Latest / Boring Science / HD 100546 b _ This Planet Is So Big It Shouldn_t Exist

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HD 100546 b _ This Planet Is So Big It Shouldn_t Exist · Boring Science

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  Speaker 1: There is a planet forming right now, 353 light years
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  Speaker 1: from Earth. And it is the biggest one we have
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  Speaker 1: ever found. Not the biggest we have guessed at. Not
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  Speaker 1: the biggest in a simulation. The biggest one astronomers have
• 0:14
  Speaker 1: actually pointed a telescope at and measured. And the measurements
• 0:17
  Speaker 1: are so extreme that the first teams to see them
• 0:20
  Speaker 1: assumed something had gone wrong. Because according to everything we
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  Speaker 1: thought we knew about how planets are built, this object
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  Speaker 1: should not exist at this size. Theoretical models set a
• 0:31
  Speaker 1: ceiling on how wide a gas giant can get. HD
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  Speaker 1: 100546b blows past that ceiling.
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  Speaker 2: It is still growing.
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  Speaker 1: Right now, as you watch this, that planet is pulling
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  Speaker 1: in gas and dust from the disk surrounding it, adding
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  Speaker 1: to a mass that is already difficult to comprehend. It
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  Speaker 1: has its own disk of material spiraling into it. It
• 0:54
  Speaker 1: may be assembling moons. It is, in every meaningful sense,
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  Speaker 1: a planet caught mid-construction, and the construction site is bigger
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  Speaker 1: than anything we have catalogued before. What makes this stranger
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  Speaker 1: is what it forces you to question. Not just how
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  Speaker 1: large a planet can get, but what a planet actually is,
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  Speaker 1: where the line falls between a planet and something else,
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  Speaker 1: and whether the way our own solar system is arranged
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  Speaker 1: is normal or just one quiet outcome in a universe
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  Speaker 1: full of something far more violent. This is the story
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  Speaker 1: of that planet. the star it is strangling, and what
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  Speaker 1: it might mean for every planet we thought we understood.
• 1:36
  Speaker 1: To understand what is growing inside the HD 100546 system,
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  Speaker 1: you first have to understand what kind of star you
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  Speaker 1: observe when you direct your gaze toward the constellation Musca.
• 1:48
  Speaker 1: Musca is a small southern constellation, faint enough that most
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  Speaker 1: people in the northern hemisphere have never thought about it.
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  Speaker 1: It sits just below the Southern Cross, tucked into a
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  Speaker 1: dense part of the Milky Way, where the sky is
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  Speaker 1: crowded with stars. If you are in the right part
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  Speaker 1: of the world, and you know exactly where to look,
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  Speaker 1: you can find HD 100546 with a reasonably powerful telescope.
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  Speaker 1: It glows at about magnitude 6.7, just at the edge
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  Speaker 1: of naked eye visibility on a perfect night. Nothing about
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  Speaker 1: it looks unusual. Nothing about it suggests that something extraordinary
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  Speaker 1: is happening there. But that is the thing about young stars,
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  Speaker 1: the chaos is hidden inside. HD 100546 is what astronomers
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  Speaker 1: call an A-type star, a classification that places it among
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  Speaker 1: the more massive stellar objects in our galaxy. It is
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  Speaker 1: significantly larger and more luminous than our own sun, burning
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  Speaker 1: through its hydrogen fuel at a rate that seems almost
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  Speaker 1: profligate when compared to the modest consumption of solar mass stars.
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  Speaker 1: The star's surface temperature reaches approximately 10,000 Kelvin, roughly twice
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  Speaker 1: that of the Sun, giving it a whitish-blue hue that
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  Speaker 1: would be visible to the naked eye if the star
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  Speaker 1: were bright enough to observe without optical aid. Yet despite
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  Speaker 1: its size and energy output, HD 100546 remains relatively unknown
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  Speaker 1: to casual stargazers, eclipsed by more famous stellar neighbours and
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  Speaker 1: dramatic celestial objects. What makes HD 100546? Truly exceptional is
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  Speaker 1: not its luminosity or its spectral classification, but.
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  Speaker 2: Rather its age.
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  Speaker 1: This star is young, remarkably young by astronomical standards. Estimates
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  Speaker 1: place it at somewhere between 5 and 10 million years old,
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  Speaker 1: making it practically an infant in a cosmos that is 13.8
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  Speaker 1: billion years ancient. For perspective, when HD 100546 was born,
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  Speaker 1: the dinosaurs had already ruled the Earth for more than
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  Speaker 1: 150 million years and were about to face their extinction event.
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  Speaker 1: In the time since HD 100546's formation, Earth's species have
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  Speaker 1: experienced dramatic evolution, humans have risen to dominance, and entire
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  Speaker 1: civilizations have flourished and fallen. Yet for a star, this
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  Speaker 1: duration represents merely the beginning of existence. The Sun by
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  Speaker 1: comparison is already 4.6 billion years old, and has billions
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  Speaker 1: of years remaining in its main sequence phase. The youth
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  Speaker 1: of HD 100546 is crucial to understanding what astronomers observe
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  Speaker 1: there today. Young stars are different from their older counterparts
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  Speaker 1: in fundamental ways. They are still contracting under their own gravity,
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  Speaker 1: still settling into the nuclear burning equilibrium that will define
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  Speaker 1: their adult years. They retain much of the material from
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  Speaker 1: their formation, material that has not yet been fully incorporated
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  Speaker 1: into the star itself or swept away by stellar winds.
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  Speaker 1: This remnant material takes the form of disks, rings, and
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  Speaker 1: clouds of gas and dust that orbit the young star,
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  Speaker 1: creating a complex architecture around it. These circumstellar disks are
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  Speaker 1: the birthplaces of planets, the nurseries where solid bodies coalesce
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  Speaker 1: from microscopic grains and grow into worlds. But they are
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  Speaker 1: also places of tremendous violence and chaos, collisions occur constantly,
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  Speaker 1: and where the basic rules of orbital mechanics are being
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  Speaker 1: tested and refined. The presence of such a disk around
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  Speaker 1: HD 10-0546 has been known for decades. Astronomers first detected
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  Speaker 1: evidence of circumstellar material through infrared observations in the 1980s
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  Speaker 1: and 1990s, when sensitive telescopes revealed that the star was
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  Speaker 1: emitting more radiation in the infrared portion of the spectrum
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  Speaker 1: than could be accounted for by the star's surface emission alone.
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  Speaker 1: This excess infrared radiation could only be explained by the
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  Speaker 1: presence of dust orbiting the star, dust that was being
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  Speaker 1: heated by the star's radiation and re-emitting that energy at
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  Speaker 1: longer wavelengths. As observational techniques improved and new telescopes came online,
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  Speaker 1: astronomers refined their understanding of this disk, measuring its extent,
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  Speaker 1: its temperature structure and its density distribution. What emerged from
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  Speaker 1: these observations was a picture of remarkable complexity. The disk
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  Speaker 1: around HD 100546 is not a simple uniform structure like
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  Speaker 1: the rings of Saturn, nor is it a smooth gradient
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  Speaker 1: of density decreasing smoothly with distance from the star. Instead,
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  Speaker 1: the observations revealed gaps, cavities, and spiral structures. There were
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  Speaker 1: regions where the disk seemed to have been cleared of materials,
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  Speaker 1: creating empty spaces where you might expect to find dust
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  Speaker 1: and gas. There were other regions where the disk showed
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  Speaker 1: intricate patterns, waves and spirals that seemed to suggest the
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  Speaker 1: presence of something massive moving through the disk, disturbing it
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  Speaker 1: like a ship moving through water. These features hinted at
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  Speaker 1: the presence of objects large enough to clear their orbital
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  Speaker 1: paths and create detectable grav, etational disturbances in the surrounding material.
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  Speaker 1: The implications of these observations were profound. Such gaps and
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  Speaker 1: cavities are not expected to form through normal processes of
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  Speaker 1: disk evolution and dust settling. They require agents of disruption,
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  Speaker 1: objects massive enough to gravitationally shepherd the disk material out
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  Speaker 1: of certain regions. In planetary systems around other stars, these
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  Speaker 1: gaps are typically attributed to planets. A forming planet, as
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  Speaker 1: it grows in mass, will clear a gap in the
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  Speaker 1: circumstellar disk, removing material through gravitational interactions. The gap grows
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  Speaker 1: as the planet grows, becoming wider and deeper as the
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  Speaker 1: planetary mass increases. Multiple planets in the same system create
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  Speaker 1: multiple gaps, producing the complex patterns that telescopes like the
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  Speaker 1: Atacama Large Millimeter Array have revealed in disks around young
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  Speaker 1: stars LED, Ike HL Tauri, and other well-studied systems. The
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  Speaker 1: conclusion was almost inescapable. HD 100546 likely harbors forming planets
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  Speaker 1: within its disk, But the evidence for these planets was indirect,
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  Speaker 1: inferred from the structure of the disk rather than observed
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  Speaker 1: directly through the light reflected or emitted by the planets themselves.
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  Speaker 1: Detecting a form in planet directly, seeing it with your
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  Speaker 1: own eyes through a telescope, represented a frontier of astronomical observation.
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  Speaker 1: Most form in planets are too faint to detect directly.
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  Speaker 1: They are small, cool objects, surrounded by material that scatters
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  Speaker 1: and absorbs their light. Yet the tantalizing possibility remained that
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  Speaker 1: somewhere within the HD 100546 system, planets were being born,
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  Speaker 1: growing from microscopic dust grains into bodies massive enough to
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  Speaker 1: reshape their cosmic environment. In 2013, a team using the
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  Speaker 1: European Southern Observatory's Very Large Telescope in Chile pointed their
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  Speaker 1: instruments at HD 100546 and picked up something that had
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  Speaker 1: never been seen before. To understand why that sentence carries weight,
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  Speaker 1: you need to understand how almost every exoplanet ever discovered has.
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  Speaker 2: Actually been found.
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  Speaker 1: The overwhelming majority were never seen directly.
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  Speaker 2: They were inferred.
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  Speaker 1: A planet passing in front of its star blocks a
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  Speaker 1: tiny fraction of the star's light, and a sensitive enough
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  Speaker 1: instrument can detect that dip, a method called transit photometry.
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  Speaker 1: Another approach watches for a star wobbling slightly in place.
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  Speaker 1: Tugged by the gravity of an orbiting planet, a way
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  Speaker 1: that shows up as a rhythmic shift in the star's
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  Speaker 1: spectral lines. Both methods are powerful. Neither one actually shows
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  Speaker 1: you the planet. What they give you is an absence,
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  Speaker 1: a wobble, a shadow. The planet itself stays invisible. Direct
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  Speaker 1: imaging is exactly what it sounds like. You point the
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  Speaker 1: telescope at the star system and you look. You try
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  Speaker 1: to actually see the planet sitting there in space. The
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  Speaker 1: problem is that stars are uncooperative in a fundamental way.
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  Speaker 1: A star like our Sun outshines any planet orbiting it
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  Speaker 1: by a factor of roughly a billion in visible light.
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  Speaker 1: Even in infrared, where planets glow more brightly from their
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  Speaker 1: own heat, the contrast ratio can be 10 million to 1.
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  Speaker 1: Finding a planet next to a star through direct imaging
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  Speaker 1: is a little like trying to spot a firefly hovering
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  Speaker 1: next to a stadium floodlight, from several miles away, in
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  Speaker 1: a photograph. The glare simply swamps everything near it. So
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  Speaker 1: why did the team try it at HD 100546? Because
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  Speaker 1: this system gave them an unusual advantage. The star is young,
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  Speaker 1: which means any planets orbiting it are also young. Young
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  Speaker 1: planets are hot. They are still radiating the energy from
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  Speaker 1: their own formation. which means they glow more intensely in
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  Speaker 1: infrared than an older, cooled-down world would. They are also,
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  Speaker 1: in some cases, still massive enough clouds of accreting material
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  Speaker 1: that they stand out against the disk background in ways
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  Speaker 1: that older, compact, finished planets do not. The system was
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  Speaker 1: already known to be surrounded by a spectacular disk, and
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  Speaker 1: there were hints in earlier observations that something was disturbing
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  Speaker 1: the disk structure from within. One of those disturbances appeared
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  Speaker 1: near a separation of roughly 53 astronomical units from the stars.
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  Speaker 1: That was where to look. What the team actually saw
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  Speaker 1: was a point source of infrared emission. Not a smear,
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  Speaker 1: not a diffuse glow.
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  Speaker 2: A point.
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  Speaker 1: It appeared embedded in the outer disk, at almost exactly
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  Speaker 1: the location the disturbance patterns had been pointing toward.
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  Speaker 2: The source was warm.
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  Speaker 1: Too warm to be a simple patch of hot dust,
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  Speaker 1: and positioned in a way that was hard to explain
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  Speaker 1: unless something with significant mass was sitting there, pulling material
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  Speaker 1: toward it and heating the surrounding gas. The researchers called
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  Speaker 1: it a protoplanet candidate, they were careful with that word, candidate,
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  Speaker 1: because a single detection through a single method is not enough.
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  Speaker 1: This is where the story slows down in the way
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  Speaker 1: science always does before it accelerates. One point of infrared
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  Speaker 1: light in an image of a young star's disk could
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  Speaker 1: be many things. It could be a clump of unusually
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  Speaker 1: dense and heated dust that had nothing to do with
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  Speaker 1: the planet. It could be a background object, something entirely
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  Speaker 1: unrelated to the HD 101. 0546 system that happened to
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  Speaker 1: appear at the same location in the sky. It could
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  Speaker 1: be an artifact of the instrument itself, a ghost left
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  Speaker 1: by the optical system. Astronomers have been burned by force
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  Speaker 1: positives before. The discipline has a long memory for those embarrassments,
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  Speaker 1: and nobody was willing to announce a landmark discovery.
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  Speaker 2: On the strength of one image.
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  Speaker 1: So they went back, multiple times with multiple approaches, The
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  Speaker 1: infrared imaging was repeated and the source held its position
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  Speaker 1: relative to the star, which ruled out a background object
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  Speaker 1: moving at a different rate. Spectroscopic observations were added, breaking
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  Speaker 1: the light from the source into its component wavelengths and
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  Speaker 1: looking for signatures that matched what a forming planet embedded
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  Speaker 1: in heated gas would produce. Spectroscopy does not give you
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  Speaker 1: a picture, it gives you chemistry and temperature.
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  Speaker 2: And the chemistry and temperature.
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  Speaker 1: Of what was sitting at 53 AU matched the expectations
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  Speaker 1: for an accreting protoplanet, not a dust clump. Then there
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  Speaker 1: was the disk itself. The structure of the surrounding material
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  Speaker 1: showed the kinds of asymmetries and perturbations that a massive
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  Speaker 1: embedded object.
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  Speaker 2: Would core, lurve out through its gravity.
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  Speaker 1: The disk was not behaving as if it were empty
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  Speaker 1: at that location. It was behaving as if something significant
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  Speaker 1: was sitting inside it, and pushing back against the flow
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  Speaker 1: of material. Three independent lines of evidence all converged on
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  Speaker 1: the same answer. Even then, the language in the published
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  Speaker 1: work was measured. Protoplanet candidate. Possible embedded planet. The field
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  Speaker 1: had earned its caution, but the convergence was striking and
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  Speaker 1: the community started paying attention. What made this different from
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  Speaker 1: every other exoplanet detection that had come before was not
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  Speaker 1: the size, not the orbit, not the mass.
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  Speaker 2: It was the timing.
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  Speaker 1: Every exoplanet discovered before this one was a finished object,
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  Speaker 1: a planet that had already formed, already settled into its orbit,
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  Speaker 1: already cooled and contracted into whatever it was going to
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  Speaker 1: be for the next several billion years. The formation process
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  Speaker 1: that had produced it was long over, leaving no trace
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  Speaker 1: in the current observations. Astronomers could infer things about how
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  Speaker 1: those planets formed from their properties, the way a detective
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  Speaker 1: can reconstruct a crime from evidence left behind, but they
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  Speaker 1: could never watch it happen. HD 10-0546b was different.
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  Speaker 2: The formation was ongoing. The accretion was active.
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  Speaker 1: The circumplanetary material was still falling inward. The planet was still,
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  Speaker 1: in the most literal sense, becoming. Observing it was not
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  Speaker 1: examining a finished structure. It was watching the construction in progress.
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  Speaker 1: That changes what you can learn. An architect studying a
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  Speaker 1: building that is already standing can measure its dimensions and
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  Speaker 1: guess at the construction techniques. But an architect who watches
• 15:10
  Speaker 1: the building going up can see exactly how the pieces
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  Speaker 1: fit together. The distinction matters enormously. The weight of what
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  Speaker 1: the 2013 team had found settled on the field slowly.
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  Speaker 1: The way significant things often do. Papers came. Follow-up observations followed.
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  Speaker 1: The debate about exactly what HD10, 0546b was, its mass,
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  Speaker 1: its radius, its temperature, that debate would continue for years,
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  Speaker 1: and in some respects continues now. But the core fact
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  Speaker 1: was not seriously contested. For the first time in the
• 15:45
  Speaker 1: history of astronomy, a planet had been caught in the
• 15:48
  Speaker 1: act of forming, still embedded in the disk that was
• 15:51
  Speaker 1: building it. Jupiter is the largest planet in our solar system,
• 15:55
  Speaker 1: and by the standards of everyday life, the numbers associated
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  Speaker 1: with it are hard to hold in your mind. Jupiter's
• 16:01
  Speaker 1: diameter is about 11 times the diameter of Earth. Its
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  Speaker 1: volume is more than 1,300 Earths. If you hollowed Jupiter
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  Speaker 1: out and started pouring in planets, you could fit every
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  Speaker 1: other world in the solar system inside it and still
• 16:14
  Speaker 1: have room. Saturn, Uranus, Neptune, Mars, Venus, Earth, Mercury, all
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  Speaker 1: of them together, rattling around inside Jupiter like pebbles in
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  Speaker 1: a barrel. and Jupiter still would not be full, by
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  Speaker 1: any measure that a human brain can actually process.
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  Speaker 2: Jupiter is enormous.
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  Speaker 1: It is the undisputed heavyweight of our solar system, and
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  Speaker 1: every other planet is essentially a footnote. Now hold that
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  Speaker 1: picture in your mind, because astronomers need a unit of
• 16:44
  Speaker 1: measurement big enough to talk about objects like HD10, 0546b,
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  Speaker 1: and that unit is the Jupiter radius. One Jupiter radius
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  Speaker 1: is roughly 71,000 kilometers, It is the standard yardstick for
• 16:58
  Speaker 1: large exoplanets, the same way astronomers use Earth radii for
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  Speaker 1: smaller rocky worlds. When the numbers involved are this extreme,
• 17:06
  Speaker 1: you need a baseline that doesn't disappear into abstraction. And
• 17:09
  Speaker 1: Jupiter is familiar enough, documented enough, that it serves as
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  Speaker 1: a useful anchor. So when a paper comes out saying
• 17:17
  Speaker 1: an exoplanet measures 3.4 Jupiter radii, you have somewhere to stand.
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  Speaker 1: You know what one Jupiter looks like. You just have
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  Speaker 1: to imagine scaling it up by a factor of three.
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  Speaker 2: And a half.
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  Speaker 1: What does 3.4 Jupiter radii actually mean in physical terms?
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  Speaker 1: A planet at that size would have a diameter of
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  Speaker 1: roughly 480,000 kilometers. Put that planet at the center of
• 17:40
  Speaker 1: our solar system where the Sun sits and its surface
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  Speaker 1: would extend outward to a distance of about 240,000 kilometers.
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  Speaker 2: From its own center.
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  Speaker 1: Mercury orbits our Sun at an average distance of roughly
• 17:52
  Speaker 1: 58 million kilometers. So HD100546b is not wider than Mercury's orbit.
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  Speaker 1: That comparison doesn't quite land that way. But the sheer
• 18:02
  Speaker 1: footprint of it dwarfs anything we have in our own neighborhood.
• 18:05
  Speaker 1: Jupiter itself, at one Jupiter radius, would fit inside HD100546b
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  Speaker 1: roughly 39 times by volume. 39 Jupiters. That is a
• 18:17
  Speaker 1: number that should feel wrong. It doesn't feel like a
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  Speaker 1: planet anymore. It starts to feel like something else entirely.
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  Speaker 1: And here is where things get stranger. The estimate of 3.4
• 18:27
  Speaker 1: Jupiter radii is the conservative one. When HD10-0546b was first
• 18:34
  Speaker 1: being studied seriously, some measurements put the radius at approximately 6.9
• 18:39
  Speaker 1: Jupiter radii, nearly 7 times the size of Jupiter. A
• 18:43
  Speaker 1: planet at that scale would be wider than the orbit
• 18:45
  Speaker 1: of Venus around our Sun. The volume would be so
• 18:48
  Speaker 1: extreme that it would contain something like 330 Jupiters. At
• 18:52
  Speaker 1: that size, the object becomes genuinely difficult to categorize using
• 18:56
  Speaker 1: any framework built around familiar planetary science. So why the range?
• 19:01
  Speaker 1: Why do two measurements of the same object produce numbers
• 19:04
  Speaker 1: that are different? The answer is that what astronomers are
• 19:07
  Speaker 1: actually seeing is not the planet cleanly against empty space.
• 19:11
  Speaker 1: HD 100546b is still forming, still wrapped in its own
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  Speaker 1: circumplanetary disk. a swirling shroud of gas and dust that
• 19:22
  Speaker 1: it is actively pulling in. When the telescope picks up
• 19:25
  Speaker 1: infrared light from the system, it is receiving the combined
• 19:28
  Speaker 1: glow of the planet itself and all that surrounding material
• 19:32
  Speaker 1: mixed together. Depending on how you model the contribution of
• 19:36
  Speaker 1: the disk versus the contribution of the planet, you get
• 19:39
  Speaker 1: a different answer for where the planet ends. Early estimates
• 19:42
  Speaker 1: were less sophisticated in disentangling those two sources and the
• 19:46
  Speaker 1: result was a radius measurement that almost certainly included a
• 19:50
  Speaker 1: large contribution.
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  Speaker 2: From the disk.
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  Speaker 1: The 2017 study that produced the 3.4 Jupiter radii figure
• 19:57
  Speaker 1: applied more careful modeling and more refined assumptions, and that
• 20:00
  Speaker 1: brought the number down. But even 3.4 is still remarkable.
• 20:05
  Speaker 1: Here is the problem. Planetary theory says it shouldn't be possible.
• 20:09
  Speaker 1: Standard models of how gas giants form and evolve place
• 20:12
  Speaker 1: a ceiling on how large a gas giant can be
• 20:15
  Speaker 1: at around 2.2 Jupiter radii. The physics behind this limit
• 20:19
  Speaker 1: is not complicated in principle. As you add mass to
• 20:22
  Speaker 1: a gas giant, gravity compresses the interior.
• 20:25
  Speaker 2: More and more efficiently. Past a certain point.
• 20:28
  Speaker 1: Adding more mass actually makes the planet smaller in radius,
• 20:32
  Speaker 1: not larger. The most massive gas giants end up more
• 20:35
  Speaker 1: compact than moderately massive ones because the compression overwhelms the
• 20:39
  Speaker 1: outward pressure. So a planet at 2.2 Jupiter radii is
• 20:43
  Speaker 1: essentially the theoretical sweet spot. The widest a gas giant
• 20:47
  Speaker 1: gets before gravity starts winning and squeezing it back down.
• 20:50
  Speaker 1: Anything claiming to be a gas giant at 3.4 Jupiter
• 20:53
  Speaker 1: radii is, on paper, break-in. G.
• 20:57
  Speaker 2: The rules.
• 20:58
  Speaker 1: What is happening in HD 1.0? 0546B' s case, is that
• 21:04
  Speaker 1: the rules were written for finished planets. A fully formed
• 21:07
  Speaker 1: gas giant has settled. Its circumplanetary disk is gone. Its
• 21:12
  Speaker 1: internal heat from formation has largely radiated away. It is
• 21:16
  Speaker 1: a completed object sitting in its final state, and the
• 21:19
  Speaker 1: radius mass models are built for exactly that kind of object.
• 21:24
  Speaker 1: HD10 0546B is none of those things. It is still
• 21:30
  Speaker 1: accumulating material. Its outer layers are still puffed up by
• 21:34
  Speaker 1: the heat of ongoing accretion. The circumplanetary disk is still
• 21:38
  Speaker 1: adding apparent size to what the telescope records. The 3.4
• 21:42
  Speaker 1: Jupiter radii figure is probably not the radius of the
• 21:45
  Speaker 1: planet itself. It is the radius of the planet plus
• 21:49
  Speaker 1: the envelope of gas and dust that has not yet
• 21:51
  Speaker 1: finished falling in. The real planet, whatever it will eventually
• 21:55
  Speaker 1: look like when the disk clears and the accretion stops,
• 21:58
  Speaker 1: is likely smaller, but we do not know by how much.
• 22:02
  Speaker 1: What makes HD10-0546b extraordinary, even if you grant every skeptical correction,
• 22:10
  Speaker 1: is that the corrected numbers still lead you to the
• 22:12
  Speaker 1: same conclusion. Strip out the circumplanetary disk contribution as best
• 22:17
  Speaker 1: you can, and you still end up with an object
• 22:19
  Speaker 1: larger than any other exoplanet in the catalog. Apply the
• 22:23
  Speaker 1: most conservative mass estimate available, and you still have something
• 22:26
  Speaker 1: behaving in ways that standard planetary models were not built
• 22:30
  Speaker 1: to accommodate. Other large exoplanets exist. HAT-P32b, WASP-79b. Objects inflated
• 22:38
  Speaker 1: by proximity to their host stars, but their inflation mechanisms
• 22:41
  Speaker 1: are understood. Their sizes are explained.
• 22:45
  Speaker 2: HD10, 0546b.
• 22:48
  Speaker 1: Size is not yet fully explained, and it is still
• 22:52
  Speaker 1: the biggest. Astronomers use the phrase anomalously large in the literature.
• 22:56
  Speaker 1: which is the careful scientific way of saying that something
• 22:59
  Speaker 1: is sitting outside the zone where the equations are comfortable.
• 23:02
  Speaker 1: That phrase shows up repeatedly in the papers on HD10.
• 23:07
  Speaker 2: 0546b.
• 23:08
  Speaker 1: It is a signal that the object is not a
• 23:10
  Speaker 1: measurement error or a modeling artifact. It is a genuine outlier.
• 23:14
  Speaker 1: The universe produced something that the best available theory did
• 23:17
  Speaker 1: not predict, and astronomers are still working out why. Even
• 23:21
  Speaker 1: stripped of every generous assumption, Even accounting for the disk
• 23:25
  Speaker 1: material inflating the apparent size, HD100546b remains the largest exoplanet
• 23:33
  Speaker 1: astronomers have ever measured. The disk surrounding HD1000546 is not
• 23:40
  Speaker 1: a minor feature of the system. It is, in a
• 23:43
  Speaker 1: real sense, the system. Everything that is happening out there,
• 23:47
  Speaker 1: the planet growing at 53 AU, the spiral arms curling outward,
• 23:52
  Speaker 1: strange cleared cavity at the center. All of it is
• 23:55
  Speaker 1: a consequence of this disk existing, and of what is
• 23:58
  Speaker 1: moving through it. To understand why that matters, you have
• 24:02
  Speaker 1: to understand what a protoplanetary disk actually is. When a
• 24:05
  Speaker 1: cloud of gas and dust in space collapses under its
• 24:08
  Speaker 1: own gravity to form a star, it does not fall
• 24:11
  Speaker 1: straight inward all at once. The cloud is rotating, even slightly,
• 24:16
  Speaker 1: and that rotation means the material cannot simply pile into
• 24:19
  Speaker 1: a single point. Instead, Most of it collapses into the
• 24:22
  Speaker 1: forming star at the center, but a fraction of it
• 24:25
  Speaker 1: spreads outward into a flat, spinning structure, a disk. This
• 24:29
  Speaker 1: is the raw material left over from star formation.
• 24:32
  Speaker 2: It is the inventory.
• 24:34
  Speaker 1: Everything that will ever become a planet, a moon, an asteroid,
• 24:38
  Speaker 1: a comet, any solid object in that system, has to
• 24:41
  Speaker 1: come from this disk. The disk is the factory floor,
• 24:44
  Speaker 1: and planetary formation is what happens when the machinery starts run.
• 24:48
  Speaker 1: In our own solar system, That factory ran and shut
• 24:53
  Speaker 1: down billions of years ago. The disk that built Earth
• 24:56
  Speaker 1: and Jupiter and Neptune dispersed long before humanity existed. We
• 25:00
  Speaker 1: can only infer what it looked like by studying the
• 25:03
  Speaker 1: finished products. HD10-0546 is different. The factory is still running.
• 25:11
  Speaker 1: The disk is still there.
• 25:13
  Speaker 2: And it is enormous. The outer edge of the HD10-0546.
• 25:15
  Speaker 1: Disk stretches out to roughly 300 AU from the star.
• 25:23
  Speaker 1: To put that in perspective, Neptune, the outermost planet in
• 25:27
  Speaker 1: our solar system, sits about 30 AU.
• 25:30
  Speaker 2: From the sun.
• 25:31
  Speaker 1: The Kuiper belt, the frozen ring of icy debris beyond Neptune,
• 25:35
  Speaker 1: extends out to around 50 AU before it thins away.
• 25:39
  Speaker 1: The disk around HD 10, 0546, reaches six times farther
• 25:46
  Speaker 1: than that.
• 25:47
  Speaker 2: Beyond the disk.
• 25:47
  Speaker 1: Itself, there is also a diffuse envelope of gas and dust,
• 25:52
  Speaker 1: extending out to approximately 1000 AU. So tenuous it barely registers,
• 25:58
  Speaker 1: but present, a reminder of the original cloud that collapsed
• 26:01
  Speaker 1: to form this system. The total scale is genuinely difficult
• 26:05
  Speaker 1: to hold in your mind. You could fit three of
• 26:08
  Speaker 1: our solar systems, edge to edge, inside just the main disk.
• 26:12
  Speaker 1: Here is where the story gets strange. If you look
• 26:16
  Speaker 1: closely at the structure of this disk, it is not
• 26:18
  Speaker 1: a uniform sheet of material thickening gradually toward the star.
• 26:23
  Speaker 1: It has a gap, a large one. Starting at around 0.2
• 26:27
  Speaker 1: AU from the star and extending all the way out
• 26:30
  Speaker 1: to about 13 AU, there is essentially nothing, an empty zone.
• 26:35
  Speaker 1: No significant gas, no significant dust, just a hollow region
• 26:39
  Speaker 1: where you would expect material to be if this were
• 26:41
  Speaker 1: a simple undisturbed disk. Then beyond 13 AU, the dense
• 26:46
  Speaker 1: outer disk picks up again full of gas and dust,
• 26:50
  Speaker 1: and embedded structure running outward until it fades at the
• 26:53
  Speaker 1: boundary near 300 AU. This is what astronomers mean when
• 26:56
  Speaker 1: they call HD 100546 a transition disk. The name refers
• 27:02
  Speaker 1: to this characteristic feature, a disk with a cleared inner cavity,
• 27:06
  Speaker 1: thought to be a disk in the process of transitioning
• 27:09
  Speaker 1: from a young full disk to something older and more dispersed.
• 27:13
  Speaker 1: Transition disks were once considered puzzling rarities, but they have
• 27:17
  Speaker 1: since been recognized as a normal phase in the life
• 27:20
  Speaker 1: of many young stellar systems. The key question has always
• 27:23
  Speaker 1: been the same, what clears the inner hole? Several mechanisms
• 27:27
  Speaker 1: have been proposed over the years. Photo evaporation, the star's
• 27:31
  Speaker 1: radiation boiling away the inner disk, can create gaps, but
• 27:35
  Speaker 1: it tends to produce gaps at specific locations and on
• 27:39
  Speaker 1: time scales that do not always match what is observed.
• 27:42
  Speaker 1: Magnetic effects can also drive material inward, and clear regions
• 27:47
  Speaker 1: of the disk. But the most powerful explanation, and the
• 27:51
  Speaker 1: one most strongly supported in the HD10-0546.
• 27:55
  Speaker 2: Case, is planets.
• 27:57
  Speaker 1: A massive planet orbiting within a disk will gravitationally capture
• 28:01
  Speaker 1: the material near its orbit, either pulling it onto the
• 28:04
  Speaker 1: planet itself or flinging it outward into different orbital paths.
• 28:09
  Speaker 1: Do this for long enough with a sufficiently massive object
• 28:13
  Speaker 1: and you hollow out the region around the planet's orbit.
• 28:16
  Speaker 1: The inner cavity in HD 100546's disk is 13.
• 28:22
  Speaker 2: AU in radius.
• 28:23
  Speaker 1: Something orbiting inside that cavity appears to have swept it clean.
• 28:28
  Speaker 1: When Hubble turned its coronagraph on HD 100546, blocking the
• 28:34
  Speaker 1: direct glare of the star and letting the surrounding disk
• 28:37
  Speaker 1: become visible, what appeared in the images was not a smooth,
• 28:40
  Speaker 1: featureless ring. The disk showed spiral arms, large sweeping structures
• 28:46
  Speaker 1: curling outward from the central region, visible in scattered light
• 28:50
  Speaker 1: as bright bands winding through the disk. Spiral arms in
• 28:53
  Speaker 1: a protoplanetary disk are not decorative. They are density waves.
• 28:58
  Speaker 1: They form when a massive object's gravity perturbs the disk material,
• 29:03
  Speaker 1: compressing it into curving bands of higher density that propagate
• 29:07
  Speaker 1: outward like ripples. The gravitational influence of a planet does
• 29:11
  Speaker 1: not just clear a local lane, It reaches across the disk,
• 29:15
  Speaker 1: pulling material into these large-scale patterns that can extend for
• 29:19
  Speaker 1: hundreds of AU. The spiral structure in HD10 shows clear asymmetries.
• 29:28
  Speaker 1: The arms are not perfectly symmetric around the star. They
• 29:31
  Speaker 1: show the kind of irregular, lopsided morphology that suggests multiple
• 29:35
  Speaker 1: sources of perturbation, which is consistent with the idea that
• 29:39
  Speaker 1: there may be more than one massive object moving through
• 29:42
  Speaker 1: the disk. The shape and pitch of spiral arms carry
• 29:46
  Speaker 1: information about the mass of whatever is causing them. More
• 29:49
  Speaker 1: massive perturbers produce wider, more loosely wound arms.
• 29:54
  Speaker 2: The patterns in.
• 29:54
  Speaker 1: HD10, 0546, point toward objects with substantial mass, not small
• 30:01
  Speaker 1: rocky bodies. Beyond the spiral arms, the disk also shows
• 30:05
  Speaker 1: brightness asymmetries in scattered light, regions where the surface of
• 30:09
  Speaker 1: the disk catches more starlight than others. This kind of
• 30:13
  Speaker 1: asymmetry can be caused by warps in the disk, by
• 30:16
  Speaker 1: density variations, or by the shadowing effect of material at
• 30:19
  Speaker 1: different heights. None of these features arise in an undisturbed
• 30:23
  Speaker 1: disk sitting quietly around a young star. They arise when
• 30:26
  Speaker 1: something is moving through the disk and stirring it. The
• 30:29
  Speaker 1: picture that emerges from all of these observations together is
• 30:32
  Speaker 1: not subtle. There is a 13 AU inner cavity where
• 30:36
  Speaker 1: material has been swept away. There are spiral arms propagating
• 30:40
  Speaker 1: through the outer disk. There are brightness asymmetries pointing to
• 30:44
  Speaker 1: density variations. There is a planet sitting at 53 AU
• 30:49
  Speaker 1: far out in the disk, still actively growing. All of
• 30:53
  Speaker 1: these features, the gap, the spirals, The asymmetries are signatures
• 30:58
  Speaker 1: of gravitational sculpting. Something massive was reshaping that disk from
• 31:03
  Speaker 1: the inside, and the shape of the cavity was pointing
• 31:06
  Speaker 1: directly at where to look. The thing that separates HD10-0546b
• 31:12
  Speaker 1: from every other exoplanet we have ever studied is not
• 31:16
  Speaker 1: its size. Every exoplanet we have catalogued before this one
• 31:19
  Speaker 1: shares a common feature.
• 31:21
  Speaker 2: It is finished.
• 31:22
  Speaker 1: Whatever forces built it collapsed into equilibrium long ago. The
• 31:26
  Speaker 1: gas settled, the accretion slowed, the surrounding disk dissipated, and
• 31:31
  Speaker 1: what remained was a planet in its final form, still orbiting,
• 31:35
  Speaker 1: still radiating heat, but fundamentally done. When astronomers study Jupiter,
• 31:40
  Speaker 1: or a hot Jupiter circling some distant star, they are
• 31:44
  Speaker 1: studying an outcome, a completed object. The recipe was followed,
• 31:48
  Speaker 1: the dish was cooked, and what sits in the pan
• 31:50
  Speaker 1: is the end product.
• 31:52
  Speaker 2: HD 100546b.
• 31:55
  Speaker 1: Is different in a way that changes what the whole
• 31:57
  Speaker 1: enterprise of exoplanet science actually means it is not a
• 32:01
  Speaker 1: finished planet it is a planet in the middle of
• 32:03
  Speaker 1: becoming one right now at this moment it is still
• 32:07
  Speaker 1: pulling in material from the disk around it still growing
• 32:11
  Speaker 1: still assembling itself into whatever it will eventually be that
• 32:15
  Speaker 1: is something astronomers have never had a clear window onto
• 32:18
  Speaker 1: before and it is the central reason this object commands
• 32:21
  Speaker 1: so much attention to understand why that matters you need
• 32:25
  Speaker 1: to understand what accretion actually is. When a giant planet forms,
• 32:30
  Speaker 1: it does not appear suddenly. It starts as a concentration
• 32:33
  Speaker 1: of material, gas and dust that has begun gravitationally collapsing
• 32:37
  Speaker 1: in on itself within the parent disk. As that concentration
• 32:41
  Speaker 1: grows denser, its gravity increases. Stronger gravity reaches further into
• 32:46
  Speaker 1: the disk and pulls in more material. More material means
• 32:50
  Speaker 1: more mass, more mass means stronger gravity, and the process
• 32:53
  Speaker 1: feeds on itself. The planet sweeps a lane through the
• 32:56
  Speaker 1: disk as it orbits, capturing gas on both sides. Some
• 33:00
  Speaker 1: of that gas falls directly into the planet. Some of
• 33:03
  Speaker 1: it enters a wide spiraling structure that wraps around the
• 33:06
  Speaker 1: planet itself, gradually funneling material inward over time. That spiraling
• 33:10
  Speaker 1: structure is what astronomers call a circumplanetary disk. It is
• 33:14
  Speaker 1: essentially a miniature version of the protoplanetary disk surrounding the star,
• 33:19
  Speaker 1: only now orbiting the planet instead of the star. HD
• 33:25
  Speaker 1: 100546b has one of these, and the fact that it
• 33:27
  Speaker 1: does tells you everything about where this object sits in
• 33:30
  Speaker 1: its own history. The circumplanetary disk around HD 100546b is
• 33:37
  Speaker 1: not a minor detail. It has its own structure, its
• 33:40
  Speaker 1: own dynamics, its own mass. Observations suggest its radius extends
• 33:45
  Speaker 1: up to roughly 0.44 AUU, which is close to the
• 33:49
  Speaker 1: distance from our Sun to Mercury. That is not a
• 33:52
  Speaker 1: thin ring clinging to the planet's surface. That is a
• 33:55
  Speaker 1: substantial spread of material rotating around the planet, feeding into
• 33:59
  Speaker 1: it from the outside edge. The estimated mass of this
• 34:02
  Speaker 1: disk runs up to about 1.44 times the mass of Earth.
• 34:07
  Speaker 1: That might sound modest compared to the mass of the
• 34:09
  Speaker 1: planet itself, but in the context of a forming moon system,
• 34:13
  Speaker 1: it is significant. Our own Jupiter built four large moons, Io, Europa, Ganymede, Callisto,
• 34:21
  Speaker 1: out of a circumplanetary disk that was probably not dramatically
• 34:24
  Speaker 1: more massive. The same physics that assembled those moons could,
• 34:28
  Speaker 1: in principle, be operating around HD10-0546i right now. The disk
• 34:36
  Speaker 1: is the raw material not just for the planet, but
• 34:39
  Speaker 1: for whatever smaller worlds might eventually orbit it. Here is
• 34:42
  Speaker 1: what makes this genuinely strange to think about. When astronomers
• 34:46
  Speaker 1: look at any other exoplanet and measure its radius, they
• 34:49
  Speaker 1: are measuring the planet.
• 34:51
  Speaker 2: Just the planet.
• 34:52
  Speaker 1: The object has a surface or a cloud layer, and
• 34:55
  Speaker 1: below that surface or cloud layer is everything that makes
• 34:59
  Speaker 1: up the planet. The radius you measure is the radius
• 35:02
  Speaker 1: of that object. When astronomers look at HD.
• 35:07
  Speaker 2: 100546b, they are not measuring the planet.
• 35:10
  Speaker 1: They are measuring the planet, plus its circumplanetary disk, plus
• 35:14
  Speaker 1: the diffuse envelope of gas and dust still raining down
• 35:18
  Speaker 1: from the surrounding protoplanetary disk. All of that material is glowing.
• 35:23
  Speaker 1: All of it is warm. All of it is sending
• 35:26
  Speaker 1: light toward the telescope simultaneously arriving mixed together in a
• 35:31
  Speaker 1: single signal that cannot be cleanly sorted by any instrument.
• 35:34
  Speaker 2: Currently in operation.
• 35:36
  Speaker 1: The circumplanetary disk is not a separate source that can
• 35:39
  Speaker 1: be pointed at and subtracted. It wraps around the planet.
• 35:43
  Speaker 1: It is geometrically entangled with the planet. Separating them is
• 35:47
  Speaker 1: not a computational inconvenience, it is a genuinely unsolved observational problem.
• 35:53
  Speaker 1: This is why the temperature estimates for HD10 range so widely.
• 36:00
  Speaker 1: One study places the effective temperature at around 932 Kelvin. Another,
• 36:05
  Speaker 1: using different assumptions about how to model the disc's contribution,
• 36:09
  Speaker 1: lands at 2630 Kelvin. Those are not small discrepancies. That
• 36:15
  Speaker 1: is the difference between a planet warm enough to glow
• 36:17
  Speaker 1: dull red and a planet hot enough to approach the
• 36:20
  Speaker 1: lower end of stellar temperatures. Both estimates come from real data.
• 36:24
  Speaker 1: Both are derived from serious analysis. The disagreement does not
• 36:28
  Speaker 1: reflect careless science. It reflects the fact that the underlying
• 36:32
  Speaker 1: object is genuinely ambiguous, because what you see depends heavily
• 36:36
  Speaker 1: on how you decide to model what you cannot see directly.
• 36:39
  Speaker 1: The same problem infects every other measurement. The radius estimates
• 36:43
  Speaker 1: range from 3.4 Jupiter radii up to earlier claims near 6.9
• 36:48
  Speaker 1: Jupiter radii. The mass estimates span from below 2 Jupiter
• 36:52
  Speaker 1: masses to well above 20. Each of these numbers comes
• 36:56
  Speaker 1: from a study that made some set of assumptions about
• 36:58
  Speaker 1: how much of the observed light belongs to the planet
• 37:01
  Speaker 1: and how much belongs to the disk. Change the assumptions,
• 37:05
  Speaker 1: change the answer. This is not how measuring finished exoplanets works.
• 37:10
  Speaker 1: When you observe a mature planet transiting its star, the
• 37:13
  Speaker 1: geometry is clean. The planet blocks a specific fraction of
• 37:17
  Speaker 1: the star's light. You measure that fraction, and the radius
• 37:20
  Speaker 1: falls out of straightforward arithmetic. HD 10-0546b does not give
• 37:27
  Speaker 1: you anything that clean.
• 37:29
  Speaker 2: It gives you a complicated, overlapping, thermally.
• 37:31
  Speaker 1: Mixed blob of emission that the planet is buried inside.
• 37:35
  Speaker 1: What astronomers have been able to do is work at
• 37:38
  Speaker 1: the edges of the problem, They can observe the disk
• 37:41
  Speaker 1: as a whole and estimate how much light should be
• 37:44
  Speaker 1: coming from the disk based on its temperature and structure.
• 37:47
  Speaker 1: They can subtract that estimate from the total and treat
• 37:50
  Speaker 1: whatever remains as the planet's contribution. But the estimate of
• 37:54
  Speaker 1: the disk's contribution depends on models of how the disk
• 37:57
  Speaker 1: is structured, which are themselves uncertain. The whole calculation is
• 38:02
  Speaker 1: iterative and sensitive to assumptions at every step, different researchers
• 38:07
  Speaker 1: following slightly different paths through the same data. have arrived
• 38:10
  Speaker 1: at numbers that barely overlap. That is the current state
• 38:14
  Speaker 1: of knowledge about this object, and it is not a
• 38:17
  Speaker 1: temporary situation. It will remain the situation until instruments powerful
• 38:22
  Speaker 1: enough to spatially resolve the planet from its disk are
• 38:26
  Speaker 1: actually pointed at it. What this actively accreting state does,
• 38:30
  Speaker 1: beyond complicating measurements, is make HD10-0546BA uniquely valuable scientific target.
• 38:40
  Speaker 1: Every other exoplanet is an answer. This one is a process.
• 38:45
  Speaker 1: The mass it will eventually have, the size it will
• 38:48
  Speaker 1: eventually reach, the structure of its atmosphere. None of those
• 38:52
  Speaker 1: things are fixed yet. They are being determined right now
• 38:55
  Speaker 1: by the rate at which material continues to fall in,
• 38:58
  Speaker 1: by the temperature of the surrounding disk, by the gravitational
• 39:02
  Speaker 1: dynamics of its orbit. Studying this planet is not studying
• 39:06
  Speaker 1: what a planet is. It is studying what a planet becomes.
• 39:10
  Speaker 1: That is a fundamentally different kind of observation, and it
• 39:13
  Speaker 1: carries information that no amount of studying finished planets can recover.
• 39:17
  Speaker 1: The planet and its disk are so thoroughly mixed together
• 39:20
  Speaker 1: in the data that pulling them apart has been one
• 39:22
  Speaker 1: of the central frustrations of studying this system for the
• 39:25
  Speaker 1: past decade. The measurements of HD 10, 0, do not agree
• 39:32
  Speaker 1: with each other. The reason for that disagreement is more
• 39:35
  Speaker 1: interesting than any single number. When astronomers first got a
• 39:38
  Speaker 1: good look at this object, the number that came back
• 39:41
  Speaker 1: was staggering. Early estimates placed the radius of HD100546b at
• 39:44
  Speaker 1: around 6.9 Jupiter radii. To put that in perspective, Jupiter
• 39:52
  Speaker 1: itself is roughly 11 times wider than Earth. A planet
• 39:55
  Speaker 1: at 6.9 Jupiter radii would be nearly 76 times wider
• 39:59
  Speaker 1: than Earth. That is not a planet by any intuitive definition.
• 40:04
  Speaker 1: That is closer in scale to a small star. The
• 40:07
  Speaker 1: number was so extreme that it immediately raised a question.
• 40:10
  Speaker 1: Was this a real measurement of a physical object? Or
• 40:13
  Speaker 1: was something else going on in the data? Something else
• 40:16
  Speaker 1: was going on, but the story of what, exactly, took
• 40:20
  Speaker 1: years to untangle, and it is still not fully resolved.
• 40:24
  Speaker 2: Here is the core problem.
• 40:25
  Speaker 1: HD10-0546b is not sitting alone in empty space, cleanly separated
• 40:34
  Speaker 1: from everything around it. It is embedded in its own
• 40:37
  Speaker 1: circumplanetary disk, a swirling structure of gas and dust that
• 40:41
  Speaker 1: is actively falling onto the planet. That disk emits its
• 40:45
  Speaker 1: own light. It scatters light from the central star. When
• 40:49
  Speaker 1: a telescope looks at the location of HD 100546b, what
• 40:55
  Speaker 1: it actually receives is a jumbled mixture of thermal emission
• 40:58
  Speaker 1: from the planet itself, emission from the circumplanetary disk, scattered
• 41:03
  Speaker 1: starlight from the surrounding protoplanetary disk. All of these signals
• 41:08
  Speaker 1: arrive at the detector blended together. There is no clean
• 41:11
  Speaker 1: way to separate them by simply staring harder. You have
• 41:14
  Speaker 1: to make assumptions. You have to build a model of
• 41:17
  Speaker 1: what the disk is doing. subtract it out, see what
• 41:21
  Speaker 1: is left. The problem is that different models of the
• 41:25
  Speaker 1: disk produce different answers for the planet. This is where
• 41:28
  Speaker 1: the early estimate of 6.9 Jupiter radii came from. If
• 41:32
  Speaker 1: you model the disk a certain way and subtract its
• 41:35
  Speaker 1: contribution from the total signal, the residual can be interpreted
• 41:39
  Speaker 1: as an object significantly larger than the most conservative estimates allow.
• 41:44
  Speaker 1: The extended gas and dust envelopes surrounding the forming planet
• 41:48
  Speaker 1: was inflating the apparent size enormously. What the telescope was
• 41:52
  Speaker 1: measuring was not really the planet's photosphere, its actual visible
• 41:56
  Speaker 1: surface layer. It was measuring the outer edge of a diffuse,
• 42:00
  Speaker 1: extended structure that included the planet at its center but
• 42:03
  Speaker 1: stretched much further out in every direction. By 2017, a
• 42:07
  Speaker 1: more careful study tried to account for this complication more rigorously.
• 42:12
  Speaker 1: That analysis came back with a revised estimate of 3.4
• 42:15
  Speaker 1: Jupiter radii, still enormous, still larger than any confirmed exoplanet
• 42:20
  Speaker 1: with better constrained measurements, but substantially smaller than the early number.
• 42:25
  Speaker 1: The reason for the difference was precisely what the earlier
• 42:28
  Speaker 1: work had not fully accounted for. The circumplanetary disk was
• 42:32
  Speaker 1: adding apparent size that did not belong to the planet itself.
• 42:35
  Speaker 1: The 2017 study also produced a temperature estimate, and that
• 42:39
  Speaker 1: number told its own complicated story. The effective temperature of
• 42:43
  Speaker 1: HD100546b in that analysis came out to roughly 2630 Kelvin.
• 42:51
  Speaker 1: Earlier work had suggested something closer to 932 Kelvin. The
• 42:56
  Speaker 1: gap between those two numbers is not small. It is
• 42:59
  Speaker 1: the difference between an object that is warm and an
• 43:01
  Speaker 1: object that is searing. At 932 Kelvin, you are roughly
• 43:05
  Speaker 1: in the range of a cool brown dwarf, an object
• 43:08
  Speaker 1: that glows a deep dim red. At 2630 Kelvin, you
• 43:13
  Speaker 1: are describing something significantly hotter, closer to the surface temperature
• 43:17
  Speaker 1: of a dim red star than to a planet in
• 43:19
  Speaker 1: any conventional sense. Why such a wide range? Again, the
• 43:24
  Speaker 1: modeling assumptions. Temperature estimates for embedded objects like HD 100546b
• 43:31
  Speaker 1: depend heavily on how you treat the extinction. the dust
• 43:35
  Speaker 1: and gas between the planet and the telescope that absorbs
• 43:38
  Speaker 1: and reddens the light before it ever reaches Earth. The
• 43:42
  Speaker 1: 2017 study described HD100546b as a highly reddened object, meaning
• 43:50
  Speaker 1: a significant amount of its light was being absorbed and
• 43:53
  Speaker 1: shifted toward redder wavelengths by intervening material. When you correct
• 43:58
  Speaker 1: aggressively for reddening, the inferred temperature of the underlying source
• 44:02
  Speaker 1: goes up dramatically. A cooler object buried behind a thick
• 44:06
  Speaker 1: dust curtain can look similar to a hotter object sitting
• 44:09
  Speaker 1: in clearer surroundings. The telescope has no immediate way to
• 44:13
  Speaker 1: distinguish between the two without additional info. Mation about what
• 44:17
  Speaker 1: the dust is doing. The mass estimate from the same
• 44:20
  Speaker 1: 2017 study sat at roughly 25 Jupiter masses. That number
• 44:25
  Speaker 1: is important. It will matter a great deal in the
• 44:28
  Speaker 1: next part.
• 44:29
  Speaker 2: Of the story.
• 44:30
  Speaker 1: This was because it puts HD 101 in uncomfortably ambiguous
• 44:36
  Speaker 1: territory when you start asking what exactly this thing is.
• 44:39
  Speaker 1: But for now, set aside the mass question and focus
• 44:43
  Speaker 1: on what these measurement disagreements collectively reveal. They reveal that
• 44:47
  Speaker 1: what astronomers are actually observing is not a clean, isolated planet.
• 44:52
  Speaker 1: It is a planet in the process of construction, still
• 44:55
  Speaker 1: wrapped in its building materials. Those materials refuse to stay
• 44:58
  Speaker 1: out of the measurement. Every attempt to pin down the
• 45:01
  Speaker 1: radius runs into the circumplanetary disk. Every attempt to pin
• 45:05
  Speaker 1: down the temperature runs into the dust. Every attempt to
• 45:08
  Speaker 1: pin down the mass runs into the difficulty of separating
• 45:11
  Speaker 1: the planet's own gravitational signature from the combined mass of
• 45:15
  Speaker 1: the surrounding structure. This is not a failure of instrumentation.
• 45:19
  Speaker 1: The telescopes used to study this system are among the most.
• 45:22
  Speaker 2: Powerful ever built.
• 45:24
  Speaker 1: It is a failure in the sense that the object
• 45:26
  Speaker 1: itself is genuinely too complex for the simple models that
• 45:29
  Speaker 1: work well.
• 45:30
  Speaker 2: On finished planets.
• 45:31
  Speaker 1: Think about how a finished planet gets measured. You observe
• 45:35
  Speaker 1: it transit across its star. You measure how much light
• 45:38
  Speaker 1: it blocks. The math is straightforward. The radius of the
• 45:41
  Speaker 1: planet is directly readable from the dip in brightness. Because
• 45:44
  Speaker 1: the planet is a solid or well-defined gas body with
• 45:47
  Speaker 1: no surrounding disk confusing the signal, the answer is clean.
• 45:51
  Speaker 1: HD10-0546b does not offer that luxury. It does not transit.
• 45:58
  Speaker 1: It does not present a clean edge. It is surrounded
• 46:01
  Speaker 1: by a circumplanetary disk of estimated radius up to 0.444 AU,
• 46:06
  Speaker 1: a disk that in our own solar system would stretch
• 46:09
  Speaker 1: nearly halfway to Jupiter from the Sun. Trying to measure
• 46:12
  Speaker 1: the planet inside that structure from 353 light-years away is
• 46:17
  Speaker 1: like trying to measure the size of a campfire ember
• 46:20
  Speaker 1: by looking at the glow of the smoke around it.
• 46:23
  Speaker 1: What the range of estimates tells you, then, is not
• 46:25
  Speaker 1: that astronomers are uncertain in some embarrassing way. It tells
• 46:29
  Speaker 1: you that HD10 is genuinely a different kind of object
• 46:36
  Speaker 1: than the thousands of exoplanets whose properties sit in neat
• 46:39
  Speaker 1: tables with small error bars. The honest answer about how
• 46:43
  Speaker 1: big HD10 actually is depends on questions that nobody has
• 46:50
  Speaker 1: yet been able to fully answer. At some point in
• 46:53
  Speaker 1: a forming solar system, a line gets crossed. Below that line,
• 46:57
  Speaker 1: you have a planet. Above it, something stranger. The object
• 47:01
  Speaker 1: is no longer just collecting gas and growing heavy. It
• 47:05
  Speaker 1: is hot enough, dense enough, and massive enough to start
• 47:08
  Speaker 1: fusing its own fuel. Not hydrogen the way a full
• 47:11
  Speaker 1: star does, but deuterium, a heavier form of hydrogen that
• 47:15
  Speaker 1: ignites at lower temperatures and pressures. That process makes the
• 47:19
  Speaker 1: object briefly luminous in its own right. It behaves, in
• 47:23
  Speaker 1: some meaningful physical sense, more like a failed star than
• 47:27
  Speaker 1: like a planet. Astronomers call these objects brown dwarfs. The
• 47:31
  Speaker 1: threshold where planetary physics gives way to brown dwarf physics
• 47:35
  Speaker 1: sits at roughly 13 times the mass of Jupiter. That
• 47:38
  Speaker 1: number is not arbitrary. It comes from the minimum conditions
• 47:42
  Speaker 1: needed to trigger deuterium fusion in an object's core. Below
• 47:45
  Speaker 1: 13 Jupiter masses, the pressure and temperature at the center
• 47:48
  Speaker 1: of a gas giant never reach the ignition point. The
• 47:51
  Speaker 1: object just sits there, slowly contracting, radiating away the heat
• 47:56
  Speaker 1: left over from its formation. Above 13 Jupiter masses, something
• 48:00
  Speaker 1: different kicks in. The core compresses hard enough that deuterium
• 48:03
  Speaker 1: begins to fuse, releasing energy, generating radiation, acting in ways
• 48:08
  Speaker 1: that no planet in our solar system has ever acted.
• 48:11
  Speaker 1: The boundary is imprecise at the edges. Deuterium fusion is
• 48:14
  Speaker 1: not a clean-on-off switch, but 13 Jupiter masses is the
• 48:17
  Speaker 1: number the field has converged on as a working dividing line.
• 48:21
  Speaker 1: Now consider what this means for HD10, 0546b. The mass
• 48:27
  Speaker 1: estimates for this object span a range so wide that
• 48:30
  Speaker 1: the dividing line between planet and brown dwarf falls somewhere
• 48:33
  Speaker 1: in the middle of it. In 2019, researchers running numerical
• 48:37
  Speaker 1: simulations of the relationship between the planet, its circumplanetary disk.
• 48:41
  Speaker 1: The surrounding circumstellar disk came back with an upper limit
• 48:45
  Speaker 1: of just 1.65 Jupiter masses. That would make HD 10,0546 b,
• 48:48
  Speaker 1: a fairly typical gas giant. Other estimates, working from infrared
• 48:56
  Speaker 1: photometry and hot start formation models, have placed the mass
• 48:59
  Speaker 1: around 8 to 15 Jupiter masses. That range straddles the
• 49:03
  Speaker 1: line directly. At 8 Jupiter masses.
• 49:06
  Speaker 2: It is a planet.
• 49:07
  Speaker 1: At 15, it might not be. And a 2017 study
• 49:11
  Speaker 1: that tried to account for the extreme reddening of the
• 49:14
  Speaker 1: object and the contaminating sign. All of the circumplanetary disk
• 49:18
  Speaker 1: settled on a mass closer to 25 Jupiter masses. That
• 49:22
  Speaker 1: lands firmly on the brown dwarf side of the boundary.
• 49:25
  Speaker 1: Three different approaches. Three very different answers. The classification of
• 49:30
  Speaker 1: the object changes depending on which one you trust. Then
• 49:34
  Speaker 1: there are the ALMA observations. Radio telescopes operating at millimeter
• 49:38
  Speaker 1: wavelengths can probe the structure of dust disks in ways
• 49:41
  Speaker 1: that infrared imaging cannot. When ALMA turned its attention toward
• 49:45
  Speaker 1: the HD 100546 system, it picked up a point source
• 49:49
  Speaker 1: embedded in the disk. The mass implied by those measurements
• 49:53
  Speaker 1: was not 1.65 Jupiter masses. It was not 25. The
• 49:58
  Speaker 1: ALMA data suggested a mass somewhere between 33 and 77
• 50:00
  Speaker 1: Jupiter masses. That range does not just cross the planet-brown
• 50:05
  Speaker 1: dwarf boundary, it clears it completely and then keeps going,
• 50:09
  Speaker 1: reaching into territory where some astronomers would not call the
• 50:12
  Speaker 1: object a brown dwarf so much as a very low-mass
• 50:15
  Speaker 1: stellar companion. An object at 77 Jupiter masses is approaching
• 50:19
  Speaker 1: the lower end of what can sustain hydrogen fusion. So
• 50:22
  Speaker 1: depending on which tell, a scope you believe, HD 10,
• 50:25
  Speaker 1: 0546 b, is either a modest.
• 50:26
  Speaker 2: Gas giant.
• 50:32
  Speaker 1: Or something that shares more physics with a dim star
• 50:34
  Speaker 1: than with Jupiter. The ALMA measurements are contested. Several researchers
• 50:39
  Speaker 1: have pointed out that the point source detected at that
• 50:41
  Speaker 1: position could be explained by a feature of the disk itself,
• 50:45
  Speaker 1: a bright region of scattered light or a density asymmetry
• 50:49
  Speaker 1: that happens to concentrate emission at one location. The disk
• 50:52
  Speaker 1: around HD 100054-6 is complicated. It has spiral arms, asymmetries,
• 51:00
  Speaker 1: and clumps of material that can mimic the signal of
• 51:02
  Speaker 1: a compact object. This does not mean the ALMA detection
• 51:06
  Speaker 1: is wrong. It means the detection is not clean enough
• 51:09
  Speaker 1: to settle the question on its own. The scientific community's
• 51:12
  Speaker 1: current position is cautious. The ALMA result exists. It is
• 51:17
  Speaker 1: taken seriously. But it is not accepted as definitive proof
• 51:21
  Speaker 1: that HD10-0546b is a brown dwarf. The debate remains open.
• 51:28
  Speaker 1: Why does any of this matter? Names are not science.
• 51:32
  Speaker 1: Calling something a planet or a brown dwarf does not
• 51:34
  Speaker 1: change what it is. But the classification carries real physical meaning,
• 51:39
  Speaker 1: because brown dwarfs and planets do not form the same way.
• 51:42
  Speaker 2: Planets grow.
• 51:44
  Speaker 1: They start as small concentrations of solid material or gas
• 51:47
  Speaker 1: in a disk. They accumulate mass over time through accretion,
• 51:51
  Speaker 1: sweeping up what the disk feeds them. The process is
• 51:54
  Speaker 1: slow and depends on the availability of material. Brown dwarfs,
• 51:58
  Speaker 1: on the other hand, form more like stars do.
• 52:01
  Speaker 2: They collapse.
• 52:02
  Speaker 1: A region of a molecular cloud or a disk becomes
• 52:05
  Speaker 1: gravitationally unstable and contracts rapidly, assembling most of its mass
• 52:10
  Speaker 1: in a short burst rather than building up grain by grain.
• 52:14
  Speaker 1: The two processes leave different signatures in the resulting object.
• 52:19
  Speaker 1: In its internal structure, its composition its relationship to the
• 52:23
  Speaker 1: disk around it. So when you ask whether HD 100546b
• 52:30
  Speaker 1: is a planet or a brown dwarf, you are really
• 52:33
  Speaker 1: asking how it came to exist. You are asking what
• 52:37
  Speaker 1: physics wrote its origin story. This is why the mass
• 52:40
  Speaker 1: question is not just a measurement problem. It is a
• 52:43
  Speaker 1: formation problem. If HD 100546b truly has a mass of 1.65
• 52:47
  Speaker 1: Jupiter masses, it almost certainly formed through accretion. Pulling in
• 52:56
  Speaker 1: material from the circumstellar disk over millions of years, if
• 53:01
  Speaker 1: it has a mass of 25 Jupiter masses or more,
• 53:04
  Speaker 1: disk instability becomes far more plausible. A runaway gravitational collapse
• 53:09
  Speaker 1: in the outer disk that assembled the bulk of the
• 53:11
  Speaker 1: object quickly without needing a long slow accretion history. The
• 53:16
  Speaker 1: two scenarios produce objects that look somewhat similar from the outside,
• 53:20
  Speaker 1: but arrived at their current state through completely different routes.
• 53:24
  Speaker 1: Getting the mass right is the only way to know
• 53:26
  Speaker 1: which story is true. What makes HD 10546b such a
• 53:32
  Speaker 1: frustrating and fascinating case is that the mass estimates are
• 53:35
  Speaker 1: not clustered around the boundary with just a little uncertainty
• 53:39
  Speaker 1: on either side. The spread runs from below 2 Jupiter
• 53:42
  Speaker 1: masses to above 70. That is not measurement noise around
• 53:45
  Speaker 1: a central value. That is a fundamental ambiguity about what
• 53:49
  Speaker 1: kind of object this is. No other known exoplanet candidate
• 53:53
  Speaker 1: has an estimated mass range that spans such wildly different
• 53:56
  Speaker 1: physical regimes. From undisputed gas giant all the way to
• 54:01
  Speaker 1: near stellar companion, with contested detections at every point along
• 54:05
  Speaker 1: the way, where exactly HD 100546b sits relative to that
• 54:11
  Speaker 1: line is a question the data has not yet settled.
• 54:15
  Speaker 1: The gap between the different estimates is wider than in
• 54:18
  Speaker 1: almost any other object in the catalogue of known exoplanets.
• 54:22
  Speaker 1: HD 100546b is not the only suspicious object in this system.
• 54:28
  Speaker 1: While astronomers were wrestling with the size and mass and
• 54:31
  Speaker 1: classification of the giant sitting at 53 AUW, a separate
• 54:36
  Speaker 1: argument was quietly developing about something much closer to the star,
• 54:40
  Speaker 1: something inside the dust cavity, something that, if real, changes
• 54:45
  Speaker 1: the entire picture of what is happening in this system.
• 54:48
  Speaker 1: Buried within 10 to 15 AU of HD 10, 0546
• 54:52
  Speaker 1: is a second candidate planet designated HD 10, 0546 C.
• 55:00
  Speaker 1: And the debate over whether it actually exists has been
• 55:02
  Speaker 1: running for over a decade with no clean resolution. The
• 55:05
  Speaker 1: way HD 10, 0546 C was first flagged is worth
• 55:10
  Speaker 1: understanding because it tells you something important about how hard
• 55:14
  Speaker 1: this kind of detection actually is. Nobody saw it directly.
• 55:18
  Speaker 1: What astronomers noticed instead was the behavior of carbon monoxide
• 55:22
  Speaker 1: gas in the inner disk. Carbon monoxide emits light at
• 55:25
  Speaker 1: very specific infrared wavelengths when it is warm enough and
• 55:28
  Speaker 1: dense enough, and the inner disk of HD1000546 has a
• 55:34
  Speaker 1: detectable signature of this emission. That alone is not surprising.
• 55:38
  Speaker 1: What was surprising was that the signature moved. Over years
• 55:42
  Speaker 1: of observation, The peak of that emission shifted back and
• 55:45
  Speaker 1: forth in a pattern that matched what you would expect
• 55:48
  Speaker 1: if a massive orbiting object were dragging the inner disk
• 55:51
  Speaker 1: gas around with it. The signal was not steady. It
• 55:55
  Speaker 1: was time variable, wobbling on a time scale consistent with
• 55:58
  Speaker 1: an orbit at roughly 10 to 15 AU from the star.
• 56:02
  Speaker 1: This is an indirect detection method. You are not seeing
• 56:06
  Speaker 1: the planet. You are seeing what the planet is doing
• 56:09
  Speaker 1: to the gas around it. In the same way you
• 56:11
  Speaker 1: might know a boat passed through a harbor, not because
• 56:14
  Speaker 1: you saw the boat, but because you saw the wake.
• 56:17
  Speaker 1: The spectroscopic signal is the wake. The planet, if it exists,
• 56:22
  Speaker 1: is somewhere in the fog. What would HD10-0546c look like
• 56:28
  Speaker 1: if it is there? The predictions are striking. A planet
• 56:32
  Speaker 1: at this location, in a disk this rich, would be
• 56:35
  Speaker 1: actively accreting material at a rapid rate. Rapidly accreting planets glow.
• 56:40
  Speaker 1: They are hot, bright at infrared wavelengths, and surrounded by
• 56:44
  Speaker 1: their own circumplanetary disk. For HD 100546C, that circumplanetary disk
• 56:52
  Speaker 1: has been estimated to extend roughly 0.1 AU in radius,
• 56:56
  Speaker 1: which is small compared to the sprawling structure around HD 100546B,
• 57:03
  Speaker 1: but still substantial. The accretion rate implied by some models
• 57:07
  Speaker 1: would make this inner planet unusually luminous for its mass.
• 57:10
  Speaker 1: bright enough that it should have shown up in direct
• 57:12
  Speaker 1: imaging by now. The fact that it has not is
• 57:15
  Speaker 1: part of what makes this detection so contested. There is
• 57:19
  Speaker 1: more evidence though, and some of it is harder to dismiss.
• 57:22
  Speaker 1: Sulfur monoxide. This molecule does not survive easily in a
• 57:26
  Speaker 1: protoplanetary disk. It breaks apart quickly unless something is actively
• 57:30
  Speaker 1: generating it. In the HD 100546 disk, sulfur monoxide has
• 57:37
  Speaker 1: been detected. and the most natural explanation for its presence
• 57:40
  Speaker 1: is shock waves. When a massive planet plows through the
• 57:44
  Speaker 1: gas in a disk, it drives a bow shock, compressing
• 57:47
  Speaker 1: and heating the gas ahead of it and on its flanks.
• 57:50
  Speaker 1: Those shock waves can trigger exactly the chemistry needed to
• 57:53
  Speaker 1: produce sulfur monoxide in detectable quantities. The detection does not
• 57:57
  Speaker 1: prove that HD100546C exists, but it does indicate that something
• 58:03
  Speaker 1: is disturbing the disk gas violently enough to rewrite its chemistry.
• 58:08
  Speaker 1: That takes a lot of mass. So why is the
• 58:10
  Speaker 1: detection contested? Because protoplanetary disks are not smooth, passive structures.
• 58:16
  Speaker 1: They have their own dynamics, their own turbulence, their own
• 58:19
  Speaker 1: chemical gradients. The carbon monoxide emission pattern that looks like
• 58:24
  Speaker 1: an orbiting planet could, in principle, be explained by the
• 58:28
  Speaker 1: geometry of the disk itself, by spiral density waves, by
• 58:32
  Speaker 1: temperature gradients in the inner region.
• 58:35
  Speaker 2: Any number of.
• 58:36
  Speaker 1: Processes that mimic the signature of an orbiting object without
• 58:39
  Speaker 1: requiring one. Scattered light data, which should in theory reveal
• 58:43
  Speaker 1: the disk structure clearly enough to confirm or deny the
• 58:46
  Speaker 1: planet's presence, has given contradictory results depending on who is
• 58:51
  Speaker 1: analysing it and what model assumptions they are using. Currie
• 58:55
  Speaker 1: and collaborators identified what they believed was a point source
• 58:58
  Speaker 1: in 2015. Later studies looked at the same data and
• 59:02
  Speaker 1: argued the feature could be a weakly polarized disk artifact.
• 59:06
  Speaker 1: The signal is right at the edge of what current
• 59:08
  Speaker 1: instruments can reliably distinguish from background structure. This is not
• 59:12
  Speaker 1: an unusual situation in exoplanet science. At the detection frontier,
• 59:17
  Speaker 1: almost everything is ambiguous. But the ambiguity here is particularly
• 59:21
  Speaker 1: frustrating because the stakes are so high. If HD10, 0546C
• 59:25
  Speaker 1: is real, It is not just a second planet. It
• 59:31
  Speaker 1: is a second forming planet. A second world actively assembling
• 59:35
  Speaker 1: itself from disk material at the same moment in time
• 59:38
  Speaker 1: as HD.
• 59:41
  Speaker 2: 100546b.
• 59:42
  Speaker 1: The system would then be hosting two massive gas giants,
• 59:45
  Speaker 1: each surrounded by its own circumplanetary disk, each still accreting,
• 59:50
  Speaker 1: each still growing, simultaneously. That has never been clearly observed
• 59:54
  Speaker 1: anywhere else. The theoretical models say it should happen. Simulations
• 59:59
  Speaker 1: of protoplanetary disk evolution have long suggested that massive disks
• 1:00:03
  Speaker 1: around intermediate-mass stars should be capable of producing multivariate planets
• 1:00:08
  Speaker 1: in parallel, not sequentially. But watching it happen, in real time,
• 1:00:13
  Speaker 1: in the same system, with the disks still intact around
• 1:00:16
  Speaker 1: both objects, would be something genuinely new. HD 10-0546c, if confirmed,
• 1:00:25
  Speaker 1: would also help explain the inner cavity. The cleared region
• 1:00:28
  Speaker 1: inside roughly 13 AU requires something to have swept it. HD10-0546b,
• 1:00:36
  Speaker 1: sitting at 53 AU, is far too distant to have
• 1:00:39
  Speaker 1: done this through its own gravity alone. A second planet
• 1:00:42
  Speaker 1: orbiting within the cavity, carving its orbital lane clean as
• 1:00:45
  Speaker 1: it goes, would account for the gap in a much
• 1:00:48
  Speaker 1: more natural way. The cavity and the planet would then
• 1:00:51
  Speaker 1: be telling the same story, one in absence and one
• 1:00:54
  Speaker 1: in signal, pointing at each other across the disk. For now,
• 1:00:58
  Speaker 1: HD 100546C remains a candidate. The evidence is suggestive, the
• 1:01:06
  Speaker 1: chemistry is pointing in the right direction, and the models
• 1:01:09
  Speaker 1: expect something to be there. But suggestive is not confirmed,
• 1:01:14
  Speaker 1: and the disk is doing its best to keep the
• 1:01:16
  Speaker 1: answer hidden. If both planets are real, The HD 100546
• 1:01:22
  Speaker 1: system would be one of the only places in the
• 1:01:25
  Speaker 1: known universe where two massive planets can be observed forming simultaneously,
• 1:01:30
  Speaker 1: side by side in the same disk. One of the
• 1:01:33
  Speaker 1: clearest pieces of evidence for what is happening inside the
• 1:01:36
  Speaker 1: HD 100546 system cannot be seen directly. There is no
• 1:01:42
  Speaker 1: point of light, no infrared glow, no spectroscopic fingerprint to chase.
• 1:01:47
  Speaker 1: What astronomers found instead was an absence, a hole, a
• 1:01:52
  Speaker 1: region of the disk where material that should exist simply
• 1:01:55
  Speaker 1: does not. The shape of that hole turns out to
• 1:01:58
  Speaker 1: tell you almost as much as seeing the planet itself would.
• 1:02:01
  Speaker 1: To understand why that matters, you need to know what
• 1:02:04
  Speaker 1: a transition disk actually is. Most young stars are surrounded
• 1:02:08
  Speaker 1: by protoplanetary disks that look more or less continuous. A
• 1:02:12
  Speaker 1: flat rotating structure of gas and dust extending from very
• 1:02:15
  Speaker 1: close to the star out to hundreds of astronomical units.
• 1:02:20
  Speaker 1: Denser in some places, thinner in others, but essentially unbroken.
• 1:02:24
  Speaker 1: A transition disk is different. A transition disk has a gap,
• 1:02:29
  Speaker 1: a cleared inner region where the material has been scooped away.
• 1:02:33
  Speaker 1: What amounts to a hole in the center of the
• 1:02:35
  Speaker 1: disk with the denser outer disk sitting further out, separated
• 1:02:39
  Speaker 1: from the star by a lane of near empty space.
• 1:02:42
  Speaker 1: Astronomers started noticing these structures decades ago, and for a
• 1:02:46
  Speaker 1: long time the explanation was not obvious. Why would a
• 1:02:50
  Speaker 1: disk develop a hole? What could remove material from the
• 1:02:53
  Speaker 1: inner region while leaving the outer disk intact? The most
• 1:02:57
  Speaker 1: compelling answer, the one that is held up best under scrutiny,
• 1:03:01
  Speaker 1: is that a.
• 1:03:01
  Speaker 2: Planet did it.
• 1:03:02
  Speaker 1: Here is how that works. When a planet forms inside
• 1:03:06
  Speaker 1: a disk, it does not sit passively in its orbit.
• 1:03:09
  Speaker 1: It is massive, and mass means gravity. And gravity means
• 1:03:14
  Speaker 1: it is constantly reaching into the surrounding material. As the
• 1:03:17
  Speaker 1: planet moves along its orbital path, it pulls nearby gas
• 1:03:21
  Speaker 1: and dust toward itself. Some of that material falls directly
• 1:03:24
  Speaker 1: onto the planet, adding to its mass. Some of it
• 1:03:28
  Speaker 1: gets captured into orbit around the planet, feeding a circumplanetary disk.
• 1:03:32
  Speaker 1: And some of it, the material that comes close enough
• 1:03:35
  Speaker 1: to be disturbed, but not close enough to be captured,
• 1:03:38
  Speaker 1: gets flung outward. kicked into higher orbits by the gravitational interaction.
• 1:03:43
  Speaker 1: Over time, this process clears a lane. The planet sweeps
• 1:03:47
  Speaker 1: its neighborhood clean, opening a gap in the disk that
• 1:03:51
  Speaker 1: widens as the planet grows. The bigger the planet, the
• 1:03:55
  Speaker 1: more gravitational reach it has, and the wider the gap
• 1:03:59
  Speaker 1: it can carve. In the HD 100546 system, the gap
• 1:04:01
  Speaker 1: is not subtle. The inner disk is essentially cleared from
• 1:04:07
  Speaker 1: about 0.2 AU all the way out to roughly 13 AU.
• 1:04:12
  Speaker 1: That is an enormous empty region. To put that in perspective,
• 1:04:16
  Speaker 1: 13 AU is roughly the orbital distance of Saturn from
• 1:04:19
  Speaker 1: our Sun. Everything inside that radius in the HD100546 disk
• 1:04:25
  Speaker 1: is close to empty. Then at 13 AU, the disk
• 1:04:29
  Speaker 1: picks back up. The dense outer disk extends from there
• 1:04:32
  Speaker 1: out to around 300 AU. That is where HD10-0546b lives
• 1:04:38
  Speaker 1: at approximately 53 AU, still embedded in all that material,
• 1:04:43
  Speaker 1: still growing. So what you have is a star, then
• 1:04:46
  Speaker 1: a thin inner region, then a vast cleared cavity, then
• 1:04:50
  Speaker 1: a wall of material marking the edge of the outer disc,
• 1:04:53
  Speaker 1: then the planet sitting further out in that outer disc,
• 1:04:57
  Speaker 1: dragging in everything around it. The evidence that this cavity
• 1:05:00
  Speaker 1: is real comes from multiple directions. Direct optical imaging confirmed it.
• 1:05:05
  Speaker 1: Infrared observations confirmed it. The Hubble Space Telescope captured scattered
• 1:05:10
  Speaker 1: light images of the disk that showed the inner region
• 1:05:13
  Speaker 1: clearly depleted compared to what disk models predict for an
• 1:05:16
  Speaker 1: unperturbed system. The spectral energy distribution of the system, that
• 1:05:21
  Speaker 1: is basically a record of how much light the disk
• 1:05:24
  Speaker 1: emits at different wavelengths, shows a clear deficit at the
• 1:05:27
  Speaker 1: wavelengths associated with warm inner disk material. Warm dust close
• 1:05:32
  Speaker 1: to the star radiates at specific infrared wavelengths. In HD 100546,
• 1:05:39
  Speaker 1: that signal is missing, suppressed far below what you would
• 1:05:42
  Speaker 1: expect from a continuous disk. That suppression is the spectral
• 1:05:46
  Speaker 1: fingerprint of a gap. Astronomers classify systems with exactly this
• 1:05:51
  Speaker 1: kind of signature as transition disks. HD 100546 is one
• 1:05:58
  Speaker 1: of the clearest examples of the type known What makes
• 1:06:01
  Speaker 1: this particularly interesting is what the inner cavity implies about
• 1:06:05
  Speaker 1: timing and process. A gap this wide, this clean, does
• 1:06:10
  Speaker 1: not open overnight. Carving out 13 AU of disk material
• 1:06:15
  Speaker 1: takes millions of years of continuous gravitational work. The fact
• 1:06:19
  Speaker 1: that the cavity exists in a system that is only
• 1:06:22
  Speaker 1: about 10 million years old tells you that whatever created
• 1:06:26
  Speaker 1: it started early. The leading candidate has always been H.D. 100546C,
• 1:06:31
  Speaker 1: the suspected inner companion, sitting somewhere in that 10 to
• 1:06:37
  Speaker 1: 15 AU range. A massive planet at that distance, still young,
• 1:06:42
  Speaker 1: still accreting rapidly, would be exactly the kind of object
• 1:06:46
  Speaker 1: capable of pushing the disk material outward and maintaining a
• 1:06:49
  Speaker 1: wide cleared zone. Some researchers think the cavity boundary itself
• 1:06:54
  Speaker 1: marks roughly where HD100546C sits, that the plan ET has
• 1:07:01
  Speaker 1: essentially bulldozed a ring around its orbit. The inner edge
• 1:07:05
  Speaker 1: of the outer disk at 13 AU is the edge
• 1:07:08
  Speaker 1: of the planet's gravitational reach. There is something almost disorienting
• 1:07:11
  Speaker 1: about this kind of planet detection. You are not looking
• 1:07:14
  Speaker 1: at the planet. You are looking at the space where
• 1:07:17
  Speaker 1: the planet has been. You are reading its gravitational history
• 1:07:20
  Speaker 1: written into the structure of the disk. The planet has
• 1:07:23
  Speaker 1: rearranged the material around it so thoroughly and so persistently
• 1:07:27
  Speaker 1: that even if you could not detect the planet directly,
• 1:07:30
  Speaker 1: Even if the signal were completely buried in noise, the
• 1:07:33
  Speaker 1: disk itself would be telling you something is there. The
• 1:07:36
  Speaker 1: cavity is not a flaw in the data.
• 1:07:38
  Speaker 2: It is data.
• 1:07:40
  Speaker 1: It is the most durable record of the planet's existence
• 1:07:42
  Speaker 1: that the system has produced, carved slowly and continuously over
• 1:07:46
  Speaker 1: millions of years of orbital motion. And that is the
• 1:07:50
  Speaker 1: thing worth sitting with. The disk gaps. The cleared inner holes.
• 1:07:55
  Speaker 1: The transition disk classifications. These are not incidental features astronomers
• 1:08:00
  Speaker 1: note on their way to finding the actual planet.
• 1:08:03
  Speaker 2: They are detections.
• 1:08:04
  Speaker 1: They are the shadow of something massive cast across the
• 1:08:07
  Speaker 1: structure of the disk. A planet announces itself not just
• 1:08:11
  Speaker 1: by appearing in your data, but by the absence it
• 1:08:14
  Speaker 1: carves out of the disk around it. When the Hubble
• 1:08:16
  Speaker 1: Space Telescope turned its coronagraph on HD 100546, blocking the
• 1:08:20
  Speaker 1: direct light of the star, What appeared in the disk
• 1:08:26
  Speaker 1: was not the smooth, featureless ring that simple disk models predicted.
• 1:08:30
  Speaker 1: What appeared instead were arms, curving, sweeping structures of compressed
• 1:08:35
  Speaker 1: gas and dust, winding outward from the inner disk in
• 1:08:38
  Speaker 1: patterns that had no business being there if the disk
• 1:08:41
  Speaker 1: was simply sitting still and undisturbed. Astronomers looking at those
• 1:08:45
  Speaker 1: images knew immediately what they were seeing. The disk was
• 1:08:48
  Speaker 1: being stirred by something inside it. To understand why spiral
• 1:08:52
  Speaker 1: arms in a protoplanetary disk are such a big deal,
• 1:08:55
  Speaker 1: You have to understand what they actually are. They are
• 1:08:58
  Speaker 1: not decorative. They are not random. A spiral arm in
• 1:09:02
  Speaker 1: a disk is a density wave, a region where the
• 1:09:04
  Speaker 1: disk material has been gravitationally squeezed into a band of
• 1:09:08
  Speaker 1: higher concentration. Think about what happens when you drag your
• 1:09:11
  Speaker 1: finger in a slow circle through shallow water. The water
• 1:09:15
  Speaker 1: piles up ahead of your finger and thins out behind it.
• 1:09:19
  Speaker 1: A massive planet doing the same thing inside a rotating
• 1:09:21
  Speaker 1: disk of gas and dust creates the same kind of pileup,
• 1:09:25
  Speaker 1: except the pileup does not stay in one place. Because
• 1:09:28
  Speaker 1: the disk is rotating, that compressed ridge gets smeared out
• 1:09:31
  Speaker 1: over time into a spiral shape, winding outward from the
• 1:09:35
  Speaker 1: planet's orbit like.
• 1:09:36
  Speaker 2: A wave frozen in stone.
• 1:09:38
  Speaker 1: That is a spiral arm, and because the disk keeps
• 1:09:40
  Speaker 1: rotating and the planet keeps.
• 1:09:42
  Speaker 2: Pulling, the arm persists. It does not dissolve.
• 1:09:46
  Speaker 1: It maintains its shape as long as the planet is
• 1:09:48
  Speaker 1: there maintaining the gravitational nudge that created it. This is
• 1:09:52
  Speaker 1: what makes spiral arms so much more compelling as evidence
• 1:09:55
  Speaker 1: than a faint point of light in an image. A
• 1:09:57
  Speaker 1: point source can be questioned. Maybe it is a background star.
• 1:10:01
  Speaker 1: Maybe it is an artifact from the telescope optics. Maybe
• 1:10:04
  Speaker 1: it is a knot of unusually hot dust that has
• 1:10:06
  Speaker 1: nothing to do with a planet. Those explanations have been
• 1:10:09
  Speaker 1: floated before in the history of exoplanet imaging, and sometimes
• 1:10:13
  Speaker 1: they have turned out to be correct. But a spiral
• 1:10:16
  Speaker 1: arm is a large-scale coherent structure. It extends across tens
• 1:10:20
  Speaker 1: of AU of disk material. It has a specific geometry,
• 1:10:24
  Speaker 1: a specific pitch angle, a specific winding direction. Explaining it
• 1:10:28
  Speaker 1: without invoking a massive perturber requires inventing something even stranger,
• 1:10:34
  Speaker 1: and astronomers are reluctant to invent things they do not need.
• 1:10:38
  Speaker 1: The pitch angle of a spiral arm, meaning how tightly
• 1:10:41
  Speaker 1: or loosely it winds around the star, carries direct information
• 1:10:45
  Speaker 1: about the mass of whatever is causing it. A more
• 1:10:48
  Speaker 1: massive planet produces a more loosely wound arm, with a
• 1:10:52
  Speaker 1: larger pitch angle. A less massive planet winds the arm
• 1:10:56
  Speaker 1: more tightly. This is not a rough intuition. There is
• 1:10:59
  Speaker 1: actual mathematical machinery behind it. Researchers can take a spiral
• 1:11:04
  Speaker 1: arm's measured geometry and work backward through the equations to
• 1:11:08
  Speaker 1: put constraints on the mass of the unseen perturber. It
• 1:11:12
  Speaker 1: is indirect. It comes with uncertainties, but it is real physics,
• 1:11:17
  Speaker 1: and it gives you a number you would not otherwise have.
• 1:11:22
  Speaker 1: The spiral structures in the HD10-0546 disk show an M
• 1:11:27
  Speaker 1: equals 2 symmetry, which means there are two main spiral
• 1:11:31
  Speaker 1: arms arranged roughly opposite each other, like the arms of
• 1:11:34
  Speaker 1: a two-bladed propeller. This particular pattern is significant. When a
• 1:11:38
  Speaker 1: planet drives spiral density waves in a disk, The response
• 1:11:42
  Speaker 1: tends to produce two symmetric arms under many conditions. The
• 1:11:45
  Speaker 1: fact that HD10, 0546's disc, shows this two-armed structure is
• 1:11:51
  Speaker 1: consistent with a single massive perturbing body driving the whole pattern.
• 1:11:55
  Speaker 1: The arms are not perfectly symmetric, which tells you the
• 1:11:58
  Speaker 1: situation is more complicated than a simple idealized model. But
• 1:12:02
  Speaker 1: the basic shape is there. And the basic shape.
• 1:12:05
  Speaker 2: Points at something real.
• 1:12:06
  Speaker 1: What do these arms tell us about HD10, 0546b specifically?
• 1:12:12
  Speaker 1: The spiral morphology is consistent with a massive body orbiting
• 1:12:15
  Speaker 1: at a large distance from the star, which matches what
• 1:12:18
  Speaker 1: direct imaging suggests about the planet's position at around 53 AU.
• 1:12:23
  Speaker 1: A planet orbiting that far out would be expected to
• 1:12:26
  Speaker 1: drive wide, loosely wound spirals covering a significant fraction of
• 1:12:30
  Speaker 1: the disk's total extent. That is roughly what the observations show.
• 1:12:35
  Speaker 1: The arms sweep outward from the region of the disc
• 1:12:37
  Speaker 1: where the planet sits and trace back toward it, like
• 1:12:40
  Speaker 1: brushstrokes that all originate from the same hand. There is
• 1:12:43
  Speaker 1: something almost satisfying about this kind of evidence, because it
• 1:12:47
  Speaker 1: is not fragile. The disc has to reorganize its structure
• 1:12:50
  Speaker 1: to produce these arms. Gas and dust across billions of
• 1:12:54
  Speaker 1: kilometers of space has to compress and align. That does
• 1:12:57
  Speaker 1: not happen because of a noise spike in a detector
• 1:13:00
  Speaker 1: or a smudge on a lens. It happens because something
• 1:13:03
  Speaker 1: with serious mass is pulling on the disk, consistently, over
• 1:13:07
  Speaker 1: timescales long enough for the pattern to develop and stabilize.
• 1:13:10
  Speaker 1: When you see spiral arms this clean and this large,
• 1:13:13
  Speaker 1: you are not looking at an artifact. You are looking
• 1:13:16
  Speaker 1: at a gravitational signature written across the face of an
• 1:13:19
  Speaker 1: entire solar system. This also helps explain why astronomers spent
• 1:13:24
  Speaker 1: years targeting HD 10, 0546, even before they had confident
• 1:13:30
  Speaker 1: direct imaging of the planet itself. The spiral arms were
• 1:13:34
  Speaker 1: already there in earlier observations. They were already suggesting that
• 1:13:38
  Speaker 1: something massive was embedded in the disk. The arms were
• 1:13:42
  Speaker 1: the accusation. The direct imaging was the attempt to find
• 1:13:46
  Speaker 1: the accused. And even in the years when the direct
• 1:13:49
  Speaker 1: imaging data was contested and uncertain, the spiral arms kept
• 1:13:53
  Speaker 1: pointing at the same location, the same region of the disk,
• 1:13:57
  Speaker 1: the same patch of sky where the planet was eventually found.
• 1:14:01
  Speaker 1: They did not waver. They did not go away. They
• 1:14:04
  Speaker 1: just kept winding outward from that spot, persistent and patient
• 1:14:09
  Speaker 1: and completely indifferent to the debates happening among the astronomers
• 1:14:12
  Speaker 1: studying them. The disk of HD 100546 is not just
• 1:14:18
  Speaker 1: a background feature against which the planet happens to exist.
• 1:14:21
  Speaker 1: It is a record of everything the planet has done
• 1:14:24
  Speaker 1: to the material around it, carved in gas and dust
• 1:14:27
  Speaker 1: across a region larger than our entire solar system.
• 1:14:30
  Speaker 2: A disk does not.
• 1:14:31
  Speaker 1: Develop spiral arms by accident, and every spiral arm is
• 1:14:35
  Speaker 1: pointing back at the thing that drew it. The planet
• 1:14:38
  Speaker 1: HD 100546 b has been sitting in plain sight for
• 1:14:42
  Speaker 1: as long as humans have had telescopes, and we still
• 1:14:45
  Speaker 1: cannot see it clearly. That sounds like it should not
• 1:14:48
  Speaker 1: be possible.
• 1:14:49
  Speaker 2: The system is 353 light years away.
• 1:14:50
  Speaker 1: Yes, But by astronomical standards that is practically next door.
• 1:14:57
  Speaker 1: We have imaged galaxies billions of light years distant. We
• 1:15:01
  Speaker 1: have mapped the surface of Pluto. We sent a spacecraft
• 1:15:04
  Speaker 1: to the edge of the solar system and watched it cross.
• 1:15:07
  Speaker 1: So why is a planet forming around a nearby star
• 1:15:10
  Speaker 1: still giving us so much trouble? The answer comes down
• 1:15:13
  Speaker 1: to a problem so basic it is almost embarrassing. The
• 1:15:16
  Speaker 1: star is too bright. Not a little too bright. Millions
• 1:15:21
  Speaker 1: of times too bright. When you point a telescope at HD10, 0546,
• 1:15:27
  Speaker 1: the star floods the detector with light the way a
• 1:15:30
  Speaker 1: flashlight floods your eyes in.
• 1:15:32
  Speaker 2: A dark room.
• 1:15:33
  Speaker 1: Everything near it disappears into the glare. A forming planet
• 1:15:37
  Speaker 1: like HD10, 0546b, even one that is genuinely enormous and
• 1:15:43
  Speaker 1: genuinely hot, is putting out a signal that the star
• 1:15:46
  Speaker 1: buries completely. You are trying to hear a whisper next
• 1:15:49
  Speaker 1: to a jet engine. This contrast problem is the fundamental
• 1:15:53
  Speaker 1: obstacle in direct imaging of exoplanets. When astronomers use indirect
• 1:15:58
  Speaker 1: methods to find planets, they sidestep the contrast issue entirely.
• 1:16:02
  Speaker 1: The transit method watches for the tiny dip in starlight
• 1:16:05
  Speaker 1: when a planet crosses in front of the disk of
• 1:16:07
  Speaker 1: the star. The radial velocity method measures the wobble that
• 1:16:11
  Speaker 1: a planet's gravity introduces into the star's motion. Neither method
• 1:16:15
  Speaker 1: requires you to actually see the planet. Direct imaging does.
• 1:16:19
  Speaker 1: You have to detect the photons coming from the planet itself,
• 1:16:23
  Speaker 1: either reflected starlight or the planet's own thermal glow. And
• 1:16:27
  Speaker 1: you have to find those photons in the same patch
• 1:16:29
  Speaker 1: of sky where the star is pouring out light that
• 1:16:32
  Speaker 1: is anywhere from a million to ten billion times more intense.
• 1:16:36
  Speaker 1: Most of the time, it simply cannot be done. The
• 1:16:39
  Speaker 1: handful of planets that have been directly imaged are mostly young, massive,
• 1:16:43
  Speaker 1: and orbiting far enough from their stars that the angular
• 1:16:46
  Speaker 1: separation is wide enough to work with. The solution astronomers
• 1:16:49
  Speaker 1: reached for is called coronagraphic imaging. The concept goes back
• 1:16:53
  Speaker 1: to a solar physicist named Bernard Lyot, who in 1931
• 1:16:58
  Speaker 1: built an instrument that could block the direct light of
• 1:17:00
  Speaker 1: the Sun to study the solar corona, the faint outer
• 1:17:03
  Speaker 1: atmosphere that is normally invisible next to the Sun's blinding disk.
• 1:17:07
  Speaker 1: The same principle applies to telescopes looking at other stars.
• 1:17:11
  Speaker 1: A physical mask inside the instrument, called a coronagraph, is
• 1:17:15
  Speaker 1: positioned to block the direct light from the star, leaving
• 1:17:18
  Speaker 1: the surrounding region visible. It is like holding your thumb
• 1:17:21
  Speaker 1: up to block a headlight, so you can see the
• 1:17:23
  Speaker 1: road around it. When you remove that central glare, veined
• 1:17:27
  Speaker 1: structures close to the star become visible for the first time.
• 1:17:30
  Speaker 1: This is how the spiral arms in HD 100546's disc
• 1:17:35
  Speaker 1: were revealed in Hubble images. This is how the disc
• 1:17:38
  Speaker 1: itself was mapped in detail. And this is the tool
• 1:17:41
  Speaker 1: that gave astronomers their first look at the region where HD.
• 1:17:46
  Speaker 2: 100546b lives.
• 1:17:48
  Speaker 1: But coronagraphic imaging has limits. It does not remove all
• 1:17:51
  Speaker 1: the star's light. Some of it diffracts around the mask
• 1:17:55
  Speaker 1: and scatters across the field of view. Some leaks through imperfections.
• 1:17:59
  Speaker 2: In the optics.
• 1:18:00
  Speaker 1: The result is a residual halo of starlight that still
• 1:18:03
  Speaker 1: contaminates the region you are trying to observe. For most
• 1:18:07
  Speaker 1: exoplanet targets, this residual halo is the main enemy. For HD10, 0546b,
• 1:18:15
  Speaker 1: there is a second enemy layered on top of it,
• 1:18:17
  Speaker 1: and this one is peculiar to this system. The planet
• 1:18:20
  Speaker 1: is embedded inside the protoplanetary disk. That disk is full
• 1:18:24
  Speaker 1: of dust and gas. That dust scatters light from the
• 1:18:28
  Speaker 1: star in all directions, and it scatters it throughout the
• 1:18:31
  Speaker 1: same spatial region where the planet is trying to announce itself.
• 1:18:35
  Speaker 1: The background is not quiet, it is bright, structured and complex.
• 1:18:40
  Speaker 1: Finding the planet's signal on top of all of that
• 1:18:43
  Speaker 1: is like trying to spot a single candle burning inside
• 1:18:46
  Speaker 1: a bonfire. There is a third problem on top of
• 1:18:49
  Speaker 1: those two. HD10 is surrounded by its own circumplanetary disk,
• 1:18:56
  Speaker 1: a smaller structure of gas and dust that the planet
• 1:18:59
  Speaker 1: is actively pulling in. This circumplanetary disk is warm, it
• 1:19:03
  Speaker 1: glows in the infrared, and when your telescope collects photons
• 1:19:07
  Speaker 1: from the direction of HD10, What arrives is a tangled
• 1:19:13
  Speaker 1: mixture of light from the planet's own thermal emission, light
• 1:19:16
  Speaker 1: from the circumplanetary disk, light from the surrounding protoplanetary disk
• 1:19:21
  Speaker 1: that happens to be in the same line of sight,
• 1:19:23
  Speaker 1: and residual scattered starlight from the coronagraph. These signals do
• 1:19:27
  Speaker 1: not come with labels. You cannot look at a photon
• 1:19:30
  Speaker 1: and ask where it came from. You get a single number,
• 1:19:34
  Speaker 1: the total flux arriving from that patch of sky. and
• 1:19:37
  Speaker 1: you have to use models to guess how much of
• 1:19:39
  Speaker 1: that flux belongs to each component.
• 1:19:41
  Speaker 2: This is where the wildly.
• 1:19:42
  Speaker 1: Different estimates for HD100546b' s properties come from.
• 1:19:45
  Speaker 2: The radius estimates range from 3.4 to 6.9 Jupiter radii.
• 1:19:48
  Speaker 1: The temperature estimates range from around 932 Kelvin to 2630 Kelvin.
• 1:19:50
  Speaker 2: The mass estimates span from.
• 1:19:51
  Speaker 1: 1.65 to 25 Jupiter masses, with some studies pushing even higher.
• 1:20:06
  Speaker 1: These are not small uncertainties. In each case, the spread
• 1:20:09
  Speaker 1: reflects a genuine disagreement about how to model the mixed signal.
• 1:20:13
  Speaker 1: If you assume most of the infrared brightness is coming
• 1:20:16
  Speaker 1: from the circumplanetary disk, you infer a cooler, smaller planet underneath.
• 1:20:21
  Speaker 1: If you weight the contribution differently, the planet itself appears
• 1:20:24
  Speaker 1: hotter and larger. Both interpretations fit the data. Neither can
• 1:20:28
  Speaker 1: be ruled out with the instruments we currently have. Future
• 1:20:32
  Speaker 1: instruments are going to change this. The extremely large telescope,
• 1:20:36
  Speaker 1: currently under construction in Chile, will have a primary mirror
• 1:20:40
  Speaker 1: 39 meters across. That gives it angular resolution roughly 10
• 1:20:44
  Speaker 1: times sharper than existing ground-based telescopes.
• 1:20:48
  Speaker 2: It will be able to.
• 1:20:49
  Speaker 1: Spatially resolve the region around HD 100546b in ways that
• 1:20:55
  Speaker 1: are simply not possible today, separating the circumplanetary disk from
• 1:20:59
  Speaker 1: the planet at a physical scale small enough to actually
• 1:21:02
  Speaker 1: distinguish the two. Instead of receiving one blended signal from
• 1:21:06
  Speaker 1: the whole region, it will be able to look at
• 1:21:08
  Speaker 1: different parts of the system independently and measure each component
• 1:21:12
  Speaker 1: on its own terms. The James Webb Space Telescope is
• 1:21:16
  Speaker 1: also contributing, though differently, its infrared sensitivity and its stable
• 1:21:21
  Speaker 1: space-based vantage. Let it detect thermal emission from young planetary
• 1:21:27
  Speaker 1: systems at wavelengths that ground-based telescopes struggle with. These instruments
• 1:21:33
  Speaker 1: represent the first real chance astronomers have had to pull
• 1:21:36
  Speaker 1: the signal of HD 100546b apart from everything surrounding it.
• 1:21:43
  Speaker 1: The reason this matters is not just that we want
• 1:21:45
  Speaker 1: cleaner numbers, though we do. It is that every fundamental
• 1:21:49
  Speaker 1: question about this object depends on untangling that signal. Is
• 1:21:55
  Speaker 1: HD 100546b a planet or a brown dwarf? You cannot
• 1:22:02
  Speaker 1: answer that without knowing the mass. Is its radius genuinely anomalous,
• 1:22:06
  Speaker 1: breaking the theoretical maximum for gas giant sizes? You cannot
• 1:22:11
  Speaker 1: answer that without knowing how much of the apparent size
• 1:22:14
  Speaker 1: belongs to the planet and how much belongs to the
• 1:22:16
  Speaker 1: disk wrapped around it. Is it forming through core accretion
• 1:22:20
  Speaker 1: or disk instability? The answer partly depends on what the
• 1:22:24
  Speaker 1: planet actually is, which requires the measurements that are currently unavailable.
• 1:22:29
  Speaker 1: The tangle is not just observational inconvenience, it is the
• 1:22:33
  Speaker 1: reason every major question about this object is still open
• 1:22:37
  Speaker 1: more than a decade after its detection. Every observation of
• 1:22:41
  Speaker 1: HD10-0546b is a negotiation between what the instruments can actually
• 1:22:48
  Speaker 1: detect and what the disk and star are willing to
• 1:22:51
  Speaker 1: let through. The debate about how HD 100546b formed cuts
• 1:22:56
  Speaker 1: to the centre of one of the oldest arguments in
• 1:22:59
  Speaker 1: planetary science. There are two competing theories for how a
• 1:23:02
  Speaker 1: giant planet like this comes into existence, and they are
• 1:23:05
  Speaker 1: not minor variations on each other. They describe fundamentally different processes,
• 1:23:10
  Speaker 1: different timescales, different physical conditions, and for decades, astronomers have
• 1:23:16
  Speaker 1: argued about which one is actually responsible for the giant
• 1:23:19
  Speaker 1: planets we find scattered across the galaxy. HD10-0546b sits right
• 1:23:26
  Speaker 1: at the center of that argument. Not because it resolves it,
• 1:23:30
  Speaker 1: but because it makes both sides harder to dismiss. The
• 1:23:33
  Speaker 1: first theory is called core accretion. The basic idea is sequential.
• 1:23:38
  Speaker 1: A forming planet starts small. Dust grains in the disk
• 1:23:41
  Speaker 1: collide and stick together, building pebbles, then boulders, then something
• 1:23:45
  Speaker 1: larger still. Eventually, a solid core accumulates enough mass that
• 1:23:49
  Speaker 1: its gravity becomes significant. At that point, the core starts
• 1:23:53
  Speaker 1: pulling in gas from the surrounding disk, wrapping itself in
• 1:23:56
  Speaker 1: a growing hydrogen and helium envelope. The core does the
• 1:23:59
  Speaker 1: hard work first. The gas envelope comes second. This is
• 1:24:04
  Speaker 1: how most astronomers believe Jupiter formed, and it is supported
• 1:24:07
  Speaker 1: by the fact that Jupiter has a distinct dense core
• 1:24:10
  Speaker 1: beneath all that gas. The model has strong theoretical backing
• 1:24:13
  Speaker 1: and matches what we see in our own solar system
• 1:24:16
  Speaker 1: reasonably well. The planets at moderate distances from their stars
• 1:24:19
  Speaker 1: within may be 10 or 15 AU. The numbers generally work.
• 1:24:23
  Speaker 1: The problem is distance. At 53 AU from HD 10
• 1:24:28
  Speaker 1: core accretion runs into serious trouble. The disk at that
• 1:24:34
  Speaker 1: distance is cold. The material is spread thin. Dust grains
• 1:24:39
  Speaker 1: are moving slowly and collisions are rare. The timescale for
• 1:24:42
  Speaker 1: building a solid core large enough to trigger rapid gas
• 1:24:45
  Speaker 1: accretion is measured in tens of millions of years, maybe longer.
• 1:24:49
  Speaker 1: But the disk itself does not last that long. Protoplanetary
• 1:24:53
  Speaker 1: disks dissipate. The star's radiation and stellar wind gradually blow
• 1:24:57
  Speaker 1: the gas away. Most disks are gone within 5 to
• 1:25:01
  Speaker 1: 10 million years. HD 10, 0546, is already nearly 10
• 1:25:07
  Speaker 1: million years old. Under standard core accretion timelines, A planet
• 1:25:12
  Speaker 1: at 53 AU should not have had time to get started,
• 1:25:15
  Speaker 1: let alone reach the size HD10. 0546B appears to be.
• 1:25:21
  Speaker 1: The disk would vanish before the core finished forming. There
• 1:25:24
  Speaker 1: would be nothing left to accrete. This is not a
• 1:25:27
  Speaker 1: subtle problem. It is a timing catastrophe for core accretion
• 1:25:30
  Speaker 1: at this location. The second theory is disk instability, and
• 1:25:34
  Speaker 1: it sidesteps the timing problem entirely. The idea here is
• 1:25:38
  Speaker 1: direct collapse. If a region of the protoplanetary disk becomes
• 1:25:42
  Speaker 1: dense enough, gravity can cause it to collapse rapidly on itself,
• 1:25:46
  Speaker 1: skipping the slow core building phase altogether.
• 1:25:49
  Speaker 2: No solid core is required.
• 1:25:51
  Speaker 1: The disk simply fragments into a self-gravitating clump, and that
• 1:25:56
  Speaker 1: clump contracts and heats up into a gas giant. The
• 1:25:59
  Speaker 1: whole process can happen in thousands of years rather than millions.
• 1:26:03
  Speaker 1: At large orbital distances, where the disk is cold and
• 1:26:06
  Speaker 1: gravity has an easier time winning against thermal pressure, disk
• 1:26:10
  Speaker 1: instability becomes much more physically plausible. The conditions at 53 AU,
• 1:26:15
  Speaker 1: the very conditions that make core accretion so difficult, actually
• 1:26:19
  Speaker 1: make disk instability more likely. So on the face of it,
• 1:26:23
  Speaker 1: HD100546b looks like a disk instability planet. The distance is right,
• 1:26:30
  Speaker 1: the timing works, the disk around HD100546 is massive and extended.
• 1:26:37
  Speaker 1: exactly the kind of disk where gravitational instability can occur.
• 1:26:41
  Speaker 1: If you had to bet based purely on orbital distance,
• 1:26:44
  Speaker 1: disk instability wins. But then the mass estimates complicate everything.
• 1:26:49
  Speaker 1: One of the key predictions of disk instability is that
• 1:26:52
  Speaker 1: planets formed this way should be massive. Gravitational collapse tends
• 1:26:56
  Speaker 1: to produce objects in the range of several Jupiter masses
• 1:26:59
  Speaker 1: or more. Some of the mass estimates for HD 100546b
• 1:27:05
  Speaker 1: higher ones clustering around 15 to 25 Jupiter masses fit
• 1:27:09
  Speaker 1: this picture. A few estimates push even further into brown
• 1:27:13
  Speaker 1: dwarf territory but the 2019 estimate placing the mass as
• 1:27:17
  Speaker 1: low as 1.65 Jupiter masses is a different story entirely.
• 1:27:22
  Speaker 1: At that mass the object might be too light to
• 1:27:25
  Speaker 1: have formed through disk instability and if it really is
• 1:27:28
  Speaker 1: that small core accretion cannot be completely ruled out even
• 1:27:32
  Speaker 1: at this distance particularly if something accelerated the formation process
• 1:27:37
  Speaker 1: or if the core built up faster than standard models predict.
• 1:27:40
  Speaker 1: What this means in practice is that neither theory can
• 1:27:43
  Speaker 1: be cleanly confirmed or eliminated. The mass uncertainty is not
• 1:27:47
  Speaker 1: just a measurement inconvenience. It is the thing keeping this
• 1:27:50
  Speaker 1: question open. Here is what makes this genuinely remarkable though.
• 1:27:55
  Speaker 1: Every other way astronomers have argued about planet formation has
• 1:27:58
  Speaker 1: involved looking at finished planets and working backward. You look
• 1:28:02
  Speaker 1: at Jupiter's compositions. and try to infer what process produced it.
• 1:28:06
  Speaker 1: You look at the orbital architecture of an exoplanet system
• 1:28:09
  Speaker 1: and try to reverse engineer how it arrived at its
• 1:28:12
  Speaker 1: current configuration. It is like trying to understand how a
• 1:28:15
  Speaker 1: building was constructed by walking around the finished structure. You
• 1:28:19
  Speaker 1: can make educated guesses. You can look for clues in
• 1:28:22
  Speaker 1: the shape of the walls or the arrangement of the rooms.
• 1:28:25
  Speaker 1: But you were not there for the construction. The working
• 1:28:28
  Speaker 1: has been erased. HD 10.0546b is different. construction is still
• 1:28:34
  Speaker 1: happening the accretion rate is not historical it is current
• 1:28:39
  Speaker 1: the circumplanet disk surrounding the planet is not a relic,
• 1:28:42
  Speaker 1: it is active. The relationship between the growing planet and
• 1:28:45
  Speaker 1: the surrounding protoplanetary material is not something that has to
• 1:28:49
  Speaker 1: be inferred from fossils in the data. It is unfolding
• 1:28:53
  Speaker 1: right now, and telescopes are watching it. The structure of
• 1:28:56
  Speaker 1: the circumplanetary disk, the temperature profile, the rate at which
• 1:29:00
  Speaker 1: mass is flowing inward toward the planet, the way the
• 1:29:03
  Speaker 1: planet is carving its path through the outer disk, all
• 1:29:06
  Speaker 1: of this carries information that a mature planetary system simply
• 1:29:09
  Speaker 1: does not preserve. Once a planet finishes forming, the disk disperses,
• 1:29:14
  Speaker 1: the circumplanetary material is consumed or ejected, and the record
• 1:29:18
  Speaker 1: of how the planet was built gets overwritten by billion.
• 1:29:22
  Speaker 1: S of years of orbital evolution. The testimony disappears. What
• 1:29:27
  Speaker 1: HD100546b offers is the testimony before it disappears.
• 1:29:33
  Speaker 2: That is rare.
• 1:29:34
  Speaker 1: That might be unprecedented at this level of detail and
• 1:29:37
  Speaker 1: at this orbital distance. And whatever the final answer turns
• 1:29:40
  Speaker 1: out to be, whether it collapses the mass estimates toward
• 1:29:43
  Speaker 1: the low end and challenges disk instability, or pushes them
• 1:29:47
  Speaker 1: toward the high end and buries core accretion, the answer
• 1:29:50
  Speaker 1: will have been read directly from a planet that was
• 1:29:52
  Speaker 1: still in the process of answering the question. Every other
• 1:29:56
  Speaker 1: exoplanet we have studied is an answer without the working shown,
• 1:30:00
  Speaker 1: and HD 100546 b is the one place where we
• 1:30:05
  Speaker 1: might actually watch the solution being calculated in real time.
• 1:30:09
  Speaker 1: The circumplanetary disk around HD 100546 b is not just
• 1:30:14
  Speaker 1: a complication for astronomers trying to measure the planet, it
• 1:30:17
  Speaker 1: is also depending on how you look at it, the
• 1:30:20
  Speaker 1: beginning of an entire world-building project.
• 1:30:23
  Speaker 2: Because we have seen this.
• 1:30:24
  Speaker 1: Before, not around HD 100546, but around the planets in
• 1:30:30
  Speaker 1: our own backyard. When Jupiter and Saturn were young and
• 1:30:33
  Speaker 1: still accreting, they were each surrounded by their own miniature
• 1:30:37
  Speaker 1: disks of gas and dust, smaller versions of the protoplanetary
• 1:30:41
  Speaker 1: disks circling the Sun. Out of those disks came moons,
• 1:30:45
  Speaker 1: dozens of them, Some of the most remarkable objects in
• 1:30:48
  Speaker 1: the solar system. Io with its volcanic surface. Europa with
• 1:30:52
  Speaker 1: its liquid ocean buried under ice. Ganymede, larger than the
• 1:30:56
  Speaker 1: planet Mercury. Callisto, ancient and cratered and strange. Around Saturn,
• 1:31:01
  Speaker 1: the same story. Titan, with its thick nitrogen atmosphere and
• 1:31:05
  Speaker 1: liquid methane lakes. A world so alien that scientists have
• 1:31:09
  Speaker 1: debated whether its chemistry could sustain some exotic form of life.
• 1:31:14
  Speaker 2: All of those.
• 1:31:14
  Speaker 1: Moons came from circumplanetary disks, assembling themselves out of leftover
• 1:31:19
  Speaker 1: material the same way the planets assembled themselves out of
• 1:31:22
  Speaker 1: the disk around the Sun. So the question is almost unavoidable.
• 1:31:27
  Speaker 1: HD 100546b has its own circumplanetary disk right now.
• 1:31:33
  Speaker 2: What might come out of it?
• 1:31:35
  Speaker 1: What astronomers have been able to measure about that disk
• 1:31:37
  Speaker 1: is limited, and the numbers carry the same uncertainties that
• 1:31:41
  Speaker 1: plague everything else in this system. The estimated mass of
• 1:31:44
  Speaker 1: the circumplanetary disk comes in at around 1.44 Earth masses,
• 1:31:49
  Speaker 1: with a radius of up to roughly 0.44 astronomical units.
• 1:31:53
  Speaker 1: To put that in perspective, 0.44 AUU is almost half
• 1:31:58
  Speaker 1: the distance between Earth and the Sun. That is a
• 1:32:01
  Speaker 1: wide diffuse structure wrapping around a planet that is itself
• 1:32:05
  Speaker 1: still growing. The mass of 1.44 Earth masses might not
• 1:32:09
  Speaker 1: sound like much, but it does not take much to
• 1:32:12
  Speaker 1: build a moon Europa, for instance, has a mass of
• 1:32:15
  Speaker 1: about 0.015 Earth masses. Ganymede clocks in around 0.025. Even Titan,
• 1:32:23
  Speaker 1: the largest moon of Saturn, is only about 0.022 Earth masses.
• 1:32:28
  Speaker 1: A circumplanetary disk massing 1.44 Earths has in no, uh,
• 1:32:34
  Speaker 1: raw material to build dozens of moons the size of
• 1:32:37
  Speaker 1: the ones we already know. Whether that material actually clumps
• 1:32:41
  Speaker 1: together into moons before the disk disperses is a different question.
• 1:32:46
  Speaker 1: The disk has to survive long enough, and the conditions
• 1:32:49
  Speaker 1: have to cooperate. Here is where it gets complicated. The
• 1:32:53
  Speaker 1: environment around Henne D100546b right now is nothing like the
• 1:32:59
  Speaker 1: environment that produced Europa or Titan. The system is less
• 1:33:03
  Speaker 1: than 10 million years old. The star is still pouring
• 1:33:07
  Speaker 1: enormous amounts of radiation into the disk, The planet itself,
• 1:33:11
  Speaker 1: based on one study's estimate, may have an effective temperature
• 1:33:14
  Speaker 1: of around 2630 Kelvin. That is not a planet cooling
• 1:33:18
  Speaker 1: quietly in the outer dark. That is an object radiating
• 1:33:22
  Speaker 1: enormous amounts of energy in every direction. Any moon forming
• 1:33:26
  Speaker 1: close to HD 10, 0546b right now, would be sitting
• 1:33:32
  Speaker 1: inside an environment that makes the surface of Venus look temperate.
• 1:33:36
  Speaker 1: The heat alone would strip away any light volatile compounds
• 1:33:39
  Speaker 1: from the surfaces of forming moonlets nearby. Water ice could
• 1:33:43
  Speaker 1: not survive at close range. Organic chemistry would be under
• 1:33:47
  Speaker 1: assault from every direction. This is not a promising nursery.
• 1:33:51
  Speaker 1: At least not yet. But stars evolve. Systems cool. The
• 1:33:56
  Speaker 1: HD 10-0546 system will not always look like this. Over
• 1:34:01
  Speaker 1: millions of years the star will stabilize onto the main sequence.
• 1:34:05
  Speaker 1: its radiation output will settle and the planet will slowly
• 1:34:08
  Speaker 1: shed its formation heat, the circumplanetary disk will eventually dissipate.
• 1:34:14
  Speaker 1: Whatever moons have managed to form by then will be
• 1:34:17
  Speaker 1: left behind, orbiting a gas giant that has grown quieter
• 1:34:20
  Speaker 1: and colder than it is today. And at that point,
• 1:34:24
  Speaker 1: depending on where they ended up and how the system evolved,
• 1:34:27
  Speaker 1: some of those moons might find themselves in conditions that
• 1:34:30
  Speaker 1: are not immediately hostile to chemistry of the interesting kind.
• 1:34:34
  Speaker 1: The planet's own residual heat of formation could provide a
• 1:34:37
  Speaker 1: source of warmth that does not depend on proximity to
• 1:34:41
  Speaker 1: the star at all. Jupiter does this today. It radiates
• 1:34:45
  Speaker 1: about 1.7 times as much energy as it receives from
• 1:34:48
  Speaker 1: the Sun, leftover heat from its gravitational collapse billions of
• 1:34:52
  Speaker 1: years ago. A planet as massive as HD 100546b, forming
• 1:34:55
  Speaker 1: in a much more energetic environment, would likely retain significant
• 1:35:02
  Speaker 1: internal heat for a very long time. This is where
• 1:35:05
  Speaker 1: the speculation starts to run ahead of the evidence. Scientists
• 1:35:09
  Speaker 1: have raised the idea that moons forming around super-Jupiters at
• 1:35:12
  Speaker 1: wide orbital separations might have access to internal heat sources
• 1:35:16
  Speaker 1: that partially compensate for their distance from the star. A
• 1:35:20
  Speaker 1: moon in the right orbit could receive enough tidal heating,
• 1:35:23
  Speaker 1: driven by gravitational flexing from the massive planet below, to
• 1:35:26
  Speaker 1: maintain liquid water. Europa's ocean exists today not because Europa
• 1:35:31
  Speaker 1: is close to the sun, but because Jupiter's gravity continuously
• 1:35:35
  Speaker 1: squeezes and releases it, generating heat from friction in its interior.
• 1:35:39
  Speaker 1: That mechanism does not require a warm star. It requires
• 1:35:43
  Speaker 1: a massive planet and a moon in an elliptical orbit.
• 1:35:46
  Speaker 1: HD 10-0546 b, if it ends up with a system
• 1:35:51
  Speaker 1: of moons, will have plenty of gravitational muscle.
• 1:35:55
  Speaker 2: To work with.
• 1:35:56
  Speaker 1: None of this is a prediction. It would be wrong
• 1:35:58
  Speaker 1: to present any of it that way. The system is young,
• 1:36:01
  Speaker 1: the measurements are uncertain, the timescales involved stretch across hundreds
• 1:36:06
  Speaker 1: of millions of years, and the conditions that would actually
• 1:36:08
  Speaker 1: allow life to emerge anywhere involve factors astronomers cannot yet
• 1:36:12
  Speaker 1: evaluate for this system. What can be said is that
• 1:36:15
  Speaker 1: the ingredients are not obviously absent. A massive planet with
• 1:36:19
  Speaker 1: an active disk, enough raw material for moon formation, internal heat,
• 1:36:24
  Speaker 1: and the potential for tidal dynamics, those are not nothing
• 1:36:27
  Speaker 1: They are the same basic checklist that produced Europa, one
• 1:36:30
  Speaker 1: of the most seriously studied candidates for life beyond Earth.
• 1:36:34
  Speaker 1: The universe apparently has no objection to setting this up
• 1:36:37
  Speaker 1: more than once, whether anything could ever survive in the
• 1:36:40
  Speaker 1: distance of Sun. But in Sun, in many countries, they
• 1:36:44
  Speaker 1: were primarily has no objection to setting this up more
• 1:36:47
  Speaker 1: than once. Whether anything could ever survive in the derived
• 1:36:51
  Speaker 1: environment around a forming super Jupiter is a question that
• 1:36:54
  Speaker 1: belongs more to the future than to current science. But
• 1:36:58
  Speaker 1: the fact that the question can be asked at all
• 1:37:01
  Speaker 1: says something about how strange and varied the universe turns
• 1:37:04
  Speaker 1: out to be. About 130 light years away, in the
• 1:37:08
  Speaker 1: constellation Pegasus, there is a star called H. Our 8,799
• 1:37:13
  Speaker 1: that is surrounded by four giant planets, all of them
• 1:37:18
  Speaker 1: imaged directly, all of them orbiting at wide separations, all
• 1:37:22
  Speaker 1: of them larger than Jupiter. This is not a small thing.
• 1:37:26
  Speaker 1: Direct imaging of exoplanets is extraordinarily rare. Most of the
• 1:37:30
  Speaker 1: thousands of worlds in the exoplanet catalogue were found indirectly,
• 1:37:34
  Speaker 1: through wobbles, through shadows, through statistical inference. HR 8799 is
• 1:37:41
  Speaker 1: one of the only systems where you can point a telescope,
• 1:37:45
  Speaker 1: block the star's direct light, and actually see the planets themselves,
• 1:37:49
  Speaker 1: four of them. hanging in the disk like stones thrown
• 1:37:52
  Speaker 1: into a slow orbit. They were confirmed in 2008 and 2010,
• 1:37:56
  Speaker 1: and for a while, HR 8799 was the most dramatic
• 1:38:01
  Speaker 1: picture planetary science had ever produced. Four super-Jupiters, ranging from
• 1:38:07
  Speaker 1: roughly 5 to 10 Jupiter masses, orbiting an intermediate-mass star
• 1:38:11
  Speaker 1: at distances between about 15 and 70 AU wide spread out. Massive,
• 1:38:17
  Speaker 1: the kind of architecture that, when it was first imaged,
• 1:38:20
  Speaker 1: Nobody had a complete explanation for. Here is the question
• 1:38:24
  Speaker 1: that immediately followed. How did they get there?
• 1:38:27
  Speaker 2: Core accretion.
• 1:38:28
  Speaker 1: The slow patient process. of building a solid core and
• 1:38:32
  Speaker 1: then pulling in a gas envelope, struggles badly at large
• 1:38:35
  Speaker 1: orbital distances. The disk material is too cold, too sparse,
• 1:38:40
  Speaker 1: too slow moving for that process to work on the
• 1:38:42
  Speaker 1: timescales involved. Disk instability, the rapid gravitational collapse of a
• 1:38:47
  Speaker 1: dense disk region directly into a gas giant, handles the
• 1:38:51
  Speaker 1: large separations better. But even that raises further questions about
• 1:38:55
  Speaker 1: what the disk looked like before the planets formed, how
• 1:38:58
  Speaker 1: massive it was, what structures existed inside it.
• 1:39:03
  Speaker 2: The problem with.
• 1:39:05
  Speaker 1: HR 8799 is that by the time we found it,
• 1:39:08
  Speaker 1: the construction was already finished, the disk was largely gone,
• 1:39:12
  Speaker 1: the planets were done, what remained was the outcome, not
• 1:39:15
  Speaker 1: the process. That is exactly where HD10 0546 enters the picture.
• 1:39:22
  Speaker 1: Astronomers looking at HD 10, 0546 noticed immediately that the
• 1:39:28
  Speaker 1: two systems share a striking family resemblance. Both have intermediate
• 1:39:32
  Speaker 1: mass host stars. HR 8799 is about 1.5 solar masses.
• 1:39:35
  Speaker 1: HD 10, 0546 sits at roughly 2.4. Both host multiple
• 1:39:37
  Speaker 1: giant planets forming or formed at moderate to wide separations.
• 1:39:49
  Speaker 1: Both systems have planets that are super Jovian in character,
• 1:39:52
  Speaker 1: far more massive than anything in our own solar system.
• 1:39:56
  Speaker 1: The difference is age. HR 8799 is somewhere between 30
• 1:39:59
  Speaker 1: and 60 million years old, depending on which estimate you trust.
• 1:40:01
  Speaker 1: HD 100546 is less than 10 million years old. The
• 1:40:04
  Speaker 1: disk around HD 100546 is still there, thick and active.
• 1:40:17
  Speaker 1: full of gas and dust and ongoing accretion. The planets
• 1:40:21
  Speaker 1: inside it are still growing. Nothing is finished. What this
• 1:40:24
  Speaker 1: suggests is not complicated, but it is genuinely striking. HD
• 1:40:30
  Speaker 1: 100546 might be an earlier version of HR 8799. Not
• 1:40:36
  Speaker 1: a copy, not a guaranteed twin, but a plausible earlier
• 1:40:40
  Speaker 1: snapshot of the same kind of system.
• 1:40:43
  Speaker 2: When astronomers look at.
• 1:40:46
  Speaker 1: HR 8799 today, they are seeing the end state of
• 1:40:49
  Speaker 1: a process that may have looked tens of millions of
• 1:40:52
  Speaker 1: years ago, something like what HD 100546 looks.
• 1:40:58
  Speaker 2: Like right now.
• 1:40:59
  Speaker 1: And when they look at HD 100546 right now, they
• 1:41:03
  Speaker 1: may be watching the early chapters of a story whose
• 1:41:06
  Speaker 1: final pages already exist, 130 light years away in a
• 1:41:11
  Speaker 1: different constellation. This is the kind of connection that gets
• 1:41:15
  Speaker 1: astronomers genuinely excited, and for good reason. The usual problem
• 1:41:20
  Speaker 1: in planetary science is that you find planets after the fact.
• 1:41:24
  Speaker 1: The disc is gone. The accretion has stopped. You measure
• 1:41:27
  Speaker 1: the mass, the orbit, the composition, and you work backward,
• 1:41:32
  Speaker 1: trying to reconstruct a formation history from the fingerprints left behind.
• 1:41:36
  Speaker 1: It is like trying to understand how a building was
• 1:41:39
  Speaker 1: constructed by studying the finished structure. You can make educated guesses,
• 1:41:44
  Speaker 1: you can infer a lot, but you are always missing
• 1:41:47
  Speaker 1: the actual process. HD100546 is the construction site. The scaffolding
• 1:41:55
  Speaker 1: is still up, the material is still moving. If the
• 1:41:59
  Speaker 1: HD100546 system really is an evolutionary predecessor to something like HR,
• 1:42:05
  Speaker 1: 8799 Then studying it gives astronomers what they have almost
• 1:42:11
  Speaker 1: never had before. A way to connect the formation process
• 1:42:15
  Speaker 1: to the outcome directly.
• 1:42:17
  Speaker 2: Not inferred.
• 1:42:19
  Speaker 1: Observed. The accretion rates. The disk structure. The circumplanetary disks.
• 1:42:26
  Speaker 1: The gap clearing mechanics. All of that is visible in
• 1:42:29
  Speaker 1: HD 100546 in ways that it is simply not visible
• 1:42:34
  Speaker 1: in mature systems. Now, there is an important caveat here.
• 1:42:38
  Speaker 1: and it would be a mistake to gloss over it.
• 1:42:41
  Speaker 1: This is a plausible evolutionary connection, not a confirmed one.
• 1:42:45
  Speaker 1: HD 100546 might develop into a system that looks nothing
• 1:42:51
  Speaker 1: like HR. 8799, the planets inside it might migrate inward,
• 1:42:57
  Speaker 1: or scatter each other into unstable orbits, or the disk
• 1:43:00
  Speaker 1: might dissipate in ways that halt the growth of the
• 1:43:03
  Speaker 1: outer planet before it matures. The comparison is a hypothesis.
• 1:43:07
  Speaker 1: grounded in real similarities, supported by the logic of stellar
• 1:43:11
  Speaker 1: aging and planet formation theory, but not yet proven in
• 1:43:15
  Speaker 1: any direct sense. The universe does not owe us a
• 1:43:18
  Speaker 1: clean narrative. What makes the comparison scientifically valuable is precisely
• 1:43:23
  Speaker 1: that it is testable.
• 1:43:25
  Speaker 2: If HD 100546.
• 1:43:25
  Speaker 1: Follows the trajectory that the HR 8799 parallel suggests, specific
• 1:43:29
  Speaker 1: predictions follow. The planets should finish accreting within the next
• 1:43:37
  Speaker 1: few million years. The disks should clear from the inside out.
• 1:43:41
  Speaker 1: The circumplanetary disks should collapse into moon systems. The spiral
• 1:43:45
  Speaker 1: arms should fade as the gravitational perturbations settle. Future telescopes
• 1:43:50
  Speaker 1: watching this system over the coming decades might actually catch
• 1:43:53
  Speaker 1: some of these transitions in progress, which would either confirm
• 1:43:56
  Speaker 1: or break the comparison against real observation.
• 1:44:00
  Speaker 2: HR 8799 has four planets.
• 1:44:00
  Speaker 1: 0546 has at least one confirmed protoplanet and evidence of
• 1:44:10
  Speaker 1: one or two more. The numbers are not far apart.
• 1:44:13
  Speaker 1: The orbital distances are not far apart. The stellar masses
• 1:44:17
  Speaker 1: are not far apart. The gap between the two systems
• 1:44:20
  Speaker 1: is almost entirely a matter of time. Tens of millions
• 1:44:24
  Speaker 1: of years of further evolution separating the younger system from
• 1:44:27
  Speaker 1: the older one. The planets of HR 8799 have already
• 1:44:29
  Speaker 1: become what the planets of HD1 and the distance between
• 1:44:39
  Speaker 1: those two pictures is the distance between watching a structure
• 1:44:42
  Speaker 1: being built and finding it already standing. Most of what
• 1:44:46
  Speaker 1: we do not yet know about HD 100546b is not
• 1:44:51
  Speaker 1: permanently unknowable. That distinction matters. There is a version of
• 1:44:55
  Speaker 1: this story where the uncertainties pile up forever, where the
• 1:44:58
  Speaker 1: planet stays blurry and contested and half-defined for the rest
• 1:45:02
  Speaker 1: of human history. that is not what is actually happening.
• 1:45:05
  Speaker 1: The reason we cannot answer basic questions about HD100546B right
• 1:45:11
  Speaker 1: now is not that the answers are hidden beyond reach.
• 1:45:15
  Speaker 1: It is that the instruments we have been using were
• 1:45:17
  Speaker 1: not built for something this complicated, this embedded, this young.
• 1:45:21
  Speaker 1: The next generation of instruments was, and several of them
• 1:45:24
  Speaker 1: are either already running or close enough to operational that
• 1:45:28
  Speaker 1: specific observations of this system are already being planned. Start
• 1:45:32
  Speaker 1: with what is already in orbit. The James Webb Space
• 1:45:35
  Speaker 1: Telescope launched in late 2021 and has been collecting data
• 1:45:39
  Speaker 1: on young disk systems ever since. What it brought to
• 1:45:42
  Speaker 1: this problem is not just sensitivity, though the sensitivity is extraordinary.
• 1:45:47
  Speaker 1: It brought access to infrared wavelengths that previous space telescopes
• 1:45:51
  Speaker 1: could not reach cleanly. Wavelengths where the thermal emission from
• 1:45:55
  Speaker 1: warm dust and warm gas glows brightest. Young protoplanetary disks
• 1:46:00
  Speaker 1: are full of exactly that material. For systems like HD10-0546,
• 1:46:06
  Speaker 1: this matters enormously. The disk and the planet both radiate
• 1:46:10
  Speaker 1: in the infrared. That is part of why they are
• 1:46:13
  Speaker 1: so difficult to untangle from the ground. Webb observes from
• 1:46:16
  Speaker 1: above the atmosphere, which eliminates the blurring and the infrared
• 1:46:20
  Speaker 1: absorption that Earth's air introduces. It can hold a target
• 1:46:24
  Speaker 1: steady and accumulate signal in ways that ground-based observatories cannot match.
• 1:46:30
  Speaker 1: Early observations of young disk systems with Webb have already
• 1:46:34
  Speaker 1: revealed structure that simply was not visible before. Gaps and
• 1:46:38
  Speaker 1: rings and asymmetries that show up cleanly in the mid-infrared
• 1:46:42
  Speaker 1: in ways that previous instruments could only hint at. For
• 1:46:45
  Speaker 1: HD10-0546 specifically, Webb has the potential to probe the thermal
• 1:46:51
  Speaker 1: emission from the circumplanetary disk around HD10-0546b with a precision
• 1:46:58
  Speaker 1: that no prior telescope achieved. the circumplanetary disk is warm.
• 1:47:03
  Speaker 1: It is actively accreting material, which generates heat, which generates
• 1:47:07
  Speaker 1: infrared radiation.
• 1:47:09
  Speaker 2: Webb can see that radiation. The question is.
• 1:47:12
  Speaker 1: Whether the signal from the circumplanetary disk can be cleanly
• 1:47:15
  Speaker 1: distinguished from the surrounding protoplanetary disk.
• 1:47:18
  Speaker 2: That is also warm, also glowing, and much larger.
• 1:47:22
  Speaker 1: This is where the specific design of Webb's instruments becomes important.
• 1:47:27
  Speaker 1: its mid-infrared camera can resolve structure at separations that are
• 1:47:31
  Speaker 1: relevant to this system.
• 1:47:32
  Speaker 2: Whether it can.
• 1:47:33
  Speaker 1: Fully separate the planet's signal from the disk background at
• 1:47:37
  Speaker 1: 53 AU from the star is still being tested, but
• 1:47:41
  Speaker 1: early results from analogous systems suggest it can get closer
• 1:47:44
  Speaker 1: to an answer than anything that came before.
• 1:47:47
  Speaker 2: Now look at what is being built on the ground.
• 1:47:49
  Speaker 1: The extremely large telescope, currently under construction in the Atacama
• 1:47:53
  Speaker 1: Desert in Chile, will have a primary mirror 39 meters across.
• 1:47:58
  Speaker 1: To put that in context, the largest optical telescope currently
• 1:48:02
  Speaker 1: operating has a mirror.
• 1:48:03
  Speaker 2: Around 10 meters.
• 1:48:05
  Speaker 1: The jump from 10 to 39 meters is not merely incremental.
• 1:48:09
  Speaker 1: The angular resolution scales with mirror diameter. That means the
• 1:48:13
  Speaker 1: extremely large telescope will be able to resolve features roughly
• 1:48:16
  Speaker 1: four times finer than the best current instruments. At wavelengths
• 1:48:21
  Speaker 1: where protoplanetary disk science actually happens, four times finer resolution,
• 1:48:26
  Speaker 1: pointed at a system like HD 100546, means the difference
• 1:48:32
  Speaker 1: between seeing a blurry extended blob of light and resolving
• 1:48:36
  Speaker 1: structure within the circumplanetary disk itself What would resolving that
• 1:48:40
  Speaker 1: structure actually tell you?
• 1:48:42
  Speaker 2: Quite a lot.
• 1:48:43
  Speaker 1: If the circumplanetary disk has internal rings or gaps, those
• 1:48:47
  Speaker 1: features would indicate that material is being concentrated into discrete orbits.
• 1:48:52
  Speaker 1: That is the first step toward forming moons. We saw
• 1:48:55
  Speaker 1: this process unfold when ALMA revealed ring structures in protoplanetary
• 1:48:59
  Speaker 1: disks around other young stars. The interpretation was immediate. Something
• 1:49:04
  Speaker 1: is sweeping those gaps, and that something is likely a
• 1:49:07
  Speaker 1: forming planet. The same logic applies inside a circumplanetary disk.
• 1:49:12
  Speaker 1: Rings in the circumplanetary disk around HD10-0546b would be a
• 1:49:18
  Speaker 1: signal that moon formation is underway. Nobody can see that
• 1:49:22
  Speaker 1: structure yet. The extremely large telescope might be able to.
• 1:49:26
  Speaker 1: There is also the question of HD10-0546c, the inner companion candidate,
• 1:49:33
  Speaker 1: sitting somewhere between 10 and 15 AU from the stars.
• 1:49:36
  Speaker 1: has been detected through carbon monoxide spectroscopy and can test
• 1:49:41
  Speaker 1: it ever since. The core of the dispute is that
• 1:49:44
  Speaker 1: the spectroscopic signal is consistent with an orbiting planet but
• 1:49:48
  Speaker 1: could also be explained by disk gas moving in non-planetary ways.
• 1:49:53
  Speaker 1: Direct imaging would settle it. The extremely large telescope, combined
• 1:49:57
  Speaker 1: with its suite of adaptive optics instruments designed specifically to
• 1:50:01
  Speaker 1: suppress starlight, may be capable of imaging a companion at
• 1:50:05
  Speaker 1: that separation around a star at this distance. If HD10
• 1:50:12
  Speaker 1: shows up as a resolved point source in direct imaging,
• 1:50:15
  Speaker 1: the debate ends. If it does not, that tells you
• 1:50:18
  Speaker 1: something too. The mass question is also within reach. Right
• 1:50:22
  Speaker 1: now the estimates for HD10 mass range from under 2
• 1:50:28
  Speaker 1: Jupiter masses to over 20, depending on the model. That
• 1:50:33
  Speaker 1: range exists because the planet's light and its disk's light
• 1:50:36
  Speaker 1: arrive at Earth mixed together. The proportions of that mixture
• 1:50:40
  Speaker 1: are uncertain. Better mid-infrared spectroscopy from Webb, combined with high-resolution
• 1:50:46
  Speaker 1: imaging from the extremely large telescope, could constrain the temperature
• 1:50:49
  Speaker 1: and luminosity of the planet independently of the disk in
• 1:50:53
  Speaker 1: ways that current data cannot. When you pin down the
• 1:50:56
  Speaker 1: luminosity of a young forming object and combine it with
• 1:50:59
  Speaker 1: models of how much energy a planet of a given
• 1:51:02
  Speaker 1: mass would be releasing during accretion at this age, you
• 1:51:05
  Speaker 1: can narrow the mass estimate dramatically, not to a single
• 1:51:08
  Speaker 1: number immediately, but to a range that is physically meaningful
• 1:51:12
  Speaker 1: rather than a range that spans an entire order of magnitude.
• 1:51:16
  Speaker 1: The radius uncertainty follows from the same problem. The apparent
• 1:51:20
  Speaker 1: size of HD100546b is inflated by the surrounding circumplanetary disk.
• 1:51:27
  Speaker 1: Until you can separate them in the data, you are
• 1:51:30
  Speaker 1: always measuring the combined system rather than the planet. Resolved
• 1:51:33
  Speaker 1: imaging that distinguishes the planet's point source from the disk's
• 1:51:36
  Speaker 1: extended emission would let astronomers assign each component its own brightness.
• 1:51:41
  Speaker 1: From there, the physical radius of the planet becomes a
• 1:51:44
  Speaker 1: tractable calculation. Within a decade, some of the most basic
• 1:51:48
  Speaker 1: facts about this planet, its true mass, its actual radius,
• 1:51:52
  Speaker 1: whether it is being orbited by smaller forming worlds, may
• 1:51:56
  Speaker 1: finally have answers that do not depend on which model
• 1:51:58
  Speaker 1: you believe. Step back from the numbers and look at
• 1:52:01
  Speaker 1: what the discovery of HD 100546b actually means for how
• 1:52:07
  Speaker 1: astronomers think about planets, because the real question underneath all
• 1:52:10
  Speaker 1: of this has never been about one object in the
• 1:52:13
  Speaker 1: constellation Musca. It has been about us, about where we fit,
• 1:52:17
  Speaker 1: about whether the solar system we grew up thinking of
• 1:52:19
  Speaker 1: as normal is actually normal at all. For most of
• 1:52:23
  Speaker 1: human history, we had no way to check. We had
• 1:52:25
  Speaker 1: one planetary system, eight planets, a belt of rocks, a
• 1:52:29
  Speaker 1: cloud of comets at the edge. That was the entire
• 1:52:32
  Speaker 1: sample size. Astronomers built models around it, made assumptions from it,
• 1:52:37
  Speaker 1: drew conclusions about how planets in general must form, and
• 1:52:40
  Speaker 1: where they must end up. The model worked because there
• 1:52:43
  Speaker 1: was nothing to contradict it. Then we started finding other systems,
• 1:52:47
  Speaker 1: and the contradictions came fast. Hot Jupiters showed up first.
• 1:52:51
  Speaker 1: Gas giants the size of Jupiter, crammed into orbits closer
• 1:52:55
  Speaker 1: to their stars than Mercury is to our sun. Nothing
• 1:52:58
  Speaker 1: in the standard model predicted them. Then came systems with
• 1:53:01
  Speaker 1: multiple super earths stacked in tight orbits, inside where Venus
• 1:53:05
  Speaker 1: would be. Then systems where the planets had no relationship
• 1:53:09
  Speaker 1: to the ecliptic plane at all, orbiting tilted, retrograde, chaotic.
• 1:53:14
  Speaker 1: Each new discovery nudged the picture further from what the
• 1:53:16
  Speaker 1: textbooks described. Our solar system started to look less like
• 1:53:20
  Speaker 1: the template, and more like one possibility among many. HD
• 1:53:24
  Speaker 1: 10 0 5 4 6 B nudges that picture again.
• 1:53:29
  Speaker 2: Hard.
• 1:53:30
  Speaker 1: If a planet can assemble itself at 53 AU from
• 1:53:33
  Speaker 1: its star, that far out, in a disk that's sparse,
• 1:53:36
  Speaker 1: through a process that's fast, then the outer reaches of
• 1:53:39
  Speaker 1: solar systems are not the quiet, half-empty places our models assumed.
• 1:53:44
  Speaker 1: They are construction zones, and the things being built out
• 1:53:47
  Speaker 1: there can be enormous, bigger than anything in our solar systems.
• 1:53:51
  Speaker 1: bigger apparently than the theoretical ceiling anyone calculated before this
• 1:53:55
  Speaker 1: object turned up in the data. What does that mean
• 1:53:58
  Speaker 1: for our own outer solar system? Neptune sits at about
• 1:54:02
  Speaker 1: 30 AU, Uranus at 19. Neither of them approaches Jupiter
• 1:54:06
  Speaker 1: in mass, let alone anything like what is growing at
• 1:54:10
  Speaker 1: 53 AU in the HD 100546 system. The outer planets
• 1:54:15
  Speaker 1: in our solar system are, by the standards of what
• 1:54:18
  Speaker 1: we now know is.
• 1:54:19
  Speaker 2: Possible, modest. Restrained.
• 1:54:22
  Speaker 1: Whatever process built our system either lacked the material, lacked
• 1:54:25
  Speaker 1: the time, or operated under conditions that kept things from
• 1:54:29
  Speaker 1: getting as extreme as they apparently can get. Whether that
• 1:54:32
  Speaker 1: makes our system unusual, or just one outcome among several
• 1:54:36
  Speaker 1: reasonable ones is a question nobody can answer yet, but
• 1:54:40
  Speaker 1: here is what we can say. Systems like H, are 8799,
• 1:54:46
  Speaker 1: with four massive giants orbiting far from their star.
• 1:54:49
  Speaker 2: Are real. They exist. We have imaged them directly.
• 1:54:54
  Speaker 1: And if HD 100546 is an early version of something
• 1:54:58
  Speaker 1: like that, then wide-orbit super-Jupiters are not freaks of nature.
• 1:55:03
  Speaker 1: They are a category, a recognizable outcome of disk instability,
• 1:55:07
  Speaker 1: working on a young massive disk around a young intermediate-mass star.
• 1:55:11
  Speaker 1: Our solar system, with its comparatively small outer planets and
• 1:55:16
  Speaker 1: its rocky inner worlds, might be the quieter result of
• 1:55:19
  Speaker 1: a process.
• 1:55:19
  Speaker 2: That often goes louder.
• 1:55:21
  Speaker 1: There is something else worth sitting with. We only found
• 1:55:24
  Speaker 1: HD 100546b because we happened to look at the right
• 1:55:30
  Speaker 1: star during an extremely narrow window. This planet is detectable
• 1:55:34
  Speaker 1: right now because it is still forming, still hot from accretion,
• 1:55:38
  Speaker 1: still wrapped in its circumplanetary disk, still pouring out infrared
• 1:55:42
  Speaker 1: radiation that our instruments can pick up from 353 light
• 1:55:45
  Speaker 1: years away. In a few tens of millions of years,
• 1:55:49
  Speaker 1: when the disk has cleared and the accretion has slowed
• 1:55:52
  Speaker 1: and the planet has settled into whatever it is going
• 1:55:55
  Speaker 1: to be, it will be dramatically harder to find.
• 1:55:58
  Speaker 2: It will cool. Its disk will dissipate.
• 1:56:01
  Speaker 1: The infrared excess that flags its presence will fade. The
• 1:56:05
  Speaker 1: window closes. How many systems like this have we missed?
• 1:56:09
  Speaker 1: How many forming super-Jupiters are out there right now in
• 1:56:12
  Speaker 1: disks around young stars we have not pointed our best
• 1:56:15
  Speaker 1: instruments at yet? The honest answer is that we do
• 1:56:18
  Speaker 1: not know, and we have no reliable way to estimate.
• 1:56:22
  Speaker 1: Every detection of a forming planet requires catching that system
• 1:56:25
  Speaker 1: in its first few million years before the evidence disappears.
• 1:56:29
  Speaker 1: The universe is old. Most solar systems finished forming billions
• 1:56:33
  Speaker 1: of years ago. The ones we can catch in the
• 1:56:36
  Speaker 1: act are the young ones, and young stars are rarer
• 1:56:39
  Speaker 1: and more distant on average than the middle-aged stars we
• 1:56:41
  Speaker 1: tend to study. We may be seeing a tiny fraction
• 1:56:44
  Speaker 1: of what happens during planet formation, and assuming it is
• 1:56:47
  Speaker 1: the whole picture. That is what makes the HD 100546
• 1:56:53
  Speaker 1: system so valuable to the people who study it. Not
• 1:56:56
  Speaker 1: just the size of the planet, not just the circumplanetary disk,
• 1:57:01
  Speaker 1: or the companion candidate, or the spectacular spiral arms in
• 1:57:04
  Speaker 1: the Hubble images. It is the timing. Somebody pointed a
• 1:57:09
  Speaker 1: telescope at this star when the process was still underway,
• 1:57:12
  Speaker 1: and what they found was a window into something that
• 1:57:14
  Speaker 1: had never been directly observed before. A planet in the
• 1:57:17
  Speaker 1: middle of becoming, not finished, not named, not classified with confidence,
• 1:57:23
  Speaker 1: still negotiating with the disk around it over how much
• 1:57:26
  Speaker 1: mass it gets to keep. Most of what we know
• 1:57:29
  Speaker 1: about planets, we know from the finished versions. We study
• 1:57:33
  Speaker 1: Jupiter and Saturn as they are today, four and a
• 1:57:35
  Speaker 1: half billion years into their lives, and try to work
• 1:57:38
  Speaker 1: backward to figure out how they got there. That is
• 1:57:41
  Speaker 1: like trying to understand how a building was constructed by
• 1:57:43
  Speaker 1: examining the completed structure without ever having seen blueprints, scaffolding,
• 1:57:48
  Speaker 1: or workers. HD100546B is the scaffolding. The cranes are still running.
• 1:57:56
  Speaker 1: Right now, 353 light years away, in a direction you
• 1:58:00
  Speaker 1: could point to with your finger on a clear night,
• 1:58:03
  Speaker 1: the largest planet we have ever found is still growing,
• 1:58:06
  Speaker 1: still pulling in the material that will eventually define what
• 1:58:08
  Speaker 1: it becomes. indifferent to the question of what we decide
• 1:58:12
  Speaker 1: to call it.