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The Kuiper Belt May Be Hiding a Giant Secret · Boring Science

• 0:00
  Speaker 1: For most of human history, the outer edge of the
• 0:03
  Solar System sat at a clean, comfortable distance, and astronomers
• 0:08
  had the numbers to prove it. Neptune, the farthest known planet,
• 0:14
  orbits roughly thirty times farther from the Sun than Earth does.
• 0:19
  Beyond that, the thinking went, there was essentially nothing, a
• 0:24
  vast stretch of cold, empty space, before the distant out
• 0:28
  cloud swallowed everything. The Solar System had a boundary, and
• 0:33
  we knew where it was. That picture was wrong, not
• 0:37
  slightly wrong, wrong in a way that should genuinely embarrass
• 0:42
  the textbooks that taught it. Beyond Neptune, starting roughly where
• 0:47
  that planet's orbit traces its path, and stretching outward for
• 0:52
  billions of miles, there is an entire province of the
• 0:56
  Solar System that almost nobody talks about. It is called
• 1:01
  the Kuiper Belt. It is enormous, It is ancient. It
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  is filled with hundreds of thousands of icy bodies, frozen
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  remnants from the formation of the Solar System, sitting out
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  there in the dark at temperatures close to absolute zero.
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  Most people have never heard of it. Most people have
• 1:23
  certainly never thought about it. And right now it is
• 1:27
  the most interesting place in planetary science. Here is what
• 1:37
  astronomers have found. There are objects sitting at distances of seventy, eighty,
• 1:43
  even ninety times the Earth's distance from the Sun, in
• 1:47
  a region where current models say almost nothing should be.
• 1:52
  There is a sharp, abrupt cliff in the population of
• 1:55
  Kuiper Belt objects at roughly fifty astronomical units, a cliff
• 2:01
  that drops off with a precision that random physical processes
• 2:05
  cannot cleanly explain. There is a gap in the Outer
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  Solar System, a structured empty zone that looks disturbingly familiar
• 2:15
  to astronomers who study debris disks around other stars in
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  other planetary systems. Gaps like this have one standard explanation.
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  A planet made it. And there is a small frozen
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  body about five hundred kilometers across sitting in the deep
• 2:34
  cold of the Outer Solar System that appears to have
• 2:38
  an atmosphere that last one should not be possible. Were
• 2:43
  we wrong about where the Solar System ends? The answer
• 2:47
  is almost certainly yes. Were we wrong about how active
• 2:52
  and complex the Outer Solar System is also yes? And
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  the question sitting underneath all of it, the one that
• 3:01
  has driven a decade of serious scientific debate is whether
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  something large and unseen is out there pulling strings, sculpting
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  the architecture of the outer Solar System from a distance
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  so extreme that centuries of sky surveys missed it entirely
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  a hidden planet, not Pluto, something far larger, far more distant,
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  and far more consequential. The evidence for it has been
• 3:31
  building for years. The machine that might finally confirm it
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  just came online. What the Kuiper Belt is actually hiding
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  may turn out to be the most important discovery in
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  the history of planetary science, and we are almost certainly
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  looking right at it. Beyond the orbit of Neptune, roughly
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  thirty times farther from the Sun than the Earth is,
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  the Solar System does something unexpected. Instead of fading into
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  empty space, it fills back up, not with planets, not
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  with anything large enough to see with the naked eye,
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  but with billions and billions of frozen objects drifting in slow,
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  cold orbits around a Sun so distant it barely qualifies
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  as a star. This region has a name, the Kuiper Belt.
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  Most people have never had a reason to think carefully
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  about it, and that is part of the problem, because
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  once you understand what it actually is. It becomes very
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  hard to think about the Solar System the same way again,
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  start with the basics. An astronomical unit is the distance
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  from the Earth to the Sun, roughly ninety three million miles.
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  That is the unit astronomers use when the numbers get
• 4:55
  too large for anything more familiar. Earth sits at one
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  astronomy unit, Mars at about one point five, Jupiter at
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  five point two, Saturn at just under ten, Uranus at nineteen,
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  and Neptune, the outermost recognized planet, sits at about thirty
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  astronomical units. That is thirty times the Earth Sun distance,
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  which works out to roughly two point eight billion miles.
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  A passenger jet flying continuously at cruising speed would take
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  somewhere around six hundred years to reach it. The number
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  is almost impossible to hold in your mind. Neptune is
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  not close to anything. Now take that distance and double it.
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  The Kuiper Belt starts right around where Neptune orbits and
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  extends outward to roughly fifty or fifty five astronomical units.
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  That range from thirty to fifty five astronomical units is
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  the classical Kuiper Belt. The inner Solar System everything from
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  the Sun out to Neptune fits inside a sphere of
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  thirty astronomical units radius. The Kuiper Belt adds another twenty
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  to twenty five astronomical units on top of that. Because
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  volume scales with the cube of distance, the sheer space
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  enclosed by the Kuiper Belt dwarfs the region containing every
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  planet most people have ever heard of. It is an
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  enormous territory, and it is not empty. The belt was
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  theorized long before any objects were actually observed. In the
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  nineteen forties, astronomers Gerard Kuiper and Frederick Whipple independently proposed
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  that a region of icy bodies must exist beyond Neptune.
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  They reasoned from orbital mechanics and the presence of certain
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  comets that no model of the Solar System made sense
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  without it. But for decades the belt remained theoretical. Actual
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  discovery of its objects began slowly in the nineteen nineties,
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  accelerated through the two thousands, and continues today. Each new
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  detection adds another piece to the picture. The belt, in
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  other words, has only recently become real to us, even
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  though it has been there since the Solar System began.
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  The objects in the Kuiper Belt are not rocky in
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  the way asteroids are. They are icy, frozen water, frozen methane,
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  frozen ammonia, sometimes mixed with silicate rock and carbon compounds
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  in proportions that vary from one object to the next.
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  The Sun's heat barely reaches them, and so these materials
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  remain locked in ice rather than boiling off into space.
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  At forty or fifty astronomical units, the temperature hovers somewhere
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  around negative two hundred twenty degrees celsius. The objects don't
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  change much. They have been sitting out there, slowly orbiting
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  since the Solar system was young. They are, in some
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  ways the best preserved material from the original disc of
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  gas and dust that everything else formed from nearly four
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  point six billion years ago. What they look like, surprisingly
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  is not uniform. Kuiper Belt objects span a remarkable range
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  of colors. Some are dead white, reflecting sunlight the way
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  fresh snow does. Others are neutral gray, and some, particularly
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  the ones found at greater distances or in specific orbital populations,
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  are extraordinarily red. Not a subtle tint, but a deep, rusty,
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  almost blood red that astronomers describe as ultra. This colour
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  comes from complex organic compounds called tholins, which form when
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  ultraviolet radiation from the sun slowly processes methane and nitrogen
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  ices over hundreds of millions of years. The colour itself
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  is a clock. The reddest objects have been cooking in
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  sunlight for the longest time, sitting undisturbed in the outer belt,
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  accumulating chemistry that has nowhere else to go. There are
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  a lot of them. Estimates suggest hundreds of thousands of
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  Kuiper Belt objects with diameters larger than one hundred kilometers,
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  That is roughly the width of the state of Kentucky.
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  Objects at that scale in the asteroid belt would be
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  notable individually. In the Kuiper Belt, there are hundreds of
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  thousands of them. Extend the countdown to smaller sizes, and
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  the number climbs into the trillions. The Kuiper Belt is
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  not a sparse scattering of lonely ice balls.
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  Speaker 2: It is a.
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  Speaker 1: Vast, crowded, structured population of frozen material spread across an
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  enormous volume of space, largely invisible from Earth. And then
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  there is Pluto. Pluto is the most famous resident of
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  the Kuiper Belt, though nobody knew it was a Kuiper
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  Belt object when it was discovered in nineteen thirty. For
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  seventy six years it was classified as the ninth planet.
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  Then in two thousand six, the International Astronomical Union downgraded
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  it to dwarf planet status, and the cultural backlash was significant.
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  People felt that something had been taken away. Here is
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  what actually happened. By the early two thousands, astronomers had
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  been finding other objects in the Outer Solar System that
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  rivaled Pluto.
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  Speaker 2: In sana.
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  Speaker 1: Eris, discovered in two thousand and five, was actually slightly
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  more massive make make how maya others. The Kuiper Belt
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  was revealing itself as a population of similarly sized bodies,
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  and Pluto was not a lonely outlier beyond Neptune. It
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  was one of many. The definition of planet had never
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  been designed to handle this situation, and when the IAU
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  finally revised it, Pluto fell below the threshold. What the
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  demotion really meant was something stranger and more interesting than
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  any reclassification. It meant the Outer Solar System was crowded
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  in a way nobody had fully appreciated. It meant Pluto
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  was a representative of a type, not a singular oddity,
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  and it meant that For most of the twentieth century,
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  astronomers had been looking at the Kuiper Belt's most famous
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  member without recognizing it as part of a much larger structure.
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  The Pluto story is not a story about scientific bureaucracy
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  making a mistake or correcting one. It is a story
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  about a part of the Solar system becoming visible for
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  the first time, slowly, one object at a time, until
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  the picture finally forced a reckoning with how large and
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  complex the outer Solar System had always been. Pluto's demotion
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  did not shrink the Solar system. It revealed just how
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  much of it had been invisible all along. In nineteen
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  ninety two, after five years of searching through images of
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  the outer Solar System by hand, David Dewett found something
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  that was not supposed to be there. The story starts
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  earlier than that, though, in the late night nineteen eighties,
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  Dewet was a young astronomer at MIT with a specific
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  and unfashionable conviction. He believed that beyond Neptune, beyond Pluto,
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  beyond the lonely edge of what most textbooks called the
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  Solar System, there had to be more. The theoretical argument
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  was not his alone. Gerard Kuiper had gestured toward it
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  in the nineteen fifties. Fred Whipple had similar instincts. The
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  mathematics of how comets behaved hinted at a reservoir of
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  icy bodies somewhere out beyond the known planets, a source
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  population that could explain where short period comets were coming from.
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  But mathematics and instinct are not the same as evidence.
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  Nobody had ever seen a single object out there, and
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  in astronomy, until you can show someone a picture, you
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  have nothing. What Jewet had was a plan and a
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  new piece of technology that most astronomers were only beginning
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  to understand how to use. The instrument was a CCD camera.
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  Charge coupled devices had been quietly transforming optical astronomy since
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  the late nineteen seventies. Where photographic film captured perhaps one
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  percent of the light falling on it, a good CCD
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  could capture eighty or ninety percent. That is not a
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  modest improvement. That is the difference between looking at the
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  outer solar system through a window and looking through a wall.
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  Objects that were genuinely invisible to photographic surveys could suddenly
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  be detected. Jewet recognized this immediately, he teamed up with
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  Jane Lou, a graduate student at MIT, who brought both
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  technical skill and extraordinary pati to the project. Together, they
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  set out to use CCD imaging to search a region
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  of sky that most of the field had quietly written off.
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  The search itself was not glamorous. It was five years
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  of pointing a telescope at patches of sky, taking exposures
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  hours apart, and then comparing the images by eye, looking
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  for any point of light that had moved. Objects in
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  the outer Solar System moved slowly Neptune takes one hundred
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  sixty five years to complete one orbit. Anything further out
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  moves even more sluggishly against the background of fixed stars,
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  but slowly is not the same as invisibly, and Dewet
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  and Lou were looking for exactly that kind of motion.
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  They were using a two point two meter telescope on
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  Mauna Kia in Hawaii, one of the best sights on
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  Earth for this kind of work. The altitude keeps you
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  above most of the atmospheres, blur the dark skies, keep
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  the background noise low. Then, on the night of August thirtieth,
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  nineteen ninety two, a point of light moved It was faint,
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  roughly one hundred times, too dim to see with the
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  naked eye. It was slow, as expected, and it was
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  sitting far out in the Solar System, well beyond Pluto,
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  in a place where nothing should have been orbiting the
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  Sun at all. The object was designated nineteen ninety two
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  QB one. It would later be given the name Albion.
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  On that single night, the known solar system got larger
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  in a way it had not since the discovery of
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  Neptune in eighteen forty six. Here is the thing worth
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  sitting with for a moment. The object had always been there.
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  It had been circling the Sun for billions of years,
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  while the dinosaurs rose and fell, while mammals evolved, while
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  human beings invented writing and telescopes and CCD cameras. The
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  Solar system had not changed our ability to see it had.
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  That distinction is one of the stranger ideas in the
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  history of astronomy. A province of the Solar System the
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  size of a continent had been invisible, not because it
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  was hidden in any dramatic sense, but simply because the
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  instruments to detect it did not exist. Within a year,
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  a second object appeared, then more the pace picked up steadily.
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  By the mid nineteen nineties, dozens of trans Neptunian objects
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  had been found, each one confirming what the discovery of
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  Albion had implied. This was not an anomaly. There was
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  a belt out there, a genuine population of icy bodies
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  spread through a wide ring beyond Neptune, orbiting in relative
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  quiet at distances that made them extraordinarily difficult to study,
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  but not with the right tools impossible to find. The
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  shift in how astronomers thought about the Outer Solar System
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  was dramatic. Before nineteen ninety two, the picture looked like this,
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  the four giant planets, then Pluto sitting awkwardly at the edge,
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  then essentially nothing until the aut cloud. At distances of
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  thousands of astronomical units. The region from roughly thirty to
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  fifty astronomical units was simply blank on every conceptual map,
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  a gap, not a mystery, just space. Nobody expected it
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  to be populated because nothing had been found there, and
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  nothing had been found there, in part because nobody had
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  looked with instruments capable of finding it. After nineteen ninety two,
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  that blank region had a name, a population, and a
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  growing catalog. The Kuiper Belt was real. Pluto, which had
• 19:18
  always seemed like an oddity, suddenly made sense as the
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  largest known member of a vast family of similar objects.
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  Pluto's strangeness resolved. It was not an outlier. It was
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  simply the first of its kind that anyone had found,
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  and it had been waiting nearly sixty years for company.
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  The catalogs grew fast. A few dozen objects became a
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  few hundred, then a thousand. Surveys improved, CCDs got more
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  sensitive telescope time devoted to Outer Solar System searches increased
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  as the scientific payoff became undeniable. The questions that ca
• 20:00
  came with each new object multiplied as quickly as the
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  objects themselves.
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  Speaker 2: Where did they.
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  Speaker 1: All come from? What was the outer boundary of this belt?
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  What determined their orbits? And was there anything even further
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  out in the dark beyond the dark. By twenty eighteen,
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  more than two thousand Kuiper Belt objects had been catalogued,
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  and the number was still climbing. But the strangest discoveries
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  were only just beginning. The Kuiper Belt does not fade
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  gradually into empty space the way most people imagine the
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  edge of the Solar System should look. Most people, if
• 20:42
  they picture the Outer Solar System at all, probably imagine
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  something like a beach fading into water. Objects getting sparser,
• 20:53
  more spread out, the density dropping off slowly until there
• 20:58
  is simply nothing left. That is a reasonable thing to imagine.
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  It is also not what happens. What actually happens at
• 21:08
  roughly fifty astronomical units from the Sun is something far stranger.
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  The population of Kuiper Belt objects falls off a cliff,
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  not a slope, not a gradual thinning, a cliff. The
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  number of objects drops sharply and dramatically, and then beyond
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  that point there is essentially nothing where the models said
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  there should be something. Astronomers have a name for this.
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  They call it the Kuiper cliff, and it has been
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  sitting in the data, largely unexplained for decades. To understand
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  why the cliff is so troubling, you have to understand
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  what the models predicted before anyone knew it was there.
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  When researchers first worked out the structure of the Outer
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  Solar System in the nineteen nineties, they built their expectations
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  on the physics of how planetary systems form. A young
• 22:04
  star surrounded by a spinning disc of gas and dust
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  is a system with momentum and mass distributed across enormous distances.
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  The disc that formed our Solar system extended far beyond
• 22:19
  the orbit of Neptune. It had to, because the outer
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  planets are where they are, and they had to have
• 22:26
  material to form from. By every reasonable estimate, that primordial
• 22:32
  disc stretched well past fifty astronomical units. Some models put
• 22:38
  its outer edge at seventy eighty even farther. The material
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  out there would have been thinner than in the inner disc,
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  but it should have been present. Objects should have formed
• 22:50
  from it. When Dewet and Lou confirmed the Kuiper Belt
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  in nineteen ninety two, and the catalog of known objects
• 22:59
  began to grow, scientists started measuring how the population changed
• 23:04
  with distance. The result matched the models reasonably well out
• 23:09
  to around fifty astronomical units. Then came the cliff. Researchers
• 23:16
  ran the numbers. They checked for observational bias. It would
• 23:20
  be easy to miss objects at extreme distances, simply because
• 23:25
  they are faint and slow moving, and surveys have limits.
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  The first obvious question was whether the drop off was
• 23:33
  real or whether it was just an artifact of what
• 23:36
  the telescopes could detect. Gary Bernstein, David Trilling, and their
• 23:42
  colleagues published careful analyzes that addressed exactly this. When they
• 23:48
  accounted for detection limits and survey coverage, the cliff remained.
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  The drop off in objects larger than one hundred kilometers
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  in radius beyond fears fifty astronomical units was real. It
• 24:04
  was not a gap in the catalog. It was a
• 24:07
  gap in the actual population. That is the part that
• 24:11
  bothers astronomers, not that the objects are hard to find
• 24:15
  beyond fifty astronomical units, but that there genuinely seemed to
• 24:20
  be far fewer of them than there should be. The
• 24:24
  primordial disc was there, the raw materials were there. Something
• 24:29
  happened to the objects that should have formed from those materials,
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  or to the materials themselves before the objects could form,
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  And whatever happened, it drew a remarkably clean line at
• 24:44
  fifty astronomical units. The leading explanations divide roughly into three categories,
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  and none of them is entirely satisfying. The first is
• 24:55
  that the material beyond fifty astronomical units was simply two
• 25:00
  sparse and two dynamically scattered to build large objects. In
• 25:05
  the first place. In the inner Kuiper belt, the density
• 25:10
  of material was high enough for small bodies to collide,
• 25:14
  stick together, and grow. Further out, those collision rates may
• 25:19
  have been too low. Objects that started growing would have
• 25:23
  had too few encounters to continue growing, and the process
• 25:27
  would have stalled before anything substantial could form. This explanation
• 25:33
  has a certain appeal. It requires no exotic physics, just
• 25:37
  the natural consequence of a thinning disc. The problem is
• 25:42
  that when you run the numbers carefully, the disc shouldn't
• 25:46
  have thinned that sharply that quickly at exactly fifty astronomical units.
• 25:54
  The cliff is too clean. The second explanation involves gravitational sculpting.
• 26:00
  During the chaotic early period of the Solar System, the
• 26:04
  giant planets, particularly Neptune, migrated outward during the first few
• 26:10
  hundred million years of Solar System history. As Neptune swept
• 26:15
  through the outer disk, it scattered enormous amounts of material.
• 26:21
  Some of it was thrown inward, some was thrown outward
• 26:24
  into the aught cloud, some was ejected entirely. It is
• 26:30
  entirely possible that the material which should have populated the
• 26:34
  outer Kuiper belt was simply cleared out by this process,
• 26:39
  leaving the cliff as the scar of Neptune's migration. This
• 26:44
  is a plausible story, but matching the exact shape of
• 26:48
  the observed drop off is difficult. The models produce a
• 26:52
  smoother decline than what the data shows. The third explanation
• 26:57
  is the one that is hardest to dismiss and hardest
• 27:00
  to prove. Something large might be out there. A massive
• 27:05
  undiscovered body sitting beyond fifty astronomical units in a distant
• 27:11
  orbit would exert gravitational influence on the surrounding population over
• 27:16
  billions of years. It would scatter nearby objects, perturb orbits,
• 27:22
  clear material from the region around it, and potentially carve
• 27:26
  a sharp edge into the Kuiper Belt's outer boundary. Patrick
• 27:31
  Lekavka of Kobe University and his colleagues have argued this case,
• 27:36
  specifically that the gravitational signature of a hidden planetary mass object,
• 27:43
  perhaps the size of Earth or Mars, is the most
• 27:46
  natural explanation for why the cliff exists where it does
• 27:51
  and why it is so abrupt. An object of that
• 27:55
  kind in an orbit far enough out to have escaped
• 27:59
  detection would do exactly what the data seems to show
• 28:03
  something did here is the strange thing. When you look
• 28:07
  at the cliff from a distance, it resembles nothing so
• 28:11
  much as a boundary that was imposed, rather than a
• 28:14
  boundary that simply emerged. Natural processes in a thinning disk
• 28:20
  produce gradual fall offs. They produce curves, not edges. The
• 28:26
  sharpness of the Kuiper cliff, the precision of it, is
• 28:30
  the feature that keeps drawing theorists back toward the idea
• 28:34
  that something active created it. This is not yet the
• 28:38
  Planet nine story that comes later, with its own evidence
• 28:43
  and its own debate, But the cliff is where the
• 28:46
  question first appears in the data. Sitting at fifty astronomical
• 28:51
  units like a wall someone built across the outer Solar System.
• 28:56
  Something cut the Kuiper belt off at fifty as astronomical
• 29:00
  units with a precision that random physical processes have no
• 29:05
  good explanation for, and the candidates for what did it
• 29:09
  are limited. On July fourteenth, twenty fifteen, after traveling more
• 29:16
  than three billion miles through space in nine years of
• 29:21
  continuous flight, New Horizons swept past Pluto at thirty one
• 29:27
  thousand miles per hour and sent back images that nobody
• 29:31
  was fully prepared for. The expectation going in was something
• 29:36
  like the Moon, a battered, frozen ball poked with ancient craters,
• 29:42
  geologically dead for billions of years. That expectation was reasonable.
• 29:49
  Pluto sits so far from the Sun that the solar
• 29:52
  heating reaching its surface is negligible. There was no obvious
• 29:57
  reason for it to be anything other than a relic,
• 30:00
  interesting as a historical artifact, but inert. What the cameras
• 30:06
  showed instead was almost unsettling. Pluto had mountains, real ones
• 30:13
  rising two miles above the surrounding plains built from water
• 30:17
  ice so cold it behaves like rock at those temperatures.
• 30:21
  It had vast pale nitrogen glaciers flowing across its surface
• 30:26
  in slow creeping sheets. It had a thin but confirmed atmosphere,
• 30:32
  haze layers stacked above the surface, glowing faintly in the
• 30:36
  back lit images that New Horizons captured as it swung past.
• 30:42
  The world that the textbooks had essentially written off turned
• 30:46
  out to be one of the more geologically complex objects
• 30:49
  in the Outer Solar System. The most striking feature was
• 30:53
  the one that became immediately famous, a broad heart shaped
• 30:58
  basin covering an area roughly the size of Texas and
• 31:02
  Oklahoma combined, now called tomboor Regio, after the astronomer who
• 31:08
  discovered Pluto in nineteen thirty. The western half of the heart,
• 31:14
  a smooth, pale expanse of nitrogen ice, showed almost no
• 31:18
  impact craters at all. No craters means a young surface,
• 31:23
  a surface being continuously reshaped. Something was happening on Pluto
• 31:29
  geologically speaking, and scientists are still debating exactly what that
• 31:34
  heat source is. The terrain elsewhere on the surface swung
• 31:39
  between extremes, dark, heavily cratered ancient highlands on one side,
• 31:46
  bright smooth plains on another, a jumbled region of chaotic,
• 31:50
  broken terrain that research is nicknamed the Bladed Lands. Whatever
• 31:57
  plutz Oh was, it was not simple. The fly by
• 32:01
  lasted roughly one day at closest approach, but the data
• 32:05
  took more than a year to fully download. New horizons
• 32:10
  was so far away that the radio signal, traveling at
• 32:13
  the speed of light took four and a half hours
• 32:17
  to make the one way trip to Earth. Every image,
• 32:21
  every measurement, every data point arrived slowly, and each one
• 32:26
  added something unexpected. Pluto was not the dead world the
• 32:30
  models predicted It was active, strange, geologically varied in ways
• 32:37
  that forced a serious rethinking of what small cold bodies
• 32:41
  at extreme distances are capable of. But New Horizons did
• 32:45
  not stop at Pluto. That was always the plan. The
• 32:49
  spacecraft continued outward into the Kuiper Belt. Mission planners had
• 32:55
  already selected a second target before the Pluto flyby even happened.
• 33:00
  A small distant object discovered by the Hubble space telescope
• 33:05
  in twenty fourteen and designated two zero one four m
• 33:09
  U six y nine. It was later named Arakoth, a
• 33:13
  word from the Powhatan language meaning sky. On January first,
• 33:18
  twenty nineteen, New Horizons made its second flyby, this time
• 33:24
  at a distance of roughly four billion miles from the Sun.
• 33:28
  No spacecraft had ever visited an object that remote. What
• 33:32
  Arakoth looked like was not what anyone had predicted. It
• 33:37
  was a contact binary, two distinct lobes pressed gently together,
• 33:43
  the larger one roughly twenty two kilometers across and the
• 33:48
  smaller one about fourteen kilometers connected at a narrow neck.
• 33:53
  The whole thing resembled in the images that came back,
• 33:58
  something between a snowman and an a peanut. It was
• 34:02
  covered in a reddish material, a kind of organic coating
• 34:06
  called tholins, produced when simple molecules like methane and nitrogen
• 34:12
  are bombarded by radiation. Over billions of years, the surface
• 34:17
  was smooth, heavily cratered, as you might expect of an
• 34:21
  object sitting undisturbed for four point six billion years, but
• 34:27
  smooth between those craters, no evidence of violent collision, no
• 34:33
  signs of a catastrophic impact history. That smoothness was the
• 34:37
  key detail. If Arikoth had formed through the violent collision
• 34:43
  and sticking process that most models assumed for small outer
• 34:47
  Solar system bodies, it should have shown damage. The collision
• 34:52
  that merged two objects into a single contact binary under
• 34:57
  the old model would have been energy meetic enough to fracture, deform,
• 35:02
  or roughen the surfaces involved. Instead, Aracoth looked like it
• 35:08
  had been assembled gently. What the data actually supported was
• 35:14
  something called the streaming instability model, a process in which
• 35:19
  a cloud of small particles in the early solar nebula
• 35:23
  gradually concentrates under its own gravity, collapses forms a bound
• 35:29
  pair without any high speed impact at all. The two
• 35:33
  lobes of Aracoth had been orbiting each other. Slowly drifting
• 35:38
  together over me lions of years until they finally made
• 35:42
  contact at low enough speed to stick rather than shatter. Quiet, deliberate,
• 35:49
  almost careful. By the standards of Solar system formation, this
• 35:54
  was not a minor refinement of existing theory. It was
• 35:58
  a significant shift. The collision based model had dominated thinking
• 36:03
  about small body formation for decades. Arikoth replaced it with
• 36:08
  something more subtle and in a way, more elegant. While
• 36:14
  all of this was happening, New Horizon's instruments were also
• 36:18
  registering something else. During the years of cruise through the
• 36:22
  Kuiper Belt, the spacecraft's dust counter and various detectors were
• 36:27
  picking up faint signals from small particles and objects in
• 36:30
  the surrounding environment. The counts did not fall off the
• 36:35
  way they were supposed to. At the classical Kuiper Belt boundary,
• 36:39
  around fifty astronomical units. There was material out further than
• 36:45
  the maps accounted for, sparse but real. It was the
• 36:50
  first in situ measurement, hinting that the Kuiper Belt's outer
• 36:54
  edge might not be where decades of observation had placed it.
• 37:00
  The cliff that surveys had identified was a feature in
• 37:04
  the large object population beneath it. In the background, something continued.
• 37:11
  That quiet instrumental signal would eventually be confirmed from the ground,
• 37:18
  would force a fundamental revision in how large the Solar
• 37:22
  System's outer disc actually is. Arakoth's gentle, two lobed shape
• 37:28
  was not the result of a collision. It was the
• 37:31
  result of two objects slowly finding each other across empty space.
• 37:36
  That single fact rewrote the leading theories of how the
• 37:40
  outer Solar System was built. In twenty twenty three, a
• 37:45
  team analyzing data from Japan's Subaru telescope quietly announced something
• 37:50
  that the planetary science community had not anticipated. They had
• 37:55
  found objects, not one or two, not a handful of
• 37:59
  bodder ligne detections that could be explained away as noise,
• 38:04
  a statistically significant population of Kuiper Belt bodies sitting at
• 38:09
  distances between seventy and ninety times the Earth's distance from
• 38:15
  the Sun. That is nearly double the classical Kuiper Belt boundary.
• 38:21
  The map said this region was empty. The maps were wrong.
• 38:26
  To understand why this matters, you have to hold two
• 38:29
  numbers in your mind. The classical Kuiper Belt extends from
• 38:34
  roughly thirty to fifty five astronomical units. One astronomical unit
• 38:40
  is the distance from the Earth to the Sun. Neptune
• 38:44
  sits at about thirty The belt runs outward from there,
• 38:49
  thinning and dropping off sharply near fifty to fifty five
• 38:53
  astronomical units. Beyond that edge, the model said there was
• 38:59
  essentially nothing until the Oort Cloud, a vast shell of
• 39:03
  comets so distant it barely counts as part of the
• 39:07
  same Solar system. The Subaru observations found objects at seventy eighty,
• 39:14
  even close to ninety astronomical units. That is not a
• 39:19
  slight extension of a known boundary. That is, discovering a
• 39:23
  room in a house you thought you had fully mapped.
• 39:27
  The team behind this work was led by researchers connected
• 39:31
  to the New Horizon's mission. The same spacecraft that flew
• 39:35
  past Pluto and then Arikoth had also accumulated compelling evidence
• 39:40
  during its journey that something was out there beyond the
• 39:43
  classical belt. The Subaru telescope gave them the power to
• 39:48
  follow that thread. The hypersuprime cam instrument mounted on Subaru
• 39:54
  is built for exactly this kind of search. Wide field
• 39:59
  deep sensorivity, the ability to detect faint slow moving objects
• 40:05
  against a crowded background of stars. Without an instrument at
• 40:09
  that level, the objects at seventy to ninety astronomical units
• 40:14
  would have remained invisible. They are not just distant, they
• 40:19
  are extraordinarily dim. Here is something worth sitting with for
• 40:24
  a moment. A Kuiper belt object at fifty astronomical units
• 40:29
  receives roughly one two thousand, five hundredth of the sunlight
• 40:34
  that Earth receives. Push that object out to eighty astronomical units,
• 40:39
  and the sunlight hitting its surface drops by another factor
• 40:43
  of more than two and a half. What little light
• 40:47
  reaches it reflects back toward Us across a vast distance,
• 40:52
  arriving at Earth as a signal so faint that distinguishing
• 40:56
  it from background noise requires patience and precision. These objects
• 41:01
  also moved slowly across the sky at those distances. Even
• 41:07
  a body traveling at tens of thousands of miles per
• 41:10
  hour appears nearly stationary. Over weeks of observation, finding them
• 41:16
  means stacking images, looking for tiny shifts in position, and
• 41:21
  ruling out artifacts. It is painstaking work. The fact that
• 41:26
  this population had gone undetected before is not really a failure.
• 41:31
  Of astronomy. It is a consequence of physics and instrument limits.
• 41:36
  The right tools simply did not exist until recently. What
• 41:41
  the Subaru data showed was not random scatter. The eleven
• 41:45
  objects detected beyond the classical belt were distributed in a
• 41:49
  way consistent with a real population, not a collection of
• 41:53
  outliers flung there by unusual gravitational kicks. Team member doctor
• 42:00
  Fumi Yoshida put it plainly, either the Kuiper Belt extends
• 42:05
  farther than anyone thought, or there is a second Kuiper
• 42:09
  belt sitting beyond the one mapped in the nineteen nineties.
• 42:13
  Both possibilities are significant. Both imply a solar system that
• 42:19
  is larger, more structured, and more populated than the standard
• 42:23
  model predicts. Researcher Wes Fraser made a point that cuts
• 42:29
  to the heart of this discovery. Our solar system had
• 42:32
  long appeared unusually small and compact compared to the debris
• 42:37
  discs observed around other stars. Astronomers studying young planetary systems
• 42:43
  in infrared light routinely see wide, extended rings of material
• 42:49
  reaching out to enormous distances from their parent stars. Our
• 42:55
  solar system, by comparison, looked truncated a little underwhelming relative
• 43:03
  to the cosmic norm. Fraser's argument was direct that impression
• 43:08
  was built on an observational bias. Previous surveys had simply
• 43:13
  not searched deeply enough at the right distances. The instruments
• 43:18
  were not sensitive enough, the survey areas were not wide enough.
• 43:23
  We had been measuring the Solar system with a ruler
• 43:26
  that stopped too soon, and concluding the Solar system was short.
• 43:31
  If the Subaru detections hold up and subsequent observations are
• 43:35
  expected to test this, the primordial solar nebula from which
• 43:40
  our Solar system formed must have extended much further than
• 43:44
  current formation models allow. The raw material for planets and
• 43:49
  minor bodies was out there at seventy eighty and ninety
• 43:54
  astronomical units when the Solar system was young. Something shaped
• 44:00
  that material into the population. We are now beginning to
• 44:04
  detect understanding what did the shaping and why the region
• 44:09
  between fifty five and seventy astronomical units appears relatively empty
• 44:16
  while material reappears beyond. It is the next layer of
• 44:20
  the problem. That gap is not random. Gaps in debris
• 44:25
  disks rarely are. There is something almost unsettling about this discovery.
• 44:31
  The Kuiper Belt was confirmed in nineteen ninety two. It
• 44:36
  has been studied intensively for more than thirty years. Thousands
• 44:40
  of objects have been catalogued, major spacecraft have been sent
• 44:45
  through it, and yet a substantial population of bodies, not
• 44:50
  single oddities, but a real statistical grouping, went undetected until
• 44:56
  a deep field survey looked carefully enough. The outer Solar
• 45:01
  system has been keeping this to itself across the entire
• 45:05
  history of modern planetary science. The comparison to other planetary
• 45:10
  systems is the part that shifts perspective most sharply. When
• 45:15
  astronomers image debris disks around distant stars, they are seeing
• 45:19
  the equivalent of our Kuiper Belt from light years away.
• 45:24
  Those discs are large, extended, often showing multiple rings separated
• 45:30
  by gaps. For years, the working assumption was that our
• 45:35
  system was different, quieter, more contained. That assumption shaped theories
• 45:42
  of how our solar system formed and influenced how astronomers
• 45:46
  compared us to the rest of the galaxy. The extended
• 45:50
  belt data suggests we were comparing ourselves to other systems
• 45:54
  while missing a significant part of our own. Our solar system,
• 46:00
  which had seemed modest and compact compared to the sprawling
• 46:03
  debris discs observed around distant stars, may have been hiding
• 46:08
  it's own outer reaches in plain sight. Between roughly fifty
• 46:13
  five and seventy times the Earth's distance from the Sun,
• 46:17
  the outer Solar System goes quiet, not gradually, not the
• 46:21
  way a city fades into countryside as you drive away
• 46:25
  from it. The transition is sharper than that. Objects exist
• 46:30
  on one side of this zone, and then there is
• 46:33
  very little on the other side of it, and then,
• 46:36
  as we discussed, objects start appearing again at much greater distances.
• 46:43
  The gap sits between the outer edge of the classical
• 46:47
  Kuiper belt and the newly detected distant population, and it
• 46:52
  has edges that are defined enough to be troubling. Random
• 46:57
  physical processes don't produce that kind of structure. Empty regions
• 47:03
  with clean boundaries are a signature of something that carved
• 47:06
  them out. The width alone is striking fifteen astronomical units
• 47:12
  of space. That's roughly the distance from the Sun to
• 47:16
  Uranus compressed into a gap between two populations of objects
• 47:20
  in the outer Solar System. If you drove that stretch
• 47:24
  at highway speed without stopping the trip would take you
• 47:28
  more than one hundred fifty million years. It is not
• 47:33
  a subtle dip in object density. It is a hole
• 47:37
  in the distribution, and it is sitting right where based
• 47:41
  on the formation models, material had every reason to exist.
• 47:46
  This is what makes the gap different from the Kuiper cliff.
• 47:50
  The cliff drops off at fifty astronomical units and could,
• 47:54
  in principle be explained by the way material was distributed
• 47:58
  in the early Solar nebula or scattered by Neptune's migration.
• 48:03
  The gap is a separate feature entirely. It sits beyond
• 48:08
  the cliff between two populations that both appear to be real,
• 48:13
  and it behaves like a cleared lane. That distinction matters
• 48:18
  because cleared lanes have a well understood cause. Here is
• 48:22
  where the comparison to other planetary systems becomes impossible to ignore.
• 48:28
  Over the past two decades, telescopes like the Atacama Large
• 48:33
  Millimeter Array ALMA have produced images of planet forming discs
• 48:38
  around young stars that look almost nothing like what we
• 48:42
  imagined the early Solar System looked like. They are not smooth,
• 48:47
  featureless discs of material. They are structured, They have rings,
• 48:53
  they have gaps. In image after image, these disks show
• 48:58
  dark bands cutting through the bright material, often at multiple radii,
• 49:04
  often with relatively clean edges. When astronomers first saw this pattern,
• 49:10
  the debate over what caused it lasted only a few years.
• 49:15
  The current consensus is that those gaps are carved by planets.
• 49:20
  A planet orbiting inside a disk of material gravitationally skulped
• 49:26
  as the material around it. Debris in its orbital path
• 49:30
  gets swept up, debris near its orbit gets ejected or
• 49:35
  pulled into orbital resonances that move it elsewhere. What's left
• 49:40
  behind is an empty ring centered on the planet's orbital path,
• 49:46
  with populations of smaller objects on either side. The physics
• 49:50
  here is not exotic. We have watched Neptune do a
• 49:54
  version of this to the Kuiper Belt itself. Over the
• 49:57
  history of the Solar System, Neptune's gravity has cleared certain
• 50:02
  orbital zones and populated others with resonant objects. Pluto is
• 50:08
  in one of those resonances. The process is known repeatable
• 50:13
  and leaves a recognisable fingerprint. What the disks around other
• 50:18
  stars show over and over is that fingerprint. At larger scales,
• 50:24
  the gap between fifty five and seventy astronomical units in
• 50:28
  our own system has that same shape. An under dense
• 50:33
  region sitting between two denser populations with edges that are
• 50:38
  more abrupt than gradual dispersal would produce. If an undiscovered
• 50:44
  body were orbiting somewhere in that range on a roughly
• 50:48
  circular or moderately elongated path, its gravitational influence over billions
• 50:55
  of years would produce something that looks very much like
• 50:59
  what we observe. It would clear objects from its immediate vicinity,
• 51:05
  creating the empty zone. It would leave the populations on
• 51:10
  either side largely intact. The structure would be stable over
• 51:15
  long time scales, because once a planet has cleared its lane,
• 51:19
  the objects that remain are the ones that have survived
• 51:23
  either far enough away to be mostly undisturbed or locked
• 51:27
  into resonances that keep them safe. Now, the critical thing
• 51:33
  to hold on to here is that the gap does
• 51:36
  not prove there is a planet. Astronomers are careful about
• 51:40
  this distinction, sometimes to the frustration of everyone outside the field.
• 51:46
  What the gap proves is that there is a structured
• 51:50
  absence of material in a region where, based purely on
• 51:54
  the distribution of objects on either side, you might have
• 51:58
  expected material to exist. There are other explanations. The primordial
• 52:05
  disc may have had a density feature there from the beginning.
• 52:09
  Dynamical processes during Neptune's outward migration may have preferentially cleared
• 52:15
  that region without leaving a body behind. These alternatives are
• 52:20
  not implausible, but they are also not as clean as
• 52:24
  the planet explanation, and they require the gap to be
• 52:28
  a coincidence, an artifact of formation or scattering that happened
• 52:33
  to produce something that looks almost precisely like what a
• 52:38
  planet would produce.
• 52:39
  Speaker 2: That is the.
• 52:40
  Speaker 1: Uncomfortable position the gap puts theorists in. To dismiss it,
• 52:46
  you have to argue that a structure which in every
• 52:49
  other planetary system we have studied would be interpreted as
• 52:53
  a gravitational signature is something different here. You have to
• 52:58
  argue that the Soul Solar system, which we know had
• 53:02
  an extremely violent early history involving migrating giant planets and
• 53:08
  massive scattering events, somehow produce this specific, bounded, relatively clean,
• 53:15
  empty zone through a process that didn't involve anything sitting there.
• 53:20
  Now that argument is possible, it is not obviously winning.
• 53:25
  What the gap does more than anything else, is force
• 53:29
  the question into the open, because the alternative to having
• 53:33
  a planet there is not having no explanation, it is
• 53:37
  having a less satisfying explanation. And in planetary science, the
• 53:42
  record of what happens when something looks like a planet
• 53:45
  has shaped the orbit of smaller bodies nearby, the record
• 53:50
  is fairly consistent. You look harder, you look more carefully,
• 53:56
  you point better instruments at the problem, and either you
• 53:59
  find something or you don't, and both outcomes tell you
• 54:04
  something real about how the Solar System works. In any
• 54:08
  other planetary system, a gap shaped like this would have
• 54:12
  astronomers reaching for the planet hypothesis almost immediately, and in
• 54:18
  our own system, that is exactly what some of them
• 54:21
  have been doing. In January of twenty sixteen, two astronomers
• 54:26
  at the California Institute of Technology published a paper that
• 54:31
  caused an immediate stir in the planetary science community. Constantine
• 54:36
  Battigin and Mike Brown had not found a new planet.
• 54:41
  They were careful to say that what they had found
• 54:45
  was something stranger in some ways, a pattern hidden inside
• 54:50
  data that already existed, a signal that nobody had thought
• 54:55
  to look for in quite the right way, and once
• 54:58
  you saw it, it was almost impossible to explain away.
• 55:03
  The starting point was a small set of objects, six
• 55:07
  Kuiper Belt objects, all of them at extreme distances from
• 55:11
  the Sun, all of them in orbits that took them
• 55:15
  far out into the cold outer Solar System before looping
• 55:19
  back in. These were not ordinary Kuiper Belt objects sitting
• 55:24
  between thirty and fifty five astronomical units. These were distant,
• 55:30
  scattered bodies, reaching hundreds of astronomical units at their farthest points. Individually,
• 55:38
  none of them looked particularly special, but Battagin and Brown
• 55:43
  noticed something when they looked at them together. The orbits
• 55:47
  were lined up, not roughly, not approximately, their closest approach
• 55:54
  points to the Sun the technical term is perihelian, were
• 55:59
  all pointing in the same general direction through space. Their
• 56:04
  orbital planes were all tilted the same way relative to
• 56:08
  the rest of the Solar system. Six objects, six independent orbits,
• 56:15
  all sharing a striking geometric alignment that had no obvious
• 56:19
  reason to exist. The probability calculation was what stopped people cold.
• 56:25
  If the orbits were distributed randomly, the chance of seeing
• 56:29
  this kind of clustering by accident was roughly one in
• 56:33
  fifteen thousand. That is not impossible, but it is the
• 56:38
  kind of number that makes careful scientists sit up straight.
• 56:43
  Random processes in the Outer Solar System do not produce clean,
• 56:48
  repeating alignments. The scattered disc is chaotic. Objects get flung
• 56:54
  to extreme distances through gravitational encounters. Their final orbits depend
• 57:01
  on the specific details of each encounter. For six objects
• 57:05
  to independently settle into orbits pointing the same direction with
• 57:11
  the same tilt without some organizing force holding them there
• 57:15
  is deeply unlikely. Here is the thing that made the
• 57:19
  hypothesis click. An orbiting planet can do exactly this. If
• 57:25
  a massive body is moving through the Outer Solar System
• 57:28
  on its own elongated orbit, its gravity reaches out over
• 57:33
  millions of years and slowly nudges nearby objects. Not through
• 57:39
  direct close encounters. The distances are too vast for that,
• 57:44
  but through a slow accumulated gravitational influence called secular resonance.
• 57:52
  The planet doesn't have to pass close to each object.
• 57:56
  It just has to exist, pulling steadily in a direction
• 58:00
  that gradually herds the orientations of smaller orbits into alignment.
• 58:06
  This is not a new concept in planetary science. Neptune
• 58:11
  has been doing the same thing to Pluto and a
• 58:13
  whole family of objects called Plutinos for billions of years,
• 58:18
  locking them into stable resonances that keep them out of
• 58:21
  Neptune's path. What Batagen and Brown were proposing was the
• 58:26
  same mechanism operating at a far greater scale. Gravitational sculpting
• 58:33
  of this kind leaves unmistakable marks on the architecture of
• 58:37
  orbital systems. The fingerprints persist even across vast time scales,
• 58:44
  evidence that some unseen architect has been at work shaping
• 58:48
  the orbits of distant bodies. Their prediction was specific, and
• 58:53
  specificity is what gives a scientific hypothesis. Teeth Planet nine,
• 58:59
  as they named it, should have a mass somewhere between
• 59:03
  five and ten times that of Earth. Its orbit should
• 59:07
  be enormously elongated, carrying it to perhaps two hundred astronomical
• 59:13
  units at its nearest approach to the Sun and far
• 59:17
  beyond one thousand astronomical units at its farthest. The orbital
• 59:23
  plane should be tilted relative to the plane of the
• 59:26
  rest of the Solar System. The long axis of its
• 59:30
  orbit should point in the opposite direction from the cluster
• 59:34
  of objects it was shepherding. These were not vague qualitative claims.
• 59:40
  They were numbers, angles, distances, things you could test once
• 59:46
  the right telescope was pointed at the right part of
• 59:49
  the sky. What made the twoenty sixteen paper land as
• 59:53
  hard as it did was partly the quality of the evidence,
• 59:57
  and partly who was making the claim. Mike Brown was
• 1:00:01
  not a peripheral figure in Kuiper Belt science. He had
• 1:00:05
  discovered Eiris, the dwarf planet whose existence directly precipitated Pluto's reclassification.
• 1:00:12
  He had found more large Kuiper Belt objects than almost
• 1:00:16
  anyone alive. When Brown said he thought there was a
• 1:00:19
  planet out there, the field paid attention. Battagen brought the
• 1:00:25
  theoretical framework, the orbital mechanics, the resonance calculations, the dynamical
• 1:00:32
  modeling needed to show that a planet of this type
• 1:00:36
  could actually produce the observed clustering. Together, they made a
• 1:00:41
  case that was difficult to dismiss with a single objection.
• 1:00:46
  The collaboration between observational expertise and theoretical rigor lent extraordinary
• 1:00:53
  weight to their conclusion, signaling to the broader scientific community
• 1:00:59
  that this was not speculative astronomy, but a serious investigation
• 1:01:04
  grounded in rigorous mathematics and empirical data. Subsequent work strengthened
• 1:01:11
  the signal rather than dissolving it. Researchers added more distant
• 1:01:15
  Kuiper Belt objects to the sample. As surveys pushed to
• 1:01:19
  greater depths, a meaningful fraction of the newly discovered objects
• 1:01:24
  fell into the same clustering pattern. A twenty twenty one
• 1:01:29
  analysis that incorporated additional objects found the alignment persisted even
• 1:01:35
  after attempting to account for potential biases in where surveys
• 1:01:40
  had been looking. The orbital plane of the distant Kuiper Belt,
• 1:01:44
  in the region where Planet nine's influence should be strongest,
• 1:01:49
  appeared to be measurably tilted relative to the plane of
• 1:01:52
  the inner Solar System. The tilt was subtle, but it
• 1:01:56
  matched the prediction. This was not sposed to happen without
• 1:02:01
  a cause. None of this constitutes proof. Battagen and Brown
• 1:02:06
  never claimed it did. What they claimed was that the
• 1:02:09
  simplest explanation for everything they were seeing, the perihelian clustering,
• 1:02:15
  the tilt of the orbital planes, the existence of objects
• 1:02:20
  in orbits that standard models have difficulty producing, was a
• 1:02:25
  single large unseen body orbiting at extreme distance, not a
• 1:02:31
  cloud of small objects, not an unusual distribution of random noise,
• 1:02:37
  but one planet pulling on everything around it, with the
• 1:02:41
  patient consistency of gravity operating over billions of years. The
• 1:02:47
  clustering was not just a curiosity, It was a fingerprint.
• 1:02:52
  Battagen and Brown believed they knew what had pressed it
• 1:02:56
  into the data. If Planet nine exists, it is nothing
• 1:03:00
  like any world in the familiar Solar System. The planets
• 1:03:04
  most people can name, Mercury, Venus, Mars, Jupiter are objects
• 1:03:10
  you can find in a basic textbook. Their masses, orbits
• 1:03:15
  and compositions have been measured with precision. They are known quantities.
• 1:03:21
  Planet nine, if it is real, belongs to a completely
• 1:03:25
  different category. It is an ice giant, something closer in
• 1:03:30
  nature to Uranus or Neptune than to anything in the
• 1:03:33
  inner Solar System. That means a world built mostly from water, methane,
• 1:03:40
  and ammonia in frozen and compressed forms, wrapped around a
• 1:03:44
  rocky core, shrouded in a thick envelope of hydrogen and
• 1:03:48
  helium gas. Not a rocky planet you could stand on,
• 1:03:53
  Not a gas giant the size of Jupiter. Something in between,
• 1:03:58
  massive enough to be unambiguously a planet strange enough to
• 1:04:03
  feel alien compared to every world we have ever visited.
• 1:04:06
  The mass estimates sit between five and ten times the
• 1:04:10
  mass of Earth. That range matters. At five Earth masses,
• 1:04:15
  planet nine would be one of the smaller ice giants imaginable.
• 1:04:20
  At ten it would be approaching a third the mass
• 1:04:23
  of Uranus. Either way, it would contain roughly five thousand
• 1:04:29
  times the mass of Pluto. This is worth holding onto
• 1:04:33
  for a moment. The debate over Pluto's planetary status consumed
• 1:04:39
  years of headlines and public argument. Planet nine would make
• 1:04:43
  that debate look almost quaint. There is no version of
• 1:04:48
  planetary definition under which an object this massive gets demoted
• 1:04:52
  to anything smaller than a full planet. It would gravitationally
• 1:04:57
  dominate a region of space large than the sphere of
• 1:05:01
  influence of any planet currently on the books. Neptune controls
• 1:05:06
  a substantial gravitational neighbourhood. Planet Nines would dwarf it. The
• 1:05:12
  orbit is where things become almost hard to picture. Planet
• 1:05:16
  nine is not proposed to sit at a fixed comfortable
• 1:05:19
  distance from the Sun. Its path would be an enormous
• 1:05:23
  ellipse stretch to extremes that have no parallel among the
• 1:05:28
  known planets. At its closest approach, what astronomers call perihelion,
• 1:05:34
  it might come within a few hundred astronomical units of
• 1:05:38
  the Sun. At its farthest point, it could swing out
• 1:05:42
  beyond a thousand astronomical units for reference Neptune orbits at
• 1:05:48
  roughly thirty astronomical units, Pluto reaches about forty nine astronomical
• 1:05:55
  units at its farthest. The inner edge of the proposed
• 1:05:59
  Planet nine orbit is already ten times farther than that.
• 1:06:04
  The outer edge is territory that has essentially never appeared
• 1:06:08
  on any map of the Solar System that meant anything.
• 1:06:11
  An orbit this large takes time, a long time. The
• 1:06:17
  estimated orbital period for planet nine falls somewhere between ten
• 1:06:21
  thousand and twenty thousand earth years one circuit of the Sun,
• 1:06:26
  takes longer than recorded human civilization has existed, multiplied several
• 1:06:32
  times over. This is why no survey has caught it moving.
• 1:06:37
  Detecting a planet requires seeing its shift position against the
• 1:06:41
  background stars. Planet nine moves so slowly that across an
• 1:06:47
  entire human lifetime of observation, across all of recorded telescopic astronomy,
• 1:06:54
  it would have covered only a tiny arc of its
• 1:06:57
  full path. Traditional skye surveys designed to catch fast moving
• 1:07:03
  nearby objects or distant but predictable ones, were never built
• 1:07:08
  to find something this slow at this distance. The faintness
• 1:07:13
  is the other wall. At distances between four hundred and
• 1:07:17
  eight hundred astronomical units, where Planet nine is most likely
• 1:07:22
  to be sitting right now, Statistically, sunlight has spread so
• 1:07:27
  thin that even a world the size of a small
• 1:07:30
  ice giant reflects almost nothing back toward us. The brightness
• 1:07:35
  of a planet depends on how much sunlight reaches it
• 1:07:38
  and how much it reflects. Sunlight falls off with the
• 1:07:43
  square of distance. At five hundred astronomical units, a planet
• 1:07:49
  receives about two hundred fifty thousand times less sunlight than
• 1:07:53
  Earth does. What little it reflects then has to travel
• 1:07:58
  that same enorrmal distance back. The result is a point
• 1:08:03
  of light so faint that most of the telescopes that
• 1:08:07
  have swept the sky for the past two centuries were
• 1:08:11
  not sensitive enough to detect it, even if they had
• 1:08:15
  been pointed directly at it. This is not a failure
• 1:08:19
  of diligence. I TEA is a physics problem. The signal
• 1:08:25
  was below the noise floor of everything we had here
• 1:08:28
  is the strange thing. We have surveyed large fractions of
• 1:08:32
  the sky. Generations of astronomers have pointed powerful instruments outward
• 1:08:38
  and catalogued what they found, and yet a planet ten
• 1:08:43
  times the mass of Earth could have been sitting in
• 1:08:46
  our own Solar System this entire time undetected, because the
• 1:08:51
  distance makes it nearly invisible, and its motion makes it
• 1:08:55
  nearly indistinguishable from a background star on any single night
• 1:09:01
  of observation. The night sky does not give up objects
• 1:09:05
  like this easily. Some researchers have gone further and asked
• 1:09:10
  where Planet nine actually came from. One theory is that
• 1:09:15
  it formed in the inner Solar System alongside Jupiter, Saturn, Uranus,
• 1:09:21
  and Neptune in the chaotic first one hundred million years
• 1:09:26
  of the Solar system's history. The early Solar System was
• 1:09:30
  not the orderly arrangement it resembles today. Giant planets were migrating,
• 1:09:36
  Their gravitational interactions were violent and unpredictable. Smaller protoplanets forming
• 1:09:43
  in that environment could be flung outward by a close
• 1:09:46
  encounter with Jupiter or Saturn, sent on to wide elongated
• 1:09:52
  orbits that carried them to the extreme Outer Solar System.
• 1:09:57
  If one of those ejected bodies were massive enough, it
• 1:10:01
  could have settled into a stable, long period orbit rather
• 1:10:05
  than being thrown out of the Solar System entirely. Planet nine,
• 1:10:12
  under this scenario, is not a foreign object captured from
• 1:10:16
  another star. It is a native of the early Solar
• 1:10:20
  System that got lost in its own backyard and has
• 1:10:24
  been orbiting in the dark ever since. Other researchers have
• 1:10:27
  proposed that planet nine might be a captured planet, a
• 1:10:31
  world born around another star and grabbed by the Sun's
• 1:10:35
  gravity during the period when the Sun was still embedded
• 1:10:38
  in its berth cluster surrounded by other young stars at
• 1:10:43
  relatively close range. Captured planets are not impossible. The dynamics
• 1:10:50
  of a star cluster can result in objects exchanging between systems.
• 1:10:56
  Whether this explains Planet nine specifically is to say, but
• 1:11:01
  it is not ruled out. What is clear is that
• 1:11:05
  nothing about this object, if it exists, is small or ambiguous.
• 1:11:12
  The object at the center of this hypothesis is not
• 1:11:15
  some small borderline body. It would be one of the
• 1:11:19
  dominant gravitational players in the Outer Solar System, and its
• 1:11:23
  absence from our catalogues after centuries of skywatching is either
• 1:11:28
  an extraordinary oversight or a sign that the hypothesis is wrong.
• 1:11:34
  The orbital clustering at the heart of the planet nine
• 1:11:37
  hypothesis is not something you can see by looking at
• 1:11:40
  a picture of the Solar System. It lives in the numbers. Specifically,
• 1:11:46
  it lives in the angles the orientations of orbits when
• 1:11:51
  you plot them mathematically and ask whether they are pointing
• 1:11:54
  in random directions or whether something has quietly pushed them
• 1:11:59
  into a line. When Battergen and Brown ran those numbers
• 1:12:04
  in twenty sixteen, what they found was not subtle. Six
• 1:12:10
  distant Kuiper Belt objects were clustered in physical space in
• 1:12:14
  a way that had roughly a one in fifteen thousand
• 1:12:17
  chants of being a coincidence. The question was what caused it,
• 1:12:24
  and the mechanism they proposed has a name, secular resonance.
• 1:12:30
  Secular resonance is one of the slower, quieter forces in
• 1:12:34
  gravitational physics, but over enough time it is extraordinarily powerful.
• 1:12:40
  When a massive planet orbits in a distant, elongated path,
• 1:12:45
  it does not simply pass by smaller objects and leave
• 1:12:48
  them undisturbed. Its gravity tugs on them with every orbit.
• 1:12:54
  Because the geometry is never quite the same twice those
• 1:12:58
  tugs accumulate. Over millions of years, the planet gradually herds
• 1:13:04
  the orbital orientations of nearby small bodies, pulling their closest
• 1:13:10
  approach points toward a preferred direction and tilting their orbital
• 1:13:15
  planes into alignment. The process is slow enough that you
• 1:13:20
  would never notice it on a human timescale, but the
• 1:13:24
  Solar System is four and a half billion years old.
• 1:13:29
  Secular resonance has had time to work. We already know
• 1:13:33
  this mechanism is real because we have been watching it
• 1:13:35
  operate for decades. Neptune does exactly this to Pluto. It
• 1:13:41
  does it to an entire population of Kuiper Belt objects
• 1:13:45
  called the Plutinos, objects locked into a two to three
• 1:13:49
  orbital resonance with Neptune, where they complete two orbits for
• 1:13:54
  every three Neptune completes. Neptune's gravity has shaped those of
• 1:13:59
  bit Roje's orbits over billions of years, herding them into
• 1:14:04
  predictable configurations that astronomers understand well enough to use as
• 1:14:09
  a calibration tool. The physics is not exotic. It is
• 1:14:15
  the same gravitational machinery that organizes ring structures around Saturn
• 1:14:20
  and Shepherd's asteroids in the inner Solar System. What Battagen
• 1:14:26
  and Brown proposed is that a more distant and more
• 1:14:29
  massive planet is doing the same thing on a larger
• 1:14:33
  sc al over longer time scales to the most remote
• 1:14:38
  objects we can detect. The specific signature they identified was twofold. First,
• 1:14:45
  the six clustered objects all had their perihelium points their
• 1:14:49
  closest approach to the Sun oriented in roughly the same direction. Statistically,
• 1:14:56
  those should be scattered randomly around the sky.
• 1:15:00
  Speaker 2: They were not.
• 1:15:02
  Speaker 1: Second, the orbital planes of those objects were all tilted
• 1:15:06
  in a consistent way relative to the plane of the
• 1:15:09
  Solar System. Again, that kind of coherence does not arise
• 1:15:14
  by chance. A planet in a specific distant orbit, they calculated,
• 1:15:20
  could produce both effects simultaneously. The clustering was not just
• 1:15:26
  an interesting pattern, It was a prediction because it told
• 1:15:31
  you where the perturbing planet had to be. The years
• 1:15:34
  after twenty sixteen brought more objects and more scrutiny. A
• 1:15:39
  twenty twenty one analysis by Battergin and collaborators incorporated a
• 1:15:44
  larger sample of distant Kuiper Belt objects and found that
• 1:15:49
  the clustering signal did not weaken it persisted in some
• 1:15:54
  respects it strengthened. Objects discovered by surveys that had had
• 1:16:00
  not been used in the original twenty sixteen study showed
• 1:16:04
  the same orientation patterns. The predicted tilt of the average
• 1:16:09
  orbital plane of the Kuiper Belt in the region where
• 1:16:13
  Planet nine's influence should dominate was compared against actual observations
• 1:16:18
  of that plane. The match was close enough to be notable.
• 1:16:23
  The tilt is small, a few degrees, but it falls
• 1:16:27
  right where the model says it should fall. Here is
• 1:16:30
  something worth holding on to the Planet nine hypothesis is
• 1:16:35
  not simply a claim that an unseen planet exists. It
• 1:16:39
  is a claim that a specific planet with a specific
• 1:16:43
  mass and orbit is producing a specific, measurable gravitational effect
• 1:16:49
  on specific objects. That level of precision makes it testable
• 1:16:54
  in a way that vague hypotheses are not. Either the
• 1:16:58
  predictions match the data, or they do not. So far
• 1:17:03
  for the objects in the original sample, and for many
• 1:17:06
  of the objects added since they match. But there is
• 1:17:11
  a serious objection, and honest science requires taking it seriously.
• 1:17:16
  Almost every one of the objects showing the clustering signature
• 1:17:20
  was discovered by surveys that did not cover the full
• 1:17:23
  sky evenly, they were concentrated in certain regions, particularly away
• 1:17:29
  from the dense star fields of the galactic plane, where
• 1:17:33
  faint objects are easier to detect. If most of the
• 1:17:38
  known extreme Kuiper Belt objects were found in overlapping patches
• 1:17:43
  of sky, then their orbital orientations might cluster simply because
• 1:17:48
  of where the telescopes were pointed, not because any planet
• 1:17:52
  herded them. This is the observational bias argument, and it
• 1:17:58
  is not a fringe objection. It was published in peer
• 1:18:02
  reviewed studies by researchers who ran careful statistical tests and
• 1:18:08
  concluded that the clustering could plausibly be explained without any
• 1:18:12
  hidden planet. The response from Planet nine proponents has been
• 1:18:17
  to model the bias explicitly. They built simulations that accounted
• 1:18:22
  for where each survey looked, then asked whether the clustering
• 1:18:26
  survived after correcting for it. Their conclusion was that it did,
• 1:18:32
  that the bias alone was insufficient to produce the pattern.
• 1:18:37
  Critics pushed back on the assumptions built into those corrections.
• 1:18:42
  The debate has continued in exactly that form, each side
• 1:18:46
  refining the analysis, each side finding the result that its
• 1:18:51
  model predicts, neither has produced evidence clean enough to end
• 1:18:56
  the argument. What the field genuinely need is a sample
• 1:19:01
  of extreme Kuiper Belt objects discovered by a survey that
• 1:19:05
  covered the entire sky uniformly, with no preferred direction, no gaps,
• 1:19:11
  no detection biases that favor one orbital orientation over another.
• 1:19:17
  With a sample like that, you could measure the clustering
• 1:19:21
  directly and know whether it reflects physical reality or telescope geometry.
• 1:19:27
  That survey does not exist yet. The debate over whether
• 1:19:32
  the clustering is real or an artifact of survey bias
• 1:19:37
  is the central unresolved tension in Planet nine research. It
• 1:19:42
  is the question that the next generation of observations is
• 1:19:46
  specifically designed to settle. The Planet nine hypothesis is the
• 1:19:51
  most famous version of the hidden planet idea, but it
• 1:19:56
  is not the only one with serious scientific backing. While
• 1:20:01
  Battagen and Brown were building their case for a distant
• 1:20:04
  ice giant ten times the mass of Earth, a separate
• 1:20:09
  line of research was pointing towards something different, smaller, closer,
• 1:20:15
  and in some ways harder to dismiss. Patrick Lekovka, an
• 1:20:21
  astronomer at Kindai University in Japan, has spent years analyzing
• 1:20:26
  the orbital structure of the Kuiper Belt from a different angle.
• 1:20:31
  What he found does not require a world the size
• 1:20:34
  of Neptune sitting a thousand astronomical units away. His proposed planet,
• 1:20:41
  sometimes called the Kuiper Belt planet sometimes Planet y, would
• 1:20:46
  have a mass somewhere between one and a half and
• 1:20:49
  three times that of Earth. Its orbit would place it
• 1:20:53
  at roughly two hundred to five hundred astronomical units from
• 1:20:58
  the Sun. That is still an extraordinary distance. Neptune sits
• 1:21:03
  at only thirty astronomical units, and even Pluto rarely ventures
• 1:21:08
  past fifty, but compared to the proposed location of planet nine,
• 1:21:13
  this is practically next door. The distinction matters. Planet nine,
• 1:21:19
  if it exists, is extreme in almost every sense. It
• 1:21:23
  would be massive, unimaginably remote, sitting in an orbit so
• 1:21:28
  elongated that its period might span tens of thousands of years.
• 1:21:33
  To explain why it hasn't been found, you have to
• 1:21:36
  pile up reasons its vast distance, its slow motion across
• 1:21:41
  the sky, the fraction of its orbits spent at maximum
• 1:21:45
  separation from the Sun. Each reason is legitimate, but the
• 1:21:50
  cumulative weight of them starts to feel like special pleading
• 1:21:55
  planet y requires far less of that. A smaller body
• 1:22:00
  at closer range should reflect more detectable light, move more
• 1:22:05
  quickly against the background of stars, in principle show up
• 1:22:10
  in a well designed sky survey far sooner. What Lekavka's
• 1:22:14
  model is specifically trying to explain are several features of
• 1:22:19
  the Kuiper Belt that standard formation theory handles poorly. The
• 1:22:24
  Kuiper Cliff is.
• 1:22:26
  Speaker 2: One of them.
• 1:22:27
  Speaker 1: That abrupt drop off in the number of objects beyond
• 1:22:30
  fifty astronomical units has never been cleanly reproduced in simulations
• 1:22:36
  that include only the four known giant planets. Something seems
• 1:22:41
  to have swept that region or sculpted its outer boundary.
• 1:22:46
  With the precision that random physical processes don't naturally produce
• 1:22:52
  a planet orbiting in the two hundred to five hundred
• 1:22:55
  astronomical units range, could over the age of the Solar
• 1:23:00
  System have exerted exactly the kind of gradual gravitational influence
• 1:23:06
  needed to thin out that population and sharpen that edge.
• 1:23:10
  There is also the question of certain resonant objects bodies
• 1:23:15
  in the Kuiper Belt whose orbits are locked into specific
• 1:23:18
  mathematical ratios with Neptune's orbital period. The distribution of these
• 1:23:24
  objects doesn't quite match what models predict. Some of them
• 1:23:29
  are in configurations that are stable today but are difficult
• 1:23:34
  to produce in simulations without invoking an additional gravitational influence
• 1:23:40
  somewhere in the outer System, a moderate sized planet at
• 1:23:45
  the distances Lekouka proposes, could have nudged these objects into
• 1:23:50
  their current configurations during the early chaotic period of Solar
• 1:23:55
  System history, and unlike some of the orbital finger prints
• 1:24:00
  attributed to Planet nine, these features have been noted in
• 1:24:05
  populations that are large enough to carry reasonable statistical weight.
• 1:24:10
  Speaker 2: Here is the.
• 1:24:11
  Speaker 1: Strange thing about Planet wise absence from our catalogs. Even
• 1:24:16
  at two hundred astronomical units, the closer end of its
• 1:24:20
  proposed range, an Earth mass object receives so little sunlight
• 1:24:25
  that its reflected brightness would be almost undetectable to most
• 1:24:29
  telescopes that have ever been pointed at the sky. It
• 1:24:33
  would appear to move slowly against background stars, though faster
• 1:24:38
  than Planet nine would. Its predicted location is not a
• 1:24:42
  broad swath of the sky, but a more targeted region.
• 1:24:46
  Based on the orbital mechanics of the objects, it's supposed
• 1:24:49
  to be influencing. That targeted prediction is both an advantage
• 1:24:54
  and a limitation. It means the search is more focused,
• 1:24:59
  but but it also means that if the predicted location
• 1:25:03
  is wrong by even a moderate amount, decades of sky
• 1:25:07
  surveys could have swept past it without noticing. What makes
• 1:25:11
  this period of Kuiper Belt research genuinely unusual is that
• 1:25:16
  two distinct planet hypotheses proposing objects of very different character
• 1:25:21
  in different parts of the Outer Solar System are both
• 1:25:25
  considered scientifically credible. At the same time, they are not
• 1:25:30
  simply variations on the same idea. Planet nine is a
• 1:25:34
  massive ice giant in an extreme elongated orbit, proposed to
• 1:25:40
  explain a clustering pattern in the most distant Kuiper Belt objects.
• 1:25:45
  Planet y is a much smaller body in a more modest,
• 1:25:49
  though still remote orbit, proposed to explain structural features in
• 1:25:55
  the classical and resonant belt populations. The orbital and n
• 1:26:00
  nonomalies they address are not identical.
• 1:26:03
  Speaker 2: It is at least.
• 1:26:04
  Speaker 1: Theoretically possible that both objects exist and that each one
• 1:26:09
  has been quietly shaping a different part of the Outer
• 1:26:12
  Solar System for billions of years. The vera Reuben observatory
• 1:26:17
  is expected to be the instrument that settles at least
• 1:26:20
  part of this. With a sky coverage and detection sensitivity
• 1:26:25
  far beyond anything previously available, Reuben should be capable of
• 1:26:30
  finding a Planet Y class object within its first few
• 1:26:34
  years of full operations, assuming the object falls anywhere near
• 1:26:39
  the predicted range of distances and sky positions. Some researchers
• 1:26:45
  believe Planet Y is actually the easier target of the two,
• 1:26:50
  not because it's brighter in any absolute sense, but because
• 1:26:54
  its predicted location is more constrained and its distance is
• 1:26:59
  less extreme. If Reuben surveys the relevant region and finds
• 1:27:04
  nothing that would impose very tight limits on where such
• 1:27:08
  a world could be hiding, may effectively rule out the
• 1:27:12
  hypothesis entirely. If it finds something, the decades of work
• 1:27:18
  building these models will have paid off in a way
• 1:27:21
  few Outer Solar System discoveries ever have. Whether Planet Y
• 1:27:27
  and Planet nine are competing explanations for the same anomalies,
• 1:27:32
  or whether they might somehow both be real, is a
• 1:27:36
  question the field has not yet been able to resolve
• 1:27:39
  with available data. Not everyone looking at the strange orbital
• 1:27:45
  clustering of distant Kuiper Belt objects, thinks a hidden planet
• 1:27:50
  is responsible. Some researchers look at the same data, the
• 1:27:54
  same orbital patterns, the same gravitational fingerprints, and arrive at
• 1:27:59
  a completely different conclusion. Not a planet, not even an
• 1:28:05
  unknown object, something far more fundamental. What if the problem
• 1:28:10
  isn't what's hiding in the outer Solar System, but rather
• 1:28:14
  what's hiding in the equations we used to describe it.
• 1:28:18
  The alternative they're pointing to has a name Modified Newtonian dynamics,
• 1:28:24
  usually shortened to MOND. It was developed in the early
• 1:28:28
  nineteen eighties by Israeli physicist Mordehai Milgram, and it was
• 1:28:33
  not designed with the Kuiper Belt in mind at all.
• 1:28:37
  Milgram was trying to solve a completely different problem. Galaxies
• 1:28:42
  rotate in a way that makes no sense under standard
• 1:28:45
  Newtonian gravity. The stars at the outer edges of galaxies
• 1:28:50
  move too fast. By Newton's equations, those stars should be
• 1:28:56
  moving slower because they're far from the gravitational star center,
• 1:29:01
  and the pull should weaken with distance. Instead, the rotation
• 1:29:06
  curves stay flat. Stars at the edges move roughly as
• 1:29:11
  fast as stars near the core. The standard explanation is
• 1:29:15
  dark matter vast invisible halos of undetected mass surrounding every galaxy,
• 1:29:21
  providing extra Gravitymond offers a different fix. It proposes that
• 1:29:28
  gravity itself behaves differently. At very low accelerations. Below a
• 1:29:33
  certain threshold, gravity doesn't fall off quite the way Newton said,
• 1:29:39
  it gets a little stronger than expected. This modification is
• 1:29:44
  small and essentially undetectable in the kinds of gravitational environments
• 1:29:49
  we normally study, but at galaxy scales and potentially at
• 1:29:54
  the extreme edges of a solar system, it starts to matter.
• 1:29:59
  Here is the thing that makes Mond relevant to the
• 1:30:02
  Kuiper Belt. At distances of several hundred astronomical units from
• 1:30:07
  the Sun, objects experience extraordinarily weak gravitational accelerations. The Sun's
• 1:30:14
  pull is real, but it is faint, and under Mond.
• 1:30:19
  At those faint acceleration levels, the gravitational influence of the
• 1:30:24
  broader galactic environment, specifically the stars packed into the center
• 1:30:29
  of the Milky Way, becomes non negligible in standard Newtonian gravity.
• 1:30:36
  That galactic pull is so small at Solar system distances
• 1:30:40
  that it gets safely ignored under Mond. The calculation changes
• 1:30:47
  the external gravitational field from the galaxy seeps in more
• 1:30:51
  effectively at the low acceleration frontier of the Solar System.
• 1:30:56
  A pair of researchers ran this calculation and found something
• 1:31:00
  under Moond, those distant Kuiper Belt objects should have their
• 1:31:05
  orbits nudged into a preferred alignment, pulled gently by the
• 1:31:09
  combined gravitational influence of the galactic center filtering through the
• 1:31:14
  modified equations. The clustering, in other words, comes out not
• 1:31:21
  from a hidden planet parked a few hundred astronomical units away,
• 1:31:26
  but from the galaxy itself, acting on the outermost reaches
• 1:31:30
  of our Solar System in a way that standard physics
• 1:31:34
  would never predict. The fingerprint looks similar the orbital grouping,
• 1:31:40
  the preferred directions the statistical pattern that Battagen and Brown
• 1:31:45
  interpreted as the work of planet nine. Moond says all
• 1:31:50
  of it could be produced by galactic gravity instead. The
• 1:31:54
  implications of this, if it holds, are almost harder to
• 1:31:58
  absorb than the planet hypothesis. A hidden ice giant is
• 1:32:03
  an astonishing discovery, but it fits comfortably inside our current
• 1:32:08
  understanding of physics. It's just a planet we haven't found yet.
• 1:32:13
  Moond being correct is a different kind of discovery.
• 1:32:17
  Speaker 2: Entirely.
• 1:32:18
  Speaker 1: It would mean that Newton's law of gravitation, which has
• 1:32:22
  been working flawlessly for three centuries across every test we've
• 1:32:26
  applied it to within the Solar System, has a blind spot.
• 1:32:32
  It behaves differently in a regime of very low acceleration
• 1:32:36
  that we haven't been able to probe carefully from here.
• 1:32:41
  That is not a small revision. Most astronomers remain deeply skeptical,
• 1:32:46
  and there are real reasons for that skepticism. MOOND has
• 1:32:51
  a complicated history. It works remarkably well for certain galaxy
• 1:32:56
  rotation problems, but it has a much harder time time
• 1:33:00
  with other observations, particularly galaxy clusters, where dark matter models
• 1:33:06
  outperform it substantially. Within the Solar System itself, Mond has
• 1:33:12
  produced predictions that don't sit cleanly with what we observe.
• 1:33:17
  The Pioneer anomaly, an unexplained drift in the trajectories of
• 1:33:22
  the Pioneer spacecraft that was once thought to be a
• 1:33:26
  candidate for Mond effects, turned out to be explained entirely
• 1:33:31
  by heat radiation from the spacecraft's own power systems. MOOND
• 1:33:37
  didn't predict that outcome, and it didn't explain away the
• 1:33:41
  anomaly either. There's also a more specific problem. The orbital
• 1:33:46
  clustering of distant Kuiper Belt objects is a very precise signal.
• 1:33:51
  It has particular statistical properties, particular orbital geometries, particular preferred directions.
• 1:33:59
  Getting all of that right from a galactic tidal effect
• 1:34:02
  under Moond is genuinely difficult. The galactic gravity hypothesis has
• 1:34:08
  to reproduce the specifics, not just the general tendency toward alignment.
• 1:34:14
  So far, that case has not been made convincingly enough
• 1:34:18
  to move most of the community. The planet nine interpretation
• 1:34:23
  still commands more support, precisely because a gravitationally dominant nearby
• 1:34:29
  body is a cleaner, more targeted explanation for a clean
• 1:34:34
  and targeted signal. But dismissing Moond entirely because it's inconvenient
• 1:34:39
  would be its own kind of error. The theory has
• 1:34:43
  survived longer than many of its critics predicted. It keeps
• 1:34:48
  finding corners of observational data where it performs better than
• 1:34:52
  it should if it were simply wrong. And the galactic
• 1:34:57
  tidal effect on the outer Solar System is a a
• 1:35:00
  real physical mechanism even in standard gravity, Mond simply makes
• 1:35:06
  it stronger. The possibility that the signal astronomers are reading
• 1:35:11
  as a planet might actually be written by the gravity
• 1:35:15
  of the entire Milky Way is exactly the kind of
• 1:35:19
  uncomfortable alternative that good science cannot simply dismiss. On a
• 1:35:25
  ridge in the Chilean Atacama Desert, a telescope, unlike anything
• 1:35:30
  previously built in the history of astronomy, is currently working
• 1:35:34
  its way through the first year of a ten year
• 1:35:36
  survey of the sky. It is called the Vera Sea
• 1:35:40
  Rubin Observatory, named for the astronomer who spent decades demonstrating
• 1:35:46
  that galaxies contain far more mass than anyone could see.
• 1:35:52
  The choice of name is appropriate. Rubin spent her career
• 1:35:56
  proving that the universe hides things in plain sight. The
• 1:36:01
  telescope bearing her name was built in no small part
• 1:36:05
  to do exactly the same work. Most telescopes operate like detectives,
• 1:36:10
  chasing specific suspects. You identify a target, you point the instrument,
• 1:36:16
  You collect light from that one object for as long
• 1:36:19
  as you need. The Vera Reuben Observatory does not work
• 1:36:23
  that way. Its survey strategy is closer to a dragnet
• 1:36:27
  than an investigation. Every few nights it images the entire
• 1:36:32
  accessible sky, then it does it again and again. Over
• 1:36:38
  a decade of operations, it will build up a massive,
• 1:36:41
  repeated record of the sky so complete that anything that moves, brightens, dims,
• 1:36:48
  or appears where it wasn't before will be caught. There
• 1:36:52
  is no hiding from a telescope that sees everything repeatedly
• 1:36:57
  for ten years straight. The engine zneering behind this is
• 1:37:01
  worth holding in your mind for a moment. The primary
• 1:37:05
  mirror is eight point four meters across. That is large
• 1:37:10
  by any measure, though there are bigger mirrors in the world.
• 1:37:15
  What makes Rubin genuinely unprecedented is its camera. It carries
• 1:37:21
  the largest digital camera ever built for astronomy, capable of
• 1:37:26
  capturing an image covering roughly forty times the area of
• 1:37:30
  the full Moon in a single exposure. Most wide field
• 1:37:35
  cameras in astronomy sacrifice depth for breadth, catching only the
• 1:37:40
  brightest objects across a wide patch of sky. Rubin is
• 1:37:45
  deep enough to detect objects that would be invisible to
• 1:37:48
  previous survey instruments while still covering the entire sky on
• 1:37:53
  a cadence of days. That combination has never existed before.
• 1:37:58
  For Kuiper Belt science. The implications are almost difficult to overstate.
• 1:38:04
  Right now, after thirty years of searching with every instrument available,
• 1:38:10
  astronomers have cataloged roughly three thousand to four thousand Kuiper
• 1:38:14
  Belt objects. Rubin is expected to discover around thirty five
• 1:38:20
  thousand in its first few years alone. That is not
• 1:38:24
  an incremental improvement, It is a transformation. The known population
• 1:38:31
  of the Outer Solar System is about to grow by
• 1:38:34
  nearly a factor of ten, and most of those new
• 1:38:38
  objects will be found in the first year or two
• 1:38:41
  of the survey, not the last. What does that mean
• 1:38:46
  for the Planet nine debate? It means the argument that
• 1:38:50
  has been standing in the middle of this problem since
• 1:38:53
  twoenty sixteen is about to become answerable. The central weakness
• 1:38:58
  in the orbital cluster during evidence has always been the same.
• 1:39:03
  The objects showing strange alignment were all discovered by surveys
• 1:39:08
  that covered limited and specific patches of sky. If the
• 1:39:13
  surveys were biased towards certain directions, the clustering they found
• 1:39:18
  could be an artifact of where the telescopes were pointed,
• 1:39:23
  rather than a genuine physical signal. Critics have made this
• 1:39:28
  argument for nearly a decade and supporters of the planet
• 1:39:32
  nine hypothesis have never been able to fully refute it
• 1:39:36
  with existing data. The data sets were simply too small,
• 1:39:42
  too patchy, and too shaped by the biases of particular
• 1:39:46
  instruments and observing programs. Rubin changes this entirely. A full
• 1:39:53
  sky survey repeated systematically over years does not have the
• 1:39:58
  same directional bias as targeted observing campaigns. When Reuben has
• 1:40:04
  added tens of thousands of new Kuiper Belt objects to
• 1:40:07
  the catalog, and when researchers run the clustering analysis on
• 1:40:11
  that full, unbiased sample, the answer will be clear. Either
• 1:40:18
  the clustering is real and shows up in the complete
• 1:40:21
  data set stronger and cleaner than before, or it dissolves
• 1:40:26
  into noise when the gaps in the older surveys are
• 1:40:29
  filled in. There is no middle ground here. The statistics
• 1:40:35
  with thirty five thousand objects instead of a few dozen
• 1:40:39
  will be overwhelming either way. Beyond clustering, Ruben will systematically
• 1:40:45
  address the extended belt. The population of objects sitting at
• 1:40:50
  seventy to ninety astronomical units from the Sun detected in
• 1:40:54
  hints by the Subaru telescope survey needs confirmation find yeing
• 1:41:00
  those distant objects is genuinely hard. They are faint, they
• 1:41:05
  move slowly. You need deep imaging and long baselines to
• 1:41:09
  distinguish them from background stars. Rubin was not designed specifically
• 1:41:15
  for this problem, but it is exactly the kind of
• 1:41:18
  instrument that solves it anyway. Repeatedly imaging the sky to
• 1:41:24
  great depth, it will catch distant objects, moven incrementally from
• 1:41:29
  frame to frame, across months and years of observations. If
• 1:41:34
  a second population of Kuiper Belt objects really does exist
• 1:41:38
  at seventy to ninety astronomical units, Rubin will map it.
• 1:41:43
  If the apparent detection was a statistical fluke, Rubin will
• 1:41:48
  reveal that too. There is something almost strange about having
• 1:41:52
  the answer this close. Astronomers have been arguing about planet
• 1:41:56
  nine for nearly a decade. They argued about whether the
• 1:42:00
  clustering was real. They argued about the mass and the
• 1:42:04
  orbit and the distance. They proposed moond as an alternative,
• 1:42:09
  and debated that the field has spent years in a
• 1:42:13
  kind of productive uncertainty, generating hypotheses faster than the data
• 1:42:18
  could test them. Ruben is the data catching up. Researchers
• 1:42:24
  have been specific about the timeline within its first year
• 1:42:28
  of scientific operations. Ruben should have enough new Kuiper Belt
• 1:42:33
  detections to begin running meaningful clustering tests within two years.
• 1:42:40
  The results should be unambiguous. The team members who have
• 1:42:43
  been working on Planet nine the longest are on record
• 1:42:47
  saying that Reuben will either find the planet or definitively
• 1:42:50
  rule it out, not narrow the range, not strengthen the evidence,
• 1:42:56
  settle it. That is a rare thing for a scientist
• 1:42:59
  to say, and the fact that they are saying it
• 1:43:02
  reflects how thoroughly Reuben's survey design addresses the specific weaknesses
• 1:43:08
  that have kept the debate alive. The Atacama is one
• 1:43:13
  of the driest places on Earth, which is why astronomers
• 1:43:17
  build there. Clear skies, minimal atmospheric distortion, almost no light pollution.
• 1:43:26
  A decade from now, the data set that Reuben accumulates
• 1:43:30
  on that ridge will be one of the most scientifically
• 1:43:33
  valuable records of the sky ever assembled. Within a year
• 1:43:38
  or two of its first data release, the VERA Reuben
• 1:43:42
  Observatory is expected to do something no previous instrument has managed,
• 1:43:48
  either find Planet nine or prove conclusively that it is
• 1:43:53
  not where the models say it should be a surprising
• 1:43:56
  fraction of Kuiper Belt objects.
• 1:43:58
  Speaker 2: Are not alone.
• 1:44:00
  Speaker 1: When astronomers began cataloging the Kuiper Belt in earnest after
• 1:44:05
  nineteen ninety two, they expected to find a collection of solitary,
• 1:44:09
  frozen bodies drifting in the dark on independent orbits. What
• 1:44:14
  they found instead, as the surveys deepened and the instruments improved,
• 1:44:20
  was something harder to explain. Roughly a third of the
• 1:44:25
  cold classical Kuiper Belt objects, the quieter, more circular population
• 1:44:31
  that sits near the heart of the belt, appear to
• 1:44:34
  have companions, not moons in the traditional sense, true binary partners,
• 1:44:41
  two roughly equal sized bodies orbiting each other as they
• 1:44:46
  moved together through the outer Solar System. This is strange.
• 1:44:51
  In the inner Solar System, among the rocky asteroids and
• 1:44:54
  the near Earth population, binaries exist, but they are relatively rare.
• 1:45:01
  The Kuiper Belt's binary fraction is much higher, and in
• 1:45:05
  the cold classical population it is higher still. That difference
• 1:45:10
  is a clue. It suggests that whatever process formed the
• 1:45:15
  cold classical objects was fundamentally different from what built the
• 1:45:20
  rocks closer to the Sun, different enough to leave paired
• 1:45:24
  systems behind at a rate that is almost impossible to
• 1:45:28
  explain through random chance alone. Here is what a binary
• 1:45:33
  KBO actually looks like. Two objects, often within a factor
• 1:45:39
  of two of each other in size, separated by distances
• 1:45:43
  that can range from a few hundred to several thousand kilometers.
• 1:45:49
  They orbit their common center of mass on time scales
• 1:45:53
  of days to months at the distances of the Kuiper Belt.
• 1:45:57
  This pairing is stable. There is nothing nearby to disrupt it.
• 1:46:03
  The Sun's gravity is weak at forty or fifty astronomical units.
• 1:46:08
  Encounters with other large bodies are rare, so once a
• 1:46:12
  binary forms out there, it tends to stay a binary.
• 1:46:16
  This is part of why so many survived. The outer
• 1:46:20
  Solar System is a quiet neighborhood, and quiet neighborhoods preserve things.
• 1:46:25
  What caused them to form in pairs in the first
• 1:46:28
  place is where the science gets genuinely interesting. For a
• 1:46:32
  long time, the default assumption was collisions. Small bodies in
• 1:46:38
  the early Solar System collided constantly. They stuck together, broke apart,
• 1:46:45
  and slowly built up larger objects through a process called accretion.
• 1:46:51
  In this model, a binary would form when a collision
• 1:46:55
  produced a loosely bound pair rather than a single merged body.
• 1:47:00
  It is a reasonable picture, and it works reasonably well
• 1:47:05
  for populations closer to the Sun. For the Kuiper Belt, though,
• 1:47:10
  it runs into trouble immediately. The cold classical objects are
• 1:47:15
  too numerous, too similarly sized, and paired too often for
• 1:47:20
  collisions to explain them cleanly. The math does not come
• 1:47:24
  out right. The competing idea is called the streaming instability.
• 1:47:30
  The concept is worth holding in mind because it changes
• 1:47:34
  the whole picture of how the outer Solar system was built.
• 1:47:39
  In the early Solar nebula, the disc of gas and
• 1:47:42
  dust surrounding the young Sun was not uniform. Aerodynamic drag
• 1:47:48
  caused small solid particles to drift inward and concentrate into
• 1:47:53
  dense filaments and clumps. At a certain density, a clump
• 1:47:58
  could become gravitation self bound. It would stop drifting and
• 1:48:03
  begin to collapse under its own weight, directly forming a
• 1:48:08
  solid body without any need for collisions to build it
• 1:48:12
  up piece by piece. This is the streaming instability, and critically,
• 1:48:19
  when researchers model this collapse in detail, the most common
• 1:48:23
  outcome is not a single object. It is two. The
• 1:48:28
  collapsing clump tends to frag meant and form a bound
• 1:48:32
  pair almost naturally, because the angular momentum of the infalling
• 1:48:37
  material does not permit a clean single body collapse. Pairs
• 1:48:42
  are the path of least resistance. Triplets also appear in
• 1:48:47
  the simulations, though less frequently. This means the binary systems
• 1:48:52
  scattered across the cold classical Kuiper Belt are not accidents.
• 1:48:57
  They are the default product of the formation mechanism. They
• 1:49:01
  are what you expect to find if the streaming instability
• 1:49:05
  is correct. Each binary pair is, in a very literal sense,
• 1:49:10
  a fossil from the moment of formation. The two components
• 1:49:15
  formed together from the same collapsing cloud of material in
• 1:49:20
  the same instant, roughly four point five billion years ago.
• 1:49:25
  They have been orbiting each other ever since. The discovery
• 1:49:29
  of triple systems pushed this further. A triple system in
• 1:49:33
  the Kuiper Belt is exactly what it sounds like, three
• 1:49:38
  objects gravitationally bound to one another. The first confirmed triple
• 1:49:43
  was already remarkable. Then a second candidate emerged. A binary
• 1:49:49
  that had been cataloged as a simple two body system
• 1:49:52
  showed subtle irregularities in how its components moved. When the
• 1:49:58
  orbital dynamics will work through carefully. The only clean explanation
• 1:50:03
  was a third body tucked in close to one of
• 1:50:06
  the existing pair, too close to be resolved directly by
• 1:50:10
  telescope imagery, but detectable through its gravitational effect on the
• 1:50:15
  orbits it shared. The inference from orbital behavior rather than
• 1:50:21
  direct detection, is the same method used to find exoplanets.
• 1:50:26
  Something is there. We can see what it is doing
• 1:50:30
  even when we cannot see it. The existence of multiple
• 1:50:34
  triple systems immediately raises a statistical point that is almost uncomfortable.
• 1:50:41
  If we have found two and one of them was
• 1:50:44
  only detectable through indirect methods, how many are we simply missing?
• 1:50:50
  The Kuiper Belt is far enough away that resolving close
• 1:50:54
  companions requires ideal conditions systems where the third body orbits
• 1:51:01
  within a few hundred kilometers of its partner, would be
• 1:51:05
  effectively invisible to current survey instruments. The true triple fraction
• 1:51:11
  could be substantially higher than what the catalogs show hidden,
• 1:51:15
  not because triples are rare, but because they are compact.
• 1:51:20
  For the formation models, this matters enormously. The streaming instability
• 1:51:26
  scenario handles binaries and triples naturally, because the gravitational collapse
• 1:51:32
  of a rotating clump of material tends to fragment at
• 1:51:36
  multiple scales. The collision based accretion model struggles to produce
• 1:51:42
  them at the observed rates, because getting two bodies to
• 1:51:46
  end up in a stable mutual orbit through a random
• 1:51:50
  collision requires a very narrow range of impact parameters. Producing
• 1:51:57
  triples through collisions requires thread an even narrower needle. The
• 1:52:03
  numbers simply favour gravitational collapse. The streaming instability passes this
• 1:52:10
  test in a way that sequential accretion does not. The
• 1:52:14
  existence of these multiple systems is not a footnote in
• 1:52:18
  Kuiper belt science. It is one of the cleanest windows
• 1:52:22
  into how the outer Solar system was actually assembled from
• 1:52:26
  the raw materials of the early solar nebula. In January
• 1:52:31
  of twenty twenty four, a small team of Japanese astronomers
• 1:52:35
  set up telescopes at multiple locations across Japan and waited
• 1:52:40
  for a frozen rock the size of a small country
• 1:52:44
  to pass in front of a distant star. The object
• 1:52:47
  they were watching is called two thousand two x FI
• 1:52:50
  nine three. It is not famous, It has no dramatic backstory.
• 1:52:57
  It sits in a three to two orbital resonance with Neptune,
• 1:53:01
  meaning it completes exactly two orbits for every three that
• 1:53:05
  Neptune completes, a gravitational arrangement that keeps it locked in
• 1:53:10
  a predictable path through the outer Solar System. Its diameter
• 1:53:16
  is roughly five hundred kilometers. That sounds large until you
• 1:53:21
  remember that Earth's moon is about three thousand, five hundred
• 1:53:25
  kilometers across in the Kuiper Belt. Five hundred kilometres is ordinary.
• 1:53:31
  There are hundreds of objects in this size range. Nothing
• 1:53:36
  about two thousand two x Fi nine three had ever
• 1:53:39
  given astronomers a reason to treat it differently.
• 1:53:42
  Speaker 2: From any of them.
• 1:53:44
  Speaker 1: What made January of twenty twenty four special was geometry.
• 1:53:50
  The object was going to pass directly in front of
• 1:53:52
  a bright background star as seen from Japan, an event
• 1:53:57
  astronomers call a stellar occultation. These alignments are rare, The
• 1:54:03
  window of opportunity is brief. The shadow of the object
• 1:54:07
  sweeps across Earth's surface at the same speed the object
• 1:54:11
  is moving relative to the star, and if you are
• 1:54:14
  not in the right place at the right moment, you
• 1:54:17
  miss it entirely. Coarrimatsu and his team had calculated where
• 1:54:23
  the shadow would fall. They positioned themselves accordingly, spread across
• 1:54:29
  multiple sights to maximize the chances of a clean detection.
• 1:54:34
  Then they waited. Here is what a stellar occultation actually
• 1:54:38
  tells you. As the object drifts in front of the star,
• 1:54:42
  the star's light drops. If the object has no atmosphere,
• 1:54:47
  the drop is sharp and abrupt. The star simply vanishes
• 1:54:51
  the instant the solid body eclipses it and reappears just
• 1:54:56
  as suddenly. When the body passes, the edges of the
• 1:55:00
  dimming curve are clean. What you get is a precise
• 1:55:03
  measurement of the object's size and shape. Astronomers have used
• 1:55:08
  this technique for decades, and for airless Kuiper belt objects,
• 1:55:13
  it almost always produces exactly this kind of clean, hard
• 1:55:17
  edged signal. An atmosphere changes everything. Gas bends light. When
• 1:55:24
  starlight passes through the edge of an atmosphere before the
• 1:55:27
  solid body blocks it entirely, the atmosphere refracts the beam,
• 1:55:32
  scattering it, dimming it gradually, rather than cutting it off.
• 1:55:37
  The star does not simply vanish, it fades. The curve
• 1:55:43
  goes soft at the edges. The shape of that softness
• 1:55:47
  tells you how thick the atmosphere is how it is structured,
• 1:55:51
  and roughly what it is made of. Every planetary atmosphere
• 1:55:56
  in the Solar System with confirmed structure has been measured
• 1:56:00
  this way at some point. The gradual dimming profile is
• 1:56:05
  the signature of something gaseous. There is no other explanation
• 1:56:10
  for it. When Arimatsu's team processed their data from January
• 1:56:15
  twenty twenty four, the curve was not clean. The star
• 1:56:20
  faded gradually. The edges were soft in a way that
• 1:56:25
  an airless five hundred kilometer rock has no business producing.
• 1:56:30
  The team check their instruments, They check the reduction pipeline.
• 1:56:35
  The signal was real. Two thousand two XV nine three
• 1:56:39
  had an atmosphere. That result was almost too strange to
• 1:56:44
  accept immediately. Pluto has an atmosphere, and Pluto is large
• 1:56:50
  enough and cold enough that nitrogen gas can persist at
• 1:56:53
  its surface without escaping into space at significant rates. Pluto
• 1:56:59
  is also in a special situation. It gets slightly closer
• 1:57:03
  to the Sun on part of its orbit, enough to
• 1:57:06
  sublimate surface ices and temporarily thicken its atmospheric envelope. Pluto
• 1:57:13
  is the exception. The expectation was that Pluto would remain
• 1:57:18
  the exception for a long time, perhaps forever. Among small
• 1:57:23
  Kuiper Belt objects, two thousand and two XV nine three
• 1:57:27
  is not Pluto. Its surface gravity is a small fraction
• 1:57:31
  of Pluto's. At five hundred kilometers across, the object barely
• 1:57:36
  holds itself into a sphere. The gravitational pull at its
• 1:57:41
  surface is so weak that a person standing on it
• 1:57:44
  could throw a ball into orbit. Under standard models of
• 1:57:49
  atmospheric physics, any volatile gas that sublimates off its surface
• 1:57:54
  should escape almost immediately. The atmosphere should not be there.
• 1:58:00
  The textbook answer was clear, and the data was contradicting it.
• 1:58:05
  Two explanations emerged, and neither is comfortable. The first is
• 1:58:11
  that the models of atmospheric retention for small cold bodies
• 1:58:15
  are wrong in some important way. Maybe at the temperatures
• 1:58:19
  and pressures relevant to the outer Kuiper Belt gases behave
• 1:58:24
  differently than the standard equations predict Maybe there are condensation
• 1:58:30
  and cold trapping effects that slow the loss of volatiles
• 1:58:34
  in ways that have not been properly accounted for. If
• 1:58:38
  this is right, other small Kuiper Belt objects might have
• 1:58:43
  thin atmospheres that we have simply never had. The geometry
• 1:58:47
  to detect the catalog of bodies considered airless might need
• 1:58:52
  to be revisited. The second explanation is more dramatic. Maybe
• 1:58:58
  two thousand two x V nine three is actively producing
• 1:59:02
  its atmosphere right now. Something on or beneath its surface
• 1:59:07
  could be venting gas, sublimating ices exposed by a recent impact,
• 1:59:13
  or outgassing from an interior that is warmer than it
• 1:59:17
  should be. If the atmosphere is being actively replenished, the
• 1:59:22
  object is not geologically dead. It is doing something. The
• 1:59:28
  frozen Outer Solar System, which astronomers have described for decades
• 1:59:32
  as inert and unchanging, would be harboring active processes in
• 1:59:38
  at least some of its smaller members. Neither possibility was predicted.
• 1:59:44
  Both have serious implications for how we think about the
• 1:59:47
  Kuiper Belt as a whole. If even a five hundred
• 1:59:51
  kilometer body in the cold dark beyond Neptune can hold
• 1:59:55
  gas against the vacuum of space, then the Outer Solar
• 1:59:59
  System is a a fundamentally more complicated environment than the
• 2:00:03
  models have been treating it.
• 2:00:05
  Speaker 2: As.
• 2:00:06
  Speaker 1: The discovery did not come with a clean resolution. Arimatsu
• 2:00:11
  and his team identified the atmosphere and laid out the
• 2:00:15
  plausible explanations, but distinguishing between them requires follow up observations
• 2:00:22
  that have not yet been made. What the detection made
• 2:00:25
  certain is that something about two thousand and two x
• 2:00:29
  v nine three does not fit the standard picture. A
• 2:00:33
  frozen rock at those distances at that size was supposed
• 2:00:37
  to be silent.
• 2:00:39
  Speaker 2: It is not.
• 2:00:41
  Speaker 1: The discovery of an atmosphere on two thousand and two
• 2:00:44
  x fied nine three did not just add a footnote
• 2:00:47
  to the catalog of known KBOs. It suggested that the
• 2:00:52
  outer Solar system was considerably more active than the standard
• 2:00:56
  models had any room to accommodate. For most of the
• 2:01:00
  time astronomers have known about it, the Kuiper Belt has
• 2:01:05
  been described the same way, a cold, dark, largely static
• 2:01:10
  collection of frozen leftovers from the Solar system's formation. That
• 2:01:16
  description made sense. At forty to fifty astronomical units from
• 2:01:21
  the Sun, temperatures hover around negative two hundred twenty degrees celsius.
• 2:01:28
  Sunlight arrives so faint it would look like little more
• 2:01:31
  than a bright star. There is no meaningful solar heating
• 2:01:36
  at those distances, nothing to drive weather, nothing to crack
• 2:01:40
  ice sheets, nothing to push material around. For billions of years.
• 2:01:47
  The picture was of objects sitting unchanged in the dark,
• 2:01:51
  essentially frozen in place. Since the Solar system was young,
• 2:01:56
  the textbook version of the Kuiper Belt was a graveyard, quiet,
• 2:02:02
  cold and finished. That picture has been breaking apart. In
• 2:02:08
  twenty twenty four, researchers using the James Webb Space telescope
• 2:02:13
  pointed at two of the largest known dwarf planets in
• 2:02:16
  the Kuiper Belt, Eris and Makemake, and found something that
• 2:02:21
  did not fit the graveyard model. The data suggested both
• 2:02:25
  bodies might be showing signs of internal geological activity, not
• 2:02:31
  dramatic activity, not volcanoes visible from orbit, but chemical signatures
• 2:02:37
  and surface features that, under careful analysis hinted at processes
• 2:02:42
  still unfolding beneath the surface, possibly in both cases liquid water.
• 2:02:49
  That last part is worth sitting with liquid water in
• 2:02:54
  the outer Kuiper Belt. The reason this is surprising has
• 2:02:59
  everything to do with where the heat would come from.
• 2:03:02
  Solar energy is essentially useless at these distances, so any
• 2:03:07
  internal activity has to be powered from within. For objects
• 2:03:11
  the size of Eris and Make Make, both roughly two
• 2:03:15
  thirds the diameter of Pluto, The most plausible internal heat
• 2:03:19
  source is radiogenic decay. Certain isotopes of uranium, thorium, and
• 2:03:26
  potassium embedded in the rocky interiors of these bodies have
• 2:03:31
  been slowly releasing heat for four point six billion years,
• 2:03:36
  the way a faintly warm stone holds heat long after
• 2:03:40
  a fire has gone out. Under the right conditions, that
• 2:03:45
  steady trickle of heat sustained over geological time scales could
• 2:03:50
  be enough to maintain a layer of liquid water deep
• 2:03:54
  beneath a frozen shell. That is the hypothesis. It is
• 2:03:59
  not proven, but it is not absurd. Not everyone in
• 2:04:04
  the field is convinced the evidence is there yet. Mike Brown,
• 2:04:09
  a professor of planetary astronomy at the California Institute of
• 2:04:13
  Technology and one of the people who knows Kuiper Belt
• 2:04:16
  objects as well as anyone alive, has been direct about
• 2:04:20
  his skepticism. Everybody wants these things to be geologically active.
• 2:04:26
  He has said they might be, but the evidence, in
• 2:04:30
  his view is sparse, and he is not wrong to
• 2:04:34
  be cautious. What Web detected are indirect signals, spectroscopic signatures
• 2:04:41
  that suggest certain chemical compositions, features that could be explained
• 2:04:46
  by internal processes, but could also be explained by other things.
• 2:04:53
  To know for certain, you would need to go there.
• 2:04:56
  A spacecraft in orbit around Eiris or make Make with
• 2:05:00
  instruments designed to look for tidal flexing, thermal gradients, or
• 2:05:05
  direct signs of subsurface liquid would answer the question definitively.
• 2:05:11
  No telescope on Earth or in low orbit can do that.
• 2:05:15
  What makes the debate harder to set aside is what
• 2:05:18
  came before this. The atmosphere detected on two thousand two
• 2:05:24
  x v nine three was not expected. Either That object
• 2:05:29
  is far smaller than eris or make Make small enough
• 2:05:33
  that its surface gravity should have been completely incapable of
• 2:05:37
  holding onto any kind of volatile atmosphere over geological time.
• 2:05:43
  Yet the stellar occultation data from January twenty twenty four
• 2:05:47
  was unambiguous. Something was refracting starlight around that object. Something
• 2:05:54
  was there. The leading explanation involves recent activity outgas, the
• 2:06:00
  release of volatiles from the surface or just below it,
• 2:06:04
  triggered by processes that are still being worked out. The
• 2:06:09
  Kuiper Belt apparently is not as finished as it looked.
• 2:06:13
  What you get when you put these findings together is
• 2:06:16
  a different kind of place than the one in the textbooks.
• 2:06:20
  Not universally active, not obviously alive in any dramatic sense,
• 2:06:27
  but not frozen solid and geologically dead either. There is
• 2:06:32
  something going on out there, spread across objects of different
• 2:06:36
  sizes at different distances, producing signatures that models built around
• 2:06:42
  cold and inert bodies were not designed to detect the
• 2:06:47
  atmosphere on a small resonant object, possible subsurface liquid on
• 2:06:52
  dwarf planets. The emerging picture is of a belt that
• 2:06:56
  retained more internal energy than anyone expected, and that is
• 2:07:00
  still in quiet ways spending it. The broader implication is
• 2:07:06
  one that would have drawn skepticism not long ago. If
• 2:07:10
  subsurface oceans exist beneath Eris or Make Make, the Kuiper
• 2:07:15
  Belt becomes part of a longer list of places in
• 2:07:18
  the Solar System where liquid water might exist today. That
• 2:07:23
  list already includes Europa, Enceladus, possibly Ganymede, possibly Titan.
• 2:07:29
  Speaker 2: In some form.
• 2:07:31
  Speaker 1: Adding dwarf planets at forty or fifty astronomical units extends
• 2:07:36
  it to distances most planetary scientists would not have seriously
• 2:07:41
  entertained twenty years ago. Liquid water at those distances sustained
• 2:07:47
  by radioactive decay alone surviving under a frozen lid for
• 2:07:52
  billions of years. Is not an impossible thing. It is
• 2:07:56
  just a thing we were not looking for and therefore
• 2:07:59
  did not. A dedicated mission would change everything. A spacecraft
• 2:08:06
  sent to orbit erris, built to measure gravitational anomalies that
• 2:08:11
  would reveal internal density variations, equipped with instruments to track
• 2:08:16
  tidal deformation, would settle the subsurface ocean question within a
• 2:08:22
  few years of arrival. No such mission is currently funded.
• 2:08:28
  The travel time alone would be measured in decades with
• 2:08:32
  existing propulsion technology. But the science case is building, and
• 2:08:37
  the case is being made in large part because of
• 2:08:40
  what the last few years of telescope data have started suggesting.
• 2:08:45
  The Kuiper Belt, it is becoming clear, is not the
• 2:08:48
  Solar System's attic. It is something considerably more complicated and
• 2:08:54
  possibly considerably more alive. The Kuiper Belt began as something
• 2:08:58
  far more violent than the frozen quiet it presents today.
• 2:09:03
  Four and a half billion years ago, there was no belt.
• 2:09:07
  There was a disk, a vast churning ring of gas, dust, ice,
• 2:09:14
  stretching far beyond where Neptune now sits, carrying somewhere between
• 2:09:18
  seven and ten times the mass of the entire Earth.
• 2:09:23
  What exists out there today is a remnant, a thin
• 2:09:27
  shadow of what was once an enormous reservoir of raw
• 2:09:31
  planetary material. Understanding how that transformation happened is one of
• 2:09:37
  the harder problems in planetary science. The leading answer is
• 2:09:42
  a story about a solar system that rearranged itself so
• 2:09:47
  violently that most of what it started with simply ceased
• 2:09:51
  to exist. The dominant framework for this story has a name.
• 2:09:56
  Scientists call it the Nice model, after the city in
• 2:10:00
  France where it was first assembled by a group of
• 2:10:03
  researchers in the early two thousands. The core idea is striking.
• 2:10:10
  In the early Solar System, the four giant planets Jupiter, Saturn, Uranus,
• 2:10:17
  Neptune were not where they sit today. They orbited closer together,
• 2:10:23
  closer to the Sun, on paths that were more circular
• 2:10:27
  and more compact than their current trajectories suggest. The outer
• 2:10:32
  disc of planetesimals extended well beyond them. For a time,
• 2:10:37
  this arrangement held a fragile stability. Then something shifted. The
• 2:10:43
  trigger was a gravitational interaction between Jupiter and Saturn. As
• 2:10:48
  these two giants slowly drifted into a specific resonance with
• 2:10:52
  each other, their combined gravitational influence destabilized the entire outer System.
• 2:10:59
  The ice giants Uranus and Neptune were flung outward. Neptune
• 2:11:05
  in particular, migrated dramatically, plowing through the outer disc like
• 2:11:10
  a wave moving through shallow water. Every small body in
• 2:11:15
  its path faced a choice it did not get to make.
• 2:11:19
  Some were pushed inward toward the Inner Solar System. Some
• 2:11:23
  were flung entirely out of the Solar System, lost to
• 2:11:27
  interstellar space. A smaller fraction survived in the chaotic wake
• 2:11:32
  Neptune left behind. That surviving population is the Kuiper Belt.
• 2:11:39
  The Nice model's predictive power is genuinely impressive. It explains
• 2:11:44
  the late Heavy bombardment that period roughly four billion years ago,
• 2:11:49
  when the Inner Solar System, including the Moon and early Earth,
• 2:11:54
  was pelted with an intense wave of impactors. The model's
• 2:11:58
  dynamics naturally reduce exactly that kind of inward surge when
• 2:12:03
  the giant planets shift. It also explains how Jupiter captured
• 2:12:08
  its trojan asteroids, the large swarms of objects locked into
• 2:12:13
  gravitational equilibrium ahead of and behind the planet in its orbit.
• 2:12:19
  Those captures require a specific dynamical window that opens and
• 2:12:24
  closes during Neptune's migration. The Nice model produces that window cleanly.
• 2:12:31
  The broad shape of the Kuiper Belt its extent. Its
• 2:12:35
  general population of objects in resonance with Neptune, also emerges
• 2:12:40
  from the model without forcing. This is what makes the
• 2:12:44
  gap so uncomfortable. A model this successful at explaining some
• 2:12:49
  things should not fail as conspicuously as the Nice model
• 2:12:54
  fails at explaining others, and it does fail. The distribute
• 2:13:00
  of classical Kuiper Belt objects, the one sitting in roughly
• 2:13:04
  circular orbits not locked into resonances with Neptune, does not
• 2:13:10
  quite match what the model produces. The actual population is
• 2:13:15
  divided into what astronomers call the cold classical and hot
• 2:13:20
  classical populations, objects with very different inclinations and orbital histories
• 2:13:26
  sitting in the same general region. The model can produce
• 2:13:31
  something like this division, but not with the exact proportions
• 2:13:35
  and orbital characteristics that observations show. There is a mismatch
• 2:13:41
  that has resisted clean resolution for two decades. The Kuiper
• 2:13:46
  cliff sits at the same problem from a different angle.
• 2:13:50
  The Nie model predicts a gradual thinning of the population
• 2:13:53
  beyond fifty astronomical units, perhaps with some complicated structure. What
• 2:14:00
  astronomers actually see is a sharp cliff like drop in
• 2:14:05
  the number of objects at that boundary. The model has
• 2:14:09
  no clean mechanism for producing an edge that abrupt. Attempts
• 2:14:14
  to explain it by adjusting Neptune's migration speed or the
• 2:14:18
  initial mass profile of the disk have produced results that
• 2:14:22
  improve the fit, but never nail it. The mass problem
• 2:14:26
  is possibly the most sobering of all. The primordial disc contained,
• 2:14:32
  by most estimates, seven to ten earth masses of material.
• 2:14:37
  The Kuiper Belt to day holds a small fraction of
• 2:14:40
  one earth mass. The Nisse model absolutely predicts massive loss.
• 2:14:46
  Neptune scattering most of the disc population is the whole
• 2:14:50
  point of the model, but getting the loss to produce
• 2:14:54
  the right final mass with the right distribution of orbital
• 2:14:58
  properties is genuinely hard. You can run simulations that deplete
• 2:15:05
  the disc appropriately, or you can run simulations that get
• 2:15:09
  the orbital distribution roughly right. Getting both at the same
• 2:15:14
  time consistently has proven frustratingly difficult. Something about the depletion
• 2:15:22
  process isn't fully captured by the model. Then there are
• 2:15:26
  the inclination and eccentricity distributions. Specific populations of Kuiper Belt
• 2:15:32
  objects have orbital tilts and shapes that the NIECE model,
• 2:15:37
  even in its most refined versions, struggles to reproduce. Some
• 2:15:43
  objects are inclined too steeply. Some resonant populations have eccentricities
• 2:15:50
  that don't match the predicted outputs. Each of these discrepancies
• 2:15:55
  is individually small enough to explain away. Together they form
• 2:16:00
  a pattern suggesting that the model is missing something important
• 2:16:04
  about what happened in the Outer Solar System. What that
• 2:16:08
  something is remains genuinely open. Some researchers argue that the
• 2:16:14
  early Solar System suffered additional disturbances beyond what the NIE
• 2:16:19
  model includes, a close passage by a neighboring star in
• 2:16:23
  the Sun's Berth cluster, perhaps, or a second gravitational instability
• 2:16:30
  that the model doesn't account for. Others argue that the
• 2:16:34
  NIE model's initial conditions are wrong, that the giant planets
• 2:16:39
  started in different positions or with different mass distributions than assumed.
• 2:16:46
  A few researchers have argued that an additional planet, something
• 2:16:50
  that was later lost or pushed to an extreme orbit,
• 2:16:54
  passed through the outer disc and did damage the model
• 2:16:58
  has no room for that possibility gets its own chapter
• 2:17:02
  in the story of how the outer Solar system was built.
• 2:17:06
  It is a chapter with considerably darker implications for our
• 2:17:10
  picture of the early solar system. What is clear is
• 2:17:15
  that the Kuiper Belt is not simply the quiet archive
• 2:17:18
  that NIE model simulations produce at the end of their runs.
• 2:17:23
  It has structure the model doesn't predict. It has an
• 2:17:27
  edge that is sharper than the dynamics allow. It has
• 2:17:31
  a mass budget that doesn't close without additional assumptions. Something
• 2:17:37
  happened out there that the best available model either glosses
• 2:17:41
  over or misses entirely. The observational pressure on this problem
• 2:17:48
  is only increasing as more distant objects are catalogued and
• 2:17:53
  their orbital properties measured with greater precision. The Nice model
• 2:17:58
  is the best story place planetary scientists have for how
• 2:18:02
  the outer Solar system was rearranged, but it is a
• 2:18:05
  story with missing pages. Finding those pages is one of
• 2:18:10
  the central projects of modern solar system research. One of
• 2:18:15
  the more unsettling conclusions to emerge from modern solar system
• 2:18:20
  dynamics is that the solar system we inhabit today is
• 2:18:24
  probably not the one that formed around the Young Sun.
• 2:18:29
  The Nice model as described gives us a reasonable account
• 2:18:33
  of how Jupiter and Saturn reshuffled the outer Solar System
• 2:18:38
  and sent Neptune migrating outward through a disk of primitive material.
• 2:18:44
  But there is a version of those same equations that
• 2:18:47
  works better, produces cleaner results, matches what we actually observe
• 2:18:53
  in the Kuiper Belt with less leftover mess. That version
• 2:18:57
  requires one extra planet, an additional ice giant roughly the
• 2:19:03
  size of Uranus or Neptune, that formed in the early
• 2:19:06
  Solar System and no longer exists here. Not destroyed, not
• 2:19:12
  quietly absorbed by another world, gone flung out into interstellar
• 2:19:18
  space by a gravitational encounter so violent that the planet
• 2:19:22
  simply never came back. This is not a fringe idea.
• 2:19:27
  Some of the researchers who built the Niece model ran
• 2:19:30
  the simulations again and again, varying the starting conditions, looking
• 2:19:36
  for configurations that produce something resembling our actual Solar system.
• 2:19:42
  What they found was that a five planets starting configuration
• 2:19:47
  four giants plus one additional ice giant produced more realistic
• 2:19:53
  outcomes than a four planet start. The Solar system we
• 2:19:57
  live in with its specifica rangin of resonances, orbital inclinations,
• 2:20:03
  scattered populations fits more naturally as the survivor of a
• 2:20:08
  five body system than a four body one. One of
• 2:20:12
  those bodies lost. The mechanics of how it happened are
• 2:20:16
  not mysterious exactly. They are brutal. During the period of
• 2:20:22
  dynamical instability that the NIE model describes, the giant planets
• 2:20:27
  were on shifting overlapping orbits. Close encounters between Jupiter and
• 2:20:33
  the smaller giants were not rare events. They were essentially inevitable.
• 2:20:39
  A close pass between Jupiter and an ice giant transfers
• 2:20:44
  an enormous amount of energy to the smaller body. If
• 2:20:48
  the geometry is right, the smaller planet gets kicked onto
• 2:20:51
  a hyperbolic trajectory, an escape path, and crosses the Outer
• 2:20:57
  Solar System at high speed, never to return. Jupiter, being
• 2:21:03
  vastly more massive, barely notices the departing planet does not
• 2:21:08
  go quietly on its way out. A planet sized body
• 2:21:12
  moving through the Outer Solar System at high velocity sweeps
• 2:21:16
  through the region that would eventually become the Kuiper Belt
• 2:21:20
  and the inner aught Cloud. It scatters objects, Some get
• 2:21:25
  flung inward toward the Inner Solar System. This may be
• 2:21:30
  part of what drove the late heavy bombardment that period
• 2:21:34
  roughly four billion years ago, when the Moon collected much
• 2:21:38
  of its crater record in a relatively short time, others
• 2:21:42
  get thrown outward, ceeded into the distant Aught cloud that
• 2:21:48
  is itself believed to be largely composed of objects that
• 2:21:52
  were gravitationally scattered from the Inner Solar System during exactly
• 2:21:57
  this kind of chaos. The orld, in other words, may
• 2:22:02
  be a graveyard for material that an ejected planet scattered
• 2:22:06
  on its way out the door. The traces of this
• 2:22:10
  event should still be readable, at least in principle, in
• 2:22:14
  the orbital distribution of small bodies in the Outer Solar System.
• 2:22:19
  The problem is that reading them requires knowing what the
• 2:22:23
  starting conditions were, how many planets in what orbits with
• 2:22:29
  what masses, and those starting conditions are precisely what we
• 2:22:33
  are trying to determine. It is circular in a way
• 2:22:37
  that makes definitive answers genuinely hard to reach. The possibility
• 2:22:43
  of disturbances beyond the niece model itself adds further complexity.
• 2:22:49
  The early Sun formed inside a stellar nursery, a cluster
• 2:22:54
  of hundreds or thousands of young stars packed into a
• 2:22:57
  relatively small volume of space. S close stellar encounters during
• 2:23:02
  this period, Another star passing within a few hundred astronomical
• 2:23:07
  units of the Sun could have reshaped the outer Solar
• 2:23:10
  System in ways that left no clean record but left
• 2:23:14
  real effects. Some researchers have proposed that a passing star
• 2:23:19
  could have tilted the early disc of planetesimals, or stripped
• 2:23:25
  material from the outer reaches of the Solar System, or
• 2:23:29
  captured objects from the passing star's own disc. The oort
• 2:23:34
  Cloud's outer population may include objects that the Sun stole
• 2:23:38
  from a neighbour it spent only a few million years near.
• 2:23:43
  The Solar System may be in some small part assembled
• 2:23:47
  from stolen parts. There's a version of this chaos that
• 2:23:52
  produced not one ejected giant but two. Some simulations produce
• 2:23:57
  better outcomes with two lost planets rather than one. The
• 2:24:02
  Solar System may have started with six giant planets. The
• 2:24:07
  number is uncertain because the evidence is indirect. What we
• 2:24:12
  know is that something extremely energetic happened in the Outer
• 2:24:16
  Solar System early in its history. The Kuiper Belt carries
• 2:24:21
  the record of that event in the form of orbital
• 2:24:24
  distributions inclinations, population gaps that our current models still struggle
• 2:24:31
  to fully reproduce. This is where the planet nine hypothesis
• 2:24:36
  takes on a different kind of significance. Most discussions of
• 2:24:40
  planet nine frame it as a planet we haven't found yet,
• 2:24:44
  something sitting quietly at four hundred or five hundred astronomical
• 2:24:49
  units waiting to be detected. But some researchers have proposed
• 2:24:54
  a different origin story. If planet nine exists, it may
• 2:24:59
  not have always been that far away. It could be
• 2:25:02
  a surviving relic of the early chaos, a planet that
• 2:25:06
  came close to ejection but not quite kicked onto an
• 2:25:11
  extreme orbit by a close encounter with Jupiter, sent to
• 2:25:15
  a distance of hundreds of astronomical units, but not quite
• 2:25:20
  given enough velocity to escape entirely. Alternatively, during the Sun's
• 2:25:26
  time in its birth cluster, a planet could have been
• 2:25:30
  captured gravitationally from another young star, pulled in by the
• 2:25:35
  Sun's gravity during a close stellar encounter, and left in
• 2:25:39
  a distant, tilted orbit that matches many of planet nine's
• 2:25:45
  predicted characteristics. Both possibilities are consistent with the orbital clustering evidence.
• 2:25:53
  Both are extraordinarily difficult to distinguish from each other with
• 2:25:57
  available data. The Kaiper Belt, in this reading is not
• 2:26:02
  just a collection of icy debris. It is a detailed
• 2:26:06
  record of the most violent era in the Solar System's history,
• 2:26:11
  a record that has been sitting in the outer darkness
• 2:26:14
  for four billion years, encoding the outcome of events we
• 2:26:19
  can barely reconstruct. The orbital distribution of Kuiper Belt objects
• 2:26:26
  is essentially a crime scene from the early Solar System.
• 2:26:30
  Reading it correctly requires first knowing how many suspects were present,
• 2:26:36
  a number that is still being debated. Every year, observatories
• 2:26:42
  around the world capture infrared images of distant stars surrounded
• 2:26:47
  by wide, glowing rings of material that look nothing like
• 2:26:52
  the asteroid belt, but look remarkably like what we are
• 2:26:56
  finding beyond Neptune. These rings glow in infrare because they
• 2:27:01
  are made of dust and ice ground down from larger bodies,
• 2:27:06
  heated just enough by their parent star to radiate at
• 2:27:10
  wavelengths our eyes cannot see. They are enormous. Some stretch
• 2:27:15
  out to hundreds of astronomical units from their stars, and
• 2:27:20
  for decades astronomers studying them have been doing something very specific.
• 2:27:27
  They have been reading the gaps when you look at
• 2:27:31
  one of these disks and you find a cleared zone,
• 2:27:34
  a ring shaped absence of material sitting between two denser populations.
• 2:27:41
  The standard interpretation is almost always the same. Something is
• 2:27:46
  in there. A planet or something close to it has
• 2:27:50
  been orbiting through that region long enough to sweep the
• 2:27:53
  material out of its path, scattering smaller bodies inward or outward,
• 2:27:59
  leaving behind a gap with relatively clean edges. This is
• 2:28:04
  not speculation. It is a technique that has been used
• 2:28:07
  to infer the presence of planets around young stars, long
• 2:28:12
  before direct imaging could confirm them. The gap is the
• 2:28:16
  fingerprint the planet is. Whoever left it here is the
• 2:28:22
  strange thing. For a long time, when astronomers compared our
• 2:28:26
  Solar system to those discs around other stars, the comparison
• 2:28:32
  was unflattering. Our debris disc the Kuiper Belt looked small.
• 2:28:39
  It appeared to cut off around fifty astronomical units, which,
• 2:28:43
  by the standards of what we were seeing around other
• 2:28:46
  Sun like stars, was almost modest. Some of the discs
• 2:28:50
  imaged around stars similar to our Sun extended to one hundred,
• 2:28:55
  one hundred, fifty, even two hundred astronomical unit. The natural
• 2:29:02
  conclusion was that our solar system was unusually compact at
• 2:29:06
  its outer edges. Some researchers suggested this might be a
• 2:29:11
  side effect of the particular dynamical history our giant planets
• 2:29:15
  went through. The upheaval that produced the NIE model's orbital
• 2:29:20
  reshuffling had maybe truncated our disc more severely than average.
• 2:29:25
  That conclusion is now in serious doubt. When the New
• 2:29:29
  Horizons team used the Subaru telescope to push observations of
• 2:29:34
  the outer Solar system to fainter detection limits and greater distances,
• 2:29:40
  they found objects at seventy eighty even close to ninety
• 2:29:45
  astronomical units, not one or two anomalous bodies, but a
• 2:29:50
  statistically significant population a second belt, or at minimum an
• 2:29:55
  extended outer edge to the belt we already knew research
• 2:30:00
  Wes Fraser put it plainly, our system had looked compact
• 2:30:04
  partly because we hadn't been searching carefully enough at the
• 2:30:08
  right distances. The signal was there, we had been missing
• 2:30:13
  it because the objects are extraordinarily faint at those distances
• 2:30:19
  and move with painful slowness across the sky. This changes
• 2:30:23
  the picture considerably. A solar system with detectable structure out
• 2:30:28
  to ninety astronomical units is no longer an outlier. It
• 2:30:33
  is consistent with the extended debris discs we observe around
• 2:30:37
  other stars. The apparent anomaly dissolves once you correct for
• 2:30:42
  what we were capable of detecting versus what was actually there,
• 2:30:47
  and that correction matters because it means our solar system
• 2:30:52
  might be far more typical than the truncated picture implied.
• 2:30:57
  The hidden outer reaches were always there, the maps were
• 2:31:02
  just wrong. What comes with that realization is something more interesting.
• 2:31:09
  If our system has a gap between roughly fifty five
• 2:31:12
  and seventy astronomical units, an extended population beyond that, and
• 2:31:18
  an abrupt inner edge somewhere around fifty astronomical units that
• 2:31:23
  we call the Kuiper cliff, that is, a complex structured architecture,
• 2:31:29
  gaps on both sides of a distant population, multiple belts,
• 2:31:34
  an abrupt boundary. These are not random features in any
• 2:31:39
  protoplanetary disk around another star. This kind of structure would
• 2:31:44
  immediately prompt a search for the bodies responsible. Astronomers studying
• 2:31:49
  those systems don't assume the structures are random. They model
• 2:31:53
  the gravitational influence required to produce each feature and work
• 2:31:58
  backward toward a predictive planet mass and orbit. It is
• 2:32:03
  systematic detective work done at distances of dozens of light years,
• 2:32:09
  using only the shape of a glowing disc as evidence.
• 2:32:12
  We are now doing the same thing, but from the inside,
• 2:32:17
  and we have far better data than we could ever
• 2:32:20
  gather on a disc around a distant star. The individual
• 2:32:24
  objects in the Kuiper Belt are measurable, their orbits are trackable.
• 2:32:30
  The clustering patterns that point toward Planet nine are a
• 2:32:34
  level of detail that no external observation of another system
• 2:32:39
  could possibly reveal. We are, in effect reading our own
• 2:32:44
  debris disc with a resolution that will never be matched
• 2:32:48
  by anything we observe from across the galaxy. The irony
• 2:32:52
  is that this comparison cuts both ways. Every time astronomers
• 2:32:57
  find a gap in a disc around another the star
• 2:33:00
  and attribute it to a hidden planet, they are applying
• 2:33:04
  reasoning that was partly built on what we understand about
• 2:33:07
  the Kuiper Belt, Neptune's resonance, sculpting of Kuiper Belt populations,
• 2:33:14
  the way large bodies clear their orbital paths over time,
• 2:33:18
  the statistical signatures of gravitational shepherding. These ideas were developed
• 2:33:24
  here using our own system as the laboratory, and they
• 2:33:28
  have been exported outward to interpret what we see everywhere else.
• 2:33:34
  And now the lessons are flowing back in the other direction.
• 2:33:39
  The extended populations, the structured gaps, the signatures of dynamical
• 2:33:44
  instability from billions of years ago. All of it is
• 2:33:49
  reminding us that our system is not a finished, settled
• 2:33:53
  thing with a neat outer edge. It is a record
• 2:33:57
  of violence and migration and sculpting that is still being read.
• 2:34:03
  Every other planetary system with a debris disc is probably
• 2:34:07
  telling a similar story. The details differ, the histories differ,
• 2:34:13
  but the processes are the same.
• 2:34:15
  Speaker 2: What we have been.
• 2:34:16
  Speaker 1: Learning about the Kuiper Belt is not just a story
• 2:34:19
  about our own solar system. It is a key for
• 2:34:23
  reading the architecture of every planetary system in the galaxy.
• 2:34:28
  Thirty years ago, the Kuiper Belt did not exist as
• 2:34:32
  a confirmed place. It was a theoretical region, a placeholder
• 2:34:37
  on a map, something astronomers believed had to be there
• 2:34:41
  but had never actually seen. Today, it is one of
• 2:34:45
  the most actively studied frontiers in planetary science, and the
• 2:34:50
  closer we look, the stranger it becomes. Think about what
• 2:34:56
  has been found in just three decades of serious observation.
• 2:35:01
  A frozen body five hundred kilometers wide carrying an atmosphere
• 2:35:06
  that the model said was physically impossible. Dwarf planets at
• 2:35:10
  the edge of the Solar System showing hints of internal
• 2:35:14
  heat and possible liquid water beneath their surfaces. Objects sitting
• 2:35:19
  at eighty and ninety astronomical units nearly double the distance
• 2:35:24
  where the Kuiper Belt was supposed to end. A gap
• 2:35:28
  in the outer Solar System between fifty five and seventy
• 2:35:32
  astronomical units that has the exact shape and character of
• 2:35:37
  a cleared orbital path, a clustering pattern in the orbits
• 2:35:42
  of distant objects that has resisted explanation for a decade,
• 2:35:47
  and that points persistently towards something large and unseen. None
• 2:35:53
  of this was in the textbooks when David Jewett found
• 2:35:57
  nineteen ninety two QB one. All of it has been
• 2:36:01
  found since the Kuiper Belt is four point six billion
• 2:36:06
  years old. It has been sitting at those distances since
• 2:36:10
  before the first multicellular life appeared on Earth, since before
• 2:36:15
  the continents reached anything close to their current shapes, since
• 2:36:19
  before the oceans had the chemistry they have now it
• 2:36:23
  is one of the oldest undisturbed archives in the Solar System,
• 2:36:28
  and for all but the last thirty of those four
• 2:36:31
  and a half billion years, we had no idea it
• 2:36:35
  was there. What we have learned since nineteen ninety two
• 2:36:39
  is genuinely extraordinary. What we have not yet learned may
• 2:36:45
  be more extraordinary. Still, here is where things stand. The
• 2:36:51
  Vera Reuben Observatory began scientific operations in twenty twenty five.
• 2:36:58
  Its camera is the largest digit imaging instrument ever built
• 2:37:02
  for astronomy. In its first year or two, it is
• 2:37:05
  expected to discover roughly thirty five thousand new Kuiper Belt objects,
• 2:37:10
  nearly ten times the entire currently known population. With that
• 2:37:14
  volume of data, the orbital clustering that has anchored the
• 2:37:18
  planet nine hypothesis either holds up under proper statistical scrutiny,
• 2:37:24
  or it doesn't. The observational bias argument, which has kept
• 2:37:29
  the debate unresolved for nearly a decade, essentially collapses under
• 2:37:34
  sample sizes that large. The answer is coming, It may
• 2:37:40
  already be sitting in the first Reuben data releases right now,
• 2:37:44
  and the answer splits into two directions, both of which
• 2:37:48
  are almost unsettling in what they would mean. If the
• 2:37:52
  clustering is real and a planet is responsible, it is
• 2:37:56
  a world somewhere between five and ten times the nad
• 2:38:00
  mass of Earth, orbiting at hundreds of astronomical units on
• 2:38:05
  an elongated path so wide that it takes between ten
• 2:38:09
  and twenty thousand years to complete a single trip around
• 2:38:13
  the Sun. Finding it would be the largest discovery in
• 2:38:17
  planetary science since Neptune, larger arguably because Neptune's existence was
• 2:38:24
  predicted from a single anomaly in one planet's orbit, Planet nine.
• 2:38:29
  If it is there, has been herding objects across the
• 2:38:33
  entire Outer Solar System for billions of years without anyone
• 2:38:37
  knowing it. That is not a minor oversight. That is
• 2:38:42
  the Solar System keeping a secret for the entirety of
• 2:38:46
  human history. If the planet is not there, the problem
• 2:38:50
  does not go away. It gets stranger. The orbital clustering
• 2:38:56
  still needs an explanation. The Kuiper cliff still has no
• 2:39:00
  clean answer. The gap between fifty five and seventy astronomical
• 2:39:05
  units still looks like the work of something that swept
• 2:39:09
  that region clear. If no planet did it, then either
• 2:39:14
  the formation history of the Outer Solar System is more
• 2:39:18
  violent and unusual than any current model captures, or the
• 2:39:22
  gravitational framework we use to describe motion at those distances
• 2:39:28
  is subtly wrong. Modified Newtonian dynamics waiting in the wings
• 2:39:33
  as an alternative is not reassuring. It means the problem
• 2:39:38
  goes deeper than a missing planet. Both outcomes are real discoveries.
• 2:39:44
  Both would reshape what we think we know. The Solar
• 2:39:48
  System either has a hidden world we have never cataloged,
• 2:39:51
  or the physics we use to describe the outer Solar
• 2:39:54
  System needs revision. At some level. There is no version
• 2:39:59
  of the answer that is small. Whatever is hiding out there,
• 2:40:03
  beyond the cliff, beyond the gap, in the cold dark,
• 2:40:07
  at distances our maps have always marked as empty, We
• 2:40:12
  are closer to finding it than we have ever been,
• 2:40:16
  and the answer, when it comes, is not going to
• 2:40:20
  be small.