Latest / Star Trails: From Backyard Astronomy to Cosmic Wonder / The Edge of the Solar System

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The Edge of the Solar System · Star Trails: From Backyard Astronomy to Cosmic Wonder

• 0:07
  Howdy Star Gazers and welcome to this episode
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  of Star Trails. My name is Drew, and I'll be
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  your guide to the night sky for the week of March
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  29th through April 4th. This week we leave the
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  familiar planets behind and journey into the
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  farthest reaches of our solar system. where the
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  sun's influence begins to fade and the boundaries
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  of our cosmic neighborhood grow uncertain. We'll
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  explore the Kuiper Belt, a vast disk of icy remnants
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  from planetary formation, and venture even farther
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  into the mysterious unseen Oort Cloud, a distant
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  spherical halo that may stretch halfway to the
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  nearest stars. Later in the show, we'll take
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  a look at what you can expect to see in this
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  week's night sky. Whether you're tuning in from
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  the backyard or the balcony, I'm glad you're
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  here. So grab a comfortable spot under the night
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  sky and let's get started. Over the past several
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  weeks, we've taken a journey through our solar
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  system. We've stood on the scorched surface of
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  Mercury. drifted through the thick clouds of
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  Venus and looked back at our fragile home from
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  orbit. We've explored the red deserts of Mars,
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  crossed the asteroid belt, and marveled at the
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  immense presence of Jupiter and Saturn. We reached
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  the outermost planets and we've looked at some
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  of the strange moons that orbit them. For much
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  of human history, that's where the story ended.
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  When Johann Gottfried Gall first observed Neptune
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  in 1846, it marked the boundary of the known
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  solar system. Even after Clyde Tombaugh discovered
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  Pluto in 1930, astronomers still thought in terms
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  of planets. Isolated worlds spaced out across
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  an otherwise empty void. But tonight we're going
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  beyond that idea. Because the solar system doesn't
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  end with Neptune. In many ways, that's just where
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  it begins to get strange. Just beyond Neptune's
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  orbit lies a vast and dimly lit region known
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  as the Kuiper Belt. This is not a place of dominant
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  planets, but a wide, flattened disk of icy debris
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  stretching from about 30 to 50 astronomical units
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  from the sun. Out here, sunlight is faint. Temperatures
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  hover just above absolute zero. and the pace
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  of motion slows to something almost imperceptible.
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  Every now and then, it sends us a short period
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  comet, like Halley's Comet for instance. These
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  distant regions are not random collections of
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  objects. They're time capsules. When the planets
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  formed billions of years ago, gravity gathered
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  material into worlds like Earth and Jupiter.
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  But not everything was used. What remained was
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  scattered outward, pushed into distant orbits
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  by the giant planets, where it's remained largely
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  unchanged ever since. The Kuiper Belt is not
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  just a region, it's actually a preserved record
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  of the solar system's formation. A construction
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  site that was never finished. The idea of such
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  a region didn't always exist. In 1951, astronomer
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  Gerard Kuyper proposed that leftover debris might
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  exist beyond Neptune, though he believed it may
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  have dissipated over time. For decades, the idea
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  remained theoretical. It wasn't until 1992 that
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  astronomers finally confirmed this distant region
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  was real. Working at the University of Hawaii,
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  David Jewett and Jane Lu spent years patiently
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  scanning the sky, searching for something incredibly
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  difficult to detect. These objects are small,
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  dark, and move very slowly against the background
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  stars. Night after night, they compared images
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  looking for a faint point of light that shifted
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  just enough to reveal itself. And then they found
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  it. A tiny object now known as 1992 QB1. It wasn't
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  a planet and it wasn't a comet. It was something
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  new. The first confirmed member of what we now
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  call the Kuiper Belt. That discovery changed
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  everything. It meant that Pluto was not an outlier.
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  It was part of a vast population of distant worlds.
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  In the years that followed, astronomers discovered
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  more and more of these objects, until it became
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  clear that the outer solar system was not empty
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  at all. It was crowded. Among the astronomers
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  leading that exploration was Mike Pluto Killer
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  Brown. In the early 2000s, Brown and his team
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  began discovering large objects in the Kuiper
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  Belt, worlds that rivaled Pluto in size. Then,
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  in 2005, they found something even more provocative.
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  Eris. Eris is slightly more massive than Pluto,
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  and travels in a distant, elongated orbit that
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  carries it far beyond Pluto's path. At times,
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  it's more than twice as far from the sun as Pluto.
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  And its discovery raised a difficult question.
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  If Pluto was a planet, Then what is Eris? Another
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  planet? The tenth? Or, had we misunderstood,
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  Pluto all along? What followed was one of the
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  most public debates in modern astronomy. In 2006,
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  the definition of a planet was formally revised,
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  and Pluto was reclassified as a dwarf planet.
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  Mike Brown took the fall as the so -called man
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  who killed Pluto, but in reality, he didn't take
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  anything away. He revealed something larger.
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  The solar system didn't really lose a planet.
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  It gained an entire new region of worlds. But
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  even the Kuiper Belt is not the edge. The idea
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  of something even farther out came from a different
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  mystery. In 1950, Dutch astronomer Jan Oort studied
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  the paths of long period comets. These rare visitors
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  that appear suddenly and may not return for thousands
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  of years. Their orbits didn't make sense. They
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  weren't confined to the mostly flat plane of
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  the solar system. Instead, they approached from
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  every direction, above, below, and at every angle
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  imaginable. Oort realized these comets must originate
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  from a spherical distribution of objects, not
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  a disk. He proposed the existence of a vast,
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  distant cloud of icy bodies surrounding the sun
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  in all directions. So far away that they're only
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  loosely bound by its gravity. A passing star
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  or even the gentle tidal forces of the Milky
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  Way could disturb one of these objects and send
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  it falling inward where we would briefly see
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  it as a comet. We have never directly observed
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  this cloud. No telescope has imaged it. and yet
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  every long period comet we see points back to
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  its existence. Today we call it the Oort cloud.
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  Some astronomers believe there may even be a
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  dense inner region, sometimes called the Hills
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  cloud, hidden within the larger structure. Taken
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  together, this region may extend tens of thousands
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  of astronomical units from the Sun, perhaps even
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  approaching halfway to the nearest star. At that
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  distance, our sun is no longer a dominant presence.
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  It becomes just another point of light in the
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  sky. When we see a comet from Earth, we're seeing
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  something ancient, a fragment of the early solar
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  system, preserved in deep freeze for billions
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  of years, now briefly illuminated by the sun
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  before returning to the darkness. When I first
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  began this series, I specifically wanted to highlight
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  places that humanity has physically explored.
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  And believe it or not, space probes are in the
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  Oort cloud right now. Of course, I'm talking
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  about the two spacecraft launched in 1977, Voyager
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  1 and Voyager 2. These are the most distant objects
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  ever created by human hands. They pass the planets,
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  cross the Kuiper Belt, and entered interstellar
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  space, moving beyond the Sun's heliosphere. That's
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  the region dominated by the solar wind. Now nearly
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  one light day away, they're deep within the broader
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  domain of the Oort cloud. Out there in the darkness,
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  the Voyagers are not just drifting silently,
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  they're still working. Both spacecraft continue
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  to send back data about the environment beyond
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  the heliosphere. measuring cosmic rays, magnetic
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  fields, and the faint plasma that exists between
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  the stars. If the distance from the Earth to
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  the Sun were reduced to a single inch, the outer
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  edge of the Oort cloud would lie nearly a mile
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  away. By that scale, the Voyagers have barely
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  begun the journey. They've left the Sun's bubble,
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  but not the Sun's backyard. Even out here, this
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  story is not complete. Astronomers have found
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  hints that something else may be lurking in the
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  outer solar system. Planet 9 is a proposed world,
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  inferred from the unusual clustering of orbits
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  among distant Kuiper belt objects. If it exists,
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  it could be several times the mass of Earth,
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  orbiting hundreds of astronomical units from
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  the Sun, taking tens of thousands of years to
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  complete a single orbit. It's never been seen.
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  Its existence is only written in the motions
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  of other objects. But the search for this hidden
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  world is happening right now. Astronomers are
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  actively looking. New observatories like the
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  Vera C. Rubin Observatory in Chile are beginning
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  to scan the sky with unprecedented depth and
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  precision, searching for faint objects that drift
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  slowly against the stars. At the same time, scientists
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  are combing through infrared data looking for
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  the faint heat signature of a distant unseen
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  planet. Others are refining the mathematics itself,
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  tracking distant Kuiper belt objects and asking
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  whether their strange orbits truly point to something
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  massive, or whether we're being misled by the
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  limits of our observations. And then there are
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  the visitors, one of them two -eye Borisov made
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  waves in the news last year as the first confirmed
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  interstellar comet. Borisov and another visitor,
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  One Eye Umauamaua, discovered in 2017, are objects
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  that do not belong to our solar system at all.
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  They arrived from elsewhere, passing briefly
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  through our neighborhood before continuing their
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  journey through the galaxy. They don't orbit
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  the sun, they arrive, pass through, and then
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  they vanish. If we can detect fragments from
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  other star systems drifting through ours, then
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  somewhere out there, other systems may be doing
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  the same. Watching a chunk of our solar system
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  drift through their domain. At some point out
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  there, it becomes difficult to say where the
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  solar system ends and where interstellar space
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  truly begins. The boundary isn't a sharp line,
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  but a gradual fading, a transition from the sun's
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  influence to the wider gravitational currents
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  of the Milky Way. So as we close out this journey,
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  it's worth remembering that the solar system
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  is not a fixed map of planets. It's a vast and
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  evolving structure, shaped by gravity, time,
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  and chance. For centuries we believed the planets
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  were the whole story. Then we discovered the
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  Kuiper Belt. Then we inferred the Oort Cloud.
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  And now we continue searching for worlds we cannot
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  yet see. After a quick break, we'll be back to
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  cover this week's night sky. Stay with us. Welcome
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  back. We're entering this week under a bright
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  and increasingly dominant moon. After reaching
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  first quarter back on March 25th, The moon is
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  now waxing toward fullness, culminating in a
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  full moon on April the 1st. This week's full
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  moon is known as the pink moon, not for its color,
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  but for the flowers that bloom beneath it, marking
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  the quiet return of spring. It's also known as
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  the egg moon, as it's linked to fertility and
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  renewal. Early in the week, you'll still have
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  some decent dark sky windows after sunset, but
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  as we move closer to midweek, Moonlight will
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  begin to wash out fainter objects, so if you're
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  planning any deep sky observing, earlier in the
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  week is your best bet. Tonight, March 29th, the
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  moon passes extremely close to Regulus, the heart
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  of the constellation Leo. In some parts of the
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  world, like Europe, observers will even see an
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  occultation where the moon passes directly in
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  front of the star, causing it to disappear and
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  reappear abruptly. Here in North America, we
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  won't witness the occultation itself, but it's
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  still a nice pairing that's easy to spot shortly
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  after sunset in the western sky. A bright moon
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  sitting right next to one of the spring sky's
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  most recognizable stars. Planet -wise, we've
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  got a few good targets this week. Jupiter is
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  still the star of the show. It's bright, unmistakable,
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  and well placed in the evening sky. sitting high
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  after sunset and lingering for hours. Venus is
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  visible low in the western sky just after sunset.
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  It's brilliant, but it doesn't stick around long,
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  so you'll want a clear horizon and good timing.
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  Uranus is still technically visible in Taurus,
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  though you'll need binoculars or a small telescope
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  to pick it out. Mercury and Mars are mostly lost
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  in the Sun's glare this week, making them difficult
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  to observe. With the full moon this week, a lot
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  of deep sky objects may be off the table. So
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  let's look at some that punch through the bright
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  moonlight. Globular clusters are fantastic in
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  moonlight because they're dense and bright. Seek
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  out Messier 3 and Canes Venetici. It's one of
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  the brightest globulars in the northern sky and
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  resolves into stars in small scopes. It will
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  be high enough for comfortable observation this
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  week. Messier 35 is a bright open cluster near
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  the foot of Gemini. It looks good in binoculars
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  and it's visible in the early evening. Open clusters
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  like the beehive cluster in Cancer remain beautiful
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  even under a bright sky, appearing as a soft
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  scattering of stars in binoculars. And if you
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  look west early in the evening, the Orion Nebula
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  is still visible, glowing faintly in the Sword
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  of Orion. Even with the moon nearby, it remains
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  one of the most rewarding objects you can observe.
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  We're in the home stretch in our book club selection.
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  Next week we're going to wrap up the final chapters
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  in Nightwatch. And looking deeper into April,
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  we're going to get a little meta and turn away
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  from the objects in the sky to the processes
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  and tools scientists actually use to study them.
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  We're going to talk about observatories, the
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  scientific method, how data is collected, used,
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  and analyzed, and in general, peel back the curtain
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  on the machinery behind the study of space. That's
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  going to do it for this week. If you found this
• 17:15
  episode interesting, please share it with a friend
• 17:18
  who might enjoy it. The easiest way to do that
• 17:21
  is by sending folks to our website StarTrails
• 17:24
  .Show. And if you'd like to support the show,
• 17:27
  use the link on the site to buy me a coffee.
• 17:30
  That really helps. Be sure to follow Star Trails
• 17:33
  on Blue Sky and YouTube. Links are in the show
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  notes. Until we meet again beneath the stars,
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  clear skies everyone!