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00:00In general, there's a massive problem with the way in which we typically teach and think
00:05of the solar system.
00:07For the most part, the emphasis is placed solely on the planets and the order of them
00:12out from the Sun.
00:13But in terms of sheer space, that doesn't tell even close to half of the story.
00:18The Kuiper Belt is the first great expanse beyond the last of the planets, Neptune.
00:24It begins 30 astronomical units away from the Sun, and is itself 20 astronomical units
00:30wide.
00:31It's only relatively recently that science has begun to understand the Kuiper Belt…
00:37and more pressingly, to ask what else could be dwelling within it.
00:45The Kuiper Belt is sometimes called the third region of the solar system, and simply put,
00:49is a vast sea of icy bodies and other chunks of space debris.
00:53It begins just beyond the orbit of Neptune and exists between 30 and 50 astronomical
00:57units away from the Sun, with one astronomical unit being the average distance between the
01:02Sun and the Earth.
01:03The Kuiper Belt has 200 times more mass than the inner asteroid belt, to the point where
01:07some astronomers believe that, if it wasn't for Neptune's strong gravity, the belt
01:11might not even have existed at all.
01:13The debris inside it could have instead formed into another planet.
01:17So, it's thanks to Neptune that the belt takes its current shape, but while the ice
01:21giant has potentially prevented another whole planet from forming, there's plenty of
01:25other interesting stuff out there.
01:26The Kuiper Belt is named after Gerard Kuiper, one of the first and leading astronomers to
01:31theorise that there could be additional objects in the solar system beyond Neptune.
01:35It wasn't Kuiper who discovered the belt, however, seeing as he died in the 1970s, almost
01:40two decades before it was confirmed.
01:42We only truly knew that the Kuiper Belt existed in 1992, when some groundbreaking discoveries
01:47of TNOs were made.
01:49A TNO is a trans-Neptunian object, which is basically any celestial body further out than
01:54Neptune but still within the Sun's heliosphere.
01:57The first trans-Neptunian object ever discovered was Pluto back in 1930, which is still the
02:02largest one we've found, though Eris is the most massive.
02:06Famously, Pluto was once deemed a planet, but it was recategorised in 2006 as a dwarf
02:11planet.
02:12There are other designations within the TNO category, however, including specific cave
02:17eos, Kuiper Belt objects, something that Pluto also is.
02:21Even further out, there are Scattered Disc Objects and Oort Cloud Objects.
02:25The Kuiper Belt is the closest to the sun of these three classifications, but there's
02:28a lot of overlap between it and the Scattered Disc, the objects of which orbit between 30
02:33and 100 AU away.
02:35The objects in the Oort Cloud orbit the sun at a much greater distance of between 2,000
02:40and 200,000 AU, a long, long way away from even the Kuiper Belt.
02:45The Kuiper Belt and the Oort Cloud are both thought to be main sources of comets.
02:49Long-period comets that orbit further from the sun come from the far-out Oort Cloud,
02:53but short-period comets, which typically burn out much more quickly, originate in the Kuiper
02:58Belt.
02:59KBOs become comets when Neptune's orbit interferes with them too much, flinging them
03:03towards the sun and Jupiter, which also has a large gravitational effect and can potentially
03:08direct these Kuiper Belt missiles towards the inner planets.
03:11As well as comets, there are plenty of other dwarf planets lurking in the Kuiper Belt,
03:15as well as the previously mentioned Pluto and Eris.
03:18And there are moons, too!
03:20Pluto is one such KBO to have moons, including its largest, Charon.
03:24But the likes of Eris, Haumea and Quaor also have moons and satellites of their own, incredibly
03:29distant worlds that make the likes of our own moon or even Mars feel really quite close.
03:34And there are objects even stranger still hiding in the darkness, including just beyond
03:39the Kuiper Belt, like the mysterious Sedna and Niku.
03:42Sedna has one of the most varied orbits of all TNOs, orbiting between 76 and 900-plus
03:48AU along a route that's estimated to take 11,000 years to complete.
03:52Niku is perhaps even more unusual.
03:54Its name translates as rebellious in Chinese, and it gets its rule-breaking reputation because
03:59it has a highly inclined orbit.
04:01It's tilted almost 110 degrees above the solar orbital plane, meaning that it's positioned
04:06above most of the sun's other satellites.
04:08The reason why objects like Niku, Sedna and even Pluto have such unusual orbits isn't
04:13conclusively known, but there are more than a few theories.
04:16Despite Neptune's strong gravity allegedly making the formation of another planet impossible,
04:21the idea that there is an extra planet is prevalent.
04:24So prevalent, in fact, that there are numerous theories for hidden planets of various sizes
04:28– and many where the Kuiper Belt is key.
04:31The proposal originally came about in the early 1900s because of perceived discrepancies
04:35within the orbits of Neptune and Uranus.
04:37The discovery of Pluto supposedly explained those discrepancies… until it was found
04:42that Pluto's gravity wasn't strong enough to affect the outer giants.
04:45So, supposedly, something else was.
04:48In time, it turned out that the original hypothesis was flawed by miscalculations, but that hasn't
04:53put other Planet 9 theories to bed.
04:55In 2017, studies held by the University of Arizona's Lunar and Planetary Laboratory
05:00suggested that there could potentially be another planet that we haven't discovered
05:04yet, though the Kuiper Belt might not stretch far enough to contain it.
05:07Again, the unusual orbits shown by KBOs were what drove scientists to investigate.
05:12According to some estimates, if the hypothetical Planet 9 does exist, it should have a mass
05:17around ten times that of Earth and to be up to 800 times further away from the sun – far
05:22beyond the belt.
05:23It'd be a bona fide super-Earth, though… were we ever to observe anything that even
05:27closely matches it.
05:29Along with Planet 9, there's the even more mysterious Planet X.
05:32Planet X differs from Planet 9 because it's said to be much smaller, with an estimated
05:36mass similar to Mars.
05:38It ties into a popular conspiracy theory called the Nibiru Cataclysm, which says that Earth
05:43is one day going to be destroyed when an unknown, additional planet crashes into it.
05:48It could be, according to the theory, that this ominous planet, Nibiru, is a rogue planet
05:52hiding in the outer solar system, perhaps in the Kuiper Belt.
05:56The majority of actual scientists and astronomers are quick to dismiss the Nibiru narrative,
06:00mind you, so there's no need to gulp in fear at the sky just yet.
06:04Not everything about the Kuiper Belt amounts to mysterious hidden worlds, however.
06:08There are some simpler explanations for the orbital anomalies, like the theory of collective
06:12gravity.
06:13This relatively new idea suggests that the Kuiper Belt could be being changed and distorted
06:17by a gravitational snowball effect, caused by smaller objects… meaning that the collective
06:22gravity of all the other, definitely non-planet TNOs could be enough to pull bodies like Sedna
06:27and Niku seemingly out of place.
06:29Bizarrely, though, mass is still a problem here.
06:32While collective gravity could be happening, researchers also speculate that the Kuiper
06:36Belt needs a lot more mass than we currently know it has for this effect to take hold.
06:41Whether that mass is a new planet or something a little less radical remains to be seen.
06:45We are discovering new KBOs and TNOs of varying sizes all the time, though, so perhaps one
06:51day, when we know all there is to know about the Belt, we'll be able to account for everything
06:54in balance after all.
06:56That day might seem as though it's incredibly far away, but despite the extreme distance
07:00between us and the Kuiper Belt, NASA is trying to investigate it as best they can, most notably
07:06with the New Horizons probe.
07:08Launched in January 2006, New Horizons passed Jupiter in 2007 and finally reached the Kuiper
07:13Belt to fly by Pluto in 2015.
07:16With the Pluto mission complete, and because it still had enough fuel and its systems were
07:20in good condition, its goals were extended in 2016 to study one or more of the mysterious
07:25KBOs.
07:26And it arrived at Ultima Thule in 2019, a peanut or snowman-shaped body made up of two
07:31small planetesimals stuck together.
07:33Ultima Thule is today the furthest object in the solar system to ever be visited by
07:37a spacecraft from Earth.
07:39There's a lot going on in this distant region of the solar system, and there's a lot left
07:43to discover… but that's what's hiding in the Kuiper Belt.
07:51What do you think?
07:52Is there anything we missed?
07:53Let us know in the comments, check out these other clips from Unveiled, and make sure you
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