How the Universe Works - S05E02 - Mystery of Planet 9
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00:00We thought we knew our solar system.
00:08Turns out, we were wrong.
00:11Groundbreaking observations suggest an unseen ninth planet may be out there on the fringes
00:18of our solar system.
00:21And it could be huge, 5,000 times more massive than Pluto and 10 times the mass of the Earth.
00:29We don't get a lot of revolutions in astronomy, and here we are, on the cusp of a discovery
00:34like this.
00:35It's crazy to think that, as much as we've looked into the universe, that there's this
00:39ninth planet out there that we've never seen.
00:43If Planet Nine really is out there, what will it be like?
00:48Is it a rocky super-Earth, an icy mega-Pluto, or a gassy mini-Neptune?
00:56Or is Planet Nine an alien world, stolen from another star?
01:02And could it provide an unlikely home for life, 100 billion miles from the sun?
01:23Take a look at the night sky.
01:26The pattern of stars that drifts overhead appears fixed.
01:30But look for longer, weeks or months, and you'll see a handful of the points move.
01:38These slow-moving points of light are the planets, the giant chunks of rock or gas that
01:43orbit our home star, the sun.
01:46We thought there were eight.
01:49We were wrong.
01:50You know, we think we understand something as simple as our solar system.
01:54We found all the planets, and right in front of us, we missed something big.
02:01A group of astronomers are studying the Kuiper Belt, a vast band of icy asteroids that sits
02:09way outside the orbit of Neptune.
02:12Most of these objects move in a neat, circular formation around the sun.
02:17But the astronomers are puzzled by a small group that appear to break the rules, swinging
02:23far outside the main belt on wild, extended orbits.
02:30Something sitting far outside the Kuiper Belt seems to be pulling these asteroids out of
02:35line, something the size of a giant planet.
02:42Caltech astronomer Mike Brown hears about the wild observations and is determined to
02:47prove the planet theory wrong.
02:51When we saw these alignments of all these objects out there, we thought, oh, everybody's
02:54going to say there's a planet.
02:55We have to very strongly prove there's not a planet because, of course, we all know there's
03:00not another planet out there.
03:02That's ridiculous.
03:05Mike asks his colleague, Konstantin Batygin, to run a computer simulation to see what effect
03:12a ninth planet should have on the Kuiper Belt.
03:15Stunningly, the simulation predicts elongated orbits identical to ones already observed.
03:22But the simulation also spits out a surprise.
03:26There should be a second set of rogue orbits that are perpendicular to the first set.
03:31If Mike can locate these weird, predicted objects inside the Kuiper Belt, planet nine
03:38is almost certainly real.
03:41I took these simulation results to Mike's office, just a couple doors down from my office,
03:47and I said, look, you know, we've got a huge problem.
03:49He said, no, there's an object called 2012 DR30, which has an orbit just like the one
03:55you were predicting.
03:59Mike's asteroid fits the prediction perfectly.
04:02He searches the records for more and finds another four that seem to be in the right
04:07area.
04:08But just how closely will they fit the prediction?
04:12I remember sitting back and thinking, OK, we're going to right now plot the data, the
04:18real observational data, on top of the model.
04:22And Mike said, if these two match up, my jaw is just going to drop to the floor.
04:27The theory says they should be right here and right here.
04:31And I did the calculations very quickly to see where they were and brought them up.
04:36And there they are, one, two, three, four, five, right on these lines, exactly where
04:42we predicted they should be.
04:44The moment we saw this, we went from cautious to, holy cow, this really is there.
04:51We have to make sure to tell everybody right away because it's actually real.
04:56Mike and Constantine had unlocked the solar system's greatest secret.
05:01Planet Nine was almost certainly real.
05:05And it had to be huge, perhaps ten times the mass of Earth.
05:10We're not talking about something like our moon or Pluto.
05:13We're talking about something that is literally planet-sized.
05:18And we're seeing its gravitational wake affecting these other objects.
05:22The idea that there could be a giant planet that we'd never seen is something I think
05:25most people wouldn't have bet on.
05:27But the evidence is remarkable.
05:31To prove Planet Nine exists, astronomers need to see it with their telescopes.
05:36But there's a problem.
05:39Computer simulations only give a broad idea of where to find it.
05:43And Planet Nine is incredibly faint and almost inconceivably far away.
05:49It's much, much farther out than we ever expected to find planets.
05:53It probably spends most of its life, if it's on an elliptical orbit, so far away from the
05:57sun that we just missed it.
06:06So just how far away is Planet Nine?
06:09The only way to truly appreciate its vast orbits is to build a scale model.
06:16Perhaps the biggest working scale model of the solar system ever attempted.
06:23Astronomical discovery scientist Kevin Walsh is here to call the shots.
06:27And he starts with the size of the sun.
06:31So what we've got here, our kickball, is going to set the scale of our mini solar system
06:36today.
06:37So everything is scaled off of its relative size compared to the size of the sun.
06:43Kevin quickly paces out the position of the inner rocky planets.
06:48All four sit within 60 yards of the sun on this scale.
06:52And each planet would appear no bigger than a peppercorn.
06:57To make this a working solar system, we need to bring on the drones.
07:16Each drone represents a different planet.
07:19And the orbital speeds have been scaled so one Earth year takes just 30 seconds.
07:28Already it's clear to see how tightly bunched these inner planets are and how the closest
07:33planets orbit faster than those farther out.
07:42Far beyond the tightly packed rocky planets lies the first of the gas giant planets.
07:48On this scale, just over a football field from the sun.
07:54So after this 400 foot walk, we made it to Jupiter, the largest planet in the solar system.
07:59But even by the size scale, Jupiter is only about the size of a lollipop.
08:06Another football field length lies ahead on the walk to Saturn.
08:10As we look back across the lake bed, I can barely see the drones.
08:15They covered a huge distance.
08:19The trek out to Uranus is bigger still.
08:22Three football fields were the length of an aircraft carrier.
08:25It turns out there's a lot of wind in the outer solar system, so I have to yell.
08:31A surprising amount of wind in the outer solar system.
08:37Tumbleweed, rattlesnakes.
08:41After Uranus, it's around 200 yards out to Neptune.
08:45Before the discovery of planet nine, we thought Neptune was the farthest planet from the sun,
08:50around half a mile on the scale of our model.
08:53But Neptune's distant orbit is nothing compared to the orbit of planet nine.
09:00So here we are.
09:01We made it to the orbit of Neptune.
09:03We're only at the tip of the iceberg.
09:05We need to stop measuring in feet and we need to start thinking in miles.
09:09We need a car to get out to planet nine.
09:18Planet nine swings out on a highly elliptical orbit.
09:22Its closest pass to the sun is a whopping 19 billion miles.
09:28That's six times wider than the orbit of Neptune.
09:31But at its farthest point, planet nine is 112 billion miles away.
09:38But on this scale, that's an incredible 18 miles from our kickball-sized sun.
09:45So we're here.
09:46End of the road.
09:47We've driven about 18 miles from where we first started setting up the solar system.
09:51But in the scale of the solar system, it's over 100 billion miles.
09:55100 billion miles to get out to the furthest part of planet nine's orbit.
10:01So to scale, and we don't know what planet nine would look like, but it's probably about
10:06the size of a BB.
10:08This is the challenge for our astronomers.
10:10How do you see a BB from 18 miles away?
10:14This is what we have to do.
10:16It could take years for our telescopes to pick out an object so impossibly faint and
10:22far away as planet nine.
10:25Until then, scientists can only speculate on what this mysterious world might be like.
10:31We're in this wonderful moment right now where we suspect that planet nine exists, but we
10:35really have no idea what it's like.
10:37And that means our imaginations can run wild.
10:40They're informed by science, but I love it when creativity takes hold and you just run
10:44with it.
10:48So what are the options?
10:50Science suggests three possibilities, and the first is astonishing.
10:55Planet nine could be made from the same materials as the Earth, but 10 times more massive.
11:02A rocky super-Earth.
11:07But what would this giant, rocky planet look like so far from the sun?
11:12A bizarre volcanic world scarred with fire somehow emerges from the cold darkness of
11:19deep space.
11:32In 2016, astronomers release astonishing evidence of a missing ninth planet on the frozen edges
11:39of our solar system, 100 billion miles from the sun.
11:45Until our telescopes find it, we can only guess what this mysterious planet nine is
11:50like.
11:51But the first option is perhaps the most surprising.
11:56Planet nine could be made from rock, just like the Earth, but 10 times more massive.
12:03A so-called rocky super-Earth.
12:05When we looked out into the universe, we realized that the most common type of planet in the
12:11entire galaxy is something we don't have, something called a super-Earth.
12:20The Kepler Space Telescope finds alien worlds by measuring the tiny dip in light as a
12:26planet passes in front of its host star.
12:30Most of the alien solar systems Kepler finds have super-Earths, so how come our star doesn't
12:36have one?
12:37Could it be possible that planet nine is our missing super-Earth?
12:43If planet nine is a rocky super-Earth, what will it look like up close?
12:54Geology geologist Janie Radebaugh imagines planet nine as a dramatic world of fire and
13:01ice.
13:02Right now we're in Iceland.
13:04We're flying over amazing, beautiful volcanic landscapes of Iceland.
13:08We think this might be the perfect landscape for thinking about what might be happening
13:13on planet nine if it's a rocky super-Earth.
13:18These black mountains and lava flows were created by leftover heat from the Earth's
13:23formation spilling out onto the surface.
13:26Planet nine, born with so much more insulating rock, should have even more of this leftover
13:32heat trapped inside it.
13:34What we're talking about is a body that's maybe ten times the mass of the Earth.
13:39I'd expect, because it's so large, that we should have lots more internal heat, and so
13:43even though it's far away in the solar system, it's far away from the sun, it's still got
13:47lots of its own energy.
13:56Touching down on the surface of planet nine, you'd find a world as inhospitable as you
14:01could imagine.
14:05Billions of miles from the sun, the surface is lit by little more than the twinkle of
14:10distant stars and the red glow of intense geological activity on the surface.
14:18We can imagine if we were on a super-rocky Earth, planet nine, we could have a landscape
14:23just like this one.
14:25There should be volcanoes erupting all the time, and the other thing we should see is
14:29lots and lots of ice and snow blanketing the landscape.
14:32This is because the atmosphere is so cold that parts of it have condensed and settled
14:37back down onto the surface.
14:39You're going to have volcanoes, you're going to have canyons, you're going to have plate
14:42tectonics, mountain building.
14:43All of these processes are still going to be going on out there in what we normally
14:47would think of as the frozen, cold and dead world of the outer solar system.
14:55As hot lava reaches the surface, it freezes suddenly in the cold of space, perhaps forming
15:01a weird volcanic glass called obsidian, another feature shared with the sub-zero volcanoes
15:09of Iceland.
15:10Okay, let's put this whole thing together.
15:12We have a landscape that's kind of dimly lit by starlight, but maybe also by the reddish
15:19glow from erupting lavas spreading across the landscape.
15:24And then behind you, you have gases that are changing immediately to snow and falling as
15:29snow down to the surface.
15:30And it would just be a beautiful, magical landscape.
15:37The case for a giant, rocky Planet Nine is compelling because it paints such a vivid
15:43picture of a living volcanic world.
15:47But there's a problem.
15:52If Planet Nine is in fact a super-Earth, how did it form and where did it form?
15:58We don't have any other super-Earths in our solar system.
16:00And the ones we see around other stars are typically really close to their star.
16:04So how did our super-Earth end up way out there at the edges of our solar system?
16:10For Planet Nine to be our rocky super-Earth, it would have had to have formed in the inner
16:15solar system and then migrated out to its current position.
16:20And that's a problem because there probably wasn't enough rocky material left over in
16:25the early solar system to create both the massive Planet Nine, as well as Mercury, Venus,
16:32Earth and Mars.
16:34It's really hard to imagine that we could have formed a 10-Earth-mass planet here and
16:39still form the rocky planets that we see today.
16:44Time for a new theory.
16:46What if Planet Nine formed from ice in the outer solar system?
16:52Calculations tell us it would have to be 10 times the mass of the Earth.
16:56And here's the kicker.
16:58An ice world that big would have an internal ocean of liquid water.
17:05A new world is revealed where icy geysers shoot through cracks in the frozen crust.
17:11And deep below it lies the largest body of liquid water in the solar system.
17:28The planets that make up our solar system seem to follow a pattern.
17:42The four closest to the sun are all made from rock.
17:47The next four are giants made mostly from gas.
17:51Beyond Neptune, gas is replaced by multiple worlds made from ice.
17:58This is the Kuiper Belt, a frozen realm of water-ice asteroids, millions of them.
18:05The Kuiper Belt is a region of space outside of Neptune's orbit that extends out about
18:1150 times the distance from the Earth to the sun, so it's really far out there.
18:16And this is populated by icy bodies.
18:18These are giant chunks of ice that have some rock and other things in them, but they're
18:22mostly ice.
18:25This planet nine is made from the same materials, an overgrown version of the Kuiper Belt's
18:31most infamous citizen, Pluto.
18:37Poor Pluto.
18:39Discovered in 1930 by Clyde Tombaugh, this tiny ice world, smaller than our moon, was
18:45quickly proclaimed the ninth planet.
18:49But in the 1990s, Mike Brown and others discovered a host of icy worlds orbiting out with Pluto.
18:58Pluto was just another Kuiper Belt object and got demoted to dwarf planet, to the dismay
19:04of much of the world.
19:06Everybody loves the idea that I killed Pluto and now I'm trying to atone for my sins by
19:14replacing it with a new ninth planet.
19:17In fact, even my daughter suggested this long before we started looking for planet nine.
19:23She said, you know, you should find a new planet and then you can have found a planet
19:27and there'll be nine planets again and everybody will like you again.
19:31If planet nine is an icy Kuiper Belt world, it'll be the biggest we've ever found.
19:38Pluto, the biggest object we know out there in the Kuiper Belt now, is less than 1% the
19:44mass of the Earth.
19:46Less than that.
19:47Planet nine, we think, is 10 times the mass of the Earth.
19:50So we're dealing with a factor of thousands of times in mass between the largest Kuiper
19:55Belt object that we know now and the size of planet nine.
20:01So you're talking about super mega ultra Pluto, something really, really big.
20:06And it's hard to know what an ice ball like that would look like.
20:12It's not crazy to speculate that there could still be activity, internal geologic activity,
20:17keeping this world from being cold and totally dead.
20:23Peering through the darkness to a hypothetical mega Pluto planet nine, we discover a giant
20:30world of ice.
20:31There's much less rock than a super Earth planet nine, but the mass of ice alone creates
20:37enough gravity to generate warmth deep in the core, even out here.
20:43The real currency of keeping a planet alive is mass.
20:47Does it have enough mass to keep the interior warm?
20:49Well, something that's 5 to 10 times the mass of the Earth probably would be warm inside.
20:56Up close, the surface explodes with activity.
21:00But these volcanoes spew water ice, not lava.
21:05If something like a giant Pluto exists, it must be the most amazing landscape to take
21:10a walk over.
21:11You'd have these ice volcanoes spewing out jets of frozen water, of ice raining down
21:16on you.
21:18Maybe you'd look out over the landscape and see hundreds of these erupting.
21:22This dramatic icy vista is a gateway to a secret world, a vast slushy ocean of liquid
21:29water mixed with ice crystals, perhaps the largest single body of water in the solar
21:35system.
21:36There's going to be enough internal heat maybe to turn this into a slushy water world.
21:41So it's not quite a terrestrial rocky planet, and it's not a Uranus or Neptune.
21:47It's a true mega ocean world, but perhaps a very cold one.
21:53Is planet nine an icy mega Pluto?
21:57The problem is scale.
21:59Pluto and the other objects in the Kuiper belt are tiny.
22:03So how could the same building materials have come together to form giants?
22:10So the idea that planet nine is simply a really scaled up Pluto, a mega Pluto, has some difficulties.
22:18We just don't think that there was enough mass out there in the far reaches of the solar
22:22system to all come together to build a planet that large.
22:26When you look at the Kuiper belt, there are all of these small icy bodies.
22:30There's nothing very big out there.
22:32And we think that's not a coincidence, that the disk of dust and gas that formed the planets
22:36had more stuff closer to the sun.
22:38And by the time you got out to where Pluto is, there wasn't much material to build planets
22:42out of, certainly not a planet five to ten times the mass of the Earth.
22:49So if planet nine didn't form in the icy outer solar system and didn't form in the rocky
22:55inner solar system, where did it come from?
22:59The more likely option?
23:01Planet nine formed in the gas-rich zone in the middle of our solar system that also created
23:07Jupiter, Saturn, and Neptune.
23:10A gassy planet nine could be similar to Neptune, but perhaps a little smaller, a mini-Neptune.
23:19But how would it get so much farther out than the other gas giants?
23:23And what would it look like?
23:26Imagine a weird, translucent world, glowing in the dark, like a giant, deep-sea creature.
23:49Something on the fringes of our solar system is upsetting orbits and causing a ruckus.
23:55Could it be a planet?
23:57It's incredible to me that we now know of thousands of other planets going around other
24:02stars in the sky, but we may have missed a big planet in our own solar system.
24:08Planet nine, a world we know almost nothing about beyond the possibility that it exists.
24:16Science suggests intriguing options.
24:20A giant, rocky world with a heart of fire, or an ice world filled with a giant, slushy
24:28ocean.
24:29But problems with each theory have led to new hunches.
24:34So if it's not a rocky, metallic super-Earth, and it's not a gigantic, ice-ball mega-Pluto,
24:42what's left?
24:43And the answer is a gas giant.
24:46And that strikes me as being the most likely prospect.
24:50When you think about the mass of planet nine, and where it is now, my best guess is it's
24:56something like a miniature version of Neptune.
25:01The gas giant planets are the monsters of our solar system.
25:06Instead of a solid surface like the Earth, the gas giants have thick, stormy atmospheres
25:12that descend for tens of thousands of miles, shrouding their small, rocky cores.
25:20Jupiter is the largest gas giant, over 300 times the mass of Earth.
25:26Moving out from Jupiter, the gas giants get progressively smaller.
25:30Saturn, then Uranus, and finally Neptune, around 17 times the mass of the Earth.
25:39If planet nine is a gas giant, it'll be even smaller, a mini-Neptune.
25:46If planet nine is a mini-Neptune, if it's a lot like Neptune, then it's not really like
25:51a terrestrial planet like Earth, but it's not really like a gas giant like Jupiter.
25:56Neptune is this weird in-between thing, where it's probably got a rocky core, but it's actually
26:01mostly what astronomers call ices.
26:03It's got methane in it, and water, and various other substances, and a very, very, very thick
26:08atmosphere on top of that.
26:13Neptune's thick clouds are stained blue with molecules of methane.
26:20But planet nine's atmosphere could be transparent.
26:25It's so cold out there, you're getting almost no extra energy from the sun.
26:30And so then anything heavy in the atmosphere, any heavier molecule, over time would have
26:33probably fallen to the surface.
26:35And only the lightest elements, the lightest molecules, would stay in your atmosphere.
26:40So maybe just almost pure hydrogen or helium, and you'd have maybe a really clear atmosphere.
26:47What would a mini-Neptune look like that far out from the sun?
26:51The thing I think of are things like jellyfish, right?
26:53That sort of beautiful, translucent look where you're looking through to the innards of the
26:58organism.
26:59In this case, you might look through to the innards of the planet in some way.
27:03The atmosphere may be transparent, but this planet is far from calm.
27:09The interior is lit by the flash of thunderstorms, and faint lights dance around the poles as
27:15solar winds from distant stars stream down the planet's magnetic fields.
27:21Looking into the innards of the planet, it would look in some ways like these gorgeous,
27:25beautiful, deep-sea organisms that are bioluminescent.
27:29And we may have the planetary equivalent of something like out there in the inky blackness
27:33of space rather than the inky blackness of the deep ocean.
27:38Could Planet 9 be a mini-Neptune?
27:41Surprisingly, the possibility of an extra-gas giant in our solar system isn't new.
27:47In 2011, scientists attempted to replicate the formation of our solar system using supercomputers.
27:55But their models didn't work, unless they added an extra-gas giant planet to the mix.
28:03It was really difficult to reproduce our current solar system.
28:07But one scientist found that if you add a fifth large planet to our solar system, then
28:13that planet will end up getting ejected from our solar system, and you'd have the planets
28:19that we have today.
28:23Is Planet 9 the missing gas giant predicted by the supercomputers?
28:28The computer model shows it being ejected by the immense gravity of Jupiter.
28:33But did Planet 9 instead cling to our solar system by the tips of its gravitational fingers?
28:41Sometimes our mathematical models predict things that we think are impossible, and then
28:44we find them.
28:46And for a while, we've known that if you throw a mini-Neptune into the mix of planets forming,
28:51the models work better.
28:53Maybe we've found that key, finally, Planet 9.
28:57We know giant planets can get thrown around.
29:00Observers have even seen ejected planets floating free in the space between stars.
29:06Did Planet 9 almost suffer the same fate?
29:10It's entirely possible that there could have been a planet forming, bigger than Earth,
29:14something like a super-Earth, well on its way to becoming a gas giant, in this wonderful
29:19area of the disk where it could have drawn in a lot of material and become a gas giant
29:24like Jupiter, except it got too close to Jupiter.
29:27And before it could do that, it was gravitationally flung away from this wonderful feeding ground
29:33out into the much sparser, more barren desert of the outer solar system.
29:41Is Planet 9 really a frozen mini-Neptune banished to the badlands of the outer solar system?
29:48Right now, it's our best bet.
29:51But there is one more option.
29:53Some scientists believe Planet 9 may not have formed around our sun at all.
30:02Is our most distant planet an alien world snatched from another star?
30:24If the mysterious Planet 9 exists, it is by far the most distant planet in the solar
30:31system, 20 times farther out than Neptune.
30:35So how did it get there?
30:37Was it made in the place it currently occupies?
30:41Or was it flung out from the inner solar system as a rocky super-Earth, or more likely a mini-Neptune?
30:49The jury's out.
30:51But there is another option, and it's out of this world.
30:55So the question is then, where did it come from if neither of these things is right?
31:00And it's possible that there is another explanation, and that is that Planet 9 is an alien visitor
31:07from outer space.
31:12The sun is just one of 200 billion stars orbiting the supermassive black hole at the center
31:19of the Milky Way galaxy.
31:21Most of these stars probably have multiple planets.
31:25And scientists now believe that from time to time, two stars might pass a little too
31:30close for comfort.
31:32The result?
31:34Planetary theft.
31:37We know that the sun moves around in the galaxy.
31:39We know that there are other stars in other solar systems.
31:42Is it possible that the sun passed so close to another solar system that it stole a planet?
31:49Today our sun drifts through space alone, like a yacht in the open ocean.
31:55But that wasn't always the case.
31:58Rewind the clock, 4.6 billion years, and our local star cluster was a much more crowded
32:04place.
32:05Ideal conditions for Planet 9 to jump ship.
32:11The sun was born in a nursery with thousands of other stars.
32:15Just like the boats in this harbor, there are so many boats around, so many neighbors.
32:20It was like that for the young sun.
32:24Stars like the sun are born in stellar nurseries, vast clouds of gas that collapse to form tens
32:30of thousands of stars, all tightly packed together.
32:37Scientists think it's possible that inside this cramped, confused playground of stars,
32:43our sun's gravity could have stolen Planet 9 from a passing neighbor.
32:48Imagine this cool scenario.
32:50You've got an alien star, and around that star forms a planet.
32:54This is Planet 9.
32:55And here comes the sun whizzing by.
32:58The sun gets so close that it steals Planet 9 on its way out into the galaxy.
33:04It sounds like science fiction, but our sun may already have a criminal record.
33:11There's some evidence that the comets in our solar system may not have started in our solar
33:16system.
33:17We may have stolen comets from other stars.
33:19If that's the case, it's not totally outrageous to think that a planet that formed around
33:25another star somehow made its way into our solar system and became part of our family.
33:32But if Planet 9 really did come from another star, how will we know for sure that it's
33:38an alien visitor?
33:39What we'd like to do is essentially a DNA test on Planet 9, scoop up some of its surface
33:45and look for material that we absolutely know couldn't have formed around our sun because
33:51we don't see it anywhere else in our solar system.
33:54We may even have to send a probe there to really get a good look at it and find out
33:58what its chemical composition is, exactly everything we can find out about its orbit.
34:02And that way we might be able to see if there are any sort of fingerprints, smoking gun
34:08pieces of evidence that'll say clearly this formed here or it formed out there.
34:16Unfortunately, before we can launch a probe to Planet 9, we first have to find it.
34:26Engineers like Mike Brown have made the challenge a little easier, using math to narrow down
34:31the zone.
34:33What we know right now is that Planet 9 is in a swath of the sky that goes about like
34:38this.
34:39It's about this big.
34:40It goes across like this.
34:41But we think we even know a little bit better.
34:43We've pinpointed, or at least slightly constrained where it is, to a patch of sky that's about
34:48this big.
34:49It's still a lot of sky to look at, but it's a lot less than having to look at the whole
34:53sky.
34:55Mike's patch of sky is close to the constellation Orion.
35:00He's going to wait until fall, when Orion is highest in the sky, to search for Planet
35:049 using the Subaru Infrared Telescope on Hawaii.
35:10The telescope is fine-tuned to pick out the faint heat signature of distant objects against
35:15the cold backdrop of deep space.
35:19Planet 9 may be frozen, but it will be warmer than space, and that tiny difference in temperature
35:25is all this incredible telescope needs.
35:28We want to see two pictures taken of the same area of the sky a few weeks apart.
35:33The stars don't move, but you see this one little thing going boop, boop, boop as you
35:37flash the pictures back and forth.
35:39That's what happens when you have an object moving around the sun against the background
35:44stars.
35:45That's how Pluto was discovered.
35:46That's how we're going to find Planet 9, if it exists.
35:51It could take years to find Planet 9, but when we do spot it, scientists will be able
35:57to analyze its light, and hidden within that faint glow could be the chemical signature
36:03for rock, ice, or gas.
36:06If it is, Planet 9's identity will finally be revealed.
36:13What lies in store beyond that is a mystery, but perhaps the most exciting prospect is
36:20Planet 9 could be home to a family of moons.
36:25And it's just possible one of these moons could provide a home for life 100 billion
36:31miles from the sun.
36:50Are we alone in the universe?
36:55For decades, scientists have scoured our closest planetary neighbor for signs of extraterrestrial
37:01life, but so far, not a trace has been found.
37:11Is it possible we're targeting the wrong planet?
37:18If Planet 9 is real, it sits on the icy outer limits of the solar system.
37:24But even here, 100 billion miles from the sun, it's just possible that life could thrive
37:31not on the planet itself, but deep inside its moons.
37:36Historically, we've always thought of moons as being these little insignificant places,
37:41but the incredible thing is they may be the best places to find life.
37:45In our solar system alone, there may be far more chances for life on moons of planets
37:49than there are on planets themselves.
37:54Moons excite astrobiologists because they can sometimes support liquid water, no matter
38:00how far they sit from the sun.
38:02The key is something called tidal heating.
38:08Moons on elliptical orbits get squashed and squeezed by the gravity of their parent planet.
38:15This generates heat and melts ice to form underground oceans, liquid water, the key
38:21ingredient for life as we know it.
38:25If Planet 9 is as big as scientists predict, it could have multiple moons, and maybe one
38:32of those moons could have warm, salty oceans primed for simple life.
38:39So if you have Planet 9 and it's got icy moons, and these icy moons are on the right kinds
38:43of orbits, the heat could be coming from within, not without.
38:48And so the sun basically doesn't matter.
38:51You could have liquid water below the surface that's heated from the internal geology.
38:56You could have geysers of water, like what we see coming off of moons around Saturn and
39:01Jupiter.
39:02You could have that all the way out there at Planet 9.
39:08Imagine Planet 9 with a system of giant moons.
39:13The closest moon is heated to melting point by Planet 9's immense gravity.
39:19There's no life here.
39:20Any water boiled away millions of years ago, creating a hot, arid ball of rock.
39:29Farther out lies a second giant moon.
39:32This new world is encased in bright, white water ice.
39:39But the crust hides a secret, a vast ocean of warm, liquid water heated by volcanic vents
39:46on the ocean floor.
39:50This hidden world is rich with organic chemistry, and it could even support a weird alien zoo
39:57of pale, aquatic creatures.
40:01We associate life with the sun.
40:03That's how we think of life originating on the Earth.
40:06But we know you don't need the sun.
40:07We have tube worms at the bottom of the ocean, which live off of hydrothermal vents.
40:12They get all the chemicals and the heat they need from basically the interior of the Earth.
40:17This is not out of the question.
40:18You know, decades ago, you'd have been laughed out of a lecture hall if you'd have said something
40:21like that.
40:22But we have learned so much about life in extreme environments since then that this
40:27is now in the realm of possibility, talking about life on a planet beyond Pluto in our
40:31own solar system.
40:32Wherever there's energy, wherever there's heat, there can be life, even all the way
40:36out by Planet 9.
40:39There is good news.
40:40If Planet 9 does have an active, watery moon, we should be able to see it with our telescopes.
40:48The active moons of Jupiter and Saturn are the brightest in the night sky, thanks to
40:53warm water gushing out from cracks in the surface and freezing in bright white layers
40:58of fresh ice.
41:02If Planet 9's moons have liquid oceans, their surfaces should be just as bright.
41:15The race is on to image Planet 9 and its moons, but what we'll see when those first pictures
41:21come back is anybody's guess.
41:24I have to admit there's some wonderful tension that I feel right now when it comes to finding
41:28Planet 9.
41:29We have giant telescopes that are scanning the sky looking for it.
41:33So any day now, I'm waiting with bated breath.
41:36My daughter believes that Planet 9 is pink with purple dots.
41:42She might be right.
41:48One thing's for sure.
41:50If and when we do find Planet 9, we'll never look at our solar system the same way again.
41:57This is tremendously exciting because if it's there, it's already telling us that there's
42:01more to know about our solar system, that there are more secrets literally under the
42:08sun than we have dreamed of in our philosophy.