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00:00Pluto, for so long a mystery, has finally been revealed.
00:13And these astounding images have rocked science.
00:18Everywhere we looked, it looked different, and that shook us to the core.
00:24Ice volcanoes, fast-flowing glaciers, and mountain ranges as big as the Rockies.
00:34We thought Pluto would be dead and boring.
00:37We couldn't have been more wrong.
00:40It was amazing.
00:41I mean, every new world is just incredible, but we had no idea that Pluto was so complex.
00:49In 2015, Pluto showed us its heart.
00:55But does its greatest secrets lie below?
00:59Could tiny Pluto harbor alien life forms three billion miles from the sun?
01:22Robotic probes, armed with scientific instruments, have been compiling a family photo album of
01:27our solar system for over 40 years.
01:31And these close-up portraits have taught us almost everything we know about our closest
01:37cosmic relatives.
01:38The lesson of planetary science is you have to go there to really resolve things in detail
01:43and to make the big discoveries.
01:46But until recently, one portrait had escaped our robotic eyes.
01:51The dwarf planet Pluto.
01:54Pluto used to be our most distant planet, until modern astronomers discovered lots of
02:00other icy objects orbiting alongside Pluto.
02:04And in 2006, poor Pluto got demoted.
02:09Pluto is tiny, smaller than our moon.
02:12And it's so far away, around three billion miles, that our finest telescope can pick
02:18out only a faint blob.
02:21The very best images we've made of Pluto were with the Hubble Space Telescope.
02:25And the Hubble Space Telescope could only get, yeah, about 20 pixels across Pluto.
02:29We knew that there were areas that were bright and dark, but we didn't know what they were,
02:33and it wasn't a very clear view at all.
02:35This fuzzy image was pretty much all we had to work out what Pluto was like.
02:41We knew that it had nitrogen ice on it, and we knew it had a moon, and we knew these other
02:45things.
02:46But still, you have to go there because it is so far away.
02:50Three billion miles, or more, we just had to go there to understand it.
02:56Summer, 2015, NASA's New Horizons probe flies past Pluto, completing a nine-year journey
03:04from Earth, and recording the first-ever close-up images of this most mysterious of worlds.
03:12Many scientists were expecting to find a flat, dead world, similar to our moon.
03:20But instead, the pictures reveal a world of dizzying diversity.
03:25High mountain ranges, winding glaciers, and vast, crater-free plains all hint at recent
03:33geological activity.
03:35Pluto, it seemed, was alive.
03:39When we saw the first truly high-resolution images that revealed Pluto in all of its glory
03:46and complexity, it was an amazing emotional release for all of us on the mission team.
03:52We suddenly got up this image that showed jagged mountains and totally bizarre hills
03:58and smooth plains, and no craters at all on that particular image, showing that this really
04:04was a geologically youthful region.
04:09Some of the features revealed by New Horizons defied simple explanation.
04:15One of the most baffling was a pair of vast mounds on the surface of Pluto, each topped
04:21by a deep depression.
04:24These mounds look just like young volcanoes.
04:27But how could that be possible on a planetary surface made mostly from ice?
04:33Now, if you were to see something like that on Earth, you'd say, that's a volcano.
04:37If you saw it on Mars, you'd say, that's a volcano.
04:40You see on Pluto, you think, what is this?
04:43There's nothing that can drive volcanoes on Pluto as far as we know.
04:47So what are these things?
04:50The mysterious mounds on Pluto are huge, over 100 miles wide and around 3 miles high.
04:58To make sense of these perplexing formations, scientists turned to similar-looking features
05:04here on Earth.
05:06Planetary geologists like Janie Radebaugh call them shield volcanoes.
05:12This volcano we're headed for is called Skjeldbrðr, and it means broad shield in Icelandic.
05:18In some ways, it's sort of the eponymous shield volcano we're about to land on.
05:25Shield volcanoes are formed by long, drawn-out eruptions of runny lava, and they're said
05:31to resemble the shape of a warrior's shield lying on the ground.
05:36This one erupted just 9,000 years ago.
05:40You can see a giant crater right here, summit crater, that's typical of shield volcanoes.
05:46And it's actually pretty deep right here, deeper than I expected.
05:49This is quite a young volcano, and so you can still really clearly see that crater.
05:53And actually, we see the summit crater on Pluto's shields very clearly, and that really
05:58kind of makes us really think they could be a shield volcano, just because of its broad
06:03shape and a summit crater, just like this.
06:07It's not unusual to find shield volcanoes on other planets.
06:11Mars, like Earth, is made mostly from rock, and it's home to the monumental volcano Olympus
06:19Mons, built up from vast eruptions of hot, runny lava millions of years ago.
06:26But lava is melted rock, and that's a problem, because Pluto should be too small and too
06:32far from the sun to have anything melted.
06:36If its broad features really are volcanic, they must be made from something very different
06:42to lava.
06:44Janie Radabaugh believes the light color of Pluto's mystery mounds offers a crucial clue.
06:51The kind of eruptions that make this shape of volcano are, you know, hundreds or thousands
06:56of individual eruptions over time.
06:59They erupt out of the fissure and flow out across the surface, and then they just pile
07:03up on top of each other and continue to flow out, building up a broad shield over time.
07:09The same thing has happened on Pluto.
07:11It's just the lava that's erupted from Pluto doesn't look anything like this.
07:15It doesn't, it's not dark in color, it's not made of basalt, instead it's made of water
07:19ice.
07:21Unlike Earth, Pluto has a surface of frozen nitrogen on top of a bedrock and mantle of
07:28solid water ice.
07:31But from time to time, some of this water ice must be melting to form explosive flows
07:36of liquid slush that spew out onto Pluto's surface just like hot, rocky lava does on
07:43Earth.
07:44The warm slush freezes rapidly on the surface, building up to form broad, icy shields just
07:50like the rocky shields we find on Earth and Mars.
07:54If the water under the surface can be melted by some thing, some energy, it can burst through
08:00the surface and flow just like lava does here on Earth.
08:03So instead of volcanoes like you have here, you get cryovolcanoes, cold volcanoes on these
08:09more distant objects.
08:11We have a myopic view of the universe thinking everything has to be the way it is here.
08:16Here on Earth, volcanoes are hot.
08:19But on Pluto, volcanoes run cold, not hot.
08:24But maybe the most exciting thing about Pluto's volcanoes is that they are virtually free
08:29from impact craters, meaning the warm slush must have flowed out of them really recently.
08:37These features are very, very young.
08:40Pluto is active today.
08:41There hasn't been enough time for the bombardments of comets impacting Pluto to build up and
08:46build up a record of craters on the surface.
08:49Pluto is active today.
08:51That's the headline.
08:53The potential for active volcanoes on Pluto stuns scientists.
08:58But they pale in comparison when close-up images of Pluto's smooth heart are revealed.
09:05Because this Texas-sized basin of ice appears to be boiling.
09:10Our solar system bears the scars of a violent past.
09:31Impact craters litter the surface of rocky planets and moons like our own.
09:37Yet on Earth, these battle scars are wiped away by lava, water, and wind.
09:44If you look at the moon now and you look at it in a thousand years,
09:46not going to be very different.
09:48However, if you look at the Earth now and wait an hour, right?
09:51We have weather, we have volcanoes, there are lakes that come and go,
09:56the sea levels rise and fall over thousands and millions of years.
10:00So with all of this geologic activity, we say that the Earth is a living world.
10:07Scientists expected Pluto to be heavily cratered,
10:10a geologically dead world similar to our moon.
10:14But when New Horizons flew past in 2015, it revealed a vast heart-shaped icy plane
10:22which appears much younger than the rest of the planet.
10:26And the western part of this plane, Sputnik Planum, was completely crater-free.
10:33Of all the things that we saw coming back, the heart, Sputnik Planum,
10:37was the most surprising and the most interesting and the most sort of,
10:41oh, look at that.
10:43The broad pale surface of Sputnik Planum offers a window into Pluto's unexpected activity
10:49because it looks an awful lot like icy glaciers do here on Earth.
10:54There's not a crater to be seen anywhere across that surface.
10:57And that immediately tells us it's young.
10:59Some of the estimates are maybe as young as 10 million years.
11:02You know, only since that stuff has been moved around and changed.
11:05That's today in geologic terms.
11:08There's got to be something actively making that surface for it to be that smooth.
11:17Something is regularly smoothing out the surface of Sputnik Planum.
11:23But what?
11:25Scientists can rule out cryovolcanoes.
11:28They make mountains, not planes.
11:32So what else could it be?
11:35The first clue comes from pale snaking lines that appear to feed into the northern rim of the plane.
11:43These sinuous features look just like the rivers of ice
11:47that flow from mountainous glaciers here on Earth.
11:53What we're looking at here is a massive glacier pouring out across the valley
11:58and emptying into a glacial lake.
12:01One of the first things we noticed when we saw the close-up images from New Horizons
12:05is not only a vast field of kind of a flat glacier,
12:08but also tiny little feeder networks into the glacier,
12:12like valley glaciers just like this one, emptying into the larger continental glacier.
12:20Ices must be forming in Pluto's highlands and then flowing downhill into Sputnik Planum,
12:26just like outlet glaciers flow from high mountains here on Earth.
12:31But on Pluto, it's too cold for water ice to flow.
12:34So the outlets feeding Sputnik Planum must be filled with a very different kind of ice.
12:42So the glaciers have to be made of things like nitrogen.
12:44Now, nitrogen is what makes up most of our atmosphere.
12:47It's a gas here.
12:48But at those temperatures, it freezes and becomes an ice and a glacier of nitrogen.
12:53On Pluto, nitrogen ice has the texture of toothpaste,
12:58and it flows down mountains made of water ice.
13:02Those glaciers are flowing.
13:03And what's more, there are no craters on them.
13:05So they're active, they're young, they're flowing right now today.
13:11We now think Sputnik Planum is a vast basin filled with frozen nitrogen
13:16and fed by mountainous glaciers to the north.
13:19This steady flow of fresh nitrogen explains why the edges of the basin are so smooth.
13:25But what about the regions that sit beyond the reach of the glacial flow?
13:31Something else must be wiping out craters in the middle of the basin.
13:37Jani Radebaugh believes a weird pattern on the surface of Sputnik Planum
13:42suggests an astonishing possibility.
13:45Pluto's surface could be boiling.
13:49Welcome to Sputnik Planum.
13:50I mean, really, this is what it would look like if we were standing on the surface of Pluto.
13:54You see a vast, flat glacier behind us, really white, extending off to the distance,
14:00and behind us, a ring of mountains.
14:03When we look at the surface of Sputnik Planum,
14:05we notice that there are regularly spaced cells,
14:08and they're a little bit rounded in the middle, they taper off at the edges,
14:12and they really have the appearance of something that formed by convection.
14:18So if you think about a pot of oatmeal,
14:21as it's boiling away, it's bringing material up to the surface,
14:24and then it's kind of pulling it back down again at the sides,
14:27convecting over and over again.
14:30The nitrogen ice of Sputnik Planum could be boiling like a pot of oatmeal,
14:35but so slowly, the roiling surface appears frozen.
14:39So slowly, the roiling surface appears frozen at any time.
14:44A similar but much faster process makes patchwork patterns in Earth's most active lava lakes.
14:52Hot globs of lava rise up, forming rounded cells on the surface.
14:57And cool lava sinks down,
15:00slipping between the gaps formed by the hottest bubbles of molten rock.
15:05As we look at the surface of Sputnik Planum,
15:07what we're seeing is basically a lava lake in slow motion.
15:11There's material rising up and then moving over and descending again as it gets cool.
15:16And basically, if we could see that, if we could speed it up over a few thousand years,
15:20we would see individual cells all across the surface,
15:23roiling and churning and boiling, moving, convecting nitrogen.
15:28You really have to step back and realize just how amazing and weird this is.
15:33The temperature is hovering near 400 degrees below zero.
15:37And things are bubbling up and moving around.
15:39There's geology happening.
15:41What you have to remember is that it doesn't take a lot of energy
15:44to make something as cold as nitrogen ice flow.
15:48But it does take some energy.
15:50And while Pluto wears its magnificent heart on its sleeve,
15:54a second, warmer heart must be beating deep below the surface.
16:00But out here, in the frozen expanse of near outer space,
16:04the question still remains.
16:06Where's the heat coming from?
16:23In 2015, the New Horizons probe stunned mission scientists
16:29when it revealed Pluto as a dynamic living world.
16:33Its glaciers, mountain ranges, and likely volcanoes
16:37are all evidence of an active geology driven by heat.
16:43But scientists are mystified as to where that warmth is coming from.
16:48Pluto is too small to have retained the heat from its violent formation
16:53over four billion years ago.
16:55And it sits so far from the sun that the same sunlight that warms the surface of our planet
17:01hardly makes an impact on Pluto.
17:05Well, it's about 20 minutes before dawn right now.
17:08And the light that we see is exactly the same
17:12as the illumination we see on the surface of Pluto at midday,
17:16when there's the maximum amount of sunlight on the surface.
17:20And because Pluto receives so little sunlight,
17:23its surface is bone chillingly cold, as low as minus 400 degrees Fahrenheit.
17:31This tiny little world, so far away from the sun,
17:34receiving so little sunlight, we never dreamed it would be an active world.
17:45If the heat that drives Pluto's dynamic geology isn't coming from sunlight,
17:50it must be coming from below.
17:53But from where?
17:55The best guess is that Pluto has a deep subterranean ocean of liquid water.
18:02And somehow, this ocean is driving heat up to the surface.
18:10There's pretty good circumstantial evidence
18:13that Pluto has a massive water ocean in its interior.
18:18And over time, as the planet cools,
18:23the water must be freezing.
18:25And as water freezes, it releases a form of energy called latent heat.
18:31And that release of energy from the freezing ocean
18:36could very well be what's powering a lot of Pluto's geology.
18:43Could freezing water really make a planet hotter?
18:46It sounds crazy, but Janie Radebaugh can demonstrate this weird quirk of physics
18:51using an ice bath to represent Pluto's frozen upper crust,
18:56and a cup of water to represent Pluto's hidden liquid ocean.
19:05At first, the ice bath causes the temperature of the water to drop.
19:11But as soon as the water freezes, the temperature drops.
19:15And the temperature inside the glass does something amazing.
19:20It rises.
19:22Okay, it's at 30, so it's definitely ready to freeze.
19:24So I just want to give it a little bit of a helping hand
19:26and see if we can start it to freeze.
19:28Here we go, just a little stir.
19:29Oh, oh, there it goes.
19:34Now it's completely frozen.
19:35And the temperature is dramatically climbing,
19:39like just seconds after it froze.
19:40It has climbed, climbed eight degrees.
19:43Look at this, it was 30.
19:45Now all of a sudden it's 38, just seconds after it froze.
19:50It might seem kind of counterintuitive,
19:51but freezing water actually gives off energy to its surroundings.
19:55All of that kinetic energy, the motion of the water molecules in the liquid state,
20:00has to be given up for those water molecules to enter a solid crystalline structure.
20:05That released energy, it's called the latent heat of fusion,
20:09it actually can warm the surroundings as water is freezing into ice.
20:15This is how scientists believe latent heat in an underground ocean
20:20could be driving volcanism on Pluto.
20:24The uppermost layers of the internal ocean freeze
20:27where liquid water meets the hard frozen ice above.
20:31This act of freezing releases latent heat,
20:35which then travels up through Pluto's crust,
20:38driving active geology on the surface.
20:41I mean, it seems like just a little bit of heat that's forming from this freezing process,
20:46but if there's a whole layer of ocean that's freezing up against the ice crust,
20:50that's a tremendous amount of heat.
20:52Maybe it could bring up cryovolcanoes
20:54driven simply by the heat from freezing in parts of the liquid water ocean.
21:00Just amazing.
21:03Incredibly, just a few degrees of heat leaking from Pluto's ocean
21:08may be all it takes to drive the dynamic surface of Pluto
21:12to raise mountain ranges, to fire up watery volcanoes,
21:17and to set nitrogen glaciers racing down icy slopes.
21:22We humans are prejudiced.
21:23We live on this warm planet.
21:25If you go down a few miles under the surface of the Earth,
21:27the rock there is almost molten.
21:29It's incredibly hot.
21:31And so we think you need a huge amount of energy
21:34to drive volcanoes and geysers and plate tectonics and all that.
21:38But that's not really the case.
21:39It's just that rock takes a lot of energy to melt and do all that.
21:43Ice doesn't take nearly that much energy.
21:45So on Pluto, if something was able to heat it up even a little bit
21:50and get that water ice to melt,
21:53that can drive the same sort of surface geology that we have here on Earth.
21:59And if, as we expect, our galaxy is filled with frozen worlds like Pluto,
22:05then the universe just got a whole lot more interesting.
22:09And so it could be that most of the worlds in the galaxy are cold worlds.
22:15And it might be that most of the volcanism in the galaxy
22:17is actually the running cold volcanism that we see on Pluto.
22:22And Pluto is actually going to end up changing
22:24the way we think of any sort of solid planet.
22:27Somehow it's still alive when it shouldn't be.
22:34New Horizons has shown us that Pluto most likely has both heat and liquid water.
22:41And that simple fact raises an astonishing possibility.
22:48Could tiny Pluto, sitting just three billion miles from the sun,
22:53provide a secret haven for life?
23:04In all the vastness of space, we only know of one planet that's home to life.
23:25Our planet, the Earth.
23:29On Earth, we have all the ingredients we needed for life to arise.
23:33Clearly, we're here.
23:34But those three things are basically a source of energy,
23:38liquid water, and organic molecules, carbon-based molecules.
23:46We used to think Earth was the only world with all three ingredients.
23:50But when robotic probes visited Jupiter and Saturn,
23:54they found multiple active moons with underground oceans warmed by hot volcanic vents.
24:01And these worlds also appeared to be spiked with the basic chemical ingredients for life.
24:08So if Jupiter's moon, Europa, and Saturn's moon, Enceladus,
24:13are considered potential havens for life, why not the subterranean oceans of Pluto too?
24:21Well, we think there's liquid water possibly on Pluto, and there's clearly a source of energy.
24:27Could it have that third ingredient?
24:29And if so, is it that bizarre to wonder if life could arise on Pluto?
24:37The third ingredient is organic chemistry,
24:39the carbon-based molecules that build the machinery of life.
24:44Surprisingly, astronomers believe these complex chemicals
24:48can form spontaneously in the cold of space.
24:52All you need are simple carbon-based gases and a source of energy, usually light.
24:59The most active natural laboratory we know of for this kind of organic chemistry
25:04is the atmosphere of Saturn's giant moon, Titan.
25:10When you look at Titan, it has a very thick atmosphere, thicker than Earth's.
25:14And it's surrounded by this haze, and that haze is basically made of organic molecules
25:21that are created from the more basic compounds that have been zapped by ultraviolet light
25:25and built up to make these more complex organic compounds.
25:31Titan's atmosphere is thick with simple gases, methane, carbon monoxide, and ammonia.
25:39And when sunlight strikes Titan's cloud tops,
25:42these gases join together to form complex organic molecules,
25:47which hang in the atmosphere, forming dense layers of haze.
25:52Scientists call these naturally occurring organic molecules tholins.
25:58It's a generic term, it's a blanket term for any sort of complex,
26:03reddish-colored organic molecule that is formed from
26:06the splitting apart and reassembling of simpler starting molecules.
26:11These organic molecules, these tholins,
26:13you can think of them as the Lego building blocks for life.
26:17On Earth, tholin-like chemicals make up the working machinery of cells,
26:23the DNA and proteins that make life tick.
26:28If, like Titan, Pluto has an atmosphere rich in carbon,
26:33could it too be producing tholins, and therefore, perhaps a shot at life?
26:40When New Horizons passed Pluto in 2015,
26:43the spaceship turned to take an image of the dwarf planet backlit against the sun.
26:50Scientists hoped to capture the unmistakable haze of organic chemistry.
26:57The results were far more spectacular than I would have expected.
27:02Absolutely, we saw that atmosphere, a beautiful blue ring of nitrogen gas surrounding Pluto,
27:08just like what we see on the Earth.
27:11These beautiful blue haze layers are chemical factories manufacturing tholins,
27:16complex organic molecules, from the simpler building blocks in the atmosphere of Pluto.
27:21The carbon monoxide, the methane, the nitrogen,
27:23all these things that are in the atmosphere of Pluto
27:25are being broken apart by sunlight and reassembled in these hazes
27:29into these just wonderful, delicious organic molecules.
27:33On Titan, newly produced tholins rain down from the atmosphere onto the surface of the Moon,
27:39producing a thick, orange-brown carpet of organic gunk.
27:45Scientists hoped to see something similar happening on Pluto,
27:48but they had to wait for New Horizons to send back
27:52its first full-color images of the dwarf planet.
27:56We've been getting a lot of black and white images from Pluto,
27:59so I was very excited to see what it would look like on Titan.
28:01We've been getting a lot of black and white images from Pluto,
28:04so I was very excited to see the color ones.
28:06And when they finally came in, and I saw these rich, red, orange-brown features on the surface,
28:13my first thought was, oh my gosh, organic chemistry.
28:17There are areas where things look almost kind of reddish-brown, even sort of pinkish.
28:21And when you see a color like that, you immediately think organics.
28:25And in fact, that's exactly what this is, pink organic snow.
28:29Life as we know it couldn't exist on the surface of Pluto.
28:33It's too cold.
28:35But if tholins are getting cycled down into the guts of the planet,
28:39they could be transported to the areas where ice melts into liquid water.
28:45And it's just possible the chemical evolution of these simple organic molecules
28:50could continue there, driven by Pluto's meager heat.
28:54And maybe, just maybe, the machinery for simple life
28:57could assemble in the subsurface oceans of Pluto,
29:02just like it probably did in the deep oceans of Earth four billion years ago.
29:08I'm intrigued by the possibilities that the sphere of life around our sun
29:13may extend much further away from the sun than we ever dreamed possible.
29:18So, you know, could there be life on Pluto or under the surface of Pluto?
29:22I couldn't say no to that at the moment.
29:24It's an intriguing possibility.
29:26Could there be life on Pluto?
29:29I don't think so.
29:31It's my own personal opinion.
29:32You know what?
29:33You can take flour and butter and eggs and chocolate chips
29:35and shake them all up and throw them in an oven.
29:37You may not get a cookie.
29:38What you're probably going to get is a glop.
29:40You're going to get a mess.
29:41While scientists debate the stunning possibility of life three billion miles from the sun,
29:48three billion miles from the sun,
29:50New Horizons turns its attention to Pluto's tiny moons.
29:57Mission scientists knew that Pluto most likely had five companion worlds,
30:02but nobody could have predicted just how plain weird these moons would turn out to be.
30:18When New Horizons arrived at Pluto, scientists held their breath,
30:23eager to see what Pluto's moons would turn out to be like.
30:27We knew nothing about them.
30:29So everything, literally, that we found out about these moons
30:33was going to be for the first time, and it was going to be a surprise.
30:38Three years before New Horizons arrived at Pluto,
30:41the Hubble Space Telescope imaged five moons on Pluto.
30:45The Hubble Space Telescope imaged five moons around the dwarf planet,
30:51one oversized moon called Charon, and four much smaller icy companions.
30:57New Horizons was reprogrammed to study these worlds
31:02and to discover any additional moons too small for Hubble to pick out.
31:08You know, before the flyby, one of the things that we surveyed people about
31:11was how many more moons would we find.
31:13And some guessed dozens, and some guessed a few more.
31:19And one of our top team members guessed zero.
31:25And I remember going to him and saying,
31:27I'll take that bet.
31:28I'll bet you a dinner anywhere in the United States that we will find at least one.
31:35Stern lost his bet.
31:36New Horizons confirmed Hubble had seen all there was to see.
31:41But what incredible worlds Pluto's five moons turned out to be.
31:47Oversized Charon was revealed alongside Styx, Nix, Kerberos, and Hydra.
31:55Four tiny ice moons, each less than 25 miles across.
32:00And they were unlike any moons astronomers had seen before.
32:05These objects are spinning crazy fast compared to what we expected.
32:10Not only that, but instead of having their poles aligned with Pluto's pole like this,
32:15they're actually spinning on their side.
32:16So they're sort of going around like this.
32:18Totally crazy behavior that we had no expectation of.
32:23To understand these crazy orbits,
32:25scientists find clues in the early history of the Earth.
32:30In the early days of the formation of the Kuiper Belt,
32:32these icy bodies were colliding with each other quite often.
32:35And just like here at the Earth, where a large Mars-sized protoplanet actually
32:40collided with the Earth to form our Earth-moon system,
32:43that's probably what happened at Pluto as well.
32:46Pluto most likely took a giant hit in its youth.
32:50And its moons are the leftovers from this mammoth collision.
32:55Giant Charon settled into a close spinning orbit with Pluto.
33:00And farther out, the four tiny moons orbit around both bodies.
33:05Like tumbling shards of icy shrapnel.
33:11The first images of oversized Charon show a gray, dead world,
33:16pockmarked with the scars of its violent past.
33:20The biggest scar is huge.
33:22It appears to almost split the moon in two.
33:26Charon is a mess.
33:29The first thing I thought of when I looked at that picture that we got in high resolution,
33:34it's like, this is Frankenstein's moon.
33:36This looks like a moon that somebody basically took a hammer and chisel to
33:39and broke it completely apart and then just mashed it back together.
33:45But what has the power to split a Texas-sized moon like Charon apart?
33:50In the frozen wastelands of the outer solar system,
33:54scientists are left with only one option.
33:57Water.
33:59Four billion years ago, Charon probably had an internal liquid ocean,
34:03just like Pluto today.
34:05But because Charon is smaller, it cooled more quickly.
34:09The entire ocean turned to ice and poor Charon burst at the seams.
34:17If you take a soda can and put it in the freezer,
34:20when the water in that soda freezes, it expands, but the metal of the can won't.
34:26And so what happens is it gets under more and more stress,
34:28more and more pressure until it ruptures and it splits open and that stuff oozes out.
34:34This system of canyons and faults across the equator of Charon
34:38really sort of represent that last gasp of geologic activity as it sort of,
34:43you know, spilled its guts out as the interior ice froze
34:47and, you know, on its way to becoming a dead world.
34:50So it was Charon's last gasp, if you will.
34:52Charon's red-stained polar cap also catches the eye of mission scientists.
34:57They name it Mordor.
35:03And this barren, red-painted terrain presents the team with perhaps their greatest challenge.
35:10Of all the surprising things on Charon, and it's a long list,
35:13probably the most surprising thing is Mordor.
35:17I love that.
35:17Mordor appears covered with tholins.
35:20But how?
35:22This frozen world doesn't have the ingredients
35:24or the atmosphere to make complex organic molecules.
35:29The tholins must be coming to Charon to produce tholins.
35:34We don't know how.
35:35But we do know that the tholins are the main elements of the tholins.
35:41The tholins are the main elements of the tholins.
35:43The tholins must be coming to Charon pre-made, but from where?
35:52The only logical answer is from Pluto, over 10,000 miles away.
35:59How would it get from being made on Pluto to getting to Charon?
36:02And really, nobody's sure.
36:04But the thinking is that somehow this stuff is getting into the atmosphere of Pluto
36:09and being transferred that way through space
36:11to basically be deposited on the North Pole of Charon.
36:15How that works is something I don't think anybody understands.
36:19And that's cool, because there are a lot of mysteries left
36:22and a lot of studying to be done, even with all of the data we have.
36:30There are still many questions to answer.
36:32But we now have a handle on how Pluto works.
36:36And that's allowed scientists to imagine the future of this frozen world.
36:42Incredibly, Pluto may be about to awaken from a deep, cold slumber.
37:042015.
37:05A tiny robotic probe shoots past Pluto and fires its photographic shutters.
37:12The pin-sharp images stunned the world.
37:16Glaciers, smooth, young plains, and even the hint of active cryovolcanoes.
37:23But one set of images at first appeared impossible.
37:28As we looked down on this brand-new world to us,
37:31we saw things that at first were very hard to explain.
37:34There seemed to be these depressions and channels
37:36that looked like lakes or even little rivers.
37:38These flow features are made from nitrogen.
37:42And although they're now frozen,
37:44they appear to have been liquid in the recent geological past.
37:48But how?
37:51Pluto is too cold and its atmosphere too thin to support liquids on the surface.
37:58In the entire universe, it is so difficult to get liquid.
38:02Everything seems to want to be a solid or a gas.
38:05You have to have just the right circumstances
38:07for that liquid phase of matter.
38:09So even for something like nitrogen,
38:11you not only just have to turn up the temperature and get nitrogen warmer,
38:14there also has to be some atmospheric pressure.
38:17A thicker atmosphere is needed to maintain liquid nitrogen on the surface.
38:23Scientists deduce that in the last million years,
38:26some significant event must have warmed Pluto.
38:30Evaporating glaciers and filling the atmosphere with nitrogen.
38:34But what could have caused such an extreme climate shift?
38:38Scientists first looked to Pluto's elongated orbit around the sun.
38:44Once every 248 Earth years, Pluto's elliptical orbit brings it close to the sun.
38:51But this brief period of summer warming isn't sufficient to thicken Pluto's atmosphere.
38:56When it comes in close to the sun, it goes faster and faster.
39:00And as it moves away from the sun, it goes much slower.
39:03So on Pluto, summer doesn't last anywhere near as long as winter.
39:08But from time to time, one half of Pluto gets a super summer,
39:13thanks to the dwarf planet's unstable tilt.
39:16We know from the way Pluto's north and south pole wobble over time,
39:20that that top that represents the spinning sphere of Pluto
39:23is not nearly as stable as the Earth.
39:25Our planet is tipped over at about 23 degrees.
39:28Our planet is tipped over at about 23 and a half degrees
39:30and sits that way for, you know, for millennia at a time.
39:35Pluto, on the other hand, is much less stable.
39:38And its poles wander over time.
39:45Once every million years or so, Pluto tips completely onto its side,
39:50exposing the northern hemisphere to constant sunlight during its close pass to the sun.
39:56And the warmth from this orbital shift transforms the surface of the planet.
40:05Picture Pluto as it warms.
40:08The atmosphere thickens and fills with clouds.
40:12A warm wind sweeps across the plains and Pluto's glaciers begin to melt.
40:19Like an animal emerging from hibernation, Pluto comes to life.
40:26It's almost as if it's undergoing these periodic changes where it's warmer and colder and warmer
40:33and colder in the past and maybe again in the future.
40:37Will Pluto have liquid on its surface, even if only temporarily?
40:41What would that mean?
40:42What would that even look like?
40:44800,000 years from now, Pluto will awaken once again.
40:49It will tilt over completely to face the sun
40:52and its mountains will fill with the sound of running nitrogen.
40:57You begin to actually see flowing rivers of nitrogen.
41:00You could stand on the shore of a nitrogen lake.
41:03There'd be pink snow with organic molecules coming down on you.
41:07What a truly magical world.
41:11New Horizons is now on its way to find new targets.
41:15So there could be more surprises yet to come.
41:18Yet the legacy of this little probe goes far beyond just Pluto.
41:23It changes the way we view frozen worlds all across our galaxy
41:28and the possibility these far-off worlds offer.
41:32It tells us that there's this huge stage for the play of life out there in the galaxy.
41:37A huge variety of worlds.
41:39You imagine the world, it probably exists out there someplace.
41:42That's kind of the lesson that Pluto has for us.
41:45It tells us that things can be a lot more interesting out there than you can possibly imagine.
41:50Pluto has really inspired me.
41:52It showed me just how wrong we can be.
41:55We thought we understood what Pluto would be and it was entirely different.
41:59And as a scientist, you've got to think,
42:01how much more out there do we have to discover?
42:03If nothing else, Pluto taught us that.