Professor Brian Cox explores the Solar System’s frozen worlds. He meets the dwarf planet where mountains of solid ice float across the surface, the black and white moon painted with frost, and a world illuminated by a strange form of ice.
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Thanks for watching. Follow for more videos.
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#solarsystem
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#episode4
#cosmology
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LearningTranscript
00:00If I ask you what is a planet made of,
00:24then you'd probably say, well, rocks and iron.
00:30And for the planets of the inner solar system, like Earth,
00:35close to the heat of the sun, you'd be right.
00:42But if you head out into the frozen outer reaches of the solar system,
00:47then even the gases that make a fire atmosphere,
00:50nitrogen, carbon dioxide, and, of course, water,
00:54are all frozen solid.
00:55And the planets and moons out there,
01:00the mountains and glaciers,
01:02and even the crust of the worlds themselves,
01:06are made of that solid, frozen, pristine ice.
01:13Ice that, in the extreme conditions we find beyond Earth,
01:18behaves in ways we never imagined possible.
01:21As we've explored the solar system,
01:30our spacecraft have encountered moons torn apart
01:34by great canyons of shifting ice.
01:43Dwarf planets where mountains of solid ice float across the surface.
01:48worlds where ice appears to cover one face,
01:55but leaves the other entirely alone.
02:05And elsewhere, alien aurora hang above the clouds,
02:09all thanks to a strange, newly discovered form of ice.
02:14Even here, on Earth,
02:21the behaviour of something as simple as ice
02:24has had, we think, profound consequences.
02:29Because without ice's counterintuitive behaviour,
02:33life on our planet may not have survived.
02:36.
02:43.
02:55.
02:55We begin our journey to the ice worlds
03:07at the freezing edge of the solar system.
03:25Out here, the sun is so far away it resembles just another star.
03:41Pluto is so remote that it was only in July 2015 that we had our first and to date only
03:48close encounter.
03:55As it flew by, the New Horizons spacecraft sent back the first close-up images of this
04:00mysterious frozen world.
04:12It discovered a great heart-shaped plane, a thousand kilometres across, that dominates
04:17one face.
04:22Around the edge of this plane, mountains made of solid ice tower over Pluto's surface.
04:46And amongst its rugged uplands, ice was detected in a form no-one ever expected to see on Pluto.
04:58Glaciers.
05:03Flowing rivers of ice on a world so far away we expected nothing would be moving.
05:12That's because the temperature here is only 40 degrees Celsius or so away from absolute
05:17zero, a temperature at which nothing should move.
05:27And yet New Horizons discovered regions of Pluto that for all the world look like the frozen
05:33reaches of our planet.
05:34So when you fly here over the years, how much does it change?
05:41It changes every day.
05:42Yeah?
05:43Yes.
05:44The shape of the glaciers change.
05:45It's never the same.
05:46It's never the same.
05:47It's never the same.
05:48It changes every day.
05:49Yeah?
05:50Yeah.
05:51I'm just imagining flying over Pluto actually.
05:52Because it's never the same.
05:53It's never the same.
05:54I'm just imagining flying over Pluto actually.
05:56because it is most remarkably similar.
05:57Really?
05:58What is the topography like?
05:59Like the céu in the sky?
06:00That's it.
06:01It's never the same.
06:02You can see it.
06:03It's never the same.
06:04Yeah.
06:05It's never the same.
06:06I'm just imagining flying over Pluto actually.
06:07Yeah.
06:08Yeah.
06:09It's never the same.
06:10I can see it.
06:11The ocean.
06:12The ocean.
06:13You can see it.
06:15I can see it.
06:16And the ocean.
06:17It's never the same.
06:18The ocean.
06:19It's never the same.
06:20I can see it.
06:21It's never the same.
06:22It's never the same.
06:24What is the topography like?
06:27It's like this.
06:28Same topography, same mountain heights.
06:30That's incredible.
06:40The discovery of Pluto's dynamic icy landscapes came as a huge shock.
06:47It forced us to rethink our understanding of this so-called dwarf planet.
06:54We're coming in for landings, so I'll just be talking to the aeroplane and not you.
06:59I respect that choice.
07:01I've had a lot of landings, but none quite like this.
07:05In fact, none like this at all.
07:09It's the world's most beautiful runway.
07:18Welcome to the glacier, you guys.
07:24Wow.
07:32You know, when we arrived, they said, oh, it's zero degrees.
07:39And I thought, that's great.
07:41Zero degrees.
07:42It's warm.
07:43Fahrenheit.
07:44Zero degrees Fahrenheit.
07:46It's about minus 20 up here.
07:48It's just, you've got a real sense, actually, coming in.
07:52It looks frigid and frozen.
07:54You know, unmoving, unchanging.
07:57But it's so dynamic.
07:58You can feel it in the wind as you land.
08:01And then, you know, you can see.
08:03You can see the way that everything flows.
08:05Just look at that glacier.
08:15You can almost feel or see it moving.
08:20It looks like a slow motion river.
08:23And indeed, it is moving.
08:25It does flow very, very slowly.
08:27And the reason this great mass can grind its way down the valley is because of the unique properties of the ice from which it's made.
08:38That bright blue ice certainly looks solid, immovable.
08:48It's formed by pressure.
08:51So these snowflakes are falling down onto the top of the glacier.
08:54And over time they build up, their weight presses down, increases the pressure.
08:59And you get that particular crystalline structure of ice which looks transparent and blue.
09:06But actually, at those pressures and temperatures, it's not completely solid.
09:11The crystals are sort of arranged in planes, a little bit like a deck of cards.
09:16And that means that as gravity is active, trying to slide this whole thing down the valley,
09:22those planes can slip and slide over each other.
09:26And that allows the whole glacier to move.
09:29You can also get liquid water between the rock and the ice.
09:32And that sort of lubricates the glacier and that allows it to slip as well.
09:36So although this looks fixed and immovable, at the conditions we find on Earth,
09:42this can almost behave like a fluid, sort of sliding very slowly and deforming down the valley.
09:51Glaciers were the last things we expected to see on Pluto.
10:05It's so cold here that we'd expect the ice crystals to be too brittle to flow.
10:14Nothing should slip.
10:16Nothing should slide.
10:21Nothing should slide.
10:23Yet that's precisely what these glaciers are doing.
10:31So if they can't be made of water ice, what are they made of?
10:36As New Horizons flew past Pluto, its detectors picked up an important clue.
10:55These are images of Pluto's surface and the colours correspond to different molecules,
11:00different substances that New Horizons detected on the surface.
11:03The purple is methane, the yellow is nitrogen, and the green is carbon monoxide.
11:11All these gases are frozen solids.
11:15Now the glaciers on Pluto are primarily made of nitrogen, solid nitrogen.
11:22The nitrogen is something that we're all familiar with.
11:25It's this stuff.
11:26Our air is pretty much made of nitrogen.
11:28So our familiar experience of it is just we can't see it.
11:33If we cool it down, then we can get it pretty easily to turn into a liquid.
11:42Now if we carried on cooling that down, it would turn into a solid.
11:45Nitrogen freezes at minus 210 degrees C, and Pluto's surface temperature at around minus 230 degrees ensures that glaciers remain solid.
11:58But, crucially, the nitrogen ice is just 20 degrees or so away from its melting point.
12:10That's very similar to the situation here on this glacier.
12:14The glacier is about, well, the air temperature today is about minus 10, minus 20 degrees Celsius, heated up by about 20 degrees, and it'll melt.
12:24So the temperature difference between the solid nitrogen ice and the nitrogen gas and the solid water ice and the water is about the same.
12:35That means that with just a small rise in temperature, Pluto's nitrogen ice should be able to move.
12:47So the discovery of its glaciers tells us something remarkable about Pluto.
12:52This tiny world must have a little heat at its core, a faint warming from radioactive decay, just enough to gently melt the bottom of these rivers of ice, sending them on their way down the valley.
13:15I think for me there are two lessons from the exploration of Pluto.
13:18Pluto. One is that geology finds a way, even so far away from the sun, where temperatures are only 40 degrees or so, above absolute zero, pretty much the coldest it can be,
13:31there can still be active geology, particularly where something is close to its freezing point.
13:37In Pluto's case, nitrogen ice.
13:40The second lesson, I think, is perhaps even more profound, is that nature's imagination far exceeds our own.
13:47Nobody expected that they would see such a beautiful, active world, so far away from the sun, on the far icy edge of the solar system.
14:07The similarities between Earth and Pluto are striking, but New Horizons discovered a wonderful difference.
14:17Pluto's glaciers flow through mountains reminiscent of Alaska's Great Ranges.
14:28But unlike Mount Denali's granite spires, Pluto's mountains are made from frozen water.
14:36But you can't imagine something that big, that high, being made of water, that's the thing that...
14:45That's crazy.
14:46...inazes me.
14:47All water, no, no rock.
14:49Yeah, pretty much, yeah.
14:52And this leads to a surreal twist.
14:54Water ice in the mountains is less dense than the nitrogen ice in the glaciers.
15:02So in places, we've seen mountains floating on the glaciers, carried away like icebergs onto the vast ice plain below.
15:19Pluto, a world sculpted by ice.
15:23Leaving Pluto and heading back towards the sun's glow, we enter the realm of the ice giants.
15:43Vast gaseous worlds, where ice storms rage.
15:49And on the innermost of these planets, we've discovered a phenomenon eerily reminiscent of home.
15:59Just above Uranus' ice clouds hang beautiful, ethereal, aurora.
16:20Found not at the poles of the planet, as on Earth, but scattered across its face.
16:36Even around the equator.
16:37So what's creating this beautiful, rare display?
16:46The basic physics of the aurora on Uranus is the same as the physics of the aurora on Earth.
17:03So the sun's constantly emitting a rain of high-energy charged particles, which is called the solar wind.
17:10And when those charged particles reach the Earth, most of them are deflected around the Earth,
17:15harmlessly off into space by our magnetic field.
17:19Now, the Earth's magnetic field looks very much like the field around the bar magnet.
17:25I'll show you that by sprinkling some iron filings around the bar magnet.
17:32And the iron filings line up with the magnetic field lines.
17:41When the solar wind hits this magnetic field, most regions of the Earth is deflected harmlessly off into space.
17:48But at the poles, those charged particles can become trapped.
17:52And then they can be accelerated down into the upper atmosphere and hit molecules in the atmosphere, oxygen and nitrogen.
17:59And that can cause those molecules to emit light, to glow.
18:03And that's what, if you're lucky, you see as the northern and southern lights.
18:08So somewhere deep inside our planet lies the equivalent of that bar magnet.
18:19And, of course, it does, in the form of a hot, molten iron core spinning away as the Earth rotates.
18:28Creating electrical currents and the magnetic field that projects out into space.
18:34But Uranus is different.
18:38The aurora are not found at the poles.
18:41And we don't think it has a molten iron or metallic core to support those electrical currents.
18:49And so the fact that Uranus does have aurora, and therefore some kind of magnetic field, is tremendous mystery.
18:57But we do have theories that allow us to piece together what might be going on.
19:11Imagine diving beyond the clouds of Uranus.
19:15Beyond the slushy ice layer that flows around the planet.
19:22And keep going towards the core.
19:25We enter a region where the pressure approaches several million times that of Earth's atmosphere.
19:34And where it's almost as hot as the Sun's surface.
19:42Rather than molten rock or metal, like we find inside our own planet.
19:47We instead find yet more frozen water.
19:52In a bizarre form of matter.
19:55Known as superionic ice.
20:02Normal water ice has a crystal structure like this.
20:06So the reds are oxygen atoms.
20:09The whites are hydrogens.
20:11And you can see that they're bonded together into this regular crystal lattice.
20:17Within the lattice, nothing that could carry an electrical current can flow.
20:22So a magnetic field can't be created.
20:27This is the crystal structure of superionic ice.
20:32The oxygens are still there, bonded together into a crystal.
20:37But now, they're a hydrogen nuclei.
20:40Electrically charged protons that can move freely through the crystal lattice.
20:46That means that this is an electrical conductor.
20:51It's this movement of the protons that could be contributing to Uranus' magnetic field.
21:03If so, then the superionic ice is, at least in part, driving the planet's mysterious aurora.
21:14Now, this story is still far from fully understood.
21:18For a long time, this strange form of ice was only a theory.
21:23But then a team pointed one of the world's most powerful lasers at a droplet of water.
21:29And recreated the conditions that are present deep down inside Uranus.
21:34And, just for a moment, cause a glimpse of superionic ice.
21:43Uranus.
21:44A world illuminated by ice.
21:54On the journey between ice worlds, we edge ever closer towards the sun.
21:59For an encounter with one of the most thoroughly explored planetary systems of them all.
22:05Saturn's rings are constructed of countless crystals,
22:26ranging in size from just a few microns to vast boulders.
22:30And all of them, made almost entirely from frozen water.
22:45The rings are joined in their orbits by at least 146 moons.
22:50And out towards the edge of the system, NASA's Cassini probe made one of its most surprising discoveries.
23:01The moon Iapetus resembles a walnut, with a mountain ridge around its middle.
23:20But that's not its strangest feature.
23:22Back in the 17th century, only about 60 years or so, actually, after the invention of the telescope,
23:32Giovanni Cassini discovered Iapetus.
23:36But he immediately noticed something strange about the moon as he watched it orbit the planet.
23:40Because he could see the moon on one side of the planet, but then on the other side, he couldn't.
23:46Now, being sensible, as a scientist after all, he said, well, it's not somehow disappearing.
23:53There must be another explanation.
23:55And he guessed that one side of the moon must be very bright, and the other side must be very dark.
24:02Now, 300 years later, we sent a spacecraft to Saturn bearing his name.
24:09And we discovered that he was right.
24:13Cassini sent back proof that one side of Iapetus is icy white,
24:21whilst the other looks as if it's been painted black.
24:29So what could be creating such a sharply defined monochromatic world?
24:37Tremendous mystery.
24:38But a clue could be found in looking at the line between the two hemispheres,
24:43because there are jet black regions on the surface there
24:47that are also some of the hottest places in the Saturnian system.
24:54Hot is relative, of course.
24:56It's still minus 140 degrees Celsius on the dark side of the moon.
25:02But that's about 20 degrees warmer than the moon's icy face.
25:08And we think that this difference is just enough to move ice around the moon
25:17in a very particular way.
25:19The sunlight falls on that dark surface as Iapetus rather languidly rotates, actually,
25:32about once every 79 Earth days, and it heats it up.
25:36The water molecules rise up, drift over to the light side,
25:41and then condense and fall onto the surface,
25:45making it brighter and brighter and brighter.
25:48It's not like what's happening here.
25:50So out there in the Pacific Ocean,
25:52the water is turning into water vapour,
25:55drifting over the cold land and falling as snow,
25:59making the whole surface bright.
26:01On the dark side of Iapetus,
26:12ice is warmed
26:13and creates a thin atmosphere of water vapour.
26:17And where this vapour meets the colder, white side of the moon,
26:28it freezes to the surface again,
26:31resembling fresh snow,
26:33maintaining the bright, icy white of this hemisphere.
26:40But a mystery remains,
26:44because Iapetus is an ice moon.
26:49So what is the dark material covering its other face?
26:59In 2009, the Spitzer Infrared Space Telescope discovered this.
27:05This is another ring around Saturn,
27:08but it's enormous.
27:10It's one of the largest structures in the solar system.
27:12This is about 12 million kilometres across.
27:21Later observations from NASA's WISE telescope
27:25suggest that the disk may extend
27:28a further 20 million kilometres out into space.
27:34At this vast scale,
27:36Saturn and its more familiar icy rings
27:39are barely visible.
27:46It might seem strange that no-one had seen
27:49one of the largest structures in the solar system
27:51until 2009.
27:53The reason is that that ring
27:55is very dark and very diffuse.
27:57If you're transported into the ring,
28:00you can look around
28:00and you wouldn't know you were in it.
28:04Spitzer saw it
28:04because Spitzer's an infrared telescope.
28:07And so it detected not visible light,
28:09but infrared light,
28:11the glow,
28:12the heat emanating from the ring.
28:16The giant outer ring
28:18is therefore very different
28:19to Saturn's ice rings.
28:22So what is it made of?
28:24And where did it come from?
28:36Phoebe is another of Saturn's outer moons.
28:39And each time a passing asteroid
28:41gets too close,
28:43the resulting impact
28:47throws dark material out into space.
28:49Over billions of years,
28:59numerous impacts
29:00have resulted in the dust from Phoebe
29:02spreading around Saturn,
29:05forming its vast, dark ring.
29:12Iapetus passes through the ring
29:14as it orbits.
29:15And so that dark material from the ring
29:19gets deposited
29:19on the surface of Iapetus.
29:22This is a really slow process.
29:25Material falls onto Iapetus
29:27and increases the size of that dark layer
29:30by about four hundredths of a millimeter
29:33every million years.
29:36It's not a bad analogy, this, actually.
29:38Some of those sort of dust particles
29:40in the ring are about this size,
29:42about the size of pepper grains.
29:44Some are bigger.
29:44There's a few centimeters across
29:46or something,
29:47but it is pretty much stuff like this.
29:52And yet a puzzle remains.
29:55Why half black and half white?
30:02Iapetus spins on its axis
30:04once every 79 days
30:05and orbits around Saturn
30:08once every 79 days.
30:10It's what's called spin orbit locked.
30:12It's like our moon.
30:12So it always leads
30:14with one hemisphere
30:16as it orbits around Saturn
30:18and passes through the ring.
30:25Iapetus, then,
30:26is a fluke of nature
30:27that exists
30:29thanks to the interaction
30:30of two moons
30:31within a dark ring
30:32right at the edge
30:34of Saturn's domain.
30:35a world painted
30:40by ice.
30:56As we return
30:58ever closer to the sun,
30:59ice becomes increasingly rare.
31:02Jupiter has 95 known moons,
31:11including three large ice worlds.
31:18and one of these
31:27is a promising target
31:29in our search
31:30for life beyond Earth.
31:31In 2022,
31:48NASA's Juno spacecraft
31:49flew by Europa
31:50and photographed
31:53a world crisscrossed
31:54with mysterious red lines.
31:56Grand canyons.
32:05Some 100 metres deep
32:07and tens of kilometres wide.
32:10In places coated
32:12in a red substance
32:13that may be
32:14a newly discovered compound
32:16of salt and water.
32:18Juno is the latest
32:30NASA mission
32:30to fly by Europa
32:32and take detailed photographs
32:34of its peculiar
32:35fractured surface.
32:43The canyons on Europa
32:45are quite unlike
32:46anything seen on Earth.
32:48or indeed
32:50anywhere
32:50in the entire
32:51solar system.
32:54The markings
32:55are geometric.
32:57They form lines
32:58that crisscross
32:59over the surface.
33:01So,
33:02what can be causing
33:03that problem?
33:06Europa's surface features
33:07are an active area
33:08of research,
33:09taking NASA scientists
33:10to the frozen reaches
33:11of our own planet
33:12in search of answers.
33:14this is an image
33:17of a region
33:17on Europa's surface
33:18called Phaedra Linea.
33:20And see this feature?
33:23It almost looks like
33:24the Grand Canyon
33:25on Earth.
33:25It's actually about
33:2650 kilometres across.
33:27A clue to what this is
33:30can be seen
33:31that if you look
33:32at the top line
33:33and the bottom line
33:34and just in your mind's eye
33:36just draw these together,
33:39you'll see that
33:40they knit together
33:41perfectly.
33:43So this looks like
33:44the crust has just spread.
33:46Now, there's only one
33:47other place
33:47in the solar system
33:48where we see
33:49features like this
33:50and it's here
33:51on Earth.
33:53It's caused by
33:53plate tectonics.
33:57On Earth
33:58is the internal heat
33:59of the planet
34:00as it forces its way
34:01through the crust,
34:03which is the driving force
34:05of plate tectonics.
34:11And no one expected
34:13to see behaviour
34:13like this
34:14on a moon.
34:19On Europa,
34:26it's not molten rock
34:27that's driving
34:28its plates apart.
34:33Density measurements
34:34of the moon
34:35suggest that beneath
34:36the thick icy crust
34:38lies a different liquid.
34:41A global subsurface ocean
34:43of water.
34:45Up to 150 kilometres deep,
34:48it may contain
34:49two or three times
34:50all the water
34:51in Earth's oceans combined.
34:55So how can all
34:57that liquid water exist
34:58just below the surface
34:59of this frigid ice moon?
35:01the answer lies
35:11with two other moons
35:14of Jupiter,
35:14with Io and Ganymede.
35:17So here's Jupiter,
35:19and then Io
35:21goes around
35:23four times,
35:24as Europa
35:28goes around
35:29two times
35:30and Ganymede,
35:31par this out,
35:33goes around
35:34once.
35:36It's called
35:36an orbital resonance.
35:38Four orbits
35:39to two orbits
35:40to one orbit.
35:42That means
35:42that these three moons
35:43line up
35:45periodically
35:45and give each other
35:47a gravitational kick,
35:49which means
35:50that the orbits
35:50don't stay
35:52as nice circles.
35:53They're all
35:53ellipses.
35:55And that
35:56means that
35:57tidal effects,
35:58just like the tides
35:59here on Earth,
36:00stretch and squash
36:01the moons
36:02and heat them up.
36:04Now the effect
36:04is strongest
36:06for Io
36:06because that's
36:07closest to the
36:07giant planet.
36:09And so that turns
36:09Io into essentially
36:11one giant volcano.
36:12For Europa,
36:13further out,
36:14that heat
36:15melts the ice.
36:18But the energy
36:19that goes
36:20into Europa
36:21from this
36:22eccentric elliptical
36:23orbit around Jupiter
36:24sort of trickles
36:26into the moon.
36:28So it really
36:28isn't enough
36:29on its own
36:30to produce
36:31the very active
36:32geology
36:33that we see
36:34on the surface.
36:40We estimate
36:41the surface ice
36:42on Europa
36:42is somewhere
36:43between 10
36:44and 25
36:45kilometres thick.
36:52So whilst
36:53the tidal forces
36:54are enough
36:55for the subsurface
36:56ocean to remain
36:56liquid,
36:57they're not enough
36:59to split apart
37:00all this ice.
37:01So to drive
37:04the high-energy
37:05geological processes
37:06we see
37:07on the surface
37:07of Europa,
37:08then there must
37:09be some kind
37:10of energy storage
37:11in the moon itself.
37:14So I've got
37:14two camping stoves
37:15here.
37:16These two pans
37:17are filled with water
37:18and it's at the same
37:19temperature,
37:20zero degrees.
37:21The only difference
37:22is that this water
37:24has ice in it
37:25and this has no ice
37:26in it.
37:27The only difference
37:28when we start
37:29the stoves.
37:33This is a thermal
37:35camera here
37:36because, you know,
37:37I wouldn't travel
37:38without one.
37:39So it will tell us
37:40that the temperature
37:41of the water
37:42is rising
37:438, 9 degrees
37:45already.
37:47Whereas this one
37:48is still
37:49zero degrees
37:50even though we're
37:51putting all the
37:51energy into it.
37:53Now look.
37:54Ha ha!
37:55You see that?
37:56So why?
38:00Well, this is a
38:02model of ice.
38:03You can see
38:03the water molecules
38:04here and here
38:05and here.
38:06And they're bonded
38:07together by these
38:08longer bonds
38:09which are called
38:10hydrogen bonds.
38:11They're the thing
38:12that hold the
38:13crystal lattice
38:13in place.
38:15And they're
38:15pretty strong.
38:17So to melt the ice
38:18you've got to break
38:19all these bonds.
38:21You've got to put
38:21a lot of energy
38:22into it.
38:23So all the energy
38:24from this camping
38:25stove at the moment
38:25is going into
38:26breaking bonds
38:27in the ice.
38:28It's not going
38:29into making
38:30all the molecules
38:30move around faster
38:32which is what
38:33temperature is.
38:34So this one's
38:35getting hotter
38:36and hotter
38:36and hotter.
38:37Nothing is
38:38happening to this one.
38:39Now these have
38:39been cooking away
38:40now and I'll show
38:41you I have
38:42confidence.
38:43I have confidence
38:44in physics.
38:45I believe in it.
38:47I would not put
38:48my hand in there.
38:49I can see it
38:49would be a stupid
38:50idea.
38:50But there.
38:52There you go.
38:54Physics works.
38:55It's actually
38:56freezing.
38:56Now reverse
39:04that idea.
39:05Reverse
39:06that argument.
39:07What happens
39:07then when I
39:08freeze water?
39:09When I turn it
39:10from a liquid
39:10to a solid?
39:13I get all
39:14that energy
39:14back out again.
39:16Huge amounts
39:17of energy
39:17as the bonds
39:18form.
39:21And this
39:22is what we think
39:22may be happening
39:23on Europa.
39:31The subsurface
39:33ocean is warmed
39:34by tidal forces
39:35from Jupiter
39:36and its moons,
39:37storing energy.
39:40then, thanks to
39:49its elliptical
39:50orbit, as Europa
39:52periodically cools,
39:53the ice begins
39:55to freeze.
40:00Releasing the
40:01stored energy.
40:02The volume
40:07of the icy crust
40:08grows
40:09as it freezes.
40:14Increasing the
40:15pressure.
40:16until the entire
40:26canyon
40:27is cleaved
40:28apart.
40:28and briny
40:38water from the
40:39ocean below
40:39surges up
40:40through the
40:41cracks.
40:44Where,
40:45bathed in
40:46Jupiter's
40:46intense radiation,
40:49it turns
40:50red.
40:51You're actually
41:00very familiar
41:00with this
41:01process.
41:01If your pipes
41:02burst in your
41:03house because
41:04they freeze,
41:05where does the
41:06energy come from
41:07to burst the
41:07pipes?
41:08It comes from
41:09water freezing
41:10into ice.
41:18Europa is far
41:19more dynamic
41:20than we'd
41:20imagined.
41:28And it's this
41:29dynamism that
41:30makes it a
41:31tantalising
41:31target in our
41:35search for life
41:36under the ice.
41:41At its
41:42simplest, life
41:43needs three
41:44things.
41:46Water, energy
41:47and the right
41:48chemical
41:48ingredients.
41:50Europa has the
41:53first two in
41:54abundance.
41:56But the
41:57chemistry for life
41:58is missing.
42:01But fortunately,
42:03Europa is not
42:04alone.
42:05orbiting close by,
42:15Io has the
42:15missing ingredients
42:16we believe
42:17necessary for
42:18life in
42:19abundance.
42:23Erupting into
42:23space in
42:25enormous quantities
42:26around Jupiter.
42:27water.
42:27Here's where the
42:34story gets even
42:35more wonderful.
42:36Because the
42:37volcanoes of Io
42:38are constantly
42:40producing chemicals,
42:41materials that
42:42rain down onto the
42:43frozen surface of
42:44Europa.
42:45But if it wasn't for
42:46the geology, then
42:47they'd be separated
42:48forever from the
42:49ocean below by
42:5010 or 20
42:52kilometers of ice.
42:54But that active
42:55geology, creating
42:57the plate tectonic
42:58like behavior, can
42:59bring those
43:00materials, those
43:01chemicals into the
43:03ocean.
43:04And then we have
43:05all the conditions
43:06we think are
43:07necessary for the
43:09origin of life.
43:14So Europa's
43:15dynamic surface may
43:17form part of an
43:18extraordinary
43:18ecosystem.
43:19one that
43:23stretches from
43:24one moon to
43:25another.
43:27And work is
43:27already underway to
43:28send robotic
43:29probes into that
43:31distant icy ocean.
43:38It would be a
43:39profound discovery to
43:41find life on Europa.
43:42But it would also be
43:43profound if we
43:45didn't.
43:46Because everything
43:47we think we know
43:48about the origin of
43:49life, all the
43:50ingredients that are
43:51necessary seem to be
43:53present on Europa.
43:55So if we go there
43:56and send a cryobot into
43:58the oceans of Europa
43:59and find nothing at
44:00all, then it may be
44:03far more likely that
44:05we are alone for
44:07millions or even
44:09billions of light
44:10years in every
44:11direction.
44:11Europa, a world
44:24completely encased in
44:26ice, couldn't exist much
44:28closer to the sun.
44:31Because just a little
44:32closer in lies the solar
44:34system's ice line.
44:36cross it and temperatures
44:41become too warm for ice
44:43to stay frozen for long.
44:51When comets fall inwards
44:53towards the sun, some of
44:56the ice they carry is
44:57transformed into water
44:59vapour.
45:07Forming tails that streak
45:09through space for hundreds
45:11of kilometres.
45:18Inside the ice line then,
45:19ice is rare.
45:21But there are places
45:23where it can hold on
45:25at the margins.
45:37Most of the ice on the
45:38surface of Mars is held
45:40at poles.
45:48Here, NASA's Mars
45:50reconnaissance orbiter has
45:51captured these
45:52extraordinary images of a
45:55strange phenomenon that
45:57takes place on the
45:58southern ice cap.
46:02Dark spider-like
46:03formations that we think
46:06are being formed as the
46:07seasons turn.
46:10During the winter, it gets
46:12so cold on Mars that the
46:15carbon dioxide in its thin
46:17atmosphere freezes.
46:20creating crystals of dry
46:25ice that fall as snow on
46:28the pole.
46:33Snowfall on Mars is
46:34nothing like snowfall on
46:36Earth.
46:37Every winter, between three
46:39and four trillion tons of
46:42carbon dioxide freezes out
46:44onto the surface.
46:45That's about 15% of the
46:47entire Martian atmosphere.
46:49And then, in the springtime,
46:52everything changes.
46:58As the sun returns in the
47:00spring, the ground is
47:02warmed.
47:04And the frozen carbon dioxide
47:06vaporises in an instant,
47:08from solid to gas.
47:11Geysers of gas that lift dark
47:13Martian dust high into the
47:15air.
47:22And it's this dust, as it
47:24settles, that's causing the
47:26fan-like spidery marks that
47:29we've seen from orbit.
47:29from Mars, it's just a short hop
47:45to our own world.
47:55And Earth, too, has permanent ice
47:57caps at its poles.
48:06But there, the similarity ends.
48:20If an alien astronomer got a
48:22powerful telescope and pointed it
48:24out of our solar system, they
48:25would immediately see there's
48:27something interesting and very
48:28rare about the third planet
48:30from the sun, about Earth.
48:33Because they'd see a place like
48:34this, a place with mountains
48:36covered in snow and flowing
48:38rivers and clouds and rain.
48:41It's a place where water exists
48:44in all three of its phases, both
48:45solid, liquid and gas, at the
48:48same time.
48:50And that's extremely unusual.
48:52Let me show you what I mean.
48:55So I'm going to draw what's
48:57called a phase diagram for
48:59water.
49:00It has pressure there and
49:03temperature along here.
49:06The Earth sits at one
49:07atmosphere pressure, that's
49:09atmospheric pressure, there.
49:12And it sits at around zero
49:15degrees Celsius, give or take.
49:16So the Earth exists somewhere in
49:20this region here.
49:22I'm going to draw a line.
49:23I'll tell you what it is after
49:24I've drawn it.
49:28So these two lines mark out the
49:30region of pressure and
49:31temperature where water can be
49:34either a solid, a liquid or a
49:38gas or vapor.
49:40And the Earth is here, a little
49:42tiny range where you can have
49:44solid, liquid and vapor.
49:47Mars sits somewhere around
49:52here.
49:53So that means that on Mars, water
49:55can either be frozen as a solid
49:57or it can be a vapor.
49:59But it can never be a liquid
50:01because the atmospheric pressure
50:02is too low.
50:04Pluto sits around here, minus
50:06230 degrees, where water can only
50:09be a solid, frozen hard as steel
50:11building the mountains of Pluto.
50:14On the other hand, Uranus sits
50:16somewhere over here at, what,
50:18millions of times atmospheric
50:20pressure and extremely high
50:21temperatures.
50:22And there we get these strange
50:24structures of ice, the supra-ionic
50:26ice.
50:28So Earth sits in a very narrow
50:30range of temperature and pressure
50:33where water can exist in all three
50:35phases.
50:36And that's what makes the Earth
50:37unique, certainly in our solar
50:39system, and perhaps for hundreds
50:42or even thousands of light years
50:44beyond.
50:44It's this that allows a complex
50:47ecosystem to exist on the surface
50:49of our planet.
50:58Earth's snow cupboard mountains,
51:02great oceans,
51:03rivers, and storm clouds can only exist
51:11together thanks to the rare and very
51:14narrow temperature and pressure range
51:16that our planet enjoys.
51:18And that's surely necessary for complex
51:31life to have emerged on just one of the
51:34solar system's ice worlds.
51:40But there is one more twist to our
51:43story of ice.
51:43ice, a strange property
51:46of the everyday ice
51:47with which we are so familiar.
51:59Ice on Earth has the unusual
52:01property that it floats
52:03on its own liquid.
52:04It's due to that complicated
52:05crystal structure with all those
52:07hydrogen bonds.
52:08Now, there are times in Earth's history
52:11when the planet almost froze solid.
52:14But because ice floats, there was always
52:16a bit of liquid water at the base of the
52:19ocean, and life could cling on in that liquid.
52:26That means that there has been an unbroken
52:29chain of life for 3.8 billion years,
52:32culminating in us.
52:34So, next time you stick a few ice cubes
52:40in your drink, just pause for a second
52:42and give a thought to the wonder of ice.
52:46aus being set because they want
53:05to be All for up to be nice at work in the
53:07icebergs.
53:08The word the beauty is
53:09on earth
53:11in the sea будем
53:12with no of the body is
53:14The three key ingredients that you need for life are, number one, liquid water, two, a
53:27source of energy, and three, various chemical elements that we associate with life.
53:33And we think that Europa has all of these ingredients.
53:37Juno has deepened our knowledge of Europa, but the mission is due to end in 2025.
53:49While we are yet to find any evidence of life on Europa, it's clear that this icy moon is
53:55worth a closer look.
54:03Tom Howell is part of a NASA team scoping a hugely ambitious attempt to explore the
54:09moon and its subsurface oceans in search of that elusive proof.
54:16It's all a guess until you go swimming in it, but we're building this picture up where we
54:22understand how salt water and rock interact on Earth and the chemistry that produces, which
54:29is likely important to the emergence of life.
54:32How are we going to prove that?
54:34We're launching the Europa Clipper mission, and that will, in the early 2030s, arrive
54:40at Jupiter and orbit Jupiter, surveying the entirety of the world.
54:48Europa Clipper is the first dedicated mission to Europa, and in fact, it's the first dedicated
54:52mission to any icy moon.
54:56Europa Clipper is set to launch from the Kennedy Space Center in October 2024.
55:03We have a payload of 10 instruments that are going to work together to characterize Europa's
55:09icy surface, its ocean, what their compositions are, and to figure out if Europa has environments
55:17that could support life.
55:18Any time you're anywhere near Jupiter, it's really dangerous.
55:26These high-energy particles that are zipping around can hit your spacecraft and damage it,
55:31and that's one of the big challenges facing Europa Clipper.
55:33And it's not just the spacecraft that must survive Jupiter's onslaught.
55:42We know that this intense radiation, that's bad for life as we know it, life as we are.
55:47But maybe life on Europa doesn't mind it too much.
55:50But what's more likely is that the thick layers of ice that are at Europa's surface shield life
55:55in the subsurface ocean.
55:59We think that the icy crust is 18 miles thick, but Europa Clipper will tell us more.
56:10I'm really excited about learning about Europa's plumes.
56:13I think they could be the key to sampling the subsurface ocean with figure out if there
56:17are traces or ideas of life in those plumes.
56:21And that's something we're going to be able to do with this amazing spacecraft.
56:26Clipper will only ever survey Europa from afar.
56:30But future missions are being developed that one day may land on the surface and explore
56:36beneath the ice.
56:38There is no ice on this planet that behaves like the surface of Europa.
56:44The ice is so thick and so hard that the upper few miles are like concrete or rock.
56:53What we really look at are ways to pack enough heat into a cylindrical probe so that it can
57:00melt all the way to that ocean, but also carry along the scientific payload with us that we
57:05want to use to explore.
57:06So is this recording video now?
57:09Yes, absolutely.
57:10Oh, yeah.
57:11So I don't know if you've ever seen yourself on camera before, but there you go.
57:16We're just going to deploy it there right into the hole and walk.
57:25And then there we go.
57:26We're down on the lake.
57:28We're looking around the interface of the ice and water just beneath us.
57:34Finding life on Europa would be extraordinarily profound because it's almost guaranteed that
57:47that would be a separate instance of an origin of life.
57:52So Europa could teach us a lot about how life begins across the universe.
58:01It's time.
58:02A powerful force creating oddball worlds of bizarre shapes and hidden secrets.
58:16These are the solar system's strange worlds.
58:23It seems like with your decline there.
58:24It seems, is rough inside thatol tem ».
58:25A power ofc vet.
58:26This process ismb了 much.
58:27This is possibly a reduction of teleportation.
58:28So the wind is which we're taking off of attention.
58:29A죠- Heaven.
58:30Diffing of Heaven
58:33Diffing of Heaven
58:36The direction of the earth at night.
58:38This is more of a transport that'sρηctive.
58:41And there continued to be difficulty.
58:43That is like the second back.
58:44Are than that?
58:45Natally' world
58:45A 가까'sому
58:50Personal Matter
58:50Is there yet?
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