0:00:05 > 0:00:09The landscapes of Earth have been shaped by volcanoes.
0:00:12 > 0:00:16We've long been in awe of their destructive beauty.
0:00:17 > 0:00:23But only recently have we discovered that volcanism exists beyond Earth.
0:00:26 > 0:00:31The planets and moons of the solar system have volcanoes that are even
0:00:31 > 0:00:34more extraordinary than those on our home planet.
0:00:36 > 0:00:39Rivers of lava once raced across our moon.
0:00:39 > 0:00:43It's an amazing thought that you could have been standing on Earth
0:00:43 > 0:00:46and looked up at the moon, and seen these massive eruptions happening.
0:00:49 > 0:00:52The largest volcano of the solar system,
0:00:52 > 0:00:56three times the height of Everest, is on Mars.
0:00:58 > 0:01:02The most violent volcano is on a moon of Jupiter.
0:01:06 > 0:01:12Huge, icy geysers fountain out into space from a moon orbiting Saturn.
0:01:12 > 0:01:16We have not closed the book on volcanism across the solar system by any means.
0:01:18 > 0:01:22But what's most remarkable is what volcanic activity elsewhere in
0:01:22 > 0:01:27the solar system has told scientists about our own planet, Earth.
0:01:30 > 0:01:34What the Earth was like at its birth,
0:01:34 > 0:01:37why we have the geology and the atmosphere we do.
0:01:39 > 0:01:44And even how life on Earth, and possibly elsewhere, originated.
0:01:58 > 0:02:00Way back in the ninth century AD,
0:02:00 > 0:02:03a band of Vikings discovered Iceland.
0:02:04 > 0:02:07They experienced volcanic eruptions for the first time.
0:02:12 > 0:02:14To explain their devastation,
0:02:14 > 0:02:19they evoked the terrible wrath of gods such as Surtr, the fire giant.
0:02:20 > 0:02:25A Viking poet wrote, "In the beginning, all was cold and grim.
0:02:26 > 0:02:29"Then came Surtr with a crashing noise.
0:02:31 > 0:02:35"Bright and burning, he bore a flaming sword."
0:02:43 > 0:02:47A millennium later, and a team of international scientists has also
0:02:47 > 0:02:50travelled to the land of fire and ice.
0:02:57 > 0:03:00This small country has more types of
0:03:00 > 0:03:03volcanoes and geological wonders packed into it
0:03:03 > 0:03:05than anywhere else in the world.
0:03:10 > 0:03:14For the team, it allows them to compare the volcanism of Earth with
0:03:14 > 0:03:17volcanoes found elsewhere in the solar system.
0:03:20 > 0:03:23You've got these continual cycles of glaciers and volcanoes.
0:03:23 > 0:03:25Absolutely brilliant.
0:03:25 > 0:03:28Yeah, you have a really diverse range of volcanic features here,
0:03:28 > 0:03:31and I think it's a good place to see the importance of volcanism.
0:03:37 > 0:03:39For geologist Jim Head,
0:03:39 > 0:03:41Iceland is a familiar landscape.
0:03:43 > 0:03:45In the 1960s,
0:03:45 > 0:03:48he was teaching the Apollo astronauts all about rocks
0:03:48 > 0:03:50before they headed off to the moon.
0:03:52 > 0:03:53We took them everywhere we could
0:03:53 > 0:03:55that would give them geological information.
0:03:55 > 0:03:57Iceland was clearly one of those.
0:03:57 > 0:04:01And I think it's completely perfect, actually,
0:04:01 > 0:04:04that we are here today in Iceland, studying the volcanoes that
0:04:04 > 0:04:07actually propelled the astronauts to go to the moon.
0:04:10 > 0:04:16Five, four, three, two, one.
0:04:16 > 0:04:19The Apollo missions weren't just about the space race.
0:04:21 > 0:04:25They were also the most ambitious geological field trips of all time.
0:04:27 > 0:04:30A key aim was to discover if volcanoes
0:04:30 > 0:04:32had helped create the moon.
0:04:33 > 0:04:36And, if so, were any still active?
0:04:37 > 0:04:38Before the Apollo programme,
0:04:38 > 0:04:41we didn't even know whether the moon had volcanism.
0:04:41 > 0:04:43For example, some people thought it was a cold moon,
0:04:43 > 0:04:45some people thought it was a warm moon,
0:04:45 > 0:04:46which had heating inside and volcanism.
0:04:46 > 0:04:49So this is a big question - was it even volcanic rock?
0:04:49 > 0:04:512,000 feet, 2,000 feet.
0:04:51 > 0:04:5447 degrees. Roger.
0:04:57 > 0:04:59These dark-looking plains of the moon
0:04:59 > 0:05:03were particularly tantalising to scientists.
0:05:03 > 0:05:07They're called the seas, or the maria.
0:05:09 > 0:05:12Beautiful view! Isn't that something?
0:05:12 > 0:05:14Magnificent desolation.
0:05:14 > 0:05:16To find out exactly what they were,
0:05:16 > 0:05:20the first Apollo landing was to Mare Tranquillitatis,
0:05:20 > 0:05:21the Sea of Tranquillity.
0:05:21 > 0:05:23OK, ready for me to come out?
0:05:23 > 0:05:26All set.
0:05:26 > 0:05:29As the astronauts explored the dusty and rocky surface,
0:05:29 > 0:05:34they recognised basalt - the most common volcanic rock found on Earth.
0:05:37 > 0:05:38And lots of it.
0:05:39 > 0:05:43When you erupt molten rock on a moon, liquid rock on the moon,
0:05:43 > 0:05:45it actually is one sixth gravity,
0:05:45 > 0:05:47so it's much less gravity than we see on the Earth.
0:05:47 > 0:05:50It looks like a collection of just about
0:05:50 > 0:05:53every variety of rock you could find.
0:05:53 > 0:05:59If the lava is coming up from great depths, given the gravity, etc,
0:05:59 > 0:06:01you'll get a lot of lava coming up,
0:06:01 > 0:06:03commonly much more than you see on the Earth,
0:06:03 > 0:06:04and so it flows great distances,
0:06:04 > 0:06:08and so we have lava flows that go over 1000 kilometres,
0:06:08 > 0:06:10like, incredible, it would go
0:06:10 > 0:06:12halfway across the United States, no problem.
0:06:13 > 0:06:16Another mysterious feature found on the moon
0:06:16 > 0:06:20was these winding canyons, or sinuous rilles.
0:06:22 > 0:06:27These channels were up to 400 metres deep and over 100km long.
0:06:29 > 0:06:33Clues as to what created them can be found back on Earth.
0:06:41 > 0:06:46Under the south-west of Iceland are curious tunnels through solid rock.
0:06:46 > 0:06:49They appear almost man-made.
0:06:52 > 0:06:55Gro Pedersen is exploring one.
0:06:57 > 0:06:59In the depths of the tunnel,
0:06:59 > 0:07:02she hopes to find evidence of what used to flow through it.
0:07:03 > 0:07:08You can actually see how the lava has been running along the wall here,
0:07:08 > 0:07:11and you can see also that it was very hot in here,
0:07:11 > 0:07:13because some of this lava re-melted,
0:07:13 > 0:07:17and basically was dribbling down the wall. You see that here.
0:07:19 > 0:07:24It's a lava tube and, long ago, lava was surging through these tunnels.
0:07:26 > 0:07:29One of the very exciting things people found on the moon
0:07:29 > 0:07:31was these sinuous rilles and,
0:07:31 > 0:07:34of course, before people actually had been on the moon,
0:07:34 > 0:07:38they were thought to potentially be water eroded.
0:07:38 > 0:07:40But then people have gone to the moon,
0:07:40 > 0:07:44and it has been studied much more and we've found out that these
0:07:44 > 0:07:49sinuous rilles were always connected with the maria,
0:07:49 > 0:07:52the moon lava that we have up there.
0:07:53 > 0:07:57Perhaps these sinuous rilles were once enclosed lava tubes.
0:08:00 > 0:08:02So one of the things that you see here, obviously,
0:08:02 > 0:08:05is that we have what we call skylights,
0:08:05 > 0:08:06so the roof has collapsed.
0:08:06 > 0:08:10If all of the roof collapses, you will end up with a valley,
0:08:10 > 0:08:12like something you see on the moon.
0:08:12 > 0:08:18But you can also see the tubes on the moon by a string of skylights,
0:08:18 > 0:08:21just as we see here, one hole after the other, and you just follow them,
0:08:21 > 0:08:25you trace them down and you can see that these are within lava flows.
0:08:27 > 0:08:30But when did these eruptions take place?
0:08:30 > 0:08:32And why did they eventually stop?
0:08:37 > 0:08:40The answer would come in small bags of volcanic rocks
0:08:40 > 0:08:42brought home by the astronauts.
0:08:44 > 0:08:47On Earth, they could be accurately dated.
0:08:47 > 0:08:50So when the moon rocks were brought back, it's, like, unbelievable.
0:08:50 > 0:08:54OK, this we can tell, four-billion-year-old rocks.
0:08:54 > 0:08:57These are the keys to the understanding of the solar system.
0:08:59 > 0:09:02Like other planetary bodies made of rock,
0:09:02 > 0:09:06the moon was a mass of hot molten magma as it was forming.
0:09:06 > 0:09:11It's an amazing thought that you could have been standing on Earth
0:09:11 > 0:09:14and looked up at the moon and seen these massive eruptions happening.
0:09:17 > 0:09:19But all the time, it was cooling -
0:09:19 > 0:09:24being relatively small, a quarter the diameter of the Earth,
0:09:24 > 0:09:26the moon cooled down quickly.
0:09:27 > 0:09:29By three billion years ago,
0:09:29 > 0:09:33almost all the lava and interior magma had solidified
0:09:33 > 0:09:35into one big lump of cold rock.
0:09:37 > 0:09:38No more volcanoes.
0:09:45 > 0:09:46But you see the remnants of it.
0:09:46 > 0:09:49I mean, when you look at the sky and you look at the moon,
0:09:49 > 0:09:52you see the evidence of the volcanism,
0:09:52 > 0:09:54because you see the dark areas, the basalt,
0:09:54 > 0:09:56which has filled in the craters.
0:09:58 > 0:10:02Understanding how the moon lost its volcanoes
0:10:02 > 0:10:05helps explain why Earth remains so active.
0:10:08 > 0:10:12Being larger allowed the Earth to retain much of its original heat.
0:10:16 > 0:10:20And so today, our planet is a dynamic and ever-changing world,
0:10:20 > 0:10:23rather than a dead one.
0:10:23 > 0:10:26So, the discovery on the moon of lava flows
0:10:26 > 0:10:29gave us pause to think about how this worked
0:10:29 > 0:10:30on other planetary bodies.
0:10:30 > 0:10:32How does volcanism work on Mars?
0:10:35 > 0:10:37So, the lunar exploration really opened up
0:10:37 > 0:10:40a field of, really, planetary volcanology.
0:10:44 > 0:10:47Exploring our neighbour, Mars,
0:10:47 > 0:10:50also reveals secrets about Earth's geology.
0:10:52 > 0:10:55When probes first reached the red planet,
0:10:55 > 0:10:58one feature stood out above swirling sandstorms.
0:10:59 > 0:11:01The volcano Olympus Mons.
0:11:06 > 0:11:10Olympus Mons is enormous, it's about 25km high.
0:11:10 > 0:11:14On Earth, you would be looking at something ridiculously high.
0:11:14 > 0:11:18Most commercial aircraft fly 10-15 kilometres.
0:11:18 > 0:11:21So you're looking at something that is towering way above
0:11:21 > 0:11:23what commercial aircraft might fly.
0:11:29 > 0:11:32Its base covers an area the size of France.
0:11:34 > 0:11:36It's three times the height of Mount Everest.
0:11:38 > 0:11:42Making it the largest volcano ever discovered in the solar system.
0:11:48 > 0:11:50Finding out how it grew to be so colossal
0:11:50 > 0:11:54tells scientists more about the volcanoes of Earth.
0:11:59 > 0:12:04That's why three of the team have come together to study this volcano.
0:12:07 > 0:12:12Icelanders call it Skjaldbreidur, which means "broad shield",
0:12:12 > 0:12:15as side on, it's reminiscent of a Viking shield.
0:12:19 > 0:12:22Although small in stature, it's of great significance.
0:12:25 > 0:12:28This shield volcano is the one over...
0:12:28 > 0:12:33about which all the other volcanoes of this type are called,
0:12:33 > 0:12:35in the solar system and on the Earth.
0:12:35 > 0:12:37So this is the first one, in many senses,
0:12:37 > 0:12:39the first one to be named the shield.
0:12:42 > 0:12:44It's only 1,000 metres high,
0:12:44 > 0:12:47a 25th the height of Olympus Mons,
0:12:47 > 0:12:51but crucially, it's the same type of shield volcano.
0:12:54 > 0:12:56At the summit is the crater.
0:12:57 > 0:12:59Wow, now you can see the crater.
0:12:59 > 0:13:02- Yeah.- Fantastic.- Wow!
0:13:02 > 0:13:03That's very nice.
0:13:03 > 0:13:07- I mean, you could even have come skiing up here.- Oh, wow.- Yeah.
0:13:07 > 0:13:10Then we can imagine, like, a lava lake.
0:13:10 > 0:13:12Yeah, just round the top.
0:13:12 > 0:13:15- Yeah.- Dribbling over where we are now.- Yeah.
0:13:15 > 0:13:18Around the rim are mysteriously-shaped rocks.
0:13:21 > 0:13:23They look almost like fossilised snakes.
0:13:26 > 0:13:29Yet they give a hint how this type of volcano forms,
0:13:29 > 0:13:32and what gives it the distinctive shield shape.
0:13:35 > 0:13:38This is a type of lava we call entrail,
0:13:38 > 0:13:42and it's a bit like the entrails from the inside of a human body
0:13:42 > 0:13:44or any animal body.
0:13:44 > 0:13:45They're characteristically quite thin.
0:13:45 > 0:13:47I mean, you can see from the shape of my hand,
0:13:47 > 0:13:49it's a couple of hand widths.
0:13:49 > 0:13:52Shield volcanoes comprise lavas that are very runny,
0:13:52 > 0:13:53because the shapes of them,
0:13:53 > 0:13:56this broad shield shape, tells us it has to have been.
0:13:56 > 0:14:00And we have the evidence in front of our eyes of these small tubes,
0:14:00 > 0:14:03these entrails running down the sides of the volcano,
0:14:03 > 0:14:05telling us that indeed, it had to be very runny.
0:14:11 > 0:14:13This fast-flowing lava creates
0:14:13 > 0:14:16the gentle slopes of all shield volcanoes,
0:14:16 > 0:14:19including the largest one of all, on Mars.
0:14:26 > 0:14:28But while shield volcanoes on Iceland
0:14:28 > 0:14:31have just one crater at the summit,
0:14:31 > 0:14:34Olympus Mons has six overlapping craters.
0:14:37 > 0:14:41That's the key. We actually can use what we see in Iceland to say,
0:14:41 > 0:14:44what we see in Mars is similar, but also different.
0:14:44 > 0:14:48It has to be much, much longer lived with multiple phases of eruptions
0:14:48 > 0:14:52to produce these multiple summit craters we see on Olympus Mons.
0:14:56 > 0:15:00When this behemoth erupted, Mars shuddered.
0:15:07 > 0:15:11Rivers of lava swept down the massive flanks of the volcano.
0:15:15 > 0:15:18But Earth is twice the size of Mars,
0:15:18 > 0:15:22so why don't we have volcanoes as enormous as Olympus Mons?
0:15:27 > 0:15:30It's all to do with plate tectonics.
0:15:32 > 0:15:35Earth is made up of seven huge plates
0:15:35 > 0:15:37drifting above a sea of magma.
0:15:42 > 0:15:46The circulation of magma recycles rocks and gases,
0:15:46 > 0:15:49bringing them to the surface and then back down again.
0:15:54 > 0:15:58Iceland is the perfect place to witness plate tectonics in action.
0:16:00 > 0:16:04This rift is where the North American plate, to the left,
0:16:04 > 0:16:07divides from its Eurasian cousin, to the right.
0:16:10 > 0:16:14The rift is widening rapidly, at over two centimetres a year.
0:16:17 > 0:16:21We've got the best evidence of plate tectonics we can find here.
0:16:21 > 0:16:25You can see the tension of the plates moving apart from each other.
0:16:25 > 0:16:28Yeah, this is the only planet that we know that's got plate tectonics.
0:16:31 > 0:16:36Mars, like all other planets we know of, has no active plate tectonics.
0:16:41 > 0:16:45The entire crust of Mars remains locked in place,
0:16:45 > 0:16:47with repercussions for its volcanoes.
0:16:54 > 0:16:57Any upwelling magma continually breaks through
0:16:57 > 0:16:59at one fixed location.
0:17:01 > 0:17:05On Mars, it's just centred, the same spot, for so long,
0:17:05 > 0:17:06building up a huge volcano.
0:17:06 > 0:17:13So it's a very focused eruption of magma for billions of years.
0:17:13 > 0:17:16And what happens is you just end up with a huge volcano,
0:17:16 > 0:17:18the biggest in the solar system.
0:17:27 > 0:17:30While Mars is no longer volcanically active,
0:17:30 > 0:17:35it does share an important feature with Earth - the polar ice caps.
0:17:38 > 0:17:40The story of these ice caps
0:17:40 > 0:17:43has been revealed through unusually shaped volcanoes.
0:17:45 > 0:17:49They have steep sides and a flat top like a table.
0:17:51 > 0:17:55Scientists now believe they might have been formed when volcanoes
0:17:55 > 0:17:58exploded through an ancient ice sheet.
0:18:04 > 0:18:07To understand how ice can change the behaviour of lava,
0:18:07 > 0:18:11scientists are carrying out an extreme experiment.
0:18:15 > 0:18:20For this, Ingo Sonder and Tracy Gregg need to make their own lava...
0:18:23 > 0:18:27..out of 50kg of basalt rock.
0:18:27 > 0:18:29We're turning it to its lava state,
0:18:29 > 0:18:31and the students have built a little ramp
0:18:31 > 0:18:34that the lava will pour down and pool at the end.
0:18:34 > 0:18:38And at the end of this lava stream, there will be a little pond of ice.
0:18:38 > 0:18:41So the lava's going to flow over the ice.
0:18:41 > 0:18:43We know this has happened on Earth.
0:18:43 > 0:18:46We think it's happened on Mars in the past.
0:18:46 > 0:18:47So we'll see what happens.
0:18:51 > 0:18:55The electrical furnace is running at 80,000 watts.
0:18:57 > 0:19:02By now, the molten rock is over 1,200 degrees Celsius.
0:19:02 > 0:19:04It's ready for the big pour.
0:19:11 > 0:19:14Look where it hits the ice, it's boiling!
0:19:14 > 0:19:17Because the ice is melting and it's flashing to steam.
0:19:17 > 0:19:21And it's creating all those bubbles there on the lava.
0:19:21 > 0:19:23Whoa! And now, this is what happens...
0:19:25 > 0:19:29..when the lava melts the ice and there's enough water,
0:19:29 > 0:19:31we're getting some little steam explosions.
0:19:33 > 0:19:36Right, there's no more lava coming out of the furnace.
0:19:36 > 0:19:39But underneath that black crust, it's still liquid,
0:19:39 > 0:19:41it's slowly flowing down.
0:19:41 > 0:19:44And you can see where it's ponded over the ice,
0:19:44 > 0:19:49there's some heaving going on as gas is trying to escape.
0:19:49 > 0:19:52The experiment lets Tracy identify
0:19:52 > 0:19:57key features as molten rock interacts with ice.
0:19:57 > 0:20:01When the lava hit the ice, a couple of things happened really fast.
0:20:01 > 0:20:03The lava started to bubble,
0:20:03 > 0:20:06as the ice melted and then flashed to steam.
0:20:06 > 0:20:08And then, as more melt occurred,
0:20:08 > 0:20:10there were actually puddles of water
0:20:10 > 0:20:12that started to boil and spatter just like
0:20:12 > 0:20:14on your stove, right, the water spattering.
0:20:14 > 0:20:19Where the ice wasn't, we have nice, neat, organised flows,
0:20:19 > 0:20:20folds in the lava.
0:20:20 > 0:20:22And right where the ice starts,
0:20:22 > 0:20:24we get these bigger bubbles on the surface.
0:20:24 > 0:20:27Look, that one's broken open, you can see inside.
0:20:27 > 0:20:29That's the kind of thing we could look for on Mars.
0:20:29 > 0:20:33Right? To see if there was any lava-ice interactions on Mars.
0:20:33 > 0:20:35Can you hear it?
0:20:35 > 0:20:36As the lava cools, it contracts,
0:20:36 > 0:20:40and it makes little pops like breakfast cereal.
0:20:40 > 0:20:41Pop, pop.
0:20:41 > 0:20:42Yep.
0:20:45 > 0:20:46That's amazing.
0:20:51 > 0:20:53The artificial volcano confirms that
0:20:53 > 0:20:57lava behaves very differently when it meets ice.
0:20:59 > 0:21:02But what happens out in the real world?
0:21:08 > 0:21:14One of the most distinctive types of volcano in Iceland is called a tuya.
0:21:16 > 0:21:19The team believe they can help explain the mountains
0:21:19 > 0:21:21with a similar shape on Mars.
0:21:23 > 0:21:26Wherever we see volcanoes that look like this,
0:21:26 > 0:21:28on Iceland we know that the ice has been there,
0:21:28 > 0:21:31and if we see the same sorts of volcanoes on Mars,
0:21:31 > 0:21:34we've got a good idea or a very good idea that there was ice present.
0:21:36 > 0:21:39There are two polar ice caps on Mars today.
0:21:43 > 0:21:44But millions of years ago,
0:21:44 > 0:21:46they were far more extensive.
0:21:49 > 0:21:52Mapping the tuyas on Mars reveals
0:21:52 > 0:21:56the coverage and depth of the ancient ice sheets.
0:22:01 > 0:22:04That's amazing, that you can actually say something about
0:22:04 > 0:22:07ice thickness in the past on a different planet,
0:22:07 > 0:22:09after the ice has gone.
0:22:09 > 0:22:11Which may have been three and a half billion years ago, as well.
0:22:11 > 0:22:15- Yeah.- It's similar processes on different planets but it's yielding
0:22:15 > 0:22:18valuable information. It's telling us about what most planets...
0:22:18 > 0:22:21how they were evolving and what was happening at the time.
0:22:22 > 0:22:28Today, Mars and our own moon are cold and desolate planetary bodies.
0:22:30 > 0:22:32Geologically inert.
0:22:35 > 0:22:38While Earth has retained active volcanoes.
0:22:41 > 0:22:43To understand how we got here,
0:22:43 > 0:22:47we need to find out what Earth was like four billion years ago.
0:22:51 > 0:22:55And scientists think they've found the perfect place to look,
0:22:55 > 0:22:58a moon far out in the solar system.
0:23:11 > 0:23:14Ashley Davies is a top planetary volcanologist.
0:23:16 > 0:23:20He's fascinated by a moon of Jupiter called Io.
0:23:23 > 0:23:28One of the most important images that's ever been collected by any
0:23:28 > 0:23:32spacecraft was obtained by Voyager at Io.
0:23:36 > 0:23:41The image revealed this crescent rising above Io's surface,
0:23:41 > 0:23:43no-one knew quite what this was.
0:23:43 > 0:23:48Could it be another moon behind Io, or some artefact in the image?
0:23:48 > 0:23:53And then it was realised that this was actually a huge volcanic plume
0:23:53 > 0:23:56rising up from Io's surface.
0:23:59 > 0:24:01For me, this was
0:24:01 > 0:24:05an image that I think shaped the rest of my life,
0:24:05 > 0:24:06because from this point...
0:24:06 > 0:24:11I was a schoolboy and I realised this was a huge step in an unknown
0:24:11 > 0:24:15direction for astronomy and planetary science.
0:24:17 > 0:24:21And in a way, this actually put me on the path through school and into
0:24:21 > 0:24:24scientific research, and finally brought me here to study
0:24:24 > 0:24:26this absolutely astonishing little world.
0:24:31 > 0:24:36We now know that crammed into Io, the same size as our moon,
0:24:36 > 0:24:39are over 400 active volcanoes.
0:24:41 > 0:24:45Compare this to just 60 on the whole of Earth.
0:24:49 > 0:24:54The most powerful eruption was seen at a volcano called Surtr,
0:24:54 > 0:24:58which is actually named after an Icelandic giant.
0:24:58 > 0:25:03A fissure opened up and a huge volume of lava literally gushed out
0:25:03 > 0:25:07of the ground to form large lava fountains kilometres high.
0:25:07 > 0:25:10It must have been an absolutely incredible sight to see
0:25:10 > 0:25:13if you were there to witness it, but not from too close by.
0:25:14 > 0:25:16When Surtr roars,
0:25:16 > 0:25:22it sends plumes of lava and ash over 500km into space.
0:25:31 > 0:25:33Io proved for the first time
0:25:33 > 0:25:36that Earth wasn't alone in having active volcanoes.
0:25:42 > 0:25:44And, perhaps more importantly,
0:25:44 > 0:25:47Io offered a clue as to the conditions
0:25:47 > 0:25:49that existed as the Earth formed.
0:25:51 > 0:25:54But first, scientists needed to discover
0:25:54 > 0:25:57where the heat driving Io's volcanism came from.
0:25:59 > 0:26:02The reason why Io is so active
0:26:02 > 0:26:09is it's caught in this gravitational tug-of-war between Jupiter, Io,
0:26:09 > 0:26:11Europa and Ganymede,
0:26:11 > 0:26:13and this pumps a lot of energy into the system.
0:26:20 > 0:26:25What happens to a squash ball is just like Io,
0:26:25 > 0:26:30as it's pulled between gigantic Jupiter and her other moons.
0:26:32 > 0:26:36A thermal camera reveals the temperature of the squash ball
0:26:36 > 0:26:38as the rallies progress.
0:26:39 > 0:26:44We hit the ball against the wall and it heated up.
0:26:46 > 0:26:48And it heated up because it was being compressed,
0:26:48 > 0:26:50twisted and turned.
0:26:51 > 0:26:54And Io is very much like that.
0:26:55 > 0:27:00With Io, it's being twisted and turned and squeezed by gravitational
0:27:00 > 0:27:03forces, and the gravitational forces
0:27:03 > 0:27:07cause a lot of interior heating and the heating manifests at the surface
0:27:07 > 0:27:09as huge volcanoes.
0:27:13 > 0:27:16Io heats up so much that it might erupt
0:27:16 > 0:27:21an extremely rare and hot form of lava called ultramafic.
0:27:25 > 0:27:29Ultramafic lava was abundant 4.5 billion years ago,
0:27:29 > 0:27:33when the Earth formed,
0:27:33 > 0:27:34but no longer.
0:27:36 > 0:27:39To discover this primitive lava on Io
0:27:39 > 0:27:42would offer scientists a window on the past.
0:27:52 > 0:27:57Volcanologist Rosaly Lopes does her research in Hawaii.
0:27:57 > 0:28:01We're studying volcanoes on Hawaii not because of Hawaii itself,
0:28:01 > 0:28:07but because Hawaiian volcanoes are such a good analogue,
0:28:07 > 0:28:11or a mirror if you like, for volcanoes on Jupiter's moon, Io.
0:28:11 > 0:28:16And it's really understanding the volcanoes on Io
0:28:16 > 0:28:18that we are after.
0:28:23 > 0:28:27Hawaii has more active volcanoes than anywhere on Earth.
0:28:29 > 0:28:33In fact, the islands are a chain of shield volcanoes,
0:28:33 > 0:28:35built up from the ocean floor.
0:28:36 > 0:28:39Rosaly looks for the most active lava flows.
0:28:41 > 0:28:44It's challenging, it's beautiful.
0:28:44 > 0:28:46I think a volcano in activity
0:28:46 > 0:28:50is just the most beautiful thing that anyone can see.
0:28:52 > 0:28:58Io is like Dante's Inferno, it's absolutely volcanoes everywhere.
0:29:00 > 0:29:04Sulphur everywhere, hot lavas everywhere,
0:29:04 > 0:29:07it is a volcanologist's paradise,
0:29:07 > 0:29:10but it would be absolute hell if you were actually there.
0:29:18 > 0:29:22Rosaly will measure the cooling rate of the lava here in Hawaii,
0:29:22 > 0:29:25and then apply it to the volcanoes of Io.
0:29:27 > 0:29:30In this way she hopes to find out if
0:29:30 > 0:29:33Io has the especially hot ultramafic lava.
0:29:35 > 0:29:37The team use a thermal camera.
0:29:39 > 0:29:42- These should be nice images. - Very nice, very nice.
0:29:42 > 0:29:44And then just really hot in the middle,
0:29:44 > 0:29:47where that's cooling so fast.
0:29:47 > 0:29:49That's beautiful, just spectacular.
0:29:51 > 0:29:54The hottest lava is the moment it emerges.
0:29:55 > 0:29:58If Jenny manages to break through the surface,
0:29:58 > 0:30:02you are going to see the hot lava spilling out.
0:30:02 > 0:30:07Oh, there we go. So that's the heart of the lava flow.
0:30:08 > 0:30:12The thermal camera reveals how quickly
0:30:12 > 0:30:13the lava cools here on Earth.
0:30:14 > 0:30:19Even on the hottest parts, it was only about 910 Celsius.
0:30:19 > 0:30:24The melting temperature of this rock is about 1,200 Celsius,
0:30:24 > 0:30:30so that tells you that even in those red hot parts, the lava has cooled,
0:30:30 > 0:30:33you know, more than a couple of hundred Celsius,
0:30:33 > 0:30:36so lava cools very, very fast.
0:30:38 > 0:30:41Rosaly suspects this also happens on Io.
0:30:44 > 0:30:48Space probes to Io have revealed that the surface hot spots
0:30:48 > 0:30:50are 1,200 degrees.
0:30:51 > 0:30:55When we get measurements of the temperatures on Io,
0:30:55 > 0:30:58we know that those temperatures likely have cooled
0:30:58 > 0:31:01by at least a couple of hundred degrees Celsius.
0:31:03 > 0:31:08It means the temperature of the lava just below the surface of Io
0:31:08 > 0:31:11must be around 1,400 degrees.
0:31:13 > 0:31:17Lava this hot is strong evidence it's ultramafic.
0:31:24 > 0:31:26An exciting finding,
0:31:26 > 0:31:30as it means Io could hold the secrets of the Earth's past.
0:31:34 > 0:31:36Io is a model of the early Earth,
0:31:36 > 0:31:42because the lavas on Io may be of the ultramafic type,
0:31:42 > 0:31:44and those are lavas that are very hot,
0:31:44 > 0:31:48very primitive and they erupted on Earth billions of years ago.
0:31:53 > 0:31:55The more we research Io,
0:31:55 > 0:31:59the more we find out what the Earth was like as it was forming -
0:31:59 > 0:32:02the type of lava flows, the form of volcanism,
0:32:02 > 0:32:05the tremendous density of volcanoes.
0:32:08 > 0:32:09By studying Io,
0:32:09 > 0:32:14we look at volcanism on a scale that has not happened on Earth
0:32:14 > 0:32:15for billions of years.
0:32:16 > 0:32:19So, Io reveals what primitive Earth was like...
0:32:22 > 0:32:25..Dante's volcanic Inferno.
0:32:34 > 0:32:36Volcanoes have played a key role
0:32:36 > 0:32:40in the evolution of planets in another way -
0:32:40 > 0:32:41by creating their atmosphere.
0:32:44 > 0:32:46And the best way of looking at that
0:32:46 > 0:32:50is the most extreme example of all - Venus.
0:32:51 > 0:32:53The planet Venus is a very hot climate.
0:32:53 > 0:32:56The atmosphere is dense
0:32:56 > 0:32:59and its primary constituent is carbon dioxide.
0:33:04 > 0:33:08It has the densest atmosphere anywhere in the solar system.
0:33:12 > 0:33:14And one of the hottest.
0:33:16 > 0:33:21This extreme atmosphere was almost certainly created by volcanism.
0:33:23 > 0:33:25It pumps out these gases.
0:33:27 > 0:33:29But the thick atmosphere
0:33:29 > 0:33:32also hid what was happening on the planet's surface.
0:33:38 > 0:33:41So, we really didn't have much of an idea of what was beneath those
0:33:41 > 0:33:43clouds, and it was a bit of guesswork.
0:33:43 > 0:33:45You know, you send the probes down, are they going to survive,
0:33:45 > 0:33:49what's the atmospheric pressure going to be, how hot is it going to be?
0:33:50 > 0:33:52So when the first probes went down onto the surface,
0:33:52 > 0:33:54they didn't last very long.
0:34:00 > 0:34:04But a new generation of probes, armed with radar,
0:34:04 > 0:34:07eventually peered through the veil of Venus
0:34:07 > 0:34:09to reveal an astonishing landscape.
0:34:12 > 0:34:14More volcanic cones and craters
0:34:14 > 0:34:17than any other planet of the solar system.
0:34:19 > 0:34:21When they eventually got
0:34:21 > 0:34:23the correct sort of radar going through the clouds
0:34:23 > 0:34:26and seeing what was going on, then it got really exciting.
0:34:26 > 0:34:29Then we thought, "This is a planet with a lot of volcanoes on it,
0:34:29 > 0:34:31"and even more fascinating,
0:34:31 > 0:34:33"volcanoes unlike any we see on the Earth."
0:34:34 > 0:34:37These volcanoes are unique to Venus.
0:34:39 > 0:34:42Some are 65km across,
0:34:42 > 0:34:46surrounded by cliffs over 1000 metres high.
0:34:48 > 0:34:53Almost perfectly circular, they're known as pancake domes.
0:34:54 > 0:34:55The pancake domes were very much a mystery.
0:34:55 > 0:35:00What we saw on the surface of Venus were just large, basically pancakes,
0:35:00 > 0:35:02stuck on top of these flat plains.
0:35:02 > 0:35:04It was just, "What are these things?"
0:35:04 > 0:35:07They are so untypical of what else we saw on Venus,
0:35:07 > 0:35:10and that's when people started thinking, "Well, the sort of lava flows on Earth,
0:35:10 > 0:35:12"where we actually have these same features,
0:35:12 > 0:35:15"and these lava flows we have in places like Iceland."
0:35:18 > 0:35:22What could pancake domes tell us about volcanism on Earth?
0:35:25 > 0:35:30These are the extraordinary lava flows at Torfajokull in Iceland.
0:35:34 > 0:35:36They end in cliffs,
0:35:36 > 0:35:39similar to the pancake domes, but on a smaller scale.
0:35:39 > 0:35:43It's like walking across a mossy Venus, isn't it?
0:35:45 > 0:35:47Dave and Ian have come here to discover
0:35:47 > 0:35:51more about the lava that created these landscapes.
0:35:52 > 0:35:55One of the things I want to do quite soon
0:35:55 > 0:36:00is to find a nice piece of this lovely lava to hit with my hammer,
0:36:00 > 0:36:03so we can have a good look at what's inside it.
0:36:08 > 0:36:10I'm going to hit this bit here, OK?
0:36:18 > 0:36:20It makes a lovely noise as well, doesn't it?
0:36:20 > 0:36:22It does indeed. And a nice smell, actually.
0:36:22 > 0:36:25I love the smell of rhyolite in the afternoon!
0:36:25 > 0:36:30So, you can see lots of little white crystals actually aligned in that
0:36:30 > 0:36:31particular direction.
0:36:31 > 0:36:34These only line up when you've got something that's very,
0:36:34 > 0:36:36very sticky, and forcing crystals
0:36:36 > 0:36:39to actually line up in the one direction.
0:36:39 > 0:36:41And in this case, I know these crystals tell me
0:36:41 > 0:36:43this rock is very high in silica.
0:36:46 > 0:36:50Silica thickens the lava, and Dave and Ian believe this was what
0:36:50 > 0:36:53created the pancake domes of Venus.
0:36:55 > 0:36:58It behaves differently from thin lava.
0:37:01 > 0:37:05The most common type of lava we have in the solar system is basalt,
0:37:05 > 0:37:08and the entire surface of the moon and the entire surface of Mars
0:37:08 > 0:37:10is covered in basalt.
0:37:10 > 0:37:13I'm going to illustrate that by using oil.
0:37:17 > 0:37:19It spreads out where it wants to go,
0:37:19 > 0:37:23beautiful little fingers coming down thin and fast.
0:37:24 > 0:37:28However, in some parts of the Earth and these pancake domes on Venus,
0:37:28 > 0:37:31which is very exciting, we have this much thicker lava flow and I'm going
0:37:31 > 0:37:35to illustrate that with treacle, and let's see how that goes.
0:37:39 > 0:37:40Beautiful.
0:37:40 > 0:37:43See how slow and how thick it is?
0:37:43 > 0:37:45That's exactly what we expect to see
0:37:45 > 0:37:47when we have these thicker lava flows
0:37:47 > 0:37:48that are much richer in silica.
0:37:48 > 0:37:50The forward edge is very thick
0:37:50 > 0:37:52because everything is getting compressed
0:37:52 > 0:37:54and squeezed forward at that forward edge.
0:37:54 > 0:37:57If this was a real lava flow,
0:37:57 > 0:38:00you would actually see blocks falling off the front of it.
0:38:00 > 0:38:02On this sort of surface that's sloping,
0:38:02 > 0:38:04you will see something that looks a little elongate,
0:38:04 > 0:38:08as we can see here. But if you pour it onto a perfectly flat surface,
0:38:08 > 0:38:10you will get, basically, a pancake, a circular pancake.
0:38:22 > 0:38:23It's utterly fascinating,
0:38:23 > 0:38:26because until recently, I thought these planets
0:38:26 > 0:38:28were very, very boring, just had basalt,
0:38:28 > 0:38:32but having found this particular type of rock on Venus,
0:38:32 > 0:38:33it excites me personally,
0:38:33 > 0:38:35because I've been working on them for 30 years.
0:38:37 > 0:38:40But are any volcanoes on Venus still active?
0:38:42 > 0:38:46Some exciting circumstantial evidence has recently been discovered.
0:38:47 > 0:38:53They found that Venus had hot spots within it that occurred over quite
0:38:53 > 0:38:56a short time interval, and this was the first evidence we had of perhaps
0:38:56 > 0:38:58something active on Venus.
0:39:01 > 0:39:07This image of the planet's surface was taken on June 22nd 2008.
0:39:07 > 0:39:10The hottest parts are yellow and red.
0:39:11 > 0:39:14And the same area, just two days later.
0:39:15 > 0:39:21The best explanation of these new hot spots is erupting lava.
0:39:21 > 0:39:26We're also seeing unexplained spikes of sulphur in the atmosphere,
0:39:26 > 0:39:28which are probably related to these bursts of hot activity
0:39:28 > 0:39:30appearing on the surface.
0:39:31 > 0:39:33That really is quite exciting, to actually see these.
0:39:33 > 0:39:36It's these active volcanoes
0:39:36 > 0:39:39that create the dense atmosphere of Venus.
0:39:48 > 0:39:52But why haven't all the volcanoes of Earth led to a similar dense
0:39:52 > 0:39:54and hostile atmosphere on our own planet?
0:40:06 > 0:40:09Claire Cousins is an astrobiologist.
0:40:09 > 0:40:12She's been coming to Iceland for ten years,
0:40:12 > 0:40:15as this is the ideal place to find out
0:40:15 > 0:40:17how volcanoes can help support life.
0:40:20 > 0:40:21Claire and her colleagues
0:40:21 > 0:40:24are tapping into the gases of a volcanic vent.
0:40:28 > 0:40:31Oh, that's interesting. That looks good, that looks good.
0:40:31 > 0:40:33Nice.
0:40:35 > 0:40:39So what kind of volcanic gases do we typically get from these systems?
0:40:39 > 0:40:42It's about 2% CO2, carbon dioxide.
0:40:42 > 0:40:45About 1% H2S, hydrogen sulphide,
0:40:45 > 0:40:48and all of the other gases are in trace amounts.
0:40:49 > 0:40:52Many of these gases are highly toxic.
0:40:54 > 0:41:00So, we wear these gas masks while we're sampling these volcanic gases
0:41:00 > 0:41:02because they're what we call acidic gases,
0:41:02 > 0:41:05so they're things like carbon dioxide or hydrogen sulphide,
0:41:05 > 0:41:08and they're basically gases that we just don't want to be breathing in.
0:41:08 > 0:41:10They're really poisonous.
0:41:13 > 0:41:18But surprisingly, the most abundant gas is actually water vapour -
0:41:18 > 0:41:2097% at this site.
0:41:22 > 0:41:26Across the entire Earth, all these gases have a global effect.
0:41:28 > 0:41:31Volcanoes, they're not just destructive processes.
0:41:31 > 0:41:34In the long-term, especially, they produce a huge amount
0:41:34 > 0:41:37of essential ingredients for life, basically.
0:41:37 > 0:41:39Particularly water vapour,
0:41:39 > 0:41:41we're just surrounded at the moment by all this
0:41:41 > 0:41:43volcanic gas and the vast majority of it is water.
0:41:47 > 0:41:52Earth's early atmosphere and oceans were created by volcanism,
0:41:52 > 0:41:55pumping water and gas into the primeval sky.
0:41:57 > 0:42:00But because the tectonic plates of the Earth
0:42:00 > 0:42:01dragged so much of this water
0:42:01 > 0:42:03and gases back inside the planet...
0:42:05 > 0:42:09..the right amount of atmosphere remained up above
0:42:09 > 0:42:10for life to evolve.
0:42:13 > 0:42:14Through this whole process,
0:42:14 > 0:42:16volcanoes actually deliver to the surface
0:42:16 > 0:42:19of the planet many fundamental ingredients required by life.
0:42:19 > 0:42:23In contrast, Venus, without plate tectonics,
0:42:23 > 0:42:26pumped ever more gases into her atmosphere.
0:42:28 > 0:42:32Over time, this dense atmosphere created a hell planet.
0:42:39 > 0:42:42All life that we know of needs heat,
0:42:42 > 0:42:45liquid water, and an energy-rich foodstuff.
0:42:47 > 0:42:50On Earth, volcanoes provide all three.
0:42:53 > 0:42:55If they can do this for life here,
0:42:55 > 0:42:59volcanoes might support life beyond Earth.
0:43:01 > 0:43:04At a volcanic hot spot in Iceland,
0:43:04 > 0:43:07Claire is searching for unusual life forms that can survive here.
0:43:14 > 0:43:19Our perspective of what's extreme is incredibly human-centric.
0:43:19 > 0:43:22We think that living at, you know, 20 Celsius
0:43:22 > 0:43:24in an oxygen-rich atmosphere is,
0:43:24 > 0:43:25that's what we like,
0:43:25 > 0:43:29and we see anything that's different to that as, you know, extreme.
0:43:29 > 0:43:30But in reality,
0:43:30 > 0:43:32that's just what we've evolved to live in,
0:43:32 > 0:43:34and microbes that live in these
0:43:34 > 0:43:36very hot or very acidic environments,
0:43:36 > 0:43:38they've evolved to live here
0:43:38 > 0:43:40and they wouldn't actually grow in our conditions.
0:43:45 > 0:43:49Mars had very similar environments where volcanism met ice.
0:43:51 > 0:43:55This makes it a good candidate for evidence of extraterrestrial life.
0:44:01 > 0:44:04Iceland acts as a useful parallel,
0:44:04 > 0:44:06and here Claire tests the water for sulphur,
0:44:06 > 0:44:08which certain bacteria can feed on.
0:44:11 > 0:44:13The intensity of the blue tells you
0:44:13 > 0:44:16how much sulphide is dissolved in the water.
0:44:16 > 0:44:18How much food there is for the microbes to eat.
0:44:18 > 0:44:24And we also get microbes which actually store the sulphur inside
0:44:24 > 0:44:25their cells for future use,
0:44:25 > 0:44:28like packing a sandwich into your bag for later.
0:44:28 > 0:44:29And they use that sulphur when
0:44:29 > 0:44:32they can't find any sulphur in the environment.
0:44:36 > 0:44:40She collects the microorganisms to study them more closely.
0:44:41 > 0:44:45We can read the DNA of these microorganisms and, you know,
0:44:45 > 0:44:47we can identify what they are,
0:44:47 > 0:44:50we can see what genes they have, you know, for certain lifestyles.
0:44:50 > 0:44:53Whether they can eat sulphur or not, for example.
0:44:53 > 0:44:56And we can really get a handle on the microbiology of these sites.
0:44:56 > 0:45:00Claire believes that life on Earth and possibly Mars
0:45:00 > 0:45:04could have originated in a volcanic hot spot just like this.
0:45:07 > 0:45:10But Mars is not the only planetary body
0:45:10 > 0:45:13where volcanism is closely linked to ice.
0:45:28 > 0:45:32Linda Spilker is head of the team that runs the Cassini probe that's
0:45:32 > 0:45:35been exploring Saturn and her moons.
0:45:36 > 0:45:41Linda is most interested in the moon called Enceladus.
0:45:41 > 0:45:44Enceladus is only about 500km across,
0:45:44 > 0:45:47and that's only about one seventh the size of our own moon.
0:45:47 > 0:45:51And that tiny moon, we think, should have been frozen solid.
0:45:51 > 0:45:53And if you look carefully,
0:45:53 > 0:45:56you notice it doesn't look like our moon at all.
0:45:56 > 0:45:58Our moon is covered with craters and it's dark,
0:45:58 > 0:46:01but this is bright, icy white, and very few craters.
0:46:03 > 0:46:06As the Cassini probe approached Enceladus,
0:46:06 > 0:46:10Linda observed something never seen before on a planetary body.
0:46:13 > 0:46:17If you look carefully, you can actually see individual geysers
0:46:17 > 0:46:20coming up and shooting out into space.
0:46:20 > 0:46:22And what a surprise.
0:46:22 > 0:46:26Everyone was in awe and amazement to see this level of activity.
0:46:30 > 0:46:34And we knew for the first time, this wasn't a dead moon.
0:46:34 > 0:46:37Enceladus was an active world.
0:46:50 > 0:46:53These eruptions are not molten rock.
0:46:56 > 0:46:58They are geysers, water and ice,
0:46:58 > 0:47:02fountaining over 700km into space.
0:47:05 > 0:47:07It means that liquid water
0:47:07 > 0:47:11deep below the surface is being forced upwards by heat.
0:47:13 > 0:47:15The material erupts so high
0:47:15 > 0:47:19that it's actually become part of Saturn's rings.
0:47:23 > 0:47:28So, all along, visible evidence of volcanic activity
0:47:28 > 0:47:30was present in the rings of Saturn,
0:47:30 > 0:47:33but scientists hadn't even realised.
0:47:37 > 0:47:39Coming out of the geysers,
0:47:39 > 0:47:42there's water vapour, there's tiny particles.
0:47:42 > 0:47:46If you'd stand near one of these cracks on Enceladus
0:47:46 > 0:47:47and put out your hand,
0:47:47 > 0:47:49it would almost be like it was snowing.
0:47:49 > 0:47:52These tiny particles would fall back down.
0:47:52 > 0:47:54And that's why there's no craters.
0:47:54 > 0:47:59That these particles go and fill in with fresh snow, on Enceladus,
0:47:59 > 0:48:01fill in all of the craters,
0:48:01 > 0:48:06and so, some pieces of Enceladus' surface are only minutes old.
0:48:06 > 0:48:10Covered by these tiny particles, falling in from space.
0:48:11 > 0:48:16So, how are these extraordinary geysers of ice and water formed?
0:48:21 > 0:48:24Again, Iceland provides a powerful analogy.
0:48:32 > 0:48:34This is the Strokkur geyser.
0:48:39 > 0:48:42Claire loves to witness its raw power.
0:48:45 > 0:48:47A great natural wonder of the world.
0:48:50 > 0:48:51So what we have here,
0:48:51 > 0:48:54rather than molten lava coming out of the ground,
0:48:54 > 0:48:57as you typically get for your regular volcano,
0:48:57 > 0:48:59what we have here is actually just water,
0:48:59 > 0:49:02just ground water which is within the ground.
0:49:02 > 0:49:04And it's being heated up by these magma chambers,
0:49:04 > 0:49:07which are actually much further, deeper underground.
0:49:07 > 0:49:09And this water gets superheated
0:49:09 > 0:49:11until it just can't stay underground any more,
0:49:11 > 0:49:14and all that steam and all that energy,
0:49:14 > 0:49:15just like in a normal volcano,
0:49:15 > 0:49:17will erupt all of that water to the surface.
0:49:22 > 0:49:26Just before the eruption, what we see is a kind of bubble forming,
0:49:26 > 0:49:28where we get this really beautiful,
0:49:28 > 0:49:31kind of almost glassy-looking dome of water,
0:49:31 > 0:49:35which is all this superheated water just coming up to the surface
0:49:35 > 0:49:36until it finally erupts.
0:49:37 > 0:49:40A thermal camera measures the heat of the water.
0:49:42 > 0:49:45What we can do when we look at the thermal camera here,
0:49:45 > 0:49:49we can get an idea of how high temperature the system is.
0:49:49 > 0:49:51It's about 70 Celsius.
0:49:51 > 0:49:55For me, Enceladus is one of the most exciting places, I think,
0:49:55 > 0:49:57in the solar system to go out and explore. It's...
0:49:57 > 0:49:59LOUD WHOOSH
0:49:59 > 0:50:00For reasons exactly like that,
0:50:00 > 0:50:03it's one of the other places in the solar system where we actually have
0:50:03 > 0:50:08this active hydrothermal activity, where we have these plumes which are
0:50:08 > 0:50:10massive in scale compared to what we have here.
0:50:16 > 0:50:20The geysers of Enceladus are so powerful,
0:50:20 > 0:50:25there must be an ocean of heated water hidden below the icy surface.
0:50:28 > 0:50:32Linda Spilker has ingeniously found out what's in this ocean.
0:50:34 > 0:50:39The Cassini spacecraft, since we can get so close to Enceladus,
0:50:39 > 0:50:44we can literally skim, fly through the jets and make measurements.
0:50:44 > 0:50:48We can measure the gas, we can measure the particles coming out,
0:50:48 > 0:50:50and figure out what they're made of.
0:50:50 > 0:50:54And the clues inside those particles, those composition,
0:50:54 > 0:50:57tells us about the ocean underneath.
0:50:59 > 0:51:02It is full of salts and organic compounds.
0:51:02 > 0:51:05Some of the key building blocks of life.
0:51:08 > 0:51:12So, we wonder, could Enceladus also have life
0:51:12 > 0:51:16very similar to the life on Earth?
0:51:16 > 0:51:19Is it like the same kind of life we have here on Earth?
0:51:19 > 0:51:22Is it something totally different that we can't imagine?
0:51:32 > 0:51:34We've had volcanism on Mars,
0:51:34 > 0:51:37we've had volcanism on Enceladus and its various different geysers.
0:51:37 > 0:51:40To find evidence of life on another planet would be...
0:51:40 > 0:51:42It would just be absolutely ground-breaking
0:51:42 > 0:51:44in terms of our understanding
0:51:44 > 0:51:46of our place, not just in the solar system,
0:51:46 > 0:51:48but in the universe as well, right?
0:51:52 > 0:51:54The hunt for volcanoes elsewhere
0:51:54 > 0:51:57continues to produce amazing breakthroughs.
0:52:01 > 0:52:05This is one of the remotest and most distant parts of the solar system.
0:52:07 > 0:52:09Pluto.
0:52:11 > 0:52:13After a nine-year odyssey,
0:52:13 > 0:52:18the New Horizons probe finally reached Pluto in July 2015.
0:52:21 > 0:52:24What it discovered was astonishing.
0:52:26 > 0:52:29The New Horizons spacecraft that just visited Pluto
0:52:29 > 0:52:33found features that have every indication of being cryovolcanic,
0:52:33 > 0:52:37mountains, shield-like mountains,
0:52:37 > 0:52:39flows on the surface.
0:52:39 > 0:52:41Completely unexpected.
0:52:41 > 0:52:43And just an extraordinary discovery
0:52:43 > 0:52:45which just shows us how exciting the game can be.
0:52:47 > 0:52:50This is Wright Mons on Pluto.
0:52:51 > 0:52:56At 150km across, and 4km high,
0:52:56 > 0:53:00it's believed to be the largest cryovolcano of the solar system.
0:53:02 > 0:53:08It's driven by a similar process of mountain formation as on Earth,
0:53:08 > 0:53:12but instead of molten rock, it's built up from flowing ice.
0:53:15 > 0:53:18In the case of Pluto, it's so cold.
0:53:18 > 0:53:20It's not water ice,
0:53:20 > 0:53:22it's actually... can be nitrogen ice that can be there.
0:53:22 > 0:53:24Or methane ice.
0:53:24 > 0:53:28Other things that can be ice in that very cold environment of Pluto.
0:53:28 > 0:53:30And there are some tantalising features
0:53:30 > 0:53:33that perhaps are cryovolcanoes - maybe something has flowed out.
0:53:33 > 0:53:36You mix a little bit of water and ammonia together and it can actually
0:53:36 > 0:53:38flow on the surface.
0:53:40 > 0:53:44A rare event on Earth called frazil ice
0:53:44 > 0:53:47reveals how freezing water can sometimes behave
0:53:47 > 0:53:49in a similar way to lava.
0:53:51 > 0:53:55During winter, it's occasionally observed in Yosemite National Park.
0:53:57 > 0:54:02A slowly flowing river of chunks of ice, given the right conditions,
0:54:02 > 0:54:05suddenly freezes solid.
0:54:07 > 0:54:09What happens when we see frazil ice on Earth,
0:54:09 > 0:54:11is it is so close to its freezing point.
0:54:11 > 0:54:13That's why it's filled with ice crystals.
0:54:13 > 0:54:17And if it cools down just enough, just another half a degree Celsius,
0:54:17 > 0:54:19a quarter of a degree Celsius,
0:54:19 > 0:54:24suddenly all the water that's liquid between those ice crystals freezes,
0:54:24 > 0:54:25and it happens just like that.
0:54:27 > 0:54:30And it's entirely possible that that same process could be happening
0:54:30 > 0:54:32on the surface of Pluto.
0:54:40 > 0:54:43It's towards the end of the Iceland expedition,
0:54:43 > 0:54:46and the team gather to discuss their findings.
0:54:50 > 0:54:53Key to this is the fascinating paradox -
0:54:53 > 0:54:57volcanoes are a violent and destructive force,
0:54:57 > 0:54:59while also essential to life.
0:55:02 > 0:55:03Whenever we find volcanism on Earth,
0:55:03 > 0:55:06we find all sorts of kind of crazy chemistry, really,
0:55:06 > 0:55:09which can just support microbial life, as it is on Earth.
0:55:09 > 0:55:11And the real question is whether
0:55:11 > 0:55:14these same kinds of processes that happen on Mars or on Enceladus,
0:55:14 > 0:55:17whether those can actually support microbial life in the same way.
0:55:17 > 0:55:20There's a lot of similarities between this type of environment,
0:55:20 > 0:55:23that we've obviously got life in, we know that.
0:55:23 > 0:55:27So this is the type of environment that would be a great target
0:55:27 > 0:55:29- to look for on Mars.- Yeah.
0:55:33 > 0:55:38But volcanoes of the solar system also give us a window
0:55:38 > 0:55:41on what might happen to our own planet in the future.
0:55:43 > 0:55:45What I think is really fascinating,
0:55:45 > 0:55:47when you look throughout the solar system,
0:55:47 > 0:55:52is that you have this diversity of bodies, and each of these bodies,
0:55:52 > 0:55:55all of them, or most of them show volcanism.
0:55:55 > 0:56:00And then you see that they have been developing in different ways,
0:56:00 > 0:56:01each of the bodies.
0:56:03 > 0:56:05In about a billion years,
0:56:05 > 0:56:10it's predicted that the plate tectonics of Earth could end.
0:56:12 > 0:56:15A catastrophe for life here.
0:56:19 > 0:56:22Plate tectonics and volcanism replenish the atmosphere
0:56:22 > 0:56:25with what we need, but won't you just lose the atmosphere
0:56:25 > 0:56:27if you stop plate tectonics?
0:56:27 > 0:56:30If Earth just literally kind of grinds to a halt, then, yeah,
0:56:30 > 0:56:34eventually the atmosphere will be stripped away by the solar wind,
0:56:34 > 0:56:37it will be just lost into space and, yeah,
0:56:37 > 0:56:39basically I think we'll end up becoming very much like Mars,
0:56:39 > 0:56:42just a very cold and dry, barren, rocky planet.
0:56:45 > 0:56:48Earth as Mars is one option.
0:56:50 > 0:56:52But another scenario is possible.
0:56:56 > 0:57:03Even if plate tectonics ended, volcanism might continue unabated,
0:57:03 > 0:57:07and our atmosphere would become thicker and hotter.
0:57:07 > 0:57:12It could go the other way and end up like Venus,
0:57:12 > 0:57:14where we have all this carbon dioxide in the atmosphere,
0:57:14 > 0:57:17and, you know, either way, the options aren't looking that great.
0:57:17 > 0:57:19So the interesting thing is
0:57:19 > 0:57:21we've got these three planets next to each other,
0:57:21 > 0:57:25and they've all got these incredibly different scenes at the present day,
0:57:25 > 0:57:30that they may be telling us a lot about the potential futures for
0:57:30 > 0:57:34the Earth, as well, and volcanoes are a big part of that story.
0:57:34 > 0:57:37So you can see the higher life forms on Earth, like human beings,
0:57:37 > 0:57:42dying out as the conditions become much more difficult for them.
0:57:42 > 0:57:44Perhaps we'll lose our atmosphere,
0:57:44 > 0:57:46perhaps actually we start losing our water.
0:57:46 > 0:57:49It's going to be very difficult for human beings to adapt to those
0:57:49 > 0:57:51- conditions, but the microbes will love them.- Yeah.
0:57:51 > 0:57:54Microbes will inherit the Earth.
0:57:57 > 0:58:00Fortunately, all this is a billion years from now.
0:58:03 > 0:58:07Way back in the ninth century, Vikings discovered Iceland,
0:58:07 > 0:58:10its landscape sculpted by volcanoes.
0:58:14 > 0:58:20Today, a new generation of explorers are looking out into space,
0:58:20 > 0:58:24discovering how volcanoes have shaped not just our planet,
0:58:24 > 0:58:27but other extraordinary worlds.