0:00:30 > 0:00:34Good evening. In this programme, we're going to talk once again
0:00:34 > 0:00:40about the giant planets Jupiter and Saturn.
0:00:40 > 0:00:43We've learned so much in the last few years. Chris Lintott.
0:00:43 > 0:00:47We certainly have and we've got a particularly exciting new mission.
0:00:47 > 0:00:49ESA, the European Space Agency,
0:00:49 > 0:00:52has decided its next big thing in space is going to be a mission
0:00:52 > 0:00:56called Juice, that's going to go to Jupiter and explore its moons.
0:00:56 > 0:00:58We've got two of the people who made Juice happen,
0:00:58 > 0:01:03Michelle Dougherty from Imperial College London, and Leigh Fletcher from Oxford.
0:01:03 > 0:01:08- Congratulations on being selected. - Thank you very much. - Michelle, what's Juice going to do?
0:01:08 > 0:01:13OK, as you say, it was recently chosen and so the plan now is we will go into a study phase.
0:01:13 > 0:01:18We will be launched in 2022. It will take eight years to get there.
0:01:18 > 0:01:21And so reach the Jupiter system in 2030.
0:01:21 > 0:01:25We'll spend at least three and a half years within the system and orbiting the moons.
0:01:25 > 0:01:30You may still be doing The Sky At Night. I sadly won't.
0:01:30 > 0:01:34Well, that remains to be seen. Which moons do you go to first?
0:01:34 > 0:01:38We will fly past Europa first. We'll have flybys over Europa.
0:01:38 > 0:01:41We will then have a Callisto phase which will be interesting,
0:01:41 > 0:01:44not only because we're going to be looking at Callisto,
0:01:44 > 0:01:47but we're going to be coming out of the equatorial plane.
0:01:47 > 0:01:50That will allow us to get into regions we haven't seen before.
0:01:50 > 0:01:54And then we will move to Ganymede and we'll spend nine months orbiting
0:01:54 > 0:01:59around Ganymede and we will end the mission by crashing on the surface.
0:01:59 > 0:02:03This is the first time a probe will have orbited a moon of one of the giant planets.
0:02:03 > 0:02:07- Why are the moons so important? - The Galilean moons, in particular,
0:02:07 > 0:02:11each one has a very different unique environment that in its own right
0:02:11 > 0:02:13would be worth studying, but the point of Juice,
0:02:13 > 0:02:17the idea behind the mission, is to compare the conditions
0:02:17 > 0:02:20that we find on those moons - Europa, Ganymede and Callisto.
0:02:20 > 0:02:24Most of the moons of the outer solar system are made of ice.
0:02:24 > 0:02:28That's simply because at the very cold temperatures
0:02:28 > 0:02:31of the outer solar system, water exists in its frozen form.
0:02:31 > 0:02:35So it makes up the large proportion of these moons.
0:02:35 > 0:02:37The tantalising thing about these three moons
0:02:37 > 0:02:42is that there is a source of energy that causes the ice to melt to become liquid water.
0:02:42 > 0:02:46We believe that a liquid ocean exists beneath the surface
0:02:46 > 0:02:49of these three icy moons.
0:02:49 > 0:02:53That has huge implications for the potential for these moons
0:02:53 > 0:02:54to be habitable.
0:02:54 > 0:02:58That's not that they do support life right now, but it's that there is
0:02:58 > 0:03:03the chance or the potential for life to exist on these icy worlds.
0:03:03 > 0:03:06Michelle, what's this source of energy that keeps
0:03:06 > 0:03:10- some of the ice liquid? - In the environment around Jupiter,
0:03:10 > 0:03:14most of the energy comes from the fast rotation of Jupiter.
0:03:14 > 0:03:18But as far as the energy sources of the interior of the moons
0:03:18 > 0:03:21is concerned, we think they're still hot in the interior
0:03:21 > 0:03:25because of the tidal forces between Jupiter and the moon.
0:03:25 > 0:03:30- As they go round Jupiter, they're pushed and pulled by its very powerful gravity.- Yes.
0:03:30 > 0:03:32And so that's what allows the interior of the moons
0:03:32 > 0:03:36to still be warm, but there are two other things you need
0:03:36 > 0:03:38if you're going to look for life.
0:03:38 > 0:03:41You need there to be complex organic compounds
0:03:41 > 0:03:47and you also need the environment to be stable over quite a long period of time.
0:03:47 > 0:03:51You need water, you need heat, you need stability and you need chemicals.
0:03:51 > 0:03:55- Is it ordinary water. H2O, like ours?- We think it is, yes.
0:03:55 > 0:03:59We also think that its conductivity,
0:03:59 > 0:04:02the amount of salt we have in the water, is probably similar to ours.
0:04:02 > 0:04:07But we're postulating from the observations we got from the Galilean spacecraft.
0:04:07 > 0:04:11We need to get a spacecraft that will orbit around Ganymede,
0:04:11 > 0:04:13make observations on the surface,
0:04:13 > 0:04:15but also understand what's underneath.
0:04:15 > 0:04:18These four ingredients Michelle was talking about,
0:04:18 > 0:04:20Juice will be able to study and look
0:04:20 > 0:04:24and so we'll finally be able to answer some of these questions
0:04:24 > 0:04:29that Galileo, back in the 1990s through to 2003, they left open.
0:04:29 > 0:04:33Planetary scientists since have been trying to resolve some of these questions.
0:04:33 > 0:04:37Let's go back to Europa. You talked about recent activity on the surface,
0:04:37 > 0:04:41but how recent are we talking about? Is this something that's happening now?
0:04:41 > 0:04:48No. People have gone back to the Galileo observations and they've compared them
0:04:48 > 0:04:51to observations that we have of the Greenland Ice Shelf.
0:04:51 > 0:04:54You could almost convince yourself you were looking at the same thing.
0:04:54 > 0:04:58The Greenland Ice Shelf changes over, what, thousands of years,
0:04:58 > 0:05:02so we should expect that sort of timescale on Europa.
0:05:02 > 0:05:06One of the interesting things about these regions of potentially
0:05:06 > 0:05:10recent activity, recent on a geologic timescale, so long periods of time,
0:05:10 > 0:05:13is there may be regions of the crust which are thinner than elsewhere,
0:05:13 > 0:05:16where you've got an exchange of say energy
0:05:16 > 0:05:20from the interior of this moon, up towards the icy surface.
0:05:20 > 0:05:25So these fractured chaotic terrains are actually really
0:05:25 > 0:05:28tantalising targets for future spacecraft like Juice,
0:05:28 > 0:05:33especially if it has the capabilities to probe deep through
0:05:33 > 0:05:36and beneath that icy crust. If we go for the thinner regions,
0:05:36 > 0:05:39- we might get access to that icy ocean beneath.- We come to Ganymede.
0:05:39 > 0:05:44- The largest satellite in the entire solar system.- That's right.
0:05:44 > 0:05:46- Juice is going to go into orbit. - That's right.
0:05:46 > 0:05:50We thought long and hard about whether we wanted
0:05:50 > 0:05:53to orbit around Europa or orbit around Ganymede and in fact,
0:05:53 > 0:06:00Ganymede is more interesting, I think. As we know, it's the largest moon in the solar system.
0:06:00 > 0:06:06It also is the only moon in the solar system that has an internal planetary field.
0:06:06 > 0:06:10- It's got a dynamo field inside. - Just like the Earth has.
0:06:10 > 0:06:14It also has a magnetic field that's induced by currents
0:06:14 > 0:06:18that are flowing in the ocean underneath, and so there's a mix
0:06:18 > 0:06:22of these different fields that we need to try and understand.
0:06:22 > 0:06:26- You care because they're telling you about the interior.- Yes.
0:06:26 > 0:06:30What do the surfaces of these outer moons look like?
0:06:30 > 0:06:34You move the largest moon, Ganymede, out to Callisto.
0:06:34 > 0:06:36Callisto has a very ancient and battered terrain.
0:06:36 > 0:06:40We think it's a remnant of the very earliest bombardments that
0:06:40 > 0:06:42took place within the solar system.
0:06:42 > 0:06:45So this, if you like, is a much more inactive moon.
0:06:45 > 0:06:49Some would say a dead moon, that isn't having resurfacing processes taking place.
0:06:49 > 0:06:53Whereas on Ganymede, there's a higher probability that we might
0:06:53 > 0:06:57see the evidence that activity has occurred in geologically recent history.
0:06:57 > 0:07:02In fact, if you have... Ground based observers are able to resolve contrasts across Ganymede
0:07:02 > 0:07:06and there's an ancient dark terrain called Galileo Regio,
0:07:06 > 0:07:10which is visible in some of the best amateur images that we see.
0:07:10 > 0:07:14Especially when Juice finally gets to Jupiter,
0:07:14 > 0:07:17we'll have a huge amateur community there along with us,
0:07:17 > 0:07:21observing the same features as the spacecraft is seeing up close and personal.
0:07:21 > 0:07:23That's going to be one to watch.
0:07:23 > 0:07:27Is this then a common way for moons in the solar system to be?
0:07:27 > 0:07:31In all three, they're icy, they have underground oceans.
0:07:31 > 0:07:35That must be telling us something about what's likely in the solar system.
0:07:35 > 0:07:38Yes. That's one of the reasons we want Juice to go to the...
0:07:38 > 0:07:40It's an unanswered question.
0:07:40 > 0:07:43What we want to try and do with the three moons
0:07:43 > 0:07:46we're going to focus on is get an understanding about why
0:07:46 > 0:07:50they're different, try and understand what the heat source is,
0:07:50 > 0:07:52we think we know what the heat source is,
0:07:52 > 0:07:56but why is it having a different effect on all three of the moons?
0:07:56 > 0:07:59But also, really try and understand
0:07:59 > 0:08:02whether there are environments in our solar system
0:08:02 > 0:08:05where the conditions are there, so that life might be able to form.
0:08:05 > 0:08:08If we can understand that at Ganymede,
0:08:08 > 0:08:11go into orbit around Ganymede and spend a lot of time
0:08:11 > 0:08:14looking at it, it will allow us to then describe how we think
0:08:14 > 0:08:18some of the bodies outside of our solar system might have formed
0:08:18 > 0:08:21and some of the extra solar work that is being done as well.
0:08:21 > 0:08:25If you can find planets in the Goldilocks Zone, around their star,
0:08:25 > 0:08:29not too hot, not too cold, they may have icy moons as well.
0:08:29 > 0:08:32And this is a revisiting of that Goldilocks hypothesis.
0:08:32 > 0:08:35The idea that you have temperatures that are just right here
0:08:35 > 0:08:38on Planet Earth for life to have existed.
0:08:38 > 0:08:43These icy moons of the solar system, which traditionally, you don't think of as being part of...
0:08:43 > 0:08:46- Cos they're far too cold. - Far too cold, way too distant,
0:08:46 > 0:08:49but actually they might have these four ingredients.
0:08:49 > 0:08:52The stability with time, the energy source that's required
0:08:52 > 0:08:56and the supply of materials in a liquid water environment.
0:08:56 > 0:09:00Be nice to have some toothed fish wandering around as well.
0:09:00 > 0:09:04I'm not sure if we can actually promise that's going to happen.
0:09:04 > 0:09:08Not yet. Well, we've talked a great deal about Jupiter.
0:09:08 > 0:09:12- On now to Saturn and its family of moons.- Yes.
0:09:12 > 0:09:17Cassini is orbiting around Saturn. Two of the moons are interesting,
0:09:17 > 0:09:21partly because we can compare them to the moons of Jupiter.
0:09:21 > 0:09:23And that is Enceladus and Titan.
0:09:23 > 0:09:28We know both of those moons have got bodies of liquid underneath
0:09:28 > 0:09:32the surface and so by learning more about Titan and Enceladus now,
0:09:32 > 0:09:34we can feed that information
0:09:34 > 0:09:38to what we're going to learn with Juice at Jupiter.
0:09:38 > 0:09:41Shall we start with Enceladus? That's the icy moon.
0:09:41 > 0:09:43So that seems closer to the Jovian examples,
0:09:43 > 0:09:46but Enceladus is a weird place.
0:09:46 > 0:09:50The Fountains of Enceladus are the weirdest things in the solar system.
0:09:50 > 0:09:54- I think they are too, but it's weird in a fascinating way.- We like weird!
0:09:54 > 0:09:58But it's very clear that there is an energy source
0:09:58 > 0:10:03at Enceladus that is keeping the interior heated.
0:10:03 > 0:10:07We know that the water ice has become liquid and we know that
0:10:07 > 0:10:09because water vapour is escaping.
0:10:09 > 0:10:15We see amazing pictures of these. You detect them with other instruments as well.
0:10:15 > 0:10:18We've flown through the plume, we've been able to measure
0:10:18 > 0:10:21the amount of organics and dust and water vapour in the plume.
0:10:21 > 0:10:24The really interesting thing from my perspective
0:10:24 > 0:10:27is the amount of activity is changing over time.
0:10:27 > 0:10:31It's very clear there are internal processes taking place,
0:10:31 > 0:10:34which are changing from one week to the next.
0:10:34 > 0:10:39So is this a special time now that we're able to view Enceladus with this happening?
0:10:39 > 0:10:44Or is this something that could have been happening over hundreds of thousands of years in the past?
0:10:44 > 0:10:49I think it must have been happening for a long period of time.
0:10:49 > 0:10:52It's now very clear that Enceladus and its plumes is the source
0:10:52 > 0:10:56of the earring and we know that the earring has been in existence...
0:10:56 > 0:10:59- One of the outer of Saturn's rings? - Yes.
0:10:59 > 0:11:02It's one of the rings that you can't visually see.
0:11:02 > 0:11:06We don't see anything like this on any of Jupiter's small moons.
0:11:06 > 0:11:10- Why just Enceladus?- Possible discoveries that we might make
0:11:10 > 0:11:15when we have Europa flybys with Juice is maybe we will see something
0:11:15 > 0:11:19at Europa, but it's very clear that Enceladus is unique, in the sense
0:11:19 > 0:11:23it's small, it has this internal heat source that we didn't expect
0:11:23 > 0:11:28to be there, and it's spewing out a large amount of water vapour.
0:11:28 > 0:11:31We know that water vapour is salty, in some sense,
0:11:31 > 0:11:37- or it's not just pure water. - That's right.- We know that because you've flown through it very bravely.
0:11:37 > 0:11:43I don't know if they would want to do it again! The closest flyby we had was 25km above the surface.
0:11:43 > 0:11:49And it was very clear after it happened that the mission planners will not do it again.
0:11:49 > 0:11:53Because the mag boom sticks off from the side of the spacecraft
0:11:53 > 0:11:55and the spacecraft moved a little bit more
0:11:55 > 0:11:59than they thought it would, as we flew through the plume.
0:11:59 > 0:12:01They don't want the spacecraft to tumble.
0:12:01 > 0:12:06- It was a really rocky ride on the way through.- I wonder why not(!)
0:12:06 > 0:12:09But nonetheless, from this brave, plucky adventure
0:12:09 > 0:12:15through the Fountains of Enceladus, it's like something out of sci-fi! Through the Fountains of Enceladus!
0:12:15 > 0:12:19We discovered the water is salty, it has other material in there.
0:12:19 > 0:12:23People have suggested that means there's a rocky core.
0:12:23 > 0:12:26There might be a rocky core. We don't know.
0:12:26 > 0:12:28A lot of work has been done at the moment,
0:12:28 > 0:12:32trying to model what the interior actually looks like.
0:12:32 > 0:12:35To understand it best, we'd need to go into orbit and that
0:12:35 > 0:12:41is difficult to do because the gravitational field of Enceladus
0:12:41 > 0:12:44is small, you need a huge amount of fuel to be able to get into orbit.
0:12:44 > 0:12:47So we're going to have to make do with lots more flybys that we have
0:12:47 > 0:12:50of Enceladus by the Cassini craft.
0:12:50 > 0:12:54- Let's turn now to Titan, unlike any of the others.- It has an atmosphere.
0:12:54 > 0:12:57- And an interesting surface.- Yes.
0:12:57 > 0:13:00We haven't really got to see the surface until very recently.
0:13:00 > 0:13:04The atmosphere is made up of ethane and methane.
0:13:04 > 0:13:09It's almost like a very smoggy place, so you can't see through it.
0:13:09 > 0:13:12It's only been with some of the instruments on board Cassini
0:13:12 > 0:13:17we've been able to see through the atmosphere and onto the surface.
0:13:17 > 0:13:21One of the initial disappointments with the Titan observations
0:13:21 > 0:13:25was that we expected to see lots of liquid on the surface.
0:13:25 > 0:13:27We didn't, for years.
0:13:27 > 0:13:31And it's only very recently that the first signatures
0:13:31 > 0:13:36of some type of liquid on the surface was seen.
0:13:36 > 0:13:37We think that's probably
0:13:37 > 0:13:42because no rain had fallen for a long period of time
0:13:42 > 0:13:44and it was only after rain had fallen we got to see it.
0:13:44 > 0:13:47We do see evolving weather through the Cassini mission.
0:13:47 > 0:13:50We've seen clouds come and go on Titan.
0:13:50 > 0:13:55We know there's something special about the north pole of Titan.
0:13:55 > 0:13:59Large bodies of standing liquid, some combination of methane
0:13:59 > 0:14:02and ethane and various hydrocarbons up there.
0:14:02 > 0:14:04- Certainly not water.- No.
0:14:04 > 0:14:08One of the closest comparisons is like the liquid natural gas
0:14:08 > 0:14:10sort of thing.
0:14:10 > 0:14:14It's a fascinating region and the first time in planetary exploration
0:14:14 > 0:14:19where we can really talk about one day exploring an ocean
0:14:19 > 0:14:24on a surface and sailing a boat on the surface of another moon.
0:14:24 > 0:14:28What strikes me from some of the shots, from Huygens,
0:14:28 > 0:14:30the probe that landed on the surface,
0:14:30 > 0:14:33you could see what looked like river valleys.
0:14:33 > 0:14:38A very easy landscape to read. It looked very Earth-like.
0:14:38 > 0:14:40Very cold, of course.
0:14:40 > 0:14:41We're talking about Titan
0:14:41 > 0:14:46because we were talking about worlds with oceans beneath the surface.
0:14:46 > 0:14:50Is that the same sort of model that we have for Titan?
0:14:50 > 0:14:53Or is the liquid confined to the surface?
0:14:53 > 0:14:58No, there have been some radar observations of Titan
0:14:58 > 0:15:04which seem to imply there is a body of liquid underneath the surface.
0:15:04 > 0:15:07We're hoping with the magnetic field instrument to be able
0:15:07 > 0:15:11to measure induced currents that are flowing in that ocean.
0:15:11 > 0:15:14But we can't get close enough.
0:15:14 > 0:15:17Because Titan has a dense atmosphere,
0:15:17 > 0:15:22because we've got the boom sticking off the side, the mission planners
0:15:22 > 0:15:25don't want to get us closer than about 950km
0:15:25 > 0:15:29because as the atmosphere gets denser,
0:15:29 > 0:15:31the spacecraft could begin to tumble.
0:15:31 > 0:15:36So we hope we will get some observations of induced currents,
0:15:36 > 0:15:39but we aren't sure we'll be able to do it.
0:15:39 > 0:15:44And we want to keep the spacecraft alive until it goes into its polar orbits.
0:15:44 > 0:15:47We've talked about some of Saturn's moons.
0:15:47 > 0:15:50Let's now talk about the ringed planet itself.
0:15:50 > 0:15:53There have been exciting times in Saturn recently.
0:15:53 > 0:15:56Back in 2010, Cassini saw this gigantic spike
0:15:56 > 0:15:59in the amount of lightning emission coming from the planet,
0:15:59 > 0:16:03showing there was a gigantic thunderstorm evolving.
0:16:03 > 0:16:08This thunderstorm grew to be what we describe as planetary in scale,
0:16:08 > 0:16:13like a single Earth storm enveloping the entire latitude circle.
0:16:13 > 0:16:17Cassini was very lucky to be there to see it.
0:16:17 > 0:16:21That thunderstorm lasted from the end of 2010
0:16:21 > 0:16:25through to the middle of 2011 when we thought things were starting
0:16:25 > 0:16:28to die down, the lightning strikes were dying away,
0:16:28 > 0:16:34and the churning convective activity of the storm had seemed to subside.
0:16:34 > 0:16:36But it's not over.
0:16:36 > 0:16:40Cassini is still tracking the remnants of this particular storm.
0:16:40 > 0:16:43It had an effect on the atmosphere really high up
0:16:43 > 0:16:47that can only been seen at infrared wavelengths of light
0:16:47 > 0:16:51- and the storm is still raging. - At infrared, you're detecting heat.
0:16:51 > 0:16:55This is energy that's being injected into the upper layers
0:16:55 > 0:16:58of the atmosphere. That's why you see it glowing.
0:16:58 > 0:17:03On Earth, you fly in a plane, you try to get above these storm cells
0:17:03 > 0:17:08to avoid all the turbulence and bumping that are inherent.
0:17:08 > 0:17:13On Saturn, we didn't we really expect the same sort of things to be taking place.
0:17:13 > 0:17:19You have this huge region of hot, heated gas,
0:17:19 > 0:17:22many hundreds of kilometres higher up than those storm clouds.
0:17:22 > 0:17:27The storm that's happening down at depth is having a huge effect
0:17:27 > 0:17:30on the atmosphere hundreds of kilometres higher up.
0:17:30 > 0:17:33We've never seen that anywhere in the solar system before.
0:17:33 > 0:17:36It's exciting to be tracking this.
0:17:36 > 0:17:40And we're seeing it as heat energy emitted by the planet Saturn
0:17:40 > 0:17:43with Cassini's instruments.
0:17:43 > 0:17:48Why do you think the atmospheres of Jupiter and Saturn are so different?
0:17:48 > 0:17:53When you look at Jupiter, you're seeing right down to the region where the clouds condense.
0:17:53 > 0:17:56You're seeing the fluffy white ammonia clouds
0:17:56 > 0:17:59and possibly the ammonium hydrogen sulphide clouds.
0:17:59 > 0:18:04On Saturn, above those clouds, there are haze particles.
0:18:04 > 0:18:09The haze is so thick it reflects the light before the light gets down.
0:18:09 > 0:18:14- It's almost like smog.- Exactly. A bit like with Titan.
0:18:14 > 0:18:18You can't see the surface because of all the smoggy hazy stuff.
0:18:18 > 0:18:22Saturn, you can't see the cloud because of the smoggy hazy stuff.
0:18:22 > 0:18:28Why are they different? Why does Saturn have this smog and Jupiter not?
0:18:28 > 0:18:31There's a difference in size between these two planets.
0:18:31 > 0:18:35It means that the gravitational acceleration on the two planets
0:18:35 > 0:18:39- is very different. - The pull of gravity.
0:18:39 > 0:18:43All the cloud decks on Saturn are more spread out with altitude.
0:18:43 > 0:18:47On Jupiter, they're more localised and squashed together.
0:18:47 > 0:18:49The amount of a particular material,
0:18:49 > 0:18:54say it's methane or ammonia or hydrogen sulphide available
0:18:54 > 0:18:56to form a cloud is very different.
0:18:56 > 0:19:00The thing that makes Jupiter have that red colour, we think,
0:19:00 > 0:19:03has got something to do with phosphorus.
0:19:03 > 0:19:06On Saturn, that phosphorus is locked away, deep in the interior.
0:19:06 > 0:19:10It isn't able to get up to cause the red colouration of the clouds.
0:19:10 > 0:19:14It's the difference in size that causes such great big differences
0:19:14 > 0:19:19in the hazes and the chemistry at work within these atmospheres.
0:19:19 > 0:19:23We've been talking about Juice. You've got a lot of work to do before you get to launch.
0:19:23 > 0:19:27You've got lots of time off between launch and getting to Jupiter, I'm sure.
0:19:27 > 0:19:32What do you think? If I had to force you all to choose one really big question,
0:19:32 > 0:19:37either Jupiter or Saturn or their moons, to answer, what would it be?
0:19:37 > 0:19:40I know what you're going to go for. You'll say Enceladus.
0:19:40 > 0:19:45Yes. The Fountains of Enceladus. These fascinate me.
0:19:45 > 0:19:48I want to know about the rings.
0:19:48 > 0:19:51I want to know how long lived Saturn's rings are.
0:19:51 > 0:19:53I want to know how long a day lasts on Saturn.
0:19:53 > 0:19:58We still don't know exactly what the rotation rate of Saturn is.
0:19:58 > 0:20:02- But you've got a probe orbiting it. - I know.
0:20:02 > 0:20:04But because it's not a solid surface
0:20:04 > 0:20:10- and there isn't something on the surface that we can follow around... - No Greenwich Meridian.
0:20:10 > 0:20:14The observations we make in the magnetic field shows
0:20:14 > 0:20:17it's around 10.7 hours, but if you're in the northern hemisphere,
0:20:17 > 0:20:21it's different to when you're in the southern hemisphere.
0:20:21 > 0:20:25That's why the end of mission when we get really close in will answer those questions.
0:20:25 > 0:20:30It's a fundamental thing. How fast Saturn rotates determines how we map features on it.
0:20:30 > 0:20:36And we don't know it. You can save your embarrassment by discovering that, what about you?
0:20:36 > 0:20:41The question I'd like to have answered is why is the great red spot the colour red.
0:20:41 > 0:20:45We don't know what the chemical is that causes it to be red in colour.
0:20:45 > 0:20:49I hope that Juice will have the answer.
0:20:49 > 0:20:51We've certainly learnt a great deal from the probes.
0:20:51 > 0:20:54There's much more to be learned. I suspect that in ten years,
0:20:54 > 0:20:59we'll have altered our ideas quite considerably.
0:20:59 > 0:21:00Thank you all very much.
0:21:02 > 0:21:08Now to Selsey Beach, where Pete and Paul are going to tell us something to look forward to.
0:21:08 > 0:21:13- We've come down to this incredibly bleak beach...- It is a bit!
0:21:13 > 0:21:16..to talk about the things we can see in the night sky
0:21:16 > 0:21:20over the next couple of months. There are some interesting things.
0:21:20 > 0:21:23There are nice gentle things which are easy to see.
0:21:23 > 0:21:28If the clouds were out of the way and it was a bit later at night,
0:21:28 > 0:21:32after the sun had gone down, this is the season where you can see
0:21:32 > 0:21:35a phenomena known as noctilucent clouds.
0:21:35 > 0:21:37- Have you ever seen them?- I haven't.
0:21:37 > 0:21:40I know they can get very bright, very powerful.
0:21:40 > 0:21:42We ought to explain what they are.
0:21:42 > 0:21:45They're basically really high altitude clouds,
0:21:45 > 0:21:48much higher than normal clouds we've got up here.
0:21:48 > 0:21:52In the summer months, going through from late May into early August,
0:21:52 > 0:21:57as the sun goes below the horizon, there's a period when the light
0:21:57 > 0:22:01from the sun can't illuminate these clouds.
0:22:01 > 0:22:05But if the sky is clear and you've got noctilucent clouds there,
0:22:05 > 0:22:08they're high enough to be able to reflect sunlight.
0:22:08 > 0:22:12Even though the sun is below the horizon, the clouds are shining away
0:22:12 > 0:22:15at night, which is why they're called night shining clouds.
0:22:15 > 0:22:18That's what noctilucent means.
0:22:18 > 0:22:22- From what I've seen, they can change as well.- They are amazing.
0:22:22 > 0:22:24I've seen loads of noctilucent clouds here.
0:22:24 > 0:22:29They sort of glow with an eerie electric blue.
0:22:29 > 0:22:32That's the best way of describing them.
0:22:32 > 0:22:36They look like a sort of network, a fine detailed network of clouds.
0:22:36 > 0:22:40The way to look for them is to wait for the sun to go down,
0:22:40 > 0:22:44a couple of hours after sunset, look in the north-west and if you can
0:22:44 > 0:22:49see some glowy clouds, keep an eye on them, they could be noctilucent.
0:22:49 > 0:22:54Also in the morning, a few hours before the sun comes up in the north-east.
0:22:54 > 0:22:58If you get a really bright display, as we have had a few years back,
0:22:58 > 0:23:00they will persist all the way through the night.
0:23:00 > 0:23:04They're on the edge of the twilight glow you can see to the north.
0:23:04 > 0:23:11- I'll hopefully get to see some this season.- Another thing is they're very photogenic.
0:23:11 > 0:23:16There are lots of beautiful photos to see on our Flickr site.
0:23:16 > 0:23:21If you don't know the address, you can go on to:
0:23:21 > 0:23:24The details are on there.
0:23:24 > 0:23:28If you get any photos of them, and they could occur at any time
0:23:28 > 0:23:33from late May through to early August, then do send them in.
0:23:33 > 0:23:36We also have another interesting event on July 15th.
0:23:36 > 0:23:41This is the occultation of Jupiter by the moon. It's not visible everywhere though.
0:23:41 > 0:23:45This is actually quite an interesting event.
0:23:45 > 0:23:50Jupiter will pass really close to the northern edge of the moon.
0:23:50 > 0:23:52Right down in the south-east is the best view.
0:23:52 > 0:23:57As you move up the country, you start to see less covering Jupiter.
0:23:57 > 0:24:01In the Midlands, it's what's known as a grazing occultation.
0:24:01 > 0:24:06Jupiter will appear to just pass over the top.
0:24:06 > 0:24:10You can catch Jupiter passing the mountains and valleys on the edge of the moon.
0:24:10 > 0:24:12That would make a lovely shot.
0:24:12 > 0:24:15Start observing from about 2:30 BST onwards.
0:24:15 > 0:24:21I hope it's a lot warmer than it is now. It can't be cloudy for all of these events.
0:24:21 > 0:24:24- Hope we get something interesting. - Definitely.
0:24:29 > 0:24:32Let's begin our News Notes with Mars.
0:24:32 > 0:24:36And there's an amazing probe, Opportunity, starting up again.
0:24:36 > 0:24:42It's had eight years on the surface of Mars, but for the Martian winter, it's been stationary.
0:24:42 > 0:24:47There isn't enough solar power in northern winter to give it enough power to drive its wheels.
0:24:47 > 0:24:50But it's now started moving again.
0:24:50 > 0:24:53It'll continue its journey around the rim of Endeavour Crater,
0:24:53 > 0:24:56which is a much larger crater than it's been to before.
0:24:56 > 0:24:59And the terrain there is much older. That's why it's there.
0:24:59 > 0:25:03It did this massive trek across the surface to get to this point,
0:25:03 > 0:25:07so we could read off billions of years of Martian history.
0:25:07 > 0:25:10Before it went into its shutdown, it found a place
0:25:10 > 0:25:14called Homestake, which had this bright material on the surface.
0:25:14 > 0:25:19Turned out to be gypsum, which we know was deposited in reasonably warm water.
0:25:19 > 0:25:23This was a lake or a sea, probably a nice temperature to go swimming in.
0:25:23 > 0:25:29We now know that this was last underwater billions of years ago.
0:25:29 > 0:25:33We're really getting to ancient Martian history.
0:25:33 > 0:25:36Next, in the long term, Opportunity will continue its exploration
0:25:36 > 0:25:42of the crater, working its way around the edge. Probably too steep to go in at any point.
0:25:42 > 0:25:46Its immediate objective is more of this gypsum that's nearby.
0:25:46 > 0:25:50We can see if Homestake was unusual or whether we need to go elsewhere.
0:25:50 > 0:25:54How long will it last? We still don't know.
0:25:54 > 0:25:58We come to Vesta, the brightest of the four largest asteroids.
0:25:58 > 0:26:02Visited at the minute by the Dawn spacecraft,
0:26:02 > 0:26:05which has just been given a few extra months at Vesta
0:26:05 > 0:26:08to finish exploring this wonderful little world.
0:26:08 > 0:26:11There's some fabulous movies that have been put together.
0:26:11 > 0:26:15These are computer animations but with real data from Dawn.
0:26:15 > 0:26:20- They're spectacular.- They're showing us the grooves around Vesta.
0:26:20 > 0:26:24We're not sure how they were created. Something to do with its violent past.
0:26:24 > 0:26:29It's clear from the shape, it's got an enormous impact basin near its south pole.
0:26:29 > 0:26:33We know that impact basin is relatively young,
0:26:33 > 0:26:36a couple of billion years.
0:26:36 > 0:26:39And mapping the surface of Vesta.
0:26:39 > 0:26:43Its southern hemisphere is different to its northern hemisphere.
0:26:43 > 0:26:46Dawn is going to be there until August this year,
0:26:46 > 0:26:49before it moves on its way to Ceres.
0:26:49 > 0:26:54- The most famous feature that Dawn's seen so far is the Snowman.- Oh, yes!
0:26:54 > 0:26:58This is over the middle of those craters that make up the Snowman.
0:26:58 > 0:27:01This gives you a real sense of the terrain of Vesta,
0:27:01 > 0:27:04what it would be like to be wandering across the surface.
0:27:04 > 0:27:09- I'd love to try! - We have to finish News Notes with at least one beautiful picture.
0:27:09 > 0:27:14My favourite this month is from the European Southern Observatory
0:27:14 > 0:27:17at La Silla in Chile.
0:27:17 > 0:27:21This image of Centaurus A. A nearby active galaxy.
0:27:21 > 0:27:24You can see the dust disc warped in the centre.
0:27:24 > 0:27:26And then the galaxy extending out
0:27:26 > 0:27:28and it's just an absolutely stunning image.
0:27:28 > 0:27:32Centaurus A one of the most fascinating galaxies in our local neighbourhood.
0:27:32 > 0:27:34It's 13 million light years away.
0:27:34 > 0:27:38It's got a massive black hole in its centre with jets coming out of it.
0:27:38 > 0:27:41In the top left, you can see some filaments of gas
0:27:41 > 0:27:44which are linked to those jets of material
0:27:44 > 0:27:48we see normally in X rays and radio waves.
0:27:48 > 0:27:52Centaurus A in the past has swallowed up another galaxy.
0:27:52 > 0:27:54It's been a cannibal.
0:27:54 > 0:27:57That's what the warped disc in the centre is,
0:27:57 > 0:28:00the remains of this smaller galaxy that got swallowed up.
0:28:00 > 0:28:06- Pity we can't see it from here. - Yes, but we can enjoy the image.
0:28:06 > 0:28:08We can do. And here it is.
0:28:10 > 0:28:12There's so much we're learning.
0:28:12 > 0:28:15Chris and Chris, thank you very much.
0:28:15 > 0:28:21Next month, we're going to talk about the inner solar system and of course the Transit of Venus.
0:28:21 > 0:28:24Until then, good night.
0:28:33 > 0:28:37Subtitles by Red Bee Media Ltd