0:00:27 > 0:00:29Good evening.
0:00:29 > 0:00:31For this programme we're going to go right out
0:00:31 > 0:00:33to the edge of our known solar system.
0:00:33 > 0:00:38Beyond Jupiter and Saturn there are two more giant planets -
0:00:38 > 0:00:41Uranus
0:00:41 > 0:00:43and Neptune.
0:00:43 > 0:00:46We call them the ice giants because they're
0:00:46 > 0:00:49very different from the two gas giants, Jupiter and Saturn.
0:00:49 > 0:00:52With me, two experts, both from Oxford.
0:00:52 > 0:00:55Dr Leigh Fletcher and Chris Lintott.
0:00:55 > 0:00:57Can I ask you, Leigh, so what are the main
0:00:57 > 0:01:01differences between the ice giants and the gas giants?
0:01:01 > 0:01:04In fact, we knew very little about the ice giants before Voyager 2
0:01:04 > 0:01:06flew past in the late 1980s.
0:01:06 > 0:01:10Voyager flew past Uranus and saw a greenish disc with very little
0:01:10 > 0:01:12cloud activity taking place over the disc itself.
0:01:12 > 0:01:16It was a really boring planet, let's be honest about this!
0:01:16 > 0:01:18Lots of scientists looked at it and were disappointed -
0:01:18 > 0:01:20we were used to Jupiter and Saturn,
0:01:20 > 0:01:24- and seeing incredible storms and banded systems.- You won't see storms and rings there.
0:01:24 > 0:01:26They happen, you won't see them.
0:01:26 > 0:01:29And in fact that's been revealed in the 25 years since Voyager 2
0:01:29 > 0:01:33that we've got a large data set of Hubble space telescope
0:01:33 > 0:01:36and ground-based observations of Uranus, which show that we simply
0:01:36 > 0:01:38flew past at a rather boring time
0:01:38 > 0:01:42and in fact it's become a lot more active now, with white spots,
0:01:42 > 0:01:45incredible colours around the north pole and the south pole.
0:01:45 > 0:01:49Uranus and Neptune are twins, they are dissimilar twins. Why?
0:01:49 > 0:01:54Voyager 2, when it flew past Uranus, gave us an idea of what we thought and ice giant should be like.
0:01:54 > 0:01:58When we got out to Neptune we realised those ideas were again wrong
0:01:58 > 0:02:01because Neptune has its own source of internal heat.
0:02:01 > 0:02:06It basically emits out more energy that it's receiving from the sun
0:02:06 > 0:02:10and that emission of heat is driving a really complicated weather pattern.
0:02:10 > 0:02:12We see incredible storms,
0:02:12 > 0:02:14such as the great dark spot which was present in Neptune
0:02:14 > 0:02:17when Voyager 2 flew past in 1989.
0:02:17 > 0:02:19But we haven't got that with Uranus.
0:02:19 > 0:02:23Apparently there there's little or no source of internal heat.
0:02:23 > 0:02:25Why not?
0:02:25 > 0:02:28Well, this has got something to do with the dim, distant past
0:02:28 > 0:02:32of our solar system and the way the ice giants formed in the first place.
0:02:32 > 0:02:35Something, back in Uranus's distant history,
0:02:35 > 0:02:39must have changed the planet into its present inclination.
0:02:39 > 0:02:43- Because it's really weird. - It's extremely strange.
0:02:43 > 0:02:48What we should say is that Uranus has been tilted completely on its side.
0:02:48 > 0:02:53Now, the Earth, and Neptune in fact, have a tilt of about 23 degrees.
0:02:53 > 0:02:57- 26 for Neptune.- So if this is the sun and this is the Earth, you're there.
0:02:57 > 0:02:58There you go.
0:02:58 > 0:03:01It means that the planet is rotating like this
0:03:01 > 0:03:05so it suffers from seasons in the same way the Earth does.
0:03:05 > 0:03:07Uranus, on the other hand,
0:03:07 > 0:03:11has got such an extreme tilt that it spends many, many years
0:03:11 > 0:03:13with just one pole of the planet
0:03:13 > 0:03:16facing towards the sun and, in fact, when we flew past
0:03:16 > 0:03:18in 1986, the south pole of Uranus
0:03:18 > 0:03:21was pointing straight back towards the sun.
0:03:21 > 0:03:23What do you mean by the south pole?
0:03:23 > 0:03:28The south pole has been defined by the International Astronomical Union
0:03:28 > 0:03:33- as being the pole which we flew past. - Yeah, so stop being awkward. Another point...- Point taken!
0:03:33 > 0:03:37There's another critical point here, as well. If this is our...
0:03:37 > 0:03:39our Uranus, and the planet's spinning like this,
0:03:39 > 0:03:42all the moons are in line with that axis as well.
0:03:42 > 0:03:45So why do people think this is tilted?
0:03:45 > 0:03:47It can't be, surely?
0:03:47 > 0:03:50Well, one of the most popular theories out there today
0:03:50 > 0:03:53is that something in the past hit Uranus...
0:03:53 > 0:03:57- A large impact.- Some kind of large impact.- Where is it now?
0:03:57 > 0:04:02The impact would have melded the two planets together, such that
0:04:02 > 0:04:05what we see as Uranus today is the agglomeration
0:04:05 > 0:04:07of multiple impacting bodies.
0:04:07 > 0:04:10- You don't sound convinced.- I'm not.
0:04:10 > 0:04:12So how would you tilt your axis?
0:04:12 > 0:04:15Years of planetary migration. Interaction with Uranus
0:04:15 > 0:04:18and the other giants gradually tilted it over.
0:04:18 > 0:04:21Well, during the migrational period, there is a very good chance
0:04:21 > 0:04:24that collisions of this sort were happening.
0:04:24 > 0:04:28In fact, the motions in these planets is causing gravitational instabilities
0:04:28 > 0:04:32and it's flinging material around all over the place.
0:04:32 > 0:04:36I have a silly question, which... You were talking earlier about ice giants, Patrick.
0:04:36 > 0:04:40- But we're not looking at ice, we're looking at gas.- Of course.
0:04:40 > 0:04:44So why do we call them ice giants - why aren't they just gas giants?
0:04:44 > 0:04:47- Cos they're icy!- Well, yes, but where's the ice?
0:04:47 > 0:04:51- It's an important point and it does confuse a lot of people.- Confuses me!
0:04:51 > 0:04:53The reason we call these things ice giants
0:04:53 > 0:04:58is because the material they're actually made of, planetary scientists call ices.
0:04:58 > 0:05:00So things like methane, ammonia, water
0:05:00 > 0:05:03that have condensed to form solids in the outer solar system.
0:05:03 > 0:05:08Now, these have all been incorporated into the interiors of these
0:05:08 > 0:05:11two ice giants, but even then they're not ices
0:05:11 > 0:05:13as you would imagine water ice being.
0:05:13 > 0:05:17If I'd come through the atmosphere and stayed alive,
0:05:17 > 0:05:19would I hit a solid icy surface?
0:05:19 > 0:05:23You won't hit solid surfaces, you'll see these ices are slowly being pressure cooked.
0:05:23 > 0:05:26The pressure is so immense at the centre of these giant planets
0:05:26 > 0:05:29that the ices take on a very alien and exotic form.
0:05:29 > 0:05:32Now, in Jupiter and Saturn it's hydrogen and helium
0:05:32 > 0:05:35which consists of most of the bulk of these planets
0:05:35 > 0:05:39and hydrogen takes on something called a metallic form and this is conducting
0:05:39 > 0:05:43and that's where we believe we get the magnetic field of the giant planets from.
0:05:43 > 0:05:45Now, on Uranus and Neptune,
0:05:45 > 0:05:46there isn't as much hydrogen helium
0:05:46 > 0:05:51cos there simply wasn't as much available in the outer disc when it formed.
0:05:51 > 0:05:54So the thing that gets pressure cooked are these ices
0:05:54 > 0:05:57that you're talking about and those ices that are in a sort of molten,
0:05:57 > 0:05:59fluid state within the interior,
0:05:59 > 0:06:01they are still conducting,
0:06:01 > 0:06:04so Uranus and Neptune do have magnetic fields,
0:06:04 > 0:06:07but even those are extremely odd - tilted and offset.
0:06:07 > 0:06:11- There's a lot that we simply don't know about them. - It occurs to me.
0:06:11 > 0:06:13I mean, we talked about the great dark spot a bit
0:06:13 > 0:06:16and you now tell me that Uranus is interesting again.
0:06:16 > 0:06:20I know I've been abusing Uranus so maybe I should stop being cruel to it.
0:06:20 > 0:06:23So over the last quarter century, Uranus, which was dull and bland
0:06:23 > 0:06:27at the beginning, seems to have taken on a more Neptune-like appearance.
0:06:27 > 0:06:30By that I mean it's become a lot more active.
0:06:30 > 0:06:35So it must now be, what, autumn or spring on different bits of Uranus?
0:06:35 > 0:06:38So the north pole of Uranus is slowly coming into sunlight
0:06:38 > 0:06:41for the first time in 40 years. It takes eight years to go round
0:06:41 > 0:06:44so it's springtime in the northern hemisphere and that means
0:06:44 > 0:06:49suddenly you've got energy being deposited from the sun into Uranus's atmosphere,
0:06:49 > 0:06:52which is triggering all these fantastic weather-like systems.
0:06:52 > 0:06:57And that's why I believe we must ultimately send another space craft back to Uranus
0:06:57 > 0:07:02other than Voyager 2. Voyager 2 flew past so quickly, it gave us just a snapshot
0:07:02 > 0:07:05- of the dynamics... - We want a Uranus orbiter.
0:07:05 > 0:07:07We would love to see something going into orbit around Uranus
0:07:07 > 0:07:10to explore the moons and to explore the rings of Uranus
0:07:10 > 0:07:12and the atmosphere and interior,
0:07:12 > 0:07:17but I think the big step change in our understanding of ice giants in general
0:07:17 > 0:07:21would be if we were to send a probe into Uranus.
0:07:21 > 0:07:23Now, we did this once with Jupiter, back in 1995.
0:07:23 > 0:07:29The Galileo probe went in and sampled the gases and figured out what the chemical make-up of Jupiter was.
0:07:29 > 0:07:31But if we did that for an ice giant as well,
0:07:31 > 0:07:34it would be a wonderful advance for our science.
0:07:34 > 0:07:40Both Uranus and Neptune have rings and satellites, so what about them?
0:07:40 > 0:07:45I think the most interesting out of all of the Uranus and Neptunian moons
0:07:45 > 0:07:49is a moon called Triton. Now, Triton is a big moon in orbit around Neptune.
0:07:49 > 0:07:52- Not a genuine moon, though. - But it's not a genuine moon.
0:07:52 > 0:07:56By that we mean that instead of forming from the same disc that Neptune formed from,
0:07:56 > 0:08:01it looks like it's been captured by Neptune's gravitational pull.
0:08:01 > 0:08:06- We know that cos it's going backwards.- It's going in a different direction to all of the other moons.
0:08:06 > 0:08:07Very like Pluto.
0:08:07 > 0:08:12That's right, in fact, the surfaces of both Pluto and Triton -
0:08:12 > 0:08:15if they did form in the same place, this shouldn't be a surprise -
0:08:15 > 0:08:19they're covered in surfaces of nitrogen and possibly methane
0:08:19 > 0:08:22and carbon monoxide, condensed onto the surface.
0:08:22 > 0:08:24Now, the interesting thing about that
0:08:24 > 0:08:27is that when Pluto and Triton get close to the sun,
0:08:27 > 0:08:29the sun's energy heats them up
0:08:29 > 0:08:32and it causes them to sublimate off - basically they form a gas
0:08:32 > 0:08:38which forms a very, very thin tenuous atmosphere around these moons.
0:08:38 > 0:08:42The last thing to say about Triton is that with Voyager's fly-by,
0:08:42 > 0:08:46we actually saw active geysers on the moon itself,
0:08:46 > 0:08:49and that makes Triton one of the most interesting places
0:08:49 > 0:08:54in our solar system in having some sort of volcanic activity.
0:08:54 > 0:08:57It's a bit like the moon is being flexed by the gravity
0:08:57 > 0:08:59of Neptune, I would assume.
0:08:59 > 0:09:03What they saw with the geysers themselves is that most of them
0:09:03 > 0:09:06were clustered around where the sun's energy was the greatest,
0:09:06 > 0:09:10so it looks like the influence of solar radiation has some effect
0:09:10 > 0:09:12on destabilising the surface,
0:09:12 > 0:09:16and that's why you see these amazing plumes in the old Voyager movies.
0:09:21 > 0:09:25Well, we've come a long way, and thank you both very much.
0:09:25 > 0:09:30Uranus was discovered in 1781 by William Herschel.
0:09:30 > 0:09:34There's a Herschel museum in Bath and Paul Abel went there.
0:09:36 > 0:09:40The Herschel Museum is in the heart of Bath
0:09:40 > 0:09:42and this beautiful Georgian house was once home
0:09:42 > 0:09:45to the great William Herschel and his sister Caroline.
0:09:47 > 0:09:51German-born Herschel arrived in England fleeing the Prussian War.
0:09:51 > 0:09:54He was penniless and made the spa town of Bath his home,
0:09:54 > 0:09:58earning his living teaching young ladies music.
0:09:58 > 0:10:01He brought over his sister Caroline to run his household,
0:10:01 > 0:10:05and together they became two of our greatest astronomers.
0:10:07 > 0:10:10Well, this is Herschel's piano because he was first a musician,
0:10:10 > 0:10:13then he became a rather prominent astronomer, and look at this -
0:10:13 > 0:10:15this is brilliant - a picture of
0:10:15 > 0:10:19the "distinguished men of science of Great Britain living in 1807"
0:10:19 > 0:10:21and there's Herschel, right on the end.
0:10:21 > 0:10:23'Wandering thought the museum,
0:10:23 > 0:10:27'you really feel Herschel's passion for astronomy.
0:10:27 > 0:10:30'These are his original telescope eyepieces.
0:10:30 > 0:10:33'Just think, Herschel would have looked through these
0:10:33 > 0:10:34'to map the night sky.'
0:10:34 > 0:10:37'Herschel also made his own mirrors,
0:10:37 > 0:10:40'striving to improve the magnification
0:10:40 > 0:10:42'so he could see further into the heavens.'
0:10:42 > 0:10:45Well, here we are in Herschel's workshop
0:10:45 > 0:10:47and it's here that he made the telescope mirrors,
0:10:47 > 0:10:50not just for himself, but for other astronomers as well.
0:10:50 > 0:10:53Back then, telescope mirrors were made of metal
0:10:53 > 0:10:56and he'd take the blank, put it in this device and spend
0:10:56 > 0:11:01many, many hours polishing the mirror until it gained the desired shape.
0:11:01 > 0:11:05It's here that he made the telescope mirror for his famous
0:11:05 > 0:11:07seven-foot telescope, which is upstairs.
0:11:07 > 0:11:10The one he used to discover Uranus. So let's go upstairs and take a look.
0:11:12 > 0:11:18Herschel was eventually to become famous for his enormous 40-foot telescope in Slough.
0:11:18 > 0:11:22But in Bath, he had a more modest reflector.
0:11:22 > 0:11:26Here it is, a replica of the seven-foot telescope
0:11:26 > 0:11:29used by Herschel to discover the planet Uranus.
0:11:29 > 0:11:32In doing so, he became the first person in human history
0:11:32 > 0:11:35to discover the existence of another large planet
0:11:35 > 0:11:37far beyond the orbit of Saturn,
0:11:37 > 0:11:40thus opening up the icy depths of the solar system to us.
0:11:40 > 0:11:43With the discovery of Uranus,
0:11:43 > 0:11:47the Herschels became overnight 18th-century celebrities.
0:11:47 > 0:11:50The King and many others came calling.
0:11:50 > 0:11:54Jonathan Hall is one of the resident astronomers helping to promote and preserve
0:11:54 > 0:11:57the work of William and his sister Caroline.
0:11:57 > 0:12:01Back in the 18th century, Herschel's night-time activities
0:12:01 > 0:12:05were viewed by the good people of Bath as unusual.
0:12:05 > 0:12:09His local reputation as being a little bit eccentric
0:12:09 > 0:12:12and very keen on the sciences and mathematics and optics.
0:12:12 > 0:12:15He would set his early telescopes up in the street
0:12:15 > 0:12:19and the horse and carriages were obliged to go round him.
0:12:19 > 0:12:23He wasn't what today we might think of as a professional scientist.
0:12:23 > 0:12:25He was purely amateur
0:12:25 > 0:12:27and he was building these telescopes
0:12:27 > 0:12:31with the aid of his brother and local craftsmen
0:12:31 > 0:12:33to arguably the best standard of the time.
0:12:33 > 0:12:35And he made mirrors for other people as well,
0:12:35 > 0:12:38- many other prominent astronomers. - He did indeed. Yes.
0:12:38 > 0:12:40Even in his youth,
0:12:40 > 0:12:43he started to read books on astronomy,
0:12:43 > 0:12:45read books on optics.
0:12:45 > 0:12:47He'd been teaching himself a little bit of Greek.
0:12:47 > 0:12:49He taught himself Italian and Latin,
0:12:49 > 0:12:51partly because of his music interests as well.
0:12:51 > 0:12:55- So much self-taught. - Incredible, yes. Very tenacious.
0:12:55 > 0:12:57But it was really when he came to Bath
0:12:57 > 0:12:59that it really started to take off.
0:12:59 > 0:13:04This is how the night sky would have looked on March 13th 1781.
0:13:04 > 0:13:08In the constellation of Gemini, there was an object, which other
0:13:08 > 0:13:13eminent astronomers such as Flamsteed and even Galileo had overlooked.
0:13:13 > 0:13:18Herschel immediately knew that this was something special.
0:13:18 > 0:13:21He wasn't actually looking for a planet.
0:13:21 > 0:13:23He'd only just moved back into the house.
0:13:23 > 0:13:25They'd been in a previous property.
0:13:25 > 0:13:28In fact, rather unusually, he was on his own.
0:13:28 > 0:13:31- Because Caroline normally observed with him.- Absolutely.
0:13:31 > 0:13:33He set the telescope up here in the garden
0:13:33 > 0:13:37doing the systematic review of the heavens and there trained it on
0:13:37 > 0:13:40the constellation of Gemini and that's where he made the discovery.
0:13:40 > 0:13:43- And that brand-new world needed to be named.- It did indeed.
0:13:43 > 0:13:47- For a long time, people wanted to call it Herschel.- Yes.
0:13:47 > 0:13:50He wanted to name it after his patron, King George III.
0:13:50 > 0:13:51In a lot of the old texts,
0:13:51 > 0:13:54you can find it listed as Georgium sidus for George's star.
0:13:54 > 0:13:55That's right.
0:13:55 > 0:13:58Herschel, of course, was no fool.
0:13:58 > 0:14:02Patronage in those days was immensely important.
0:14:02 > 0:14:05The other link, of course, is that King George III,
0:14:05 > 0:14:08part of the Hanoverian Empire.
0:14:08 > 0:14:10Herschel was from Hanover.
0:14:10 > 0:14:12So, as part of the patronage,
0:14:12 > 0:14:14the King created a brand-new post for him.
0:14:14 > 0:14:19He had to leave his life here in Bath
0:14:19 > 0:14:22so he could be at the beck and call of the King and the Royal Family
0:14:22 > 0:14:27to be able to go and show them the wonders of the heavens.
0:14:27 > 0:14:29It's remarkable, over the two or three years
0:14:29 > 0:14:33immediately following the discovery, all the eminent people
0:14:33 > 0:14:36from around the world and Europe, who would come and pay homage
0:14:36 > 0:14:40and their respects and want to look through a Herschelian telescope.
0:14:42 > 0:14:44The planet was eventually named Uranus,
0:14:44 > 0:14:48which in Greek mythology is the father of Saturn.
0:14:48 > 0:14:50It's in our night sky at the moment
0:14:50 > 0:14:53in the constellation of Pisces, the fishes.
0:14:53 > 0:14:55It took some time to find it,
0:14:55 > 0:14:58but I made this drawing of it the other night.
0:14:58 > 0:15:02Herschel discovered this strange world over 200 years ago.
0:15:02 > 0:15:04It changed his life for ever and guaranteed him
0:15:04 > 0:15:07a place in astronomical history.
0:15:11 > 0:15:15The Herschel Museum, well worth a visit if you are in Bath.
0:15:15 > 0:15:17Herschel always makes me think of you,
0:15:17 > 0:15:20because he was a musician and an astronomer as well.
0:15:20 > 0:15:22You've played some of Herschel's music?
0:15:22 > 0:15:26I'm a very amateur musician. I've never had a lesson in my life.
0:15:26 > 0:15:29But I borrowed some of Herschel's music once
0:15:29 > 0:15:32and played it live on the piano.
0:15:32 > 0:15:33Was it any good?
0:15:33 > 0:15:37- His music is!- I wasn't asking about your piano playing!
0:15:37 > 0:15:38I got through it.
0:15:38 > 0:15:40GENTLE PIANO MUSIC
0:15:56 > 0:15:58We've come a long way now,
0:15:58 > 0:16:01so let's go even further out of the solar system
0:16:01 > 0:16:03and come to the Kuiper Belt,
0:16:03 > 0:16:07from which the best-known member is of course Pluto.
0:16:07 > 0:16:11Pluto is a very similar object to Triton,
0:16:11 > 0:16:13in that, it has, over the surface,
0:16:13 > 0:16:17ices of things like nitrogen and carbon monoxide,
0:16:17 > 0:16:21that over the course of Pluto's extremely long orbit around the sun,
0:16:21 > 0:16:24will sublimate off to form a kind of atmosphere.
0:16:24 > 0:16:26When it was discovered, by my old friend Clyde Tombaugh,
0:16:26 > 0:16:30it was thought to be at least the size of Mars, probably larger,
0:16:30 > 0:16:32and therefore of planetary status.
0:16:32 > 0:16:35So we regarded it as a planet
0:16:35 > 0:16:37and it has been demoted.
0:16:37 > 0:16:40It's been demoted, that's true,
0:16:40 > 0:16:42but I'm not sure it's particularly because
0:16:42 > 0:16:44Pluto's smaller than we thought -
0:16:44 > 0:16:46though it is, it's smaller than Mercury.
0:16:46 > 0:16:50- But it's more that we've found lots of other things this size. - It's not the only one.- No.
0:16:50 > 0:16:52So we have the choice of having eight planets,
0:16:52 > 0:16:55as we do, from Mercury out to Neptune,
0:16:55 > 0:16:56or many, many, many planets.
0:16:56 > 0:16:58And we call those the Kuiper Belt -
0:16:58 > 0:17:02Pluto and Pluto-like objects on one part of it.
0:17:02 > 0:17:05Of course, the most exciting thing about Pluto
0:17:05 > 0:17:07is that's there's a spacecraft on the way, New Horizons,
0:17:07 > 0:17:10which was planned - not that it matters -
0:17:10 > 0:17:12but it was planned while Pluto was still a planet,
0:17:12 > 0:17:14and a big part of their pitch
0:17:14 > 0:17:17- was this was the last planet that we haven't seen.- Quite.
0:17:17 > 0:17:20But where's New Horizons got to now? It's a few years away yet.
0:17:20 > 0:17:22So it's still on its way to Pluto,
0:17:22 > 0:17:24it's going to get there in July of 2015
0:17:24 > 0:17:27and it's just got past the orbit of Uranus.
0:17:27 > 0:17:29That doesn't mean it visited Uranus,
0:17:29 > 0:17:32but it's on its way to do a slingshot by Pluto.
0:17:32 > 0:17:33And after Pluto,
0:17:33 > 0:17:36it's going to go on to look at another Kuiper Belt object.
0:17:36 > 0:17:38- Which hasn't been discovered yet.- No.
0:17:38 > 0:17:41It's something that we're still looking for at the moment.
0:17:41 > 0:17:44Pluto is the brightest member of the Kuiper Belt,
0:17:44 > 0:17:47it's certainly nothing more than that.
0:17:47 > 0:17:51Recently there was a big conference in France about these things
0:17:51 > 0:17:54and Dr Chris North went there
0:17:54 > 0:17:57and brings us back news from the Kuiper Belt.
0:17:57 > 0:18:01This year's annual gathering of planetary scientists in Nantes
0:18:01 > 0:18:03was the largest for many years.
0:18:03 > 0:18:05For space scientists,
0:18:05 > 0:18:07it's a great place to talk about missions to the planets,
0:18:07 > 0:18:09and for the astronomers,
0:18:09 > 0:18:11a platform to launch their new ideas.
0:18:11 > 0:18:14This year, the icy, dark depths
0:18:14 > 0:18:17of our solar system have caused a bit of a stir.
0:18:20 > 0:18:23The Kuiper Belt stretches beyond Neptune
0:18:23 > 0:18:27and has previously been dismissed as the dustbin of the solar system,
0:18:27 > 0:18:29the leftovers of its formation.
0:18:30 > 0:18:33Meg Schwamb has been raking through the rubbish,
0:18:33 > 0:18:35to find clues about the Kuiper Belt and its formation.
0:18:38 > 0:18:42We now know that there are lots of exotic objects out there.
0:18:42 > 0:18:44They come in a range of sizes
0:18:44 > 0:18:47and some, such as Pluto, even have moons.
0:18:47 > 0:18:51While many formed in these icy outer depths,
0:18:51 > 0:18:52others formed closer in
0:18:52 > 0:18:56and were flung out there by the movement of the giant planets.
0:18:57 > 0:18:59The Kuiper Belt really is
0:18:59 > 0:19:01the icy remnants left over from planet formation.
0:19:01 > 0:19:04You can think of it as the embryos and the failed planets
0:19:04 > 0:19:07that didn't form into the terrestrial planets
0:19:07 > 0:19:09or the cores of the giant planets
0:19:09 > 0:19:11and have been scattered out, or may have formed out,
0:19:11 > 0:19:13in orbits beyond Neptune.
0:19:13 > 0:19:17And so Pluto is one of the well-known and largest of these objects
0:19:17 > 0:19:21and there are now many Pluto-sized bodies known in this region,
0:19:21 > 0:19:24as well as many hundreds of thousands of other smaller bodies
0:19:24 > 0:19:27that orbit well beyond Neptune.
0:19:27 > 0:19:32In 2007, Meg discovered an object nicknamed Snow White,
0:19:32 > 0:19:34one of the largest Kuiper Belt objects
0:19:34 > 0:19:36at around half the size of Pluto.
0:19:36 > 0:19:40Despite its name, Snow White is actually red.
0:19:40 > 0:19:44The colour is caused by a tarry gloop called tholins,
0:19:44 > 0:19:46a term coined by Carl Sagan.
0:19:46 > 0:19:50We think tholins are methane and other chemicals
0:19:50 > 0:19:53broken down by weak sunlight over billions of years.
0:19:55 > 0:19:59I don't think we've quite touched tholins in the outer solar system,
0:19:59 > 0:20:04but we think that if you take these methane ices and nitrogen ices
0:20:04 > 0:20:06and you keep radiating the methane,
0:20:06 > 0:20:08you get a higher and higher order of hydrocarbons,
0:20:08 > 0:20:10and so you get more gunk and tar.
0:20:10 > 0:20:12And so, that's what we think it is
0:20:12 > 0:20:14and we think it's reddened their surface.
0:20:14 > 0:20:18And so it's sort of this red crust, or radiation crust,
0:20:18 > 0:20:19sitting on the surface.
0:20:19 > 0:20:21- It's goo. - It's goo, it's sort of, yeah...
0:20:21 > 0:20:24- It comes from the Greek word for muddy, I believe.- Yes.
0:20:24 > 0:20:28Kuiper Belt objects are the preserved remnants of our early solar system
0:20:28 > 0:20:31and they tell us what is was like billions of years ago
0:20:31 > 0:20:32when the planets were forming.
0:20:32 > 0:20:35But studying it can be very frustrating,
0:20:35 > 0:20:38as the objects are so small and so very far away.
0:20:38 > 0:20:40Occasionally, however,
0:20:40 > 0:20:44we get visitors from the outer limits - comets.
0:20:47 > 0:20:51'Mike Ahern has led one of the most successful mission to not one,
0:20:51 > 0:20:52'but two comets.
0:20:52 > 0:20:55'In July 2005,'
0:20:55 > 0:20:59part of the Deep Impact probe was smashed into Comet Tempel 1,
0:20:59 > 0:21:02giving our first view of material from inside a comet.
0:21:02 > 0:21:05Following this successful mission,
0:21:05 > 0:21:07the Deep Impact spacecraft was re-routed
0:21:07 > 0:21:09and in November 2010,
0:21:09 > 0:21:11flew past Comet Hartley 2
0:21:11 > 0:21:13where it saw a very different world.
0:21:13 > 0:21:14Every comet we've visited
0:21:14 > 0:21:16has been very different
0:21:16 > 0:21:21from what we would have predicted from the previous one we visited.
0:21:21 > 0:21:23So that's the reason for going to multiple ones -
0:21:23 > 0:21:25to try to find a pattern.
0:21:25 > 0:21:28One difference between Tempel 1 and Hartley 2,
0:21:28 > 0:21:30the two that Deep Impact spacecraft visited,
0:21:30 > 0:21:32is they're very different sizes
0:21:32 > 0:21:35and very different activity for their size.
0:21:35 > 0:21:39On Tempel 1 we saw differences in the outgassing
0:21:39 > 0:21:42from different parts of the comet.
0:21:42 > 0:21:44Now, does this mean different parts of the comet
0:21:44 > 0:21:47came from different parts of the proto-planetary disc?
0:21:47 > 0:21:48It was hard to tell...
0:21:48 > 0:21:51- Because they're made of different stuff.- Yeah.
0:21:51 > 0:21:54But there could be still strong seasonal effects on Tempel 1.
0:21:54 > 0:21:57Now, at Hartley 2, it's in this excited state rotation
0:21:57 > 0:22:00where in addition to going around like this, it rolls.
0:22:00 > 0:22:02So everything gets illuminated all the time
0:22:02 > 0:22:04and there are no strong seasonal effects.
0:22:04 > 0:22:06And we still see big differences
0:22:06 > 0:22:08between the outgassing at the two ends,
0:22:08 > 0:22:10which says that they really must have come,
0:22:10 > 0:22:14in the early solar system, from different distances from the sun.
0:22:14 > 0:22:16- So they are different? - They really are different.
0:22:17 > 0:22:20Comets, the archaeological remains of our early solar system,
0:22:20 > 0:22:22will help us understand
0:22:22 > 0:22:24how the planet Earth became such a unique world.
0:22:24 > 0:22:27It's important, because, for one thing,
0:22:27 > 0:22:29we think the comets bring all the water to Earth,
0:22:29 > 0:22:31or at least some of us have thought that all along.
0:22:31 > 0:22:36Is that just because Earth's the only planet we know with standing water...
0:22:36 > 0:22:39- That's correct.- ..on its surface. - Yes.- And the early Earth,
0:22:39 > 0:22:41- that should have all boiled off. - Exactly.
0:22:41 > 0:22:45- So where did it come from? - So it has to have been brought in at a somewhat later stage -
0:22:45 > 0:22:49- only half a billion years after the formation, but...- A long time ago.
0:22:51 > 0:22:54The Kuiper Belt is clearly not the dustbin of the solar system
0:22:54 > 0:22:58and the exotic objects that live there are far more than just rubbish
0:22:58 > 0:23:00thrown out during its formation.
0:23:00 > 0:23:04Instead, each one is a fascinating world
0:23:04 > 0:23:06and the more we find out about them,
0:23:06 > 0:23:09the more we find out about our own origins.
0:23:10 > 0:23:12Plenty of news this month
0:23:12 > 0:23:15so we'll go now to Chris North and Chris Lintott.
0:23:15 > 0:23:19A huge storm going on on Saturn.
0:23:19 > 0:23:22A huge storm that's been going on for most of the last year.
0:23:22 > 0:23:26It was discovered last December as this white spot,
0:23:26 > 0:23:28which is the form storms on Saturn normally take,
0:23:28 > 0:23:32but this one spread out until it covered quite a lot of the disc.
0:23:32 > 0:23:35- Huge.- You can see it in these new images that we just got from Cassini
0:23:35 > 0:23:37that were taken over the last year.
0:23:37 > 0:23:39Of course, the amateurs saw this as well.
0:23:39 > 0:23:42Then they saw the storm fade over time
0:23:42 > 0:23:44and it seemed like all was quiet on Saturn.
0:23:44 > 0:23:46But if you talk to the professionals who can use
0:23:46 > 0:23:49some really big telescopes and they can look in the infrared,
0:23:49 > 0:23:52they see that actually what's happened is up in the top
0:23:52 > 0:23:56of Saturn's atmosphere, in what would be the stratosphere,
0:23:56 > 0:23:58there's still a lot going on.
0:23:58 > 0:24:01The storm now covers about a quarter of the disc,
0:24:01 > 0:24:05so all of the northern bit you can see on one side.
0:24:05 > 0:24:07But as it emerges in January, we're going to see
0:24:07 > 0:24:10some interesting things happening
0:24:10 > 0:24:12where this storm was last year.
0:24:12 > 0:24:15- I wonder what we'll see. - We'll find out.
0:24:15 > 0:24:19Coming into Jupiter and the second moon there, Europa,
0:24:19 > 0:24:20interesting news?
0:24:20 > 0:24:23Europa's this moon that's got the very weird terrain.
0:24:23 > 0:24:27We call it chaotic terrain. It was terrain that the Voyager probes and Galileo saw
0:24:27 > 0:24:31covered in cracks and fissures and all sorts.
0:24:31 > 0:24:34- Map-maker's nightmare.- Indeed. Map-maker's complete nightmare.
0:24:34 > 0:24:37What we think is happening still is that that's cracked
0:24:37 > 0:24:42and broken up by the motion of a sub-surface ocean.
0:24:42 > 0:24:45We can compare that to stuff we see on the Earth.
0:24:45 > 0:24:49Some of the features look like things we've seen in Antarctica,
0:24:49 > 0:24:52with a sub-surface sea or lake that's not quite that deep.
0:24:52 > 0:24:53I'm quite excited about this because
0:24:53 > 0:24:57it's been my favourite idea for a mission anywhere in the solar system,
0:24:57 > 0:25:00which is you land on Europa, melt your way through the surface
0:25:00 > 0:25:03and you see something with teeth coming towards you.
0:25:03 > 0:25:07The reason people care about this ocean is
0:25:07 > 0:25:09it's an interesting place to think about life.
0:25:09 > 0:25:10It could well be.
0:25:10 > 0:25:13Life on Earth, we think, started in deep oceans
0:25:13 > 0:25:16without much sunlight, so Europa's a fascinating world.
0:25:16 > 0:25:19They all are. Of course, you can't get away from Mars.
0:25:19 > 0:25:21Always something new there and,
0:25:21 > 0:25:24of course, this new probe Phobos-Grunt.
0:25:24 > 0:25:29Yes, this was a Russian probe that was meant to go to Mars's moon, Phobos,
0:25:29 > 0:25:31collect a sample, bring it back to Earth.
0:25:31 > 0:25:35Unfortunately, it made it into orbit, it's been stuck there.
0:25:35 > 0:25:39It's not sure what will happen, which is very sad.
0:25:39 > 0:25:41The Russians have never had any success there.
0:25:41 > 0:25:45It was incredibly ambitious. That would have been the first sample-return mission,
0:25:45 > 0:25:49BUT we shouldn't forget there's good news for Mars this month as well,
0:25:49 > 0:25:53which is that the American Curiosity rover is successfully on its way.
0:25:53 > 0:25:57Lift off of the Atlas V with Curiosity.
0:25:57 > 0:26:01We're going to find out a huge amount about Mars's past
0:26:01 > 0:26:04and about whether there are the conditions for life there.
0:26:04 > 0:26:07- So I'm really excited about Curiosity.- So far, all goes well.
0:26:07 > 0:26:09We have spacecraft separation.
0:26:09 > 0:26:11APPLAUSE
0:26:11 > 0:26:13One more news item.
0:26:13 > 0:26:15We found a long-lost Sky At Night programme
0:26:15 > 0:26:18on a recording machine and here it is.
0:26:23 > 0:26:25I'm talking about moon bases tonight for two reasons.
0:26:25 > 0:26:28First, because they are very topical
0:26:28 > 0:26:31and we've just shown you one new design study.
0:26:31 > 0:26:34But secondly because I am delighted to have with me
0:26:34 > 0:26:36my old friend Arthur Clarke.
0:26:36 > 0:26:38Arthur, you, of course,
0:26:38 > 0:26:42were forecasting developments of this kind more than 20 years ago.
0:26:42 > 0:26:43Thank you, Pat.
0:26:43 > 0:26:46I'd like to begin with a flashback to the communication satellite
0:26:46 > 0:26:48which you mentioned,
0:26:48 > 0:26:53by showing this illustration which has some sentimental interest to me
0:26:53 > 0:26:57because I displayed this on BBC TV about ten years ago.
0:26:57 > 0:27:00This was undoubtedly the first time that anything
0:27:00 > 0:27:04about communication satellites appeared on TV anywhere in the world.
0:27:04 > 0:27:07So, this is a programme from 1963.
0:27:07 > 0:27:10To put us in context, that was before Apollo.
0:27:10 > 0:27:12Apollo was still in the planning.
0:27:12 > 0:27:17We'd had people into space, but only a few probes whizzing past the moon.
0:27:17 > 0:27:21Arthur C Clarke was predicting not only these communication satellites,
0:27:21 > 0:27:25which were starting to become a reality back then,
0:27:25 > 0:27:29but also was talking about bases on the moon, bases on Mars,
0:27:29 > 0:27:31all incredibly exciting for what we might do
0:27:31 > 0:27:34from then, in the next 20, 30 years.
0:27:34 > 0:27:36I think a great deal has depended there upon
0:27:36 > 0:27:38the question of the lunar atmosphere
0:27:38 > 0:27:41because if the moon had proved to have anything of an atmosphere,
0:27:41 > 0:27:44then the surface dome would have been the answer.
0:27:44 > 0:27:47Do you think that this means that the lunar base
0:27:47 > 0:27:48has got to go underground?
0:27:48 > 0:27:53If it turns out that a meteor bombardment is a serious danger,
0:27:53 > 0:27:56then, undoubtedly, we will have to put our bases underground.
0:27:56 > 0:28:00But I rather hope that the necessity of a lunar underground movement
0:28:00 > 0:28:02does not arise.
0:28:02 > 0:28:04- I hope we can stay on the surface and look at the stars.- So do I.
0:28:04 > 0:28:06He and I were great friends.
0:28:06 > 0:28:09This is one of the few recordings we made together
0:28:09 > 0:28:11that's actually been preserved.
0:28:11 > 0:28:12Yes, it's wonderful.
0:28:12 > 0:28:16If you could have picked one Sky At Night out of those that were lost,
0:28:16 > 0:28:18- this one would have been high on the list.- I would agree.
0:28:18 > 0:28:20You can see more clips
0:28:20 > 0:28:24on the website, which is...
0:28:24 > 0:28:28I'm going to watch it again and dream of Mars bases.
0:28:28 > 0:28:30Thank you both very much indeed.
0:28:30 > 0:28:33When I come back next month, we're going even further
0:28:33 > 0:28:36and look at planets on other stars.
0:28:36 > 0:28:38Until then, good night.
0:28:44 > 0:28:48Subtitles by Red Bee Media Ltd
0:28:48 > 0:28:51E-mail subtitling@bbc.co.uk