0:00:02 > 0:00:05We've been observing the planets with telescopes
0:00:05 > 0:00:09for hundreds of years and sending probes out into space for over 50.
0:00:09 > 0:00:12So you might have thought that our cosmic neighbourhood would be
0:00:12 > 0:00:14pretty well explored. But the truth is,
0:00:14 > 0:00:17we've only just scratched the surface.
0:00:17 > 0:00:21The reality is that most of the Solar System still remains a mystery.
0:00:23 > 0:00:26Once you head out beyond Neptune, you enter a realm that was,
0:00:26 > 0:00:30until recently, almost completely unknown.
0:00:31 > 0:00:35Yet we now know that it's full of extraordinary objects.
0:00:36 > 0:00:39So tonight we're going to explore this unknown area.
0:00:39 > 0:00:43We're going to venture out into this dark zone.
0:01:11 > 0:01:14Since Pluto's relegation to dwarf planet status,
0:01:14 > 0:01:17the planets of the Solar System now end at Neptune.
0:01:17 > 0:01:19And if you think that all the exciting stuff
0:01:19 > 0:01:22happens between there and the Sun, you're totally mistaken.
0:01:22 > 0:01:27We now know that that dark realm beyond Neptune's orbit is filled
0:01:27 > 0:01:30with a vast number of strange icy bodies.
0:01:30 > 0:01:33And, as we've discovered them over the last couple of decades,
0:01:33 > 0:01:36it's become clear that they play a critical role
0:01:36 > 0:01:40in the evolution of the whole Solar System.
0:01:41 > 0:01:44Tonight, from the Observatory at Herstmonceux,
0:01:44 > 0:01:46we'll explore the incredible objects
0:01:46 > 0:01:49that we're finding in the outer Solar System.
0:01:49 > 0:01:51Some are on uniquely baffling orbits,
0:01:51 > 0:01:55while others spin surprisingly rapidly.
0:01:55 > 0:01:59And Marcus du Sautoy investigates the surprising mathematical laws
0:01:59 > 0:02:03that govern these objects, and how they reveal that our Solar System is
0:02:03 > 0:02:08potentially on the brink of catastrophic instability.
0:02:08 > 0:02:11This group of strange new worlds needed a name,
0:02:11 > 0:02:13and we call them the Trans-Neptunian Objects.
0:02:13 > 0:02:17But to understand the role they play in the Solar System,
0:02:17 > 0:02:19you really have to see them in context.
0:02:24 > 0:02:26Let me paint you a picture of our Solar System.
0:02:26 > 0:02:30At the centre, we have our local star, the Sun.
0:02:30 > 0:02:32Then, the inner planets.
0:02:32 > 0:02:34Mercury, Venus,
0:02:34 > 0:02:36Earth, which of course we're on,
0:02:36 > 0:02:39and then, a little beyond, Mars.
0:02:39 > 0:02:42Then we move on to the outer planets.
0:02:42 > 0:02:44Jupiter, Saturn.
0:02:44 > 0:02:47Over here is Uranus.
0:02:47 > 0:02:50And way over here is Neptune.
0:02:50 > 0:02:534.5 billion kilometres away from the sun.
0:02:53 > 0:02:56Now, the images of the planets aren't drawn to scale,
0:02:56 > 0:03:00but the distances from the Sun are about proportional.
0:03:00 > 0:03:03Except this isn't the outer edge.
0:03:03 > 0:03:05Not by a long way.
0:03:08 > 0:03:12Because beyond is the realm of the Trans-Neptunian Objects.
0:03:14 > 0:03:16Most are in a region called the Kuiper Belt.
0:03:18 > 0:03:20Pluto, for instance, is here.
0:03:21 > 0:03:24One called Haumea is here.
0:03:25 > 0:03:27Another, called Eris, sits here.
0:03:28 > 0:03:30And some are even further out,
0:03:30 > 0:03:34or in strange orbits outside the plane of the Solar System.
0:03:36 > 0:03:38The Kuiper Belt alone is huge,
0:03:38 > 0:03:41some 16 billion kilometres wide.
0:03:42 > 0:03:46It forms a flat disc, lying in the same plane as the planets.
0:03:47 > 0:03:51And within it are hundreds of thousands of new objects,
0:03:51 > 0:03:53maybe millions.
0:03:55 > 0:03:59Trans-Neptunian Object hunter Michelle Bannister has been using
0:03:59 > 0:04:02some of the most powerful telescopes in the world
0:04:02 > 0:04:04to search through this dark zone.
0:04:04 > 0:04:07She tells Chris about some of her most exciting discoveries.
0:04:09 > 0:04:12Well, the outer Solar System is a fascinating and interesting place,
0:04:12 > 0:04:14but what's been found recently?
0:04:14 > 0:04:18Well, we've just wrapped up one of the largest surveys ever made
0:04:18 > 0:04:21of the outer Solar System, and we've been able to double the number
0:04:21 > 0:04:25of Trans-Neptunian objects orbiting outside Neptune, that are known,
0:04:25 > 0:04:27that have really well understood orbits.
0:04:27 > 0:04:31We've been able to discover more than 800 icy worlds,
0:04:31 > 0:04:35little objects about 50 to maybe 300 or so kilometres in size,
0:04:35 > 0:04:38most of them, that orbit beyond Neptune.
0:04:38 > 0:04:40These are leftover pieces, planetesimals,
0:04:40 > 0:04:43from the formation and evolution of the giant planets.
0:04:43 > 0:04:44Just very excited, I've got
0:04:44 > 0:04:47a picture of one of your discoveries here.
0:04:47 > 0:04:51This goes by the delightful moniker of 2015RR245.
0:04:51 > 0:04:56So RR245, it's a lot bigger than some of these others.
0:04:56 > 0:04:58This is bright, this is really bright,
0:04:58 > 0:05:00and when we found it,
0:05:00 > 0:05:02it's moving across the sky over three hours
0:05:02 > 0:05:04in these three images you see here,
0:05:04 > 0:05:09really slowly, and because it's bright and slow,
0:05:09 > 0:05:11that means it has to be very far away.
0:05:11 > 0:05:15It turns out it's about 700km across.
0:05:15 > 0:05:18It's one of the 20 largest dwarf objects in the outer Solar System.
0:05:18 > 0:05:21So, what's a world like this actually like? What's it made of?
0:05:21 > 0:05:23What would it be like to be there?
0:05:23 > 0:05:27What you probably would see is a surface of complex ices.
0:05:27 > 0:05:28Definitely water ice.
0:05:28 > 0:05:31On Pluto, we know that water ice makes mountains.
0:05:31 > 0:05:34So here maybe you'd see terraces
0:05:34 > 0:05:36and small mountains of some water ice.
0:05:37 > 0:05:40You'd also see reddish layers on the surface.
0:05:40 > 0:05:45And that's because RR245 is probably large enough that it has
0:05:45 > 0:05:50some of the complex molecules that form on icy surfaces over time,
0:05:50 > 0:05:53from hydrocarbon molecules being bombarded
0:05:53 > 0:05:55by the slow rain of cosmic rays.
0:05:55 > 0:05:58So, I've got a picture of one of my favourites.
0:05:58 > 0:06:00This is an artist's impression of Haumea,
0:06:00 > 0:06:03which is one of the first to be discovered.
0:06:03 > 0:06:05Yes, it was discovered back in 2003,
0:06:05 > 0:06:08and we now know a lot more about this wonderful icy world,
0:06:08 > 0:06:11this is one of the strangest objects in the outer Solar System.
0:06:11 > 0:06:14It's shaped in this elongated way, like a rugby ball,
0:06:14 > 0:06:17cos its spin axis is actually here.
0:06:17 > 0:06:21So it's spinning like this, and it spins every 3.9 hours or so.
0:06:21 > 0:06:23That's really fast. These are big things.
0:06:23 > 0:06:26It's one of the fastest things in the Solar System, spinning, yeah.
0:06:26 > 0:06:29This is spinning so fast that the solid rock itself
0:06:29 > 0:06:33that makes up most of this object is actually flowing out,
0:06:33 > 0:06:35and that gives it this elongated shape.
0:06:35 > 0:06:39- How are they arranged? - Some of them are in a flat disc,
0:06:39 > 0:06:41so they have round orbits that are flat.
0:06:41 > 0:06:44These are probably the ones that have changed the least
0:06:44 > 0:06:47since the formation of the Solar System in the Kuiper Belt.
0:06:47 > 0:06:49Then you have ones where their orbits have been
0:06:49 > 0:06:52dynamically changed, so they're actually excited,
0:06:52 > 0:06:54they have tilted orbits out of the plane of the System.
0:06:54 > 0:06:58Not a whole lot, but, you know, a few tens of degrees.
0:06:58 > 0:07:01What are the big new discoveries still lurking out there?
0:07:01 > 0:07:05There's some fun indications that we could have another dwarf planet
0:07:05 > 0:07:07out beyond Neptune, that we haven't yet found.
0:07:07 > 0:07:09This could be as big as a Mars-sized object,
0:07:09 > 0:07:12and this ties into an object
0:07:12 > 0:07:14that was found about a year and a half ago now,
0:07:14 > 0:07:16by a different survey in Hawaii.
0:07:16 > 0:07:18And this object, it actually orbits perpendicular
0:07:18 > 0:07:21- to the plane of the Solar System. - Oh, is it called Niku?
0:07:21 > 0:07:23- It's called Niku. - OK, I was going to talk to you.
0:07:23 > 0:07:25- There's Niku in all its glory.- Yes!
0:07:25 > 0:07:27I have to say, it doesn't look like much.
0:07:27 > 0:07:29- It's got charisma.- All right, we'll go to the theory.
0:07:29 > 0:07:31There you go, there's the theory.
0:07:31 > 0:07:34We've watched this object move across the sky for several years,
0:07:34 > 0:07:36and therefore able to do the computation of its orbit
0:07:36 > 0:07:38and show this orbit is strange.
0:07:38 > 0:07:41So, this is Jupiter, Saturn, Uranus, Neptune, all in a plane,
0:07:41 > 0:07:43- and the Earth would be in this plane as well.- Right.
0:07:43 > 0:07:47But this object orbits perpendicular to the plane of the Solar System,
0:07:47 > 0:07:51and this is a mechanism that we don't have a clear idea yet
0:07:51 > 0:07:52of how to form orbits like this.
0:07:52 > 0:07:55You can make a comet that goes way out,
0:07:55 > 0:07:58and then comes back in on such a perpendicular orbit,
0:07:58 > 0:08:01but making something that's relatively small and close...
0:08:01 > 0:08:04This dips in amongst the giant planets, and then zips out as far as
0:08:04 > 0:08:08the Kuiper Belt. Except the Kuiper Belt's over here, it's, you know,
0:08:08 > 0:08:10in a nice, relatively even disc.
0:08:10 > 0:08:13Nothing does this in the Kuiper Belt.
0:08:13 > 0:08:16Every time I talk to anyone who studies the outer Solar System,
0:08:16 > 0:08:19I end up with more questions, so I hope you find more things,
0:08:19 > 0:08:21I hope you come back and tell us about them.
0:08:21 > 0:08:22- Thank you very much.- Thank you.
0:08:24 > 0:08:28The more we peer in to this dark zone beyond Neptune,
0:08:28 > 0:08:30the more mysteries we discover.
0:08:33 > 0:08:35For most of astronomical history,
0:08:35 > 0:08:38these Trans-Neptunian Objects have been hidden
0:08:38 > 0:08:40from even the most powerful telescopes,
0:08:40 > 0:08:43and that's why they've never got the attention they really deserve.
0:08:43 > 0:08:46But these days, are they so impossible to spot?
0:08:46 > 0:08:49To find out, we set Pete Lawrence a challenge -
0:08:49 > 0:08:54to try and see a Trans-Neptunian Object using amateur equipment.
0:08:59 > 0:09:02I've been given tough challenges on The Sky At Night before,
0:09:02 > 0:09:06but this one has to be up with some of the hardest I've ever had.
0:09:06 > 0:09:11These objects are, after all, tiny, dark and a long, long way away.
0:09:11 > 0:09:14But I've decided to try and observe Haumea.
0:09:15 > 0:09:18The reason I've chosen that particular one
0:09:18 > 0:09:20is that it's really well placed at present.
0:09:20 > 0:09:24It's actually located just between the midpoint,
0:09:24 > 0:09:27or just south of the midpoint between the stars
0:09:27 > 0:09:29Arcturus and Muphrid,
0:09:29 > 0:09:31and both of those stars are in the constellation of Bootes.
0:09:32 > 0:09:36I know the exact position of Haumea because I've looked it up
0:09:36 > 0:09:39on the JPL Horizons Ephemeris Generator.
0:09:39 > 0:09:41That's a free online resource.
0:09:41 > 0:09:45And I can tell you, it's pretty faint, it's about magnitude 17.6,
0:09:45 > 0:09:47which is about 36,000 times fainter
0:09:47 > 0:09:51than the faintest star you can see with the naked eye.
0:09:51 > 0:09:56To attempt this observation, I'm using my 130mm telescope,
0:09:56 > 0:10:01with a DSLR camera and my laptop to process the images.
0:10:04 > 0:10:08We are trying to capture this very close to the June Solstice,
0:10:08 > 0:10:11so the sky is still really bright.
0:10:11 > 0:10:13In fact, the threshold of brightness is too high, really,
0:10:13 > 0:10:16to pick out anything really faint.
0:10:16 > 0:10:19It's a little bit frustrating because I'm confident
0:10:19 > 0:10:22that under darker skies, for instance, later in the year,
0:10:22 > 0:10:24I'd be able to make this work.
0:10:24 > 0:10:28I did have an inkling this was going to happen, so a month ago,
0:10:28 > 0:10:33I did dial into a remote telescope set-up in New Mexico.
0:10:34 > 0:10:37This is a commercially available telescope
0:10:37 > 0:10:39that anyone can book time with on the internet.
0:10:39 > 0:10:43The one I'm using is actually smaller than mine,
0:10:43 > 0:10:47but the skies in New Mexico are fantastically dark.
0:10:47 > 0:10:49And these are the results.
0:10:50 > 0:10:54Well, looking at the New Mexico results, they're much clearer,
0:10:54 > 0:10:58those dark, transparent skies have really worked for us.
0:10:58 > 0:11:02But how am I going to find Haumea amongst all those stars?
0:11:02 > 0:11:04Well, I'm going to use a classic technique
0:11:04 > 0:11:06which is known as the blink method.
0:11:07 > 0:11:09So, the blink method works like this.
0:11:09 > 0:11:13The object I'm looking for will move over a period of days.
0:11:13 > 0:11:16So if I take a picture on one day and then wait a few days,
0:11:16 > 0:11:18take another picture,
0:11:18 > 0:11:21and then I align the stars between those two pictures,
0:11:21 > 0:11:23and then blink between them,
0:11:23 > 0:11:27anything that moves should stand out like a sore thumb.
0:11:28 > 0:11:31This is the same technique that was used in the 1930s
0:11:31 > 0:11:34by Clyde Tombaugh to spot Pluto.
0:11:34 > 0:11:37And these are the images he took over a week
0:11:37 > 0:11:41that eventually revealed Pluto's existence.
0:11:41 > 0:11:44Hopefully, that same technique should work for me.
0:11:46 > 0:11:48And there it is! I can see it,
0:11:48 > 0:11:52I can see the dot moving backwards and forwards.
0:11:52 > 0:11:56Now, that represents the movement of Haumea over six days.
0:11:56 > 0:11:58So the blink method has worked.
0:11:58 > 0:12:01That's incredible, isn't it? I mean, that's an object which is
0:12:01 > 0:12:04just a few hundred kilometres across,
0:12:04 > 0:12:08and about 7.5 billion kilometres away.
0:12:08 > 0:12:09That's amazing!
0:12:10 > 0:12:14If you'd like to try and spot a Trans-Neptunian Object,
0:12:14 > 0:12:17we've put some information about the positions of Haumea,
0:12:17 > 0:12:21Makemake and Niku on our website.
0:12:21 > 0:12:25And please do drop us a line to let us know how you do.
0:12:28 > 0:12:31It's not just our instruments that have improved.
0:12:31 > 0:12:35We now get much more information about objects in deep space
0:12:35 > 0:12:38from missions like New Horizons.
0:12:38 > 0:12:40Three, two, one...
0:12:40 > 0:12:45We have ignition and lift-off of Nasa's New Horizons spacecraft...
0:12:45 > 0:12:50Nasa's space explorer, New Horizons, reached Pluto in 2015,
0:12:50 > 0:12:54and it's still exploring, venturing deeper into the Kuiper Belt.
0:12:56 > 0:13:01It revealed new information about both Pluto and its moon, Charon.
0:13:01 > 0:13:04It found unexpected warmth on Pluto
0:13:04 > 0:13:08and a mysterious dark red area on Charon's North Pole.
0:13:10 > 0:13:14Maggie spoke to New Horizons team member Carly Howett
0:13:14 > 0:13:18from her base in Colorado, for the latest updates on these mysteries,
0:13:18 > 0:13:22and to see where they're going next in this dark zone.
0:13:23 > 0:13:26- Hi, Carly, good to see you again. - Yeah, you, too. Good to be here.
0:13:26 > 0:13:29Now, last time we spoke, it was incredibly exciting,
0:13:29 > 0:13:32because New Horizons had just flown past Pluto.
0:13:32 > 0:13:34So what have been the most exciting findings so far?
0:13:34 > 0:13:38So, I think there's two that really jumped out for me.
0:13:38 > 0:13:40One is actually to do with Charon.
0:13:40 > 0:13:42So, Charon, of course, is Pluto's biggest moon.
0:13:42 > 0:13:45It's most of the same size as Pluto,
0:13:45 > 0:13:48it's very large indeed, compared to its orbital parent body,
0:13:48 > 0:13:50and so we didn't know it had a red pole.
0:13:50 > 0:13:53And so there was a lot of work that's gone into
0:13:53 > 0:13:55trying to understand what's going on.
0:13:55 > 0:13:58And now, after two years of analysis,
0:13:58 > 0:14:02Carly's team think they finally have an answer.
0:14:02 > 0:14:05Charon is stealing Pluto's atmosphere,
0:14:05 > 0:14:10which is freezing at its poles, then turning slowly red.
0:14:10 > 0:14:14So, we think that Charon's poles are red because they're sort of nabbing
0:14:14 > 0:14:17some of Pluto's atmosphere as it's being lost,
0:14:17 > 0:14:19which I think is phenomenal.
0:14:19 > 0:14:21But this process happens incredibly slowly.
0:14:21 > 0:14:24So, Pluto has a very thin atmosphere,
0:14:24 > 0:14:28and so you end up with about 1.5 millimetres
0:14:28 > 0:14:30- per million Earth years.- Whoa!
0:14:30 > 0:14:34So this process is not something that's happening overnight,
0:14:34 > 0:14:37this is a very, very slow process, and it tells you, really,
0:14:37 > 0:14:39that Charon's surface must be incredibly stable.
0:14:39 > 0:14:42There's not an overturning, there's not a change in the surface,
0:14:42 > 0:14:44because otherwise that reddening couldn't have happened.
0:14:44 > 0:14:47But there's also talk that Pluto has a heat source.
0:14:47 > 0:14:48Has that been confirmed?
0:14:48 > 0:14:51The origins of that is that there's these shapes
0:14:51 > 0:14:52that have very discrete boundaries,
0:14:52 > 0:14:55and what we think is, they're like lava lamps,
0:14:55 > 0:14:57so they're getting heated from the bottom,
0:14:57 > 0:15:00slowly the material is rising up, and then falling back down again.
0:15:00 > 0:15:01Now, there's two ideas,
0:15:01 > 0:15:04one is that the energy source from that is from the interior
0:15:04 > 0:15:06and it's leftover radioactive decay.
0:15:06 > 0:15:09If it's radioactivity, wouldn't it have decayed long ago?
0:15:09 > 0:15:12So, we think that, actually, there's enough remnant radiation,
0:15:12 > 0:15:15because you just don't need enough, you just need a little bit.
0:15:15 > 0:15:18We're still trying to figure out whether it's just purely sunlight,
0:15:18 > 0:15:21whether sunlight's enough to drive it, or whether we do need
0:15:21 > 0:15:25to sort of invoke extra radiation, um...sort of a superpower
0:15:25 > 0:15:28for Pluto, for radiation to allow this convection to happen.
0:15:28 > 0:15:31But we certainly don't need a lot of heat for it to happen,
0:15:31 > 0:15:33a few degrees is all that's needed.
0:15:33 > 0:15:35We've got all these fantastic results,
0:15:35 > 0:15:36but what's next for New Horizons?
0:15:36 > 0:15:40New Horizons is still busy, we found another target for it to visit.
0:15:40 > 0:15:44It's got a very catchy name of 2014 MU69,
0:15:44 > 0:15:48and this is a very small object
0:15:48 > 0:15:50that's located in the Kuiper Belt.
0:15:50 > 0:15:53We think it's never been heated up, so again, it's this sort of remnant
0:15:53 > 0:15:54of the early Solar System.
0:15:54 > 0:15:57Which is, again, important in order to understand
0:15:57 > 0:16:00our own Solar System formation theory.
0:16:00 > 0:16:01It hasn't been modified since
0:16:01 > 0:16:05basically the dawn of our Solar System, so it's very exciting.
0:16:05 > 0:16:07So, we're observing things en route,
0:16:07 > 0:16:11but our next target we reach on the 1st of January in 2019.
0:16:11 > 0:16:14So, there's going to be quite a lot of scientists that are going to be
0:16:14 > 0:16:18- very sober on New Year's Eve 2018. - THEY LAUGH
0:16:18 > 0:16:21So, Carly, what have we learned from its journey?
0:16:21 > 0:16:23Oh, we've learned so many things.
0:16:23 > 0:16:27I think we've learned that this region of space is not boring,
0:16:27 > 0:16:29it's not dead. Activity is happening,
0:16:29 > 0:16:32there's variation across different targets.
0:16:32 > 0:16:34This is a region of space that really wasn't known
0:16:34 > 0:16:37very much at all, and it's completely revolutionised
0:16:37 > 0:16:39our understanding of these targets.
0:16:39 > 0:16:41Well, Carly, thank you for talking to us again,
0:16:41 > 0:16:44and we look forward to getting the latest results as they come through.
0:16:44 > 0:16:46Thanks for your time.
0:16:48 > 0:16:50Most of the Trans-Neptunian Objects
0:16:50 > 0:16:53are leftovers from the origins of the Solar System.
0:16:54 > 0:16:59This means they contain important clues as to how it evolved.
0:17:01 > 0:17:04Scientists believe they've played a significant part
0:17:04 > 0:17:07in the Solar System's most turbulent period,
0:17:07 > 0:17:11a time when the orbits of the planets changed dramatically,
0:17:11 > 0:17:15and they suggest there's a chance that this might happen again.
0:17:16 > 0:17:20To understand how such relatively small objects
0:17:20 > 0:17:22play such an important role,
0:17:22 > 0:17:24you need a very particular tool...
0:17:24 > 0:17:26mathematics.
0:17:26 > 0:17:28Marcus du Sautoy explains.
0:17:35 > 0:17:38For a mathematician like me, what's so fascinating
0:17:38 > 0:17:40is that the planets, the Moon, the stars, all move
0:17:40 > 0:17:44through the night sky following very strict mathematical rules.
0:17:44 > 0:17:48And this idea is perfectly captured by this thing here.
0:17:48 > 0:17:50It's called an orrery.
0:17:51 > 0:17:56An orrery is a model of the planets revolving around the sun
0:17:56 > 0:18:00that runs on one of the most beautiful mathematical systems,
0:18:00 > 0:18:01clockwork.
0:18:01 > 0:18:06Mathematics describes the clockwork nature of the way the planets move
0:18:06 > 0:18:09around the Sun with such remarkable detail
0:18:09 > 0:18:12that we're able to make predictions about where the planets will be
0:18:12 > 0:18:15into the future with pinpoint accuracy.
0:18:17 > 0:18:20This is because of Newton's theory of gravity -
0:18:20 > 0:18:24a mathematical equation that shows how objects attract each other
0:18:24 > 0:18:26through gravitational force.
0:18:28 > 0:18:32Crucially, this means that as the planets and other objects move,
0:18:32 > 0:18:36they can influence each other in ways that can be very profound.
0:18:36 > 0:18:40Let's suppose this metal ball is a planet orbiting the Sun.
0:18:40 > 0:18:42Let's set it off on its orbit.
0:18:44 > 0:18:45I'm going to use this magnet
0:18:45 > 0:18:48to represent the influence of a second planet.
0:18:48 > 0:18:50So I should be able to give a kick
0:18:50 > 0:18:53to the stable orbit of this first planet.
0:19:00 > 0:19:03There, see, we're starting to influence the orbit
0:19:03 > 0:19:05of the first planet in quite a dramatic way.
0:19:07 > 0:19:11When one object or planet affects another via gravity,
0:19:11 > 0:19:13we call it perturbation,
0:19:13 > 0:19:17and it's an influence which has had a major effect on the Solar System.
0:19:17 > 0:19:21And over the years, we've used the mathematics of perturbation
0:19:21 > 0:19:25to solve some of the great mysteries of the Solar System.
0:19:25 > 0:19:27For instance, in the 19th century,
0:19:27 > 0:19:32the predictions of the position of Uranus were discovered to be wrong.
0:19:33 > 0:19:37And mathematicians guessed this could actually be due
0:19:37 > 0:19:40to another planet perturbing the orbit of Uranus.
0:19:41 > 0:19:44And within 20 years, they found it.
0:19:44 > 0:19:47It was named after the Roman god of the sea,
0:19:47 > 0:19:48Neptune.
0:19:49 > 0:19:51Mathematics doesn't just help us
0:19:51 > 0:19:54to predict where objects will be in the future,
0:19:54 > 0:19:58it also helps us to understand the very structure of the Solar System,
0:19:58 > 0:20:02how it evolved and how it might eventually end.
0:20:03 > 0:20:07And many believe that the Trans-Neptunian Objects
0:20:07 > 0:20:09are evidence of this mathematics at work,
0:20:09 > 0:20:12because of my second mathematical principle -
0:20:12 > 0:20:13resonance.
0:20:16 > 0:20:18This is a Barton pendulum,
0:20:18 > 0:20:21and it shows how, under certain circumstances,
0:20:21 > 0:20:24a regular pattern can powerfully influence another
0:20:24 > 0:20:27through something called resonance.
0:20:27 > 0:20:30I've got a series of pendulums hanging from a string here,
0:20:30 > 0:20:32and I've got a driver pendulum.
0:20:32 > 0:20:34And when I set this off,
0:20:34 > 0:20:37the energy is going to get transferred to the other pendulums,
0:20:37 > 0:20:39but they're not all going to react in the same way.
0:20:39 > 0:20:42LANGUID PIANO MUSIC PLAYS
0:20:44 > 0:20:47What we see is that these two pendulums are swinging much more
0:20:47 > 0:20:51than the others, and this is because they're in resonance.
0:20:52 > 0:20:57Resonance occurs when a pendulum absorbs the momentum easily
0:20:57 > 0:21:00from the driver and relates to its length.
0:21:00 > 0:21:03And some lengths work better than others.
0:21:03 > 0:21:08So, here, the length of the string is the same as the driver,
0:21:08 > 0:21:12and this one is in a 2:3 ratio.
0:21:12 > 0:21:16Amazingly, the same thing can happen with the planets and the moons.
0:21:16 > 0:21:19The gravitational attraction as they orbit means that,
0:21:19 > 0:21:23under certain circumstances, they can begin to resonate.
0:21:23 > 0:21:27So they kind of get locked in, creating a regular pattern.
0:21:29 > 0:21:32For instance, Pluto resonates with Neptune,
0:21:32 > 0:21:36orbiting twice for Neptune's three times.
0:21:37 > 0:21:40And the Trans-Neptunian Objects resonate too.
0:21:42 > 0:21:46Although this resonance seems to create order and balance,
0:21:46 > 0:21:51it's not guaranteed, because, as with any finely balanced object,
0:21:51 > 0:21:54it's easy for it to become destabilised.
0:21:57 > 0:22:00Which brings us on to another mathematical subject
0:22:00 > 0:22:01called chaos theory.
0:22:05 > 0:22:10Roughly speaking, the idea reveals how a small change in the present
0:22:10 > 0:22:13can have dramatic implications for the future.
0:22:13 > 0:22:15Consider this pendulum here.
0:22:15 > 0:22:19If I set it off, then it does exactly what you'd expect it to do.
0:22:22 > 0:22:27If I now add a magnet to the base, then it perturbs the orbit.
0:22:27 > 0:22:30It's still pretty predictable, but it's beginning to wobble.
0:22:31 > 0:22:34But now, if I add two more magnets to the base,
0:22:34 > 0:22:38the orbit becomes wildly unpredictable.
0:22:38 > 0:22:41More accurately, what mathematicians mean by chaos
0:22:41 > 0:22:45is that a small change in the starting position
0:22:45 > 0:22:47can cause a completely different outcome
0:22:47 > 0:22:49for the trajectory of the pendulum.
0:22:53 > 0:22:56What we've come to realise in the last few years
0:22:56 > 0:22:59is that our Solar System has much more in common
0:22:59 > 0:23:02with this chaotic pendulum than we ever imagined.
0:23:04 > 0:23:07Far from being stable and predictable,
0:23:07 > 0:23:10it's actually unstable and chaotic.
0:23:10 > 0:23:15And a small wobble of a tiny object could theoretically change
0:23:15 > 0:23:18the whole structure of the Solar System completely.
0:23:19 > 0:23:22But how about this for a thought?
0:23:22 > 0:23:26Scientists now believe that chaotic disturbances have already played
0:23:26 > 0:23:28a critical role in the history of our Solar System.
0:23:32 > 0:23:36In particular, they suggest there may have been
0:23:36 > 0:23:41a chaotic resonance catastrophe around 4.5 billion years ago.
0:23:42 > 0:23:45As well as messing with the planets,
0:23:45 > 0:23:47this might also finally explain
0:23:47 > 0:23:50the weird orbits, spins and positions
0:23:50 > 0:23:52of the Trans-Neptunian Objects.
0:23:53 > 0:23:55To find out more,
0:23:55 > 0:23:59Chris met up with Marek Kukula of Greenwich Observatory.
0:24:00 > 0:24:01So what's the story?
0:24:01 > 0:24:04What did happen 4.5, 5 billion years ago?
0:24:04 > 0:24:07Well, the most popular model for what might have happened is
0:24:07 > 0:24:09called the Nice model.
0:24:09 > 0:24:11It's named after the Observatoire de la Cote d'Azur,
0:24:11 > 0:24:16down in Nice in France, where the model was first come up with,
0:24:16 > 0:24:18in 2005, I think.
0:24:18 > 0:24:21And the idea here is that the giant planets -
0:24:21 > 0:24:23Jupiter, Saturn, Uranus and Neptune -
0:24:23 > 0:24:28were all in very neat orbits, but closer to the Sun than they are now,
0:24:28 > 0:24:31and beyond them was this very thick, dense Kuiper Belt,
0:24:31 > 0:24:34very different to the one that we have today.
0:24:34 > 0:24:35So, although it looked,
0:24:35 > 0:24:37perhaps from the outside, very neat and stable,
0:24:37 > 0:24:41actually the seeds of its own destruction were already there.
0:24:41 > 0:24:44And what happens is that the giant planets are able to pull in
0:24:44 > 0:24:47the smaller objects from the Kuiper Belt and they flick them inwards.
0:24:47 > 0:24:51But when the small objects start to get into the realm of Jupiter,
0:24:51 > 0:24:53then something a little bit different happens.
0:24:53 > 0:24:55Jupiter, obviously, the most massive planet,
0:24:55 > 0:24:57its gravity is very powerful.
0:24:57 > 0:24:59It's able, actually, to flick these objects
0:24:59 > 0:25:01not further in, but further out,
0:25:01 > 0:25:04it's flicking them perhaps even out of the Solar System entirely.
0:25:04 > 0:25:06And of course, if it's flicking them out,
0:25:06 > 0:25:08it has to move further in.
0:25:08 > 0:25:10So, Saturn, the other giant planets are moving out,
0:25:10 > 0:25:14Jupiter is moving in, and then you get to the situation where we have
0:25:14 > 0:25:18a resonance, where Jupiter is going around the sun twice
0:25:18 > 0:25:21for every one orbit that Saturn makes.
0:25:21 > 0:25:24That resonance is a very powerful situation,
0:25:24 > 0:25:26and that means that, as they do that,
0:25:26 > 0:25:28they're giving very regular gravitational tugs
0:25:28 > 0:25:31to Uranus, to Neptune and to the Kuiper Belt objects.
0:25:31 > 0:25:33So what you get is,
0:25:33 > 0:25:36as Jupiter and Saturn are doing this resonance thing,
0:25:36 > 0:25:40they are pushing Uranus and Neptune further out
0:25:40 > 0:25:43and they've pushed them out into this dense Kuiper Belt.
0:25:43 > 0:25:44That's very chaotic.
0:25:44 > 0:25:47These smaller objects are being thrown in all directions.
0:25:47 > 0:25:49Many of them are being flung into the Solar System,
0:25:49 > 0:25:53and this is where all hell breaks loose.
0:25:53 > 0:25:57This computer simulation shows this moment of resonance,
0:25:57 > 0:25:59followed by chaos.
0:25:59 > 0:26:02The Kuiper Belt is in green and the outer planets are in the centre.
0:26:03 > 0:26:06Suddenly, Jupiter and Saturn wreak havoc,
0:26:06 > 0:26:09and the Kuiper Belt is scattered.
0:26:09 > 0:26:10When that process is finished,
0:26:10 > 0:26:13Uranus and Neptune perhaps swap places.
0:26:13 > 0:26:16They and Saturn have moved further out from the Sun,
0:26:16 > 0:26:19the Kuiper Belt has been scattered in all directions.
0:26:19 > 0:26:22It's now much less dense and much more extensive,
0:26:22 > 0:26:25and this is why we have the Solar System that we have today.
0:26:25 > 0:26:27So, when we think about the chaos
0:26:27 > 0:26:29that still exists in the Solar System,
0:26:29 > 0:26:32the potential for chaos, the fact that things could change,
0:26:32 > 0:26:34what's the worst that could happen?
0:26:34 > 0:26:35Should we be worried?
0:26:35 > 0:26:37Well, perhaps a little bit worried.
0:26:37 > 0:26:40If you look at the Solar System as it is today,
0:26:40 > 0:26:43it does look fairly stable, but in fact that's an illusion.
0:26:43 > 0:26:46And if you look at all of the orbits of the planets, the other objects,
0:26:46 > 0:26:50the Kuiper Belt, the asteroids, it is still rather a chaotic system.
0:26:50 > 0:26:54It turns out that Mercury's orbit is not particularly stable
0:26:54 > 0:26:56and there is a small, perhaps 1% chance,
0:26:56 > 0:27:00that over the next few tens or hundreds of millions of years,
0:27:00 > 0:27:02Jupiter's influence on Mercury could cause it
0:27:02 > 0:27:04either to crash into the Sun,
0:27:04 > 0:27:06to fly out of the Solar System entirely,
0:27:06 > 0:27:10or perhaps even to crash into either Venus or the Earth.
0:27:10 > 0:27:13So, no sign that that's happening, but we can't be certain.
0:27:13 > 0:27:14We can't rule it out.
0:27:14 > 0:27:19It's a small possibility, but it is a real, finite possibility,
0:27:19 > 0:27:24so we're still living in chaotic times, the chaos isn't over yet.
0:27:26 > 0:27:28It seems now that the exploration
0:27:28 > 0:27:31of the weird world of Trans-Neptunian Objects
0:27:31 > 0:27:35is presenting us with a new chaotic picture of our Solar System.
0:27:36 > 0:27:40This is light years away from the stable, predictable one
0:27:40 > 0:27:42we thought we knew before.
0:27:43 > 0:27:47And there's still so much more to explore.
0:27:52 > 0:27:55I'm so impressed by what's being found in the outer Solar System -
0:27:55 > 0:27:58the diversity of worlds, but also their sheer number.
0:27:58 > 0:28:01800 new places in that one survey alone,
0:28:01 > 0:28:03and who knows what else is out there?
0:28:03 > 0:28:05But that's the exciting thing, I think.
0:28:05 > 0:28:07We're discovering new things all the time,
0:28:07 > 0:28:10and by looking at these objects so far away from the Sun,
0:28:10 > 0:28:12we're discovering about the evolution
0:28:12 > 0:28:14of the whole of the Solar System.
0:28:14 > 0:28:16That's all we have time for in this programme,
0:28:16 > 0:28:18but do join us next month
0:28:18 > 0:28:20when we'll be looking at the profound effect
0:28:20 > 0:28:22that space has here on Earth,
0:28:22 > 0:28:26from a deluge of space dust to the beauty of a meteor storm,
0:28:26 > 0:28:28to the potential for life itself.
0:28:28 > 0:28:34And in the meantime, do check out our website at bbc.co.uk/skyatnight,
0:28:34 > 0:28:37where you'll find exclusive content, including a star guide.
0:28:37 > 0:28:40In the meantime, of course, get outside and...
0:28:40 > 0:28:42get looking up.
0:28:42 > 0:28:43Goodnight.