0:00:02 > 0:00:0430 years ago, two astronomers made a remarkable discovery,
0:00:04 > 0:00:07one which would change the way we view the universe for ever.
0:00:07 > 0:00:12A planet outside our solar system, orbiting a distant star -
0:00:12 > 0:00:13an exoplanet.
0:00:15 > 0:00:19Since then, we have found worlds where it rains diamonds,
0:00:19 > 0:00:22ones that boil at 3,000 degrees centigrade
0:00:22 > 0:00:24and even a world with four suns in its sky.
0:00:27 > 0:00:32But the big question is - will we ever find another Earth?
0:00:32 > 0:00:34Welcome to The Sky At Night.
0:01:02 > 0:01:07Our solar system is filled with an incredible variety of planets.
0:01:08 > 0:01:11From small, airless and rocky worlds like Mercury
0:01:11 > 0:01:15to gas giants like Saturn, with its spectacular rings of ice.
0:01:18 > 0:01:24Surely our solar system couldn't be the only one to host such a wonderful variety of worlds?
0:01:27 > 0:01:30And yet, until the 1990s, astronomers hadn't found
0:01:30 > 0:01:33a single planet outside our solar system.
0:01:34 > 0:01:37And then, in 1995, they found it -
0:01:37 > 0:01:39the first really convincing evidence
0:01:39 > 0:01:42for a planet orbiting another star.
0:01:42 > 0:01:44Since then, we've discovered nearly 2,000, and it's involved
0:01:44 > 0:01:47some pretty extraordinary science detective work.
0:01:47 > 0:01:50In fact, we've found so many planets that we've reached
0:01:50 > 0:01:52a remarkable conclusion.
0:01:52 > 0:01:54That almost all the stars in our galaxy
0:01:54 > 0:01:57have their own families of planets.
0:01:57 > 0:01:59It's a really hot topic in astronomy right now.
0:01:59 > 0:02:01We're all desperate to find another Earth.
0:02:01 > 0:02:06Although, as we'll see later, quite what that means is open to question.
0:02:08 > 0:02:10Coming up tonight, we'll be examining some of the latest
0:02:10 > 0:02:16discoveries made here at the Cambridge Exoplanet Research Centre.
0:02:16 > 0:02:19And finding out how the hunt for a second Earth,
0:02:19 > 0:02:23a habitable planet like our own. is coming along.
0:02:23 > 0:02:26We have found planets in all size, in all masses
0:02:26 > 0:02:28and in many different kind of structure
0:02:28 > 0:02:30from the one we have in the solar system.
0:02:32 > 0:02:35Hollywood has no doubts that there are habitable planets out there.
0:02:35 > 0:02:36Dallas Campbell finds out
0:02:36 > 0:02:40whether exoplanets in the movies have any basis in reality.
0:02:40 > 0:02:43And you can see there's the binary star, one is
0:02:43 > 0:02:45a little bit whiter, one is a bit red.
0:02:45 > 0:02:47Almost exactly like in Star Wars.
0:02:49 > 0:02:52We'll tackle a controversial discovery that my own research
0:02:52 > 0:02:54group have been involved in.
0:02:54 > 0:02:58Could this really be the first discovery of an alien civilisation?
0:03:00 > 0:03:04But first, how do you go about finding an exoplanet amongst
0:03:04 > 0:03:06the 100 billion stars in our galaxy?
0:03:12 > 0:03:14The first true exoplanet was discovered
0:03:14 > 0:03:16by two astronomers in 1992.
0:03:17 > 0:03:19Scientists found not just one
0:03:19 > 0:03:23but at least two planetary objects orbiting around a star.
0:03:24 > 0:03:26It was a stunning achievement.
0:03:26 > 0:03:29These planets were four times the mass of the Earth
0:03:29 > 0:03:34and orbited a type of star called a pulsar - a remnant of a supernova.
0:03:36 > 0:03:39Because the pulsar permanently bathed its planets
0:03:39 > 0:03:42in high-energy radiation, there was no chance for life.
0:03:43 > 0:03:46So in terms of finding another Earth,
0:03:46 > 0:03:48these planets were non-starters.
0:03:49 > 0:03:51Nevertheless, it was a thrilling discovery,
0:03:51 > 0:03:54and left us hungry for more.
0:03:54 > 0:03:57What we wanted next was a planet orbiting a main sequence star
0:03:57 > 0:03:58just like our own.
0:04:00 > 0:04:03And, in a small observatory in France,
0:04:03 > 0:04:05a young PhD student struck lucky.
0:04:05 > 0:04:11Didier Queloz discovered a planet around the star 51 Pegasi.
0:04:11 > 0:04:1451 Pegasi was the right kind of star,
0:04:14 > 0:04:18one that wouldn't bathe its planet with deadly radiation.
0:04:18 > 0:04:21But in other respects the planet in orbit around it was
0:04:21 > 0:04:23spectacularly weird.
0:04:24 > 0:04:25It was the size of Jupiter
0:04:25 > 0:04:28yet it took just four days to orbit its star.
0:04:30 > 0:04:34And its surface temperature exceeded 1,000 degrees Celsius.
0:04:34 > 0:04:38It was a type of planet that has come to be known as a "hot Jupiter".
0:04:38 > 0:04:40It was an extraordinary discovery that
0:04:40 > 0:04:44rewrote our understanding of what exoplanets might be like.
0:04:44 > 0:04:46And it was just the beginning.
0:04:46 > 0:04:48I caught up with Didier to find out
0:04:48 > 0:04:52more about his original discovery, and what's he's been up to since.
0:04:52 > 0:04:55Tell me about the day you discovered 51 Pegasi b?
0:04:55 > 0:04:57Yeah, I was a PhD student at that time
0:04:57 > 0:05:00so the first time I've saw something
0:05:00 > 0:05:06a bit strange going on on the series of measurements I made on 51 Peg,
0:05:06 > 0:05:09I never thought it would be a planet because it was just impossible.
0:05:09 > 0:05:11I thought it was a bug into the instrument,
0:05:11 > 0:05:14something was wrong with the instrument, with the machinery.
0:05:14 > 0:05:17And it took me a long time to figure out exactly what it was.
0:05:17 > 0:05:21Did you hope that the planet you had discovered was going to be Earth-like?
0:05:21 > 0:05:25Well, it was impossible because the, the, the, the instrument
0:05:25 > 0:05:29we're using, the best it could do is detecting something like Jupiter.
0:05:29 > 0:05:31It was designed to do that.
0:05:31 > 0:05:33It was already a tremendous achievement at that time.
0:05:33 > 0:05:37We can do Earth right now, but at 20 years ago it was not possible.
0:05:37 > 0:05:41But it was already so much amazing to find a planet
0:05:41 > 0:05:44so bizarre than this one, so I didn't care at all.
0:05:44 > 0:05:46I mean, it was really a kind of game changer situation.
0:05:46 > 0:05:49So what method did you use to find 51 Peg?
0:05:50 > 0:05:53So at the time, the only way to find a planet was to observe
0:05:53 > 0:05:57the stars, and, uh, by observing the star we are measuring
0:05:57 > 0:06:01the speed of the star, looking for tiny change of that speed.
0:06:01 > 0:06:04So, you have a star and you have a planet going round it.
0:06:04 > 0:06:06And as the planet goes round it caused the star to
0:06:06 > 0:06:10move by a little bit and you're measuring that movement, that speed.
0:06:10 > 0:06:12It's a very tiny effect. You don't see it right away,
0:06:12 > 0:06:15you need to use quite sophisticated algorithms to build
0:06:15 > 0:06:17the average motion that tell you
0:06:17 > 0:06:20at the end that there is something orbiting that star.
0:06:20 > 0:06:21So that's one method,
0:06:21 > 0:06:24but are there other methods for detecting these exoplanets?
0:06:24 > 0:06:27People started to look for transit at that time.
0:06:27 > 0:06:31What will happen is there will be for short amount of time
0:06:31 > 0:06:33a slightly change of the light, a dimming of the light
0:06:33 > 0:06:37of the star, like, like a cloud just hiding us the sun.
0:06:37 > 0:06:40Uh, we can use that to get the size of the planet as well
0:06:40 > 0:06:42as the period of the planet.
0:06:42 > 0:06:45We can also combine the two, you can get the mass from the radial
0:06:45 > 0:06:47velocity and you can get the size from the transit
0:06:47 > 0:06:51and we doing that today to get the density of the planet.
0:06:51 > 0:06:54And the density helps you to understand the structure of the planet.
0:06:54 > 0:06:55And it was really the beginning.
0:06:55 > 0:06:59So it was a massive trigger and that's why at that time
0:06:59 > 0:07:01we were maybe 20 people in the world doing that,
0:07:01 > 0:07:03now there must be 5,000 people working on this.
0:07:03 > 0:07:06So we've found these hot Jupiters and now we're finding sort of
0:07:06 > 0:07:09smaller and smaller planets with the better sophisticated equipment.
0:07:09 > 0:07:11Do you ever think we'll find another Earth?
0:07:11 > 0:07:15Oh, yes, I mean, we have found already, Earth-size planet,
0:07:15 > 0:07:17or Earth-mass planet,
0:07:17 > 0:07:21most of them they're not exactly Earth equivalent because very often
0:07:21 > 0:07:24they're too close to the stars, much too hot.
0:07:24 > 0:07:26So we don't really, really know what we're finding these days.
0:07:26 > 0:07:30But we have planet in all, in all size, in all masses,
0:07:30 > 0:07:34and in many different kind of structure from the one
0:07:34 > 0:07:35we have in the solar system.
0:07:35 > 0:07:38So we're finding more and more and hopefully, that um,
0:07:38 > 0:07:41- another Earth will be out there one day.- Oh, yeah, there are.
0:07:41 > 0:07:45Because right now we're finding an average one planet for each star.
0:07:45 > 0:07:48So if you look at the star, uh, tonight,
0:07:48 > 0:07:51on all the star you seeing by the naked eyes they're planets.
0:07:51 > 0:07:54Some of them we are found them, other we have not yet found them.
0:07:54 > 0:07:57It means that maybe they are solar system equivalent just
0:07:57 > 0:07:58waiting for us to be found.
0:07:58 > 0:08:01- Hm, exciting times ahead. - It is definitely exciting, yes.
0:08:01 > 0:08:04Well, thank you, that was wonderful.
0:08:13 > 0:08:15As we hunt for a second Earth,
0:08:15 > 0:08:19we have to think about what it is that we are really looking for.
0:08:19 > 0:08:22What is it that makes a planet earthlike?
0:08:22 > 0:08:26Is it rocky? Is there liquid water on it surface?
0:08:26 > 0:08:28What gravity would it have?
0:08:28 > 0:08:32And would we be able to breathe if we were standing on the planet?
0:08:34 > 0:08:37Astronomers are only just beginning to work out what
0:08:37 > 0:08:39conditions are like on exoplanets.
0:08:39 > 0:08:44But that hasn't stopped Hollywood from creating its own alien worlds.
0:08:44 > 0:08:47And most of them are very much habitable.
0:08:47 > 0:08:50Dallas Campbell investigates how plausible Hollywood's
0:08:50 > 0:08:52exoplanets really are.
0:09:01 > 0:09:05I went to see Star Wars when it first came out, aged seven,
0:09:05 > 0:09:09at the ABC Cinema Haymarket, Newcastle-upon-Tyne.
0:09:09 > 0:09:15It was one of those cinema experiences that will be forever etched on my brain.
0:09:15 > 0:09:19It ignited my lifelong love affair with science fiction movies.
0:09:21 > 0:09:24Amazingly, many of the distant worlds featured in these films were
0:09:24 > 0:09:26being imagined by writers
0:09:26 > 0:09:30and directors decades before the first exoplanets were found.
0:09:31 > 0:09:35The planet Tatooine from Star Wars, for example, you've got this
0:09:35 > 0:09:42wonderful, evocative desert landscape, and Luke Skywalker stands there contemplating his destiny,
0:09:42 > 0:09:47bathed in the afternoon light from not one but two suns.
0:09:58 > 0:09:59Although it has two suns,
0:09:59 > 0:10:04in almost every other respect Tatooine feels reassuringly earthlike,
0:10:04 > 0:10:07which makes sense, given that it was filmed in Tunisia.
0:10:07 > 0:10:09But the same can't be said for this planet.
0:10:10 > 0:10:12If I owned this place and hell,
0:10:12 > 0:10:15I'd rent this place out and live in hell.
0:10:17 > 0:10:20This is Crematoria from The Chronicles Of Riddick,
0:10:20 > 0:10:24and in it the protagonist has to deal with furnace-like temperatures during the day,
0:10:24 > 0:10:26so up to 372 degrees,
0:10:26 > 0:10:30and then at night it gets down to minus 182 degrees -
0:10:30 > 0:10:35with only a 20-minute window where the characters can actually
0:10:35 > 0:10:37walk about safely on the surface.
0:10:50 > 0:10:53Interstellar is about the search for a second Earth.
0:10:53 > 0:10:57As food resources run out humanity must find a new home.
0:10:57 > 0:11:02And en route they have a close encounter with a very strange water world called Miller,
0:11:02 > 0:11:04which has 30% more gravity than Earth,
0:11:04 > 0:11:10huge tidal waves and is orbiting an enormous black hole called Gargantua.
0:11:10 > 0:11:13It's our only chance to save people on Earth.
0:11:13 > 0:11:16If I can find a way to transmit the quantum data I'll find in there,
0:11:16 > 0:11:17they might still make it.
0:11:19 > 0:11:22Let's just hope there's still someone there to save.
0:11:24 > 0:11:29That's just a few examples of the artistic licence used by writers and directors
0:11:29 > 0:11:32in describing exoplanets.
0:11:32 > 0:11:33But what about real life?
0:11:33 > 0:11:37How close are we to finding anything like what we see in the movies?
0:11:37 > 0:11:41I'm going to go and see exoplanet expert Ruth Angus to find out.
0:11:43 > 0:11:46So how realistic are some of these exoplanets that we
0:11:46 > 0:11:47see in the movies?
0:11:47 > 0:11:50I guess the most famous one is Tatooine in Star Wars,
0:11:50 > 0:11:51with its binary star system.
0:11:51 > 0:11:53Could something like that happen?
0:11:53 > 0:11:57- If so, have we found anything like that?- Yes, absolutely.
0:11:57 > 0:11:58We've found more than one, actually.
0:11:58 > 0:12:02The first one we found was Kepler-16b, we found it in 2011,
0:12:02 > 0:12:06and it's the first circumbinary planet.
0:12:06 > 0:12:10So that means it's a binary star, two stars that orbit each other,
0:12:10 > 0:12:13and a planet on the outside that orbits both of them.
0:12:13 > 0:12:16- So the planet has two stars.- So the stars are orbiting each other,
0:12:16 > 0:12:19in a little sort of merry dance, and the planet is going round - oh, wow!
0:12:19 > 0:12:23So here's a video of that system and you can see there's the binary
0:12:23 > 0:12:26star in the centre, one is a little bit more massive than the other
0:12:26 > 0:12:30and it's slightly whiter, and the other is a little red.
0:12:30 > 0:12:31Almost exactly like in Star Wars.
0:12:31 > 0:12:34It is, it is almost exactly like in Star Wars, yeah.
0:12:34 > 0:12:36And is the planet that's orbiting this system, would it be a rocky
0:12:36 > 0:12:41planet looking a little bit like Tunisia by any chance?
0:12:41 > 0:12:42We should be so lucky!
0:12:42 > 0:12:45No, unfortunately, this planet is a Saturn-like planet.
0:12:45 > 0:12:48The reason why this is such a benchmark system is
0:12:48 > 0:12:51because before we found Kepler-16b, we didn't actually know
0:12:51 > 0:12:54whether you could form an exoplanet in a binary system.
0:12:54 > 0:12:57And that's because the gravitational pull acting on the planet
0:12:57 > 0:13:00varies all the time because these two stars are moving.
0:13:00 > 0:13:03So that means that the planet is kind of, like,
0:13:03 > 0:13:07walking drunkenly around in space, and if that kind of drunken walk
0:13:07 > 0:13:11gets too extreme it's going to spiral inwards and plunge into
0:13:11 > 0:13:14- the surface of one of the stars or it will be flung outwards completely.- Right.
0:13:14 > 0:13:18So we didn't know whether we would find any planets in stable
0:13:18 > 0:13:20orbits around binary stars.
0:13:20 > 0:13:23Kepler-16b showed us that they do exist and we can find them.
0:13:23 > 0:13:25What about some of these exotic exoplanets that we
0:13:25 > 0:13:27see in the movies?
0:13:27 > 0:13:28Something like Crematoria, which is
0:13:28 > 0:13:31the aptly named planet in The Chronicles Of Riddick.
0:13:31 > 0:13:36This sort of extremely hot during the day, extremely cold at night.
0:13:36 > 0:13:39Is that just complete fantasy or is that possible?
0:13:39 > 0:13:44Well, we have managed to map the temperature on the planet WASP-43b,
0:13:44 > 0:13:48so we actually know what the temperature of the day side is
0:13:48 > 0:13:50and we know what the temperature of the night side is.
0:13:50 > 0:13:51And in this graphic,
0:13:51 > 0:13:57we can see in the day it's really hovering up around 1,500 Kelvin,
0:13:57 > 0:14:02and in the night it drops all the way back down to, almost to zero.
0:14:02 > 0:14:05I find it amazing that we have the technology that enables us
0:14:05 > 0:14:06to do that.
0:14:06 > 0:14:09One of the things about the planet Miller in Interstellar,
0:14:09 > 0:14:12is that it's orbiting a black hole and you get into all
0:14:12 > 0:14:16kinds of exotic physics - time dilation and all this sort of stuff.
0:14:16 > 0:14:18But the fact that its orbiting a black hole, is,
0:14:18 > 0:14:20is a really interesting idea.
0:14:20 > 0:14:22Is that at all feasible?
0:14:22 > 0:14:23Yeah.
0:14:23 > 0:14:26There's no reason why you can't have a planet orbiting a black hole.
0:14:26 > 0:14:31And in fact there is some evidence to suggest that we've even
0:14:31 > 0:14:35seen a super Jupiter being eaten by a black hole.
0:14:35 > 0:14:38Uh, and so this, this graphic shows you.
0:14:38 > 0:14:40So this is the planet here
0:14:40 > 0:14:44and the black hole is somewhere in here, you can't quite see it,
0:14:44 > 0:14:48but material is streaming from the planet onto the black hole.
0:14:48 > 0:14:50I'm trying to imagine what you might see,
0:14:50 > 0:14:53because obviously a black hole, it's not actually emitting anything.
0:14:53 > 0:14:55So what would the view be like?
0:14:55 > 0:14:57Well, in this example, you'd see this very bizarre
0:14:57 > 0:15:02kind of arc of light stretching from you to the black hole.
0:15:02 > 0:15:04So what's that? What is that light?
0:15:04 > 0:15:05Where is that light coming from?
0:15:05 > 0:15:09That's, that's the dust and gas falling off the planet into
0:15:09 > 0:15:13- the black hole and crossing the event horizon.- So the raw materials that we find that makes up planets.
0:15:13 > 0:15:15The raw materials, yeah, exactly.
0:15:15 > 0:15:18So this material as it's falling into the black hole gets
0:15:18 > 0:15:22extremely hot and it starts to give off radiation, it glows.
0:15:22 > 0:15:25So you would see the kind of glowing signature
0:15:25 > 0:15:27of this accreting material.
0:15:27 > 0:15:30Do science fiction writers, are they creative enough, do you think?
0:15:30 > 0:15:33Do you think they are slightly limited by their own imagination?
0:15:33 > 0:15:36And actually what's really interesting is the stuff that's actually out there?
0:15:36 > 0:15:40Things like, uh, you know, a super Jupiter being eaten by a black hole
0:15:40 > 0:15:43and a planet made of diamonds and this sort of stuff?
0:15:43 > 0:15:46I'm sure that's true. The old expression "stranger than fiction"
0:15:46 > 0:15:48is absolutely applicable to exoplanets.
0:15:48 > 0:15:51There are lots of things that we've found that are stranger than things we can imagine
0:15:51 > 0:15:55and that's the beauty of the exoplanet world - we are discovering things we didn't even
0:15:55 > 0:15:58know were possible and new physics is being discovered all the time.
0:15:58 > 0:16:00Thank you very much, that was fascinating.
0:16:07 > 0:16:10One of the greatest success stories in exoplanet research has been
0:16:10 > 0:16:12Nasa's Kepler space telescope.
0:16:12 > 0:16:17It has found over half of the exoplanets we know about today.
0:16:17 > 0:16:20Five, four, three, two...
0:16:20 > 0:16:21engine start.
0:16:21 > 0:16:27One, zero, and lift off of the Delta Two rocket with Kepler,
0:16:27 > 0:16:30on a search for planets in some way like our own.
0:16:32 > 0:16:34Kepler was launched in March 2009.
0:16:34 > 0:16:38Its mission was to survey our region of the Milky Way,
0:16:38 > 0:16:40to try and find another Earth.
0:16:42 > 0:16:45And it's discovered more than a thousand planets.
0:16:47 > 0:16:49One of most interesting findings of the Kepler space mission
0:16:49 > 0:16:52to date has been the discovery of a class of planet
0:16:52 > 0:16:54known as "Super Earths".
0:16:54 > 0:16:57They seem to be fairly common throughout the galaxy
0:16:57 > 0:17:00and yet none exist within our own solar system.
0:17:00 > 0:17:03They're larger than Earth but smaller than an icy giant.
0:17:03 > 0:17:07We don't know what they're made of. Are they rocky or icy?
0:17:07 > 0:17:09It remains a mystery, at least for now.
0:17:11 > 0:17:14Perhaps even more exciting is the recent discovery of
0:17:14 > 0:17:18Kepler-452b, 1,400 light years away.
0:17:18 > 0:17:22It's probably the most earthlike planet we've found so far.
0:17:22 > 0:17:25It's a rocky world that's orbiting in the habitable zone
0:17:25 > 0:17:29of its parent star, where there could be liquid water.
0:17:29 > 0:17:32But there's still a lot we don't know about the planet,
0:17:32 > 0:17:35for example what its atmosphere is made of.
0:17:37 > 0:17:39Kepler has done a tremendous job in finding
0:17:39 > 0:17:44exoplanets virtually everywhere it's looked, but it's not designed to
0:17:44 > 0:17:48give us the detailed information to tell us what those planets would be like.
0:17:48 > 0:17:51Our best bet for finding another Earth is to build
0:17:51 > 0:17:53new instruments that can take a closer look.
0:17:55 > 0:17:58That's what Nasa is doing.
0:17:58 > 0:18:01Its Tess planet finder launches in just two years' time.
0:18:03 > 0:18:07Its mission is to detect small planets orbiting bright host stars.
0:18:09 > 0:18:11Bright stars will reveal more detailed
0:18:11 > 0:18:14information about their planets, enabling us
0:18:14 > 0:18:17to better identify those that are truly earthlike.
0:18:22 > 0:18:25Of course, the ultimate prize isn't just
0:18:25 > 0:18:30finding a planet that is like Earth, it's finding intelligent life.
0:18:31 > 0:18:34We don't really know how that would manifest itself,
0:18:34 > 0:18:37but Chris has recently been involved in a discovery that has got
0:18:37 > 0:18:39some people very excited.
0:18:41 > 0:18:43I don't normally talk about my own research on the programme,
0:18:43 > 0:18:47but in the last few weeks we've announced a remarkable, strange discovery,
0:18:47 > 0:18:52probably the strangest thing we've seen in the universe in the last 20 years.
0:18:52 > 0:18:55And according to the internet and the newspapers we've discovered
0:18:55 > 0:19:00alien spaceships in orbit around a star 1,500 light years away.
0:19:00 > 0:19:02That's not quite what happened.
0:19:02 > 0:19:05We've been running a project for the last few years called Planet Hunters
0:19:05 > 0:19:09which has invited hundreds of thousands of people to go online
0:19:09 > 0:19:13and to look through this data from Kepler and try and find planets.
0:19:13 > 0:19:17And we've found planets, but a few of the volunteers pointed us
0:19:17 > 0:19:20to this one particular star which is behaving really oddly.
0:19:20 > 0:19:25This is its brightness over the course of three or four years.
0:19:25 > 0:19:28You can see most of the time it's fairly stable,
0:19:28 > 0:19:29but there are these dips.
0:19:29 > 0:19:31Just like you'd expect if there was a planet,
0:19:31 > 0:19:33but the dips happen randomly,
0:19:33 > 0:19:34some of them are huge,
0:19:34 > 0:19:38so at one point something blocks out 20% of the star's light.
0:19:38 > 0:19:41That's way too much for this to be a normal planet
0:19:41 > 0:19:44and the fact that they're irregular means this can't be something
0:19:44 > 0:19:48on a circular orbit that blocks out the star's light again and again and again.
0:19:48 > 0:19:50Something really odd is going on here.
0:19:50 > 0:19:54In fact, this is the only star amongst the 150,000
0:19:54 > 0:19:56that's doing anything like this.
0:19:56 > 0:19:59So the obvious question is what's blocking the light from the star?
0:19:59 > 0:20:01We think this might be not exoplanets,
0:20:01 > 0:20:04but a family of exocomets.
0:20:04 > 0:20:08If you have a comet on an elliptical orbit about the star
0:20:08 > 0:20:12AND that comet has broken up, so that you have a string of comets -
0:20:12 > 0:20:15rather like what happened to Shoemaker-Levy 9
0:20:15 > 0:20:17when it hit Jupiter a couple of decades ago -
0:20:17 > 0:20:21then, as each of those pieces of comet pass by the star,
0:20:21 > 0:20:22we'd see a dip.
0:20:22 > 0:20:25And so you see there's one here, there's one here,
0:20:25 > 0:20:29and then this sudden flurry of large bits that block light out.
0:20:29 > 0:20:31But we don't really understand what's going on and
0:20:31 > 0:20:33so we should consider everything,
0:20:33 > 0:20:37including the idea that this is some sort of alien civilisation.
0:20:37 > 0:20:41In fact, people are taking the idea so seriously,
0:20:41 > 0:20:44that astronomers have already pointed radio telescopes at
0:20:44 > 0:20:47this star just to listen out, Seti-style, for any signals
0:20:47 > 0:20:52that might be coming our way from what's become the most interesting star in the galaxy.
0:21:00 > 0:21:02When it comes to finding exoplanets,
0:21:02 > 0:21:06you need more than even the best home telescope.
0:21:06 > 0:21:07But Pete's here to show us
0:21:07 > 0:21:11another way we can all connect with the thrill of exoplanet discovery.
0:21:12 > 0:21:14It's actually not too bad an evening,
0:21:14 > 0:21:18it started off rather cloudy today but the skies have cleared
0:21:18 > 0:21:21and I can see some stars shining away up there,
0:21:21 > 0:21:24there's a bit of haze in the west, but that was forecast to come in.
0:21:24 > 0:21:25I'm just glad we can see some stars.
0:21:25 > 0:21:29What I'm looking for is a huge pattern in the sky that
0:21:29 > 0:21:33looks like a giant square, and that's the square of Pegasus.
0:21:33 > 0:21:37And early evening about this time of year, it's quite high up
0:21:37 > 0:21:41in the sky towards the south-east direction.
0:21:41 > 0:21:44It's pretty prominent, just look for this giant square.
0:21:44 > 0:21:49Once you've located it, look to the right-hand side of the square.
0:21:49 > 0:21:52Close to the mid point there is a faint star,
0:21:52 > 0:21:53and that's called 51 Pegasi.
0:21:57 > 0:22:00OK, well, I think I have a photograph of 51 Pegasi there,
0:22:00 > 0:22:04and of course on the back of my camera it'll look just like a regular star.
0:22:04 > 0:22:07The planet is there, we know it's there, it's been detected
0:22:07 > 0:22:10and confirmed by a number of different sources.
0:22:10 > 0:22:14The planet going around 51 Pegasi has a name, it's formal name is
0:22:14 > 0:22:1851 Pegasi b, but there is an unofficial name as well, which is Bellerophon.
0:22:18 > 0:22:23Now Bellerophon in mythology was the person that tamed the flying horse
0:22:23 > 0:22:27Pegasus, so it's rather nice being in the constellation of Pegasus itself.
0:22:28 > 0:22:33So, I think with exoplanets and regular telescopes it's really
0:22:33 > 0:22:36a journey of the imagination, you can see the star there
0:22:36 > 0:22:39through the eyepiece or on the back of the camera, but it's your
0:22:39 > 0:22:44mind that takes you into that system to imagine what it must look like.
0:22:44 > 0:22:46Absolutely fantastic.
0:22:48 > 0:22:51Go to the website to find out more about how to locate 51 Pegasi,
0:22:51 > 0:22:56to see this month's Star Guide, and also to learn about an exciting
0:22:56 > 0:22:58new project The Sky At Night has been involved in.
0:23:00 > 0:23:04This month, we're trying out a brand-new BBC messaging tool
0:23:04 > 0:23:06called Whispering Stars.
0:23:06 > 0:23:10It's a prototype at the moment but we'd love you to have a go.
0:23:10 > 0:23:14On the star map, you can click on any star with a circle round it.
0:23:14 > 0:23:17Not only will you see information from Pete about that star,
0:23:17 > 0:23:20but you can also leave your own message.
0:23:21 > 0:23:25Then I can share a link to that message via e-mail or social media.
0:23:26 > 0:23:30The recipient can find your message using a computer or a smartphone.
0:23:31 > 0:23:34I've got a new message, just have to click to find it
0:23:34 > 0:23:38and it points me up into the sky towards whichever star
0:23:38 > 0:23:39the message is attached to,
0:23:39 > 0:23:41so apparently I should keep going.
0:23:41 > 0:23:43Back this way, it's this one here,
0:23:43 > 0:23:47which looks like it is...Vega.
0:23:47 > 0:23:50And here's the message from Maggie, which says,
0:23:50 > 0:23:52"Dear Chris, I know you like astrophotography
0:23:52 > 0:23:56"but did you know that Vega was the first star to be photographed?"
0:23:56 > 0:24:00So a message sent through the stars - sort of - and you can go to our
0:24:00 > 0:24:05website at bbc.co.uk/skyatnight to use Whispering Stars for yourself.
0:24:05 > 0:24:09We'll be using it to try and send you information over the next few months.
0:24:16 > 0:24:19Even if we find another rocky planet, just like ours,
0:24:19 > 0:24:24orbiting a star similar to ours, even orbiting at the right distance,
0:24:24 > 0:24:26there's another piece of information
0:24:26 > 0:24:29we need before we can confirm we've found another Earth.
0:24:29 > 0:24:33And that information is the atmospheric composition of that exoplanet.
0:24:33 > 0:24:36And rather astonishingly, we're doing just that.
0:24:36 > 0:24:40Chris has been talking to Nikku Madhusudhan, who is leading
0:24:40 > 0:24:44the research into exoplanet atmospheres here at Cambridge.
0:24:44 > 0:24:47So we've discovered all of these planets, we know, I dunno,
0:24:47 > 0:24:50what size they are, what mass they are, but it's not really enough.
0:24:50 > 0:24:51I want to know what they're like.
0:24:51 > 0:24:54Do we have any prospect of trying to understand that?
0:24:54 > 0:24:57- To, to investigating these planets properly?- No, absolutely.
0:24:57 > 0:25:00So the way you do that is, you know, transiting planets, for example,
0:25:00 > 0:25:02what the transit method is
0:25:02 > 0:25:04is when the planet's star system is aligned
0:25:04 > 0:25:09in such a way that you can infer the planet going in front of the star.
0:25:09 > 0:25:11- Yeah, we see these dips in the star light.- Exactly.
0:25:11 > 0:25:13And we say, OK, there's a planet there.
0:25:13 > 0:25:16As it turns out, the dip in the starlight is just a little
0:25:16 > 0:25:19bit more if you have an atmosphere on top of the planet.
0:25:19 > 0:25:22Because the atmosphere blocks the light from the star as well.
0:25:22 > 0:25:25Yeah, yeah, but the key point is that the atmosphere blocks
0:25:25 > 0:25:28the light in some wavelengths and not in others.
0:25:28 > 0:25:31And so that means if you have a transiting planet you can say
0:25:31 > 0:25:33something about what its atmosphere is made of?
0:25:33 > 0:25:36Exactly, you can infer its chemical composition.
0:25:36 > 0:25:38OK, so Earth is mostly nitrogen, bit of oxygen,
0:25:38 > 0:25:41bit of carbon dioxide, what do we see on these exoplanets?
0:25:41 > 0:25:45Yep, so the exoplanets, um, that we are most
0:25:45 > 0:25:49able to study today are the big and hot ones.
0:25:49 > 0:25:50It's because the bigger the planet,
0:25:50 > 0:25:52the bigger the starlight you're blocking.
0:25:52 > 0:25:54Yeah, the bigger the dip.
0:25:54 > 0:25:56The bigger the dip, so it's just easier to find them.
0:25:56 > 0:26:00And hot because the hotter the atmosphere is the more
0:26:00 > 0:26:05- puffier it is.- Hm.- Right, so, so the bigger it is.
0:26:05 > 0:26:09So the hotter the atmosphere, the bigger the atmosphere, and the more light it blocks.
0:26:09 > 0:26:13Right, so most of the results to date have come from these
0:26:13 > 0:26:14objects called hot Jupiters.
0:26:14 > 0:26:16What do we know about the conditions?
0:26:16 > 0:26:19We know they're large, that means they must be made of gas, mostly.
0:26:19 > 0:26:24- What do we know about the atmosphere?- We are finding less water than we would expect
0:26:24 > 0:26:27if the planets formed in a solar-like environment
0:26:27 > 0:26:31- Oh, OK.- And they could be less by even a factor of ten.
0:26:31 > 0:26:37One explanation is that maybe these objects have clouds in their atmospheres.
0:26:37 > 0:26:40So you're, you're saying the water would be hidden? By the clouds?
0:26:40 > 0:26:44- Yeah, exactly.- So you only see the bit of the atmosphere above the clouds?
0:26:44 > 0:26:48- Exactly, so, so that's one way.- So it's a straightforward explanation -
0:26:48 > 0:26:52astronomers being confused by clouds is common here on Earth as well.
0:26:52 > 0:26:55It's not only on Earth, not only a terrestrial experience,
0:26:55 > 0:26:58even when you go to exoplanets clouds are a headache.
0:26:58 > 0:26:59But there is a subtlety.
0:26:59 > 0:27:03Clouds are not the same clouds we have here.
0:27:03 > 0:27:05Right, so on Earth they are water clouds.
0:27:05 > 0:27:09- But these are planets at a few thousand degrees.- Of course, so...
0:27:09 > 0:27:11So you can't have water clouds.
0:27:11 > 0:27:14So you may have to invoke iron clouds,
0:27:14 > 0:27:16or silicate clouds, you see it in rocks,
0:27:16 > 0:27:19on Earth rocks are made of silicates,
0:27:19 > 0:27:20so you might be able to make
0:27:20 > 0:27:24clouds out of those same silicates, hanging up in the atmosphere.
0:27:24 > 0:27:25Wow, suddenly it's a place to me,
0:27:25 > 0:27:28because we are talking about what they're like.
0:27:28 > 0:27:30I can, I sort of feel they're real.
0:27:30 > 0:27:32- Yeah.- Remarkable stuff, and we'll come back
0:27:32 > 0:27:34and see how you're getting on in a few years perhaps.
0:27:34 > 0:27:37- Thank you very much. - Thank you, thank you.
0:27:37 > 0:27:40It's amazing we've come so far in just 20 years.
0:27:40 > 0:27:42Going from no exoplanets to about 2,000 now!
0:27:42 > 0:27:45And turning them from just points on a graph, from just data,
0:27:45 > 0:27:49to real places with atmospheres, and rain,
0:27:49 > 0:27:52and even clouds to annoy the astronomers!
0:27:52 > 0:27:55What I'm fascinated by, is if we did find an earthlike planet,
0:27:55 > 0:27:57I mean, even signs of life, what would we do then?
0:27:57 > 0:27:59We'd have to go, wouldn't we?
0:27:59 > 0:28:02If you looked at the sky and you could say that star has an earthlike planet,
0:28:02 > 0:28:06the right temperature, with life in its atmosphere - you'd have to send a probe.
0:28:06 > 0:28:10- It'd take thousands of years to get there!- We still should send something, I mean, maybe not us,
0:28:10 > 0:28:14- but we should send something just so we know we're on our way.- I have to agree, you're right!
0:28:19 > 0:28:22That's it for this month. Next month we have a Christmas special!
0:28:22 > 0:28:25We'll be taking an astronomical look at the mystery surrounding
0:28:25 > 0:28:27the Star of Bethlehem.
0:28:27 > 0:28:29Was it just a conjunction of planets
0:28:29 > 0:28:31or something more exciting like a comet,
0:28:31 > 0:28:32or a supernova?
0:28:32 > 0:28:36In the meanwhile, get outside and get looking up.
0:28:36 > 0:28:37Goodnight.