1 00:00:00,400 --> 00:00:05,100 20 years ago, two astronomers made a remarkable discovery, 2 00:00:05,100 --> 00:00:08,060 one which would change the way we view the universe for ever. 3 00:00:08,060 --> 00:00:12,420 A planet outside our solar system, orbiting a distant star - 4 00:00:12,420 --> 00:00:13,660 an exoplanet. 5 00:00:15,300 --> 00:00:19,540 Since then, we have found worlds where it rains diamonds, 6 00:00:19,540 --> 00:00:22,420 ones that boil at 3,000 degrees centigrade 7 00:00:22,420 --> 00:00:24,500 and even a world with four suns in its sky. 8 00:00:27,860 --> 00:00:32,300 But the big question is - will we ever find another Earth? 9 00:00:32,300 --> 00:00:34,140 Welcome to The Sky At Night. 10 00:01:02,660 --> 00:01:07,140 Our solar system is filled with an incredible variety of planets. 11 00:01:08,260 --> 00:01:11,740 From small, airless and rocky worlds like Mercury 12 00:01:11,740 --> 00:01:15,780 to gas giants like Saturn, with its spectacular rings of ice. 13 00:01:18,820 --> 00:01:25,060 Surely our solar system couldn't be the only one to host such a wonderful variety of worlds? 14 00:01:27,740 --> 00:01:30,660 And yet, until the 1990s, astronomers hadn't found 15 00:01:30,660 --> 00:01:33,260 a single planet outside our solar system. 16 00:01:35,020 --> 00:01:37,540 And then, in 1995, they found it - 17 00:01:37,540 --> 00:01:40,020 the first really convincing evidence 18 00:01:40,020 --> 00:01:42,140 for a planet orbiting another star. 19 00:01:42,140 --> 00:01:45,060 Since then, we've discovered nearly 2,000, and it's involved 20 00:01:45,060 --> 00:01:48,060 some pretty extraordinary science detective work. 21 00:01:48,060 --> 00:01:50,580 In fact, we've found so many planets that we've reached 22 00:01:50,580 --> 00:01:52,340 a remarkable conclusion. 23 00:01:52,340 --> 00:01:54,820 That almost all the stars in our galaxy 24 00:01:54,820 --> 00:01:57,260 have their own families of planets. 25 00:01:57,260 --> 00:01:59,700 It's a really hot topic in astronomy right now. 26 00:01:59,700 --> 00:02:02,140 We're all desperate to find another Earth. 27 00:02:02,140 --> 00:02:06,620 Although, as we'll see later, quite what that means is open to question. 28 00:02:08,260 --> 00:02:11,140 Coming up tonight, we'll be examining some of the latest 29 00:02:11,140 --> 00:02:16,380 discoveries made here at the Cambridge Exoplanet Research Centre. 30 00:02:16,380 --> 00:02:19,660 And finding out how the hunt for a second Earth, 31 00:02:19,660 --> 00:02:23,300 a habitable planet like our own. is coming along. 32 00:02:23,300 --> 00:02:26,700 We have found planets in all size, in all masses 33 00:02:26,700 --> 00:02:28,580 and in many different kind of structure 34 00:02:28,580 --> 00:02:30,740 from the one we have in the solar system. 35 00:02:32,180 --> 00:02:35,260 Hollywood has no doubts that there are habitable planets out there. 36 00:02:35,260 --> 00:02:36,780 Dallas Campbell finds out 37 00:02:36,780 --> 00:02:40,980 whether exoplanets in the movies have any basis in reality. 38 00:02:40,980 --> 00:02:43,300 And you can see there's the binary star, one is 39 00:02:43,300 --> 00:02:45,300 a little bit whiter, one is a bit red. 40 00:02:45,300 --> 00:02:47,220 Almost exactly like in Star Wars. 41 00:02:49,980 --> 00:02:52,900 We'll tackle a controversial discovery that my own research 42 00:02:52,900 --> 00:02:54,700 group have been involved in. 43 00:02:54,700 --> 00:02:58,780 Could this really be the first discovery of an alien civilisation? 44 00:03:00,420 --> 00:03:04,540 But first, how do you go about finding an exoplanet amongst 45 00:03:04,540 --> 00:03:06,900 the 100 billion stars in our galaxy? 46 00:03:12,380 --> 00:03:14,820 The first true exoplanet was discovered 47 00:03:14,820 --> 00:03:16,540 by two astronomers in 1992. 48 00:03:18,060 --> 00:03:20,100 Scientists found not just one 49 00:03:20,100 --> 00:03:23,340 but at least two planetary objects orbiting around a star. 50 00:03:24,580 --> 00:03:26,660 It was a stunning achievement. 51 00:03:26,660 --> 00:03:29,700 These planets were four times the mass of the Earth 52 00:03:29,700 --> 00:03:34,940 and orbited a type of star called a pulsar - a remnant of a supernova. 53 00:03:36,220 --> 00:03:39,180 Because the pulsar permanently bathed its planets 54 00:03:39,180 --> 00:03:42,580 in high-energy radiation, there was no chance for life. 55 00:03:44,100 --> 00:03:46,140 So in terms of finding another Earth, 56 00:03:46,140 --> 00:03:48,100 these planets were non-starters. 57 00:03:49,780 --> 00:03:51,780 Nevertheless, it was a thrilling discovery, 58 00:03:51,780 --> 00:03:54,260 and left us hungry for more. 59 00:03:54,260 --> 00:03:57,740 What we wanted next was a planet orbiting a main sequence star 60 00:03:57,740 --> 00:03:59,020 just like our own. 61 00:04:00,940 --> 00:04:03,380 And, in a small observatory in France, 62 00:04:03,380 --> 00:04:05,620 a young PhD student struck lucky. 63 00:04:05,620 --> 00:04:11,380 Didier Queloz discovered a planet around the star 51 Pegasi. 64 00:04:11,380 --> 00:04:14,140 51 Pegasi was the right kind of star, 65 00:04:14,140 --> 00:04:18,300 one that wouldn't bathe its planet with deadly radiation. 66 00:04:18,300 --> 00:04:21,940 But in other respects the planet in orbit around it was 67 00:04:21,940 --> 00:04:23,300 spectacularly weird. 68 00:04:24,420 --> 00:04:25,940 It was the size of Jupiter 69 00:04:25,940 --> 00:04:28,860 yet it took just four days to orbit its star. 70 00:04:30,780 --> 00:04:34,260 And its surface temperature exceeded 1,000 degrees Celsius. 71 00:04:34,260 --> 00:04:38,300 It was a type of planet that has come to be known as a "hot Jupiter". 72 00:04:38,300 --> 00:04:40,940 It was an extraordinary discovery that 73 00:04:40,940 --> 00:04:44,700 rewrote our understanding of what exoplanets might be like. 74 00:04:44,700 --> 00:04:46,900 And it was just the beginning. 75 00:04:46,900 --> 00:04:48,980 I caught up with Didier to find out 76 00:04:48,980 --> 00:04:52,940 more about his original discovery, and what's he's been up to since. 77 00:04:52,940 --> 00:04:55,940 Tell me about the day you discovered 51 Pegasi b? 78 00:04:55,940 --> 00:04:58,020 Yeah, I was a PhD student at that time 79 00:04:58,020 --> 00:05:00,300 so the first time I've saw something 80 00:05:00,300 --> 00:05:06,820 a bit strange going on on the series of measurements I made on 51 Peg, 81 00:05:06,820 --> 00:05:09,780 I never thought it would be a planet because it was just impossible. 82 00:05:09,780 --> 00:05:11,820 I thought it was a bug into the instrument, 83 00:05:11,820 --> 00:05:14,820 something was wrong with the instrument, with the machinery. 84 00:05:14,820 --> 00:05:18,140 And it took me a long time to figure out exactly what it was. 85 00:05:18,140 --> 00:05:21,580 Did you hope that the planet you had discovered was going to be Earth-like? 86 00:05:21,580 --> 00:05:25,700 Well, it was impossible because the, the, the, the instrument 87 00:05:25,700 --> 00:05:29,780 we're using, the best it could do is detecting something like Jupiter. 88 00:05:29,780 --> 00:05:31,540 It was designed to do that. 89 00:05:31,540 --> 00:05:34,100 It was already a tremendous achievement at that time. 90 00:05:34,100 --> 00:05:37,940 We can do Earth right now, but at 20 years ago it was not possible. 91 00:05:37,940 --> 00:05:41,340 But it was already so much amazing to find a planet 92 00:05:41,340 --> 00:05:44,300 so bizarre than this one, so I didn't care at all. 93 00:05:44,300 --> 00:05:46,980 I mean, it was really a kind of game changer situation. 94 00:05:46,980 --> 00:05:49,260 So what method did you use to find 51 Peg? 95 00:05:50,620 --> 00:05:53,860 So at the time, the only way to find a planet was to observe 96 00:05:53,860 --> 00:05:57,500 the stars, and, uh, by observing the star we are measuring 97 00:05:57,500 --> 00:06:01,620 the speed of the star, looking for tiny change of that speed. 98 00:06:01,620 --> 00:06:04,660 So, you have a star and you have a planet going round it. 99 00:06:04,660 --> 00:06:07,020 And as the planet goes round it caused the star to 100 00:06:07,020 --> 00:06:10,100 move by a little bit and you're measuring that movement, that speed. 101 00:06:10,100 --> 00:06:12,980 It's a very tiny effect. You don't see it right away, 102 00:06:12,980 --> 00:06:16,020 you need to use quite sophisticated algorithms to build 103 00:06:16,020 --> 00:06:18,060 the average motion that tell you 104 00:06:18,060 --> 00:06:20,820 at the end that there is something orbiting that star. 105 00:06:20,820 --> 00:06:22,020 So that's one method, 106 00:06:22,020 --> 00:06:25,060 but are there other methods for detecting these exoplanets? 107 00:06:25,060 --> 00:06:27,260 People started to look for transit at that time. 108 00:06:27,260 --> 00:06:31,460 What will happen is there will be for short amount of time 109 00:06:31,460 --> 00:06:33,740 a slightly change of the light, a dimming of the light 110 00:06:33,740 --> 00:06:37,500 of the star, like, like a cloud just hiding us the sun. 111 00:06:37,500 --> 00:06:40,900 Uh, we can use that to get the size of the planet as well 112 00:06:40,900 --> 00:06:42,420 as the period of the planet. 113 00:06:42,420 --> 00:06:45,460 We can also combine the two, you can get the mass from the radial 114 00:06:45,460 --> 00:06:47,700 velocity and you can get the size from the transit 115 00:06:47,700 --> 00:06:51,340 and we doing that today to get the density of the planet. 116 00:06:51,340 --> 00:06:54,300 And the density helps you to understand the structure of the planet. 117 00:06:54,300 --> 00:06:55,740 And it was really the beginning. 118 00:06:55,740 --> 00:06:59,140 So it was a massive trigger and that's why at that time 119 00:06:59,140 --> 00:07:01,300 we were maybe 20 people in the world doing that, 120 00:07:01,300 --> 00:07:03,780 now there must be 5,000 people working on this. 121 00:07:03,780 --> 00:07:06,420 So we've found these hot Jupiters and now we're finding sort of 122 00:07:06,420 --> 00:07:09,460 smaller and smaller planets with the better sophisticated equipment. 123 00:07:09,460 --> 00:07:11,780 Do you ever think we'll find another Earth? 124 00:07:11,780 --> 00:07:15,300 Oh, yes, I mean, we have found already, Earth-size planet, 125 00:07:15,300 --> 00:07:17,220 or Earth-mass planet, 126 00:07:17,220 --> 00:07:21,820 most of them they're not exactly Earth equivalent because very often 127 00:07:21,820 --> 00:07:24,180 they're too close to the stars, much too hot. 128 00:07:24,180 --> 00:07:26,980 So we don't really, really know what we're finding these days. 129 00:07:26,980 --> 00:07:30,980 But we have planet in all, in all size, in all masses, 130 00:07:30,980 --> 00:07:34,300 and in many different kind of structure from the one 131 00:07:34,300 --> 00:07:35,980 we have in the solar system. 132 00:07:35,980 --> 00:07:38,620 So we're finding more and more and hopefully, that um, 133 00:07:38,620 --> 00:07:41,500 another Earth will be out there one day. Oh, yeah, there are. 134 00:07:41,500 --> 00:07:45,300 Because right now we're finding an average one planet for each star. 135 00:07:45,300 --> 00:07:48,220 So if you look at the star, uh, tonight, 136 00:07:48,220 --> 00:07:51,620 on all the star you seeing by the naked eyes they're planets. 137 00:07:51,620 --> 00:07:54,820 Some of them we are found them, other we have not yet found them. 138 00:07:54,820 --> 00:07:57,540 It means that maybe they are solar system equivalent just 139 00:07:57,540 --> 00:07:59,140 waiting for us to be found. 140 00:07:59,140 --> 00:08:02,020 Hm, exciting times ahead. It is definitely exciting, yes. 141 00:08:02,020 --> 00:08:04,060 Well, thank you, that was wonderful. 142 00:08:13,620 --> 00:08:15,380 As we hunt for a second Earth, 143 00:08:15,380 --> 00:08:19,460 we have to think about what it is that we are really looking for. 144 00:08:19,460 --> 00:08:22,660 What is it that makes a planet earthlike? 145 00:08:22,660 --> 00:08:26,340 Is it rocky? Is there liquid water on it surface? 146 00:08:26,340 --> 00:08:28,540 What gravity would it have? 147 00:08:28,540 --> 00:08:32,100 And would we be able to breathe if we were standing on the planet? 148 00:08:34,540 --> 00:08:37,220 Astronomers are only just beginning to work out what 149 00:08:37,220 --> 00:08:40,140 conditions are like on exoplanets. 150 00:08:40,140 --> 00:08:44,660 But that hasn't stopped Hollywood from creating its own alien worlds. 151 00:08:44,660 --> 00:08:47,740 And most of them are very much habitable. 152 00:08:47,740 --> 00:08:51,020 Dallas Campbell investigates how plausible Hollywood's 153 00:08:51,020 --> 00:08:52,780 exoplanets really are. 154 00:09:01,540 --> 00:09:05,620 I went to see Star Wars when it first came out, aged seven, 155 00:09:05,620 --> 00:09:09,900 at the ABC Cinema Haymarket, Newcastle-upon-Tyne. 156 00:09:09,900 --> 00:09:15,740 It was one of those cinema experiences that will be forever etched on my brain. 157 00:09:15,740 --> 00:09:19,460 It ignited my lifelong love affair with science fiction movies. 158 00:09:21,260 --> 00:09:25,060 Amazingly, many of the distant worlds featured in these films were 159 00:09:25,060 --> 00:09:26,660 being imagined by writers 160 00:09:26,660 --> 00:09:30,260 and directors decades before the first exoplanets were found. 161 00:09:32,020 --> 00:09:35,540 The planet Tatooine from Star Wars, for example, you've got this 162 00:09:35,540 --> 00:09:42,860 wonderful, evocative desert landscape, and Luke Skywalker stands there contemplating his destiny, 163 00:09:42,860 --> 00:09:47,420 bathed in the afternoon light from not one but two suns. 164 00:09:58,500 --> 00:09:59,860 Although it has two suns, 165 00:09:59,860 --> 00:10:04,300 in almost every other respect Tatooine feels reassuringly earthlike, 166 00:10:04,300 --> 00:10:07,340 which makes sense, given that it was filmed in Tunisia. 167 00:10:07,340 --> 00:10:09,660 But the same can't be said for this planet. 168 00:10:10,820 --> 00:10:12,460 If I owned this place and hell, 169 00:10:12,460 --> 00:10:15,500 I'd rent this place out and live in hell. 170 00:10:17,500 --> 00:10:20,460 This is Crematoria from The Chronicles Of Riddick, 171 00:10:20,460 --> 00:10:24,860 and in it the protagonist has to deal with furnace-like temperatures during the day, 172 00:10:24,860 --> 00:10:26,860 so up to 372 degrees, 173 00:10:26,860 --> 00:10:31,020 and then at night it gets down to minus 182 degrees - 174 00:10:31,020 --> 00:10:35,460 with only a 20-minute window where the characters can actually 175 00:10:35,460 --> 00:10:37,420 walk about safely on the surface. 176 00:10:50,620 --> 00:10:53,460 Interstellar is about the search for a second Earth. 177 00:10:53,460 --> 00:10:57,380 As food resources run out humanity must find a new home. 178 00:10:57,380 --> 00:11:02,260 And en route they have a close encounter with a very strange water world called Miller, 179 00:11:02,260 --> 00:11:05,140 which has 30% more gravity than Earth, 180 00:11:05,140 --> 00:11:11,100 huge tidal waves and is orbiting an enormous black hole called Gargantua. 181 00:11:11,100 --> 00:11:13,420 It's our only chance to save people on Earth. 182 00:11:13,420 --> 00:11:16,420 If I can find a way to transmit the quantum data I'll find in there, 183 00:11:16,420 --> 00:11:17,860 they might still make it. 184 00:11:19,900 --> 00:11:22,820 Let's just hope there's still someone there to save. 185 00:11:24,860 --> 00:11:29,780 That's just a few examples of the artistic licence used by writers and directors 186 00:11:29,780 --> 00:11:32,300 in describing exoplanets. 187 00:11:32,300 --> 00:11:33,940 But what about real life? 188 00:11:33,940 --> 00:11:37,740 How close are we to finding anything like what we see in the movies? 189 00:11:37,740 --> 00:11:41,580 I'm going to go and see exoplanet expert Ruth Angus to find out. 190 00:11:43,460 --> 00:11:46,460 So how realistic are some of these exoplanets that we 191 00:11:46,460 --> 00:11:47,500 see in the movies? 192 00:11:47,500 --> 00:11:50,340 I guess the most famous one is Tatooine in Star Wars, 193 00:11:50,340 --> 00:11:52,020 with its binary star system. 194 00:11:52,020 --> 00:11:53,900 Could something like that happen? 195 00:11:53,900 --> 00:11:57,140 If so, have we found anything like that? Yes, absolutely. 196 00:11:57,140 --> 00:11:58,860 We've found more than one, actually. 197 00:11:58,860 --> 00:12:02,700 The first one we found was Kepler-16b, we found it in 2011, 198 00:12:02,700 --> 00:12:06,260 and it's the first circumbinary planet. 199 00:12:06,260 --> 00:12:10,260 So that means it's a binary star, two stars that orbit each other, 200 00:12:10,260 --> 00:12:13,220 and a planet on the outside that orbits both of them. 201 00:12:13,220 --> 00:12:16,180 So the planet has two stars. So the stars are orbiting each other, 202 00:12:16,180 --> 00:12:19,980 in a little sort of merry dance, and the planet is going round - oh, wow! 203 00:12:19,980 --> 00:12:23,780 So here's a video of that system and you can see there's the binary 204 00:12:23,780 --> 00:12:26,980 star in the centre, one is a little bit more massive than the other 205 00:12:26,980 --> 00:12:30,180 and it's slightly whiter, and the other is a little red. 206 00:12:30,180 --> 00:12:31,820 Almost exactly like in Star Wars. 207 00:12:31,820 --> 00:12:34,260 It is, it is almost exactly like in Star Wars, yeah. 208 00:12:34,260 --> 00:12:37,100 And is the planet that's orbiting this system, would it be a rocky 209 00:12:37,100 --> 00:12:41,140 planet looking a little bit like Tunisia by any chance? 210 00:12:41,140 --> 00:12:43,140 We should be so lucky! 211 00:12:43,140 --> 00:12:45,980 No, unfortunately, this planet is a Saturn-like planet. 212 00:12:45,980 --> 00:12:48,700 The reason why this is such a benchmark system is 213 00:12:48,700 --> 00:12:51,580 because before we found Kepler-16b, we didn't actually know 214 00:12:51,580 --> 00:12:54,540 whether you could form an exoplanet in a binary system. 215 00:12:54,540 --> 00:12:58,020 And that's because the gravitational pull acting on the planet 216 00:12:58,020 --> 00:13:01,180 varies all the time because these two stars are moving. 217 00:13:01,180 --> 00:13:03,740 So that means that the planet is kind of, like, 218 00:13:03,740 --> 00:13:07,780 walking drunkenly around in space, and if that kind of drunken walk 219 00:13:07,780 --> 00:13:11,740 gets too extreme it's going to spiral inwards and plunge into 220 00:13:11,740 --> 00:13:14,980 the surface of one of the stars or it will be flung outwards completely. Right. 221 00:13:14,980 --> 00:13:18,300 So we didn't know whether we would find any planets in stable 222 00:13:18,300 --> 00:13:20,380 orbits around binary stars. 223 00:13:20,380 --> 00:13:23,460 Kepler-16b showed us that they do exist and we can find them. 224 00:13:23,460 --> 00:13:25,820 What about some of these exotic exoplanets that we 225 00:13:25,820 --> 00:13:27,260 see in the movies? 226 00:13:27,260 --> 00:13:28,980 Something like Crematoria, which is 227 00:13:28,980 --> 00:13:32,140 the aptly named planet in The Chronicles Of Riddick. 228 00:13:32,140 --> 00:13:36,740 This sort of extremely hot during the day, extremely cold at night. 229 00:13:36,740 --> 00:13:39,660 Is that just complete fantasy or is that possible? 230 00:13:39,660 --> 00:13:45,060 Well, we have managed to map the temperature on the planet WASP-43b, 231 00:13:45,060 --> 00:13:48,580 so we actually know what the temperature of the day side is 232 00:13:48,580 --> 00:13:50,740 and we know what the temperature of the night side is. 233 00:13:50,740 --> 00:13:52,180 And in this graphic, 234 00:13:52,180 --> 00:13:58,060 we can see in the day it's really hovering up around 1,500 Kelvin, 235 00:13:58,060 --> 00:14:02,820 and in the night it drops all the way back down to, almost to zero. 236 00:14:02,820 --> 00:14:05,660 I find it amazing that we have the technology that enables us 237 00:14:05,660 --> 00:14:07,060 to do that. 238 00:14:07,060 --> 00:14:09,700 One of the things about the planet Miller in Interstellar, 239 00:14:09,700 --> 00:14:12,900 is that it's orbiting a black hole and you get into all 240 00:14:12,900 --> 00:14:16,620 kinds of exotic physics - time dilation and all this sort of stuff. 241 00:14:16,620 --> 00:14:18,980 But the fact that its orbiting a black hole, is, 242 00:14:18,980 --> 00:14:20,580 is a really interesting idea. 243 00:14:20,580 --> 00:14:22,300 Is that at all feasible? 244 00:14:22,300 --> 00:14:23,420 Yeah. 245 00:14:23,420 --> 00:14:26,980 There's no reason why you can't have a planet orbiting a black hole. 246 00:14:26,980 --> 00:14:31,260 And in fact there is some evidence to suggest that we've even 247 00:14:31,260 --> 00:14:35,420 seen a super Jupiter being eaten by a black hole. 248 00:14:35,420 --> 00:14:38,940 Uh, and so this, this graphic shows you. 249 00:14:38,940 --> 00:14:40,980 So this is the planet here 250 00:14:40,980 --> 00:14:44,420 and the black hole is somewhere in here, you can't quite see it, 251 00:14:44,420 --> 00:14:48,500 but material is streaming from the planet onto the black hole. 252 00:14:48,500 --> 00:14:50,420 I'm trying to imagine what you might see, 253 00:14:50,420 --> 00:14:53,580 because obviously a black hole, it's not actually emitting anything. 254 00:14:53,580 --> 00:14:55,260 So what would the view be like? 255 00:14:55,260 --> 00:14:57,980 Well, in this example, you'd see this very bizarre 256 00:14:57,980 --> 00:15:02,860 kind of arc of light stretching from you to the black hole. 257 00:15:02,860 --> 00:15:04,380 So what's that? What is that light? 258 00:15:04,380 --> 00:15:05,900 Where is that light coming from? 259 00:15:05,900 --> 00:15:09,700 That's, that's the dust and gas falling off the planet into 260 00:15:09,700 --> 00:15:13,700 the black hole and crossing the event horizon. So the raw materials that we find that makes up planets. 261 00:15:13,700 --> 00:15:15,900 The raw materials, yeah, exactly. 262 00:15:15,900 --> 00:15:18,580 So this material as it's falling into the black hole gets 263 00:15:18,580 --> 00:15:22,460 extremely hot and it starts to give off radiation, it glows. 264 00:15:22,460 --> 00:15:25,580 So you would see the kind of glowing signature 265 00:15:25,580 --> 00:15:27,500 of this accreting material. 266 00:15:27,500 --> 00:15:30,540 Do science fiction writers, are they creative enough, do you think? 267 00:15:30,540 --> 00:15:33,420 Do you think they are slightly limited by their own imagination? 268 00:15:33,420 --> 00:15:37,100 And actually what's really interesting is the stuff that's actually out there? 269 00:15:37,100 --> 00:15:41,140 Things like, uh, you know, a super Jupiter being eaten by a black hole 270 00:15:41,140 --> 00:15:43,660 and a planet made of diamonds and this sort of stuff? 271 00:15:43,660 --> 00:15:46,620 I'm sure that's true. The old expression "stranger than fiction" 272 00:15:46,620 --> 00:15:48,460 is absolutely applicable to exoplanets. 273 00:15:48,460 --> 00:15:52,020 There are lots of things that we've found that are stranger than things we can imagine 274 00:15:52,020 --> 00:15:55,580 and that's the beauty of the exoplanet world - we are discovering things we didn't even 275 00:15:55,580 --> 00:15:58,460 know were possible and new physics is being discovered all the time. 276 00:15:58,460 --> 00:16:00,780 Thank you very much, that was fascinating. 277 00:16:07,420 --> 00:16:10,980 One of the greatest success stories in exoplanet research has been 278 00:16:10,980 --> 00:16:13,020 Nasa's Kepler space telescope. 279 00:16:13,020 --> 00:16:17,180 It has found over half of the exoplanets we know about today. 280 00:16:17,180 --> 00:16:20,260 Five, four, three, two... 281 00:16:20,260 --> 00:16:21,980 engine start. 282 00:16:21,980 --> 00:16:27,140 One, zero, and lift off of the Delta Two rocket with Kepler, 283 00:16:27,140 --> 00:16:30,420 on a search for planets in some way like our own. 284 00:16:32,380 --> 00:16:34,860 Kepler was launched in March 2009. 285 00:16:34,860 --> 00:16:38,340 Its mission was to survey our region of the Milky Way, 286 00:16:38,340 --> 00:16:40,340 to try and find another Earth. 287 00:16:42,860 --> 00:16:45,700 And it's discovered more than a thousand planets. 288 00:16:47,260 --> 00:16:50,060 One of most interesting findings of the Kepler space mission 289 00:16:50,060 --> 00:16:52,940 to date has been the discovery of a class of planet 290 00:16:52,940 --> 00:16:55,060 known as "Super Earths". 291 00:16:55,060 --> 00:16:57,460 They seem to be fairly common throughout the galaxy 292 00:16:57,460 --> 00:17:00,540 and yet none exist within our own solar system. 293 00:17:00,540 --> 00:17:03,900 They're larger than Earth but smaller than an icy giant. 294 00:17:03,900 --> 00:17:07,380 We don't know what they're made of. Are they rocky or icy? 295 00:17:07,380 --> 00:17:09,460 It remains a mystery, at least for now. 296 00:17:11,420 --> 00:17:14,420 Perhaps even more exciting is the recent discovery of 297 00:17:14,420 --> 00:17:18,700 Kepler-452b, 1,400 light years away. 298 00:17:18,700 --> 00:17:23,060 It's probably the most earthlike planet we've found so far. 299 00:17:23,060 --> 00:17:26,140 It's a rocky world that's orbiting in the habitable zone 300 00:17:26,140 --> 00:17:29,660 of its parent star, where there could be liquid water. 301 00:17:29,660 --> 00:17:33,060 But there's still a lot we don't know about the planet, 302 00:17:33,060 --> 00:17:35,860 for example what its atmosphere is made of. 303 00:17:37,500 --> 00:17:39,860 Kepler has done a tremendous job in finding 304 00:17:39,860 --> 00:17:44,220 exoplanets virtually everywhere it's looked, but it's not designed to 305 00:17:44,220 --> 00:17:48,620 give us the detailed information to tell us what those planets would be like. 306 00:17:48,620 --> 00:17:51,180 Our best bet for finding another Earth is to build 307 00:17:51,180 --> 00:17:53,860 new instruments that can take a closer look. 308 00:17:55,900 --> 00:17:58,260 That's what Nasa is doing. 309 00:17:58,260 --> 00:18:01,660 Its Tess planet finder launches in just two years' time. 310 00:18:03,660 --> 00:18:07,980 Its mission is to detect small planets orbiting bright host stars. 311 00:18:09,300 --> 00:18:11,500 Bright stars will reveal more detailed 312 00:18:11,500 --> 00:18:14,580 information about their planets, enabling us 313 00:18:14,580 --> 00:18:17,500 to better identify those that are truly earthlike. 314 00:18:23,140 --> 00:18:25,620 Of course, the ultimate prize isn't just 315 00:18:25,620 --> 00:18:30,100 finding a planet that is like Earth, it's finding intelligent life. 316 00:18:31,500 --> 00:18:34,340 We don't really know how that would manifest itself, 317 00:18:34,340 --> 00:18:37,820 but Chris has recently been involved in a discovery that has got 318 00:18:37,820 --> 00:18:39,660 some people very excited. 319 00:18:41,140 --> 00:18:44,100 I don't normally talk about my own research on the programme, 320 00:18:44,100 --> 00:18:48,060 but in the last few weeks we've announced a remarkable, strange discovery, 321 00:18:48,060 --> 00:18:52,500 probably the strangest thing we've seen in the universe in the last 20 years. 322 00:18:52,500 --> 00:18:55,500 And according to the internet and the newspapers we've discovered 323 00:18:55,500 --> 00:19:00,380 alien spaceships in orbit around a star 1,500 light years away. 324 00:19:00,380 --> 00:19:02,340 That's not quite what happened. 325 00:19:02,340 --> 00:19:06,060 We've been running a project for the last few years called Planet Hunters 326 00:19:06,060 --> 00:19:09,740 which has invited hundreds of thousands of people to go online 327 00:19:09,740 --> 00:19:13,700 and to look through this data from Kepler and try and find planets. 328 00:19:13,700 --> 00:19:17,700 And we've found planets, but a few of the volunteers pointed us 329 00:19:17,700 --> 00:19:21,140 to this one particular star which is behaving really oddly. 330 00:19:21,140 --> 00:19:26,060 This is its brightness over the course of three or four years. 331 00:19:26,060 --> 00:19:28,220 You can see most of the time it's fairly stable, 332 00:19:28,220 --> 00:19:29,460 but there are these dips. 333 00:19:29,460 --> 00:19:31,780 Just like you'd expect if there was a planet, 334 00:19:31,780 --> 00:19:33,500 but the dips happen randomly, 335 00:19:33,500 --> 00:19:34,540 some of them are huge, 336 00:19:34,540 --> 00:19:38,620 so at one point something blocks out 20% of the star's light. 337 00:19:38,620 --> 00:19:41,620 That's way too much for this to be a normal planet 338 00:19:41,620 --> 00:19:44,900 and the fact that they're irregular means this can't be something 339 00:19:44,900 --> 00:19:48,900 on a circular orbit that blocks out the star's light again and again and again. 340 00:19:48,900 --> 00:19:51,180 Something really odd is going on here. 341 00:19:51,180 --> 00:19:54,540 In fact, this is the only star amongst the 150,000 342 00:19:54,540 --> 00:19:57,060 that's doing anything like this. 343 00:19:57,060 --> 00:19:59,940 So the obvious question is what's blocking the light from the star? 344 00:19:59,940 --> 00:20:02,060 We think this might be not exoplanets, 345 00:20:02,060 --> 00:20:04,500 but a family of exocomets. 346 00:20:04,500 --> 00:20:08,460 If you have a comet on an elliptical orbit about the star 347 00:20:08,460 --> 00:20:12,900 AND that comet has broken up, so that you have a string of comets - 348 00:20:12,900 --> 00:20:15,580 rather like what happened to Shoemaker-Levy 9 349 00:20:15,580 --> 00:20:18,020 when it hit Jupiter a couple of decades ago - 350 00:20:18,020 --> 00:20:21,620 then, as each of those pieces of comet pass by the star, 351 00:20:21,620 --> 00:20:23,060 we'd see a dip. 352 00:20:23,060 --> 00:20:25,940 And so you see there's one here, there's one here, 353 00:20:25,940 --> 00:20:29,220 and then this sudden flurry of large bits that block light out. 354 00:20:29,220 --> 00:20:31,980 But we don't really understand what's going on and 355 00:20:31,980 --> 00:20:33,700 so we should consider everything, 356 00:20:33,700 --> 00:20:38,140 including the idea that this is some sort of alien civilisation. 357 00:20:38,140 --> 00:20:41,140 In fact, people are taking the idea so seriously, 358 00:20:41,140 --> 00:20:44,420 that astronomers have already pointed radio telescopes at 359 00:20:44,420 --> 00:20:47,620 this star just to listen out, Seti-style, for any signals 360 00:20:47,620 --> 00:20:52,380 that might be coming our way from what's become the most interesting star in the galaxy. 361 00:21:01,060 --> 00:21:02,900 When it comes to finding exoplanets, 362 00:21:02,900 --> 00:21:06,300 you need more than even the best home telescope. 363 00:21:06,300 --> 00:21:07,740 But Pete's here to show us 364 00:21:07,740 --> 00:21:11,780 another way we can all connect with the thrill of exoplanet discovery. 365 00:21:13,020 --> 00:21:15,060 It's actually not too bad an evening, 366 00:21:15,060 --> 00:21:18,780 it started off rather cloudy today but the skies have cleared 367 00:21:18,780 --> 00:21:21,340 and I can see some stars shining away up there, 368 00:21:21,340 --> 00:21:24,260 there's a bit of haze in the west, but that was forecast to come in. 369 00:21:24,260 --> 00:21:26,020 I'm just glad we can see some stars. 370 00:21:26,020 --> 00:21:29,660 What I'm looking for is a huge pattern in the sky that 371 00:21:29,660 --> 00:21:33,220 looks like a giant square, and that's the square of Pegasus. 372 00:21:33,220 --> 00:21:37,300 And early evening about this time of year, it's quite high up 373 00:21:37,300 --> 00:21:41,300 in the sky towards the south-east direction. 374 00:21:41,300 --> 00:21:44,900 It's pretty prominent, just look for this giant square. 375 00:21:44,900 --> 00:21:49,580 Once you've located it, look to the right-hand side of the square. 376 00:21:49,580 --> 00:21:52,220 Close to the mid point there is a faint star, 377 00:21:52,220 --> 00:21:54,060 and that's called 51 Pegasi. 378 00:21:57,420 --> 00:22:00,860 OK, well, I think I have a photograph of 51 Pegasi there, 379 00:22:00,860 --> 00:22:04,380 and of course on the back of my camera it'll look just like a regular star. 380 00:22:04,380 --> 00:22:07,700 The planet is there, we know it's there, it's been detected 381 00:22:07,700 --> 00:22:10,500 and confirmed by a number of different sources. 382 00:22:10,500 --> 00:22:14,900 The planet going around 51 Pegasi has a name, it's formal name is 383 00:22:14,900 --> 00:22:18,620 51 Pegasi b, but there is an unofficial name as well, which is Bellerophon. 384 00:22:18,620 --> 00:22:23,340 Now Bellerophon in mythology was the person that tamed the flying horse 385 00:22:23,340 --> 00:22:27,380 Pegasus, so it's rather nice being in the constellation of Pegasus itself. 386 00:22:28,900 --> 00:22:33,580 So, I think with exoplanets and regular telescopes it's really 387 00:22:33,580 --> 00:22:37,060 a journey of the imagination, you can see the star there 388 00:22:37,060 --> 00:22:39,740 through the eyepiece or on the back of the camera, but it's your 389 00:22:39,740 --> 00:22:44,860 mind that takes you into that system to imagine what it must look like. 390 00:22:44,860 --> 00:22:46,220 Absolutely fantastic. 391 00:22:48,140 --> 00:22:51,740 Go to the website to find out more about how to locate 51 Pegasi, 392 00:22:51,740 --> 00:22:56,300 to see this month's Star Guide, and also to learn about an exciting 393 00:22:56,300 --> 00:22:58,980 new project The Sky At Night has been involved in. 394 00:23:00,780 --> 00:23:04,820 This month, we're trying out a brand-new BBC messaging tool 395 00:23:04,820 --> 00:23:06,580 called Whispering Stars. 396 00:23:06,580 --> 00:23:10,500 It's a prototype at the moment but we'd love you to have a go. 397 00:23:10,500 --> 00:23:14,740 On the star map, you can click on any star with a circle round it. 398 00:23:14,740 --> 00:23:17,940 Not only will you see information from Pete about that star, 399 00:23:17,940 --> 00:23:20,100 but you can also leave your own message. 400 00:23:21,540 --> 00:23:25,140 Then I can share a link to that message via e-mail or social media. 401 00:23:26,300 --> 00:23:30,340 The recipient can find your message using a computer or a smartphone. 402 00:23:32,020 --> 00:23:35,140 I've got a new message, just have to click to find it 403 00:23:35,140 --> 00:23:38,380 and it points me up into the sky towards whichever star 404 00:23:38,380 --> 00:23:40,100 the message is attached to, 405 00:23:40,100 --> 00:23:41,820 so apparently I should keep going. 406 00:23:41,820 --> 00:23:43,540 Back this way, it's this one here, 407 00:23:43,540 --> 00:23:47,620 which looks like it is...Vega. 408 00:23:47,620 --> 00:23:50,260 And here's the message from Maggie, which says, 409 00:23:50,260 --> 00:23:52,580 "Dear Chris, I know you like astrophotography 410 00:23:52,580 --> 00:23:56,300 "but did you know that Vega was the first star to be photographed?" 411 00:23:56,300 --> 00:24:00,260 So a message sent through the stars - sort of - and you can go to our 412 00:24:00,260 --> 00:24:05,940 website at bbc.co.uk/skyatnight to use Whispering Stars for yourself. 413 00:24:05,940 --> 00:24:09,540 We'll be using it to try and send you information over the next few months. 414 00:24:16,260 --> 00:24:19,740 Even if we find another rocky planet, just like ours, 415 00:24:19,740 --> 00:24:24,260 orbiting a star similar to ours, even orbiting at the right distance, 416 00:24:24,260 --> 00:24:26,260 there's another piece of information 417 00:24:26,260 --> 00:24:29,300 we need before we can confirm we've found another Earth. 418 00:24:29,300 --> 00:24:33,420 And that information is the atmospheric composition of that exoplanet. 419 00:24:33,420 --> 00:24:36,580 And rather astonishingly, we're doing just that. 420 00:24:36,580 --> 00:24:40,220 Chris has been talking to Nikku Madhusudhan, who is leading 421 00:24:40,220 --> 00:24:44,140 the research into exoplanet atmospheres here at Cambridge. 422 00:24:44,140 --> 00:24:47,340 So we've discovered all of these planets, we know, I dunno, 423 00:24:47,340 --> 00:24:50,300 what size they are, what mass they are, but it's not really enough. 424 00:24:50,300 --> 00:24:51,860 I want to know what they're like. 425 00:24:51,860 --> 00:24:54,580 Do we have any prospect of trying to understand that? 426 00:24:54,580 --> 00:24:57,500 To, to investigating these planets properly? No, absolutely. 427 00:24:57,500 --> 00:25:01,100 So the way you do that is, you know, transiting planets, for example, 428 00:25:01,100 --> 00:25:02,580 what the transit method is 429 00:25:02,580 --> 00:25:04,820 is when the planet's star system is aligned 430 00:25:04,820 --> 00:25:09,300 in such a way that you can infer the planet going in front of the star. 431 00:25:09,300 --> 00:25:11,700 Yeah, we see these dips in the star light. Exactly. 432 00:25:11,700 --> 00:25:13,500 And we say, OK, there's a planet there. 433 00:25:13,500 --> 00:25:16,380 As it turns out, the dip in the starlight is just a little 434 00:25:16,380 --> 00:25:19,580 bit more if you have an atmosphere on top of the planet. 435 00:25:19,580 --> 00:25:22,700 Because the atmosphere blocks the light from the star as well. 436 00:25:22,700 --> 00:25:25,940 Yeah, yeah, but the key point is that the atmosphere blocks 437 00:25:25,940 --> 00:25:28,940 the light in some wavelengths and not in others. 438 00:25:28,940 --> 00:25:31,540 And so that means if you have a transiting planet you can say 439 00:25:31,540 --> 00:25:33,740 something about what its atmosphere is made of? 440 00:25:33,740 --> 00:25:36,660 Exactly, you can infer its chemical composition. 441 00:25:36,660 --> 00:25:38,900 OK, so Earth is mostly nitrogen, bit of oxygen, 442 00:25:38,900 --> 00:25:41,700 bit of carbon dioxide, what do we see on these exoplanets? 443 00:25:41,700 --> 00:25:45,620 Yep, so the exoplanets, um, that we are most 444 00:25:45,620 --> 00:25:49,140 able to study today are the big and hot ones. 445 00:25:49,140 --> 00:25:50,940 It's because the bigger the planet, 446 00:25:50,940 --> 00:25:53,020 the bigger the starlight you're blocking. 447 00:25:53,020 --> 00:25:54,220 Yeah, the bigger the dip. 448 00:25:54,220 --> 00:25:56,700 The bigger the dip, so it's just easier to find them. 449 00:25:56,700 --> 00:26:01,100 And hot because the hotter the atmosphere is the more 450 00:26:01,100 --> 00:26:05,820 puffier it is. Hm. Right, so, so the bigger it is. 451 00:26:05,820 --> 00:26:09,380 So the hotter the atmosphere, the bigger the atmosphere, and the more light it blocks. 452 00:26:09,380 --> 00:26:13,140 Right, so most of the results to date have come from these 453 00:26:13,140 --> 00:26:14,900 objects called hot Jupiters. 454 00:26:14,900 --> 00:26:17,100 What do we know about the conditions? 455 00:26:17,100 --> 00:26:20,020 We know they're large, that means they must be made of gas, mostly. 456 00:26:20,020 --> 00:26:25,100 What do we know about the atmosphere? We are finding less water than we would expect 457 00:26:25,100 --> 00:26:28,060 if the planets formed in a solar-like environment 458 00:26:28,060 --> 00:26:31,820 Oh, OK. And they could be less by even a factor of ten. 459 00:26:31,820 --> 00:26:37,180 One explanation is that maybe these objects have clouds in their atmospheres. 460 00:26:37,180 --> 00:26:41,060 So you're, you're saying the water would be hidden? By the clouds? 461 00:26:41,060 --> 00:26:44,580 Yeah, exactly. So you only see the bit of the atmosphere above the clouds? 462 00:26:44,580 --> 00:26:48,460 Exactly, so, so that's one way. So it's a straightforward explanation - 463 00:26:48,460 --> 00:26:52,940 astronomers being confused by clouds is common here on Earth as well. 464 00:26:52,940 --> 00:26:55,580 It's not only on Earth, not only a terrestrial experience, 465 00:26:55,580 --> 00:26:58,740 even when you go to exoplanets clouds are a headache. 466 00:26:58,740 --> 00:27:00,100 But there is a subtlety. 467 00:27:00,100 --> 00:27:03,380 Clouds are not the same clouds we have here. 468 00:27:03,380 --> 00:27:06,020 Right, so on Earth they are water clouds. 469 00:27:06,020 --> 00:27:09,300 But these are planets at a few thousand degrees. Of course, so... 470 00:27:09,300 --> 00:27:11,540 So you can't have water clouds. 471 00:27:11,540 --> 00:27:14,380 So you may have to invoke iron clouds, 472 00:27:14,380 --> 00:27:17,020 or silicate clouds, you see it in rocks, 473 00:27:17,020 --> 00:27:19,140 on Earth rocks are made of silicates, 474 00:27:19,140 --> 00:27:20,820 so you might be able to make 475 00:27:20,820 --> 00:27:24,100 clouds out of those same silicates, hanging up in the atmosphere. 476 00:27:24,100 --> 00:27:26,020 Wow, suddenly it's a place to me, 477 00:27:26,020 --> 00:27:28,300 because we are talking about what they're like. 478 00:27:28,300 --> 00:27:30,380 I can, I sort of feel they're real. 479 00:27:30,380 --> 00:27:32,820 Yeah. Remarkable stuff, and we'll come back 480 00:27:32,820 --> 00:27:35,100 and see how you're getting on in a few years perhaps. 481 00:27:35,100 --> 00:27:37,740 Thank you very much. Thank you, thank you. 482 00:27:37,740 --> 00:27:40,180 It's amazing we've come so far in just 20 years. 483 00:27:40,180 --> 00:27:43,020 Going from no exoplanets to about 2,000 now! 484 00:27:43,020 --> 00:27:45,820 And turning them from just points on a graph, from just data, 485 00:27:45,820 --> 00:27:49,340 to real places with atmospheres, and rain, 486 00:27:49,340 --> 00:27:52,740 and even clouds to annoy the astronomers! 487 00:27:52,740 --> 00:27:55,740 What I'm fascinated by, is if we did find an earthlike planet, 488 00:27:55,740 --> 00:27:57,940 I mean, even signs of life, what would we do then? 489 00:27:57,940 --> 00:27:59,380 We'd have to go, wouldn't we? 490 00:27:59,380 --> 00:28:02,780 If you looked at the sky and you could say that star has an earthlike planet, 491 00:28:02,780 --> 00:28:06,460 the right temperature, with life in its atmosphere - you'd have to send a probe. 492 00:28:06,460 --> 00:28:10,180 It'd take thousands of years to get there! We still should send something, I mean, maybe not us, 493 00:28:10,180 --> 00:28:14,140 but we should send something just so we know we're on our way. I have to agree, you're right! 494 00:28:19,180 --> 00:28:22,380 That's it for this month. Next month we have a Christmas special! 495 00:28:22,380 --> 00:28:25,380 We'll be taking an astronomical look at the mystery surrounding 496 00:28:25,380 --> 00:28:27,140 the Star of Bethlehem. 497 00:28:27,140 --> 00:28:29,340 Was it just a conjunction of planets 498 00:28:29,340 --> 00:28:31,580 or something more exciting like a comet, 499 00:28:31,580 --> 00:28:32,980 or a supernova? 500 00:28:32,980 --> 00:28:36,460 In the meanwhile, get outside and get looking up. 501 00:28:36,460 --> 00:28:37,700 Goodnight.