1 00:00:01,500 --> 00:00:05,300 Tonight on The Sky At Night, we're going interstellar. 2 00:00:05,300 --> 00:00:08,340 Travelling to the stars has always seemed like an impossible dream, 3 00:00:08,340 --> 00:00:10,420 but now some scientists believe 4 00:00:10,420 --> 00:00:12,860 that it may be possible within our lifetimes. 5 00:00:12,860 --> 00:00:15,540 And that prospect has just become even more enticing 6 00:00:15,540 --> 00:00:18,020 because we have a target to aim for. 7 00:00:18,020 --> 00:00:20,580 Within the last few weeks, astronomers have announced 8 00:00:20,580 --> 00:00:24,860 the discovery of a hospitable planet around the Sun's nearest neighbour, 9 00:00:24,860 --> 00:00:25,940 Proxima Centauri. 10 00:00:27,060 --> 00:00:28,500 On tonight's programme, 11 00:00:28,500 --> 00:00:31,420 we'll be finding out how this new planet was detected 12 00:00:31,420 --> 00:00:33,780 and why it's such an important discovery. 13 00:00:35,220 --> 00:00:38,940 And Jim Al-Khalili will be exploring the revolutionary new technology 14 00:00:38,940 --> 00:00:41,940 that might take us deep into space. 15 00:00:41,940 --> 00:00:43,940 Welcome to The Sky At Night. 16 00:01:14,020 --> 00:01:18,460 On August 24th, astronomers made an extraordinary announcement. 17 00:01:18,460 --> 00:01:20,700 Scientists are hailing a major discovery - 18 00:01:20,700 --> 00:01:23,540 a new planet which they've called Proxima b. 19 00:01:23,540 --> 00:01:26,860 At just four light years away, it's relatively close to us. 20 00:01:26,860 --> 00:01:28,540 It's roughly the same size as Earth, 21 00:01:28,540 --> 00:01:31,540 and because it's just the right distance away from its star, 22 00:01:31,540 --> 00:01:34,380 it could be the right temperature to have liquid water 23 00:01:34,380 --> 00:01:36,100 and possibly life. 24 00:01:37,620 --> 00:01:39,300 Over the last few years, 25 00:01:39,300 --> 00:01:44,260 we have identified over 3,000 planets orbiting other stars, 26 00:01:44,260 --> 00:01:46,820 but this one is special. 27 00:01:46,820 --> 00:01:49,980 It's already been called one of the discoveries of the century. 28 00:01:49,980 --> 00:01:53,220 So what makes this planet such an enticing target 29 00:01:53,220 --> 00:01:55,060 for our first interstellar mission? 30 00:01:57,060 --> 00:02:00,300 Proxima b is in orbit around Proxima Centauri, 31 00:02:00,300 --> 00:02:02,940 the closest star to our sun. 32 00:02:02,940 --> 00:02:08,380 Only discovered in 1915, Proxima is an apparently unremarkable star. 33 00:02:08,380 --> 00:02:10,500 It's the smallest of the three stars 34 00:02:10,500 --> 00:02:13,020 that make up the Alpha Centauri system. 35 00:02:13,020 --> 00:02:17,220 A red dwarf, like 70% of the stars in the Milky Way, 36 00:02:17,220 --> 00:02:19,620 it's just 12% of the mass of the sun. 37 00:02:23,900 --> 00:02:28,060 That small size means the pressure and the temperature at the core 38 00:02:28,060 --> 00:02:30,220 are much less than in our sun, 39 00:02:30,220 --> 00:02:33,420 and so the processes of nuclear fusion that power the star 40 00:02:33,420 --> 00:02:35,100 proceed much more slowly. 41 00:02:36,460 --> 00:02:39,340 And so, Proxima Centauri is cool. 42 00:02:39,340 --> 00:02:42,180 Its surface temperature is only half that of the sun 43 00:02:42,180 --> 00:02:45,740 and its luminosity is 500 times lower. 44 00:02:45,740 --> 00:02:49,900 In fact, it's so dim that even though it's the closest star to us, 45 00:02:49,900 --> 00:02:53,380 it can't be seen from Earth with the naked eye. 46 00:02:53,380 --> 00:02:56,500 But the discovery of a planet around Proxima Centauri 47 00:02:56,500 --> 00:02:58,700 makes it a much more exciting neighbour. 48 00:03:01,260 --> 00:03:04,540 This is the paper published in Nature just last month 49 00:03:04,540 --> 00:03:07,340 that announced the discovery of the planet 50 00:03:07,340 --> 00:03:09,460 that the team called Proxima b. 51 00:03:09,460 --> 00:03:12,740 I've come here to Queen Mary University of London 52 00:03:12,740 --> 00:03:14,620 to meet Guillem Anglada-Escude, 53 00:03:14,620 --> 00:03:17,700 the leader of the team that made this remarkable discovery. 54 00:03:19,820 --> 00:03:23,300 Anglada was part of a project called the Pale Red Dot 55 00:03:23,300 --> 00:03:26,420 that used the European Southern Observatory's telescopes 56 00:03:26,420 --> 00:03:31,180 in Chile to observe the star for 60 straight nights last spring, 57 00:03:31,180 --> 00:03:34,060 and it's only now, after careful analysis, 58 00:03:34,060 --> 00:03:36,260 that the results have been released. 59 00:03:36,260 --> 00:03:37,700 Congratulations. Thank you. 60 00:03:37,700 --> 00:03:40,060 It's a wonderful, wonderful discovery, 61 00:03:40,060 --> 00:03:43,020 but how on Earth do you tell that this tiny planet is there 62 00:03:43,020 --> 00:03:45,540 going around the star? 63 00:03:45,540 --> 00:03:48,220 Well, that... Well, that took some time. 64 00:03:48,220 --> 00:03:50,860 It was not something that happened from one day to the next. 65 00:03:50,860 --> 00:03:52,740 But I think the thing that's difficult for me 66 00:03:52,740 --> 00:03:55,420 to get my head round is I sort of imagine you taking a picture 67 00:03:55,420 --> 00:03:58,460 and looking for the planet in the image, but that's not how it works. 68 00:03:58,460 --> 00:03:59,980 No. No, not in these cases. 69 00:03:59,980 --> 00:04:02,020 And most of the planets don't work this way because 70 00:04:02,020 --> 00:04:04,220 the planets are very faint compared to the stars. 71 00:04:04,220 --> 00:04:06,220 So what you see is the star, 72 00:04:06,220 --> 00:04:08,180 and we are using a method that is indirect. 73 00:04:08,180 --> 00:04:10,580 So we see what the planet is doing to the star because 74 00:04:10,580 --> 00:04:12,460 the planet and the star both have mass 75 00:04:12,460 --> 00:04:14,980 and therefore they attract gravitationally, 76 00:04:14,980 --> 00:04:18,260 and the planet going around the star moves the star itself, 77 00:04:18,260 --> 00:04:20,060 and that is what we are trying to measure. 78 00:04:20,060 --> 00:04:21,300 I was going to say, 79 00:04:21,300 --> 00:04:24,340 because the planets are small compared to the stars, 80 00:04:24,340 --> 00:04:26,380 so this motion must be very subtle. 81 00:04:26,380 --> 00:04:29,020 For example, the Earth can't have much effect on the sun. 82 00:04:29,020 --> 00:04:31,100 The effect of the Earth on the sun is small - 83 00:04:31,100 --> 00:04:32,820 it's about 10 centimetres per second. 84 00:04:32,820 --> 00:04:36,660 So you can think of just moving like this, like an ant. 85 00:04:36,660 --> 00:04:40,540 For planets around stars that are much smaller, like Proxima, 86 00:04:40,540 --> 00:04:44,740 the star is smaller, so the planet is making the star move more, 87 00:04:44,740 --> 00:04:49,020 and in that case, the motion is about metre per second level. 88 00:04:49,020 --> 00:04:53,380 Wow, so you are able to detect that a whole star is moving 89 00:04:53,380 --> 00:04:55,660 at a metre per second, which is... 90 00:04:55,660 --> 00:04:57,460 That's sort of walking pace. 91 00:04:57,460 --> 00:05:01,340 Exactly. And it's not a trivial thing to do because what you have is 92 00:05:01,340 --> 00:05:03,980 the planet going around the star periodically, 93 00:05:03,980 --> 00:05:07,220 and we see this motion going up and down, up and down. 94 00:05:07,220 --> 00:05:10,180 So you see a wave, like something like this. 95 00:05:10,180 --> 00:05:12,860 And that's the signature that tells you that there's a planet. 96 00:05:12,860 --> 00:05:15,940 When you see something like this in a star that repeats over time, 97 00:05:15,940 --> 00:05:19,740 that is always consistent and a number of other things, 98 00:05:19,740 --> 00:05:22,460 this is when you're convinced that you have a planet around a star. 99 00:05:22,460 --> 00:05:24,980 Excellent. And then from there, the next question is, 100 00:05:24,980 --> 00:05:26,740 what do we know about this planet? 101 00:05:26,740 --> 00:05:28,900 What can we tell, other than the fact that it's there 102 00:05:28,900 --> 00:05:30,620 and it's making the star move? 103 00:05:30,620 --> 00:05:33,820 So, just from the motion that we detect, this time, 104 00:05:33,820 --> 00:05:37,020 sorry, this curve, this oscillation, we know the period. 105 00:05:37,020 --> 00:05:39,260 And for this planet, what is that number? 106 00:05:39,260 --> 00:05:40,780 It's 11.2 days. 107 00:05:40,780 --> 00:05:43,380 So it's going round pretty quickly. Yes. 108 00:05:43,380 --> 00:05:47,580 From that we can infer the distance between the star and the planet. 109 00:05:47,580 --> 00:05:49,780 Just from knowing how gravity works, basically. 110 00:05:49,780 --> 00:05:52,260 Yes. This is Kepler's law, the first Kepler's law. 111 00:05:52,260 --> 00:05:54,380 And so what is that separation for this planet? 112 00:05:54,380 --> 00:05:57,980 In this case, it is around 5% an astronomical unit. 113 00:05:57,980 --> 00:05:59,820 OK. So that's what? 114 00:05:59,820 --> 00:06:03,460 That something like 7.5 million kilometres, something like that? 115 00:06:03,460 --> 00:06:05,260 You're faster than me. Yeah, OK. 116 00:06:05,260 --> 00:06:07,060 But it's very close to the star. 117 00:06:07,060 --> 00:06:09,860 That's much closer to the star than Mercury is to the sun. 118 00:06:09,860 --> 00:06:13,420 Yes. Yeah. It's about a tenth of the distance 119 00:06:13,420 --> 00:06:15,260 between Mercury and the sun. 120 00:06:15,260 --> 00:06:20,180 And the other thing we get from this curve is the mass of the planet. 121 00:06:20,180 --> 00:06:21,540 And what is that mass? 122 00:06:21,540 --> 00:06:25,780 This mass is 1.3, 1.4 Earth masses. 123 00:06:25,780 --> 00:06:29,340 So for this system, we've got a one and a third Earth mass planet 124 00:06:29,340 --> 00:06:32,260 going around its star every 11 days. 125 00:06:32,260 --> 00:06:33,820 So, just thinking about that, 126 00:06:33,820 --> 00:06:37,020 I expect... That's much closer to the star than Mercury is to the sun, 127 00:06:37,020 --> 00:06:38,780 so I'd expect that to be hot. 128 00:06:38,780 --> 00:06:42,020 Yes, you would expect that to be hot if that was the sun, 129 00:06:42,020 --> 00:06:45,820 but this is Proxima and it's a red star, it's a red dwarf. 130 00:06:45,820 --> 00:06:48,100 And it's a small red dwarf, 131 00:06:48,100 --> 00:06:51,820 so Proxima has around 12% of the mass of the sun, 132 00:06:51,820 --> 00:06:54,060 so this means that if you want to keep warm, 133 00:06:54,060 --> 00:06:56,060 you have to be much closer to the star. 134 00:06:56,060 --> 00:06:58,380 Right. And this is when the magic happens, 135 00:06:58,380 --> 00:07:00,900 where you put all the numbers together and you can estimate 136 00:07:00,900 --> 00:07:03,660 how much light, how much energy is reaching the planet. 137 00:07:03,660 --> 00:07:05,860 And this amount of energy is about 70%, 138 00:07:05,860 --> 00:07:09,460 the amount of energy that Earth is receiving from the sun. 139 00:07:09,460 --> 00:07:12,700 And so it's actually pretty warm by planetary standards. 140 00:07:12,700 --> 00:07:14,540 By planetary standards. 141 00:07:14,540 --> 00:07:16,780 The next calculation you can do is try to estimate 142 00:07:16,780 --> 00:07:19,140 the temperature that this planet would have. 143 00:07:19,140 --> 00:07:21,500 And you do the numbers and you get 240 Kelvins. 144 00:07:21,500 --> 00:07:23,700 That's what? -30 centigrade. 145 00:07:23,700 --> 00:07:26,460 -30, -40 Celsius, something like this. 146 00:07:26,460 --> 00:07:28,660 But you would say, oh, that would be frozen, 147 00:07:28,660 --> 00:07:30,500 but the same would happen to Earth. 148 00:07:30,500 --> 00:07:33,620 Earth is about 255 Kelvins, 149 00:07:33,620 --> 00:07:37,620 which means it's -20 Celsius. And this is not -20, right? 150 00:07:37,620 --> 00:07:41,460 And what happens there is that Earth has an atmosphere and keeps it warm. 151 00:07:41,460 --> 00:07:44,260 So in principle, this planet, if it has an atmosphere, 152 00:07:44,260 --> 00:07:47,460 it would have a greenhouse effect, and that would keep the planet warm. 153 00:07:47,460 --> 00:07:50,380 So with an atmosphere, it might be warm enough to have liquid water. 154 00:07:50,380 --> 00:07:51,940 Yes. That's the... 155 00:07:51,940 --> 00:07:54,380 That's also the highlight of the discovery. 156 00:07:54,380 --> 00:07:56,420 Well, it's great to be talking about this. 157 00:07:56,420 --> 00:07:57,980 Congratulations again. 158 00:07:57,980 --> 00:08:00,260 I can't wait to see what further research comes out 159 00:08:00,260 --> 00:08:02,820 and what else is there. Thanks a lot. Thank you. 160 00:08:04,980 --> 00:08:09,060 The discovery of a potential earthlike planet so close to us 161 00:08:09,060 --> 00:08:11,820 instantly raises another question - 162 00:08:11,820 --> 00:08:14,500 could we send a spacecraft to visit it? 163 00:08:16,100 --> 00:08:19,540 Everybody ready to say goodbye to our solar system? 164 00:08:19,540 --> 00:08:23,820 In science fiction, interstellar travel always seems easy. 165 00:08:23,820 --> 00:08:25,940 Here we go. 166 00:08:25,940 --> 00:08:27,460 In the film Interstellar, 167 00:08:27,460 --> 00:08:30,540 it's simply a matter of dropping through a wormhole. 168 00:08:32,300 --> 00:08:34,620 Maximum warp. Punch it. 169 00:08:34,620 --> 00:08:38,860 In Star Trek, a warp drive is used to bend the shape of space-time. 170 00:08:42,100 --> 00:08:43,100 Compressor. 171 00:08:47,140 --> 00:08:50,180 And in the Star Wars universe, you just need to throw a switch 172 00:08:50,180 --> 00:08:53,500 to accelerate past light speed and into hyperspace. 173 00:08:57,620 --> 00:08:59,780 But in reality, travelling to the stars 174 00:08:59,780 --> 00:09:02,420 has always seemed an impossible dream. 175 00:09:02,420 --> 00:09:03,660 Until now. 176 00:09:05,060 --> 00:09:08,460 We asked Jim Al-Khalili to explain why it's so difficult 177 00:09:08,460 --> 00:09:12,180 to travel to the stars and to investigate the technology 178 00:09:12,180 --> 00:09:15,660 that might be about to make interstellar travel possible. 179 00:09:17,420 --> 00:09:19,700 For decades, centuries, even, 180 00:09:19,700 --> 00:09:23,100 we've been wondering what kind of fast engines would be needed 181 00:09:23,100 --> 00:09:24,900 to carry us to the stars. 182 00:09:24,900 --> 00:09:28,820 There's one simple overwhelming problem when it comes to 183 00:09:28,820 --> 00:09:31,180 travelling across interstellar space. 184 00:09:31,180 --> 00:09:35,740 As Douglas Adams once said, "Space is big. Really big." 185 00:09:37,420 --> 00:09:41,380 And so far we've only been able to explore the tiniest fraction of it. 186 00:09:43,340 --> 00:09:47,780 The craft that we've sent furthest into space is Voyager 1. 187 00:09:47,780 --> 00:09:49,700 Launched in 1977, 188 00:09:49,700 --> 00:09:53,260 it visited Jupiter and Saturn before heading for the outer edges 189 00:09:53,260 --> 00:09:57,180 of the solar system. Now, nearly 40 years later, 190 00:09:57,180 --> 00:10:00,180 it's escaped the solar system and has started the journey 191 00:10:00,180 --> 00:10:02,500 through interstellar space. 192 00:10:02,500 --> 00:10:04,780 But it has a very, very long way to go 193 00:10:04,780 --> 00:10:06,620 to get as far as Proxima Centauri. 194 00:10:08,300 --> 00:10:11,340 Any practical mission to the stars would need to get there 195 00:10:11,340 --> 00:10:15,020 in a reasonable amount of time - say 20 years. 196 00:10:15,020 --> 00:10:17,660 But that means going incredibly fast. 197 00:10:19,140 --> 00:10:22,180 The distance between Earth and Proxima Centauri 198 00:10:22,180 --> 00:10:26,500 is just under 4.25 light years. 199 00:10:26,500 --> 00:10:30,620 Now, that works out at roughly 40 trillion kilometres, 200 00:10:30,620 --> 00:10:35,020 or 4 x 10 to the 13. 201 00:10:35,020 --> 00:10:38,460 Now, in order to cover this vast distance in 20 years, 202 00:10:38,460 --> 00:10:43,060 a spacecraft would have to travel at 20% the speed of light. 203 00:10:43,060 --> 00:10:48,940 That's roughly 64,000 kilometres per second. 204 00:10:50,300 --> 00:10:53,740 If you compare this with the speed that Voyager currently travels at - 205 00:10:53,740 --> 00:10:57,900 a mere 17km per second. 206 00:10:57,900 --> 00:11:01,340 It is this disparity between the speed that is required 207 00:11:01,340 --> 00:11:05,900 and what is commonly achievable that has always made interstellar travel 208 00:11:05,900 --> 00:11:07,740 seem almost impossible. 209 00:11:10,340 --> 00:11:13,020 The biggest problem in reaching the speeds needed 210 00:11:13,020 --> 00:11:17,020 for interstellar travel is the sheer amount of energy required 211 00:11:17,020 --> 00:11:19,020 to produce the acceleration. 212 00:11:19,020 --> 00:11:23,620 The Saturn V was the largest and most powerful rocket ever built. 213 00:11:23,620 --> 00:11:28,300 It weighed nearly 3,000 tonnes and almost all of that was the fuel 214 00:11:28,300 --> 00:11:33,340 required to propel its meagre 44-tonne payload to the moon. 215 00:11:33,340 --> 00:11:36,860 Accelerating a spacecraft to the speeds needed to reach the stars 216 00:11:36,860 --> 00:11:40,260 would require much more energy than you could ever produce 217 00:11:40,260 --> 00:11:42,060 with a conventional rocket. 218 00:11:42,060 --> 00:11:45,380 It would need a completely new type of propulsion system. 219 00:11:47,180 --> 00:11:50,380 In the 1970s, the British Interplanetary Society 220 00:11:50,380 --> 00:11:53,540 set out to see if it was possible to design a spacecraft 221 00:11:53,540 --> 00:11:56,500 that could travel at 12% the speed of light. 222 00:11:56,500 --> 00:12:01,020 Such a craft would reach Proxima Centauri in about 40 years. 223 00:12:01,020 --> 00:12:03,580 They called it Project Daedalus. 224 00:12:03,580 --> 00:12:04,900 And here it is. 225 00:12:04,900 --> 00:12:08,620 It was to be huge craft - 200 metres along - 226 00:12:08,620 --> 00:12:11,940 and to save on the energy of getting it off the Earth's surface, 227 00:12:11,940 --> 00:12:14,060 it was to be built in orbit. 228 00:12:14,060 --> 00:12:17,420 Now, it would be powered by a nuclear pulse engine 229 00:12:17,420 --> 00:12:21,300 using nuclear fusion, a technology that hasn't even been invented yet, 230 00:12:21,300 --> 00:12:24,940 but that was seen to provide much more energy than chemical rockets 231 00:12:24,940 --> 00:12:27,940 that we use today. Still, to get it up to speed, 232 00:12:27,940 --> 00:12:32,860 it would need 50,000 tonnes of deuterium helium-3 fuel 233 00:12:32,860 --> 00:12:36,020 that would be stored in these vast tanks. 234 00:12:36,020 --> 00:12:38,780 Now, there's not enough helium on Earth for this, 235 00:12:38,780 --> 00:12:42,140 so they suggested that helium could be harvested 236 00:12:42,140 --> 00:12:44,300 from the surface of Jupiter. 237 00:12:44,300 --> 00:12:45,300 Easy, really. 238 00:12:46,300 --> 00:12:47,900 Perhaps, unsurprisingly, 239 00:12:47,900 --> 00:12:50,340 Project Daedalus never made it off the drawing board. 240 00:12:53,820 --> 00:12:57,700 But, more than 40 years later, there's another suggestion. 241 00:12:57,700 --> 00:13:01,620 In April, Stephen Hawking and Internet billionaire Yuri Milner 242 00:13:01,620 --> 00:13:05,340 announced that they were putting up $100 million to develop 243 00:13:05,340 --> 00:13:09,460 a new interstellar project called Breakthrough Starshot. 244 00:13:09,460 --> 00:13:12,460 For the first time in human history, 245 00:13:12,460 --> 00:13:15,940 we can do more than just gaze at the stars. 246 00:13:15,940 --> 00:13:17,380 We can actually reach them. 247 00:13:19,140 --> 00:13:22,020 There are two key features to this new system. 248 00:13:22,020 --> 00:13:26,060 The first is that the spacecraft won't be carrying its own engines. 249 00:13:26,060 --> 00:13:30,380 Instead, it will have a sail that is propelled by the force of light. 250 00:13:31,980 --> 00:13:33,900 Released from a launcher in orbit, 251 00:13:33,900 --> 00:13:37,900 the spacecraft will be accelerated by the second new concept - 252 00:13:37,900 --> 00:13:40,700 a vast array of lasers fired from Earth. 253 00:13:42,780 --> 00:13:45,540 Theoretically, the planned 100 gigawatt laser 254 00:13:45,540 --> 00:13:50,020 that has about the same power output as 100 nuclear power stations 255 00:13:50,020 --> 00:13:52,900 could accelerate a spacecraft to nearly a quarter 256 00:13:52,900 --> 00:13:55,220 of the speed of light in about two minutes. 257 00:13:57,420 --> 00:14:00,620 It would reach Mars in just half an hour. 258 00:14:00,620 --> 00:14:03,580 It would overtake Voyager in about four days 259 00:14:03,580 --> 00:14:07,980 and it would get to Proxima Centauri in little over 20 years. 260 00:14:09,220 --> 00:14:11,140 There's only one problem - 261 00:14:11,140 --> 00:14:14,220 to reach those speeds, the spacecraft will have to be 262 00:14:14,220 --> 00:14:18,100 incredibly light, probably weighing no more than one gram. 263 00:14:19,340 --> 00:14:21,740 It's not exactly the Starship Enterprise, 264 00:14:21,740 --> 00:14:25,620 but what could you achieve with a one-gram spacecraft? 265 00:14:25,620 --> 00:14:28,220 I called up Harvard cosmologist Avi Loeb, 266 00:14:28,220 --> 00:14:30,860 one of the scientists behind the project, to find out more. 267 00:14:32,860 --> 00:14:35,340 Avi, this is a hugely ambitious project. 268 00:14:35,340 --> 00:14:37,620 Do you really think it's possible? 269 00:14:37,620 --> 00:14:40,340 Yes, we hope that we can achieve the goals 270 00:14:40,340 --> 00:14:42,220 of this very ambitious project 271 00:14:42,220 --> 00:14:44,900 within the lifetime of our generation. 272 00:14:46,060 --> 00:14:50,580 This project is as ambitious as was building the pyramids 273 00:14:50,580 --> 00:14:55,460 or building cathedrals in ancient times. 274 00:14:55,460 --> 00:15:00,020 You can think of it as the cathedral of our generation. 275 00:15:00,020 --> 00:15:03,860 The only difference from past cathedrals is that it reaches 276 00:15:03,860 --> 00:15:05,980 all the way out the stars. 277 00:15:05,980 --> 00:15:07,940 And what about the cost? 278 00:15:07,940 --> 00:15:09,860 Presumably this is going to be hugely expensive. 279 00:15:11,500 --> 00:15:15,180 The cost is up to $10 billion - 280 00:15:15,180 --> 00:15:20,860 of the order of the biggest science projects that we encountered so far, 281 00:15:20,860 --> 00:15:25,180 such as Cern or the James Webb Space Telescope. 282 00:15:25,180 --> 00:15:30,460 A critic will say that's a lot of money to send a one-gram spacecraft 283 00:15:30,460 --> 00:15:35,500 through space. How much science can you do with a one-gram payload? 284 00:15:35,500 --> 00:15:40,540 Fortunately, these days we can pack a lot of smart electronics 285 00:15:40,540 --> 00:15:44,500 into a single gram. If you look at a cellphone and strip it 286 00:15:44,500 --> 00:15:48,340 from the protective case 287 00:15:48,340 --> 00:15:50,900 and strip it from the human interface, 288 00:15:50,900 --> 00:15:54,940 you're left roughly with a gram, and that includes a camera, 289 00:15:54,940 --> 00:15:58,460 a communication device, navigation - 290 00:15:58,460 --> 00:16:02,620 all of the ingredients we need in the Starshot spacecraft. 291 00:16:02,620 --> 00:16:06,140 And presumably, if the technology is successful, 292 00:16:06,140 --> 00:16:09,500 it could be used for other than just interstellar travel. 293 00:16:09,500 --> 00:16:13,660 Yes, this technology can be used to explore the space in between us 294 00:16:13,660 --> 00:16:15,580 and the nearest star. 295 00:16:15,580 --> 00:16:20,260 For example, we could search for life within the solar system. 296 00:16:20,260 --> 00:16:24,140 It would take us only a few days to reach Pluto, 297 00:16:24,140 --> 00:16:28,340 instead of about a decade that it took New Horizons to get there. 298 00:16:28,340 --> 00:16:31,060 And so, in principle, the technology that we develop 299 00:16:31,060 --> 00:16:34,340 will allow us to probe the edge of the solar system 300 00:16:34,340 --> 00:16:36,700 within a relatively short time. 301 00:16:36,700 --> 00:16:39,540 And what's the timescale for the project? 302 00:16:39,540 --> 00:16:40,900 What happens next? 303 00:16:40,900 --> 00:16:45,260 The first five to ten years will be dedicated to a feasibility study, 304 00:16:45,260 --> 00:16:50,660 where we will demonstrate the technology of reaching a speed 305 00:16:50,660 --> 00:16:54,700 far larger than previously reached with chemical rocketry 306 00:16:54,700 --> 00:16:56,420 in a laboratory set-up. 307 00:16:56,420 --> 00:17:02,140 And after demonstrating that, we hope to expand the system 308 00:17:02,140 --> 00:17:05,060 until we reach the final design 309 00:17:05,060 --> 00:17:08,420 within about 20 to 30 years from now. 310 00:17:08,420 --> 00:17:11,580 Following that, we hope to launch the spacecrafts, 311 00:17:11,580 --> 00:17:15,700 and it will take them about 20 years to reach Alpha Centauri, 312 00:17:15,700 --> 00:17:20,300 and another four years for the signal from them to teach us. 313 00:17:20,300 --> 00:17:22,660 And so, altogether, 314 00:17:22,660 --> 00:17:28,780 we hope to get those signals while we are still alive. 315 00:17:28,780 --> 00:17:30,260 I'm the same age as you, 316 00:17:30,260 --> 00:17:33,940 so I just hope we're both around to see this project completed 317 00:17:33,940 --> 00:17:35,940 and successful in our lifetime. 318 00:17:35,940 --> 00:17:37,900 I wish you the very best of luck. 319 00:17:37,900 --> 00:17:38,940 Thank you so much. 320 00:17:42,340 --> 00:17:44,260 Before the system becomes a reality, 321 00:17:44,260 --> 00:17:46,900 there are many other technical problems to solve... 322 00:17:48,700 --> 00:17:52,860 ..like building a material that can withstand a 100 gigawatt laser 323 00:17:52,860 --> 00:17:55,220 without burning up, 324 00:17:55,220 --> 00:17:58,900 and how to get a signal back from a tiny spacecraft 325 00:17:58,900 --> 00:18:02,140 hurtling away from us at 20% the speed of light. 326 00:18:03,820 --> 00:18:05,700 It's an exciting prospect. 327 00:18:05,700 --> 00:18:08,820 There are still many practical problems to solve and, you know, 328 00:18:08,820 --> 00:18:11,660 it's still hard to believe that it would succeed. 329 00:18:11,660 --> 00:18:15,940 But looking at this project makes me realise that something I always 330 00:18:15,940 --> 00:18:20,260 thought was unreachable may actually be possible. 331 00:18:20,260 --> 00:18:23,500 If it succeeds, it wouldn't just revolutionise space travel, 332 00:18:23,500 --> 00:18:27,140 it would vastly increase our knowledge of the universe around us. 333 00:18:27,140 --> 00:18:30,180 And who knows? With the will and the money, 334 00:18:30,180 --> 00:18:32,820 it may actually happen in my lifetime. 335 00:18:36,420 --> 00:18:39,420 If we do develop the means to travel to the stars, 336 00:18:39,420 --> 00:18:43,020 Proxima Centauri won't be our only destination. 337 00:18:43,020 --> 00:18:45,140 There are other nearby stars we could visit. 338 00:18:46,780 --> 00:18:50,420 Pete has been identifying some of the other potential targets. 339 00:18:53,820 --> 00:18:58,700 Within 15 light years of the sun, there are approximately 58 stars 340 00:18:58,700 --> 00:19:02,260 in 39 separate stellar systems, each being very different. 341 00:19:03,420 --> 00:19:06,300 This group of stars are the closest to being within reach 342 00:19:06,300 --> 00:19:08,180 of an interstellar mission. 343 00:19:08,180 --> 00:19:11,900 Many of them are cool red dwarfs like Proxima Centauri, 344 00:19:11,900 --> 00:19:15,180 and the more optimistic studies place at least one planet 345 00:19:15,180 --> 00:19:18,460 in the habitable zone around each one. 346 00:19:18,460 --> 00:19:21,620 One of the closest red dwarfs is Barnard's Star. 347 00:19:21,620 --> 00:19:23,300 Just six light years away, 348 00:19:23,300 --> 00:19:27,020 it has the highest proper motion of any star in the sky. 349 00:19:27,020 --> 00:19:31,980 At present, it's well placed in the west-southwest at around 9pm, 350 00:19:31,980 --> 00:19:35,940 positioned off the eastern shoulder of Ophiuchus. 351 00:19:35,940 --> 00:19:41,140 To find it, look for a faint V in the sky known as Poniatovski's Bull. 352 00:19:41,140 --> 00:19:43,860 Barnard's Star sits to the top right. 353 00:19:43,860 --> 00:19:47,780 The closest sunlike star to ours is Tau Ceti. 354 00:19:47,780 --> 00:19:52,540 11.9 light years away, it sits low in the constellation of Cetus, 355 00:19:52,540 --> 00:19:54,620 rising in the east-southeast, 356 00:19:54,620 --> 00:19:57,300 and is one of my favourite stars to observe. 357 00:19:57,300 --> 00:20:00,460 It's at its highest from 3am. 358 00:20:00,460 --> 00:20:02,580 Locate the Great Square of Pegasus, 359 00:20:02,580 --> 00:20:05,580 then follow the left-hand side down 360 00:20:05,580 --> 00:20:08,500 to a bright star known as Deneb Kaitos. 361 00:20:08,500 --> 00:20:12,060 Off to the left is a quadrilateral of fainter stars, 362 00:20:12,060 --> 00:20:14,340 Tau being the southernmost of these four. 363 00:20:15,900 --> 00:20:18,460 With a possible system of five planets in orbit, 364 00:20:18,460 --> 00:20:20,500 including one in the habitable zone, 365 00:20:20,500 --> 00:20:24,260 Tau Ceti would make an exciting target for an interstellar mission. 366 00:20:25,700 --> 00:20:28,940 There are likely to be unique and bizarre planets in orbit 367 00:20:28,940 --> 00:20:31,260 around almost all of the stars in the sky. 368 00:20:34,260 --> 00:20:38,340 And if we could send a tiny probe to just one of these stars, 369 00:20:38,340 --> 00:20:41,180 imagine how amazing it would be to be able to look at 370 00:20:41,180 --> 00:20:43,740 another solar system at close quarters. 371 00:20:47,460 --> 00:20:50,940 Proxima b is undoubtedly an exciting discovery, 372 00:20:50,940 --> 00:20:53,780 but just because it could have liquid water on the surface 373 00:20:53,780 --> 00:20:56,500 doesn't mean it's going to turn out like Earth. 374 00:20:56,500 --> 00:20:59,420 And it certainly doesn't mean that it will be habitable, 375 00:20:59,420 --> 00:21:02,220 because planets in very similar environments 376 00:21:02,220 --> 00:21:04,740 can develop in very different ways. 377 00:21:06,740 --> 00:21:09,300 Just look at Earth and Venus - 378 00:21:09,300 --> 00:21:11,740 twin planets of about the same size 379 00:21:11,740 --> 00:21:14,300 and at a similar distance from the sun. 380 00:21:14,300 --> 00:21:17,380 But they've developed very differently. 381 00:21:17,380 --> 00:21:22,220 Where the Earth became a warm and temperate world, a haven for life, 382 00:21:22,220 --> 00:21:26,540 Venus lost its water and succumbed to a runaway greenhouse effect. 383 00:21:29,020 --> 00:21:31,740 Its sulphurous atmosphere heated its surface 384 00:21:31,740 --> 00:21:35,180 to more than 450 degrees centigrade. 385 00:21:35,180 --> 00:21:38,100 It is completely unsuitable for life. 386 00:21:40,060 --> 00:21:42,020 Proxima b might be like Earth, 387 00:21:42,020 --> 00:21:44,580 but it could equally well be like Venus, 388 00:21:44,580 --> 00:21:46,820 or like something else entirely. 389 00:21:46,820 --> 00:21:49,820 And so, what can we say about conditions on the planet 390 00:21:49,820 --> 00:21:52,620 and about its chances of being hospitable to life? 391 00:21:53,740 --> 00:21:58,940 Maggie has been talking to expert on planetary atmospheres Jo Barstow. 392 00:21:58,940 --> 00:21:59,860 Yes. 393 00:22:02,980 --> 00:22:05,660 So, Joanna, can you tell me how excited you are about 394 00:22:05,660 --> 00:22:07,900 the discovery of this new exoplanet? 395 00:22:07,900 --> 00:22:09,860 Well, incredibly excited. 396 00:22:09,860 --> 00:22:13,820 I think this is pretty much going to transform the field that I work in. 397 00:22:13,820 --> 00:22:16,420 How is it similar to Earth, or how is it different? 398 00:22:16,420 --> 00:22:19,420 Well, one of the things we think is the same based on the mass 399 00:22:19,420 --> 00:22:21,700 that's been measured with these new results 400 00:22:21,700 --> 00:22:24,580 is that it's likely to be rocky, and that's a good sign. 401 00:22:24,580 --> 00:22:26,700 That means that it should have a solid surface, 402 00:22:26,700 --> 00:22:29,060 that means that there should be potential, maybe, 403 00:22:29,060 --> 00:22:31,300 for something to live on that surface. 404 00:22:31,300 --> 00:22:34,700 The major difference is driven by the fact that it's orbiting 405 00:22:34,700 --> 00:22:36,780 much closer to that star, 406 00:22:36,780 --> 00:22:41,220 and that introduces all sorts of potential problems. 407 00:22:41,220 --> 00:22:43,940 And one of those is that we think the planet 408 00:22:43,940 --> 00:22:46,740 is something we call tidally locked. 409 00:22:46,740 --> 00:22:49,420 And I have here a very small star. 410 00:22:49,420 --> 00:22:51,140 Oh, yes. 411 00:22:51,140 --> 00:22:54,140 And a very large planet. And a very large, not to scale, planet at all. 412 00:22:55,260 --> 00:22:59,100 So what's happening, because the planet is so close to the star, 413 00:22:59,100 --> 00:23:02,420 tidal forces mean that the same side of the planet 414 00:23:02,420 --> 00:23:04,500 is always facing the star. 415 00:23:04,500 --> 00:23:07,860 So as it goes round the star, it's rotating like this. 416 00:23:07,860 --> 00:23:11,260 Its day is actually the same length as its year. 417 00:23:11,260 --> 00:23:14,140 So that's like the moon? Exactly like the moon. 418 00:23:14,140 --> 00:23:17,260 From Earth we can only see one side of the moon because that's the side 419 00:23:17,260 --> 00:23:18,940 that always faces the Earth. 420 00:23:18,940 --> 00:23:21,860 And so what that means is that one side is getting all of the light 421 00:23:21,860 --> 00:23:24,460 from the star and therefore getting much hotter 422 00:23:24,460 --> 00:23:26,340 than the other side of the planet. 423 00:23:26,340 --> 00:23:28,300 And that could potentially produce 424 00:23:28,300 --> 00:23:30,300 very extreme temperature differences. 425 00:23:30,300 --> 00:23:32,380 So, looking at life, how does that impact? 426 00:23:32,380 --> 00:23:35,100 Is there any way of evening out that temperature or do you always have 427 00:23:35,100 --> 00:23:37,580 that sort of dichotomy - the hot side and the cold side? 428 00:23:37,580 --> 00:23:41,380 Well, thankfully, if the planet has an atmosphere, then it might help 429 00:23:41,380 --> 00:23:43,340 to even out that temperature difference. 430 00:23:43,340 --> 00:23:45,820 The atmosphere actually sort of lets the heat be distributed 431 00:23:45,820 --> 00:23:47,180 around the planet? Yes. 432 00:23:47,180 --> 00:23:50,220 Basically, it enables the heat to be distributed from 433 00:23:50,220 --> 00:23:53,140 what we call the day side, the side that's receiving all the light, 434 00:23:53,140 --> 00:23:56,100 round to the night side, and it evens everything out. 435 00:23:56,100 --> 00:23:58,540 What is the likelihood of having an atmosphere? 436 00:23:58,540 --> 00:24:00,460 I mean, because it's closer to that star. 437 00:24:00,460 --> 00:24:02,540 Yes, and that is also a bit of a problem. 438 00:24:02,540 --> 00:24:05,420 I mean, we want it to have an atmosphere quite apart from the fact 439 00:24:05,420 --> 00:24:09,340 that it can even out temperature differences to give any life there 440 00:24:09,340 --> 00:24:12,340 something to breathe. And if you were going to have an ocean 441 00:24:12,340 --> 00:24:16,100 or liquid water, then you also need to have an atmosphere. 442 00:24:16,100 --> 00:24:20,340 But because it's so close to the star, it's possible it may no longer 443 00:24:20,340 --> 00:24:22,540 have an atmosphere, even if it did once. 444 00:24:22,540 --> 00:24:26,020 So this star doesn't give out as much light as the sun, 445 00:24:26,020 --> 00:24:29,300 but what it does do is it gives out about the same amount of X-rays 446 00:24:29,300 --> 00:24:32,740 as the sun does. And for us out at Earth, 447 00:24:32,740 --> 00:24:34,980 the sun's X-rays are not an enormous problem, 448 00:24:34,980 --> 00:24:37,660 but if you imagine being 20 times closer, 449 00:24:37,660 --> 00:24:41,020 then suddenly those X-rays do become a bit of a problem. 450 00:24:41,020 --> 00:24:43,340 X-rays are not great for life. 451 00:24:44,620 --> 00:24:48,740 Also, when this star experiences what we call coronal mass ejections, 452 00:24:48,740 --> 00:24:52,100 which are events where some of the material actually leaves the star 453 00:24:52,100 --> 00:24:53,860 and goes out into space, 454 00:24:53,860 --> 00:24:56,900 that causes on Earth beautiful auroral displays, 455 00:24:56,900 --> 00:24:58,940 but for a planet like Proxima Cen b... 456 00:24:58,940 --> 00:25:02,180 That much closer. ..then you're going to have problems, potentially, 457 00:25:02,180 --> 00:25:05,100 because those coronal mass ejections could actually start 458 00:25:05,100 --> 00:25:07,420 to eat away at the atmosphere of that planet. 459 00:25:07,420 --> 00:25:09,300 And if it experiences enough of those, 460 00:25:09,300 --> 00:25:11,820 then eventually the atmosphere could potentially 461 00:25:11,820 --> 00:25:13,300 get physically stripped away. 462 00:25:13,300 --> 00:25:15,540 Let's assume that this planet has an atmosphere 463 00:25:15,540 --> 00:25:18,260 and it's a benign atmosphere, it has liquid water - 464 00:25:18,260 --> 00:25:21,260 what sort of life do you think could possibly live on this planet? 465 00:25:21,260 --> 00:25:24,620 Well, I think we can fairly safely say it isn't going to look 466 00:25:24,620 --> 00:25:26,700 exactly like life on Earth. 467 00:25:26,700 --> 00:25:29,580 And one of the things that I think you're very unlikely to see 468 00:25:29,580 --> 00:25:32,260 are lots of beautiful green, leafy plants. 469 00:25:32,260 --> 00:25:33,940 If there is any kind of plant life, 470 00:25:33,940 --> 00:25:35,900 it's likely to be a different colour. 471 00:25:35,900 --> 00:25:39,300 And the reason for that is that plant life on Earth has evolved 472 00:25:39,300 --> 00:25:42,420 to take advantage of exactly the kind of light 473 00:25:42,420 --> 00:25:44,260 that we receive from the sun. 474 00:25:44,260 --> 00:25:48,900 Now, the star Proxima Centauri is a much redder star than the sun, 475 00:25:48,900 --> 00:25:53,220 so it puts out much more light in the red part of the spectrum. 476 00:25:53,220 --> 00:25:55,660 It also puts out quite a lot of infrared radiation 477 00:25:55,660 --> 00:25:57,860 that we can't even perceive. 478 00:25:57,860 --> 00:26:02,260 And so that means plant life on that planet, if there is any, 479 00:26:02,260 --> 00:26:05,780 it could look red or it could even look black or grey. 480 00:26:05,780 --> 00:26:08,100 What do you think the probability is of going there? 481 00:26:08,100 --> 00:26:10,820 I mean, there are really exciting projects like Starshot. 482 00:26:10,820 --> 00:26:12,900 Do you think we'll ever get there within our lifetime? 483 00:26:12,900 --> 00:26:14,500 I think, actually, it's possible, 484 00:26:14,500 --> 00:26:17,100 and that's the first time I've ever thought it's possible, 485 00:26:17,100 --> 00:26:19,140 which is why I'm so excited about this. 486 00:26:19,140 --> 00:26:22,820 The thing about Starshot is that, unlike most of the ideas 487 00:26:22,820 --> 00:26:25,500 that are thrown around about interstellar travel, 488 00:26:25,500 --> 00:26:29,900 there aren't actually any hard theoretical barriers to doing that. 489 00:26:29,900 --> 00:26:32,140 It is theoretically possible. 490 00:26:32,140 --> 00:26:36,900 It's a technological challenge, but it's perhaps of a magnitude 491 00:26:36,900 --> 00:26:39,660 similar to challenges we've already overcome as a species. 492 00:26:39,660 --> 00:26:42,380 I can see why you're excited. Yes! 493 00:26:42,380 --> 00:26:45,180 Well, thank you. That's been fascinating. Thank you. 494 00:26:47,780 --> 00:26:49,660 Well, Maggie, you're the engineer here. 495 00:26:49,660 --> 00:26:53,460 Do you really think this idea of an interstellar probe is possible? 496 00:26:53,460 --> 00:26:54,740 I'd like to think so, 497 00:26:54,740 --> 00:26:56,860 but the problem is the stars are so far away, 498 00:26:56,860 --> 00:26:59,180 so the technical challenge is quite huge. 499 00:26:59,180 --> 00:27:02,020 But looking at the theory, it does seem viable. 500 00:27:02,020 --> 00:27:03,860 It's an exciting solution as well. 501 00:27:03,860 --> 00:27:06,060 It's like something out of science fiction - 502 00:27:06,060 --> 00:27:09,540 we have a giant laser pushing this probe towards the stars. 503 00:27:09,540 --> 00:27:11,220 It's a wonderful story to tell. 504 00:27:11,220 --> 00:27:13,220 It is. And I think it's going to be expensive, 505 00:27:13,220 --> 00:27:15,060 but I think it might be worth the effort. 506 00:27:15,060 --> 00:27:17,380 Space science is great at doing miniaturisation, 507 00:27:17,380 --> 00:27:19,500 and this space probe is going to have to be tiny, 508 00:27:19,500 --> 00:27:21,140 have an onboard camera, a transmitter 509 00:27:21,140 --> 00:27:23,380 to send information back, and so the technology 510 00:27:23,380 --> 00:27:25,060 that goes into that can help us all. 511 00:27:25,060 --> 00:27:27,460 Yeah. I suppose if we've got one of these things 512 00:27:27,460 --> 00:27:29,900 to go to Proxima Centauri we can send them to other stars 513 00:27:29,900 --> 00:27:33,300 with other planets, we could shoot around the solar system as well. 514 00:27:33,300 --> 00:27:35,340 I do find the cost difficult, though. 515 00:27:35,340 --> 00:27:38,180 From a scientific point of view, I think there's probably 516 00:27:38,180 --> 00:27:39,660 other places to spend the money. 517 00:27:39,660 --> 00:27:41,460 But the inspirational value is great. 518 00:27:41,460 --> 00:27:43,100 Knowing that that planet's there, 519 00:27:43,100 --> 00:27:45,740 it would be sad if we weren't trying to get there, don't you think? 520 00:27:45,740 --> 00:27:48,540 I think so. It's our next-door neighbour star, 521 00:27:48,540 --> 00:27:50,780 it's got something that looks fairly earthlike - 522 00:27:50,780 --> 00:27:53,660 we've just got to go there, and this seems like a good way of doing it. 523 00:27:53,660 --> 00:27:56,940 Yeah. Just knowing the probe is on the way would be so exciting. 524 00:27:56,940 --> 00:27:59,260 Well, that's all we've got time for this month, 525 00:27:59,260 --> 00:28:02,340 but do make sure you check out the star guide, which is on the website. 526 00:28:03,780 --> 00:28:08,380 We'll be back next month with a final update on the Rosetta mission, 527 00:28:08,380 --> 00:28:11,700 including the latest exciting images that reveal the fate 528 00:28:11,700 --> 00:28:15,300 of the Philae lander that disappeared on the surface 529 00:28:15,300 --> 00:28:17,500 of a comet nearly two years ago. 530 00:28:17,500 --> 00:28:20,260 But, in the meantime, get outside and... 531 00:28:20,260 --> 00:28:21,660 get looking up. Goodnight.