WEBVTT FILE 1 00:00:00.200 --> 00:00:04.390 Technology Sounds 2 00:00:04.390 --> 00:00:08.450 Technology Sounds 3 00:00:08.450 --> 00:00:12.530 Technology Sounds 4 00:00:12.530 --> 00:00:16.710 //applause// 5 00:00:16.710 --> 00:00:20.890 //applause// 6 00:00:20.890 --> 00:00:25.080 Dr. John Holdren: Life is the most complex thing in the known universe. 7 00:00:25.080 --> 00:00:29.150 Just ask anybody in the White House. Abundant on Earth, 8 00:00:29.150 --> 00:00:33.250 hugely successful in colonizing every available 9 00:00:33.250 --> 00:00:37.310 niche. It seems that once started, life is 10 00:00:37.310 --> 00:00:41.400 unstoppable. But does that mean there's life on other planets, 11 00:00:41.400 --> 00:00:45.510 elsewhere in the universe? So far we have not seen signs 12 00:00:45.510 --> 00:00:49.610 of life elsewhere, and not for lack of trying. 13 00:00:49.610 --> 00:00:53.790 Is there other life or traces of former life out there? 14 00:00:53.790 --> 00:00:57.960 Is there now or has there ever been intelligent life 15 00:00:57.960 --> 00:01:02.130 anywhere but on our Earth? With a hundred billion 16 00:01:02.130 --> 00:01:06.180 galaxies, the order of a hundred billion galaxies, 17 00:01:06.180 --> 00:01:10.250 each containing the order of a hundred billion stars, most of which we 18 00:01:10.250 --> 00:01:14.410 now know have their own planets, 19 00:01:14.410 --> 00:01:18.600 the probability of life having evolved elsewhere 20 00:01:18.600 --> 00:01:22.780 seems very, very high. Indeed, on the numbers, 21 00:01:22.780 --> 00:01:26.840 it seems highly likely that intelligent life has 22 00:01:26.840 --> 00:01:30.930 evolved in the universe at some other time, at some other 23 00:01:30.930 --> 00:01:35.080 place, and maybe is out there now. 24 00:01:35.080 --> 00:01:39.270 How will we find out for sure? Tonight, we're going to take you on a 25 00:01:39.270 --> 00:01:43.470 journey from Earth, through the solar system, to planets around 26 00:01:43.470 --> 00:01:47.540 other stars in the search for life. 27 00:01:47.540 --> 00:01:51.630 Let's start with the Earth, and I note that some have asked whether there's intelligent 28 00:01:51.630 --> 00:01:55.780 life on Earth I believe there is, but let me turn 29 00:01:55.780 --> 00:01:59.940 it over now to Gavin Schmidt. Gavin? 30 00:01:59.940 --> 00:02:04.150 //applause// 31 00:02:04.150 --> 00:02:08.220 Dr. Gavin Schmidt: Earth is the only example we have 32 00:02:08.220 --> 00:02:12.310 so far of a planet with a biosphere. As we get 33 00:02:12.310 --> 00:02:16.400 further away, Earth shrinks from a recognizably inhabited 34 00:02:16.400 --> 00:02:20.570 place, to a blue dot and then to just a tiny point 35 00:02:20.570 --> 00:02:24.700 in orbit around the sun. The further out we go, 36 00:02:24.700 --> 00:02:28.730 the harder it is to tell that there is life on Earth. 37 00:02:28.730 --> 00:02:32.800 But there has been life on Earth for more than three billion years. 38 00:02:32.800 --> 00:02:36.880 The universe has existed for 13.8 billion years 39 00:02:36.880 --> 00:02:40.990 since the Big Bang, and our solar system has been around for the last 40 00:02:40.990 --> 00:02:45.130 4.6 billion years of those. But 41 00:02:45.130 --> 00:02:49.320 remarkably quickly after the solar system formed and rocky planets 42 00:02:49.320 --> 00:02:53.360 condensed and cooled, there was liquid water on the surface of our 43 00:02:53.360 --> 00:02:57.440 planet. For a planet 4.5 billion years old, 44 00:02:57.440 --> 00:03:01.540 we have evidence of water from only .2 billion years later. 45 00:03:01.540 --> 00:03:05.690 But it took life perhaps another 46 00:03:05.690 --> 00:03:09.870 500 million years to appear. Early life 47 00:03:09.870 --> 00:03:14.080 forms weren't much to look at, but life itself has been here 48 00:03:14.080 --> 00:03:18.160 a long time. We don't yet know how life got started, 49 00:03:18.160 --> 00:03:22.310 there are many theories, but we do know that it got going 50 00:03:22.310 --> 00:03:26.400 under some very challenging conditions. 51 00:03:26.400 --> 00:03:30.590 The sun was 30 percent dimmer than today, but with more 52 00:03:30.590 --> 00:03:34.630 solar flares. There was no oxygen, and therefore 53 00:03:34.630 --> 00:03:38.670 no ozone layer to protect the surface from harsh ultraviolet 54 00:03:38.670 --> 00:03:42.750 rays. But Earth did have the ingredients necessary 55 00:03:42.750 --> 00:03:46.870 to support life. A solvent like water, an energy 56 00:03:46.870 --> 00:03:51.050 source, and abundant nutrients. 57 00:03:51.050 --> 00:03:55.240 For 1.5 billion years, this primitive life survived 58 00:03:55.240 --> 00:03:59.290 in the oceans, protected by the water's opacity. 59 00:03:59.290 --> 00:04:03.470 But around 2.5 billion years ago, 60 00:04:03.470 --> 00:04:07.490 bacteria started to use sunlight directly to fuse 61 00:04:07.490 --> 00:04:11.510 water and carbon dioxide to make sugars, which were then used as food. 62 00:04:11.510 --> 00:04:15.590 But for every molecule of carbon dioxide they used, 63 00:04:15.590 --> 00:04:19.730 and there was a lot of carbon dioxide in the atmosphere, 64 00:04:19.730 --> 00:04:23.940 they released a molecule of oxygen. Those bacteria were followed 65 00:04:23.940 --> 00:04:28.130 by photosynthesizing algae, mosses, and plants. 66 00:04:28.130 --> 00:04:32.170 And eventually, after a number of false starts, 67 00:04:32.170 --> 00:04:36.240 the oxygen built up in the atmosphere until around 500 million years ago, 68 00:04:36.240 --> 00:04:40.360 it got close to present day concentrations, giving a start 69 00:04:40.360 --> 00:04:44.470 to the huge variety of land animals, insects, and 70 00:04:44.470 --> 00:04:48.640 plants we see today. Meanwhile, the 71 00:04:48.640 --> 00:04:52.830 climate was not static. The planet went through cycles of snowballs 72 00:04:52.830 --> 00:04:56.910 and hot houses, driven by plate tectonics, volcanism, greenhouse 73 00:04:56.910 --> 00:05:00.980 gases and impacts. Indeed, it was only 74 00:05:00.980 --> 00:05:05.030 after the last snowball Earth event that set the stage-- 75 00:05:05.030 --> 00:05:09.110 that the stage was set for the evolution of multicellular life in the 76 00:05:09.110 --> 00:05:13.210 Edicarian 600 million years ago. The new 77 00:05:13.210 --> 00:05:17.350 species that were rapidly born, evolved and died 78 00:05:17.350 --> 00:05:21.400 changed the planet forever. The surface became completely covered, 79 00:05:21.400 --> 00:05:25.580 you could say infected, infested, with life. 80 00:05:25.580 --> 00:05:29.620 And that life affected the climate, changing the 81 00:05:29.620 --> 00:05:33.670 composition of the atmosphere, the reflectivity of the surface, and the cycling 82 00:05:33.670 --> 00:05:37.720 of water, radically transforming the view from space. 83 00:05:37.720 --> 00:05:41.770 Life co-created the broad 84 00:05:41.770 --> 00:05:45.890 array of special, unique ecosystems and microclimates that 85 00:05:45.890 --> 00:05:50.010 characterize the Earth today, visible even from a million miles away. 86 00:05:50.010 --> 00:05:54.190 But remember, for most of the time 87 00:05:54.190 --> 00:05:58.210 that life existed on Earth, it did not have a land fingerprint, 88 00:05:58.210 --> 00:06:02.310 and the oxygen that we now rely on wasn't detectable 89 00:06:02.310 --> 00:06:06.400 for perhaps half that time. Under those conditions, 90 00:06:06.400 --> 00:06:10.520 or any others in Earth's history, how can we know what would have been 91 00:06:10.520 --> 00:06:14.710 seen from further away? This is where our 92 00:06:14.710 --> 00:06:18.890 understanding of current climates, and of processes that control 93 00:06:18.890 --> 00:06:22.950 composition, clouds and dynamics come into play. 94 00:06:22.950 --> 00:06:27.060 We can simulate the impacts of climate on life, and the impacts of 95 00:06:27.060 --> 00:06:31.200 life on climate at each stage of our planet's history. 96 00:06:31.200 --> 00:06:35.380 Simulations which include the physics of clouds, 97 00:06:35.380 --> 00:06:39.560 oceans, ice, and of atmospheric particles like dust. 98 00:06:39.560 --> 00:06:43.610 We can take those results and then project how those 99 00:06:43.610 --> 00:06:47.680 climates would look from space, from beyond even the solar system. 100 00:06:47.680 --> 00:06:51.810 But we can go further, we can even 101 00:06:51.810 --> 00:06:55.970 simulate the climates of Venus and Mars three billion years ago, 102 00:06:55.970 --> 00:07:00.160 when they were both very different places. Places that 103 00:07:00.160 --> 00:07:04.210 perhaps also had the seeds of life. And Jen can discuss that. 104 00:07:04.210 --> 00:07:08.280 //applause// 105 00:07:08.280 --> 00:07:12.400 //applause// 106 00:07:12.400 --> 00:07:16.600 Dr. Jen Eigenbrode: If life ever existed in our solar system 107 00:07:16.600 --> 00:07:20.800 then it found a way to adapt to extreme conditions. 108 00:07:20.800 --> 00:07:24.880 Conditions that may be more extreme than what we have on Earth. 109 00:07:24.880 --> 00:07:28.940 I am constantly amazed to find that life has adapted 110 00:07:28.940 --> 00:07:33.080 to every niche, no matter how harsh the environment. 111 00:07:33.080 --> 00:07:37.260 Take for example, the extraordinary springs of Dallol in the 112 00:07:37.260 --> 00:07:41.450 Danakil Desert of Ethiopia. These springs are hot, 113 00:07:41.450 --> 00:07:45.530 salty, rich in heavy metals, and they're 114 00:07:45.530 --> 00:07:49.680 acidic. Microorganisms thrive in these pools, 115 00:07:49.680 --> 00:07:53.830 even the pools of pH less than one. That's more acidic than battery acid. 116 00:07:53.830 --> 00:07:58.010 Life adapted. 117 00:07:58.010 --> 00:08:02.180 Another example, the Atacama Desert in the rain shadow of the Andes 118 00:08:02.180 --> 00:08:06.230 Mountains. It is the driest land desert on Earth. This 119 00:08:06.230 --> 00:08:10.290 Martian-like landscape has been shaped by the wind and salty aerosols 120 00:08:10.290 --> 00:08:14.370 for millions of years. It has been one of the most 121 00:08:14.370 --> 00:08:18.480 challenging places to find evidence of life. 122 00:08:18.480 --> 00:08:22.610 And yet it's there, a few cells here and there. Life adapted. 123 00:08:22.610 --> 00:08:26.840 One last example, and this one really 124 00:08:26.840 --> 00:08:30.930 me, Chernobyl. This diverse life 125 00:08:30.930 --> 00:08:35.090 in this agricultural region is punctuated by the presence of 126 00:08:35.090 --> 00:08:39.280 fungi that live off the radiation from the 1986 127 00:08:39.280 --> 00:08:43.480 meltdown of reactor four. These fungi 128 00:08:43.480 --> 00:08:47.550 use the radiation, the gamma radiation, in the same way 129 00:08:47.550 --> 00:08:51.640 plants use sunlight to grow. Life adapted on Earth. 130 00:08:51.640 --> 00:08:55.780 Could life have arisen and adapted to the extreme 131 00:08:55.780 --> 00:08:59.960 conditions of other places in the solar system? 132 00:08:59.960 --> 00:09:04.160 We're going to find out. We will search for biomolecules, 133 00:09:04.160 --> 00:09:08.180 the organic compounds that make up life, its food and waste products. 134 00:09:08.180 --> 00:09:12.340 We may need to extend that search to other types of signatures, 135 00:09:12.340 --> 00:09:16.470 to build confidence in that detection. We might search for active 136 00:09:16.470 --> 00:09:20.650 cells, and catch extraterrestrial life in action. 137 00:09:20.650 --> 00:09:24.790 We might search for fossilized cells 138 00:09:24.790 --> 00:09:28.840 in ancient rocks and ice. Gavin explained that 139 00:09:28.840 --> 00:09:32.900 Earth is the only known biosphere. However, Mars is a 140 00:09:32.900 --> 00:09:37.000 close neighbor. Although it looks like a rusty, 141 00:09:37.000 --> 00:09:41.210 barren planet today, its history was very similar to Earth's in the beginning. 142 00:09:41.210 --> 00:09:45.390 Did life arise on Mars around the same time that life 143 00:09:45.390 --> 00:09:49.430 arose on Earth? Why are these 144 00:09:49.430 --> 00:09:53.490 two planets so vastly different today? 145 00:09:53.490 --> 00:09:57.600 Both Earth and Mars had a liquid core when they 146 00:09:57.600 --> 00:10:01.720 formed. Movement of this molten iron 147 00:10:01.720 --> 00:10:05.890 generate a magnetic field that shield the atmosphere and surface from being 148 00:10:05.890 --> 00:10:09.980 blasted by ionizing radiation. Earth maintains its 149 00:10:09.980 --> 00:10:14.020 magnetic field, but not so for Mars. Convection of the 150 00:10:14.020 --> 00:10:18.120 Martian core slowed or stopped four billion years ago. 151 00:10:18.120 --> 00:10:22.290 Without the protection of the magnetic field, the powerful solar 152 00:10:22.290 --> 00:10:26.480 wind streaming continuously from the young sun crashed into the 153 00:10:26.480 --> 00:10:30.660 red planet, piling up in front of it like a bow wave of a ship, except in this case, 154 00:10:30.660 --> 00:10:34.710 the wave is charged particles that electrically strip away the 155 00:10:34.710 --> 00:10:38.820 Martian atmosphere. This process continued 156 00:10:38.820 --> 00:10:42.990 for eons regulated by the sun's activity, and slowly stripped 157 00:10:42.990 --> 00:10:47.110 away gases from the volcanoes and the rocks. 158 00:10:47.110 --> 00:10:51.280 With the magnetic field and atmosphere mostly gone, the rocky 159 00:10:51.280 --> 00:10:55.330 surface of Mars was bombarded by ionizing radiation from the 160 00:10:55.330 --> 00:10:59.390 galaxy and the sun. This radiation 161 00:10:59.390 --> 00:11:03.540 comes in the form of photons, such as UV, x-ray, 162 00:11:03.540 --> 00:11:07.720 and gamma rays, as well as charged particles. However, unlike what we experience 163 00:11:07.720 --> 00:11:11.930 here on Earth, all of these forms have an enormous amount of energy. 164 00:11:11.930 --> 00:11:16.000 When ionizing radiation encounters 165 00:11:16.000 --> 00:11:20.140 molecules, it changes them. Radiation damage 166 00:11:20.140 --> 00:11:24.330 to molecules means damage to life and the 167 00:11:24.330 --> 00:11:28.530 signatures that we seek. We know that life 168 00:11:28.530 --> 00:11:32.570 adapts. If life ever existed on Mars, 169 00:11:32.570 --> 00:11:36.650 did it adapt to the harsh radiation environment at or near its 170 00:11:36.650 --> 00:11:40.760 surface? Life has surprised us on Earth and perhaps 171 00:11:40.760 --> 00:11:44.880 life will surprise us on Mars too. 172 00:11:44.880 --> 00:11:49.060 I have spent the last four years exploring Mars through the imagers and the 173 00:11:49.060 --> 00:11:53.240 instruments of the Curiosity rover. We have discovered that Mars is not 174 00:11:53.240 --> 00:11:57.310 really red, it's grey with a rusty skin. 175 00:11:57.310 --> 00:12:01.390 Mars is not really dry, either. Liquid 176 00:12:01.390 --> 00:12:05.570 water on Mars formed rivers, deltas, lakes, 177 00:12:05.570 --> 00:12:09.760 maybe seas. It has been cold and warm, acidic and 178 00:12:09.760 --> 00:12:13.960 alkaline. Its surface and atmospheric chemistry evolved. 179 00:12:13.960 --> 00:12:18.020 It has organic matter and the key nutrients needed 180 00:12:18.020 --> 00:12:22.140 for life. We have only scratched the 181 00:12:22.140 --> 00:12:26.340 surface of Mars and begun to decipher its story. 182 00:12:26.340 --> 00:12:30.540 Did life ever live there? Is there life 183 00:12:30.540 --> 00:12:34.580 on Mars now? And could life live here 184 00:12:34.580 --> 00:12:38.660 in the future? Beyond Mars, we will 185 00:12:38.660 --> 00:12:42.760 search for life in the ocean worlds of the moons of Jupiter and Saturn. 186 00:12:42.760 --> 00:12:46.910 Jupiter has a magnetic field 187 00:12:46.910 --> 00:12:51.020 20.000 times stronger than Earth's. The field 188 00:12:51.020 --> 00:12:55.230 produces a donut-shaped belt around the planet in which charged particles get trapped. 189 00:12:55.230 --> 00:12:59.300 Europa is a water ice-covered ocean 190 00:12:59.300 --> 00:13:03.370 world, and one of great interest as a possible abode for life. 191 00:13:03.370 --> 00:13:07.460 It sits right smack in the middle of Jupiter's magnetic belt, 192 00:13:07.460 --> 00:13:11.630 which means that it is being bombarded by intense amounts of radiation. 193 00:13:11.630 --> 00:13:15.810 Although the Europan surface 194 00:13:15.810 --> 00:13:19.860 is inhospitable, it may offer a glimpse of 195 00:13:19.860 --> 00:13:23.980 the chemistry of what lies beneath. Europa's thick crust 196 00:13:23.980 --> 00:13:28.120 is sufficient for protecting the underlying 197 00:13:28.120 --> 00:13:32.300 global ocean from radiation. And it is hypothesized 198 00:13:32.300 --> 00:13:36.500 that Europa may have hydrothermal vents stemming from its rocky 199 00:13:36.500 --> 00:13:40.540 interior. And if so, these are ideal sites for life, 200 00:13:40.540 --> 00:13:44.600 and they support the potential of life in the ocean. 201 00:13:44.600 --> 00:13:48.690 Now let's go to Saturn, where the moons are embedded in 202 00:13:48.690 --> 00:13:52.830 the rings, where we think life may exist on some of these moons. 203 00:13:52.830 --> 00:13:56.990 Like Europa, Enceladus is an icy 204 00:13:56.990 --> 00:14:01.130 ocean world. And in 2005, the Cassini spacecraft witnessed 205 00:14:01.130 --> 00:14:05.200 geysers of gas arising from the surface. These 206 00:14:05.200 --> 00:14:09.260 plumes are direct conduits to a deep ocean. We might search 207 00:14:09.260 --> 00:14:13.380 for signs of life by flying through these plumes. 208 00:14:13.380 --> 00:14:17.510 And then there's Titan. A rocky moon 209 00:14:17.510 --> 00:14:21.700 with seas of liquid methane and an atmosphere of organic smog. 210 00:14:21.700 --> 00:14:25.900 Titan is drenched in hydrocarbons, and it's cold enough 211 00:14:25.900 --> 00:14:29.990 to freeze most of them. Life as we know it is largely 212 00:14:29.990 --> 00:14:34.100 made of hydrocarbons. Although it may be a stretch of our imagination 213 00:14:34.100 --> 00:14:38.290 to think that life might live here, it is considered 214 00:14:38.290 --> 00:14:42.490 potentially habitable. Did life arise on 215 00:14:42.490 --> 00:14:46.570 Titan? There are 216 00:14:46.570 --> 00:14:50.680 possibilities for extraterrestrial life in our solar system. However, as 217 00:14:50.680 --> 00:14:54.840 Aki will explain, there even more possibilities of life outside of it. 218 00:14:54.840 --> 00:14:59.010 //applause// 219 00:14:59.010 --> 00:15:03.210 //applause// 220 00:15:03.210 --> 00:15:07.260 Dr. Aki Roberge: If we're going to look for life that's really Earth-like, we need to look for planets 221 00:15:07.260 --> 00:15:11.350 around other stars. Exoplanets, for short. When I started 222 00:15:11.350 --> 00:15:15.490 undergrad, we only knew of nine planets in the solar system. Actually, eight 223 00:15:15.490 --> 00:15:19.690 now. //audience laughter// And in grad school we thought exoplanets 224 00:15:19.690 --> 00:15:23.900 would be rare. Twenty years ago we discovered the first planet around another 225 00:15:23.900 --> 00:15:27.990 star. Since that time, we've gone from a few planets in the solar system 226 00:15:27.990 --> 00:15:32.180 to literally thousands of exoplanets orbiting other stars. 227 00:15:32.180 --> 00:15:36.350 And we have only searched a tiny portion of the galaxy with the Kepler 228 00:15:36.350 --> 00:15:40.540 'space mission. We think there's at least one exoplanet 229 00:15:40.540 --> 00:15:44.610 for every star in the galaxy, which would mean over 100 billion planets in the 230 00:15:44.610 --> 00:15:48.690 Milky Way alone. So that's at least 14 planets for every human 231 00:15:48.690 --> 00:15:52.830 on Earth. And the Milky Way is only one of a myriad 232 00:15:52.830 --> 00:15:57.000 of galaxies in the universe. We've found that the planet formation process 233 00:15:57.000 --> 00:16:01.180 is more robust and easy than we thought, and exoplanets 234 00:16:01.180 --> 00:16:05.210 are common. They can form around all different 235 00:16:05.210 --> 00:16:09.260 kinds of stars, even ones not like the sun. There are even planets around binary 236 00:16:09.260 --> 00:16:13.340 stars, just like Tatooine in Star Wars. To our delighted 237 00:16:13.340 --> 00:16:17.450 surprise, exoplanets are not only common, but diverse. 238 00:16:17.450 --> 00:16:21.630 The first planets discovered are unlike anything we have in the solar system. 239 00:16:21.630 --> 00:16:25.830 They are hot Jupiters, massive, gassy planets orbiting closer 240 00:16:25.830 --> 00:16:29.890 to their stars than Mercury orbits our sun. 241 00:16:29.890 --> 00:16:33.970 So in the solar system we have two basic classes of planets. We have 242 00:16:33.970 --> 00:16:38.090 massive gas giants like Jupiter, and small rocky planets like Earth. 243 00:16:38.090 --> 00:16:42.090 But there's all sizes of planets out there. From super Jupiters 244 00:16:42.090 --> 00:16:46.270 to Neptunes, to rocky planets several times more massive 245 00:16:46.270 --> 00:16:50.470 than Earth, all the way down to true Earth-size planets. 246 00:16:50.470 --> 00:16:54.510 So with all this richness of planetary real estate, 247 00:16:54.510 --> 00:16:58.630 it encourages us to start thinking more ambitiously. To search for 248 00:16:58.630 --> 00:17:02.790 those rocky planets that are actually like Earth. We may have 249 00:17:02.790 --> 00:17:06.920 already found some, but we can't actually tell right now what their surfaces are really 250 00:17:06.920 --> 00:17:11.090 like. So as Gavin mentioned, Earth's abundant 251 00:17:11.090 --> 00:17:15.120 surface life makes it unique in the solar system. And this is probably 252 00:17:15.120 --> 00:17:19.230 the only kind of life that we can detect from really far away. 253 00:17:19.230 --> 00:17:23.410 There might be other kinds of life on other kinds of worlds out there, but we 254 00:17:23.410 --> 00:17:27.590 probably won't be able to recognize it. So astronomers are really 255 00:17:27.590 --> 00:17:31.790 focused on finding the true Earth twins out there, and we will look for them 256 00:17:31.790 --> 00:17:35.880 in the habitable zones of nearby stars. So, 257 00:17:35.880 --> 00:17:40.030 the habitable zone is the region around a star where an Earth-like planet 258 00:17:40.030 --> 00:17:44.200 is just the right temperature to have liquid water on its surface, the key ingredient 259 00:17:44.200 --> 00:17:48.380 for Earth life. So for the sun, the habitable zone stretches from 260 00:17:48.380 --> 00:17:52.410 just outside Venus' orbit to Mars. For bigger, brighter stars, 261 00:17:52.410 --> 00:17:56.470 the habitable zone moves out, to cool off, like moving away from a campfire. 262 00:17:56.470 --> 00:18:00.590 And then for smaller, dimmer stars, the habitable zone moves in 263 00:18:00.590 --> 00:18:04.820 to keep the planet warm. Now this spectrum 264 00:18:04.820 --> 00:18:09.010 is how astronomers want to look for life on other worlds. It's the light from the 265 00:18:09.010 --> 00:18:13.080 Earth as if it were really far away, separated by color. Don't panic, we'll go through it. 266 00:18:13.080 --> 00:18:17.190 So this rise in brightness on the 267 00:18:17.190 --> 00:18:21.290 far left is literally our blue sky. And this narrow dip 268 00:18:21.290 --> 00:18:25.540 comes from oxygen, which is produced by plants. These several deep 269 00:18:25.540 --> 00:18:29.750 dips come from water vapor. And then over here is a methane 270 00:18:29.750 --> 00:18:33.810 feature. So methane in our atmosphere 271 00:18:33.810 --> 00:18:37.840 largely comes from bacteria in the guts of our livestock, and in swamps. 272 00:18:37.840 --> 00:18:41.960 So the Earth's atmosphere is full of bio signatures, gases 273 00:18:41.960 --> 00:18:46.150 that wouldn't be present in our atmosphere without life. 274 00:18:46.150 --> 00:18:50.340 Now, the technical challenge of ever seeing something like this is one of the hardest things 275 00:18:50.340 --> 00:18:54.380 scientists have ever thought of trying, and here's why. The Earth is 276 00:18:54.380 --> 00:18:58.420 10 billion times fainter than the sun. So. if the 277 00:18:58.420 --> 00:19:02.520 Luxor Sky Beam, the brightest man-made light in the world, is the sun, 278 00:19:02.520 --> 00:19:06.630 the Earth is four candles on your dinner table. But 279 00:19:06.630 --> 00:19:10.750 astronomers actually observe things that faint all the time. The real problem 280 00:19:10.750 --> 00:19:14.930 is those four candles are sitting right next to the bright lights. If we're 281 00:19:14.930 --> 00:19:19.010 looking at the solar system from 33 light years away, which is not that far, 282 00:19:19.010 --> 00:19:23.030 it's pretty nearby, the separation between the Earth and the sun 283 00:19:23.030 --> 00:19:27.120 .1 arc seconds, or the width of a human hair from the distance of two 284 00:19:27.120 --> 00:19:31.260 football fields. So imagine trying to see those candles if they were right on top of 285 00:19:31.260 --> 00:19:35.440 the Luxor Sky Beam. We have to suppress the light 286 00:19:35.440 --> 00:19:39.630 from the star before we can see the faint blue dot next to it. 287 00:19:39.630 --> 00:19:43.700 There are a couple of different technologies people have come up with to do this. One of 288 00:19:43.700 --> 00:19:47.790 them is a star shade, a gigantic deployed screen that would fly tens of thousands of 289 00:19:47.790 --> 00:19:51.810 kilometers in front of a telescope. You'd be aligned with a star 290 00:19:51.810 --> 00:19:55.900 to block its bright light. But this telescope is a relatively 291 00:19:55.900 --> 00:20:00.090 small one. If we really want to get a spectrum like the Earth 292 00:20:00.090 --> 00:20:04.140 one I showed, we need a bigger telescope. So, NASA has 293 00:20:04.140 --> 00:20:08.220 begun a concept study for a super-duper Hubble called LUVOIR, 294 00:20:08.220 --> 00:20:12.360 which will search for dozens of Earth-like planets and probe their atmospheres. 295 00:20:12.360 --> 00:20:16.570 In addition, it would enable a wide range of general astronomy, 296 00:20:16.570 --> 00:20:20.780 just like Hubble did. With powerful future missions, 297 00:20:20.780 --> 00:20:24.870 we could see the pale blue dot of Carl Sagan's imagining, and have a fighting 298 00:20:24.870 --> 00:20:28.990 chance of finding life out there among the stars. So to 299 00:20:28.990 --> 00:20:33.180 put this grand endeavor into perspective, we turn to Piers. 300 00:20:33.180 --> 00:20:37.380 //applause// 301 00:20:37.380 --> 00:20:41.440 //applause// 302 00:20:41.440 --> 00:20:45.470 Dr. Piers Sellers: The universe is really big and really old. 303 00:20:45.470 --> 00:20:49.590 Life has been on Earth for about four 304 00:20:49.590 --> 00:20:53.670 billion years. Now we know that in the universe, physics and chemistry 305 00:20:53.670 --> 00:20:57.840 are the same everywhere. A Hydrogen atom here 306 00:20:57.840 --> 00:21:02.040 is just the same as a Hydrogen atom on the other end of the universe. 307 00:21:02.040 --> 00:21:06.120 The laws of physics and chemistry work the same everywhere. 308 00:21:06.120 --> 00:21:10.230 Now we strongly suspect, based on an example of one, 309 00:21:10.230 --> 00:21:14.410 our Earth, that the laws of biology work the same everywhere too. 310 00:21:14.410 --> 00:21:18.600 And by that I mean the laws that Charles Darwin discovered for us. 311 00:21:18.600 --> 00:21:22.780 We think that based on these laws, that 312 00:21:22.780 --> 00:21:26.970 evolution can drive life. To greater complexity, 313 00:21:26.970 --> 00:21:31.170 and ultimately to intelligence. It's the smart thing to do. 314 00:21:31.170 --> 00:21:35.240 Now look at this tree of life. We can see intelligent 315 00:21:35.240 --> 00:21:39.320 animals that we're familiar with. Humans, 316 00:21:39.320 --> 00:21:43.440 elephants, dolphins. These creatures are very 317 00:21:43.440 --> 00:21:47.620 closely related to us. But look over here on the far right. 318 00:21:47.620 --> 00:21:51.830 There's one other intelligence, an invertebrate 319 00:21:51.830 --> 00:21:55.910 intelligence, that evolved completely separately from the rest of us. 320 00:21:55.910 --> 00:21:59.950 They split off from us before brains were even thought of, 321 00:21:59.950 --> 00:22:04.070 when all creatures had were just a few nerve cells. 322 00:22:04.070 --> 00:22:08.270 Octopuses have an intelligence that's comparable to quite a lot of 323 00:22:08.270 --> 00:22:12.450 mammals, and it evolved completely separately. 324 00:22:12.450 --> 00:22:16.500 These guys are like little aliens 325 00:22:16.500 --> 00:22:20.600 living with us on our own planet. If you look at an 326 00:22:20.600 --> 00:22:24.700 octopus, you can see that its brains are actually distributed all over 327 00:22:24.700 --> 00:22:28.820 its body. Most of its brains are in its feet, or in its legs, 328 00:22:28.820 --> 00:22:33.000 and they're connected to the nerve center in its head by a neural 329 00:22:33.000 --> 00:22:41.260 network. It's a distributed intelligence. 330 00:22:41.260 --> 00:22:45.380 But it turns out that they think pretty much the same way that mammals do. 331 00:22:45.380 --> 00:22:49.580 They have a short-term memory and a long-term memory, 332 00:22:49.580 --> 00:22:53.770 they learn, and they get mad. They basically tackle the 333 00:22:53.770 --> 00:22:57.800 business of living in a complex environment the same way that we mammals do. 334 00:22:57.800 --> 00:23:01.860 We think that we understand 335 00:23:01.860 --> 00:23:05.960 how an octopus thinks. So the secret of intelligence 336 00:23:05.960 --> 00:23:10.110 is in the software, it's not in the hardware. 337 00:23:10.110 --> 00:23:14.300 It's very likely that an alien intelligence would be 338 00:23:14.300 --> 00:23:18.490 comprehensible to us in the same way that an octopus' 339 00:23:18.490 --> 00:23:22.560 thoughts are more or less comprehensible to us too. 340 00:23:22.560 --> 00:23:26.670 We should be able to communicate with them if we met them. 341 00:23:26.670 --> 00:23:30.860 So, you'd think there'd be plenty of opportunities for life to evolve 342 00:23:30.860 --> 00:23:35.070 somewhere else, and maybe swing by the Earth, or at least call on the radio. 343 00:23:35.070 --> 00:23:39.270 But we haven't found any alien monoliths, 344 00:23:39.270 --> 00:23:43.370 or beer cans, or cigarette ends, 345 00:23:43.370 --> 00:23:47.520 and we have not heard them tweeting on the radio either. 346 00:23:47.520 --> 00:23:51.710 So, where are they? That's what Johnny von Neumann asked. 347 00:23:51.710 --> 00:23:55.910 Where are they? There are lots of theories about that, 348 00:23:55.910 --> 00:23:59.980 but I'm going to concentrate on the more plausible ones. 349 00:23:59.980 --> 00:24:04.090 First of all, there's the water trap. Maybe the worlds 350 00:24:04.090 --> 00:24:08.210 that have water on them are all ocean, for the most part. 351 00:24:08.210 --> 00:24:12.410 And if that's the case you can't discover combustion, you can't 352 00:24:12.410 --> 00:24:16.600 make metals, so you can't make a radio or a spaceship. 353 00:24:16.600 --> 00:24:20.660 If our dolphin friends lived on an ocean planet, they would be stuck where 354 00:24:20.660 --> 00:24:24.790 they are, in the Stone Age, forever. 355 00:24:24.790 --> 00:24:28.960 We might discover intelligent life here, but they could be incredibly 356 00:24:28.960 --> 00:24:33.160 boring. Talking endlessly about the flavors of different kinds of plankton, 357 00:24:33.160 --> 00:24:37.350 and that sort of thing. Or maybe on a 358 00:24:37.350 --> 00:24:41.450 planet that has dry land but no metals, 359 00:24:41.450 --> 00:24:45.610 same problem. You can't develop a technology. 360 00:24:45.610 --> 00:24:49.790 And how about the difficulty of interstellar travel? 361 00:24:49.790 --> 00:24:53.990 Maybe it's just too hard. It looks like a real challenge for us, 362 00:24:53.990 --> 00:24:58.060 it could be a couple of hundred years before we try that. Maybe it's just too hard. 363 00:24:58.060 --> 00:25:02.090 And then there's the great sci-fi standbys, hostile 364 00:25:02.090 --> 00:25:06.200 races evolve, they wipe out everyone else, that's sort of an ugly end. 365 00:25:06.200 --> 00:25:10.400 I think we should move on quickly, this is meant to be a fun evening. 366 00:25:10.400 --> 00:25:14.600 And then there's another theory, which is that we could be the first. 367 00:25:14.600 --> 00:25:18.800 We could be the first intelligence to evolve 368 00:25:18.800 --> 00:25:22.900 in this part of the galaxy. Someone has to be. We could be 369 00:25:22.900 --> 00:25:27.050 the elder race. So here's a time history of Earth. 370 00:25:27.050 --> 00:25:31.240 When you look at all the time that life has been here. Nearly four 371 00:25:31.240 --> 00:25:35.450 billion years, humans have only been around for a couple of 372 00:25:35.450 --> 00:25:39.560 hundred thousand years, civilization for about 6,000 years, 373 00:25:39.560 --> 00:25:43.680 depending how you count it, and our technical era 374 00:25:43.680 --> 00:25:47.810 only for 200 years. When you look at this picture, 375 00:25:47.810 --> 00:25:52.030 it is obvious that the most likely first alien life forms 376 00:25:52.030 --> 00:25:56.100 that we discover will not be intelligent. They will be somewhere back 377 00:25:56.100 --> 00:26:00.250 here, equivalent to life on Earth during the first three billion years 378 00:26:00.250 --> 00:26:04.280 of evolution. Similarly, 379 00:26:04.280 --> 00:26:08.480 nearby life on an exoplanet is probably plodding its way 380 00:26:08.480 --> 00:26:12.680 up the evolutionary ladder. Remember how long 381 00:26:12.680 --> 00:26:16.750 it took us to get where we are. Where we could even think about life 382 00:26:16.750 --> 00:26:20.820 elsewhere. So, what are the chances 383 00:26:20.820 --> 00:26:24.950 of us finding anything, or anybody, soon? 384 00:26:24.950 --> 00:26:29.100 Here's a timeline of missions for exploring the solar system 385 00:26:29.100 --> 00:26:33.250 with some notional ideas of what we'll be doing in the next 386 00:26:33.250 --> 00:26:37.450 50 years. I think that over the next 30 to 50 387 00:26:37.450 --> 00:26:41.530 years, we will have thoroughly explored every nook and cranny of the solar system, 388 00:26:41.530 --> 00:26:45.650 and seen or determined where there is life here, or past life, 389 00:26:45.650 --> 00:26:49.800 or not. I think there's a good chance we'll nail that one flat. 390 00:26:49.800 --> 00:26:53.960 And then there's a chance of looking for bio signatures 391 00:26:53.960 --> 00:26:58.080 in the atmospheres of exoplanets. 392 00:26:58.080 --> 00:27:02.130 Here's the missions, again, pretty notional, and it's all the 30 393 00:27:02.130 --> 00:27:06.180 to 50-year timeframe, in the future that we could see looking at exoplanets 394 00:27:06.180 --> 00:27:10.280 where we'd be looking for traces of life in their 395 00:27:10.280 --> 00:27:14.470 atmospheres. It turns out 396 00:27:14.470 --> 00:27:18.660 that we Earthlings have the prime real estate in our solar system, 397 00:27:18.660 --> 00:27:22.730 as far as having a habitable environment is concerned. 398 00:27:22.730 --> 00:27:26.810 Most of the rest of the solar system looks like a really tough place to live. 399 00:27:26.810 --> 00:27:30.960 But, you never know. We need to 400 00:27:30.960 --> 00:27:35.170 thoroughly check out our own backyard as well as the planets around other stars. 401 00:27:35.170 --> 00:27:39.370 We'd look like idiots if we failed to check for life 402 00:27:39.370 --> 00:27:43.490 close to home, and failed for lack of trying. 403 00:27:43.490 --> 00:27:47.610 Now back to the beginning. John Holdren's question. 404 00:27:47.610 --> 00:27:51.820 Why do we even care about this stuff? We think it goes 405 00:27:51.820 --> 00:27:56.120 beyond just intellectual curiosity. It's in our nature 406 00:27:56.120 --> 00:28:00.190 because we humans grew up as part of nature, and need to pay attention to it. 407 00:28:00.190 --> 00:28:04.290 I want you to imagine what humans could do in a couple of 408 00:28:04.290 --> 00:28:08.450 hundred years or so. Imagine a probe 409 00:28:08.450 --> 00:28:12.650 from Earth entering the solar system of another star 410 00:28:12.650 --> 00:28:16.840 after a journey of decades, maybe a century. 411 00:28:16.840 --> 00:28:20.900 Note the MSBR logo. 412 00:28:20.900 --> 00:28:25.020 What would it find? My advice to you is eat 413 00:28:25.020 --> 00:28:29.160 healthy, don't smoke, don't jaywalk, 414 00:28:29.160 --> 00:28:33.350 and you might find out. It'd be good to find out we're not alone. 415 00:28:33.350 --> 00:28:37.560 Thank you for your attention. 416 00:28:37.560 --> 00:28:41.650 //applause// 417 00:28:41.650 --> 00:28:43.438 //applause//