WEBVTT FILE 1 00:00:01.066 --> 00:00:01.700 When considering 2 00:00:01.700 --> 00:00:05.466 the possibility of life beyond Earth, we look for three main ingredients. 3 00:00:05.500 --> 00:00:10.166 The first one is key elements such as carbon, hydrogen, oxygen and sulfur. 4 00:00:10.300 --> 00:00:12.833 The second is a source of energy. 5 00:00:13.133 --> 00:00:17.033 And the third, and perhaps most important, is the existence of liquid water. 6 00:00:17.333 --> 00:00:20.900 Water is a necessary solvent in all chemical reactions that have to do with 7 00:00:20.900 --> 00:00:21.466 life. 8 00:00:21.466 --> 00:00:24.466 Energy is required to drive these chemical reactions, 9 00:00:24.666 --> 00:00:28.400 and organic matter is the material from which all life that we know of is made. 10 00:00:28.700 --> 00:00:31.066 Life as we know it requires liquid water. 11 00:00:31.233 --> 00:00:34.466 Scientists believe that life on earth started in our oceans. 12 00:00:34.600 --> 00:00:36.666 Now through our exploration of the solar system. 13 00:00:36.700 --> 00:00:40.400 We've realized that the moons around the giant planets have the right 14 00:00:40.400 --> 00:00:44.166 conditions, that there could be liquid water underneath their surfaces. 15 00:00:44.166 --> 00:00:47.133 And so that really sort of expands our whole concept 16 00:00:47.133 --> 00:00:50.400 of where you could have a habitat where we might find life. 17 00:00:54.933 --> 00:00:56.833 Water is fairly common in the universe. 18 00:00:56.833 --> 00:01:00.800 We've seen traces of water in large molecular clouds between stars. 19 00:01:00.833 --> 00:01:03.933 We've seen traces of water in protoplanetary disks. 20 00:01:03.966 --> 00:01:05.800 We've also seen traces of water 21 00:01:05.800 --> 00:01:09.433 as water vapor in the atmospheres of giant planets around other stars. 22 00:01:09.600 --> 00:01:10.833 And we know that water 23 00:01:10.833 --> 00:01:14.366 is in the atmospheres and interiors of our solar system's giant planets. 24 00:01:14.666 --> 00:01:17.833 So we know that water is ubiquitous throughout the universe. 25 00:01:17.833 --> 00:01:20.700 As far as liquid water, that's a little less common. 26 00:01:20.900 --> 00:01:21.333 Earth is 27 00:01:21.333 --> 00:01:25.100 the only planet in the solar system where we see liquid water at our surface. 28 00:01:25.200 --> 00:01:29.700 Moons such as Enceladus and Europa may have liquid water beneath layers of ice. 29 00:01:30.133 --> 00:01:34.133 We're really expanding our understanding of what makes a place habitable. 30 00:01:34.200 --> 00:01:38.266 Instead of just looking for an Earth like terrestrial planet, 31 00:01:38.266 --> 00:01:41.300 that's a very specific distance from its star, we're learning 32 00:01:41.300 --> 00:01:44.266 that there can be hidden habitats that are underneath 33 00:01:44.266 --> 00:01:47.733 icy layers, and they can be a lot further out from the sun. 34 00:01:48.100 --> 00:01:51.833 So we believe icy moons in the solar system actually harbor 35 00:01:51.833 --> 00:01:55.800 kilometers-thick oceans underneath their icy surfaces. 36 00:01:55.933 --> 00:01:59.733 These icy moons and their subsurface oceans may be 37 00:01:59.733 --> 00:02:03.533 some of the best places to search for life elsewhere in our solar system. 38 00:02:08.733 --> 00:02:10.433 Enceladus is one of Saturn's 39 00:02:10.433 --> 00:02:14.666 many moons, and it's a very small moon that people tend to kind of ignore. 40 00:02:14.800 --> 00:02:17.066 It's so small, about five or ten kilometers in diameter. 41 00:02:17.233 --> 00:02:20.100 But decades ago, in the 1980s, from ground-based 42 00:02:20.100 --> 00:02:24.466 observing, we found out that the location of Enceladus relative to Saturn 43 00:02:24.633 --> 00:02:27.500 happened to coincide nicely with Saturn's E ring. 44 00:02:27.600 --> 00:02:31.566 And so we were thinking that Enceladus had something to do with the E ring 45 00:02:31.566 --> 00:02:34.466 particulates, the icy material, but we weren't sure. 46 00:02:34.566 --> 00:02:38.966 What we later find from Cassini was that we directly determined 47 00:02:38.966 --> 00:02:42.200 that there are indeed plumes jetting out of the south polar region 48 00:02:42.200 --> 00:02:45.566 from cracks in the south pole of Enceladus in the crust, 49 00:02:45.633 --> 00:02:49.300 and it's dominantly water rich material just jetting out into space. 50 00:02:49.500 --> 00:02:51.000 And so the way we saw it, 51 00:02:51.000 --> 00:02:55.566 Cassini happened to be located where Enceladus was backlit from the sun. 52 00:02:55.600 --> 00:02:59.500 And so you saw this curtain of beautiful, diffuse material jetting 53 00:02:59.500 --> 00:03:01.000 out of the south polar region. 54 00:03:01.000 --> 00:03:02.766 Quite breathtaking, actually. 55 00:03:02.766 --> 00:03:05.900 Even more, we were able to use the different complements of instruments 56 00:03:05.900 --> 00:03:10.166 on board Cassini to go after the chemical composition of the plumes. 57 00:03:10.166 --> 00:03:12.266 And that's where things got really interesting. 58 00:03:12.533 --> 00:03:15.300 So, number one, that's because of liquid water. 59 00:03:15.300 --> 00:03:17.566 There is definitely a liquid water reservoir. 60 00:03:17.800 --> 00:03:20.533 It's subsurface below the icy crust, but that is there. 61 00:03:20.700 --> 00:03:23.666 Number two, the chemical composition of the plumes 62 00:03:23.833 --> 00:03:26.100 told us that there's a lot of organics, things 63 00:03:26.100 --> 00:03:29.400 that make up amino acid and things on life that are very interesting. 64 00:03:29.500 --> 00:03:30.900 And number three, 65 00:03:30.900 --> 00:03:35.100 what we are really looking for is a source of energy on Enceladus. 66 00:03:35.100 --> 00:03:38.766 Photons from the sun aren't going to work because you can't penetrate the tens 67 00:03:38.766 --> 00:03:42.833 of kilometers of icy crust to get down to where the liquid water reservoir is. 68 00:03:42.933 --> 00:03:46.866 But what Enceladus does have is hydrothermal vents. 69 00:03:47.033 --> 00:03:49.100 It's very hot, and the liquid water, 70 00:03:49.200 --> 00:03:52.933 that has a lot of analogies with the ocean floor, where we have a form 71 00:03:52.933 --> 00:03:57.300 of releasing chemical energy via something called serpentinization. 72 00:03:57.300 --> 00:04:00.533 And so we think that Enceladus might have that potential 73 00:04:00.533 --> 00:04:04.633 to have an energy source being chemical, not sunlight. 74 00:04:04.833 --> 00:04:07.733 And so you put all that together and Enceladus 75 00:04:08.100 --> 00:04:11.966 has all the ingredients or most of what we need for life. 76 00:04:12.100 --> 00:04:16.000 That makes it a very astrobiologically interesting object to study. 77 00:04:23.300 --> 00:04:26.566 Europa is one of the largest moons of Jupiter, and we believe that 78 00:04:26.566 --> 00:04:31.700 Europa has a subsurface ocean tens to hundreds of kilometers thick. 79 00:04:31.866 --> 00:04:33.466 And so this ocean 80 00:04:33.466 --> 00:04:37.200 may be one of the best places to search for life in the solar system. 81 00:04:37.500 --> 00:04:40.533 There's been three space missions that have provided 82 00:04:40.533 --> 00:04:43.600 evidence for Europa harboring liquid water. 83 00:04:43.800 --> 00:04:46.666 The first one is Voyager in the late seventies. 84 00:04:46.866 --> 00:04:50.933 The second one is the Galileo mission in the late 1980s 85 00:04:51.066 --> 00:04:54.533 and most recently Hubble, which detected plume-like 86 00:04:54.600 --> 00:04:57.733 emission from hydrogen and oxygen, which is closely 87 00:04:57.733 --> 00:05:01.366 related to the existence of water beneath its surface. 88 00:05:01.800 --> 00:05:06.600 These plumes may be directly ejected through cracks in the surface of the moon 89 00:05:06.600 --> 00:05:11.500 and therefore what we're seeing in water vapor plumes is the actual ocean water 90 00:05:11.700 --> 00:05:17.133 from the subsurface of the moon as these plume particles are ejected to space. 91 00:05:17.166 --> 00:05:18.133 Solar radiation 92 00:05:18.133 --> 00:05:21.933 is going to excite these water particles creating vibrational modes. 93 00:05:22.333 --> 00:05:26.400 Now, these vibrational modes are signatures that can be detected 94 00:05:26.633 --> 00:05:29.533 at infrared wavelengths by the Keck Observatory. 95 00:05:30.000 --> 00:05:33.033 So we observe Europa on 17 days. 96 00:05:33.166 --> 00:05:39.333 What we found is that the majority of observations have no presence of water. 97 00:05:39.900 --> 00:05:43.233 However, on one of those dates we detected water. 98 00:05:43.333 --> 00:05:45.333 We detected H2O. 99 00:05:45.333 --> 00:05:48.666 In the past, Hubble provided indirect 100 00:05:48.666 --> 00:05:51.766 measurements of water by detecting hydrogen and oxygen. 101 00:05:52.000 --> 00:05:55.800 But now we have directly detected water for the first time. 102 00:05:56.333 --> 00:06:00.433 Both the Webb Telescope and the Europa Clipper mission will give us a much 103 00:06:00.433 --> 00:06:05.466 more detailed picture of the surface of Europa, its cracks and crevices, 104 00:06:05.466 --> 00:06:09.300 detailed pictures of the water vapor, as well as other molecules 105 00:06:09.300 --> 00:06:13.000 that may also be emanating from the subsurface of Europa. 106 00:06:13.233 --> 00:06:14.400 So both of these missions 107 00:06:14.400 --> 00:06:18.366 will give us a great picture of whether Europa is truly habitable. 108 00:06:27.600 --> 00:06:29.633 Titan is a moon of Saturn. 109 00:06:29.633 --> 00:06:34.566 It's the second largest moon in the solar system and it is about two times 110 00:06:34.566 --> 00:06:38.600 larger than Earth's Moon and actually bigger than the planet Mercury. 111 00:06:38.733 --> 00:06:39.966 And Titan is also interesting. 112 00:06:39.966 --> 00:06:42.833 It's the only moon in our solar system with an atmosphere. 113 00:06:42.833 --> 00:06:43.566 It's surrounded 114 00:06:43.566 --> 00:06:47.700 by sort of an envelope of gaseous nitrogen, just like our own earth is. 115 00:06:48.200 --> 00:06:52.966 Titan was first discovered by telescope observation back in the mid 1600’s. 116 00:06:53.200 --> 00:06:56.966 The first spacecraft observations were made of Titan during flybys 117 00:06:56.966 --> 00:06:58.200 through the outer solar system. 118 00:06:58.200 --> 00:07:00.800 That was in the late seventies and in the eighties. 119 00:07:01.033 --> 00:07:05.000 But we really were able to explore Titan in depth with the Cassini-Huygens mission. 120 00:07:05.166 --> 00:07:09.066 The Huygens probe was dropped into the atmosphere of Titan 121 00:07:09.066 --> 00:07:13.200 and it made measurements of chemistry and it took images as it fell to the surface. 122 00:07:13.400 --> 00:07:15.300 And that was back in 2005. 123 00:07:15.300 --> 00:07:19.266 And since then, the Cassini orbiter made over 100 close flybys of Titan. 124 00:07:19.500 --> 00:07:22.200 Cassini in its design with the different instruments 125 00:07:22.266 --> 00:07:25.266 - we purposely were picking instruments that could go into longer 126 00:07:25.266 --> 00:07:29.533 wavelengths, into the infrared, so we could really understand the moon. 127 00:07:29.633 --> 00:07:32.200 We were able to basically peel back 128 00:07:32.366 --> 00:07:35.866 the layers of Titan to really see what was below. 129 00:07:36.066 --> 00:07:39.133 And it was remarkable, very Earth-like. 130 00:07:39.300 --> 00:07:43.000 The landscape is similar to Earth's in many, many ways, 131 00:07:43.000 --> 00:07:44.933 but with a little bit of a twist. 132 00:07:44.933 --> 00:07:50.100 So on Titan, you can find dunes, you find lakes, there are river channels. 133 00:07:50.100 --> 00:07:55.766 The atmosphere is very dense and you can get clouds and smog and you even get rain. 134 00:07:55.833 --> 00:07:58.833 We saw winds, we saw seasons. 135 00:07:58.833 --> 00:08:02.200 And one really important thing we saw was liquids 136 00:08:02.200 --> 00:08:05.533 pooling in the polar regions on the surface, a lot of it. 137 00:08:05.666 --> 00:08:09.566 But because Titan is so cold, those features are all made of 138 00:08:09.766 --> 00:08:13.200 very exotic materials compared to what we would find on Earth. 139 00:08:13.400 --> 00:08:16.300 So the lakes and the rain are made of liquid methane. 140 00:08:16.466 --> 00:08:19.433 The crust that forms the surface of Titan is actually 141 00:08:19.433 --> 00:08:22.466 water ice, but it's so cold that it's as hard as rock. 142 00:08:22.733 --> 00:08:26.200 And in the atmosphere, we get this organic chemistry 143 00:08:26.200 --> 00:08:29.033 that forms large organic molecules and particulates. 144 00:08:29.033 --> 00:08:32.633 They fall down to the surface and then behave like dust or like sand does. 145 00:08:32.866 --> 00:08:35.733 So it makes us want to go back to really understand 146 00:08:35.733 --> 00:08:39.100 the complex organic environment of that surface 147 00:08:39.233 --> 00:08:42.533 and what it means for either past life or maybe future life. 148 00:08:45.300 --> 00:08:47.200 Dragonfly is a mission that 149 00:08:47.200 --> 00:08:52.133 was just selected by NASA to fly to Titan and arrive in the mid 2030s. 150 00:08:52.266 --> 00:08:55.600 Dragonfly is going to make a whole bunch of measurements to help us understand 151 00:08:55.600 --> 00:08:58.700 the environment on Titan and its potential for habitability. 152 00:08:58.866 --> 00:08:59.833 We'll be taking measurements 153 00:08:59.833 --> 00:09:04.300 of the atmosphere that includes things like pressure, temperature, winds. 154 00:09:04.300 --> 00:09:05.566 We’ll probe the surface 155 00:09:05.566 --> 00:09:08.833 to try to understand what materials the surface made out of. 156 00:09:08.866 --> 00:09:12.933 We’ll also be drilling into the surface to look for the types of organic molecules 157 00:09:12.933 --> 00:09:16.833 that are present and to try to see if we can find any examples of compounds 158 00:09:16.833 --> 00:09:19.800 that mimic the types of building blocks we know we need for life on Earth. 159 00:09:20.700 --> 00:09:22.933 We don't really know how life started on Earth. 160 00:09:23.266 --> 00:09:24.200 We don't exactly know 161 00:09:24.200 --> 00:09:27.300 what the chemical environment of Earth was like before life started. 162 00:09:27.733 --> 00:09:30.866 So with Titan, we have this really unique opportunity. 163 00:09:30.900 --> 00:09:33.466 There are times in Titan's past where there could be liquid 164 00:09:33.500 --> 00:09:34.600 water on the surface. 165 00:09:34.600 --> 00:09:38.800 Impact craters can generate impact melt, and there's a potential for possible 166 00:09:38.833 --> 00:09:41.866 cryovolcanism to erupt some liquid water onto the surface. 167 00:09:42.000 --> 00:09:45.433 And so we know that there's a rich organic chemistry going on in the atmosphere. 168 00:09:45.433 --> 00:09:47.400 We know that's depositing to the surface. 169 00:09:47.400 --> 00:09:50.433 If there were times where those organics and the liquid water 170 00:09:50.433 --> 00:09:51.866 environments were mixing, 171 00:09:51.866 --> 00:09:54.700 then there may be some really interesting chemistry taking place. 172 00:09:54.933 --> 00:09:58.233 When you have these processes operating for hundreds of millions of years, 173 00:09:58.466 --> 00:10:01.566 how far can they get you down that path of chemical complexity? 174 00:10:01.566 --> 00:10:05.666 And can we see reactions and molecules that start to look something like what 175 00:10:05.666 --> 00:10:10.166 we think of as essential elements for our biochemistry for life on Earth? 176 00:10:10.233 --> 00:10:11.233 In the future, 177 00:10:11.233 --> 00:10:14.166 looking forward as opposed to looking back and thinking about Titan 178 00:10:14.166 --> 00:10:17.933 as a chemical laboratory for the prebiotic Earth, I like to look forward 179 00:10:17.933 --> 00:10:21.266 thinking about what's going to happen when the Sun evolves and warms 180 00:10:21.266 --> 00:10:24.666 up and the habitable zone actually moves out to where Titan is? 181 00:10:24.766 --> 00:10:25.633 And it will. 182 00:10:25.633 --> 00:10:27.066 You have all the organics. 183 00:10:27.066 --> 00:10:28.500 You're going to have a source of energy. 184 00:10:28.500 --> 00:10:30.866 All we have to do is melt the frozen water 185 00:10:30.866 --> 00:10:34.166 and we're going to have a pool of organics just embedded in liquid. 186 00:10:34.300 --> 00:10:37.766 Titan might actually have a chance at that point to harbor life. 187 00:10:43.600 --> 00:10:45.233 So when we think about ocean worlds, it's 188 00:10:45.233 --> 00:10:47.333 good to compare them to what we know about Earth. 189 00:10:47.333 --> 00:10:50.800 In total proportion, Earth is about 0.1% water. 190 00:10:50.900 --> 00:10:54.300 An ocean world is a body that has in proportion about ten times 191 00:10:54.300 --> 00:10:55.733 more water than Earth does. 192 00:10:55.733 --> 00:11:00.100 And when we think of the TRAPPIST planets, those planets have about 50 times 193 00:11:00.100 --> 00:11:02.300 more water in proportion to what Earth does. 194 00:11:02.700 --> 00:11:05.100 Ocean worlds do appear to be common in our galaxy. 195 00:11:05.100 --> 00:11:06.966 As far back as the early 2000’s, 196 00:11:06.966 --> 00:11:09.600 we had astronomers, some of them still here at NASA Goddard, 197 00:11:09.600 --> 00:11:13.866 that suggested that we would have ocean worlds orbiting low mass stars. 198 00:11:13.966 --> 00:11:17.433 Recently, we've looked at about 52 exoplanets, 199 00:11:17.433 --> 00:11:19.100 and these are low-mass exoplanets. 200 00:11:19.100 --> 00:11:23.666 And what we found is of these 52 planets, one out of every four 201 00:11:23.700 --> 00:11:25.233 may be an ocean planet. 202 00:11:25.233 --> 00:11:26.600 And when it comes to these 203 00:11:26.600 --> 00:11:30.966 ocean planets over half of them may be ice-covered ocean worlds. 204 00:11:30.966 --> 00:11:35.366 And so Enceladus and Europa may serve as small scale analogs of these planets. 205 00:11:36.066 --> 00:11:37.733 So there are a number of different ways 206 00:11:37.733 --> 00:11:41.400 to search for life on planets around other stars. 207 00:11:41.400 --> 00:11:44.966 But the key method is the study of the atmospheres. 208 00:11:45.100 --> 00:11:47.966 We can search for signs of life - biosignatures, 209 00:11:47.966 --> 00:11:52.400 as we call them - things like oxygen, water vapor, carbon dioxide. 210 00:11:52.466 --> 00:11:56.666 Even more unusual biosignatures, things like chlorofluorocarbons 211 00:11:56.666 --> 00:11:59.433 or other things that are only produced by intelligent life. 212 00:11:59.633 --> 00:12:04.000 By looking for these key constituents of planetary atmospheres that signal life, 213 00:12:04.000 --> 00:12:06.933 we can discover life-forms on other planets 214 00:12:07.200 --> 00:12:09.533 that we could never actually visit in our lifetime. 215 00:12:09.700 --> 00:12:13.833 So this is very analogous to how we study the atmospheres of moons and planets 216 00:12:13.833 --> 00:12:17.266 in our own solar system and really makes the connection between studying 217 00:12:17.266 --> 00:12:21.433 the plumes of Europa and the atmospheres of planets around other stars. 218 00:12:21.766 --> 00:12:26.600 What I would like to see is the definition of a habitable zone expanded. 219 00:12:26.633 --> 00:12:30.900 We don't want to keep thinking too narrow about liquid on the surface - broaden 220 00:12:30.900 --> 00:12:35.166 the scope and really try to embrace other worlds that might seem too far 221 00:12:35.166 --> 00:12:39.300 from the host star and frozen out, when they really aren't frozen at all. 222 00:12:39.300 --> 00:12:44.733 At great depths, they harbor a warm, hydrothermal-driven, liquid water environment.