WEBVTT FILE 1 00:00:00.166 --> 00:00:00.700 [ Music ] 2 00:00:00.700 --> 00:00:05.133 When considering the possibility of life beyond Earth, we look for three main ingredients: 3 00:00:05.133 --> 00:00:09.933 the first one is key elements such as carbon, hydrogen, oxygen, and sulfur. 4 00:00:09.933 --> 00:00:12.766 The second is a source of energy, 5 00:00:12.766 --> 00:00:16.866 and the third, and perhaps most important, is the existence of liquid water. 6 00:00:16.866 --> 00:00:21.100 Water is a necessary solvent in all chemical reactions that have to do with life. 7 00:00:21.100 --> 00:00:24.266 Energy is required to drive these chemical reactions 8 00:00:24.266 --> 00:00:28.333 and organic matter is the material from which all life that we know of is made. 9 00:00:28.333 --> 00:00:30.833 Life as we know it requires liquid water. 10 00:00:30.833 --> 00:00:34.200 Scientists believe that life on Earth started in our oceans. 11 00:00:34.200 --> 00:00:38.066 Now through our exploration of the Solar System, we’ve realized that the moons 12 00:00:38.066 --> 00:00:42.333 around the giant planets have the right conditions that there could be liquid water 13 00:00:42.333 --> 00:00:43.800 underneath their surfaces. 14 00:00:43.800 --> 00:00:48.566 So that really sort of expands our whole concept of where you could have a habitat 15 00:00:48.566 --> 00:00:50.300 where we might find life. 16 00:00:50.300 --> 00:00:54.633 [ Music ] 17 00:00:54.633 --> 00:00:56.400 Water is fairly common in the universe. 18 00:00:56.400 --> 00:01:00.466 We’ve seen traces of water in large molecular clouds between stars. 19 00:01:00.466 --> 00:01:03.633 We’ve seen traces of water in protoplanetary disks. 20 00:01:03.633 --> 00:01:07.866 We’ve also seen traces of water as water vapor in the atmospheres of giant planets 21 00:01:07.866 --> 00:01:11.900 around other stars, and we know that water is in the atmospheres and interiors 22 00:01:11.900 --> 00:01:14.300 of our Solar System’s giant planets. 23 00:01:14.300 --> 00:01:17.366 So, we know that water is ubiquitous throughout the universe. 24 00:01:17.366 --> 00:01:20.500 As far as liquid water, that’s a little less common. 25 00:01:20.500 --> 00:01:24.800 Earth is the only planet in the Solar System where we see liquid water at our surface. 26 00:01:24.800 --> 00:01:29.833 Moons such as Enceladus and Europa may have liquid water beneath layers of ice. 27 00:01:29.833 --> 00:01:33.866 We’re really expanding our understanding of what makes a place habitable. 28 00:01:33.866 --> 00:01:39.266 Instead of just looking for an Earthlike, terrestrial planet that’s a very specific distance 29 00:01:39.266 --> 00:01:42.866 from its star, we’re learning that there can be hidden habitats 30 00:01:42.866 --> 00:01:44.966 that are underneath icy layers, 31 00:01:44.966 --> 00:01:47.700 and they can be a lot further out from the Sun. 32 00:01:47.700 --> 00:01:53.366 So we believe icy moons in the Solar System actually harbor kilometers-thick oceans 33 00:01:53.366 --> 00:01:55.566 underneath their icy surfaces. 34 00:01:55.566 --> 00:01:59.500 These icy moons and their subsurface oceans may be some of 35 00:01:59.500 --> 00:02:03.633 the best places to search for life elsewhere in our Solar System. 36 00:02:03.933 --> 00:02:08.333 [ Music ] 37 00:02:08.333 --> 00:02:12.733 Enceladus is one of Saturn’s many moons, and it’s a very small moon 38 00:02:12.733 --> 00:02:14.900 that people tend to kind of ignore because it is so small 39 00:02:14.900 --> 00:02:16.800 about 500 kilometers in diameter. 40 00:02:16.800 --> 00:02:20.333 But decades ago, in the 1980's from ground-based observing, 41 00:02:20.333 --> 00:02:24.100 we found out that the location of Enceladus relative to Saturn 42 00:02:24.100 --> 00:02:27.400 happened to coincide nicely with Saturn’s E ring 43 00:02:27.400 --> 00:02:31.066 and so we were thinking that Enceladus had something to do with the E ring 44 00:02:31.066 --> 00:02:34.233 particulates, that icy material, but we weren’t sure. 45 00:02:34.233 --> 00:02:38.533 What we later find from Cassini was that we directly determined 46 00:02:38.533 --> 00:02:42.800 that there are indeed plumes jetting out of the south polar region from cracks 47 00:02:42.800 --> 00:02:45.266 in the south pole of Enceladus in the crust. 48 00:02:45.266 --> 00:02:49.066 And it’s dominantly water-rich material just jetting out into space. 49 00:02:49.066 --> 00:02:54.233 And so the way we saw it, Cassini happened to be located where Enceladus was backlit 50 00:02:54.233 --> 00:02:58.700 from the Sun, and so you saw this curtain of beautiful, diffuse material 51 00:02:58.700 --> 00:03:02.400 jetting out of the south polar region – quite breathtaking actually. 52 00:03:02.400 --> 00:03:05.400 Even more, we were able to use the different compliments of instruments 53 00:03:05.400 --> 00:03:09.666 onboard Cassini to go after the chemical composition of the plumes, 54 00:03:09.666 --> 00:03:14.866 and that’s where things got really interesting. So number one, that’s because of liquid water. 55 00:03:14.866 --> 00:03:20.333 There’s definitely a liquid water reservoir subsurface below the icy crust, but that is there. 56 00:03:20.333 --> 00:03:25.433 Number two, the chemical composition of the plumes told us that there is a lot of organics 57 00:03:25.433 --> 00:03:29.133 things that make up amino acids and things on life that are very interesting. 58 00:03:29.133 --> 00:03:33.600 And number three, what we were really looking for was a source of energy. 59 00:03:33.600 --> 00:03:37.800 On Enceladus, photons from the Sun aren’t going to work because you can’t penetrate 60 00:03:37.800 --> 00:03:42.600 the tens of kilometers of icy crust to get down to where the liquid water reservoir is. 61 00:03:42.600 --> 00:03:46.600 But, what Enceladus does have is hydrothermal vents. 62 00:03:46.600 --> 00:03:51.400 It’s very hot with the liquid water, that has a lot of analogies with the ocean floor 63 00:03:51.400 --> 00:03:57.000 where we have a form of releasing chemical energy via something called serpentinization. 64 00:03:57.000 --> 00:04:00.100 And so we think that Enceladus might have that potential 65 00:04:00.100 --> 00:04:04.400 to have an energy source being chemical, not sunlight. 66 00:04:04.400 --> 00:04:08.900 And so you put all that together and Enceladus has all the ingredients, 67 00:04:08.900 --> 00:04:11.600 or most of what we need for life. 68 00:04:11.600 --> 00:04:15.800 That makes it a very astrobiologically interesting object to study. 69 00:04:15.800 --> 00:04:18.833 [ Music ] 70 00:04:22.933 --> 00:04:27.000 Europa is one of the largest moons of Jupiter, and we believe that Europa has 71 00:04:27.000 --> 00:04:31.500 a subsurface ocean tens to hundreds of kilometers thick 72 00:04:31.500 --> 00:04:37.200 And so this ocean may be one of the best places to search for life in the Solar System. 73 00:04:37.200 --> 00:04:41.300 There’s been three space missions that have provided evidence for 74 00:04:41.300 --> 00:04:43.433 Europa harboring liquid water. 75 00:04:43.433 --> 00:04:49.066 The first one is Voyager in the late 70's, the second one is the Galileo mission 76 00:04:49.066 --> 00:04:54.700 in the late 90's, and most recently Hubble, which detected plume-like emission 77 00:04:54.700 --> 00:04:59.500 from hydrogen and oxygen which is closely related to the existence of water 78 00:04:59.500 --> 00:05:01.500 beneath its surface. 79 00:05:01.500 --> 00:05:06.233 These plumes may be directly ejected through cracks in the surface of the moon, 80 00:05:06.233 --> 00:05:09.066 and therefore what we are seeing in water vapor plumes 81 00:05:09.066 --> 00:05:13.300 is the actual ocean water from the subsurface of the moon. 82 00:05:13.300 --> 00:05:18.833 As these plume particles are ejected to space, solar radiation is going to excite these 83 00:05:18.833 --> 00:05:24.733 water particles, creating vibrational modes. Now, these vibrational modes are signatures 84 00:05:24.733 --> 00:05:29.600 that can be detected at infrared wavelengths by the Keck Observatory. 85 00:05:29.600 --> 00:05:35.866 So, we observe Europa on seventeen dates. What we found is that the majority 86 00:05:35.866 --> 00:05:41.600 of observations have no presence of water; however, on one of those dates 87 00:05:41.600 --> 00:05:45.833 we detected water. We detected H2O. 88 00:05:45.833 --> 00:05:51.633 In the past, Hubble provided indirect measurements of water by detecting hydrogen and oxygen, 89 00:05:51.633 --> 00:05:56.000 but now we have directly detected water for the first time. 90 00:05:56.000 --> 00:05:58.866 Both the Webb Telescope and the Europa Clipper mission will give us 91 00:05:58.866 --> 00:06:05.166 us a much more detailed picture of the surface of Europa, its cracks and crevices, 92 00:06:05.166 --> 00:06:09.900 detailed pictures of the water vapor, as well as other molecules that may also 93 00:06:09.900 --> 00:06:12.866 be emanating from the subsurface of Europa. 94 00:06:12.866 --> 00:06:18.133 So both of these missions will give us a great picture of whether Europa is truly habitable. 95 00:06:18.133 --> 00:06:27.133 [ Music ] 96 00:06:27.133 --> 00:06:29.266 Titan is a moon of Saturn. 97 00:06:29.266 --> 00:06:34.533 It’s the second largest moon in the Solar System and it is about two times larger 98 00:06:34.533 --> 00:06:38.333 than Earth’s Moon and actually bigger than the planet Mercury. 99 00:06:38.333 --> 00:06:42.433 Titan is also interesting – it’s the only moon in our Solar System with an atmosphere. 100 00:06:42.433 --> 00:06:45.900 It’s surrounded by sort of an envelope of gaseous nitrogen 101 00:06:45.900 --> 00:06:47.733 just like our own Earth is. 102 00:06:47.733 --> 00:06:52.633 Titan was first discovered by telescope observations back in the mid-1600's. 103 00:06:52.633 --> 00:06:56.700 The first spacecraft observations were made of Titan during flybys through 104 00:06:56.700 --> 00:07:00.633 the outer Solar System – that was in the late seventies and in the eighties. 105 00:07:00.633 --> 00:07:04.800 But we really were able to explore Titan in-depth with the Cassini-Huygens mission. 106 00:07:04.800 --> 00:07:08.700 The Huygens probe was dropped into the atmosphere of Titan, 107 00:07:08.700 --> 00:07:13.000 and it made measurements of chemistry, and it took images as it fell to the surface, 108 00:07:13.000 --> 00:07:14.900 and that was back in 2005. 109 00:07:14.900 --> 00:07:19.033 And since then, the Cassini Orbiter made over a hundred close flybys of Titan. 110 00:07:19.033 --> 00:07:23.333 Cassini in its design with the different instruments – we purposely were picking 111 00:07:23.333 --> 00:07:26.533 instruments that could go into longer wavelengths into the infrared 112 00:07:26.533 --> 00:07:29.300 so we could really understand the moon. 113 00:07:29.300 --> 00:07:33.433 We were able to basically peel back the layers of Titan 114 00:07:33.433 --> 00:07:38.866 to really see what was below, and it was remarkable – very Earthlike. 115 00:07:38.866 --> 00:07:44.400 The landscape is similar to Earth’s in many, many ways, but with a little bit of a twist. 116 00:07:44.400 --> 00:07:49.800 So on Titan, you can find dunes, you find lakes, there are river channels, 117 00:07:49.800 --> 00:07:55.500 the atmosphere is very dense and you can get clouds and smog and you even get rain. 118 00:07:55.500 --> 00:08:01.800 We saw winds, we saw seasons, and one really important thing we saw was liquids 119 00:08:01.800 --> 00:08:05.266 pooling in the polar regions on the surface – a lot of it. 120 00:08:05.266 --> 00:08:10.633 But because Titan is so cold, those features are all made of very exotic materials 121 00:08:10.633 --> 00:08:13.033 compared to what we would find on Earth. 122 00:08:13.033 --> 00:08:17.766 So the lakes and the rain are made of liquid methane, the crust that forms 123 00:08:17.766 --> 00:08:22.366 the surface of Titan is actually water ice, but it’s so cold that it's as hard as rock, 124 00:08:22.366 --> 00:08:26.766 and in the atmosphere we get this organic chemistry that forms large 125 00:08:26.766 --> 00:08:29.866 organic molecules and particulates – they fall down to the surface 126 00:08:29.866 --> 00:08:32.466 and then behave like dust or like sand does. 127 00:08:32.466 --> 00:08:36.066 So it makes us want to go back to really understand the complex, 128 00:08:36.066 --> 00:08:39.600 organic environment of that surface and what it means 129 00:08:39.600 --> 00:08:42.133 for either past life or maybe future life. 130 00:08:42.133 --> 00:08:44.900 [ Music ] 131 00:08:44.900 --> 00:08:49.500 Dragonfly is a mission that was just selected by NASA to fly to Titan 132 00:08:49.500 --> 00:08:51.933 Titan and arrive in the mid-2030’s. 133 00:08:51.933 --> 00:08:55.166 Dragonfly is going to make a whole bunch of measurements to help us understand 134 00:08:55.166 --> 00:08:58.500 the environment on Titan and its potential for habitability. 135 00:08:58.500 --> 00:09:01.033 We’ll be taking measurements of the atmosphere – that includes 136 00:09:01.033 --> 00:09:03.933 things like pressure, temperature, winds. 137 00:09:03.933 --> 00:09:08.500 We’ll probe the surface to try to understand what materials the surface is made out of. 138 00:09:08.500 --> 00:09:12.500 We’ll also be drilling into the surface to look for the types of organic molecules 139 00:09:12.500 --> 00:09:17.033 that are present and to try to see if we can find any examples of compounds that mimic 140 00:09:17.033 --> 00:09:20.133 the types of building blocks that we know we need for life on Earth. 141 00:09:20.133 --> 00:09:24.300 We don’t really know how life started on Earth. We don’t exactly know what the chemical 142 00:09:24.300 --> 00:09:30.500 environment of Earth was like before life started. So with Titan we have this really unique opportunity 143 00:09:30.500 --> 00:09:34.200 There are times in Titan’s past where there could be liquid water on the surface. 144 00:09:34.200 --> 00:09:39.200 Impact craters can generate impact melt, and there’s a potential for possible cryovolcanism 145 00:09:39.200 --> 00:09:41.633 to erupt some liquid water onto the surface. 146 00:09:41.633 --> 00:09:45.033 And so we know that there’s a rich organic chemistry going on in the atmosphere 147 00:09:45.033 --> 00:09:47.066 we know that’s depositing to the surface. 148 00:09:47.066 --> 00:09:51.500 If there were times where those organics in the liquid water environments were mixing, 149 00:09:51.500 --> 00:09:54.533 then there may be some really interesting chemistry taking place. 150 00:09:54.533 --> 00:09:58.033 When you have these processes operating for hundreds of millions of years, 151 00:09:58.033 --> 00:10:01.166 how far can they get you down that path of chemical complexity 152 00:10:01.166 --> 00:10:04.966 and can we see reactions and molecules that start to look something like 153 00:10:04.966 --> 00:10:09.800 what we think of as essential elements for our biochemistry for life on Earth? 154 00:10:09.800 --> 00:10:13.700 In the future, looking forward as opposed to looking back and thinking about Titan 155 00:10:13.700 --> 00:10:16.333 as a chemical laboratory for the pre-biotic Earth, 156 00:10:16.333 --> 00:10:20.200 I like to look forward thinking about what’s going to happen when the Sun evolves 157 00:10:20.200 --> 00:10:25.266 and warms up and the habitable zone actually moves outward to where Titan is, and it will. 158 00:10:25.266 --> 00:10:28.133 You have all the organics, you’re going to have a source of energy, 159 00:10:28.133 --> 00:10:32.466 all we have to do is melt the frozen water and we’re going to have a pool of organics 160 00:10:32.466 --> 00:10:33.933 just embedded in liquid. 161 00:10:33.933 --> 00:10:37.566 Titan might actually have a chance at that point to harbor life. 162 00:10:37.566 --> 00:10:43.200 [ Music ] 163 00:10:43.200 --> 00:10:45.800 So when we think about ocean worlds, it's good to compare them to what 164 00:10:45.800 --> 00:10:50.533 we know about Earth. In total proportion, Earth is about point-one-percent water. 165 00:10:50.533 --> 00:10:54.433 An ocean world is a body that has, in proportion, about ten times more water 166 00:10:54.433 --> 00:10:55.400 than Earth does. 167 00:10:55.400 --> 00:10:59.666 And when we think of the TRAPPIST planets, those planets have about fifty times 168 00:10:59.666 --> 00:11:02.266 more water in proportion to what Earth does. 169 00:11:02.266 --> 00:11:06.566 Ocean worlds do appear to be common in our galaxy. As far back as the early 2000's, 170 00:11:06.566 --> 00:11:10.200 We had astronomers, some of them still here at NASA Goddard that suggested that we would 171 00:11:10.200 --> 00:11:13.366 have ocean worlds orbiting low-mass stars. 172 00:11:13.366 --> 00:11:18.566 Recently we've looked at about fifty-two exoplanets, and these are low-mass exoplanets 173 00:11:18.566 --> 00:11:23.200 and what we've found is, of these fifty-two planets one out of every four 174 00:11:23.200 --> 00:11:24.900 may be an ocean planet. 175 00:11:24.900 --> 00:11:29.766 And when it comes to these ocean planets, over half of them may be ice-covered 176 00:11:29.766 --> 00:11:34.000 ocean worlds, and so Enceladus and Europa may serve as small-scale analogues 177 00:11:34.000 --> 00:11:35.633 of these planets. 178 00:11:35.633 --> 00:11:41.033 So there are a number of different ways to search for life on planets around other stars, 179 00:11:41.033 --> 00:11:44.766 but the key method is the study of the atmospheres. 180 00:11:44.766 --> 00:11:49.833 We can search for signs of life - biosignatures, we call them, things like oxygen, 181 00:11:49.833 --> 00:11:54.133 water vapor, carbon dioxide, even more unusual biosignatures - 182 00:11:54.133 --> 00:11:59.266 things like chlorofluorocarbons, or other things that are only produced by intelligent life. 183 00:11:59.266 --> 00:12:03.666 By looking for these key constituents of planetary atmospheres that signal life, 184 00:12:03.666 --> 00:12:09.233 We can discover lifeforms on other planets that we could never actually visit in our lifetime. 185 00:12:09.233 --> 00:12:13.366 So this is very analogous to how we study the atmospheres of moons and planets 186 00:12:13.366 --> 00:12:17.366 in our own solar system, and really makes the connection between studying the plumes 187 00:12:17.366 --> 00:12:21.300 of Europa, and the atmospheres of planets around other stars. 188 00:12:21.300 --> 00:12:26.133 What I would like to see is the definition of a habitable zone expanded 189 00:12:26.133 --> 00:12:31.333 We don't want to keep thinking too narrow about liquid on the surface, broaden the scope 190 00:12:31.333 --> 00:12:35.766 and really try to embrace other worlds that might seem too far from their host star, 191 00:12:35.766 --> 00:12:40.300 and frozen out, when they really aren't frozen at all. At great depths, they harbor 192 00:12:40.300 --> 00:12:45.266 a warm, hydrothermal-driven, liquid water environment. 193 00:12:45.266 --> 00:13:06.433 [ Music ]