1 00:00:02,333 --> 00:00:04,466 NARRATOR: When we look beyond Earth, 2 00:00:04,466 --> 00:00:07,533 we discover dynamic worlds. 3 00:00:07,533 --> 00:00:10,566 KATHERINE DE KLEER: As we're exploring the solar system, 4 00:00:10,566 --> 00:00:12,166 we are finding 5 00:00:12,166 --> 00:00:14,500 remarkably diverse 6 00:00:14,500 --> 00:00:17,100 and ferociously active worlds. 7 00:00:18,100 --> 00:00:21,100 CLARA SOUSA-SILVA: Where lava flows, where volcanoes erupt, 8 00:00:21,100 --> 00:00:24,333 where rumblings beneath crack the surface. 9 00:00:26,033 --> 00:00:28,066 NARRATOR: From giant, dead volcanoes 10 00:00:28,066 --> 00:00:30,500 on the planet next door... 11 00:00:30,500 --> 00:00:33,700 JAMES DOTTIN: It's absolutely mind-boggling 12 00:00:33,700 --> 00:00:36,933 that there are volcanoes that can get that big 13 00:00:36,933 --> 00:00:40,466 that it can tip a planet. That's absolutely crazy. 14 00:00:40,466 --> 00:00:43,566 NARRATOR: ...to active ice-cold eruptions 15 00:00:43,566 --> 00:00:46,500 on frozen moons. 16 00:00:46,500 --> 00:00:48,100 PAUL BYRNE: Where everything's frozen over, 17 00:00:48,100 --> 00:00:51,866 we see volcanic eruptions blasting out into space, 18 00:00:51,866 --> 00:00:53,800 and that's a real surprise. 19 00:00:53,800 --> 00:00:56,233 NARRATOR: These explosive worlds 20 00:00:56,233 --> 00:00:58,166 could even provide a clue 21 00:00:58,166 --> 00:01:01,133 to one of the biggest questions of them all. 22 00:01:01,133 --> 00:01:04,433 JEN GUPTA: Studying volcanoes in the solar system 23 00:01:04,433 --> 00:01:06,666 is incredibly important. 24 00:01:06,666 --> 00:01:10,600 It can help answer that question of where you and I came from 25 00:01:10,600 --> 00:01:13,133 and even how life first began. 26 00:01:14,366 --> 00:01:18,033 NARRATOR: But ultimately, volcanoes, fiery or frozen, 27 00:01:18,033 --> 00:01:23,666 reveal the incredible activity that lies within. 28 00:01:23,666 --> 00:01:24,833 When I think of a volcano, 29 00:01:24,833 --> 00:01:28,000 I think of awesomeness and... 30 00:01:28,000 --> 00:01:29,700 how can I get a ticket to go there? 31 00:01:29,700 --> 00:01:32,600 NARRATOR: How can there be so many 32 00:01:32,600 --> 00:01:36,500 different kinds of eruptions across our solar system? 33 00:01:37,500 --> 00:01:40,300 And what might Earth's volcanoes tell us 34 00:01:40,300 --> 00:01:43,500 about the possibilities of life elsewhere? 35 00:01:45,233 --> 00:01:48,333 "Solar System: Volcano Worlds." 36 00:01:48,333 --> 00:01:51,166 Right now, on "NOVA." 37 00:01:51,166 --> 00:01:53,200 ♪ ♪ 38 00:02:23,066 --> 00:02:25,100 NARRATOR: Humans have only set foot 39 00:02:25,100 --> 00:02:27,433 on one world beyond our own. 40 00:02:30,166 --> 00:02:34,233 On the moon, we found a barren landscape, 41 00:02:34,233 --> 00:02:38,266 appearing unchanged for more than a billion years. 42 00:02:40,366 --> 00:02:44,900 Its surface, scarred with craters and dark patches. 43 00:02:46,000 --> 00:02:49,266 This was activity that occurred early on in the moon's history. 44 00:02:49,266 --> 00:02:52,400 The moon now, there isn't much going on there. 45 00:02:53,800 --> 00:02:57,066 NARRATOR: Our moon is an inactive world, 46 00:02:57,066 --> 00:02:58,666 frozen in time. 47 00:03:01,600 --> 00:03:03,500 In stark contrast with Earth. 48 00:03:04,866 --> 00:03:08,633 Which seethes with activity beneath the surface. 49 00:03:10,033 --> 00:03:12,000 Who doesn't love a volcano? I mean, hot stuff 50 00:03:12,000 --> 00:03:14,033 jumping out of the ground at you. 51 00:03:14,033 --> 00:03:16,600 It would be really exciting. 52 00:03:16,600 --> 00:03:18,600 OLUSEYI: I've seen erupting volcanoes, 53 00:03:18,600 --> 00:03:20,800 and I just love active geology. 54 00:03:20,800 --> 00:03:23,233 It just tells me that the planet is alive, 55 00:03:23,233 --> 00:03:25,766 not literally, but figuratively. 56 00:03:26,900 --> 00:03:31,000 NARRATOR: And when we look beyond Earth and its moon, 57 00:03:31,000 --> 00:03:33,600 out into our solar system, 58 00:03:33,600 --> 00:03:38,400 other dynamic worlds like ours do exist. 59 00:03:41,166 --> 00:03:42,666 As we're exploring the solar system, 60 00:03:42,666 --> 00:03:44,800 both with telescopes and with spacecraft, 61 00:03:44,800 --> 00:03:48,900 we are finding remarkably diverse 62 00:03:48,900 --> 00:03:52,833 and ferociously active worlds throughout the solar system. 63 00:03:55,266 --> 00:03:59,033 NARRATOR: Many hold clues to our own planet's story. 64 00:04:00,100 --> 00:04:02,100 JASON HOFGARTNER: Looking at volcanoes elsewhere in the solar system, 65 00:04:02,100 --> 00:04:06,000 we see that Earth has a special type of volcanic activity, 66 00:04:06,000 --> 00:04:08,400 and so, by understanding other volcanoes, 67 00:04:08,400 --> 00:04:10,333 we might understand how Earth 68 00:04:10,333 --> 00:04:12,600 had eruptions in the past or in the future. 69 00:04:15,000 --> 00:04:18,300 NARRATOR: And since many scientists think volcanic activity 70 00:04:18,300 --> 00:04:20,466 might have played a major role 71 00:04:20,466 --> 00:04:22,500 in the origins of life on Earth... 72 00:04:25,566 --> 00:04:28,133 ...other active worlds in our solar system 73 00:04:28,133 --> 00:04:31,033 are especially intriguing. 74 00:04:31,033 --> 00:04:33,033 SOUSA-SILVA: We know that there's a relationship 75 00:04:33,033 --> 00:04:35,000 between volcanism and life, 76 00:04:35,000 --> 00:04:37,333 but we don't know where it ends and where it begins, 77 00:04:37,333 --> 00:04:40,366 and that's why we need to keep exploring. 78 00:04:42,366 --> 00:04:44,400 ♪ ♪ 79 00:05:03,833 --> 00:05:05,400 NARRATOR: The largest volcanoes 80 00:05:05,400 --> 00:05:08,866 discovered in the solar system so far 81 00:05:08,866 --> 00:05:10,933 are right next door. 82 00:05:17,266 --> 00:05:21,100 Mars is one of the most explored and photographed 83 00:05:21,100 --> 00:05:23,900 of all the planets beyond Earth. 84 00:05:24,866 --> 00:05:27,366 We've captured its stark beauty. 85 00:05:28,566 --> 00:05:30,666 From ice frosted dunes 86 00:05:30,666 --> 00:05:34,066 to canyons just over six miles deep. 87 00:05:36,066 --> 00:05:38,500 And many of the most detailed images 88 00:05:38,500 --> 00:05:41,733 have come from the Mars Reconnaissance Orbiter. 89 00:05:43,100 --> 00:05:45,433 Launched in 2005, 90 00:05:45,433 --> 00:05:48,700 it is still orbiting the planet today. 91 00:05:50,033 --> 00:05:53,200 JORGE NÚÑEZ: It carries instruments, high-resolution instruments, 92 00:05:53,200 --> 00:05:56,933 that allows us to view and explore 93 00:05:56,933 --> 00:05:59,933 the surface of Mars in such detail 94 00:05:59,933 --> 00:06:02,600 that we could map out 95 00:06:02,600 --> 00:06:06,066 things the size of a desk on the surface. 96 00:06:11,633 --> 00:06:13,100 OLUSEYI: It's the length of a school bus 97 00:06:13,100 --> 00:06:16,233 with these two big solar panels to power it, 98 00:06:16,233 --> 00:06:18,466 and as it's going about its business, 99 00:06:18,466 --> 00:06:20,866 it's sent back more data to Earth 100 00:06:20,866 --> 00:06:22,800 than any mission ever. 101 00:06:30,600 --> 00:06:35,300 NARRATOR: These images show in greater detail than ever before 102 00:06:35,300 --> 00:06:37,433 giant volcanoes 103 00:06:37,433 --> 00:06:40,733 that dwarf anything seen on Earth. 104 00:06:42,033 --> 00:06:44,333 One so wide... 105 00:06:46,866 --> 00:06:49,266 ...it would cover the length of Nevada. 106 00:06:51,300 --> 00:06:53,900 And one so tall... 107 00:06:55,700 --> 00:06:59,433 ...it reaches over twice the height of Mount Everest. 108 00:07:01,333 --> 00:07:04,900 It's the largest volcano in the solar system. 109 00:07:08,433 --> 00:07:11,933 Lava once flowed from these giants, 110 00:07:11,933 --> 00:07:15,766 spilling across the land in all directions. 111 00:07:16,766 --> 00:07:19,033 So much molten rock 112 00:07:19,033 --> 00:07:20,833 that the combined mass 113 00:07:20,833 --> 00:07:23,533 tipped the planet over on its axis 114 00:07:23,533 --> 00:07:25,800 by about 20 degrees. 115 00:07:27,266 --> 00:07:30,366 How did these monsters get so big? 116 00:07:33,166 --> 00:07:37,200 A hint comes from studying active volcanoes 117 00:07:37,200 --> 00:07:40,033 here on Earth. 118 00:07:41,733 --> 00:07:44,166 OLUSEYI: If you want to understand volcanism on Earth, 119 00:07:44,166 --> 00:07:45,200 or if you just want 120 00:07:45,200 --> 00:07:46,366 to understand Earth at all, 121 00:07:46,366 --> 00:07:48,566 you need to start with plate tectonics. 122 00:07:51,466 --> 00:07:55,433 NARRATOR: Earth's crust is made up of seven large plates 123 00:07:55,433 --> 00:07:57,633 and several smaller ones, 124 00:07:57,633 --> 00:08:01,700 which interact with each other at their boundaries. 125 00:08:02,700 --> 00:08:04,833 AISHA MORRIS: And they interact in multiple different ways. 126 00:08:04,833 --> 00:08:07,100 They can be smashing into each other, 127 00:08:07,100 --> 00:08:08,700 pulling apart from each other, 128 00:08:08,700 --> 00:08:11,333 or grinding against each other as they move around. 129 00:08:14,133 --> 00:08:15,500 DOTTIN: So at plate boundaries, 130 00:08:15,500 --> 00:08:17,033 what happens is that 131 00:08:17,033 --> 00:08:19,466 you end up with rock instabilities 132 00:08:19,466 --> 00:08:22,133 and, ultimately, the rock melts. 133 00:08:22,133 --> 00:08:24,266 NARRATOR: Creating the conditions 134 00:08:24,266 --> 00:08:26,966 that have formed the majority of volcanoes on Earth. 135 00:08:31,566 --> 00:08:35,500 But it's the volcanoes that don't form at plate boundaries 136 00:08:35,500 --> 00:08:38,666 that tell us the most about Martian volcanoes. 137 00:08:42,533 --> 00:08:45,300 GUPTA: On Earth, we also have volcanoes 138 00:08:45,300 --> 00:08:48,633 in the middle of a plate, not just the boundary. 139 00:08:48,633 --> 00:08:50,700 These are called hotspot volcanoes, 140 00:08:50,700 --> 00:08:53,600 and Hawaii is a great example of this. 141 00:08:54,566 --> 00:08:56,000   DOTTIN: Hotspot volcanoes 142 00:08:56,000 --> 00:08:58,066 are typically created by a plume, 143 00:08:58,066 --> 00:09:00,133 like a bubble of hot magma 144 00:09:00,133 --> 00:09:02,966 welling up directly from the interior, 145 00:09:02,966 --> 00:09:06,433 hitting the bottom of the plate and bursting through. 146 00:09:10,500 --> 00:09:15,033 NARRATOR: Hawaii is a chain of hotspot volcanoes, 147 00:09:15,033 --> 00:09:17,266 created by a tectonic plate 148 00:09:17,266 --> 00:09:20,433 moving across a single plume of magma, 149 00:09:20,433 --> 00:09:23,866 erupting onto the surface 150 00:09:23,866 --> 00:09:26,566 forming a line of islands. 151 00:09:27,866 --> 00:09:30,233 Like on Earth, 152 00:09:30,233 --> 00:09:32,700 Mars has hotspot volcanoes, 153 00:09:32,700 --> 00:09:34,866 but with one major difference, 154 00:09:34,866 --> 00:09:37,666 no plate tectonics. 155 00:09:40,200 --> 00:09:42,100 On Mars, instead of the plate moving over the plume 156 00:09:42,100 --> 00:09:44,166 and making a chain of volcanoes, 157 00:09:44,166 --> 00:09:48,033 you get the plume stationary, with respect to the ground, 158 00:09:48,033 --> 00:09:49,400 and that means, 159 00:09:49,400 --> 00:09:52,200 over millions or even billions of years, 160 00:09:52,200 --> 00:09:54,600 Mars has been able to build up volcanoes 161 00:09:54,600 --> 00:09:57,033 that dwarf anything that we see on Earth. 162 00:09:59,800 --> 00:10:03,900 NARRATOR: But all of those monster volcanoes have quieted. 163 00:10:05,933 --> 00:10:09,700 Still and cold for millions of years. 164 00:10:12,933 --> 00:10:14,100 Why? 165 00:10:15,633 --> 00:10:17,300 To find the answer, 166 00:10:17,300 --> 00:10:21,133 scientists look deep within, 167 00:10:21,133 --> 00:10:24,800 tracing the source of heat that drives volcanism 168 00:10:24,800 --> 00:10:28,533 on rocky planets like ours. 169 00:10:31,933 --> 00:10:34,300 Four and a half billion years ago, 170 00:10:34,300 --> 00:10:36,033 with the rest of the solar system, 171 00:10:36,033 --> 00:10:38,400 the Earth formed from the collapse 172 00:10:38,400 --> 00:10:40,400 of a cloud of gas and dust 173 00:10:40,400 --> 00:10:43,066 being smashed together 174 00:10:43,066 --> 00:10:45,700 under the force of its own gravity. 175 00:10:45,700 --> 00:10:48,966 NARRATOR: Much of the energy that went into these collisions 176 00:10:48,966 --> 00:10:53,400 turned into heat, trapped inside Earth. 177 00:10:54,633 --> 00:10:57,566 Added to that is heat from radioactive elements 178 00:10:57,566 --> 00:11:01,000 inside the planet, like uranium. 179 00:11:02,366 --> 00:11:03,633 So over time, 180 00:11:03,633 --> 00:11:05,766 these elements actually decay 181 00:11:05,766 --> 00:11:07,266 into lighter elements 182 00:11:07,266 --> 00:11:08,666 and as they do so, 183 00:11:08,666 --> 00:11:12,233 they are constantly warming and heating our planet 184 00:11:12,233 --> 00:11:14,233 from the inside. 185 00:11:14,233 --> 00:11:15,633 When you stop and think about it, 186 00:11:15,633 --> 00:11:19,166 it really just is incredible that all of this heat 187 00:11:19,166 --> 00:11:22,000 that is powering volcanoes here on Earth 188 00:11:22,000 --> 00:11:24,800 can be traced back four and a half billion years ago 189 00:11:24,800 --> 00:11:26,733 to the formation of the Earth. 190 00:11:26,733 --> 00:11:29,266 ♪ ♪ 191 00:11:29,266 --> 00:11:32,400 NARRATOR: Mars shares Earth's origin story. 192 00:11:33,600 --> 00:11:35,666 It formed in the same way... 193 00:11:37,033 --> 00:11:38,733 ...at the same time... 194 00:11:41,466 --> 00:11:44,600 ...capturing enough heat to drive volcanism 195 00:11:44,600 --> 00:11:46,633 on a staggering scale. 196 00:11:55,600 --> 00:11:58,700 But now the volcanoes are cold and silent. 197 00:12:01,266 --> 00:12:04,033 Where did all that heat go? 198 00:12:05,733 --> 00:12:09,500 A clue exists within this volcanic landscape. 199 00:12:11,333 --> 00:12:16,200 In Mars's northern hemisphere lies the Marte Vallis area... 200 00:12:17,300 --> 00:12:18,700 ...where cliffs are built 201 00:12:18,700 --> 00:12:21,133 from an intricate array of pillars. 202 00:12:22,600 --> 00:12:25,066 Arranged in uniform patterns, 203 00:12:25,066 --> 00:12:28,600 these structures are made of solidified lava. 204 00:12:30,900 --> 00:12:34,366 Similar structures also exist here on Earth... 205 00:12:36,800 --> 00:12:38,933 ...and they can help unravel the mystery 206 00:12:38,933 --> 00:12:43,200 behind why Mars's volcanoes are now silent. 207 00:12:47,466 --> 00:12:48,833 PAUL BYRNE: We see columnar jointing 208 00:12:48,833 --> 00:12:50,400 in lots of places on Earth. 209 00:12:55,033 --> 00:12:57,333 There's a particularly beautiful example 210 00:12:57,333 --> 00:13:00,100 in the Studlagil Canyon in Iceland. 211 00:13:01,200 --> 00:13:03,133 NARRATOR: Hot lava once flowed here. 212 00:13:04,266 --> 00:13:07,633 As it cooled, it did something extraordinary. 213 00:13:09,400 --> 00:13:11,300 PAUL BYRNE: As that lava's cooling down, 214 00:13:11,300 --> 00:13:13,533 it's shrinking, it's contracting. 215 00:13:13,533 --> 00:13:16,700 And as the lava pulls apart from itself, as it contracts, 216 00:13:16,700 --> 00:13:18,466 it makes these fractures 217 00:13:18,466 --> 00:13:20,933 and these fractures form this very regular, 218 00:13:20,933 --> 00:13:22,300 even pattern. 219 00:13:24,000 --> 00:13:26,233 NARRATOR: Exactly what conditions cause 220 00:13:26,233 --> 00:13:29,366 these unusual structures to form is complex. 221 00:13:30,833 --> 00:13:32,233 But they do reveal 222 00:13:32,233 --> 00:13:36,000 one of the most fundamental laws of nature. 223 00:13:36,000 --> 00:13:37,100 DOTTIN: The simplest explanation 224 00:13:37,100 --> 00:13:40,133 for the second law of thermodynamics 225 00:13:40,133 --> 00:13:43,233 is that heat flows from hot to cold. 226 00:13:43,233 --> 00:13:45,933 So if you were to go outside on a cold day 227 00:13:45,933 --> 00:13:48,433 with a hot cup of coffee, eventually, 228 00:13:48,433 --> 00:13:51,200 that hot cup of coffee will be the same temperature 229 00:13:51,200 --> 00:13:55,166 as your outdoor surroundings. 230 00:13:56,533 --> 00:13:59,200 NARRATOR: More than 65 feet tall, 231 00:13:59,200 --> 00:14:02,700 these columns show this very principle in action. 232 00:14:04,166 --> 00:14:07,200 BYRNE: So we can think of how, say, columnar joints form 233 00:14:07,200 --> 00:14:11,166 through that lens of energy flowing from hot to cold. 234 00:14:11,166 --> 00:14:14,200 When the lava flow is flowing over the surface, 235 00:14:14,200 --> 00:14:15,866 in the case of Earth, at least, 236 00:14:15,866 --> 00:14:18,666 it's much hotter than both the ground and the air. 237 00:14:20,700 --> 00:14:22,766 NARRATOR: As the lava cools, 238 00:14:22,766 --> 00:14:25,966 its heat rises into the atmosphere 239 00:14:25,966 --> 00:14:27,866 and then out into space, 240 00:14:27,866 --> 00:14:31,033 slowly cooling the entire planet. 241 00:14:31,033 --> 00:14:33,033 ♪ ♪ 242 00:14:33,033 --> 00:14:35,366 TRIPATHI: The beautiful truth about physics 243 00:14:35,366 --> 00:14:38,700 is that the laws are the same everywhere. 244 00:14:38,700 --> 00:14:41,633 So the laws of thermodynamics work on Earth, 245 00:14:41,633 --> 00:14:43,933 they work on Mars, they work beyond. 246 00:14:46,466 --> 00:14:48,933 NARRATOR: The physics may be the same: 247 00:14:48,933 --> 00:14:52,433 volcanoes driven by ancient internal heat 248 00:14:52,433 --> 00:14:54,400 moving towards equilibrium 249 00:14:54,400 --> 00:14:56,600 with the coldness of outer space. 250 00:14:59,100 --> 00:15:00,333 But one key difference 251 00:15:00,333 --> 00:15:02,800 caused a big change in how quickly 252 00:15:02,800 --> 00:15:04,500 Mars lost its heat. 253 00:15:07,066 --> 00:15:08,666 OLUSEYI: If we look at these two balls 254 00:15:08,666 --> 00:15:12,433 as an example for Earth-- the baseball-- 255 00:15:12,433 --> 00:15:15,266 and Mars-- the golf ball-- 256 00:15:15,266 --> 00:15:16,733 then they're different sizes. 257 00:15:16,733 --> 00:15:19,300 So as the object gets bigger, 258 00:15:19,300 --> 00:15:22,966 the volume grows faster than the surface area grows. 259 00:15:22,966 --> 00:15:28,133 In spite of having a volume that's only 15% of the Earth, 260 00:15:28,133 --> 00:15:31,100 Mars's surface area is, actually, bigger proportionally. 261 00:15:31,100 --> 00:15:32,733 It's got about 28% 262 00:15:32,733 --> 00:15:35,166 of the surface area of the Earth. 263 00:15:35,166 --> 00:15:36,766 You can think of it this way. 264 00:15:36,766 --> 00:15:40,233 If I make a big pot of coffee, it's gonna stay warm for hours. 265 00:15:40,233 --> 00:15:42,900 If I pour some of that coffee into a mug, 266 00:15:42,900 --> 00:15:45,433 it'll cool down much faster because there's less of it, 267 00:15:45,433 --> 00:15:46,933 but there's more surface area. 268 00:15:46,933 --> 00:15:49,100 And these differences have resulted 269 00:15:49,100 --> 00:15:51,666 in so much of what we see today, 270 00:15:51,666 --> 00:15:54,733 including the geologic and volcanic history 271 00:15:54,733 --> 00:15:56,133 on the two worlds. 272 00:15:56,133 --> 00:15:58,166 ♪ ♪ 273 00:16:02,166 --> 00:16:04,066 NARRATOR: Earth and Mars started out 274 00:16:04,066 --> 00:16:09,900 with similar materials: heat and volcanic activity. 275 00:16:11,666 --> 00:16:15,866 But while Mars's heat and its volcanism ebbed away, 276 00:16:15,866 --> 00:16:19,400 Earth's volcanoes continue erupting to this day. 277 00:16:21,500 --> 00:16:24,433 And many scientists believe that on Earth, 278 00:16:24,433 --> 00:16:28,000 volcanism on the ocean floor played a role 279 00:16:28,000 --> 00:16:29,866 in life's beginnings. 280 00:16:32,100 --> 00:16:34,900 So with such similar origin stories... 281 00:16:35,866 --> 00:16:38,900 ...could there once have been life on Mars? 282 00:16:40,433 --> 00:16:42,533 NÚÑEZ: Mars is like Earth's cousin. 283 00:16:42,533 --> 00:16:45,166 And so very early in their history as they formed, 284 00:16:45,166 --> 00:16:47,433 they had this volcanic activity, and we found evidence 285 00:16:47,433 --> 00:16:51,100 that Mars had liquid water on its surface. 286 00:16:51,100 --> 00:16:53,800 It had a thicker atmosphere. 287 00:16:53,800 --> 00:16:55,533 And around the same time 288 00:16:55,533 --> 00:16:58,433 that we know that life emerged here on Earth, 289 00:16:58,433 --> 00:17:02,466 there was liquid water on the surface of Mars 290 00:17:02,466 --> 00:17:07,500 and it had conditions very similar to early Earth. 291 00:17:09,133 --> 00:17:13,733 NARRATOR: Today the Perseverance rover, on Mars since 2021, 292 00:17:13,733 --> 00:17:18,300 is creating packages of rock samples with the intention 293 00:17:18,300 --> 00:17:22,000 that a later mission will one day return them to Earth. 294 00:17:23,666 --> 00:17:27,333 Could they contain evidence of Martian life? 295 00:17:29,100 --> 00:17:32,166 DOTTIN: So generally, in these rock samples from Mars, 296 00:17:32,166 --> 00:17:33,733 we're looking for signatures 297 00:17:33,733 --> 00:17:36,200 that there was life on the planet. 298 00:17:36,200 --> 00:17:38,900 But it would be absolutely amazing 299 00:17:38,900 --> 00:17:42,833 if we actually found cells or something similar 300 00:17:42,833 --> 00:17:44,466 in these rocks that indicated 301 00:17:44,466 --> 00:17:46,800 that there is life on Mars today. 302 00:17:48,233 --> 00:17:53,033 NARRATOR: For now, any secrets of life on Mars remain a mystery. 303 00:17:54,300 --> 00:17:57,066 But what Mars does demonstrate 304 00:17:57,066 --> 00:18:01,966 is the smaller the planet, the more quickly it loses heat. 305 00:18:06,166 --> 00:18:09,566 Still, there is a rule breaker: 306 00:18:09,566 --> 00:18:12,100 a world even smaller than Mars 307 00:18:12,100 --> 00:18:15,566 that is somehow the most ferociously active body 308 00:18:15,566 --> 00:18:17,133 in the solar system. 309 00:18:22,966 --> 00:18:26,733 Leaving the quiet volcanoes of Mars behind... 310 00:18:27,733 --> 00:18:30,500 ...passing through the asteroid belt, 311 00:18:30,500 --> 00:18:32,233 the cold rubble left over 312 00:18:32,233 --> 00:18:34,100 from the formation of the planets... 313 00:18:36,133 --> 00:18:39,533 ...we reach the first of the gas giants. 314 00:18:42,933 --> 00:18:46,300 Twice the mass of all the other planets combined, 315 00:18:46,300 --> 00:18:50,733 Jupiter is circled by more than 80 moons. 316 00:18:52,933 --> 00:18:54,666 Some are icy. 317 00:18:55,933 --> 00:18:58,733 Like the frozen expanses of Ganymede. 318 00:18:59,766 --> 00:19:01,366 And Europa. 319 00:19:03,200 --> 00:19:06,433 But then, there is Io. 320 00:19:12,366 --> 00:19:14,600 About the size of our moon, 321 00:19:14,600 --> 00:19:18,866 Io orbits closer to Jupiter than any other moon of its size. 322 00:19:22,366 --> 00:19:24,400 Since 2016, 323 00:19:24,400 --> 00:19:27,033 the space probe Juno has been our eyes 324 00:19:27,033 --> 00:19:28,900 on Jupiter and its moons. 325 00:19:29,900 --> 00:19:32,333 With an elongated orbit, 326 00:19:32,333 --> 00:19:35,433 it has made regular flybys past Io... 327 00:19:39,366 --> 00:19:42,300 ...witnessing violent eruptions, 328 00:19:42,300 --> 00:19:46,000 which shoot out columns of gas and dust 329 00:19:46,000 --> 00:19:48,833 that reach far out into space... 330 00:19:52,633 --> 00:19:57,800 ...and send rivers of lava pouring across the landscape... 331 00:19:59,133 --> 00:20:03,200 ...creating a surface dotted with lakes of lava. 332 00:20:04,633 --> 00:20:08,100 Io is a volcanic powerhouse, 333 00:20:08,100 --> 00:20:11,066 defying all expectations. 334 00:20:12,266 --> 00:20:15,333 DE KLEER: Considering how small Io is, 335 00:20:15,333 --> 00:20:18,466 the heat sources like we have on Earth, 336 00:20:18,466 --> 00:20:21,233 the heat of formation and the radioactive decay, 337 00:20:21,233 --> 00:20:24,266 those should be, essentially, completely gone on Io by now. 338 00:20:25,266 --> 00:20:28,600 OLUSEYI: This little, tiny, small world of Io, 339 00:20:28,600 --> 00:20:31,400 you'd expect it to be geologically inactive. 340 00:20:31,400 --> 00:20:32,833 Instead, it's the most 341 00:20:32,833 --> 00:20:34,066 volcanically active body 342 00:20:34,066 --> 00:20:36,366 in our solar system. 343 00:20:36,366 --> 00:20:38,100 That's a surprise. 344 00:20:40,866 --> 00:20:45,333 NARRATOR: Eruptions continue day in, day out, 345 00:20:45,333 --> 00:20:48,566 across the entire surface. 346 00:20:50,733 --> 00:20:54,200 A world like no other in our solar system. 347 00:20:55,433 --> 00:20:57,466 ♪ ♪ 348 00:20:59,133 --> 00:21:02,433 But similarities can be found 349 00:21:02,433 --> 00:21:05,433 by taking a closer look beneath the surface 350 00:21:05,433 --> 00:21:08,866 inside volcanoes here on Earth. 351 00:21:16,400 --> 00:21:20,400 Astrophysicist Jen Gupta is entering a chamber 352 00:21:20,400 --> 00:21:22,866 created by a volcanic eruption 353 00:21:22,866 --> 00:21:25,933 over 4,000 years ago. 354 00:21:28,866 --> 00:21:31,333 GUPTA: The incredible thing about this place 355 00:21:31,333 --> 00:21:33,233 is that as the magma drained away, 356 00:21:33,233 --> 00:21:35,433 it left behind these colors 357 00:21:35,433 --> 00:21:38,366 that we can see here on the walls, 358 00:21:38,366 --> 00:21:40,033 from elements and minerals 359 00:21:40,033 --> 00:21:42,500 that were dragged up from the interior of the Earth 360 00:21:42,500 --> 00:21:44,400 during that volcanic eruption. 361 00:21:45,900 --> 00:21:49,066 The one that immediately grabbed my attention is the yellow. 362 00:21:49,066 --> 00:21:52,166 This is from sulphates and sulphur, 363 00:21:52,166 --> 00:21:53,433 and these are the exact same colors 364 00:21:53,433 --> 00:21:56,366 that we see covering the entire surface of Io. 365 00:22:03,133 --> 00:22:05,133 NARRATOR: Images of Io are dominated 366 00:22:05,133 --> 00:22:07,400 by its yellow surface, 367 00:22:07,400 --> 00:22:11,700 created by the same sulphates and sulphur 368 00:22:11,700 --> 00:22:15,233 that line the chamber walls here in Iceland. 369 00:22:18,933 --> 00:22:21,533 GUPTA: The scale of this place is just astonishing, 370 00:22:21,533 --> 00:22:24,900 and to think that there are chambers like this 371 00:22:24,900 --> 00:22:26,766 under the surface of Io, 372 00:22:26,766 --> 00:22:31,066 filled with molten magma ready to erupt out. 373 00:22:31,066 --> 00:22:33,766 It's easy to think that Earth, our home planet, 374 00:22:33,766 --> 00:22:35,866 is completely unique, 375 00:22:35,866 --> 00:22:38,133 but the more we discover about the solar system, 376 00:22:38,133 --> 00:22:41,000 the more we see these remarkable similarities, 377 00:22:41,000 --> 00:22:42,700 like having volcanoes on Io. 378 00:22:45,733 --> 00:22:49,166 NARRATOR: And unlike Mars's ancient dead volcanoes, 379 00:22:49,166 --> 00:22:55,233 Io's are continually erupting, 380 00:22:55,233 --> 00:22:58,633 creating a thin atmosphere of volcanic gases. 381 00:23:05,300 --> 00:23:08,500 As Jupiter blocks the sun, 382 00:23:08,500 --> 00:23:11,100 Io passes into its shadow. 383 00:23:14,200 --> 00:23:17,466 Even with such constant activity, 384 00:23:17,466 --> 00:23:19,566 temperatures plummet, 385 00:23:21,266 --> 00:23:26,466 so low that the thin atmosphere begins to freeze, 386 00:23:26,466 --> 00:23:28,966 creating an incredible frost. 387 00:23:34,266 --> 00:23:35,933 Made not of water, 388 00:23:35,933 --> 00:23:40,733 but of delicate crystals of sulphur dioxide. 389 00:23:46,466 --> 00:23:49,266 A few hours later, 390 00:23:49,266 --> 00:23:52,466 they are gone, 391 00:23:52,466 --> 00:23:55,533 evaporating away 392 00:23:55,533 --> 00:23:57,633 as the sun returns. 393 00:23:59,633 --> 00:24:01,600 DOTTIN: Sulphur is a major component 394 00:24:01,600 --> 00:24:03,533 of volcanic eruptions. 395 00:24:03,533 --> 00:24:05,633 And so it's not surprising 396 00:24:05,633 --> 00:24:09,366 that the surface of Io is 397 00:24:09,366 --> 00:24:10,600 covered with sulphur crystals 398 00:24:10,600 --> 00:24:12,933 because there's so much volcanic activity 399 00:24:12,933 --> 00:24:14,900 going on there. 400 00:24:20,133 --> 00:24:21,633 NARRATOR: Io isn't big enough 401 00:24:21,633 --> 00:24:24,000 to have retained heat from its formation. 402 00:24:25,200 --> 00:24:27,300 So the heat that drives this much sulphur 403 00:24:27,300 --> 00:24:30,133 to the surface 404 00:24:30,133 --> 00:24:32,666 must be coming from somewhere else. 405 00:24:34,633 --> 00:24:36,133 DE KLEER: So, the question is, 406 00:24:36,133 --> 00:24:38,666 why is an object this small 407 00:24:38,666 --> 00:24:40,366 still volcanically active? 408 00:24:40,366 --> 00:24:43,000 Why hasn't it run out of heat yet? 409 00:24:47,766 --> 00:24:49,300 GUPTA: The thing about Io 410 00:24:49,300 --> 00:24:53,200 is it doesn't orbit Jupiter in a circular orbit. 411 00:24:53,200 --> 00:24:55,000 What it does instead is travel round 412 00:24:55,000 --> 00:24:58,600 in an elliptical orbit like this. 413 00:24:58,600 --> 00:25:00,466 And it's that elliptical orbit 414 00:25:00,466 --> 00:25:02,300 that's one of the driving forces 415 00:25:02,300 --> 00:25:04,566 behind the level of volcanic activity 416 00:25:04,566 --> 00:25:07,133 on the moon. 417 00:25:07,133 --> 00:25:09,166 NARRATOR: Jupiter is the largest planet 418 00:25:09,166 --> 00:25:10,600 in our solar system, 419 00:25:10,600 --> 00:25:14,833 and its gravitational pull on Io is enormous. 420 00:25:16,433 --> 00:25:19,400 GUPTA: As Io comes in towards the planet, 421 00:25:19,400 --> 00:25:21,566 the gravitational pull of Jupiter is stronger, 422 00:25:21,566 --> 00:25:24,100 causing the very rock on Io 423 00:25:24,100 --> 00:25:26,766 to bulge out towards its host planet. 424 00:25:26,766 --> 00:25:29,700 Then as Io moves further away, 425 00:25:29,700 --> 00:25:32,000 the bulge shrinks and moves, 426 00:25:32,000 --> 00:25:35,500 causing a tide of rock on Io 427 00:25:35,500 --> 00:25:38,666 that's over 300 feet tall. 428 00:25:38,666 --> 00:25:42,333 That's rock the height of this chamber 429 00:25:42,333 --> 00:25:46,033 bulging and moving on that rocky moon. 430 00:25:46,033 --> 00:25:49,133 This is rock rubbing against rock 431 00:25:49,133 --> 00:25:51,700 in a similar way to when we rub our hands together, 432 00:25:51,700 --> 00:25:53,033 and they warm up. 433 00:25:53,033 --> 00:25:54,800 It's generating huge amounts 434 00:25:54,800 --> 00:25:57,366 of heat underneath the surface of Io. 435 00:26:00,100 --> 00:26:02,800 NARRATOR: A process known as "tidal heating." 436 00:26:04,233 --> 00:26:08,033 But this bulging movement generates only some of the heat 437 00:26:08,033 --> 00:26:10,700 that drives Io's violent volcanoes. 438 00:26:12,800 --> 00:26:15,433 So where is the rest of the heat coming from? 439 00:26:16,566 --> 00:26:18,866 DOTTIN: When we think about our moon, 440 00:26:18,866 --> 00:26:22,333 we understand that we only see one side of the moon, 441 00:26:22,333 --> 00:26:23,666 and this is because 442 00:26:23,666 --> 00:26:25,766 the Earth and the moon are tidally locked. 443 00:26:25,766 --> 00:26:28,033 NARRATOR: But as the moon travels 444 00:26:28,033 --> 00:26:30,633 its elliptical path around Earth, 445 00:26:30,633 --> 00:26:33,200 we actually see it at slightly different angles. 446 00:26:34,566 --> 00:26:35,800 OLUSEYI: It's sort of like 447 00:26:35,800 --> 00:26:37,800 if I was to shake my head and say "no." 448 00:26:39,366 --> 00:26:41,666 Right? You see my face the entire time, 449 00:26:41,666 --> 00:26:43,700 but because it rocks back and forth, 450 00:26:43,700 --> 00:26:46,133 you see slightly more of my head 451 00:26:46,133 --> 00:26:49,266 than if I just kept it pointing right at it. 452 00:26:49,266 --> 00:26:52,066 So, it's like the moon is looking down on the Earth 453 00:26:52,066 --> 00:26:54,766 and going, "Mm, mm, mm. 454 00:26:54,766 --> 00:26:56,766 Look at those humans." 455 00:26:58,266 --> 00:27:00,000 NARRATOR: Just like our moon, 456 00:27:00,000 --> 00:27:03,266 Io is tidally locked to its planet 457 00:27:03,266 --> 00:27:05,133 and has an elliptical orbit. 458 00:27:06,800 --> 00:27:09,633 Which means that as Io orbits Jupiter, 459 00:27:09,633 --> 00:27:13,366 it appears to rock back and forth by around one degree. 460 00:27:14,800 --> 00:27:18,033 But there's one big difference between our moon and Io. 461 00:27:19,533 --> 00:27:22,233 OLUSEYI: Jupiter is way more massive than the Earth, 462 00:27:22,233 --> 00:27:24,800 and Io is similar to the moon, 463 00:27:24,800 --> 00:27:27,700 so the tidal effects are more extreme. 464 00:27:28,866 --> 00:27:30,333 NARRATOR: Io's tidal bulge 465 00:27:30,333 --> 00:27:33,833 is continuously pulled towards Jupiter. 466 00:27:33,833 --> 00:27:36,933 So as Io faces the planet at slightly different angles 467 00:27:36,933 --> 00:27:38,833 throughout its orbit, 468 00:27:38,833 --> 00:27:43,433 Jupiter not only raises the rock tide 300 feet up and down, 469 00:27:43,433 --> 00:27:48,133 but also drags that tidal bulge back and forth 470 00:27:48,133 --> 00:27:50,433 40 miles across Io's surface. 471 00:27:51,666 --> 00:27:54,833 Earth's heat was captured billions of years ago, 472 00:27:54,833 --> 00:27:57,766 locked inside the planet at the time of formation. 473 00:27:58,733 --> 00:28:02,600 But on Io, its heat is constantly replenished 474 00:28:02,600 --> 00:28:04,800 by its elliptical orbit. 475 00:28:08,033 --> 00:28:10,366 NARRATOR: As Io deforms, 476 00:28:10,366 --> 00:28:12,266 the intense friction generated 477 00:28:12,266 --> 00:28:16,100 by these tidal forces produces enough heat 478 00:28:16,100 --> 00:28:20,800 to drive Io's spectacularly violent volcanism. 479 00:28:23,033 --> 00:28:25,033 But could all that heat have driven out 480 00:28:25,033 --> 00:28:28,666 some common planetary ingredients, like water? 481 00:28:31,700 --> 00:28:33,366 Io doesn't seem to have any water today, 482 00:28:33,366 --> 00:28:36,566 and we actually don't entirely know why that is. 483 00:28:36,566 --> 00:28:40,300 Maybe it was never able to form with any water, 484 00:28:40,300 --> 00:28:42,966 but maybe it just lost all of its water over time 485 00:28:42,966 --> 00:28:44,766 because of this tremendous amount of heat 486 00:28:44,766 --> 00:28:47,533 that's produced in it. 487 00:28:50,566 --> 00:28:52,900 FRANCK MARCHIS: So, there is no water on Io. 488 00:28:52,900 --> 00:28:55,333 Is there life? We don't know. 489 00:28:55,333 --> 00:28:56,666 If there is life, it would be a life 490 00:28:56,666 --> 00:28:58,133 which is very different 491 00:28:58,133 --> 00:29:01,133 to the life we have on our own planet, 492 00:29:01,133 --> 00:29:03,066 and the only way for us to find it will be 493 00:29:03,066 --> 00:29:05,366 to go there and to explore directly. 494 00:29:06,333 --> 00:29:08,500 DE KLEER: Every time I point a telescope at Io, 495 00:29:08,500 --> 00:29:10,433 I still have that new excitement 496 00:29:10,433 --> 00:29:11,966 because you don't know what's going to be happening. 497 00:29:11,966 --> 00:29:13,833 You take an image of Io, 498 00:29:13,833 --> 00:29:16,200 and you're saying, "Which volcanoes are active?" 499 00:29:16,200 --> 00:29:18,600 And you look at it, and you can just immediately see 500 00:29:18,600 --> 00:29:20,333 from the picture and identify 501 00:29:20,333 --> 00:29:23,700 which volcanoes are going off at that time. 502 00:29:25,966 --> 00:29:27,833 NARRATOR: As scientists learn more, 503 00:29:27,833 --> 00:29:29,700 they are finding the effects 504 00:29:29,700 --> 00:29:33,766 of tidal heating on an even stranger world. 505 00:29:34,733 --> 00:29:37,400 That same source of heat, 506 00:29:37,400 --> 00:29:39,600 caused by an elliptical orbit, 507 00:29:39,600 --> 00:29:43,933 drives volcanic eruptions that aren't even hot. 508 00:29:46,200 --> 00:29:49,066 Even farther from Earth than Jupiter, 509 00:29:49,066 --> 00:29:52,766 across a great gulf of space, 510 00:29:52,766 --> 00:29:55,166 lies the next planet. 511 00:30:00,866 --> 00:30:05,366 Saturn's rings loop for hundreds of thousands of miles. 512 00:30:09,700 --> 00:30:11,300 And just beyond them, 513 00:30:11,300 --> 00:30:14,100 one of its largest moons changed everything 514 00:30:14,100 --> 00:30:17,066 we thought we knew about volcanic activity 515 00:30:17,066 --> 00:30:19,300 this far out in the solar system. 516 00:30:25,266 --> 00:30:29,466 ♪ ♪ 517 00:30:29,466 --> 00:30:32,533 With a hard, frozen exterior, 518 00:30:32,533 --> 00:30:35,833 Enceladus' surface averages a chilly 519 00:30:35,833 --> 00:30:39,300 -330 degrees Fahrenheit. 520 00:30:40,966 --> 00:30:45,266 It's one of the coldest places in the Saturn system. 521 00:30:45,266 --> 00:30:48,200 An ice world, 522 00:30:48,200 --> 00:30:51,966 where we'd expect everything to be completely still, 523 00:30:51,966 --> 00:30:54,466 frozen and unchanging. 524 00:30:58,966 --> 00:31:01,033 But in 2005, 525 00:31:01,033 --> 00:31:05,133 NASA's Cassini spacecraft travelled to the South Pole 526 00:31:05,133 --> 00:31:08,033 and discovered that stillness shattered. 527 00:31:10,333 --> 00:31:13,533 It captured explosive jets 528 00:31:13,533 --> 00:31:16,033 constantly erupting from the surface. 529 00:31:16,033 --> 00:31:18,066 ♪ ♪ 530 00:31:20,466 --> 00:31:22,533 NÚÑEZ: So, when we first saw those plumes 531 00:31:22,533 --> 00:31:24,166 coming out of Enceladus, 532 00:31:24,166 --> 00:31:27,933 it was just... mind-boggling 533 00:31:27,933 --> 00:31:30,500 that to see this tiny world 534 00:31:30,500 --> 00:31:32,666 spewing material out, 535 00:31:32,666 --> 00:31:35,600 indicating that it was geologically active. 536 00:31:38,200 --> 00:31:40,100 Discovering the jets at Enceladus's south pole 537 00:31:40,100 --> 00:31:42,466 completely changed the way that we see icy worlds. 538 00:31:42,466 --> 00:31:45,700 It changed the way that we see small, icy worlds in particular. 539 00:31:49,033 --> 00:31:53,100 NARRATOR: Giant plumes far bigger than the moon they erupt from 540 00:31:53,100 --> 00:31:55,066 are an incredible sight. 541 00:31:56,966 --> 00:32:01,166 But how is it possible to have such powerful eruptions 542 00:32:01,166 --> 00:32:03,233 on a frozen moon? 543 00:32:09,300 --> 00:32:11,900 Our usual experience of volcanic eruptions 544 00:32:11,900 --> 00:32:13,633 is of molten rock 545 00:32:13,633 --> 00:32:16,033 bursting onto the surface. 546 00:32:19,233 --> 00:32:22,966 But eruptions on Enceladus are different, 547 00:32:22,966 --> 00:32:25,066 more like what's happening here. 548 00:32:27,200 --> 00:32:29,633 At a geothermal power plant in Iceland. 549 00:32:31,366 --> 00:32:34,000 A mile below the surface 550 00:32:34,000 --> 00:32:37,300 lies a reservoir of superheated water. 551 00:32:38,466 --> 00:32:41,766 Drilling down into it allows steam and water 552 00:32:41,766 --> 00:32:45,933 to erupt out and generate electricity. 553 00:32:48,066 --> 00:32:50,266 HOWETT: To be here is amazing! 554 00:32:50,266 --> 00:32:53,666 I spent most of my entire adult life studying Enceladus, 555 00:32:53,666 --> 00:32:56,300 but I've never heard it, I've never seen it, 556 00:32:56,300 --> 00:32:58,600 I've never felt it, and this is one-tenth 557 00:32:58,600 --> 00:33:01,966 of what one of the jets on Enceladus would be like. 558 00:33:01,966 --> 00:33:04,366 It's astounding. 559 00:33:06,800 --> 00:33:09,833 NARRATOR: Over 660 pounds of water 560 00:33:09,833 --> 00:33:14,333 erupt from the surface of Enceladus every second, 561 00:33:14,333 --> 00:33:16,266 creating visible eruptions 562 00:33:16,266 --> 00:33:19,633 that can thrust up to 6,000 miles into space. 563 00:33:22,233 --> 00:33:25,300 It's called cryovolcanism. 564 00:33:25,300 --> 00:33:27,933 "Cryo" from the Greek for cold. 565 00:33:29,900 --> 00:33:32,966 Cryovolcanism is absolutely volcanism. 566 00:33:32,966 --> 00:33:35,200 When we study the planets, we learned that, 567 00:33:35,200 --> 00:33:38,200 even though they have different chemistry or slight differences, 568 00:33:38,200 --> 00:33:41,533 that these processes are common throughout the planets, 569 00:33:41,533 --> 00:33:43,500 and volcanism is one of them. 570 00:33:46,700 --> 00:33:47,800 MARCHIS: What is surprising 571 00:33:47,800 --> 00:33:50,166 is not only the presence of the jets, 572 00:33:50,166 --> 00:33:52,833 but their size, the fact that this is 573 00:33:52,833 --> 00:33:54,866 an extreme cryovolcanism 574 00:33:54,866 --> 00:33:57,300 coming from such a small body. 575 00:34:00,233 --> 00:34:03,133 NARRATOR: But where does such an enormous amount of water 576 00:34:03,133 --> 00:34:05,733 come from on a frigid ice moon? 577 00:34:09,100 --> 00:34:11,866 There is a hint. 578 00:34:11,866 --> 00:34:14,766 As Enceladus orbits Saturn, 579 00:34:14,766 --> 00:34:19,233 it wobbles by about 0.12 degrees on its axis. 580 00:34:22,866 --> 00:34:25,533 A tiny but significant movement... 581 00:34:26,866 --> 00:34:30,066 ...that tells us something about the moon's interior. 582 00:34:31,066 --> 00:34:32,533 HOWETT: A simple way to think about 583 00:34:32,533 --> 00:34:34,500 what's happening inside Enceladus 584 00:34:34,500 --> 00:34:38,133 is to consider what happens when we rotate two eggs, 585 00:34:38,133 --> 00:34:41,166 one of which is hard-boiled and the other one isn't. 586 00:34:41,166 --> 00:34:44,366 So, we'll start with this one. 587 00:34:44,366 --> 00:34:45,733 If we spin the egg... 588 00:34:49,366 --> 00:34:51,700 (laughs) Just with eggs, 589 00:34:51,700 --> 00:34:53,133 doesn't seem like the most obvious solution. 590 00:34:53,133 --> 00:34:55,200 You can see that it... 591 00:34:55,200 --> 00:34:57,233 As it rotates, it's got a bit of a wobble to it, 592 00:34:57,233 --> 00:34:59,600 and if we rotate it a bit faster and then stop it, 593 00:34:59,600 --> 00:35:01,600 it'll continue to rotate. 594 00:35:02,900 --> 00:35:04,300 Whereas this one, 595 00:35:04,300 --> 00:35:05,600 we do the same thing. 596 00:35:05,600 --> 00:35:08,300 It rotates more smoothly, 597 00:35:08,300 --> 00:35:10,366 and if we rotate it and stop it, 598 00:35:10,366 --> 00:35:12,600 you can see it stops. 599 00:35:13,933 --> 00:35:15,800 NARRATOR: The reason the first one wobbles 600 00:35:15,800 --> 00:35:18,366 is because it is raw. 601 00:35:18,366 --> 00:35:20,566 Whereas this one... 602 00:35:23,833 --> 00:35:25,733 ...is hard-boiled. 603 00:35:28,033 --> 00:35:30,233 The raw one, of course, has a liquid in the middle, 604 00:35:30,233 --> 00:35:32,333 and so, even after you stop the shell, 605 00:35:32,333 --> 00:35:34,233 the liquid continues to rotate, 606 00:35:34,233 --> 00:35:36,233 and that causes the shell to rotate. 607 00:35:36,233 --> 00:35:38,500 It also caused that wobbly rotation 608 00:35:38,500 --> 00:35:40,033 that we see all the way along. 609 00:35:40,033 --> 00:35:42,800 Whereas the hard-boiled one is solid all the way through. 610 00:35:42,800 --> 00:35:44,900 When you stop the shell, you stop all of it. 611 00:35:44,900 --> 00:35:47,733 It also causes it to rotate very nicely. 612 00:35:47,733 --> 00:35:49,500 But it's the liquid one, the raw one, 613 00:35:49,500 --> 00:35:50,700 that's like Enceladus. 614 00:35:52,900 --> 00:35:56,466 NARRATOR: Enceladus is unlikely to crack like a raw egg. 615 00:35:57,433 --> 00:35:59,700 But it does wobble like one. 616 00:36:02,666 --> 00:36:07,000 And that tells us that there is an outer shell of ice, 617 00:36:07,000 --> 00:36:10,966 sitting on top of a global ocean of water. 618 00:36:14,500 --> 00:36:18,166 But how does that water manage to erupt 619 00:36:18,166 --> 00:36:22,366 through a shell of around three miles of solid ice? 620 00:36:23,833 --> 00:36:26,200 QUICK: When the liquid ocean is heated from below 621 00:36:26,200 --> 00:36:29,166 by energy from tidal heating, it expands, 622 00:36:29,166 --> 00:36:31,600 so the liquid wants to take up more space. 623 00:36:31,600 --> 00:36:33,866 As it seeks to take up more space, 624 00:36:33,866 --> 00:36:36,166 it pushes up against the bottom of the ice shell. 625 00:36:37,633 --> 00:36:41,100 NARRATOR: Once there, another force comes into action. 626 00:36:42,400 --> 00:36:44,633 Once that water goes through a crack 627 00:36:44,633 --> 00:36:47,533 and then is exposed to the vacuum of space, 628 00:36:47,533 --> 00:36:49,033 it's like a suction. 629 00:36:49,033 --> 00:36:50,966 That's what vacuum does. 630 00:36:50,966 --> 00:36:52,866 BYRNE: The reason water behaves this way 631 00:36:52,866 --> 00:36:54,866 when it's exposed to zero pressure 632 00:36:54,866 --> 00:36:56,733 is because there's nothing acting 633 00:36:56,733 --> 00:36:58,066 to keep the water together. 634 00:36:58,066 --> 00:37:00,400 So, the water will try its best to expand 635 00:37:00,400 --> 00:37:02,300 as much as it possibly can. 636 00:37:04,266 --> 00:37:05,666 One force pushes the water up, 637 00:37:05,666 --> 00:37:08,233 and the other force pulls it out onto the surface, 638 00:37:08,233 --> 00:37:10,466 and that's why we have these magnificent jets. 639 00:37:12,233 --> 00:37:14,333 NARRATOR: And they carry with them the secrets 640 00:37:14,333 --> 00:37:17,600 of what lies beneath the ice. 641 00:37:19,533 --> 00:37:22,633 These plumes contain traces of silica 642 00:37:22,633 --> 00:37:24,700 and molecular hydrogen 643 00:37:24,700 --> 00:37:26,900 that could've come from the ocean water 644 00:37:26,900 --> 00:37:29,633 interacting with hot volcanic rocks. 645 00:37:32,000 --> 00:37:35,700 Suggesting that, in the depths of Enceladus's ocean, 646 00:37:35,700 --> 00:37:38,766 there may be hydrothermal vents, 647 00:37:38,766 --> 00:37:41,866 towering structures created by water flowing 648 00:37:41,866 --> 00:37:44,733 into the volcanic rocks on the seabed. 649 00:37:46,900 --> 00:37:48,000 I think the chances are pretty high 650 00:37:48,000 --> 00:37:49,133 that there are hydrothermal vents 651 00:37:49,133 --> 00:37:51,066 at the bottom of Enceladus' ocean. 652 00:37:51,066 --> 00:37:52,566 Just like Earth's ocean, 653 00:37:52,566 --> 00:37:55,266 Enceladus's ocean sits right on top of its rocky mantle. 654 00:37:56,266 --> 00:37:59,300 NARRATOR: And with probable hydrothermal vents, 655 00:37:59,300 --> 00:38:02,666 an exciting possibility for life. 656 00:38:02,666 --> 00:38:07,000 NÚÑEZ: We think that life could've originated on Earth 657 00:38:07,000 --> 00:38:08,800 in hydrothermal vents. 658 00:38:08,800 --> 00:38:10,700 And these hydrothermal vents 659 00:38:10,700 --> 00:38:12,166 have those ingredients 660 00:38:12,166 --> 00:38:14,666 that are essential for life. 661 00:38:17,366 --> 00:38:20,233 NARRATOR: And it isn't just the possibility of heat 662 00:38:20,233 --> 00:38:23,933 that makes Enceladus a compelling incubator for life. 663 00:38:25,466 --> 00:38:26,866 HOFGARTNER: There are three key ingredients 664 00:38:26,866 --> 00:38:28,566 to a habitable environment: 665 00:38:28,566 --> 00:38:31,433 liquid water, chemical nutrients, 666 00:38:31,433 --> 00:38:33,233 and an energy source to use, 667 00:38:33,233 --> 00:38:37,266 and now we know that Enceladus has all three within its ocean. 668 00:38:40,333 --> 00:38:43,466 QUICK: A 2023 study showed that Enceladus's jets 669 00:38:43,466 --> 00:38:45,133 have phosphates in it, 670 00:38:45,133 --> 00:38:48,400 anywhere from 100 to 1,000 times the amount of phosphates 671 00:38:48,400 --> 00:38:49,866 that we find in Earth's oceans. 672 00:38:49,866 --> 00:38:54,100 Phosphates, we know, are a key component of DNA, 673 00:38:54,100 --> 00:38:55,666 which is the building block of life. 674 00:38:58,733 --> 00:39:01,166 NÚÑEZ: Does that mean that we found life? 675 00:39:01,166 --> 00:39:02,600 Well, we don't know. 676 00:39:02,600 --> 00:39:04,000 Just because we found phosphates, 677 00:39:04,000 --> 00:39:07,033 it's-it's a potential ingredient, 678 00:39:07,033 --> 00:39:08,333 but it's not a slam dunk, 679 00:39:08,333 --> 00:39:11,633 and so, we need to go back and really explore 680 00:39:11,633 --> 00:39:13,433 in more detail to see 681 00:39:13,433 --> 00:39:16,000 what is the origin of this phosphate. 682 00:39:18,866 --> 00:39:22,300 NARRATOR: Any mission to Enceladus is a ways off. 683 00:39:23,800 --> 00:39:27,333 But there is another world much closer to home 684 00:39:27,333 --> 00:39:30,733 that has more volcanoes strewn across its surface 685 00:39:30,733 --> 00:39:32,833 than any other planet. 686 00:39:42,166 --> 00:39:44,200 To find it, we have to return 687 00:39:44,200 --> 00:39:47,533 all the way back into the inner solar system. 688 00:39:49,566 --> 00:39:51,566 Past Mars's ancient peaks... 689 00:39:53,700 --> 00:39:55,366 ...and beyond Earth. 690 00:39:56,400 --> 00:39:59,700 ...to a mysterious, cloud-covered planet. 691 00:40:10,133 --> 00:40:13,300 Venus's dense atmosphere of carbon dioxide 692 00:40:13,300 --> 00:40:16,666 and clouds of sulfuric acid 693 00:40:16,666 --> 00:40:18,800 obscure the surface. 694 00:40:22,900 --> 00:40:26,200 For decades, orbiting probes have used radar 695 00:40:26,200 --> 00:40:28,500 to peer through the clouds. 696 00:40:31,500 --> 00:40:33,866 Revealing a landscape dominated 697 00:40:33,866 --> 00:40:36,766 by more than 85,000 volcanoes. 698 00:40:39,733 --> 00:40:41,866 But it was hard to see in the images 699 00:40:41,866 --> 00:40:44,066 if any were recently active, 700 00:40:44,066 --> 00:40:46,766 or if, like Mars, 701 00:40:46,766 --> 00:40:49,000 they were relics of the past. 702 00:40:50,566 --> 00:40:54,433 So why does Venus have so many volcanoes? 703 00:40:56,700 --> 00:40:59,133 And are they still erupting today? 704 00:41:02,766 --> 00:41:06,566 To find out, scientists are studying Iceland, 705 00:41:06,566 --> 00:41:10,100 one of the most volcanically active places on Earth. 706 00:41:19,433 --> 00:41:24,000 Here they are investigating recent lava flow activity 707 00:41:24,000 --> 00:41:26,833 to help prepare for future missions to Venus. 708 00:41:29,966 --> 00:41:32,133 SUE SMREKAR: I have remained fascinated by Venus 709 00:41:32,133 --> 00:41:35,466 because it tells us so much about the Earth. 710 00:41:35,466 --> 00:41:36,466 They really are twin planets 711 00:41:36,466 --> 00:41:39,533 evolving down different paths. 712 00:41:42,300 --> 00:41:45,100 NARRATOR: Sue Smrekar is leading the Veritas mission 713 00:41:45,100 --> 00:41:48,466 preparing to launch to Venus in the next decade. 714 00:41:50,100 --> 00:41:52,000 She uses radar data, 715 00:41:52,000 --> 00:41:54,033 which creates black-and-white images 716 00:41:54,033 --> 00:41:56,533 that reveal the texture of the surface. 717 00:41:59,500 --> 00:42:02,766 ♪ ♪ 718 00:42:04,433 --> 00:42:06,833 SMREKAR: I try to see things with my radar eyes, 719 00:42:06,833 --> 00:42:08,433 just imagining what they look like. 720 00:42:09,833 --> 00:42:13,200 When it's a nice smooth surface, the radar wave comes down, 721 00:42:13,200 --> 00:42:14,633 and it looks dark. 722 00:42:14,633 --> 00:42:17,466 But these areas that are super rough, 723 00:42:17,466 --> 00:42:19,266 you'll get a lot more reflection, so, 724 00:42:19,266 --> 00:42:23,133 in radar, these areas will be much brighter. 725 00:42:26,400 --> 00:42:28,700 NARRATOR: Whether new lava flows like we see on Earth 726 00:42:28,700 --> 00:42:33,733 exist on Venus was a much debated subject, 727 00:42:33,733 --> 00:42:35,966 as scientists had no direct evidence 728 00:42:35,966 --> 00:42:38,266 of recent volcanic activity on Venus. 729 00:42:40,733 --> 00:42:42,766 Until now. 730 00:42:43,733 --> 00:42:45,000 ROBERT HERRICK: It's really 731 00:42:45,000 --> 00:42:47,600 only been in the last decade or so 732 00:42:47,600 --> 00:42:50,000 that technology has made it possible 733 00:42:50,000 --> 00:42:51,633 to be able to zoom in and out 734 00:42:51,633 --> 00:42:54,800 and flip back and forth between data. 735 00:42:56,466 --> 00:42:58,766   NARRATOR: Using today's faster computers, 736 00:42:58,766 --> 00:43:02,633 Robert Herrick and his team reanalyzed images taken 737 00:43:02,633 --> 00:43:05,166 by the Magellan orbiter... 738 00:43:05,166 --> 00:43:07,966 over 30 years ago, 739 00:43:07,966 --> 00:43:10,266 and spotted a volcanic crater 740 00:43:10,266 --> 00:43:13,133 that had doubled in size over eight months. 741 00:43:14,100 --> 00:43:16,700 Proving that a volcano, 742 00:43:16,700 --> 00:43:20,066 about the size of Mount Everest, 743 00:43:20,066 --> 00:43:22,666 was erupting from its northern flank. 744 00:43:24,000 --> 00:43:26,166 HERRICK: When an investigation actually works out, 745 00:43:26,166 --> 00:43:28,500 and you learn something important, and you're like, 746 00:43:28,500 --> 00:43:29,933 "Oh, this is... this is cool." 747 00:43:32,000 --> 00:43:34,400 So, yes, it's a thrill to, you know, 748 00:43:34,400 --> 00:43:37,266 "Wow, I've-I've made my mark on the field." 749 00:43:37,266 --> 00:43:39,633 I was so excited when we saw those images 750 00:43:39,633 --> 00:43:41,500 because what that tells us is that everything 751 00:43:41,500 --> 00:43:43,900 we've been thinking about Venus is right, 752 00:43:43,900 --> 00:43:46,366 that this world probably is volcanically active, 753 00:43:46,366 --> 00:43:49,200 and that just makes us hungry for more. 754 00:43:51,100 --> 00:43:54,566 NARRATOR: But evidence of one probable eruption can't reveal 755 00:43:54,566 --> 00:43:57,733 if the rest of Venus's volcanoes are still active. 756 00:43:59,000 --> 00:44:02,000 And another mystery remains. 757 00:44:03,033 --> 00:44:05,200 Venus could have been Earth's twin. 758 00:44:06,166 --> 00:44:09,700 It is roughly the same size and built of the same stuff. 759 00:44:12,800 --> 00:44:15,666 So why are the two planets so different today? 760 00:44:18,433 --> 00:44:22,333 Understanding where volcanoes are found may solve this puzzle 761 00:44:22,333 --> 00:44:26,233 and explain why Venus is now a planet 762 00:44:26,233 --> 00:44:29,100 with such extreme conditions. 763 00:44:33,800 --> 00:44:35,433 SMREKAR: So, this map shows the distribution 764 00:44:35,433 --> 00:44:37,066 of volcanoes on the Earth. 765 00:44:37,066 --> 00:44:39,066 And you can see there's a big line of them 766 00:44:39,066 --> 00:44:41,433 that goes down the coast of North America 767 00:44:41,433 --> 00:44:43,933 on down to South America, 768 00:44:43,933 --> 00:44:46,933 and their location is really controlled 769 00:44:46,933 --> 00:44:50,666 to a large degree by the location of plate boundaries. 770 00:44:51,733 --> 00:44:54,033 NARRATOR: Most volcanoes on Earth are found 771 00:44:54,033 --> 00:44:57,733 where two plates meet, or are pulling apart, 772 00:44:57,733 --> 00:45:00,566 creating lines of volcanoes along their edges. 773 00:45:01,666 --> 00:45:05,133 But on Venus, the pattern is very different. 774 00:45:05,133 --> 00:45:08,100 SMREKAR: So, this is a map of the volcanism on Venus, 775 00:45:08,100 --> 00:45:10,133 the volcanoes, and you can see 776 00:45:10,133 --> 00:45:11,833 that they are all over the place. 777 00:45:11,833 --> 00:45:13,066 They don't follow any nice, 778 00:45:13,066 --> 00:45:15,633 uh, tight line of volcanism 779 00:45:15,633 --> 00:45:17,500 the way we saw for Earth. 780 00:45:17,500 --> 00:45:19,100 And, you know, the difference is 781 00:45:19,100 --> 00:45:21,833 that, uh, on Venus, we don't have plate tectonics. 782 00:45:21,833 --> 00:45:24,266 Venus has some entirely different system. 783 00:45:28,033 --> 00:45:30,500 NARRATOR: Not only are there numerous volcanoes 784 00:45:30,500 --> 00:45:33,100 scattered across Venus' landscape, 785 00:45:33,100 --> 00:45:35,666 they take on odd forms. 786 00:45:38,133 --> 00:45:41,766 From lines of flattened volcanic domes 787 00:45:41,766 --> 00:45:44,133 that look like chains of pancakes... 788 00:45:46,633 --> 00:45:48,400 ...to strange volcanoes 789 00:45:48,400 --> 00:45:51,833 whose rutted sides make them look almost like insects, 790 00:45:51,833 --> 00:45:54,800 clamped to the surface. 791 00:45:55,800 --> 00:45:58,866 Venus is a volcanic zoo, 792 00:45:58,866 --> 00:46:01,666 with a variety of volcanoes, 793 00:46:01,666 --> 00:46:04,866 including some that are unique in the solar system. 794 00:46:07,266 --> 00:46:08,900 Venus doesn't have plate tectonics, 795 00:46:08,900 --> 00:46:12,700 but its crust has uneven thickness, 796 00:46:12,700 --> 00:46:15,633 and so, magma from within 797 00:46:15,633 --> 00:46:18,166 can climb and poke into the crust and then cool. 798 00:46:19,866 --> 00:46:23,000 NARRATOR: The inner heat drives vast lava flows 799 00:46:23,000 --> 00:46:26,933 that can run for thousands of miles, 800 00:46:26,933 --> 00:46:29,200 and creates far more blemishes and bubbles 801 00:46:29,200 --> 00:46:31,733 on the surface than here on Earth. 802 00:46:34,333 --> 00:46:36,633 But the lack of plate tectonics 803 00:46:36,633 --> 00:46:40,000 points to a far more profound difference 804 00:46:40,000 --> 00:46:42,233 between Earth and Venus. 805 00:46:44,666 --> 00:46:46,000 DOTTIN: So on Earth, 806 00:46:46,000 --> 00:46:47,033 there have been times where 807 00:46:47,033 --> 00:46:50,300 there were volcanic eruptions 808 00:46:50,300 --> 00:46:52,700 that were so large and so constant 809 00:46:52,700 --> 00:46:55,400   that it was filling the atmosphere 810 00:46:55,400 --> 00:46:58,766 with tons of toxic gases and greenhouse gases. 811 00:47:00,466 --> 00:47:02,766 NARRATOR: Venus's greenhouse gases trapped heat, 812 00:47:02,766 --> 00:47:05,433 increasing the temperature, 813 00:47:05,433 --> 00:47:08,433 but thanks to plate tectonics, 814 00:47:08,433 --> 00:47:11,066 Earth had a way to balance this effect. 815 00:47:12,066 --> 00:47:13,500 MORRIS: On Earth, 816 00:47:13,500 --> 00:47:14,533 carbon dioxide is actually 817 00:47:14,533 --> 00:47:16,266 pulled out of the atmosphere 818 00:47:16,266 --> 00:47:18,033 when it rains, 819 00:47:18,033 --> 00:47:20,833 and those molecules interact with the rocks 820 00:47:20,833 --> 00:47:23,866 and the carbon dioxide gets deposited in the rocks, 821 00:47:23,866 --> 00:47:26,800 and as the plate tectonics cycle occurs, 822 00:47:26,800 --> 00:47:30,833 that material gets then pulled into the subsurface 823 00:47:30,833 --> 00:47:32,966 and removed from the atmosphere. 824 00:47:32,966 --> 00:47:34,300 BYRNE: When we have 825 00:47:34,300 --> 00:47:36,300 these huge volcanic eruptions 826 00:47:36,300 --> 00:47:38,133 injecting all this CO2 827 00:47:38,133 --> 00:47:39,433 into the atmosphere, 828 00:47:39,433 --> 00:47:43,033 we see substantial and severe climate change, 829 00:47:43,033 --> 00:47:44,333 at least for a while, 830 00:47:44,333 --> 00:47:46,300 until plate tectonics is able 831 00:47:46,300 --> 00:47:50,100 to regulate things and get them back under control. 832 00:47:50,100 --> 00:47:51,266 DOTTIN: So, plate tectonics 833 00:47:51,266 --> 00:47:54,366 is probably one of the main reasons 834 00:47:54,366 --> 00:47:57,566 why we've been able to maintain the climate 835 00:47:57,566 --> 00:47:59,300 that we have on our planet. 836 00:48:01,733 --> 00:48:04,333 NARRATOR: As Venus's volcanoes erupted, 837 00:48:04,333 --> 00:48:06,400 it seems there was no mechanism 838 00:48:06,400 --> 00:48:08,900 to remove those gases from the atmosphere 839 00:48:08,900 --> 00:48:10,733 back to the interior. 840 00:48:14,166 --> 00:48:18,600 So the planet got hotter and hotter, 841 00:48:18,600 --> 00:48:22,666 turning it into the hellish landscape we see today. 842 00:48:24,233 --> 00:48:27,666 Venus shows the importance of plate tectonics 843 00:48:27,666 --> 00:48:30,866 in helping to control not just volcanoes, 844 00:48:30,866 --> 00:48:33,000 but the climate, too. 845 00:48:34,566 --> 00:48:36,833 MORRIS: So, the lesson that we can learn from Venus 846 00:48:36,833 --> 00:48:38,766 is that on Earth, 847 00:48:38,766 --> 00:48:41,833 the planet is actually able to stabilize itself 848 00:48:41,833 --> 00:48:43,800 through the process of plate tectonics, 849 00:48:43,800 --> 00:48:46,100 and we see on Venus what happens 850 00:48:46,100 --> 00:48:47,600 when the planet's not able 851 00:48:47,600 --> 00:48:49,800 to maintain that stability in the atmosphere. 852 00:48:53,566 --> 00:48:55,300 NARRATOR: But human activity emits 853 00:48:55,300 --> 00:48:58,233 at least 60 times more carbon dioxide 854 00:48:58,233 --> 00:49:01,500 than all the volcanoes on Earth each year, 855 00:49:01,500 --> 00:49:05,800 and plate tectonics is a slow process. 856 00:49:07,133 --> 00:49:09,800 OLUSEYI: What we see in Venus's atmosphere is a cautionary tale 857 00:49:09,800 --> 00:49:13,466 for the situation that Earth is in at this very moment. 858 00:49:13,466 --> 00:49:15,733 We have a greenhouse effect taking place 859 00:49:15,733 --> 00:49:17,766 that's warming our planet. 860 00:49:18,800 --> 00:49:21,766 Venus is a runaway greenhouse effect 861 00:49:21,766 --> 00:49:23,566 just gone rampant, 862 00:49:23,566 --> 00:49:26,666 and the whole planet is now a hotbox of it. 863 00:49:31,533 --> 00:49:32,900 NARRATOR: Scientists don't think 864 00:49:32,900 --> 00:49:35,466 human emissions alone can send us 865 00:49:35,466 --> 00:49:37,500 to those extremes. 866 00:49:38,966 --> 00:49:41,200 But with Venus, we have another planet 867 00:49:41,200 --> 00:49:43,900 that's identical in many ways. 868 00:49:43,900 --> 00:49:48,166 And by understanding why it's so different today, 869 00:49:48,166 --> 00:49:52,833 we can appreciate the unique habitability of our own planet. 870 00:49:52,833 --> 00:49:55,866 (explosive pop) 871 00:49:55,866 --> 00:49:59,133 SMREKAR: Venus is kind of a... like a teenager. 872 00:49:59,133 --> 00:50:02,533 We go back in time to the early part of Earth's geology 873 00:50:02,533 --> 00:50:04,033 when we study Venus. 874 00:50:04,033 --> 00:50:06,766 So, it's a... it's a really a fascinating, you know, 875 00:50:06,766 --> 00:50:09,466 look at our... the evolution of our own planet. 876 00:50:11,266 --> 00:50:14,433 NARRATOR: Future missions like the Veritas orbiter 877 00:50:14,433 --> 00:50:16,866 will help explain the different processes 878 00:50:16,866 --> 00:50:19,266 behind volcanism on Venus. 879 00:50:20,666 --> 00:50:22,033 SMREKAR: With Veritas, we have just 880 00:50:22,033 --> 00:50:25,466 all kinds of ways to look for new volcanism. 881 00:50:26,866 --> 00:50:30,333 We can actually see the surface deforming at the scale of, 882 00:50:30,333 --> 00:50:31,933 you know, an inch or so. 883 00:50:31,933 --> 00:50:35,100 And I think we're just going to see vastly more flows 884 00:50:35,100 --> 00:50:36,966 that are young and even, 885 00:50:36,966 --> 00:50:38,500 I predict, happening during our mission. 886 00:50:40,500 --> 00:50:43,000 NARRATOR: With new insights into Venus, 887 00:50:43,000 --> 00:50:44,800 we can better understand the role 888 00:50:44,800 --> 00:50:49,433 plate tectonics plays in balancing our own environment, 889 00:50:49,433 --> 00:50:53,100 creating the conditions for life to thrive. 890 00:50:57,500 --> 00:51:00,100 One of the revelations in our exploration 891 00:51:00,100 --> 00:51:03,433 of the solar system is what we are finding 892 00:51:03,433 --> 00:51:06,000 isn't a collection of inactive worlds. 893 00:51:08,266 --> 00:51:09,733 HOFGARTNER: There is a great diversity 894 00:51:09,733 --> 00:51:12,366 of geological activity in the solar system, 895 00:51:12,366 --> 00:51:14,066 and sometimes nature 896 00:51:14,066 --> 00:51:17,200 makes it occur in surprising places. 897 00:51:19,100 --> 00:51:23,533 NARRATOR: From the tiny, explosive moon of Io... 898 00:51:23,533 --> 00:51:27,366 to the stunning cryovolcanoes on Enceladus, 899 00:51:27,366 --> 00:51:32,066 they are telling us so much about Earth. 900 00:51:32,066 --> 00:51:34,233 SOUSA-SILVA: When we look at other planets and moons, 901 00:51:34,233 --> 00:51:37,533 we see snippets of Earth's past and future. 902 00:51:37,533 --> 00:51:41,166 We were once covered in volcanoes like Io is now, 903 00:51:41,166 --> 00:51:43,266 and in Venus, we see what happens 904 00:51:43,266 --> 00:51:46,566 when greenhouse gases get out of control. 905 00:51:48,233 --> 00:51:50,033 NARRATOR: But they also tell us 906 00:51:50,033 --> 00:51:53,366 just how remarkable Earth is, 907 00:51:53,366 --> 00:51:56,100 for one very special reason. 908 00:51:59,000 --> 00:52:01,100 Amongst all these geologically active worlds, 909 00:52:01,100 --> 00:52:04,066 it's still pretty amazing that the only place 910 00:52:04,066 --> 00:52:07,500 where we saw these active geology become biology 911 00:52:07,500 --> 00:52:08,966 is here on Earth. 912 00:52:08,966 --> 00:52:11,433 ♪ ♪ 913 00:52:35,100 --> 00:52:37,966 ♪ ♪ 914 00:52:38,900 --> 00:52:46,433 ♪ ♪ 915 00:52:50,266 --> 00:52:57,800 ♪ ♪ 916 00:53:01,700 --> 00:53:09,233 ♪ ♪ 917 00:53:10,866 --> 00:53:18,400 ♪ ♪ 918 00:53:20,033 --> 00:53:27,566 ♪ ♪