1 00:00:01,538 --> 00:00:05,005 NARRATOR: Our solar system is home to eight planets, 2 00:00:05,005 --> 00:00:06,938 near-perfect spheres 3 00:00:06,938 --> 00:00:10,905 spinning through the darkness of space. 4 00:00:13,805 --> 00:00:16,938 But the more we explore, 5 00:00:16,938 --> 00:00:20,971 the more weird and wonderful worlds we discover. 6 00:00:22,638 --> 00:00:24,371 ANJALI TRIPATHI: Our solar system is filled 7 00:00:24,371 --> 00:00:28,705 with these strange worlds that defy all expectations. 8 00:00:28,705 --> 00:00:31,038 NAOMI ROWE-GURNEY: Patchwork worlds that look like they've been 9 00:00:31,038 --> 00:00:33,438 stuck together like Frankenstein monsters. 10 00:00:33,438 --> 00:00:35,171 AMY BARR MLINAR: The images were shocking. 11 00:00:35,171 --> 00:00:38,238 Nobody expected to see enormous ice cliffs 12 00:00:38,238 --> 00:00:40,271 on a moon in the outer solar system. 13 00:00:40,271 --> 00:00:44,605 NARRATOR: Worlds that don't seem to play by the rules. 14 00:00:44,605 --> 00:00:46,271 HAKEEM OLUSEYI: There is so much strange activity 15 00:00:46,271 --> 00:00:50,505 out there in the solar system that we don't understand. 16 00:00:50,505 --> 00:00:52,738 Sometimes it does feel like being a detective, 17 00:00:52,738 --> 00:00:57,038 trying to find out why it's there, what it's doing. 18 00:00:57,038 --> 00:00:58,571 NARRATOR: Each discovery 19 00:00:58,571 --> 00:01:04,271 offers new clues to how our solar system works. 20 00:01:04,271 --> 00:01:06,105 A lot of the weirdness that we find 21 00:01:06,105 --> 00:01:08,471 has something to do with gravity. 22 00:01:08,471 --> 00:01:12,271 NARRATOR: But other forces are also at play. 23 00:01:12,271 --> 00:01:15,771 LYNNAE QUICK: Each planet and each moon in our solar system 24 00:01:15,771 --> 00:01:17,571 are examples of how the rules of physics 25 00:01:17,571 --> 00:01:19,571 can play out differently. 26 00:01:19,571 --> 00:01:21,405 GEOFFREY COLLINS: And sometimes we don't understand 27 00:01:21,405 --> 00:01:24,371 which rules can be broken. 28 00:01:25,938 --> 00:01:30,338 NARRATOR: "Solar System: Strange Worlds." 29 00:01:33,305 --> 00:01:36,271 Right now on "NOVA." 30 00:01:36,271 --> 00:01:38,305 ♪ ♪ 31 00:01:50,638 --> 00:01:54,871 ♪ ♪ 32 00:02:10,371 --> 00:02:15,405 NARRATOR: On the edge of the solar system is the Kuiper Belt. 33 00:02:17,805 --> 00:02:21,971 As we travel farther from the warmth of the sun, 34 00:02:21,971 --> 00:02:26,005 we find a world like no other. 35 00:02:32,405 --> 00:02:33,638 Haumea was a really exciting discovery 36 00:02:33,638 --> 00:02:35,338 because it's a Kuiper Belt object 37 00:02:35,338 --> 00:02:37,538 that doesn't seem to follow any of the rules. 38 00:02:38,638 --> 00:02:40,971 NARRATOR: One of the most basic rules 39 00:02:40,971 --> 00:02:44,605 is that gravity usually shapes planetary bodies like this 40 00:02:44,605 --> 00:02:45,971 into spheres. 41 00:02:48,205 --> 00:02:50,538 The force of gravity is always pulling mass 42 00:02:50,538 --> 00:02:52,105 toward a central point. 43 00:02:52,105 --> 00:02:56,538 A sphere is the shape that packs the most material 44 00:02:56,538 --> 00:02:58,905 closest to the center as possible. 45 00:03:01,838 --> 00:03:06,838 NARRATOR: But Haumea's shape is a little harder to define. 46 00:03:06,838 --> 00:03:09,105 Haumea is shaped sort of like a football. 47 00:03:11,271 --> 00:03:12,505 It's a bit of a stretched egg. 48 00:03:12,505 --> 00:03:15,071 COLLINS: Haumea looks like a rounded pebble 49 00:03:15,071 --> 00:03:16,705 that you would find on the beach. 50 00:03:16,705 --> 00:03:19,838 Haumea is definitely one of the strangest worlds out there. 51 00:03:23,305 --> 00:03:26,838 NARRATOR: And the solar system has even more worlds 52 00:03:26,838 --> 00:03:28,905 that defy our expectations. 53 00:03:33,171 --> 00:03:34,671 COLLINS: As we explore the solar system, 54 00:03:34,671 --> 00:03:38,105 we find more and more bizarre objects out there. 55 00:03:38,105 --> 00:03:39,438 Oh man, I just love everything weird, 56 00:03:39,438 --> 00:03:41,571 and what's weirder than outer space? 57 00:03:41,571 --> 00:03:43,338 No two worlds are the same, 58 00:03:43,338 --> 00:03:46,471 and there's always something new to find. 59 00:03:47,505 --> 00:03:50,405 NARRATOR: Oddly-shaped worlds, 60 00:03:50,405 --> 00:03:54,238 moons that look like they've been torn apart 61 00:03:54,238 --> 00:03:57,505 and strange water worlds. 62 00:03:57,505 --> 00:03:59,371 TRIPATHI: How did we get so many different 63 00:03:59,371 --> 00:04:02,238 and unique worlds in our solar system? 64 00:04:02,238 --> 00:04:04,471 That's the million-dollar question. 65 00:04:04,471 --> 00:04:09,505 ♪ ♪ 66 00:04:14,671 --> 00:04:17,071 (eerie static whirring) 67 00:04:19,438 --> 00:04:21,471 ♪ ♪ 68 00:04:29,871 --> 00:04:33,071 NARRATOR: From a cloud of gas and dust... 69 00:04:36,505 --> 00:04:42,238 ...gravity, the great sculptor of our universe, 70 00:04:42,238 --> 00:04:45,405 fashioned our star 71 00:04:45,405 --> 00:04:47,771 and the planets and moons around it... 72 00:04:55,005 --> 00:04:58,171 ...creating the solar system. 73 00:05:06,038 --> 00:05:07,838 And gravity has continued 74 00:05:07,838 --> 00:05:12,638 to shape these myriad worlds ever since. 75 00:05:12,638 --> 00:05:14,305 But how? 76 00:05:14,305 --> 00:05:17,438 What exactly is gravity? 77 00:05:17,438 --> 00:05:19,538 Michele DOUGHERTY: It depends who you ask. 78 00:05:19,538 --> 00:05:22,838 If you ask Newton, he would say that gravity is a force 79 00:05:22,838 --> 00:05:24,605 that helps pull things together. 80 00:05:24,605 --> 00:05:28,538 It's what's keeping me seated on the Earth at the moment. 81 00:05:28,538 --> 00:05:31,438 QUICK: It builds planets, stars and galaxies 82 00:05:31,438 --> 00:05:34,105 by pulling together the dust and the gas and the rocks 83 00:05:34,105 --> 00:05:35,805 that make them up. 84 00:05:35,805 --> 00:05:40,571 NARRATOR: But Einstein saw it a little differently. 85 00:05:40,571 --> 00:05:43,571 DOUGHERTY: If you asked Einstein, he said 86 00:05:43,571 --> 00:05:48,505 it wasn't a force but that it curved space and time. 87 00:05:48,505 --> 00:05:52,871 Very simply put, space and time were linked to him, 88 00:05:52,871 --> 00:05:54,538 as if they were a fabric. 89 00:05:54,538 --> 00:05:58,105 So any kind of object with mass, uh, would, um, 90 00:05:58,105 --> 00:06:02,138 kind of bend that fabric and, um, things would fall into it. 91 00:06:03,838 --> 00:06:06,171 NARRATOR: At the center of our solar system 92 00:06:06,171 --> 00:06:10,205 is the most massive object in it, our sun, 93 00:06:10,205 --> 00:06:14,671 curving the fabric of space-time around it. 94 00:06:14,671 --> 00:06:17,938 The planets follow this curvature, 95 00:06:17,938 --> 00:06:22,071 creating their orbits. 96 00:06:22,071 --> 00:06:25,105 The sun binds everything in the solar system together 97 00:06:25,105 --> 00:06:27,405 within its gravity, and without that, 98 00:06:27,405 --> 00:06:28,971 uh, there wouldn't be anything. 99 00:06:28,971 --> 00:06:30,305 There wouldn't be a solar system, 100 00:06:30,305 --> 00:06:31,938 and we wouldn't exist, either. 101 00:06:34,505 --> 00:06:36,405 NARRATOR: But gravity is not alone 102 00:06:36,405 --> 00:06:40,171 when it comes to shaping our solar system. 103 00:06:40,171 --> 00:06:42,205 The solar system would be a really boring place 104 00:06:42,205 --> 00:06:44,938 if it was only gravity that was acting on all of these things. 105 00:06:44,938 --> 00:06:49,105 It would mean that everything was spherical and, uh, the same. 106 00:06:50,271 --> 00:06:52,505 QUICK: We see such a variety of shapes 107 00:06:52,505 --> 00:06:55,105 because gravity is not the only force at play. 108 00:06:55,105 --> 00:06:58,105 TRIPATHI: Even though it's counter to what we think about 109 00:06:58,105 --> 00:07:00,405 when we talk about the planets and gravity, 110 00:07:00,405 --> 00:07:03,538 it's actually the weakest force in day-to-day life. 111 00:07:03,538 --> 00:07:08,205 PROUDFOOT: So, although gravity likes making spherical planets, 112 00:07:08,205 --> 00:07:12,205 sometimes rocks are just strong enough to resist gravity. 113 00:07:12,205 --> 00:07:13,871 We don't live in a universe of marbles 114 00:07:13,871 --> 00:07:16,305 because you have to have enough mass 115 00:07:16,305 --> 00:07:19,205 for gravity to pull everything into the spherical shape. 116 00:07:21,171 --> 00:07:24,505 NARRATOR: So how much mass does gravity need 117 00:07:24,505 --> 00:07:27,405 to overcome the strength of rock 118 00:07:27,405 --> 00:07:30,438 and make planets spherical? 119 00:07:36,571 --> 00:07:40,071 James Dottin is a planetary scientist 120 00:07:40,071 --> 00:07:44,038 who studies rocks to understand the evolution of planets. 121 00:07:46,005 --> 00:07:49,071 DOTTIN: Gravity is directly proportional to mass. 122 00:07:49,071 --> 00:07:51,171 The more mass an object has, 123 00:07:51,171 --> 00:07:54,205 the stronger the gravitational force. 124 00:07:54,205 --> 00:07:55,405 So, in order to iron out 125 00:07:55,405 --> 00:07:56,638 all the lumps and bumps 126 00:07:56,638 --> 00:07:58,838 of rocky objects in our solar system, 127 00:07:58,838 --> 00:08:01,905 it requires a lot of gravitational force. 128 00:08:03,571 --> 00:08:05,171   NARRATOR: For a planet's gravity 129 00:08:05,171 --> 00:08:07,305 to overcome the strength of rock, 130 00:08:07,305 --> 00:08:10,405 it must reach a critical size. 131 00:08:12,571 --> 00:08:15,038 We think that, in order for them to form into a sphere, 132 00:08:15,038 --> 00:08:19,171 they need to have a radius of about 200 miles, 133 00:08:19,171 --> 00:08:23,005 so that they're massive enough for gravitational forces 134 00:08:23,005 --> 00:08:25,938 to be strong enough to form them into a sphere. 135 00:08:25,938 --> 00:08:29,238 It's called the potato radius because objects that are smaller 136 00:08:29,238 --> 00:08:31,271 end up looking like potatoes. 137 00:08:33,705 --> 00:08:38,305 NARRATOR: A rocky world with a radius under 200 miles... 138 00:08:39,538 --> 00:08:42,238 ...will tend to be oddly-shaped. 139 00:08:48,138 --> 00:08:53,171 While everything with a radius larger than about 200 miles 140 00:08:53,171 --> 00:08:55,171 is a sphere. 141 00:08:55,171 --> 00:08:59,738 That is, almost everything. 142 00:08:59,738 --> 00:09:03,038 Haumea, out in the depths of the solar system, 143 00:09:03,038 --> 00:09:05,771 is a rule breaker. 144 00:09:06,971 --> 00:09:11,371 This is a world about 1,300 miles long, 145 00:09:11,371 --> 00:09:13,971 1,000 miles wide, 146 00:09:13,971 --> 00:09:17,971 and less than 700 miles high pole to pole... 147 00:09:20,938 --> 00:09:22,471 ...and it isn't alone. 148 00:09:27,271 --> 00:09:33,271 Two icy moons in a thin ring of rock and ice orbit Haumea, 149 00:09:33,271 --> 00:09:37,005 making an unexpected and odd system... 150 00:09:38,105 --> 00:09:43,105 ...the first like it ever discovered. 151 00:09:43,105 --> 00:09:44,638 Haumea was such an exciting discovery 152 00:09:44,638 --> 00:09:46,905 because it's large enough to be round, 153 00:09:46,905 --> 00:09:50,305 but for some strange reason, it's shaped like a football. 154 00:09:51,538 --> 00:09:53,038 NARRATOR: So, if its odd shape 155 00:09:53,038 --> 00:09:57,205 is not due to its size, then what is it? 156 00:09:58,538 --> 00:10:02,605 There is a clue we can see at work here on Earth, 157 00:10:02,605 --> 00:10:05,071 if you know how to look. 158 00:10:08,871 --> 00:10:11,971 We've left this camera out all morning, 159 00:10:11,971 --> 00:10:13,938 fixed on a single point in the sky. 160 00:10:15,771 --> 00:10:19,271 NARRATOR: In this case, the sun, 161 00:10:19,271 --> 00:10:22,771 and that helps to visualize the rotation of the planet. 162 00:10:24,738 --> 00:10:27,571 DOTTIN: Wow. I mean, how cool is that? 163 00:10:27,571 --> 00:10:29,238 Now that's no camera trick, 164 00:10:29,238 --> 00:10:32,271 that's literally the Earth rotating 165 00:10:32,271 --> 00:10:34,838 at about 1,000 miles per hour. 166 00:10:34,838 --> 00:10:39,105 And although that's superfast, I can't feel it, 167 00:10:39,105 --> 00:10:41,805 and that's because everything around me 168 00:10:41,805 --> 00:10:43,805 is rotating with the Earth. 169 00:10:45,405 --> 00:10:49,005 NARRATOR: But even if we cannot feel Earth's rotation 170 00:10:49,005 --> 00:10:51,338 we can still feel the forces created 171 00:10:51,338 --> 00:10:53,838 by a rapidly spinning object. 172 00:10:55,771 --> 00:10:58,305 MLINAR: So a merry-go-round on a playground 173 00:10:58,305 --> 00:11:01,371 is this big spinning disc, it has handles, 174 00:11:01,371 --> 00:11:03,405 you can hold onto it, you get on, 175 00:11:03,405 --> 00:11:05,938 your friends start to spin the merry-go-round faster 176 00:11:05,938 --> 00:11:09,338 and faster and faster, eventually, it goes so fast 177 00:11:09,338 --> 00:11:12,205 that you can't hang on anymore and you kind of fly off. 178 00:11:12,205 --> 00:11:13,605 So when that happens, 179 00:11:13,605 --> 00:11:15,638 you're experiencing centrifugal force. 180 00:11:18,371 --> 00:11:22,771 NARRATOR: And it turns out, Haumea is spinning incredibly quickly. 181 00:11:25,238 --> 00:11:27,705 This world is spinning so fast, 182 00:11:27,705 --> 00:11:32,071 it experiences an entire day and night in under four hours. 183 00:11:34,238 --> 00:11:38,338 It's the fastest known rotating object in the Kuiper Belt. 184 00:11:42,605 --> 00:11:44,571 So if this is our model of Haumea, 185 00:11:44,571 --> 00:11:46,238 gravity is acting to try and make it 186 00:11:46,238 --> 00:11:47,505 into a sphere, 187 00:11:47,505 --> 00:11:49,638 but because Haumea is spinning so quickly, 188 00:11:49,638 --> 00:11:52,505 it actually means that centrifugal forces 189 00:11:52,505 --> 00:11:55,338 can make it propel away from itself. 190 00:11:55,338 --> 00:11:58,438 And you'll notice that it starts to become more egg-shaped 191 00:11:58,438 --> 00:12:00,105 as it spins. 192 00:12:00,105 --> 00:12:01,838 Oh, cool, it's really egg-shaped now. 193 00:12:01,838 --> 00:12:03,838 I'm gonna turn it off before it kills us. 194 00:12:03,838 --> 00:12:05,338 (laughs) 195 00:12:05,338 --> 00:12:09,171 The immensely fast rotation of Haumea spinning around is 196 00:12:09,171 --> 00:12:13,138 what explains the shape that we see as a stretched out oval 197 00:12:13,138 --> 00:12:15,771 as opposed to a perfectly round sphere. 198 00:12:15,771 --> 00:12:17,071 MLINAR: It's just been 199 00:12:17,071 --> 00:12:18,838 forced to deform 200 00:12:18,838 --> 00:12:22,771 into this completely football, egg shape. 201 00:12:22,771 --> 00:12:25,305 It has no choice, it has to be that shape. 202 00:12:27,838 --> 00:12:31,438 NARRATOR: And Haumea's spin may also be responsible 203 00:12:31,438 --> 00:12:34,271 for the formation of the two icy moons 204 00:12:34,271 --> 00:12:36,771 orbiting this strange world. 205 00:12:38,805 --> 00:12:40,605 PROUDFOOT: So most people generally think 206 00:12:40,605 --> 00:12:43,238 that Haumea was formed in a giant collision. 207 00:12:43,238 --> 00:12:47,838 That impact probably got Haumea spinning really, really fast. 208 00:12:47,838 --> 00:12:51,171 When something spins too fast, centrifugal force beats gravity 209 00:12:51,171 --> 00:12:55,005 and things can actually become detached from the body. 210 00:12:55,005 --> 00:12:56,671 So if we go back to the analogy 211 00:12:56,671 --> 00:12:59,171 of kids riding on a merry-go-round, 212 00:12:59,171 --> 00:13:02,105 these would be the kids that fell off the merry-go-round 213 00:13:02,105 --> 00:13:03,405 when it was going too fast. 214 00:13:04,438 --> 00:13:08,805 So that's one way of making tiny little icy moons around Haumea. 215 00:13:10,838 --> 00:13:13,305 NARRATOR: Haumea and its moons formed 216 00:13:13,305 --> 00:13:16,371 in an ongoing battle 217 00:13:16,371 --> 00:13:18,738 with gravity pulling the world together... 218 00:13:20,438 --> 00:13:23,171 ...and its spin pushing it apart. 219 00:13:25,838 --> 00:13:28,505 The battle between these two forces-- 220 00:13:28,505 --> 00:13:33,371 gravity and spin-- creates a truly strange world. 221 00:13:34,871 --> 00:13:36,838 ♪ ♪ 222 00:13:36,838 --> 00:13:40,871 But it isn't the only oddball in our solar system. 223 00:13:40,871 --> 00:13:43,871 Travel in from the Kuiper Belt... 224 00:13:45,171 --> 00:13:47,371 ...past the ice giants... 225 00:13:50,438 --> 00:13:52,838 ...and past Saturn.... 226 00:13:53,871 --> 00:13:55,671 ...and we discover what happens 227 00:13:55,671 --> 00:13:58,138 if we dial up a planet's gravity. 228 00:14:01,538 --> 00:14:05,538 This is a world so enormous 229 00:14:05,538 --> 00:14:08,538 you could fit all the other planets inside it 230 00:14:08,538 --> 00:14:10,371 with room to spare. 231 00:14:11,871 --> 00:14:15,938 And such a gargantuan planet has massive moons 232 00:14:15,938 --> 00:14:19,071 that also feel the effects of Jupiter's pull. 233 00:14:25,171 --> 00:14:27,371 Since 2016, 234 00:14:27,371 --> 00:14:30,738 NASA's Juno spacecraft has been exploring Jupiter 235 00:14:30,738 --> 00:14:32,738 and its many moons... 236 00:14:35,338 --> 00:14:39,638 ...including one unlike any other in the solar system. 237 00:14:46,971 --> 00:14:48,671 SCHENK: Ganymede is really big. 238 00:14:48,671 --> 00:14:50,905 It's about 3,000 miles across. 239 00:14:50,905 --> 00:14:53,138 It's almost as big as the planet Mars. 240 00:14:53,138 --> 00:14:54,871 It's really big. 241 00:14:55,871 --> 00:14:58,038 NARRATOR: But it's not just the size of the moon 242 00:14:58,038 --> 00:15:00,571 that makes Ganymede unusual. 243 00:15:01,638 --> 00:15:04,538 DOUGHERTY: The surface of Ganymede looks 244 00:15:04,538 --> 00:15:07,005 weird in that it's got lots of 245 00:15:07,005 --> 00:15:08,238 craters on the surface. 246 00:15:08,238 --> 00:15:10,905 It's got grooves and cracks 247 00:15:10,905 --> 00:15:12,305 on the surface. 248 00:15:12,305 --> 00:15:14,738 COLLINS: The surface is mostly ice, 249 00:15:14,738 --> 00:15:17,205 in some places there's a thin layer 250 00:15:17,205 --> 00:15:19,571 of rocky dust on top of the ice. 251 00:15:19,571 --> 00:15:21,738 And you might see some icy mountains in the background. 252 00:15:24,405 --> 00:15:27,471 NARRATOR: And above this icy surface, 253 00:15:27,471 --> 00:15:30,705 Juno witnessed strange ribbons of light, 254 00:15:32,505 --> 00:15:34,905 An aurora 255 00:15:34,905 --> 00:15:37,605 dancing above the poles of the moon. 256 00:15:43,138 --> 00:15:45,171 A spectacular light show 257 00:15:45,171 --> 00:15:47,938 that has helped reveal something even stranger 258 00:15:47,938 --> 00:15:49,971 about this world. 259 00:15:54,305 --> 00:15:55,938 We think that Ganymede might have a secret 260 00:15:55,938 --> 00:15:57,371 hiding beneath the surface. 261 00:15:59,571 --> 00:16:02,038 NARRATOR: The aurora above the surface 262 00:16:02,038 --> 00:16:04,005 helps us peer beneath it. 263 00:16:05,905 --> 00:16:08,238 O'DONOGHUE: The aurora of Ganymede are produced when 264 00:16:08,238 --> 00:16:09,971 electrically charged particles are 265 00:16:09,971 --> 00:16:11,838 flowing down magnetic field lines 266 00:16:11,838 --> 00:16:14,505 and they're hitting the atmosphere, 267 00:16:14,505 --> 00:16:16,238 which is made of oxygen 268 00:16:16,238 --> 00:16:18,038 and they're causing it to glow 269 00:16:18,038 --> 00:16:19,871 in green and red lights. 270 00:16:21,238 --> 00:16:23,538 SCHENK: Ganymede's magnetic field is a lot like Earth's. 271 00:16:24,538 --> 00:16:27,305 It's generated by a liquid magnetic 272 00:16:27,305 --> 00:16:28,638 iron core. 273 00:16:28,638 --> 00:16:30,438 If you stood on the surface of Ganymede 274 00:16:30,438 --> 00:16:32,971 with a compass and you looked at it, 275 00:16:32,971 --> 00:16:35,971 the needle of the compass would point to the north pole 276 00:16:35,971 --> 00:16:38,305 of the magnetic field, just like it does on the Earth, 277 00:16:38,305 --> 00:16:40,605 it is the only moon that you can do it on 278 00:16:40,605 --> 00:16:42,605 because it's the only moon in our solar system 279 00:16:42,605 --> 00:16:44,871 that has an internal magnetic field. 280 00:16:46,505 --> 00:16:48,505 NARRATOR: And Ganymede's aurora 281 00:16:48,505 --> 00:16:51,171 rocked back and forth across the moon. 282 00:16:52,338 --> 00:16:54,705 QUICK: Because Jupiter also has a magnetic field 283 00:16:54,705 --> 00:16:57,271 and Ganymede sits within Jupiter's magnetic field, 284 00:16:57,271 --> 00:16:59,105 it should cause Ganymede's aurora 285 00:16:59,105 --> 00:17:00,738 to rock back and forth. 286 00:17:04,905 --> 00:17:06,805 NARRATOR: But when scientists used 287 00:17:06,805 --> 00:17:09,038 the Hubble Space Telescope to look 288 00:17:09,038 --> 00:17:11,371 at Ganymede's aurora, 289 00:17:11,371 --> 00:17:13,438 something didn't add up. 290 00:17:15,038 --> 00:17:17,505 DOUGHERTY: The images of the aurora at Ganymede 291 00:17:17,505 --> 00:17:20,305 showed that they weren't rocking back and forth 292 00:17:20,305 --> 00:17:22,438 as much as we expected them to. 293 00:17:22,438 --> 00:17:24,371 Because the motion of Ganymede's aurora 294 00:17:24,371 --> 00:17:25,938 don't match scientific predictions, 295 00:17:25,938 --> 00:17:28,271 we think there must be something else there 296 00:17:28,271 --> 00:17:30,305 that's affecting them. 297 00:17:33,771 --> 00:17:36,605 NARRATOR: If there were a second magnetic field being generated 298 00:17:36,605 --> 00:17:38,538 within Ganymede, 299 00:17:38,538 --> 00:17:41,005 that would interfere with the aurora, 300 00:17:41,005 --> 00:17:44,038 reducing the rocking. 301 00:17:46,638 --> 00:17:49,671 But the only way to generate that extra field 302 00:17:49,671 --> 00:17:51,871 would be if another layer, 303 00:17:51,871 --> 00:17:55,738 besides the molten core, were conducting electricity. 304 00:17:57,205 --> 00:17:59,871 There has to be something else. 305 00:18:01,805 --> 00:18:02,805 SCHENK: That something else 306 00:18:02,805 --> 00:18:05,138 turns out to be a liquid layer, 307 00:18:05,138 --> 00:18:07,471 an ocean underneath the surface. 308 00:18:07,471 --> 00:18:10,271 Ganymede's internal ocean is damping down 309 00:18:10,271 --> 00:18:12,938 the oscillation that we see. 310 00:18:12,938 --> 00:18:14,505 QUICK: It's extremely cool 311 00:18:14,505 --> 00:18:16,105 that we can tell that there's an ocean 312 00:18:16,105 --> 00:18:17,371 beneath Ganymede's surface, 313 00:18:17,371 --> 00:18:19,738 despite never having a lander there. 314 00:18:24,305 --> 00:18:26,705 NARRATOR: Scientists estimate 315 00:18:26,705 --> 00:18:29,805 Ganymede has a global ocean. 316 00:18:33,305 --> 00:18:35,605 60 miles deep, 317 00:18:35,605 --> 00:18:40,538 hidden beneath around 95 miles of rock-hard ice. 318 00:18:41,505 --> 00:18:42,838 DOUGHERTY: It's pretty mind-blowing, 319 00:18:42,838 --> 00:18:44,005 if you think about it. 320 00:18:44,005 --> 00:18:47,138 This moon out in the outer solar system, 321 00:18:47,138 --> 00:18:49,471 which is much smaller than the Earth, 322 00:18:49,471 --> 00:18:51,971 could potentially have more water within it 323 00:18:51,971 --> 00:18:55,471 than we have in our own oceans on the Earth. 324 00:18:55,471 --> 00:18:58,538 NARRATOR: Of all the water worlds in the solar system, 325 00:18:58,538 --> 00:19:02,005 Ganymede's ocean is the largest. 326 00:19:02,005 --> 00:19:04,671 DOUGHERTY: One of the questions I always ask myself 327 00:19:04,671 --> 00:19:08,405 is how does an icy moon like Ganymede get this huge ocean. 328 00:19:11,371 --> 00:19:14,571 NARRATOR: Strange gouges on the surface of Ganymede 329 00:19:14,571 --> 00:19:17,438 hint at a fascinating theory. 330 00:19:18,438 --> 00:19:20,838 These are impact craters, 331 00:19:20,838 --> 00:19:24,838 not individual ones like we see on most other worlds 332 00:19:24,838 --> 00:19:27,571 but a long chain of them. 333 00:19:29,138 --> 00:19:31,805 To understand how these form, 334 00:19:31,805 --> 00:19:35,538 we have to look back to the monster living next door... 335 00:19:37,038 --> 00:19:39,238 ...Jupiter. 336 00:19:44,538 --> 00:19:46,271 Veronica Bray Durfey 337 00:19:46,271 --> 00:19:50,571 is a planetary scientist who studies impact craters... 338 00:19:51,571 --> 00:19:54,171 ...on the surface of Ganymede. 339 00:19:57,338 --> 00:19:59,705 DURFEY: A lot of planetary science these days is, 340 00:19:59,705 --> 00:20:02,238 you know, I-I wait for the pictures to come back 341 00:20:02,238 --> 00:20:05,105 from spacecraft that have been to the planets. 342 00:20:05,105 --> 00:20:07,471 But there's something a lot more personal 343 00:20:07,471 --> 00:20:09,471 about getting it through a telescope. 344 00:20:09,471 --> 00:20:13,071 And to-to see all of the Galilean moons out tonight, 345 00:20:13,071 --> 00:20:15,805 that's always extra special. 346 00:20:15,805 --> 00:20:19,671 This pinprick of light just on the edge of Jupiter, 347 00:20:19,671 --> 00:20:21,738 that's Ganymede. 348 00:20:21,738 --> 00:20:24,071 It's the biggest of the Galilean moons. 349 00:20:24,071 --> 00:20:26,571 It's the biggest moon in the solar system. 350 00:20:26,571 --> 00:20:28,438 It's bigger than the planet Mercury. 351 00:20:29,405 --> 00:20:31,971 NARRATOR: And Ganymede's location, 352 00:20:31,971 --> 00:20:33,438 orbiting Jupiter, 353 00:20:33,438 --> 00:20:37,771 may play a part in how the moon got its hidden ocean. 354 00:20:43,171 --> 00:20:44,805 Any objects that have mass 355 00:20:44,805 --> 00:20:46,838 will have a force of attraction between them, 356 00:20:46,838 --> 00:20:48,505 and that's gravity. 357 00:20:48,505 --> 00:20:50,171 The larger the mass, 358 00:20:50,171 --> 00:20:52,105 the larger the gravitational attraction 359 00:20:52,105 --> 00:20:53,605 between the two objects. 360 00:20:53,605 --> 00:20:56,005 Because Jupiter's so massive, 361 00:20:56,005 --> 00:20:59,005 it has a really massive gravitational pull. 362 00:20:59,005 --> 00:21:00,905 So this means that it attracts 363 00:21:00,905 --> 00:21:04,671 a lot of bodies of the solar system towards it. 364 00:21:05,738 --> 00:21:08,371 If an asteroid or a comet gets close enough, 365 00:21:08,371 --> 00:21:10,971 it can feel the pull of Jupiter. 366 00:21:12,171 --> 00:21:13,671 COLLINS: So if you're drawn in toward Jupiter 367 00:21:13,671 --> 00:21:16,471 by its gravity and you don't 368 00:21:16,471 --> 00:21:19,805 quite hit Jupiter, but you get very close... 369 00:21:19,805 --> 00:21:21,905 Jupiter's gravity is so strong 370 00:21:21,905 --> 00:21:24,338 that it will start to pull 371 00:21:24,338 --> 00:21:26,338 bodies apart. 372 00:21:27,305 --> 00:21:29,738 SCHENK: We've actually seen the process. 373 00:21:29,738 --> 00:21:31,771 This was back in 1993 374 00:21:31,771 --> 00:21:35,505 when astronomers observed a comet 375 00:21:35,505 --> 00:21:39,638 broken up after a close passage of Jupiter. 376 00:21:39,638 --> 00:21:42,505 And it was called Shoemaker-Levy 9 377 00:21:42,505 --> 00:21:44,738 after the astronomers who discovered it. 378 00:21:44,738 --> 00:21:46,238 COLLINS: It had been disrupted 379 00:21:46,238 --> 00:21:48,005 by Jupiter's gravity into... 380 00:21:48,005 --> 00:21:49,971 a string of objects. 381 00:21:49,971 --> 00:21:52,371 And looking at its orbit, they realized 382 00:21:52,371 --> 00:21:54,038 that it was going to come back 383 00:21:54,038 --> 00:21:57,038 a year later and actually hit Jupiter. 384 00:22:00,438 --> 00:22:03,638 NARRATOR: Watching this series of comet fragments explode 385 00:22:03,638 --> 00:22:06,438 as they hit the dark side of Jupiter 386 00:22:06,438 --> 00:22:08,505 provided scientists with clues 387 00:22:08,505 --> 00:22:11,605 as to how these strange crater chains 388 00:22:11,605 --> 00:22:13,305 were formed on Ganymede. 389 00:22:14,471 --> 00:22:18,038 SCHENK: So on Ganymede we observed these chains of craters, 390 00:22:18,038 --> 00:22:20,171 all nicely lined up in a row, 391 00:22:20,171 --> 00:22:22,071 evenly spaced, very peculiar. 392 00:22:22,071 --> 00:22:25,871 So when we saw the chain of cometary fragments 393 00:22:25,871 --> 00:22:28,505 that make up Shoemaker-Levy 9 394 00:22:28,505 --> 00:22:30,805 and we saw that in 1993, 395 00:22:30,805 --> 00:22:32,438 it suddenly occurred to us, 396 00:22:32,438 --> 00:22:36,238 that same set of cometary fragments, 397 00:22:36,238 --> 00:22:37,838 if it the moon on the way out, 398 00:22:37,838 --> 00:22:40,771 would form a crater chain just like this. 399 00:22:50,571 --> 00:22:54,105 NARRATOR: Ferocious, high energy impacts 400 00:22:54,105 --> 00:22:57,605 create these incredible chains of craters. 401 00:23:02,038 --> 00:23:05,205 But Jupiter's gravity means that so much more 402 00:23:05,205 --> 00:23:08,871 has hit Ganymede than just these torn apart objects. 403 00:23:10,971 --> 00:23:13,138 And it is these violent collisions 404 00:23:13,138 --> 00:23:16,905 that may help explain the moon's vast hidden ocean. 405 00:23:25,138 --> 00:23:28,305 COLLINS: The early history of the solar system was a very chaotic place. 406 00:23:28,305 --> 00:23:31,638 There were more asteroids and comets 407 00:23:31,638 --> 00:23:34,938 flying around, impacts were just 408 00:23:34,938 --> 00:23:36,805 a much more common occurrence. 409 00:23:38,471 --> 00:23:40,771 Nothing was spared the chaos 410 00:23:40,771 --> 00:23:42,905 of the early solar system. 411 00:23:45,005 --> 00:23:48,571 NARRATOR: As Jupiter drew in countless asteroids and comets 412 00:23:48,571 --> 00:23:50,505 with its immense gravity... 413 00:23:51,505 --> 00:23:54,238 ...Ganymede was caught in the crossfire. 414 00:23:58,238 --> 00:24:01,971 Each impact delivers huge amounts of heat 415 00:24:01,971 --> 00:24:04,205 and energy to the early moon. 416 00:24:06,138 --> 00:24:08,471 DURFEY: And this allowed Ganymede to heat up 417 00:24:08,471 --> 00:24:11,305 and some of its components to become molten. 418 00:24:11,305 --> 00:24:13,871 And once you have that molten mix, 419 00:24:13,871 --> 00:24:16,105 you're going to get differentiation. 420 00:24:18,238 --> 00:24:20,105 NARRATOR: Differentiation 421 00:24:20,105 --> 00:24:22,605 is where gravity organizes material 422 00:24:22,605 --> 00:24:24,538 based on its density. 423 00:24:26,905 --> 00:24:29,371 DURFEY: We can visualize this differentiation. 424 00:24:29,371 --> 00:24:34,171 So if this oil is our low density material... 425 00:24:36,338 --> 00:24:37,671 ...we can add 426 00:24:37,671 --> 00:24:39,438 a higher density material. 427 00:24:39,438 --> 00:24:41,071 This sand. 428 00:24:42,671 --> 00:24:44,605 NARRATOR: Shaking the jar lets us imagine 429 00:24:44,605 --> 00:24:47,538 what Ganymede would've been like at the beginning. 430 00:24:49,805 --> 00:24:53,238 A mixture of high and low-density materials. 431 00:24:53,238 --> 00:24:54,905 DURFEY: And then over time 432 00:24:54,905 --> 00:24:57,105 the gravitational pull 433 00:24:57,105 --> 00:24:59,238 will help this separate out. 434 00:24:59,238 --> 00:25:01,271 And so in Ganymede's case, 435 00:25:01,271 --> 00:25:04,705 that is the high-density metals 436 00:25:04,705 --> 00:25:07,505 falling towards its core 437 00:25:07,505 --> 00:25:09,005 and the low-density ices 438 00:25:09,005 --> 00:25:11,705 remaining at its surface. 439 00:25:12,871 --> 00:25:16,738 Differentiation takes millions and millions of years. 440 00:25:16,738 --> 00:25:18,471 But this will not take that long. 441 00:25:19,805 --> 00:25:23,938 NARRATOR: But gravity had one more trick to play. 442 00:25:23,938 --> 00:25:25,205 DURFEY: As the dense material 443 00:25:25,205 --> 00:25:27,205 heads towards the core of Ganymede, 444 00:25:27,205 --> 00:25:30,271 it flows past the less dense material, 445 00:25:30,271 --> 00:25:33,305 and this creates heat through friction, 446 00:25:33,305 --> 00:25:35,771 keeping Ganymede molten for longer 447 00:25:35,771 --> 00:25:38,205 and making its differentiation 448 00:25:38,205 --> 00:25:40,271 almost a self-sustaining system. 449 00:25:42,238 --> 00:25:44,871 NARRATOR: And this continued until Ganymede's interior 450 00:25:44,871 --> 00:25:47,605 separated out into different layers. 451 00:25:49,505 --> 00:25:52,738 MLINAR: So we know that Ganymede got hot enough to melt completely. 452 00:25:52,738 --> 00:25:55,071 And not just to separate the ice 453 00:25:55,071 --> 00:25:56,605 from the rock, 454 00:25:56,605 --> 00:25:58,171 but actually to separate 455 00:25:58,171 --> 00:25:59,438 the metal from the rock 456 00:25:59,438 --> 00:26:01,038 inside of Ganymede, as well. 457 00:26:01,038 --> 00:26:04,338 NARRATOR: And over hundreds of millions of years 458 00:26:04,338 --> 00:26:06,705 the moon started to cool. 459 00:26:06,705 --> 00:26:09,605 MLINAR: What will happen is that the ice 460 00:26:09,605 --> 00:26:11,371 deep inside Ganymede starts 461 00:26:11,371 --> 00:26:14,305 to freeze from below, but it also freezes from above, 462 00:26:14,305 --> 00:26:17,071 and then you get left with this layer 463 00:26:17,071 --> 00:26:19,838 of salty water that just won't freeze. 464 00:26:20,838 --> 00:26:24,171 NARRATOR: But this is just one theory about Ganymede's ocean 465 00:26:24,171 --> 00:26:26,838 and how it got the heat to form. 466 00:26:30,105 --> 00:26:32,105 When I get asked the question will we ever know 467 00:26:32,105 --> 00:26:33,538 exactly what happened at Ganymede, 468 00:26:33,538 --> 00:26:35,671 and the answer's probably no, 469 00:26:35,671 --> 00:26:37,938 we will be able to come up with suggestions 470 00:26:37,938 --> 00:26:39,838 as to what might've happened. 471 00:26:39,838 --> 00:26:43,571 Um, but we'll probably never know it completely. 472 00:26:43,571 --> 00:26:45,205 But to me that's part of what makes it 473 00:26:45,205 --> 00:26:46,838 so interesting to study. 474 00:26:46,838 --> 00:26:48,671 Because there are always new ideas. 475 00:26:48,671 --> 00:26:50,638 There are always new things that we can measure. 476 00:26:50,638 --> 00:26:53,271 Always new techniques that we can try. 477 00:27:00,505 --> 00:27:04,138 NARRATOR: Leaving this hidden ocean world behind, 478 00:27:04,138 --> 00:27:06,371 with its bizarre surface... 479 00:27:09,438 --> 00:27:11,671 ...we head out away from the sun... 480 00:27:14,105 --> 00:27:15,938 ...past Saturn... 481 00:27:17,138 --> 00:27:19,905 ...to see what strange things can happen 482 00:27:19,905 --> 00:27:22,705 when you pair a massive world 483 00:27:22,705 --> 00:27:24,738 with a tiny one. 484 00:27:29,638 --> 00:27:32,238 Uranus is pretty odd to begin with. 485 00:27:35,005 --> 00:27:38,905 The entire planet knocked onto its side, 486 00:27:38,905 --> 00:27:42,105 likely by some massive impact in the past. 487 00:27:43,538 --> 00:27:47,038 But that's nothing compared to how weird 488 00:27:47,038 --> 00:27:49,005 one of its moons is. 489 00:27:53,338 --> 00:27:55,905 GROUND CONTROLLER: Four, three, two, 490 00:27:55,905 --> 00:27:58,338 one. 491 00:27:58,338 --> 00:28:02,038 We have ignition and we have lift off. 492 00:28:03,638 --> 00:28:06,705 NARRATOR: On August 20, 1977, 493 00:28:06,705 --> 00:28:09,438 spacecraft Voyager 2 494 00:28:09,438 --> 00:28:11,805 was launched to explore the outer planets 495 00:28:11,805 --> 00:28:15,338 of the solar system. 496 00:28:15,338 --> 00:28:16,871 The Voyager mission was really exciting, it was... 497 00:28:16,871 --> 00:28:21,371 a rare mission of first exploration. 498 00:28:29,505 --> 00:28:32,071 NARRATOR: And after more than eight years... 499 00:28:33,805 --> 00:28:36,571 ...Voyager 2 reached Uranus. 500 00:28:36,571 --> 00:28:40,238 It was the first, and remains the only spacecraft 501 00:28:40,238 --> 00:28:43,405 to visit this planet and its moons. 502 00:28:44,738 --> 00:28:46,871 COLLINS: And we'll never have that 503 00:28:46,871 --> 00:28:48,838 experience again of seeing those places 504 00:28:48,838 --> 00:28:50,371 for the first time. 505 00:28:52,905 --> 00:28:56,338 NARRATOR: As it flew past Miranda's south pole... 506 00:28:58,905 --> 00:29:02,438 Voyager 2's cameras captured images of one 507 00:29:02,438 --> 00:29:04,605 of the most astonishing surfaces 508 00:29:04,605 --> 00:29:07,038 in the entire solar system. 509 00:29:10,038 --> 00:29:11,871 MLINAR: I think the images of Miranda 510 00:29:11,871 --> 00:29:14,271 were shocking when they came back. 511 00:29:15,271 --> 00:29:17,871 SCHENK: Because we weren't really expecting much. 512 00:29:17,871 --> 00:29:21,005 We were expecting it to be cold and dead. 513 00:29:21,005 --> 00:29:22,405 Not much happening. 514 00:29:22,405 --> 00:29:27,105 And yet there's signs of some kind of activity inside. 515 00:29:28,871 --> 00:29:31,071 It looks like somebody 516 00:29:31,071 --> 00:29:33,471 was making an art project. 517 00:29:33,471 --> 00:29:35,371 Like somebody ripped up 518 00:29:35,371 --> 00:29:36,838 pictures of two different moons 519 00:29:36,838 --> 00:29:38,538 and glued them back together again. 520 00:29:38,538 --> 00:29:41,905 It didn't look real to me the first time I saw it. 521 00:29:43,471 --> 00:29:47,471 NARRATOR: Scientists spotted plunging canyons. 522 00:29:47,471 --> 00:29:50,038 With cliffs taller than Mount Everest. 523 00:29:50,038 --> 00:29:53,771 And ridged patches that punctuate the surface. 524 00:29:57,305 --> 00:30:01,638 All on a moon only 293 miles in diameter. 525 00:30:02,671 --> 00:30:04,671 Less than the width of Arizona. 526 00:30:06,771 --> 00:30:08,838 MLINAR: It raised a lot of questions 527 00:30:08,838 --> 00:30:12,438 as to what's going on, on those small icy moons? 528 00:30:12,438 --> 00:30:15,205 SCHENK: It was a real resetting event. 529 00:30:15,205 --> 00:30:17,771 It told us that, you know, small bodies can be 530 00:30:17,771 --> 00:30:20,671 very interesting and dynamic, too. 531 00:30:20,671 --> 00:30:22,205 And we had to sort of go back 532 00:30:22,205 --> 00:30:24,371 and understand why that was the case. 533 00:30:26,571 --> 00:30:29,405 NARRATOR: The moon's size offers a clue. 534 00:30:30,671 --> 00:30:32,971 MLINAR: So Miranda is much, much smaller than the Earth. 535 00:30:32,971 --> 00:30:35,638 So the surface gravity on Miranda is about... 536 00:30:35,638 --> 00:30:38,071 1/100th that on the surface of the Earth. 537 00:30:39,638 --> 00:30:42,571 NARRATOR: And that means the cliffs can soar 538 00:30:42,571 --> 00:30:44,938 to unbelievable heights. 539 00:30:44,938 --> 00:30:47,505 QUICK: Miranda's tallest cliff is pretty high 540 00:30:47,505 --> 00:30:49,371 compared to its overall size. 541 00:30:49,371 --> 00:30:51,238 The tallest cliff is six miles high. 542 00:30:51,238 --> 00:30:53,038 That's equivalent to 2% 543 00:30:53,038 --> 00:30:54,571 of Miranda's diameter. 544 00:30:56,638 --> 00:30:58,938   NARRATOR: That would be like Earth having a cliff 545 00:30:58,938 --> 00:31:01,738 160 miles high. 546 00:31:01,738 --> 00:31:03,505 QUICK: The reason that Earth's tallest mountain 547 00:31:03,505 --> 00:31:05,605 is only five and a half miles tall 548 00:31:05,605 --> 00:31:07,771 is because Earth is more massive and because it's 549 00:31:07,771 --> 00:31:10,005 more massive, it has much stronger gravity, 550 00:31:10,005 --> 00:31:11,938 and gravity won't allow 551 00:31:11,938 --> 00:31:14,738 mountains or cliffs to grow that tall on Earth. 552 00:31:20,638 --> 00:31:22,605 NARRATOR: Like other worlds, 553 00:31:22,605 --> 00:31:26,305 Miranda suffers the occasional meteorite strike. 554 00:31:29,971 --> 00:31:32,338 But because of its weak gravity... 555 00:31:33,305 --> 00:31:36,305 ...the results play out in slow motion. 556 00:31:41,105 --> 00:31:43,738 With the debris taking over eight minutes 557 00:31:43,738 --> 00:31:47,105 to fall the height of its tallest cliffs. 558 00:31:54,038 --> 00:31:55,838 Compare that to Earth, 559 00:31:55,838 --> 00:31:59,371 where the same drop would take less than a minute. 560 00:32:02,638 --> 00:32:04,938 COLLINS: Jumping on Miranda would be a lot of fun. 561 00:32:04,938 --> 00:32:07,371 You could jump really high in the air 562 00:32:07,371 --> 00:32:09,971 because gravity is so low. 563 00:32:09,971 --> 00:32:12,705 In fact, just trying to walk normally would be difficult. 564 00:32:14,271 --> 00:32:17,171 NARRATOR: There are countless other small, icy worlds 565 00:32:17,171 --> 00:32:20,138 also with weak gravity, 566 00:32:20,138 --> 00:32:24,671 but we've only seen strange patches like this on Miranda. 567 00:32:26,205 --> 00:32:28,838 So where did this weird patchwork surface 568 00:32:28,838 --> 00:32:30,971 come from in the first place? 569 00:32:33,005 --> 00:32:37,071 All scientists have to go on are those images... 570 00:32:38,705 --> 00:32:44,338 ...grabbed in 1986 as Voyager 2 streaked past. 571 00:32:46,738 --> 00:32:48,871 SCHENK: One of the keys to understanding Miranda 572 00:32:48,871 --> 00:32:51,238 is to recognize that there is actually order 573 00:32:51,238 --> 00:32:53,638 to this apparently chaotic picture. 574 00:32:53,638 --> 00:32:57,405 COLLINS: You've got this ancient, cratered terrain over here 575 00:32:57,405 --> 00:33:02,505 and then these patches like here, here and up here 576 00:33:02,505 --> 00:33:04,171 that we call coronae. 577 00:33:05,138 --> 00:33:09,538 NARRATOR: Where regions of Miranda's surface have been remade. 578 00:33:09,538 --> 00:33:11,771 COLLINS: And inside that patch, 579 00:33:11,771 --> 00:33:13,671 you see are these ridges and troughs 580 00:33:13,671 --> 00:33:16,005 that are like stretch marks on the surfaces. 581 00:33:17,438 --> 00:33:20,405 NARRATOR: It looks as if the surface has been ripped apart... 582 00:33:21,538 --> 00:33:26,371 ...suggesting these scars were formed by internal forces. 583 00:33:29,205 --> 00:33:30,838 COLLINS: If you had some kind of 584 00:33:30,838 --> 00:33:33,038 warm material inside Miranda, 585 00:33:33,038 --> 00:33:36,005 it's less dense and it starts rising up 586 00:33:36,005 --> 00:33:37,838 uh, in a big blob. 587 00:33:37,838 --> 00:33:39,905 And as it comes up toward the surface, 588 00:33:39,905 --> 00:33:42,538 it pushes the material out of its way... 589 00:33:43,738 --> 00:33:45,938 ...ripping the surface apart. 590 00:33:45,938 --> 00:33:48,238 QUICK: It cracks and it fractures open 591 00:33:48,238 --> 00:33:50,238 and we're left with a corona. 592 00:33:52,971 --> 00:33:56,371 NARRATOR: This left hundreds of miles of canyons... 593 00:33:57,638 --> 00:34:00,705 ...where the surface cracked open along fault lines... 594 00:34:01,671 --> 00:34:04,905 ...creating this incredible landscape. 595 00:34:08,238 --> 00:34:09,905 I think since the Voyager images came back 596 00:34:09,905 --> 00:34:11,971 people have been wondering 597 00:34:11,971 --> 00:34:14,538 how a body so small could be so active. 598 00:34:14,538 --> 00:34:16,605 Small bodies lose their heat rapidly, 599 00:34:16,605 --> 00:34:18,138 so we were expecting it to 600 00:34:18,138 --> 00:34:21,005 not have any real geologic history. 601 00:34:21,771 --> 00:34:23,038 COLLINS: So the big question is, 602 00:34:23,038 --> 00:34:24,505 where did the heat come from 603 00:34:24,505 --> 00:34:26,938 to drive the creation of this bizarre landscape? 604 00:34:29,238 --> 00:34:33,105 NARRATOR: For that, we have to look to Miranda's history. 605 00:34:34,438 --> 00:34:37,905 Our best theory involves the moon's giant parent planet, 606 00:34:37,905 --> 00:34:39,005 Uranus... 607 00:34:39,971 --> 00:34:42,338 ...and another quirk of gravity. 608 00:34:43,671 --> 00:34:44,971 QUICK: Billions of years ago, 609 00:34:44,971 --> 00:34:46,971 Miranda had a more eccentric orbit. 610 00:34:46,971 --> 00:34:51,271 And what that means is that when Miranda orbited Uranus, 611 00:34:51,271 --> 00:34:52,638 it wasn't a perfect circle, 612 00:34:52,638 --> 00:34:54,471 it was more in the shape of an ellipse. 613 00:34:54,471 --> 00:34:56,005 So, when Miranda 614 00:34:56,005 --> 00:34:58,271 is very, very close to Uranus, 615 00:34:58,271 --> 00:34:59,938 the gravity from Uranus 616 00:34:59,938 --> 00:35:02,705 sort of deforms it into more like an egg shape. 617 00:35:02,705 --> 00:35:05,505 And then when Miranda's farther away, it's more round. 618 00:35:05,505 --> 00:35:08,338 And that stretching and squeezing 619 00:35:08,338 --> 00:35:10,705 causes a lot of friction on the inside 620 00:35:10,705 --> 00:35:12,605 and that friction results in heat, 621 00:35:12,605 --> 00:35:14,271 which we call tidal heating. 622 00:35:15,938 --> 00:35:18,038 NARRATOR: And it's this tidal heating 623 00:35:18,038 --> 00:35:20,371 that drives Miranda's geology 624 00:35:20,371 --> 00:35:22,271 and forms the coronae. 625 00:35:25,071 --> 00:35:27,105 SCHENK: Not only is the gravity responsible 626 00:35:27,105 --> 00:35:28,605 for bringing the material together 627 00:35:28,605 --> 00:35:31,838 that created Miranda in the first place, 628 00:35:31,838 --> 00:35:33,871 but because of its gravitational interaction 629 00:35:33,871 --> 00:35:39,638 with Uranus, it's also responsible for the energy 630 00:35:39,638 --> 00:35:41,238 that remade Miranda later on. 631 00:35:42,538 --> 00:35:46,238 NARRATOR: Today, Miranda has a nearly circular orbit. 632 00:35:46,238 --> 00:35:49,505 And scientists think that heat is mostly gone. 633 00:35:50,438 --> 00:35:51,971 QUICK: Because Miranda's so small, 634 00:35:51,971 --> 00:35:53,471 it would've been difficult for it to hold onto 635 00:35:53,471 --> 00:35:54,838 its heat for a long time. 636 00:35:54,838 --> 00:35:57,671 But the Uranus system is not very well explored. 637 00:35:57,671 --> 00:35:59,405 There are a lot of things we don't understand 638 00:35:59,405 --> 00:36:01,705 about Uranus and its moons. 639 00:36:01,705 --> 00:36:04,238 And we should prepare to be surprised 640 00:36:04,238 --> 00:36:05,905 next time we go back. 641 00:36:07,338 --> 00:36:08,971 NARRATOR: Though now frozen, 642 00:36:08,971 --> 00:36:11,171 Miranda reveals how small worlds 643 00:36:11,171 --> 00:36:15,471 can be shaped through gravity by larger ones. 644 00:36:17,305 --> 00:36:21,238 But traveling inwards towards the sun, we see evidence 645 00:36:21,238 --> 00:36:25,371 that small worlds can also leave a big mark of their own. 646 00:36:27,771 --> 00:36:32,005 On one of the most spectacular structures in the solar system. 647 00:36:39,338 --> 00:36:42,638 Glimmering rings of rock and ice... 648 00:36:43,605 --> 00:36:47,038 ...they are one of the hallmarks of our cosmic neighborhood. 649 00:36:51,771 --> 00:36:54,305 And when examined more closely, 650 00:36:54,305 --> 00:36:57,838 show signs of remarkable organization. 651 00:36:59,171 --> 00:37:03,771 Lumps of ice and rock spread out in a thin disc, 652 00:37:03,771 --> 00:37:08,338 split into hundreds of repeating tracks and gaps 653 00:37:08,338 --> 00:37:10,505 that look like grooves on a record. 654 00:37:11,571 --> 00:37:14,771 Looping for hundreds of thousands of miles 655 00:37:14,771 --> 00:37:15,805 through space. 656 00:37:18,071 --> 00:37:21,505 Saturn's rings are amazingly complex. 657 00:37:21,505 --> 00:37:22,938 And the more we zoom into them, 658 00:37:22,938 --> 00:37:25,005 the more complex seem to be. 659 00:37:25,971 --> 00:37:28,771 It is one of the wonders of the solar system. 660 00:37:35,171 --> 00:37:38,471 NARRATOR: Scientists think the rings may have first formed 661 00:37:38,471 --> 00:37:41,838 when a moon strayed too close to Saturn... 662 00:37:42,838 --> 00:37:46,138 ...and was pulled apart by its gravity... 663 00:37:48,338 --> 00:37:50,238 ...creating a jumble of trillions 664 00:37:50,238 --> 00:37:54,105 of individual fragments of rock and ice. 665 00:38:00,138 --> 00:38:02,405 So what turns such chaos 666 00:38:02,405 --> 00:38:05,871 into the ordered beauty we see today? 667 00:38:10,038 --> 00:38:11,971 NASA's Cassini spacecraft 668 00:38:11,971 --> 00:38:16,671 gave us the best view of the rings we've ever had. 669 00:38:16,671 --> 00:38:18,338 OLUSEYI: The photographs from Cassini 670 00:38:18,338 --> 00:38:21,071 gave us Saturn's rings at all angles. 671 00:38:21,071 --> 00:38:24,605   We saw them reflecting light from the sun, 672 00:38:24,605 --> 00:38:27,705 we saw Cassini look through them toward the sun. 673 00:38:27,705 --> 00:38:31,171 Just the spectacular beauty of them. 674 00:38:31,171 --> 00:38:33,138 Just mind-blowing. 675 00:38:34,071 --> 00:38:38,971 NARRATOR: And lurking among the loops of rock and ice... 676 00:38:38,971 --> 00:38:43,505 Cassini imaged one of the most startling moons 677 00:38:43,505 --> 00:38:45,338 in the entire Saturn system. 678 00:38:54,238 --> 00:38:57,205 EL MOUTAMID: So, Pan is this weird, tiny object. 679 00:38:57,205 --> 00:39:00,605 It is only 17 miles across. 680 00:39:00,605 --> 00:39:03,471 And it looks, for me, like a walnut. 681 00:39:03,471 --> 00:39:07,038 And, uh, it looks like it has a dusting of material around it 682 00:39:07,038 --> 00:39:09,405 that could easily break off if you were to touch it. 683 00:39:11,271 --> 00:39:15,738 NARRATOR: Despite its small size, Pan has a big impact 684 00:39:15,738 --> 00:39:17,738 on the structure of the rings. 685 00:39:19,038 --> 00:39:22,805 BROOKS: Pan is a great example of how gravitational interactions 686 00:39:22,805 --> 00:39:24,038 can shape Saturn's rings 687 00:39:24,038 --> 00:39:25,871 and create the gaps that we see. 688 00:39:28,605 --> 00:39:32,371 NARRATOR: Pan orbits inside a wide track within Saturn's rings 689 00:39:32,371 --> 00:39:34,138 called the Encke Gap. 690 00:39:36,171 --> 00:39:39,138 EL MOUTAMID: We think Pan created the Encke Gap 691 00:39:39,138 --> 00:39:42,338 by cleaning the orbit and by accumulating 692 00:39:42,338 --> 00:39:46,705 all this ring material, dust and ice, around it. 693 00:39:46,705 --> 00:39:49,338 O'DONOGHUE: This ring material has settled 694 00:39:49,338 --> 00:39:50,605 specifically on Pan's equator 695 00:39:50,605 --> 00:39:53,238 again and again and again and that meant 696 00:39:53,238 --> 00:39:56,571 there is this large, uh, ridge around Pan itself. 697 00:39:56,571 --> 00:39:58,838 OLUSEYI: It looks like an empanada 698 00:39:58,838 --> 00:40:00,238 because so much water and ice from the rings 699 00:40:00,238 --> 00:40:02,271 have built up around its equator. 700 00:40:05,171 --> 00:40:06,871 NARRATOR: For millions of years, 701 00:40:06,871 --> 00:40:09,905 Pan has been nibbling away, 702 00:40:09,905 --> 00:40:12,705 clearing particles out of its orbit... 703 00:40:13,771 --> 00:40:16,438 ...and creating this pathway... 704 00:40:17,405 --> 00:40:20,971 ...only that can't be the full story. 705 00:40:24,971 --> 00:40:28,771 Pan is just 17 miles across, 706 00:40:28,771 --> 00:40:31,305 yet it orbits within the Encke Gap 707 00:40:31,305 --> 00:40:33,571 that's 200 miles wide... 708 00:40:37,971 --> 00:40:40,671 ...far broader than Pan could clear 709 00:40:40,671 --> 00:40:42,905 through simply snacking alone. 710 00:40:45,471 --> 00:40:48,405 So the big question is, how can a small moon like Pan 711 00:40:48,405 --> 00:40:51,038 carve out such a huge gap in Saturn's rings? 712 00:40:51,038 --> 00:40:53,738 In addition to sweeping up ring particles, 713 00:40:53,738 --> 00:40:56,405 Pan also managed to open up the Encke Gap 714 00:40:56,405 --> 00:40:59,705 by pushing away the particles on either side of the gap 715 00:40:59,705 --> 00:41:02,005 through gravitational interactions. 716 00:41:04,838 --> 00:41:09,371 NARRATOR: This turns out to be a quirk of orbital physics. 717 00:41:09,371 --> 00:41:12,338 If a particle of ice gets close to Pan, 718 00:41:12,338 --> 00:41:16,071 the moon's gravity gives it a tug, 719 00:41:16,071 --> 00:41:19,405 speeding the particle up or slowing it down. 720 00:41:21,171 --> 00:41:24,405 That moves it to a new orbit, 721 00:41:24,405 --> 00:41:27,171 clearing a path through the rings. 722 00:41:28,805 --> 00:41:30,905 And Pan is not alone. 723 00:41:32,238 --> 00:41:36,371 The Cassini spacecraft also spotted tiny Daphnis... 724 00:41:38,171 --> 00:41:40,338 ...just five miles across, 725 00:41:40,338 --> 00:41:43,005 clearing its own gap in the rings. 726 00:41:46,805 --> 00:41:52,705 Even tiny, odd worlds can create structures of staggering scale. 727 00:41:56,305 --> 00:41:58,905 But not all the gaps have moons embedded in them, 728 00:41:58,905 --> 00:42:01,971 including one of the biggest, 729 00:42:01,971 --> 00:42:05,038 the massive Cassini Division, 730 00:42:05,038 --> 00:42:07,638 almost 3,000 miles wide. 731 00:42:12,371 --> 00:42:15,605 So how did these gaps in the rings form 732 00:42:15,605 --> 00:42:18,271 without a moon inside clearing the way? 733 00:42:29,305 --> 00:42:32,305 James O'Donoghue is a planetary scientist 734 00:42:32,305 --> 00:42:34,505 who studies Saturn and its rings. 735 00:42:42,171 --> 00:42:44,205 O'DONOGHUE: Saturn's rings are an amazing example 736 00:42:44,205 --> 00:42:47,038 of the most beautiful and complex patterns 737 00:42:47,038 --> 00:42:49,338 being produced by a single event 738 00:42:49,338 --> 00:42:51,638 occurring over time again and again. 739 00:42:51,638 --> 00:42:54,771 We see these patterns occurring all across nature 740 00:42:54,771 --> 00:42:56,305 in various forms, as we can see here, 741 00:42:56,305 --> 00:42:59,838 with ripples running across these sand dunes. 742 00:42:59,838 --> 00:43:02,238 The ripples form when the wind 743 00:43:02,238 --> 00:43:04,671 is gliding over the surface of the sand dunes, 744 00:43:04,671 --> 00:43:07,105 and it's lifting up small pieces of sand 745 00:43:07,105 --> 00:43:09,238 and bouncing them along the surface. 746 00:43:12,305 --> 00:43:14,671 NARRATOR: When the bouncing grains hit the surface, 747 00:43:14,671 --> 00:43:17,238 they kick up more grains. 748 00:43:18,171 --> 00:43:21,138 And as this process repeats, 749 00:43:21,138 --> 00:43:22,805 the ripples form. 750 00:43:25,138 --> 00:43:27,605 And just like wind creates structure 751 00:43:27,605 --> 00:43:29,705 in these sandy dunes, 752 00:43:29,705 --> 00:43:32,938 over 700 million miles away, 753 00:43:32,938 --> 00:43:35,438 in the Saturn system, 754 00:43:35,438 --> 00:43:38,905 regular, repeating gravitational interactions 755 00:43:38,905 --> 00:43:42,171 form the structures of the rings. 756 00:43:44,738 --> 00:43:46,171 O'DONOGHUE: This is Saturn and its rings-- 757 00:43:46,171 --> 00:43:48,271 it's not to scale-- and we also have 758 00:43:48,271 --> 00:43:50,038 a selection of moons. 759 00:43:50,038 --> 00:43:53,505 Here is Pan and here is Pandora, 760 00:43:53,505 --> 00:43:56,005 and we also have the moon Mimas. 761 00:43:56,005 --> 00:43:57,438 And we also have Titan, 762 00:43:57,438 --> 00:43:59,205 which is 50% larger than our moon, 763 00:43:59,205 --> 00:44:01,438 which is much further out. 764 00:44:01,438 --> 00:44:03,738 Saturn has over 140 moons. 765 00:44:03,738 --> 00:44:07,438 We only show four here because it would be too busy, 766 00:44:07,438 --> 00:44:08,471 and they interact 767 00:44:08,471 --> 00:44:09,505 with each other gravitationally, 768 00:44:09,505 --> 00:44:10,838 in a really complex way, 769 00:44:10,838 --> 00:44:14,338 and it weirdly leads to a lot of order. 770 00:44:17,171 --> 00:44:19,938 NARRATOR: One of these moons, Mimas, 771 00:44:19,938 --> 00:44:22,638 which has more than a passing resemblance 772 00:44:22,638 --> 00:44:25,038 to the Death Star from "Star Wars," 773 00:44:25,038 --> 00:44:27,005 creates the Cassini Division, 774 00:44:27,005 --> 00:44:31,171 despite being around 40,000 miles away from it. 775 00:44:34,238 --> 00:44:38,105 And it does this all thanks to gravity. 776 00:44:41,971 --> 00:44:44,371 O'DONOGHUE: The Cassini Division is the biggest gap in the rings, 777 00:44:44,371 --> 00:44:46,871 and it's produced by a gravitational interaction 778 00:44:46,871 --> 00:44:49,305 between Mimas and the ring particles 779 00:44:49,305 --> 00:44:50,505 around about here. 780 00:44:51,438 --> 00:44:54,838 NARRATOR: Mimas is in a two to one orbital resonance 781 00:44:54,838 --> 00:44:57,905 with the ring particles of rock and ice 782 00:44:57,905 --> 00:45:00,505 that would be found in the Cassini Division. 783 00:45:01,505 --> 00:45:02,938 O'DONOGHUE: And what that means is 784 00:45:02,938 --> 00:45:05,671 that Mimas, for every one orbit 785 00:45:05,671 --> 00:45:08,438 that it makes around the planet, 786 00:45:08,438 --> 00:45:10,938 the ring particle makes two. 787 00:45:13,671 --> 00:45:15,105 And because these are in resonance, 788 00:45:15,105 --> 00:45:16,405 every time Mimas 789 00:45:16,405 --> 00:45:17,971 and the ring particle meet, 790 00:45:17,971 --> 00:45:21,938 they actually meet at the same point in space around Saturn, 791 00:45:21,938 --> 00:45:23,738 and Mimas implants a gravitational tug 792 00:45:23,738 --> 00:45:27,038 onto the ring particle, which changes its orbit. 793 00:45:29,371 --> 00:45:33,038 NARRATOR: And Mimas has this gravitational relationship, 794 00:45:33,038 --> 00:45:36,271 not with just a single ring particle, 795 00:45:36,271 --> 00:45:39,571 but all the ring particles in the same orbit. 796 00:45:41,271 --> 00:45:45,705 Each time the moon and the ring particles align, 797 00:45:45,705 --> 00:45:50,105 Mimas's gravity tugs at the fragments of ice and rock, 798 00:45:50,105 --> 00:45:52,238 like an invisible hand... 799 00:45:55,138 --> 00:45:57,538 ...opening up the giant gap. 800 00:46:02,605 --> 00:46:05,405 And there are more moons sitting outside the main rings 801 00:46:05,405 --> 00:46:07,971 creating structures within them. 802 00:46:11,271 --> 00:46:13,338 EL MOUTAMID: It is fascinating that, 803 00:46:13,338 --> 00:46:16,038 even if the moons are far away from the ring, 804 00:46:16,038 --> 00:46:18,338 they still have an impact on the ring, 805 00:46:18,338 --> 00:46:21,538 and this is the magic of gravity. 806 00:46:21,538 --> 00:46:24,138 Gravity is the main force, 807 00:46:24,138 --> 00:46:26,905 that it is shaping everything in universe, 808 00:46:26,905 --> 00:46:30,738 including the Saturnian system. 809 00:46:36,638 --> 00:46:39,671 NARRATOR: The orbital dance of Saturn's moons 810 00:46:39,671 --> 00:46:42,971 create the constantly changing 811 00:46:42,971 --> 00:46:45,871 and dynamic pattern within the rings. 812 00:46:47,871 --> 00:46:50,938 One we are lucky to see. 813 00:47:00,405 --> 00:47:04,338 Saturn's rings allow us to see gravity at work, 814 00:47:04,338 --> 00:47:07,738 constantly shaping our solar system. 815 00:47:10,105 --> 00:47:14,038 But leave these beautiful patterns behind... 816 00:47:15,171 --> 00:47:17,505 ...and we see how a planet's size 817 00:47:17,505 --> 00:47:19,638 and the influence of gravity 818 00:47:19,638 --> 00:47:22,638 can have astonishing consequences for life. 819 00:47:28,571 --> 00:47:32,405 More than half a billion miles closer to the sun... 820 00:47:33,471 --> 00:47:36,005 ...through the asteroid belt, 821 00:47:36,005 --> 00:47:37,405 rubble left over 822 00:47:37,405 --> 00:47:40,971 when gravity failed to pull a planet together, 823 00:47:40,971 --> 00:47:44,438 and we reach the inner rocky worlds 824 00:47:44,438 --> 00:47:48,405 where we find perhaps the most bizarre world of all. 825 00:47:51,471 --> 00:47:56,071 A true outlier unlike anything else. 826 00:48:03,071 --> 00:48:06,771 Our solar system's beautiful blue marble. 827 00:48:07,638 --> 00:48:08,838 TRIPATHI: We're living in this 828 00:48:08,838 --> 00:48:11,071 amazing period of the Earth's history 829 00:48:11,071 --> 00:48:14,271 when we have liquid water in the form of oceans 830 00:48:14,271 --> 00:48:15,671 on the surface of our planet, 831 00:48:15,671 --> 00:48:17,705   and that is remarkably unique across, 832 00:48:17,705 --> 00:48:20,538 not only the solar system, 833 00:48:20,538 --> 00:48:22,305 but the thousands of other planets 834 00:48:22,305 --> 00:48:23,371 we've discovered to date. 835 00:48:26,171 --> 00:48:29,605 NARRATOR: The fact that Earth has oceans on the surface 836 00:48:29,605 --> 00:48:31,305 turns out to be, again, 837 00:48:31,305 --> 00:48:34,871 thanks in part to gravity, 838 00:48:34,871 --> 00:48:37,271 which pulls down on the atmosphere. 839 00:48:39,271 --> 00:48:41,938 ROWE-GURNEY: So our atmosphere is made up of lots of gasses, 840 00:48:41,938 --> 00:48:44,871 and that gas exerts a pressure 841 00:48:44,871 --> 00:48:46,838 on the surface of the Earth, 842 00:48:46,838 --> 00:48:49,438 and that pressure stops water 843 00:48:49,438 --> 00:48:51,705 from evaporating into space. 844 00:48:55,871 --> 00:48:58,671 NARRATOR: But if Earth were smaller, 845 00:48:58,671 --> 00:49:01,938 it might have been a different story. 846 00:49:03,271 --> 00:49:06,305 TRIPATHI: If it was much smaller, it wouldn't have enough mass, 847 00:49:06,305 --> 00:49:10,105 and, therefore, enough gravity to hold on to an atmosphere. 848 00:49:10,105 --> 00:49:12,205 We're lucky to live on a rocky planet 849 00:49:12,205 --> 00:49:15,405 that is large enough to keep its atmosphere in place. 850 00:49:17,071 --> 00:49:19,205 NARRATOR: With little to no atmosphere 851 00:49:19,205 --> 00:49:21,271 to press down on the oceans... 852 00:49:22,271 --> 00:49:25,871 ...water would boil at much lower temperatures, 853 00:49:25,871 --> 00:49:30,705 and Earth would become a desolate, barren ball. 854 00:49:33,005 --> 00:49:34,438 ROWE-GURNEY: So, without the atmosphere, 855 00:49:34,438 --> 00:49:36,571 Earth wouldn't have life on it, 856 00:49:36,571 --> 00:49:39,638 uh, and we wouldn't have the ability to breathe, 857 00:49:39,638 --> 00:49:41,905 um, there wouldn't be oceans, 858 00:49:41,905 --> 00:49:44,471 uh, and forests and trees. 859 00:49:44,471 --> 00:49:46,138 Uh, we wouldn't have anything 860 00:49:46,138 --> 00:49:48,071 like the Earth that we know today. 861 00:49:52,171 --> 00:49:56,371 NARRATOR: Earth's size has helped shape its destiny. 862 00:49:56,371 --> 00:49:58,371 Too small, 863 00:49:58,371 --> 00:50:01,305 and Earth could've been a misshapen potato 864 00:50:01,305 --> 00:50:02,871 with no atmosphere. 865 00:50:02,871 --> 00:50:04,738 Too big, 866 00:50:04,738 --> 00:50:07,438 about ten times its current mass, 867 00:50:07,438 --> 00:50:10,571 it could've grown to become a gas giant... 868 00:50:11,605 --> 00:50:14,671 ...with little hope for life as we know it. 869 00:50:15,971 --> 00:50:17,538 It turns out, 870 00:50:17,538 --> 00:50:21,005 life can run riot across the surface of the planet... 871 00:50:22,705 --> 00:50:25,805 ...because Earth is the right size 872 00:50:25,805 --> 00:50:29,505 with just the right amount of gravity. 873 00:50:34,538 --> 00:50:38,471 The same force that has helped shape all the other 874 00:50:38,471 --> 00:50:40,405 radically different, 875 00:50:40,405 --> 00:50:43,538 wonderfully strange worlds out there. 876 00:50:45,505 --> 00:50:48,771 The more we go out and visit our solar system in detail, 877 00:50:48,771 --> 00:50:53,038 the more we discover things we've never seen before. 878 00:50:53,038 --> 00:50:55,571 SCHENK: We're not entirely sure why we see so many 879 00:50:55,571 --> 00:50:57,838 different sizes and shapes 880 00:50:57,838 --> 00:51:00,271 and complexity of planetary bodies, 881 00:51:00,271 --> 00:51:02,838 uh, but we think that gravity 882 00:51:02,838 --> 00:51:05,305 has a very strong role to play in it. 883 00:51:06,505 --> 00:51:09,938 Without gravity, the universe would be a pretty boring place. 884 00:51:09,938 --> 00:51:13,371 It's gravity that assembles 885 00:51:13,371 --> 00:51:14,605 the materials of the universe 886 00:51:14,605 --> 00:51:16,671 into the large structures that we see. 887 00:51:17,671 --> 00:51:19,371 TRIPATHI: Gravity is the backdrop 888 00:51:19,371 --> 00:51:22,505 that's setting the stage for other forces to get to work. 889 00:51:24,605 --> 00:51:27,471 ROWE-GURNEY: We need to study these strange worlds in the solar system 890 00:51:27,471 --> 00:51:29,738 because, without them, we wouldn't understand 891 00:51:29,738 --> 00:51:32,205 how all of these forces come together to create them. 892 00:51:33,505 --> 00:51:36,205 NARRATOR: But our solar system only contains 893 00:51:36,205 --> 00:51:39,305 a fraction of the strange worlds out there. 894 00:51:39,305 --> 00:51:42,771 DOUGHERTY: We talk a lot about strange worlds in our solar system, 895 00:51:42,771 --> 00:51:45,171 but there are certainly stranger worlds out there 896 00:51:45,171 --> 00:51:46,438 that we haven't found yet. 897 00:51:46,438 --> 00:51:48,038 NARRATOR: And scientists 898 00:51:48,038 --> 00:51:52,038 will never stop looking for new, weird worlds. 899 00:51:52,038 --> 00:51:54,838 I don't think I'm ever gonna get bored of strange worlds. 900 00:51:54,838 --> 00:51:58,205 There's so much out there to explore and discover. 901 00:51:58,205 --> 00:52:01,138 It's what gets me out of bed every day. 902 00:52:01,138 --> 00:52:04,005 So, the strangeness is only just beginning. 903 00:52:04,005 --> 00:52:09,038 ♪ ♪ 904 00:52:19,705 --> 00:52:23,938 ♪ ♪ 905 00:52:35,171 --> 00:52:38,038 ♪ ♪ 906 00:52:38,971 --> 00:52:46,505 ♪ ♪ 907 00:52:50,338 --> 00:52:57,871 ♪ ♪ 908 00:53:01,771 --> 00:53:09,305 ♪ ♪ 909 00:53:10,938 --> 00:53:18,471 ♪ ♪ 910 00:53:20,105 --> 00:53:27,638 ♪ ♪