1 00:00:01,533 --> 00:00:05,000 NARRATOR: Our solar system is home to eight planets, 2 00:00:05,000 --> 00:00:06,933 near-perfect spheres 3 00:00:06,933 --> 00:00:10,900 spinning through the darkness of space. 4 00:00:13,800 --> 00:00:16,933 But the more we explore, 5 00:00:16,933 --> 00:00:20,966 the more weird and wonderful worlds we discover. 6 00:00:22,633 --> 00:00:24,366 ANJALI TRIPATHI: Our solar system is filled 7 00:00:24,366 --> 00:00:28,700 with these strange worlds that defy all expectations. 8 00:00:28,700 --> 00:00:31,033 NAOMI ROWE-GURNEY: Patchwork worlds that look like they've been 9 00:00:31,033 --> 00:00:33,433 stuck together like Frankenstein monsters. 10 00:00:33,433 --> 00:00:35,166 AMY BARR MLINAR: The images were shocking. 11 00:00:35,166 --> 00:00:38,233 Nobody expected to see enormous ice cliffs 12 00:00:38,233 --> 00:00:40,266 on a moon in the outer solar system. 13 00:00:40,266 --> 00:00:44,600 NARRATOR: Worlds that don't seem to play by the rules. 14 00:00:44,600 --> 00:00:46,266 HAKEEM OLUSEYI: There is so much strange activity 15 00:00:46,266 --> 00:00:50,500 out there in the solar system that we don't understand. 16 00:00:50,500 --> 00:00:52,733 Sometimes it does feel like being a detective, 17 00:00:52,733 --> 00:00:57,033 trying to find out why it's there, what it's doing. 18 00:00:57,033 --> 00:00:58,566 NARRATOR: Each discovery 19 00:00:58,566 --> 00:01:04,266 offers new clues to how our solar system works. 20 00:01:04,266 --> 00:01:06,100 A lot of the weirdness that we find 21 00:01:06,100 --> 00:01:08,466 has something to do with gravity. 22 00:01:08,466 --> 00:01:12,266 NARRATOR: But other forces are also at play. 23 00:01:12,266 --> 00:01:15,766 LYNNAE QUICK: Each planet and each moon in our solar system 24 00:01:15,766 --> 00:01:17,566 are examples of how the rules of physics 25 00:01:17,566 --> 00:01:19,566 can play out differently. 26 00:01:19,566 --> 00:01:21,400 GEOFFREY COLLINS: And sometimes we don't understand 27 00:01:21,400 --> 00:01:24,366 which rules can be broken. 28 00:01:25,933 --> 00:01:30,333 NARRATOR: "Solar System: Strange Worlds." 29 00:01:33,300 --> 00:01:36,266 Right now on "NOVA." 30 00:01:36,266 --> 00:01:38,300 ♪ ♪ 31 00:01:50,633 --> 00:01:54,866 ♪ ♪ 32 00:02:10,366 --> 00:02:15,400 NARRATOR: On the edge of the solar system is the Kuiper Belt. 33 00:02:17,800 --> 00:02:21,966 As we travel farther from the warmth of the sun, 34 00:02:21,966 --> 00:02:26,000 we find a world like no other. 35 00:02:32,400 --> 00:02:33,633 Haumea was a really exciting discovery 36 00:02:33,633 --> 00:02:35,333 because it's a Kuiper Belt object 37 00:02:35,333 --> 00:02:37,533 that doesn't seem to follow any of the rules. 38 00:02:38,633 --> 00:02:40,966 NARRATOR: One of the most basic rules 39 00:02:40,966 --> 00:02:44,600 is that gravity usually shapes planetary bodies like this 40 00:02:44,600 --> 00:02:45,966 into spheres. 41 00:02:48,200 --> 00:02:50,533 The force of gravity is always pulling mass 42 00:02:50,533 --> 00:02:52,100 toward a central point. 43 00:02:52,100 --> 00:02:56,533 A sphere is the shape that packs the most material 44 00:02:56,533 --> 00:02:58,900 closest to the center as possible. 45 00:03:01,833 --> 00:03:06,833 NARRATOR: But Haumea's shape is a little harder to define. 46 00:03:06,833 --> 00:03:09,100 Haumea is shaped sort of like a football. 47 00:03:11,266 --> 00:03:12,500 It's a bit of a stretched egg. 48 00:03:12,500 --> 00:03:15,066 COLLINS: Haumea looks like a rounded pebble 49 00:03:15,066 --> 00:03:16,700 that you would find on the beach. 50 00:03:16,700 --> 00:03:19,833 Haumea is definitely one of the strangest worlds out there. 51 00:03:23,300 --> 00:03:26,833 NARRATOR: And the solar system has even more worlds 52 00:03:26,833 --> 00:03:28,900 that defy our expectations. 53 00:03:33,166 --> 00:03:34,666 COLLINS: As we explore the solar system, 54 00:03:34,666 --> 00:03:38,100 we find more and more bizarre objects out there. 55 00:03:38,100 --> 00:03:39,433 Oh man, I just love everything weird, 56 00:03:39,433 --> 00:03:41,566 and what's weirder than outer space? 57 00:03:41,566 --> 00:03:43,333 No two worlds are the same, 58 00:03:43,333 --> 00:03:46,466 and there's always something new to find. 59 00:03:47,500 --> 00:03:50,400 NARRATOR: Oddly-shaped worlds, 60 00:03:50,400 --> 00:03:54,233 moons that look like they've been torn apart 61 00:03:54,233 --> 00:03:57,500 and strange water worlds. 62 00:03:57,500 --> 00:03:59,366 TRIPATHI: How did we get so many different 63 00:03:59,366 --> 00:04:02,233 and unique worlds in our solar system? 64 00:04:02,233 --> 00:04:04,466 That's the million-dollar question. 65 00:04:04,466 --> 00:04:09,500 ♪ ♪ 66 00:04:14,666 --> 00:04:17,066 (eerie static whirring) 67 00:04:19,433 --> 00:04:21,466 ♪ ♪ 68 00:04:29,866 --> 00:04:33,066 NARRATOR: From a cloud of gas and dust... 69 00:04:36,500 --> 00:04:42,233 ...gravity, the great sculptor of our universe, 70 00:04:42,233 --> 00:04:45,400 fashioned our star 71 00:04:45,400 --> 00:04:47,766 and the planets and moons around it... 72 00:04:55,000 --> 00:04:58,166 ...creating the solar system. 73 00:05:06,033 --> 00:05:07,833 And gravity has continued 74 00:05:07,833 --> 00:05:12,633 to shape these myriad worlds ever since. 75 00:05:12,633 --> 00:05:14,300 But how? 76 00:05:14,300 --> 00:05:17,433 What exactly is gravity? 77 00:05:17,433 --> 00:05:19,533 Michele DOUGHERTY: It depends who you ask. 78 00:05:19,533 --> 00:05:22,833 If you ask Newton, he would say that gravity is a force 79 00:05:22,833 --> 00:05:24,600 that helps pull things together. 80 00:05:24,600 --> 00:05:28,533 It's what's keeping me seated on the Earth at the moment. 81 00:05:28,533 --> 00:05:31,433 QUICK: It builds planets, stars and galaxies 82 00:05:31,433 --> 00:05:34,100 by pulling together the dust and the gas and the rocks 83 00:05:34,100 --> 00:05:35,800 that make them up. 84 00:05:35,800 --> 00:05:40,566 NARRATOR: But Einstein saw it a little differently. 85 00:05:40,566 --> 00:05:43,566 DOUGHERTY: If you asked Einstein, he said 86 00:05:43,566 --> 00:05:48,500 it wasn't a force but that it curved space and time. 87 00:05:48,500 --> 00:05:52,866 Very simply put, space and time were linked to him, 88 00:05:52,866 --> 00:05:54,533 as if they were a fabric. 89 00:05:54,533 --> 00:05:58,100 So any kind of object with mass, uh, would, um, 90 00:05:58,100 --> 00:06:02,133 kind of bend that fabric and, um, things would fall into it. 91 00:06:03,833 --> 00:06:06,166 NARRATOR: At the center of our solar system 92 00:06:06,166 --> 00:06:10,200 is the most massive object in it, our sun, 93 00:06:10,200 --> 00:06:14,666 curving the fabric of space-time around it. 94 00:06:14,666 --> 00:06:17,933 The planets follow this curvature, 95 00:06:17,933 --> 00:06:22,066 creating their orbits. 96 00:06:22,066 --> 00:06:25,100 The sun binds everything in the solar system together 97 00:06:25,100 --> 00:06:27,400 within its gravity, and without that, 98 00:06:27,400 --> 00:06:28,966 uh, there wouldn't be anything. 99 00:06:28,966 --> 00:06:30,300 There wouldn't be a solar system, 100 00:06:30,300 --> 00:06:31,933 and we wouldn't exist, either. 101 00:06:34,500 --> 00:06:36,400 NARRATOR: But gravity is not alone 102 00:06:36,400 --> 00:06:40,166 when it comes to shaping our solar system. 103 00:06:40,166 --> 00:06:42,200 The solar system would be a really boring place 104 00:06:42,200 --> 00:06:44,933 if it was only gravity that was acting on all of these things. 105 00:06:44,933 --> 00:06:49,100 It would mean that everything was spherical and, uh, the same. 106 00:06:50,266 --> 00:06:52,500 QUICK: We see such a variety of shapes 107 00:06:52,500 --> 00:06:55,100 because gravity is not the only force at play. 108 00:06:55,100 --> 00:06:58,100 TRIPATHI: Even though it's counter to what we think about 109 00:06:58,100 --> 00:07:00,400 when we talk about the planets and gravity, 110 00:07:00,400 --> 00:07:03,533 it's actually the weakest force in day-to-day life. 111 00:07:03,533 --> 00:07:08,200 PROUDFOOT: So, although gravity likes making spherical planets, 112 00:07:08,200 --> 00:07:12,200 sometimes rocks are just strong enough to resist gravity. 113 00:07:12,200 --> 00:07:13,866 We don't live in a universe of marbles 114 00:07:13,866 --> 00:07:16,300 because you have to have enough mass 115 00:07:16,300 --> 00:07:19,200 for gravity to pull everything into the spherical shape. 116 00:07:21,166 --> 00:07:24,500 NARRATOR: So how much mass does gravity need 117 00:07:24,500 --> 00:07:27,400 to overcome the strength of rock 118 00:07:27,400 --> 00:07:30,433 and make planets spherical? 119 00:07:36,566 --> 00:07:40,066 James Dottin is a planetary scientist 120 00:07:40,066 --> 00:07:44,033 who studies rocks to understand the evolution of planets. 121 00:07:46,000 --> 00:07:49,066 DOTTIN: Gravity is directly proportional to mass. 122 00:07:49,066 --> 00:07:51,166 The more mass an object has, 123 00:07:51,166 --> 00:07:54,200 the stronger the gravitational force. 124 00:07:54,200 --> 00:07:55,400 So, in order to iron out 125 00:07:55,400 --> 00:07:56,633 all the lumps and bumps 126 00:07:56,633 --> 00:07:58,833 of rocky objects in our solar system, 127 00:07:58,833 --> 00:08:01,900 it requires a lot of gravitational force. 128 00:08:03,566 --> 00:08:05,166   NARRATOR: For a planet's gravity 129 00:08:05,166 --> 00:08:07,300 to overcome the strength of rock, 130 00:08:07,300 --> 00:08:10,400 it must reach a critical size. 131 00:08:12,566 --> 00:08:15,033 We think that, in order for them to form into a sphere, 132 00:08:15,033 --> 00:08:19,166 they need to have a radius of about 200 miles, 133 00:08:19,166 --> 00:08:23,000 so that they're massive enough for gravitational forces 134 00:08:23,000 --> 00:08:25,933 to be strong enough to form them into a sphere. 135 00:08:25,933 --> 00:08:29,233 It's called the potato radius because objects that are smaller 136 00:08:29,233 --> 00:08:31,266 end up looking like potatoes. 137 00:08:33,700 --> 00:08:38,300 NARRATOR: A rocky world with a radius under 200 miles... 138 00:08:39,533 --> 00:08:42,233 ...will tend to be oddly-shaped. 139 00:08:48,133 --> 00:08:53,166 While everything with a radius larger than about 200 miles 140 00:08:53,166 --> 00:08:55,166 is a sphere. 141 00:08:55,166 --> 00:08:59,733 That is, almost everything. 142 00:08:59,733 --> 00:09:03,033 Haumea, out in the depths of the solar system, 143 00:09:03,033 --> 00:09:05,766 is a rule breaker. 144 00:09:06,966 --> 00:09:11,366 This is a world about 1,300 miles long, 145 00:09:11,366 --> 00:09:13,966 1,000 miles wide, 146 00:09:13,966 --> 00:09:17,966 and less than 700 miles high pole to pole... 147 00:09:20,933 --> 00:09:22,466 ...and it isn't alone. 148 00:09:27,266 --> 00:09:33,266 Two icy moons in a thin ring of rock and ice orbit Haumea, 149 00:09:33,266 --> 00:09:37,000 making an unexpected and odd system... 150 00:09:38,100 --> 00:09:43,100 ...the first like it ever discovered. 151 00:09:43,100 --> 00:09:44,633 Haumea was such an exciting discovery 152 00:09:44,633 --> 00:09:46,900 because it's large enough to be round, 153 00:09:46,900 --> 00:09:50,300 but for some strange reason, it's shaped like a football. 154 00:09:51,533 --> 00:09:53,033 NARRATOR: So, if its odd shape 155 00:09:53,033 --> 00:09:57,200 is not due to its size, then what is it? 156 00:09:58,533 --> 00:10:02,600 There is a clue we can see at work here on Earth, 157 00:10:02,600 --> 00:10:05,066 if you know how to look. 158 00:10:08,866 --> 00:10:11,966 We've left this camera out all morning, 159 00:10:11,966 --> 00:10:13,933 fixed on a single point in the sky. 160 00:10:15,766 --> 00:10:19,266 NARRATOR: In this case, the sun, 161 00:10:19,266 --> 00:10:22,766 and that helps to visualize the rotation of the planet. 162 00:10:24,733 --> 00:10:27,566 DOTTIN: Wow. I mean, how cool is that? 163 00:10:27,566 --> 00:10:29,233 Now that's no camera trick, 164 00:10:29,233 --> 00:10:32,266 that's literally the Earth rotating 165 00:10:32,266 --> 00:10:34,833 at about 1,000 miles per hour. 166 00:10:34,833 --> 00:10:39,100 And although that's superfast, I can't feel it, 167 00:10:39,100 --> 00:10:41,800 and that's because everything around me 168 00:10:41,800 --> 00:10:43,800 is rotating with the Earth. 169 00:10:45,400 --> 00:10:49,000 NARRATOR: But even if we cannot feel Earth's rotation 170 00:10:49,000 --> 00:10:51,333 we can still feel the forces created 171 00:10:51,333 --> 00:10:53,833 by a rapidly spinning object. 172 00:10:55,766 --> 00:10:58,300 MLINAR: So a merry-go-round on a playground 173 00:10:58,300 --> 00:11:01,366 is this big spinning disc, it has handles, 174 00:11:01,366 --> 00:11:03,400 you can hold onto it, you get on, 175 00:11:03,400 --> 00:11:05,933 your friends start to spin the merry-go-round faster 176 00:11:05,933 --> 00:11:09,333 and faster and faster, eventually, it goes so fast 177 00:11:09,333 --> 00:11:12,200 that you can't hang on anymore and you kind of fly off. 178 00:11:12,200 --> 00:11:13,600 So when that happens, 179 00:11:13,600 --> 00:11:15,633 you're experiencing centrifugal force. 180 00:11:18,366 --> 00:11:22,766 NARRATOR: And it turns out, Haumea is spinning incredibly quickly. 181 00:11:25,233 --> 00:11:27,700 This world is spinning so fast, 182 00:11:27,700 --> 00:11:32,066 it experiences an entire day and night in under four hours. 183 00:11:34,233 --> 00:11:38,333 It's the fastest known rotating object in the Kuiper Belt. 184 00:11:42,600 --> 00:11:44,566 So if this is our model of Haumea, 185 00:11:44,566 --> 00:11:46,233 gravity is acting to try and make it 186 00:11:46,233 --> 00:11:47,500 into a sphere, 187 00:11:47,500 --> 00:11:49,633 but because Haumea is spinning so quickly, 188 00:11:49,633 --> 00:11:52,500 it actually means that centrifugal forces 189 00:11:52,500 --> 00:11:55,333 can make it propel away from itself. 190 00:11:55,333 --> 00:11:58,433 And you'll notice that it starts to become more egg-shaped 191 00:11:58,433 --> 00:12:00,100 as it spins. 192 00:12:00,100 --> 00:12:01,833 Oh, cool, it's really egg-shaped now. 193 00:12:01,833 --> 00:12:03,833 I'm gonna turn it off before it kills us. 194 00:12:03,833 --> 00:12:05,333 (laughs) 195 00:12:05,333 --> 00:12:09,166 The immensely fast rotation of Haumea spinning around is 196 00:12:09,166 --> 00:12:13,133 what explains the shape that we see as a stretched out oval 197 00:12:13,133 --> 00:12:15,766 as opposed to a perfectly round sphere. 198 00:12:15,766 --> 00:12:17,066 MLINAR: It's just been 199 00:12:17,066 --> 00:12:18,833 forced to deform 200 00:12:18,833 --> 00:12:22,766 into this completely football, egg shape. 201 00:12:22,766 --> 00:12:25,300 It has no choice, it has to be that shape. 202 00:12:27,833 --> 00:12:31,433 NARRATOR: And Haumea's spin may also be responsible 203 00:12:31,433 --> 00:12:34,266 for the formation of the two icy moons 204 00:12:34,266 --> 00:12:36,766 orbiting this strange world. 205 00:12:38,800 --> 00:12:40,600 PROUDFOOT: So most people generally think 206 00:12:40,600 --> 00:12:43,233 that Haumea was formed in a giant collision. 207 00:12:43,233 --> 00:12:47,833 That impact probably got Haumea spinning really, really fast. 208 00:12:47,833 --> 00:12:51,166 When something spins too fast, centrifugal force beats gravity 209 00:12:51,166 --> 00:12:55,000 and things can actually become detached from the body. 210 00:12:55,000 --> 00:12:56,666 So if we go back to the analogy 211 00:12:56,666 --> 00:12:59,166 of kids riding on a merry-go-round, 212 00:12:59,166 --> 00:13:02,100 these would be the kids that fell off the merry-go-round 213 00:13:02,100 --> 00:13:03,400 when it was going too fast. 214 00:13:04,433 --> 00:13:08,800 So that's one way of making tiny little icy moons around Haumea. 215 00:13:10,833 --> 00:13:13,300 NARRATOR: Haumea and its moons formed 216 00:13:13,300 --> 00:13:16,366 in an ongoing battle 217 00:13:16,366 --> 00:13:18,733 with gravity pulling the world together... 218 00:13:20,433 --> 00:13:23,166 ...and its spin pushing it apart. 219 00:13:25,833 --> 00:13:28,500 The battle between these two forces-- 220 00:13:28,500 --> 00:13:33,366 gravity and spin-- creates a truly strange world. 221 00:13:34,866 --> 00:13:36,833 ♪ ♪ 222 00:13:36,833 --> 00:13:40,866 But it isn't the only oddball in our solar system. 223 00:13:40,866 --> 00:13:43,866 Travel in from the Kuiper Belt... 224 00:13:45,166 --> 00:13:47,366 ...past the ice giants... 225 00:13:50,433 --> 00:13:52,833 ...and past Saturn.... 226 00:13:53,866 --> 00:13:55,666 ...and we discover what happens 227 00:13:55,666 --> 00:13:58,133 if we dial up a planet's gravity. 228 00:14:01,533 --> 00:14:05,533 This is a world so enormous 229 00:14:05,533 --> 00:14:08,533 you could fit all the other planets inside it 230 00:14:08,533 --> 00:14:10,366 with room to spare. 231 00:14:11,866 --> 00:14:15,933 And such a gargantuan planet has massive moons 232 00:14:15,933 --> 00:14:19,066 that also feel the effects of Jupiter's pull. 233 00:14:25,166 --> 00:14:27,366 Since 2016, 234 00:14:27,366 --> 00:14:30,733 NASA's Juno spacecraft has been exploring Jupiter 235 00:14:30,733 --> 00:14:32,733 and its many moons... 236 00:14:35,333 --> 00:14:39,633 ...including one unlike any other in the solar system. 237 00:14:46,966 --> 00:14:48,666 SCHENK: Ganymede is really big. 238 00:14:48,666 --> 00:14:50,900 It's about 3,000 miles across. 239 00:14:50,900 --> 00:14:53,133 It's almost as big as the planet Mars. 240 00:14:53,133 --> 00:14:54,866 It's really big. 241 00:14:55,866 --> 00:14:58,033 NARRATOR: But it's not just the size of the moon 242 00:14:58,033 --> 00:15:00,566 that makes Ganymede unusual. 243 00:15:01,633 --> 00:15:04,533 DOUGHERTY: The surface of Ganymede looks 244 00:15:04,533 --> 00:15:07,000 weird in that it's got lots of 245 00:15:07,000 --> 00:15:08,233 craters on the surface. 246 00:15:08,233 --> 00:15:10,900 It's got grooves and cracks 247 00:15:10,900 --> 00:15:12,300 on the surface. 248 00:15:12,300 --> 00:15:14,733 COLLINS: The surface is mostly ice, 249 00:15:14,733 --> 00:15:17,200 in some places there's a thin layer 250 00:15:17,200 --> 00:15:19,566 of rocky dust on top of the ice. 251 00:15:19,566 --> 00:15:21,733 And you might see some icy mountains in the background. 252 00:15:24,400 --> 00:15:27,466 NARRATOR: And above this icy surface, 253 00:15:27,466 --> 00:15:30,700 Juno witnessed strange ribbons of light, 254 00:15:32,500 --> 00:15:34,900 An aurora 255 00:15:34,900 --> 00:15:37,600 dancing above the poles of the moon. 256 00:15:43,133 --> 00:15:45,166 A spectacular light show 257 00:15:45,166 --> 00:15:47,933 that has helped reveal something even stranger 258 00:15:47,933 --> 00:15:49,966 about this world. 259 00:15:54,300 --> 00:15:55,933 We think that Ganymede might have a secret 260 00:15:55,933 --> 00:15:57,366 hiding beneath the surface. 261 00:15:59,566 --> 00:16:02,033 NARRATOR: The aurora above the surface 262 00:16:02,033 --> 00:16:04,000 helps us peer beneath it. 263 00:16:05,900 --> 00:16:08,233 O'DONOGHUE: The aurora of Ganymede are produced when 264 00:16:08,233 --> 00:16:09,966 electrically charged particles are 265 00:16:09,966 --> 00:16:11,833 flowing down magnetic field lines 266 00:16:11,833 --> 00:16:14,500 and they're hitting the atmosphere, 267 00:16:14,500 --> 00:16:16,233 which is made of oxygen 268 00:16:16,233 --> 00:16:18,033 and they're causing it to glow 269 00:16:18,033 --> 00:16:19,866 in green and red lights. 270 00:16:21,233 --> 00:16:23,533 SCHENK: Ganymede's magnetic field is a lot like Earth's. 271 00:16:24,533 --> 00:16:27,300 It's generated by a liquid magnetic 272 00:16:27,300 --> 00:16:28,633 iron core. 273 00:16:28,633 --> 00:16:30,433 If you stood on the surface of Ganymede 274 00:16:30,433 --> 00:16:32,966 with a compass and you looked at it, 275 00:16:32,966 --> 00:16:35,966 the needle of the compass would point to the north pole 276 00:16:35,966 --> 00:16:38,300 of the magnetic field, just like it does on the Earth, 277 00:16:38,300 --> 00:16:40,600 it is the only moon that you can do it on 278 00:16:40,600 --> 00:16:42,600 because it's the only moon in our solar system 279 00:16:42,600 --> 00:16:44,866 that has an internal magnetic field. 280 00:16:46,500 --> 00:16:48,500 NARRATOR: And Ganymede's aurora 281 00:16:48,500 --> 00:16:51,166 rocked back and forth across the moon. 282 00:16:52,333 --> 00:16:54,700 QUICK: Because Jupiter also has a magnetic field 283 00:16:54,700 --> 00:16:57,266 and Ganymede sits within Jupiter's magnetic field, 284 00:16:57,266 --> 00:16:59,100 it should cause Ganymede's aurora 285 00:16:59,100 --> 00:17:00,733 to rock back and forth. 286 00:17:04,900 --> 00:17:06,800 NARRATOR: But when scientists used 287 00:17:06,800 --> 00:17:09,033 the Hubble Space Telescope to look 288 00:17:09,033 --> 00:17:11,366 at Ganymede's aurora, 289 00:17:11,366 --> 00:17:13,433 something didn't add up. 290 00:17:15,033 --> 00:17:17,500 DOUGHERTY: The images of the aurora at Ganymede 291 00:17:17,500 --> 00:17:20,300 showed that they weren't rocking back and forth 292 00:17:20,300 --> 00:17:22,433 as much as we expected them to. 293 00:17:22,433 --> 00:17:24,366 Because the motion of Ganymede's aurora 294 00:17:24,366 --> 00:17:25,933 don't match scientific predictions, 295 00:17:25,933 --> 00:17:28,266 we think there must be something else there 296 00:17:28,266 --> 00:17:30,300 that's affecting them. 297 00:17:33,766 --> 00:17:36,600 NARRATOR: If there were a second magnetic field being generated 298 00:17:36,600 --> 00:17:38,533 within Ganymede, 299 00:17:38,533 --> 00:17:41,000 that would interfere with the aurora, 300 00:17:41,000 --> 00:17:44,033 reducing the rocking. 301 00:17:46,633 --> 00:17:49,666 But the only way to generate that extra field 302 00:17:49,666 --> 00:17:51,866 would be if another layer, 303 00:17:51,866 --> 00:17:55,733 besides the molten core, were conducting electricity. 304 00:17:57,200 --> 00:17:59,866 There has to be something else. 305 00:18:01,800 --> 00:18:02,800 SCHENK: That something else 306 00:18:02,800 --> 00:18:05,133 turns out to be a liquid layer, 307 00:18:05,133 --> 00:18:07,466 an ocean underneath the surface. 308 00:18:07,466 --> 00:18:10,266 Ganymede's internal ocean is damping down 309 00:18:10,266 --> 00:18:12,933 the oscillation that we see. 310 00:18:12,933 --> 00:18:14,500 QUICK: It's extremely cool 311 00:18:14,500 --> 00:18:16,100 that we can tell that there's an ocean 312 00:18:16,100 --> 00:18:17,366 beneath Ganymede's surface, 313 00:18:17,366 --> 00:18:19,733 despite never having a lander there. 314 00:18:24,300 --> 00:18:26,700 NARRATOR: Scientists estimate 315 00:18:26,700 --> 00:18:29,800 Ganymede has a global ocean. 316 00:18:33,300 --> 00:18:35,600 60 miles deep, 317 00:18:35,600 --> 00:18:40,533 hidden beneath around 95 miles of rock-hard ice. 318 00:18:41,500 --> 00:18:42,833 DOUGHERTY: It's pretty mind-blowing, 319 00:18:42,833 --> 00:18:44,000 if you think about it. 320 00:18:44,000 --> 00:18:47,133 This moon out in the outer solar system, 321 00:18:47,133 --> 00:18:49,466 which is much smaller than the Earth, 322 00:18:49,466 --> 00:18:51,966 could potentially have more water within it 323 00:18:51,966 --> 00:18:55,466 than we have in our own oceans on the Earth. 324 00:18:55,466 --> 00:18:58,533 NARRATOR: Of all the water worlds in the solar system, 325 00:18:58,533 --> 00:19:02,000 Ganymede's ocean is the largest. 326 00:19:02,000 --> 00:19:04,666 DOUGHERTY: One of the questions I always ask myself 327 00:19:04,666 --> 00:19:08,400 is how does an icy moon like Ganymede get this huge ocean. 328 00:19:11,366 --> 00:19:14,566 NARRATOR: Strange gouges on the surface of Ganymede 329 00:19:14,566 --> 00:19:17,433 hint at a fascinating theory. 330 00:19:18,433 --> 00:19:20,833 These are impact craters, 331 00:19:20,833 --> 00:19:24,833 not individual ones like we see on most other worlds 332 00:19:24,833 --> 00:19:27,566 but a long chain of them. 333 00:19:29,133 --> 00:19:31,800 To understand how these form, 334 00:19:31,800 --> 00:19:35,533 we have to look back to the monster living next door... 335 00:19:37,033 --> 00:19:39,233 ...Jupiter. 336 00:19:44,533 --> 00:19:46,266 Veronica Bray Durfey 337 00:19:46,266 --> 00:19:50,566 is a planetary scientist who studies impact craters... 338 00:19:51,566 --> 00:19:54,166 ...on the surface of Ganymede. 339 00:19:57,333 --> 00:19:59,700 DURFEY: A lot of planetary science these days is, 340 00:19:59,700 --> 00:20:02,233 you know, I-I wait for the pictures to come back 341 00:20:02,233 --> 00:20:05,100 from spacecraft that have been to the planets. 342 00:20:05,100 --> 00:20:07,466 But there's something a lot more personal 343 00:20:07,466 --> 00:20:09,466 about getting it through a telescope. 344 00:20:09,466 --> 00:20:13,066 And to-to see all of the Galilean moons out tonight, 345 00:20:13,066 --> 00:20:15,800 that's always extra special. 346 00:20:15,800 --> 00:20:19,666 This pinprick of light just on the edge of Jupiter, 347 00:20:19,666 --> 00:20:21,733 that's Ganymede. 348 00:20:21,733 --> 00:20:24,066 It's the biggest of the Galilean moons. 349 00:20:24,066 --> 00:20:26,566 It's the biggest moon in the solar system. 350 00:20:26,566 --> 00:20:28,433 It's bigger than the planet Mercury. 351 00:20:29,400 --> 00:20:31,966 NARRATOR: And Ganymede's location, 352 00:20:31,966 --> 00:20:33,433 orbiting Jupiter, 353 00:20:33,433 --> 00:20:37,766 may play a part in how the moon got its hidden ocean. 354 00:20:43,166 --> 00:20:44,800 Any objects that have mass 355 00:20:44,800 --> 00:20:46,833 will have a force of attraction between them, 356 00:20:46,833 --> 00:20:48,500 and that's gravity. 357 00:20:48,500 --> 00:20:50,166 The larger the mass, 358 00:20:50,166 --> 00:20:52,100 the larger the gravitational attraction 359 00:20:52,100 --> 00:20:53,600 between the two objects. 360 00:20:53,600 --> 00:20:56,000 Because Jupiter's so massive, 361 00:20:56,000 --> 00:20:59,000 it has a really massive gravitational pull. 362 00:20:59,000 --> 00:21:00,900 So this means that it attracts 363 00:21:00,900 --> 00:21:04,666 a lot of bodies of the solar system towards it. 364 00:21:05,733 --> 00:21:08,366 If an asteroid or a comet gets close enough, 365 00:21:08,366 --> 00:21:10,966 it can feel the pull of Jupiter. 366 00:21:12,166 --> 00:21:13,666 COLLINS: So if you're drawn in toward Jupiter 367 00:21:13,666 --> 00:21:16,466 by its gravity and you don't 368 00:21:16,466 --> 00:21:19,800 quite hit Jupiter, but you get very close... 369 00:21:19,800 --> 00:21:21,900 Jupiter's gravity is so strong 370 00:21:21,900 --> 00:21:24,333 that it will start to pull 371 00:21:24,333 --> 00:21:26,333 bodies apart. 372 00:21:27,300 --> 00:21:29,733 SCHENK: We've actually seen the process. 373 00:21:29,733 --> 00:21:31,766 This was back in 1993 374 00:21:31,766 --> 00:21:35,500 when astronomers observed a comet 375 00:21:35,500 --> 00:21:39,633 broken up after a close passage of Jupiter. 376 00:21:39,633 --> 00:21:42,500 And it was called Shoemaker-Levy 9 377 00:21:42,500 --> 00:21:44,733 after the astronomers who discovered it. 378 00:21:44,733 --> 00:21:46,233 COLLINS: It had been disrupted 379 00:21:46,233 --> 00:21:48,000 by Jupiter's gravity into... 380 00:21:48,000 --> 00:21:49,966 a string of objects. 381 00:21:49,966 --> 00:21:52,366 And looking at its orbit, they realized 382 00:21:52,366 --> 00:21:54,033 that it was going to come back 383 00:21:54,033 --> 00:21:57,033 a year later and actually hit Jupiter. 384 00:22:00,433 --> 00:22:03,633 NARRATOR: Watching this series of comet fragments explode 385 00:22:03,633 --> 00:22:06,433 as they hit the dark side of Jupiter 386 00:22:06,433 --> 00:22:08,500 provided scientists with clues 387 00:22:08,500 --> 00:22:11,600 as to how these strange crater chains 388 00:22:11,600 --> 00:22:13,300 were formed on Ganymede. 389 00:22:14,466 --> 00:22:18,033 SCHENK: So on Ganymede we observed these chains of craters, 390 00:22:18,033 --> 00:22:20,166 all nicely lined up in a row, 391 00:22:20,166 --> 00:22:22,066 evenly spaced, very peculiar. 392 00:22:22,066 --> 00:22:25,866 So when we saw the chain of cometary fragments 393 00:22:25,866 --> 00:22:28,500 that make up Shoemaker-Levy 9 394 00:22:28,500 --> 00:22:30,800 and we saw that in 1993, 395 00:22:30,800 --> 00:22:32,433 it suddenly occurred to us, 396 00:22:32,433 --> 00:22:36,233 that same set of cometary fragments, 397 00:22:36,233 --> 00:22:37,833 if it the moon on the way out, 398 00:22:37,833 --> 00:22:40,766 would form a crater chain just like this. 399 00:22:50,566 --> 00:22:54,100 NARRATOR: Ferocious, high energy impacts 400 00:22:54,100 --> 00:22:57,600 create these incredible chains of craters. 401 00:23:02,033 --> 00:23:05,200 But Jupiter's gravity means that so much more 402 00:23:05,200 --> 00:23:08,866 has hit Ganymede than just these torn apart objects. 403 00:23:10,966 --> 00:23:13,133 And it is these violent collisions 404 00:23:13,133 --> 00:23:16,900 that may help explain the moon's vast hidden ocean. 405 00:23:25,133 --> 00:23:28,300 COLLINS: The early history of the solar system was a very chaotic place. 406 00:23:28,300 --> 00:23:31,633 There were more asteroids and comets 407 00:23:31,633 --> 00:23:34,933 flying around, impacts were just 408 00:23:34,933 --> 00:23:36,800 a much more common occurrence. 409 00:23:38,466 --> 00:23:40,766 Nothing was spared the chaos 410 00:23:40,766 --> 00:23:42,900 of the early solar system. 411 00:23:45,000 --> 00:23:48,566 NARRATOR: As Jupiter drew in countless asteroids and comets 412 00:23:48,566 --> 00:23:50,500 with its immense gravity... 413 00:23:51,500 --> 00:23:54,233 ...Ganymede was caught in the crossfire. 414 00:23:58,233 --> 00:24:01,966 Each impact delivers huge amounts of heat 415 00:24:01,966 --> 00:24:04,200 and energy to the early moon. 416 00:24:06,133 --> 00:24:08,466 DURFEY: And this allowed Ganymede to heat up 417 00:24:08,466 --> 00:24:11,300 and some of its components to become molten. 418 00:24:11,300 --> 00:24:13,866 And once you have that molten mix, 419 00:24:13,866 --> 00:24:16,100 you're going to get differentiation. 420 00:24:18,233 --> 00:24:20,100 NARRATOR: Differentiation 421 00:24:20,100 --> 00:24:22,600 is where gravity organizes material 422 00:24:22,600 --> 00:24:24,533 based on its density. 423 00:24:26,900 --> 00:24:29,366 DURFEY: We can visualize this differentiation. 424 00:24:29,366 --> 00:24:34,166 So if this oil is our low density material... 425 00:24:36,333 --> 00:24:37,666 ...we can add 426 00:24:37,666 --> 00:24:39,433 a higher density material. 427 00:24:39,433 --> 00:24:41,066 This sand. 428 00:24:42,666 --> 00:24:44,600 NARRATOR: Shaking the jar lets us imagine 429 00:24:44,600 --> 00:24:47,533 what Ganymede would've been like at the beginning. 430 00:24:49,800 --> 00:24:53,233 A mixture of high and low-density materials. 431 00:24:53,233 --> 00:24:54,900 DURFEY: And then over time 432 00:24:54,900 --> 00:24:57,100 the gravitational pull 433 00:24:57,100 --> 00:24:59,233 will help this separate out. 434 00:24:59,233 --> 00:25:01,266 And so in Ganymede's case, 435 00:25:01,266 --> 00:25:04,700 that is the high-density metals 436 00:25:04,700 --> 00:25:07,500 falling towards its core 437 00:25:07,500 --> 00:25:09,000 and the low-density ices 438 00:25:09,000 --> 00:25:11,700 remaining at its surface. 439 00:25:12,866 --> 00:25:16,733 Differentiation takes millions and millions of years. 440 00:25:16,733 --> 00:25:18,466 But this will not take that long. 441 00:25:19,800 --> 00:25:23,933 NARRATOR: But gravity had one more trick to play. 442 00:25:23,933 --> 00:25:25,200 DURFEY: As the dense material 443 00:25:25,200 --> 00:25:27,200 heads towards the core of Ganymede, 444 00:25:27,200 --> 00:25:30,266 it flows past the less dense material, 445 00:25:30,266 --> 00:25:33,300 and this creates heat through friction, 446 00:25:33,300 --> 00:25:35,766 keeping Ganymede molten for longer 447 00:25:35,766 --> 00:25:38,200 and making its differentiation 448 00:25:38,200 --> 00:25:40,266 almost a self-sustaining system. 449 00:25:42,233 --> 00:25:44,866 NARRATOR: And this continued until Ganymede's interior 450 00:25:44,866 --> 00:25:47,600 separated out into different layers. 451 00:25:49,500 --> 00:25:52,733 MLINAR: So we know that Ganymede got hot enough to melt completely. 452 00:25:52,733 --> 00:25:55,066 And not just to separate the ice 453 00:25:55,066 --> 00:25:56,600 from the rock, 454 00:25:56,600 --> 00:25:58,166 but actually to separate 455 00:25:58,166 --> 00:25:59,433 the metal from the rock 456 00:25:59,433 --> 00:26:01,033 inside of Ganymede, as well. 457 00:26:01,033 --> 00:26:04,333 NARRATOR: And over hundreds of millions of years 458 00:26:04,333 --> 00:26:06,700 the moon started to cool. 459 00:26:06,700 --> 00:26:09,600 MLINAR: What will happen is that the ice 460 00:26:09,600 --> 00:26:11,366 deep inside Ganymede starts 461 00:26:11,366 --> 00:26:14,300 to freeze from below, but it also freezes from above, 462 00:26:14,300 --> 00:26:17,066 and then you get left with this layer 463 00:26:17,066 --> 00:26:19,833 of salty water that just won't freeze. 464 00:26:20,833 --> 00:26:24,166 NARRATOR: But this is just one theory about Ganymede's ocean 465 00:26:24,166 --> 00:26:26,833 and how it got the heat to form. 466 00:26:30,100 --> 00:26:32,100 When I get asked the question will we ever know 467 00:26:32,100 --> 00:26:33,533 exactly what happened at Ganymede, 468 00:26:33,533 --> 00:26:35,666 and the answer's probably no, 469 00:26:35,666 --> 00:26:37,933 we will be able to come up with suggestions 470 00:26:37,933 --> 00:26:39,833 as to what might've happened. 471 00:26:39,833 --> 00:26:43,566 Um, but we'll probably never know it completely. 472 00:26:43,566 --> 00:26:45,200 But to me that's part of what makes it 473 00:26:45,200 --> 00:26:46,833 so interesting to study. 474 00:26:46,833 --> 00:26:48,666 Because there are always new ideas. 475 00:26:48,666 --> 00:26:50,633 There are always new things that we can measure. 476 00:26:50,633 --> 00:26:53,266 Always new techniques that we can try. 477 00:27:00,500 --> 00:27:04,133 NARRATOR: Leaving this hidden ocean world behind, 478 00:27:04,133 --> 00:27:06,366 with its bizarre surface... 479 00:27:09,433 --> 00:27:11,666 ...we head out away from the sun... 480 00:27:14,100 --> 00:27:15,933 ...past Saturn... 481 00:27:17,133 --> 00:27:19,900 ...to see what strange things can happen 482 00:27:19,900 --> 00:27:22,700 when you pair a massive world 483 00:27:22,700 --> 00:27:24,733 with a tiny one. 484 00:27:29,633 --> 00:27:32,233 Uranus is pretty odd to begin with. 485 00:27:35,000 --> 00:27:38,900 The entire planet knocked onto its side, 486 00:27:38,900 --> 00:27:42,100 likely by some massive impact in the past. 487 00:27:43,533 --> 00:27:47,033 But that's nothing compared to how weird 488 00:27:47,033 --> 00:27:49,000 one of its moons is. 489 00:27:53,333 --> 00:27:55,900 GROUND CONTROLLER: Four, three, two, 490 00:27:55,900 --> 00:27:58,333 one. 491 00:27:58,333 --> 00:28:02,033 We have ignition and we have lift off. 492 00:28:03,633 --> 00:28:06,700 NARRATOR: On August 20, 1977, 493 00:28:06,700 --> 00:28:09,433 spacecraft Voyager 2 494 00:28:09,433 --> 00:28:11,800 was launched to explore the outer planets 495 00:28:11,800 --> 00:28:15,333 of the solar system. 496 00:28:15,333 --> 00:28:16,866 The Voyager mission was really exciting, it was... 497 00:28:16,866 --> 00:28:21,366 a rare mission of first exploration. 498 00:28:29,500 --> 00:28:32,066 NARRATOR: And after more than eight years... 499 00:28:33,800 --> 00:28:36,566 ...Voyager 2 reached Uranus. 500 00:28:36,566 --> 00:28:40,233 It was the first, and remains the only spacecraft 501 00:28:40,233 --> 00:28:43,400 to visit this planet and its moons. 502 00:28:44,733 --> 00:28:46,866 COLLINS: And we'll never have that 503 00:28:46,866 --> 00:28:48,833 experience again of seeing those places 504 00:28:48,833 --> 00:28:50,366 for the first time. 505 00:28:52,900 --> 00:28:56,333 NARRATOR: As it flew past Miranda's south pole... 506 00:28:58,900 --> 00:29:02,433 Voyager 2's cameras captured images of one 507 00:29:02,433 --> 00:29:04,600 of the most astonishing surfaces 508 00:29:04,600 --> 00:29:07,033 in the entire solar system. 509 00:29:10,033 --> 00:29:11,866 MLINAR: I think the images of Miranda 510 00:29:11,866 --> 00:29:14,266 were shocking when they came back. 511 00:29:15,266 --> 00:29:17,866 SCHENK: Because we weren't really expecting much. 512 00:29:17,866 --> 00:29:21,000 We were expecting it to be cold and dead. 513 00:29:21,000 --> 00:29:22,400 Not much happening. 514 00:29:22,400 --> 00:29:27,100 And yet there's signs of some kind of activity inside. 515 00:29:28,866 --> 00:29:31,066 It looks like somebody 516 00:29:31,066 --> 00:29:33,466 was making an art project. 517 00:29:33,466 --> 00:29:35,366 Like somebody ripped up 518 00:29:35,366 --> 00:29:36,833 pictures of two different moons 519 00:29:36,833 --> 00:29:38,533 and glued them back together again. 520 00:29:38,533 --> 00:29:41,900 It didn't look real to me the first time I saw it. 521 00:29:43,466 --> 00:29:47,466 NARRATOR: Scientists spotted plunging canyons. 522 00:29:47,466 --> 00:29:50,033 With cliffs taller than Mount Everest. 523 00:29:50,033 --> 00:29:53,766 And ridged patches that punctuate the surface. 524 00:29:57,300 --> 00:30:01,633 All on a moon only 293 miles in diameter. 525 00:30:02,666 --> 00:30:04,666 Less than the width of Arizona. 526 00:30:06,766 --> 00:30:08,833 MLINAR: It raised a lot of questions 527 00:30:08,833 --> 00:30:12,433 as to what's going on, on those small icy moons? 528 00:30:12,433 --> 00:30:15,200 SCHENK: It was a real resetting event. 529 00:30:15,200 --> 00:30:17,766 It told us that, you know, small bodies can be 530 00:30:17,766 --> 00:30:20,666 very interesting and dynamic, too. 531 00:30:20,666 --> 00:30:22,200 And we had to sort of go back 532 00:30:22,200 --> 00:30:24,366 and understand why that was the case. 533 00:30:26,566 --> 00:30:29,400 NARRATOR: The moon's size offers a clue. 534 00:30:30,666 --> 00:30:32,966 MLINAR: So Miranda is much, much smaller than the Earth. 535 00:30:32,966 --> 00:30:35,633 So the surface gravity on Miranda is about... 536 00:30:35,633 --> 00:30:38,066 1/100th that on the surface of the Earth. 537 00:30:39,633 --> 00:30:42,566 NARRATOR: And that means the cliffs can soar 538 00:30:42,566 --> 00:30:44,933 to unbelievable heights. 539 00:30:44,933 --> 00:30:47,500 QUICK: Miranda's tallest cliff is pretty high 540 00:30:47,500 --> 00:30:49,366 compared to its overall size. 541 00:30:49,366 --> 00:30:51,233 The tallest cliff is six miles high. 542 00:30:51,233 --> 00:30:53,033 That's equivalent to 2% 543 00:30:53,033 --> 00:30:54,566 of Miranda's diameter. 544 00:30:56,633 --> 00:30:58,933   NARRATOR: That would be like Earth having a cliff 545 00:30:58,933 --> 00:31:01,733 160 miles high. 546 00:31:01,733 --> 00:31:03,500 QUICK: The reason that Earth's tallest mountain 547 00:31:03,500 --> 00:31:05,600 is only five and a half miles tall 548 00:31:05,600 --> 00:31:07,766 is because Earth is more massive and because it's 549 00:31:07,766 --> 00:31:10,000 more massive, it has much stronger gravity, 550 00:31:10,000 --> 00:31:11,933 and gravity won't allow 551 00:31:11,933 --> 00:31:14,733 mountains or cliffs to grow that tall on Earth. 552 00:31:20,633 --> 00:31:22,600 NARRATOR: Like other worlds, 553 00:31:22,600 --> 00:31:26,300 Miranda suffers the occasional meteorite strike. 554 00:31:29,966 --> 00:31:32,333 But because of its weak gravity... 555 00:31:33,300 --> 00:31:36,300 ...the results play out in slow motion. 556 00:31:41,100 --> 00:31:43,733 With the debris taking over eight minutes 557 00:31:43,733 --> 00:31:47,100 to fall the height of its tallest cliffs. 558 00:31:54,033 --> 00:31:55,833 Compare that to Earth, 559 00:31:55,833 --> 00:31:59,366 where the same drop would take less than a minute. 560 00:32:02,633 --> 00:32:04,933 COLLINS: Jumping on Miranda would be a lot of fun. 561 00:32:04,933 --> 00:32:07,366 You could jump really high in the air 562 00:32:07,366 --> 00:32:09,966 because gravity is so low. 563 00:32:09,966 --> 00:32:12,700 In fact, just trying to walk normally would be difficult. 564 00:32:14,266 --> 00:32:17,166 NARRATOR: There are countless other small, icy worlds 565 00:32:17,166 --> 00:32:20,133 also with weak gravity, 566 00:32:20,133 --> 00:32:24,666 but we've only seen strange patches like this on Miranda. 567 00:32:26,200 --> 00:32:28,833 So where did this weird patchwork surface 568 00:32:28,833 --> 00:32:30,966 come from in the first place? 569 00:32:33,000 --> 00:32:37,066 All scientists have to go on are those images... 570 00:32:38,700 --> 00:32:44,333 ...grabbed in 1986 as Voyager 2 streaked past. 571 00:32:46,733 --> 00:32:48,866 SCHENK: One of the keys to understanding Miranda 572 00:32:48,866 --> 00:32:51,233 is to recognize that there is actually order 573 00:32:51,233 --> 00:32:53,633 to this apparently chaotic picture. 574 00:32:53,633 --> 00:32:57,400 COLLINS: You've got this ancient, cratered terrain over here 575 00:32:57,400 --> 00:33:02,500 and then these patches like here, here and up here 576 00:33:02,500 --> 00:33:04,166 that we call coronae. 577 00:33:05,133 --> 00:33:09,533 NARRATOR: Where regions of Miranda's surface have been remade. 578 00:33:09,533 --> 00:33:11,766 COLLINS: And inside that patch, 579 00:33:11,766 --> 00:33:13,666 you see are these ridges and troughs 580 00:33:13,666 --> 00:33:16,000 that are like stretch marks on the surfaces. 581 00:33:17,433 --> 00:33:20,400 NARRATOR: It looks as if the surface has been ripped apart... 582 00:33:21,533 --> 00:33:26,366 ...suggesting these scars were formed by internal forces. 583 00:33:29,200 --> 00:33:30,833 COLLINS: If you had some kind of 584 00:33:30,833 --> 00:33:33,033 warm material inside Miranda, 585 00:33:33,033 --> 00:33:36,000 it's less dense and it starts rising up 586 00:33:36,000 --> 00:33:37,833 uh, in a big blob. 587 00:33:37,833 --> 00:33:39,900 And as it comes up toward the surface, 588 00:33:39,900 --> 00:33:42,533 it pushes the material out of its way... 589 00:33:43,733 --> 00:33:45,933 ...ripping the surface apart. 590 00:33:45,933 --> 00:33:48,233 QUICK: It cracks and it fractures open 591 00:33:48,233 --> 00:33:50,233 and we're left with a corona. 592 00:33:52,966 --> 00:33:56,366 NARRATOR: This left hundreds of miles of canyons... 593 00:33:57,633 --> 00:34:00,700 ...where the surface cracked open along fault lines... 594 00:34:01,666 --> 00:34:04,900 ...creating this incredible landscape. 595 00:34:08,233 --> 00:34:09,900 I think since the Voyager images came back 596 00:34:09,900 --> 00:34:11,966 people have been wondering 597 00:34:11,966 --> 00:34:14,533 how a body so small could be so active. 598 00:34:14,533 --> 00:34:16,600 Small bodies lose their heat rapidly, 599 00:34:16,600 --> 00:34:18,133 so we were expecting it to 600 00:34:18,133 --> 00:34:21,000 not have any real geologic history. 601 00:34:21,766 --> 00:34:23,033 COLLINS: So the big question is, 602 00:34:23,033 --> 00:34:24,500 where did the heat come from 603 00:34:24,500 --> 00:34:26,933 to drive the creation of this bizarre landscape? 604 00:34:29,233 --> 00:34:33,100 NARRATOR: For that, we have to look to Miranda's history. 605 00:34:34,433 --> 00:34:37,900 Our best theory involves the moon's giant parent planet, 606 00:34:37,900 --> 00:34:39,000 Uranus... 607 00:34:39,966 --> 00:34:42,333 ...and another quirk of gravity. 608 00:34:43,666 --> 00:34:44,966 QUICK: Billions of years ago, 609 00:34:44,966 --> 00:34:46,966 Miranda had a more eccentric orbit. 610 00:34:46,966 --> 00:34:51,266 And what that means is that when Miranda orbited Uranus, 611 00:34:51,266 --> 00:34:52,633 it wasn't a perfect circle, 612 00:34:52,633 --> 00:34:54,466 it was more in the shape of an ellipse. 613 00:34:54,466 --> 00:34:56,000 So, when Miranda 614 00:34:56,000 --> 00:34:58,266 is very, very close to Uranus, 615 00:34:58,266 --> 00:34:59,933 the gravity from Uranus 616 00:34:59,933 --> 00:35:02,700 sort of deforms it into more like an egg shape. 617 00:35:02,700 --> 00:35:05,500 And then when Miranda's farther away, it's more round. 618 00:35:05,500 --> 00:35:08,333 And that stretching and squeezing 619 00:35:08,333 --> 00:35:10,700 causes a lot of friction on the inside 620 00:35:10,700 --> 00:35:12,600 and that friction results in heat, 621 00:35:12,600 --> 00:35:14,266 which we call tidal heating. 622 00:35:15,933 --> 00:35:18,033 NARRATOR: And it's this tidal heating 623 00:35:18,033 --> 00:35:20,366 that drives Miranda's geology 624 00:35:20,366 --> 00:35:22,266 and forms the coronae. 625 00:35:25,066 --> 00:35:27,100 SCHENK: Not only is the gravity responsible 626 00:35:27,100 --> 00:35:28,600 for bringing the material together 627 00:35:28,600 --> 00:35:31,833 that created Miranda in the first place, 628 00:35:31,833 --> 00:35:33,866 but because of its gravitational interaction 629 00:35:33,866 --> 00:35:39,633 with Uranus, it's also responsible for the energy 630 00:35:39,633 --> 00:35:41,233 that remade Miranda later on. 631 00:35:42,533 --> 00:35:46,233 NARRATOR: Today, Miranda has a nearly circular orbit. 632 00:35:46,233 --> 00:35:49,500 And scientists think that heat is mostly gone. 633 00:35:50,433 --> 00:35:51,966 QUICK: Because Miranda's so small, 634 00:35:51,966 --> 00:35:53,466 it would've been difficult for it to hold onto 635 00:35:53,466 --> 00:35:54,833 its heat for a long time. 636 00:35:54,833 --> 00:35:57,666 But the Uranus system is not very well explored. 637 00:35:57,666 --> 00:35:59,400 There are a lot of things we don't understand 638 00:35:59,400 --> 00:36:01,700 about Uranus and its moons. 639 00:36:01,700 --> 00:36:04,233 And we should prepare to be surprised 640 00:36:04,233 --> 00:36:05,900 next time we go back. 641 00:36:07,333 --> 00:36:08,966 NARRATOR: Though now frozen, 642 00:36:08,966 --> 00:36:11,166 Miranda reveals how small worlds 643 00:36:11,166 --> 00:36:15,466 can be shaped through gravity by larger ones. 644 00:36:17,300 --> 00:36:21,233 But traveling inwards towards the sun, we see evidence 645 00:36:21,233 --> 00:36:25,366 that small worlds can also leave a big mark of their own. 646 00:36:27,766 --> 00:36:32,000 On one of the most spectacular structures in the solar system. 647 00:36:39,333 --> 00:36:42,633 Glimmering rings of rock and ice... 648 00:36:43,600 --> 00:36:47,033 ...they are one of the hallmarks of our cosmic neighborhood. 649 00:36:51,766 --> 00:36:54,300 And when examined more closely, 650 00:36:54,300 --> 00:36:57,833 show signs of remarkable organization. 651 00:36:59,166 --> 00:37:03,766 Lumps of ice and rock spread out in a thin disc, 652 00:37:03,766 --> 00:37:08,333 split into hundreds of repeating tracks and gaps 653 00:37:08,333 --> 00:37:10,500 that look like grooves on a record. 654 00:37:11,566 --> 00:37:14,766 Looping for hundreds of thousands of miles 655 00:37:14,766 --> 00:37:15,800 through space. 656 00:37:18,066 --> 00:37:21,500 Saturn's rings are amazingly complex. 657 00:37:21,500 --> 00:37:22,933 And the more we zoom into them, 658 00:37:22,933 --> 00:37:25,000 the more complex seem to be. 659 00:37:25,966 --> 00:37:28,766 It is one of the wonders of the solar system. 660 00:37:35,166 --> 00:37:38,466 NARRATOR: Scientists think the rings may have first formed 661 00:37:38,466 --> 00:37:41,833 when a moon strayed too close to Saturn... 662 00:37:42,833 --> 00:37:46,133 ...and was pulled apart by its gravity... 663 00:37:48,333 --> 00:37:50,233 ...creating a jumble of trillions 664 00:37:50,233 --> 00:37:54,100 of individual fragments of rock and ice. 665 00:38:00,133 --> 00:38:02,400 So what turns such chaos 666 00:38:02,400 --> 00:38:05,866 into the ordered beauty we see today? 667 00:38:10,033 --> 00:38:11,966 NASA's Cassini spacecraft 668 00:38:11,966 --> 00:38:16,666 gave us the best view of the rings we've ever had. 669 00:38:16,666 --> 00:38:18,333 OLUSEYI: The photographs from Cassini 670 00:38:18,333 --> 00:38:21,066 gave us Saturn's rings at all angles. 671 00:38:21,066 --> 00:38:24,600   We saw them reflecting light from the sun, 672 00:38:24,600 --> 00:38:27,700 we saw Cassini look through them toward the sun. 673 00:38:27,700 --> 00:38:31,166 Just the spectacular beauty of them. 674 00:38:31,166 --> 00:38:33,133 Just mind-blowing. 675 00:38:34,066 --> 00:38:38,966 NARRATOR: And lurking among the loops of rock and ice... 676 00:38:38,966 --> 00:38:43,500 Cassini imaged one of the most startling moons 677 00:38:43,500 --> 00:38:45,333 in the entire Saturn system. 678 00:38:54,233 --> 00:38:57,200 EL MOUTAMID: So, Pan is this weird, tiny object. 679 00:38:57,200 --> 00:39:00,600 It is only 17 miles across. 680 00:39:00,600 --> 00:39:03,466 And it looks, for me, like a walnut. 681 00:39:03,466 --> 00:39:07,033 And, uh, it looks like it has a dusting of material around it 682 00:39:07,033 --> 00:39:09,400 that could easily break off if you were to touch it. 683 00:39:11,266 --> 00:39:15,733 NARRATOR: Despite its small size, Pan has a big impact 684 00:39:15,733 --> 00:39:17,733 on the structure of the rings. 685 00:39:19,033 --> 00:39:22,800 BROOKS: Pan is a great example of how gravitational interactions 686 00:39:22,800 --> 00:39:24,033 can shape Saturn's rings 687 00:39:24,033 --> 00:39:25,866 and create the gaps that we see. 688 00:39:28,600 --> 00:39:32,366 NARRATOR: Pan orbits inside a wide track within Saturn's rings 689 00:39:32,366 --> 00:39:34,133 called the Encke Gap. 690 00:39:36,166 --> 00:39:39,133 EL MOUTAMID: We think Pan created the Encke Gap 691 00:39:39,133 --> 00:39:42,333 by cleaning the orbit and by accumulating 692 00:39:42,333 --> 00:39:46,700 all this ring material, dust and ice, around it. 693 00:39:46,700 --> 00:39:49,333 O'DONOGHUE: This ring material has settled 694 00:39:49,333 --> 00:39:50,600 specifically on Pan's equator 695 00:39:50,600 --> 00:39:53,233 again and again and again and that meant 696 00:39:53,233 --> 00:39:56,566 there is this large, uh, ridge around Pan itself. 697 00:39:56,566 --> 00:39:58,833 OLUSEYI: It looks like an empanada 698 00:39:58,833 --> 00:40:00,233 because so much water and ice from the rings 699 00:40:00,233 --> 00:40:02,266 have built up around its equator. 700 00:40:05,166 --> 00:40:06,866 NARRATOR: For millions of years, 701 00:40:06,866 --> 00:40:09,900 Pan has been nibbling away, 702 00:40:09,900 --> 00:40:12,700 clearing particles out of its orbit... 703 00:40:13,766 --> 00:40:16,433 ...and creating this pathway... 704 00:40:17,400 --> 00:40:20,966 ...only that can't be the full story. 705 00:40:24,966 --> 00:40:28,766 Pan is just 17 miles across, 706 00:40:28,766 --> 00:40:31,300 yet it orbits within the Encke Gap 707 00:40:31,300 --> 00:40:33,566 that's 200 miles wide... 708 00:40:37,966 --> 00:40:40,666 ...far broader than Pan could clear 709 00:40:40,666 --> 00:40:42,900 through simply snacking alone. 710 00:40:45,466 --> 00:40:48,400 So the big question is, how can a small moon like Pan 711 00:40:48,400 --> 00:40:51,033 carve out such a huge gap in Saturn's rings? 712 00:40:51,033 --> 00:40:53,733 In addition to sweeping up ring particles, 713 00:40:53,733 --> 00:40:56,400 Pan also managed to open up the Encke Gap 714 00:40:56,400 --> 00:40:59,700 by pushing away the particles on either side of the gap 715 00:40:59,700 --> 00:41:02,000 through gravitational interactions. 716 00:41:04,833 --> 00:41:09,366 NARRATOR: This turns out to be a quirk of orbital physics. 717 00:41:09,366 --> 00:41:12,333 If a particle of ice gets close to Pan, 718 00:41:12,333 --> 00:41:16,066 the moon's gravity gives it a tug, 719 00:41:16,066 --> 00:41:19,400 speeding the particle up or slowing it down. 720 00:41:21,166 --> 00:41:24,400 That moves it to a new orbit, 721 00:41:24,400 --> 00:41:27,166 clearing a path through the rings. 722 00:41:28,800 --> 00:41:30,900 And Pan is not alone. 723 00:41:32,233 --> 00:41:36,366 The Cassini spacecraft also spotted tiny Daphnis... 724 00:41:38,166 --> 00:41:40,333 ...just five miles across, 725 00:41:40,333 --> 00:41:43,000 clearing its own gap in the rings. 726 00:41:46,800 --> 00:41:52,700 Even tiny, odd worlds can create structures of staggering scale. 727 00:41:56,300 --> 00:41:58,900 But not all the gaps have moons embedded in them, 728 00:41:58,900 --> 00:42:01,966 including one of the biggest, 729 00:42:01,966 --> 00:42:05,033 the massive Cassini Division, 730 00:42:05,033 --> 00:42:07,633 almost 3,000 miles wide. 731 00:42:12,366 --> 00:42:15,600 So how did these gaps in the rings form 732 00:42:15,600 --> 00:42:18,266 without a moon inside clearing the way? 733 00:42:29,300 --> 00:42:32,300 James O'Donoghue is a planetary scientist 734 00:42:32,300 --> 00:42:34,500 who studies Saturn and its rings. 735 00:42:42,166 --> 00:42:44,200 O'DONOGHUE: Saturn's rings are an amazing example 736 00:42:44,200 --> 00:42:47,033 of the most beautiful and complex patterns 737 00:42:47,033 --> 00:42:49,333 being produced by a single event 738 00:42:49,333 --> 00:42:51,633 occurring over time again and again. 739 00:42:51,633 --> 00:42:54,766 We see these patterns occurring all across nature 740 00:42:54,766 --> 00:42:56,300 in various forms, as we can see here, 741 00:42:56,300 --> 00:42:59,833 with ripples running across these sand dunes. 742 00:42:59,833 --> 00:43:02,233 The ripples form when the wind 743 00:43:02,233 --> 00:43:04,666 is gliding over the surface of the sand dunes, 744 00:43:04,666 --> 00:43:07,100 and it's lifting up small pieces of sand 745 00:43:07,100 --> 00:43:09,233 and bouncing them along the surface. 746 00:43:12,300 --> 00:43:14,666 NARRATOR: When the bouncing grains hit the surface, 747 00:43:14,666 --> 00:43:17,233 they kick up more grains. 748 00:43:18,166 --> 00:43:21,133 And as this process repeats, 749 00:43:21,133 --> 00:43:22,800 the ripples form. 750 00:43:25,133 --> 00:43:27,600 And just like wind creates structure 751 00:43:27,600 --> 00:43:29,700 in these sandy dunes, 752 00:43:29,700 --> 00:43:32,933 over 700 million miles away, 753 00:43:32,933 --> 00:43:35,433 in the Saturn system, 754 00:43:35,433 --> 00:43:38,900 regular, repeating gravitational interactions 755 00:43:38,900 --> 00:43:42,166 form the structures of the rings. 756 00:43:44,733 --> 00:43:46,166 O'DONOGHUE: This is Saturn and its rings-- 757 00:43:46,166 --> 00:43:48,266 it's not to scale-- and we also have 758 00:43:48,266 --> 00:43:50,033 a selection of moons. 759 00:43:50,033 --> 00:43:53,500 Here is Pan and here is Pandora, 760 00:43:53,500 --> 00:43:56,000 and we also have the moon Mimas. 761 00:43:56,000 --> 00:43:57,433 And we also have Titan, 762 00:43:57,433 --> 00:43:59,200 which is 50% larger than our moon, 763 00:43:59,200 --> 00:44:01,433 which is much further out. 764 00:44:01,433 --> 00:44:03,733 Saturn has over 140 moons. 765 00:44:03,733 --> 00:44:07,433 We only show four here because it would be too busy, 766 00:44:07,433 --> 00:44:08,466 and they interact 767 00:44:08,466 --> 00:44:09,500 with each other gravitationally, 768 00:44:09,500 --> 00:44:10,833 in a really complex way, 769 00:44:10,833 --> 00:44:14,333 and it weirdly leads to a lot of order. 770 00:44:17,166 --> 00:44:19,933 NARRATOR: One of these moons, Mimas, 771 00:44:19,933 --> 00:44:22,633 which has more than a passing resemblance 772 00:44:22,633 --> 00:44:25,033 to the Death Star from "Star Wars," 773 00:44:25,033 --> 00:44:27,000 creates the Cassini Division, 774 00:44:27,000 --> 00:44:31,166 despite being around 40,000 miles away from it. 775 00:44:34,233 --> 00:44:38,100 And it does this all thanks to gravity. 776 00:44:41,966 --> 00:44:44,366 O'DONOGHUE: The Cassini Division is the biggest gap in the rings, 777 00:44:44,366 --> 00:44:46,866 and it's produced by a gravitational interaction 778 00:44:46,866 --> 00:44:49,300 between Mimas and the ring particles 779 00:44:49,300 --> 00:44:50,500 around about here. 780 00:44:51,433 --> 00:44:54,833 NARRATOR: Mimas is in a two to one orbital resonance 781 00:44:54,833 --> 00:44:57,900 with the ring particles of rock and ice 782 00:44:57,900 --> 00:45:00,500 that would be found in the Cassini Division. 783 00:45:01,500 --> 00:45:02,933 O'DONOGHUE: And what that means is 784 00:45:02,933 --> 00:45:05,666 that Mimas, for every one orbit 785 00:45:05,666 --> 00:45:08,433 that it makes around the planet, 786 00:45:08,433 --> 00:45:10,933 the ring particle makes two. 787 00:45:13,666 --> 00:45:15,100 And because these are in resonance, 788 00:45:15,100 --> 00:45:16,400 every time Mimas 789 00:45:16,400 --> 00:45:17,966 and the ring particle meet, 790 00:45:17,966 --> 00:45:21,933 they actually meet at the same point in space around Saturn, 791 00:45:21,933 --> 00:45:23,733 and Mimas implants a gravitational tug 792 00:45:23,733 --> 00:45:27,033 onto the ring particle, which changes its orbit. 793 00:45:29,366 --> 00:45:33,033 NARRATOR: And Mimas has this gravitational relationship, 794 00:45:33,033 --> 00:45:36,266 not with just a single ring particle, 795 00:45:36,266 --> 00:45:39,566 but all the ring particles in the same orbit. 796 00:45:41,266 --> 00:45:45,700 Each time the moon and the ring particles align, 797 00:45:45,700 --> 00:45:50,100 Mimas's gravity tugs at the fragments of ice and rock, 798 00:45:50,100 --> 00:45:52,233 like an invisible hand... 799 00:45:55,133 --> 00:45:57,533 ...opening up the giant gap. 800 00:46:02,600 --> 00:46:05,400 And there are more moons sitting outside the main rings 801 00:46:05,400 --> 00:46:07,966 creating structures within them. 802 00:46:11,266 --> 00:46:13,333 EL MOUTAMID: It is fascinating that, 803 00:46:13,333 --> 00:46:16,033 even if the moons are far away from the ring, 804 00:46:16,033 --> 00:46:18,333 they still have an impact on the ring, 805 00:46:18,333 --> 00:46:21,533 and this is the magic of gravity. 806 00:46:21,533 --> 00:46:24,133 Gravity is the main force, 807 00:46:24,133 --> 00:46:26,900 that it is shaping everything in universe, 808 00:46:26,900 --> 00:46:30,733 including the Saturnian system. 809 00:46:36,633 --> 00:46:39,666 NARRATOR: The orbital dance of Saturn's moons 810 00:46:39,666 --> 00:46:42,966 create the constantly changing 811 00:46:42,966 --> 00:46:45,866 and dynamic pattern within the rings. 812 00:46:47,866 --> 00:46:50,933 One we are lucky to see. 813 00:47:00,400 --> 00:47:04,333 Saturn's rings allow us to see gravity at work, 814 00:47:04,333 --> 00:47:07,733 constantly shaping our solar system. 815 00:47:10,100 --> 00:47:14,033 But leave these beautiful patterns behind... 816 00:47:15,166 --> 00:47:17,500 ...and we see how a planet's size 817 00:47:17,500 --> 00:47:19,633 and the influence of gravity 818 00:47:19,633 --> 00:47:22,633 can have astonishing consequences for life. 819 00:47:28,566 --> 00:47:32,400 More than half a billion miles closer to the sun... 820 00:47:33,466 --> 00:47:36,000 ...through the asteroid belt, 821 00:47:36,000 --> 00:47:37,400 rubble left over 822 00:47:37,400 --> 00:47:40,966 when gravity failed to pull a planet together, 823 00:47:40,966 --> 00:47:44,433 and we reach the inner rocky worlds 824 00:47:44,433 --> 00:47:48,400 where we find perhaps the most bizarre world of all. 825 00:47:51,466 --> 00:47:56,066 A true outlier unlike anything else. 826 00:48:03,066 --> 00:48:06,766 Our solar system's beautiful blue marble. 827 00:48:07,633 --> 00:48:08,833 TRIPATHI: We're living in this 828 00:48:08,833 --> 00:48:11,066 amazing period of the Earth's history 829 00:48:11,066 --> 00:48:14,266 when we have liquid water in the form of oceans 830 00:48:14,266 --> 00:48:15,666 on the surface of our planet, 831 00:48:15,666 --> 00:48:17,700   and that is remarkably unique across, 832 00:48:17,700 --> 00:48:20,533 not only the solar system, 833 00:48:20,533 --> 00:48:22,300 but the thousands of other planets 834 00:48:22,300 --> 00:48:23,366 we've discovered to date. 835 00:48:26,166 --> 00:48:29,600 NARRATOR: The fact that Earth has oceans on the surface 836 00:48:29,600 --> 00:48:31,300 turns out to be, again, 837 00:48:31,300 --> 00:48:34,866 thanks in part to gravity, 838 00:48:34,866 --> 00:48:37,266 which pulls down on the atmosphere. 839 00:48:39,266 --> 00:48:41,933 ROWE-GURNEY: So our atmosphere is made up of lots of gasses, 840 00:48:41,933 --> 00:48:44,866 and that gas exerts a pressure 841 00:48:44,866 --> 00:48:46,833 on the surface of the Earth, 842 00:48:46,833 --> 00:48:49,433 and that pressure stops water 843 00:48:49,433 --> 00:48:51,700 from evaporating into space. 844 00:48:55,866 --> 00:48:58,666 NARRATOR: But if Earth were smaller, 845 00:48:58,666 --> 00:49:01,933 it might have been a different story. 846 00:49:03,266 --> 00:49:06,300 TRIPATHI: If it was much smaller, it wouldn't have enough mass, 847 00:49:06,300 --> 00:49:10,100 and, therefore, enough gravity to hold on to an atmosphere. 848 00:49:10,100 --> 00:49:12,200 We're lucky to live on a rocky planet 849 00:49:12,200 --> 00:49:15,400 that is large enough to keep its atmosphere in place. 850 00:49:17,066 --> 00:49:19,200 NARRATOR: With little to no atmosphere 851 00:49:19,200 --> 00:49:21,266 to press down on the oceans... 852 00:49:22,266 --> 00:49:25,866 ...water would boil at much lower temperatures, 853 00:49:25,866 --> 00:49:30,700 and Earth would become a desolate, barren ball. 854 00:49:33,000 --> 00:49:34,433 ROWE-GURNEY: So, without the atmosphere, 855 00:49:34,433 --> 00:49:36,566 Earth wouldn't have life on it, 856 00:49:36,566 --> 00:49:39,633 uh, and we wouldn't have the ability to breathe, 857 00:49:39,633 --> 00:49:41,900 um, there wouldn't be oceans, 858 00:49:41,900 --> 00:49:44,466 uh, and forests and trees. 859 00:49:44,466 --> 00:49:46,133 Uh, we wouldn't have anything 860 00:49:46,133 --> 00:49:48,066 like the Earth that we know today. 861 00:49:52,166 --> 00:49:56,366 NARRATOR: Earth's size has helped shape its destiny. 862 00:49:56,366 --> 00:49:58,366 Too small, 863 00:49:58,366 --> 00:50:01,300 and Earth could've been a misshapen potato 864 00:50:01,300 --> 00:50:02,866 with no atmosphere. 865 00:50:02,866 --> 00:50:04,733 Too big, 866 00:50:04,733 --> 00:50:07,433 about ten times its current mass, 867 00:50:07,433 --> 00:50:10,566 it could've grown to become a gas giant... 868 00:50:11,600 --> 00:50:14,666 ...with little hope for life as we know it. 869 00:50:15,966 --> 00:50:17,533 It turns out, 870 00:50:17,533 --> 00:50:21,000 life can run riot across the surface of the planet... 871 00:50:22,700 --> 00:50:25,800 ...because Earth is the right size 872 00:50:25,800 --> 00:50:29,500 with just the right amount of gravity. 873 00:50:34,533 --> 00:50:38,466 The same force that has helped shape all the other 874 00:50:38,466 --> 00:50:40,400 radically different, 875 00:50:40,400 --> 00:50:43,533 wonderfully strange worlds out there. 876 00:50:45,500 --> 00:50:48,766 The more we go out and visit our solar system in detail, 877 00:50:48,766 --> 00:50:53,033 the more we discover things we've never seen before. 878 00:50:53,033 --> 00:50:55,566 SCHENK: We're not entirely sure why we see so many 879 00:50:55,566 --> 00:50:57,833 different sizes and shapes 880 00:50:57,833 --> 00:51:00,266 and complexity of planetary bodies, 881 00:51:00,266 --> 00:51:02,833 uh, but we think that gravity 882 00:51:02,833 --> 00:51:05,300 has a very strong role to play in it. 883 00:51:06,500 --> 00:51:09,933 Without gravity, the universe would be a pretty boring place. 884 00:51:09,933 --> 00:51:13,366 It's gravity that assembles 885 00:51:13,366 --> 00:51:14,600 the materials of the universe 886 00:51:14,600 --> 00:51:16,666 into the large structures that we see. 887 00:51:17,666 --> 00:51:19,366 TRIPATHI: Gravity is the backdrop 888 00:51:19,366 --> 00:51:22,500 that's setting the stage for other forces to get to work. 889 00:51:24,600 --> 00:51:27,466 ROWE-GURNEY: We need to study these strange worlds in the solar system 890 00:51:27,466 --> 00:51:29,733 because, without them, we wouldn't understand 891 00:51:29,733 --> 00:51:32,200 how all of these forces come together to create them. 892 00:51:33,500 --> 00:51:36,200 NARRATOR: But our solar system only contains 893 00:51:36,200 --> 00:51:39,300 a fraction of the strange worlds out there. 894 00:51:39,300 --> 00:51:42,766 DOUGHERTY: We talk a lot about strange worlds in our solar system, 895 00:51:42,766 --> 00:51:45,166 but there are certainly stranger worlds out there 896 00:51:45,166 --> 00:51:46,433 that we haven't found yet. 897 00:51:46,433 --> 00:51:48,033 NARRATOR: And scientists 898 00:51:48,033 --> 00:51:52,033 will never stop looking for new, weird worlds. 899 00:51:52,033 --> 00:51:54,833 I don't think I'm ever gonna get bored of strange worlds. 900 00:51:54,833 --> 00:51:58,200 There's so much out there to explore and discover. 901 00:51:58,200 --> 00:52:01,133 It's what gets me out of bed every day. 902 00:52:01,133 --> 00:52:04,000 So, the strangeness is only just beginning. 903 00:52:04,000 --> 00:52:09,033 ♪ ♪ 904 00:52:19,700 --> 00:52:23,933 ♪ ♪ 905 00:52:35,166 --> 00:52:38,033 ♪ ♪ 906 00:52:38,966 --> 00:52:46,500 ♪ ♪ 907 00:52:50,333 --> 00:52:57,866 ♪ ♪ 908 00:53:01,766 --> 00:53:09,300 ♪ ♪ 909 00:53:10,933 --> 00:53:18,466 ♪ ♪ 910 00:53:20,100 --> 00:53:27,633 ♪ ♪