1 00:00:01,070 --> 00:00:03,244 Viewers like you make this program possible. 2 00:00:03,244 --> 00:00:05,350 Support your local PBS station. 3 00:00:07,697 --> 00:00:11,666 NARRATOR: Our solar system is filled with mysterious worlds... 4 00:00:13,910 --> 00:00:17,189 ...wandering between and beyond the planets. 5 00:00:17,189 --> 00:00:19,053 [collision pounds] 6 00:00:19,053 --> 00:00:21,745 MALENA RICE: The objects that lie between the planets 7 00:00:21,745 --> 00:00:23,851 are actually the key to understanding 8 00:00:23,851 --> 00:00:25,301 how our solar system formed. 9 00:00:26,474 --> 00:00:29,167 NARRATOR: Imposters, and oddballs, 10 00:00:29,167 --> 00:00:33,723 rewriting our understanding of our place in space. 11 00:00:35,104 --> 00:00:38,072 JESSICA SUNSHINE: It is two pieces that are stuck together. 12 00:00:38,072 --> 00:00:39,280 It was really quite remarkable. 13 00:00:39,280 --> 00:00:41,213 [explodes] 14 00:00:41,213 --> 00:00:45,217 QUEENIE HOI SHAN CHAN: It is possible that after 30 million years, 15 00:00:45,217 --> 00:00:47,495 Mars might have a ring of its own. 16 00:00:47,495 --> 00:00:50,429 ♪ 17 00:00:50,429 --> 00:00:53,639 NARRATOR: Studying these wandering worlds 18 00:00:53,639 --> 00:00:57,885 allows scientists to explore regions of the solar system 19 00:00:57,885 --> 00:01:00,750 we have no chance of visiting. 20 00:01:00,750 --> 00:01:02,821 WANDA DIÍAZ MERCED: I cannot go to the asteroid belt, 21 00:01:02,821 --> 00:01:04,926 so when a meteorite lands on Earth, 22 00:01:04,926 --> 00:01:10,311 we will have a chunk of history right in our hands. 23 00:01:10,311 --> 00:01:11,795 ASHLEY KING: The Winchcombe meteorite 24 00:01:11,795 --> 00:01:13,659 was like a little treasure box for planetary scientists. 25 00:01:13,659 --> 00:01:15,247 [geyser bursts] 26 00:01:15,247 --> 00:01:18,147 NARRATOR: And the misfits of our solar system 27 00:01:18,147 --> 00:01:20,218 are full of surprises. 28 00:01:20,218 --> 00:01:22,599 VERONICA BRAY DURFEY: There are many, many worlds out there 29 00:01:22,599 --> 00:01:24,256 that we are yet to discover 30 00:01:24,256 --> 00:01:26,603 and that we haven't even imagined yet. 31 00:01:27,742 --> 00:01:29,434 SCOTT SHEPPARD: It's like a box of chocolates. 32 00:01:29,434 --> 00:01:31,470 You never know what you're gonna get in our images. 33 00:01:31,470 --> 00:01:33,610 This model of the solar system, 34 00:01:33,610 --> 00:01:37,200 it's missing all of the most interesting bits. 35 00:01:38,443 --> 00:01:40,824 NARRATOR: What secrets do these wandering worlds 36 00:01:40,824 --> 00:01:43,482 reveal about our solar system? 37 00:01:43,482 --> 00:01:46,623 And what else is lurking out there 38 00:01:46,623 --> 00:01:47,762 in the dark? 39 00:01:47,762 --> 00:01:49,626 [bursting] 40 00:01:49,626 --> 00:01:53,320 "Solar System: Wandering Worlds," 41 00:01:53,320 --> 00:01:56,116 right now on "NOVA." 42 00:01:58,221 --> 00:02:03,261 ♪ 43 00:02:18,897 --> 00:02:23,212 ♪ 44 00:02:26,525 --> 00:02:30,253 NARRATOR: There's something out there in the darkness. 45 00:02:32,807 --> 00:02:37,433 We don't know for sure where it came from 46 00:02:37,433 --> 00:02:39,400 or how long it's been there. 47 00:02:42,127 --> 00:02:45,165 But we know it's not alone. 48 00:02:47,201 --> 00:02:50,756 It was discovered in 2018. 49 00:02:53,242 --> 00:02:57,211 A world with no official name. 50 00:02:57,211 --> 00:03:01,422 So distant, it has been called simply 51 00:03:01,422 --> 00:03:03,700 FarFarOut. 52 00:03:03,700 --> 00:03:05,702 SHEPPARD: FarFarOut, 53 00:03:05,702 --> 00:03:07,566 as its name implies, is very far away. 54 00:03:07,566 --> 00:03:09,982 So, it's just a, a very faint point of light 55 00:03:09,982 --> 00:03:11,501 that, uh, we discovered 56 00:03:11,501 --> 00:03:13,400 with one of the largest telescopes in the world. 57 00:03:13,400 --> 00:03:15,540 JANE LUU: Its notoriety comes from the fact 58 00:03:15,540 --> 00:03:17,127 that it's the most distant object 59 00:03:17,127 --> 00:03:19,164 that we have found in the solar system. 60 00:03:19,164 --> 00:03:22,029 SHEPPARD: And the big question is, what do we call the next one? 61 00:03:22,029 --> 00:03:23,789 Do we just add another "far" or not? 62 00:03:23,789 --> 00:03:28,000 LUU: "ExtremelyFarOut," and then "StupendouslyFarOut," 63 00:03:28,000 --> 00:03:29,761 and it just keeps going. [laughs] 64 00:03:29,761 --> 00:03:31,383 ♪ 65 00:03:31,383 --> 00:03:34,248 NARRATOR: 12 billion miles from the sun, 66 00:03:34,248 --> 00:03:38,218 FarFarOut is not alone. 67 00:03:38,218 --> 00:03:41,531 Out here, there could be countless other worlds 68 00:03:41,531 --> 00:03:44,983 yet to be discovered, 69 00:03:44,983 --> 00:03:49,298 wandering in the dark. 70 00:03:49,298 --> 00:03:53,302 Even closer to home, we are only just beginning 71 00:03:53,302 --> 00:03:58,859 to explore the vast spaces between the planets. 72 00:03:59,860 --> 00:04:02,518 Home to a myriad of worlds, 73 00:04:02,518 --> 00:04:06,487 many too small or too dark to see. 74 00:04:08,972 --> 00:04:11,458 NANCY CHABOT: When we think about our solar system, 75 00:04:11,458 --> 00:04:13,805 we think about the sun, it's in the center, 76 00:04:13,805 --> 00:04:15,669 everything else is kind of going around it, 77 00:04:15,669 --> 00:04:18,741 and we've got the big planets, Jupiter and Saturn, 78 00:04:18,741 --> 00:04:20,294 and the most important planet, Earth. 79 00:04:20,294 --> 00:04:23,746 But there are so many more secrets and mysteries 80 00:04:23,746 --> 00:04:27,301 than just these planets that are shown in the model. 81 00:04:27,301 --> 00:04:29,269 So, to me, the most exciting thing 82 00:04:29,269 --> 00:04:32,824 about studying the solar system is not the planets themselves, 83 00:04:32,824 --> 00:04:36,621 but it's all the bits in between the planets. 84 00:04:36,621 --> 00:04:41,522 NARRATOR: These worlds could provide clues to our own planet's story. 85 00:04:43,352 --> 00:04:45,526 RICE: In a lot of ways, studying the solar system 86 00:04:45,526 --> 00:04:49,254 is a way of trying to understand ourselves. 87 00:04:49,254 --> 00:04:51,118 How did we come to be in the first place, 88 00:04:51,118 --> 00:04:53,845 and what does it mean that we're on this rock 89 00:04:53,845 --> 00:04:56,779 that is sailing through space? 90 00:04:56,779 --> 00:05:01,473 NARRATOR: With distances so vast, there's still much to discover. 91 00:05:01,473 --> 00:05:02,854 KING: There's so much stuff 92 00:05:02,854 --> 00:05:04,752 that we just don't know about our solar system, 93 00:05:04,752 --> 00:05:06,961 and what we do know is, it is constantly surprising us. 94 00:05:06,961 --> 00:05:10,931 So we need to go out there, look at these wandering worlds. 95 00:05:10,931 --> 00:05:13,589 NARRATOR: And many questions remain unanswered. 96 00:05:13,589 --> 00:05:16,177 LYNNAE QUICK: Are these lost and wandering worlds 97 00:05:16,177 --> 00:05:18,456 worthy of exploration in their own right? 98 00:05:18,456 --> 00:05:22,356 CHABOT: How far do these dark regions extend 99 00:05:22,356 --> 00:05:24,772 beyond, to the edge of our solar system? 100 00:05:24,772 --> 00:05:28,086 Are there more planets in the dark region 101 00:05:28,086 --> 00:05:29,536 waiting to be discovered? 102 00:05:29,536 --> 00:05:33,125 ♪ 103 00:06:01,222 --> 00:06:04,329 [dog barking in distance] 104 00:06:04,329 --> 00:06:08,747 NARRATOR: It was the sound that most people noticed. 105 00:06:08,747 --> 00:06:12,717 [explosion echoing in distance] 106 00:06:12,717 --> 00:06:16,410 A sonic boom in the night. 107 00:06:18,067 --> 00:06:20,656 But this was no fighter jet. 108 00:06:24,038 --> 00:06:27,904 Traveling at around 30,000 miles per hour, 109 00:06:27,904 --> 00:06:31,356 it tore through the atmosphere. 110 00:06:33,289 --> 00:06:35,981 ♪ 111 00:06:38,121 --> 00:06:39,778 Broke up. 112 00:06:41,331 --> 00:06:44,404 And rained down across the fields. 113 00:06:48,442 --> 00:06:52,032 A visitor from a distant realm. 114 00:06:54,690 --> 00:06:57,486 One of the biggest chunks 115 00:06:57,486 --> 00:07:01,904 landed on a driveway in front of a house. 116 00:07:01,904 --> 00:07:04,354 KING: When I first saw it, it was kind of a splat. 117 00:07:04,354 --> 00:07:07,047 I mean, it's so soft, it kind of just made a powder 118 00:07:07,047 --> 00:07:09,014 and it threw fragments all over the driveway. 119 00:07:09,014 --> 00:07:10,499 SARA RUSSELL: The Winchcombe meteorite fall 120 00:07:10,499 --> 00:07:14,054 was the first U.K. meteorite fall recovered for 30 years, 121 00:07:14,054 --> 00:07:15,987 so we've been waiting such a long time. 122 00:07:15,987 --> 00:07:19,231 KING: I couldn't believe that we had a new meteorite in the U.K. 123 00:07:19,231 --> 00:07:20,543 Yeah, it was incredibly exciting. 124 00:07:20,543 --> 00:07:22,476 And all meteorites are scientifically priceless. 125 00:07:22,476 --> 00:07:25,548 RUSSELL: I feel amazed and privileged 126 00:07:25,548 --> 00:07:28,309 to be able to hold something 127 00:07:28,309 --> 00:07:29,966 that may tell us about thesecrets 128 00:07:29,966 --> 00:07:31,865 of the origins of our solarsystem, 129 00:07:31,865 --> 00:07:33,694 and how we got to be here. 130 00:07:35,662 --> 00:07:40,494 NARRATOR: It's estimated as many as 50 meteorites hit Earth every day. 131 00:07:40,494 --> 00:07:43,877 Many burn up in our atmosphere, 132 00:07:43,877 --> 00:07:48,571 creating shooting stars and meteor showers. 133 00:07:48,571 --> 00:07:52,506 But some of the largest ones do make it to Earth. 134 00:07:52,506 --> 00:07:57,442 In 2018, the Hamburg meteor fireball 135 00:07:57,442 --> 00:08:01,239 streaked across the American Midwest sky. 136 00:08:03,655 --> 00:08:06,209 WOMAN: What was that? 137 00:08:06,209 --> 00:08:08,522 Did you see a light flash out there? 138 00:08:08,522 --> 00:08:10,179 It's particularly pristine, because it landed 139 00:08:10,179 --> 00:08:14,217 on a frozen lake, so that keeps it in cold storage. 140 00:08:14,217 --> 00:08:19,913 It was like the meteor selected where to land, 141 00:08:19,913 --> 00:08:21,984 because it wanted to be studied. 142 00:08:23,813 --> 00:08:25,194 NARRATOR: A few years later, 143 00:08:25,194 --> 00:08:28,231 a meteorite the weight of a grand piano 144 00:08:28,231 --> 00:08:31,303 exploded in the skies near McAllen, Texas. 145 00:08:31,303 --> 00:08:33,685 [explosion pounds in distance] 146 00:08:33,685 --> 00:08:36,895 MERCED: Ah! 147 00:08:36,895 --> 00:08:39,415 It's like a, like an explosion of dynamite. 148 00:08:39,415 --> 00:08:41,900 [explosion echoes] 149 00:08:41,900 --> 00:08:45,559 That big explosion, that was a sonic boom. 150 00:08:52,186 --> 00:08:56,501 ♪ 151 00:08:56,501 --> 00:08:58,227 NARRATOR: The cows weren't the only witnesses 152 00:08:58,227 --> 00:09:00,678 that night in Winchcombe. 153 00:09:03,128 --> 00:09:08,686 Doorbell and CCTV cameras never sleep. 154 00:09:08,686 --> 00:09:11,723 And networks of dedicated meteor cameras 155 00:09:11,723 --> 00:09:14,554 captured it from different angles. 156 00:09:17,142 --> 00:09:20,663 That meant it was possible to calculate its trajectory. 157 00:09:22,423 --> 00:09:24,564 [cows mooing] 158 00:09:24,564 --> 00:09:30,155 Back over the skies of England, 159 00:09:30,155 --> 00:09:34,850 out of Earth's atmosphere, 160 00:09:34,850 --> 00:09:38,647 past the orbit of Mars, 161 00:09:38,647 --> 00:09:41,788 into the dark. 162 00:09:41,788 --> 00:09:46,862 This is where the meteorite's journey began, 163 00:09:46,862 --> 00:09:51,487 a mysterious realm of countless rocky worlds, 164 00:09:51,487 --> 00:09:57,182 rubble left over from the formation of the solar system: 165 00:09:57,182 --> 00:09:58,667 asteroids. 166 00:10:01,083 --> 00:10:04,914 There could be at least a million out here. 167 00:10:04,914 --> 00:10:08,538 But they're so dark, reflecting little light, 168 00:10:08,538 --> 00:10:12,128 they're incredibly difficult to detect. 169 00:10:15,753 --> 00:10:20,102 But asteroids don't always stay in the asteroid belt. 170 00:10:22,622 --> 00:10:25,452 [collision pounds] 171 00:10:25,452 --> 00:10:28,317 When two collide, 172 00:10:28,317 --> 00:10:33,529 they blast fragments in all directions, 173 00:10:33,529 --> 00:10:37,602 sending some out of the asteroid belt forever. 174 00:10:39,362 --> 00:10:43,988 Sometimes wreaking havoc on planets they encounter. 175 00:10:43,988 --> 00:10:48,717 ♪ 176 00:10:55,896 --> 00:10:58,209 Including our own. 177 00:11:00,142 --> 00:11:02,662 And asteroids that leave the belt 178 00:11:02,662 --> 00:11:05,803 can transform planets nearby. 179 00:11:08,495 --> 00:11:11,671 ♪ 180 00:11:11,671 --> 00:11:18,022 A planet covered in scars from the asteroid belt is Mars. 181 00:11:20,369 --> 00:11:25,995 Around 80 fresh impact sites are found on Mars every year. 182 00:11:25,995 --> 00:11:31,242 ♪ 183 00:11:33,002 --> 00:11:34,832 And some amazing meteorites 184 00:11:34,832 --> 00:11:38,456 have even been snapped by NASA's rovers. 185 00:11:47,051 --> 00:11:50,295 But there's another dark rock here, 186 00:11:50,295 --> 00:11:53,920 imaged by the Perseverance rover, 187 00:11:53,920 --> 00:11:58,683 not on Mars's surface, but orbiting overhead... 188 00:11:58,683 --> 00:12:03,032 ♪ 189 00:12:03,032 --> 00:12:04,862 ...captured during an eclipse, 190 00:12:04,862 --> 00:12:07,761 as it passed in front of the sun. 191 00:12:10,246 --> 00:12:14,285 This is Mars's moon Phobos. 192 00:12:19,048 --> 00:12:22,534 Today, the orbiting probe Mars Express 193 00:12:22,534 --> 00:12:26,228 regularly flies between Mars and Phobos. 194 00:12:26,228 --> 00:12:30,232 ♪ 195 00:12:30,232 --> 00:12:34,512 Its high-resolution camera 196 00:12:34,512 --> 00:12:40,173 captured incredibly detailed images of Phobos, 197 00:12:40,173 --> 00:12:44,349 showing a surface covered in strange grooves. 198 00:12:46,835 --> 00:12:52,357 Phobos looks like someone has ridden a giant bike all over it. 199 00:12:59,917 --> 00:13:04,611 Astrophysicist Sean Raymond is investigating 200 00:13:04,611 --> 00:13:08,615 how objects like Phobos could have formed. 201 00:13:14,069 --> 00:13:15,656 Phobos is a strange-lookingmoon. 202 00:13:15,656 --> 00:13:19,315 Like this beach, it's covered ingrooves. 203 00:13:19,315 --> 00:13:20,627 You might say it's 204 00:13:20,627 --> 00:13:22,629 the grooviest moon in the solar system. 205 00:13:24,734 --> 00:13:28,014 NARRATOR: The magnificent grooves here in Spain 206 00:13:28,014 --> 00:13:30,533 are formed by geological processes 207 00:13:30,533 --> 00:13:34,710 and erosion from relentless, crashing waves. 208 00:13:34,710 --> 00:13:38,162 RAYMOND: It's so cool-- the grooves are amazing here. 209 00:13:38,162 --> 00:13:41,337 NARRATOR: But Phobos isn't anything like Earth, 210 00:13:41,337 --> 00:13:44,685 so what's going on? 211 00:13:44,685 --> 00:13:47,171 RAYMOND: Phobos certainly looks like an asteroid. 212 00:13:47,171 --> 00:13:50,381 It's covered in craters, and it's dark in color. 213 00:13:50,381 --> 00:13:52,590 So you might think it's just an asteroid that got 214 00:13:52,590 --> 00:13:57,043 too close to Mars and then was captured in orbit. 215 00:13:57,043 --> 00:14:02,220 NARRATOR: It turns out it's not that simple. 216 00:14:02,220 --> 00:14:05,879 Phobos orbits Mars in an almost perfect circle, 217 00:14:05,879 --> 00:14:08,882 right along Mars's equator, 218 00:14:08,882 --> 00:14:10,573 and this makes us question whether Phobos 219 00:14:10,573 --> 00:14:13,783 is really the asteroid it appears to be, 220 00:14:13,783 --> 00:14:16,890 because captured asteroids usually orbit planets 221 00:14:16,890 --> 00:14:19,203 on very elliptical orbits 222 00:14:19,203 --> 00:14:21,722 that sometimes take them very far from their planet 223 00:14:21,722 --> 00:14:24,035 and sometimes being much closer. 224 00:14:24,035 --> 00:14:27,349 NARRATOR: So, if it's not an asteroid, 225 00:14:27,349 --> 00:14:31,042 where did this funny little moon come from? 226 00:14:34,149 --> 00:14:36,116 CHABOT: So, in planetary science, 227 00:14:36,116 --> 00:14:38,463 the joke is that you just add an impact event, 228 00:14:38,463 --> 00:14:41,156 and an impact event can explain everything. 229 00:14:41,156 --> 00:14:43,503 That might actually be true in this case, though. 230 00:14:43,503 --> 00:14:45,746 It's this one-off event, and it might have been 231 00:14:45,746 --> 00:14:47,783 that an object hit Mars, 232 00:14:47,783 --> 00:14:50,786 and Phobos is the result of that impact collision 233 00:14:50,786 --> 00:14:54,031 between those objects, and that's what we're seeing. 234 00:14:54,031 --> 00:14:57,931 ♪ 235 00:14:57,931 --> 00:15:04,317 NARRATOR: Phobos may not be a captured asteroid at all, 236 00:15:04,317 --> 00:15:07,320 but formed from debris thrown into orbit 237 00:15:07,320 --> 00:15:12,118 after a massive asteroid impact. 238 00:15:12,118 --> 00:15:15,155 However, this still doesn't explain 239 00:15:15,155 --> 00:15:19,780 why it's covered in grooves. 240 00:15:22,922 --> 00:15:28,203 Phobos is about 3,700 miles from Mars's surface, 241 00:15:28,203 --> 00:15:33,760 and every hundred years, moves closer by about six feet. 242 00:15:33,760 --> 00:15:39,490 And as it does, the tidal forces caused by Mars's gravity 243 00:15:39,490 --> 00:15:42,976 become stronger. 244 00:15:42,976 --> 00:15:45,979 RAYMOND: So, just like the moon pulls on the Earth, 245 00:15:45,979 --> 00:15:49,500 dragging the oceans and causing the tide, 246 00:15:49,500 --> 00:15:53,987 Mars pulls on Phobos, causing tides, as well. 247 00:15:53,987 --> 00:15:56,162 So, as you can see behind me right now, 248 00:15:56,162 --> 00:15:59,027 the tide is coming in as the moon is pulling on 249 00:15:59,027 --> 00:16:00,718 the water on the Earth. 250 00:16:00,718 --> 00:16:03,686 The same process happens on Phobos, due to Mars, 251 00:16:03,686 --> 00:16:06,551 except on Phobos, it's sand and rock that's moving, 252 00:16:06,551 --> 00:16:08,968 instead of water. 253 00:16:10,797 --> 00:16:15,215 NARRATOR: Those tidal forces are pulling Phobos apart. 254 00:16:15,215 --> 00:16:21,118 And with every orbit, the grooves widen and deepen. 255 00:16:26,054 --> 00:16:30,541 Eventually, Phobos will drift so close, 256 00:16:30,541 --> 00:16:35,132 Mars's gravity will destroy it. 257 00:16:35,132 --> 00:16:37,893 As Phobos breaks apart... 258 00:16:40,413 --> 00:16:44,796 ...most of the debris will fall to the surface of Mars. 259 00:16:48,455 --> 00:16:52,045 ♪ 260 00:16:52,045 --> 00:16:56,877 But the rest will remain in close orbit, 261 00:16:56,877 --> 00:17:03,643 spreading out to encircle the entire planet, 262 00:17:03,643 --> 00:17:07,785 giving Mars a wispy ring. 263 00:17:11,271 --> 00:17:13,411 CHAN: It would be quite impressive. 264 00:17:13,411 --> 00:17:16,069 I love ring planets, I love Saturn, 265 00:17:16,069 --> 00:17:19,969 and it's not bad to have another ring planet in our solar system. 266 00:17:22,455 --> 00:17:26,424 NARRATOR: It seems Mars will one day be transformed 267 00:17:26,424 --> 00:17:29,496 by the asteroid belt. 268 00:17:34,639 --> 00:17:38,643 But the asteroid belt itself is still an enigma. 269 00:17:41,129 --> 00:17:43,407 We've flown several spacecraft 270 00:17:43,407 --> 00:17:47,618 through this mysterious region, 271 00:17:47,618 --> 00:17:49,861 but only one has orbited the rocks 272 00:17:49,861 --> 00:17:53,175 in the asteroid belt itself: 273 00:17:53,175 --> 00:17:58,525 NASA's Dawn probe. 274 00:17:58,525 --> 00:18:02,633 Most of these ancient remnants are misshapen boulders. 275 00:18:04,083 --> 00:18:07,155 But one stands out. 276 00:18:12,263 --> 00:18:14,921 Ceres is much bigger than the others 277 00:18:14,921 --> 00:18:20,099 and almost perfectly spherical. 278 00:18:20,099 --> 00:18:21,583 QUICK: I joined the Dawn mission 279 00:18:21,583 --> 00:18:23,688 right after it reached Ceres, 280 00:18:23,688 --> 00:18:25,034 and it was so exciting. 281 00:18:25,034 --> 00:18:29,177 Dawn collected thousands of images of Ceres. 282 00:18:29,177 --> 00:18:31,248 They showed us areas of the surface 283 00:18:31,248 --> 00:18:33,284 that we'd never seen before. 284 00:18:33,284 --> 00:18:34,527 We thought that it's kind of 285 00:18:34,527 --> 00:18:36,011 a dead planetary body. 286 00:18:36,011 --> 00:18:38,393 Looking at those images, 287 00:18:38,393 --> 00:18:40,636 we could not, basically, believe our eyes, 288 00:18:40,636 --> 00:18:43,122 and it was, like, "Uh, what's going on over there?" 289 00:18:43,122 --> 00:18:46,815 ♪ 290 00:18:46,815 --> 00:18:50,474 NARRATOR: At first, it appears dark and heavily cratered, 291 00:18:50,474 --> 00:18:53,787 like its fellow asteroids. 292 00:18:53,787 --> 00:18:56,031 But Ceres is different. 293 00:18:57,895 --> 00:19:03,107 Its surface is peppered with white crystals. 294 00:19:03,107 --> 00:19:06,628 But what are they? 295 00:19:06,628 --> 00:19:10,873 Clues come from another planet in our solar system, 296 00:19:10,873 --> 00:19:15,602 where white crystals are also found on the surface. 297 00:19:17,673 --> 00:19:20,711 Earth. 298 00:19:27,235 --> 00:19:31,653 HAKEEM OLUSEYI: This mountain is made up almost entirely of sea salt, 299 00:19:31,653 --> 00:19:33,827 the exact same stuff that you put on your food 300 00:19:33,827 --> 00:19:35,070 at the dinner table. 301 00:19:36,658 --> 00:19:38,970 NARRATOR: 40 million years ago, 302 00:19:38,970 --> 00:19:43,803 this whole area was under an ancient sea. 303 00:19:47,634 --> 00:19:50,637 Over time, it dried out, 304 00:19:50,637 --> 00:19:55,953 leaving behind a layer of salt a mile thick. 305 00:19:57,437 --> 00:19:59,577 Holy moly! 306 00:19:59,577 --> 00:20:01,648 Whoa! 307 00:20:03,616 --> 00:20:06,481 ♪ 308 00:20:09,277 --> 00:20:10,899 It's definitely salty. 309 00:20:10,899 --> 00:20:12,763 And the thing about salt deposits like this 310 00:20:12,763 --> 00:20:15,731 is that they're only formed in the presence of water. 311 00:20:15,731 --> 00:20:19,390 So, that raises an intriguing possibility. 312 00:20:19,390 --> 00:20:23,739 Could the white spots on Ceres also be salts 313 00:20:23,739 --> 00:20:27,709 that were deposited by water? 314 00:20:27,709 --> 00:20:30,470 NARRATOR: Finding water on Ceres today 315 00:20:30,470 --> 00:20:32,645 would be an astonishing discovery. 316 00:20:32,645 --> 00:20:36,062 ♪ 317 00:20:36,062 --> 00:20:40,135 Dawn made tight orbits of Ceres. 318 00:20:41,757 --> 00:20:45,382 And by bouncing light off the crystal deposits, 319 00:20:45,382 --> 00:20:51,284 it determined what they were made of: 320 00:20:51,284 --> 00:20:55,392 sodium carbonate, a common type of salt. 321 00:20:57,635 --> 00:21:01,121 A tantalizing sign that Ceres, 322 00:21:01,121 --> 00:21:03,917 which is 13 times smaller than Earth, 323 00:21:03,917 --> 00:21:08,267 had an ocean in the past. 324 00:21:08,267 --> 00:21:12,857 Flying just over 20 miles from the surface, 325 00:21:12,857 --> 00:21:18,484 Dawn finds something else in the white spots: 326 00:21:18,484 --> 00:21:21,349 hydrohalite crystals, 327 00:21:21,349 --> 00:21:27,182 another salt found on Earth in the presence of water. 328 00:21:27,182 --> 00:21:30,875 Could Ceres still be a water world today? 329 00:21:33,844 --> 00:21:36,398 So, "hydro" is water and "halite" is salt-- 330 00:21:36,398 --> 00:21:37,399 table salt. 331 00:21:37,399 --> 00:21:39,919 So, if you imagine a table salt 332 00:21:39,919 --> 00:21:42,749 that's got water molecules in the structure, 333 00:21:42,749 --> 00:21:45,338 that's what hydrohalite is. 334 00:21:45,338 --> 00:21:47,582 It was very surprising that there were hydrohalites 335 00:21:47,582 --> 00:21:49,584 on the surface of Ceres. 336 00:21:49,584 --> 00:21:51,862 CHAN: Hydrohalite would be very unstable 337 00:21:51,862 --> 00:21:54,209 at the surface of Ceres. 338 00:21:54,209 --> 00:21:56,211 At that pressure, 339 00:21:56,211 --> 00:21:59,352 the water molecule would have been vaporized. 340 00:21:59,352 --> 00:22:03,425 That implies that water was recently emplaced on Ceres, 341 00:22:03,425 --> 00:22:07,153 bound to salt crystals within the past few hundred years. 342 00:22:07,153 --> 00:22:08,879 This replenishment of hydrohalite 343 00:22:08,879 --> 00:22:11,191 at Ceres' surface leads us to wonder 344 00:22:11,191 --> 00:22:12,986 if Ceres might be an ocean world 345 00:22:12,986 --> 00:22:15,748 that's masquerading as an asteroid. 346 00:22:15,748 --> 00:22:19,407 ♪ 347 00:22:19,407 --> 00:22:23,169 NARRATOR: Scientists suspect that pools of salty water exist 348 00:22:23,169 --> 00:22:27,691 about 25 miles underground, 349 00:22:27,691 --> 00:22:30,038 raising another question: 350 00:22:30,038 --> 00:22:34,214 how did these salts end up on the surface? 351 00:22:34,214 --> 00:22:38,495 A clue lies in Ceres' location, 352 00:22:38,495 --> 00:22:41,532 right in the heart of the asteroid belt, 353 00:22:41,532 --> 00:22:43,603 where collisions are common... 354 00:22:43,603 --> 00:22:45,950 [collision pounds] 355 00:22:45,950 --> 00:22:49,885 ...and incoming asteroids can form cracks in the surface 356 00:22:49,885 --> 00:22:53,544 reaching the pools below. 357 00:22:53,544 --> 00:22:55,891 Exposed to the vacuum of space, 358 00:22:55,891 --> 00:23:01,310 the water vaporizes, 359 00:23:01,310 --> 00:23:05,901 leaving its cargo of salt behind 360 00:23:05,901 --> 00:23:09,905 and peppering Ceres with white spots. 361 00:23:12,080 --> 00:23:14,013 QUICK: There's still one big twist 362 00:23:14,013 --> 00:23:15,842 to the story of Ceres' past. 363 00:23:15,842 --> 00:23:19,605 The Dawn spacecraft found ammonia salts on the surface. 364 00:23:21,296 --> 00:23:24,920 NARRATOR: Ammonia salts could be traces of ammonia ices 365 00:23:24,920 --> 00:23:28,303 that once covered Ceres' surface. 366 00:23:28,303 --> 00:23:30,788 Frozen ammonia is common in colder parts 367 00:23:30,788 --> 00:23:35,137 of the solar system, but not here. 368 00:23:35,137 --> 00:23:41,005 CHAN: Ammonia doesn't really exist as ice at where Ceres is now. 369 00:23:41,005 --> 00:23:44,008 It has to be formed at a distance 370 00:23:44,008 --> 00:23:46,459 further away from the sun, 371 00:23:46,459 --> 00:23:48,944 where the distance is cold enough 372 00:23:48,944 --> 00:23:51,740 for ammonia to exist as ice. 373 00:23:51,740 --> 00:23:53,915 This suggests that Ceres didn't form 374 00:23:53,915 --> 00:23:56,124 where it stands currently in our solar system. 375 00:23:57,505 --> 00:24:01,992 NARRATOR: Instead, scientists think it formed much farther out, 376 00:24:01,992 --> 00:24:04,684 and as it wandered towards the sun, 377 00:24:04,684 --> 00:24:07,376 the ammonia ices melted, 378 00:24:07,376 --> 00:24:12,968 leaving behind the ammonia salts we see today. 379 00:24:12,968 --> 00:24:17,179 An imposter lurking in the asteroid belt, 380 00:24:17,179 --> 00:24:22,012 exposed by its salty secrets. 381 00:24:22,012 --> 00:24:24,704 Ceres has a journey of relocation 382 00:24:24,704 --> 00:24:27,949 just written all across the surface. 383 00:24:30,952 --> 00:24:35,784 NARRATOR: But just how did Ceres end up where it is today? 384 00:24:35,784 --> 00:24:38,131 OLUSEYI: The best explanation is that it wandered. 385 00:24:38,131 --> 00:24:39,719 Well, actually, it was pulled. 386 00:24:39,719 --> 00:24:40,962 So let's say this is Ceres. 387 00:24:40,962 --> 00:24:41,997 Okay? 388 00:24:41,997 --> 00:24:44,517 We think that Ceres formed beyond 389 00:24:44,517 --> 00:24:46,139 what is known as the ice line 390 00:24:46,139 --> 00:24:47,900 for ammonium ices. 391 00:24:47,900 --> 00:24:49,695 NARRATOR: Beyond this ice line, 392 00:24:49,695 --> 00:24:51,731 ammonia freezes, 393 00:24:51,731 --> 00:24:55,494 and this is where Ceres likely started forming, 394 00:24:55,494 --> 00:24:58,566 alongside Neptune and Uranus. 395 00:24:58,566 --> 00:25:00,844 OLUSEYI: And here we have Saturn and Jupiter. 396 00:25:00,844 --> 00:25:02,639 Now, normally, these planets 397 00:25:02,639 --> 00:25:03,847 aren't lined up like this. 398 00:25:03,847 --> 00:25:05,642 They're moving around the solar system. 399 00:25:05,642 --> 00:25:08,852 And what happens is, as Ceres 400 00:25:08,852 --> 00:25:10,854 orbited the solar system, 401 00:25:10,854 --> 00:25:13,650 Jupiter tugged on it with its gravity, 402 00:25:13,650 --> 00:25:16,445 and Ceres ended up right there, 403 00:25:16,445 --> 00:25:19,207 in the asteroid belt, where we find it today. 404 00:25:21,520 --> 00:25:23,798 NARRATOR: In the heart of the asteroid belt, 405 00:25:23,798 --> 00:25:27,111 Ceres, once a much icier world, 406 00:25:27,111 --> 00:25:31,150 has migrated far from where it formed, 407 00:25:31,150 --> 00:25:35,810 evidence that our solar system is ever changing. 408 00:25:35,810 --> 00:25:37,777 ♪ 409 00:25:37,777 --> 00:25:41,643 Ceres isn't the only displaced world. 410 00:25:41,643 --> 00:25:45,129 Farther from the sun, there is another icy world 411 00:25:45,129 --> 00:25:48,754 that doesn't seem to belong where it's found today. 412 00:25:50,203 --> 00:25:54,587 Beyond Jupiter, 413 00:25:54,587 --> 00:25:57,797 the space between the planets gets wider 414 00:25:57,797 --> 00:26:00,213 and wider. 415 00:26:01,352 --> 00:26:04,459 And temperatures plummet. 416 00:26:07,013 --> 00:26:11,259 ♪ 417 00:26:11,259 --> 00:26:16,747 And a billion miles past Uranus, 418 00:26:16,747 --> 00:26:20,682 we finally reach the farthest planet from the sun. 419 00:26:23,512 --> 00:26:26,515 Neptune. 420 00:26:26,515 --> 00:26:32,521 ♪ 421 00:26:32,521 --> 00:26:36,733 Wrapped in a dense blue blanket, 422 00:26:36,733 --> 00:26:42,635 Neptune has no detectable surface, 423 00:26:42,635 --> 00:26:46,674 with clouds of methane and ammonia. 424 00:26:48,986 --> 00:26:53,612 But there are rocky worlds nearby. 425 00:26:53,612 --> 00:26:57,788 Neptune has at least 16 moons. 426 00:26:57,788 --> 00:27:02,344 And one is very unusual. 427 00:27:07,556 --> 00:27:12,354 Triton is the largest of Neptune's moons. 428 00:27:12,354 --> 00:27:15,150 Its surface is coated with ice. 429 00:27:19,189 --> 00:27:21,881 And, unlike the other moons, 430 00:27:21,881 --> 00:27:24,677 Triton is an active world. 431 00:27:24,677 --> 00:27:28,785 [geyser bursts] 432 00:27:28,785 --> 00:27:31,684 Geyser-like plumes of gas and dust 433 00:27:31,684 --> 00:27:35,654 stretch five miles high into Triton's atmosphere... 434 00:27:37,483 --> 00:27:39,485 ...which flattens them abruptly 435 00:27:39,485 --> 00:27:42,074 by 90 degrees, 436 00:27:42,074 --> 00:27:46,561 creating a vista so strange, 437 00:27:46,561 --> 00:27:49,737 it's hard to believe it's real. 438 00:27:54,086 --> 00:27:59,885 How did a moon 2.8 billion miles from the sun 439 00:27:59,885 --> 00:28:02,957 become so active? 440 00:28:08,307 --> 00:28:11,241 A clue lies with how the planets and moons 441 00:28:11,241 --> 00:28:14,934 move around each other in the solar system. 442 00:28:19,214 --> 00:28:21,044 CARLY HOWETT: Every day, the sun rises in the east 443 00:28:21,044 --> 00:28:23,184 and sets in the west. 444 00:28:23,184 --> 00:28:25,393 And the moon follows the same course. 445 00:28:25,393 --> 00:28:27,084 And there's a reason for that. 446 00:28:28,465 --> 00:28:30,294 NARRATOR: To understand why, 447 00:28:30,294 --> 00:28:34,057 we need to go all the way back. 448 00:28:36,162 --> 00:28:40,304 To the birth of the solar system. 449 00:28:40,304 --> 00:28:42,272 DURFEY: In the beginning of our solar system, 450 00:28:42,272 --> 00:28:43,722 the sun was surrounded 451 00:28:43,722 --> 00:28:46,138 by a disc of dust and gas. 452 00:28:46,138 --> 00:28:49,486 And it was within this spinning disc 453 00:28:49,486 --> 00:28:52,282 that the planets formed. 454 00:28:52,282 --> 00:28:53,732 PAREKH: So that's the reason 455 00:28:53,732 --> 00:28:55,354 the planets and the moon continued 456 00:28:55,354 --> 00:28:57,218 orbiting also in the same direction 457 00:28:57,218 --> 00:29:00,186 around the sun. 458 00:29:00,186 --> 00:29:02,671 NARRATOR: Moons that form around their planets 459 00:29:02,671 --> 00:29:05,847 tend to follow this pattern, 460 00:29:05,847 --> 00:29:08,091 orbiting and spinning in the direction 461 00:29:08,091 --> 00:29:11,957 of the planet's rotation. 462 00:29:11,957 --> 00:29:16,306 But while the inner moons orbit Neptune in the same direction, 463 00:29:16,306 --> 00:29:19,619 Triton goes the other way, 464 00:29:19,619 --> 00:29:24,763 suggesting it didn't form alongside Neptune, 465 00:29:24,763 --> 00:29:29,595 but came from elsewhere. 466 00:29:33,772 --> 00:29:35,256 HOWETT: What a planet's made from 467 00:29:35,256 --> 00:29:38,086 can tell you where it formed in our solar system. 468 00:29:38,086 --> 00:29:40,364 And that's because, in our early solar system, 469 00:29:40,364 --> 00:29:42,850 the ingredients that a planet could be built from 470 00:29:42,850 --> 00:29:45,266 varied as the distance from the sun. 471 00:29:45,266 --> 00:29:48,200 So if we take Earth, for example, 472 00:29:48,200 --> 00:29:49,857 it's got a lot of rocks and metals, too: 473 00:29:49,857 --> 00:29:51,893 aluminium and iron. 474 00:29:51,893 --> 00:29:53,308 And Mars is prettysimilar. 475 00:29:53,308 --> 00:29:56,139 Iron, metals, and other rocks. 476 00:29:56,139 --> 00:29:59,107 So these can be paired together. 477 00:29:59,107 --> 00:30:01,144 If we do the same thing 478 00:30:01,144 --> 00:30:04,837 for the ice giants, Neptune and Uranus, 479 00:30:04,837 --> 00:30:06,839 with big atmospheres made of hydrogen, 480 00:30:06,839 --> 00:30:08,634 helium, and a bit of methane, 481 00:30:08,634 --> 00:30:10,291 they're huge, too. 482 00:30:10,291 --> 00:30:12,811 So we can pair those together. 483 00:30:12,811 --> 00:30:14,985 So how does Triton fit in? 484 00:30:14,985 --> 00:30:16,849 Well, its surface is mainly nitrogen ice, 485 00:30:16,849 --> 00:30:18,264 and it's much smaller. 486 00:30:18,264 --> 00:30:21,233 It doesn't fit with either of these two groupings. 487 00:30:21,233 --> 00:30:23,373 To understand where it could fit, 488 00:30:23,373 --> 00:30:25,030 we have to look at Pluto. 489 00:30:25,030 --> 00:30:28,723 Pluto has a, a nitrogen ice surface with methane, 490 00:30:28,723 --> 00:30:31,105 carbon monoxide, and water ice. 491 00:30:31,105 --> 00:30:34,073 And it's about the same size as Triton, too. 492 00:30:34,073 --> 00:30:35,868 These are a good pairing. 493 00:30:35,868 --> 00:30:38,906 NARRATOR: With such similar ingredients, 494 00:30:38,906 --> 00:30:42,771 Triton and Pluto could've formed in the same place, 495 00:30:42,771 --> 00:30:46,154 but they aren't anywhere near each other today. 496 00:30:46,154 --> 00:30:49,502 HOWETT: Triton's located one billion miles from Pluto. 497 00:30:49,502 --> 00:30:51,056 So how did that happen? 498 00:30:52,643 --> 00:30:56,889 NARRATOR: Neptune might be the farthest planet from the sun, 499 00:30:56,889 --> 00:31:00,893 but it's not the edge of our solar system. 500 00:31:00,893 --> 00:31:04,863 Not even close. 501 00:31:04,863 --> 00:31:08,314 Almost a billion miles farther out 502 00:31:08,314 --> 00:31:10,799 lies Pluto. 503 00:31:10,799 --> 00:31:13,802 And it's not alone. 504 00:31:13,802 --> 00:31:19,153 There are hundreds of thousands of other worlds out here. 505 00:31:19,153 --> 00:31:23,605 This is the Kuiper Belt, 506 00:31:23,605 --> 00:31:28,507 a vast, doughnut-shaped ring of icy bodies 507 00:31:28,507 --> 00:31:30,578 billions of miles wide. 508 00:31:32,683 --> 00:31:34,375 So dark and distant, 509 00:31:34,375 --> 00:31:40,312 it remained undiscovered until 1992. 510 00:31:40,312 --> 00:31:42,555 LUU: We had been searching for, uh, the Kuiper Belt 511 00:31:42,555 --> 00:31:45,593 for, uh, for five years before we finally found it. 512 00:31:45,593 --> 00:31:49,045 So when we spotted the first Kuiper Belt object, 513 00:31:49,045 --> 00:31:51,357 1992 QB1, 514 00:31:51,357 --> 00:31:53,290 there was jumping up and down, and there was... 515 00:31:53,290 --> 00:31:55,948 I think we gave each other a high five. [laughs] 516 00:31:55,948 --> 00:31:57,846 The discovery of the Kuiper Belt 517 00:31:57,846 --> 00:32:00,125 helped us to better understand our solar system 518 00:32:00,125 --> 00:32:02,921 as it is now, and also its history. 519 00:32:02,921 --> 00:32:06,338 LUU: The Kuiper Belt is really the frontier 520 00:32:06,338 --> 00:32:09,272 if you want to understand the solar system. 521 00:32:09,272 --> 00:32:11,446 But it is very difficult to study it, 522 00:32:11,446 --> 00:32:15,312 because it is so far away. 523 00:32:15,312 --> 00:32:17,936 NARRATOR: Despite the challenges, 524 00:32:17,936 --> 00:32:20,386 more than 4,000 Kuiper Belt objects 525 00:32:20,386 --> 00:32:23,424 have been discovered to date. 526 00:32:26,358 --> 00:32:28,394 And scientists estimate 527 00:32:28,394 --> 00:32:31,466 there may be 200 dwarf planets. 528 00:32:34,642 --> 00:32:38,404 Some have rings and moons. 529 00:32:38,404 --> 00:32:43,754 Some are bizarre and misshapen. 530 00:32:43,754 --> 00:32:46,309 But they all share one thing in common. 531 00:32:49,036 --> 00:32:52,625 They're made of icy materials, similar to Triton. 532 00:32:55,525 --> 00:32:59,770 This is where Triton belongs. 533 00:32:59,770 --> 00:33:03,015 So how did it end up around a billion miles away, 534 00:33:03,015 --> 00:33:07,399 in orbit around Neptune? 535 00:33:07,399 --> 00:33:11,472 ♪ 536 00:33:15,994 --> 00:33:18,237 HOWETT: So, to understand Triton, 537 00:33:18,237 --> 00:33:20,274 you have to understand the Kuiper Belt. 538 00:33:20,274 --> 00:33:21,896 If this is our sun, 539 00:33:21,896 --> 00:33:24,588 the one population of Kuiper Belt objects 540 00:33:24,588 --> 00:33:27,936 orbit it in a nice circle. 541 00:33:27,936 --> 00:33:30,698 Another population of Kuiper Belt objects 542 00:33:30,698 --> 00:33:34,046 have a highly elliptical orbit. 543 00:33:34,046 --> 00:33:36,600 So the question is, why are these so different? 544 00:33:36,600 --> 00:33:40,052 What caused them to be in this weird orbit? 545 00:33:40,052 --> 00:33:42,054 Well, the answer is, some of these objects 546 00:33:42,054 --> 00:33:44,953 are in resonance with another planet, Neptune. 547 00:33:44,953 --> 00:33:48,198 Resonance is when two objects have paths 548 00:33:48,198 --> 00:33:50,304 that meet up occasionally. 549 00:33:50,304 --> 00:33:52,306 And we see this throughout the solar system. 550 00:33:52,306 --> 00:33:54,308 If you look, for example, at Pluto, 551 00:33:54,308 --> 00:33:55,619 it'll go around 552 00:33:55,619 --> 00:33:58,553 on this elliptical orbittwice 553 00:33:58,553 --> 00:34:02,454 in the same time Neptune has gone around three times. 554 00:34:02,454 --> 00:34:05,215 And this resonance is an important clue 555 00:34:05,215 --> 00:34:07,804 in understanding how disruptive 556 00:34:07,804 --> 00:34:10,220 Neptune is to Kuiper Belt objects. 557 00:34:14,500 --> 00:34:16,709 ♪ 558 00:34:16,709 --> 00:34:19,091 NARRATOR: Scientists think Neptune formed 559 00:34:19,091 --> 00:34:22,646 much closer to the sun, 560 00:34:22,646 --> 00:34:25,063 then slowly drifted out. 561 00:34:28,652 --> 00:34:31,448 Its huge gravity disrupted the orbits 562 00:34:31,448 --> 00:34:34,451 of the Kuiper Belt worlds it encountered, 563 00:34:34,451 --> 00:34:36,902 kicking them into the elliptical orbits 564 00:34:36,902 --> 00:34:40,216 we see today. 565 00:34:40,216 --> 00:34:43,667 DURFEY: The early solar system was complete chaos, 566 00:34:43,667 --> 00:34:47,533 filled with small bodies growing larger 567 00:34:47,533 --> 00:34:49,328 and smashing into each other, 568 00:34:49,328 --> 00:34:52,124 sometimes destroying. 569 00:34:52,124 --> 00:34:54,333 Complete chaos. 570 00:34:55,403 --> 00:34:57,371 NARRATOR: During all the commotion, 571 00:34:57,371 --> 00:35:02,030 Triton became trapped by Neptune's gravity, 572 00:35:02,030 --> 00:35:06,311 slipping into its backward orbit. 573 00:35:06,311 --> 00:35:11,730 And being this close to a giant has consequences. 574 00:35:13,318 --> 00:35:16,907 Just as our moon raises tides on Earth, 575 00:35:16,907 --> 00:35:21,498 Neptune raises tides on Triton, 576 00:35:21,498 --> 00:35:24,984 stretching and squashing it like a stress ball, 577 00:35:24,984 --> 00:35:29,851 heating it up. 578 00:35:29,851 --> 00:35:32,544 HOWETT: Triton being captured by Neptune 579 00:35:32,544 --> 00:35:35,133 fundamentally changed how it works. 580 00:35:35,133 --> 00:35:38,032 On Earth, we experience energy every day. 581 00:35:38,032 --> 00:35:39,999 You might be able to hear it in the roar 582 00:35:39,999 --> 00:35:42,761 that comes from the tide coming in underneath us. 583 00:35:42,761 --> 00:35:45,004 [waves pounding] 584 00:35:45,004 --> 00:35:47,006 Tidal energy can force water up through cracks 585 00:35:47,006 --> 00:35:48,491 in the Earth, like the one in front of us, 586 00:35:48,491 --> 00:35:53,634 creating plumes erupting up to the sky. 587 00:35:53,634 --> 00:35:58,777 NARRATOR: On Triton, the plumes are even more spectacular. 588 00:35:58,777 --> 00:36:02,505 HOWETT: The plumes on Triton would be magnificent to behold. 589 00:36:02,505 --> 00:36:06,957 Erupting from the surface, cracks like this, 590 00:36:06,957 --> 00:36:11,134 but going five miles into the sky. 591 00:36:11,134 --> 00:36:12,998 I mean, it'd just be absolutely phenomenal. 592 00:36:12,998 --> 00:36:15,207 [geyser bursts] 593 00:36:15,207 --> 00:36:18,659 NARRATOR: What creates Triton's plumes is a mystery. 594 00:36:18,659 --> 00:36:24,112 But one theory lies in its unusual orbit. 595 00:36:24,112 --> 00:36:27,495 HOWETT: It's highly tilted, and Triton orbits backwards. 596 00:36:27,495 --> 00:36:29,601 Meaning as it goes around Neptune, 597 00:36:29,601 --> 00:36:31,775 its pull and push that it receives 598 00:36:31,775 --> 00:36:33,674 from Neptune and its moons changes. 599 00:36:33,674 --> 00:36:35,779 This creates a kind of friction, 600 00:36:35,779 --> 00:36:37,333 similar to the one that you get 601 00:36:37,333 --> 00:36:39,576 when you rub your hands together on a cold day. 602 00:36:39,576 --> 00:36:42,234 Your hands warm up, and so might Triton. 603 00:36:42,234 --> 00:36:45,410 We call that kind of energy tidal heating. 604 00:36:48,067 --> 00:36:51,450 NARRATOR: As Neptune's gravity stretches and squashes 605 00:36:51,450 --> 00:36:53,487 its giant moon... 606 00:36:53,487 --> 00:36:56,386 [plume roaring] 607 00:36:56,386 --> 00:36:58,492 ...the tidal heating produced 608 00:36:58,492 --> 00:37:02,358 melts Triton's frozen interior... 609 00:37:02,358 --> 00:37:05,464 ♪ 610 00:37:05,464 --> 00:37:10,573 ...powering its spectacular plumes. 611 00:37:10,573 --> 00:37:12,333 DURFEY: Triton is a great example 612 00:37:12,333 --> 00:37:15,716 of how interconnected our solar system is. 613 00:37:15,716 --> 00:37:17,856 And it also serves as a goodexample 614 00:37:17,856 --> 00:37:21,308 of how a large, giant planet 615 00:37:21,308 --> 00:37:23,275 straying into a belt of objects 616 00:37:23,275 --> 00:37:26,416 can really mess up your system. 617 00:37:34,390 --> 00:37:39,326 NARRATOR: Triton was plucked from the Kuiper Belt, 618 00:37:39,326 --> 00:37:44,676 a distant realm filled with mysterious worlds 619 00:37:44,676 --> 00:37:47,161 so far away 620 00:37:47,161 --> 00:37:51,510 we can't make them out in much detail. 621 00:37:51,510 --> 00:37:54,306 But we have sent one spacecraft. 622 00:38:00,174 --> 00:38:04,385 It took over nine years for New Horizons to get here 623 00:38:04,385 --> 00:38:08,044 and home in on its primary target. 624 00:38:14,361 --> 00:38:16,363 ♪ 625 00:38:16,363 --> 00:38:21,022 The tiny spacecraft captured the first close-up images 626 00:38:21,022 --> 00:38:25,958 of this Kuiper Belt world, 627 00:38:25,958 --> 00:38:28,720 revealing unexpectedly complex 628 00:38:28,720 --> 00:38:32,689 and dynamic surface features: 629 00:38:32,689 --> 00:38:36,969 mountains as high as the Alps, made from water, 630 00:38:36,969 --> 00:38:42,285 frozen as hard as granite. 631 00:38:42,285 --> 00:38:46,047 But there's something else odd out here. 632 00:38:46,047 --> 00:38:49,257 Another world close by. 633 00:38:58,025 --> 00:39:02,995 How did Charon and Pluto end up almost touching? 634 00:39:07,621 --> 00:39:09,657 Charon orbits about 12,000 miles 635 00:39:09,657 --> 00:39:11,072 from the surface of Pluto, 636 00:39:11,072 --> 00:39:13,040 which sounds like a really largenumber, 637 00:39:13,040 --> 00:39:14,628 but is actually really close 638 00:39:14,628 --> 00:39:16,906 for the scale of the Kuiper Belt. 639 00:39:16,906 --> 00:39:19,564 It's very common in our solar system 640 00:39:19,564 --> 00:39:24,534 for moons that are close enough to their parent body 641 00:39:24,534 --> 00:39:26,778 to become tidally locked. 642 00:39:26,778 --> 00:39:29,297 And that is where one orbit 643 00:39:29,297 --> 00:39:32,404 will also be one spin, 644 00:39:32,404 --> 00:39:34,924 so that the same face of that moon 645 00:39:34,924 --> 00:39:38,030 is presented to the planet at all times. 646 00:39:42,518 --> 00:39:45,279 NARRATOR: All large moons in the solar system, 647 00:39:45,279 --> 00:39:48,731 including our own, are tidally locked, 648 00:39:48,731 --> 00:39:53,805 only showing one face to their parent planet. 649 00:39:53,805 --> 00:39:56,601 But in the case of Pluto and Charon, 650 00:39:56,601 --> 00:40:01,399 it isn't just Charon that is tidally locked to Pluto. 651 00:40:01,399 --> 00:40:05,437 Pluto is also tidally locked to Charon. 652 00:40:05,437 --> 00:40:10,373 Both worlds constantly face each other at all times. 653 00:40:12,720 --> 00:40:15,205 RICE: And what that means is, if you're on the side of Pluto 654 00:40:15,205 --> 00:40:17,311 where you're able to see Charon, 655 00:40:17,311 --> 00:40:20,659 then it'll look like it's just hanging there all the time. 656 00:40:20,659 --> 00:40:22,558 It's not going to rise, it's not going to set. 657 00:40:22,558 --> 00:40:26,389 It's just going to constantly be in your sky. 658 00:40:26,389 --> 00:40:32,464 ♪ 659 00:40:32,464 --> 00:40:38,574 NARRATOR: This isn't just a dwarf planet and its moon, 660 00:40:38,574 --> 00:40:41,784 but a binary pair. 661 00:40:41,784 --> 00:40:46,374 ♪ 662 00:40:46,374 --> 00:40:51,552 New Horizons is still studying Kuiper Belt worlds today. 663 00:40:55,211 --> 00:40:58,801 During the most distant fly-by in history, 664 00:40:58,801 --> 00:41:04,565 it encountered Arrokoth, 665 00:41:04,565 --> 00:41:07,603 a bizarre snowman-shaped object. 666 00:41:14,610 --> 00:41:16,715 SUNSHINE: It is two pieces that are stuck together, 667 00:41:16,715 --> 00:41:20,892 and those two pieces must have come together very gently. 668 00:41:20,892 --> 00:41:23,515 To actually see it was really quite remarkable. 669 00:41:23,515 --> 00:41:26,760 Any time you see a new world, it's remarkable. 670 00:41:30,177 --> 00:41:33,525 NARRATOR: Why do the worlds out here in the Kuiper Belt 671 00:41:33,525 --> 00:41:37,667 form these partnerships? 672 00:41:37,667 --> 00:41:39,738 LUU: Things become slower and slower 673 00:41:39,738 --> 00:41:41,637 as you go further away from the sun. 674 00:41:41,637 --> 00:41:44,778 In the Kuiper Belt, things might collide 675 00:41:44,778 --> 00:41:47,988 at the speed of a few hundred feet per second. 676 00:41:47,988 --> 00:41:51,785 They occur at such low-impact velocity 677 00:41:51,785 --> 00:41:54,270 that a lot of the collisions are constructive 678 00:41:54,270 --> 00:41:59,275 rather than destructive. 679 00:41:59,275 --> 00:42:05,108 NARRATOR: At some point in their history, Pluto and Charon collided. 680 00:42:11,390 --> 00:42:15,774 But their slow movements 681 00:42:15,774 --> 00:42:19,053 meant this was less of an impact 682 00:42:19,053 --> 00:42:22,540 and more of an embrace. 683 00:42:27,545 --> 00:42:32,342 The Kuiper Belt is so vast and far from the sun 684 00:42:32,342 --> 00:42:35,863 that many mysteries still remain. 685 00:42:38,763 --> 00:42:40,937 I am often pretty amazed that we're actually able 686 00:42:40,937 --> 00:42:43,664 to study things like the Big Bang 687 00:42:43,664 --> 00:42:45,942 and the early universe and distant galaxies, 688 00:42:45,942 --> 00:42:48,669 and yet we still actually don't know everything 689 00:42:48,669 --> 00:42:50,257 that there is to know about our own solar system 690 00:42:50,257 --> 00:42:51,672 and our own backyard. 691 00:42:51,672 --> 00:42:55,262 I'm very confident that there are many, many worlds 692 00:42:55,262 --> 00:42:57,713 out there that we are yet to discover, 693 00:42:57,713 --> 00:43:01,337 and that we haven't even imagined yet. 694 00:43:01,337 --> 00:43:06,963 ♪ 695 00:43:13,383 --> 00:43:17,387 NARRATOR: We can see distant stars in the night sky 696 00:43:17,387 --> 00:43:21,219 because they burn so bright. 697 00:43:21,219 --> 00:43:23,531 Telescopes can detect planets 698 00:43:23,531 --> 00:43:27,950 as they pass in front of their parent stars. 699 00:43:27,950 --> 00:43:30,884 Seeing worlds in our own solar system 700 00:43:30,884 --> 00:43:33,611 is much harder, 701 00:43:33,611 --> 00:43:36,614 but not impossible. 702 00:43:36,614 --> 00:43:40,652 ♪ 703 00:43:40,652 --> 00:43:42,792 In 2018, 704 00:43:42,792 --> 00:43:45,899 a faint point of light was detected 705 00:43:45,899 --> 00:43:50,697 about 12 billion miles from the sun. 706 00:43:50,697 --> 00:43:54,183 It's thought to be a dwarf planet 707 00:43:54,183 --> 00:43:57,255 nicknamed FarFarOut. 708 00:44:02,640 --> 00:44:07,403 This is the most distant object yet seen in our solar system 709 00:44:07,403 --> 00:44:11,925 by some of our most powerful telescopes. 710 00:44:11,925 --> 00:44:16,723 But it's not the limit of what could be out there. 711 00:44:16,723 --> 00:44:22,349 ♪ 712 00:44:22,349 --> 00:44:25,939 OLUSEYI: How far do you expect the solar system to extend? 713 00:44:25,939 --> 00:44:27,699 You may imagine that it ends 714 00:44:27,699 --> 00:44:29,839 at the last major planet, Neptune. 715 00:44:29,839 --> 00:44:31,979 However, that's not exactly the case, 716 00:44:31,979 --> 00:44:33,360 and let me show you why. 717 00:44:33,360 --> 00:44:35,776 Here I'm gonna make a model of the solar system. 718 00:44:35,776 --> 00:44:38,676 This rock is my sun, 719 00:44:38,676 --> 00:44:40,401 and I'm gonna place it right there, 720 00:44:40,401 --> 00:44:42,749 and an inch away, I'm gonna place the Earth. 721 00:44:42,749 --> 00:44:45,027 And so this will be my scale, one inch equals 722 00:44:45,027 --> 00:44:47,961 the average distance between the Earth and the sun. 723 00:44:47,961 --> 00:44:50,239 So now, if I go a second inch, 724 00:44:50,239 --> 00:44:53,656 I arrive at the asteroid belt. 725 00:44:53,656 --> 00:44:57,867 And to get to the most distant major planet, Neptune, 726 00:44:57,867 --> 00:45:00,214 that's gonna be about 30 inches. 727 00:45:00,214 --> 00:45:02,389 Now, we have to keep going and going, 728 00:45:02,389 --> 00:45:03,908 because out here is 729 00:45:03,908 --> 00:45:06,462 the most distantly observed object ever 730 00:45:06,462 --> 00:45:08,291 in the history of our solar system, 731 00:45:08,291 --> 00:45:10,086 11 feet away from the sun, 732 00:45:10,086 --> 00:45:11,985 132 inches, 733 00:45:11,985 --> 00:45:13,469 12 billion miles, 734 00:45:13,469 --> 00:45:16,783 is FarFarOut. 735 00:45:16,783 --> 00:45:20,683 NARRATOR: But the solar system doesn't end here. 736 00:45:20,683 --> 00:45:23,721 OLUSEYI: I have to walk another 50 paces... 737 00:45:32,626 --> 00:45:37,079 ...another 186 billion miles, 738 00:45:37,079 --> 00:45:39,219 and now we've reached our destination, 739 00:45:39,219 --> 00:45:42,049 a vast region known as the Oort Cloud. 740 00:45:42,049 --> 00:45:45,156 ♪ 741 00:45:45,156 --> 00:45:47,745 NARRATOR: Clinging on at the very edge 742 00:45:47,745 --> 00:45:51,162 of the sun's gravitational influence, 743 00:45:51,162 --> 00:45:54,959 the Oort Cloud is our solar system's largest 744 00:45:54,959 --> 00:45:58,031 and most mysterious realm. 745 00:46:03,208 --> 00:46:05,797 It's so deep into the darkness, 746 00:46:05,797 --> 00:46:09,042 it's almost impossible to imagine, 747 00:46:09,042 --> 00:46:11,699 let alone see, 748 00:46:11,699 --> 00:46:14,772 filled with billions upon billions 749 00:46:14,772 --> 00:46:18,568 of strange worlds. 750 00:46:18,568 --> 00:46:21,295 Most are thought to be icy objects 751 00:46:21,295 --> 00:46:24,298 the size of mountains. 752 00:46:24,298 --> 00:46:29,303 But it's likely some are made of rock. 753 00:46:29,303 --> 00:46:34,343 And if we were able to go there, we'd discover they are pristine. 754 00:46:34,343 --> 00:46:37,691 ♪ 755 00:46:37,691 --> 00:46:42,558 Barely changed since the dawn of the solar system. 756 00:46:42,558 --> 00:46:46,631 It's thought some could be older than the sun. 757 00:46:48,633 --> 00:46:50,877 The Oort Cloud's existence is hypothetical, 758 00:46:50,877 --> 00:46:53,017 but science doesn't deal in fairy tales, 759 00:46:53,017 --> 00:46:57,193 so how do we know it's actually there if we've never seen it? 760 00:46:57,193 --> 00:47:01,646 ♪ 761 00:47:01,646 --> 00:47:05,339 NARRATOR: For as long as we've been looking into the night sky, 762 00:47:05,339 --> 00:47:09,999 we've seen signs that the Oort Cloud is real. 763 00:47:09,999 --> 00:47:13,071 And this is one of them. 764 00:47:18,766 --> 00:47:20,872 For hundreds of years, 765 00:47:20,872 --> 00:47:24,876 it's been locked in a deep, frozen slumber. 766 00:47:27,327 --> 00:47:29,950 ♪ 767 00:47:29,950 --> 00:47:32,504 But now it stirs. 768 00:47:32,504 --> 00:47:36,370 ♪ 769 00:47:36,370 --> 00:47:39,960 As it nears the sun, 770 00:47:39,960 --> 00:47:42,756 warm rays bathe its surface... 771 00:47:47,795 --> 00:47:50,798 ...and it begins to thaw. 772 00:47:50,798 --> 00:47:56,114 [hissing] 773 00:48:08,092 --> 00:48:11,026 ♪ 774 00:48:11,026 --> 00:48:16,652 So much debris is torn from the surface, 775 00:48:16,652 --> 00:48:20,276 it stretches out, forming a tail... 776 00:48:22,002 --> 00:48:26,041 ...around 14 million miles long. 777 00:48:27,766 --> 00:48:31,805 This is the comet Nishimura. 778 00:48:36,499 --> 00:48:41,194 It's visible from Earth for just a few weeks, 779 00:48:41,194 --> 00:48:46,199 before eventually heading back into the darkness, 780 00:48:46,199 --> 00:48:50,928 just the latest in a long line of icy visitors. 781 00:48:56,209 --> 00:48:58,245 Hale-Bopp. 782 00:49:01,248 --> 00:49:04,596 Neowise. 783 00:49:04,596 --> 00:49:10,671 They lit up our skies for weeks, or even months, on end. 784 00:49:10,671 --> 00:49:12,501 Humans have been captivated by comets 785 00:49:12,501 --> 00:49:14,330 because, frankly, they're spectacular. 786 00:49:14,330 --> 00:49:16,988 CHABOT: And the fact that they do wander 787 00:49:16,988 --> 00:49:19,577 around the solar system from time to time 788 00:49:19,577 --> 00:49:22,925 really is a unique scientific opportunity. 789 00:49:26,549 --> 00:49:28,862 NARRATOR: When scientists followed the trajectories 790 00:49:28,862 --> 00:49:30,898 of these comets back, 791 00:49:30,898 --> 00:49:35,006 they discovered they came from the same region, 792 00:49:35,006 --> 00:49:40,529 more than 200 billion miles from the sun. 793 00:49:40,529 --> 00:49:41,875 SUNSHINE: If you calculate 794 00:49:41,875 --> 00:49:44,740 where the orbit took you back to, 795 00:49:44,740 --> 00:49:46,224 it was way out, 796 00:49:46,224 --> 00:49:51,436 unbelievably far out, what we now call the Oort Cloud. 797 00:49:51,436 --> 00:49:55,544 NARRATOR: It's thought the gravity of other objects in the galaxy 798 00:49:55,544 --> 00:50:00,859 can occasionally knock these icy objects inwards. 799 00:50:00,859 --> 00:50:02,413 SUNSHINE: But the really interesting thing 800 00:50:02,413 --> 00:50:05,657 was that they were coming from all directions in space, 801 00:50:05,657 --> 00:50:07,935 and there had to be a cloud. 802 00:50:07,935 --> 00:50:11,387 ♪ 803 00:50:11,387 --> 00:50:14,597 NARRATOR: Although we can't see this far out, 804 00:50:14,597 --> 00:50:17,600 comets with orbits starting in the Oort Cloud 805 00:50:17,600 --> 00:50:22,157 streak across our skies. 806 00:50:22,157 --> 00:50:24,366 RICE: The Oort Cloud is kind of incredible. 807 00:50:24,366 --> 00:50:25,919 No one's actually been there, 808 00:50:25,919 --> 00:50:28,370 no one's actually observed anything within the Oort Cloud. 809 00:50:28,370 --> 00:50:31,166 They've only seen the wanderers that have escaped 810 00:50:31,166 --> 00:50:33,271 from the Oort Cloud for a brief moment, 811 00:50:33,271 --> 00:50:34,617 which I think is what makes it 812 00:50:34,617 --> 00:50:37,965 so spectacular and so exciting to me. 813 00:50:37,965 --> 00:50:41,900 CHABOT: If I could visit one of those dark regions, 814 00:50:41,900 --> 00:50:44,075 I would have to choose the Oort Cloud. 815 00:50:44,075 --> 00:50:46,008 We don't know that region at all, 816 00:50:46,008 --> 00:50:48,907 we haven't ever explored it, so for me, 817 00:50:48,907 --> 00:50:51,324 that would be the most exciting place to go. 818 00:50:51,324 --> 00:50:54,223 ♪ 819 00:50:54,223 --> 00:50:55,914 NARRATOR: We think of the solar system 820 00:50:55,914 --> 00:51:01,472 as the sun and all the planets. 821 00:51:01,472 --> 00:51:04,095 But that's just what's close to Earth. 822 00:51:07,271 --> 00:51:10,205 As wandering worlds give us rare glimpses 823 00:51:10,205 --> 00:51:13,035 into what is beyond 824 00:51:13,035 --> 00:51:16,521 and technology improves, 825 00:51:16,521 --> 00:51:21,975 we're discovering more and more. 826 00:51:21,975 --> 00:51:24,011 RUSSELL: We're really only scratching the surface, 827 00:51:24,011 --> 00:51:27,014 so there are millions of these tiny bodies out there, 828 00:51:27,014 --> 00:51:31,088 and we still have so many secrets to unlock from them. 829 00:51:31,088 --> 00:51:35,057 MERCED: There is so much information in darkness. 830 00:51:35,057 --> 00:51:37,059 If we pay more attention 831 00:51:37,059 --> 00:51:40,787 and we trust what we perceive 832 00:51:40,787 --> 00:51:44,618 with all our senses, 833 00:51:44,618 --> 00:51:47,932 we will gain much more information 834 00:51:47,932 --> 00:51:51,970 from those dark regions of not only our solar system, 835 00:51:51,970 --> 00:51:54,111 but of the universe. 836 00:51:54,111 --> 00:51:56,147 This model of the solar system, 837 00:51:56,147 --> 00:52:00,117 it's missing all of the most interesting bits. 838 00:52:00,117 --> 00:52:02,119 ♪