1 00:00:04,892 --> 00:00:07,959 We thought we knew our solar system. 2 00:00:07,960 --> 00:00:11,522 Turns out we were wrong. 3 00:00:11,523 --> 00:00:13,768 Groundbreaking observations suggest 4 00:00:13,769 --> 00:00:16,282 an unseen ninth planet 5 00:00:16,283 --> 00:00:20,933 may be out there on the fringes of our solar system. 6 00:00:20,934 --> 00:00:23,013 And it could be huge, 7 00:00:23,023 --> 00:00:26,348 5,000 times more massive than Pluto 8 00:00:26,358 --> 00:00:28,990 and 10 times the mass of the Earth. 9 00:00:29,000 --> 00:00:31,335 We don't get a lot of revolutions in astronomy. 10 00:00:31,336 --> 00:00:35,234 And here we are on the cusp of a discovery like this. 11 00:00:35,235 --> 00:00:36,689 It's crazy to think that, 12 00:00:36,690 --> 00:00:38,539 as much as we've looked into the universe, 13 00:00:38,540 --> 00:00:42,567 that there's this ninth planet out there that we've never seen. 14 00:00:42,568 --> 00:00:45,536 If planet 9 really is out there, 15 00:00:45,537 --> 00:00:47,852 what will it be like? 16 00:00:47,853 --> 00:00:50,227 Is it a rocky super-Earth, 17 00:00:50,228 --> 00:00:52,602 an icy mega-Pluto, 18 00:00:52,603 --> 00:00:55,809 or a gassy mini-Neptune? 19 00:00:55,810 --> 00:00:58,710 Or is planet 9 an alien world 20 00:00:58,720 --> 00:01:01,490 stolen from another star? 21 00:01:01,491 --> 00:01:05,023 And could it provide an unlikely home for life 22 00:01:05,024 --> 00:01:08,853 100 billion miles from the Sun? 23 00:01:22,887 --> 00:01:24,964 Take a look at the night sky. 24 00:01:24,965 --> 00:01:26,419 The pattern of stars 25 00:01:26,420 --> 00:01:29,716 that drifts overhead appears fixed. 26 00:01:29,725 --> 00:01:32,792 But look for longer, weeks or months, 27 00:01:32,793 --> 00:01:37,285 and you'll see a handful of the points move. 28 00:01:37,286 --> 00:01:40,353 These slow-moving points of light are the planets, 29 00:01:40,354 --> 00:01:42,531 the giant chunks of rock or gas 30 00:01:42,532 --> 00:01:45,539 that orbit our home star, the Sun. 31 00:01:45,540 --> 00:01:48,182 We thought there were eight. 32 00:01:48,183 --> 00:01:49,498 We were wrong. 33 00:01:49,499 --> 00:01:51,676 You know, we think we understand something 34 00:01:51,686 --> 00:01:53,100 as simple as our solar system. 35 00:01:53,101 --> 00:01:55,149 We've found all the planets. 36 00:01:55,150 --> 00:01:59,732 And, right in front of us, we missed something big. 37 00:01:59,742 --> 00:02:04,125 A group of astronomers are studying the Kuiper belt, 38 00:02:04,126 --> 00:02:06,501 a vast band of icy asteroids 39 00:02:06,511 --> 00:02:11,062 that sits way, way outside the orbit of Neptune. 40 00:02:11,063 --> 00:02:14,467 Most of these objects move in a neat, circular formation 41 00:02:14,468 --> 00:02:16,210 around the Sun. 42 00:02:16,220 --> 00:02:19,386 But the astronomers are puzzled by a small group 43 00:02:19,386 --> 00:02:21,593 that appear to break the rules, 44 00:02:21,603 --> 00:02:24,403 swinging far outside the main belt 45 00:02:24,404 --> 00:02:28,005 on wild, extended orbits. 46 00:02:28,006 --> 00:02:31,440 Something sitting far outside the Kuiper belt 47 00:02:31,441 --> 00:02:35,132 seems to be pulling these asteroids out of line, 48 00:02:35,142 --> 00:02:38,705 something the size of a giant planet. 49 00:02:40,753 --> 00:02:42,891 Caltech astronomer Mike Brown hears 50 00:02:42,901 --> 00:02:45,107 about the wild observations 51 00:02:45,108 --> 00:02:49,432 and is determined to prove the planet theory wrong. 52 00:02:49,432 --> 00:02:50,659 When we saw these alignments of all 53 00:02:50,660 --> 00:02:52,470 these objects out there, we thought, 54 00:02:52,471 --> 00:02:53,994 "ugh, everybody's gonna say there's a planet. 55 00:02:53,995 --> 00:02:57,091 We have to very strongly prove there's not a planet." 56 00:02:57,092 --> 00:02:58,714 Because, of course, we all know 57 00:02:58,715 --> 00:03:03,208 there's not another planet out there. That's ridiculous. 58 00:03:03,209 --> 00:03:06,345 Mike asked his colleague, Konstantin Batygin, 59 00:03:06,346 --> 00:03:08,187 to run a computer simulation 60 00:03:08,196 --> 00:03:11,095 to see what effect a ninth planet 61 00:03:11,096 --> 00:03:13,470 should have on the Kuiper belt. 62 00:03:13,471 --> 00:03:15,649 Stunningly, the simulation predicts 63 00:03:15,658 --> 00:03:18,458 elongated orbits identical 64 00:03:18,459 --> 00:03:20,705 to ones already observed. 65 00:03:20,706 --> 00:03:23,872 But the simulation also spits out a surprise. 66 00:03:23,873 --> 00:03:26,949 There should be a second set of rogue orbits 67 00:03:26,950 --> 00:03:29,592 that are perpendicular to the first set. 68 00:03:29,593 --> 00:03:31,769 If Mike can locate these weird 69 00:03:31,770 --> 00:03:35,165 predicted objects inside the Kuiper belt, 70 00:03:35,174 --> 00:03:39,231 planet 9 is almost certainly real. 71 00:03:39,232 --> 00:03:42,566 I took these simulation results to Mike's office 72 00:03:42,567 --> 00:03:45,209 just a couple doors down from my office. 73 00:03:45,210 --> 00:03:47,386 And I said, "look!" You know, "we've got a huge problem!" 74 00:03:47,387 --> 00:03:48,703 He said, "no!" 75 00:03:48,713 --> 00:03:52,205 There's an object called 2012 dr30 76 00:03:52,206 --> 00:03:56,332 "which has an orbit just like the one you're predicting." 77 00:03:56,333 --> 00:03:59,371 Mike's asteroid fits the prediction perfectly. 78 00:03:59,372 --> 00:04:03,369 He searches the records for more and finds another four 79 00:04:03,370 --> 00:04:05,615 that seem to be in the right area. 80 00:04:05,616 --> 00:04:09,841 But just how closely will they fit the prediction? 81 00:04:09,842 --> 00:04:12,780 I remember sitting back and thinking, 82 00:04:12,781 --> 00:04:15,749 "okay, we're going to, right now, plot the data, 83 00:04:15,750 --> 00:04:19,916 the real observational data on top of the model." 84 00:04:19,917 --> 00:04:21,956 And Mike said, "if these two match up, 85 00:04:21,965 --> 00:04:24,301 my jaw is just gonna drop to the floor." 86 00:04:24,311 --> 00:04:28,428 The theory says they should be right here and right here. 87 00:04:28,438 --> 00:04:30,248 And I did the calculations very quickly 88 00:04:30,249 --> 00:04:33,454 to see where they were and brought them up. 89 00:04:33,455 --> 00:04:37,048 And there they are. One, two, three, four, five, 90 00:04:37,058 --> 00:04:38,571 right on these lines 91 00:04:38,572 --> 00:04:41,609 exactly where we predicted they should be. 92 00:04:41,610 --> 00:04:44,153 The moment we saw this, 93 00:04:44,154 --> 00:04:46,003 we went from cautious 94 00:04:46,004 --> 00:04:48,340 to "holy cow! This really is there!" 95 00:04:48,350 --> 00:04:50,586 We have to make sure to tell everybody right away 96 00:04:50,596 --> 00:04:53,267 "because it's actually real!" 97 00:04:53,268 --> 00:04:55,771 Mike and Konstantin had unlocked 98 00:04:55,772 --> 00:04:58,315 the solar system's greatest secret. 99 00:04:58,316 --> 00:05:02,382 Planet 9 was almost certainly real. 100 00:05:02,383 --> 00:05:03,995 And it had to be huge, 101 00:05:03,996 --> 00:05:07,202 perhaps 10 times the mass of Earth. 102 00:05:07,203 --> 00:05:09,577 We're not talking about something like our moon 103 00:05:09,578 --> 00:05:11,428 or Pluto. We're talking about something 104 00:05:11,429 --> 00:05:14,565 that is literally planet-sized. 105 00:05:14,566 --> 00:05:17,138 And we're seeing its gravitational wake 106 00:05:17,139 --> 00:05:18,464 affecting these other objects. 107 00:05:18,465 --> 00:05:20,572 The idea that there could be a giant planet 108 00:05:20,573 --> 00:05:22,353 that we've never seen is something I think 109 00:05:22,354 --> 00:05:24,402 most of people wouldn't have bet on. 110 00:05:24,403 --> 00:05:27,638 But the evidence is remarkable! 111 00:05:27,639 --> 00:05:29,915 To prove planet 9 exists, 112 00:05:29,925 --> 00:05:33,091 astronomers need to see it with their telescopes. 113 00:05:33,092 --> 00:05:35,199 But there's a problem. 114 00:05:35,200 --> 00:05:37,911 Computer simulations only give a broad idea 115 00:05:37,912 --> 00:05:40,020 of where to find it. 116 00:05:40,030 --> 00:05:42,800 And planet 9 is incredibly faint 117 00:05:42,801 --> 00:05:45,967 and almost inconceivably far away. 118 00:05:45,968 --> 00:05:47,779 It's much, much farther out 119 00:05:47,789 --> 00:05:50,025 than we ever expected to find planets. 120 00:05:50,035 --> 00:05:51,647 It probably spends most of its life, 121 00:05:51,648 --> 00:05:52,934 if it's on an elliptical orbit, 122 00:05:52,935 --> 00:05:55,805 so far away from the Sun that we just missed it. 123 00:06:02,218 --> 00:06:05,878 So just how far away is planet 9? 124 00:06:05,879 --> 00:06:09,145 The only way to truly appreciate its vast orbit 125 00:06:09,155 --> 00:06:12,321 is to build a scale model, 126 00:06:12,322 --> 00:06:15,884 perhaps the biggest working model of the solar system 127 00:06:15,885 --> 00:06:19,151 ever attempted. 128 00:06:19,161 --> 00:06:23,118 Planetary scientist Kevin Walsh is here to call the shots. 129 00:06:23,119 --> 00:06:26,712 And he starts with the size of the Sun. 130 00:06:26,722 --> 00:06:29,255 So what we've got here, our kickball, 131 00:06:29,265 --> 00:06:32,857 is going to set the scale of our mini-solar system today. 132 00:06:32,858 --> 00:06:36,162 So everything is scaled off of its relative size 133 00:06:36,163 --> 00:06:39,527 compared to the size of the Sun. 134 00:06:39,528 --> 00:06:41,744 Kevin quickly paces out the position 135 00:06:41,745 --> 00:06:43,882 of the inner rocky planets. 136 00:06:43,892 --> 00:06:48,473 All four sit within 60 yards of the Sun on this scale. 137 00:06:48,474 --> 00:06:52,739 And each planet would appear no bigger than a peppercorn. 138 00:06:52,740 --> 00:06:55,442 To make this a working solar system, 139 00:06:55,451 --> 00:06:57,332 we need to bring on the drones. 140 00:07:11,721 --> 00:07:14,630 Each drone represents a different planet. 141 00:07:14,631 --> 00:07:16,016 And the orbital speeds 142 00:07:16,016 --> 00:07:18,788 have been scaled so one Earth year 143 00:07:18,797 --> 00:07:21,232 takes just 30 seconds. 144 00:07:23,251 --> 00:07:24,665 Already, it's clear to see 145 00:07:24,666 --> 00:07:27,703 how tightly bunched these inner planets are, 146 00:07:27,704 --> 00:07:29,623 and how the closest planets 147 00:07:29,624 --> 00:07:32,128 orbit faster than those farther out. 148 00:07:37,551 --> 00:07:40,618 Far beyond the tightly packed rocky planets 149 00:07:40,619 --> 00:07:43,983 lies the first of the gas giant planets, 150 00:07:43,984 --> 00:07:47,616 on this scale, just over a football field from the Sun. 151 00:07:49,734 --> 00:07:52,535 So, after this 400-foot walk, we made to to Jupiter, 152 00:07:52,545 --> 00:07:54,820 the largest planet in the solar system. 153 00:07:54,821 --> 00:07:56,107 But, even by this size scale, 154 00:07:56,108 --> 00:07:59,245 Jupiter is only about the size of a lollipop. 155 00:08:01,254 --> 00:08:03,935 Another football-field length lies ahead 156 00:08:03,936 --> 00:08:06,607 on the walk to Saturn. 157 00:08:06,608 --> 00:08:09,310 As we look back across the lake bed, 158 00:08:09,319 --> 00:08:10,734 I can barely see the drones. 159 00:08:10,735 --> 00:08:13,802 We covered a huge distance. 160 00:08:13,803 --> 00:08:16,681 The trek out to Uranus is bigger still, 161 00:08:16,682 --> 00:08:18,196 three football fields 162 00:08:18,197 --> 00:08:20,541 or the length of an aircraft carrier. 163 00:08:20,542 --> 00:08:23,609 Turns out there's a lot of wind in the outer solar system! 164 00:08:23,610 --> 00:08:27,281 So I have to yell. 165 00:08:27,282 --> 00:08:29,588 Surprising amount of wind in the outer solar system. 166 00:08:31,903 --> 00:08:35,366 Tumbleweed, rattlesnakes. 167 00:08:35,367 --> 00:08:39,493 After Uranus, it's around 200 yards out to Neptune. 168 00:08:39,494 --> 00:08:41,770 Before the discovery of planet 9, 169 00:08:41,780 --> 00:08:45,243 we thought Neptune was the farthest planet from the Sun, 170 00:08:45,244 --> 00:08:47,885 around half a mile on the scale of our model. 171 00:08:47,886 --> 00:08:50,854 But Neptune's distant orbit is nothing 172 00:08:50,855 --> 00:08:54,190 compared to the orbit of planet 9. 173 00:08:54,191 --> 00:08:55,377 So here we are. 174 00:08:55,378 --> 00:08:57,495 We made it to the orbit of Neptune. 175 00:08:57,496 --> 00:08:59,840 We're only at the tip of the iceberg. 176 00:08:59,841 --> 00:09:01,583 We need to stop measuring in feet. 177 00:09:01,593 --> 00:09:03,176 And we need to start thinking in miles. 178 00:09:03,177 --> 00:09:05,750 We need a car to get out to planet 9. 179 00:09:12,192 --> 00:09:16,417 Planet 9 swings out on a highly elliptical orbit. 180 00:09:16,418 --> 00:09:18,358 Its closest pass to the Sun 181 00:09:18,368 --> 00:09:21,831 is a whopping 19 billion miles. 182 00:09:21,832 --> 00:09:25,028 That's six times wider than the orbit of Neptune. 183 00:09:25,038 --> 00:09:27,313 But, at its farthest point, 184 00:09:27,314 --> 00:09:31,896 planet 9 is 112 billion miles away. 185 00:09:31,906 --> 00:09:36,290 And, on this scale, that's an incredible 18 miles 186 00:09:36,291 --> 00:09:39,001 from our kickball-sized Sun. 187 00:09:39,002 --> 00:09:41,050 So we're here, end of the road. 188 00:09:41,051 --> 00:09:43,098 We've driven about 18 miles 189 00:09:43,099 --> 00:09:45,435 from where we first started setting up the solar system. 190 00:09:45,445 --> 00:09:47,354 But, in the scale of the solar system, 191 00:09:47,355 --> 00:09:49,274 it's over 100 billion miles. 192 00:09:49,275 --> 00:09:51,778 100 billion miles 193 00:09:51,779 --> 00:09:55,083 to get out to the furthest part of planet 9's orbit. 194 00:09:55,084 --> 00:09:56,538 So, to scale, 195 00:09:56,539 --> 00:09:58,776 and we don't know what planet 9 would look like, 196 00:09:58,785 --> 00:10:02,347 but it's probably about the size of a B.B. 197 00:10:02,348 --> 00:10:04,555 So this is the challenge for our astronomers. 198 00:10:04,565 --> 00:10:07,830 How do you see a b.B. From 18 miles away? 199 00:10:07,831 --> 00:10:10,137 This is what we have to do. 200 00:10:10,147 --> 00:10:12,422 It could take years for our telescopes 201 00:10:12,423 --> 00:10:16,084 to pick out an object so impossibly faint, 202 00:10:16,085 --> 00:10:18,261 far away as planet 9. 203 00:10:18,262 --> 00:10:21,330 Until then, scientists can only speculate 204 00:10:21,340 --> 00:10:24,931 on what this mysterious world might be like. 205 00:10:24,932 --> 00:10:27,307 We're in this wonderful moment right now 206 00:10:27,317 --> 00:10:28,999 where we suspect that planet 9 exists. 207 00:10:29,000 --> 00:10:30,909 But we really have no idea what it's like. 208 00:10:30,910 --> 00:10:33,879 And that means our imaginations can run wild. 209 00:10:33,889 --> 00:10:35,402 They're informed by science. 210 00:10:35,403 --> 00:10:37,709 But I love it when creativity takes hold, 211 00:10:37,719 --> 00:10:38,966 and you just run with it. 212 00:10:41,182 --> 00:10:42,834 So what are the options? 213 00:10:42,835 --> 00:10:45,734 Science suggests three possibilities. 214 00:10:45,735 --> 00:10:48,515 And the first is astonishing. 215 00:10:48,516 --> 00:10:50,159 Planet 9 could be made 216 00:10:50,168 --> 00:10:52,998 from the same materials as the Earth, 217 00:10:52,999 --> 00:10:55,145 but 10 times more massive, 218 00:10:55,146 --> 00:10:57,591 a rocky super-Earth. 219 00:10:59,808 --> 00:11:02,647 But what would this giant, rocky planet 220 00:11:02,648 --> 00:11:05,289 look like so far from the Sun? 221 00:11:05,290 --> 00:11:08,882 A bizarre volcanic world scarred with fire 222 00:11:08,883 --> 00:11:13,574 somehow emerges from the cold darkness of deep space. 223 00:11:27,973 --> 00:11:31,802 In 2016, astronomers release astonishing evidence 224 00:11:31,803 --> 00:11:34,049 of a missing ninth planet 225 00:11:34,050 --> 00:11:36,752 on the frozen edges of our solar system, 226 00:11:36,762 --> 00:11:41,016 100 billion miles from the Sun. 227 00:11:41,017 --> 00:11:42,768 Until our telescopes find it, 228 00:11:42,769 --> 00:11:47,450 we can only guess what this mysterious planet 9 is like. 229 00:11:47,460 --> 00:11:51,417 But the first option is perhaps the most surprising. 230 00:11:51,418 --> 00:11:54,584 Planet 9 could be made from rock, 231 00:11:54,585 --> 00:11:56,039 just like the Earth, 232 00:11:56,040 --> 00:11:58,810 but 10 times more massive, 233 00:11:58,811 --> 00:12:02,086 a so-called rocky super-Earth. 234 00:12:02,087 --> 00:12:04,225 When we looked out into the universe, we realized 235 00:12:04,234 --> 00:12:06,905 that the most common type of planet 236 00:12:06,906 --> 00:12:08,093 in the entire galaxy 237 00:12:08,094 --> 00:12:09,806 is something we don't have, 238 00:12:09,816 --> 00:12:12,191 something called a super-Earth. 239 00:12:15,259 --> 00:12:18,366 The Kepler space telescope finds alien worlds 240 00:12:18,367 --> 00:12:21,305 by measuring the tiny dip in light 241 00:12:21,306 --> 00:12:25,462 as a planet passes in front of its host star. 242 00:12:25,463 --> 00:12:29,856 Most of the alien solar systems Kepler finds have super-Earths. 243 00:12:29,857 --> 00:12:33,616 So how come our star doesn't have one? 244 00:12:33,617 --> 00:12:38,179 Could it be possible that planet 9 is our missing super-Earth? 245 00:12:38,180 --> 00:12:41,316 If planet 9 is a rocky super-Earth, 246 00:12:41,317 --> 00:12:43,553 what will it look like up close? 247 00:12:49,076 --> 00:12:53,163 Planetary geologist Jani Radebaugh imagines planet 9 248 00:12:53,173 --> 00:12:58,190 as a dramatic world of fire and ice. 249 00:12:58,191 --> 00:12:59,377 Right now, we're in Iceland. 250 00:12:59,378 --> 00:13:01,386 We're flying over amazing, 251 00:13:01,387 --> 00:13:04,296 beautiful volcanic landscapes of Iceland. 252 00:13:04,297 --> 00:13:06,641 We think this might be the perfect landscape 253 00:13:06,642 --> 00:13:09,679 for thinking about what might be happening on planet 9 254 00:13:09,680 --> 00:13:13,213 if it's a rocky super-Earth. 255 00:13:13,214 --> 00:13:15,321 These black mountains and lava flows 256 00:13:15,331 --> 00:13:17,438 were created by leftover heat 257 00:13:17,439 --> 00:13:21,100 from the Earth's formation spilling out onto the surface. 258 00:13:21,101 --> 00:13:25,197 Planet 9, born with so much more insulating rock, 259 00:13:25,198 --> 00:13:29,522 should have even more of this leftover heat trapped inside it. 260 00:13:29,523 --> 00:13:30,809 What we're talking about is a body 261 00:13:30,810 --> 00:13:33,718 that's maybe 10 times the mass of the Earth. 262 00:13:33,719 --> 00:13:35,827 I'd expect, because it's so large, 263 00:13:35,837 --> 00:13:37,944 that we should have lots more internal heat. 264 00:13:37,945 --> 00:13:40,191 And so, even though it's far away in the solar system, 265 00:13:40,192 --> 00:13:41,408 it's far away from the Sun, 266 00:13:41,409 --> 00:13:43,596 it's still got lots of its own energy. 267 00:13:50,563 --> 00:13:53,462 Touching down on the surface of planet 9, 268 00:13:53,463 --> 00:13:55,937 you'd find a world as inhospitable 269 00:13:55,947 --> 00:13:59,439 as you could imagine. 270 00:13:59,440 --> 00:14:01,290 Billions of miles from the Sun, 271 00:14:01,291 --> 00:14:03,764 the surface is lit by little more 272 00:14:03,765 --> 00:14:06,239 than the twinkle of distant stars 273 00:14:06,249 --> 00:14:09,940 and the red glow of intense geological activity 274 00:14:09,941 --> 00:14:12,483 on the surface. 275 00:14:12,484 --> 00:14:14,007 We can imagine, if we were on 276 00:14:14,008 --> 00:14:16,283 a super rocky Earth planet 9, 277 00:14:16,284 --> 00:14:19,153 we could have a landscape just like this one. 278 00:14:19,154 --> 00:14:21,370 There should be volcanoes erupting all the time. 279 00:14:21,371 --> 00:14:23,082 And the other thing we should see 280 00:14:23,083 --> 00:14:25,992 is lots and lots of ice and snow blanketing the landscape. 281 00:14:25,993 --> 00:14:28,931 This is because the atmosphere is so cold 282 00:14:28,932 --> 00:14:30,683 that parts of it have condensed 283 00:14:30,684 --> 00:14:32,593 and settled back down onto the surface. 284 00:14:32,594 --> 00:14:35,037 You're gonna have volcanoes. You're gonna have canyons. 285 00:14:35,038 --> 00:14:37,581 You're gonna have plate tectonics, mountain-building. 286 00:14:37,582 --> 00:14:40,352 All of these processes are still gonna be going on out there 287 00:14:40,353 --> 00:14:43,093 in what we normally would think of as the frozen, cold, 288 00:14:43,094 --> 00:14:45,568 and dead world of the outer solar system. 289 00:14:48,943 --> 00:14:51,119 As hot lava reaches the surface, 290 00:14:51,120 --> 00:14:54,287 it freezes suddenly in the cold of space, 291 00:14:54,297 --> 00:14:56,275 perhaps forming a weird, 292 00:14:56,276 --> 00:14:59,967 volcanic glass called obsidian, 293 00:14:59,968 --> 00:15:01,224 another feature shared 294 00:15:01,225 --> 00:15:03,668 with the sub-zero volcanoes of Iceland. 295 00:15:03,669 --> 00:15:06,509 Okay, let's put this whole thing together. 296 00:15:06,509 --> 00:15:08,686 We have a landscape 297 00:15:08,687 --> 00:15:11,062 that's kind of dimly lit by starlight, 298 00:15:11,072 --> 00:15:13,347 but maybe also by the reddish glow 299 00:15:13,348 --> 00:15:17,969 from erupting lavas spreading across the landscape. 300 00:15:17,970 --> 00:15:20,215 And then, behind you, you have gases 301 00:15:20,216 --> 00:15:21,760 that are changing immediately to snow 302 00:15:21,770 --> 00:15:24,243 and falling as snow down to the surface. 303 00:15:24,244 --> 00:15:27,639 And it would just be a beautiful, magical landscape. 304 00:15:31,013 --> 00:15:35,002 The case for a giant, rocky planet 9 is compelling 305 00:15:35,012 --> 00:15:37,248 because it paints such a vivid picture 306 00:15:37,258 --> 00:15:40,751 of a living volcanic world. 307 00:15:40,752 --> 00:15:42,206 But there's a problem. 308 00:15:45,740 --> 00:15:48,945 If planet 9 is, in fact, a super-Earth, 309 00:15:48,946 --> 00:15:50,985 how did it form? Where did it form? 310 00:15:50,995 --> 00:15:52,310 We don't have any other super-Earths 311 00:15:52,311 --> 00:15:53,528 in our solar system. 312 00:15:53,538 --> 00:15:55,112 And the ones we see around other stars 313 00:15:55,121 --> 00:15:57,457 are typically really close to their star. 314 00:15:57,467 --> 00:16:00,564 So how did our super-Earth end up way out there 315 00:16:00,565 --> 00:16:03,701 at the edges of our solar system? 316 00:16:03,702 --> 00:16:06,670 For planet 9 to be our rocky super-Earth, 317 00:16:06,671 --> 00:16:09,708 it would've had to have formed in the inner solar system 318 00:16:09,709 --> 00:16:12,746 and then migrated out to its current position. 319 00:16:12,747 --> 00:16:14,529 And that's a problem, 320 00:16:14,539 --> 00:16:17,932 because there probably wasn't enough rocky material left over 321 00:16:17,933 --> 00:16:19,318 in the early solar system 322 00:16:19,319 --> 00:16:22,920 to create both the massive planet 9 323 00:16:22,921 --> 00:16:27,275 as well as Mercury, Venus, Earth, and Mars. 324 00:16:27,285 --> 00:16:28,729 It's really hard to imagine 325 00:16:28,730 --> 00:16:31,540 that we could have formed a 10-Earth-mass planet here 326 00:16:31,541 --> 00:16:33,391 and still formed the rocky planets 327 00:16:33,392 --> 00:16:36,726 that we see today. 328 00:16:36,727 --> 00:16:38,903 - '- Time for a new theory. 329 00:16:38,904 --> 00:16:42,010 What if planet 9 formed from ice 330 00:16:42,011 --> 00:16:44,941 in the outer solar system? 331 00:16:44,951 --> 00:16:47,919 Calculations tell us it would have to be 10 times 332 00:16:47,920 --> 00:16:49,235 the mass of the Earth. 333 00:16:49,236 --> 00:16:51,185 And here's the kicker. 334 00:16:51,186 --> 00:16:53,363 An ice world that big 335 00:16:53,373 --> 00:16:57,391 would have an internal ocean of liquid water. 336 00:16:57,401 --> 00:16:59,537 A new world is revealed 337 00:16:59,538 --> 00:17:02,081 where icy geysers shoot through cracks 338 00:17:02,082 --> 00:17:03,665 in the frozen crust. 339 00:17:03,675 --> 00:17:05,060 And deep below it 340 00:17:05,061 --> 00:17:07,464 lies the largest body of liquid water 341 00:17:07,465 --> 00:17:09,118 in the solar system. 342 00:17:32,464 --> 00:17:34,245 The planets that make up our solar system 343 00:17:34,246 --> 00:17:37,748 seem to follow a pattern. 344 00:17:37,749 --> 00:17:42,043 The four closest to the Sun are all made from rock. 345 00:17:42,044 --> 00:17:46,764 The next four are giants made mostly from gas. 346 00:17:46,765 --> 00:17:49,565 Beyond Neptune, gas is replaced 347 00:17:49,575 --> 00:17:52,939 by multiple worlds made from ice. 348 00:17:52,940 --> 00:17:54,750 This is the Kuiper belt, 349 00:17:54,751 --> 00:17:57,986 a frozen realm of water-ice asteroids, 350 00:17:57,987 --> 00:18:00,332 millions of them. 351 00:18:00,333 --> 00:18:02,776 The Kuiper belt is a region of space 352 00:18:02,777 --> 00:18:04,627 outside of Neptune's orbit 353 00:18:04,628 --> 00:18:06,309 that extends out, 354 00:18:06,310 --> 00:18:09,120 eh, about 50 times the distance from the Earth to the Sun. 355 00:18:09,121 --> 00:18:10,971 So it's really far out there. 356 00:18:10,972 --> 00:18:13,109 And this is populated by icy bodies. 357 00:18:13,119 --> 00:18:15,424 These are giant chunks of ice 358 00:18:15,425 --> 00:18:17,404 that have some rock and other things in them. 359 00:18:17,405 --> 00:18:19,879 But they're mostly ice. 360 00:18:19,889 --> 00:18:23,252 Perhaps planet 9 is made from the same materials, 361 00:18:23,253 --> 00:18:25,955 an overgrown version of the Kuiper belt's 362 00:18:25,965 --> 00:18:29,162 most infamous citizen, Pluto. 363 00:18:31,576 --> 00:18:33,090 Poor Pluto. 364 00:18:33,091 --> 00:18:36,128 Discovered in 1930 by Clyde Tombaugh, 365 00:18:36,129 --> 00:18:38,077 this tiny ice world, 366 00:18:38,078 --> 00:18:39,562 smaller than our moon, 367 00:18:39,563 --> 00:18:43,293 was quickly proclaimed the ninth planet. 368 00:18:43,294 --> 00:18:47,618 But, in the 1990s, Mike brown and others discovered 369 00:18:47,619 --> 00:18:51,913 a host of icy worlds orbiting out with Pluto. 370 00:18:51,914 --> 00:18:55,248 Pluto was just another Kuiper belt object 371 00:18:55,249 --> 00:18:57,692 and got demoted to dwarf planet, 372 00:18:57,693 --> 00:19:00,335 to the dismay of much of the world. 373 00:19:00,336 --> 00:19:04,689 Everybody loves the idea that I killed Pluto, 374 00:19:04,690 --> 00:19:07,866 and now I'm trying to atone for my sins 375 00:19:07,867 --> 00:19:11,330 by replacing it with a new ninth planet. 376 00:19:11,331 --> 00:19:13,576 In fact, even my daughter suggested this 377 00:19:13,577 --> 00:19:16,249 long before we started looking for planet 9. 378 00:19:16,250 --> 00:19:19,386 She said, you know, "you should find a new planet." 379 00:19:19,387 --> 00:19:21,167 And then you can have found a planet. 380 00:19:21,168 --> 00:19:22,988 And there'll be nine planets again. 381 00:19:22,989 --> 00:19:25,136 "And everybody will like you again." 382 00:19:25,137 --> 00:19:29,292 If planet 9 is an icy Kuiper belt world, 383 00:19:29,293 --> 00:19:33,221 it'll be the biggest we've ever found. 384 00:19:33,222 --> 00:19:35,438 Pluto, the biggest object 385 00:19:35,439 --> 00:19:37,388 we know out there in the Kuiper belt now, 386 00:19:37,389 --> 00:19:39,922 is less than 1% the mass of the Earth, 387 00:19:39,932 --> 00:19:41,445 less than that. 388 00:19:41,446 --> 00:19:44,256 Planet 9, we think, is 10 times the mass of the Earth. 389 00:19:44,257 --> 00:19:47,591 So we're dealing with a factor of thousands of times in mass 390 00:19:47,592 --> 00:19:50,035 between the largest Kuiper belt object 391 00:19:50,036 --> 00:19:51,847 that we know now 392 00:19:51,848 --> 00:19:54,321 and the size of planet 9. 393 00:19:54,322 --> 00:19:58,350 So you're talking about super-mega-ultra-Pluto. 394 00:19:58,359 --> 00:20:00,239 It's really, really big. 395 00:20:00,240 --> 00:20:03,376 And it's hard to know what an ice ball 396 00:20:03,377 --> 00:20:05,652 like that would look like. 397 00:20:05,653 --> 00:20:09,611 It's not crazy to speculate that there could still be activity, 398 00:20:09,612 --> 00:20:11,234 internal geologic activity, 399 00:20:11,235 --> 00:20:13,807 keeping this world from being cold 400 00:20:13,808 --> 00:20:16,380 and totally dead. 401 00:20:16,381 --> 00:20:18,102 Peering through the darkness 402 00:20:18,103 --> 00:20:21,863 to a hypothetical mega-Pluto planet 9, 403 00:20:21,864 --> 00:20:25,099 we discover a giant world of ice. 404 00:20:25,100 --> 00:20:28,503 There's much less rock than a super-Earth planet 9. 405 00:20:28,504 --> 00:20:31,542 But the mass of ice alone creates enough gravity 406 00:20:31,543 --> 00:20:36,431 to generate warmth deep in the core, even out here. 407 00:20:36,432 --> 00:20:40,221 The real currency of keeping a planet alive is mass. 408 00:20:40,222 --> 00:20:43,131 Does it have enough mass to keep the interior warm? 409 00:20:43,132 --> 00:20:44,981 Well, something that's 5 to 10 times 410 00:20:44,982 --> 00:20:49,474 the mass of the Earth probably would be warm inside. 411 00:20:49,475 --> 00:20:53,661 Up close, the surface explodes with activity. 412 00:20:53,662 --> 00:20:58,481 But these volcanoes spew water ice, not lava. 413 00:20:58,491 --> 00:21:00,697 If something like a giant Pluto exists, 414 00:21:00,698 --> 00:21:02,647 it must be the most amazing landscape 415 00:21:02,648 --> 00:21:04,032 to take a walk over. 416 00:21:04,033 --> 00:21:07,466 You'd have these ice volcanoes spewing out jets 417 00:21:07,467 --> 00:21:10,435 of frozen water, of ice raining down on you. 418 00:21:10,436 --> 00:21:12,218 Maybe you'd look out over the landscape 419 00:21:12,227 --> 00:21:14,662 and see hundreds of these erupting. 420 00:21:14,672 --> 00:21:17,997 This dramatic, icy vista is a gateway 421 00:21:18,007 --> 00:21:19,787 to a secret world, 422 00:21:19,788 --> 00:21:22,786 a vast, slushy ocean of liquid water 423 00:21:22,787 --> 00:21:24,766 mixed with ice crystals, 424 00:21:24,776 --> 00:21:26,220 perhaps the largest 425 00:21:26,221 --> 00:21:28,833 single body of water in the solar system. 426 00:21:28,834 --> 00:21:31,041 There's gonna be enough internal heat, maybe, 427 00:21:31,051 --> 00:21:34,147 to turn this into a slushy water world. 428 00:21:34,148 --> 00:21:37,018 So it's not quite a terrestrial, rocky planet. 429 00:21:37,028 --> 00:21:39,501 And it's not a Uranus or Neptune. 430 00:21:39,502 --> 00:21:42,500 It's a true mega-ocean world, 431 00:21:42,501 --> 00:21:46,399 but perhaps a very cold one. 432 00:21:46,400 --> 00:21:49,932 Is planet 9 an icy mega-Pluto? 433 00:21:49,933 --> 00:21:51,843 The problem is scale. 434 00:21:51,853 --> 00:21:55,910 Pluto and the other objects in the Kuiper belt are tiny. 435 00:21:55,911 --> 00:21:58,415 So how could the same building materials 436 00:21:58,425 --> 00:22:02,481 have come together to form a giant? 437 00:22:02,482 --> 00:22:04,392 So, the idea that planet 9 438 00:22:04,402 --> 00:22:08,756 is simply a really scaled-up Pluto, a mega-Pluto, 439 00:22:08,757 --> 00:22:10,408 has some difficulties. 440 00:22:10,409 --> 00:22:14,070 We just don't think that there was enough mass out there 441 00:22:14,071 --> 00:22:15,921 in the far reaches of the solar system 442 00:22:15,922 --> 00:22:18,327 to all come together to build a planet that large. 443 00:22:18,337 --> 00:22:20,315 When you look at the Kuiper belt, 444 00:22:20,316 --> 00:22:22,195 there are all of these small, icy bodies. 445 00:22:22,196 --> 00:22:24,205 There's nothing very big out there. 446 00:22:24,215 --> 00:22:26,253 And we think that's not a coincidence, 447 00:22:26,254 --> 00:22:28,470 that the disk of dust and gas that formed the planets 448 00:22:28,471 --> 00:22:30,647 had more stuff closer to the Sun. 449 00:22:30,648 --> 00:22:32,567 And by the time you got out to where Pluto is, 450 00:22:32,568 --> 00:22:35,269 there wasn't much material to build planets out of, 451 00:22:35,270 --> 00:22:36,595 certainly not a planet 452 00:22:36,596 --> 00:22:40,949 5 to 10 times the mass of the Earth. 453 00:22:40,950 --> 00:22:45,571 So, if planet 9 didn't form in the icy outer system 454 00:22:45,572 --> 00:22:49,203 and didn't form in the rocky, inner solar system, 455 00:22:49,204 --> 00:22:51,123 where did it come from? 456 00:22:51,124 --> 00:22:53,133 The more likely option, 457 00:22:53,143 --> 00:22:56,111 planet 9 formed in the gas-rich zone 458 00:22:56,112 --> 00:22:58,219 in the middle of our solar system 459 00:22:58,220 --> 00:23:02,484 that also created Jupiter, Saturn, and Neptune. 460 00:23:02,485 --> 00:23:05,522 A gassy planet 9 could be similar to Neptune, 461 00:23:05,523 --> 00:23:08,957 but perhaps a little smaller, 462 00:23:08,958 --> 00:23:10,867 a mini-Neptune. 463 00:23:10,868 --> 00:23:13,479 But how would it get so much farther out 464 00:23:13,480 --> 00:23:15,360 than the other gas giants? 465 00:23:15,361 --> 00:23:18,299 And what would it look like? 466 00:23:18,300 --> 00:23:21,535 Imagine a weird, translucent world 467 00:23:21,536 --> 00:23:25,693 glowing in the dark like a giant deep-sea creature. 468 00:23:43,170 --> 00:23:45,604 Something on the fringes of our solar system 469 00:23:45,605 --> 00:23:49,039 is upsetting orbits and causing a ruckus. 470 00:23:49,049 --> 00:23:51,848 Could it be a planet? 471 00:23:51,849 --> 00:23:53,957 It's incredible to me that we now know 472 00:23:53,967 --> 00:23:55,579 of thousands of other planets 473 00:23:55,580 --> 00:23:57,628 going around other stars in the sky, 474 00:23:57,629 --> 00:24:00,399 but we may have missed a big planet 475 00:24:00,400 --> 00:24:02,517 in our own solar system. 476 00:24:02,518 --> 00:24:06,209 Planet 9, a world we know almost nothing about, 477 00:24:06,219 --> 00:24:10,177 beyond the possibility that it exists. 478 00:24:10,178 --> 00:24:14,868 Science suggests intriguing options... 479 00:24:14,869 --> 00:24:18,262 a giant, rocky world with a heart of fire, 480 00:24:18,263 --> 00:24:20,905 or an ice world filled 481 00:24:20,906 --> 00:24:23,913 with a giant, slushy ocean. 482 00:24:23,914 --> 00:24:28,268 But problems with each theory have led to new hunches. 483 00:24:28,269 --> 00:24:31,247 So, if it's not a rocky, metallic super-Earth 484 00:24:31,248 --> 00:24:35,403 and it's not a gigantic, ice-ball, mega-Pluto, 485 00:24:35,404 --> 00:24:36,888 what's left? 486 00:24:36,889 --> 00:24:39,530 And the answer is a gas giant. 487 00:24:39,531 --> 00:24:43,726 And that strikes me as being the most likely prospect. 488 00:24:43,727 --> 00:24:46,893 When you think about the mass of planet 9 489 00:24:46,894 --> 00:24:49,733 and where it is now, my best guess, 490 00:24:49,734 --> 00:24:54,494 it's something like a miniature version of Neptune. 491 00:24:54,495 --> 00:24:56,404 The gas giant planets 492 00:24:56,405 --> 00:24:59,374 are the monsters of our solar system. 493 00:24:59,384 --> 00:25:01,818 Instead of a solid surface, like the Earth, 494 00:25:01,828 --> 00:25:05,320 the gas giants have thick, stormy atmospheres 495 00:25:05,321 --> 00:25:08,428 that descend for tens of thousands of miles, 496 00:25:08,429 --> 00:25:11,269 shrouding their small, rocky cores. 497 00:25:13,447 --> 00:25:15,950 Jupiter is the largest gas giant, 498 00:25:15,960 --> 00:25:19,582 over 300 times the mass of Earth. 499 00:25:19,592 --> 00:25:20,878 Moving out from Jupiter, 500 00:25:20,879 --> 00:25:24,371 the gas giants get progressively smaller, 501 00:25:24,372 --> 00:25:28,301 Saturn, then Uranus, and finally Neptune, 502 00:25:28,311 --> 00:25:32,131 around 17 times the mass of the Earth. 503 00:25:32,141 --> 00:25:34,972 If planet 9 is a gas giant, 504 00:25:34,981 --> 00:25:37,019 it'll be even smaller, 505 00:25:37,020 --> 00:25:39,167 a mini-Neptune. 506 00:25:39,168 --> 00:25:41,345 If planet 9 is a mini-Neptune, 507 00:25:41,355 --> 00:25:43,165 if it's a lot like Neptune, 508 00:25:43,166 --> 00:25:44,977 then it's not really like 509 00:25:44,987 --> 00:25:46,500 a terrestrial planet, like Earth. 510 00:25:46,501 --> 00:25:49,044 But it's not really like a gas giant, like Jupiter. 511 00:25:49,045 --> 00:25:51,350 Neptune is this weird, in-between thing 512 00:25:51,360 --> 00:25:53,735 where it's probably got a rocky core. 513 00:25:53,736 --> 00:25:56,605 But it's actually, mostly, what astronomers call ices. 514 00:25:56,606 --> 00:26:00,207 It's got methane in it and water and various other substances 515 00:26:00,208 --> 00:26:03,305 and a very, very, very thick atmosphere on top of that. 516 00:26:07,769 --> 00:26:10,470 Neptune's thick clouds are stained blue 517 00:26:10,471 --> 00:26:12,587 with molecules of methane. 518 00:26:12,588 --> 00:26:17,209 But planet 9's atmosphere could be transparent. 519 00:26:17,210 --> 00:26:20,218 It's so cold out there, you're getting almost 520 00:26:20,219 --> 00:26:22,296 no extra energy from the Sun. 521 00:26:22,297 --> 00:26:24,176 And so then anything heavy in the atmosphere, 522 00:26:24,177 --> 00:26:26,225 any heavier molecule, over time, 523 00:26:26,226 --> 00:26:28,274 would have probably fallen to the surface. 524 00:26:28,275 --> 00:26:30,184 And only the lightest elements, 525 00:26:30,185 --> 00:26:33,123 the lightest molecules, would stay in your atmosphere, 526 00:26:33,124 --> 00:26:36,260 so maybe just almost pure hydrogen or helium. 527 00:26:36,261 --> 00:26:39,595 And you'd have, maybe, a really clear atmosphere. 528 00:26:39,596 --> 00:26:41,644 What would a mini-Neptune look like 529 00:26:41,645 --> 00:26:43,326 that far out from the Sun? 530 00:26:43,327 --> 00:26:45,900 The thing I think of are things like jellyfish, right? 531 00:26:45,910 --> 00:26:47,621 That sort of beautiful, translucent look, 532 00:26:47,622 --> 00:26:50,957 where you're looking through to the innards of the organism. 533 00:26:50,957 --> 00:26:52,411 In this case, you might look through 534 00:26:52,412 --> 00:26:55,807 to the innards of the planet in some way. 535 00:26:55,817 --> 00:26:58,350 The atmosphere may be transparent. 536 00:26:58,360 --> 00:27:01,031 But this planet is far from calm. 537 00:27:01,032 --> 00:27:04,526 The interior is lit by the flash of thunderstorms. 538 00:27:04,536 --> 00:27:07,168 And faint lights dance around the poles 539 00:27:07,178 --> 00:27:09,750 as solar winds from distant stars 540 00:27:09,751 --> 00:27:12,689 stream down the planet's magnetic fields. 541 00:27:12,690 --> 00:27:14,698 Looking into the innards of the planet, 542 00:27:14,699 --> 00:27:17,272 it would look, in some ways, like these gorgeous, 543 00:27:17,282 --> 00:27:21,240 beautiful deep-sea organisms that are bioluminescent. 544 00:27:21,241 --> 00:27:23,190 And we may have the planetary equivalent 545 00:27:23,191 --> 00:27:25,961 of something like out there in the inky blackness of space, 546 00:27:25,962 --> 00:27:30,285 rather than the inky blackness of the deep ocean. 547 00:27:30,286 --> 00:27:33,353 Could planet 9 be a mini-Neptune? 548 00:27:33,354 --> 00:27:36,926 Surprisingly, the possibility of an extra gas giant 549 00:27:36,927 --> 00:27:39,994 in our solar system isn't new. 550 00:27:39,995 --> 00:27:42,567 In 2011, scientists attempted 551 00:27:42,568 --> 00:27:43,824 to replicate the formation 552 00:27:43,825 --> 00:27:47,159 of our solar system using supercomputers. 553 00:27:47,160 --> 00:27:49,208 But their models didn't work 554 00:27:49,209 --> 00:27:54,621 unless they added an extra gas giant planet to the mix. 555 00:27:54,622 --> 00:27:56,799 It was really difficult to reproduce 556 00:27:56,809 --> 00:27:58,887 our current solar system. 557 00:27:58,888 --> 00:28:00,668 But one scientist found that, 558 00:28:00,669 --> 00:28:03,508 if you add a fifth large planet 559 00:28:03,509 --> 00:28:04,894 to our solar system, 560 00:28:04,895 --> 00:28:07,536 then that planet will end up 561 00:28:07,537 --> 00:28:09,743 getting ejected from our solar system. 562 00:28:09,744 --> 00:28:12,654 And you'd have the planets that we have today. 563 00:28:14,574 --> 00:28:16,978 Is planet 9 the missing gas giant 564 00:28:16,979 --> 00:28:19,689 predicted by the supercomputers? 565 00:28:19,690 --> 00:28:21,965 The computer model shows it being ejected 566 00:28:21,966 --> 00:28:24,371 by the immense gravity of Jupiter. 567 00:28:24,381 --> 00:28:28,665 But did planet 9 instead cling to our solar system 568 00:28:28,666 --> 00:28:32,337 by the tips of its gravitational fingers? 569 00:28:32,338 --> 00:28:34,019 Sometimes, our mathematical models 570 00:28:34,020 --> 00:28:35,900 predict things that we think are impossible. 571 00:28:35,901 --> 00:28:37,454 And then we find them. 572 00:28:37,455 --> 00:28:39,106 And, for a while, we've known that, 573 00:28:39,107 --> 00:28:40,591 if you throw a mini-Neptune 574 00:28:40,592 --> 00:28:42,699 into the mix of planets forming, 575 00:28:42,700 --> 00:28:44,223 the models work better. 576 00:28:44,224 --> 00:28:48,053 Maybe we found that key, finally... planet 9. 577 00:28:48,054 --> 00:28:51,190 We know giant planets can get thrown around. 578 00:28:51,191 --> 00:28:53,794 Observers have even seen ejected planets 579 00:28:53,804 --> 00:28:57,426 floating free in the space between stars. 580 00:28:57,436 --> 00:29:01,492 Did planet 9 almost suffer the same fate? 581 00:29:01,493 --> 00:29:04,135 It's entirely possible that there could've been 582 00:29:04,136 --> 00:29:05,550 a planet forming bigger than Earth, 583 00:29:05,551 --> 00:29:07,569 something like a super-Earth, well on its way 584 00:29:07,570 --> 00:29:09,083 to becoming a gas giant 585 00:29:09,084 --> 00:29:12,092 in this wonderful area of the disk, 586 00:29:12,093 --> 00:29:13,843 where it could've drawn in a lot of material 587 00:29:13,844 --> 00:29:15,892 and become a gas giant like Jupiter, 588 00:29:15,893 --> 00:29:18,237 except it got too close to Jupiter. 589 00:29:18,238 --> 00:29:19,751 And, before it could do that, 590 00:29:19,752 --> 00:29:22,028 it was gravitationally thrown away 591 00:29:22,029 --> 00:29:24,343 from this wonderful feeding ground 592 00:29:24,344 --> 00:29:26,194 out into the much sparser, 593 00:29:26,195 --> 00:29:29,065 more barren desert of the outer solar system. 594 00:29:32,004 --> 00:29:35,368 Is planet 9 really a frozen mini-Neptune 595 00:29:35,369 --> 00:29:38,802 banished to the badlands of the outer solar system? 596 00:29:38,803 --> 00:29:41,484 Right now, it's our best bet. 597 00:29:41,485 --> 00:29:44,186 But there is one more option. 598 00:29:44,187 --> 00:29:46,007 Some scientists believe 599 00:29:46,008 --> 00:29:49,798 planet 9 may not have formed around our Sun at all. 600 00:29:53,144 --> 00:29:55,349 Is our most distant planet 601 00:29:55,350 --> 00:29:58,884 an alien world snatched from another star? 602 00:30:18,667 --> 00:30:21,437 If the mysterious planet 9 exists, 603 00:30:21,438 --> 00:30:23,942 it is by far the most distant planet 604 00:30:23,952 --> 00:30:25,336 in the solar system, 605 00:30:25,337 --> 00:30:28,176 20 times farther out than Neptune. 606 00:30:28,177 --> 00:30:30,720 So how did it get there? 607 00:30:30,721 --> 00:30:34,451 Was it made in the place it currently occupies? 608 00:30:34,452 --> 00:30:37,054 Or was it flung out from the inner solar system 609 00:30:37,055 --> 00:30:38,578 as a rocky super-Earth 610 00:30:38,579 --> 00:30:42,012 or, more likely, a mini-Neptune? 611 00:30:42,013 --> 00:30:43,694 The jury's out. 612 00:30:43,695 --> 00:30:46,595 But there is another option. 613 00:30:46,605 --> 00:30:48,385 And it's out of this world. 614 00:30:48,386 --> 00:30:51,087 So the question is, then, where did it come from 615 00:30:51,088 --> 00:30:52,542 if neither of these things is right? 616 00:30:52,543 --> 00:30:56,075 And it's possible that there is another explanation. 617 00:30:56,076 --> 00:30:59,905 And that is that planet 9 is an alien visitor 618 00:30:59,906 --> 00:31:01,727 from outer space. 619 00:31:04,666 --> 00:31:08,099 The Sun is just 1 of 200 billion stars 620 00:31:08,100 --> 00:31:10,742 orbiting the supermassive black hole 621 00:31:10,743 --> 00:31:13,809 at the center of the milky way galaxy. 622 00:31:13,810 --> 00:31:17,244 Most of these stars probably have multiple planets. 623 00:31:17,245 --> 00:31:20,777 And scientists now believe that, from time to time, 624 00:31:20,778 --> 00:31:24,736 two stars might pass a little too close for comfort. 625 00:31:24,746 --> 00:31:29,160 The result... planetary theft. 626 00:31:29,170 --> 00:31:31,376 We know that the Sun moves around in the galaxy. 627 00:31:31,377 --> 00:31:32,959 We know that there are other stars 628 00:31:32,960 --> 00:31:34,147 and other solar systems. 629 00:31:34,148 --> 00:31:36,859 Is it possible that the Sun passed so close 630 00:31:36,860 --> 00:31:38,145 to another solar system 631 00:31:38,146 --> 00:31:41,678 that it stole a planet? 632 00:31:41,679 --> 00:31:44,549 Today, our Sun drifts through space alone, 633 00:31:44,559 --> 00:31:47,488 like a yacht in the open ocean. 634 00:31:47,489 --> 00:31:49,803 But that wasn't always the case. 635 00:31:49,804 --> 00:31:53,040 Rewind the clock 4.6 billion years, 636 00:31:53,041 --> 00:31:57,265 and our local star cluster was a much more crowded place, 637 00:31:57,266 --> 00:32:01,126 ideal conditions for planet 9 to jump ship. 638 00:32:03,145 --> 00:32:04,995 The Sun was born in a nursery 639 00:32:04,996 --> 00:32:07,073 with thousands of other stars. 640 00:32:07,074 --> 00:32:08,924 Just like the boats in this harbor, 641 00:32:08,925 --> 00:32:12,061 there are so many boats around, so many neighbors. 642 00:32:12,062 --> 00:32:13,972 It was like that for the young Sun. 643 00:32:15,921 --> 00:32:19,355 Stars like the Sun are born in stellar nurseries, 644 00:32:19,355 --> 00:32:21,731 vast clouds of gas that collapse 645 00:32:21,741 --> 00:32:24,639 to form tens of thousands of stars, 646 00:32:24,640 --> 00:32:26,986 all tightly packed together. 647 00:32:28,965 --> 00:32:31,043 Astronomers think it's possible 648 00:32:31,053 --> 00:32:35,209 that, inside this cramped, confused playground of stars, 649 00:32:35,210 --> 00:32:38,445 our Sun's gravity could've stolen planet 9 650 00:32:38,446 --> 00:32:40,395 from a passing neighbor. 651 00:32:40,396 --> 00:32:42,107 Imagine this cool scenario. 652 00:32:42,108 --> 00:32:44,087 You've got an alien star. 653 00:32:44,097 --> 00:32:46,234 And around that star forms a planet. 654 00:32:46,235 --> 00:32:47,620 This is planet 9. 655 00:32:47,630 --> 00:32:49,668 And here comes the Sun whizzing by. 656 00:32:49,669 --> 00:32:52,409 The Sun gets so close that it steals planet 9 657 00:32:52,410 --> 00:32:56,081 on its way out into the galaxy. 658 00:32:56,082 --> 00:32:58,357 It sounds like science fiction. 659 00:32:58,358 --> 00:33:02,445 But our Sun may already have a criminal record. 660 00:33:02,455 --> 00:33:05,750 There's some evidence that the comets in our solar system 661 00:33:05,751 --> 00:33:07,829 may not have started in our solar system. 662 00:33:07,839 --> 00:33:10,966 We may have stolen comets from other stars. 663 00:33:10,976 --> 00:33:12,489 If that's the case, 664 00:33:12,490 --> 00:33:14,103 it's not totally outrageous 665 00:33:14,113 --> 00:33:17,903 to think that a planet that formed around another star 666 00:33:17,904 --> 00:33:20,675 somehow made its way into our solar system 667 00:33:20,685 --> 00:33:24,147 and became part of our family. 668 00:33:24,148 --> 00:33:26,918 But if planet 9 really did come from another star, 669 00:33:26,919 --> 00:33:30,353 how will we know for sure that it's an alien visitor? 670 00:33:30,354 --> 00:33:32,302 What we'd like to do is essentially 671 00:33:32,303 --> 00:33:34,677 a DNA test on planet 9, 672 00:33:34,678 --> 00:33:36,627 scoop up some of its surface 673 00:33:36,628 --> 00:33:40,587 and look for material that we absolutely know 674 00:33:40,596 --> 00:33:42,278 couldn't have formed around our Sun, 675 00:33:42,279 --> 00:33:44,653 because we don't see it anywhere else in our solar system. 676 00:33:44,654 --> 00:33:46,563 We may even have to send a probe there 677 00:33:46,564 --> 00:33:48,285 to really get a good look at it 678 00:33:48,286 --> 00:33:50,561 and find out what its chemical composition is, 679 00:33:50,562 --> 00:33:53,570 exactly everything we can find out about its orbit. 680 00:33:53,571 --> 00:33:54,985 And, that way, we might be able to see 681 00:33:54,986 --> 00:33:57,856 if there are any sort of fingerprints, 682 00:33:57,866 --> 00:34:00,004 smoking-gun pieces of evidence 683 00:34:00,014 --> 00:34:02,942 that'll say clearly this formed here 684 00:34:02,943 --> 00:34:05,259 or it formed out there. 685 00:34:08,891 --> 00:34:13,017 Unfortunately, before we can 686 00:34:13,018 --> 00:34:16,778 we first have to find it. 687 00:34:16,788 --> 00:34:18,232 Astronomers like Mike brown 688 00:34:18,233 --> 00:34:20,410 have made the challenge a little easier, 689 00:34:20,420 --> 00:34:23,913 using math to narrow down the zone. 690 00:34:23,914 --> 00:34:26,328 What we know right now is that planet 9 691 00:34:26,329 --> 00:34:29,425 is in a swath of the sky that goes about like this. 692 00:34:29,426 --> 00:34:31,741 It's about this big. It goes across like this. 693 00:34:31,742 --> 00:34:33,987 But we think we even know a little bit better. 694 00:34:33,988 --> 00:34:36,363 We've pinpointed, or at least slightly constrained 695 00:34:36,364 --> 00:34:39,926 where it is, to a patch of sky that's about this big. 696 00:34:39,936 --> 00:34:41,647 It's still a lot of sky to look at. 697 00:34:41,648 --> 00:34:45,705 But it's a lot less than having to look at the whole sky. 698 00:34:45,706 --> 00:34:50,328 Mike's patch of sky is close 699 00:34:50,338 --> 00:34:51,752 he's going to wait until fall, 700 00:34:51,753 --> 00:34:53,663 when Orion is highest in the sky, 701 00:34:53,673 --> 00:34:55,483 to search for planet 9 702 00:34:55,484 --> 00:35:00,234 using the Subaru infrared telescope on Hawaii. 703 00:35:00,244 --> 00:35:01,728 The telescope is fine-tuned 704 00:35:01,729 --> 00:35:03,767 to pick out the faint heat signature 705 00:35:03,777 --> 00:35:05,360 of distant objects 706 00:35:05,361 --> 00:35:08,893 against the cold backdrop of deep space. 707 00:35:08,894 --> 00:35:11,199 Planet 9 may be frozen. 708 00:35:11,200 --> 00:35:13,119 But it will be warmer than space. 709 00:35:13,120 --> 00:35:15,424 And that tiny difference in temperature 710 00:35:15,425 --> 00:35:18,532 is all this incredible telescope needs. 711 00:35:18,533 --> 00:35:20,680 We want to see two pictures taken 712 00:35:20,681 --> 00:35:23,283 of the same area of the sky a few weeks apart. 713 00:35:23,293 --> 00:35:24,905 The stars don't move. 714 00:35:24,906 --> 00:35:27,182 But you see this one, little thing going, "boop, boop, boop," 715 00:35:27,183 --> 00:35:28,904 as you flash the pictures back and forth. 716 00:35:28,905 --> 00:35:30,685 That's what happens when you have an object 717 00:35:30,686 --> 00:35:32,338 moving around the Sun 718 00:35:32,339 --> 00:35:34,050 against the background of stars. 719 00:35:34,051 --> 00:35:35,970 That's how Pluto was discovered. 720 00:35:35,971 --> 00:35:38,811 That's how we're gonna find planet 9 if it exists. 721 00:35:40,959 --> 00:35:43,531 It could take years to find planet 9. 722 00:35:43,532 --> 00:35:45,579 But when we do spot it, 723 00:35:45,580 --> 00:35:48,746 scientists will be able to analyze its light. 724 00:35:48,747 --> 00:35:51,121 And hidden within that faint glow 725 00:35:51,122 --> 00:35:53,041 could be the chemical signature 726 00:35:53,042 --> 00:35:56,239 for rock, ice, or gas. 727 00:35:56,249 --> 00:35:59,118 If it is, planet 9's identity 728 00:35:59,119 --> 00:36:03,107 will finally be revealed. 729 00:36:03,117 --> 00:36:06,283 What lies in store beyond that is a mystery. 730 00:36:06,284 --> 00:36:09,420 But perhaps the most exciting prospect 731 00:36:09,421 --> 00:36:14,566 is planet 9 could be home to a family of moons. 732 00:36:14,567 --> 00:36:17,377 And it's just possible one of these moons 733 00:36:17,378 --> 00:36:19,554 could provide a home for life 734 00:36:19,555 --> 00:36:22,623 100 billion miles from the Sun. 735 00:36:42,050 --> 00:36:44,425 Are we alone in the universe? 736 00:36:47,028 --> 00:36:49,442 For decades, scientists have scoured 737 00:36:49,443 --> 00:36:51,293 our closest planetary neighbor 738 00:36:51,294 --> 00:36:54,035 for signs of extraterrestrial life. 739 00:36:56,014 --> 00:36:58,953 But so far, not a trace has been found. 740 00:37:02,981 --> 00:37:06,247 Is it possible we're targeting the wrong planet? 741 00:37:10,147 --> 00:37:12,125 If planet 9 is real, 742 00:37:12,126 --> 00:37:15,689 it sits on the icy outer limits of the solar system. 743 00:37:15,698 --> 00:37:19,815 But even here, 100 billion miles from the Sun, 744 00:37:19,825 --> 00:37:23,120 it's just possible that life could thrive 745 00:37:23,121 --> 00:37:25,337 not on the planet itself, 746 00:37:25,338 --> 00:37:28,108 but deep inside its moons. 747 00:37:28,109 --> 00:37:30,424 Historically, we've always thought of moons 748 00:37:30,425 --> 00:37:32,730 as being these little, insignificant places. 749 00:37:32,730 --> 00:37:34,382 But the incredible thing is they may be 750 00:37:34,383 --> 00:37:36,491 the best places to find life. 751 00:37:36,501 --> 00:37:38,045 In our solar system alone, 752 00:37:38,055 --> 00:37:40,587 there may be far more chances for life on moons of planets 753 00:37:40,588 --> 00:37:43,033 than there are on planets themselves. 754 00:37:45,052 --> 00:37:47,495 Moons excite astrobiologists 755 00:37:47,496 --> 00:37:51,157 because they can sometimes support liquid water, 756 00:37:51,158 --> 00:37:53,799 no matter how far they sit from the Sun. 757 00:37:53,800 --> 00:37:57,036 The key is something called tidal heating. 758 00:37:59,709 --> 00:38:02,617 Moons on elliptical orbits get squashed 759 00:38:02,618 --> 00:38:06,051 and squeezed by the gravity of their parent planet. 760 00:38:06,052 --> 00:38:08,426 This generates heat and melts ice 761 00:38:08,427 --> 00:38:12,256 to form underground oceans of liquid water, 762 00:38:12,257 --> 00:38:16,779 the key ingredient for life as we know it. 763 00:38:16,780 --> 00:38:20,015 If planet 9 is as big as scientists predict, 764 00:38:20,016 --> 00:38:22,331 it could have multiple moons. 765 00:38:22,332 --> 00:38:24,677 And maybe one of those moons 766 00:38:24,678 --> 00:38:27,180 could have warm, salty oceans 767 00:38:27,181 --> 00:38:30,318 primed for simple life. 768 00:38:30,319 --> 00:38:32,199 So, if you have planet 9, 769 00:38:32,209 --> 00:38:34,019 and it's got icy moons, and these icy moons 770 00:38:34,020 --> 00:38:36,167 are on the right kinds of orbits, 771 00:38:36,168 --> 00:38:39,205 the heat could be coming from within, not without. 772 00:38:39,206 --> 00:38:42,007 And so the Sun basically doesn't matter. 773 00:38:42,016 --> 00:38:45,479 You could have liquid water below the surface 774 00:38:45,480 --> 00:38:47,687 that's heated from the internal geology. 775 00:38:47,697 --> 00:38:49,477 You could have geysers of water 776 00:38:49,478 --> 00:38:50,923 like what we see coming off of moons 777 00:38:50,933 --> 00:38:52,516 around Saturn and Jupiter. 778 00:38:52,517 --> 00:38:54,852 You could have that all the way out there at planet 9. 779 00:38:58,494 --> 00:39:03,570 Imagine planet 9 with a system of giant moons. 780 00:39:03,571 --> 00:39:06,351 The closest moon is heated to melting point 781 00:39:06,352 --> 00:39:09,548 by planet 9's immense gravity. 782 00:39:09,549 --> 00:39:11,072 There's no life here. 783 00:39:11,073 --> 00:39:13,972 Any water boiled away millions of years ago, 784 00:39:13,982 --> 00:39:16,882 creating a hot, arid ball of rock. 785 00:39:19,851 --> 00:39:22,492 Farther out lies a second giant moon. 786 00:39:22,493 --> 00:39:26,887 This new world is encased in bright, white water ice. 787 00:39:29,500 --> 00:39:31,539 But the crust hides a secret... 788 00:39:31,549 --> 00:39:34,517 a vast ocean of warm liquid water 789 00:39:34,518 --> 00:39:37,714 heated by volcanic vents on the ocean floor. 790 00:39:39,931 --> 00:39:43,295 This hidden world is rich with organic chemistry. 791 00:39:43,296 --> 00:39:48,154 And it could even support a weird, alien zoo 792 00:39:48,155 --> 00:39:51,192 of pale aquatic creatures. 793 00:39:51,193 --> 00:39:53,469 We associate life with the Sun. 794 00:39:53,470 --> 00:39:56,012 That's how we think of life originating on the Earth. 795 00:39:56,013 --> 00:39:57,626 But we know you don't need the Sun. 796 00:39:57,636 --> 00:40:00,170 We have tube worms at the bottom of the ocean 797 00:40:00,180 --> 00:40:02,158 which live off of hydrothermal vents. 798 00:40:02,159 --> 00:40:04,198 They get all the chemicals and the heat they need 799 00:40:04,207 --> 00:40:06,483 from, basically, the interior of the Earth. 800 00:40:06,484 --> 00:40:08,729 This is not out of the question. You know, decades ago, 801 00:40:08,730 --> 00:40:10,709 you'd have been laughed out of a lecture hall 802 00:40:10,709 --> 00:40:12,688 if you'd have said something like that. 803 00:40:12,689 --> 00:40:14,736 But we have learned so much about life 804 00:40:14,737 --> 00:40:16,053 in extreme environments since then 805 00:40:16,054 --> 00:40:18,330 that this is now in the realm of possibility, 806 00:40:18,340 --> 00:40:19,884 talking about life on a planet 807 00:40:19,894 --> 00:40:21,872 beyond Pluto in our own solar system. 808 00:40:21,873 --> 00:40:23,455 Wherever there's energy, 809 00:40:23,456 --> 00:40:25,435 wherever there's heat, there can be life, 810 00:40:25,436 --> 00:40:28,770 even all the way out by planet 9. 811 00:40:28,771 --> 00:40:30,254 There is good news. 812 00:40:30,255 --> 00:40:33,224 If planet 9 does have an active watery moon, 813 00:40:33,234 --> 00:40:35,837 we should be able to see it with our telescopes. 814 00:40:38,153 --> 00:40:40,161 The active moons of Jupiter and Saturn 815 00:40:40,162 --> 00:40:42,437 are the brightest in the night sky, 816 00:40:42,438 --> 00:40:46,138 thanks to warm water gushing out from cracks in the surface 817 00:40:46,139 --> 00:40:51,423 and freezing in bright white layers of fresh ice. 818 00:40:51,424 --> 00:40:54,324 If planet 9's moons have liquid oceans, 819 00:40:54,334 --> 00:40:57,500 their surfaces should be just as bright. 820 00:41:04,893 --> 00:41:08,623 The race is on to image planet 9 and its moons. 821 00:41:08,624 --> 00:41:12,097 But what we'll see when those pictures come back 822 00:41:12,098 --> 00:41:13,611 is anybody's guess. 823 00:41:13,612 --> 00:41:15,689 I have to admit, there's some wonderful tension 824 00:41:15,690 --> 00:41:18,470 that I feel right now when it comes to finding planet 9. 825 00:41:18,471 --> 00:41:20,015 We have giant telescopes 826 00:41:20,025 --> 00:41:22,261 that are scanning the sky looking for it. 827 00:41:22,262 --> 00:41:25,665 So, any day now, I'm waiting with baited breath. 828 00:41:25,666 --> 00:41:26,883 My daughter believes 829 00:41:26,893 --> 00:41:30,158 that planet 9 is pink with purple dots. 830 00:41:30,159 --> 00:41:32,930 Um, she might be right. 831 00:41:37,324 --> 00:41:38,709 One thing's for sure. 832 00:41:38,710 --> 00:41:41,915 If and when we do find planet 9, 833 00:41:41,916 --> 00:41:46,042 we'll never look at our solar system the same way again. 834 00:41:46,043 --> 00:41:47,725 This is tremendously exciting, 835 00:41:47,726 --> 00:41:49,902 because, if it's there, it's already telling us 836 00:41:49,903 --> 00:41:54,494 that there's more to know about our solar system, 837 00:41:54,495 --> 00:41:57,463 that there are more secrets literally under the Sun 838 00:41:57,464 --> 00:41:59,908 than we have dreamed of in our philosophy.