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These are the user uploaded subtitles that are being translated: 1 00:00:01,420 --> 00:00:04,720 Our solar system is a strange thing. 2 00:00:04,720 --> 00:00:08,190 It's radically different from all the other planetary systems 3 00:00:08,190 --> 00:00:10,460 we see across the galaxy. 4 00:00:10,460 --> 00:00:13,390 We are an exception rather than the rule. 5 00:00:13,400 --> 00:00:16,200 To understand why, scientists peer deep 6 00:00:16,200 --> 00:00:19,270 into our solar system's secret history 7 00:00:19,270 --> 00:00:24,610 and find a dark and violent past of planetary homicide 8 00:00:24,610 --> 00:00:26,440 on a mass scale. 9 00:00:28,810 --> 00:00:32,150 The solar system is a ghost of what it used to be. 10 00:00:32,150 --> 00:00:33,910 You end up with the last survivors 11 00:00:33,920 --> 00:00:36,080 being a bunch of freaks. 12 00:00:38,690 --> 00:00:41,920 Our home could be one of those freaks. 13 00:00:41,920 --> 00:00:43,960 The rock beneath our feet could have been 14 00:00:43,960 --> 00:00:45,660 from long-dead planets. 15 00:00:45,660 --> 00:00:48,730 And those long-dead planets could help explain 16 00:00:48,730 --> 00:00:52,130 why there's life on Earth. 17 00:01:16,290 --> 00:01:20,430 In a spiral arm of a huge galaxy called the milky way 18 00:01:20,430 --> 00:01:24,370 spins an extraordinary planetary system, 19 00:01:24,370 --> 00:01:27,000 our solar system. 20 00:01:27,000 --> 00:01:31,570 For millennia, it was the only one we knew, 21 00:01:31,570 --> 00:01:34,640 but all that has changed. 22 00:01:34,640 --> 00:01:39,780 Astronomers have discovered more than 2,600 planetary systems 23 00:01:39,780 --> 00:01:44,450 to date, but none of them are quite like our own. 24 00:01:46,860 --> 00:01:48,820 The incredible thing about astronomy 25 00:01:48,820 --> 00:01:50,760 is when you look out into the universe, 26 00:01:50,760 --> 00:01:53,060 and you realize you have completely misinterpreted 27 00:01:53,060 --> 00:01:54,300 your own home. 28 00:01:56,900 --> 00:01:58,300 So one important thing we've learned 29 00:01:58,300 --> 00:02:00,230 in discovering planets around other stars 30 00:02:00,240 --> 00:02:03,270 is that our system isn't the normal system. 31 00:02:03,270 --> 00:02:05,340 It's not what we see everywhere. 32 00:02:05,340 --> 00:02:07,140 In fact, as we discover more planets 33 00:02:07,140 --> 00:02:08,610 orbiting other stars, 34 00:02:08,610 --> 00:02:11,180 we see that ours is an oddball. 35 00:02:11,180 --> 00:02:15,220 Most other solar systems look completely different than ours. 36 00:02:15,220 --> 00:02:19,890 February 2017, NASA makes a huge announcement 37 00:02:19,890 --> 00:02:23,160 about a system in the Aquarius constellation, 38 00:02:23,160 --> 00:02:26,260 Trappist-1. 39 00:02:26,260 --> 00:02:28,200 Trappist-1 is a little unusual. 40 00:02:28,200 --> 00:02:31,130 It's a little bit smaller and cooler than the Sun, 41 00:02:31,130 --> 00:02:33,130 but it has seven planets orbiting it. 42 00:02:33,140 --> 00:02:35,770 And you think, "well, that's not that peculiar. We have eight." 43 00:02:35,770 --> 00:02:38,940 But these are seven roughly Earth-sized planets. 44 00:02:38,940 --> 00:02:40,610 There's not a lot of variety there, 45 00:02:40,610 --> 00:02:44,350 and they also orbit the star very close in. 46 00:02:44,350 --> 00:02:47,820 All seven planets somehow orbit closer 47 00:02:47,820 --> 00:02:49,980 to their star than Mercury, 48 00:02:49,990 --> 00:02:53,690 our innermost planet, does to our sun. 49 00:02:53,690 --> 00:02:56,020 Perhaps one of the greatest puzzles 50 00:02:56,030 --> 00:03:00,260 that have come out of finding planets around other stars 51 00:03:00,260 --> 00:03:03,100 is that they typically have orbits 52 00:03:03,100 --> 00:03:05,600 well inside the orbit of Mercury. 53 00:03:05,600 --> 00:03:08,270 It's really odd, in my view, 54 00:03:08,270 --> 00:03:10,270 that the solar system is hollowed out. 55 00:03:10,270 --> 00:03:12,410 There's nothing inside of Mercury's orbit. 56 00:03:12,410 --> 00:03:13,910 Why is that? 57 00:03:17,250 --> 00:03:19,980 The mystery of the missing inner planets 58 00:03:19,980 --> 00:03:22,080 is like a cosmic whodunit, 59 00:03:22,080 --> 00:03:26,020 turning scientists into detectives asking, 60 00:03:26,020 --> 00:03:31,460 "do we really know how the story of our solar system unfolds?" 61 00:03:31,460 --> 00:03:35,400 The whole process is, like, cosmic CSI. 62 00:03:35,400 --> 00:03:39,030 You're trying to put together the clues to find out something 63 00:03:39,040 --> 00:03:40,970 that happened when nobody else 64 00:03:40,970 --> 00:03:42,800 was there to watch it happen. 65 00:03:44,940 --> 00:03:46,740 Like detectives, scientists start 66 00:03:46,740 --> 00:03:48,480 with the simplest explanation. 67 00:03:52,980 --> 00:03:54,150 So in some ways, the early solar system 68 00:03:54,150 --> 00:03:55,750 is like a pool game. 69 00:03:55,750 --> 00:03:59,290 All the billiard balls represent the pieces, the building blocks, 70 00:03:59,290 --> 00:04:01,620 the planetesimals or the planetary embryos 71 00:04:01,620 --> 00:04:02,920 that are going to come together 72 00:04:02,930 --> 00:04:06,360 eventually to build the final system of planets. 73 00:04:06,360 --> 00:04:07,830 In planetary formation, 74 00:04:07,830 --> 00:04:10,360 the simplest theory is that the planets all formed 75 00:04:10,370 --> 00:04:13,730 where we find them now. 76 00:04:13,740 --> 00:04:15,440 It's called the classical model. 77 00:04:17,840 --> 00:04:19,510 How does this play out? 78 00:04:19,510 --> 00:04:21,310 We start with a few planetesimals 79 00:04:21,310 --> 00:04:22,510 that collide with each other, 80 00:04:22,510 --> 00:04:24,080 and they grow a little bit larger 81 00:04:24,080 --> 00:04:26,750 in this region of the solar system. 82 00:04:26,750 --> 00:04:29,950 This process continues, and you grow all the way up to planets, 83 00:04:29,950 --> 00:04:32,590 with each planet in each of the zone of the solar system 84 00:04:32,590 --> 00:04:34,660 creating material just from its neighborhood 85 00:04:34,660 --> 00:04:38,030 and no one's really moving around very far. 86 00:04:38,030 --> 00:04:40,890 But this classical model can't explain why 87 00:04:40,900 --> 00:04:42,800 our inner solar system 88 00:04:42,800 --> 00:04:46,500 is missing all kinds of material. 89 00:04:46,500 --> 00:04:49,270 The classical model has no natural explanation 90 00:04:49,270 --> 00:04:52,340 for why Mercury is the last thing that we know of, 91 00:04:52,340 --> 00:04:53,770 inward towards the Sun, 92 00:04:53,780 --> 00:04:55,680 that there are no planets, no asteroids, 93 00:04:55,680 --> 00:04:57,610 nothing inside Mercury, is still a mystery 94 00:04:57,610 --> 00:05:00,310 that the classical model can't easily explain. 95 00:05:04,720 --> 00:05:09,360 The area close to our sun isn't just missing asteroids 96 00:05:09,360 --> 00:05:12,690 and small planets. 97 00:05:12,700 --> 00:05:17,230 It's also missing really big ones. 98 00:05:17,230 --> 00:05:18,830 The very first exoplanets, 99 00:05:18,830 --> 00:05:21,500 the very first alien worlds we discovered, 100 00:05:21,500 --> 00:05:23,700 were Jupiter-mass or bigger planets 101 00:05:23,710 --> 00:05:26,170 orbiting their starts very closely, 102 00:05:26,180 --> 00:05:28,640 even closer than Mercury orbits the Sun. 103 00:05:31,210 --> 00:05:33,550 Astronomers have so far discovered 104 00:05:33,550 --> 00:05:35,620 around 300 gas giants 105 00:05:35,620 --> 00:05:39,290 scorchingly close to their suns. 106 00:05:39,290 --> 00:05:42,660 They call them hot Jupiters... 107 00:05:42,660 --> 00:05:46,330 But how they form is a mystery. 108 00:05:48,360 --> 00:05:52,070 Gas giants like Jupiter should be born out of the cold, 109 00:05:52,070 --> 00:05:54,540 far from their suns. 110 00:05:54,540 --> 00:05:57,840 It's very hard to imagine hot Jupiters forming 111 00:05:57,840 --> 00:05:59,370 where we see them today. 112 00:05:59,380 --> 00:06:02,540 The temperatures, the distances from the star, 113 00:06:02,550 --> 00:06:04,650 where we find hot Jupiters are so hot, 114 00:06:04,650 --> 00:06:06,950 it's hard to imagine any material 115 00:06:06,950 --> 00:06:09,320 condensing out of the solar nebula. 116 00:06:09,320 --> 00:06:10,680 This kick-started the idea 117 00:06:10,690 --> 00:06:13,720 that maybe these hot Jupiters, as they were called, 118 00:06:13,720 --> 00:06:15,720 may have actually formed farther out, 119 00:06:15,720 --> 00:06:17,860 like near where our Jupiter is now, 120 00:06:17,860 --> 00:06:19,760 and in the early solar system 121 00:06:19,760 --> 00:06:24,030 they started migrating inward toward their star. 122 00:06:24,030 --> 00:06:26,730 So what happens when a planet the size of Jupiter 123 00:06:26,740 --> 00:06:28,200 moves inward? 124 00:06:28,200 --> 00:06:31,610 Can this help explain the inner solar system's missing mass 125 00:06:31,610 --> 00:06:35,140 and answer why we don't have a hot Jupiter? 126 00:06:36,610 --> 00:06:39,750 To find out, Kevin Walsh and colleagues simulate 127 00:06:39,750 --> 00:06:43,050 the first 10 million years of the solar system. 128 00:06:43,050 --> 00:06:46,220 They call this model the grand tack. 129 00:06:46,220 --> 00:06:48,720 The grand tack model is a scenario 130 00:06:48,720 --> 00:06:49,960 designed to help understand 131 00:06:49,960 --> 00:06:52,660 how the terrestrial planets could have formed, 132 00:06:52,660 --> 00:06:54,560 thinking about what the giant planets 133 00:06:54,560 --> 00:06:56,930 might have been doing in the early solar system. 134 00:06:59,270 --> 00:07:03,170 The planets form within a thick disk of gas and debris 135 00:07:03,170 --> 00:07:06,740 that surrounds the newly-formed sun. 136 00:07:06,740 --> 00:07:10,780 The grand tack model simulates what happens if Jupiter moves 137 00:07:10,780 --> 00:07:15,050 in towards the Sun through this disk. 138 00:07:15,050 --> 00:07:17,250 It's pushing all of the asteroids in its path 139 00:07:17,250 --> 00:07:19,450 into the inner solar system. 140 00:07:19,460 --> 00:07:21,460 All of that material is what is going to come together 141 00:07:21,460 --> 00:07:23,890 to form the rocky planets. 142 00:07:23,890 --> 00:07:26,330 Jupiter's immense gravity pulls in more 143 00:07:26,330 --> 00:07:27,690 and more material, 144 00:07:27,700 --> 00:07:31,670 forming a dense wave of debris bulging out behind it. 145 00:07:34,470 --> 00:07:39,540 The pressure of this bulge pushes Jupiter further inwards. 146 00:07:39,540 --> 00:07:42,340 Like a wrecking ball, Jupiter should clear out 147 00:07:42,340 --> 00:07:43,910 all the planet-building material 148 00:07:43,910 --> 00:07:46,610 from the entire inner solar system 149 00:07:46,620 --> 00:07:51,420 and become a sun-hugging hot Jupiter, 150 00:07:51,420 --> 00:07:56,460 but something checks Jupiter's path of destruction. 151 00:07:56,460 --> 00:07:57,990 If Jupiter had hung around much longer 152 00:07:57,990 --> 00:08:00,430 in the inner solar system, we wouldn't be here, 153 00:08:00,430 --> 00:08:02,930 so something must have drawn it out very rapidly. 154 00:08:02,930 --> 00:08:06,800 And what could possibly move a big, massive planet rapidly? 155 00:08:06,800 --> 00:08:09,900 And the answer is another big, massive planet. 156 00:08:13,640 --> 00:08:17,110 Saturn... 157 00:08:17,110 --> 00:08:19,510 It forms just after Jupiter, 158 00:08:19,520 --> 00:08:21,520 and is hot on Jupiter's heels, 159 00:08:21,520 --> 00:08:24,650 as it, too, migrates towards the Sun. 160 00:08:29,860 --> 00:08:32,190 Saturn is pretty big itself. 161 00:08:32,190 --> 00:08:35,100 The combined effect of the two giant planets 162 00:08:35,100 --> 00:08:37,060 migrating is that once 163 00:08:37,070 --> 00:08:40,300 Saturn is large enough, it can actually change the way 164 00:08:40,300 --> 00:08:43,440 that the gas disk is interacting with both the planets. 165 00:08:43,440 --> 00:08:47,170 And it can stop Jupiter's inward migration and help to turn 166 00:08:47,180 --> 00:08:48,410 Jupiter around 167 00:08:48,410 --> 00:08:50,840 and almost pulls it back to the outer solar system. 168 00:08:54,850 --> 00:08:57,050 Like a sailboat switching direction, 169 00:08:57,050 --> 00:09:01,320 Jupiter tacks away from the Sun. 170 00:09:01,320 --> 00:09:03,390 The behavior of the giant outer planets 171 00:09:03,390 --> 00:09:07,260 leaves our solar system with no hot Jupiter 172 00:09:07,260 --> 00:09:11,530 and has dramatic effect on the small inner planets, too. 173 00:09:11,530 --> 00:09:13,730 As it's coming back outwards, 174 00:09:13,740 --> 00:09:16,140 what has Jupiter done to the inner solar system? 175 00:09:16,140 --> 00:09:18,540 It has removed all of the material in its path, 176 00:09:18,540 --> 00:09:20,710 all the way down to where we find the Earth today. 177 00:09:20,710 --> 00:09:23,610 And all of that material pushed into essentially a narrow band 178 00:09:23,610 --> 00:09:25,950 in the inner solar system is what is going to come together 179 00:09:25,950 --> 00:09:28,520 to form the rocky planets as we find them today. 180 00:09:32,620 --> 00:09:34,490 According to the grand tack model, 181 00:09:34,490 --> 00:09:37,260 without Jupiter, the rocky terrestrial planets 182 00:09:37,260 --> 00:09:41,360 of the inner solar system might have never formed. 183 00:09:41,360 --> 00:09:45,500 One of those planets is Earth. 184 00:09:45,500 --> 00:09:48,300 So as much as we owe our existence to Jupiter, 185 00:09:48,300 --> 00:09:49,700 we also owe it to Saturn 186 00:09:49,710 --> 00:09:52,540 because if Jupiter had kept moving in closer to the Sun, 187 00:09:52,540 --> 00:09:54,640 we almost certainly wouldn't be here now. 188 00:09:59,080 --> 00:10:01,880 The grand tack may provide a vital chapter 189 00:10:01,880 --> 00:10:04,320 in the story of Earth's formation. 190 00:10:04,320 --> 00:10:06,590 That answers why we're missing a hot Jupiter 191 00:10:06,590 --> 00:10:08,320 but doesn't explain why there's nothing 192 00:10:08,320 --> 00:10:11,690 between Mercury and the Sun, 193 00:10:11,690 --> 00:10:15,300 nor why we're missing one of the most common types of planet 194 00:10:15,300 --> 00:10:17,900 in the whole galaxy, 195 00:10:17,900 --> 00:10:20,930 a giant rocky world up to 10 times 196 00:10:20,940 --> 00:10:24,910 the size of Earth... A super-Earth. 197 00:10:45,090 --> 00:10:46,550 The Kepler space telescope 198 00:10:46,560 --> 00:10:47,790 leads the charge in the hunt 199 00:10:47,790 --> 00:10:51,430 for exoplanets around other stars. 200 00:10:51,430 --> 00:10:55,130 It's confirmed over 2,000 new worlds. 201 00:10:55,130 --> 00:10:58,070 The single-largest finding to date, 202 00:10:58,070 --> 00:11:03,200 over one-third of those planets are super-Earths. 203 00:11:03,210 --> 00:11:05,370 A super-Earth is a type of rocky planet 204 00:11:05,380 --> 00:11:07,880 that has a mass a few times the mass of the Earth, 205 00:11:07,880 --> 00:11:11,880 and as we look around the galaxy, we find them all over. 206 00:11:11,880 --> 00:11:13,750 Our solar system doesn't have one, 207 00:11:13,750 --> 00:11:15,750 and you have to ask the question... why not? 208 00:11:15,750 --> 00:11:19,420 What's different about us? 209 00:11:19,420 --> 00:11:21,920 In our solar system, planets range in mass, 210 00:11:21,930 --> 00:11:23,690 with Jupiter being the largest 211 00:11:23,690 --> 00:11:27,560 and Mercury the smallest. 212 00:11:27,560 --> 00:11:31,470 But weirdly, we have nothing in the super-Earth-size range, 213 00:11:31,470 --> 00:11:35,040 which is between Earth and Uranus. 214 00:11:35,040 --> 00:11:36,700 Why is there such a big gap in masses 215 00:11:36,710 --> 00:11:38,270 between the Earth and Uranus, 216 00:11:38,270 --> 00:11:41,780 which is roughly a dozen times the Earth's mass? 217 00:11:41,780 --> 00:11:44,550 It's a big jump from one to a dozen. 218 00:11:44,550 --> 00:11:47,850 Why? 219 00:11:47,850 --> 00:11:49,350 In 2015, 220 00:11:49,350 --> 00:11:52,420 Konstantin Batygin tries to find the answer 221 00:11:52,420 --> 00:11:55,320 to why we have no super-Earths, 222 00:11:55,330 --> 00:11:58,490 and why there is nothing within the orbit of Mercury. 223 00:12:02,400 --> 00:12:06,230 He reconstructs the grand tack model with one key difference... 224 00:12:10,070 --> 00:12:12,810 The simulations start with six super-Earths 225 00:12:12,810 --> 00:12:14,540 in our solar system center 226 00:12:14,540 --> 00:12:17,650 in a tight orbit around the Sun, 227 00:12:17,650 --> 00:12:21,720 typical of other systems we've observed. 228 00:12:21,720 --> 00:12:25,090 He calls this new model the grand attack. 229 00:12:28,320 --> 00:12:30,260 One of the realizations that has come out 230 00:12:30,260 --> 00:12:32,930 of studying the grand tack scenario 231 00:12:32,930 --> 00:12:36,430 is that Jupiter's migration would have really unleashed 232 00:12:36,430 --> 00:12:38,230 a veritable grand attack 233 00:12:38,230 --> 00:12:41,900 upon the inner solar system. 234 00:12:41,910 --> 00:12:45,470 The grand attack model ramps up Jupiter's action 235 00:12:45,480 --> 00:12:49,380 so it sends swarms of giant asteroids and planetary 236 00:12:49,380 --> 00:12:53,550 embryos into the inner solar system on tight-knit, 237 00:12:53,550 --> 00:12:55,520 overlapping orbits. 238 00:12:55,520 --> 00:12:57,020 The result? 239 00:12:57,020 --> 00:12:58,120 Carnage. 240 00:13:01,490 --> 00:13:04,530 Each big body will experience a collision 241 00:13:04,530 --> 00:13:09,000 with another big body once every 20 to 200 orbits. 242 00:13:09,000 --> 00:13:12,470 This is exceptionally fast on cosmic-time scales. 243 00:13:15,510 --> 00:13:18,040 What this means is that you take the entirety 244 00:13:18,040 --> 00:13:20,270 of that overlapped population of bodies, 245 00:13:20,280 --> 00:13:23,210 and you smash them up into smaller debris. 246 00:13:23,210 --> 00:13:25,050 Jupiter is like a little kid with a hammer, you know? 247 00:13:25,050 --> 00:13:27,920 It just comes in and is whacking around at everything, 248 00:13:27,920 --> 00:13:32,220 and it's making a mess of the inner solar system. 249 00:13:32,220 --> 00:13:36,860 It's a game of cosmic pool on steroids. 250 00:13:41,400 --> 00:13:42,730 Let's start with our Jupiter, 251 00:13:42,730 --> 00:13:44,570 for our model here of the solar system. 252 00:13:54,810 --> 00:13:56,840 It's causing a bunch of very violent collisions 253 00:13:56,850 --> 00:13:59,680 between all of this debris that it's sweeping up. 254 00:13:59,680 --> 00:14:02,120 These huge collisions are making an enormous amount 255 00:14:02,120 --> 00:14:03,950 of really small material, 256 00:14:03,950 --> 00:14:06,850 which can drift really fast inward in the solar system 257 00:14:06,860 --> 00:14:11,330 due to the drag from the gas around the Sun. 258 00:14:11,330 --> 00:14:14,730 These planetesimals collide over and over, 259 00:14:14,730 --> 00:14:17,770 pulverized to the size of gravel. 260 00:14:17,770 --> 00:14:20,900 For the smaller debris, hitting this dense gas cloud 261 00:14:20,900 --> 00:14:25,710 around the Sun is like plowing into a headwind. 262 00:14:25,710 --> 00:14:29,040 The swarm of rubble loses the momentum that keeps it 263 00:14:29,050 --> 00:14:33,180 in orbit around the Sun and starts spiraling in, 264 00:14:33,180 --> 00:14:36,820 but it hits roadblocks. 265 00:14:36,820 --> 00:14:40,050 So as all this debris rushes inward in a big wave, 266 00:14:40,060 --> 00:14:43,560 it gets dragged in until it gets stuck behind the super-Earths. 267 00:14:47,060 --> 00:14:51,230 Debris builds up until the super-Earths finally give way. 268 00:14:55,140 --> 00:14:56,540 The super-Earths are like a dam 269 00:14:56,540 --> 00:14:59,270 that can't quite resist the flow of water 270 00:14:59,280 --> 00:15:02,840 and begins to recede and eventually gets 271 00:15:02,850 --> 00:15:05,010 kind of pushed onto the surface of the Sun, 272 00:15:05,010 --> 00:15:09,120 together with the flux of collisional debris. 273 00:15:09,120 --> 00:15:11,790 It's a remarkably swift process. 274 00:15:11,790 --> 00:15:17,490 In just 20,000 years, all the super-Earths crash into the Sun. 275 00:15:22,530 --> 00:15:24,270 After the dramatic evolution 276 00:15:24,270 --> 00:15:26,600 of the inner solar system, there's only a fraction 277 00:15:26,600 --> 00:15:28,200 of the original mass left. 278 00:15:28,200 --> 00:15:31,410 The solar system is a ghost of what it used to be. 279 00:15:34,380 --> 00:15:37,240 There's nothing in the first 39 million miles 280 00:15:37,250 --> 00:15:38,250 from the Sun. 281 00:15:40,480 --> 00:15:42,950 But slightly farther out, 282 00:15:42,950 --> 00:15:45,990 there's a narrow ring of rocky debris, 283 00:15:45,990 --> 00:15:51,290 about 10% of the original material swept in by Jupiter, 284 00:15:51,290 --> 00:15:54,730 just enough to rebuild the inner solar system. 285 00:15:57,100 --> 00:16:02,340 A few survivors, small planetesimals start to regroup. 286 00:16:02,340 --> 00:16:04,070 Over millions of years, 287 00:16:04,070 --> 00:16:08,440 four small, rocky planets form. 288 00:16:08,440 --> 00:16:10,140 Mercury, Venus, Earth, and Mars 289 00:16:10,150 --> 00:16:12,580 form from this leftover debris. 290 00:16:12,580 --> 00:16:15,780 The planet that we're standing on may not be 291 00:16:15,790 --> 00:16:20,590 an original generation solar system planet. 292 00:16:20,590 --> 00:16:23,520 It's kind of like building a house with cinder blocks 293 00:16:23,530 --> 00:16:27,360 from a house that sat on that spot but was demolished. 294 00:16:27,360 --> 00:16:30,900 Not only are we breathing the atmospheres of long-dead stars, 295 00:16:30,900 --> 00:16:32,300 the rock beneath our feet 296 00:16:32,300 --> 00:16:36,440 could have been from long-dead planets. 297 00:16:36,440 --> 00:16:39,210 So Earth could be second-generation planet 298 00:16:39,210 --> 00:16:41,640 formed from the wreckage of the grand attack., 299 00:16:44,150 --> 00:16:46,350 But there was one thing the super-Earths 300 00:16:46,350 --> 00:16:49,250 took with them to their fiery grave... 301 00:16:49,250 --> 00:16:51,790 The supply of hydrogen and helium 302 00:16:51,790 --> 00:16:55,190 in the inner solar system. 303 00:16:55,190 --> 00:16:56,590 When you look at the Earth's atmosphere now, 304 00:16:56,590 --> 00:16:58,930 we don't have any hydrogen or helium in it. 305 00:16:58,930 --> 00:17:01,160 There was hydrogen and helium in the disk 306 00:17:01,160 --> 00:17:03,300 where the inner planets formed, 307 00:17:03,300 --> 00:17:05,230 but that became part of the super-Earths, 308 00:17:05,230 --> 00:17:07,130 the first generation planets. 309 00:17:07,140 --> 00:17:09,870 When Jupiter came in and dropped them into the Sun, 310 00:17:09,870 --> 00:17:12,140 they took their hydrogen and helium with them. 311 00:17:12,140 --> 00:17:14,840 So the composition of the the air around you right now 312 00:17:14,840 --> 00:17:16,010 may be due to the fact 313 00:17:16,010 --> 00:17:17,980 that we're a second-generation planet. 314 00:17:21,180 --> 00:17:23,680 Coming in second might not sound great, 315 00:17:23,690 --> 00:17:28,660 but maybe second place is the reason we're here. 316 00:17:28,660 --> 00:17:32,230 So, the Earth we now see is Earth 2.0. 317 00:17:32,230 --> 00:17:36,100 Would Earth 1.0 have been conducive to life? 318 00:17:36,100 --> 00:17:38,930 That's an interesting question. 319 00:17:38,940 --> 00:17:42,500 Earth's atmosphere is a fertile blend of gases 320 00:17:42,510 --> 00:17:46,640 that allows life as we know it to flourish, 321 00:17:46,640 --> 00:17:50,140 an atmosphere that might have been completely different 322 00:17:50,150 --> 00:17:53,950 if Earth was a first-generation planet. 323 00:17:53,950 --> 00:17:58,090 It's entirely possible that life, like us, 324 00:17:58,090 --> 00:18:01,090 needs to have a second-generation planet 325 00:18:01,090 --> 00:18:04,790 to arise in the first place. 326 00:18:04,790 --> 00:18:07,160 Could our planet be more unusual 327 00:18:07,160 --> 00:18:08,500 than we'd ever thought? 328 00:18:11,000 --> 00:18:14,970 How special is the Earth in a cosmic setting? 329 00:18:14,970 --> 00:18:17,640 We don't really know the final answer to this question, 330 00:18:17,640 --> 00:18:19,840 but evidence is beginning to point to the fact 331 00:18:19,840 --> 00:18:22,510 that the Earth is actually kind of rare, 332 00:18:22,510 --> 00:18:25,180 and we should really appreciate our planet. 333 00:18:27,350 --> 00:18:29,980 Finding out what happened to our solar system 334 00:18:29,990 --> 00:18:34,620 is like studying a cosmic crime scene. 335 00:18:34,620 --> 00:18:37,290 To reveal the solar system's secret history, 336 00:18:37,290 --> 00:18:41,200 we need to look in unusual places, 337 00:18:41,200 --> 00:18:44,100 the last surviving pieces of the violence 338 00:18:44,100 --> 00:18:45,930 from which our home was born. 339 00:19:04,620 --> 00:19:08,080 Our solar system is a celestial cold case, 340 00:19:08,090 --> 00:19:11,850 and it's hiding the traces of its violent past. 341 00:19:11,860 --> 00:19:16,790 What you have now is a crime scene that has dried up, 342 00:19:16,790 --> 00:19:19,130 and you're trying to find little clues as to 343 00:19:19,130 --> 00:19:21,930 what happened 4 1/2 billion years ago. 344 00:19:21,930 --> 00:19:26,840 It's a really, really difficult problem to solve. 345 00:19:26,840 --> 00:19:29,670 Solid evidence could be hard to find, 346 00:19:29,670 --> 00:19:32,910 but sometimes we get lucky. 347 00:19:32,910 --> 00:19:34,940 We don't have a time machine, so it's hard to go back 348 00:19:34,950 --> 00:19:36,350 in time 4 1/2 billion years 349 00:19:36,350 --> 00:19:40,620 and look at the solar system and see what it was doing back then. 350 00:19:40,620 --> 00:19:43,350 However, sometimes nature provides, 351 00:19:43,350 --> 00:19:45,020 and if you don't have a time machine, 352 00:19:45,020 --> 00:19:48,420 sometimes a time capsule will do just as well. 353 00:19:48,430 --> 00:19:50,360 And in fact, we have time capsules 354 00:19:50,360 --> 00:19:51,760 of the early solar system, 355 00:19:51,760 --> 00:19:53,700 and we call them meteorites. 356 00:19:56,970 --> 00:19:59,430 Most meteorites are chunks of asteroids 357 00:19:59,440 --> 00:20:00,840 that fall to Earth. 358 00:20:00,840 --> 00:20:02,400 Depending on their origin, 359 00:20:02,410 --> 00:20:05,810 they come in different shapes and sizes. 360 00:20:05,810 --> 00:20:08,110 Asteroids really are like space fossils 361 00:20:08,110 --> 00:20:12,610 because they were formed 4 1/2 billion years ago, 362 00:20:12,620 --> 00:20:15,780 but they've basically remained dead. 363 00:20:15,790 --> 00:20:18,550 They are the leftovers, the remnants of planet formation. 364 00:20:18,560 --> 00:20:22,320 They're the last little bits that haven't become planets yet. 365 00:20:22,330 --> 00:20:26,760 To understand why meteorites are such useful clues, 366 00:20:26,760 --> 00:20:30,400 we first need to know how planets form. 367 00:20:30,400 --> 00:20:33,740 It's a process called accretion. 368 00:20:33,740 --> 00:20:37,040 The cloud of hot gas swirling around the Sun condenses 369 00:20:37,040 --> 00:20:40,040 and clumps into larger and larger bodies. 370 00:20:40,040 --> 00:20:44,110 We find traces of this process inside meteorites, 371 00:20:44,110 --> 00:20:49,550 in tiny mineral beads called chondrules. 372 00:20:49,550 --> 00:20:51,620 Chondrules are literally the seeds 373 00:20:51,620 --> 00:20:54,920 of all of the structure in our solar system. 374 00:20:54,930 --> 00:20:56,630 Most chondrules condense 375 00:20:56,630 --> 00:20:58,430 out of the cloud of hot gas 376 00:20:58,430 --> 00:21:02,760 around the Sun as the solar system forms. 377 00:21:02,770 --> 00:21:05,570 Chondrules have been described poetically 378 00:21:05,570 --> 00:21:09,500 as droplets of fiery rain that have solidified. 379 00:21:09,510 --> 00:21:14,280 They are little globules of silicate melt 380 00:21:14,280 --> 00:21:17,310 that were produced in the very earliest history 381 00:21:17,310 --> 00:21:18,780 of our solar system. 382 00:21:18,780 --> 00:21:21,420 These globules of melt solidified to form 383 00:21:21,420 --> 00:21:23,120 these little spheres. 384 00:21:23,120 --> 00:21:25,690 It really tells us about the process of agglomeration 385 00:21:25,690 --> 00:21:30,790 of smaller objects to form larger bodies. 386 00:21:30,790 --> 00:21:32,630 But some chondrules tell us 387 00:21:32,630 --> 00:21:34,960 not only about a planet's birth, 388 00:21:34,970 --> 00:21:36,770 but also its death. 389 00:21:47,210 --> 00:21:49,040 A meteorite called gujba 390 00:21:49,050 --> 00:21:53,480 contains two very different kinds of globules. 391 00:21:53,480 --> 00:21:57,250 So a gujba is a type of meteorite 392 00:21:57,250 --> 00:22:00,760 that's made up of little spherials 393 00:22:00,760 --> 00:22:02,620 of silicate material 394 00:22:02,630 --> 00:22:05,590 as well as spherials of iron-nickel metal, 395 00:22:05,600 --> 00:22:08,360 and it's very unusual in that regard. 396 00:22:08,370 --> 00:22:12,530 These metal spherials that we find in gujba are formed, 397 00:22:12,540 --> 00:22:15,470 we think, around 5 or 6 million years 398 00:22:15,470 --> 00:22:19,310 after the solar system forms. 399 00:22:19,310 --> 00:22:21,710 At that point, there was not enough hot gas 400 00:22:21,710 --> 00:22:23,110 lingering in the disk 401 00:22:23,110 --> 00:22:27,120 to form the chondrules we see in the gujba. 402 00:22:27,120 --> 00:22:30,750 So how did this globules form? 403 00:22:30,750 --> 00:22:33,060 The only way to really produce these globules 404 00:22:33,060 --> 00:22:35,620 is another process, 405 00:22:35,630 --> 00:22:38,260 and we think in this case it was some kind of process 406 00:22:38,260 --> 00:22:41,830 like collisions. 407 00:22:41,830 --> 00:22:44,430 Collisions so violent they vaporized 408 00:22:44,440 --> 00:22:46,970 the silicates and metals. 409 00:22:46,970 --> 00:22:52,770 Solid turns to gas, and then gas to liquid. 410 00:22:52,780 --> 00:22:55,810 But what planetary body contains enough metal to be able 411 00:22:55,810 --> 00:23:00,780 to produce the droplets we see in gujba? 412 00:23:00,780 --> 00:23:04,650 Only something big enough to have an iron core. 413 00:23:06,520 --> 00:23:08,060 When an object grows large enough, 414 00:23:08,060 --> 00:23:10,890 its gravity become strong enough that it differentiates, 415 00:23:10,890 --> 00:23:12,690 and what we mean by that is, 416 00:23:12,700 --> 00:23:15,160 heavy stuff is pulled down and sinks into the center, 417 00:23:15,170 --> 00:23:16,900 and lighter stuff floats to the top, 418 00:23:16,900 --> 00:23:22,840 so you have a differentiation of material. 419 00:23:22,840 --> 00:23:23,656 Earth is a classic example of a body that is differentiated. 420 00:23:29,410 --> 00:23:33,550 while heavy metals remain in the crust 421 00:23:33,550 --> 00:23:36,120 The crust and the core are separated 422 00:23:36,120 --> 00:23:41,560 by a molten silicate layer known as the mantle. 423 00:23:41,560 --> 00:23:45,160 Gujba is a perfect example of the fact 424 00:23:45,160 --> 00:23:48,360 that you had large planetary bodies 425 00:23:48,370 --> 00:23:52,000 that were differentiated into irons and silicates, 426 00:23:52,000 --> 00:23:54,000 and they were colliding at velocities 427 00:23:54,000 --> 00:23:56,140 great enough to scatter their pieces 428 00:23:56,140 --> 00:23:57,740 out into the nebula again. 429 00:23:57,740 --> 00:23:59,940 That is just amazing to me, 430 00:23:59,940 --> 00:24:03,510 that this really, really violent process 431 00:24:03,510 --> 00:24:07,780 in history that's captured in these tiny little fragments. 432 00:24:10,950 --> 00:24:13,420 Gujba reveals the differentiated planets 433 00:24:13,420 --> 00:24:16,590 were commonplace as early as 5 million years 434 00:24:16,590 --> 00:24:19,160 after the formation of the solar system. 435 00:24:21,600 --> 00:24:23,330 There were so many of these planets, 436 00:24:23,330 --> 00:24:25,870 they often smashed together. 437 00:24:28,340 --> 00:24:31,370 If you go down this path of planet formation 438 00:24:31,380 --> 00:24:32,870 by giant impacts, 439 00:24:32,880 --> 00:24:34,680 you end up with the last survivors 440 00:24:34,680 --> 00:24:38,380 being a bunch of freaks. 441 00:24:38,380 --> 00:24:40,380 Freaks built from the dead embers 442 00:24:40,380 --> 00:24:41,820 of past generations. 443 00:24:44,620 --> 00:24:48,390 And this violent scenario raises the question, 444 00:24:48,390 --> 00:24:50,390 just how many planets did it take 445 00:24:50,390 --> 00:24:52,530 to build the inner solar system? 446 00:24:54,670 --> 00:24:58,600 Simulations say at least 30, 447 00:24:58,600 --> 00:25:00,770 but just four survived. 448 00:25:19,180 --> 00:25:21,280 The secret history of the solar system 449 00:25:21,290 --> 00:25:24,250 is hard to interpret, 450 00:25:24,260 --> 00:25:27,260 but astronomers devise radical new solutions 451 00:25:27,260 --> 00:25:28,760 to connect the dots. 452 00:25:31,260 --> 00:25:33,530 The grand tack model helps explain why we see 453 00:25:33,530 --> 00:25:35,270 no hot Jupiter planet. 454 00:25:37,540 --> 00:25:40,300 The grand attack model provides an answer 455 00:25:40,310 --> 00:25:43,040 to the lack of material within Mercury's orbit 456 00:25:43,040 --> 00:25:46,110 and why our solar system has no super-Earths. 457 00:25:48,510 --> 00:25:53,220 These are theories designed to crack the cosmic cold case, 458 00:25:53,220 --> 00:25:55,990 but to understand our red neighbor, Mars, 459 00:25:55,990 --> 00:26:00,390 scientists need another simulation, a 30-planet pileup. 460 00:26:03,800 --> 00:26:05,730 When you look at the action in a solar system, 461 00:26:05,730 --> 00:26:08,100 you essentially have our smallest planet on the inside 462 00:26:08,100 --> 00:26:09,400 and then it gets larger and larger 463 00:26:09,400 --> 00:26:11,230 as you go from Venus to the Earth, 464 00:26:11,240 --> 00:26:14,970 so you would naturally expect Mars to be larger than it is. 465 00:26:14,970 --> 00:26:18,110 It should be 10 times bigger than it is, but it's not. 466 00:26:21,250 --> 00:26:24,510 Mars' size isn't its only mystery. 467 00:26:24,520 --> 00:26:28,020 It's also much older than we expected. 468 00:26:28,020 --> 00:26:31,350 Scientists have refined the age of Mars' mantle 469 00:26:31,360 --> 00:26:32,990 based on the chemical composition 470 00:26:32,990 --> 00:26:37,090 of a piece of martian meteorite. 471 00:26:37,100 --> 00:26:40,500 The sample blew off from the planet during a violent impact 472 00:26:40,500 --> 00:26:44,800 and made its way to Earth. 473 00:26:44,800 --> 00:26:47,270 It revealed that Mars formed rapidly, 474 00:26:47,270 --> 00:26:51,980 within the first 2 million years of the solar system's birth, 475 00:26:51,980 --> 00:26:54,980 well before the Earth. 476 00:26:54,980 --> 00:26:57,580 Mars is small, and Mars formed really, 477 00:26:57,580 --> 00:27:01,180 really fast compared to what it should have. 478 00:27:01,190 --> 00:27:02,820 The Earth is 10 times more massive. 479 00:27:02,820 --> 00:27:04,920 It formed in 100 million years. 480 00:27:04,920 --> 00:27:06,620 Mars formed in 2 million years. 481 00:27:06,630 --> 00:27:08,060 This doesn't make sense. It's our neighbor. 482 00:27:08,060 --> 00:27:10,130 It should look just like us. 483 00:27:10,130 --> 00:27:14,430 Everything about Mars feels wrong. 484 00:27:14,430 --> 00:27:17,300 These two mysteries might help explain one another. 485 00:27:17,300 --> 00:27:18,940 Scientists think it's possible 486 00:27:18,940 --> 00:27:21,600 that around 30 other similar planets 487 00:27:21,610 --> 00:27:23,710 formed alongside Mars 488 00:27:23,710 --> 00:27:26,410 within the first 2 million years of the solar system. 489 00:27:29,750 --> 00:27:32,520 So what happened to this 30-planet pileup? 490 00:27:32,520 --> 00:27:34,820 Time for another game of cosmic pool. 491 00:27:40,130 --> 00:27:43,230 So in this model, we very quickly form 492 00:27:43,230 --> 00:27:45,900 20 or 30 Mars-sized planets. 493 00:27:45,900 --> 00:27:47,530 This is a pretty jam-packed system. 494 00:27:47,530 --> 00:27:49,200 The planets are pretty close to each other, 495 00:27:49,200 --> 00:27:54,070 and it's just on the hairy edge of stability. 496 00:27:54,070 --> 00:27:57,340 This colony of Mars-sized planets builds rapidly. 497 00:27:59,080 --> 00:28:00,940 In the early days of the solar system, 498 00:28:00,950 --> 00:28:03,180 there's enough gas around to keep their orbits 499 00:28:03,180 --> 00:28:07,380 from crossing each other, 500 00:28:07,390 --> 00:28:10,790 but after 20 million years, the gas has gone, 501 00:28:10,790 --> 00:28:13,460 and their orbits start to intersect. 502 00:28:15,530 --> 00:28:17,360 When it goes unstable, 503 00:28:17,360 --> 00:28:19,760 it's then a pretty loud and chaotic place. 504 00:28:19,760 --> 00:28:21,930 As Mars-sized bodies collide with each other 505 00:28:21,930 --> 00:28:23,900 to build the Earth and Venus, 506 00:28:23,900 --> 00:28:26,570 we get a series of huge, violent collisions. 507 00:28:29,740 --> 00:28:31,740 Over the next 100 million years, 508 00:28:31,740 --> 00:28:35,210 the Mars-sized protoplanets annihilate each other 509 00:28:35,210 --> 00:28:38,820 to eventually form second-generation planets, 510 00:28:38,820 --> 00:28:42,320 Venus and Earth. 511 00:28:42,320 --> 00:28:45,920 Yet one planet stood back and watched from the sidelines. 512 00:28:48,160 --> 00:28:53,460 That planet was Mars, and that is the secret to its old age, 513 00:28:53,470 --> 00:28:56,600 compared to Earth. 514 00:28:56,600 --> 00:28:59,340 If Mars is indeed older than the Earth, 515 00:28:59,340 --> 00:29:03,510 that would imply that it's one of the original planetary 516 00:29:03,510 --> 00:29:05,240 embryos of the solar system. 517 00:29:05,240 --> 00:29:07,340 Mars is essentially done early. 518 00:29:07,350 --> 00:29:09,510 It is on the outside of this whole process, 519 00:29:09,510 --> 00:29:11,980 sitting out not accreting any more mass 520 00:29:11,980 --> 00:29:13,780 and watching while the Earth and Venus 521 00:29:13,790 --> 00:29:16,350 form out of the other big bodies that have been built. 522 00:29:18,690 --> 00:29:20,890 So what prevented Mars from colliding 523 00:29:20,890 --> 00:29:23,330 with the rest of the planetary embryos? 524 00:29:25,760 --> 00:29:30,170 The answer... Jupiter. 525 00:29:30,170 --> 00:29:33,670 During the grand tack, Jupiter moved to the same distance 526 00:29:33,670 --> 00:29:36,740 from the Sun that we find Mars today, 527 00:29:36,740 --> 00:29:41,040 and in the process ate the red planet's lunch. 528 00:29:41,050 --> 00:29:42,850 Jupiter removes all of the material 529 00:29:42,850 --> 00:29:45,550 that Mars otherwise would have been building on 530 00:29:45,550 --> 00:29:47,680 for the next tens of millions of years, 531 00:29:47,690 --> 00:29:50,020 essentially clears out a big chunk of the solar system 532 00:29:50,020 --> 00:29:51,850 and starves Mars. 533 00:29:51,860 --> 00:29:53,420 If Jupiter were not there, 534 00:29:53,430 --> 00:29:54,760 than we would have expected Mars 535 00:29:54,760 --> 00:29:57,590 to have formed a fully-fledged super-Earth planet. 536 00:29:59,730 --> 00:30:03,000 Earth formed from the wreckage of this pileup, 537 00:30:03,000 --> 00:30:06,170 but a reminder of this population lives on, 538 00:30:06,170 --> 00:30:11,640 every time we look to the night sky... The Moon. 539 00:30:11,640 --> 00:30:14,780 We were convinced we knew how the Moon formed. 540 00:30:14,780 --> 00:30:18,550 Turns out, we were completely wrong. 541 00:30:39,730 --> 00:30:42,870 A distance observer studying our solar system 542 00:30:42,870 --> 00:30:47,070 would notice something strange right away... 543 00:30:47,070 --> 00:30:50,710 The size of Earth's moon. 544 00:30:50,710 --> 00:30:54,880 Most planet's moons are tiny by comparison. 545 00:30:54,880 --> 00:30:57,010 How did we get a moon so big? 546 00:30:59,220 --> 00:31:01,220 For a while we've realized it couldn't have formed 547 00:31:01,220 --> 00:31:02,550 at the same time as the Earth. 548 00:31:02,560 --> 00:31:04,720 It just doesn't make sense. 549 00:31:04,720 --> 00:31:06,860 The standard idea of the Moon's formation 550 00:31:06,860 --> 00:31:08,990 is that an object about the size of Mars 551 00:31:09,000 --> 00:31:10,760 collided with the early Earth. 552 00:31:10,760 --> 00:31:13,500 A lot of the debris was thrown into orbit around the Earth, 553 00:31:13,500 --> 00:31:16,630 and it coalesced to form the Moon. 554 00:31:16,640 --> 00:31:20,910 We call this Mars-sized object Thea, 555 00:31:20,910 --> 00:31:24,440 but exactly when and how the Moon formed 556 00:31:24,440 --> 00:31:27,650 remains a mystery. 557 00:31:27,650 --> 00:31:29,710 Ever since the Apollo missions, 558 00:31:29,720 --> 00:31:32,280 we've been searching for a piece of lunar rock 559 00:31:32,290 --> 00:31:33,920 that can unlock this secret. 560 00:31:36,360 --> 00:31:40,290 Melanie Barboni's team at UCLA is one of the few groups 561 00:31:40,290 --> 00:31:44,630 authorized to analyze these precious lunar samples. 562 00:31:47,500 --> 00:31:48,930 But there's a problem... 563 00:31:48,940 --> 00:31:51,100 Most moon rock is contaminated 564 00:31:51,100 --> 00:31:56,570 and damaged by violent events in the more recent past. 565 00:31:56,580 --> 00:31:58,340 Asteroids hit the Moon, and there are geological 566 00:31:58,340 --> 00:31:59,810 processes that do a lot of mixing, 567 00:31:59,810 --> 00:32:02,910 and it's very difficult to find a pristine sample 568 00:32:02,920 --> 00:32:07,080 from the Moon's very formation. 569 00:32:07,090 --> 00:32:09,520 Melanie and her team have come up with a novel 570 00:32:09,520 --> 00:32:11,320 answer to that problem. 571 00:32:11,320 --> 00:32:13,660 Rather than date the entire rock, 572 00:32:13,660 --> 00:32:18,200 they isolate a tiny, pristine crystal within a lunar sample, 573 00:32:18,200 --> 00:32:20,730 known as a zircon. 574 00:32:20,730 --> 00:32:22,370 Now we don't want the whole rock, 575 00:32:22,370 --> 00:32:26,700 we want only tiny zircon that are inside those rocks. 576 00:32:28,610 --> 00:32:29,940 These zircons formed 577 00:32:29,940 --> 00:32:32,840 just after Thea's collision with Earth. 578 00:32:32,850 --> 00:32:34,850 Once the molten crust of the Moon, 579 00:32:34,850 --> 00:32:37,720 it cooled and solidified. 580 00:32:37,720 --> 00:32:40,320 This is much smaller than the grain of sand 581 00:32:40,320 --> 00:32:42,320 you find on the beach. 582 00:32:42,320 --> 00:32:44,890 Zircon is the most perfect clock 583 00:32:44,890 --> 00:32:46,890 that nature gave us to date the Moon 584 00:32:46,890 --> 00:32:49,230 because it's very resistant. 585 00:32:49,230 --> 00:32:52,030 Here you can see its surface is very smooth. 586 00:32:52,030 --> 00:32:55,130 There is no fractures on it. 587 00:32:55,130 --> 00:32:58,140 Zircons tick off time like clocks. 588 00:32:58,140 --> 00:33:00,710 They contain large radioactive elements 589 00:33:00,710 --> 00:33:03,240 that decay into smaller ones. 590 00:33:03,240 --> 00:33:05,210 Scientists can tell how old the crystal 591 00:33:05,210 --> 00:33:09,010 is by measuring the radioactive decay. 592 00:33:09,020 --> 00:33:14,890 The zircons Melanie found rewrite the history of the Moon. 593 00:33:14,890 --> 00:33:20,120 The Moon is around 140 million years older 594 00:33:20,130 --> 00:33:21,760 than what we thought. 595 00:33:21,760 --> 00:33:23,690 This means the Moon formed 596 00:33:23,700 --> 00:33:26,300 no later than 60 million years 597 00:33:26,300 --> 00:33:28,670 after the birth of the Sun. 598 00:33:28,670 --> 00:33:32,070 This places the formation of the Moon right in the middle 599 00:33:32,070 --> 00:33:35,810 of the destruction of the 30-planet pileup. 600 00:33:35,810 --> 00:33:39,540 It's entirely possible that Thea was once a member 601 00:33:39,550 --> 00:33:43,610 of this colony of Mars-sized objects. 602 00:33:43,620 --> 00:33:45,580 It wasn't just some Mars object 603 00:33:45,590 --> 00:33:47,020 that was out in the outer solar system 604 00:33:47,020 --> 00:33:49,150 and came careening in and smashed into us. 605 00:33:49,160 --> 00:33:53,020 It was one of these no-longer-existing planetesimals 606 00:33:53,030 --> 00:33:56,760 that slammed into us and formed the Moon. 607 00:33:56,760 --> 00:33:59,430 But scientists looking for traces of Thea 608 00:33:59,430 --> 00:34:03,370 on the Moon draw blanks. 609 00:34:03,370 --> 00:34:04,970 One of the intriguing things about moon rocks 610 00:34:04,970 --> 00:34:07,810 is how similar they are, chemically, to rocks on Earth. 611 00:34:07,810 --> 00:34:09,940 It has the same geochemical fingerprints, 612 00:34:09,940 --> 00:34:12,140 the oxygen isotopes, of the Earth, 613 00:34:12,150 --> 00:34:14,250 and all the other chemical isotopes of the Earth. 614 00:34:14,250 --> 00:34:16,650 It looks just like Earth rock. 615 00:34:16,650 --> 00:34:19,480 If the Moon really is the product of one giant collision, 616 00:34:19,490 --> 00:34:21,320 well, whatever hit the Earth, 617 00:34:21,320 --> 00:34:23,620 there should be different proportions of that on the Earth 618 00:34:23,620 --> 00:34:26,590 as opposed to the Moon, but we don't find that. 619 00:34:28,460 --> 00:34:31,730 The Moon is identical to material from the Earth, 620 00:34:31,730 --> 00:34:35,870 except it's missing heavy elements, iron and nickel, 621 00:34:35,870 --> 00:34:37,740 found in the Earth's core. 622 00:34:37,740 --> 00:34:41,840 Instead, it mainly contains lighter rocky elements 623 00:34:41,840 --> 00:34:44,640 found in the Earth's crust and mantle. 624 00:34:44,640 --> 00:34:46,910 Why? 625 00:34:46,910 --> 00:34:48,210 It wasn't a head-on collision. 626 00:34:48,210 --> 00:34:49,980 It was a grazing collision. 627 00:34:49,980 --> 00:34:51,780 Now, that's important because the heavy material 628 00:34:51,780 --> 00:34:54,220 was starting to sink into the center of the Earth, 629 00:34:54,220 --> 00:34:55,951 and the lighter stuff was floating to the top. 630 00:34:55,960 --> 00:34:58,090 And if this were a grazing collision, 631 00:34:58,090 --> 00:35:00,620 then that lighter material would have been splashed out, 632 00:35:00,630 --> 00:35:02,660 and that's what would have formed the Moon. 633 00:35:02,660 --> 00:35:05,030 And the Moon is, in fact, less dense than the Earth, 634 00:35:05,030 --> 00:35:07,830 which makes sense if it formed from this lighter material 635 00:35:07,830 --> 00:35:09,330 that was near the top. 636 00:35:09,340 --> 00:35:11,800 It looks like you took a blob of the Earth's mantle 637 00:35:11,800 --> 00:35:14,070 and just put it into space around the Earth. 638 00:35:14,070 --> 00:35:17,010 A single head-on collision would leave traces 639 00:35:17,010 --> 00:35:21,550 of both Thea and Earth's core on the Moon, 640 00:35:21,550 --> 00:35:25,250 but a glancing blow wouldn't knock off enough material 641 00:35:25,250 --> 00:35:28,790 to form a moon as big as ours. 642 00:35:28,790 --> 00:35:30,920 One way we can end up with the Earth-moon system 643 00:35:30,920 --> 00:35:33,490 that we see today and solve all these problems, 644 00:35:33,490 --> 00:35:36,190 is that instead of having one big collision, 645 00:35:36,200 --> 00:35:39,400 there were a series of several smaller collisions. 646 00:35:43,240 --> 00:35:47,070 Each impact grazes off a section of Earth's crust 647 00:35:47,070 --> 00:35:49,770 that forms a ring around our planet. 648 00:35:49,780 --> 00:35:51,380 With each small collision, 649 00:35:51,380 --> 00:35:54,710 material would have been thrown into orbit around the Earth. 650 00:35:54,710 --> 00:35:57,280 Eventually this collisional debris merges 651 00:35:57,280 --> 00:36:01,290 to form a small, new moon, a moonlet. 652 00:36:01,290 --> 00:36:03,990 Now after several of these collisions, 653 00:36:03,990 --> 00:36:07,120 you'll have debris from each collision circling the Earth. 654 00:36:07,130 --> 00:36:09,090 Some of it is still in the form of debris, 655 00:36:09,100 --> 00:36:11,300 some of it is in the form of moonlets. 656 00:36:11,300 --> 00:36:16,130 Eventually they coalesce to form our current moon. 657 00:36:16,140 --> 00:36:18,270 It seems our moon may well be 658 00:36:18,270 --> 00:36:19,940 the product of a series 659 00:36:19,940 --> 00:36:24,110 of cosmic collisions in the early solar system. 660 00:36:24,110 --> 00:36:28,610 What we see when we look up in the sky now isn't the moon, 661 00:36:28,610 --> 00:36:31,920 but it's basically the last moon that survived. 662 00:36:31,920 --> 00:36:34,450 It was just the one that happened to be there 663 00:36:34,450 --> 00:36:36,620 when all of these impacts stopped. 664 00:36:40,330 --> 00:36:43,560 The closer we come to understanding our violent past, 665 00:36:43,560 --> 00:36:47,670 the more we appreciate the calm of the present, 666 00:36:47,670 --> 00:36:50,330 but as we try to predict our future, 667 00:36:50,340 --> 00:36:54,140 it seems we are destined for chaos once again, 668 00:36:54,140 --> 00:36:58,510 as a distant mystery planet in the outer solar system 669 00:36:58,510 --> 00:37:00,880 moves in from the cold. 670 00:37:19,730 --> 00:37:22,230 The birth of our solar system... 671 00:37:22,230 --> 00:37:26,670 Violent, chaotic, catastrophic. 672 00:37:26,670 --> 00:37:29,570 When we look at the solar system when it was very young, 673 00:37:29,570 --> 00:37:31,740 all of our models pretty much say the same thing. 674 00:37:31,740 --> 00:37:33,710 It was not nice and orderly. 675 00:37:33,710 --> 00:37:35,240 It was a disaster. 676 00:37:35,240 --> 00:37:37,280 And then things settled down. 677 00:37:37,280 --> 00:37:40,710 Life had a chance to take hold and evolve under very stable, 678 00:37:40,720 --> 00:37:42,480 very friendly conditions. 679 00:37:42,480 --> 00:37:44,050 So when you look around right now, 680 00:37:44,050 --> 00:37:47,550 you're seeing the story of an ancient, violent past 681 00:37:47,560 --> 00:37:50,220 that has smoothed out into the wonderful environment 682 00:37:50,220 --> 00:37:51,990 we know today. 683 00:37:51,990 --> 00:37:54,290 Our solar system might seem stable, 684 00:37:54,300 --> 00:37:57,560 but there is still something very strange about it. 685 00:37:57,570 --> 00:38:00,030 There is still one enduring mystery, 686 00:38:00,030 --> 00:38:03,940 and that is why the solar system tilted? 687 00:38:03,940 --> 00:38:05,300 The eight planets orbit 688 00:38:05,310 --> 00:38:08,540 in roughly the same flat plane, 689 00:38:08,540 --> 00:38:11,610 but compared to the spin axis of the Sun, 690 00:38:11,610 --> 00:38:17,750 that plane is tilted, making the Sun look lopsided. 691 00:38:17,750 --> 00:38:19,550 And it turns out, when you look at the Sun's tilt, 692 00:38:19,550 --> 00:38:21,950 it's actually tipped by 6 degrees, 693 00:38:21,960 --> 00:38:23,690 the plane of the solar system. 694 00:38:23,690 --> 00:38:25,190 And that may not sound like a lot, 695 00:38:25,190 --> 00:38:26,730 but it's actually quite a bit 696 00:38:26,730 --> 00:38:29,630 compared to the tilts of all the planets of the solar system, 697 00:38:29,630 --> 00:38:31,060 and this is an outlier. 698 00:38:31,070 --> 00:38:32,430 It's strange. 699 00:38:32,430 --> 00:38:34,630 What could have done that? 700 00:38:34,640 --> 00:38:37,000 The tilt contradicts what we know about 701 00:38:37,000 --> 00:38:39,000 how the solar system formed, 702 00:38:39,010 --> 00:38:43,740 a spinning cloud collapses into a disk. 703 00:38:43,740 --> 00:38:48,350 The spinning disk then becomes the Sun and all the planets. 704 00:38:48,350 --> 00:38:52,550 It should all be spinning on the same axis. 705 00:38:52,550 --> 00:38:55,990 So one possible way that you could change the orientation 706 00:38:55,990 --> 00:38:58,520 of the pull of the Sun relative to the plane the planets are in, 707 00:38:58,530 --> 00:39:00,290 is if there was something out there 708 00:39:00,290 --> 00:39:03,660 tugging on the planets for a very long time. 709 00:39:03,660 --> 00:39:06,530 2016, Cal tech astronomers 710 00:39:06,530 --> 00:39:09,540 Konstantin Batygin and Mike Brown 711 00:39:09,540 --> 00:39:13,940 claim they've found the missing something... 712 00:39:13,940 --> 00:39:20,650 Planet 9, a theoretical giant orbiting off-kilter 713 00:39:20,650 --> 00:39:23,720 in the far reaches of the solar system. 714 00:39:23,720 --> 00:39:28,190 Planet 9 resides on a long and substantial orbit, 715 00:39:28,190 --> 00:39:33,430 and it itself is pretty massive, about 10 Earth masses or so. 716 00:39:33,430 --> 00:39:36,600 If it's orbiting the Sun on a highly elliptical tilted orbit, 717 00:39:36,600 --> 00:39:38,200 every time it gets close to the Sun, 718 00:39:38,200 --> 00:39:40,930 it's going to tug on the planets just a little bit. 719 00:39:40,940 --> 00:39:44,400 But over hundreds and thousands of orbits, it can actually tip 720 00:39:44,410 --> 00:39:46,940 the orbits of all the planets in the solar system, 721 00:39:46,940 --> 00:39:49,340 but it won't tip the Sun. 722 00:39:49,340 --> 00:39:52,340 Over billions of years, the planetary system 723 00:39:52,350 --> 00:39:57,150 slowly twists out of alignment with its original plane. 724 00:39:57,150 --> 00:39:59,220 Planet 9's distant reach 725 00:39:59,220 --> 00:40:03,260 may solve the mystery of the solar system's tilt, 726 00:40:03,260 --> 00:40:06,990 but it might also have a disastrous effect 727 00:40:06,990 --> 00:40:10,800 on the outer planets as the Sun starts to die. 728 00:40:19,010 --> 00:40:21,240 the Sun, just like every other star in the universe, 729 00:40:21,240 --> 00:40:22,670 has a life cycle. 730 00:40:22,680 --> 00:40:23,810 It was born. 731 00:40:23,810 --> 00:40:26,280 It is currently living its life, and it will die. 732 00:40:26,280 --> 00:40:29,820 As it dies, it will bloat up into a red giant star, 733 00:40:29,820 --> 00:40:32,780 and then the outer layers will begin to drift away. 734 00:40:32,790 --> 00:40:34,090 Now what that means is that 735 00:40:34,090 --> 00:40:36,820 the Sun will be losing mass very quickly. 736 00:40:36,820 --> 00:40:39,690 The thing that holds us in orbit around the Sun 737 00:40:39,690 --> 00:40:42,260 is the gravitational pull of the Sun. 738 00:40:42,260 --> 00:40:45,400 Jupiter, Saturn, Uranus, and Neptune 739 00:40:45,400 --> 00:40:46,800 will move away from the Sun 740 00:40:46,800 --> 00:40:49,430 as its outer layers expand, 741 00:40:49,440 --> 00:40:52,740 but that's not the case for distant Planet 9. 742 00:40:52,740 --> 00:40:55,170 Scientists think that Planet 9 orbits 743 00:40:55,180 --> 00:40:58,040 so far out that as the Sun dies, 744 00:40:58,050 --> 00:41:01,550 it will loosen its gravitational grip on the planet. 745 00:41:01,550 --> 00:41:05,480 Planet 9 starts to feel the influence of other objects 746 00:41:05,490 --> 00:41:07,520 more than the Sun. 747 00:41:07,520 --> 00:41:10,260 It turns out a passing star, for example, 748 00:41:10,260 --> 00:41:11,490 could affect its orbit, 749 00:41:11,490 --> 00:41:14,760 or even tides from the galaxy itself, 750 00:41:14,760 --> 00:41:18,000 our galaxy's gravitational field can affect this planet, 751 00:41:18,000 --> 00:41:20,370 and drop it into the inner solar system. 752 00:41:20,370 --> 00:41:22,700 This change in Planet 9's orbits 753 00:41:22,700 --> 00:41:25,370 could be disastrous for the solar system. 754 00:41:25,370 --> 00:41:26,710 And if that happens, 755 00:41:26,710 --> 00:41:29,680 it could actually wreak havoc on the gas giants 756 00:41:29,680 --> 00:41:31,610 Jupiter, Saturn, Uranus, and Neptune 757 00:41:31,610 --> 00:41:33,210 and distort their orbits, 758 00:41:33,210 --> 00:41:35,080 maybe dropping them into the Sun 759 00:41:35,080 --> 00:41:37,480 or flinging them out of the solar system, as well. 760 00:41:40,620 --> 00:41:43,290 Planet 9 could make the death of the solar system 761 00:41:43,290 --> 00:41:46,430 just as violent as its birth. 762 00:41:46,430 --> 00:41:48,960 Right now we're in this wonderful sweet spot 763 00:41:48,960 --> 00:41:51,460 where life can evolve and take hold between 764 00:41:51,470 --> 00:41:54,970 two eras of almost unimaginable violence. 765 00:41:54,970 --> 00:41:58,400 If there is a Planet 9, then it's kind of a rehash 766 00:41:58,410 --> 00:42:00,170 of what happened in the early solar system, 767 00:42:00,170 --> 00:42:01,840 when everything was really chaotic 768 00:42:01,840 --> 00:42:04,110 because of a giant planet moving inward. 769 00:42:04,110 --> 00:42:07,710 The same thing could happen again. 770 00:42:07,720 --> 00:42:09,210 Born in chaos. 771 00:42:09,220 --> 00:42:11,850 Perhaps ending in worse. 772 00:42:11,850 --> 00:42:13,420 One thing is clear... 773 00:42:13,420 --> 00:42:16,460 What we thought we knew of our cosmic home 774 00:42:16,460 --> 00:42:18,120 grows more intriguing 775 00:42:18,130 --> 00:42:22,490 with each new clue to this once cold case, 776 00:42:22,500 --> 00:42:25,400 now a very hot one. 777 00:42:25,701 --> 00:42:27,901 I have spent hours for You, please spend 5 seconds for me Visit www.nicolascanni.com + click on the Ads - Thank You! 62041

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