1 00:00:04,237 --> 00:00:06,535 Our solar system... 2 00:00:06,606 --> 00:00:08,597 8 planets and over 300 moons 3 00:00:08,675 --> 00:00:12,338 circling the Sun like clockwork. 4 00:00:12,412 --> 00:00:14,972 But it didn't start that way. 5 00:00:15,048 --> 00:00:19,508 Our solar system has a long history of violence. 6 00:00:19,586 --> 00:00:21,747 The solar system we see today 7 00:00:21,821 --> 00:00:25,882 is really just the final survivors of the early chaos. 8 00:00:25,959 --> 00:00:29,019 And in the future, that chaos will return. 9 00:00:29,095 --> 00:00:33,259 The entire house of cards that is our solar system 10 00:00:33,333 --> 00:00:34,800 will completely fall apart. 11 00:00:34,868 --> 00:00:37,166 From start to finish, 12 00:00:37,237 --> 00:00:40,206 this is how solar systems work. 13 00:00:55,522 --> 00:00:59,288 There are billions of stars in the Milky Way galaxy. 14 00:00:59,359 --> 00:01:01,793 One of them is our Sun. 15 00:01:06,433 --> 00:01:11,029 And around the Sun orbits a system of planets and moons... 16 00:01:11,104 --> 00:01:13,197 a solar system. 17 00:01:18,478 --> 00:01:22,915 Our solar system is clearly a precious planetary system. 18 00:01:22,982 --> 00:01:25,678 And it begs the question, 19 00:01:25,752 --> 00:01:29,279 are there other planetary systems like ours 20 00:01:29,355 --> 00:01:31,789 orbiting other stars? 21 00:01:31,858 --> 00:01:35,954 To find out, Marcy scans the skies with the Keck... 22 00:01:36,029 --> 00:01:39,226 one of the world's largest optical telescopes. 23 00:01:39,299 --> 00:01:43,998 Perched at 14,000 feet, on top of Mauna Kea in Hawaii, 24 00:01:44,070 --> 00:01:47,335 it hunts for new, distant solar systems. 25 00:01:51,578 --> 00:01:55,173 The marvelous reality is that our own Milky Way galaxy 26 00:01:55,248 --> 00:01:59,947 contains some 200 billion stars or so, 27 00:02:00,019 --> 00:02:03,455 and many of those stars have their own planetary systems. 28 00:02:06,526 --> 00:02:09,689 Our solar system, with its eight major planets, 29 00:02:09,762 --> 00:02:11,286 is not alone. 30 00:02:11,364 --> 00:02:14,765 There are other brethren planetary systems 31 00:02:14,834 --> 00:02:16,893 out there by the billions. 32 00:02:16,970 --> 00:02:20,997 Of course, astronomers hope to find another solar system 33 00:02:21,074 --> 00:02:24,510 with a planet like Earth, and they're off to a good start. 34 00:02:24,577 --> 00:02:26,807 So far, Marcy and other astronomers 35 00:02:26,880 --> 00:02:31,840 have discovered over 360 stars with orbiting planets. 36 00:02:31,918 --> 00:02:35,376 One of the exciting discoveries that we've made 37 00:02:35,455 --> 00:02:37,685 is that stars tend to be orbited 38 00:02:37,757 --> 00:02:39,190 not just by one planet 39 00:02:39,259 --> 00:02:42,820 but usually two, three, four, or a multitude of planets. 40 00:02:42,896 --> 00:02:44,864 Planets come in families, 41 00:02:44,931 --> 00:02:47,365 not unlike the family of planets 42 00:02:47,433 --> 00:02:50,197 we enjoy here around our own Sun. 43 00:02:52,906 --> 00:02:54,874 For the first time, 44 00:02:54,941 --> 00:02:57,535 scientists can study them in some detail. 45 00:02:57,610 --> 00:03:00,511 We can actually observe how planets heat up 46 00:03:00,580 --> 00:03:02,377 as they go around their sun. 47 00:03:02,448 --> 00:03:05,417 For example, we actually saw that one planet 48 00:03:05,485 --> 00:03:08,477 got hotter and colder as it orbited its star. 49 00:03:08,555 --> 00:03:10,682 And we realized that we were actually seeing 50 00:03:10,757 --> 00:03:12,054 the night side of the planet 51 00:03:12,125 --> 00:03:13,922 and then the day side of the planet. 52 00:03:13,993 --> 00:03:15,790 That was the temperature difference. 53 00:03:18,131 --> 00:03:21,259 We were observing sunrise and sunset on a planet 54 00:03:21,334 --> 00:03:22,892 in another solar system. 55 00:03:26,406 --> 00:03:29,432 But that planet is nothing like Earth, 56 00:03:29,509 --> 00:03:32,501 and most of these newly discovered solar systems 57 00:03:32,579 --> 00:03:34,137 are nothing like our own. 58 00:03:37,183 --> 00:03:40,619 Their planets are huge... much bigger than Jupiter. 59 00:03:43,690 --> 00:03:45,749 Some follow wild orbits, 60 00:03:45,825 --> 00:03:49,158 some orbit in the opposite direction, 61 00:03:49,229 --> 00:03:53,359 and some shoot billions of miles out into space, 62 00:03:53,433 --> 00:03:56,630 then dive back toward their star. 63 00:03:56,703 --> 00:03:59,331 A few orbit so close to the star, 64 00:03:59,405 --> 00:04:02,272 their surfaces vaporize. 65 00:04:02,342 --> 00:04:08,008 It's bizarre, at the least, if not completely frightening. 66 00:04:08,081 --> 00:04:11,312 Planetary systems offer a wide diversity 67 00:04:11,384 --> 00:04:14,251 of different architectures, sizes, 68 00:04:14,320 --> 00:04:17,084 masses of the planets, and so on, 69 00:04:17,156 --> 00:04:20,057 rendering our solar system just one type 70 00:04:20,126 --> 00:04:22,959 of a planetary system out of thousands. 71 00:04:23,029 --> 00:04:27,898 It could be that each and every solar system is a one-of-a-kind. 72 00:04:27,967 --> 00:04:31,528 But they all have one thing in common... 73 00:04:31,604 --> 00:04:35,335 each one begins with a star. 74 00:04:35,408 --> 00:04:40,846 First, a star is born in a cloud of dust and gas called a nebula. 75 00:04:40,913 --> 00:04:44,906 This is the Eagle nebula. 76 00:04:44,984 --> 00:04:48,078 These are the Pillars of Creation. 77 00:04:51,824 --> 00:04:55,260 And this is the Horsehead nebula, 78 00:04:55,328 --> 00:04:57,762 an enormous star nursery. 79 00:05:01,801 --> 00:05:05,168 What scientists have been trying to figure out 80 00:05:05,238 --> 00:05:09,174 is what triggers the star-making process. 81 00:05:09,242 --> 00:05:13,702 One possibility is that a nearby supernova explosion 82 00:05:13,780 --> 00:05:15,805 took place... 83 00:05:21,254 --> 00:05:23,313 ...and rammed into 84 00:05:23,389 --> 00:05:26,825 this otherwise innocuous molecular cloud... 85 00:05:28,795 --> 00:05:30,592 ...smushing it, smashing it, 86 00:05:30,663 --> 00:05:34,030 compressing it down so that gravity could take over. 87 00:05:41,741 --> 00:05:44,039 Once gravity takes over, 88 00:05:44,110 --> 00:05:45,771 the cloud begins to shrink, 89 00:05:45,845 --> 00:05:50,873 sucking in more and more gas into a giant, spinning disk. 90 00:05:50,950 --> 00:05:54,545 Gravity at the center crushes everything 91 00:05:54,620 --> 00:05:57,145 into a dense, superhot ball... 92 00:06:01,728 --> 00:06:04,162 ...that gets hotter and hotter. 93 00:06:06,666 --> 00:06:10,762 Suddenly, atoms in the gas begin to fuse, 94 00:06:10,837 --> 00:06:13,397 and the star ignites. 95 00:06:20,446 --> 00:06:22,846 The leftover dust and debris 96 00:06:22,915 --> 00:06:26,646 forms a disk spinning around the new star. 97 00:06:26,719 --> 00:06:29,119 It contains the seeds 98 00:06:29,188 --> 00:06:32,715 of planets, moons, comets, 99 00:06:32,792 --> 00:06:35,158 and asteroids. 100 00:06:38,631 --> 00:06:41,725 In 2001, the Hubble space telescope 101 00:06:41,801 --> 00:06:44,201 was scanning the Orion nebula 102 00:06:44,270 --> 00:06:47,364 and took this image of a young star 103 00:06:47,440 --> 00:06:50,432 surrounded by one of these disks. 104 00:06:50,510 --> 00:06:54,606 It's a picture of a solar system being born. 105 00:06:54,680 --> 00:06:57,672 Whenever I look at these beautiful pictures of nebulae, 106 00:06:57,750 --> 00:06:59,479 the thing that really gets me 107 00:06:59,552 --> 00:07:02,919 is that these are baby pictures of our own solar system. 108 00:07:02,989 --> 00:07:04,513 We looked like that once. 109 00:07:04,590 --> 00:07:08,117 These fuzzy images have opened the door 110 00:07:08,194 --> 00:07:11,391 to understanding how planetary systems form. 111 00:07:11,464 --> 00:07:14,399 We have this marvelous first-ever tool 112 00:07:14,467 --> 00:07:17,527 by which we can take pictures of planets 113 00:07:17,603 --> 00:07:20,697 caught in the act of formation. 114 00:07:20,773 --> 00:07:23,469 It's quite a marvelous opportunity 115 00:07:23,543 --> 00:07:27,445 for us to see the planets around other stars forming, 116 00:07:27,513 --> 00:07:29,242 thereby giving us a glimpse 117 00:07:29,315 --> 00:07:32,807 as to how our own solar system must surely have formed. 118 00:07:35,688 --> 00:07:39,215 Scientists understood where stars come from 119 00:07:39,292 --> 00:07:42,955 but not how planets grow from the disk of gas and dust. 120 00:07:43,029 --> 00:07:45,725 The answer was discovered by accident 121 00:07:45,798 --> 00:07:48,631 aboard the International Space Station. 122 00:07:50,470 --> 00:07:51,994 Astronaut Don Pettit 123 00:07:52,071 --> 00:07:55,563 was experimenting with grains of sugar and salt 124 00:07:55,641 --> 00:07:57,871 in the weightlessness of space. 125 00:07:57,944 --> 00:08:00,936 Stanley Love was watching from Mission Control 126 00:08:01,013 --> 00:08:03,504 when Pettit stumbled onto the process 127 00:08:03,583 --> 00:08:07,519 of how planets form from cosmic dust. 128 00:08:07,587 --> 00:08:09,248 Well, one of Don's 129 00:08:09,322 --> 00:08:11,722 Saturday-morning science projects 130 00:08:11,791 --> 00:08:14,817 was to take the bags that we store drinks in 131 00:08:14,894 --> 00:08:18,762 and he put other stuff in it, like salt and sugar, 132 00:08:18,831 --> 00:08:22,062 and there was one bag that he just left the coffee powder in. 133 00:08:22,134 --> 00:08:23,863 Then he inflated the bags, 134 00:08:23,936 --> 00:08:26,268 and with these particles in them, 135 00:08:26,339 --> 00:08:29,433 noticed that the particles would just clump up immediately. 136 00:08:29,509 --> 00:08:30,908 They make a little dust bunny. 137 00:08:30,977 --> 00:08:33,275 We'll be spending some time watching that. 138 00:08:33,346 --> 00:08:35,678 I said, "Don, this is incredible! 139 00:08:35,748 --> 00:08:39,809 You've just solved a 40-year-old problem in planetary science!" 140 00:08:39,886 --> 00:08:43,913 Astronaut Pettit had discovered something big. 141 00:08:43,990 --> 00:08:47,517 In the zero gravity of space, 142 00:08:47,593 --> 00:08:50,790 particles of dust don't float apart, 143 00:08:50,863 --> 00:08:52,592 they clump together. 144 00:08:52,665 --> 00:08:57,125 This is how mighty planets are made from cosmic dust. 145 00:08:57,203 --> 00:09:01,264 The dust particles would collide and stick and grow 146 00:09:01,340 --> 00:09:03,706 into ever larger dust particles 147 00:09:03,776 --> 00:09:06,574 and eventually rocks and eventually boulders. 148 00:09:08,714 --> 00:09:10,875 The bigger the boulder, 149 00:09:10,950 --> 00:09:12,417 the more gravity it has. 150 00:09:12,485 --> 00:09:16,922 It begins to eat up everything around it and grows bigger. 151 00:09:21,928 --> 00:09:24,863 It becomes larger, heavier, 152 00:09:24,931 --> 00:09:27,764 and consumes bigger and bigger rocks. 153 00:09:35,341 --> 00:09:39,300 Eventually, some of these rocks grow into planets. 154 00:09:46,252 --> 00:09:49,312 This is what happened in our solar system 155 00:09:49,388 --> 00:09:51,879 4.6 billion years ago. 156 00:10:00,066 --> 00:10:02,728 There were about 100 young planets 157 00:10:02,802 --> 00:10:05,566 all orbiting the new Sun. 158 00:10:09,709 --> 00:10:12,735 Collisions were inevitable. 159 00:10:21,454 --> 00:10:26,118 At the beginning, solar systems are violent. 160 00:10:26,192 --> 00:10:29,093 Ours was no different. 161 00:10:30,596 --> 00:10:35,693 It began with about 100 small, new planets. 162 00:10:35,768 --> 00:10:39,397 So, how did it go from 100 small planets 163 00:10:39,472 --> 00:10:42,498 to the 8 major planets of today? 164 00:10:42,575 --> 00:10:44,008 We got the answer 165 00:10:44,076 --> 00:10:48,012 by studying the evolution of other solar systems. 166 00:10:48,080 --> 00:10:51,572 We see solar systems forming planets, 167 00:10:51,651 --> 00:10:55,143 and all of a sudden, they had these giant disks around them. 168 00:10:55,221 --> 00:10:57,712 Those disks must be from huge collisions. 169 00:11:03,262 --> 00:11:06,789 If planets are smashing together in other systems, 170 00:11:06,866 --> 00:11:09,596 they probably smashed together in our own. 171 00:11:15,741 --> 00:11:18,335 We now know that all solar systems do this 172 00:11:18,411 --> 00:11:19,844 before they settle down. 173 00:11:23,082 --> 00:11:25,107 It's the way they're built. 174 00:11:32,391 --> 00:11:35,554 The nice, neat, orderly solar system that we see today 175 00:11:35,628 --> 00:11:37,289 has not always been the case. 176 00:11:37,363 --> 00:11:39,661 In the early days... a few million years, basically, 177 00:11:39,732 --> 00:11:41,393 after the planets started forming... 178 00:11:41,467 --> 00:11:45,801 there were dozens, maybe even hundreds of these young planets 179 00:11:45,871 --> 00:11:48,169 that were bouncing around the solar system. 180 00:11:54,447 --> 00:11:56,540 They would smash into each other. 181 00:11:56,615 --> 00:11:59,982 Sometimes they would collect and get to be bigger planets. 182 00:12:00,052 --> 00:12:02,486 Sometimes they would smash each other 183 00:12:02,555 --> 00:12:04,182 and turn into little bits. 184 00:12:07,827 --> 00:12:11,228 There was heavy traffic in the new solar system, 185 00:12:11,297 --> 00:12:14,460 objects of all sizes. 186 00:12:14,533 --> 00:12:17,400 They were bound to collide. 187 00:12:19,505 --> 00:12:22,201 Some of the planets grew larger, 188 00:12:22,274 --> 00:12:24,504 and so did the collisions. 189 00:12:24,577 --> 00:12:26,374 I like to try to imagine what it would have been like 190 00:12:26,445 --> 00:12:27,742 to actually stand on the early Earth 191 00:12:27,813 --> 00:12:29,371 and look up into the night sky. 192 00:12:29,448 --> 00:12:31,348 Things would have looked different. 193 00:12:36,122 --> 00:12:39,114 Planet hit planet. 194 00:12:39,191 --> 00:12:42,524 Only the largest survive. 195 00:12:42,595 --> 00:12:46,224 The rest are smashed to pieces. 196 00:12:51,704 --> 00:12:55,162 Something very large struck the young planet Mercury. 197 00:12:56,976 --> 00:12:58,876 It blew the crust off 198 00:12:58,944 --> 00:13:02,209 and left behind just the iron core. 199 00:13:10,122 --> 00:13:13,250 And the young planet Earth did not escape, either. 200 00:13:13,325 --> 00:13:15,486 A planet-sized object 201 00:13:15,561 --> 00:13:17,756 slammed into the Earth off-center 202 00:13:17,830 --> 00:13:21,231 and blew a huge amount of the Earth's crust into space. 203 00:13:35,147 --> 00:13:37,911 The debris circled around the Earth... 204 00:13:37,983 --> 00:13:41,441 And eventually coalesced to become the moon. 205 00:13:59,905 --> 00:14:04,035 This demolition derby raged for 500 million years. 206 00:14:04,109 --> 00:14:05,576 What we see now... 207 00:14:05,644 --> 00:14:07,544 Mars and Earth and Mercury and Venus... 208 00:14:07,613 --> 00:14:09,604 these planets in the inner solar system... 209 00:14:09,682 --> 00:14:11,274 they're the survivors. 210 00:14:11,350 --> 00:14:15,218 They're the ones who lived through these giant impacts. 211 00:14:15,287 --> 00:14:18,256 Debris from smashed infant planets 212 00:14:18,324 --> 00:14:20,383 ended up in the Asteroid Belt... 213 00:14:20,459 --> 00:14:24,088 a junkyard of rocky, leftover planet parts. 214 00:14:28,934 --> 00:14:30,799 Most of the big impacts happened 215 00:14:30,870 --> 00:14:32,428 in the inner solar system. 216 00:14:34,974 --> 00:14:38,432 But one of the outer planets, Uranus, 217 00:14:38,510 --> 00:14:41,707 was also hit and knocked on its side. 218 00:14:46,252 --> 00:14:50,348 A mystery, since the outer planets formed mostly from gas 219 00:14:50,422 --> 00:14:54,620 and largely escaped the violence of the inner solar system. 220 00:14:54,693 --> 00:14:58,459 These rocky cores formed. The gas accumulated around them. 221 00:14:58,530 --> 00:15:02,193 This process actually happened very rapidly, 222 00:15:02,268 --> 00:15:06,432 in astronomical terms, in only about a million years. 223 00:15:08,741 --> 00:15:12,006 And those are the giant planets we see today. 224 00:15:19,451 --> 00:15:23,114 Beyond the gas giants, Jupiter and Saturn, 225 00:15:23,188 --> 00:15:24,849 are Uranus and Neptune. 226 00:15:27,359 --> 00:15:31,523 These two are made of gas and ice. 227 00:15:41,840 --> 00:15:44,934 And beyond them lies the Kuiper Belt, 228 00:15:45,010 --> 00:15:48,776 a band of orbiting icy rocks and dwarf planets. 229 00:15:50,983 --> 00:15:55,113 We used to think that one Kuiper Belt object, Pluto, 230 00:15:55,187 --> 00:15:56,916 was the ninth planet. 231 00:16:00,059 --> 00:16:04,826 We've since decided that Pluto is, in fact, a dwarf planet... 232 00:16:04,897 --> 00:16:08,162 one of many orbiting more than 3 billion miles 233 00:16:08,233 --> 00:16:10,793 from the Sun. 234 00:16:10,869 --> 00:16:13,133 There are millions of these things out there. 235 00:16:15,908 --> 00:16:19,503 They're so far away and so faint that they're hard to see. 236 00:16:19,578 --> 00:16:22,809 These are left over from the formation 237 00:16:22,881 --> 00:16:24,508 of the solar system itself. 238 00:16:28,954 --> 00:16:32,981 The Kuiper Belt marks the edge of the Sun's influence. 239 00:16:33,058 --> 00:16:35,549 There is no warmth and not much light 240 00:16:35,627 --> 00:16:37,788 way out here. 241 00:16:40,599 --> 00:16:44,763 But the Kuiper Belt is not the end of our solar system. 242 00:16:44,837 --> 00:16:47,772 A shell of trillions of icy objects, 243 00:16:47,840 --> 00:16:51,207 called the Oort Cloud, is even further out. 244 00:16:53,679 --> 00:16:56,113 The Oort Cloud is so far away, 245 00:16:56,181 --> 00:17:00,277 light from the Sun takes a full year to reach it. 246 00:17:06,392 --> 00:17:10,624 From the cold outer edge to the hot star at the center, 247 00:17:10,696 --> 00:17:12,994 our solar system seems stable. 248 00:17:15,701 --> 00:17:19,728 Everything appears orderly and in its proper place. 249 00:17:23,142 --> 00:17:25,633 But something isn't right. 250 00:17:27,646 --> 00:17:31,104 Uranus and Neptune are in the wrong place. 251 00:17:40,359 --> 00:17:41,849 The planets of the solar system 252 00:17:41,927 --> 00:17:45,454 grew from a giant disk of dust and gas... 253 00:17:45,531 --> 00:17:50,298 the four inner rocky planets close to the Sun, 254 00:17:50,369 --> 00:17:53,566 and the giant gas planets farther out. 255 00:17:55,941 --> 00:17:59,377 But Uranus and Neptune seem out of place. 256 00:18:03,849 --> 00:18:06,784 There wasn't enough stuff this far from the Sun 257 00:18:06,852 --> 00:18:09,412 to make such big planets. 258 00:18:09,488 --> 00:18:12,946 So, what are they doing out here? 259 00:18:13,025 --> 00:18:16,358 That led us to a theory where Uranus and Neptune 260 00:18:16,428 --> 00:18:18,328 formed very close to the Sun 261 00:18:18,397 --> 00:18:21,423 and were actually violently pushed outward. 262 00:18:25,437 --> 00:18:28,497 So, what could shove two massive planets 263 00:18:28,574 --> 00:18:30,371 clear across the solar system? 264 00:18:30,442 --> 00:18:32,273 We believe that Jupiter and Saturn 265 00:18:32,344 --> 00:18:34,107 got into this funny configuration 266 00:18:34,179 --> 00:18:37,546 where Jupiter went around the Sun exactly twice 267 00:18:37,616 --> 00:18:41,143 every time Saturn went around once. 268 00:18:41,220 --> 00:18:43,745 And that configuration 269 00:18:43,822 --> 00:18:46,347 allows the planets to kick each other more 270 00:18:46,425 --> 00:18:47,892 as they pass one another, 271 00:18:47,960 --> 00:18:50,588 and that caused the whole system to go nuts. 272 00:18:54,166 --> 00:18:57,533 The combined gravity of Jupiter and Saturn 273 00:18:57,603 --> 00:18:59,901 yanked hard on Uranus and Neptune 274 00:18:59,972 --> 00:19:03,806 and pulled them away from the Sun. 275 00:19:03,876 --> 00:19:05,366 As they moved outward, 276 00:19:05,444 --> 00:19:09,210 the two planets plowed through asteroids and other debris 277 00:19:09,281 --> 00:19:12,648 left over from the formation of the other planets. 278 00:19:26,331 --> 00:19:30,495 This sent billions of chunks of rock flying in all directions. 279 00:19:37,910 --> 00:19:41,505 Some rocks formed the Asteroid Belt. 280 00:19:41,580 --> 00:19:47,041 But most were thrown out to create the vast Kuiper Belt. 281 00:19:51,190 --> 00:19:53,784 The analogy I like to use is, think of a bowling match. 282 00:19:53,859 --> 00:19:57,158 And the bowling balls go down, and the pins just go kaplooey. 283 00:19:57,229 --> 00:19:59,322 That's what happened in the outer part of the solar system. 284 00:20:02,467 --> 00:20:04,526 The gravitational push 285 00:20:04,603 --> 00:20:07,003 from Jupiter and Saturn was so strong, 286 00:20:07,072 --> 00:20:10,235 it may have reversed the position of the two planets. 287 00:20:10,309 --> 00:20:13,403 It looks like it's possible that Uranus and Neptune 288 00:20:13,478 --> 00:20:15,912 actually formed in the opposite order. 289 00:20:15,981 --> 00:20:18,506 Neptune was closer to the Sun than Uranus, 290 00:20:18,584 --> 00:20:20,814 but these gravitational interactions 291 00:20:20,886 --> 00:20:22,945 actually swapped their positions. 292 00:20:27,326 --> 00:20:29,317 It was the blizzard of rocks 293 00:20:29,394 --> 00:20:30,952 that Uranus and Neptune ran into 294 00:20:31,029 --> 00:20:32,860 that acted like a brake 295 00:20:32,931 --> 00:20:36,697 and slowed them into the orbits they keep today. 296 00:20:38,637 --> 00:20:42,266 The idea of planets changing orbits may sound crazy, 297 00:20:42,341 --> 00:20:46,300 but scientists have seen it happen in other solar systems. 298 00:20:46,378 --> 00:20:52,044 So now they think it's just the way all solar systems work. 299 00:20:52,117 --> 00:20:54,608 When we look out into the galaxy 300 00:20:54,686 --> 00:20:57,951 and look at planets around other stars, 301 00:20:58,023 --> 00:20:59,354 we see lots of evidence 302 00:20:59,424 --> 00:21:01,984 of those kind of events happening elsewhere. 303 00:21:04,896 --> 00:21:06,295 In one far-off system, 304 00:21:06,365 --> 00:21:07,855 scientists have spotted 305 00:21:07,933 --> 00:21:10,527 something completely off the charts... 306 00:21:10,602 --> 00:21:12,695 a planet as big as Jupiter, 307 00:21:12,771 --> 00:21:16,400 but it's not acting like the Jupiter we know. 308 00:21:18,610 --> 00:21:20,339 Some of these giant planets 309 00:21:20,412 --> 00:21:23,575 are found orbiting very close to their host star, 310 00:21:23,649 --> 00:21:25,947 taking only days... a few days... 311 00:21:26,018 --> 00:21:28,043 to go around the host star. 312 00:21:30,622 --> 00:21:33,420 Obviously, such close-in Jupiters 313 00:21:33,492 --> 00:21:35,687 are blowtorched by the star, 314 00:21:35,761 --> 00:21:38,355 raising the temperature of the planet 315 00:21:38,430 --> 00:21:41,024 up to 1,000 or 2,000 degrees Celsius. 316 00:21:41,099 --> 00:21:45,900 There's no way a gas giant could have formed this close in. 317 00:21:45,971 --> 00:21:47,404 It's way too hot. 318 00:21:47,472 --> 00:21:51,772 The only explanation is that it must have formed out there 319 00:21:51,843 --> 00:21:54,607 and then moved in here. 320 00:22:01,386 --> 00:22:03,616 The same thing could have happened 321 00:22:03,689 --> 00:22:05,156 in our own solar system. 322 00:22:07,326 --> 00:22:11,126 Scientists have found large amounts of the element lithium 323 00:22:11,196 --> 00:22:12,925 on the surface of the Sun. 324 00:22:16,735 --> 00:22:20,000 Lithium doesn't normally exist in stars, 325 00:22:20,072 --> 00:22:22,438 but it is found in gas planets. 326 00:22:26,144 --> 00:22:28,704 Maybe there was another gas giant 327 00:22:28,780 --> 00:22:30,441 in our own solar system 328 00:22:30,515 --> 00:22:33,643 that spiraled in and crashed into the Sun. 329 00:22:33,719 --> 00:22:36,517 That would explain how the lithium got there. 330 00:22:47,399 --> 00:22:49,162 Something very violent happened. 331 00:22:51,970 --> 00:22:54,461 Could it have been one of these Jupiter-size planets 332 00:22:54,539 --> 00:22:56,632 getting thrown in toward the Sun long ago? 333 00:22:56,708 --> 00:22:59,541 In the beginning, 334 00:22:59,611 --> 00:23:02,842 solar systems are violent and messy, 335 00:23:02,914 --> 00:23:07,647 but, over time, they settle down and become more stable. 336 00:23:07,719 --> 00:23:10,483 But stability is an illusion. 337 00:23:10,555 --> 00:23:12,682 Any planet in the solar system 338 00:23:12,758 --> 00:23:17,252 is always in danger of total annihilation. 339 00:23:22,634 --> 00:23:24,431 There are all kinds of solar systems 340 00:23:24,503 --> 00:23:26,266 in the Milky Way galaxy. 341 00:23:26,338 --> 00:23:29,830 Most seem strange compared to our own. 342 00:23:29,908 --> 00:23:33,071 Some planets follow crazy orbits. 343 00:23:33,145 --> 00:23:36,410 Some smash into each other. 344 00:23:42,287 --> 00:23:45,484 Others dive into their stars. 345 00:23:53,198 --> 00:23:56,998 So, why are the orbits of our own planets 346 00:23:57,068 --> 00:23:59,093 so regular and stable? 347 00:23:59,171 --> 00:24:02,436 Well, that's because all the planets have motion left over 348 00:24:02,507 --> 00:24:04,839 from the formation of the solar system. 349 00:24:04,910 --> 00:24:07,606 When the nebula collapsed around the Sun, 350 00:24:07,679 --> 00:24:11,115 as the Sun was forming, there was an intrinsic motion, 351 00:24:11,183 --> 00:24:13,617 and that gave our planet a velocity. 352 00:24:13,685 --> 00:24:17,451 Literally, we are falling freely toward the Sun at all times, 353 00:24:17,522 --> 00:24:20,320 but we're going so fast, we keep missing it. 354 00:24:20,392 --> 00:24:21,916 That's what an orbit is. 355 00:24:25,831 --> 00:24:27,992 Think of a merry-go-round. 356 00:24:28,066 --> 00:24:29,363 The faster it spins, 357 00:24:29,434 --> 00:24:32,631 the farther and farther you're thrown from the center. 358 00:24:32,704 --> 00:24:35,002 When it slows down, 359 00:24:35,073 --> 00:24:38,975 you lose momentum and fall back inwards. 360 00:24:41,346 --> 00:24:44,144 It's something like that with planets. 361 00:24:44,216 --> 00:24:48,915 The disk that gave birth to the planets was spinning, 362 00:24:48,987 --> 00:24:51,421 and the momentum left over from that 363 00:24:51,490 --> 00:24:54,288 keeps everything going around to this day. 364 00:24:56,761 --> 00:24:59,491 Moving at 66,000 miles an hour, 365 00:24:59,564 --> 00:25:02,465 the Earth takes one year to orbit the Sun. 366 00:25:02,534 --> 00:25:05,765 Planets farther from the Sun have bigger orbits, 367 00:25:05,837 --> 00:25:09,034 move slower, and take longer. 368 00:25:09,107 --> 00:25:13,407 Saturn orbits the Sun once every 29 years. 369 00:25:16,147 --> 00:25:20,982 Neptune takes 164 years. 370 00:25:21,052 --> 00:25:25,318 Each planet stays on a precise path around the Sun, 371 00:25:25,390 --> 00:25:28,018 and for us, that's a good thing. 372 00:25:30,028 --> 00:25:33,657 Our solar system has a somewhat fortunate 373 00:25:33,732 --> 00:25:35,461 spacing of the planets, 374 00:25:35,534 --> 00:25:37,729 with nearly circular orbits, 375 00:25:37,802 --> 00:25:40,828 which keeps the whole house of cards 376 00:25:40,906 --> 00:25:44,433 from falling apart, crumbling, scattering to the wind. 377 00:25:50,315 --> 00:25:52,476 If our solar system did not have 378 00:25:52,551 --> 00:25:55,577 nice, neat, stable, nearly circular orbits, 379 00:25:55,654 --> 00:25:57,121 the Earth wouldn't be here 380 00:25:57,188 --> 00:25:59,554 and we wouldn't be here talking about it. 381 00:26:04,362 --> 00:26:07,490 The planets are on safe, stable orbits... 382 00:26:10,068 --> 00:26:13,196 ...but billions of comets and asteroids are not. 383 00:26:17,676 --> 00:26:22,136 Many come streaking into the inner solar system. 384 00:26:22,213 --> 00:26:25,273 And when they do, watch out. 385 00:26:33,858 --> 00:26:37,589 The meteor crater which we see here today 386 00:26:37,662 --> 00:26:41,621 formed as a result of a 150-foot rocky iron object 387 00:26:41,700 --> 00:26:44,760 coming in and slamming into the Earth 388 00:26:44,836 --> 00:26:46,827 roughly 50,000 years ago. 389 00:26:46,905 --> 00:26:52,275 Some of the objects coming our way can be much bigger. 390 00:26:52,344 --> 00:26:54,141 Look at the moon. 391 00:26:54,212 --> 00:26:58,205 It's covered with large impact craters. 392 00:26:58,283 --> 00:27:01,582 Earth has been hit, too... a lot. 393 00:27:07,192 --> 00:27:09,183 But the craters have eroded. 394 00:27:10,862 --> 00:27:14,662 We know that a huge asteroid smashed into the Earth, 395 00:27:14,733 --> 00:27:18,169 off the coast of Mexico, 65 million years ago. 396 00:27:18,236 --> 00:27:21,967 It was going 45,000 miles an hour, 397 00:27:22,040 --> 00:27:23,769 and when it hit, 398 00:27:23,842 --> 00:27:27,608 it released more energy than 5 billion Hiroshima bombs. 399 00:28:01,880 --> 00:28:05,816 It wiped out 70% of life on Earth. 400 00:28:12,290 --> 00:28:16,852 A few more impacts like that could destroy all life on Earth. 401 00:28:16,928 --> 00:28:21,365 But, believe it or not, Earth has a giant bodyguard. 402 00:28:23,902 --> 00:28:26,063 Jupiter is more than just another pretty face 403 00:28:26,137 --> 00:28:27,331 through the telescope. 404 00:28:27,405 --> 00:28:29,600 It's actually really important for life on Earth. 405 00:28:29,674 --> 00:28:31,164 Jupiter's gravity is so huge 406 00:28:31,242 --> 00:28:34,143 and it's just in the right place in the solar system, 407 00:28:34,212 --> 00:28:36,407 that it protects the Earth from comets 408 00:28:36,481 --> 00:28:38,711 that come from deep in the solar system 409 00:28:38,783 --> 00:28:43,345 and swing by the Sun and could possibly hit the Earth. 410 00:28:43,421 --> 00:28:45,651 Jupiter plays the role 411 00:28:45,724 --> 00:28:48,659 of the biggest baseball bat in the solar system. 412 00:28:48,727 --> 00:28:50,126 As these comets come by, 413 00:28:50,195 --> 00:28:53,631 most of them get knocked out of the solar system by Jupiter. 414 00:28:56,634 --> 00:28:58,124 In 1994, 415 00:28:58,203 --> 00:29:02,799 comet Shoemaker-Levy 9 raced toward the inner solar system. 416 00:29:05,510 --> 00:29:07,978 But it never got past Jupiter. 417 00:29:10,682 --> 00:29:14,118 Astronomers watched as Jupiter tore it to pieces 418 00:29:14,185 --> 00:29:17,916 and dragged its remains down to the planet's surface. 419 00:29:20,925 --> 00:29:22,825 We have seen comets smash into Jupiter, 420 00:29:22,894 --> 00:29:25,260 creating fireballs that were bigger than the Earth. 421 00:29:31,136 --> 00:29:33,764 They were the biggest explosions 422 00:29:33,838 --> 00:29:35,635 ever seen in our solar system. 423 00:29:39,210 --> 00:29:41,644 Had that comet hit us, 424 00:29:41,713 --> 00:29:43,203 it would have resurfaced the planet. 425 00:29:43,281 --> 00:29:45,112 It would have been the end of life as we know it. 426 00:29:45,183 --> 00:29:46,309 If Jupiter wasn't there, 427 00:29:46,384 --> 00:29:48,682 we believe that the impact rate on the Earth 428 00:29:48,753 --> 00:29:52,587 would be something like 1,000 times more than we see today. 429 00:30:00,498 --> 00:30:03,990 Lucky for us, Earth has the perfect orbit. 430 00:30:05,603 --> 00:30:09,095 Jupiter protects us from asteroids and comets. 431 00:30:11,976 --> 00:30:14,638 We're close enough to the Sun for liquid water 432 00:30:14,712 --> 00:30:17,738 but not so close that it boils away. 433 00:30:17,816 --> 00:30:22,617 It's just the right combination for life. 434 00:30:25,056 --> 00:30:26,318 Question is, 435 00:30:26,391 --> 00:30:29,224 if our solar system could create the perfect conditions, 436 00:30:29,294 --> 00:30:31,592 could other solar systems do it, too? 437 00:30:33,264 --> 00:30:36,358 Planet hunters have spotted a solar system 438 00:30:36,434 --> 00:30:37,924 20 light-years away, 439 00:30:38,002 --> 00:30:40,937 and it has a planet just the right size 440 00:30:41,005 --> 00:30:42,973 in just the right place. 441 00:30:48,646 --> 00:30:51,843 Astronomers around the world are looking for new planets 442 00:30:51,916 --> 00:30:54,749 in distant solar systems. 443 00:30:56,855 --> 00:31:00,723 So far, they've discovered more than 420. 444 00:31:06,764 --> 00:31:09,756 Most are huge gas giants, like Jupiter... 445 00:31:13,938 --> 00:31:16,839 ...but they're either very close to the star 446 00:31:16,908 --> 00:31:18,876 or much farther away. 447 00:31:26,951 --> 00:31:31,615 Then, in 2005, astronomers made an exciting discovery. 448 00:31:35,126 --> 00:31:39,756 They detected a solar system with rocky planets like our own. 449 00:31:42,734 --> 00:31:48,434 These planets orbit a star called Gliese 581. 450 00:31:48,506 --> 00:31:51,942 This star, Gliese 581, and its 4 planets 451 00:31:52,010 --> 00:31:55,776 is, frankly, quite bizarre relative to our solar system. 452 00:31:55,847 --> 00:31:59,010 The four planets we know of 453 00:31:59,083 --> 00:32:01,745 all orbit very close to the host star, 454 00:32:01,819 --> 00:32:03,912 all four of them orbiting closer 455 00:32:03,988 --> 00:32:06,980 than the planet Mercury, our closest planet, 456 00:32:07,058 --> 00:32:08,150 orbits the Sun. 457 00:32:12,997 --> 00:32:15,830 But Gliese 581 is a small star. 458 00:32:15,900 --> 00:32:17,697 It doesn't burn as brightly 459 00:32:17,769 --> 00:32:20,329 or give off as much heat as our Sun, 460 00:32:20,405 --> 00:32:23,704 so the planets can orbit much closer 461 00:32:23,775 --> 00:32:25,868 without being vaporized. 462 00:32:25,944 --> 00:32:30,074 We know of four planets going around this star, 463 00:32:30,148 --> 00:32:32,878 and a few of them are quite interesting. 464 00:32:32,951 --> 00:32:36,216 There's one that's only about twice the mass of Earth. 465 00:32:36,287 --> 00:32:39,051 Now, that particular one is very close to the star. 466 00:32:39,123 --> 00:32:41,489 It's probably very hot... too hot for life. 467 00:32:41,559 --> 00:32:42,753 But there's another one, 468 00:32:42,827 --> 00:32:44,920 about eight times the mass of the Earth, 469 00:32:44,996 --> 00:32:47,362 which is getting far enough away from the star 470 00:32:47,432 --> 00:32:49,457 that it might be in the habitable zone. 471 00:32:49,534 --> 00:32:51,593 Like Earth, 472 00:32:51,669 --> 00:32:55,537 this planet orbits at a distance where water is a liquid. 473 00:32:58,309 --> 00:33:03,110 And where there's liquid water, there could be oceans and life. 474 00:33:18,096 --> 00:33:22,499 In March 2009, NASA launched the Kepler Space Telescope. 475 00:33:22,567 --> 00:33:23,795 Its mission... 476 00:33:23,868 --> 00:33:27,099 to search for planets similar to our own 477 00:33:27,171 --> 00:33:29,696 in new solar systems. 478 00:33:32,010 --> 00:33:35,002 We may find planets that have methane atmospheres... 479 00:33:41,019 --> 00:33:43,385 ...that have ammonia atmospheres. 480 00:33:47,225 --> 00:33:50,786 We may find planets that are covered in heavy organics... 481 00:33:52,663 --> 00:33:54,961 ...a tarlike material. 482 00:33:58,069 --> 00:34:00,833 We may find some that are covered by water. 483 00:34:03,741 --> 00:34:05,936 I think one of the glorious quests here 484 00:34:06,010 --> 00:34:08,240 in the next decade or two 485 00:34:08,312 --> 00:34:11,110 is to learn the full diversity 486 00:34:11,182 --> 00:34:13,082 of the family of Earth-like planets 487 00:34:13,151 --> 00:34:15,142 that may be out there in the universe. 488 00:34:19,557 --> 00:34:20,956 With Kepler, 489 00:34:21,025 --> 00:34:23,653 astronomers expect to discover hundreds, 490 00:34:23,728 --> 00:34:26,390 possibly thousands, of new solar systems. 491 00:34:30,535 --> 00:34:33,436 Think about our own Milky Way galaxy. 492 00:34:33,504 --> 00:34:37,998 The galaxy has roughly 500 billion to a trillion stars. 493 00:34:38,076 --> 00:34:42,979 Some fairly large percentage of that have planets. 494 00:34:43,047 --> 00:34:45,982 Now, think about how many galaxies we know of. 495 00:34:46,050 --> 00:34:48,951 We certainly haven't found all the galaxies 496 00:34:49,020 --> 00:34:50,351 in the universe yet. 497 00:34:50,421 --> 00:34:52,981 But the ones we can take a picture of 498 00:34:53,057 --> 00:34:55,719 are actually about 60 billion galaxies. 499 00:34:59,297 --> 00:35:02,425 When you look up at the night sky tonight, 500 00:35:02,500 --> 00:35:05,060 simply in the path of your sight, 501 00:35:05,136 --> 00:35:08,594 even if you can't see it, 502 00:35:08,673 --> 00:35:13,372 there are billions of solar systems all around you. 503 00:35:13,444 --> 00:35:16,345 And there could be a solar system 504 00:35:16,414 --> 00:35:19,247 with a planet just like Earth. 505 00:35:21,285 --> 00:35:25,119 If it happened once, it could happen again. 506 00:35:30,962 --> 00:35:34,454 Solar systems don't last forever. 507 00:35:34,532 --> 00:35:36,432 Orbits fall apart. 508 00:35:36,501 --> 00:35:38,093 Planets collide. 509 00:35:38,169 --> 00:35:40,228 It might happen to us. 510 00:35:40,304 --> 00:35:42,465 But even if it doesn't, 511 00:35:42,540 --> 00:35:45,008 in another 5 billion years, 512 00:35:45,076 --> 00:35:49,638 a catastrophe will end our solar system as we know it. 513 00:35:58,422 --> 00:36:02,415 Nothing lasts forever, not even solar systems. 514 00:36:02,493 --> 00:36:04,586 Ours may seem stable now, 515 00:36:04,662 --> 00:36:08,564 but, actually, it's very slowly coming apart. 516 00:36:14,338 --> 00:36:17,307 If the solar system was chaotic in the past, 517 00:36:17,375 --> 00:36:19,843 that doesn't mean it's all settled down now. 518 00:36:19,911 --> 00:36:21,674 There is still a possibility 519 00:36:21,746 --> 00:36:24,340 of a little bit of chaos in the future. 520 00:36:24,415 --> 00:36:26,042 In the future, 521 00:36:26,117 --> 00:36:29,575 the gravitational pull of the planets on each other 522 00:36:29,654 --> 00:36:32,214 will gradually disrupt their orbits. 523 00:36:32,290 --> 00:36:35,782 Perhaps, over the billions of years, 524 00:36:35,860 --> 00:36:39,557 the planets will jostle each other in this gravitational way 525 00:36:39,630 --> 00:36:40,961 so that, eventually, 526 00:36:41,032 --> 00:36:44,126 two of the planets will come close to each other. 527 00:36:48,139 --> 00:36:51,040 When that happens... and it will... 528 00:36:51,108 --> 00:36:55,442 those two planets will engage in a sort of a do-si-do, 529 00:36:55,513 --> 00:36:59,074 flinging one or the other of them, maybe both, 530 00:36:59,150 --> 00:37:00,549 into wild orbits, 531 00:37:00,618 --> 00:37:04,611 perhaps ejecting one or both of them from the solar system. 532 00:37:07,024 --> 00:37:10,255 Mars could be thrown out of the solar system, 533 00:37:10,328 --> 00:37:12,762 and Mercury might crash into the Earth. 534 00:37:24,642 --> 00:37:28,271 The entire house of cards that is our solar system 535 00:37:28,346 --> 00:37:30,337 would completely fall apart. 536 00:37:30,414 --> 00:37:34,475 Solar systems begin and end 537 00:37:34,552 --> 00:37:38,010 with a lot of collisions and destruction. 538 00:37:38,089 --> 00:37:39,886 But don't panic yet. 539 00:37:41,659 --> 00:37:44,025 This is gonna take billions of years, 540 00:37:44,095 --> 00:37:46,222 but over the lifetime of the solar system, 541 00:37:46,297 --> 00:37:48,857 these are eventualities that could come to pass. 542 00:37:48,933 --> 00:37:52,699 But one way or another, 543 00:37:52,770 --> 00:37:55,898 our solar system is doomed. 544 00:37:58,776 --> 00:38:01,438 Like all solar systems, the end will come 545 00:38:01,512 --> 00:38:05,448 when the star at the center dies. 546 00:38:05,516 --> 00:38:08,917 In 5 billion years, 547 00:38:08,986 --> 00:38:11,921 our own star will run out of fuel 548 00:38:11,989 --> 00:38:14,480 and become a red giant. 549 00:38:16,727 --> 00:38:21,027 It'll heat up, swell, and engulf the inner planets. 550 00:38:27,204 --> 00:38:30,332 The Earth's surface will be scorched... 551 00:38:33,678 --> 00:38:37,045 ...the seas will evaporate... 552 00:38:37,114 --> 00:38:39,912 And the land will melt. 553 00:38:45,356 --> 00:38:49,315 The Sun will become about as big as where the Earth's orbit is, 554 00:38:49,393 --> 00:38:51,759 so a likely scenario for the end of the world 555 00:38:51,829 --> 00:38:54,559 is that we're going to be inside the Sun for a while. 556 00:39:06,811 --> 00:39:10,144 The Earth's gonna get swallowed right up into the Sun, 557 00:39:10,214 --> 00:39:12,580 and it's gonna be toast... vapor, literally. 558 00:39:14,218 --> 00:39:15,742 After a while, 559 00:39:15,820 --> 00:39:18,050 the red giant will fall apart, too, 560 00:39:18,122 --> 00:39:23,082 leaving behind a tiny corpse of a star called a white dwarf. 561 00:39:33,804 --> 00:39:36,170 Lt'll be about the size of the Earth, 562 00:39:36,240 --> 00:39:39,038 and it will cool off over many millions or billions of years. 563 00:39:43,848 --> 00:39:46,749 That will be the real end of our solar system. 564 00:39:52,823 --> 00:39:54,415 From the Earth... 565 00:39:54,492 --> 00:39:57,461 this dead, rocky planet that used to harbor 566 00:39:57,528 --> 00:40:00,122 an enormously vibrant civilization... 567 00:40:00,197 --> 00:40:03,189 we will look out... 568 00:40:03,267 --> 00:40:07,397 And there will be this fairly faint dot which is our Sun, 569 00:40:07,471 --> 00:40:11,498 now a white dwarf, a dying, almost dead star. 570 00:40:15,012 --> 00:40:17,037 The remains of the inner planets 571 00:40:17,114 --> 00:40:19,048 will continue to orbit the white dwarf. 572 00:40:25,289 --> 00:40:29,555 But the giant outer planets will live on, untouched. 573 00:40:33,097 --> 00:40:34,724 They will have warmed up 574 00:40:34,799 --> 00:40:36,733 during the red-giant phase of the Sun. 575 00:40:36,801 --> 00:40:39,565 But once the Sun is a white dwarf, 576 00:40:39,637 --> 00:40:43,198 those giant planets will survive just as well, 577 00:40:43,274 --> 00:40:45,868 holding on to their hydrogen and helium, 578 00:40:45,943 --> 00:40:48,241 albeit colder than they used to be, 579 00:40:48,312 --> 00:40:51,611 because that white dwarf will no longer be warming them up. 580 00:40:58,088 --> 00:41:01,546 Even though this is 5 billion years in the future 581 00:41:01,625 --> 00:41:02,887 for our solar system, 582 00:41:02,960 --> 00:41:04,552 it may already have happened 583 00:41:04,628 --> 00:41:07,358 to many other systems throughout the universe. 584 00:41:11,168 --> 00:41:14,569 Our solar system emerged from chaos 585 00:41:14,638 --> 00:41:16,629 to eventually support life. 586 00:41:16,707 --> 00:41:17,901 We were lucky. 587 00:41:17,975 --> 00:41:21,069 We've just the right amount of planets, 588 00:41:21,145 --> 00:41:22,373 in the right place, 589 00:41:22,446 --> 00:41:24,937 at the right distance from each other, 590 00:41:25,015 --> 00:41:27,415 all orbiting the right type of star. 591 00:41:27,485 --> 00:41:32,445 But it could have been a very different story. 592 00:41:32,523 --> 00:41:34,286 There are so many things 593 00:41:34,358 --> 00:41:36,326 that are fortunate about our solar system, 594 00:41:36,393 --> 00:41:37,382 starting with the Sun. 595 00:41:37,461 --> 00:41:40,396 The Sun is a very stable, easy star... 596 00:41:40,464 --> 00:41:43,661 a perfect thing for life to evolve around. 597 00:41:43,734 --> 00:41:45,668 That's probably not a coincidence that we're here. 598 00:41:47,671 --> 00:41:50,037 An extraordinary chain of events 599 00:41:50,107 --> 00:41:51,574 over billions of years 600 00:41:51,642 --> 00:41:54,611 have made our solar system the perfect place 601 00:41:54,678 --> 00:41:57,010 for life to evolve. 602 00:42:03,354 --> 00:42:06,983 What we see today is not the way things have always been 603 00:42:07,057 --> 00:42:09,184 and not the way things will always be. 604 00:42:09,260 --> 00:42:10,318 We're not unique, 605 00:42:10,394 --> 00:42:12,521 but it is just the way things worked out. 606 00:42:15,399 --> 00:42:17,594 The Earth has to be in the right place. 607 00:42:17,668 --> 00:42:19,465 The planets had to be in the right place. 608 00:42:19,537 --> 00:42:22,438 The giant planets have to be in the right place 609 00:42:22,506 --> 00:42:24,838 to protect us from impacts. 610 00:42:27,411 --> 00:42:31,142 All that has to be right in order to get life on Earth. 611 00:42:34,852 --> 00:42:38,049 Ours is the only planetary system we know 612 00:42:38,122 --> 00:42:39,350 that supports life. 613 00:42:39,423 --> 00:42:41,118 As solar systems go, 614 00:42:41,191 --> 00:42:45,423 does that make us extraordinary or perfectly normal? 615 00:42:45,496 --> 00:42:47,555 We don't know. 616 00:42:47,631 --> 00:42:48,859 But every week, 617 00:42:48,933 --> 00:42:51,731 we're discovering new solar systems 618 00:42:51,802 --> 00:42:53,167 with new planets. 619 00:42:53,237 --> 00:42:55,831 It could be just a matter of time 620 00:42:55,906 --> 00:42:57,464 before we discover... 621 00:42:57,541 --> 00:42:59,771 We're not alone.