1 00:00:01,968 --> 00:00:05,504 MIKE ROWE: We're discovering the cosmos is full of alien planets. 2 00:00:05,605 --> 00:00:08,273 It's so exciting -- In my lifetime, 3 00:00:08,375 --> 00:00:10,809 we didn't even know if exoplanets existed, 4 00:00:10,910 --> 00:00:12,811 and now, they're everywhere. 5 00:00:12,912 --> 00:00:15,681 - It's incredible. - ROWE: Exoplanets, 6 00:00:15,782 --> 00:00:18,884 Strange worlds outside our solar system. 7 00:00:18,985 --> 00:00:22,755 Hellishly hot worlds, violently colliding worlds, 8 00:00:22,856 --> 00:00:24,990 worlds getting eaten by their stars. 9 00:00:25,091 --> 00:00:27,493 There's much, much more out there than we had ever imagined. 10 00:00:30,096 --> 00:00:34,466 ROWE: Exoplanets are rewriting what makes a planet a planet. 11 00:00:34,567 --> 00:00:38,437 It's a bit of a mystery how these planets can even exist. 12 00:00:38,538 --> 00:00:41,473 It seems to defy the laws of physics. 13 00:00:41,574 --> 00:00:44,309 ROWE: Alien worlds that challenge our understanding 14 00:00:44,411 --> 00:00:46,545 of planetary systems. 15 00:00:46,646 --> 00:00:48,447 It's actually been a bit of a wake-up call. 16 00:00:48,548 --> 00:00:51,116 We keep thinking we understand what's happening, 17 00:00:51,217 --> 00:00:52,785 and then the universe surprises us with something 18 00:00:52,886 --> 00:00:54,486 completely different. 19 00:00:54,587 --> 00:00:56,555 ROWE: Exoplanets are shaking up 20 00:00:56,656 --> 00:00:58,190 our understanding of the universe. 21 00:00:59,359 --> 00:01:02,928 The cosmos is a chaotic array of the odd, 22 00:01:03,029 --> 00:01:06,131 the weird, and the wonderful. 23 00:01:06,232 --> 00:01:09,902 The more we find, the less we know. 24 00:01:10,003 --> 00:01:12,037 [electricity buzzing] 25 00:01:13,540 --> 00:01:16,341 [explosion blasts] 26 00:01:20,880 --> 00:01:24,650 We've now found over 4,000 exoplanets, 27 00:01:24,751 --> 00:01:30,289 a rapidly increasing array of strange alien worlds, 28 00:01:30,390 --> 00:01:34,093 and the more we uncover, the weirder they get. 29 00:01:34,194 --> 00:01:35,661 They don't act at all like 30 00:01:35,762 --> 00:01:37,596 what we're seeing in our solar system. 31 00:01:37,697 --> 00:01:39,765 There are planets out there interacting, there are planets 32 00:01:39,866 --> 00:01:42,234 dive-bombing their sun, gigantic planets 33 00:01:42,368 --> 00:01:45,437 orbiting really close in -- Everything, in every kind of 34 00:01:45,538 --> 00:01:48,340 combination you can possibly imagine. 35 00:01:48,441 --> 00:01:51,076 ROWE: One alien world truly stands out. 36 00:01:52,846 --> 00:01:54,847 This is the planet from hell. 37 00:01:57,450 --> 00:01:59,451 When we examine the atmosphere of this planet, 38 00:01:59,552 --> 00:02:01,720 what we find is liquid iron. 39 00:02:01,821 --> 00:02:03,222 The iron is heated up so much, 40 00:02:03,323 --> 00:02:05,324 it's been vaporized, and it's falling out of 41 00:02:05,425 --> 00:02:06,725 the sky like rain. 42 00:02:08,628 --> 00:02:10,362 ROWE: But why is this planet so much more 43 00:02:10,463 --> 00:02:13,532 extreme than the ones in our solar system? 44 00:02:13,633 --> 00:02:16,368 What this is telling us is that the universe is really 45 00:02:16,469 --> 00:02:18,203 good at making lots of planets 46 00:02:18,304 --> 00:02:21,073 that are wildly different than the one we live on. 47 00:02:23,276 --> 00:02:25,043 SHIELDS: Outside of our apparently 48 00:02:25,145 --> 00:02:28,947 stable and calm solar system, it is the wild, 49 00:02:29,048 --> 00:02:32,751 wild West out in the cosmos, where crazy stuff is happening, 50 00:02:32,852 --> 00:02:35,487 completely unchecked. 51 00:02:35,555 --> 00:02:39,925 ROWE: WASP-76b is 640 light-years away, 52 00:02:40,026 --> 00:02:43,195 in the Pisces constellation. 53 00:02:43,296 --> 00:02:45,764 At first, this planet looks like nothing out of 54 00:02:45,865 --> 00:02:46,765 the ordinary. 55 00:02:46,866 --> 00:02:50,002 WASP-76b orbits its star, just like our sun, 56 00:02:50,103 --> 00:02:52,404 which is really reassuring in a universe which is full of 57 00:02:52,505 --> 00:02:54,239 the unfamiliar. 58 00:02:54,340 --> 00:02:58,043 ROWE: WASP-76b is a gas giant, 59 00:02:58,144 --> 00:03:01,313 a bit like Jupiter in our solar system, 60 00:03:01,414 --> 00:03:04,816 but its location makes a big difference. 61 00:03:04,918 --> 00:03:07,352 You take a star similar to ours, 62 00:03:07,453 --> 00:03:09,721 you take a planet similar to Jupiter, 63 00:03:09,822 --> 00:03:11,423 but instead of parking it in the outer solar system, 64 00:03:11,524 --> 00:03:14,826 you put it really, really, really close to the star. 65 00:03:16,729 --> 00:03:20,899 ROWE: Jupiter is almost 500 million miles away from the sun. 66 00:03:21,000 --> 00:03:27,072 WASP-76b is just three million miles from its star, 67 00:03:27,173 --> 00:03:32,010 and that's what makes this planet a hot Jupiter. 68 00:03:33,680 --> 00:03:39,484 Temperatures on WASP-76b exceed 4,000 degrees Fahrenheit, 69 00:03:39,586 --> 00:03:41,687 creating one of the most extreme environments 70 00:03:41,788 --> 00:03:43,121 in the universe. 71 00:03:44,290 --> 00:03:47,159 If I were fortunate enough to be able to go and visit 72 00:03:47,260 --> 00:03:48,994 this world, I would have 73 00:03:49,095 --> 00:03:51,597 to take a lot of precautions, because it is 74 00:03:51,698 --> 00:03:54,866 essentially a hellscape on that planet. 75 00:03:54,968 --> 00:03:57,336 RADEBAUGH: The heat is absolutely insane. 76 00:03:57,437 --> 00:03:59,271 There is nothing like it in our solar system. 77 00:04:01,107 --> 00:04:02,374 ROWE: The fact that it's so close 78 00:04:02,475 --> 00:04:05,611 to its star has another consequence. 79 00:04:05,745 --> 00:04:11,149 WASP-76b's spin is locked to its star. 80 00:04:11,251 --> 00:04:13,952 The gravity from the star will grip onto the planet, 81 00:04:14,053 --> 00:04:17,489 slow its rotation over time, if it had any to start with, and 82 00:04:17,590 --> 00:04:21,426 lock it so that one face always faces toward the star. 83 00:04:21,527 --> 00:04:24,830 ROWE: This gravitational grip is called tidal locking. 84 00:04:26,332 --> 00:04:28,000 We're used to the idea of tidally locking 85 00:04:28,101 --> 00:04:30,736 with our own moon -- we only ever see one side of the moon. 86 00:04:30,837 --> 00:04:33,372 The far side of the moon continues to face space. 87 00:04:33,473 --> 00:04:36,241 There are consequences for being a tidally locked planet, 88 00:04:36,342 --> 00:04:38,010 and not all of them are good. 89 00:04:38,111 --> 00:04:40,846 That can set up some pretty extreme weather conditions, 90 00:04:40,947 --> 00:04:43,115 very hot on the daytime side 91 00:04:43,216 --> 00:04:46,118 and extremely cold on the nighttime side. 92 00:04:47,954 --> 00:04:49,921 ROWE: In 2020, we took a closer look at 93 00:04:50,023 --> 00:04:53,592 the atmosphere between the day and night side of the planet. 94 00:04:56,596 --> 00:04:59,364 This twilight zone has plenty of rain, 95 00:04:59,465 --> 00:05:02,434 but here, it rains molten iron. 96 00:05:06,005 --> 00:05:08,307 RADEBAUGH: I mean, this thing has iron rain. 97 00:05:08,408 --> 00:05:09,274 How lazy is that 98 00:05:09,375 --> 00:05:10,442 if you were writing a sci-fi novel? 99 00:05:10,543 --> 00:05:12,844 Oh, let's make some iron rain, but this is reality. 100 00:05:12,945 --> 00:05:15,747 It is hot enough to vaporize iron and make it rain. 101 00:05:19,018 --> 00:05:22,521 When I grew up watching sci-fi on TV and reading novels, 102 00:05:22,622 --> 00:05:24,256 there would always be some planet where there was some 103 00:05:24,357 --> 00:05:25,324 strange condition. 104 00:05:25,425 --> 00:05:28,126 Oh, iron rains out of the sky, and I'd be like, 105 00:05:28,227 --> 00:05:29,227 that's ridiculous. 106 00:05:29,329 --> 00:05:31,563 And now what I found out is that nature 107 00:05:31,664 --> 00:05:34,633 is way nuttier than anything we could have thought of. 108 00:05:34,734 --> 00:05:38,370 How do you get vaporized iron? 109 00:05:38,471 --> 00:05:41,039 Well, most materials can exist in different states, 110 00:05:41,140 --> 00:05:42,841 so think about water, right? 111 00:05:42,942 --> 00:05:45,310 THALLER: Water can be a solid when it's ice, 112 00:05:45,411 --> 00:05:48,179 and then when you heat it up, it becomes water, 113 00:05:48,247 --> 00:05:50,549 the liquid part of water, and then if you heat it up more, 114 00:05:50,650 --> 00:05:52,784 it becomes steam, like out of a kettle. 115 00:05:52,885 --> 00:05:54,953 And this is true of every chemical element. 116 00:05:55,054 --> 00:05:58,423 So for iron, if you heat it even more up, it becomes a gas, 117 00:05:58,524 --> 00:06:03,061 so you really can have clouds of iron vapor condensing 118 00:06:03,162 --> 00:06:04,863 and raining liquid iron. 119 00:06:05,965 --> 00:06:08,200 ROWE: These nightmare weather conditions are 120 00:06:08,301 --> 00:06:10,869 a direct result of WASP-76b's 121 00:06:10,970 --> 00:06:13,805 proximity to its star. 122 00:06:13,906 --> 00:06:17,242 WASP-76b is so close to its star that its star 123 00:06:17,343 --> 00:06:18,643 is super heating its atmosphere. 124 00:06:18,745 --> 00:06:22,080 So the upper atmosphere is heated and rises. 125 00:06:22,181 --> 00:06:23,949 ROWE: The atmosphere on the day side 126 00:06:24,050 --> 00:06:27,519 reaches over 4,000 degrees Fahrenheit. 127 00:06:27,620 --> 00:06:31,790 The planet's night side is cooler at 2,730 128 00:06:31,891 --> 00:06:34,226 degrees Fahrenheit. 129 00:06:34,327 --> 00:06:36,261 This difference in temperature 130 00:06:36,362 --> 00:06:38,630 sets up spectacular wind streams. 131 00:06:40,333 --> 00:06:42,768 One of the really cool things about this brand-new class 132 00:06:42,869 --> 00:06:45,170 of planets we found is discovering weather 133 00:06:45,271 --> 00:06:46,671 we've never seen before. 134 00:06:46,773 --> 00:06:49,908 These hot Jupiters have these equatorial jets of wind that 135 00:06:50,009 --> 00:06:52,677 are supersonic, traveling at thousands of miles per hour, 136 00:06:52,779 --> 00:06:54,813 and that wind is pulling the rain around 137 00:06:54,914 --> 00:06:56,281 to the night side. 138 00:06:56,382 --> 00:06:58,583 The air on the hot side expands, because it's 139 00:06:58,684 --> 00:07:01,319 being heated and will flow over to the other side. 140 00:07:01,421 --> 00:07:03,555 So you get these torrential winds blowing 141 00:07:03,656 --> 00:07:05,557 that hot air to the cooler side. 142 00:07:05,658 --> 00:07:09,728 If there is vaporized iron, gaseous iron, in the atmosphere 143 00:07:09,829 --> 00:07:10,762 on the hot side, 144 00:07:10,863 --> 00:07:13,832 it will blow over to the cooler side. 145 00:07:13,933 --> 00:07:17,068 ROWE: On Earth, the fastest recorded winds have reached 146 00:07:17,170 --> 00:07:21,606 speeds in excess of 250 miles an hour. 147 00:07:21,707 --> 00:07:24,709 On WASP-76b, winds hit speeds 148 00:07:24,811 --> 00:07:28,246 in excess of 11,000 miles an hour, 149 00:07:28,347 --> 00:07:32,818 strong enough to move millions of tons of iron vapor to 150 00:07:32,919 --> 00:07:34,653 the planet's night side, 151 00:07:34,720 --> 00:07:38,223 where it undergoes a dramatic change. 152 00:07:38,324 --> 00:07:41,226 It's cooler there, can't be maintained as a gas, 153 00:07:41,327 --> 00:07:45,096 so it condenses and becomes a liquid and then rains out. 154 00:07:45,198 --> 00:07:47,799 RADEBAUGH: There are clouds coming up and forming, 155 00:07:47,900 --> 00:07:48,800 and then rain is falling, 156 00:07:48,901 --> 00:07:50,802 but it's iron, it's iron vapor. 157 00:07:50,903 --> 00:07:51,770 It's iron rain. 158 00:07:51,871 --> 00:07:54,072 It would be spectacular to see in that 159 00:07:54,173 --> 00:07:56,408 brief moment you have before you vaporized, too. 160 00:08:00,213 --> 00:08:02,247 ROWE: You might think that having clouds of iron 161 00:08:02,348 --> 00:08:06,251 rain is WASP-76b's strangest feature. 162 00:08:08,054 --> 00:08:09,821 But astronomers are even more puzzled 163 00:08:09,922 --> 00:08:12,357 by the location of this gas giant. 164 00:08:14,160 --> 00:08:16,528 When you look at the planets in our solar system, you can 165 00:08:16,629 --> 00:08:20,365 divide them into gas giants like Jupiter and rocky planets 166 00:08:20,466 --> 00:08:22,868 like the Earth. - ROWE: In our solar system, 167 00:08:22,969 --> 00:08:26,638 rocky planets are close to the sun, and gas giants are 168 00:08:26,739 --> 00:08:28,473 farther away. 169 00:08:28,574 --> 00:08:31,510 But in exosystems, the positions of 170 00:08:31,611 --> 00:08:34,713 different kinds of planets are all messed up. 171 00:08:34,814 --> 00:08:37,516 WALSH: We're finding Jupiter-sized planets 172 00:08:37,617 --> 00:08:39,451 super close to their stars instead of 173 00:08:39,552 --> 00:08:41,419 in the outer parts of the solar system. 174 00:08:41,521 --> 00:08:43,355 And we're finding rocky planets really close to 175 00:08:43,456 --> 00:08:46,992 stars and packed in really tight and weird configurations. 176 00:08:48,294 --> 00:08:50,428 ROWE: These planets orbiting close to their stars 177 00:08:50,530 --> 00:08:53,932 survive being blasted with intense radiation. 178 00:08:54,033 --> 00:08:55,901 They're taking part in the ultimate 179 00:08:56,002 --> 00:08:58,069 endurance challenge. 180 00:08:58,170 --> 00:09:00,539 But not all worlds are so tough. 181 00:09:00,640 --> 00:09:03,208 Some are so light and delicate, 182 00:09:03,309 --> 00:09:04,910 they're barely there at all. 183 00:09:05,011 --> 00:09:08,747 Are these weird puffballs even planets? 184 00:09:19,258 --> 00:09:21,059 ROWE: The more exoplanets we find, 185 00:09:21,160 --> 00:09:26,831 the more we realize how weird these new worlds really are. 186 00:09:26,933 --> 00:09:30,936 Some planets are so unlikely, so odd, and so bizarre, 187 00:09:31,037 --> 00:09:34,039 scientists wonder, how can they even exist? 188 00:09:35,908 --> 00:09:38,543 Before we discovered exoplanets, we thought that our 189 00:09:38,644 --> 00:09:40,145 solar system would be representative, 190 00:09:40,246 --> 00:09:42,347 that other solar systems would look like ours. 191 00:09:42,448 --> 00:09:45,016 Rocky planets, gas giants, ice giants. 192 00:09:45,117 --> 00:09:47,152 But when we went out there and found them, 193 00:09:47,253 --> 00:09:49,421 they don't look anything like our solar system. 194 00:09:52,124 --> 00:09:55,794 ROWE: In 2012, we discovered three gas giants 195 00:09:55,895 --> 00:09:57,662 orbiting the sun-like star, 196 00:09:57,763 --> 00:10:03,134 Kepler-51, located 2,615 light-years away 197 00:10:03,235 --> 00:10:05,170 in the constellation of Cygnus. 198 00:10:08,174 --> 00:10:09,541 At first, there seemed to be 199 00:10:09,642 --> 00:10:12,210 little to distinguish these planets from Jupiter. 200 00:10:12,311 --> 00:10:16,982 Then, in 2019, we took a closer look. 201 00:10:17,083 --> 00:10:20,518 You go into a system like Kepler-51, a sun-like star, 202 00:10:20,586 --> 00:10:23,154 and you kind of go in expecting or hoping to find, 203 00:10:23,255 --> 00:10:25,824 you know, Earth-like planets, planets familiar from our own 204 00:10:25,925 --> 00:10:27,092 solar system. 205 00:10:27,193 --> 00:10:28,693 And then you find something like this, 206 00:10:28,794 --> 00:10:31,496 and you're kind of like, you know, what the heck is that? 207 00:10:31,597 --> 00:10:34,499 We've been hunting for exoplanets, and we've gotten 208 00:10:34,600 --> 00:10:35,967 used to some weird things, 209 00:10:36,068 --> 00:10:38,203 but this is truly out there. 210 00:10:38,304 --> 00:10:41,740 This is a truly alien scenario. 211 00:10:41,841 --> 00:10:44,209 ROWE: According to how we think planets are formed, 212 00:10:44,310 --> 00:10:48,446 the worlds orbiting Kepler-51 shouldn't exist. 213 00:10:48,547 --> 00:10:51,049 These three objects orbiting Kepler-51 214 00:10:51,150 --> 00:10:54,352 are kind of like cosmic conmen, because they appear to be 215 00:10:54,453 --> 00:10:56,021 like Jupiter, but in fact, 216 00:10:56,122 --> 00:10:58,456 their masses are just a few times that of Earth. 217 00:10:58,557 --> 00:11:01,726 These are planets that have like 1/10 of the density 218 00:11:01,827 --> 00:11:02,861 of water. 219 00:11:02,962 --> 00:11:05,096 If you could throw these things into a giant ocean, 220 00:11:05,197 --> 00:11:06,297 they would float. 221 00:11:07,566 --> 00:11:09,300 ROWE: The super-puff planets form from 222 00:11:09,402 --> 00:11:13,171 helium and hydrogen, just like Jupiter. 223 00:11:13,272 --> 00:11:15,707 But unlike Jupiter, gas on 224 00:11:15,808 --> 00:11:18,576 the super-puffs is not densely packed together. 225 00:11:18,678 --> 00:11:23,381 It's loose, creating big, fluffy balls. 226 00:11:23,482 --> 00:11:26,484 So even though they're the same size as Jupiter, 227 00:11:26,585 --> 00:11:29,187 their mass is just one percent. 228 00:11:29,288 --> 00:11:31,156 That's like a heavyweight fighter with 229 00:11:31,257 --> 00:11:33,692 the mass of a prairie dog. 230 00:11:33,793 --> 00:11:37,095 The super-puff planets, which is the greatest name ever 231 00:11:37,196 --> 00:11:39,964 for a planet, is really a very low density planet. 232 00:11:40,066 --> 00:11:42,333 Really, what it means is that it's very, very fluffy 233 00:11:42,435 --> 00:11:44,602 and light -- it's almost like it has a light, 234 00:11:44,704 --> 00:11:46,571 snow-like consistency. 235 00:11:47,840 --> 00:11:50,308 ROWE: The extremely low mass of these planets 236 00:11:50,409 --> 00:11:54,245 presents a problem for planetary scientists. 237 00:11:54,346 --> 00:11:57,482 This is an incredibly unlikely situation. 238 00:11:57,583 --> 00:12:02,020 How can these super-puff worlds even exist? 239 00:12:04,290 --> 00:12:08,393 ROWE: Gas giants like Jupiter start with an ice and rock core. 240 00:12:08,494 --> 00:12:10,729 This core grows until it generates 241 00:12:10,830 --> 00:12:13,965 enough gravity to pull in gas, 242 00:12:14,066 --> 00:12:17,836 building an atmosphere almost 2,000 miles deep. 243 00:12:19,472 --> 00:12:22,407 Do the super-puff planets form the same way? 244 00:12:23,876 --> 00:12:26,511 It's a bit of a mystery how these planets can 245 00:12:26,612 --> 00:12:29,781 even exist just based on what we know about planet formation. 246 00:12:29,882 --> 00:12:33,651 It's really an unusual thing to have something that is so 247 00:12:33,753 --> 00:12:37,422 light, because that's not how planets that we recognize 248 00:12:37,523 --> 00:12:39,491 typically form. 249 00:12:39,592 --> 00:12:41,926 ROWE: Scientists have a theory about how 250 00:12:42,027 --> 00:12:44,028 the super-puff planets formed. 251 00:12:44,096 --> 00:12:46,331 DURDA: We see these three planets relatively close 252 00:12:46,432 --> 00:12:48,133 to their parent star today, 253 00:12:48,234 --> 00:12:51,035 but very likely, given their composition, they probably 254 00:12:51,137 --> 00:12:52,237 formed a lot farther away, 255 00:12:52,338 --> 00:12:54,639 beyond the snow line, as we call it. 256 00:12:54,740 --> 00:12:57,675 ROWE: Star systems split into two regions, 257 00:12:57,777 --> 00:13:01,846 a warm inner region close to the star, and a colder 258 00:13:01,947 --> 00:13:03,848 outer region farther away. 259 00:13:03,949 --> 00:13:07,218 The snow line separates the two zones. 260 00:13:08,921 --> 00:13:12,090 Gas planets only form outside the snow line, 261 00:13:12,191 --> 00:13:15,727 far from the star, where gas can clump together. 262 00:13:17,429 --> 00:13:19,364 You're actually able to grab onto a lot 263 00:13:19,465 --> 00:13:23,067 of hydrogen and helium and build up an atmosphere. 264 00:13:23,169 --> 00:13:25,003 ROWE: Beyond the snow line, 265 00:13:25,104 --> 00:13:28,273 water condenses to a solid form. 266 00:13:28,374 --> 00:13:31,376 This process greatly boosts the formation of 267 00:13:31,477 --> 00:13:32,811 minute planets. 268 00:13:32,912 --> 00:13:36,614 These icy planetesimals jumpstart the rapid 269 00:13:36,715 --> 00:13:40,251 growth of what will become gas giants. 270 00:13:41,787 --> 00:13:44,889 The super-puffs formed even further out than Jupiter, in 271 00:13:44,990 --> 00:13:48,793 a far colder area -- Compared to Jupiter, 272 00:13:48,894 --> 00:13:51,796 the super-puffs had a relatively small core, 273 00:13:51,897 --> 00:13:55,433 but because they developed in this colder region, they still 274 00:13:55,534 --> 00:13:58,403 pulled in a huge quantity of hydrogen and helium. 275 00:13:58,504 --> 00:14:02,807 You end up with something that is kind of large in size 276 00:14:02,908 --> 00:14:05,076 but still really low density, 277 00:14:05,177 --> 00:14:06,711 low in mass. 278 00:14:06,812 --> 00:14:09,647 ROWE: These planets have been growing in size for around 279 00:14:09,748 --> 00:14:11,416 500 million years, 280 00:14:11,517 --> 00:14:15,119 and as they've been growing, they've also been moving. 281 00:14:15,221 --> 00:14:18,556 SUTTER: The gravity of their parent star can pull 282 00:14:18,657 --> 00:14:21,993 these planets closer, so we can see chains of 283 00:14:22,094 --> 00:14:25,096 super-puff planets like -- Like cars on a train, 284 00:14:25,197 --> 00:14:28,266 all marching inwards towards the star. 285 00:14:28,367 --> 00:14:30,534 ROWE: The closer they get to the star, 286 00:14:30,603 --> 00:14:33,805 the more stellar winds batter the super-puffs. 287 00:14:33,906 --> 00:14:36,474 The winds blast off the loose, 288 00:14:36,575 --> 00:14:41,779 puffy atmosphere in a process called photoevaporation. 289 00:14:41,881 --> 00:14:45,984 This process of photoevaporation results in these planets 290 00:14:46,085 --> 00:14:47,785 losing their atmospheres, 291 00:14:47,887 --> 00:14:51,456 literally losing billions of tons of atmosphere 292 00:14:51,557 --> 00:14:52,657 every second. 293 00:14:52,758 --> 00:14:56,761 These super-puffs are like orbiting dandelions 294 00:14:56,862 --> 00:15:00,565 that are getting blown away in the wind. 295 00:15:00,666 --> 00:15:04,736 ROWE: Scientists predict that over the next 4.5 billion years, 296 00:15:04,837 --> 00:15:06,905 the super-puff planet closest to 297 00:15:07,006 --> 00:15:10,141 its star will lose all its atmosphere, 298 00:15:10,242 --> 00:15:13,711 leaving a planet with a radius smaller than Neptune. 299 00:15:13,812 --> 00:15:15,079 The other two super-puff 300 00:15:15,180 --> 00:15:18,449 planets will escape largely unscathed. 301 00:15:21,320 --> 00:15:22,854 We are rapidly discovering 302 00:15:22,955 --> 00:15:26,024 a wide range of weird, oddball worlds. 303 00:15:26,125 --> 00:15:29,160 Planet hunters are also searching for something 304 00:15:29,261 --> 00:15:30,995 more familiar, 305 00:15:31,096 --> 00:15:34,999 something critical for life as we know it. 306 00:15:35,100 --> 00:15:38,436 We now think there could be planets dominated 307 00:15:38,537 --> 00:15:39,570 by water. 308 00:15:39,672 --> 00:15:42,707 But are these water worlds the oasis 309 00:15:42,808 --> 00:15:44,075 we've been searching for? 310 00:15:53,585 --> 00:15:56,654 ROWE: On the search for alien worlds, we've uncovered plenty 311 00:15:56,755 --> 00:15:58,823 of the strange, the scary, 312 00:15:58,891 --> 00:16:03,695 and the incredible, but we still haven't detected 313 00:16:03,796 --> 00:16:06,664 anything remotely like our planet. 314 00:16:07,933 --> 00:16:10,568 For all these treasures that we've been digging up, 315 00:16:10,669 --> 00:16:13,037 we haven't found the crown jewels -- 316 00:16:13,138 --> 00:16:15,907 A planet similar to Earth. 317 00:16:18,544 --> 00:16:20,745 ROWE: Finding an exoplanet with conditions suitable 318 00:16:20,846 --> 00:16:24,315 for life takes a lot of luck. 319 00:16:24,416 --> 00:16:27,151 Sifting through these exoplanets, looking for 320 00:16:27,252 --> 00:16:28,820 something that's habitable 321 00:16:28,921 --> 00:16:34,659 for life, is like an interstellar dating app. 322 00:16:34,760 --> 00:16:38,596 If we have molten iron rain, that's definitely out. 323 00:16:38,697 --> 00:16:40,932 You see toxic atmosphere, and you swipe, and you see 324 00:16:41,033 --> 00:16:42,867 red giant, and you swipe. 325 00:16:42,968 --> 00:16:44,836 So it's like oh, too hot, too cold, 326 00:16:44,937 --> 00:16:46,771 too small, too thick in atmosphere. 327 00:16:46,872 --> 00:16:48,506 No UV rays. No, no, no. 328 00:16:48,607 --> 00:16:49,841 Doesn't even have a star. 329 00:16:49,942 --> 00:16:51,809 Ba-da-da, like it's just not working 330 00:16:51,910 --> 00:16:54,145 again and again and again. 331 00:16:54,246 --> 00:16:55,947 ROWE: When it comes to finding life, 332 00:16:56,048 --> 00:16:58,883 there is one basic element that everyone agrees 333 00:16:58,984 --> 00:17:00,118 is necessary. 334 00:17:00,219 --> 00:17:02,186 SHIELDS: There is a phrase that we use whenever 335 00:17:02,287 --> 00:17:05,056 we talk about the search for life elsewhere -- 336 00:17:05,157 --> 00:17:06,457 Follow the water. 337 00:17:08,494 --> 00:17:10,695 ROWE: And now we think there could be lots 338 00:17:10,796 --> 00:17:13,531 of worlds out there that do contain water. 339 00:17:13,632 --> 00:17:15,733 But is there a catch? 340 00:17:15,834 --> 00:17:19,404 Could they hold too much water? 341 00:17:19,505 --> 00:17:23,908 A 2019 study suggests the Milky Way might contain 342 00:17:24,009 --> 00:17:25,009 many worlds, 343 00:17:25,077 --> 00:17:28,212 with thousands of times more water than Earth. 344 00:17:28,313 --> 00:17:31,115 Many of these planets are a bit smaller than Neptune. 345 00:17:31,216 --> 00:17:33,618 We call them sub-Neptunes. 346 00:17:34,820 --> 00:17:37,488 What they found were these sub-Neptunes, 347 00:17:37,589 --> 00:17:39,924 planets smaller than Neptune but bigger than Earth, 348 00:17:40,025 --> 00:17:42,326 ROWE: unlike any planets we'd seen before. 349 00:17:42,428 --> 00:17:46,864 We think we found such a planet just 40 light-years 350 00:17:46,965 --> 00:17:50,001 from Earth in the constellation Ophiuchus. 351 00:17:51,570 --> 00:17:55,673 Scientists have nicknamed the planet the Waterworld. 352 00:17:55,774 --> 00:17:58,709 GJ 1214 b could be one of these sub-Neptunes, 353 00:17:58,811 --> 00:18:00,845 with more water than we would know what to do with. 354 00:18:02,848 --> 00:18:07,218 ROWE: So far, we're not too sure what GJ 1214 b 355 00:18:07,319 --> 00:18:10,788 looks like -- though Earth is called the Blue Planet, 356 00:18:10,889 --> 00:18:14,258 It's only .05 percent water by mass. 357 00:18:15,861 --> 00:18:20,498 As much as 70 percent of GJ 1214 b's mass 358 00:18:20,599 --> 00:18:22,100 could be water. 359 00:18:22,201 --> 00:18:25,069 The planet is thought to have a rocky core, 360 00:18:25,170 --> 00:18:28,806 strange oceans, and a hot, steamy atmosphere of 361 00:18:28,907 --> 00:18:30,608 water vapor. 362 00:18:30,709 --> 00:18:33,845 We spent a lot of time looking for very small amounts of 363 00:18:33,946 --> 00:18:36,948 water to establish whether or not a planet could even 364 00:18:37,049 --> 00:18:38,116 be habitable, 365 00:18:38,217 --> 00:18:40,284 and so it's kind of amazing that we just 366 00:18:40,385 --> 00:18:43,121 found this planet that was essentially nothing but water. 367 00:18:44,623 --> 00:18:49,594 ROWE: Unlike Earth, GJ 1214 b most likely has no complex 368 00:18:49,695 --> 00:18:52,430 arrangement of water and land masses. 369 00:18:52,531 --> 00:18:54,031 WALSH: The lack of interaction 370 00:18:54,133 --> 00:18:57,602 between stable land masses and a healthy, 371 00:18:57,703 --> 00:19:01,172 long-term stable ocean might really be a killer, 372 00:19:01,273 --> 00:19:02,740 and you might need that land 373 00:19:02,841 --> 00:19:06,177 interacting with that water to have a good location for life. 374 00:19:07,946 --> 00:19:09,647 ROWE: We think life began in the oceans, 375 00:19:09,748 --> 00:19:12,950 but it needed chemicals from rocks to start. 376 00:19:13,051 --> 00:19:16,454 Without the interaction between land and oceans, 377 00:19:16,555 --> 00:19:18,923 life might not have evolved. 378 00:19:21,426 --> 00:19:26,030 Not only is there no land-sea relationship on GJ 1214 b, 379 00:19:26,131 --> 00:19:30,601 evolution here may be limited in another way. 380 00:19:30,702 --> 00:19:33,404 Earth's oceans are replenished with chemicals 381 00:19:33,505 --> 00:19:34,939 from hydrothermal vents 382 00:19:35,040 --> 00:19:37,808 thousands of feet down on the seabed. 383 00:19:37,910 --> 00:19:43,181 GJ 1214 b's ocean floors are thousands of miles deep, 384 00:19:44,483 --> 00:19:46,817 Right at the bottom of these incredibly deep oceans, 385 00:19:46,919 --> 00:19:48,686 you've got very high pressures. 386 00:19:48,787 --> 00:19:50,521 You've got so much water above you, 387 00:19:50,622 --> 00:19:52,190 and you got very cold temperatures. 388 00:19:52,291 --> 00:19:54,659 You're really being shielded from any incoming 389 00:19:54,760 --> 00:19:56,694 solar radiation or sunlight, 390 00:19:56,795 --> 00:19:59,697 so the water itself could turn to ice. 391 00:19:59,798 --> 00:20:03,467 ROWE: Most ice on Earth is called Ice I. 392 00:20:03,569 --> 00:20:06,137 When ice is subject to increasing pressure, 393 00:20:06,238 --> 00:20:08,673 its categorization number goes up. 394 00:20:08,807 --> 00:20:11,576 We think the ice on GJ 1214 b 395 00:20:11,677 --> 00:20:14,178 is Ice VII, the type of ice 396 00:20:14,279 --> 00:20:19,083 we believe to be on moons like Enceladus and Europa. 397 00:20:19,184 --> 00:20:21,552 On GJ 1214 b, 398 00:20:21,653 --> 00:20:24,488 we believe Ice VII seals off the seabed, 399 00:20:24,590 --> 00:20:28,025 preventing potential nutrients from the rocky core from 400 00:20:28,126 --> 00:20:29,493 passing into the ocean. 401 00:20:29,595 --> 00:20:33,798 We've been following the water, that's been the key to trying 402 00:20:33,899 --> 00:20:35,233 to understand astrobiology, 403 00:20:35,334 --> 00:20:37,935 and then we find these worlds where it's too much 404 00:20:38,036 --> 00:20:39,303 of a good thing, there's too much 405 00:20:39,404 --> 00:20:40,938 water for -- Perhaps for life to exist, 406 00:20:41,039 --> 00:20:44,275 so it's certainly one of those things that a little you need, 407 00:20:44,376 --> 00:20:46,844 but maybe too much is bad, too. 408 00:20:46,945 --> 00:20:50,281 ROWE: We need to find worlds with just the right 409 00:20:50,382 --> 00:20:53,150 amount of water and land for life to evolve. 410 00:20:54,453 --> 00:21:00,224 GJ 1214 b looks like a dead end, but the hunt goes on. 411 00:21:02,327 --> 00:21:05,463 Space is big, and I like the idea that it's not just 412 00:21:05,564 --> 00:21:07,465 for us, so I'm hopeful, 413 00:21:07,566 --> 00:21:09,367 whether it'll be in my lifetime or my daughter's, 414 00:21:09,468 --> 00:21:11,669 I don't know, but I'm hopeful. 415 00:21:11,770 --> 00:21:13,938 ROWE: As we continue to probe the cosmos, 416 00:21:14,039 --> 00:21:19,477 we've discovered one hopeful, distant object, a moon. 417 00:21:19,578 --> 00:21:22,346 But this exomoon is a monster. 418 00:21:22,447 --> 00:21:24,782 It's four times larger than Earth. 419 00:21:24,883 --> 00:21:28,686 So how did it get so big? 420 00:21:38,263 --> 00:21:41,265 ROWE: Each time we find new stars and their weird worlds, 421 00:21:41,366 --> 00:21:45,503 we have to rethink the rules of our own planetary system. 422 00:21:45,604 --> 00:21:49,040 We keep thinking we understand what's happening, 423 00:21:49,141 --> 00:21:50,741 and then the universe surprises us with something 424 00:21:50,842 --> 00:21:52,476 completely different. 425 00:21:52,577 --> 00:21:56,914 ROWE: Our search for exoplanets has been remarkably successful, 426 00:21:57,015 --> 00:22:01,285 but we've yet to spot those highly familiar objects that 427 00:22:01,386 --> 00:22:04,488 orbit many planets in the solar system. 428 00:22:04,589 --> 00:22:06,924 It's been an incredibly exciting time finding over 429 00:22:07,025 --> 00:22:08,626 4,000 exoplanets, 430 00:22:08,727 --> 00:22:11,128 but there's still something we haven't found that we're really 431 00:22:11,229 --> 00:22:13,064 excited by -- exomoons. 432 00:22:13,165 --> 00:22:18,135 ROWE: We expect to see exomoons around exoplanets, 433 00:22:18,236 --> 00:22:21,138 because our own solar system is full of moons. 434 00:22:21,239 --> 00:22:23,974 CHRISTIANSEN: Almost all the planets in our solar system 435 00:22:24,076 --> 00:22:25,810 have moons around them. 436 00:22:25,911 --> 00:22:28,846 In fact, Earth is the only planet that only has one moon. 437 00:22:28,947 --> 00:22:31,382 Most have more. 438 00:22:31,483 --> 00:22:33,417 LANZA: So the question is, 439 00:22:33,518 --> 00:22:36,220 you know, are moons unusual in general for planets? 440 00:22:36,321 --> 00:22:39,924 Or are we just not seeing the moons that are out there? 441 00:22:43,562 --> 00:22:46,230 Astronomers find exoplanets when they pass in front of 442 00:22:46,331 --> 00:22:48,165 a star. 443 00:22:48,266 --> 00:22:51,702 It's called a transit and creates a dip 444 00:22:51,803 --> 00:22:54,004 or a wobble in the light from the star. 445 00:22:54,106 --> 00:22:57,408 But moons pose a problem. 446 00:22:57,509 --> 00:23:00,678 They're incredibly small, so to find even one, 447 00:23:00,779 --> 00:23:02,713 we'd have to be very lucky. 448 00:23:02,814 --> 00:23:06,684 ROWE: In October 2017, astronomers took a closer 449 00:23:06,785 --> 00:23:10,287 look at a star 8,000 light-years away. 450 00:23:10,389 --> 00:23:13,391 The light dipped as a Jupiter-sized 451 00:23:13,492 --> 00:23:15,960 exoplanet passed in front of the star. 452 00:23:16,061 --> 00:23:21,232 Then, 3.5 hours later, they saw the light dip again. 453 00:23:21,333 --> 00:23:25,136 There was actually evidence as this planet transited 454 00:23:25,237 --> 00:23:26,437 and went across the star, 455 00:23:26,538 --> 00:23:28,606 blocking out a little bit of light of the star, that there 456 00:23:28,707 --> 00:23:31,642 was another large object rotating around the planet. 457 00:23:31,743 --> 00:23:37,481 ROWE: The planet, Kepler-1625b, appeared to have a companion 458 00:23:37,582 --> 00:23:39,049 orbiting around it. 459 00:23:39,151 --> 00:23:41,986 By looking at the light that was coming 460 00:23:42,087 --> 00:23:44,922 from the system and how it was changing, 461 00:23:45,023 --> 00:23:47,925 they thought they discovered the first exomoon, 462 00:23:48,026 --> 00:23:50,194 and that was really exciting. 463 00:23:50,295 --> 00:23:54,565 ROWE: Known as Kepler-1625b I, 464 00:23:54,666 --> 00:23:56,333 this exomoon candidate 465 00:23:56,435 --> 00:23:59,136 caused a significant dip in the light. 466 00:23:59,237 --> 00:24:00,771 And that can only mean one thing. 467 00:24:02,240 --> 00:24:05,309 When we analyze the signal caused by this potential moon, 468 00:24:05,410 --> 00:24:07,812 it must have been caused by something four times the width 469 00:24:07,913 --> 00:24:10,080 of Earth, so something like the size of Neptune, 470 00:24:10,182 --> 00:24:11,649 and we have no moons in our solar system 471 00:24:11,750 --> 00:24:13,284 that are Neptune-sized. 472 00:24:13,385 --> 00:24:15,553 ROWE: In our solar system, 473 00:24:15,654 --> 00:24:17,321 objects the size of Neptune 474 00:24:17,422 --> 00:24:18,956 are planets, not moons. 475 00:24:19,057 --> 00:24:22,460 Neptune and planets of a similar mass are ice 476 00:24:22,561 --> 00:24:24,929 and gas giants. 477 00:24:25,030 --> 00:24:29,233 Moons in our solar system don't have this composition. 478 00:24:29,334 --> 00:24:30,367 They're all solid. 479 00:24:30,469 --> 00:24:34,205 Just when we thought we understood moons 480 00:24:34,306 --> 00:24:35,639 and how they worked, 481 00:24:35,740 --> 00:24:39,043 now here comes an exoplanet to tell us not so fast. 482 00:24:39,144 --> 00:24:40,744 One problem with this system is we don't 483 00:24:40,846 --> 00:24:43,013 have many good ideas for how it formed. 484 00:24:43,114 --> 00:24:46,884 ROWE: Everything we know about moon formation comes from 485 00:24:46,985 --> 00:24:48,719 solid moons. 486 00:24:48,820 --> 00:24:51,188 There are two main ways that we think moons can form. 487 00:24:51,289 --> 00:24:53,591 The first is you have a rocky world, 488 00:24:53,692 --> 00:24:55,326 something comes in and smacks it, 489 00:24:58,730 --> 00:25:01,899 and the thing that smacks it, plus the debris that's ejected 490 00:25:02,000 --> 00:25:03,667 from that world, then go on to form 491 00:25:03,768 --> 00:25:04,869 a new moon, which is how we think 492 00:25:04,970 --> 00:25:06,737 the Earth's moon formed. 493 00:25:06,838 --> 00:25:08,038 Another way, 494 00:25:08,139 --> 00:25:10,908 potentially, is that when that planet was forming and there 495 00:25:11,009 --> 00:25:13,110 was a big cloud of dust and it was swirling 496 00:25:13,211 --> 00:25:15,412 around that the moons formed out of that 497 00:25:15,514 --> 00:25:17,147 dust at the same time of the planet. 498 00:25:18,350 --> 00:25:19,483 ROWE: But there may be another way 499 00:25:19,584 --> 00:25:23,153 the moon orbiting Kepler-1625b could have formed. 500 00:25:23,255 --> 00:25:24,989 RADEBAUGH: An exomoon 501 00:25:25,090 --> 00:25:27,558 doesn't have to form around the planet itself like we see 502 00:25:27,659 --> 00:25:28,893 around Jupiter or Saturn. 503 00:25:28,994 --> 00:25:31,495 But instead, let's imagine there's some kind of rogue 504 00:25:31,596 --> 00:25:33,430 planet wandering by a larger planet, 505 00:25:33,532 --> 00:25:35,533 and it gets captured and becomes a moon. 506 00:25:37,903 --> 00:25:40,204 ROWE: Perhaps billions of years ago, 507 00:25:40,305 --> 00:25:43,807 the planetary core of Kepler-1625b 508 00:25:43,909 --> 00:25:46,977 grows in a disk of gas and dust. 509 00:25:48,613 --> 00:25:50,848 It's not alone. 510 00:25:50,949 --> 00:25:53,751 Nearby, another protoplanet forms. 511 00:25:55,320 --> 00:25:56,854 RADEBAUGH: It's a little bit like twins. 512 00:25:56,955 --> 00:25:59,323 Each twin is gonna try to argue for their own amount of 513 00:25:59,424 --> 00:26:00,491 resources in the womb, 514 00:26:00,592 --> 00:26:02,192 and that's sort of the same thing happening here. 515 00:26:02,294 --> 00:26:04,395 It's a battle for resources. 516 00:26:04,496 --> 00:26:08,198 Kepler-1625b grabs more gas and dust 517 00:26:08,266 --> 00:26:11,135 than its twin, growing larger and larger. 518 00:26:13,138 --> 00:26:15,506 The now huge exoplanet slowly 519 00:26:15,607 --> 00:26:17,808 drags its smaller sibling closer, 520 00:26:19,344 --> 00:26:22,846 eventually pulling it into orbit. 521 00:26:22,948 --> 00:26:28,752 The smaller, protoplanet becomes Kepler-1625b's moon. 522 00:26:28,853 --> 00:26:31,155 The one thing that exoplanets have taught us is that we 523 00:26:31,256 --> 00:26:35,459 have no idea how systems in our universe have to evolve. 524 00:26:35,560 --> 00:26:38,495 And so it's completely feasible that this -- there is 525 00:26:38,597 --> 00:26:40,397 a really large Neptune-sized moon around 526 00:26:40,498 --> 00:26:44,101 a host planet, and we just need more evidence in order to 527 00:26:44,202 --> 00:26:45,936 make sure that that's true. 528 00:26:49,207 --> 00:26:51,742 ROWE: Scientists are confident that such evidence will 529 00:26:51,843 --> 00:26:55,412 be found when new technology comes online. 530 00:26:57,148 --> 00:26:59,617 But sometimes astronomers spot things that 531 00:26:59,718 --> 00:27:02,419 make them doubt their own instruments, 532 00:27:02,520 --> 00:27:05,889 events like a planet disappearing. 533 00:27:19,638 --> 00:27:22,873 ROWE: We've discovered some extraordinary exoplanets, 534 00:27:22,974 --> 00:27:26,310 super-hot worlds with molten iron rain, 535 00:27:26,411 --> 00:27:31,048 super-puff planets so fragile they might blow away, 536 00:27:31,149 --> 00:27:34,051 exoplanets that defy physics. 537 00:27:34,152 --> 00:27:39,323 But stranger still is the case of the disappearing planet. 538 00:27:39,424 --> 00:27:43,961 Over a decade ago, the Hubble telescope spotted a planet 539 00:27:44,062 --> 00:27:45,496 orbiting Fomalhaut, 540 00:27:45,597 --> 00:27:50,000 one of the brightest stars in the night sky. 541 00:27:50,101 --> 00:27:54,304 Fomalhaut is a very nearby, very young star. 542 00:27:54,406 --> 00:27:56,707 And the images of this system are incredible, because what 543 00:27:56,808 --> 00:28:00,778 you see is the central star surrounded by a bright ring. 544 00:28:00,879 --> 00:28:03,414 It looks just like the Eye of Sauron. 545 00:28:05,083 --> 00:28:08,619 ROWE: We observed the new planet, called Fomalhaut b, 546 00:28:08,720 --> 00:28:10,054 for six years. 547 00:28:10,155 --> 00:28:14,358 Then something surprising happened. 548 00:28:14,459 --> 00:28:16,960 All of a sudden, it just wasn't there anymore. 549 00:28:17,062 --> 00:28:20,464 Where did this planet go? - For it to suddenly be gone, 550 00:28:20,565 --> 00:28:23,067 it was amazing. It was astounding. 551 00:28:23,168 --> 00:28:24,635 It was terrifying. 552 00:28:26,337 --> 00:28:28,572 ROWE: If Fomalhaut b can suddenly vanish, 553 00:28:28,673 --> 00:28:31,942 what could that mean for other planets and us? 554 00:28:32,043 --> 00:28:35,779 We live on a planet, so we have a vested interest 555 00:28:35,880 --> 00:28:39,016 in understanding how planets could disappear, if that's 556 00:28:39,117 --> 00:28:40,517 a phenomenon that exists. 557 00:28:42,821 --> 00:28:45,622 ROWE: October 2019. 558 00:28:45,724 --> 00:28:49,159 Astronomers investigate the idea of a vanishing planet 559 00:28:49,260 --> 00:28:52,796 by looking at BD 20307, 560 00:28:52,897 --> 00:28:56,200 a star system straight out of the movies. 561 00:28:56,301 --> 00:28:59,470 Just like that iconic image from Star Wars from Tatooine, 562 00:28:59,571 --> 00:29:00,537 where you look up, 563 00:29:00,638 --> 00:29:02,673 and there's two stars in the sky. 564 00:29:02,774 --> 00:29:05,375 That's actually not that crazy. 565 00:29:05,443 --> 00:29:07,311 Out there in the wild, wild West of the universe, 566 00:29:07,412 --> 00:29:09,346 you have lots of different kinds of star systems. 567 00:29:09,447 --> 00:29:11,315 In fact, it's more common to have pairs of 568 00:29:11,416 --> 00:29:14,284 stars orbiting each other than have stars by themselves. 569 00:29:14,385 --> 00:29:17,221 ROWE: If two star systems are the norm, 570 00:29:17,322 --> 00:29:22,092 what makes BD 20307 different? 571 00:29:22,193 --> 00:29:24,895 The two stars lie within a bright 572 00:29:24,996 --> 00:29:27,898 disk of gas and dust like Fomalhaut. 573 00:29:27,999 --> 00:29:30,033 But Fomalhaut is a young 574 00:29:30,135 --> 00:29:32,970 system less than 500 million years old. 575 00:29:34,038 --> 00:29:38,308 BD 20307 is a billion years old, 576 00:29:38,409 --> 00:29:42,212 and that's weird, because the material in the disk is so 577 00:29:42,313 --> 00:29:46,250 old, it should have formed new planets long ago. 578 00:29:46,351 --> 00:29:47,251 So what's going on? 579 00:29:48,720 --> 00:29:51,355 OLUSEYI: Rings of dust are characteristic of 580 00:29:51,456 --> 00:29:52,890 young planetary systems. 581 00:29:52,991 --> 00:29:56,593 What does it mean when we see a disk of material surrounding 582 00:29:56,694 --> 00:29:57,795 an older star, 583 00:29:57,896 --> 00:29:59,830 a star over a billion years old? 584 00:29:59,931 --> 00:30:03,367 Well, one thing could be the collisions of planets. 585 00:30:03,468 --> 00:30:07,204 We think that, in this system, 586 00:30:07,305 --> 00:30:10,407 planets collided, and that formed the disk that we see. 587 00:30:12,544 --> 00:30:13,977 ROWE: When planets collide, 588 00:30:14,078 --> 00:30:17,314 they don't just spew out masses of material. 589 00:30:17,415 --> 00:30:19,016 The violence of the event 590 00:30:19,117 --> 00:30:21,785 shakes up the whole planetary neighborhood. 591 00:30:21,886 --> 00:30:24,822 Planetary objects come in with such energy 592 00:30:24,923 --> 00:30:28,792 and such speed that essentially they are vaporizing each other. 593 00:30:28,893 --> 00:30:32,329 Observing a planet essentially being destroyed 594 00:30:32,430 --> 00:30:33,697 tells us something 595 00:30:33,798 --> 00:30:37,167 about what might happen in our own solar system. 596 00:30:37,268 --> 00:30:40,070 Our planets feel very stable in their orbits, 597 00:30:40,171 --> 00:30:44,942 but we don't realize that, in the future, those orbits might 598 00:30:45,043 --> 00:30:47,077 be very different than they are today. 599 00:30:48,379 --> 00:30:51,949 ROWE: Early in its existence, our solar system was 600 00:30:52,050 --> 00:30:53,350 a demolition derby, 601 00:30:54,686 --> 00:30:56,820 with many, many collisions. 602 00:30:58,656 --> 00:31:01,058 It's how rocky planets like ours formed. 603 00:31:02,527 --> 00:31:03,994 DURDA: Back then, there were more than eight 604 00:31:04,095 --> 00:31:05,362 or nine planets in our solar system. 605 00:31:05,463 --> 00:31:07,831 There were hundreds, and planets were running 606 00:31:07,932 --> 00:31:10,500 into each other and interacting with each other all the time. 607 00:31:12,203 --> 00:31:14,771 ROWE: Eventually, the planets we see today formed, 608 00:31:14,873 --> 00:31:15,906 and our solar system 609 00:31:16,007 --> 00:31:19,343 settled into a nice, regular arrangement. 610 00:31:20,912 --> 00:31:25,249 Finding strange systems like BD 20307 611 00:31:25,350 --> 00:31:28,218 makes us question that narrative. 612 00:31:28,319 --> 00:31:30,354 One of the really valuable lessons that astronomers have 613 00:31:30,455 --> 00:31:32,456 learned from studying planets around other stars is 614 00:31:32,557 --> 00:31:36,693 that it appears very clear now that planets don't necessarily 615 00:31:36,794 --> 00:31:38,896 stay where they are in a solar system. 616 00:31:38,997 --> 00:31:42,266 ROWE: Over time, the orbits of planets 617 00:31:42,367 --> 00:31:45,302 in our solar system slowly shift. 618 00:31:45,370 --> 00:31:47,037 The repercussions of these orbital 619 00:31:47,138 --> 00:31:51,074 fluctuations could shatter our cosmic neighborhood. 620 00:31:51,175 --> 00:31:54,611 The odds are slim, but billions of years from now, 621 00:31:54,712 --> 00:31:58,315 Mercury could be pulled out of its orbit by gravitational 622 00:31:58,416 --> 00:32:00,450 interactions with Jupiter. 623 00:32:00,551 --> 00:32:04,688 This action would set Mercury on a fateful course. 624 00:32:04,789 --> 00:32:10,027 One potential future that our solar system may have is 625 00:32:10,128 --> 00:32:14,298 actually that Mercury could collide with Earth, 626 00:32:14,399 --> 00:32:18,702 which sounds crazy but would also be a real bummer. 627 00:32:18,803 --> 00:32:22,439 So what we see in BD 20307 628 00:32:22,540 --> 00:32:25,208 is theoretically possible in our own solar system. 629 00:32:27,612 --> 00:32:30,514 DURDA: It's actually been a bit of a wake-up call. 630 00:32:30,615 --> 00:32:33,116 It's a transformation in our understanding 631 00:32:33,217 --> 00:32:35,385 of how our solar system works. 632 00:32:35,486 --> 00:32:37,321 ROWE: Studying other systems shows us 633 00:32:37,422 --> 00:32:40,190 just how vulnerable planets can be. 634 00:32:40,291 --> 00:32:44,695 Things can change at any time in a planetary system, that we 635 00:32:44,796 --> 00:32:48,932 could be watching a planet on its orbit one day and poof, 636 00:32:49,000 --> 00:32:53,070 it could suffer that really big collision the next. 637 00:32:53,171 --> 00:32:55,005 SHIELDS:: But could this all explain 638 00:32:55,106 --> 00:32:57,174 the case of the Fomalhaut b system? 639 00:32:57,275 --> 00:32:59,109 Could it have collided with another planet, 640 00:32:59,210 --> 00:33:00,777 wiping it out completely? 641 00:33:02,246 --> 00:33:03,780 ROWE: Well, maybe. 642 00:33:05,550 --> 00:33:08,552 April 2020. 643 00:33:08,653 --> 00:33:11,588 Astronomers at the University of Arizona come 644 00:33:11,689 --> 00:33:14,524 up with a new theory about Fomalhaut. 645 00:33:14,625 --> 00:33:18,428 Every good mystery needs a shocking twist at the end, 646 00:33:18,529 --> 00:33:22,432 and the twist in this tale could be that the planet 647 00:33:22,533 --> 00:33:24,501 disappeared before Hubble's eyes, 648 00:33:24,602 --> 00:33:27,738 because it never was there to begin with. 649 00:33:29,507 --> 00:33:31,475 CHRISTIANSEN: Instead of a planet that we thought 650 00:33:31,576 --> 00:33:33,310 we captured inside the ring, 651 00:33:33,411 --> 00:33:35,112 it was actually a collision between two 652 00:33:35,213 --> 00:33:39,116 smaller objects called planetesimals. 653 00:33:39,217 --> 00:33:41,918 ROWE: Planetesimals are infant planets, 654 00:33:42,020 --> 00:33:46,623 bodies that measure from a few miles to hundreds of 655 00:33:46,724 --> 00:33:48,558 miles across. 656 00:33:48,659 --> 00:33:50,127 CHRISTIANSEN: They smashed together 657 00:33:50,228 --> 00:33:51,661 and created a huge dust cloud, 658 00:33:51,763 --> 00:33:53,497 which we caught up with Hubble. 659 00:33:53,598 --> 00:33:55,032 All we saw was a bright blob 660 00:33:55,133 --> 00:33:57,267 of light that looked like a planet. 661 00:33:57,368 --> 00:33:59,703 ROWE: They didn't spot a planet, 662 00:33:59,804 --> 00:34:02,839 but they did learn a very important lesson. 663 00:34:02,940 --> 00:34:05,142 DURDA: We were actually observing a process, part of 664 00:34:05,243 --> 00:34:07,577 the way that solar systems grow and are born. 665 00:34:07,678 --> 00:34:09,446 And, in many ways, that's, I think, 666 00:34:09,547 --> 00:34:13,683 more important and more useful to us than having spotted yet 667 00:34:13,785 --> 00:34:15,018 another planet. 668 00:34:16,621 --> 00:34:19,189 ROWE: Exoplanets are opening our eyes to the way 669 00:34:19,290 --> 00:34:21,224 the universe works. 670 00:34:21,325 --> 00:34:23,994 We must question some long-held assumptions. 671 00:34:25,830 --> 00:34:27,564 One standard text predicts 672 00:34:27,665 --> 00:34:30,333 the sun will eventually engulf the Earth. 673 00:34:31,903 --> 00:34:34,438 But could there be a way out? 674 00:34:34,539 --> 00:34:37,240 Do some planets cheat death? 675 00:34:48,786 --> 00:34:51,188 ROWE: In 4.5 billion years, our sun 676 00:34:51,289 --> 00:34:54,524 will expand to become a red giant. 677 00:34:54,625 --> 00:34:56,927 RADEBAUGH: When our own star turns into 678 00:34:57,028 --> 00:34:59,796 a red giant in 4.5 billion years from now, 679 00:34:59,897 --> 00:35:03,300 then it will expand, and it will engulf Mercury and Venus 680 00:35:03,401 --> 00:35:04,668 and the Earth and the moon, 681 00:35:04,769 --> 00:35:08,038 and it will cook the surfaces of all of those bodies. 682 00:35:08,139 --> 00:35:11,675 ROWE: But is there a way of escaping this apocalypse? 683 00:35:16,314 --> 00:35:18,248 When we look beyond our solar system to 684 00:35:18,349 --> 00:35:21,651 the Aquarius constellation, we find hope. 685 00:35:24,122 --> 00:35:29,926 Planet HD 203949 b is living on borrowed time. 686 00:35:30,027 --> 00:35:33,430 It orbits a red giant star. 687 00:35:33,531 --> 00:35:36,333 Red giant stars have burned up all the hydrogen in 688 00:35:36,434 --> 00:35:38,301 the middle, and they've moved to the next stage of 689 00:35:38,402 --> 00:35:40,003 their development. 690 00:35:40,104 --> 00:35:44,174 ROWE: A stage that's terminal for a planet orbiting this star. 691 00:35:44,275 --> 00:35:46,042 LANZA: If you're a planet, and you've been orbiting 692 00:35:46,144 --> 00:35:48,612 fairly close to your star for billions of years, 693 00:35:48,713 --> 00:35:51,281 you might feel like you've got a good relationship, 694 00:35:51,382 --> 00:35:52,616 that it's pretty safe. 695 00:35:52,717 --> 00:35:54,751 But in fact, you would be wrong. 696 00:35:54,852 --> 00:35:57,587 In fact, this star that has been taking care of 697 00:35:57,688 --> 00:36:00,891 you for billions of years is now going to destroy you. 698 00:36:02,860 --> 00:36:05,262 After billions of years of generating heat 699 00:36:05,363 --> 00:36:08,765 and light, a star's hydrogen fuel runs out. 700 00:36:10,334 --> 00:36:14,037 The star's core becomes unstable and contracts. 701 00:36:14,138 --> 00:36:16,139 CHRISTIANSEN: Gravity just pulls everything to the center. 702 00:36:17,909 --> 00:36:18,842 And then there's a rebound. 703 00:36:18,943 --> 00:36:21,111 Everything comes back again, and that creates 704 00:36:21,212 --> 00:36:24,147 this big envelope of gas around the star. 705 00:36:25,950 --> 00:36:30,220 ROWE: The outer layers of gas blow off and expand outwards. 706 00:36:30,321 --> 00:36:32,522 As the gas envelope gets bigger, 707 00:36:32,623 --> 00:36:35,725 the surface cools to under 10,000 degrees Fahrenheit. 708 00:36:37,728 --> 00:36:42,432 The coolest stars appear red, so late in stars' lives, they're 709 00:36:42,533 --> 00:36:45,402 big, bloated red giants. 710 00:36:49,273 --> 00:36:51,241 RADEBAUGH: When a star goes red giant, it expands, 711 00:36:51,342 --> 00:36:52,442 and it expands outward, 712 00:36:52,543 --> 00:36:54,678 and it's likely that it's going to come and engulf some 713 00:36:54,779 --> 00:36:56,680 of the planets that orbit that star. 714 00:36:56,781 --> 00:36:59,282 ROWE: The surface is cooled, 715 00:36:59,383 --> 00:37:02,986 but temperatures still exceed 8,000 degrees Fahrenheit. 716 00:37:03,087 --> 00:37:07,457 If you're in the red giant expansion zone, 717 00:37:07,558 --> 00:37:08,825 you're gonna get cooked. 718 00:37:10,261 --> 00:37:16,633 ROWE: Exoplanet HD 203949 B orbits within this zone. 719 00:37:16,734 --> 00:37:20,237 So is this planet toast? 720 00:37:24,242 --> 00:37:26,409 September 2019. 721 00:37:26,510 --> 00:37:28,878 We take a closer look at the red giant 722 00:37:28,980 --> 00:37:32,382 threatening the planet using a technique called 723 00:37:32,483 --> 00:37:34,618 astroseismology. 724 00:37:34,719 --> 00:37:38,455 Astroseismology measures the vibrations of stars. 725 00:37:38,556 --> 00:37:42,158 Astroseismology applied to these stars is a really useful 726 00:37:42,260 --> 00:37:43,793 way to get at more information 727 00:37:43,894 --> 00:37:45,929 than we might normally get by just looking at 728 00:37:46,030 --> 00:37:47,297 their brightness or their temperatures. 729 00:37:47,398 --> 00:37:49,799 Vibrations go back and forth within the stars, 730 00:37:49,900 --> 00:37:52,068 and we can see those by monitoring the surface. 731 00:37:52,169 --> 00:37:54,738 One of the things that happens when these stars get to 732 00:37:54,839 --> 00:37:58,508 their red giant phase is they start ringing like a bell. 733 00:37:58,609 --> 00:38:00,744 [dinging sound] 734 00:38:00,845 --> 00:38:03,713 When we hear these stars ringing, 735 00:38:03,814 --> 00:38:06,283 it actually gives us the most precise information we have 736 00:38:06,384 --> 00:38:07,484 about any stars. 737 00:38:07,585 --> 00:38:09,386 We can measure their mass, their radius, 738 00:38:09,487 --> 00:38:11,688 their density much more exquisitely than any 739 00:38:11,789 --> 00:38:12,856 other star. 740 00:38:12,957 --> 00:38:15,925 ROWE: The vibrations from the red giant star 741 00:38:16,027 --> 00:38:18,995 reveal something highly surprising. 742 00:38:19,096 --> 00:38:21,598 CHRISTIANSEN: When we analyzed the way this star was ringing, 743 00:38:21,699 --> 00:38:24,067 we realized it was actually less massive than we determined 744 00:38:24,168 --> 00:38:25,068 from other methods. 745 00:38:25,169 --> 00:38:27,003 It told us that star probably has 746 00:38:27,104 --> 00:38:30,307 already gone through its red giant phase. 747 00:38:30,408 --> 00:38:33,209 Um, the star we see today is a little smaller than it should 748 00:38:33,277 --> 00:38:35,345 have been quite a while back. 749 00:38:35,446 --> 00:38:37,981 ROWE: This star has lost some of 750 00:38:38,082 --> 00:38:41,718 its outer layers and has started to shrink. 751 00:38:41,819 --> 00:38:45,021 If this star has already gone through its red giant phase 752 00:38:45,122 --> 00:38:46,256 and is shrinking again, 753 00:38:46,357 --> 00:38:48,692 that means at one point, it was bigger than the orbit of 754 00:38:48,793 --> 00:38:50,026 this planet. 755 00:38:50,127 --> 00:38:52,629 ROWE: If the planet was within the red giant zone, 756 00:38:52,730 --> 00:38:54,297 it should have been destroyed. 757 00:38:54,398 --> 00:38:56,866 But somehow, it remained intact. 758 00:38:56,967 --> 00:38:59,169 By all accounts, this planet shouldn't exist. 759 00:38:59,270 --> 00:39:01,004 But somehow, we see it there today, 760 00:39:01,105 --> 00:39:03,206 cheating death -- What a survivor. 761 00:39:03,307 --> 00:39:07,377 ROWE: So how can we explain this escape act? 762 00:39:07,478 --> 00:39:10,413 Could it be of this planet changed its orbital position 763 00:39:10,514 --> 00:39:12,749 to allow it to cheat death? 764 00:39:12,850 --> 00:39:19,723 ROWE: Or maybe HD 203949 b was never even in the kill zone. 765 00:39:19,824 --> 00:39:22,926 Perhaps this planet originally formed further out 766 00:39:23,027 --> 00:39:26,930 and migrated in after the red giant phase was completed. 767 00:39:28,332 --> 00:39:30,367 ROWE: Maybe some of the clouds of gas 768 00:39:30,468 --> 00:39:33,203 shed from the star reached the planet. 769 00:39:33,304 --> 00:39:35,472 This gas dragged on the planet, 770 00:39:35,573 --> 00:39:37,574 slowing its orbit down. 771 00:39:37,675 --> 00:39:41,177 Gradually, the planet migrated inwards after 772 00:39:41,278 --> 00:39:44,114 the star reached its maximum size. 773 00:39:44,215 --> 00:39:47,851 And we then evolve down to the system that we see today, 774 00:39:47,952 --> 00:39:50,954 a post red giant star with a planet 775 00:39:51,055 --> 00:39:52,722 that shouldn't be there, so to speak. 776 00:39:54,492 --> 00:39:57,093 ROWE: This exoplanet may have escaped oblivion, 777 00:39:57,194 --> 00:39:59,929 but its future doesn't look bright. 778 00:40:01,198 --> 00:40:05,969 Its star will shrink down to a cool, dim white dwarf. 779 00:40:06,070 --> 00:40:07,504 LANZA: If I were a planet, you know, 780 00:40:07,605 --> 00:40:10,340 I would be sad at the existence that I would live 781 00:40:10,441 --> 00:40:11,641 afterward, just because it would 782 00:40:11,742 --> 00:40:14,177 be so different, it would be cold and dark, 783 00:40:14,278 --> 00:40:17,147 and I would still be bound with a star 784 00:40:17,248 --> 00:40:19,983 that is no longer there in the same way that it was. 785 00:40:21,652 --> 00:40:24,354 ROWE: This is our future, 786 00:40:24,455 --> 00:40:27,056 but it won't happen for another five billion years. 787 00:40:28,759 --> 00:40:31,728 In the meantime, we can be thankful we live on Earth 788 00:40:31,829 --> 00:40:33,563 rather than one of the weird worlds 789 00:40:33,664 --> 00:40:35,765 we've discovered in our galaxy. 790 00:40:38,035 --> 00:40:40,970 The more and more exoplanets we find, 791 00:40:41,071 --> 00:40:44,007 the more we realize how lucky we really are. 792 00:40:44,108 --> 00:40:46,810 We see planets that are too big, too small, 793 00:40:46,911 --> 00:40:47,944 too much atmosphere, 794 00:40:48,045 --> 00:40:50,280 too little atmosphere, too close to their star, 795 00:40:50,381 --> 00:40:51,448 too far from their star. 796 00:40:51,549 --> 00:40:54,250 Too little water, too much water. 797 00:40:54,351 --> 00:40:57,654 Everything on Earth is just right. 798 00:40:57,755 --> 00:40:59,722 ROWE: Compared to our home world, 799 00:40:59,824 --> 00:41:02,192 exoplanets push and twist 800 00:41:02,293 --> 00:41:05,895 and stretch the boundaries of planetary science. 801 00:41:05,996 --> 00:41:09,365 But every new world we discover expands our 802 00:41:09,467 --> 00:41:14,971 knowledge and moves us closer to understanding our place 803 00:41:15,072 --> 00:41:16,372 in the universe. 804 00:41:16,474 --> 00:41:19,742 If we can understand how planets form and why they form 805 00:41:19,844 --> 00:41:22,212 the way they do and how they evolve, 806 00:41:22,313 --> 00:41:26,883 then we can know our past, present, and future even better. 807 00:41:28,853 --> 00:41:30,753 PLAIT: I think as we find more and more of these planets, 808 00:41:30,855 --> 00:41:33,857 we're going to find out more about our own solar system 809 00:41:33,958 --> 00:41:35,992 and our place in this menagerie. 810 00:41:37,862 --> 00:41:40,163 BULLOCK: A lot of times, we think about other planets 811 00:41:40,264 --> 00:41:41,998 and even life in the universe as resembling 812 00:41:42,099 --> 00:41:43,166 very much our own. 813 00:41:43,267 --> 00:41:46,035 But these weird worlds open the possibility that 814 00:41:46,136 --> 00:41:48,438 there's much, much more out there than we had ever imagined. 815 00:41:50,241 --> 00:41:52,408 CHRISTIANSEN: We found so many different kinds of crazy worlds 816 00:41:52,510 --> 00:41:55,044 in crazy places, doing crazy things. 817 00:41:55,145 --> 00:41:56,312 It's so interesting. 818 00:41:56,413 --> 00:41:58,047 Imagine how boring it would be if 819 00:41:58,148 --> 00:42:00,316 we only found our solar system everywhere else.