WEBVTT 1 00:00:03.399 --> 00:00:07.719 Welcome to Bedtime Astronomy. Explore the wonders of the cosmos 2 00:00:07.759 --> 00:00:12.279 with our soothing Bedtime Astronomie podcast. Each episode offers a 3 00:00:12.359 --> 00:00:16.320 gentle journey through the stars, planets, and beyond, perfect for 4 00:00:16.399 --> 00:00:20.239 unwinding after a long day. Let's travel through the mysteries 5 00:00:20.239 --> 00:00:22.440 of the universe as you drift off into a peaceful 6 00:00:22.480 --> 00:00:25.839 slumber under the night sky. 7 00:00:26.960 --> 00:00:29.079 You know the image, I mean, it's basically burned into 8 00:00:29.120 --> 00:00:31.000 our brains at this point, the pale blue dot. 9 00:00:31.039 --> 00:00:35.280 Oh yeah, Voyager one, Carl Sagan's whole speech. It's iconic. 10 00:00:35.359 --> 00:00:38.399 It is right, that one tiny pixel of light just 11 00:00:38.479 --> 00:00:41.159 hanging there in a sunbeam, and for what the last 12 00:00:41.200 --> 00:00:44.320 thirty plus years, that's been our shorthand for life in 13 00:00:44.320 --> 00:00:47.320 the universe. If you look for aliens, you look for 14 00:00:47.359 --> 00:00:50.079 the blue, you look for oceans, you look for that 15 00:00:50.479 --> 00:00:54.679 specific shade that says earth like. It's almost romantic. 16 00:00:54.960 --> 00:00:59.359 It is. It's a beautiful thought, but it's also well, 17 00:01:00.000 --> 00:01:01.880 it's a bit of a trap. A trap how so, 18 00:01:02.000 --> 00:01:04.719 it's a cognitive trap because it locks us into looking 19 00:01:04.760 --> 00:01:07.599 for a mirror. We're looking for ourselves, but ourselves today. 20 00:01:07.799 --> 00:01:11.640 It just assumes that habitable always equals blue, and that 21 00:01:11.799 --> 00:01:13.760 is exactly where we're going today. 22 00:01:13.959 --> 00:01:16.840 I want you to just for a second reimagine that dot. 23 00:01:17.319 --> 00:01:21.200 Forget the blue. Instead, picture of that pixel is a deep, 24 00:01:21.439 --> 00:01:22.359 vibrant purple. 25 00:01:22.599 --> 00:01:24.799 Or get this, What if the oceans on that dot 26 00:01:24.879 --> 00:01:28.560 weren't blue at all, but like a bright, almost neon green. 27 00:01:28.640 --> 00:01:31.079 And here's the kicker. This isn't science fiction. We're not 28 00:01:31.120 --> 00:01:33.159 talking about some far flown alien world. 29 00:01:33.239 --> 00:01:35.599 Yeah, no, not at all. We are talking about Earth. 30 00:01:35.680 --> 00:01:39.200 This is our own history. If alien astronomers had been 31 00:01:39.239 --> 00:01:41.439 looking at our planet at different times, they wouldn't have 32 00:01:41.439 --> 00:01:42.439 seen a pale blue dot. 33 00:01:42.640 --> 00:01:45.000 They have seen a purple world, oh or a green 34 00:01:45.040 --> 00:01:45.680 ocean world. 35 00:01:45.719 --> 00:01:48.599 And that simple fact that our planet changes its color 36 00:01:48.680 --> 00:01:52.879 over billions of years is at the heart of this. Well, 37 00:01:52.920 --> 00:01:56.200 this really intense debate happening inside NASA right now. 38 00:01:56.280 --> 00:01:59.519 It's a huge struggle. We're talking about giant space telescopes, 39 00:02:00.000 --> 00:02:04.920 million dollar budget fights, ancient bacteria, and even rocks that 40 00:02:04.959 --> 00:02:07.000 are trying to trick us exactly. We're looking at a 41 00:02:07.000 --> 00:02:09.439 new white paper that just came out January twenty twenty 42 00:02:09.439 --> 00:02:12.520 six on the Arts of pre Print Server. It's from 43 00:02:12.560 --> 00:02:14.240 the Living World's Working group. 44 00:02:14.039 --> 00:02:16.919 Which is a very very cool name for a committee 45 00:02:16.960 --> 00:02:17.560 of scientists. 46 00:02:17.560 --> 00:02:20.560 It sounds like a superhero team, doesn't it. But their 47 00:02:20.639 --> 00:02:23.840 job is actually really practical. They're trying to define the 48 00:02:23.879 --> 00:02:27.759 capabilities of the next great space telescope, the Happible World's 49 00:02:27.759 --> 00:02:30.039 Observatory or HWO. 50 00:02:29.919 --> 00:02:32.039 Right, and the argument they're making in this paper is, 51 00:02:32.240 --> 00:02:34.879 to put it simply, if we build this thing on 52 00:02:34.919 --> 00:02:37.280 the cheap, if we cut corners on the sensors to 53 00:02:37.319 --> 00:02:38.039 save a few. 54 00:02:37.840 --> 00:02:39.439 Billion dollars, which always happens. 55 00:02:39.639 --> 00:02:42.120 It always happens, then we might stare right at a 56 00:02:42.120 --> 00:02:45.479 living planet and have absolutely no idea what we're looking at. 57 00:02:45.719 --> 00:02:47.919 Or and I think this might be worse, we might 58 00:02:47.960 --> 00:02:50.360 stare at a dead, toxic rock and convince ourselves we 59 00:02:50.439 --> 00:02:51.120 found a jungle. 60 00:02:51.360 --> 00:02:54.199 That's the fear, that's the big false positive nightmare. 61 00:02:54.280 --> 00:02:58.479 So that's the mission today. We're going hunting for purple earths, 62 00:02:58.919 --> 00:03:02.120 green oceans, and the cosmic impostors trying to fool us. 63 00:03:02.319 --> 00:03:02.879 Let's do it. 64 00:03:03.039 --> 00:03:05.800 Okay, So before we even get to the cool biology, 65 00:03:05.840 --> 00:03:08.159 the purple bacteria and all that, we haven't talked about 66 00:03:08.199 --> 00:03:12.280 the machine, the tool, this Habitable World's Observatory. 67 00:03:11.680 --> 00:03:13.280 The HWO yeah. 68 00:03:13.560 --> 00:03:16.280 I mean, we've all been obsessed with the James Web 69 00:03:16.319 --> 00:03:19.960 Telescope JWST for the last few years. The images are 70 00:03:20.000 --> 00:03:24.039 just stunning. So why do we need another huge, expensive telescope. 71 00:03:24.280 --> 00:03:26.599 What can HWO do that Web can't. 72 00:03:26.840 --> 00:03:29.319 That is the multi billion dollar question, isn't it? And 73 00:03:29.360 --> 00:03:31.520 it really comes down to how they look at planets. 74 00:03:31.680 --> 00:03:34.199 JWST is an absolute marvel, don't get me wrong, but 75 00:03:34.280 --> 00:03:37.759 for exoplanets planets around other stars, it mostly uses a 76 00:03:37.800 --> 00:03:39.960 method called transit spectroscopy. 77 00:03:40.159 --> 00:03:42.319 Transit's okay, so that's the shadow method. 78 00:03:42.080 --> 00:03:44.879 Right, The shadow method exactly, you have to wait for 79 00:03:44.919 --> 00:03:47.159 a planet to pass directly in front of its star 80 00:03:47.319 --> 00:03:48.560 from our point of view. 81 00:03:48.400 --> 00:03:50.960 And as it does, a tiny bit of the starlight 82 00:03:51.439 --> 00:03:53.039 shines through the planet's. 83 00:03:52.599 --> 00:03:56.639 Atmosphere precisely like sunlight through a stained glass window, and 84 00:03:56.680 --> 00:03:59.280 by looking at what colors get filtered out, you can 85 00:03:59.319 --> 00:04:02.520 tell what gases are in that atmosphere. Oh, there's methane here, 86 00:04:02.599 --> 00:04:06.439 there's water, vapor. It's incredible, Like there's a butt, there's 87 00:04:06.439 --> 00:04:09.680 a big butt. You're only seeing the edges. You're basically 88 00:04:09.719 --> 00:04:13.199 looking at a backlit silhouette of the planet. You're sniffing 89 00:04:13.199 --> 00:04:15.439 its air, but you're not seeing its surface. 90 00:04:15.479 --> 00:04:16.240 You can't see the ground. 91 00:04:16.279 --> 00:04:19.519 You can't see the ground. The Habitable World's Observatory is 92 00:04:19.560 --> 00:04:22.519 designed to do something much much harder. It's designed for 93 00:04:22.759 --> 00:04:24.160 direct imaging. 94 00:04:23.800 --> 00:04:26.439 Which sounds simple. It just means taking a picture of 95 00:04:26.480 --> 00:04:27.360 the planet itself. 96 00:04:27.480 --> 00:04:30.040 It sounds simple. We take pictures all day, but the 97 00:04:30.079 --> 00:04:33.480 physics of it are just staggering. You're trying to photograph 98 00:04:33.600 --> 00:04:38.600 a tiny firefly floating right next to a giant, blinding searchlight. 99 00:04:38.319 --> 00:04:39.920 From miles and miles away. 100 00:04:40.040 --> 00:04:43.959 From light years away. The star is billions of times 101 00:04:44.000 --> 00:04:47.439 brighter than the planet. If you just point a telescope, 102 00:04:47.560 --> 00:04:49.920 the planet is completely lost in the glare. 103 00:04:50.480 --> 00:04:51.959 So how do you solve that? What's the trick? 104 00:04:52.120 --> 00:04:54.759 The trick is a very clever piece of engineering called 105 00:04:54.759 --> 00:04:58.279 a coronagraph. A coronagraph, Yeah, think of it this way. 106 00:04:58.639 --> 00:05:01.120 If you're outside and the sun is in your eyes, 107 00:05:01.160 --> 00:05:03.360 but you want to see, I don't know, a bird 108 00:05:03.399 --> 00:05:04.160 flying near. 109 00:05:04.000 --> 00:05:06.560 It, what do you do instinctively and put my hand 110 00:05:06.639 --> 00:05:08.560 up block the sun with my thumb. 111 00:05:08.480 --> 00:05:12.920 Exactly, you create a tiny artificial eclipse just for your eye. 112 00:05:13.319 --> 00:05:17.759 A coronagraph is a super high tech hand inside the telescope. 113 00:05:18.040 --> 00:05:21.120 It's a system of masks and mirrors that physically block 114 00:05:21.199 --> 00:05:22.360 the light from the star. 115 00:05:22.319 --> 00:05:24.680 So it creates a little shadow right where the star is. 116 00:05:24.800 --> 00:05:27.480 A perfect little shadow. It suppresses that glare by an 117 00:05:27.519 --> 00:05:31.000 insane amount, like it blocks ninety nine point nine percent 118 00:05:31.079 --> 00:05:33.920 of the starlight, and suddenly the faint little speck of 119 00:05:33.959 --> 00:05:36.600 light reflecting off the planet next to it can actually 120 00:05:36.600 --> 00:05:37.040 be seen. 121 00:05:37.240 --> 00:05:40.079 And that's the revolution, because if you can block the star, 122 00:05:40.399 --> 00:05:42.199 you're not just seeing the atmosphere anymore. 123 00:05:42.399 --> 00:05:44.120 Now you're seeing the surface. 124 00:05:43.959 --> 00:05:47.720 You're seeing the light bouncing off the continents, off the oceans. 125 00:05:47.839 --> 00:05:49.040 You can actually see its color. 126 00:05:49.240 --> 00:05:52.079 And that's where all the trouble starts because seeing color 127 00:05:52.120 --> 00:05:54.720 sounds easy, but to do it from that distance, you 128 00:05:54.800 --> 00:05:58.399 need incredibly clean data. The whole point of this new 129 00:05:58.439 --> 00:06:02.399 white paper is that the aged needs an exceptionally high 130 00:06:02.800 --> 00:06:05.399 signal to noise ratio signal to noise. 131 00:06:05.399 --> 00:06:08.000 We talk about that in audio production. So it's about clarity. 132 00:06:08.120 --> 00:06:10.319 It's all about clarity. It's not just about getting more light, 133 00:06:10.360 --> 00:06:13.120 it's about getting clean light. Imagine you're at a really 134 00:06:13.160 --> 00:06:15.560 loud concert and someone across the room is trying to 135 00:06:15.600 --> 00:06:19.519 whisper a secret password to you, Okay, The loud music 136 00:06:19.600 --> 00:06:22.680 is the noise, all the stray light from the star, 137 00:06:23.000 --> 00:06:26.439 from dust in space, even heat from the telescope itself. 138 00:06:26.920 --> 00:06:29.920 The whisper is the signal, that little sliver of colored 139 00:06:29.959 --> 00:06:31.399 light that might indicate life. 140 00:06:31.519 --> 00:06:33.839 And if the signal to noise is low, the music 141 00:06:33.879 --> 00:06:34.240 is too. 142 00:06:34.199 --> 00:06:36.839 Loud, you can't hear the password. You might hear a murmur, 143 00:06:36.920 --> 00:06:38.519 You might think they said the right word, but you 144 00:06:38.519 --> 00:06:41.000 can't be sure. The scientists are saying they need a 145 00:06:41.000 --> 00:06:44.279 system so quiet, so sensitive that they can pick out 146 00:06:44.319 --> 00:06:46.120 that whisper with total confidence. 147 00:06:46.439 --> 00:06:48.600 And this gets us back to the horse trading you mentioned, 148 00:06:49.199 --> 00:06:51.639 because making a quiet telescope is. 149 00:06:51.600 --> 00:06:57.199 Expensive, unbelievably expensive. Every little bit of improved performance costs 150 00:06:57.319 --> 00:07:00.959 millions or tens of millions, and the financial managers at NASA, 151 00:07:01.040 --> 00:07:03.560 their job is to look at the plans and say, Okay, 152 00:07:03.600 --> 00:07:06.079 do you really need the deluxe sensor package. Can't you 153 00:07:06.160 --> 00:07:07.920 just make do with the standard one cage? 154 00:07:08.040 --> 00:07:09.920 Just fix it in photoshop later. 155 00:07:09.920 --> 00:07:13.680 Exactly, And this paper from the Living World's Group is 156 00:07:13.720 --> 00:07:17.000 their response. It's them saying, look, this isn't a luxury feature, 157 00:07:17.240 --> 00:07:19.639 this isn't just gold plating. If we don't have this 158 00:07:19.720 --> 00:07:23.160 specific capability, the entire mission could fail. We won't be 159 00:07:23.160 --> 00:07:24.199 able to hear the whisper. 160 00:07:24.360 --> 00:07:26.160 Okay, so let's get into what they're trying to hear. 161 00:07:26.680 --> 00:07:29.639 What's the whisker? If an alien astronomer is looking at 162 00:07:29.680 --> 00:07:36.600 Earth right now, what's the gold standard signal that screams life. 163 00:07:35.720 --> 00:07:40.000 For modern Earth? The clearest, most unambiguous surface biosignature is 164 00:07:40.040 --> 00:07:41.959 something called the vegetation red edge. 165 00:07:42.040 --> 00:07:44.319 The red edge, it sounds like a spy movie, A. 166 00:07:44.279 --> 00:07:45.959 Cliff is actually the best way to think about it. 167 00:07:45.959 --> 00:07:48.879 So we all know plants are green because chlorophyll absorbs 168 00:07:48.879 --> 00:07:51.319 red and blue light for photosynthesis. 169 00:07:50.600 --> 00:07:52.720 Right right, and it reflects the green light, which is 170 00:07:52.720 --> 00:07:53.680 why we see it as green. 171 00:07:53.800 --> 00:07:56.279 But that's not the whole story. There's something else happening 172 00:07:56.319 --> 00:07:59.319 that our eyes can't see. Plants are also reflecting a 173 00:07:59.399 --> 00:08:01.199 huge amount of near infrared light. 174 00:08:01.439 --> 00:08:04.040 Okay, why, what's the evolutionary advantage there? 175 00:08:04.120 --> 00:08:08.759 It's a radiator, it's thermal regulation. Infrared light is basically heat. 176 00:08:09.560 --> 00:08:12.399 If plants absorbed all that infrared energy from the sun, 177 00:08:12.639 --> 00:08:14.959 they literally cook themselves from the inside out. 178 00:08:15.199 --> 00:08:16.839 Ah, So they need to get rid of it. 179 00:08:16.879 --> 00:08:18.399 They need to get rid of it fast. So they 180 00:08:18.480 --> 00:08:22.600 evolved this amazing trick where their cell structures act like 181 00:08:22.720 --> 00:08:25.519 perfect mirrors for a near infrared light. They just bounce 182 00:08:25.560 --> 00:08:26.600 it right back into space. 183 00:08:26.720 --> 00:08:28.120 That's genius, it is. 184 00:08:28.160 --> 00:08:30.120 And if you plot this on a graph of light, 185 00:08:30.240 --> 00:08:34.759 a spectrogram, it creates this incredibly dramatic feature. The brightness 186 00:08:34.879 --> 00:08:37.240 is low in the red part of the spectrum because 187 00:08:37.240 --> 00:08:39.200 the plants are eating that light. And then as soon 188 00:08:39.240 --> 00:08:42.519 as you cross over into the near infrared, boom, the 189 00:08:42.559 --> 00:08:45.519 line shoots straight up like a vertical wall, a cliff, 190 00:08:45.639 --> 00:08:49.720 a cliff. That sharp sudden jump is the vegetation red edge. 191 00:08:49.799 --> 00:08:50.919 And rocks don't do that. 192 00:08:51.360 --> 00:08:54.519 Rocks and sand and dirt they don't do that. Their 193 00:08:54.559 --> 00:08:57.879 reflection spectra are usually smooth slopes, they don't have sharp edges. 194 00:08:58.720 --> 00:09:01.000 If you see that cliff, it's one of the strongest 195 00:09:01.039 --> 00:09:04.240 signs of widespread complex life you could ever hope for. 196 00:09:04.559 --> 00:09:07.639 But and I'm sensing the catch here, the thing the 197 00:09:07.639 --> 00:09:10.759 white paper is worried about. You can only see that 198 00:09:10.840 --> 00:09:13.320 cliff if your camera can see into the infrared. 199 00:09:13.440 --> 00:09:17.360 There's the catch. If the budget committee says, hey, those 200 00:09:17.480 --> 00:09:20.919 near infrared sensors are too complex, too expensive, let's just 201 00:09:20.919 --> 00:09:23.600 stick to the visible light our eyes can see. Then 202 00:09:23.639 --> 00:09:25.200 you completely miss the red edge. 203 00:09:25.279 --> 00:09:26.519 The cliff is invisible to you. 204 00:09:26.639 --> 00:09:28.919 It's invisible. You could be looking at a planet covered 205 00:09:28.919 --> 00:09:31.120 in the Amazon rainforest and it would just look like 206 00:09:31.159 --> 00:09:34.639 a dark, unremarkable smudge. You miss the smoking gun. 207 00:09:35.279 --> 00:09:39.200 So that's argument number one for the expensive model. We 208 00:09:39.240 --> 00:09:42.679 need infrared to see earth like life today. But the 209 00:09:42.679 --> 00:09:46.000 paper goes deeper, doesn't it, because looking for modern Earth 210 00:09:46.039 --> 00:09:46.840 isn't enough. 211 00:09:47.159 --> 00:09:49.039 Not even close. I mean, this is where it gets 212 00:09:49.080 --> 00:09:53.399 really mind bending for me. We're so biased towards green chlorophyll, 213 00:09:53.799 --> 00:09:56.919 but chlorophyll is in the grand scheme of things, a 214 00:09:56.960 --> 00:10:01.480 fairly recent invention for a huge chunk of our planet's history. 215 00:10:01.720 --> 00:10:04.720 The world wasn't green, it was purple. It was purple. 216 00:10:04.799 --> 00:10:08.039 The purple Earth hypothesis. I love this, So take us back. 217 00:10:08.080 --> 00:10:09.240 What's going on purple Earth. 218 00:10:09.320 --> 00:10:14.440 We're talking maybe three billion, two point five billion years ago. 219 00:10:15.200 --> 00:10:17.960 The most advanced life forms on the planet were these 220 00:10:18.000 --> 00:10:22.519 single celled organisms purple and oxygenic phototrufs. 221 00:10:22.919 --> 00:10:24.600 Okay, that's a mouseful it is. 222 00:10:24.600 --> 00:10:27.240 Let's just call them purple bacteria. The key thing is 223 00:10:27.360 --> 00:10:30.279 they didn't use chlorophyll for photosynthesis. They used a different 224 00:10:30.360 --> 00:10:31.960 kind of pigment called retinal. 225 00:10:31.679 --> 00:10:34.759 Retinal wait as in this stuff in our retinas in 226 00:10:34.799 --> 00:10:35.720 our eyes, very. 227 00:10:35.679 --> 00:10:38.559 Very similar chemical structure, the same pigments your eyes used 228 00:10:38.559 --> 00:10:41.960 to detect light. These ancient bacteria used to harvest energy 229 00:10:41.960 --> 00:10:45.639 from the sun, and they work differently from chlorophyll. Chlorophyll 230 00:10:45.759 --> 00:10:49.759 absorbs red and blue, reflects green. Retinal is basically the opposite. 231 00:10:49.879 --> 00:10:52.639 It's most efficient at absorbing green and yellow light, which 232 00:10:52.639 --> 00:10:55.039 by the way, is the peak of the Sun's energy output. 233 00:10:55.240 --> 00:10:57.799 So it's absorbing the most powerful part of the sunlight. 234 00:10:58.440 --> 00:10:59.879 And if it absorbs green. 235 00:11:00.080 --> 00:11:02.519 Flex the other parts. It reflects red and blue light. 236 00:11:02.639 --> 00:11:04.879 And if you mix red and blue paint you get you. 237 00:11:04.799 --> 00:11:07.320 Get purple, a deep, rich purple. 238 00:11:07.559 --> 00:11:11.799 So for a billion years, maybe more, any continents or 239 00:11:12.039 --> 00:11:15.320 shallow coastal areas on Earth would have been covered in 240 00:11:15.360 --> 00:11:17.960 these vast purple mats of bacteria. 241 00:11:18.440 --> 00:11:20.440 And this isn't just a theory. We still have them. 242 00:11:20.480 --> 00:11:23.000 If you go to super salty places like the Great 243 00:11:23.000 --> 00:11:25.399 Salt Lake or certain salt flats, you can see these 244 00:11:25.480 --> 00:11:29.120 organisms called halo bacteria. They turn the water that shocking 245 00:11:29.240 --> 00:11:31.159 brilliant pink or purple color. 246 00:11:30.960 --> 00:11:32.799 So we can see what ancient Earth looked like today 247 00:11:32.840 --> 00:11:33.399 we can. 248 00:11:33.320 --> 00:11:35.759 And here's the number from the paper that just flings me. 249 00:11:36.679 --> 00:11:40.080 This purple Earth phase might have lasted for nearly one 250 00:11:40.080 --> 00:11:41.759 point five billion years. 251 00:11:42.159 --> 00:11:45.320 That's staggering. That's more than twice as long as complex 252 00:11:45.360 --> 00:11:46.559 animals have even existed. 253 00:11:46.879 --> 00:11:49.720 Exactly, for a huge percentage of the time that Earth 254 00:11:49.759 --> 00:11:52.639 has been alive, it was a purple planet. So now 255 00:11:52.720 --> 00:11:54.559 apply that to the telescope problem. 256 00:11:54.639 --> 00:11:58.279 Okay, So if HWO is scanning the galaxy and it 257 00:11:58.320 --> 00:11:59.960 finds a planet that happens to be in its own 258 00:12:00.000 --> 00:12:02.600 own purple phase, right now. 259 00:12:02.360 --> 00:12:03.320 What do we see. 260 00:12:03.519 --> 00:12:05.879 Well, if we don't have the right sensors, we see nothing. 261 00:12:06.000 --> 00:12:10.159 We see nothing. These purple bacteria, they're retinal pigments. They 262 00:12:10.200 --> 00:12:14.279 absorb light well into the infrared, so their spectral signature, 263 00:12:14.320 --> 00:12:18.120 their edge is different from chlorophylls. If we build a 264 00:12:18.120 --> 00:12:20.320 telescope that is only looking for the red edge of 265 00:12:20.440 --> 00:12:21.519 modern plants. 266 00:12:21.200 --> 00:12:22.720 We're wearing the wrong color glasses. 267 00:12:22.799 --> 00:12:24.720 You're wearing the wrong glasses. You would look at a 268 00:12:24.720 --> 00:12:29.759 world that is absolutely teeming with life, a thriving global biosphere, 269 00:12:30.120 --> 00:12:32.639 and your multi billion dollar instrument would tell you it's 270 00:12:32.639 --> 00:12:33.159 a dead rock. 271 00:12:33.519 --> 00:12:37.399 That is the ultimate nightmare scenario. We spend twenty years 272 00:12:37.440 --> 00:12:39.960 building this thing pointed at a second Earth and just 273 00:12:40.039 --> 00:12:41.639 completely fail to recognize it. 274 00:12:41.879 --> 00:12:45.519 That's the argument. The Living World's Working Group is basically screaming, 275 00:12:45.919 --> 00:12:48.879 you cannot design this machine just to find us today. 276 00:12:49.039 --> 00:12:51.519 You have to design it to find who we were yesterday. 277 00:12:52.080 --> 00:12:55.360 Because statistically, for any given planet, it might be more 278 00:12:55.519 --> 00:12:58.200 likely to be in its purple phase than its green phase. 279 00:12:58.240 --> 00:13:01.360 Okay, so we've got purple Earth. But the story doesn't 280 00:13:01.399 --> 00:13:04.519 just jump from purple to the green forest we see today. 281 00:13:04.840 --> 00:13:06.759 There was an intermediate step in the outline. 282 00:13:06.799 --> 00:13:11.240 There was a middle chapter, the green Ocean hypothesis. 283 00:13:11.039 --> 00:13:12.759 Where the oceans themselves turned green. 284 00:13:13.039 --> 00:13:17.639 Yes, this is a fascinating period geologically and biologically. We're 285 00:13:17.639 --> 00:13:20.279 talking about the rchae and eon. So maybe between four 286 00:13:20.279 --> 00:13:23.679 and two point five billion years ago, the world was different. 287 00:13:23.799 --> 00:13:25.440 The atmosphere had no oxygen. 288 00:13:25.559 --> 00:13:27.799 So what made the water green? Was it some kind 289 00:13:27.799 --> 00:13:28.720 of early algae? 290 00:13:29.000 --> 00:13:32.279 No? Not, At first, it was the rock the planet's geology. 291 00:13:32.440 --> 00:13:34.840 The oceans were full of dissolved iron that was being 292 00:13:34.879 --> 00:13:38.960 pumped out of hydrothermal events. On the seafloor, specifically. 293 00:13:38.320 --> 00:13:40.120 Ferric iron, and that colors the water. 294 00:13:40.480 --> 00:13:43.120 It does. Ferrisc iron in a solution is really good 295 00:13:43.159 --> 00:13:45.320 at absorbing light at the blue and red ends of 296 00:13:45.320 --> 00:13:48.440 the spectrum, but it doesn't absorb green light very well. 297 00:13:48.279 --> 00:13:51.399 So it reflects the green the ocean itself. Just the 298 00:13:51.440 --> 00:13:54.000 water and iron would have looked green, that. 299 00:13:54.080 --> 00:13:58.759 Kind of murky olive green probably, But then life adapts. 300 00:13:58.919 --> 00:14:03.039 Evolution is always an opportunist. You have these early cyanobacteria 301 00:14:03.080 --> 00:14:06.200 floating in the water. They need sunlight, but the water 302 00:14:06.240 --> 00:14:08.399 they're living in is filtering out all the good red 303 00:14:08.399 --> 00:14:09.679 and blue light, so. 304 00:14:09.600 --> 00:14:11.639 The only light that's making it down to them is 305 00:14:11.639 --> 00:14:14.919 the green light that the iron isn't absorbing the leftovers. 306 00:14:15.320 --> 00:14:17.840 So what do they do? They evolve a new tool. 307 00:14:18.120 --> 00:14:22.840 They develop special accessory pigments called phycobilins that are perfectly 308 00:14:22.879 --> 00:14:25.799 tuned to capture and use green light for photosynthesis. 309 00:14:26.159 --> 00:14:28.879 It's like they're tuning their antenna to the only radio 310 00:14:28.919 --> 00:14:29.600 station that's. 311 00:14:29.480 --> 00:14:32.840 Broadcasting perfect analogy, and so you get this layered effect. 312 00:14:32.879 --> 00:14:35.600 You have a geological green signal from the iron and 313 00:14:35.639 --> 00:14:38.639 then a biological green signal from the bacteria living in it. 314 00:14:38.720 --> 00:14:40.480 Now from the telescope's point of view, that's got to 315 00:14:40.519 --> 00:14:41.080 be confusing. 316 00:14:41.360 --> 00:14:43.840 It's extremely confusing because if you just look at the 317 00:14:43.879 --> 00:14:46.360 overall color, a bionet with a green ocean full of 318 00:14:46.399 --> 00:14:50.399 cyanobacteria looks very, very similar to a planet with continents 319 00:14:50.440 --> 00:14:51.840 covered in green forests. 320 00:14:52.159 --> 00:14:55.000 So if we saw that, would it even matter? I mean, 321 00:14:55.039 --> 00:14:57.480 green is green? Life is life? We pop the champagne, right, 322 00:14:57.720 --> 00:14:58.639 I mean yes and no. 323 00:14:58.919 --> 00:15:01.080 On the one hand, any row bust green signal is 324 00:15:01.120 --> 00:15:03.960 a huge deal, But scientifically we'd want to know what 325 00:15:03.960 --> 00:15:07.879 we're looking at. Is this a primitive oxygen poor world 326 00:15:08.320 --> 00:15:10.080 with simple bacteria or. 327 00:15:10.039 --> 00:15:13.759 Is it a mature, oxygen rich world with complex plants. 328 00:15:14.120 --> 00:15:18.360 Those are two fundamentally different stages of planetary evolution. Telling 329 00:15:18.360 --> 00:15:22.519 them apart requires incredibly high spectral resolution. You need to 330 00:15:22.559 --> 00:15:25.080 be able to see the subtle little bumps and wiggles 331 00:15:25.080 --> 00:15:29.440 in the spectrum that differentiate a phycobilin pigment from a 332 00:15:29.519 --> 00:15:30.559 chlorophyll pigment. 333 00:15:30.679 --> 00:15:32.759 So again it comes back to the quality of the instrument. 334 00:15:32.840 --> 00:15:35.279 Don't give us a blurry, low res camera exactly. 335 00:15:35.600 --> 00:15:39.039 But it gets even more complicated because sometimes a color 336 00:15:39.039 --> 00:15:42.240 that looks like life isn't life at all. Sometimes it's 337 00:15:42.279 --> 00:15:43.679 just a rock trying to fool you. 338 00:15:43.960 --> 00:15:46.279 This is the part that gives me anxiety. The mimics, 339 00:15:46.879 --> 00:15:47.960 the false positives. 340 00:15:48.360 --> 00:15:51.080 This is the core of the engineering argument in the paper. 341 00:15:51.360 --> 00:15:55.000 It's about being sure. We are so desperate to find life, 342 00:15:55.000 --> 00:15:58.320 there's a huge risk of confirmation bias. We want to believe. 343 00:15:59.000 --> 00:16:01.879 The universe, however, is full of minerals that can look 344 00:16:01.919 --> 00:16:03.840 an awful lot like biology. 345 00:16:03.960 --> 00:16:06.320 So let's go through the list of suspects. What's mimic 346 00:16:06.480 --> 00:16:07.080 number one? 347 00:16:07.200 --> 00:16:11.799 The most obvious one is iron oxide rust Mars. Mars 348 00:16:11.879 --> 00:16:13.960 is the poster child. It's the red planet because it's 349 00:16:13.960 --> 00:16:18.799 covered in rust. Spectrally, rust creates what's called a red slope. 350 00:16:18.879 --> 00:16:20.879 It just reflects more and more light as you go 351 00:16:20.960 --> 00:16:22.600 from green to red to infrared. 352 00:16:22.679 --> 00:16:25.519 And if you have a blurry instrument, a gentle slope 353 00:16:25.720 --> 00:16:27.720 can look a lot like a sharp edge. 354 00:16:27.840 --> 00:16:30.320 They can blur together. Think about looking at a ramp 355 00:16:30.440 --> 00:16:33.120 versus a single step from really far away. If your 356 00:16:33.200 --> 00:16:35.559 vision is bad, they can look the same. You could 357 00:16:35.600 --> 00:16:39.440 absolutely mistake a dead, rusty desert planet for a world 358 00:16:39.480 --> 00:16:40.399 covered in vegetation. 359 00:16:40.519 --> 00:16:41.960 So how do you tell them apart. 360 00:16:41.799 --> 00:16:43.720 You need high resolution. You need to be able to 361 00:16:43.720 --> 00:16:47.159 see the sharpness of the feature. Biology creates sharp, well 362 00:16:47.159 --> 00:16:51.399 defined edges. Geology is usually smoother, more sloped. You need 363 00:16:51.440 --> 00:16:52.919 an instrument that can tell the difference. 364 00:16:53.240 --> 00:16:55.600 Okay, so rust is a big one, but the paper 365 00:16:55.879 --> 00:17:00.879 mentioned another mineral that was much more exotic. Cinebar. 366 00:17:01.159 --> 00:17:05.000 Cinebar. Yeah, mercury sulfide. It's this brilliant red mineral, and 367 00:17:05.039 --> 00:17:05.680 it's mercury. 368 00:17:05.799 --> 00:17:07.279 It's incredibly toxic. 369 00:17:07.519 --> 00:17:09.240 You would not want to land on a planet made 370 00:17:09.240 --> 00:17:12.559 of cinebar. But here's the universe playing a cruel joke 371 00:17:12.640 --> 00:17:15.759 on us. Cinebar has a spectral feature. It has a 372 00:17:15.920 --> 00:17:19.240 very strong, very sharp reflective edge. 373 00:17:19.559 --> 00:17:20.200 It's like plants. 374 00:17:20.200 --> 00:17:24.480 Doo, just like plants, but there's one tiny critical difference. 375 00:17:24.880 --> 00:17:27.799 The vegetation red edge happens at a wavelength of about 376 00:17:27.839 --> 00:17:31.119 seven hundred animeters. Okay, the cinnabar edge happens at about 377 00:17:31.119 --> 00:17:32.160 six hundred animeters. 378 00:17:32.200 --> 00:17:34.200 That's one hundred animeters. That sounds like almost nothing. 379 00:17:34.279 --> 00:17:36.720 It is almost nothing. And if your telescope has low 380 00:17:36.799 --> 00:17:41.119 spectral resolution, if your pixels are too fat, then six 381 00:17:41.240 --> 00:17:43.960 hundred nanimeters and seven hundred animeters can fall into the 382 00:17:44.000 --> 00:17:46.680 same data bin, they blur together into one signal. 383 00:17:46.720 --> 00:17:49.119 So imagine the press conference. NASA gets up and says, 384 00:17:49.440 --> 00:17:52.400 we found it a planet with a clear biological edge. 385 00:17:52.400 --> 00:17:53.720 It's covered in red forests. 386 00:17:53.839 --> 00:17:55.880 And then ten years later a better instrument goes up 387 00:17:55.880 --> 00:17:59.880 and we realize, oh, whoops, it's actually a giant poison 388 00:18:00.119 --> 00:18:01.039 us mercury rock. 389 00:18:01.359 --> 00:18:02.440 That would be devastating. 390 00:18:02.519 --> 00:18:05.200 That is the nightmare. That is why they are fighting 391 00:18:05.240 --> 00:18:08.119 for this high resolution. They're saying, we have to be 392 00:18:08.160 --> 00:18:10.279 able to tell the difference between six hundred and seven 393 00:18:10.359 --> 00:18:13.759 hundred nanimeters with absolute certainty. We need to be able 394 00:18:13.759 --> 00:18:16.240 to distinguish a tree from a toxic rock. 395 00:18:16.960 --> 00:18:20.000 Wow. Okay, and there was one more mimic, right, sulfur 396 00:18:20.559 --> 00:18:21.480 elemental sulfur. 397 00:18:21.559 --> 00:18:24.000 Yeah, it has its own edge, but it's down around 398 00:18:24.000 --> 00:18:26.799 four hundred and fifty to five hundred nanometers. It's a 399 00:18:26.839 --> 00:18:29.119 little easier to spot because it's further away from the 400 00:18:29.200 --> 00:18:32.720 vegetation signal, but the principle is the same. A planet 401 00:18:32.759 --> 00:18:35.880