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 --> 00:00:25.239 slumber under the night sky. 7 00:00:26.920 --> 00:00:30.039 Okay, let's dive in. We're setting coordinates way out there today, 8 00:00:30.079 --> 00:00:33.880 folks past Jupiter, past Saturn, all the way out to 9 00:00:33.920 --> 00:00:34.600 the ice Giant. 10 00:00:35.000 --> 00:00:37.399 You're in this deep space. Yeah, and we're looking at 11 00:00:37.399 --> 00:00:40.240 one of its moons, aerial. There's some really fascinating new 12 00:00:40.240 --> 00:00:41.679 research out published in Chorus. 13 00:00:41.840 --> 00:00:45.359 Fascinating is almost an understatement. The main takeaway, the big 14 00:00:45.399 --> 00:00:49.799 headline here is that this research suggests Aerial, well, it 15 00:00:49.960 --> 00:00:52.000 used to have a massive ocean under. 16 00:00:51.840 --> 00:00:55.479 Its icy crust, a really massive one. We're talking potentially 17 00:00:56.640 --> 00:00:58.679 over one hundred miles deep. That's about one hundred and 18 00:00:58.719 --> 00:00:59.479 seventy kilometers. 19 00:00:59.439 --> 00:01:01.719 Okay, hold on, let's put that in perspective for everyone listening. 20 00:01:01.719 --> 00:01:04.040 One hundred and seventy kilometers deep. How does that stack 21 00:01:04.159 --> 00:01:06.560 up against say, Earth's oceans. 22 00:01:06.719 --> 00:01:09.799 Well, think about the Pacific Ocean. Its average depth is 23 00:01:09.840 --> 00:01:12.840 only about four kilometers maybe two point five miles, So 24 00:01:12.879 --> 00:01:16.159 this potential pasted ocean on Aerial it could have been 25 00:01:16.200 --> 00:01:19.599 something like forty times deeper on average than the. 26 00:01:19.519 --> 00:01:22.040 Pacific, twenty times on a moon. That's what much smaller 27 00:01:22.079 --> 00:01:24.040 than Earth. That's kind of mind bending. 28 00:01:24.040 --> 00:01:27.920 It absolutely is. We're picturing this relatively small, icy world 29 00:01:28.280 --> 00:01:30.400 way out in the cold, dark part of the Solar System, 30 00:01:30.400 --> 00:01:34.000 and it might have had this colossal hidden layer of 31 00:01:34.159 --> 00:01:36.799 liquid water. Yeah, it really makes you rethink. 32 00:01:36.519 --> 00:01:39.879 Thing, completely makes you rethink the potential for water and 33 00:01:39.920 --> 00:01:43.040 maybe even heat way out there. So Okay, the big 34 00:01:43.120 --> 00:01:47.879 question then is how how did scientists figure this out? 35 00:01:48.040 --> 00:01:50.680 Just by looking at the surface. What cleaves did they find? 36 00:01:50.920 --> 00:01:53.640 Yeah, that's the core of the research. Led by folks 37 00:01:53.680 --> 00:01:57.239 like Caleb Strom and Alex Patoff. They were basically doing 38 00:01:57.280 --> 00:01:59.040 geological detective work. 39 00:01:58.879 --> 00:02:01.439 Forensics on a planet terry scale exactly. 40 00:02:01.560 --> 00:02:05.120 They looked at Aerial's surface geology, which is pretty dramatic, 41 00:02:05.239 --> 00:02:07.760 that's a huge cracks and riches, and they tried to 42 00:02:07.760 --> 00:02:10.560 connect those features to what must have been going on 43 00:02:10.759 --> 00:02:13.960 inside the Moon and how it must have been orbiting Urinus. 44 00:02:13.639 --> 00:02:16.560 In the past, so reverse engineering the forces involved, that's 45 00:02:16.599 --> 00:02:17.000 the idea. 46 00:02:17.360 --> 00:02:19.240 What kind of stress would you need to break the 47 00:02:19.240 --> 00:02:21.759 Moon's crust in exactly the way we see it broken? 48 00:02:21.960 --> 00:02:24.560 All right, let's zoom in on aerial itself. Then the 49 00:02:24.599 --> 00:02:27.680 researchers called it pretty unique in terms of icy moons. 50 00:02:27.719 --> 00:02:29.120 What makes it stand out? Well? 51 00:02:29.159 --> 00:02:31.879 First off, its location and brightness. Is the brightest moon 52 00:02:31.919 --> 00:02:33.919 of Uranus and the second one out from the planet. 53 00:02:34.039 --> 00:02:36.759 It's the fourth largest, but still pretty modest in size. 54 00:02:36.919 --> 00:02:38.080 How modest are we? Talking? 55 00:02:38.319 --> 00:02:42.599 Only about seven hundred and twenty miles across eleven hundred 56 00:02:42.599 --> 00:02:45.120 and fifty nine kilometers give you a sense of that. 57 00:02:45.199 --> 00:02:49.159 It's roughly the driving distance from say, Tucson, Arizona, up 58 00:02:49.240 --> 00:02:52.240 to Salt Lake City, Utah. That's the entire width of 59 00:02:52.280 --> 00:02:52.599 the moon. 60 00:02:53.159 --> 00:02:56.560 Wow. Okay, so not huge, but clearly something dramatic happened 61 00:02:56.560 --> 00:02:59.960 on its surface. You mentioned this geological paradox. What's that about? 62 00:03:00.080 --> 00:03:04.240 It's this weird mix of really old and really young 63 00:03:04.240 --> 00:03:06.000 looking Kraine side by side. 64 00:03:06.000 --> 00:03:07.639 Old and young. How can you tell? 65 00:03:07.719 --> 00:03:10.240 The old parts are just covered in impact craters. Tells 66 00:03:10.240 --> 00:03:13.080 you that surface hasn't really changed much in maybe billions 67 00:03:13.120 --> 00:03:15.199 of years, it's just been sitting there getting hit. 68 00:03:15.360 --> 00:03:16.240 Okay, makes sense. 69 00:03:16.360 --> 00:03:19.080 But right next to those ancient battered areas you find 70 00:03:19.120 --> 00:03:23.919 these stretches of remarkably smooth terrain, and that smoothness suggests 71 00:03:23.919 --> 00:03:28.719 something wipe the slate clean relatively recently geologically. 72 00:03:28.120 --> 00:03:30.280 Speaking, like paving over the old roads. 73 00:03:30.639 --> 00:03:36.199 Kind of yeah. The prime suspect is cryovulcanism, icy eruptions 74 00:03:36.199 --> 00:03:39.759 from inside the moon that float out, froze, and smooths 75 00:03:39.759 --> 00:03:40.960 over the older crust. 76 00:03:41.199 --> 00:03:46.120 So internal heat, slushy ice, or water erupting that already 77 00:03:46.199 --> 00:03:48.560 hints at something interesting happening below it does. 78 00:03:49.280 --> 00:03:52.360 But even more compelling than the smooth plains were the 79 00:03:52.479 --> 00:03:56.199 giant cracks and faults, the sheer scale of the deformation. 80 00:03:56.479 --> 00:03:58.560 Right, you mentioned those, what kind of features are we 81 00:03:58.599 --> 00:03:59.120 talking about? 82 00:03:59.280 --> 00:04:03.759 Massive fraction, really long ridges, and these complex systems called grabins. 83 00:04:04.360 --> 00:04:06.919 A grabin is basically where a big block of the 84 00:04:07.000 --> 00:04:10.360 crust is just dropped down between two parallel faults. 85 00:04:10.159 --> 00:04:13.159 Like a valley formed by stretching and cracking exactly. 86 00:04:13.680 --> 00:04:15.800 And the key thing here, according to the paper, is 87 00:04:15.840 --> 00:04:18.959 the scale. These features on aerial are described as being 88 00:04:19.040 --> 00:04:22.399 at scales larger than almost anywhere else in the Solar. 89 00:04:22.120 --> 00:04:25.160 System late larger than almost anywhere. That's a huge statement, 90 00:04:25.279 --> 00:04:28.319 bigger than the cracks on Europa or the canyons on Mars. 91 00:04:28.519 --> 00:04:31.879 That's the claim. We're talking features that might stretch for hundreds, 92 00:04:31.879 --> 00:04:34.439 maybe over one thousand kilometers, and these seem to be 93 00:04:34.480 --> 00:04:37.560 part of a global pattern, suggesting the entire crust was 94 00:04:37.639 --> 00:04:38.680 under immense tension. 95 00:04:38.839 --> 00:04:41.079 Okay, if the cracks are that big, the forces must 96 00:04:41.120 --> 00:04:44.360 have been equally enormous. You don't get solar system scale 97 00:04:44.399 --> 00:04:48.839 cracks without solar system scale stress. Precisely, that's the fossil 98 00:04:48.839 --> 00:04:51.399 record we were talking about. To crack and drop sections 99 00:04:51.399 --> 00:04:54.879 of crust that large, the stress had to be intense, widespread, 100 00:04:54.920 --> 00:04:59.519 and probably prolonged. Points to two things working together, serious 101 00:04:59.600 --> 00:05:03.920 interurn heat softening things up, and really powerful external forces. 102 00:05:04.319 --> 00:05:09.040 And those external forces would be tides from Uranus. 103 00:05:09.240 --> 00:05:12.879 That's the prime candidate. Tidal forces, the gravitational push and 104 00:05:12.920 --> 00:05:16.560 pull from orbiting Uranus. This incredibly fractured landscape became the 105 00:05:16.600 --> 00:05:18.199 input data for their computer models. 106 00:05:18.399 --> 00:05:21.560 So they had the crime scene, these giant fractures. How 107 00:05:21.560 --> 00:05:23.680 do they use the models to find the culprit, the 108 00:05:23.720 --> 00:05:24.680 engine driving it all? 109 00:05:24.720 --> 00:05:27.360 Well, the first step was meticulously mapping the locations and 110 00:05:27.399 --> 00:05:30.519 orientations of all these major structures using the old Voyager 111 00:05:30.560 --> 00:05:32.600 two fly by images from back in the eighties. 112 00:05:32.759 --> 00:05:34.439 Right, our only close up looks so far. 113 00:05:34.680 --> 00:05:38.439 Yeah. Then they fed this map, this pattern of fractures 114 00:05:38.680 --> 00:05:42.240 into a computer program. This program was designed to simulate 115 00:05:42.319 --> 00:05:45.319 how an icy moon's crust would respond to different kinds 116 00:05:45.360 --> 00:05:47.839 of stress, specifically tidal stresses. 117 00:05:47.920 --> 00:05:50.720 Okay, let's break down tidal stress. We hear the term 118 00:05:50.720 --> 00:05:54.079 a lot with moons like Europa or Eo. How does 119 00:05:54.120 --> 00:05:54.480 it work? 120 00:05:54.519 --> 00:05:58.399 Basically, it's all about gravity changing depending on distance. When 121 00:05:58.399 --> 00:06:01.199 a moon orbits a big planet like Uranus, the side 122 00:06:01.240 --> 00:06:04.199 of the Moon closest to the planet gets pulled harder 123 00:06:04.240 --> 00:06:06.879 by gravity than the center of the moon does okay, 124 00:06:07.120 --> 00:06:09.439 and the center in turn gets pulled harder than the 125 00:06:09.439 --> 00:06:13.120 far side. So the overall effect is that the planet's 126 00:06:13.160 --> 00:06:14.920 gravity tries to stretch the Moon. 127 00:06:14.759 --> 00:06:18.360 Out, stretching it like along the line pointing towards Uranus exactly. 128 00:06:18.360 --> 00:06:20.560 And as the Moon moves in its orbit, maybe getting 129 00:06:20.560 --> 00:06:23.079 closer and farther away if the orbit isn't perfectly circular, 130 00:06:23.360 --> 00:06:25.920 the amount of stretching changes. The Moon gets squeezed and 131 00:06:26.079 --> 00:06:28.199 stretched squeezed in stretched. 132 00:06:27.839 --> 00:06:29.040 Ah like kneading dough. 133 00:06:29.199 --> 00:06:33.160 Almost yeah, Or imagine flexing a rubber ball. It constantly 134 00:06:33.240 --> 00:06:37.000 changes shape slightly. For a moon, it might bulge towards 135 00:06:37.040 --> 00:06:40.319 and away from the planet, relaxing back towards the sphere 136 00:06:40.319 --> 00:06:43.759 as it moves. That constant flexing is the tidal. 137 00:06:43.439 --> 00:06:47.240 Stress, and that flexing generates heat, right. 138 00:06:47.240 --> 00:06:52.079 Friction, That's the key. It's called tidal dissipation, where tidal heating, 139 00:06:52.680 --> 00:06:56.279 all that bending and flexing creates friction inside the moon, 140 00:06:56.680 --> 00:06:59.279 converting the energy of its orbit into internal heat. 141 00:06:59.360 --> 00:07:01.160 Like rubbing your hand ends together to warm them up, 142 00:07:01.160 --> 00:07:02.759 but on a planetary scale. 143 00:07:02.480 --> 00:07:05.040 Precisely you bend a paper clip back and forth, it 144 00:07:05.079 --> 00:07:09.839 gets warm eventually breaks a moon flexing under gravity, same principle, 145 00:07:09.959 --> 00:07:13.040 just over millions or billions of years, and that internal 146 00:07:13.040 --> 00:07:15.920 heat is what could potentially melt ice deep inside, creating 147 00:07:15.959 --> 00:07:16.399 an ocean. 148 00:07:16.680 --> 00:07:19.800 Got it. So the strength of this tidal heating, this 149 00:07:19.920 --> 00:07:22.040 flexing depends on the orbit. 150 00:07:21.959 --> 00:07:25.199 Crucially, Yes, and the most important factor dictating the strength 151 00:07:25.199 --> 00:07:27.879 of the tides is the shape of the orbit. Specifically, 152 00:07:27.920 --> 00:07:28.879 it's eccentricity. 153 00:07:28.959 --> 00:07:31.040 Eccentricity, Okay, what does that mean exactly. 154 00:07:31.279 --> 00:07:34.120 Eccentricity is just a measure of how much an orbit 155 00:07:34.160 --> 00:07:37.160 deviates from being a perfect circle. A perfect circle has 156 00:07:37.160 --> 00:07:41.600 an eccentricity of zero. The more elongated or oval shape 157 00:07:41.600 --> 00:07:42.279 the orbit. 158 00:07:42.160 --> 00:07:43.759 Is like a squashed circle. 159 00:07:43.839 --> 00:07:45.920 Yeah. The bigger the difference between its closest point to 160 00:07:45.959 --> 00:07:49.680 the planet and its farthest point, the higher the eccentricity value. 161 00:07:49.720 --> 00:07:51.319 And why does that matter for tidal stress? 162 00:07:51.720 --> 00:07:54.720 Because a higher eccentricity means a much bigger change in 163 00:07:54.720 --> 00:07:58.399 the gravitational pull the Moon experiences during each orbit. It 164 00:07:58.439 --> 00:08:00.680 gets stretched a lot more when it's closed and relaxes 165 00:08:00.680 --> 00:08:03.600 more when it's far. That bigger change in shape means 166 00:08:03.720 --> 00:08:07.639 much stronger flexing, more friction, and way more internal heat generated. 167 00:08:08.600 --> 00:08:12.120 Okay, so the modeling team basically asked how eccentric, how 168 00:08:12.160 --> 00:08:15.040 non circular did aerials orbit need to be in the 169 00:08:15.079 --> 00:08:18.480 past to generate enough tidal stress to create those gigantic 170 00:08:18.519 --> 00:08:20.560 fractures we see today exactly. 171 00:08:20.600 --> 00:08:23.839 They ran the models backwards essentially, and the answer they 172 00:08:23.839 --> 00:08:26.240 came up with was that aeriel needed a past orbital 173 00:08:26.279 --> 00:08:28.639 eccentricity of about zero point zero four. 174 00:08:28.879 --> 00:08:31.079 Zero point zero four Is that a lot? How does 175 00:08:31.079 --> 00:08:32.039 that compare it to its orbit. 176 00:08:32.120 --> 00:08:36.000 Now. Ah, here's where it gets really interesting. Ariel's current 177 00:08:36.039 --> 00:08:40.840 eccentricity is tiny, almost zero. That calculated past value of 178 00:08:40.879 --> 00:08:44.320 point zero four about forty times larger than its current value. 179 00:08:44.480 --> 00:08:48.240 Forty times. That's a massive difference. So its orbit used 180 00:08:48.279 --> 00:08:50.320 to be significantly more stretched. 181 00:08:49.960 --> 00:08:53.519 Out, significantly more effective at generating tides. Yes, even though 182 00:08:53.519 --> 00:08:55.919 in orbit with e eor a point zero four would 183 00:08:55.919 --> 00:08:58.879 still look pretty circular to the naked eye, the effect 184 00:08:58.960 --> 00:09:02.039 on tidal forces isn't linear. It ramps up much faster. 185 00:09:02.279 --> 00:09:05.080 Wait why isn't it linear? Why does a forty x 186 00:09:05.080 --> 00:09:07.960 increase in eccentricity cause way more than a forty x 187 00:09:08.000 --> 00:09:08.879 increase in stress. 188 00:09:09.159 --> 00:09:11.240 It comes down to the physics of how that energy 189 00:09:11.279 --> 00:09:14.159 turns into heat. The amount of tidal heating generated goes 190 00:09:14.240 --> 00:09:18.080 up much faster than the eccentricity itself. It's often related 191 00:09:18.120 --> 00:09:21.279 to the eccentricity squared or even higher powers depending on 192 00:09:21.279 --> 00:09:21.960 the specifics. 193 00:09:22.000 --> 00:09:25.159 Okay, so small changes in orbital shape can have these huge, 194 00:09:25.320 --> 00:09:27.120 outsized effects on the inside of the Moon. 195 00:09:27.440 --> 00:09:30.120 Massive effects. It means that this past orbit at point 196 00:09:30.279 --> 00:09:33.639 zero four eccentricity would have been incredibly efficient at churning 197 00:09:33.720 --> 00:09:37.159 up aerials interior, generating a ton of heat, enough heat 198 00:09:37.200 --> 00:09:39.559 potentially to melt a very deep layer of ice. 199 00:09:39.759 --> 00:09:42.080 That really puts it in perspective, especially when you compare 200 00:09:42.120 --> 00:09:45.600 it to a moon like Europa. Right, Jupiter's moon, Europa 201 00:09:45.679 --> 00:09:48.360 is kind of the poster child for tidal stress cracking 202 00:09:48.360 --> 00:09:51.679 its surface. It is Europa's surface is famously fractured by 203 00:09:51.720 --> 00:09:55.159 Jupiter's tides. But get this. The model suggests that for 204 00:09:55.200 --> 00:09:59.240 Aerial to get its specific massive fractures, its past orbit 205 00:09:59.320 --> 00:10:01.720 needed to be about four times more eccentric than Europe's 206 00:10:01.720 --> 00:10:04.600 current orbit. Four times more eccentric than Europa. Wow. 207 00:10:04.759 --> 00:10:08.240 Yeah, So if you think Europa looks beat up, aerials 208 00:10:08.320 --> 00:10:11.440 pass must have involved forces that were, in a sense, 209 00:10:11.600 --> 00:10:15.320 four times more intense than what Europa experiences today. It 210 00:10:15.360 --> 00:10:18.480 really drives home why the researchers described aerials features as 211 00:10:18.519 --> 00:10:21.200 being on a scale larger than almost anywhere else. The 212 00:10:21.240 --> 00:10:24.159 forces involved were just monumental. Okay, so we've got the 213 00:10:24.200 --> 00:10:29.240 cause this incredibly eccentric past orbit generating immense tidal stress 214 00:10:29.720 --> 00:10:32.200 way more than even Europa feels now. And we've got 215 00:10:32.240 --> 00:10:36.080 the effect these absolutely enormous fractures and grobins on the surface. 216 00:10:36.159 --> 00:10:39.919 Oh but why does that require an ocean. Why couldn't 217 00:10:39.919 --> 00:10:42.039 the moon just be solid ice all the way through 218 00:10:42.279 --> 00:10:44.600 and it just cracked under that incredible stress. 219 00:10:44.799 --> 00:10:46.840 Ah, that's the lynchpin of the argument. It comes down 220 00:10:46.840 --> 00:10:49.600 to how the ice shell breaks. The model showed something 221 00:10:49.639 --> 00:10:52.240 crucial about the style of fracturing. Okay, to get those 222 00:10:52.240 --> 00:10:56.039 specific features, these really long, parallel grobins where huge sections 223 00:10:56.039 --> 00:10:59.600 of crust drop down uniformly over vast distances, you need 224 00:10:59.600 --> 00:11:01.840 the outer ice shell to be able to flex significantly 225 00:11:01.960 --> 00:11:03.919 and globally in response to the stress. 226 00:11:04.000 --> 00:11:06.120 And a completely solid moon wouldn't do that. It would 227 00:11:06.159 --> 00:11:09.919 just shatter differently exactly if aerial was solid ice from 228 00:11:09.919 --> 00:11:12.639 surface to core, even if it got warm and a 229 00:11:12.639 --> 00:11:15.879 bit soft inside, it would still basically behave as a 230 00:11:15.879 --> 00:11:19.399 single rigid unit. When you subject a rigid body to 231 00:11:19.399 --> 00:11:22.759 those kinds of massive oscillating tidal forces, it tends to 232 00:11:22.759 --> 00:11:26.039 crack in a more brittle, maybe localized way. You wouldn't 233 00:11:26.039 --> 00:11:29.679 necessarily expect these huge, consistent, globe spanning fracture systems. 234 00:11:29.960 --> 00:11:33.039 So what does adding a liquid layer the ocean change? 235 00:11:33.039 --> 00:11:36.840 How does that allow for these specific giant gravens. 236 00:11:36.240 --> 00:11:39.559 The liquid water layer acts as a decoupling zone. Think 237 00:11:39.600 --> 00:11:41.519 of it like a layer of lubricant between the outer 238 00:11:41.639 --> 00:11:44.679 brittle ice shell and the solid rocky interior or. 239 00:11:44.639 --> 00:11:48.519 Core the moon decoupling, meaning the shell can move somewhat independently. 240 00:11:48.639 --> 00:11:51.879 Precisely because the ice shell is essentially floating on this 241 00:11:51.960 --> 00:11:55.639 liquid layer, it's not rigidly locked to the core. This 242 00:11:55.679 --> 00:11:59.159 allows the entire shell to flex, stretch, and relax much 243 00:11:59.240 --> 00:12:02.000 more easily in uniformly as a whole unit in response 244 00:12:02.039 --> 00:12:02.919 to those tidle poles. 245 00:12:02.960 --> 00:12:05.480 Ah I see, So the ocean allows the entire crust 246 00:12:05.480 --> 00:12:08.000 to participate in the flexing, leading to these large scale, 247 00:12:08.080 --> 00:12:09.919 consistent cracks when it finally breaks. 248 00:12:10.159 --> 00:12:13.799 That's the idea. Without that liquid layer providing the slipplane 249 00:12:14.039 --> 00:12:17.559 the decoupling, you likely wouldn't get the specific type and 250 00:12:17.639 --> 00:12:21.559 scale of features like the massive parallel gravins that dominate 251 00:12:21.600 --> 00:12:26.320 aerials observed terrain. The liquid layer facilitates that particular style 252 00:12:26.480 --> 00:12:27.600 of crustal failure. 253 00:12:27.840 --> 00:12:30.159 Okay, that makes a lot of sense. The ocean isn't 254 00:12:30.159 --> 00:12:33.000 just a consequence of the heat. Its presence is actually 255 00:12:33.039 --> 00:12:35.919 necessary to explain the way the surface broke. Yes, the 256 00:12:35.960 --> 00:12:39.120 researchers put it really well. In order to create those fractures, 257 00:12:39.200 --> 00:12:41.519 you have to have either a really thin ice shell 258 00:12:41.559 --> 00:12:44.440 on a really big ocean, or a higher eccentricity and 259 00:12:44.480 --> 00:12:47.039 a smaller ocean. So there's a trade off between how 260 00:12:47.080 --> 00:12:48.759 thick the ice is and how big the ocean is 261 00:12:49.080 --> 00:12:50.320 or how strong the tides were. 262 00:12:50.600 --> 00:12:53.720 Right, but the key point is, under the plausible conditions 263 00:12:53.759 --> 00:12:57.519 dictated by the past eccentricity, you need that liquid layer. 264 00:12:58.000 --> 00:13:00.480 The ocean is the non negotiable part of the equation 265 00:13:00.600 --> 00:13:02.440 to explain the geology. 266 00:13:01.960 --> 00:13:04.519 Which brings us back to that mind boggling depth one 267 00:13:04.559 --> 00:13:07.320 hundred and seventy kilometers. How did they land on that 268 00:13:07.360 --> 00:13:08.279 specific number? 269 00:13:08.440 --> 00:13:11.639 That figure represents the kind of ocean depth that would 270 00:13:11.639 --> 00:13:15.279 be compatible with the strongest plausible tidal stresses, the ones 271 00:13:15.320 --> 00:13:19.120 generated by that calculated past eccentricity of point zero four. 272 00:13:19.279 --> 00:13:22.039 So it's like the maximum possible ocean size given the 273 00:13:22.080 --> 00:13:23.000 forces involved. 274 00:13:23.159 --> 00:13:26.159 Essentially yes, given that level of intense tidle heating over 275 00:13:26.159 --> 00:13:29.559 a long period, the model suggests a significant fraction of 276 00:13:29.600 --> 00:13:33.639 Aerial's original water ice mantle could have melted, potentially creating 277 00:13:33.639 --> 00:13:36.519 an ocean that deep overlying the rocky core. 278 00:13:36.679 --> 00:13:39.600 It's still incredible that we can pieces together from fractures 279 00:13:39.600 --> 00:13:42.399 scene decades ago. But you mentioned a limitation the timing. 280 00:13:42.559 --> 00:13:44.559 Do we know when all this was happening? When did 281 00:13:44.600 --> 00:13:47.720 Ariel have the super eccentric orbit in this deep ocean. 282 00:13:47.919 --> 00:13:50.799 That's the big unknown right now and definitely a focus 283 00:13:50.799 --> 00:13:54.440 for future work. Orbital mechanics and moon systems are really complex. 284 00:13:54.600 --> 00:13:58.320 Moons interact, orbits evolve, Tidal forces themselves tend to make 285 00:13:58.399 --> 00:14:00.919 orbits more circular over very long, long time scales. 286 00:14:01.039 --> 00:14:04.519 So this highly eccentric phase was likely temporary, maybe billions 287 00:14:04.519 --> 00:14:05.080 of years ago. 288 00:14:05.360 --> 00:14:09.240 Probably likely happened earlier in the Solar system's history, but 289 00:14:09.320 --> 00:14:12.320 pinning down the exact timing is tough. What this study 290 00:14:12.360 --> 00:14:16.600 does is established the conditions required. It sets the physical boundaries, 291 00:14:16.600 --> 00:14:20.720 the eccentricity needed, the maximum ocean depth possible that any 292 00:14:20.759 --> 00:14:24.159 future model trying to trace Aerieal's history will have to match. 293 00:14:24.480 --> 00:14:25.720 It's a crucial baseline. 294 00:14:25.799 --> 00:14:28.320 Okay, let's broaden the view now. This research wasn't done 295 00:14:28.360 --> 00:14:30.559 in isolation, right, It's part of a larger look at 296 00:14:30.600 --> 00:14:31.720 the Uranian system. 297 00:14:31.759 --> 00:14:34.519 That's right. This is actually the second paper in a 298 00:14:34.600 --> 00:14:38.480 series from the same team. They previously published similar findings 299 00:14:38.679 --> 00:14:41.480 for another one of Uranus's inner moons, Miranda. 300 00:14:41.639 --> 00:14:43.799 Miranda, that's the one that looks like it was smashed 301 00:14:43.799 --> 00:14:46.759 apart and badly put back together, right, really bizarre surface. 302 00:14:46.840 --> 00:14:51.120 Yeah, Miranda's geology is famously chaotic, and the team's earlier 303 00:14:51.159 --> 00:14:53.600 work suggested that its weird features could also be explained 304 00:14:53.600 --> 00:14:56.600 by pass tidal heating driven by a period of high 305 00:14:56.679 --> 00:15:00.039 orbital eccentricity, likely also requiring a subsurface over. 306 00:15:00.879 --> 00:15:04.279 So the researchers are talking about potentially twin ocean worlds 307 00:15:04.399 --> 00:15:06.679 orbiting Urinus Aerial and Miranda. 308 00:15:06.840 --> 00:15:11.039 That's the tantalizing possibility they raise. It suggests that maybe 309 00:15:11.039 --> 00:15:15.279 the conditions for generating significant internal heat via tides weren't 310 00:15:15.360 --> 00:15:18.200 just a fluke for one moon, but perhaps a more 311 00:15:18.200 --> 00:15:21.639 common occurrence or a phase that multiple inner moons went 312 00:15:21.679 --> 00:15:23.320 through in the Uranian system. 313 00:15:23.600 --> 00:15:26.639 That really changes the picture of the Uranian system, doesn't it. 314 00:15:26.720 --> 00:15:29.399 We tend to think of it as just this cold, distant, 315 00:15:29.600 --> 00:15:32.799 relatively quiet place compared to Jupiter or Saturn. 316 00:15:32.840 --> 00:15:36.000 Absolutely, for a long time, Uranus and its moons seemed 317 00:15:36.080 --> 00:15:38.320 kind of dormant, just because they're so far from the 318 00:15:38.360 --> 00:15:42.679 Sun and the initial flyby didn't reveal obvious ongoing activity 319 00:15:42.720 --> 00:15:46.720 like Geyser's. But if Aerial and Miranda both potentially hosted 320 00:15:46.799 --> 00:15:50.399 deep liquid water oceans in their past driven by internal 321 00:15:50.440 --> 00:15:53.159 tidal heat, well, that paints a picture of a much 322 00:15:53.159 --> 00:15:56.320 more dynamic and geologically active system history than we assumed. 323 00:15:56.559 --> 00:15:59.399 It really underscores how important tidal heating is as an 324 00:15:59.480 --> 00:16:02.720 energy source, potentially everywhere in the outer Solar System, completely 325 00:16:02.720 --> 00:16:03.559 separate from sunlight. 326 00:16:03.679 --> 00:16:06.480 Definitely, it's a game changer for thinking about potentially habitable 327 00:16:06.600 --> 00:16:07.879 environments far from the star. 328 00:16:08.159 --> 00:16:12.759 But we're still working with pretty limited data here, aren't we. 329 00:16:13.120 --> 00:16:16.240 All of this is inferred from that single Voyager two 330 00:16:16.399 --> 00:16:18.240 flyby back in nineteen eighty six. 331 00:16:18.480 --> 00:16:21.799 That's the frustrating part. Yes, our only close up images 332 00:16:21.840 --> 00:16:24.960 are decades old, and because of the flyby trajectory and 333 00:16:25.000 --> 00:16:27.480 the way Uranus was tilted at the time, Voyager two 334 00:16:27.559 --> 00:16:30.200 only got good views of the southern hemispheres of these. 335 00:16:30.080 --> 00:16:31.919 Moons, so we've only seen half the picture. 336 00:16:32.159 --> 00:16:36.799 Literally, exactly as Tom Nordheim, one of the studies co authors, emphasized, 337 00:16:37.120 --> 00:16:39.519 we just haven't seen the northern halves of Aerial or 338 00:16:39.559 --> 00:16:42.519 Miranda up close. It's kind of amazing we can deduce 339 00:16:42.639 --> 00:16:44.960 this much from half a moon view decades ago. 340 00:16:45.240 --> 00:16:47.799 Does that limit how confident we can be in these 341 00:16:47.840 --> 00:16:48.600 ocean models. 342 00:16:48.679 --> 00:16:52.159 It certainly introduces uncertainty, but that's also where the predictive 343 00:16:52.200 --> 00:16:54.519 power of this modeling work becomes so valuable. 344 00:16:54.559 --> 00:16:56.200 Predictive power how so. 345 00:16:56.399 --> 00:16:58.840 Because the models aren't just explaining the features we have 346 00:16:58.960 --> 00:17:02.360 seen based on the physics of how the entire Moon 347 00:17:02.399 --> 00:17:05.759 should respond to those global tidal stresses. So the models 348 00:17:05.799 --> 00:17:09.599 actually make specific predictions about what kind of features like 349 00:17:09.680 --> 00:17:12.759 the orientation and location of major fractures and ridges, we 350 00:17:12.799 --> 00:17:16.119 should find on the unseen northern hemispheres if this whole 351 00:17:16.119 --> 00:17:17.200 scenario is correct. 352 00:17:17.359 --> 00:17:20.200 Ah, So it's like they've drawn a map for a 353 00:17:20.240 --> 00:17:23.880 future mission. If we're right, you should find giant cracks 354 00:17:23.960 --> 00:17:25.079 running this way up north. 355 00:17:25.200 --> 00:17:29.720 Precisely, they've provided testable hypotheses. They've essentially laid out the 356 00:17:29.880 --> 00:17:33.480 geological treasure map for a future orbitor or probe going 357 00:17:33.519 --> 00:17:35.960 back to Urinus. It makes the scientific case for a 358 00:17:36.000 --> 00:17:37.359 return mission much stronger. 359 00:17:37.680 --> 00:17:40.200 Yeah, you can see why they'd be pushing for it. Absolutely, 360 00:17:40.400 --> 00:17:44.519 the evidence is compelling. Potentially two ancient ocean worlds with 361 00:17:44.599 --> 00:17:48.559 specific predictions waiting to be verified. It really boils down 362 00:17:48.559 --> 00:17:51.559 to what the researchers themselves say. Ultimately, we just need 363 00:17:51.599 --> 00:17:54.880 to go back to the Urinus system and see for ourselves. Okay, 364 00:17:54.960 --> 00:17:56.960 let's try and pull this all together. We journeyed out 365 00:17:57.000 --> 00:18:01.000 to Ariel, this fairly small moon of Uranus. Its surface 366 00:18:01.039 --> 00:18:05.440 is covered in these absolutely enormous fractures and grabins, some 367 00:18:05.480 --> 00:18:08.799 of the biggest geological scars seen anywhere. 368 00:18:08.359 --> 00:18:10.599 Right evidence of massive past stress. 369 00:18:10.960 --> 00:18:13.559 The only way to generate that much stress, the model show, 370 00:18:13.880 --> 00:18:16.759 was through intense tidal forces from a past orbit that 371 00:18:16.880 --> 00:18:19.920 was way more eccentric, about forty times more than today, 372 00:18:20.000 --> 00:18:20.680 an orbit. 373 00:18:20.480 --> 00:18:23.759 Potentially four times more eccentric than even Europe's current one. 374 00:18:23.839 --> 00:18:27.359 And crucially, the way the crust broke forming those specific 375 00:18:27.440 --> 00:18:31.640 global features required the ice shell to be floating decoupled 376 00:18:31.640 --> 00:18:32.000 from the. 377 00:18:31.960 --> 00:18:34.440 Core, which means there had to be a liquid layer 378 00:18:34.480 --> 00:18:37.079 in between a subsurface ocean. 379 00:18:36.799 --> 00:18:39.519 A notion that under those extreme past conditions could have 380 00:18:39.559 --> 00:18:42.839 been over one hundred miles one hundred and seventy kilometers. 381 00:18:42.440 --> 00:18:44.440 Deep, just a staggering volume of water. 382 00:18:44.559 --> 00:18:47.480 And this isn't just aerial. Similar evidence points to its 383 00:18:47.480 --> 00:18:51.519 neighbor Miranda, potentially being a twin ocean world. It completely 384 00:18:51.599 --> 00:18:53.319 recasts the Uranian system. 385 00:18:53.400 --> 00:18:55.680 Yeah, it shifts review from seeing it as just cold 386 00:18:55.759 --> 00:18:59.279 endorment to a place that was likely once incredibly dynamic, 387 00:18:59.599 --> 00:19:02.480 wet and warm inside thanks to tidal energy. 388 00:19:02.960 --> 00:19:04.559 What stands out most to you from all this? 389 00:19:04.880 --> 00:19:07.640 For me, it's the sheer implication for water in the universe. 390 00:19:08.279 --> 00:19:11.920 If these relatively small moons orbiting a distant ice giant 391 00:19:12.359 --> 00:19:16.079 could generate enough internal heat to sustain oceans this massive, 392 00:19:17.160 --> 00:19:20.839 it just reinforces that the ingredients for potentially habitable environments 393 00:19:21.079 --> 00:19:24.160 liquid water and energy might be far more common out 394 00:19:24.160 --> 00:19:26.559 there than we used to think, even in the really cold, 395 00:19:26.640 --> 00:19:30.039 dark places. It definitely makes you wonder, and it leads 396 00:19:30.079 --> 00:19:32.960 to a final thought building on that idea of pass oceans. 397 00:19:33.759 --> 00:19:36.720 If Aerial and maybe Miranda really did have these deep 398 00:19:36.720 --> 00:19:40.480 oceans billions of years ago, how long could they have lasted? 399 00:19:40.519 --> 00:19:43.279 That's a billion dollar question, isn't it? How long can 400 00:19:43.359 --> 00:19:46.480 liquid water persist inside an icy moon once the period 401 00:19:46.519 --> 00:19:49.880