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 Astronomy 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 --> 00:00:23.800 slumber under the night sky. 7 00:00:27.000 --> 00:00:30.079 When you picture an asteroid, I can almost guarantee what's 8 00:00:30.079 --> 00:00:33.200 playing in your head right now. It's that iconic, totally 9 00:00:33.280 --> 00:00:35.479 chaotic chase scene from the Empire Strikes Back. 10 00:00:35.520 --> 00:00:38.920 Oh yeah, the Millennium Falcon, just darting through that densely 11 00:00:38.960 --> 00:00:42.240 packed field of tumbling space rock. 12 00:00:42.200 --> 00:00:45.600 Exactly just bouncing off each other, creating this impossible three 13 00:00:45.600 --> 00:00:48.960 dimensional maze. And I mean it's a thrilling visual for 14 00:00:49.039 --> 00:00:52.000 you as a viewer, but it is a complete. 15 00:00:51.719 --> 00:00:55.240 Just massive violation of arble mechanics. It's really a masterclass 16 00:00:55.280 --> 00:00:56.159 in terrible. 17 00:00:55.799 --> 00:00:59.240 Astrophysics, right because the reality of the main asteroid belt 18 00:00:59.399 --> 00:01:01.479 is well, it's profoundly lonelier than that. 19 00:01:02.280 --> 00:01:05.840 Vastly lonelier. The objects out there are separated by these 20 00:01:06.319 --> 00:01:10.079 just incomprehensible distances. I mean, if you were actually standing 21 00:01:10.079 --> 00:01:12.439 on an asteroid in the main belt, you would likely 22 00:01:12.480 --> 00:01:14.799 need a telescope just to see the next closest one. 23 00:01:15.079 --> 00:01:15.400 Wow. 24 00:01:15.560 --> 00:01:19.040 Yeah, it's a vast, mostly empty expanse. It is definitely 25 00:01:19.079 --> 00:01:20.959 not a cosmic pinball machine. 26 00:01:21.040 --> 00:01:23.079 And I think that emptiness sets us up for an 27 00:01:23.120 --> 00:01:26.760 even bigger misconception, you know, because we just assume that 28 00:01:26.840 --> 00:01:29.640 every single one of these sparsely distributed objects is well 29 00:01:29.799 --> 00:01:31.319 just a dusty. 30 00:01:31.040 --> 00:01:34.400 Gray rock, right, the standard floating rock assumption. 31 00:01:34.680 --> 00:01:39.359 Yeah, but today we're totally dismantling that Hollywood myth because 32 00:01:39.439 --> 00:01:41.760 out there in the dark, there is an object that 33 00:01:41.840 --> 00:01:45.879 completely defies that assumption. It isn't rock at all. We're 34 00:01:45.920 --> 00:01:48.319 talking about asteroid sixteen Psyche. 35 00:01:48.480 --> 00:01:49.519 Psyche is amazing. 36 00:01:50.280 --> 00:01:52.159 It's roughly the size of Massachusetts, right. 37 00:01:52.159 --> 00:01:55.519 Roughly, Yeah, the Massachusetts size, kind of lumpy potato shaped 38 00:01:55.519 --> 00:01:59.159 body that is comprised almost entirely of metal. 39 00:01:59.000 --> 00:02:01.400 Which is just wild to think about, just a giant 40 00:02:01.480 --> 00:02:02.680 metal potato. 41 00:02:02.280 --> 00:02:05.040 And space iron and nickel to be specific. And the 42 00:02:05.079 --> 00:02:07.959 working hypothesis in the planetary science community right now is 43 00:02:08.000 --> 00:02:11.719 that sixteenth Hyche isn't just some random clump of heavy 44 00:02:11.719 --> 00:02:14.400 metals that happened to stick together, Right, it's actually the 45 00:02:14.439 --> 00:02:19.199 exposed frozen core of a lost protoplanet, a world was 46 00:02:19.280 --> 00:02:22.439 violently stopped from forming during the very earliest days of 47 00:02:22.439 --> 00:02:23.199 the Solar System. 48 00:02:23.319 --> 00:02:26.639 So we are looking at a dead planet's heart basically. 49 00:02:26.520 --> 00:02:31.479 Essentially, Yes, And by looking at this massive impact basin 50 00:02:31.520 --> 00:02:36.479 on Psyche's north pole and running these incredibly complex computational 51 00:02:36.520 --> 00:02:40.560 simulations of how that specific crater formed, we can start 52 00:02:40.599 --> 00:02:44.199 to sort of reverse engineer the exact mechanics of the 53 00:02:44.240 --> 00:02:46.680 demolition derby that gave rise to the planets we have today. 54 00:02:46.719 --> 00:02:49.039 Okay, let's untack this, because if we think of the 55 00:02:49.080 --> 00:02:52.840 early Solar System as this chaotic construction site I'm trying 56 00:02:52.840 --> 00:02:55.879 to picture, is Psyche essentially leftover rebar? 57 00:02:56.280 --> 00:02:59.599 I like that leftover rebar is actually a highly accurate 58 00:02:59.639 --> 00:03:03.639 way to conceptualize the kinematics of the early Solar System. 59 00:03:03.439 --> 00:03:05.680 Because, I mean, we know that in a fully formed planet, 60 00:03:05.719 --> 00:03:09.240 the dense metals sink to the center to form a core, right, 61 00:03:09.560 --> 00:03:12.120 and then the lighter silicates float up to form the 62 00:03:12.159 --> 00:03:13.039 mantle in the crust. 63 00:03:13.159 --> 00:03:14.520 Exactly, that's differentiation. 64 00:03:14.759 --> 00:03:16.960 So for a planet's core to end up just floating 65 00:03:16.960 --> 00:03:19.719 completely naked in the vacuum of space. It had to 66 00:03:19.800 --> 00:03:22.280 have been entirely stripped of all those outer rocky layer. 67 00:03:22.400 --> 00:03:25.280 Yeah, totally stripped, because back then we didn't have these 68 00:03:25.319 --> 00:03:28.479 neat orderly planetary orbits the ease. Today we had a 69 00:03:28.520 --> 00:03:29.840 swirling accretion. 70 00:03:29.560 --> 00:03:32.120 Disk, just a mess of material. 71 00:03:31.879 --> 00:03:36.039 A total mess. Gravity pulled gas and dust into small 72 00:03:36.080 --> 00:03:40.159 clumps which collided to form planet tesimals. And as these 73 00:03:40.199 --> 00:03:44.400 planet casimals accreted mass, the kinetic energy of constant impacts 74 00:03:44.759 --> 00:03:48.240 combined with the decay of short lived radioactive isotopes like 75 00:03:48.280 --> 00:03:51.919 aluminum twenty six, it generated immense paternal heat. 76 00:03:51.879 --> 00:03:54.639 Right, and that heat is what triggers the differentiation you 77 00:03:54.719 --> 00:03:55.680 mentioned exactly. 78 00:03:55.719 --> 00:03:58.680 You get this global magma ocean phase. The iron and 79 00:03:58.759 --> 00:04:02.240 nickel physically separate from the silicates and sink down into 80 00:04:02.240 --> 00:04:03.560 the gravity well of the body. 81 00:04:03.599 --> 00:04:04.800 They just dropped to the center. 82 00:04:04.960 --> 00:04:08.599 Yes, the silicate metal partitioning. And the thing is Psyche 83 00:04:08.680 --> 00:04:11.840 was on that exact trajectory. It had differentiated. It had 84 00:04:11.879 --> 00:04:15.319 an iron core and a thick rocky mantle and a crust. 85 00:04:15.520 --> 00:04:17.439 It was on its way to being a real planet. 86 00:04:17.560 --> 00:04:21.639 It was, but the environment was defined by just catastrophic violence. 87 00:04:21.959 --> 00:04:25.480 The prevailing model suggests Psyche was subjected to a series 88 00:04:25.519 --> 00:04:28.120 of what we call hid and run collisions. 89 00:04:27.800 --> 00:04:30.199 Hit and run, like they didn't just smash together and merge. 90 00:04:30.439 --> 00:04:34.519 Not always, No, we're talking about other massive planetesimals, you know, 91 00:04:34.519 --> 00:04:37.560 perhaps hundreds of kilometers across, slamming into it at velocities 92 00:04:37.560 --> 00:04:39.240 of five to twenty kilometers per second. 93 00:04:39.480 --> 00:04:42.000 Oh my god, five to twenty kilometers a second. 94 00:04:42.120 --> 00:04:45.959 Yeah, And at those velocities, the kinetic energy transferred during 95 00:04:45.959 --> 00:04:49.879 the impact is well, it's staggering. It wouldn't just leave 96 00:04:49.879 --> 00:04:53.360 a crater, it would actually overcome the gravitational binding energy 97 00:04:53.600 --> 00:04:54.680 of the mantle itself. 98 00:04:54.759 --> 00:04:56.839 So it's hitting it so hard that the rock just 99 00:04:57.279 --> 00:04:58.399 it can't hold on anymore. 100 00:04:58.439 --> 00:05:01.240 The sheer physics of it are brutal. The shock waves 101 00:05:01.240 --> 00:05:04.160 from a collision of that magnitude, they travel through the body, 102 00:05:04.399 --> 00:05:07.519 compressing the material, and then they reflect back as rare 103 00:05:07.560 --> 00:05:08.319 faction waves. 104 00:05:08.399 --> 00:05:09.600 Where are faction waves? 105 00:05:09.720 --> 00:05:12.319 Yeah, tensile waves that literally tear the rock apart from 106 00:05:12.319 --> 00:05:16.120 the inside out. And if the impact angles oblique enough, 107 00:05:16.160 --> 00:05:19.000 like a grazing blow rather than a dead on center mass. 108 00:05:18.839 --> 00:05:21.720 Strike, it just takes the top right off exactly. 109 00:05:22.079 --> 00:05:25.279 The kinetic energy shears the outer rocky layers completely off 110 00:05:25.279 --> 00:05:30.199 the protoplanet, it accelerates that silicate debris well beyond escape velocity. 111 00:05:30.199 --> 00:05:33.800 Wow, so the rock just flies off into space forever. 112 00:05:33.959 --> 00:05:38.319 Right, But it leaves the much denser, highly cohesive iron 113 00:05:38.399 --> 00:05:41.199 core intact. And if you do this a few times, 114 00:05:41.639 --> 00:05:44.920 just strip away layer after layer, the crust and mantle 115 00:05:44.959 --> 00:05:48.839 are gone. You're left with this unyielding metallic core totally 116 00:05:48.879 --> 00:05:50.360 stripped of its protective layers. 117 00:05:50.759 --> 00:05:52.720 So looking at Psyche out there and the main belt 118 00:05:52.839 --> 00:05:55.079 is really like looking at a ghost. It's the skeletal 119 00:05:55.120 --> 00:05:57.560 remains of a world that could have been a neighbored 120 00:05:57.639 --> 00:06:00.519 Earth or Mars or Venus world. 121 00:06:00.600 --> 00:06:05.360 Yeah, but from a purely scientific standpoint, this planetary casualty 122 00:06:05.800 --> 00:06:08.519 is just a massive, massive opportunity. 123 00:06:07.920 --> 00:06:10.879 For us because it solves that fundamental limitation we have 124 00:06:11.000 --> 00:06:13.439 when we try to study the deep interior of our 125 00:06:13.480 --> 00:06:14.120 own planet. 126 00:06:14.279 --> 00:06:18.000 Yes, it's the ultimate irony of our discipline, honestly. I mean, 127 00:06:18.040 --> 00:06:20.720 we have rovers analyzing the isotopic composition of. 128 00:06:20.720 --> 00:06:23.079 Martian regolith right millions of miles away. 129 00:06:23.000 --> 00:06:26.399 Millions of miles away, but we are embarrassingly ignorant about 130 00:06:26.399 --> 00:06:29.000 the deep interior of the very sphere we are standing on. 131 00:06:29.240 --> 00:06:31.160 I mean, if you're wondering why we don't just drill 132 00:06:31.240 --> 00:06:33.079 down to find out what's the center of the earth, 133 00:06:33.319 --> 00:06:35.240 the math is incredibly. 134 00:06:34.720 --> 00:06:38.360 Humbling, extremely humbling. The distance from the surface to the 135 00:06:38.399 --> 00:06:41.839 center of the Earth is roughly six three hundred kilometers. 136 00:06:41.360 --> 00:06:44.279 Which is almost four thousand miles straight down. 137 00:06:44.079 --> 00:06:48.079 Straight down. Now compare that to the deepest artificial whole 138 00:06:48.199 --> 00:06:52.879 humanity has ever created, the Cola super deep borehole in Russia. 139 00:06:53.160 --> 00:06:54.399 Right, how deep did they get? 140 00:06:54.639 --> 00:06:58.560 They reached twelve point two six kilometers before the project 141 00:06:58.560 --> 00:06:59.319 had to be abandoned. 142 00:06:59.439 --> 00:07:02.480 Twelve point two six kilometers, So out of sixy three 143 00:07:02.560 --> 00:07:03.639 hundred we've gone. 144 00:07:03.680 --> 00:07:06.120 Twelve yep, which is roughly zer point two percent of 145 00:07:06.160 --> 00:07:06.600 the way down. 146 00:07:07.000 --> 00:07:09.000 I always think of the apple analogy. We live on 147 00:07:09.040 --> 00:07:11.120 the absolute thinnest part of the skin of the apple, 148 00:07:11.480 --> 00:07:14.240 and we've barely even managed to scratch that skin, let 149 00:07:14.279 --> 00:07:16.519 alone get anywhere near the seeds in the center. 150 00:07:16.600 --> 00:07:19.600 It's a perfect analogy. We haven't even pierced the crust entirely, 151 00:07:19.720 --> 00:07:21.920 let alone reached the mantle of the core. And the 152 00:07:21.959 --> 00:07:25.000 limitation isn't just a lack of engineering willpower. It's the 153 00:07:25.079 --> 00:07:27.480 geothermal gradient and the extreme pressure. 154 00:07:27.199 --> 00:07:29.879 Because it just gets hotter and heavier the deeper you go. 155 00:07:30.120 --> 00:07:33.120 Right, It's a matter of fundamental thermodynamics and material science. 156 00:07:34.160 --> 00:07:38.199 As you descend, the pressure increases to millions of atmospheres, 157 00:07:38.839 --> 00:07:41.639 and the temperature at the core mantle boundary, it's hot 158 00:07:41.759 --> 00:07:45.399 enough to melt literally any drill bit we could conceivably manufacture. 159 00:07:45.519 --> 00:07:47.920 It just turns to liquid instantly yea. 160 00:07:48.079 --> 00:07:50.560 And the rock down there it ceases to behave like 161 00:07:50.560 --> 00:07:54.160 a brittle solid. Altogether, it acts like a highly viscous, 162 00:07:54.199 --> 00:07:58.560 flowing plastic. We are functionally permanently locked out. 163 00:07:58.800 --> 00:08:01.160 So if we can't physically go down there, how do 164 00:08:01.199 --> 00:08:02.839 we know what's in our core at all? 165 00:08:03.040 --> 00:08:07.560 We have to rely on indirect measurements, specifically seismic tomography. 166 00:08:08.000 --> 00:08:11.040 We watch how pways and s ways from earthquakes propagate 167 00:08:11.319 --> 00:08:14.040 and how they refract and reflect through the Earth's internal 168 00:08:14.079 --> 00:08:14.720 layers like. 169 00:08:14.639 --> 00:08:16.360 An ultrasound for the planet. 170 00:08:16.120 --> 00:08:19.319 Exactly like an ultrasound. Yeah, but seismic data is essentially 171 00:08:19.360 --> 00:08:22.319 a blurry sonogram. We can see density changes like the 172 00:08:22.399 --> 00:08:24.399 Leman discontinuity. 173 00:08:23.639 --> 00:08:26.439 Which is the boundary that separates the liquid outer core 174 00:08:26.480 --> 00:08:27.879 from the solid inner core. 175 00:08:27.879 --> 00:08:31.720 Right spot on. We can see that boundary exists, but 176 00:08:31.759 --> 00:08:34.399 we can't sample the material. We can't put it in 177 00:08:34.480 --> 00:08:38.279 a mass spectrometer. We are just guessing based on how 178 00:08:38.399 --> 00:08:39.960 sound waves bend, which. 179 00:08:39.720 --> 00:08:43.159 Makes sixteen Psyche the ultimate proxy. I mean, if we 180 00:08:43.200 --> 00:08:45.200 can't go down into our own planet to see a core, 181 00:08:45.320 --> 00:08:47.960 we have to look up because the universe has conveniently 182 00:08:48.000 --> 00:08:50.799 cracked a planet open and left its core just sitting 183 00:08:50.879 --> 00:08:52.799 in the freezer space for us to look at. 184 00:08:52.879 --> 00:08:55.879 Yes, it's the only place in the entire Solar System 185 00:08:56.159 --> 00:08:59.279 where we can directly observe the engine room of a planet. 186 00:09:00.080 --> 00:09:04.200 And that is exactly why NASA launched the Psyche spacecraft 187 00:09:04.279 --> 00:09:05.519 in late twenty twenty. 188 00:09:05.279 --> 00:09:08.879 Three, just a mission dedicated entirely to flying alongside this 189 00:09:09.000 --> 00:09:11.120 asteroid to take direct measurements right. 190 00:09:11.000 --> 00:09:13.080 To finally get some ground truth data on what a 191 00:09:13.120 --> 00:09:15.320 planetary core actually looks like up close. 192 00:09:15.600 --> 00:09:18.200 But the wait time on orbital mechanics is just brutal. 193 00:09:18.200 --> 00:09:20.720 I mean, the probe won't arrive until August of twenty 194 00:09:20.759 --> 00:09:21.279 twenty nine. 195 00:09:21.360 --> 00:09:22.720 It takes a long time to get out there. 196 00:09:22.799 --> 00:09:25.519 So in the meantime, with the spacecraft still years away, 197 00:09:25.840 --> 00:09:29.240 planetary scientists aren't just twiddling their thumbs waiting for photos 198 00:09:29.240 --> 00:09:29.799 to download. 199 00:09:30.039 --> 00:09:33.919 Oh, definitely not. We already have some ground based telescope data, 200 00:09:34.120 --> 00:09:36.919 radar imaging, and light curve inversion. 201 00:09:36.519 --> 00:09:40.120 Models, and that gives us a fuzzy, low resolution shape 202 00:09:40.120 --> 00:09:41.320 model of the asteroid. 203 00:09:41.519 --> 00:09:44.919 Very fuzzy, but we can see it's that lumpy potato shape, 204 00:09:45.039 --> 00:09:47.360 and we can make out a massive impact basin near 205 00:09:47.360 --> 00:09:48.399 its north polar region. 206 00:09:48.559 --> 00:09:51.120 But trying to figure out the internal structure based on 207 00:09:51.399 --> 00:09:55.080 a blurry silhouette millions of miles away, that requires some 208 00:09:55.399 --> 00:09:57.879 intense computational forensics, right. 209 00:09:57.799 --> 00:10:00.559 Exactly, And this is where they reach and break through 210 00:10:00.559 --> 00:10:02.799 research led by Namia by All at the University of 211 00:10:02.799 --> 00:10:07.039 Arizona really comes into play. If we can't physically sample 212 00:10:07.039 --> 00:10:10.159 the asteroid yet, we have to use advanced hydrocodes to 213 00:10:10.200 --> 00:10:13.240 simulate the specific impact that created that North Pole crater. 214 00:10:13.360 --> 00:10:15.440 Okay, wait, what exactly is a hydrocode. 215 00:10:15.519 --> 00:10:19.200 Hydrocode is a highly specialized computational tool. It's used to 216 00:10:19.279 --> 00:10:23.080 model the behavior of continuous media under extreme conditions. 217 00:10:22.639 --> 00:10:24.600 Like a hypervelocity asteroid impact. 218 00:10:24.919 --> 00:10:27.559 Right, Because things don't behave normally when they hit each 219 00:10:27.600 --> 00:10:31.440 other at ten kilometers a second, solid rock and metals 220 00:10:31.440 --> 00:10:34.600 start acting almost like fluids, and you can't just model 221 00:10:34.600 --> 00:10:38.080 a generic sphere colliding with a flat surface. The geometry 222 00:10:38.080 --> 00:10:41.720 of the target dictates how the shockwave propagates. 223 00:10:41.279 --> 00:10:44.159 Because hitting a curved ridge line on a potato shaped 224 00:10:44.200 --> 00:10:47.440 asteroid is going to yield a completely different crater geometry 225 00:10:47.519 --> 00:10:48.759 than hitting a flat plane. 226 00:10:48.799 --> 00:10:53.600 Precisely so, Byell's team had to painstakingly program in Psyche's lumpy, 227 00:10:53.639 --> 00:10:56.000 irregular shape into the simulation. 228 00:10:56.639 --> 00:10:59.799 Wow, And they also had to test different internal structures, right, 229 00:11:00.039 --> 00:11:02.480 since we don't know the exact composition beneath the surface. 230 00:11:02.600 --> 00:11:05.840 Yes, they ran simulations with two very different internal models. 231 00:11:06.320 --> 00:11:09.399 First a homogeneous model, which assumes Psyche is just a solid, 232 00:11:09.480 --> 00:11:12.480 uniform block of iron nickel alloy all the way from 233 00:11:12.519 --> 00:11:13.759 the surface to the center. 234 00:11:13.600 --> 00:11:14.919 Like a giant cannon ball. 235 00:11:15.000 --> 00:11:15.159 Right. 236 00:11:15.679 --> 00:11:18.039 And then they also ran a layered model, testing the 237 00:11:18.080 --> 00:11:21.440 hypothesis that maybe the core still retains a thin outer 238 00:11:21.600 --> 00:11:23.399 shell of different material. 239 00:11:23.120 --> 00:11:26.159 Like maybe some heavily shocked silicates or volcanic rock that 240 00:11:26.279 --> 00:11:28.960 somehow survived those ancient hit and run collisions. 241 00:11:29.360 --> 00:11:33.519 Exactly when they run these simulations, literally firing virtual projectiles 242 00:11:33.519 --> 00:11:37.399 at virtual metal potatoes in a supercomputer. They are analyzing 243 00:11:37.440 --> 00:11:41.840 the resulting creter morphology, and specifically, they are looking at 244 00:11:41.840 --> 00:11:44.360 a metric known as the depth diameter ratio. 245 00:11:44.440 --> 00:11:47.120 The depth diameter ratio eye. So, just to visualize this, 246 00:11:47.200 --> 00:11:50.440 if I drop a heavy steel ball bearing into a 247 00:11:50.480 --> 00:11:53.919 bowl of loose flour, the flower yields really easily, right, 248 00:11:53.919 --> 00:11:56.440 and I get a deep, relatively narrow crater. Yes, But 249 00:11:56.480 --> 00:11:58.879 if I drop that same ball bearing into a dense 250 00:11:58.879 --> 00:12:03.000 block of wet clay, the clay resists the kinetic energy differently, 251 00:12:03.360 --> 00:12:05.679 resulting in a wider or much shallower crater. 252 00:12:05.919 --> 00:12:07.960 That's a great way to think about it. The physical 253 00:12:08.000 --> 00:12:11.519 properties of the target material, its density, it's yield strength, 254 00:12:11.519 --> 00:12:14.679 it's equation of state. Those dictate the final geometry of 255 00:12:14.679 --> 00:12:16.840 the crater, how deep it is compared to how wide 256 00:12:16.840 --> 00:12:17.120 it is. 257 00:12:17.240 --> 00:12:18.600 It's like a cosmic fingerprint. 258 00:12:18.799 --> 00:12:21.519 It really is. By altering the internal structure in the 259 00:12:21.600 --> 00:12:25.240 hydrocode and measuring the resulting depth diameter ratio of the 260 00:12:25.320 --> 00:12:30.240 virtual crater, Bisel's team is reverse engineering a multi billion 261 00:12:30.320 --> 00:12:34.440 year old impact. They are hunting for the simulated interior 262 00:12:34.480 --> 00:12:38.159 that produces a crater that perfectly matches the dim blurry 263 00:12:38.159 --> 00:12:40.200 depression we can currently observe from Earth. 264 00:12:40.399 --> 00:12:44.279 That is so clever. But in running these models, here's 265 00:12:44.279 --> 00:12:47.799 where it gets really interesting. They isolated a hidden variable 266 00:12:47.919 --> 00:12:51.879 that completely upends how we assume a solid metal asteroid 267 00:12:51.960 --> 00:12:52.600 should behave. 268 00:12:53.039 --> 00:12:54.279 Yes, porosity. 269 00:12:54.360 --> 00:12:57.120 They found that porosity is actually the driving factor in 270 00:12:57.159 --> 00:12:58.799 crater formation on Psyche. 271 00:12:58.879 --> 00:13:03.120 Macro porosity specif the amount of empty space, deep voids 272 00:13:03.159 --> 00:13:05.480 and internal fracturing inside the asteroid. 273 00:13:05.600 --> 00:13:08.360 But wait, if Psyche is a metallic core that formed 274 00:13:08.440 --> 00:13:10.919 under immense pressure at the center of a proto planet, 275 00:13:11.240 --> 00:13:14.240 its initial state would be incredibly dense, right, like virtually 276 00:13:14.360 --> 00:13:15.240 zero porosity. 277 00:13:15.360 --> 00:13:16.320 It would have been pristine. 278 00:13:16.399 --> 00:13:19.080 Yes, So why would a giant chunk of iron and 279 00:13:19.200 --> 00:13:21.679 nickel floating in space be porous? I mean, a solid 280 00:13:21.679 --> 00:13:23.679 block of steel doesn't avoids in it, It's solid. 281 00:13:23.919 --> 00:13:27.399 The initial core was undoubtedly dense, But you have to 282 00:13:27.440 --> 00:13:31.799 remember the apocalyptic violence of Psyche's history. When you slam 283 00:13:32.039 --> 00:13:35.080 massive planet tesimols into it at ten kilometers per second, 284 00:13:35.519 --> 00:13:37.799 the kinetic energy doesn't just vaporize the crust and. 285 00:13:37.799 --> 00:13:39.759 Stop there, right, The energy has to go somewhere. 286 00:13:39.799 --> 00:13:43.639 The shockwaves travel deep into the metallic core. Now, the 287 00:13:43.679 --> 00:13:47.960 metal is incredibly strong, obviously, but it isn't invincible. These 288 00:13:48.000 --> 00:13:52.120 impacts can actually exceed what's called the hugoniot elastic limit 289 00:13:52.240 --> 00:13:53.120 of the iron alloy. 290 00:13:53.279 --> 00:13:56.600 The hugonia elastic limit, meaning it hits it so hard 291 00:13:56.720 --> 00:13:59.320 it permanently deforms or breaks the metal. 292 00:13:59.080 --> 00:14:02.919 Brutally fractures it. It creates massive internal fault lines. The 293 00:14:02.960 --> 00:14:06.240 metal is shattered into a tightly packed rubble pile, essentially 294 00:14:06.559 --> 00:14:08.720 held together only by its own weak gravity. 295 00:14:08.840 --> 00:14:11.120 Okay, so it's less like a pristine bowling ball of 296 00:14:11.159 --> 00:14:13.879 steel and more like, I don't know, a heavily fractured 297 00:14:13.919 --> 00:14:16.399 medieval shield that's just taken way too many hits. 298 00:14:16.600 --> 00:14:19.080 That's yeah, exactly. It holds its macro shape. It looks 299 00:14:19.120 --> 00:14:23.000 solid from the outside, but internally there are vast networks 300 00:14:23.000 --> 00:14:25.320 of cracks and gaps. It's a metallic sponge. 301 00:14:25.440 --> 00:14:30.759 A metallic sponge. Wow. And that internal empty space completely 302 00:14:30.840 --> 00:14:34.879 changes how the material absorbs the kinetic energy of a 303 00:14:34.919 --> 00:14:35.600 new impact. 304 00:14:35.759 --> 00:14:39.200 It changes the energy partitioning entirely, because think about it, 305 00:14:39.240 --> 00:14:42.559 If you strike a solid block of dense steel, the 306 00:14:42.679 --> 00:14:45.960 energy of the blow is transmitted almost perfectly through the 307 00:14:45.960 --> 00:14:49.279 material as an elastic wave. It just rings through it, right, 308 00:14:49.320 --> 00:14:51.919 and much of that energy goes into excavating the crater 309 00:14:52.519 --> 00:14:53.639 throwing material outwork. 310 00:14:53.759 --> 00:14:56.759 Okay, But if the target is highly porous, like our 311 00:14:56.879 --> 00:14:58.279 metallic sponge, then. 312 00:14:58.200 --> 00:15:01.159 The energy does what we call pdvwork pressure volume work. 313 00:15:01.679 --> 00:15:05.480 The shockwave energy is literally consumed by physically crushing the 314 00:15:05.519 --> 00:15:08.519 voids and compressing the material inward on itself. 315 00:15:08.120 --> 00:15:09.600 So the empty space collapses. 316 00:15:09.639 --> 00:15:10.799 It collapses, and that. 317 00:15:10.720 --> 00:15:13.720 Compression that generates intense localized heat. 318 00:15:14.000 --> 00:15:16.639 Massive heat. So instead of just blasting material away and 319 00:15:16.679 --> 00:15:20.440 excavating a deep hole, a highly porous Psyche would crush inward, 320 00:15:20.799 --> 00:15:24.879 absorbing the blow locally, which fundamentally alters that depth diamber 321 00:15:24.960 --> 00:15:26.279 ratio of the crater. We see. 322 00:15:26.320 --> 00:15:29.480 It's like hitting a crumple zone in a car, exactly. 323 00:15:29.080 --> 00:15:32.120 Like a crumple zone. And this leads to a fascinating 324 00:15:32.159 --> 00:15:36.399 paradox regarding the fate of the impactor itself. You know, 325 00:15:36.440 --> 00:15:40.000 the alien rock that actually crashed into Psyche's north pole 326 00:15:40.080 --> 00:15:41.000 to make the crater. 327 00:15:41.039 --> 00:15:42.519 Right, what happens to the bullet? 328 00:15:42.679 --> 00:15:47.919 Well, the hydrocode simulations revealed something totally counterintuitive. A stronger, 329 00:15:48.120 --> 00:15:52.399 more solid, low porosity interior actually preserves large amounts of 330 00:15:52.440 --> 00:15:56.879 the impactor really, yes, while a weaker, highly porous interior 331 00:15:57.240 --> 00:16:01.759 results in the impact or vaporizing or shattering into microscopic fragments. 332 00:16:01.799 --> 00:16:04.279 But if the target is highly porous and crushes inward, 333 00:16:04.320 --> 00:16:07.039 wouldn't that like trap the heat of the impact. It 334 00:16:07.039 --> 00:16:09.480 sounds like the impactor would just be cooked inside the 335 00:16:09.519 --> 00:16:11.159 crater rather than bouncing off. 336 00:16:11.200 --> 00:16:14.840 That is exactly the thermodynamic mechanism at play. The crushing 337 00:16:14.879 --> 00:16:17.679 action acts as an energy trap. The extreme heat and 338 00:16:17.759 --> 00:16:21.000 pressure are localized right at the point of contact, enveloping 339 00:16:21.000 --> 00:16:23.399 the impactor in the zone of extreme violence, so. 340 00:16:23.399 --> 00:16:24.080 It just melts. 341 00:16:24.720 --> 00:16:27.559 The temperature spikes so rapidly that the impact is subjected 342 00:16:27.559 --> 00:16:31.320 to shock melting or outright vaporization. But if the target 343 00:16:31.360 --> 00:16:35.159 is solid, dense metal, it cannot easily crush inward. 344 00:16:35.120 --> 00:16:38.200 Right there are no voids to collapse, so the energy 345 00:16:38.279 --> 00:16:43.200 propagates outward in a massive shock wave, violently excavating the crater. 346 00:16:43.840 --> 00:16:47.360 The impactor is heavily fragmented, sure, but larger chunks of 347 00:16:47.360 --> 00:16:50.879 it can actually survive the initial contact and become embedded 348 00:16:50.919 --> 00:16:53.639 in the solid metal floor of the crater because that 349 00:16:53.720 --> 00:16:55.720 localized thermal trap never formed. 350 00:16:56.000 --> 00:16:56.559 Wow. 351 00:16:56.879 --> 00:17:00.440 So when the Psyche spacecraft finally arrives in twenty twenty nine. 352 00:17:00.639 --> 00:17:02.679 Its instrument payload is going to be hunting for those 353 00:17:02.720 --> 00:17:03.720 exact fragments. 354 00:17:04.079 --> 00:17:07.920 Yes, the probe is carrying a gamma ray and neutron spectrometer, 355 00:17:08.359 --> 00:17:10.160 the GRNs. 356 00:17:09.640 --> 00:17:11.759 Right, And the GRNs is a vital piece of this 357 00:17:11.839 --> 00:17:15.359 puzzle because it detects the energy signatures of cosmic rays 358 00:17:15.400 --> 00:17:17.160 interacting with the asteroid surface. 359 00:17:17.359 --> 00:17:20.640 Correct Different elements emit different spectraa of gamma rays and 360 00:17:20.720 --> 00:17:22.720 neutrons when struck by cosmic rays. 361 00:17:22.839 --> 00:17:25.759 So by mapping those elemental signatures, the probe will be 362 00:17:25.799 --> 00:17:28.920 able to see if there are high concentrations of exogenous 363 00:17:28.920 --> 00:17:31.480 silicates basically alien rock, sitting in the bottom of that 364 00:17:31.640 --> 00:17:33.240 North Pole crater exactly. 365 00:17:33.279 --> 00:17:36.559 And if the spectrometer detects large chunks of rocky material 366 00:17:36.720 --> 00:17:38.599 embedded in the metal, it tells. 367 00:17:38.440 --> 00:17:41.279 Us that Psyche's interior is dense and solid. 368 00:17:41.640 --> 00:17:45.920 Yes, But if it finds very little rocky material, it 369 00:17:45.960 --> 00:17:49.599 tells us Psyche is a heavily fractured porous sponge that 370 00:17:49.720 --> 00:17:51.000 vaporized its attacker. 371 00:17:51.200 --> 00:17:54.839 It's literally planetary forensics via orbital spectrometry. 372 00:17:54.920 --> 00:17:58.559 It's beautiful science, and the hypotheses generated by Bazal's three 373 00:17:58.640 --> 00:18:02.079 D models are essential here because they calibrate the instruments 374 00:18:02.079 --> 00:18:04.799 on the spacecraft. We aren't flying blind and we get 375 00:18:04.799 --> 00:18:07.680 there in twenty twenty nine. The hydrocods tell us exactly 376 00:18:07.720 --> 00:18:10.640 what elemental signatures and creater morphology is to look for 377 00:18:10.799 --> 00:18:11.839 to answer these questions. 378 00:18:12.039 --> 00:18:14.680 I mean, just studying the microscopic thermal dynamics of a 379 00:18:14.680 --> 00:18:17.400 crater on a dead metal potato is an incredible display 380 00:18:17.440 --> 00:18:19.720 of physics on its own, it really is. But you know, 381 00:18:19.799 --> 00:18:23.400 as we zoom out, the implications of understanding psyche stretch far, 382 00:18:23.599 --> 00:18:25.720 far beyond just the main asteroid belt. 383 00:18:25.759 --> 00:18:26.440 Oh definitely. 384 00:18:27.039 --> 00:18:29.079 So what does this all mean for us? Because this 385 00:18:29.200 --> 00:18:31.480 data actually scales up to one of the most significant 386 00:18:31.559 --> 00:18:36.079 questions in modern astrophysics, right, the search for habitable exoplanets. 387 00:18:36.160 --> 00:18:38.640 It does, and to understand that connection we have to 388 00:18:38.640 --> 00:18:40.279 look at planetary geodynamos. 389 00:18:40.279 --> 00:18:43.319 Geodynamos the engines inside a planet. 390 00:18:43.680 --> 00:18:47.039 Right, Planetary cores are not static lumps of metal deep 391 00:18:47.079 --> 00:18:49.799 inside the Earth. The iron core is partitioned into a 392 00:18:49.839 --> 00:18:52.279 solid inner core and a liquid outer core. 393 00:18:52.200 --> 00:18:55.200 And the immense heat radiating from that inner core, combined 394 00:18:55.240 --> 00:18:58.640 with the Coriolis force from the Earth spinning creates these 395 00:18:58.759 --> 00:19:02.960 massive twisting convection currents in the liquid metal. 396 00:19:03.079 --> 00:19:07.319 Yes, magneto hydrodynamics, because the liquid metal is a conductor, 397 00:19:07.559 --> 00:19:11.799 that turbulent churning motion generates a massive electromagnetic field that 398 00:19:11.880 --> 00:19:14.359 extends far out into space around our planet. 399 00:19:14.440 --> 00:19:17.880 And that magnetic field is the absolute prerequisite for habitability 400 00:19:17.920 --> 00:19:19.079 on the surface, isn't it. 401 00:19:18.960 --> 00:19:23.200