WEBVTT 1 00:00:03.439 --> 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 --> 00:00:23.800 slumber under the night sky. 7 00:00:26.879 --> 00:00:28.800 I want you to just take a second and picture 8 00:00:28.879 --> 00:00:29.879 volcanic magma. 9 00:00:30.039 --> 00:00:32.439 Oh yeah, the classic mental image right. 10 00:00:32.359 --> 00:00:36.000 Like you probably immediately think of this thick, glowing red, 11 00:00:36.200 --> 00:00:38.000 slowly creeping lava. 12 00:00:37.880 --> 00:00:41.520 Like something you'd see in Hawaii or Iceland exactly. 13 00:00:41.560 --> 00:00:44.799 And that image, that whole process is totally driven by 14 00:00:44.799 --> 00:00:48.079 the familiar elements we have right here on Earth, you know, 15 00:00:48.479 --> 00:00:49.679 mainly oxygen and iron. 16 00:00:49.799 --> 00:00:51.240 Yeah, those are the big players for us. 17 00:00:51.479 --> 00:00:56.679 But we need to completely shatter that mental image right 18 00:00:56.719 --> 00:00:58.560 out of the gate today. Oh, absolutely, throw it right 19 00:00:58.560 --> 00:01:02.280 out the window, because we are heading to Mercury. It's 20 00:01:02.320 --> 00:01:05.680 the smallest, innermost planet in our Solar system, but it 21 00:01:05.719 --> 00:01:08.840 is hiding this massive, fundamentally alien secret. 22 00:01:09.040 --> 00:01:11.159 It really is. It's just a totally different world. 23 00:01:11.319 --> 00:01:14.120 Yeah, on Mercury, the familiar rules of geology, all that 24 00:01:14.200 --> 00:01:17.200 oxygen and iron stuff, it's just it's gone. It's replaced 25 00:01:17.239 --> 00:01:20.760 by a chemical reality that is so bizarre it forces 26 00:01:20.840 --> 00:01:24.120 us to basically rethink how planets are even born. 27 00:01:24.239 --> 00:01:27.400 It's wild. It completely flips our understanding of planetary evolution. 28 00:01:27.760 --> 00:01:30.040 So that's our mission for you today. We are going 29 00:01:30.040 --> 00:01:33.560 to journey far away from this comfortable Earth centric view 30 00:01:33.599 --> 00:01:37.239 of planetary science, and we're dropping into a world where 31 00:01:37.239 --> 00:01:41.079 a totally different element, sulfur just reigns supreme. 32 00:01:41.319 --> 00:01:43.680 Lfer is the king on Mercury, right, and. 33 00:01:43.719 --> 00:01:46.920 Our goal is to understand how this one single element 34 00:01:47.079 --> 00:01:51.519 completely rewrites Mercury's history. It creates a crust and a 35 00:01:51.599 --> 00:01:55.560 geologic timeline that looks honestly nothing like. 36 00:01:55.519 --> 00:01:57.079 Our own, not even close to our own. 37 00:01:57.400 --> 00:01:59.359 And it's so easy, right, It's so easy to just 38 00:01:59.400 --> 00:02:02.400 assume all rocky planets are basically variations of Earth, like 39 00:02:02.599 --> 00:02:04.799 Mars is a cold Earth, Venus is a hotter Earth. 40 00:02:04.879 --> 00:02:08.000 Yeah, it's the single biggest trap in planetary science, honestly. 41 00:02:07.680 --> 00:02:09.159 I mean, it makes sense why we do it, of 42 00:02:09.159 --> 00:02:09.759 course it does. 43 00:02:09.960 --> 00:02:13.560 We live here. We have naturally built our entire understanding 44 00:02:13.599 --> 00:02:18.639 of you know, planetary accretion, mantle convection, crust formation, all 45 00:02:18.680 --> 00:02:23.000 of it. The chemistry of Earth, Mars, and well Venus, 46 00:02:23.240 --> 00:02:25.840 because that's what we can see and measure easily exactly. 47 00:02:26.159 --> 00:02:28.680 And in those systems, the oxygen and fugacity, which is 48 00:02:28.680 --> 00:02:31.319 basically just the availability and the chemical activity of oxygen. 49 00:02:31.319 --> 00:02:34.199 When the planet was forming, that was relatively high. 50 00:02:34.000 --> 00:02:36.400 So there's plenty of oxygen to go around. 51 00:02:36.360 --> 00:02:40.000 Tons of it. Oxygen totally dominates the chemical structure on Earth. 52 00:02:40.479 --> 00:02:43.719 It dictates which elements bond together, it decides at what 53 00:02:43.800 --> 00:02:47.800 temperature rocks melt, and really importantly, how a planet loses 54 00:02:47.840 --> 00:02:50.120 its internal heat over bions of years. 55 00:02:50.840 --> 00:02:52.879 But mercury is playing a different game. 56 00:02:52.960 --> 00:02:56.199 A completely different game. It formed under entirely different initial 57 00:02:56.240 --> 00:02:59.759 conditions in the Solar nebula. The rules that govern how 58 00:02:59.759 --> 00:03:03.919 magma evolves on Earth, they just fail, They literally fail 59 00:03:04.039 --> 00:03:05.840 when you apply them to mercury. 60 00:03:05.439 --> 00:03:08.360 Because oxygen isn't the boss there, right, We're. 61 00:03:08.199 --> 00:03:11.400 Dealing with environment governed by a completely different primary driver, 62 00:03:11.759 --> 00:03:13.319 which is, like you said, sulfur. 63 00:03:14.000 --> 00:03:16.319 Okay, So let's look at the actual data that broke 64 00:03:16.360 --> 00:03:19.000 this Earth centric model, because I think that's fascinating. 65 00:03:19.039 --> 00:03:20.759 The NASA Messenger mission. 66 00:03:20.560 --> 00:03:25.039 Yes, Messenger because before Messenger, our understanding of mercury surface 67 00:03:25.159 --> 00:03:27.680 was pretty much just you know, educated guessing. 68 00:03:27.960 --> 00:03:30.439 Yeah, we had some fly by data from Mariner ten 69 00:03:30.840 --> 00:03:34.080 back in the seventies and some telescope observations from the ground, 70 00:03:34.120 --> 00:03:35.439 but it was really speculative. 71 00:03:35.639 --> 00:03:39.039 But then Messenger finally gets into orbit around Mercury and 72 00:03:39.080 --> 00:03:42.240 it starts using this X ray spectrometer. 73 00:03:41.719 --> 00:03:43.919 Which is such a cool instrument by the way it is. 74 00:03:44.000 --> 00:03:46.800 It basically waits for solar flares from the Sun to 75 00:03:46.960 --> 00:03:50.680 blast the planet's surface and then measures the secondary X 76 00:03:50.800 --> 00:03:52.319 rays that bounce off the rocks. 77 00:03:52.400 --> 00:03:55.840 Exactly. It uses the Sun as its own giant radiation 78 00:03:56.000 --> 00:03:58.319 source to light up the planet's chemistry. 79 00:03:58.400 --> 00:04:01.879 And the chemical signature at back was just shocking. It 80 00:04:01.960 --> 00:04:04.360 was entirely incompatible with an. 81 00:04:04.280 --> 00:04:08.120 Earth like mantle, totally incompatible. It threw everyone for a loop. 82 00:04:08.280 --> 00:04:11.759 It showed that Mercury's crust was incredibly depleted in iron, 83 00:04:11.840 --> 00:04:16.000 like missing so much iron, but it was extraordinarily enriched 84 00:04:16.120 --> 00:04:16.759 in sulfur. 85 00:04:17.000 --> 00:04:19.519 We are talking about sulfur levels on the surface that 86 00:04:19.560 --> 00:04:23.720 are orders of magnitude higher than anything we ever see on. 87 00:04:23.639 --> 00:04:26.360 Earth, which is crazy. And this immediately tells us there's 88 00:04:26.399 --> 00:04:29.519 a huge difference in the planet's bulk chemistry. It points 89 00:04:29.519 --> 00:04:32.360 to this thing called an extreme reducing environment, right. 90 00:04:32.279 --> 00:04:36.040 Yeah, a highly reduced environment. That's the absolute key to 91 00:04:36.360 --> 00:04:38.360 interpreting all this messenger data. 92 00:04:38.439 --> 00:04:41.399 Okay, So help us out here break down what it 93 00:04:41.439 --> 00:04:45.040 actually means for a planetary body to be highly reduced 94 00:04:45.079 --> 00:04:47.800 because that sounds like a very dense chemistry term. 95 00:04:47.959 --> 00:04:51.120 Oh sure, So when planetary scientists talk about the redock 96 00:04:51.160 --> 00:04:53.639 state of a planet, we're really just talking about the 97 00:04:53.639 --> 00:04:57.279 balance between reduction and oxidation when the planet was first 98 00:04:57.319 --> 00:04:58.000 clumping together. 99 00:04:58.120 --> 00:04:58.439 Okay. 100 00:04:58.920 --> 00:05:03.519 In an oxidized in environment like Earth, oxygen is superabundant, 101 00:05:03.639 --> 00:05:06.920 and oxygen is highly electronegative. 102 00:05:06.240 --> 00:05:07.800 Meaning it really wants electrons. 103 00:05:07.839 --> 00:05:11.319 It loves electrons. It aggressively pulls electrons away from other 104 00:05:11.360 --> 00:05:15.480 elements to form oxides. So iron, for example, easily oxidizes 105 00:05:15.560 --> 00:05:18.160 to form silicate minerals, and those make up the bulk 106 00:05:18.160 --> 00:05:19.680 of Earth's mantle and crust. 107 00:05:19.839 --> 00:05:22.279 So an oxidized Earth is kind of like, well, it's 108 00:05:22.279 --> 00:05:24.160 like a rusting piece of iron sitting out in the. 109 00:05:24.160 --> 00:05:26.279 Brain right now that oxygen is grabbing onto everything. 110 00:05:26.360 --> 00:05:29.920 That's a perfect analogy. Actually, Earth is basically fully rusted. 111 00:05:29.680 --> 00:05:31.399 But mercury isn't rusting. 112 00:05:31.480 --> 00:05:33.720 No, not at all. Mercury formed way closer to the 113 00:05:33.720 --> 00:05:36.000 proto Sun in a part of the early Solar nebula 114 00:05:36.000 --> 00:05:39.360 where the oxygen fugacity that the availability we talked about 115 00:05:39.600 --> 00:05:41.000 was incredibly low. 116 00:05:40.879 --> 00:05:44.160 So no free oxygen, almost none. It's the most chemically 117 00:05:44.240 --> 00:05:47.120 reduced terrestrial planet we have in the Solar System. In 118 00:05:47.160 --> 00:05:50.319 this kind of environment, elements don't lose their electrons to 119 00:05:50.319 --> 00:05:54.560 oxygen to keep them right. The whole system favors retaining electrons. 120 00:05:55.399 --> 00:05:58.240 So without enough oxygen around to bond with the iron 121 00:05:58.279 --> 00:06:01.920 in this big molten protoplanet, the way the iron behaves 122 00:06:02.160 --> 00:06:03.480 shifts dramatically. 123 00:06:03.519 --> 00:06:05.040 Okay, but wait, let me push back on this a 124 00:06:05.040 --> 00:06:09.279 little bit. We know as a planetary fact that Mercury 125 00:06:09.480 --> 00:06:13.920 has a disproportionately massive iron core, right, Like, the core 126 00:06:14.000 --> 00:06:15.639 is huge compared to the rest of the planet. 127 00:06:15.639 --> 00:06:19.040 Oh, absolutely massive. It's essentially a giant iron cannonball with 128 00:06:19.160 --> 00:06:20.639 a thin, little rocky shell. 129 00:06:20.720 --> 00:06:23.160 Right. So if it has this giant iron core, how 130 00:06:23.240 --> 00:06:26.199 can its crust be so incredibly poor and iron? Where 131 00:06:26.199 --> 00:06:27.000 did it all go? 132 00:06:27.279 --> 00:06:30.199 That is the magic of the reduced state, because the 133 00:06:30.240 --> 00:06:33.560 iron wasn't bonding with oxygen to form light silicate rocks 134 00:06:33.560 --> 00:06:37.680 in the mantle. It stayed as unbound heavy metallic iron. 135 00:06:37.800 --> 00:06:40.399 Oh I see, and gravity just took over. In a 136 00:06:40.439 --> 00:06:44.680 totally molten young planet, all that heavy unbound iron just 137 00:06:45.120 --> 00:06:46.839 sank rapidly right to the center. 138 00:06:46.959 --> 00:06:48.879 Wow, So it basically filtered itself out. 139 00:06:49.279 --> 00:06:54.519 Exactly, the extreme reducing conditions caused super efficient planetary differentiation. 140 00:06:55.079 --> 00:06:58.680 The iron partitioned almost completely into the core, and it 141 00:06:58.759 --> 00:07:01.879 left behind a mantle that is just stripped bear of iron. 142 00:07:02.079 --> 00:07:03.839 That makes so much sense, but that brings up a 143 00:07:03.879 --> 00:07:07.360 really big chemical mystery, then the sulfur mystery. Exactly. If 144 00:07:07.360 --> 00:07:10.199 the mantle has no iron but it has tons of sulfur, 145 00:07:10.879 --> 00:07:13.360 what is the sulfur doing Because here on Earth, sulfur 146 00:07:13.439 --> 00:07:16.920 is a home wrecker, but it specifically loves iron, right Yeah. 147 00:07:16.920 --> 00:07:19.360 On Earth, sulfur is what we call a chalcophile element. 148 00:07:19.480 --> 00:07:22.160 It has a super strong affinity for iron. It constantly 149 00:07:22.160 --> 00:07:25.279 seeks out iron to form these dense sulfide melts. 150 00:07:25.399 --> 00:07:27.839 But if all the iron on mercury already sank to 151 00:07:27.879 --> 00:07:28.600 the center. 152 00:07:28.399 --> 00:07:31.000 Then the sulfur in the outer layers the mantle is 153 00:07:31.040 --> 00:07:34.959 basically stranded. It's stuck up there without its favorite bonding partner. 154 00:07:34.680 --> 00:07:36.319 So it has to find someone else to dance with. 155 00:07:36.519 --> 00:07:39.839 Exactly that total absence of iron forces a huge shift 156 00:07:39.879 --> 00:07:42.800 in the mineral pathways. On Earth, sulfur and iron get 157 00:07:42.800 --> 00:07:46.000 together in four minerals like pyrite, which you know as 158 00:07:46.040 --> 00:07:49.600 fool's gold. But on mercury, the sulfur has to interact 159 00:07:49.879 --> 00:07:54.040 with the next best things available, and in this highly 160 00:07:54.079 --> 00:08:00.600 reduced iron poor molten rock, sulfur starts bonding aggressively with magnesium. 161 00:08:00.160 --> 00:08:01.600 Calcium, magnesium and calcium. 162 00:08:01.720 --> 00:08:04.519 Yeah, and that is a pathway that is almost entirely 163 00:08:04.560 --> 00:08:06.839 shut down on Earth. We just don't see it much here, 164 00:08:07.319 --> 00:08:10.920 But on mercury it becomes the dominant chemical mechanism. 165 00:08:11.199 --> 00:08:14.240 Okay, so sulfur is suddenly best friends with magnesium and calcium. 166 00:08:14.680 --> 00:08:17.680 But how does that atomic level chemistry actually change the 167 00:08:17.680 --> 00:08:21.279 physical magma? Like, what is it doing to the rock itself? 168 00:08:21.399 --> 00:08:24.240 It completely changes the structural integrity of the magma. Think 169 00:08:24.279 --> 00:08:27.519 about how molden rock where silicon melt is built in 170 00:08:27.560 --> 00:08:30.560 a normal Earth magma, the structure is this really complex 171 00:08:30.639 --> 00:08:32.840 network of silicon, oxygen tetrahedrol. 172 00:08:32.919 --> 00:08:35.279 Okay, silicon and oxygen linking up right. 173 00:08:35.440 --> 00:08:38.320 Oxygen acts as the glue or the bridging ion. It 174 00:08:38.360 --> 00:08:41.399 links these structures together into a really robust three dimensional web. 175 00:08:41.440 --> 00:08:45.559 So it's strong, very strong, and that interconnected web dictates everything. 176 00:08:45.679 --> 00:08:49.000 It controls how thick and viscous the magma is, its density, 177 00:08:49.240 --> 00:08:51.120 and crucially its liquidst temperature. 178 00:08:51.360 --> 00:08:54.519 The liquidst temperature meaning the exact point where it stops 179 00:08:54.519 --> 00:08:57.559 being liquid and starts forming solid crystals exactly. 180 00:08:57.639 --> 00:09:01.240 So if you have all this sulfur for forming complexes 181 00:09:01.279 --> 00:09:04.679 with magnesium and calcium on mercury, it isn't just floating 182 00:09:04.720 --> 00:09:09.720 around doing nothing. It actively attacks that silicon oxygen framework. 183 00:09:09.799 --> 00:09:13.240 It's actively breaking it. Like Okay, think about Earth's magma 184 00:09:13.279 --> 00:09:17.519 as a building. The oxygen atoms are these strong steel 185 00:09:17.600 --> 00:09:20.679 bolts holding the steel beams together. I like that, But 186 00:09:20.759 --> 00:09:24.559 on molcury, because of all this weird chemistry, those steel 187 00:09:24.600 --> 00:09:27.840 bolts get replaced by a softer metal, yes, exactly, like 188 00:09:27.919 --> 00:09:31.039 lead or something. So it fundamentally compromises the rigidity of 189 00:09:31.039 --> 00:09:33.080 the whole building. It's way easier to collapse. 190 00:09:33.159 --> 00:09:37.000 That's spot on. The sulfur actively substitutes for oxygen in 191 00:09:37.039 --> 00:09:39.360 the network because sulfur is in the same group as 192 00:09:39.399 --> 00:09:42.360 oxygen on the periodic table, it can technically fit into 193 00:09:42.399 --> 00:09:45.240 those same spots. It's like an impostor a very clumsy imposter. 194 00:09:45.559 --> 00:09:48.559 Sulfur is a much larger ion than oxygen, and it 195 00:09:48.600 --> 00:09:51.559 doesn't hold onto electrons as tightly, So when sulfur forces 196 00:09:51.600 --> 00:09:54.399 its way in and replaces a bridging oxygen atom, it 197 00:09:54.480 --> 00:09:55.519 bends the bond. 198 00:09:55.279 --> 00:09:57.200 Angles, it warps the structure, It. 199 00:09:57.240 --> 00:10:00.679 Totally warps it. The bond between sulfur and silic is 200 00:10:00.799 --> 00:10:04.080 just much weaker and way easier to break than the 201 00:10:04.120 --> 00:10:08.360 normal oxygen silicon bond, so the milt to polymizes. 202 00:10:07.759 --> 00:10:09.679 To polymerizes, meaning it just falls apart. 203 00:10:09.799 --> 00:10:13.240 It breaks up those long, strong chains. Now, a strong 204 00:10:13.480 --> 00:10:16.320 oxidized magma on Earth needs a huge amount of heat 205 00:10:16.480 --> 00:10:19.559 just to stay liquid. But if you introduce sulfur and 206 00:10:19.679 --> 00:10:23.000 break all those bonds, you're lowering the amount of energy. 207 00:10:22.799 --> 00:10:25.600 Needed, which means it stays liquid at much cooler temperatures. 208 00:10:25.720 --> 00:10:28.919 Exactly the thermal energy required to prevent it from freezing 209 00:10:28.919 --> 00:10:31.279 into solid rock drops significantly. 210 00:10:31.360 --> 00:10:33.519 Okay, so that's the theory, But how do we actually 211 00:10:33.559 --> 00:10:36.639 know this Because we haven't brought any rocks back from Mercury. 212 00:10:36.840 --> 00:10:39.639 No, we haven't. And that's where the lab work comes. 213 00:10:39.399 --> 00:10:41.919 In, right, because you can't just run a computer simulation 214 00:10:42.000 --> 00:10:43.360 and call it a day. You have to prove it. 215 00:10:43.399 --> 00:10:45.440 You have to physically cook a rock and see what happens. 216 00:10:45.519 --> 00:10:48.399 Yeah, you have to subject the exact chemical recipe of 217 00:10:48.440 --> 00:10:52.440 mercury's mantle to the massive pressures and temperatures deep inside 218 00:10:52.440 --> 00:10:53.480 the planet. 219 00:10:53.120 --> 00:10:55.960 Which brings us to this mind blowing research from twenty 220 00:10:56.000 --> 00:10:59.159 twenty six. This was done at Rice University. 221 00:10:58.960 --> 00:11:04.440 Yes, pecifically by a postdoctoral researcher named Yushen Zang working 222 00:11:04.480 --> 00:11:08.399 in roj Deep Dusk Gupta's lab. They wanted to physically replicate. 223 00:11:07.919 --> 00:11:10.960 Early mercury, but again, no rocks for mercury. So they 224 00:11:10.960 --> 00:11:12.759 needed a stand in proxy and. 225 00:11:12.720 --> 00:11:16.000 They found the perfect proxy, the in Darsch meteorite. 226 00:11:16.120 --> 00:11:18.120 Okay, we have to talk up the backstory of this 227 00:11:18.200 --> 00:11:20.840 meteorite because it is just incredible to me that this 228 00:11:21.000 --> 00:11:23.960 rock fell out of the sky in Azerbaijan in eighteen 229 00:11:24.039 --> 00:11:24.639 ninety one. 230 00:11:24.559 --> 00:11:27.200 Eighteen ninety one, way before we even knew what mercury 231 00:11:27.240 --> 00:11:27.639 really was. 232 00:11:27.840 --> 00:11:31.200 Yeah, it's just astounding. A rock falls from space in 233 00:11:31.200 --> 00:11:33.679 the nineteenth century sits in a drawer somewhere for one 234 00:11:33.720 --> 00:11:36.000 hundred and thirty years, and now we're using it to 235 00:11:36.000 --> 00:11:40.840 simulate an unreachable planet. Why this specific rock though, What 236 00:11:40.960 --> 00:11:42.799 makes in dark so special. 237 00:11:42.559 --> 00:11:44.679 In darts is a very rare type of rock called 238 00:11:44.679 --> 00:11:47.480 an ensteatite chondrite. They make up only about two percent 239 00:11:47.519 --> 00:11:48.759 of all meteorites that hit Earth. 240 00:11:48.799 --> 00:11:51.159 Wow, so very rare, extremely. 241 00:11:50.759 --> 00:11:53.159 Rare, and their chemistry is key. When we look at 242 00:11:53.159 --> 00:11:56.639 their isotopes like oxygen, titanium, and calcium, they look a 243 00:11:56.639 --> 00:11:58.799 lot like the rocks in the Earth Moon system, which 244 00:11:58.840 --> 00:12:01.600 tells us they formed in inner solar nebula. 245 00:12:01.240 --> 00:12:01.840 Toast of the Sun. 246 00:12:02.240 --> 00:12:07.480 Right. But unlike Earth rocks, their mineral makeup is aggressively reduced. 247 00:12:07.840 --> 00:12:09.879 There's that word again, reduced, Right. 248 00:12:09.960 --> 00:12:13.320 They're packed with minerals that simply cannot exist if there's 249 00:12:13.320 --> 00:12:17.799 any free oxygen around. Minerals like oldamite, which is calcium sulfide, 250 00:12:18.000 --> 00:12:21.159 and nineiningerite, which is a magnesium iron sulfide. 251 00:12:21.200 --> 00:12:25.039 So this meteorite basically has the exact same weird low 252 00:12:25.120 --> 00:12:28.159 iron high sulfur recipe as mercury's crust. 253 00:12:28.279 --> 00:12:31.039 It's practically a perfect match for the messenger data. It 254 00:12:31.120 --> 00:12:34.039 is a surviving piece of the exact type of material 255 00:12:34.360 --> 00:12:36.039 that clump together to build mercury. 256 00:12:36.240 --> 00:12:39.480 Okay, so Zang and the team at Rice University have 257 00:12:39.600 --> 00:12:42.039 this piece of the in darch meteorite. But you can't 258 00:12:42.039 --> 00:12:44.840 just stick it in a microwave. How do you simulate 259 00:12:44.879 --> 00:12:46.639 the inside of a planet? How do you cook this 260 00:12:46.879 --> 00:12:50.559 rock at those kinds of pressures without destroying the laboratory? 261 00:12:50.679 --> 00:12:50.840 Oh? 262 00:12:50.919 --> 00:12:53.720 It requires some serious heavy duty engineering. They use what's 263 00:12:53.759 --> 00:12:55.120 called a multianvil press. 264 00:12:55.440 --> 00:13:00.000 Multi anvil sounds heavy, it's massive. These machines generate gigab 265 00:13:00.080 --> 00:13:01.120 has scals of pressure. 266 00:13:01.279 --> 00:13:03.879 You get pascals. What does that feel life? It's basically 267 00:13:03.960 --> 00:13:07.200 equivalent to the crushing weight of hundreds of kilometers of 268 00:13:07.240 --> 00:13:10.159 solid planetary rock pressing down on you all at once. 269 00:13:10.320 --> 00:13:13.000 Oh wow, Okay, So how does the machine do that? 270 00:13:13.320 --> 00:13:16.360 They take the rock, sample, powder it, and put it 271 00:13:16.399 --> 00:13:18.919 inside this tiny capsule, usually made a graphite or a 272 00:13:18.960 --> 00:13:22.200 special metal alloy. Then they put that tiny capsule inside 273 00:13:22.240 --> 00:13:26.519 an octaegal pressure medium, basically an eight sided block. Then 274 00:13:27.120 --> 00:13:32.000 massive hydraulic rams drive heavy tungsten carbide andles together from 275 00:13:32.080 --> 00:13:35.519 all sides at the exact same time from all side. Yeah, 276 00:13:35.600 --> 00:13:39.399 so the pressure's perfectly even, simulating depth, and while it's 277 00:13:39.440 --> 00:13:43.080 being crushed, a tiny internal heater like a rhanium furnace 278 00:13:43.440 --> 00:13:46.000 cranks the heat up to thousands of degrees celsius. 279 00:13:46.080 --> 00:13:48.679 That is insane. Maintaining that kind of heat and pressure 280 00:13:48.679 --> 00:13:50.159 without the whole thing just exploding. 281 00:13:50.279 --> 00:13:52.960 The precision is unbelievable, but they have to do it 282 00:13:52.960 --> 00:13:55.639 to track exactly when the rock melts and when it freezes. 283 00:13:56.000 --> 00:13:57.679 They map the liquidus and the solidus. 284 00:13:57.720 --> 00:14:00.279 It's the solidus being the point where it's totally hundred 285 00:14:00.279 --> 00:14:01.279 percent solid rock. 286 00:14:01.440 --> 00:14:03.799 Right, So they get the rock to the exact pressure 287 00:14:03.799 --> 00:14:06.559 and temperature they want, wait for the chemistry to balance out, 288 00:14:06.600 --> 00:14:08.399 and then they do a rabid quench, a. 289 00:14:08.440 --> 00:14:10.799 Quench like plunging a hot sword into water. 290 00:14:11.240 --> 00:14:14.879 Essentially, Yes, they instantly drop the temperature while keeping the 291 00:14:14.879 --> 00:14:18.000 crushing pressure on. It freezes the molten rock into glass 292 00:14:18.000 --> 00:14:18.919 in a split second. 293 00:14:19.039 --> 00:14:22.039 So it basically takes a chemical snapshot of what the 294 00:14:22.080 --> 00:14:25.840 magma look like at that exact depth and temperature exactly. 295 00:14:25.519 --> 00:14:27.200 And then they slice it open and look at it 296 00:14:27.360 --> 00:14:29.679 under an electron microprobe. 297 00:14:29.120 --> 00:14:31.600 And so the big reveal when they finally looked at 298 00:14:31.639 --> 00:14:36.360 these cooked, quenched samples of this mercury like rock. What 299 00:14:36.480 --> 00:14:38.960 did they actually see? Did the sulfur do what they 300 00:14:38.960 --> 00:14:39.559 thought it would? 301 00:14:39.639 --> 00:14:43.000 It did exactly what they predicted. The data was crystal clear. 302 00:14:43.360 --> 00:14:47.399 The sulfur aggressively substituted into the silicate network, weakened it 303 00:14:47.679 --> 00:14:49.679 and actively suppressed crystallization. 304 00:14:49.960 --> 00:14:51.480 So the anti freeze theory worked. 305 00:14:51.679 --> 00:14:56.360 It worked perfectly. These reduced sulfur rich melts stayed liquid 306 00:14:56.440 --> 00:15:00.120 at significantly lower temperatures than an equivalent Earth rock would have. 307 00:15:00.279 --> 00:15:03.519 Which brings up that great quote from Rajdeep Dascupta, the 308 00:15:03.559 --> 00:15:04.240 head of the lab. 309 00:15:04.399 --> 00:15:07.519 Oh I love this quote. He said, what water or 310 00:15:07.600 --> 00:15:11.879 carbon does to magmatic evolution on Earth, sulfur does on mercury. 311 00:15:12.159 --> 00:15:14.600 It's such a perfect summary because on Earth, if you 312 00:15:14.639 --> 00:15:17.440 add water to hot rock deep underground, like at a 313 00:15:17.440 --> 00:15:20.799 subduction zone, it acts as a flux. It lowers the 314 00:15:20.840 --> 00:15:22.679 melting point and triggers volcanoes. 315 00:15:22.799 --> 00:15:25.759 Right The water physically gets into the rock structure and 316 00:15:25.879 --> 00:15:26.519 breaks up the. 317 00:15:26.440 --> 00:15:30.200 Polymers, like pouring salt on an icy road exactly. 318 00:15:29.799 --> 00:15:32.440 It forces the ice to melt even though it's freezing outside. 319 00:15:32.720 --> 00:15:36.720 On mercury, sulfur is the salt. It's the planetary anti freeze. 320 00:15:36.759 --> 00:15:40.639 But the difference is water on Earth is kind of localized. 321 00:15:40.679 --> 00:15:44.840 It happens at specific tectonic plates. On Mercury, this sulfur 322 00:15:44.960 --> 00:15:47.120 is everywhere. It's built into the whole planet. 323 00:15:47.279 --> 00:15:50.879 Yes, it operates globally. It depressed the melting point across 324 00:15:50.919 --> 00:15:52.600 the entire mantle of the planet. 325 00:15:52.679 --> 00:15:54.919 Okay, so let's zoom out. Now we've got the lab data. 326 00:15:55.000 --> 00:15:56.919 We know the atomic bonds are weaker. We know the 327 00:15:56.960 --> 00:16:00.159 magma stays liquid at cooler temperatures. How does it's that 328 00:16:00.240 --> 00:16:04.080 atomic level chemistry translate to the huge planet wide features 329 00:16:04.120 --> 00:16:05.279 we see on Mercury today. 330 00:16:05.480 --> 00:16:08.960 Well, if the magma stays liquid longer at cooler temperatures, 331 00:16:09.559 --> 00:16:13.879 it drastically extends the life span of Mercury's early magma oceans. 332 00:16:14.080 --> 00:16:17.639 So instead of freezing solid quickly, the planet just sloshed 333 00:16:17.639 --> 00:16:20.279 around as a giant ball of liquid rock for millions 334 00:16:20.320 --> 00:16:22.159 of years, longer than we thought exactly. 335 00:16:22.559 --> 00:16:26.240 And because the magma had a weaker structureless polymerized, it 336 00:16:26.279 --> 00:16:28.240 was also runnier, less. 337 00:16:28.080 --> 00:16:30.559 Viscous like water instead of honey. 338 00:16:30.360 --> 00:16:34.200 Right, and a running mantle moves heat really efficiently. It 339 00:16:34.240 --> 00:16:37.320 convects faster, pulling heat from the core to the surface. 340 00:16:37.480 --> 00:16:39.919 Wait, if it's moving heat to the surface faster, wouldn't 341 00:16:39.919 --> 00:16:42.600 the planet cool down faster. That seems like a contradiction. 342 00:16:42.840 --> 00:16:45.000 It does seem like one. Yeah, but remember the anti 343 00:16:45.000 --> 00:16:48.360 freeze effect. Even though the planet is losing heat rapidly, 344 00:16:48.759 --> 00:16:52.600 the sulfur ensures the rock simply refuses to solidify until 345 00:16:52.639 --> 00:16:54.440 the temperature drops incredibly low. 346 00:16:54.639 --> 00:16:57.600 Oh man, So it's cooling off, but it's trapped in 347 00:16:57.600 --> 00:16:58.440 a liquid. 348 00:16:58.120 --> 00:17:01.200 State precisely, and this extended period of cooling as a 349 00:17:01.200 --> 00:17:05.119 liquid completely changes what kind of rocks eventually form. As 350 00:17:05.119 --> 00:17:08.640 the temperature slowly drops toward that new super low freezing point. 351 00:17:09.000 --> 00:17:10.960 The very first minerals to pop out of the liquid 352 00:17:11.039 --> 00:17:14.079 and crystallize are those sulfur compounds. 353 00:17:13.759 --> 00:17:17.640 The calcium and magnesium sulfides we talked about earlier oldamite 354 00:17:17.680 --> 00:17:18.559 and nininjurite. 355 00:17:18.799 --> 00:17:23.400 Yes, because they crystallized early while the mantle was still fluid, 356 00:17:23.720 --> 00:17:25.640 they were able to concentrate in the upper. 357 00:17:25.359 --> 00:17:29.160 Crust, which perfectly explains why messengers saw all that calcium 358 00:17:29.200 --> 00:17:31.160 and magnesium on the surface exactly. 359 00:17:31.319 --> 00:17:34.680 The entire surface composition is a direct result of this 360 00:17:34.880 --> 00:17:38.119 prolonged low temperature crystallization that is. 361 00:17:38.039 --> 00:17:41.440 So incredibly elegant. It just ties everything together. 362 00:17:41.279 --> 00:17:45.039 It really does. It also explains Mercury's volcanic history, oh. 363 00:17:44.960 --> 00:17:49.079 Right, because Mercury has these huge, smooth volcanic planes. 364 00:17:48.759 --> 00:17:51.720 Right, vast plains of cured lava that sit on top 365 00:17:51.759 --> 00:17:55.920 of older, cratered terrain, which means these massive volcanic eruptions 366 00:17:56.000 --> 00:17:58.319 happened relatively late in the planet's youth. 367 00:17:58.559 --> 00:18:00.720 But if Mercury was an Earth like rock, it's so 368 00:18:00.880 --> 00:18:03.279 small it should have cooled and formed a thick, solid 369 00:18:03.279 --> 00:18:06.119 crust really early. The volcano should have choked off and 370 00:18:06.200 --> 00:18:07.400 died exactly. 371 00:18:07.960 --> 00:18:11.720 The thermal models for a normal rocky planet of Mercury 372 00:18:11.839 --> 00:18:15.279 size say the volcano should have shut down quickly, but 373 00:18:15.319 --> 00:18:18.000 the sulfur kept the engine running. It kept the mantle 374 00:18:18.079 --> 00:18:21.319 partially melted and fluid enough to erupt onto the surface 375 00:18:21.759 --> 00:18:23.440 long after it should have frozen solid. 376 00:18:23.519 --> 00:18:26.079 Okay, but this leads me to another question, a pushback. 377 00:18:26.119 --> 00:18:27.240 Actually, let's hear it. 378 00:18:27.400 --> 00:18:30.440 If the sulfur kept the magma hot and fluid for 379 00:18:30.480 --> 00:18:32.839 such a long time, how does that fit with the 380 00:18:32.880 --> 00:18:33.400 low bait. 381 00:18:33.319 --> 00:18:34.880 Scarps us the scarps? 382 00:18:35.000 --> 00:18:37.319 Yeah, for people who don't know mercury is covered in 383 00:18:37.359 --> 00:18:40.920 these massive cliffs and ridges called scarps. They look like wrinkles. 384 00:18:41.279 --> 00:18:44.559 The planet literally contracted and shrank like a raisin. 385 00:18:44.400 --> 00:18:46.160 A giant iron filled raisin. 386 00:18:46.319 --> 00:18:48.640 Right, But you can't wrinkle a liquid. If the mantle 387 00:18:48.680 --> 00:18:51.720 was fluid for so long, a shrinking core wouldn't cause 388 00:18:51.720 --> 00:18:54.359 the surface to snap and form cliffs. The liquid would 389 00:18:54.400 --> 00:18:57.400 just adjust. So how did the scarps form? 390 00:18:57.480 --> 00:19:00.000 That is a brilliant point. The mechanics have scarp formed 391 00:19:00.680 --> 00:19:05.440 absolutely require a rigid, solid, thick outer shell lithosphere. So 392 00:19:05.480 --> 00:19:09.000 the timeline is everything here. The global contraction, the shrinking 393 00:19:09.039 --> 00:19:12.039 that made those cliffs. It had to happen primarily after 394 00:19:12.079 --> 00:19:16.119 the sulfur rich magma ocean finally cooled past its super 395 00:19:16.160 --> 00:19:17.960 low freezing point and locked up. 396 00:19:18.119 --> 00:19:20.319 Oh I see, So it stayed liquid for a long time, 397 00:19:20.400 --> 00:19:23.839 letting the volcanoes erupt but eventually even the anti freeze 398 00:19:23.839 --> 00:19:25.759 couldn't stop it from freezing exactly. 399 00:19:26.079 --> 00:19:28.960 The temperature eventually dropped low enough that even those weakened 400 00:19:29.039 --> 00:19:31.640 sulfur silicate networks froze solid. 401 00:19:31.359 --> 00:19:34.000