Speaker 1: Welcome to Bedtime Astronomy. Explore the wonders of the cosmos
Speaker 1: with our soothing Bedtime Astronomie podcast. Each episode offers a
Speaker 1: gentle journey through the stars, planets, and beyond, perfect for
Speaker 1: unwinding after a long day. Let's travel through the mysteries
Speaker 1: of the universe as you drift off into a peaceful
Speaker 1: slumber under the night sky.
Speaker 2: I want you to just take a second and picture
Speaker 2: volcanic magma.
Speaker 3: Oh yeah, the classic mental image right.
Speaker 2: Like you probably immediately think of this thick, glowing red,
Speaker 2: slowly creeping lava.
Speaker 3: Like something you'd see in Hawaii or Iceland exactly.
Speaker 2: And that image, that whole process is totally driven by
Speaker 2: the familiar elements we have right here on Earth, you know,
Speaker 2: mainly oxygen and iron.
Speaker 3: Yeah, those are the big players for us.
Speaker 2: But we need to completely shatter that mental image right
Speaker 2: out of the gate today. Oh, absolutely, throw it right
Speaker 2: out the window, because we are heading to Mercury. It's
Speaker 2: the smallest, innermost planet in our Solar system, but it
Speaker 2: is hiding this massive, fundamentally alien secret.
Speaker 3: It really is. It's just a totally different world.
Speaker 2: Yeah, on Mercury, the familiar rules of geology, all that
Speaker 2: oxygen and iron stuff, it's just it's gone. It's replaced
Speaker 2: by a chemical reality that is so bizarre it forces
Speaker 2: us to basically rethink how planets are even born.
Speaker 3: It's wild. It completely flips our understanding of planetary evolution.
Speaker 2: So that's our mission for you today. We are going
Speaker 2: to journey far away from this comfortable Earth centric view
Speaker 2: of planetary science, and we're dropping into a world where
Speaker 2: a totally different element, sulfur just reigns supreme.
Speaker 3: Lfer is the king on Mercury, right, and.
Speaker 2: Our goal is to understand how this one single element
Speaker 2: completely rewrites Mercury's history. It creates a crust and a
Speaker 2: geologic timeline that looks honestly nothing like.
Speaker 3: Our own, not even close to our own.
Speaker 2: And it's so easy, right, It's so easy to just
Speaker 2: assume all rocky planets are basically variations of Earth, like
Speaker 2: Mars is a cold Earth, Venus is a hotter Earth.
Speaker 3: Yeah, it's the single biggest trap in planetary science, honestly.
Speaker 2: I mean, it makes sense why we do it, of
Speaker 2: course it does.
Speaker 3: We live here. We have naturally built our entire understanding
Speaker 3: of you know, planetary accretion, mantle convection, crust formation, all
Speaker 3: of it. The chemistry of Earth, Mars, and well Venus,
Speaker 3: because that's what we can see and measure easily exactly.
Speaker 3: And in those systems, the oxygen and fugacity, which is
Speaker 3: basically just the availability and the chemical activity of oxygen.
Speaker 3: When the planet was forming, that was relatively high.
Speaker 2: So there's plenty of oxygen to go around.
Speaker 3: Tons of it. Oxygen totally dominates the chemical structure on Earth.
Speaker 3: It dictates which elements bond together, it decides at what
Speaker 3: temperature rocks melt, and really importantly, how a planet loses
Speaker 3: its internal heat over bions of years.
Speaker 2: But mercury is playing a different game.
Speaker 3: A completely different game. It formed under entirely different initial
Speaker 3: conditions in the Solar nebula. The rules that govern how
Speaker 3: magma evolves on Earth, they just fail, They literally fail
Speaker 3: when you apply them to mercury.
Speaker 2: Because oxygen isn't the boss there, right, We're.
Speaker 3: Dealing with environment governed by a completely different primary driver,
Speaker 3: which is, like you said, sulfur.
Speaker 2: Okay, So let's look at the actual data that broke
Speaker 2: this Earth centric model, because I think that's fascinating.
Speaker 3: The NASA Messenger mission.
Speaker 2: Yes, Messenger because before Messenger, our understanding of mercury surface
Speaker 2: was pretty much just you know, educated guessing.
Speaker 3: Yeah, we had some fly by data from Mariner ten
Speaker 3: back in the seventies and some telescope observations from the ground,
Speaker 3: but it was really speculative.
Speaker 2: But then Messenger finally gets into orbit around Mercury and
Speaker 2: it starts using this X ray spectrometer.
Speaker 3: Which is such a cool instrument by the way it is.
Speaker 2: It basically waits for solar flares from the Sun to
Speaker 2: blast the planet's surface and then measures the secondary X
Speaker 2: rays that bounce off the rocks.
Speaker 3: Exactly. It uses the Sun as its own giant radiation
Speaker 3: source to light up the planet's chemistry.
Speaker 2: And the chemical signature at back was just shocking. It
Speaker 2: was entirely incompatible with an.
Speaker 3: Earth like mantle, totally incompatible. It threw everyone for a loop.
Speaker 2: It showed that Mercury's crust was incredibly depleted in iron,
Speaker 2: like missing so much iron, but it was extraordinarily enriched
Speaker 2: in sulfur.
Speaker 3: We are talking about sulfur levels on the surface that
Speaker 3: are orders of magnitude higher than anything we ever see on.
Speaker 2: Earth, which is crazy. And this immediately tells us there's
Speaker 2: a huge difference in the planet's bulk chemistry. It points
Speaker 2: to this thing called an extreme reducing environment, right.
Speaker 3: Yeah, a highly reduced environment. That's the absolute key to
Speaker 3: interpreting all this messenger data.
Speaker 2: Okay, So help us out here break down what it
Speaker 2: actually means for a planetary body to be highly reduced
Speaker 2: because that sounds like a very dense chemistry term.
Speaker 3: Oh sure, So when planetary scientists talk about the redock
Speaker 3: state of a planet, we're really just talking about the
Speaker 3: balance between reduction and oxidation when the planet was first
Speaker 3: clumping together.
Speaker 2: Okay.
Speaker 3: In an oxidized in environment like Earth, oxygen is superabundant,
Speaker 3: and oxygen is highly electronegative.
Speaker 2: Meaning it really wants electrons.
Speaker 3: It loves electrons. It aggressively pulls electrons away from other
Speaker 3: elements to form oxides. So iron, for example, easily oxidizes
Speaker 3: to form silicate minerals, and those make up the bulk
Speaker 3: of Earth's mantle and crust.
Speaker 2: So an oxidized Earth is kind of like, well, it's
Speaker 2: like a rusting piece of iron sitting out in the.
Speaker 3: Brain right now that oxygen is grabbing onto everything.
Speaker 2: That's a perfect analogy. Actually, Earth is basically fully rusted.
Speaker 3: But mercury isn't rusting.
Speaker 2: No, not at all. Mercury formed way closer to the
Speaker 2: proto Sun in a part of the early Solar nebula
Speaker 2: where the oxygen fugacity that the availability we talked about
Speaker 2: was incredibly low.
Speaker 3: So no free oxygen, almost none. It's the most chemically
Speaker 3: reduced terrestrial planet we have in the Solar System. In
Speaker 3: this kind of environment, elements don't lose their electrons to
Speaker 3: oxygen to keep them right. The whole system favors retaining electrons.
Speaker 3: So without enough oxygen around to bond with the iron
Speaker 3: in this big molten protoplanet, the way the iron behaves
Speaker 3: shifts dramatically.
Speaker 2: Okay, but wait, let me push back on this a
Speaker 2: little bit. We know as a planetary fact that Mercury
Speaker 2: has a disproportionately massive iron core, right, Like, the core
Speaker 2: is huge compared to the rest of the planet.
Speaker 3: Oh, absolutely massive. It's essentially a giant iron cannonball with
Speaker 3: a thin, little rocky shell.
Speaker 2: Right. So if it has this giant iron core, how
Speaker 2: can its crust be so incredibly poor and iron? Where
Speaker 2: did it all go?
Speaker 3: That is the magic of the reduced state, because the
Speaker 3: iron wasn't bonding with oxygen to form light silicate rocks
Speaker 3: in the mantle. It stayed as unbound heavy metallic iron.
Speaker 3: Oh I see, and gravity just took over. In a
Speaker 3: totally molten young planet, all that heavy unbound iron just
Speaker 3: sank rapidly right to the center.
Speaker 2: Wow, So it basically filtered itself out.
Speaker 3: Exactly, the extreme reducing conditions caused super efficient planetary differentiation.
Speaker 3: The iron partitioned almost completely into the core, and it
Speaker 3: left behind a mantle that is just stripped bear of iron.
Speaker 2: That makes so much sense, but that brings up a
Speaker 2: really big chemical mystery, then the sulfur mystery. Exactly. If
Speaker 2: the mantle has no iron but it has tons of sulfur,
Speaker 2: what is the sulfur doing Because here on Earth, sulfur
Speaker 2: is a home wrecker, but it specifically loves iron, right Yeah.
Speaker 3: On Earth, sulfur is what we call a chalcophile element.
Speaker 3: It has a super strong affinity for iron. It constantly
Speaker 3: seeks out iron to form these dense sulfide melts.
Speaker 2: But if all the iron on mercury already sank to
Speaker 2: the center.
Speaker 3: Then the sulfur in the outer layers the mantle is
Speaker 3: basically stranded. It's stuck up there without its favorite bonding partner.
Speaker 2: So it has to find someone else to dance with.
Speaker 3: Exactly that total absence of iron forces a huge shift
Speaker 3: in the mineral pathways. On Earth, sulfur and iron get
Speaker 3: together in four minerals like pyrite, which you know as
Speaker 3: fool's gold. But on mercury, the sulfur has to interact
Speaker 3: with the next best things available, and in this highly
Speaker 3: reduced iron poor molten rock, sulfur starts bonding aggressively with magnesium.
Speaker 2: Calcium, magnesium and calcium.
Speaker 3: Yeah, and that is a pathway that is almost entirely
Speaker 3: shut down on Earth. We just don't see it much here,
Speaker 3: But on mercury it becomes the dominant chemical mechanism.
Speaker 2: Okay, so sulfur is suddenly best friends with magnesium and calcium.
Speaker 2: But how does that atomic level chemistry actually change the
Speaker 2: physical magma? Like, what is it doing to the rock itself?
Speaker 3: It completely changes the structural integrity of the magma. Think
Speaker 3: about how molden rock where silicon melt is built in
Speaker 3: a normal Earth magma, the structure is this really complex
Speaker 3: network of silicon, oxygen tetrahedrol.
Speaker 2: Okay, silicon and oxygen linking up right.
Speaker 3: Oxygen acts as the glue or the bridging ion. It
Speaker 3: links these structures together into a really robust three dimensional web.
Speaker 3: So it's strong, very strong, and that interconnected web dictates everything.
Speaker 3: It controls how thick and viscous the magma is, its density,
Speaker 3: and crucially its liquidst temperature.
Speaker 2: The liquidst temperature meaning the exact point where it stops
Speaker 2: being liquid and starts forming solid crystals exactly.
Speaker 3: So if you have all this sulfur for forming complexes
Speaker 3: with magnesium and calcium on mercury, it isn't just floating
Speaker 3: around doing nothing. It actively attacks that silicon oxygen framework.
Speaker 2: It's actively breaking it. Like Okay, think about Earth's magma
Speaker 2: as a building. The oxygen atoms are these strong steel
Speaker 2: bolts holding the steel beams together. I like that, But
Speaker 2: on molcury, because of all this weird chemistry, those steel
Speaker 2: bolts get replaced by a softer metal, yes, exactly, like
Speaker 2: lead or something. So it fundamentally compromises the rigidity of
Speaker 2: the whole building. It's way easier to collapse.
Speaker 3: That's spot on. The sulfur actively substitutes for oxygen in
Speaker 3: the network because sulfur is in the same group as
Speaker 3: oxygen on the periodic table, it can technically fit into
Speaker 3: those same spots. It's like an impostor a very clumsy imposter.
Speaker 3: Sulfur is a much larger ion than oxygen, and it
Speaker 3: doesn't hold onto electrons as tightly, So when sulfur forces
Speaker 3: its way in and replaces a bridging oxygen atom, it
Speaker 3: bends the bond.
Speaker 2: Angles, it warps the structure, It.
Speaker 3: Totally warps it. The bond between sulfur and silic is
Speaker 3: just much weaker and way easier to break than the
Speaker 3: normal oxygen silicon bond, so the milt to polymizes.
Speaker 2: To polymerizes, meaning it just falls apart.
Speaker 3: It breaks up those long, strong chains. Now, a strong
Speaker 3: oxidized magma on Earth needs a huge amount of heat
Speaker 3: just to stay liquid. But if you introduce sulfur and
Speaker 3: break all those bonds, you're lowering the amount of energy.
Speaker 2: Needed, which means it stays liquid at much cooler temperatures.
Speaker 3: Exactly the thermal energy required to prevent it from freezing
Speaker 3: into solid rock drops significantly.
Speaker 2: Okay, so that's the theory, But how do we actually
Speaker 2: know this Because we haven't brought any rocks back from Mercury.
Speaker 3: No, we haven't. And that's where the lab work comes.
Speaker 2: In, right, because you can't just run a computer simulation
Speaker 2: and call it a day. You have to prove it.
Speaker 2: You have to physically cook a rock and see what happens.
Speaker 3: Yeah, you have to subject the exact chemical recipe of
Speaker 3: mercury's mantle to the massive pressures and temperatures deep inside
Speaker 3: the planet.
Speaker 2: Which brings us to this mind blowing research from twenty
Speaker 2: twenty six. This was done at Rice University.
Speaker 3: Yes, pecifically by a postdoctoral researcher named Yushen Zang working
Speaker 3: in roj Deep Dusk Gupta's lab. They wanted to physically replicate.
Speaker 2: Early mercury, but again, no rocks for mercury. So they
Speaker 2: needed a stand in proxy and.
Speaker 3: They found the perfect proxy, the in Darsch meteorite.
Speaker 2: Okay, we have to talk up the backstory of this
Speaker 2: meteorite because it is just incredible to me that this
Speaker 2: rock fell out of the sky in Azerbaijan in eighteen
Speaker 2: ninety one.
Speaker 3: Eighteen ninety one, way before we even knew what mercury
Speaker 3: really was.
Speaker 2: Yeah, it's just astounding. A rock falls from space in
Speaker 2: the nineteenth century sits in a drawer somewhere for one
Speaker 2: hundred and thirty years, and now we're using it to
Speaker 2: simulate an unreachable planet. Why this specific rock though, What
Speaker 2: makes in dark so special.
Speaker 3: In darts is a very rare type of rock called
Speaker 3: an ensteatite chondrite. They make up only about two percent
Speaker 3: of all meteorites that hit Earth.
Speaker 2: Wow, so very rare, extremely.
Speaker 3: Rare, and their chemistry is key. When we look at
Speaker 3: their isotopes like oxygen, titanium, and calcium, they look a
Speaker 3: lot like the rocks in the Earth Moon system, which
Speaker 3: tells us they formed in inner solar nebula.
Speaker 2: Toast of the Sun.
Speaker 3: Right. But unlike Earth rocks, their mineral makeup is aggressively reduced.
Speaker 2: There's that word again, reduced, Right.
Speaker 3: They're packed with minerals that simply cannot exist if there's
Speaker 3: any free oxygen around. Minerals like oldamite, which is calcium sulfide,
Speaker 3: and nineiningerite, which is a magnesium iron sulfide.
Speaker 2: So this meteorite basically has the exact same weird low
Speaker 2: iron high sulfur recipe as mercury's crust.
Speaker 3: It's practically a perfect match for the messenger data. It
Speaker 3: is a surviving piece of the exact type of material
Speaker 3: that clump together to build mercury.
Speaker 2: Okay, so Zang and the team at Rice University have
Speaker 2: this piece of the in darch meteorite. But you can't
Speaker 2: just stick it in a microwave. How do you simulate
Speaker 2: the inside of a planet? How do you cook this
Speaker 2: rock at those kinds of pressures without destroying the laboratory?
Speaker 1: Oh?
Speaker 3: It requires some serious heavy duty engineering. They use what's
Speaker 3: called a multianvil press.
Speaker 2: Multi anvil sounds heavy, it's massive. These machines generate gigab
Speaker 2: has scals of pressure.
Speaker 3: You get pascals. What does that feel life? It's basically
Speaker 3: equivalent to the crushing weight of hundreds of kilometers of
Speaker 3: solid planetary rock pressing down on you all at once.
Speaker 2: Oh wow, Okay, So how does the machine do that?
Speaker 3: They take the rock, sample, powder it, and put it
Speaker 3: inside this tiny capsule, usually made a graphite or a
Speaker 3: special metal alloy. Then they put that tiny capsule inside
Speaker 3: an octaegal pressure medium, basically an eight sided block. Then
Speaker 3: massive hydraulic rams drive heavy tungsten carbide andles together from
Speaker 3: all sides at the exact same time from all side. Yeah,
Speaker 3: so the pressure's perfectly even, simulating depth, and while it's
Speaker 3: being crushed, a tiny internal heater like a rhanium furnace
Speaker 3: cranks the heat up to thousands of degrees celsius.
Speaker 2: That is insane. Maintaining that kind of heat and pressure
Speaker 2: without the whole thing just exploding.
Speaker 3: The precision is unbelievable, but they have to do it
Speaker 3: to track exactly when the rock melts and when it freezes.
Speaker 3: They map the liquidus and the solidus.
Speaker 2: It's the solidus being the point where it's totally hundred
Speaker 2: percent solid rock.
Speaker 3: Right, So they get the rock to the exact pressure
Speaker 3: and temperature they want, wait for the chemistry to balance out,
Speaker 3: and then they do a rabid quench, a.
Speaker 2: Quench like plunging a hot sword into water.
Speaker 3: Essentially, Yes, they instantly drop the temperature while keeping the
Speaker 3: crushing pressure on. It freezes the molten rock into glass
Speaker 3: in a split second.
Speaker 2: So it basically takes a chemical snapshot of what the
Speaker 2: magma look like at that exact depth and temperature exactly.
Speaker 3: And then they slice it open and look at it
Speaker 3: under an electron microprobe.
Speaker 2: And so the big reveal when they finally looked at
Speaker 2: these cooked, quenched samples of this mercury like rock. What
Speaker 2: did they actually see? Did the sulfur do what they
Speaker 2: thought it would?
Speaker 3: It did exactly what they predicted. The data was crystal clear.
Speaker 3: The sulfur aggressively substituted into the silicate network, weakened it
Speaker 3: and actively suppressed crystallization.
Speaker 2: So the anti freeze theory worked.
Speaker 3: It worked perfectly. These reduced sulfur rich melts stayed liquid
Speaker 3: at significantly lower temperatures than an equivalent Earth rock would have.
Speaker 2: Which brings up that great quote from Rajdeep Dascupta, the
Speaker 2: head of the lab.
Speaker 3: Oh I love this quote. He said, what water or
Speaker 3: carbon does to magmatic evolution on Earth, sulfur does on mercury.
Speaker 2: It's such a perfect summary because on Earth, if you
Speaker 2: add water to hot rock deep underground, like at a
Speaker 2: subduction zone, it acts as a flux. It lowers the
Speaker 2: melting point and triggers volcanoes.
Speaker 3: Right The water physically gets into the rock structure and
Speaker 3: breaks up the.
Speaker 2: Polymers, like pouring salt on an icy road exactly.
Speaker 3: It forces the ice to melt even though it's freezing outside.
Speaker 3: On mercury, sulfur is the salt. It's the planetary anti freeze.
Speaker 2: But the difference is water on Earth is kind of localized.
Speaker 2: It happens at specific tectonic plates. On Mercury, this sulfur
Speaker 2: is everywhere. It's built into the whole planet.
Speaker 3: Yes, it operates globally. It depressed the melting point across
Speaker 3: the entire mantle of the planet.
Speaker 2: Okay, so let's zoom out. Now we've got the lab data.
Speaker 2: We know the atomic bonds are weaker. We know the
Speaker 2: magma stays liquid at cooler temperatures. How does it's that
Speaker 2: atomic level chemistry translate to the huge planet wide features
Speaker 2: we see on Mercury today.
Speaker 3: Well, if the magma stays liquid longer at cooler temperatures,
Speaker 3: it drastically extends the life span of Mercury's early magma oceans.
Speaker 2: So instead of freezing solid quickly, the planet just sloshed
Speaker 2: around as a giant ball of liquid rock for millions
Speaker 2: of years, longer than we thought exactly.
Speaker 3: And because the magma had a weaker structureless polymerized, it
Speaker 3: was also runnier, less.
Speaker 2: Viscous like water instead of honey.
Speaker 3: Right, and a running mantle moves heat really efficiently. It
Speaker 3: convects faster, pulling heat from the core to the surface.
Speaker 2: Wait, if it's moving heat to the surface faster, wouldn't
Speaker 2: the planet cool down faster. That seems like a contradiction.
Speaker 3: It does seem like one. Yeah, but remember the anti
Speaker 3: freeze effect. Even though the planet is losing heat rapidly,
Speaker 3: the sulfur ensures the rock simply refuses to solidify until
Speaker 3: the temperature drops incredibly low.
Speaker 2: Oh man, So it's cooling off, but it's trapped in
Speaker 2: a liquid.
Speaker 3: State precisely, and this extended period of cooling as a
Speaker 3: liquid completely changes what kind of rocks eventually form. As
Speaker 3: the temperature slowly drops toward that new super low freezing point.
Speaker 3: The very first minerals to pop out of the liquid
Speaker 3: and crystallize are those sulfur compounds.
Speaker 2: The calcium and magnesium sulfides we talked about earlier oldamite
Speaker 2: and nininjurite.
Speaker 3: Yes, because they crystallized early while the mantle was still fluid,
Speaker 3: they were able to concentrate in the upper.
Speaker 2: Crust, which perfectly explains why messengers saw all that calcium
Speaker 2: and magnesium on the surface exactly.
Speaker 3: The entire surface composition is a direct result of this
Speaker 3: prolonged low temperature crystallization that is.
Speaker 2: So incredibly elegant. It just ties everything together.
Speaker 3: It really does. It also explains Mercury's volcanic history, oh.
Speaker 2: Right, because Mercury has these huge, smooth volcanic planes.
Speaker 3: Right, vast plains of cured lava that sit on top
Speaker 3: of older, cratered terrain, which means these massive volcanic eruptions
Speaker 3: happened relatively late in the planet's youth.
Speaker 2: But if Mercury was an Earth like rock, it's so
Speaker 2: small it should have cooled and formed a thick, solid
Speaker 2: crust really early. The volcano should have choked off and
Speaker 2: died exactly.
Speaker 3: The thermal models for a normal rocky planet of Mercury
Speaker 3: size say the volcano should have shut down quickly, but
Speaker 3: the sulfur kept the engine running. It kept the mantle
Speaker 3: partially melted and fluid enough to erupt onto the surface
Speaker 3: long after it should have frozen solid.
Speaker 2: Okay, but this leads me to another question, a pushback.
Speaker 3: Actually, let's hear it.
Speaker 2: If the sulfur kept the magma hot and fluid for
Speaker 2: such a long time, how does that fit with the
Speaker 2: low bait.
Speaker 3: Scarps us the scarps?
Speaker 2: Yeah, for people who don't know mercury is covered in
Speaker 2: these massive cliffs and ridges called scarps. They look like wrinkles.
Speaker 2: The planet literally contracted and shrank like a raisin.
Speaker 3: A giant iron filled raisin.
Speaker 2: Right, But you can't wrinkle a liquid. If the mantle
Speaker 2: was fluid for so long, a shrinking core wouldn't cause
Speaker 2: the surface to snap and form cliffs. The liquid would
Speaker 2: just adjust. So how did the scarps form?
Speaker 3: That is a brilliant point. The mechanics have scarp formed
Speaker 3: absolutely require a rigid, solid, thick outer shell lithosphere. So
Speaker 3: the timeline is everything here. The global contraction, the shrinking
Speaker 3: that made those cliffs. It had to happen primarily after
Speaker 3: the sulfur rich magma ocean finally cooled past its super
Speaker 3: low freezing point and locked up.
Speaker 2: Oh I see, So it stayed liquid for a long time,
Speaker 2: letting the volcanoes erupt but eventually even the anti freeze
Speaker 2: couldn't stop it from freezing exactly.
Speaker 3: The temperature eventually dropped low enough that even those weakened
Speaker 3: sulfur silicate networks froze solid.
Speaker 2: And once it formed that thick, hard shell.
Speaker 3: Once that rigid lithosphere was in place, the massive iron
Speaker 3: core underneath continued to slowly cool and shrink over billions.
Speaker 2: Of years, and the crust had nowhere to go right, it.
Speaker 3: Induced immense compressive stress on the solid rock above it.
Speaker 3: The crust had no choice but to snap, fail catastrophically,
Speaker 3: and thrust up over itself to create those huge cliffs.
Speaker 2: So the timing of the whole tectonic history is dictated
Speaker 2: by the atomic behavior of sulfur.
Speaker 3: Yes, down to the very atoms, and it goes even deeper.
Speaker 3: It affects the magnetic field too.
Speaker 2: Wait, really, the sulfur on the rocks affects the magnetic
Speaker 2: field of the core.
Speaker 3: Oh. Absolutely, Mercury has a global magnetic field generated by
Speaker 3: a churning, convecting liquid iron core, a geodynamo.
Speaker 2: Just like Earth.
Speaker 3: Just like Earth, But for a geodynamo to work, you
Speaker 3: need a very specific rate of heat escaping from the
Speaker 3: core into the mantle. If the mantle acts like a
Speaker 3: thick thermal blanket, the core stops churning and the magnetic
Speaker 3: field dies.
Speaker 2: But we just said the sulfur made the mantle runnier
Speaker 2: and more efficient at moving heat.
Speaker 3: Exactly by proving that the sulfur rich mantle stayed fluid
Speaker 3: and less viscous for longer. The researchers basically re rode
Speaker 3: the equations for how heat moves across that boundary. The
Speaker 3: chemistry of the rock directly controlled the cooling rate of
Speaker 3: the iron core.
Speaker 2: Which means the sulfur literally dictated the strength and the
Speaker 2: longevity of the magnetic field we still measure today.
Speaker 3: It's all connected. The microscopic chemistry of the rock is
Speaker 3: inextricably linked to the massive geophysical engine inside the planet.
Speaker 2: That is just phenomenal. It's a cohesive start to finish
Speaker 2: explanation for every weird thing about mercury, the surface chemistry,
Speaker 2: the extended volcanoes, the cliffs, the magnetic field, it all
Speaker 2: tracks back to sulfur.
Speaker 3: It's a total paradigm shift, and it really validates the
Speaker 3: incredible work done by the Rice University team.
Speaker 2: Supported by NASA grants and the Rice Space Institute Center
Speaker 2: for Planetary Origins to Habitability, which you know is a
Speaker 2: long name, but they are doing vital work.
Speaker 3: Vital work because honestly, this goes way beyond mercury.
Speaker 2: Yes, this is what I really want to get into.
Speaker 2: Why does this single case study matter for the rest
Speaker 2: of the universe.
Speaker 3: Because it exposes our severe terrestrial bias, our Earth centric
Speaker 3: trap exactly because we live here. All our instruments are math,
Speaker 3: our thermodynamic assumptions. They are all grounded in the oxidized,
Speaker 3: iron rich chemistry of Earth.
Speaker 2: So when we look at other planets, we just assume
Speaker 2: they're built the same way.
Speaker 3: We project our local rules onto the rest of the galaxy.
Speaker 3: And Mercury just proved that if you apply an oxidized
Speaker 3: model to a highly reduced planet, you get totally wrong answers.
Speaker 3: You predict the wrong thermal history, the wrong structure, everything.
Speaker 2: And we are discovering so many planets right now.
Speaker 3: Thousands of them with advanced telescopes like James Web. We
Speaker 3: aren't just finding rocky exoplanets, super earths and sub neptunes.
Speaker 3: We're actually starting to look at their atmospheres and figure
Speaker 3: out what they're made of.
Speaker 2: And they aren't all like Earth, not at all.
Speaker 3: Many of them orbit stars with totally different chemistry in
Speaker 3: primordial discs that are vastly different from our own. Statistically,
Speaker 3: a huge number of these rocky exoplanets formed under highly
Speaker 3: reduced conditions.
Speaker 2: Meaning the universe is likely just teeming with these sulfur dominated,
Speaker 2: iron poor worlds absolutely teeming with them, which is kind
Speaker 2: of ironic. Right. By turning our focus inward to the
Speaker 2: absolute smallest closest planet to our Sun, we've basically built
Speaker 2: a decoder ring to understand the farthest most alien exoplanets
Speaker 2: in the galaxy.
Speaker 3: That's a great way to put it, because if we
Speaker 3: look at a distant super Earth through a telescope and
Speaker 3: try to model its interior using Earth math, we will fail.
Speaker 2: We'd calculate the wrong melting points, the wrong crust thickness.
Speaker 3: The wrong timeline for when it might release gases into
Speaker 3: an atmosphere. We would completely misunderstand its capacity to be
Speaker 3: a stable, maybe even habitable environment.
Speaker 2: But thanks to the data from crushing that little in
Speaker 2: darch media.
Speaker 3: Right, we now have the actual thermodynamic framework. We have
Speaker 3: the correct phase boundaries to model the geology of reduced
Speaker 3: exoplanets accurately.
Speaker 2: It's incredible. It lets us predict when a sulfur rich
Speaker 2: planet light years away will solidify, when its volcanoes will stop,
Speaker 2: and how its crust will deform.
Speaker 3: We can anticipate that its surface might be covered in
Speaker 3: old mite instead of basalt. We can adjust our models
Speaker 3: for its magnetic field. We are learning how to read
Speaker 3: the geological history of worlds we can't even see clearly yet.
Speaker 2: It's just a remarkable progression of knowledge. To summarize this
Speaker 2: whole journey, we started with one anomalous, weirdly reduced rock
Speaker 2: that fell in Azerbaijan in eighteen ninety one.
Speaker 3: The indarge and statype chondrite.
Speaker 2: Right, and by recognizing that its chemistry matched the weird
Speaker 2: data from mercury, researchers in twenty twenty six used it
Speaker 2: as a proxy. They subjected it to gigapascals of pressure
Speaker 2: and thousands of degrees of heat.
Speaker 3: They mapped the phase boundaries of a sulfur rich.
Speaker 2: Mantle and prove that sulfur acts as a planetary anti freeze.
Speaker 2: It depalmerizes the melt, lowers the energy needed to stay liquid,
Speaker 2: and pushes the freezing point way down.
Speaker 3: Which subsequently rewrites the entire geological timeline of mercury. It
Speaker 3: explains the sulfide crust, the long lasting magma oceans, the
Speaker 3: late forming scarps, and the magnetic dynamo.
Speaker 2: And more importantly, it proves how much our understanding of
Speaker 2: the universe is biased by our own backyard. Sometimes just
Speaker 2: swapping out one single element, oxygen for sulfur, can rewrite
Speaker 2: an entire planet's history.
Speaker 3: It changes the architecture from the atomic scale all the
Speaker 3: way up to the global features.
Speaker 2: Which leaves us with a really provoked could have thought
Speaker 2: to end on today? We now know the profound consequences
Speaker 2: of swapping oxygen for sulfur. But sulfur is just one variable,
Speaker 2: just one of many. Right as we keep looking at
Speaker 2: distant star systems, we are going to find protoplanetary discs
Speaker 2: with entirely alien elemental recipes. If a relatively simple swap
Speaker 2: like sulfur can create a world as bizarre as mercury,
Speaker 2: what else is out there?
Speaker 3: The possibilities are endless.
Speaker 2: What happens to a planet's mantle if it's heavily enriched
Speaker 2: with carbon? How does a planet dissipate heat if it's
Speaker 2: dominated by exotic refractory metals. What kind of wild, unpredicted
Speaker 2: rocks are currently shaping worlds where the initial chemistry forces
Speaker 2: elements into configurations we haven't even thought to synthesize in
Speaker 2: a lab.
Speaker 3: It's mind boggling.
Speaker 2: Mercury is proof that our familiar Earth chemistry is just
Speaker 2: one specific lucky outcome in a universe that is capable
Speaker 2: of building planets through an almost infinite number of distinct
Speaker 2: alien pathways.