Speaker 1: When we set out to understand the universe, we usually
Speaker 1: start by looking up. After all, that's where the best
Speaker 1: views are of the glittery cosmos stretched across billions of miles.
Speaker 1: We wonder, are we alone? Is there anyone up there
Speaker 1: looking back at us? But what if the best way
Speaker 1: to find answers to questions about what's up there is
Speaker 1: actually to look down under our feet. Hi, I'm Daniel.
Speaker 1: I'm a particle physicist and a professor at UC Irvine,
Speaker 1: and I desperately want to know who's out there in
Speaker 1: the universe and if they are wondering the same things
Speaker 1: we are. And Welcome to the podcast Daniel and Horace
Speaker 1: Explain the Universe in which we do just that, wonder
Speaker 1: about the nature of the universe and try to explain
Speaker 1: all of it to you. Regular listeners the podcast, know
Speaker 1: that I am desperate to understand the nature of the universe,
Speaker 1: how it all works, and to explain all of that
Speaker 1: knowledge and all of that confusion to you. One of
Speaker 1: the deepest questions we wrestle with on the pod is
Speaker 1: not just about the universe, but kind of about ourselves.
Speaker 1: How weird? Are we are? There more like us out
Speaker 1: there in the universe, or are we alone? How rare
Speaker 1: and special is the Earth anyway? Are we one of
Speaker 1: a kind out of a trillion planets, or are we
Speaker 1: one of many rocky balls covered in Curious Life. We're
Speaker 1: frustratingly limited by what we can learn about distant planets,
Speaker 1: though we're doing our best. But something we can do
Speaker 1: right now is drill deeper into our own planet, understand
Speaker 1: the forces that shaped it and whether those are finely
Speaker 1: balanced in a rare way or naturally in harmony, in
Speaker 1: a way we'll find everywhere in the universe. So today
Speaker 1: on the podcast, we'll be answering the question what's hidden
Speaker 1: inside planets? And to help me explore this fascinating topic,
Speaker 1: I'm pleasing to be speaking to Professor Sabina Stanley, author
Speaker 1: of a very recent book of that same title. All right, well,
Speaker 1: then it's my great pleasure to introduce the podcast Professor
Speaker 1: Sabina Stanley. She's the Bloomberg Distinguished Professor of Planetary Physics
Speaker 1: at Johns Hopkins University, where she focuses on magnetic fields
Speaker 1: and other geophysical elements as a means of studying the
Speaker 1: interiors of planets, moons, and asteroids. She's an Alfred Peasloan
Speaker 1: Research Fellow, and has also received the William Gilbert Award
Speaker 1: of the American Geophysical Union. Sabina, Welcome to the podcast,
Speaker 1: and thank you for coming to talk to us.
Speaker 2: Thanks so much for having me.
Speaker 1: So one thing we always wonder about as we look
Speaker 1: out into the night sky is all the other planets
Speaker 1: that are out there. Of course we can't study mnie
Speaker 1: them up close, and so often on this podcast we've
Speaker 1: tried to dig into what's under our feet, the mysteries
Speaker 1: that are right here in our Earth. And so I
Speaker 1: really enjoyed your recent book, What's Hidden Inside Planets, and
Speaker 1: I'd love to talk to you about what's in our planet.
Speaker 1: Could you start us off by taking us sort of
Speaker 1: on a brief tour of like what is under our feet,
Speaker 1: layer by layer, all the way down to the core.
Speaker 2: Yeah, absolutely, great question.
Speaker 3: So I think it's interesting to note that when you
Speaker 3: start on the surface, as you go deeper and deeper,
Speaker 3: stuff gets kind of weirder and weirder and much more
Speaker 3: different than what we're used to on the surface.
Speaker 2: So we start on the crust.
Speaker 3: This is where we live, This is where all the
Speaker 3: stuff happens that we're used to crust can vary in
Speaker 3: thickness five about you know, five kilometers depth to almost
Speaker 3: one hundred kilometers depth. But under that you get to
Speaker 3: the mantle that's also still mostly rocky, the type of
Speaker 3: rocks that are rich in magnesium and silicates, but still
Speaker 3: what we would recognize as rocks. So about half the
Speaker 3: radius of the Earth are those rocks. It goes down
Speaker 3: about two thousand miles deep.
Speaker 1: So what distinguishes then between the crust and the mantle.
Speaker 1: Is it like how squeezed they are and how much
Speaker 1: they flow, or is it a different kind of rock?
Speaker 2: Great question.
Speaker 3: Yeah, it's a little bit different kind of rock. So
Speaker 3: essentially the crust layer of the earth. I sometimes refer
Speaker 3: to it as like the scum of the earth. So
Speaker 3: it's kind of like, you know, like when you're making
Speaker 3: a soup and you're boiling your broth and you've got
Speaker 3: all that light, floaty stuff that comes to the top.
Speaker 3: So the stuff that's the most buoyant when you have
Speaker 3: certain heat, thermal reactions and chemical reactions happening with rocks
Speaker 3: near the surface, all of that percolates up to the
Speaker 3: top and that ends up becoming the crust, and then
Speaker 3: sort of the stuff underneath might be less scummy, less
Speaker 3: you know, it's been less reworked, and it's sort of
Speaker 3: more kind of pristine rock.
Speaker 1: I see, we're going to get started very quickly with
Speaker 1: the food analogies.
Speaker 2: Yeah, I'm sorry, it's just going to be how it goes.
Speaker 3: It's going to be food involved in almost every analogy
Speaker 3: I make.
Speaker 2: Here.
Speaker 1: Are you a big fan of soup or you a
Speaker 1: cook at home?
Speaker 3: So I'm a terrible cook, but I grew up in
Speaker 3: a restaurant family, so I've been around sort of good
Speaker 3: food my whole life.
Speaker 1: All right, Well, then let's do our best to at
Speaker 1: least use tasty food analogies. I don't want any want
Speaker 1: to think that the earth is like a disgusting bowl
Speaker 1: of soup. Maybe it's like, you know, bubbling hot cocoa,
Speaker 1: and this is that delicious film that forms on top.
Speaker 2: I love that so much. You don't even know. So
Speaker 2: that's amazing, all right.
Speaker 1: So the crust is the sort of coolest part that
Speaker 1: floats to the top, and underneath that it's still rock,
Speaker 1: but it's able to flow. How do we visualize that?
Speaker 1: I mean, it's not like liquid lava that's flowing on
Speaker 1: the surface. This is still like solid rock, but it's flowing.
Speaker 1: How does solid rock flow is something I've always tried
Speaker 1: to visualize and failed.
Speaker 2: Yeah, So the answer to that question is very slowly.
Speaker 1: Right.
Speaker 3: So, yes, it's solid, but it's still deformable, right, And
Speaker 3: I think we have experience with different types of solids
Speaker 3: in our everyday life, and that some are more deformable
Speaker 3: than other.
Speaker 2: Right, Like you might have clay.
Speaker 3: Clay is solid, but you can still deform it, whereas
Speaker 3: a metal also is kind of deformable. But then you
Speaker 3: have some rocks that are really like a diamond, really
Speaker 3: hard to deform. But the rocks in the mantle, they
Speaker 3: are solid, but they can be deformed, and if they
Speaker 3: can be deformed, then they start being influenced by the
Speaker 3: forces like gravity such that you can get them to flow.
Speaker 1: I see, all right, So we have the crust and
Speaker 1: we have the mantle. Both the wiz are still really rock.
Speaker 1: Take us down below that, right.
Speaker 3: So then you get down about halfway through the Earth
Speaker 3: and you suddenly hit a very big boundary, complete change
Speaker 3: of environment. Now you're at the iron core. So the
Speaker 3: inner half of the planet about it's mostly made of iron.
Speaker 3: There's a little bit of nickel mixed in there, and
Speaker 3: about ten percent of some sort of lighter elements that
Speaker 3: we have a whole sort of platter of possibilities for,
Speaker 3: but we don't actually know what they are. And that
Speaker 3: makes up the core. The core has two parts to it.
Speaker 3: The outer port is liquid. It can flow very easily,
Speaker 3: much faster timescales than the mantle, and it's really important
Speaker 3: for us because that's where our magnetic field is generated
Speaker 3: in that liquid iron core. Then below that, the innermost
Speaker 3: thirteen hundred kilometers of our planet, is a solid iron core.
Speaker 1: And so what distinguishes then the mantle, which can flow
Speaker 1: but is a solid not a liquid, from the outer core,
Speaker 1: which can flow but is a liquid and not a solid, Like,
Speaker 1: is there really a distinction here? Are we just putting
Speaker 1: labels on things?
Speaker 3: When we study fluid dynamics, we talk a lot about
Speaker 3: there being a spectrum of fluids. Right, nothing's ever purely
Speaker 3: a solid or purely a fluid. It's all about the
Speaker 3: time scales. So the mantle, for example, if you want
Speaker 3: to talk about how materials flow in the mantle, a
Speaker 3: parcel at the bottom of the mantle could take hundreds
Speaker 3: of millions of years to make it to the top
Speaker 3: of the mantle, whereas a parcel at the bottom of
Speaker 3: the core could take a couple of years to get
Speaker 3: the top of the core. So it's a very different
Speaker 3: timescale of the flow. You could actually see changes in
Speaker 3: material in the core flowing.
Speaker 1: But this is also like a boundary. It's not like
Speaker 1: there's a smooth, very gradual transition. There's like a line.
Speaker 1: You can say, this is the core and this is
Speaker 1: the mantle.
Speaker 3: Yeah, And that happens because mantle, rocks, and iron in
Speaker 3: the core have very different densities, and at one time
Speaker 3: in the past in our planet, it was mostly molten
Speaker 3: and so the heaviest stuff, when you have a bunch
Speaker 3: of stuff mixed together, the heaviest stuff's going to sync
Speaker 3: to the bottom. And so that's what happened in Earth.
Speaker 3: All the iron, most of the irons, sunk to the
Speaker 3: center of the Earth and made.
Speaker 1: Up the core like the big chunks in a stew
Speaker 1: or something exactly.
Speaker 2: Yes, I like it.
Speaker 1: So the reason that there's a boundary there and like
Speaker 1: a transition or rather than just like a smooth gradation
Speaker 1: from more liquid to less liquid, that reflects like the
Speaker 1: phase transitions and materials. Is that right, the way that
Speaker 1: like ice turns solid at some moment and doesn't just
Speaker 1: like gradually become more and more solid.
Speaker 3: I would say that's more representative of what kind of
Speaker 3: happens at the inner core outer core boundary, so where
Speaker 3: the iron becomes solid. But above that it's more kind
Speaker 3: of like a maybe you go with an oil and
Speaker 3: water type thing. You've got two materials with very different
Speaker 3: density and very different properties, so it's really hard to
Speaker 3: mix them.
Speaker 1: Wonderful and tell us about how we know about this.
Speaker 1: I was reading in your book this really exciting description
Speaker 1: of the mantle race, basically like a parallel to the
Speaker 1: space race, but into the Earth. Tell us about our
Speaker 1: humanity's efforts to like literally tunnel to the center of
Speaker 1: the Earth.
Speaker 3: Yeah, So if you imagine you want to figure what's
Speaker 3: inside the Earth, right, your first instinct might be, hey,
Speaker 3: why don't we dig down as far as we can
Speaker 3: and actually sample it?
Speaker 2: Right?
Speaker 3: And it's a great instinct. Unfortunately, it's incredibly challenging to do.
Speaker 3: And that's because pressure increases so fast as you go
Speaker 3: deeper inside the planet, and so do temperatures. So as
Speaker 3: you can imagine, humans don't like really high pressures and temperatures.
Speaker 3: Neither does equipment, and the farthest we've been able to
Speaker 3: dig with sort of a really concerted effort to do so, right,
Speaker 3: Like this was something on the scale of moonshot to
Speaker 3: the Moon in the late sixties. This is something very
Speaker 3: similar to that, And you could get only down to
Speaker 3: about eight miles in depth, and the radius of the
Speaker 3: Earth you're talking about four thousand miles, so tiny, tiny
Speaker 3: scrape of the surface by going down that deep. Equipment
Speaker 3: does not like high pressures and temperatures.
Speaker 1: But how do you even get eight miles deep? I mean,
Speaker 1: I remember digging in my backyard with a shovel, wondering
Speaker 1: how far I could get, and it's not very far.
Speaker 1: How do you get eight miles down?
Speaker 3: This is like high tech technology kind of stuff. It's
Speaker 3: at the limits of what we can do for drilling
Speaker 3: that we do now to drill for resources, et cetera.
Speaker 3: So it's a lot of fancy equipment and challenges that
Speaker 3: are over met that way. So we can't dig and
Speaker 3: we can't drill, But that's okay because there are other
Speaker 3: ways we can figure out what's going on deeper inside
Speaker 3: the earth.
Speaker 1: Yeah, So tell us about some of those ways you
Speaker 1: were talking in the book about diamonds, how we can
Speaker 1: use diamonds to give us little snapshots of what's inside
Speaker 1: the planet.
Speaker 3: Yeah, so you know, it would be great if we
Speaker 3: could dig down, but would it also be great if
Speaker 3: the stuff down there came to us. And that's really
Speaker 3: what happens with diamonds. Diamonds are produced deeper inside the Earth,
Speaker 3: and then they come up to the surface, usually in
Speaker 3: volcanic vent things known as kimber like pipes and those diamonds.
Speaker 3: You know, Jewelers love diamonds when they're as pure as possible.
Speaker 3: Geologists love diamonds when they're as impure as possible. So
Speaker 3: sometimes diamonds, when they form, they can enclose a little
Speaker 3: capsule of some of the material where they formed inside them, right,
Speaker 3: So you might get a little bit of garnet in
Speaker 3: the diamond or a little bit of something that was
Speaker 3: created deeper in the earth. And when it it up,
Speaker 3: because diamonds so strong, it actually keeps the material in
Speaker 3: its like pristine form, So you really have this like
Speaker 3: sample from the interior of the Earth come to the
Speaker 3: surface for us to investigate. So that's a great way
Speaker 3: and we've used that, for example, to figure out that
Speaker 3: there is actually water deeper inside the Earth because we've
Speaker 3: found water inside diamond inclusions.
Speaker 1: It's fascinating to me though, that this thing that you
Speaker 1: make in a high pressure environment, when you bring it
Speaker 1: up to low pressure, it doesn't explode. Is that just
Speaker 1: because of the incredible structure of diamond?
Speaker 2: Yeah.
Speaker 3: When they say diamonds are forever, that's technically not true, right,
Speaker 3: They just have a really really long lifetime before they
Speaker 3: revert back to their carbon phase.
Speaker 2: So yeah, it's just a great property of diamond.
Speaker 1: So is it's sort of like you know, you put
Speaker 1: a pan of brownies in the oven and it changes
Speaker 1: into something else, and when you take it out, cool
Speaker 1: it down, it doesn't revert back into batter.
Speaker 2: That's an excellent way of thinking about it.
Speaker 1: Yeah, okay, And so then what have we learned from
Speaker 1: these diamond samples? Like what's inside these diamonds that we
Speaker 1: didn't realize other than water?
Speaker 2: Yeah? I think water is the big thing.
Speaker 3: Sometimes it's a lot about sort of the smaller amounts
Speaker 3: of elements that we don't know about, Right, how much
Speaker 3: of a particular kind of silicon down there is sulfur,
Speaker 3: down there these kinds of questions, and those all just
Speaker 3: help us understand what the building blocks of Earth were
Speaker 3: when Earth formed, and what the geochemistry the kind of
Speaker 3: chemical reactions that can occur as material descends into the Earth.
Speaker 3: That's really where we get that information. But even with diamonds, right,
Speaker 3: we're talking about the outermost layers of the mantle, right, diamonds.
Speaker 3: We don't get diamonds safe from the core mantle boundary
Speaker 3: or anywhere deeper than that. So we can't use the
Speaker 3: diamonds to learn about the deeper parts.
Speaker 1: Is that because diamonds aren't made deeper or because diamonds
Speaker 1: from that far down just don't make it up to
Speaker 1: the surface.
Speaker 3: Mostly the latter, I think also, like if you get
Speaker 3: carbon down there, yeah, it doesn't necessarily join into making
Speaker 3: diamond at that depth.
Speaker 1: All right, So there aren't like huge diamonds buried deep
Speaker 1: in the earth that we are not on Earth, not
Speaker 1: on Earth. Well, that was my whole motivation for digging
Speaker 1: so deeply when I was a kid, fantasizing about revealing
Speaker 1: some you know, boulder sized diamond. All right, So diamonds
Speaker 1: give us one sample of what else can we do?
Speaker 1: What about gravity? What about just studying like the variation
Speaker 1: in Earth's gravity as we you know, orbit to planate
Speaker 1: or look around it. What does that tell us about
Speaker 1: what's inside the Earth.
Speaker 3: The way I like to think about it is, you know,
Speaker 3: if you want to figure out what's going on inside
Speaker 3: the Earth, try and make an analogy to a human body.
Speaker 3: Right if you if you have an ache and you
Speaker 3: go to your doctor and you're like this hurts. Hopefully
Speaker 3: they're not. Their first kind of instinct is not to
Speaker 3: drill a hole in you to figure that out. Right,
Speaker 3: There are ways that they can use different fields and
Speaker 3: different scans to figure out what's wrong with your insides,
Speaker 3: And we can do the same thing for the inside
Speaker 3: of the Earth. So we can scan gravity as you mentioned,
Speaker 3: that's one, Magnetic fields is another one.
Speaker 2: And we can also determine.
Speaker 3: Properties of waves that travel through the Earth from earthquakes
Speaker 3: through seismology. So we can use all these scanning techniques
Speaker 3: to figure out what's going on deeper inside the Earth.
Speaker 1: So what do you mean by using gravity? Is it
Speaker 1: just like measuring the variations of gravity so that we
Speaker 1: understand how the Earth is not a perfect sphere or
Speaker 1: how they'rear is not homogeneous in density. What is it
Speaker 1: we're learning?
Speaker 2: Yeah, great question.
Speaker 3: So, yeah, it really is the fact that both isn't
Speaker 3: a perfect sphere and has some inhomogeneous material below it. Right,
Speaker 3: So if you were walking around with a griviminter that
Speaker 3: could measure gravity and it was really really good and
Speaker 3: you walked around, you would get slightly different values everywhere
Speaker 3: you walk, and that would be determined by the mass
Speaker 3: directly under your feet. And so we can use that information.
Speaker 3: We have spacecraft that orbit the Earth that measure Earth's
Speaker 3: gravity feel to really high precision, and we can use
Speaker 3: that to figure out what is the distribution of density
Speaker 3: inside the Earth. And that kind of allows us to
Speaker 3: kind of image what's going on. Where's the denser stuff
Speaker 3: in the Earth, where's the lighter stuff? And we can
Speaker 3: actually see things like convection cells in the mantle and
Speaker 3: plumes of magma coming up for volcanoes, things like this.
Speaker 1: But gravity is such a weak force. How do you
Speaker 1: identify these variations in density with such an incredibly weak force.
Speaker 1: They must be pretty big effects.
Speaker 3: They aren't. They are very very tiny effect. We're just
Speaker 3: really good at measuring them.
Speaker 1: Emitter, you mentioned this might seem like a weird object
Speaker 1: or listeners. But I guess, like my bathroom scale is
Speaker 1: a gravi emitter. If I walked around the Earth with
Speaker 1: my bathroom scale, I would measure different weights before and
Speaker 1: after lunch, of course, but also if I didn't need anything,
Speaker 1: or I user reference mass, then I guess I would
Speaker 1: measure different accelerations due to gravity.
Speaker 2: Yeah.
Speaker 3: Absolutely, And if you are someone on the surface taking
Speaker 3: gravity measurements, that's exactly the kind of instrument you would use. Interestingly,
Speaker 3: once we get into orbiting around a planet like Earth
Speaker 3: to take measurements, we use a completely different technique. We
Speaker 3: basically use the fact that if we have a spacecraft
Speaker 3: in orbit around the Earth, we know it's in orbit
Speaker 3: around the Earth, and its orbital speed and altitude is
Speaker 3: completely determined by the mass of the planet.
Speaker 2: So we can use things.
Speaker 3: Like two spacecraft just slightly at different locations from each
Speaker 3: other kind of moving around, and we can use the
Speaker 3: distance between the two spacecraft as like a proxy for
Speaker 3: how much g is right where they are, how much
Speaker 3: the gravity is right where they are. So that's actually
Speaker 3: how it's done in practice with spacecraft.
Speaker 1: Wow, that's incredible, And how sensitive are they? I mean,
Speaker 1: like one part in a thousand, one part in a million.
Speaker 2: Yeah, one part in a million. That's where we're getting to.
Speaker 1: Wow, So they can really tell if I've eaten lunch.
Speaker 1: Some spacecraft up there can tell that the mass of
Speaker 1: the Earth has changed.
Speaker 3: One thing they're actually used for. So the Grace satellites,
Speaker 3: which orbited Earth for about ten years, one of their
Speaker 3: main applications was to follow water flow on the surface,
Speaker 3: so you could see, for example, when water was filling
Speaker 3: reservoirs underground reservoirs in certain parts of the country or
Speaker 3: different countries if you wanted to see are we going
Speaker 3: to have a drought, are we in a rainstorm season,
Speaker 3: or what's the water situation going on here?
Speaker 2: So we can even use gravity to tract climate change.
Speaker 1: Wow, that sounds like modern day divining rods. But you're
Speaker 1: actually using science to find the water underground. That's incredible,
Speaker 1: all right, So gravity's one way to do it. You
Speaker 1: also mentioned seismic probes. These are like waves inside the earth.
Speaker 1: How do we use that to see what's going on?
Speaker 3: So every time there's an earthquake, it's like sort of
Speaker 3: something kind of punched the inside of the Earth at
Speaker 3: some point and it causes the Earth to ring. It
Speaker 3: causes waves to travel through the interior of the Earth
Speaker 3: and on the surface of the Earth. If we put
Speaker 3: out a bunch of instruments that can kind of measure
Speaker 3: the shaking, so seismographs, then we can figure out a
Speaker 3: few things.
Speaker 2: About the earthquake waves.
Speaker 3: We can figure out when they arrive at different locations
Speaker 3: around the planet, and how big the waves are, the
Speaker 3: amplitude of the waves.
Speaker 2: And the speed.
Speaker 3: The timing of when the waves arrive is completely directly
Speaker 3: related to the material properties that the waves traveled through.
Speaker 3: So for example, we can figure out the density of
Speaker 3: material that a wave traveled safe from. Let's say an
Speaker 3: earthquake happens in California and the wave travels up to
Speaker 3: Seattle in Washington. You can use that to figure out
Speaker 3: kind of what's the material just under the surface there,
Speaker 3: Whereas if you try to go across the globe to
Speaker 3: another part on the other side, the waves might travel
Speaker 3: through the entire planet and we could actually sample the
Speaker 3: material in the.
Speaker 2: Core for example.
Speaker 3: So you can use all those different measurements. The more
Speaker 3: locations you have on the Earth for these seismic measurements
Speaker 3: to be made, the more you can kind of discern
Speaker 3: what is the lateral structure of the.
Speaker 2: Interior of the Earth.
Speaker 1: And we're really talking about sound waves, right, These are
Speaker 1: pressure waves in the rock, and so we can think
Speaker 1: about how denser materials have sound travel faster, and less
Speaker 1: dense materials sound travels lower. So you're measuring the density
Speaker 1: of the material by measuring the speed of sound. But again,
Speaker 1: these are rocks that are like pushing on each other, right,
Speaker 1: Like sound waves through rock is a very weird thing
Speaker 1: to think about.
Speaker 3: Yeah, absolutely, So there are the sound waves that The
Speaker 3: other type of wave that goes through are these sheer waves.
Speaker 3: So those are kind of more like waves you'd experience
Speaker 3: in a fluid, let's say, or not in fluid, sorry,
Speaker 3: waves that you would experience if you try to kind
Speaker 3: of bend peanut butter or something like that. Right, So
Speaker 3: there's multiple kinds of waves, and some of them are
Speaker 3: very diagnostic of what's going on in certain types of materials.
Speaker 1: Well, I never thought we'd be talking about peanut butter waves,
Speaker 1: but here we are. So when did we get this picture, Like,
Speaker 1: what is the first technique that really gave us a
Speaker 1: view of the inside of the earth. Was it the
Speaker 1: seismographs or is it something else.
Speaker 2: That's a good question.
Speaker 3: It's not like there was a sun moment where suddenly
Speaker 3: we had this picture of the Earth. I think we
Speaker 3: develop our understanding to higher and higher precision as time
Speaker 3: went on.
Speaker 2: Right, I think early studies.
Speaker 3: Of gravity, going back to Newton, let's say, was able
Speaker 3: to tell us this is the mass of the Earth,
Speaker 3: and then you could take, for example, samples of crustal
Speaker 3: rocks and figure out what their density was and infer, hey,
Speaker 3: there must be a lot more mass deeper in the center.
Speaker 3: So that was kind of first order information you might
Speaker 3: get so through both seismology. So early nineteen hundreds was
Speaker 3: when we were doing some really great seismology figuring out
Speaker 3: things like, oh, look we have a core. Right, that
Speaker 3: was where the core was first discovered. The inner core
Speaker 3: was discovered in the early nineteen hundreds. The first sort
Speaker 3: of real profile of density through the Earth happened, I
Speaker 3: think it was in the seventies with what was called
Speaker 3: the Preliminary Reference Earth Model, which really used a whole
Speaker 3: bunch of seismic data to really kind of do an
Speaker 3: inverse problem and figure out here's what the seismic wave
Speaker 3: speed and the density has to be at every depth
Speaker 3: the in sort of like a won d earth. So
Speaker 3: that was a big step forward there too. But at
Speaker 3: the same time, gravity was being used, and so we
Speaker 3: were getting pictures from different types.
Speaker 1: Of information, But were the only a few hundred years
Speaker 1: that we've had any sort of reasonable idea of what's
Speaker 1: under our feet. And it sounds like only the last
Speaker 1: few decades, maybe fifty years, that we've had any sort
Speaker 1: of detailed picture of what's actually inside our own planet.
Speaker 1: It's incredible how long we can remain ignorant about really
Speaker 1: basic science about our own lives.
Speaker 3: Yeah, when I talk to people, I tell them geophysics
Speaker 3: is really modern physics because all of the stuff we're
Speaker 3: doing now is all stuff that's happened sort of in
Speaker 3: the last sixty seventy years. So I'd like to think
Speaker 3: of it as a modern physics.
Speaker 1: Approach, right, And now we've extended this frontier two other planets.
Speaker 1: We've talked in the podcast before about the Insite mission,
Speaker 1: and I think you worked on that measuring Mars quakes
Speaker 1: to see what's inside Mars. Did the same principles apply there?
Speaker 3: Yes, absolutely, So the amazing thing with the Inside mission
Speaker 3: is brought a seismometer, and that seismometer had to be
Speaker 3: placed onto the surface of Mars so that it could
Speaker 3: measure the ground shaking essentially, and it worked, like it
Speaker 3: was just amazing that it worked. But it was a
Speaker 3: very interesting experience because for most of the mission, and
Speaker 3: especially in the big all the Mars quakes we were
Speaker 3: seeing were quite weak.
Speaker 2: We were looking for.
Speaker 3: The big one, right, We're looking for the big Mars quake,
Speaker 3: because the bigger the quake, the more ways we'll travel
Speaker 3: through the deeper parts of Mars. And so we really
Speaker 3: wanted to study or I really wanted to study the core,
Speaker 3: and for that we needed some big Mars quakes, and
Speaker 3: they really didn't happen for the first few years, and
Speaker 3: then right near when the mission was about to end,
Speaker 3: we suddenly had a few. So that was really amazing
Speaker 3: to get that data at the end. So Mars kind
Speaker 3: of kept us hoping for a while and then finally delivered.
Speaker 1: And before you landed on Mars with this seismometer, did
Speaker 1: you have much reason to expect that there were Mars quakes?
Speaker 1: Or it could be that Mars was totally silent.
Speaker 3: I mean it could have been we didn't have any
Speaker 3: direct evidence from Mars quakes. But my geologist friends who
Speaker 3: are used to looking at say tectonic features on the surface,
Speaker 3: looking at things like where are the cracks in the surface,
Speaker 3: where are the mountains, they would have told me to
Speaker 3: expect Mars quakes because they see movements geologically, they see
Speaker 3: movements on the surface. But also, luckily, we kind of
Speaker 3: have our own source of Mars quakes. In a way,
Speaker 3: when meteors hit planet, they crash into them. They're kind
Speaker 3: of like a hammer that's smashing into a bell, right,
Speaker 3: And so a lot of the Mars quakes we measured
Speaker 3: were actually caused by meteors that hit Mars as opposed
Speaker 3: to just tectonic activity happening in the interior.
Speaker 1: Well, it's terrifying to me or feel a little conflicted
Speaker 1: the geologists are rooting for quakes and rooting for like
Speaker 1: big impacts because they're like, ooh, yay data.
Speaker 2: Yes exactly, I will.
Speaker 3: I mean, as a funny story on the mission, we
Speaker 3: did at one point, so the Insight mission was on
Speaker 3: the surface when the Perseverance rover was planning to land,
Speaker 3: and we did kind of do a calculation where if
Speaker 3: the landing didn't go so well would be able to
Speaker 3: detect the way from that.
Speaker 2: Luckily that didn't happen. We had a very nice landing.
Speaker 1: Congratulations on your landing. Too bad we didn't get some
Speaker 1: cool data though from your explosion of your huge project.
Speaker 1: Oh my gosh. All right, this is really fun and
Speaker 1: I want to hear a lot more about what's going
Speaker 1: on inside our planet. But first let's take a quick break. Okay,
Speaker 1: we're back. We're talking to Professor Sabina Stanley, author of
Speaker 1: the book What's Hidden Inside Planets, about what's inside our planet.
Speaker 1: You mentioned earlier that it was amazing that insight worked.
Speaker 1: Is that just because it's hard to land stuff on
Speaker 1: Mars and operate a robot on another planet or was
Speaker 1: there something particularly challenging about a seismometer on another planet.
Speaker 3: Yeah, Inside had a lot of firsts, I would say, right,
Speaker 3: it wasn't the first lander. We've had other landers on
Speaker 3: the surface, but this was the first time we were
Speaker 3: going to take equipment that was stored on top of
Speaker 3: the lander and actually physically move it to put it
Speaker 3: on the surface. So there were lots of ways that
Speaker 3: could have gone wrong. Right, This lander had this arm
Speaker 3: type device that had to pick up the seismometer on
Speaker 3: the lander and move it onto the surface. So that required,
Speaker 3: you know, tons of work to get that to just
Speaker 3: work properly. Then it had to put a windshield on
Speaker 3: top of the seismometer to make sure that we didn't
Speaker 3: measure a bunch of wind basically because wind also shakes schismometers.
Speaker 3: Then you know that the seismometer wasn't the only instrument
Speaker 3: on Insight. There was also a thermal probe what we
Speaker 3: called the mole, which was supposed to dig down about
Speaker 3: ten meters and take temperature measurements at depth, which would
Speaker 3: have told us about the heat flow coming out of Mars.
Speaker 2: Again, this was going to be the first time.
Speaker 3: Anything like this was tried, and unfortunately we couldn't get
Speaker 3: the mole to dig deeper than about tens of centimeters.
Speaker 3: The properties of the soils kind of a word we use,
Speaker 3: but the properties of the sand on Mars were not
Speaker 3: as we expected, and just the device couldn't actually use
Speaker 3: friction to dig down deeper and deeper. So that was
Speaker 3: a struggle and we actually the Insight engineering team that
Speaker 3: worked on this and the scientists that worked on this,
Speaker 3: you know, I wasn't part of this. It was just
Speaker 3: amazing the things that they tried, and in the end
Speaker 3: we actually did get some good science out of it.
Speaker 2: We measured more sort of the thermal.
Speaker 3: Properties at the upper part of the cross as opposed
Speaker 3: to deeper down. But it was just amazing to see
Speaker 3: how much they tried to work on doing this first
Speaker 3: digging on here. You know, we talked about digging on
Speaker 3: the Earth is hard. Now imagine digging on another planet
Speaker 3: without humans, and it's even harder.
Speaker 1: Wonderful, And then what are the plans for the future.
Speaker 1: Is NASA planning to dig into the surfaces of any
Speaker 1: other objects in the Solar System or put seismometers on
Speaker 1: any other surfaces.
Speaker 3: So I think seismometers is definitely something that's going to go.
Speaker 3: So there is a big push right now to send
Speaker 3: spacecraft back to the Moon so that we can better
Speaker 3: understand our closest celestial body, let's say. And so there
Speaker 3: is a mission that will involve putting a seismometer, putting
Speaker 3: more seismometers on the Moon. We already have some seismometers
Speaker 3: on the Moon that were turned off a while ago
Speaker 3: for budgetary reasons, right, So it'll be great to get
Speaker 3: seismology again on the Moon. But for me, the most
Speaker 3: exciting is that an upcoming mission that's planned to go
Speaker 3: to Titan, which is a moon of Saturn, is actually
Speaker 3: going to have a seismometer on it as well. So
Speaker 3: it'll be interesting to see what we can learn about
Speaker 3: the interior of.
Speaker 1: Titan, and what do we know right now about the
Speaker 1: interior of Titan, And how could we know anything about
Speaker 1: it just from like looking at a few photons that
Speaker 1: happened to reflect off of it.
Speaker 3: So Titan is one of my favorite places, so it's
Speaker 3: really exciting to think about what they're going to see.
Speaker 3: So Titan's a unique place. First of all, it's the
Speaker 3: only other planetary body in the Solar System that has
Speaker 3: a nitrogen based atmosphere that's thick like the Earth's right,
Speaker 3: So earth Is atmosphere is mostly nitrogen, and the surface
Speaker 3: pressure on Titan is about one and a half bars,
Speaker 3: so one and a half Earth atmospheres. But the cool
Speaker 3: thing about Titan is that it's a small planet and
Speaker 3: so it has very little mass and so its gravity
Speaker 3: is really low. So if you were to go to
Speaker 3: Titan and put some cardboard on your arms and flap them,
Speaker 3: you would be able to fly on Titan because you
Speaker 3: have ideal buoyancy situation there. You've got thick atmosphere, low gravity,
Speaker 3: so it's really easy to fly there.
Speaker 1: So in contrast, like they had the helicopter on Mars,
Speaker 1: that was a real challenge because the atmosphere was thin
Speaker 1: and the helicopter needs atmosphere exactly exactly.
Speaker 3: So the Dragonfly mission, which is going to Titan, should
Speaker 3: get there in the mid twenty thirties. It is going
Speaker 3: to involve a dual quad copter. So this thing has
Speaker 3: basically eight rotors and this to me, because I'm Canadian,
Speaker 3: it looks like a skidoo or a snowmobile because it
Speaker 3: has these sled tracks underneath it. But it's basically going
Speaker 3: to fly around land somewhere, do a bunch of science,
Speaker 3: then take off again, look for a new location, scout somewhat,
Speaker 3: then fly to a new location, land again. And so
Speaker 3: it's going to be able to do ground local science
Speaker 3: right at an individual location for a bunch of locations
Speaker 3: over the surface. And that's really the challenge in planetary
Speaker 3: science is this kind of combination of get lots of
Speaker 3: data from lots of different places really locally, really close
Speaker 3: to the surface. So that's going to be a very
Speaker 3: exciting mission.
Speaker 1: We'd have to ask you about that. Is that going
Speaker 1: to be self directed? Is it going to decide on
Speaker 1: its own where to go or is it going to
Speaker 1: wait for signals for minutes and minutes from Earth?
Speaker 3: Full disclosure here, I have no involvement in the Dragonfly mission.
Speaker 3: I'm just a super fan. But my understanding is what
Speaker 3: it's going to do is when it kind of goes
Speaker 3: up the one time.
Speaker 2: When it flies up one time.
Speaker 3: It's going to survey, It's going to look around, then
Speaker 3: it'll come back down recharge its batteries. And during that time,
Speaker 3: when the data gets back to Earth, people are going
Speaker 3: to look around and say, let's go here, right that
Speaker 3: place over there looks kind of interesting. So it'll be
Speaker 3: a combination. Some of the in time flight stuff is
Speaker 3: going to have to be done by the spacecraft by itself,
Speaker 3: but when it comes to making decisions about where to
Speaker 3: go next in terms of big steps, that's going to
Speaker 3: be done by the people.
Speaker 2: Back here on Earth.
Speaker 1: I really liked your comment about needing to sample several places.
Speaker 1: It seems obvious that if you only land on Earth
Speaker 1: in one place, you might conclude, oh, this whole place
Speaker 1: is granted or oh, look, it's all beautiful marble or something.
Speaker 1: Obviously you need to look around to get a better sample.
Speaker 1: And so when we only land on one place on
Speaker 1: the Moon, like the Apollo astronauts, you know, only looked
Speaker 1: or near where they landed, we may have gotten a
Speaker 1: bias sample of what's going on up there. So that's
Speaker 1: really cool that they're going to explore it. So other
Speaker 1: than landing on the surface. In your book, you were
Speaker 1: talking about seeing what's inside a planet by basically how
Speaker 1: it wobbles. Can you walk us through the physics of that,
Speaker 1: the moment off and how it gives us a picture
Speaker 1: of what's inside.
Speaker 2: Yeah.
Speaker 3: Absolutely, So all of the planets spin to some amount, right,
Speaker 3: That's why we have a day on the Earth. And
Speaker 3: when it spins, a planet doesn't just stay a perfect sphere.
Speaker 3: It kind of gets fatter at the equator than it
Speaker 3: does at the poles. Now, it turns out that how
Speaker 3: fat it gets at the equator versus the poles is
Speaker 3: directly related to what the material properties of the object are. So,
Speaker 3: for example, if you had a perfect water planet, right,
Speaker 3: imagine the small planet made of water and you spun
Speaker 3: it there's a specific like ellipsoidal shape you would get
Speaker 3: for a liquid planet, Whereas if you had a dense
Speaker 3: core inside the planet and with a solid layer and
Speaker 3: then a water ocean on the outside, you're going to
Speaker 3: get a different amount of flattening or a different amount
Speaker 3: of kind of bulging at the equator from that. So
Speaker 3: we can actually use the amount of bulging of these
Speaker 3: planets when they're spinning to get information about what's inside.
Speaker 1: So, for example, you spin a basketball, it stays a sphere,
Speaker 1: but if you spin a blog a pizza dough, it
Speaker 1: becomes a disc, right, and so it tells you pizza
Speaker 1: do softer than basketballs. I guess we already knew that,
Speaker 1: But you're saying we can apply the same thing to planets.
Speaker 1: By the deformation of the sphere, we can tell basically
Speaker 1: how rigid it is.
Speaker 3: Yes, absolutely, and also where the dense, how dense it
Speaker 3: is essentially in different parts. So for example, Saturn, Saturn
Speaker 3: is the bulgiest of all the planets in our solar systems.
Speaker 3: Even if if you look at through a telescope, it
Speaker 3: doesn't look like a sphere, It actually looks like more
Speaker 3: of an oblate spheroid. So it's really interesting to look
Speaker 3: at Saturn through a telescope.
Speaker 1: You mean Saturn looks like squished, like somebody sat on it.
Speaker 2: Yes, Saturn looks like someone satur on it.
Speaker 1: In the best possible way. I mean Saturn's beautiful, Yes, yes, absolutely.
Speaker 3: But because of that, we know that Saturn isn't just
Speaker 3: a ball of hydrogen helium. We know that there have
Speaker 3: to be some rocks inside kind of condensed at the center,
Speaker 3: and then the gas sphere is kind of more on
Speaker 3: the outside of it. So we've actually been able to
Speaker 3: figure that out from the size of its equatorial bulge.
Speaker 2: So that's the first way we can use rotation. There
Speaker 2: are other ways.
Speaker 3: So for example, as planets orbit and rotate, they can
Speaker 3: actually as they're rotating, they don't always point their north
Speaker 3: pole to exactly the same location, so they can actually process,
Speaker 3: so their rotational axis can move around in a circle
Speaker 3: about their orbit axis. And if you've ever played with
Speaker 3: like a top, like a toy top, and you've spun
Speaker 3: it and you've seen it make this little wobbly circlar pattern,
Speaker 3: planets do the same thing. So planetary rotation axis wobble,
Speaker 3: they process, and they also do this thing called nutating
Speaker 3: where they kind of dip down a little bit, and
Speaker 3: the period of those procession motions and the kind of
Speaker 3: how cyclical they are really tells us about the interior
Speaker 3: properties as well.
Speaker 1: But why does it happen in the first place, I mean,
Speaker 1: does an angular momentum tell us that it should we
Speaker 1: spin along the same axis? Is this the effect of
Speaker 1: like other things pulling on it?
Speaker 2: Yes, exactly.
Speaker 3: So if Earth were alone, if it was just the Earth,
Speaker 3: then nothing else was around, we would not have any
Speaker 3: procession or mutation. But we've got the Sun, we've got
Speaker 3: the Moon nearby, and both of those things causecessional motions
Speaker 3: and wobbling nutational motions that affect our orbit in our day.
Speaker 1: So Jupiter and the other things are pulling on the
Speaker 1: Earth and changing the direction of its spin axis basically
Speaker 1: like where the north pole is pointing in the galaxy.
Speaker 1: And you're saying that tells us something about what's inside
Speaker 1: the Earth. People, I think are used to thinking about
Speaker 1: the gravitational model of like, well, you can treat the
Speaker 1: whole planet as a point mass at its center of mass,
Speaker 1: you can't learn anything else about it. So how is
Speaker 1: it possible to know something about the distribution of mass
Speaker 1: inside the planet from how it's spin wobbles.
Speaker 3: So the wobbling and the spin can tell you things,
Speaker 3: for example, like if you have a liquid layer inside
Speaker 3: the planet. So I don't know if you've ever played
Speaker 3: this game, but if you take a beach ball and
Speaker 3: you put like a little pocket of water in it
Speaker 3: and you try to throw it to someone, it moves
Speaker 3: completely differently than if you don't. Or even easier, take
Speaker 3: an egg. Take a raw egg and take a cooked egg,
Speaker 3: both still in their shells, and put them on your counter.
Speaker 2: And spin them, and you will see that they spin.
Speaker 3: Very differently because one of them has liquids inside of
Speaker 3: it and the other one is fully solid. So we
Speaker 3: can use the way that the spin axis wobbles to
Speaker 3: figure out where are there liquid layers in this place?
Speaker 2: Is it fully solid that sort of thing I see?
Speaker 1: Is this planet more like a soft or hard boiled egg.
Speaker 1: That's incredible, And can't you also measure the moment of
Speaker 1: inertia of the planet and tell like where the mass
Speaker 1: is distributed, Like you can tell the difference between like
Speaker 1: all the mass being at the core versus all the
Speaker 1: mass being at the surface.
Speaker 3: Yeah, so it's a bit complicated in the math, but
Speaker 3: it turns out that the precession rate, so how fast
Speaker 3: the axis of the rotation processes about the orbit normal.
Speaker 2: I'll give you any example.
Speaker 3: So on the Earth right now, our north pole points
Speaker 3: to the North Star. It was named lat Way for
Speaker 3: a very specific reason. But it's moving around and in
Speaker 3: about twenty it takes about twenty six thousand years for
Speaker 3: that pole to get back to the North Star. Right,
Speaker 3: So the period of our orbit is twenty six thousand years,
Speaker 3: and that period can be used to actually determine the
Speaker 3: moment of inertia of the Earth through some fancy math formulas.
Speaker 3: And so if we can measure the precession rate or
Speaker 3: the period for other planetary bodies, we can also figure
Speaker 3: out their moment of inertia.
Speaker 1: Wow, twenty six thousand years. How long have we been
Speaker 1: making these measurements? Couldn't have been more than a thousand
Speaker 1: years that maximum?
Speaker 3: Yeah, yeah, it's definitely less than that. But you know,
Speaker 3: you can you can trace out a little arc of
Speaker 3: a circle, then you can pretty much draw out the
Speaker 3: rest of the circle.
Speaker 1: Yeah, I guess we have a model and we can
Speaker 1: fit to that little arc. That's amazing, incredible. We can
Speaker 1: learn so much about what's inside these objects without even
Speaker 1: ever going inside. All right, I can't wait to talk
Speaker 1: about this some more, but first we have to take
Speaker 1: another break. Okay, we're back and we're talking to Professor
Speaker 1: Sabina Stanley, author of the new book What's Hidden Inside
Speaker 1: Planets about what's inside the Earth and other planets. Now,
Speaker 1: I want to talk about sort of how the inside
Speaker 1: affects the outside, because obviously, if you're just curious about
Speaker 1: how the solar system is formed, you want to know,
Speaker 1: like what's inside the Earth. But even if you're not,
Speaker 1: like it has an effect on living on the surface, right,
Speaker 1: tell us about how the magnetic field of these things
Speaker 1: is generated and how it relates to bubbling soup.
Speaker 2: Yeah, so magnetic fields are my favorite topic. Not gonna lie.
Speaker 2: So here's this amazing thing. Right.
Speaker 3: We're on the surface of the Earth, and one of
Speaker 3: the reasons it's such a nice place to live at
Speaker 3: the moment is because we have this beautiful magnetic field
Speaker 3: that completely envelops the Earth. And that magnetic field what
Speaker 3: it does for us is it shields the surface from
Speaker 3: high energy particles that come from the solar wind, which
Speaker 3: come from the Sun and from cosmic rays that come
Speaker 3: from deep space, and those very high energy particles. If
Speaker 3: we didn't have our magnetic field, they would kind of
Speaker 3: blast the surface of the Earth and they would do
Speaker 3: some terrible things. First of all, they would cause high
Speaker 3: radiation environments, so we'd likely have higher rates of cancer,
Speaker 3: for example. But also they cause lots of electrical disturbances.
Speaker 3: And if you think about our power grid, our power
Speaker 3: grid does not like there to be large fluctuations in
Speaker 3: electromagnetic fields.
Speaker 2: That's another thing that is not so good.
Speaker 3: It also tends to these solar winds that bombard planets.
Speaker 3: They can actually erode the atmosphere of a planet, so
Speaker 3: they can take they can basically, you know, it's like
Speaker 3: pointing a hair dryer at the Earth. You're going to
Speaker 3: be able to blow off all the gas from it.
Speaker 3: So there are all these things that the magnetic field
Speaker 3: actually shields us from. But this magnetic field that surrounds
Speaker 3: us is actually created deep inside the Earth in the
Speaker 3: iron core. So iron is great electrical conductor. When you
Speaker 3: have a great electrical conductor, if you can get it
Speaker 3: moving around in the right way, then you can actually
Speaker 3: generate magnetic fields And the best kind of analogy I
Speaker 3: can think of for this is if anyone has a
Speaker 3: home generator or if they have a bike light that
Speaker 3: they can pedal to get going, you're basically converting the
Speaker 3: kinetic energy of that motion into electromagnetic energy.
Speaker 2: So you either you know.
Speaker 3: You're pedaling, causes your bike light causes currents to flow
Speaker 3: that causes your bike light to shine right, or similar
Speaker 3: in your generator. So in the core of the earth,
Speaker 3: convection which occurs because the center is hotter than the
Speaker 3: outer parts of the core, So you kind of have
Speaker 3: bubbling up like like you would if you put a
Speaker 3: pot of soup on the stove, right, you get the
Speaker 3: bottom of the pot is hot, the top of the
Speaker 3: pot is cold, So you get these overturning motions in
Speaker 3: the soup. Same thing happens in the core, and so
Speaker 3: that overturning motions they create magnetic fields and you get
Speaker 3: what called a dynamo. So the dynamo in the center
Speaker 3: of the earth generates this magnetic field that protects us
Speaker 3: on the surface.
Speaker 1: Amazing, And so you're saying that it's the convection cells
Speaker 1: that generate the magnetic field, not for example, the spinning
Speaker 1: of the planet.
Speaker 3: Right, So there's a somewhat common misunderstanding out there that
Speaker 3: the reason that Earth has a magnetic field, for example,
Speaker 3: is due to its spinning. And this has been used sometimes,
Speaker 3: for example, to explain why Venus, which is spinning very slowly,
Speaker 3: doesn't have a magnetic field.
Speaker 2: And it turns out.
Speaker 3: That you don't need spinning at all to generate a
Speaker 3: magnetic field. So magnetic fields can be generated through dynamo
Speaker 3: processes without spinning. Now, spinning sometimes helps in organizing motions
Speaker 3: and stuff like that, but it's not actually a requirement.
Speaker 3: So it's the convective motions, not the spinning, right.
Speaker 1: And so in your analogy, you're talking about like peddling
Speaker 1: your bicycle to generate electricity, And we haven't seen any
Speaker 1: magnetic monopoles in our universe, so we know that to
Speaker 1: generate magnetic fields you have to take a charge and
Speaker 1: put it in motion, which is how electrical generators work.
Speaker 1: But what is the charge here? Like we have flows
Speaker 1: of iron. Iron is obviously metallic and it conducts, but
Speaker 1: don't you need some ion in motion in order to
Speaker 1: get a current going? What generates the actual current? If
Speaker 1: you just have neutral iron how does that generate a
Speaker 1: magnetic field.
Speaker 3: Yeah, it's actually an induction process. So what it is
Speaker 3: is you've got a good electrical conductor and imagine you
Speaker 3: have a magnetic field and it's frozen into a good
Speaker 3: electrical conductor. So magnetic fields tend to stick inside good conductors.
Speaker 2: They don't like to change. But imagine then that.
Speaker 3: You start moving that conductor around relative to itself, so
Speaker 3: you shear it, you pull it apart a little bit.
Speaker 3: That magnetic field has to go with it, so you
Speaker 3: stretch and twist the magnetic fields through the motion itself
Speaker 3: to create new magnetic fields.
Speaker 1: Wow. Fascinating. And the Earth's magnetic field, though it's pretty reliable,
Speaker 1: is not actually constant. Isn't it gradually changing?
Speaker 2: Yes?
Speaker 3: Absolutely, So we have records from the rocks in our crust.
Speaker 3: They can be magnetized at the time that they form,
Speaker 3: and those records tell us that Earth's magnetic field has
Speaker 3: changed over time. We at least have data that shows
Speaker 3: it's been around for about three billion years, if not longer.
Speaker 3: But it hasn't always been the same. So there are
Speaker 3: times in the past where the field has gotten weaker.
Speaker 3: There are times in the past where the field has
Speaker 3: flipped polarity, so the north magnetic pole became the south
Speaker 3: magnetic pole and vice versa. And even today, on like
Speaker 3: weekly time scales, we can measure the small changes in
Speaker 3: the earth magnetic field that are happening from a variety
Speaker 3: of things. Some things are external, but sometimes we can
Speaker 3: also see on a yearly scale we can see the
Speaker 3: changes due to different flows happening in the core of
Speaker 3: the Earth.
Speaker 1: Can we use these changes in the magnetic field to
Speaker 1: sort of image those flows the same way we can
Speaker 1: see changes in the gravitational field to give us a
Speaker 1: picture of what's inside the Earth.
Speaker 3: Yeah, it gets a little more challenging the deeper you go.
Speaker 3: And with magnetic fields, what we can see, for example,
Speaker 3: is because we know it's a good electrical conductor, if
Speaker 3: we see a magnetic field pattern drifting.
Speaker 2: In one direction.
Speaker 3: So for example, there's this kind of famous thing we
Speaker 3: talk about in geomagnetism called the westward drift. So if
Speaker 3: you follow certain features of the magnetic field, you see
Speaker 3: they all kind of drift westward, and we interpret that
Speaker 3: to being there's flow generally in the westward direction.
Speaker 2: There's like a jet.
Speaker 3: Stream in the core of the Earth. That's flowing westward,
Speaker 3: that's taking the magnetic field with us.
Speaker 1: Wow, and so how well do we understand this process?
Speaker 1: Are there still open questions about like why it's flipping
Speaker 1: and why it's changing or is it something that we
Speaker 1: understand pretty well?
Speaker 3: So many open questions. So the amazing thing about this process,
Speaker 3: so fluid dynamics. If you've had any experience with climate
Speaker 3: modeling or trying to study flows that happen in pipes
Speaker 3: and so forth, fluids are really complicated. They can they
Speaker 3: can display turbulence for example, or laminar flows depending on
Speaker 3: what types of you know, what what the situation is like.
Speaker 2: Now, if you add to that.
Speaker 3: Add to fluid dynamics magnetic fields and all the things
Speaker 3: that happen with magnetic fields, you almost get an added complication.
Speaker 3: And so when we try to think about, well, how
Speaker 3: do we study the dynamo process, right, we can't really
Speaker 3: wait thousands of years to watch the real system over time.
Speaker 3: We want to study it faster. So you can either
Speaker 3: do experiments or you can try to write a computer
Speaker 3: model that can mimic what's going on in a core
Speaker 3: when it's generating a magnetic field. Experiments are really hard
Speaker 3: turns out that dynamos they like three things. They like
Speaker 3: really good electrical conductors, they like really fast motions, and
Speaker 3: they like really large length scales. And then you start saying, Okay,
Speaker 3: I'm going to build my giant sphere of a really
Speaker 3: good electrical conductor and then spin it really fast, and
Speaker 3: you just you end up with a huge challenging problem.
Speaker 3: The biggest dynamo experiment out there is the three meter
Speaker 3: Dynamo Sphere in Maryland, and it has yet to generate
Speaker 3: an active dynamo, so that's a challenging problem. We use
Speaker 3: computer simulations to study dynamos inside planets. The problem there
Speaker 3: is that planets, the motions, the scales, and the motions
Speaker 3: are so tiny and so fast that there isn't enough
Speaker 3: computer power on the planet to run a simulation accurately.
Speaker 3: So we have to make a lot of assumptions and
Speaker 3: simplifying type conditions, so we aren't able to fully study
Speaker 3: the system the way.
Speaker 2: We want to. We have to be very nuanced in
Speaker 2: how we study it. Well.
Speaker 1: Do we understand why the Earth's flipping of the magnetic
Speaker 1: field seems so irregular compared to, for example, the Sun,
Speaker 1: which has this rock solid solar cycle of eleven years.
Speaker 3: Yeah, we don't fully understand why at all. We can't
Speaker 3: even kind of predict what we would expect for other
Speaker 3: planets as well. We have what I would call a
Speaker 3: hand way the understanding, and that we would describe the
Speaker 3: core fluid as being a very nonlinear system that can
Speaker 3: have different attractors or different stable systems. And sometimes it's
Speaker 3: in one stable position, sometimes it's another. And so if
Speaker 3: you have something near a stable position, imagine you have
Speaker 3: a ball sitting and you have like a nice valley
Speaker 3: in two hill on the side, and you stick the
Speaker 3: ball on one of the tops of the hills, right,
Speaker 3: it'll pretty much stay there, but maybe if you shake
Speaker 3: it a little bit too much, give it a bit
Speaker 3: too many perturbations, it'll sink down and go to the
Speaker 3: other stable position. So we think that some perturbations in
Speaker 3: the fluid can sometimes cause the field of flip, but
Speaker 3: we don't have a good way to, for example, predict
Speaker 3: when the next flip is going to happen, what's the
Speaker 3: key factor that causes such a flip for example?
Speaker 2: And these are all areas of current research.
Speaker 1: Wow. And then as we discover planets in other solar systems.
Speaker 1: How do we begin to do geology of those planets?
Speaker 1: And first, I guess there's a trivial question is would
Speaker 1: you call it geology? Geology is to study the Earth,
Speaker 1: so it is this like exo planetology, what do you
Speaker 1: call it?
Speaker 2: This is a great question.
Speaker 3: I think the norm has been to refer to geology
Speaker 3: as looking at rocks.
Speaker 2: And it doesn't matter where those rocks are. So rocks.
Speaker 3: There are Mars geologists, I'll just get that out there,
Speaker 3: instead of mars oologists or whatever you would call them instead. Yeah,
Speaker 3: with exoplanets, the challenge there is the type of information
Speaker 3: you can get can be quite limitted compared to what
Speaker 3: we can get when we're in our own Solar system
Speaker 3: or here on the Earth. But even with the standard
Speaker 3: techniques that can discover exoplanets, right, if you think about
Speaker 3: the methods involving radial velocity detection, so where you measure
Speaker 3: fluctuations in the stars light curve caused by the motion
Speaker 3: of a planet around it, you get information about the
Speaker 3: period of the orbit, and that can also give you
Speaker 3: measurements about the mass of the planet. Then if you
Speaker 3: use transit where a planet passes in front of or
Speaker 3: behind a star, you can get information about the size
Speaker 3: of the planet. So as soon as you have the
Speaker 3: size and the mass, you already have kind of an
Speaker 3: average density, a bulk density of the planet. So we
Speaker 3: have sense of whether when we discover these exoplanets, is
Speaker 3: it a gas giant, is it an Earth like planet?
Speaker 3: Is it an ice world like Uranus and Neptune. So
Speaker 3: we can do some very broad geology, let's say, from
Speaker 3: that type of information. But what I'm most excited about
Speaker 3: is the possibilities that are going to come forward with
Speaker 3: JWST because this new telescope is going to be able
Speaker 3: to measure the atmospheres of exoplanets and tell us what
Speaker 3: they're made of. That's going to be crucial information to
Speaker 3: figure out what's actually going on deeper inside the planet.
Speaker 3: Right our atmosphere on Earth is the way it is
Speaker 3: because of interactions with the interior of the Earth, and
Speaker 3: so we're going to be able to use information about
Speaker 3: the atmospheres of these exoplanets to also tell us something
Speaker 3: about the interior.
Speaker 1: What do you mean by that? I know our atmosphere
Speaker 1: is different because we have a magnetic field and because
Speaker 1: of the surface gravity. What else does our atmosphere tell
Speaker 1: us about what's inside the Earth.
Speaker 3: Right, So if there was an alien flying by our
Speaker 3: solar system, and all it could measure is kind of
Speaker 3: the spectrum of our atmosphere, it would be able to
Speaker 3: tell that there was life here most likely.
Speaker 2: Right.
Speaker 3: We've done things to our environment to make it very
Speaker 3: obvious that there is industrial action happening on the surface.
Speaker 2: Right.
Speaker 3: But also, for example, a lot of the processes that
Speaker 3: regulate some of the key species in our atmospheres, like
Speaker 3: carbon dioxide. On Earth, there's the carbon cycle. The carbon
Speaker 3: cycle not only involves the atmosphere, it involves the ocean,
Speaker 3: the surface, and the deep interior. So carbon gets recycled
Speaker 3: inside the Earth, and so we can actually learn about
Speaker 3: how exchanges of materials happen with the interior and the
Speaker 3: atmosphere by looking at how much carbon there is around,
Speaker 3: for example, right. And so the same is true for
Speaker 3: other element cycles, and so the same could be true
Speaker 3: for exoplanets.
Speaker 1: We had Professor Shields on the podcast recently, and she
Speaker 1: does exoplanet climate simulations. We're basically building models of these
Speaker 1: planets and then trying to make them consistent with what
Speaker 1: we might understand from JWST. It sounds like you're talking
Speaker 1: about doing something similar, but you're building models of the
Speaker 1: internals of these planets to explain then the climate in
Speaker 1: the atmosphere, which then tells us about the light we're
Speaker 1: seeing from these planets. So it seems like quite a
Speaker 1: few steps there from the photons we're getting in JWST
Speaker 1: to our model of what's happening inside those planets. Incredible
Speaker 1: that we could learn.
Speaker 2: Anything, Yes, absolutely agree.
Speaker 1: And what about future missions? I know there are space
Speaker 1: telescopes that are going to be looking specifically for planets.
Speaker 1: Are those going to have the toy to tell us
Speaker 1: more about these planets or do we need to wait
Speaker 1: until we can send landers to listen for exoplanet quakes.
Speaker 3: What I'm most excited about for future exoplanet data has
Speaker 3: to do with magnetic fields again, right, So if we
Speaker 3: think Earth having a magnetic field is so important for
Speaker 3: shielding life on the surface, then it might be nice
Speaker 3: if we knew that exoplanets had magnetic fields. It maybe
Speaker 3: it's something we should add to the conditions for a habitable.
Speaker 2: Planet out there.
Speaker 3: And there have been some signs, some evidence that we
Speaker 3: might actually be able to measure magnetic fields of exoplanets
Speaker 3: so there's hope that with even more measurements and so forth,
Speaker 3: we might actually be able to tell in the future
Speaker 3: if an exoplanet has a magnetic field.
Speaker 1: Today, how would that be possible? Are you looking for
Speaker 1: like the Northern lights equivalent on the planet, seeing the
Speaker 1: effect of the magnetic field on the atmosphere.
Speaker 3: So that's one way kind of so it's not the
Speaker 3: Northern lights itself, but actually the way we found out
Speaker 3: Jupiter had a magnetic field. We knew that Jupiter had
Speaker 3: a magnet field in the nineteen sixties even though we'd
Speaker 3: never been there, because electrons that spire roll along the
Speaker 3: magnetic field lines of Jupiter get really close to the
Speaker 3: poles into the atmosphere there right, and that causes aurora
Speaker 3: on Jupiter as well. But it also causes a type
Speaker 3: of radio emissions to come off of Jupiter, and those
Speaker 3: radio emissions get beamed out into space and we could
Speaker 3: actually measure them here on the surface of the Earth.
Speaker 3: So we knew about Jupiter's magnetic field in the nineteen
Speaker 3: sixties before we'd ever gone there, because we received these
Speaker 3: radio emissions. Same is true for any other planet. Now,
Speaker 3: it turns out that the intensity of those radio emissions
Speaker 3: is really important, so you need really strong magnetic fields
Speaker 3: in order to be able to measure them. On the
Speaker 3: surface of the Earth. We have this horrible atmosphere on
Speaker 3: Earth and it blocks a lot of radio emissions, which
Speaker 3: is very frustrating, although kind of good for breathing. So
Speaker 3: I guess, you know, let's say we put a radio
Speaker 3: telescope on the far side of the Moon. That would
Speaker 3: be great for helping to detect radio emissions from exoplanets.
Speaker 3: So there's that method, but they're also what I would
Speaker 3: call sneakier methods.
Speaker 2: Right.
Speaker 3: For example, if you look at the transit spectrum, so
Speaker 3: if you look at a planet that's going in front
Speaker 3: of a sign or a star and you see kind
Speaker 3: of how wide the planet is. People can already kind
Speaker 3: of tell if a planet has an atmosphere by the
Speaker 3: fact that it could have different thicknesses or different radius
Speaker 3: in different wavelengths, and that you know, sometimes the atmosphere
Speaker 3: will let light through, whereas the planet itself won't, right,
Speaker 3: And so that's how we can tell whether something has
Speaker 3: an atmosphere, is what particular wavelengths of light get through
Speaker 3: at different distances. The same can be true about a
Speaker 3: magnetic field. Sometimes a magnetic field can cause certain light
Speaker 3: spectra light frequencies to not get through, so we might
Speaker 3: be actually able to measure a magnetosphere surrounding a planet
Speaker 3: by looking at transit spectra. You can also maybe see
Speaker 3: if a planet has like a tail, right, and so
Speaker 3: sometimes if atmosphere is being blown off a planet, you
Speaker 3: might be able to see that in a transit spectrum
Speaker 3: or through other types of light detection. So there might
Speaker 3: be some sneaky ways to look for magnet fields of
Speaker 3: exoplanets as well.
Speaker 1: Wonderful well, I expect that the next generation of scientists
Speaker 1: will be even more creative about coming up with ways
Speaker 1: to extract a me information from these tiny little blips
Speaker 1: in our telescopes.
Speaker 2: Yes, hopefully so.
Speaker 1: Wonderful well. Thank you very much for coming on the
Speaker 1: podcast and telling us so much about the mysteries that
Speaker 1: are under our feet and the mysteries that are out
Speaker 1: there in the universe.
Speaker 2: Thanks so much.
Speaker 1: This was fun, all right. That was my chat with
Speaker 1: Professor Sabina Stanley again. She's the author of the book
Speaker 1: What's Hidden Inside Plants, which you can get now at
Speaker 1: all reputable booksellers. Thanks very much for listening. Tune in
Speaker 1: next time. Thanks for listening, and remember that Daniel and
Speaker 1: Jorge Explain the Universe is a production of iHeart Radio.
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