Latest / Daniel and Kelly’s Extraordinary Universe / What's hidden inside planets?

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What's hidden inside planets? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: When we set out to understand the universe, we usually
• 0:11
  Speaker 1: start by looking up. After all, that's where the best
• 0:14
  Speaker 1: views are of the glittery cosmos stretched across billions of miles.
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  Speaker 1: We wonder, are we alone? Is there anyone up there
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  Speaker 1: looking back at us? But what if the best way
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  Speaker 1: to find answers to questions about what's up there is
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  Speaker 1: actually to look down under our feet. Hi, I'm Daniel.
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  Speaker 1: I'm a particle physicist and a professor at UC Irvine,
• 0:51
  Speaker 1: and I desperately want to know who's out there in
• 0:53
  Speaker 1: the universe and if they are wondering the same things
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  Speaker 1: we are. And Welcome to the podcast Daniel and Horace
• 1:00
  Speaker 1: Explain the Universe in which we do just that, wonder
• 1:03
  Speaker 1: about the nature of the universe and try to explain
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  Speaker 1: all of it to you. Regular listeners the podcast, know
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  Speaker 1: that I am desperate to understand the nature of the universe,
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  Speaker 1: how it all works, and to explain all of that
• 1:15
  Speaker 1: knowledge and all of that confusion to you. One of
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  Speaker 1: the deepest questions we wrestle with on the pod is
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  Speaker 1: not just about the universe, but kind of about ourselves.
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  Speaker 1: How weird? Are we are? There more like us out
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  Speaker 1: there in the universe, or are we alone? How rare
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  Speaker 1: and special is the Earth anyway? Are we one of
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  Speaker 1: a kind out of a trillion planets, or are we
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  Speaker 1: one of many rocky balls covered in Curious Life. We're
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  Speaker 1: frustratingly limited by what we can learn about distant planets,
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  Speaker 1: though we're doing our best. But something we can do
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  Speaker 1: right now is drill deeper into our own planet, understand
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  Speaker 1: the forces that shaped it and whether those are finely
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  Speaker 1: balanced in a rare way or naturally in harmony, in
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  Speaker 1: a way we'll find everywhere in the universe. So today
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  Speaker 1: on the podcast, we'll be answering the question what's hidden
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  Speaker 1: inside planets? And to help me explore this fascinating topic,
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  Speaker 1: I'm pleasing to be speaking to Professor Sabina Stanley, author
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  Speaker 1: of a very recent book of that same title. All right, well,
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  Speaker 1: then it's my great pleasure to introduce the podcast Professor
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  Speaker 1: Sabina Stanley. She's the Bloomberg Distinguished Professor of Planetary Physics
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  Speaker 1: at Johns Hopkins University, where she focuses on magnetic fields
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  Speaker 1: and other geophysical elements as a means of studying the
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  Speaker 1: interiors of planets, moons, and asteroids. She's an Alfred Peasloan
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  Speaker 1: Research Fellow, and has also received the William Gilbert Award
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  Speaker 1: of the American Geophysical Union. Sabina, Welcome to the podcast,
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  Speaker 1: and thank you for coming to talk to us.
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  Speaker 2: Thanks so much for having me.
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  Speaker 1: So one thing we always wonder about as we look
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  Speaker 1: out into the night sky is all the other planets
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  Speaker 1: that are out there. Of course we can't study mnie
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  Speaker 1: them up close, and so often on this podcast we've
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  Speaker 1: tried to dig into what's under our feet, the mysteries
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  Speaker 1: that are right here in our Earth. And so I
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  Speaker 1: really enjoyed your recent book, What's Hidden Inside Planets, and
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  Speaker 1: I'd love to talk to you about what's in our planet.
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  Speaker 1: Could you start us off by taking us sort of
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  Speaker 1: on a brief tour of like what is under our feet,
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  Speaker 1: layer by layer, all the way down to the core.
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  Speaker 2: Yeah, absolutely, great question.
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  Speaker 3: So I think it's interesting to note that when you
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  Speaker 3: start on the surface, as you go deeper and deeper,
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  Speaker 3: stuff gets kind of weirder and weirder and much more
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  Speaker 3: different than what we're used to on the surface.
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  Speaker 2: So we start on the crust.
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  Speaker 3: This is where we live, This is where all the
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  Speaker 3: stuff happens that we're used to crust can vary in
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  Speaker 3: thickness five about you know, five kilometers depth to almost
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  Speaker 3: one hundred kilometers depth. But under that you get to
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  Speaker 3: the mantle that's also still mostly rocky, the type of
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  Speaker 3: rocks that are rich in magnesium and silicates, but still
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  Speaker 3: what we would recognize as rocks. So about half the
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  Speaker 3: radius of the Earth are those rocks. It goes down
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  Speaker 3: about two thousand miles deep.
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  Speaker 1: So what distinguishes then between the crust and the mantle.
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  Speaker 1: Is it like how squeezed they are and how much
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  Speaker 1: they flow, or is it a different kind of rock?
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  Speaker 2: Great question.
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  Speaker 3: Yeah, it's a little bit different kind of rock. So
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  Speaker 3: essentially the crust layer of the earth. I sometimes refer
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  Speaker 3: to it as like the scum of the earth. So
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  Speaker 3: it's kind of like, you know, like when you're making
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  Speaker 3: a soup and you're boiling your broth and you've got
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  Speaker 3: all that light, floaty stuff that comes to the top.
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  Speaker 3: So the stuff that's the most buoyant when you have
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  Speaker 3: certain heat, thermal reactions and chemical reactions happening with rocks
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  Speaker 3: near the surface, all of that percolates up to the
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  Speaker 3: top and that ends up becoming the crust, and then
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  Speaker 3: sort of the stuff underneath might be less scummy, less
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  Speaker 3: you know, it's been less reworked, and it's sort of
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  Speaker 3: more kind of pristine rock.
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  Speaker 1: I see, we're going to get started very quickly with
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  Speaker 1: the food analogies.
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  Speaker 2: Yeah, I'm sorry, it's just going to be how it goes.
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  Speaker 3: It's going to be food involved in almost every analogy
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  Speaker 3: I make.
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  Speaker 2: Here.
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  Speaker 1: Are you a big fan of soup or you a
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  Speaker 1: cook at home?
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  Speaker 3: So I'm a terrible cook, but I grew up in
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  Speaker 3: a restaurant family, so I've been around sort of good
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  Speaker 3: food my whole life.
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  Speaker 1: All right, Well, then let's do our best to at
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  Speaker 1: least use tasty food analogies. I don't want any want
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  Speaker 1: to think that the earth is like a disgusting bowl
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  Speaker 1: of soup. Maybe it's like, you know, bubbling hot cocoa,
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  Speaker 1: and this is that delicious film that forms on top.
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  Speaker 2: I love that so much. You don't even know. So
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  Speaker 2: that's amazing, all right.
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  Speaker 1: So the crust is the sort of coolest part that
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  Speaker 1: floats to the top, and underneath that it's still rock,
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  Speaker 1: but it's able to flow. How do we visualize that?
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  Speaker 1: I mean, it's not like liquid lava that's flowing on
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  Speaker 1: the surface. This is still like solid rock, but it's flowing.
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  Speaker 1: How does solid rock flow is something I've always tried
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  Speaker 1: to visualize and failed.
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  Speaker 2: Yeah, So the answer to that question is very slowly.
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  Speaker 1: Right.
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  Speaker 3: So, yes, it's solid, but it's still deformable, right, And
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  Speaker 3: I think we have experience with different types of solids
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  Speaker 3: in our everyday life, and that some are more deformable
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  Speaker 3: than other.
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  Speaker 2: Right, Like you might have clay.
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  Speaker 3: Clay is solid, but you can still deform it, whereas
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  Speaker 3: a metal also is kind of deformable. But then you
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  Speaker 3: have some rocks that are really like a diamond, really
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  Speaker 3: hard to deform. But the rocks in the mantle, they
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  Speaker 3: are solid, but they can be deformed, and if they
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  Speaker 3: can be deformed, then they start being influenced by the
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  Speaker 3: forces like gravity such that you can get them to flow.
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  Speaker 1: I see, all right, So we have the crust and
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  Speaker 1: we have the mantle. Both the wiz are still really rock.
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  Speaker 1: Take us down below that, right.
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  Speaker 3: So then you get down about halfway through the Earth
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  Speaker 3: and you suddenly hit a very big boundary, complete change
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  Speaker 3: of environment. Now you're at the iron core. So the
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  Speaker 3: inner half of the planet about it's mostly made of iron.
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  Speaker 3: There's a little bit of nickel mixed in there, and
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  Speaker 3: about ten percent of some sort of lighter elements that
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  Speaker 3: we have a whole sort of platter of possibilities for,
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  Speaker 3: but we don't actually know what they are. And that
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  Speaker 3: makes up the core. The core has two parts to it.
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  Speaker 3: The outer port is liquid. It can flow very easily,
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  Speaker 3: much faster timescales than the mantle, and it's really important
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  Speaker 3: for us because that's where our magnetic field is generated
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  Speaker 3: in that liquid iron core. Then below that, the innermost
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  Speaker 3: thirteen hundred kilometers of our planet, is a solid iron core.
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  Speaker 1: And so what distinguishes then the mantle, which can flow
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  Speaker 1: but is a solid not a liquid, from the outer core,
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  Speaker 1: which can flow but is a liquid and not a solid, Like,
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  Speaker 1: is there really a distinction here? Are we just putting
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  Speaker 1: labels on things?
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  Speaker 3: When we study fluid dynamics, we talk a lot about
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  Speaker 3: there being a spectrum of fluids. Right, nothing's ever purely
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  Speaker 3: a solid or purely a fluid. It's all about the
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  Speaker 3: time scales. So the mantle, for example, if you want
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  Speaker 3: to talk about how materials flow in the mantle, a
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  Speaker 3: parcel at the bottom of the mantle could take hundreds
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  Speaker 3: of millions of years to make it to the top
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  Speaker 3: of the mantle, whereas a parcel at the bottom of
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  Speaker 3: the core could take a couple of years to get
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  Speaker 3: the top of the core. So it's a very different
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  Speaker 3: timescale of the flow. You could actually see changes in
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  Speaker 3: material in the core flowing.
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  Speaker 1: But this is also like a boundary. It's not like
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  Speaker 1: there's a smooth, very gradual transition. There's like a line.
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  Speaker 1: You can say, this is the core and this is
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  Speaker 1: the mantle.
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  Speaker 3: Yeah, And that happens because mantle, rocks, and iron in
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  Speaker 3: the core have very different densities, and at one time
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  Speaker 3: in the past in our planet, it was mostly molten
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  Speaker 3: and so the heaviest stuff, when you have a bunch
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  Speaker 3: of stuff mixed together, the heaviest stuff's going to sync
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  Speaker 3: to the bottom. And so that's what happened in Earth.
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  Speaker 3: All the iron, most of the irons, sunk to the
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  Speaker 3: center of the Earth and made.
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  Speaker 1: Up the core like the big chunks in a stew
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  Speaker 1: or something exactly.
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  Speaker 2: Yes, I like it.
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  Speaker 1: So the reason that there's a boundary there and like
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  Speaker 1: a transition or rather than just like a smooth gradation
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  Speaker 1: from more liquid to less liquid, that reflects like the
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  Speaker 1: phase transitions and materials. Is that right, the way that
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  Speaker 1: like ice turns solid at some moment and doesn't just
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  Speaker 1: like gradually become more and more solid.
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  Speaker 3: I would say that's more representative of what kind of
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  Speaker 3: happens at the inner core outer core boundary, so where
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  Speaker 3: the iron becomes solid. But above that it's more kind
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  Speaker 3: of like a maybe you go with an oil and
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  Speaker 3: water type thing. You've got two materials with very different
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  Speaker 3: density and very different properties, so it's really hard to
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  Speaker 3: mix them.
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  Speaker 1: Wonderful and tell us about how we know about this.
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  Speaker 1: I was reading in your book this really exciting description
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  Speaker 1: of the mantle race, basically like a parallel to the
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  Speaker 1: space race, but into the Earth. Tell us about our
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  Speaker 1: humanity's efforts to like literally tunnel to the center of
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  Speaker 1: the Earth.
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  Speaker 3: Yeah, So if you imagine you want to figure what's
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  Speaker 3: inside the Earth, right, your first instinct might be, hey,
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  Speaker 3: why don't we dig down as far as we can
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  Speaker 3: and actually sample it?
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  Speaker 2: Right?
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  Speaker 3: And it's a great instinct. Unfortunately, it's incredibly challenging to do.
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  Speaker 3: And that's because pressure increases so fast as you go
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  Speaker 3: deeper inside the planet, and so do temperatures. So as
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  Speaker 3: you can imagine, humans don't like really high pressures and temperatures.
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  Speaker 3: Neither does equipment, and the farthest we've been able to
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  Speaker 3: dig with sort of a really concerted effort to do so, right,
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  Speaker 3: Like this was something on the scale of moonshot to
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  Speaker 3: the Moon in the late sixties. This is something very
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  Speaker 3: similar to that, And you could get only down to
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  Speaker 3: about eight miles in depth, and the radius of the
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  Speaker 3: Earth you're talking about four thousand miles, so tiny, tiny
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  Speaker 3: scrape of the surface by going down that deep. Equipment
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  Speaker 3: does not like high pressures and temperatures.
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  Speaker 1: But how do you even get eight miles deep? I mean,
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  Speaker 1: I remember digging in my backyard with a shovel, wondering
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  Speaker 1: how far I could get, and it's not very far.
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  Speaker 1: How do you get eight miles down?
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  Speaker 3: This is like high tech technology kind of stuff. It's
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  Speaker 3: at the limits of what we can do for drilling
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  Speaker 3: that we do now to drill for resources, et cetera.
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  Speaker 3: So it's a lot of fancy equipment and challenges that
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  Speaker 3: are over met that way. So we can't dig and
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  Speaker 3: we can't drill, But that's okay because there are other
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  Speaker 3: ways we can figure out what's going on deeper inside
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  Speaker 3: the earth.
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  Speaker 1: Yeah, So tell us about some of those ways you
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  Speaker 1: were talking in the book about diamonds, how we can
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  Speaker 1: use diamonds to give us little snapshots of what's inside
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  Speaker 1: the planet.
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  Speaker 3: Yeah, so you know, it would be great if we
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  Speaker 3: could dig down, but would it also be great if
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  Speaker 3: the stuff down there came to us. And that's really
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  Speaker 3: what happens with diamonds. Diamonds are produced deeper inside the Earth,
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  Speaker 3: and then they come up to the surface, usually in
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  Speaker 3: volcanic vent things known as kimber like pipes and those diamonds.
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  Speaker 3: You know, Jewelers love diamonds when they're as pure as possible.
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  Speaker 3: Geologists love diamonds when they're as impure as possible. So
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  Speaker 3: sometimes diamonds, when they form, they can enclose a little
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  Speaker 3: capsule of some of the material where they formed inside them, right,
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  Speaker 3: So you might get a little bit of garnet in
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  Speaker 3: the diamond or a little bit of something that was
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  Speaker 3: created deeper in the earth. And when it it up,
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  Speaker 3: because diamonds so strong, it actually keeps the material in
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  Speaker 3: its like pristine form, So you really have this like
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  Speaker 3: sample from the interior of the Earth come to the
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  Speaker 3: surface for us to investigate. So that's a great way
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  Speaker 3: and we've used that, for example, to figure out that
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  Speaker 3: there is actually water deeper inside the Earth because we've
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  Speaker 3: found water inside diamond inclusions.
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  Speaker 1: It's fascinating to me though, that this thing that you
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  Speaker 1: make in a high pressure environment, when you bring it
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  Speaker 1: up to low pressure, it doesn't explode. Is that just
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  Speaker 1: because of the incredible structure of diamond?
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  Speaker 2: Yeah.
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  Speaker 3: When they say diamonds are forever, that's technically not true, right,
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  Speaker 3: They just have a really really long lifetime before they
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  Speaker 3: revert back to their carbon phase.
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  Speaker 2: So yeah, it's just a great property of diamond.
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  Speaker 1: So is it's sort of like you know, you put
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  Speaker 1: a pan of brownies in the oven and it changes
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  Speaker 1: into something else, and when you take it out, cool
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  Speaker 1: it down, it doesn't revert back into batter.
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  Speaker 2: That's an excellent way of thinking about it.
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  Speaker 1: Yeah, okay, And so then what have we learned from
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  Speaker 1: these diamond samples? Like what's inside these diamonds that we
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  Speaker 1: didn't realize other than water?
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  Speaker 2: Yeah? I think water is the big thing.
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  Speaker 3: Sometimes it's a lot about sort of the smaller amounts
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  Speaker 3: of elements that we don't know about, Right, how much
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  Speaker 3: of a particular kind of silicon down there is sulfur,
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  Speaker 3: down there these kinds of questions, and those all just
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  Speaker 3: help us understand what the building blocks of Earth were
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  Speaker 3: when Earth formed, and what the geochemistry the kind of
• 12:20
  Speaker 3: chemical reactions that can occur as material descends into the Earth.
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  Speaker 3: That's really where we get that information. But even with diamonds, right,
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  Speaker 3: we're talking about the outermost layers of the mantle, right, diamonds.
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  Speaker 3: We don't get diamonds safe from the core mantle boundary
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  Speaker 3: or anywhere deeper than that. So we can't use the
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  Speaker 3: diamonds to learn about the deeper parts.
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  Speaker 1: Is that because diamonds aren't made deeper or because diamonds
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  Speaker 1: from that far down just don't make it up to
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  Speaker 1: the surface.
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  Speaker 3: Mostly the latter, I think also, like if you get
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  Speaker 3: carbon down there, yeah, it doesn't necessarily join into making
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  Speaker 3: diamond at that depth.
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  Speaker 1: All right, So there aren't like huge diamonds buried deep
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  Speaker 1: in the earth that we are not on Earth, not
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  Speaker 1: on Earth. Well, that was my whole motivation for digging
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  Speaker 1: so deeply when I was a kid, fantasizing about revealing
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  Speaker 1: some you know, boulder sized diamond. All right, So diamonds
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  Speaker 1: give us one sample of what else can we do?
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  Speaker 1: What about gravity? What about just studying like the variation
• 13:10
  Speaker 1: in Earth's gravity as we you know, orbit to planate
• 13:13
  Speaker 1: or look around it. What does that tell us about
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  Speaker 1: what's inside the Earth.
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  Speaker 3: The way I like to think about it is, you know,
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  Speaker 3: if you want to figure out what's going on inside
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  Speaker 3: the Earth, try and make an analogy to a human body.
• 13:23
  Speaker 3: Right if you if you have an ache and you
• 13:24
  Speaker 3: go to your doctor and you're like this hurts. Hopefully
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  Speaker 3: they're not. Their first kind of instinct is not to
• 13:29
  Speaker 3: drill a hole in you to figure that out. Right,
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  Speaker 3: There are ways that they can use different fields and
• 13:33
  Speaker 3: different scans to figure out what's wrong with your insides,
• 13:36
  Speaker 3: And we can do the same thing for the inside
• 13:38
  Speaker 3: of the Earth. So we can scan gravity as you mentioned,
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  Speaker 3: that's one, Magnetic fields is another one.
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  Speaker 2: And we can also determine.
• 13:44
  Speaker 3: Properties of waves that travel through the Earth from earthquakes
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  Speaker 3: through seismology. So we can use all these scanning techniques
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  Speaker 3: to figure out what's going on deeper inside the Earth.
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  Speaker 1: So what do you mean by using gravity? Is it
• 13:54
  Speaker 1: just like measuring the variations of gravity so that we
• 13:57
  Speaker 1: understand how the Earth is not a perfect sphere or
• 13:59
  Speaker 1: how they'rear is not homogeneous in density. What is it
• 14:02
  Speaker 1: we're learning?
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  Speaker 2: Yeah, great question.
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  Speaker 3: So, yeah, it really is the fact that both isn't
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  Speaker 3: a perfect sphere and has some inhomogeneous material below it. Right,
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  Speaker 3: So if you were walking around with a griviminter that
• 14:13
  Speaker 3: could measure gravity and it was really really good and
• 14:15
  Speaker 3: you walked around, you would get slightly different values everywhere
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  Speaker 3: you walk, and that would be determined by the mass
• 14:20
  Speaker 3: directly under your feet. And so we can use that information.
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  Speaker 3: We have spacecraft that orbit the Earth that measure Earth's
• 14:27
  Speaker 3: gravity feel to really high precision, and we can use
• 14:30
  Speaker 3: that to figure out what is the distribution of density
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  Speaker 3: inside the Earth. And that kind of allows us to
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  Speaker 3: kind of image what's going on. Where's the denser stuff
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  Speaker 3: in the Earth, where's the lighter stuff? And we can
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  Speaker 3: actually see things like convection cells in the mantle and
• 14:42
  Speaker 3: plumes of magma coming up for volcanoes, things like this.
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  Speaker 1: But gravity is such a weak force. How do you
• 14:49
  Speaker 1: identify these variations in density with such an incredibly weak force.
• 14:53
  Speaker 1: They must be pretty big effects.
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  Speaker 3: They aren't. They are very very tiny effect. We're just
• 14:58
  Speaker 3: really good at measuring them.
• 15:00
  Speaker 1: Emitter, you mentioned this might seem like a weird object
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  Speaker 1: or listeners. But I guess, like my bathroom scale is
• 15:05
  Speaker 1: a gravi emitter. If I walked around the Earth with
• 15:06
  Speaker 1: my bathroom scale, I would measure different weights before and
• 15:10
  Speaker 1: after lunch, of course, but also if I didn't need anything,
• 15:13
  Speaker 1: or I user reference mass, then I guess I would
• 15:15
  Speaker 1: measure different accelerations due to gravity.
• 15:18
  Speaker 2: Yeah.
• 15:18
  Speaker 3: Absolutely, And if you are someone on the surface taking
• 15:20
  Speaker 3: gravity measurements, that's exactly the kind of instrument you would use. Interestingly,
• 15:25
  Speaker 3: once we get into orbiting around a planet like Earth
• 15:28
  Speaker 3: to take measurements, we use a completely different technique. We
• 15:31
  Speaker 3: basically use the fact that if we have a spacecraft
• 15:34
  Speaker 3: in orbit around the Earth, we know it's in orbit
• 15:36
  Speaker 3: around the Earth, and its orbital speed and altitude is
• 15:40
  Speaker 3: completely determined by the mass of the planet.
• 15:42
  Speaker 2: So we can use things.
• 15:43
  Speaker 3: Like two spacecraft just slightly at different locations from each
• 15:47
  Speaker 3: other kind of moving around, and we can use the
• 15:49
  Speaker 3: distance between the two spacecraft as like a proxy for
• 15:52
  Speaker 3: how much g is right where they are, how much
• 15:54
  Speaker 3: the gravity is right where they are. So that's actually
• 15:56
  Speaker 3: how it's done in practice with spacecraft.
• 15:58
  Speaker 1: Wow, that's incredible, And how sensitive are they? I mean,
• 16:00
  Speaker 1: like one part in a thousand, one part in a million.
• 16:03
  Speaker 2: Yeah, one part in a million. That's where we're getting to.
• 16:05
  Speaker 1: Wow, So they can really tell if I've eaten lunch.
• 16:07
  Speaker 1: Some spacecraft up there can tell that the mass of
• 16:09
  Speaker 1: the Earth has changed.
• 16:11
  Speaker 3: One thing they're actually used for. So the Grace satellites,
• 16:13
  Speaker 3: which orbited Earth for about ten years, one of their
• 16:16
  Speaker 3: main applications was to follow water flow on the surface,
• 16:19
  Speaker 3: so you could see, for example, when water was filling
• 16:21
  Speaker 3: reservoirs underground reservoirs in certain parts of the country or
• 16:25
  Speaker 3: different countries if you wanted to see are we going
• 16:27
  Speaker 3: to have a drought, are we in a rainstorm season,
• 16:30
  Speaker 3: or what's the water situation going on here?
• 16:31
  Speaker 2: So we can even use gravity to tract climate change.
• 16:34
  Speaker 1: Wow, that sounds like modern day divining rods. But you're
• 16:37
  Speaker 1: actually using science to find the water underground. That's incredible,
• 16:40
  Speaker 1: all right, So gravity's one way to do it. You
• 16:42
  Speaker 1: also mentioned seismic probes. These are like waves inside the earth.
• 16:46
  Speaker 1: How do we use that to see what's going on?
• 16:48
  Speaker 3: So every time there's an earthquake, it's like sort of
• 16:52
  Speaker 3: something kind of punched the inside of the Earth at
• 16:54
  Speaker 3: some point and it causes the Earth to ring. It
• 16:55
  Speaker 3: causes waves to travel through the interior of the Earth
• 17:00
  Speaker 3: and on the surface of the Earth. If we put
• 17:02
  Speaker 3: out a bunch of instruments that can kind of measure
• 17:04
  Speaker 3: the shaking, so seismographs, then we can figure out a
• 17:08
  Speaker 3: few things.
• 17:08
  Speaker 2: About the earthquake waves.
• 17:09
  Speaker 3: We can figure out when they arrive at different locations
• 17:12
  Speaker 3: around the planet, and how big the waves are, the
• 17:14
  Speaker 3: amplitude of the waves.
• 17:16
  Speaker 2: And the speed.
• 17:17
  Speaker 3: The timing of when the waves arrive is completely directly
• 17:20
  Speaker 3: related to the material properties that the waves traveled through.
• 17:24
  Speaker 3: So for example, we can figure out the density of
• 17:26
  Speaker 3: material that a wave traveled safe from. Let's say an
• 17:29
  Speaker 3: earthquake happens in California and the wave travels up to
• 17:34
  Speaker 3: Seattle in Washington. You can use that to figure out
• 17:38
  Speaker 3: kind of what's the material just under the surface there,
• 17:40
  Speaker 3: Whereas if you try to go across the globe to
• 17:43
  Speaker 3: another part on the other side, the waves might travel
• 17:45
  Speaker 3: through the entire planet and we could actually sample the
• 17:48
  Speaker 3: material in the.
• 17:49
  Speaker 2: Core for example.
• 17:50
  Speaker 3: So you can use all those different measurements. The more
• 17:52
  Speaker 3: locations you have on the Earth for these seismic measurements
• 17:54
  Speaker 3: to be made, the more you can kind of discern
• 17:57
  Speaker 3: what is the lateral structure of the.
• 17:59
  Speaker 2: Interior of the Earth.
• 18:00
  Speaker 1: And we're really talking about sound waves, right, These are
• 18:02
  Speaker 1: pressure waves in the rock, and so we can think
• 18:05
  Speaker 1: about how denser materials have sound travel faster, and less
• 18:08
  Speaker 1: dense materials sound travels lower. So you're measuring the density
• 18:12
  Speaker 1: of the material by measuring the speed of sound. But again,
• 18:14
  Speaker 1: these are rocks that are like pushing on each other, right,
• 18:17
  Speaker 1: Like sound waves through rock is a very weird thing
• 18:20
  Speaker 1: to think about.
• 18:21
  Speaker 3: Yeah, absolutely, So there are the sound waves that The
• 18:23
  Speaker 3: other type of wave that goes through are these sheer waves.
• 18:26
  Speaker 3: So those are kind of more like waves you'd experience
• 18:29
  Speaker 3: in a fluid, let's say, or not in fluid, sorry,
• 18:31
  Speaker 3: waves that you would experience if you try to kind
• 18:34
  Speaker 3: of bend peanut butter or something like that. Right, So
• 18:36
  Speaker 3: there's multiple kinds of waves, and some of them are
• 18:39
  Speaker 3: very diagnostic of what's going on in certain types of materials.
• 18:43
  Speaker 1: Well, I never thought we'd be talking about peanut butter waves,
• 18:45
  Speaker 1: but here we are. So when did we get this picture, Like,
• 18:48
  Speaker 1: what is the first technique that really gave us a
• 18:50
  Speaker 1: view of the inside of the earth. Was it the
• 18:52
  Speaker 1: seismographs or is it something else.
• 18:54
  Speaker 2: That's a good question.
• 18:56
  Speaker 3: It's not like there was a sun moment where suddenly
• 18:58
  Speaker 3: we had this picture of the Earth. I think we
• 18:59
  Speaker 3: develop our understanding to higher and higher precision as time
• 19:03
  Speaker 3: went on.
• 19:03
  Speaker 2: Right, I think early studies.
• 19:05
  Speaker 3: Of gravity, going back to Newton, let's say, was able
• 19:08
  Speaker 3: to tell us this is the mass of the Earth,
• 19:10
  Speaker 3: and then you could take, for example, samples of crustal
• 19:12
  Speaker 3: rocks and figure out what their density was and infer, hey,
• 19:15
  Speaker 3: there must be a lot more mass deeper in the center.
• 19:17
  Speaker 3: So that was kind of first order information you might
• 19:19
  Speaker 3: get so through both seismology. So early nineteen hundreds was
• 19:23
  Speaker 3: when we were doing some really great seismology figuring out
• 19:26
  Speaker 3: things like, oh, look we have a core. Right, that
• 19:28
  Speaker 3: was where the core was first discovered. The inner core
• 19:30
  Speaker 3: was discovered in the early nineteen hundreds. The first sort
• 19:33
  Speaker 3: of real profile of density through the Earth happened, I
• 19:37
  Speaker 3: think it was in the seventies with what was called
• 19:38
  Speaker 3: the Preliminary Reference Earth Model, which really used a whole
• 19:42
  Speaker 3: bunch of seismic data to really kind of do an
• 19:44
  Speaker 3: inverse problem and figure out here's what the seismic wave
• 19:47
  Speaker 3: speed and the density has to be at every depth
• 19:49
  Speaker 3: the in sort of like a won d earth. So
• 19:51
  Speaker 3: that was a big step forward there too. But at
• 19:54
  Speaker 3: the same time, gravity was being used, and so we
• 19:56
  Speaker 3: were getting pictures from different types.
• 19:58
  Speaker 1: Of information, But were the only a few hundred years
• 20:01
  Speaker 1: that we've had any sort of reasonable idea of what's
• 20:03
  Speaker 1: under our feet. And it sounds like only the last
• 20:05
  Speaker 1: few decades, maybe fifty years, that we've had any sort
• 20:08
  Speaker 1: of detailed picture of what's actually inside our own planet.
• 20:11
  Speaker 1: It's incredible how long we can remain ignorant about really
• 20:14
  Speaker 1: basic science about our own lives.
• 20:16
  Speaker 3: Yeah, when I talk to people, I tell them geophysics
• 20:20
  Speaker 3: is really modern physics because all of the stuff we're
• 20:22
  Speaker 3: doing now is all stuff that's happened sort of in
• 20:24
  Speaker 3: the last sixty seventy years. So I'd like to think
• 20:27
  Speaker 3: of it as a modern physics.
• 20:28
  Speaker 1: Approach, right, And now we've extended this frontier two other planets.
• 20:32
  Speaker 1: We've talked in the podcast before about the Insite mission,
• 20:34
  Speaker 1: and I think you worked on that measuring Mars quakes
• 20:37
  Speaker 1: to see what's inside Mars. Did the same principles apply there?
• 20:41
  Speaker 3: Yes, absolutely, So the amazing thing with the Inside mission
• 20:44
  Speaker 3: is brought a seismometer, and that seismometer had to be
• 20:47
  Speaker 3: placed onto the surface of Mars so that it could
• 20:50
  Speaker 3: measure the ground shaking essentially, and it worked, like it
• 20:53
  Speaker 3: was just amazing that it worked. But it was a
• 20:55
  Speaker 3: very interesting experience because for most of the mission, and
• 20:59
  Speaker 3: especially in the big all the Mars quakes we were
• 21:02
  Speaker 3: seeing were quite weak.
• 21:04
  Speaker 2: We were looking for.
• 21:04
  Speaker 3: The big one, right, We're looking for the big Mars quake,
• 21:07
  Speaker 3: because the bigger the quake, the more ways we'll travel
• 21:09
  Speaker 3: through the deeper parts of Mars. And so we really
• 21:11
  Speaker 3: wanted to study or I really wanted to study the core,
• 21:14
  Speaker 3: and for that we needed some big Mars quakes, and
• 21:16
  Speaker 3: they really didn't happen for the first few years, and
• 21:18
  Speaker 3: then right near when the mission was about to end,
• 21:21
  Speaker 3: we suddenly had a few. So that was really amazing
• 21:23
  Speaker 3: to get that data at the end. So Mars kind
• 21:25
  Speaker 3: of kept us hoping for a while and then finally delivered.
• 21:27
  Speaker 1: And before you landed on Mars with this seismometer, did
• 21:30
  Speaker 1: you have much reason to expect that there were Mars quakes?
• 21:33
  Speaker 1: Or it could be that Mars was totally silent.
• 21:36
  Speaker 3: I mean it could have been we didn't have any
• 21:37
  Speaker 3: direct evidence from Mars quakes. But my geologist friends who
• 21:40
  Speaker 3: are used to looking at say tectonic features on the surface,
• 21:43
  Speaker 3: looking at things like where are the cracks in the surface,
• 21:45
  Speaker 3: where are the mountains, they would have told me to
• 21:47
  Speaker 3: expect Mars quakes because they see movements geologically, they see
• 21:52
  Speaker 3: movements on the surface. But also, luckily, we kind of
• 21:55
  Speaker 3: have our own source of Mars quakes. In a way,
• 21:58
  Speaker 3: when meteors hit planet, they crash into them. They're kind
• 22:02
  Speaker 3: of like a hammer that's smashing into a bell, right,
• 22:05
  Speaker 3: And so a lot of the Mars quakes we measured
• 22:07
  Speaker 3: were actually caused by meteors that hit Mars as opposed
• 22:10
  Speaker 3: to just tectonic activity happening in the interior.
• 22:12
  Speaker 1: Well, it's terrifying to me or feel a little conflicted
• 22:14
  Speaker 1: the geologists are rooting for quakes and rooting for like
• 22:18
  Speaker 1: big impacts because they're like, ooh, yay data.
• 22:21
  Speaker 2: Yes exactly, I will.
• 22:23
  Speaker 3: I mean, as a funny story on the mission, we
• 22:25
  Speaker 3: did at one point, so the Insight mission was on
• 22:27
  Speaker 3: the surface when the Perseverance rover was planning to land,
• 22:32
  Speaker 3: and we did kind of do a calculation where if
• 22:34
  Speaker 3: the landing didn't go so well would be able to
• 22:37
  Speaker 3: detect the way from that.
• 22:39
  Speaker 2: Luckily that didn't happen. We had a very nice landing.
• 22:42
  Speaker 1: Congratulations on your landing. Too bad we didn't get some
• 22:45
  Speaker 1: cool data though from your explosion of your huge project.
• 22:48
  Speaker 1: Oh my gosh. All right, this is really fun and
• 22:51
  Speaker 1: I want to hear a lot more about what's going
• 22:53
  Speaker 1: on inside our planet. But first let's take a quick break. Okay,
• 23:09
  Speaker 1: we're back. We're talking to Professor Sabina Stanley, author of
• 23:12
  Speaker 1: the book What's Hidden Inside Planets, about what's inside our planet.
• 23:17
  Speaker 1: You mentioned earlier that it was amazing that insight worked.
• 23:20
  Speaker 1: Is that just because it's hard to land stuff on
• 23:22
  Speaker 1: Mars and operate a robot on another planet or was
• 23:25
  Speaker 1: there something particularly challenging about a seismometer on another planet.
• 23:29
  Speaker 3: Yeah, Inside had a lot of firsts, I would say, right,
• 23:32
  Speaker 3: it wasn't the first lander. We've had other landers on
• 23:34
  Speaker 3: the surface, but this was the first time we were
• 23:36
  Speaker 3: going to take equipment that was stored on top of
• 23:38
  Speaker 3: the lander and actually physically move it to put it
• 23:41
  Speaker 3: on the surface. So there were lots of ways that
• 23:43
  Speaker 3: could have gone wrong. Right, This lander had this arm
• 23:46
  Speaker 3: type device that had to pick up the seismometer on
• 23:48
  Speaker 3: the lander and move it onto the surface. So that required,
• 23:53
  Speaker 3: you know, tons of work to get that to just
• 23:54
  Speaker 3: work properly. Then it had to put a windshield on
• 23:57
  Speaker 3: top of the seismometer to make sure that we didn't
• 24:00
  Speaker 3: measure a bunch of wind basically because wind also shakes schismometers.
• 24:03
  Speaker 3: Then you know that the seismometer wasn't the only instrument
• 24:07
  Speaker 3: on Insight. There was also a thermal probe what we
• 24:11
  Speaker 3: called the mole, which was supposed to dig down about
• 24:14
  Speaker 3: ten meters and take temperature measurements at depth, which would
• 24:18
  Speaker 3: have told us about the heat flow coming out of Mars.
• 24:21
  Speaker 2: Again, this was going to be the first time.
• 24:23
  Speaker 3: Anything like this was tried, and unfortunately we couldn't get
• 24:27
  Speaker 3: the mole to dig deeper than about tens of centimeters.
• 24:31
  Speaker 3: The properties of the soils kind of a word we use,
• 24:35
  Speaker 3: but the properties of the sand on Mars were not
• 24:38
  Speaker 3: as we expected, and just the device couldn't actually use
• 24:42
  Speaker 3: friction to dig down deeper and deeper. So that was
• 24:45
  Speaker 3: a struggle and we actually the Insight engineering team that
• 24:49
  Speaker 3: worked on this and the scientists that worked on this,
• 24:51
  Speaker 3: you know, I wasn't part of this. It was just
• 24:52
  Speaker 3: amazing the things that they tried, and in the end
• 24:55
  Speaker 3: we actually did get some good science out of it.
• 24:57
  Speaker 2: We measured more sort of the thermal.
• 24:58
  Speaker 3: Properties at the upper part of the cross as opposed
• 25:00
  Speaker 3: to deeper down. But it was just amazing to see
• 25:03
  Speaker 3: how much they tried to work on doing this first
• 25:06
  Speaker 3: digging on here. You know, we talked about digging on
• 25:08
  Speaker 3: the Earth is hard. Now imagine digging on another planet
• 25:10
  Speaker 3: without humans, and it's even harder.
• 25:12
  Speaker 1: Wonderful, And then what are the plans for the future.
• 25:15
  Speaker 1: Is NASA planning to dig into the surfaces of any
• 25:18
  Speaker 1: other objects in the Solar System or put seismometers on
• 25:21
  Speaker 1: any other surfaces.
• 25:22
  Speaker 3: So I think seismometers is definitely something that's going to go.
• 25:25
  Speaker 3: So there is a big push right now to send
• 25:28
  Speaker 3: spacecraft back to the Moon so that we can better
• 25:31
  Speaker 3: understand our closest celestial body, let's say. And so there
• 25:35
  Speaker 3: is a mission that will involve putting a seismometer, putting
• 25:37
  Speaker 3: more seismometers on the Moon. We already have some seismometers
• 25:40
  Speaker 3: on the Moon that were turned off a while ago
• 25:42
  Speaker 3: for budgetary reasons, right, So it'll be great to get
• 25:45
  Speaker 3: seismology again on the Moon. But for me, the most
• 25:48
  Speaker 3: exciting is that an upcoming mission that's planned to go
• 25:52
  Speaker 3: to Titan, which is a moon of Saturn, is actually
• 25:55
  Speaker 3: going to have a seismometer on it as well. So
• 25:56
  Speaker 3: it'll be interesting to see what we can learn about
• 25:59
  Speaker 3: the interior of.
• 26:00
  Speaker 1: Titan, and what do we know right now about the
• 26:02
  Speaker 1: interior of Titan, And how could we know anything about
• 26:05
  Speaker 1: it just from like looking at a few photons that
• 26:07
  Speaker 1: happened to reflect off of it.
• 26:08
  Speaker 3: So Titan is one of my favorite places, so it's
• 26:10
  Speaker 3: really exciting to think about what they're going to see.
• 26:12
  Speaker 3: So Titan's a unique place. First of all, it's the
• 26:14
  Speaker 3: only other planetary body in the Solar System that has
• 26:17
  Speaker 3: a nitrogen based atmosphere that's thick like the Earth's right,
• 26:20
  Speaker 3: So earth Is atmosphere is mostly nitrogen, and the surface
• 26:24
  Speaker 3: pressure on Titan is about one and a half bars,
• 26:27
  Speaker 3: so one and a half Earth atmospheres. But the cool
• 26:29
  Speaker 3: thing about Titan is that it's a small planet and
• 26:31
  Speaker 3: so it has very little mass and so its gravity
• 26:33
  Speaker 3: is really low. So if you were to go to
• 26:36
  Speaker 3: Titan and put some cardboard on your arms and flap them,
• 26:39
  Speaker 3: you would be able to fly on Titan because you
• 26:41
  Speaker 3: have ideal buoyancy situation there. You've got thick atmosphere, low gravity,
• 26:45
  Speaker 3: so it's really easy to fly there.
• 26:47
  Speaker 1: So in contrast, like they had the helicopter on Mars,
• 26:49
  Speaker 1: that was a real challenge because the atmosphere was thin
• 26:52
  Speaker 1: and the helicopter needs atmosphere exactly exactly.
• 26:56
  Speaker 3: So the Dragonfly mission, which is going to Titan, should
• 26:59
  Speaker 3: get there in the mid twenty thirties. It is going
• 27:02
  Speaker 3: to involve a dual quad copter. So this thing has
• 27:04
  Speaker 3: basically eight rotors and this to me, because I'm Canadian,
• 27:09
  Speaker 3: it looks like a skidoo or a snowmobile because it
• 27:12
  Speaker 3: has these sled tracks underneath it. But it's basically going
• 27:16
  Speaker 3: to fly around land somewhere, do a bunch of science,
• 27:19
  Speaker 3: then take off again, look for a new location, scout somewhat,
• 27:23
  Speaker 3: then fly to a new location, land again. And so
• 27:24
  Speaker 3: it's going to be able to do ground local science
• 27:28
  Speaker 3: right at an individual location for a bunch of locations
• 27:30
  Speaker 3: over the surface. And that's really the challenge in planetary
• 27:33
  Speaker 3: science is this kind of combination of get lots of
• 27:36
  Speaker 3: data from lots of different places really locally, really close
• 27:39
  Speaker 3: to the surface. So that's going to be a very
• 27:41
  Speaker 3: exciting mission.
• 27:42
  Speaker 1: We'd have to ask you about that. Is that going
• 27:43
  Speaker 1: to be self directed? Is it going to decide on
• 27:46
  Speaker 1: its own where to go or is it going to
• 27:47
  Speaker 1: wait for signals for minutes and minutes from Earth?
• 27:50
  Speaker 3: Full disclosure here, I have no involvement in the Dragonfly mission.
• 27:53
  Speaker 3: I'm just a super fan. But my understanding is what
• 27:56
  Speaker 3: it's going to do is when it kind of goes
• 27:58
  Speaker 3: up the one time.
• 28:00
  Speaker 2: When it flies up one time.
• 28:00
  Speaker 3: It's going to survey, It's going to look around, then
• 28:03
  Speaker 3: it'll come back down recharge its batteries. And during that time,
• 28:06
  Speaker 3: when the data gets back to Earth, people are going
• 28:08
  Speaker 3: to look around and say, let's go here, right that
• 28:11
  Speaker 3: place over there looks kind of interesting. So it'll be
• 28:13
  Speaker 3: a combination. Some of the in time flight stuff is
• 28:16
  Speaker 3: going to have to be done by the spacecraft by itself,
• 28:19
  Speaker 3: but when it comes to making decisions about where to
• 28:21
  Speaker 3: go next in terms of big steps, that's going to
• 28:23
  Speaker 3: be done by the people.
• 28:24
  Speaker 2: Back here on Earth.
• 28:24
  Speaker 1: I really liked your comment about needing to sample several places.
• 28:28
  Speaker 1: It seems obvious that if you only land on Earth
• 28:30
  Speaker 1: in one place, you might conclude, oh, this whole place
• 28:32
  Speaker 1: is granted or oh, look, it's all beautiful marble or something.
• 28:36
  Speaker 1: Obviously you need to look around to get a better sample.
• 28:39
  Speaker 1: And so when we only land on one place on
• 28:41
  Speaker 1: the Moon, like the Apollo astronauts, you know, only looked
• 28:43
  Speaker 1: or near where they landed, we may have gotten a
• 28:46
  Speaker 1: bias sample of what's going on up there. So that's
• 28:49
  Speaker 1: really cool that they're going to explore it. So other
• 28:51
  Speaker 1: than landing on the surface. In your book, you were
• 28:53
  Speaker 1: talking about seeing what's inside a planet by basically how
• 28:56
  Speaker 1: it wobbles. Can you walk us through the physics of that,
• 28:59
  Speaker 1: the moment off and how it gives us a picture
• 29:01
  Speaker 1: of what's inside.
• 29:02
  Speaker 2: Yeah.
• 29:03
  Speaker 3: Absolutely, So all of the planets spin to some amount, right,
• 29:07
  Speaker 3: That's why we have a day on the Earth. And
• 29:10
  Speaker 3: when it spins, a planet doesn't just stay a perfect sphere.
• 29:14
  Speaker 3: It kind of gets fatter at the equator than it
• 29:16
  Speaker 3: does at the poles. Now, it turns out that how
• 29:18
  Speaker 3: fat it gets at the equator versus the poles is
• 29:21
  Speaker 3: directly related to what the material properties of the object are. So,
• 29:24
  Speaker 3: for example, if you had a perfect water planet, right,
• 29:26
  Speaker 3: imagine the small planet made of water and you spun
• 29:28
  Speaker 3: it there's a specific like ellipsoidal shape you would get
• 29:31
  Speaker 3: for a liquid planet, Whereas if you had a dense
• 29:34
  Speaker 3: core inside the planet and with a solid layer and
• 29:37
  Speaker 3: then a water ocean on the outside, you're going to
• 29:39
  Speaker 3: get a different amount of flattening or a different amount
• 29:42
  Speaker 3: of kind of bulging at the equator from that. So
• 29:45
  Speaker 3: we can actually use the amount of bulging of these
• 29:47
  Speaker 3: planets when they're spinning to get information about what's inside.
• 29:52
  Speaker 1: So, for example, you spin a basketball, it stays a sphere,
• 29:54
  Speaker 1: but if you spin a blog a pizza dough, it
• 29:57
  Speaker 1: becomes a disc, right, and so it tells you pizza
• 29:59
  Speaker 1: do softer than basketballs. I guess we already knew that,
• 30:02
  Speaker 1: But you're saying we can apply the same thing to planets.
• 30:04
  Speaker 1: By the deformation of the sphere, we can tell basically
• 30:07
  Speaker 1: how rigid it is.
• 30:08
  Speaker 3: Yes, absolutely, and also where the dense, how dense it
• 30:11
  Speaker 3: is essentially in different parts. So for example, Saturn, Saturn
• 30:15
  Speaker 3: is the bulgiest of all the planets in our solar systems.
• 30:18
  Speaker 3: Even if if you look at through a telescope, it
• 30:19
  Speaker 3: doesn't look like a sphere, It actually looks like more
• 30:22
  Speaker 3: of an oblate spheroid. So it's really interesting to look
• 30:25
  Speaker 3: at Saturn through a telescope.
• 30:26
  Speaker 1: You mean Saturn looks like squished, like somebody sat on it.
• 30:29
  Speaker 2: Yes, Saturn looks like someone satur on it.
• 30:31
  Speaker 1: In the best possible way. I mean Saturn's beautiful, Yes, yes, absolutely.
• 30:35
  Speaker 3: But because of that, we know that Saturn isn't just
• 30:37
  Speaker 3: a ball of hydrogen helium. We know that there have
• 30:40
  Speaker 3: to be some rocks inside kind of condensed at the center,
• 30:43
  Speaker 3: and then the gas sphere is kind of more on
• 30:45
  Speaker 3: the outside of it. So we've actually been able to
• 30:47
  Speaker 3: figure that out from the size of its equatorial bulge.
• 30:50
  Speaker 2: So that's the first way we can use rotation. There
• 30:52
  Speaker 2: are other ways.
• 30:53
  Speaker 3: So for example, as planets orbit and rotate, they can
• 30:57
  Speaker 3: actually as they're rotating, they don't always point their north
• 31:00
  Speaker 3: pole to exactly the same location, so they can actually process,
• 31:04
  Speaker 3: so their rotational axis can move around in a circle
• 31:08
  Speaker 3: about their orbit axis. And if you've ever played with
• 31:10
  Speaker 3: like a top, like a toy top, and you've spun
• 31:13
  Speaker 3: it and you've seen it make this little wobbly circlar pattern,
• 31:15
  Speaker 3: planets do the same thing. So planetary rotation axis wobble,
• 31:18
  Speaker 3: they process, and they also do this thing called nutating
• 31:21
  Speaker 3: where they kind of dip down a little bit, and
• 31:24
  Speaker 3: the period of those procession motions and the kind of
• 31:28
  Speaker 3: how cyclical they are really tells us about the interior
• 31:31
  Speaker 3: properties as well.
• 31:32
  Speaker 1: But why does it happen in the first place, I mean,
• 31:34
  Speaker 1: does an angular momentum tell us that it should we
• 31:37
  Speaker 1: spin along the same axis? Is this the effect of
• 31:39
  Speaker 1: like other things pulling on it?
• 31:41
  Speaker 2: Yes, exactly.
• 31:42
  Speaker 3: So if Earth were alone, if it was just the Earth,
• 31:45
  Speaker 3: then nothing else was around, we would not have any
• 31:47
  Speaker 3: procession or mutation. But we've got the Sun, we've got
• 31:50
  Speaker 3: the Moon nearby, and both of those things causecessional motions
• 31:54
  Speaker 3: and wobbling nutational motions that affect our orbit in our day.
• 31:58
  Speaker 1: So Jupiter and the other things are pulling on the
• 32:00
  Speaker 1: Earth and changing the direction of its spin axis basically
• 32:04
  Speaker 1: like where the north pole is pointing in the galaxy.
• 32:07
  Speaker 1: And you're saying that tells us something about what's inside
• 32:10
  Speaker 1: the Earth. People, I think are used to thinking about
• 32:12
  Speaker 1: the gravitational model of like, well, you can treat the
• 32:14
  Speaker 1: whole planet as a point mass at its center of mass,
• 32:17
  Speaker 1: you can't learn anything else about it. So how is
• 32:19
  Speaker 1: it possible to know something about the distribution of mass
• 32:21
  Speaker 1: inside the planet from how it's spin wobbles.
• 32:24
  Speaker 3: So the wobbling and the spin can tell you things,
• 32:27
  Speaker 3: for example, like if you have a liquid layer inside
• 32:29
  Speaker 3: the planet. So I don't know if you've ever played
• 32:30
  Speaker 3: this game, but if you take a beach ball and
• 32:33
  Speaker 3: you put like a little pocket of water in it
• 32:36
  Speaker 3: and you try to throw it to someone, it moves
• 32:37
  Speaker 3: completely differently than if you don't. Or even easier, take
• 32:40
  Speaker 3: an egg. Take a raw egg and take a cooked egg,
• 32:44
  Speaker 3: both still in their shells, and put them on your counter.
• 32:47
  Speaker 2: And spin them, and you will see that they spin.
• 32:49
  Speaker 3: Very differently because one of them has liquids inside of
• 32:51
  Speaker 3: it and the other one is fully solid. So we
• 32:54
  Speaker 3: can use the way that the spin axis wobbles to
• 32:58
  Speaker 3: figure out where are there liquid layers in this place?
• 33:00
  Speaker 2: Is it fully solid that sort of thing I see?
• 33:03
  Speaker 1: Is this planet more like a soft or hard boiled egg.
• 33:06
  Speaker 1: That's incredible, And can't you also measure the moment of
• 33:10
  Speaker 1: inertia of the planet and tell like where the mass
• 33:12
  Speaker 1: is distributed, Like you can tell the difference between like
• 33:15
  Speaker 1: all the mass being at the core versus all the
• 33:17
  Speaker 1: mass being at the surface.
• 33:19
  Speaker 3: Yeah, so it's a bit complicated in the math, but
• 33:21
  Speaker 3: it turns out that the precession rate, so how fast
• 33:24
  Speaker 3: the axis of the rotation processes about the orbit normal.
• 33:27
  Speaker 2: I'll give you any example.
• 33:28
  Speaker 3: So on the Earth right now, our north pole points
• 33:31
  Speaker 3: to the North Star. It was named lat Way for
• 33:33
  Speaker 3: a very specific reason. But it's moving around and in
• 33:35
  Speaker 3: about twenty it takes about twenty six thousand years for
• 33:38
  Speaker 3: that pole to get back to the North Star. Right,
• 33:41
  Speaker 3: So the period of our orbit is twenty six thousand years,
• 33:45
  Speaker 3: and that period can be used to actually determine the
• 33:49
  Speaker 3: moment of inertia of the Earth through some fancy math formulas.
• 33:53
  Speaker 3: And so if we can measure the precession rate or
• 33:56
  Speaker 3: the period for other planetary bodies, we can also figure
• 33:59
  Speaker 3: out their moment of inertia.
• 34:00
  Speaker 1: Wow, twenty six thousand years. How long have we been
• 34:04
  Speaker 1: making these measurements? Couldn't have been more than a thousand
• 34:06
  Speaker 1: years that maximum?
• 34:07
  Speaker 3: Yeah, yeah, it's definitely less than that. But you know,
• 34:10
  Speaker 3: you can you can trace out a little arc of
• 34:11
  Speaker 3: a circle, then you can pretty much draw out the
• 34:13
  Speaker 3: rest of the circle.
• 34:14
  Speaker 1: Yeah, I guess we have a model and we can
• 34:16
  Speaker 1: fit to that little arc. That's amazing, incredible. We can
• 34:19
  Speaker 1: learn so much about what's inside these objects without even
• 34:22
  Speaker 1: ever going inside. All right, I can't wait to talk
• 34:25
  Speaker 1: about this some more, but first we have to take
• 34:27
  Speaker 1: another break. Okay, we're back and we're talking to Professor
• 34:42
  Speaker 1: Sabina Stanley, author of the new book What's Hidden Inside
• 34:46
  Speaker 1: Planets about what's inside the Earth and other planets. Now,
• 34:49
  Speaker 1: I want to talk about sort of how the inside
• 34:51
  Speaker 1: affects the outside, because obviously, if you're just curious about
• 34:55
  Speaker 1: how the solar system is formed, you want to know,
• 34:57
  Speaker 1: like what's inside the Earth. But even if you're not,
• 35:00
  Speaker 1: like it has an effect on living on the surface, right,
• 35:03
  Speaker 1: tell us about how the magnetic field of these things
• 35:06
  Speaker 1: is generated and how it relates to bubbling soup.
• 35:09
  Speaker 2: Yeah, so magnetic fields are my favorite topic. Not gonna lie.
• 35:12
  Speaker 2: So here's this amazing thing. Right.
• 35:14
  Speaker 3: We're on the surface of the Earth, and one of
• 35:16
  Speaker 3: the reasons it's such a nice place to live at
• 35:18
  Speaker 3: the moment is because we have this beautiful magnetic field
• 35:21
  Speaker 3: that completely envelops the Earth. And that magnetic field what
• 35:24
  Speaker 3: it does for us is it shields the surface from
• 35:27
  Speaker 3: high energy particles that come from the solar wind, which
• 35:29
  Speaker 3: come from the Sun and from cosmic rays that come
• 35:31
  Speaker 3: from deep space, and those very high energy particles. If
• 35:35
  Speaker 3: we didn't have our magnetic field, they would kind of
• 35:37
  Speaker 3: blast the surface of the Earth and they would do
• 35:39
  Speaker 3: some terrible things. First of all, they would cause high
• 35:41
  Speaker 3: radiation environments, so we'd likely have higher rates of cancer,
• 35:44
  Speaker 3: for example. But also they cause lots of electrical disturbances.
• 35:49
  Speaker 3: And if you think about our power grid, our power
• 35:51
  Speaker 3: grid does not like there to be large fluctuations in
• 35:53
  Speaker 3: electromagnetic fields.
• 35:55
  Speaker 2: That's another thing that is not so good.
• 35:57
  Speaker 3: It also tends to these solar winds that bombard planets.
• 36:02
  Speaker 3: They can actually erode the atmosphere of a planet, so
• 36:05
  Speaker 3: they can take they can basically, you know, it's like
• 36:07
  Speaker 3: pointing a hair dryer at the Earth. You're going to
• 36:10
  Speaker 3: be able to blow off all the gas from it.
• 36:12
  Speaker 3: So there are all these things that the magnetic field
• 36:13
  Speaker 3: actually shields us from. But this magnetic field that surrounds
• 36:16
  Speaker 3: us is actually created deep inside the Earth in the
• 36:20
  Speaker 3: iron core. So iron is great electrical conductor. When you
• 36:24
  Speaker 3: have a great electrical conductor, if you can get it
• 36:26
  Speaker 3: moving around in the right way, then you can actually
• 36:29
  Speaker 3: generate magnetic fields And the best kind of analogy I
• 36:33
  Speaker 3: can think of for this is if anyone has a
• 36:34
  Speaker 3: home generator or if they have a bike light that
• 36:38
  Speaker 3: they can pedal to get going, you're basically converting the
• 36:41
  Speaker 3: kinetic energy of that motion into electromagnetic energy.
• 36:44
  Speaker 2: So you either you know.
• 36:45
  Speaker 3: You're pedaling, causes your bike light causes currents to flow
• 36:49
  Speaker 3: that causes your bike light to shine right, or similar
• 36:52
  Speaker 3: in your generator. So in the core of the earth,
• 36:55
  Speaker 3: convection which occurs because the center is hotter than the
• 36:59
  Speaker 3: outer parts of the core, So you kind of have
• 37:01
  Speaker 3: bubbling up like like you would if you put a
• 37:03
  Speaker 3: pot of soup on the stove, right, you get the
• 37:05
  Speaker 3: bottom of the pot is hot, the top of the
• 37:07
  Speaker 3: pot is cold, So you get these overturning motions in
• 37:11
  Speaker 3: the soup. Same thing happens in the core, and so
• 37:14
  Speaker 3: that overturning motions they create magnetic fields and you get
• 37:17
  Speaker 3: what called a dynamo. So the dynamo in the center
• 37:20
  Speaker 3: of the earth generates this magnetic field that protects us
• 37:22
  Speaker 3: on the surface.
• 37:23
  Speaker 1: Amazing, And so you're saying that it's the convection cells
• 37:27
  Speaker 1: that generate the magnetic field, not for example, the spinning
• 37:30
  Speaker 1: of the planet.
• 37:31
  Speaker 3: Right, So there's a somewhat common misunderstanding out there that
• 37:36
  Speaker 3: the reason that Earth has a magnetic field, for example,
• 37:38
  Speaker 3: is due to its spinning. And this has been used sometimes,
• 37:41
  Speaker 3: for example, to explain why Venus, which is spinning very slowly,
• 37:45
  Speaker 3: doesn't have a magnetic field.
• 37:47
  Speaker 2: And it turns out.
• 37:47
  Speaker 3: That you don't need spinning at all to generate a
• 37:50
  Speaker 3: magnetic field. So magnetic fields can be generated through dynamo
• 37:53
  Speaker 3: processes without spinning. Now, spinning sometimes helps in organizing motions
• 37:58
  Speaker 3: and stuff like that, but it's not actually a requirement.
• 38:01
  Speaker 3: So it's the convective motions, not the spinning, right.
• 38:03
  Speaker 1: And so in your analogy, you're talking about like peddling
• 38:06
  Speaker 1: your bicycle to generate electricity, And we haven't seen any
• 38:09
  Speaker 1: magnetic monopoles in our universe, so we know that to
• 38:12
  Speaker 1: generate magnetic fields you have to take a charge and
• 38:15
  Speaker 1: put it in motion, which is how electrical generators work.
• 38:18
  Speaker 1: But what is the charge here? Like we have flows
• 38:21
  Speaker 1: of iron. Iron is obviously metallic and it conducts, but
• 38:24
  Speaker 1: don't you need some ion in motion in order to
• 38:27
  Speaker 1: get a current going? What generates the actual current? If
• 38:30
  Speaker 1: you just have neutral iron how does that generate a
• 38:32
  Speaker 1: magnetic field.
• 38:33
  Speaker 3: Yeah, it's actually an induction process. So what it is
• 38:36
  Speaker 3: is you've got a good electrical conductor and imagine you
• 38:39
  Speaker 3: have a magnetic field and it's frozen into a good
• 38:42
  Speaker 3: electrical conductor. So magnetic fields tend to stick inside good conductors.
• 38:46
  Speaker 2: They don't like to change. But imagine then that.
• 38:48
  Speaker 3: You start moving that conductor around relative to itself, so
• 38:51
  Speaker 3: you shear it, you pull it apart a little bit.
• 38:53
  Speaker 3: That magnetic field has to go with it, so you
• 38:56
  Speaker 3: stretch and twist the magnetic fields through the motion itself
• 38:59
  Speaker 3: to create new magnetic fields.
• 39:01
  Speaker 1: Wow. Fascinating. And the Earth's magnetic field, though it's pretty reliable,
• 39:05
  Speaker 1: is not actually constant. Isn't it gradually changing?
• 39:08
  Speaker 2: Yes?
• 39:08
  Speaker 3: Absolutely, So we have records from the rocks in our crust.
• 39:12
  Speaker 3: They can be magnetized at the time that they form,
• 39:15
  Speaker 3: and those records tell us that Earth's magnetic field has
• 39:19
  Speaker 3: changed over time. We at least have data that shows
• 39:21
  Speaker 3: it's been around for about three billion years, if not longer.
• 39:25
  Speaker 3: But it hasn't always been the same. So there are
• 39:27
  Speaker 3: times in the past where the field has gotten weaker.
• 39:29
  Speaker 3: There are times in the past where the field has
• 39:31
  Speaker 3: flipped polarity, so the north magnetic pole became the south
• 39:34
  Speaker 3: magnetic pole and vice versa. And even today, on like
• 39:38
  Speaker 3: weekly time scales, we can measure the small changes in
• 39:41
  Speaker 3: the earth magnetic field that are happening from a variety
• 39:44
  Speaker 3: of things. Some things are external, but sometimes we can
• 39:46
  Speaker 3: also see on a yearly scale we can see the
• 39:49
  Speaker 3: changes due to different flows happening in the core of
• 39:51
  Speaker 3: the Earth.
• 39:52
  Speaker 1: Can we use these changes in the magnetic field to
• 39:54
  Speaker 1: sort of image those flows the same way we can
• 39:57
  Speaker 1: see changes in the gravitational field to give us a
• 39:59
  Speaker 1: picture of what's inside the Earth.
• 40:01
  Speaker 3: Yeah, it gets a little more challenging the deeper you go.
• 40:04
  Speaker 3: And with magnetic fields, what we can see, for example,
• 40:06
  Speaker 3: is because we know it's a good electrical conductor, if
• 40:09
  Speaker 3: we see a magnetic field pattern drifting.
• 40:11
  Speaker 2: In one direction.
• 40:12
  Speaker 3: So for example, there's this kind of famous thing we
• 40:14
  Speaker 3: talk about in geomagnetism called the westward drift. So if
• 40:17
  Speaker 3: you follow certain features of the magnetic field, you see
• 40:19
  Speaker 3: they all kind of drift westward, and we interpret that
• 40:22
  Speaker 3: to being there's flow generally in the westward direction.
• 40:25
  Speaker 2: There's like a jet.
• 40:25
  Speaker 3: Stream in the core of the Earth. That's flowing westward,
• 40:29
  Speaker 3: that's taking the magnetic field with us.
• 40:31
  Speaker 1: Wow, and so how well do we understand this process?
• 40:34
  Speaker 1: Are there still open questions about like why it's flipping
• 40:37
  Speaker 1: and why it's changing or is it something that we
• 40:39
  Speaker 1: understand pretty well?
• 40:40
  Speaker 3: So many open questions. So the amazing thing about this process,
• 40:44
  Speaker 3: so fluid dynamics. If you've had any experience with climate
• 40:46
  Speaker 3: modeling or trying to study flows that happen in pipes
• 40:50
  Speaker 3: and so forth, fluids are really complicated. They can they
• 40:54
  Speaker 3: can display turbulence for example, or laminar flows depending on
• 40:58
  Speaker 3: what types of you know, what what the situation is like.
• 41:02
  Speaker 2: Now, if you add to that.
• 41:04
  Speaker 3: Add to fluid dynamics magnetic fields and all the things
• 41:06
  Speaker 3: that happen with magnetic fields, you almost get an added complication.
• 41:10
  Speaker 3: And so when we try to think about, well, how
• 41:12
  Speaker 3: do we study the dynamo process, right, we can't really
• 41:14
  Speaker 3: wait thousands of years to watch the real system over time.
• 41:18
  Speaker 3: We want to study it faster. So you can either
• 41:20
  Speaker 3: do experiments or you can try to write a computer
• 41:23
  Speaker 3: model that can mimic what's going on in a core
• 41:26
  Speaker 3: when it's generating a magnetic field. Experiments are really hard
• 41:29
  Speaker 3: turns out that dynamos they like three things. They like
• 41:34
  Speaker 3: really good electrical conductors, they like really fast motions, and
• 41:37
  Speaker 3: they like really large length scales. And then you start saying, Okay,
• 41:40
  Speaker 3: I'm going to build my giant sphere of a really
• 41:44
  Speaker 3: good electrical conductor and then spin it really fast, and
• 41:47
  Speaker 3: you just you end up with a huge challenging problem.
• 41:49
  Speaker 3: The biggest dynamo experiment out there is the three meter
• 41:53
  Speaker 3: Dynamo Sphere in Maryland, and it has yet to generate
• 41:56
  Speaker 3: an active dynamo, so that's a challenging problem. We use
• 42:00
  Speaker 3: computer simulations to study dynamos inside planets. The problem there
• 42:04
  Speaker 3: is that planets, the motions, the scales, and the motions
• 42:07
  Speaker 3: are so tiny and so fast that there isn't enough
• 42:10
  Speaker 3: computer power on the planet to run a simulation accurately.
• 42:13
  Speaker 3: So we have to make a lot of assumptions and
• 42:16
  Speaker 3: simplifying type conditions, so we aren't able to fully study
• 42:19
  Speaker 3: the system the way.
• 42:20
  Speaker 2: We want to. We have to be very nuanced in
• 42:23
  Speaker 2: how we study it. Well.
• 42:23
  Speaker 1: Do we understand why the Earth's flipping of the magnetic
• 42:27
  Speaker 1: field seems so irregular compared to, for example, the Sun,
• 42:29
  Speaker 1: which has this rock solid solar cycle of eleven years.
• 42:32
  Speaker 3: Yeah, we don't fully understand why at all. We can't
• 42:35
  Speaker 3: even kind of predict what we would expect for other
• 42:37
  Speaker 3: planets as well. We have what I would call a
• 42:39
  Speaker 3: hand way the understanding, and that we would describe the
• 42:42
  Speaker 3: core fluid as being a very nonlinear system that can
• 42:46
  Speaker 3: have different attractors or different stable systems. And sometimes it's
• 42:51
  Speaker 3: in one stable position, sometimes it's another. And so if
• 42:53
  Speaker 3: you have something near a stable position, imagine you have
• 42:55
  Speaker 3: a ball sitting and you have like a nice valley
• 42:59
  Speaker 3: in two hill on the side, and you stick the
• 43:01
  Speaker 3: ball on one of the tops of the hills, right,
• 43:03
  Speaker 3: it'll pretty much stay there, but maybe if you shake
• 43:05
  Speaker 3: it a little bit too much, give it a bit
• 43:07
  Speaker 3: too many perturbations, it'll sink down and go to the
• 43:10
  Speaker 3: other stable position. So we think that some perturbations in
• 43:13
  Speaker 3: the fluid can sometimes cause the field of flip, but
• 43:16
  Speaker 3: we don't have a good way to, for example, predict
• 43:18
  Speaker 3: when the next flip is going to happen, what's the
• 43:20
  Speaker 3: key factor that causes such a flip for example?
• 43:23
  Speaker 2: And these are all areas of current research.
• 43:24
  Speaker 1: Wow. And then as we discover planets in other solar systems.
• 43:29
  Speaker 1: How do we begin to do geology of those planets?
• 43:33
  Speaker 1: And first, I guess there's a trivial question is would
• 43:35
  Speaker 1: you call it geology? Geology is to study the Earth,
• 43:37
  Speaker 1: so it is this like exo planetology, what do you
• 43:40
  Speaker 1: call it?
• 43:40
  Speaker 2: This is a great question.
• 43:42
  Speaker 3: I think the norm has been to refer to geology
• 43:44
  Speaker 3: as looking at rocks.
• 43:46
  Speaker 2: And it doesn't matter where those rocks are. So rocks.
• 43:48
  Speaker 3: There are Mars geologists, I'll just get that out there,
• 43:51
  Speaker 3: instead of mars oologists or whatever you would call them instead. Yeah,
• 43:54
  Speaker 3: with exoplanets, the challenge there is the type of information
• 43:58
  Speaker 3: you can get can be quite limitted compared to what
• 44:00
  Speaker 3: we can get when we're in our own Solar system
• 44:03
  Speaker 3: or here on the Earth. But even with the standard
• 44:05
  Speaker 3: techniques that can discover exoplanets, right, if you think about
• 44:10
  Speaker 3: the methods involving radial velocity detection, so where you measure
• 44:13
  Speaker 3: fluctuations in the stars light curve caused by the motion
• 44:17
  Speaker 3: of a planet around it, you get information about the
• 44:19
  Speaker 3: period of the orbit, and that can also give you
• 44:21
  Speaker 3: measurements about the mass of the planet. Then if you
• 44:24
  Speaker 3: use transit where a planet passes in front of or
• 44:27
  Speaker 3: behind a star, you can get information about the size
• 44:30
  Speaker 3: of the planet. So as soon as you have the
• 44:31
  Speaker 3: size and the mass, you already have kind of an
• 44:33
  Speaker 3: average density, a bulk density of the planet. So we
• 44:36
  Speaker 3: have sense of whether when we discover these exoplanets, is
• 44:40
  Speaker 3: it a gas giant, is it an Earth like planet?
• 44:43
  Speaker 3: Is it an ice world like Uranus and Neptune. So
• 44:45
  Speaker 3: we can do some very broad geology, let's say, from
• 44:49
  Speaker 3: that type of information. But what I'm most excited about
• 44:52
  Speaker 3: is the possibilities that are going to come forward with
• 44:55
  Speaker 3: JWST because this new telescope is going to be able
• 44:59
  Speaker 3: to measure the atmospheres of exoplanets and tell us what
• 45:04
  Speaker 3: they're made of. That's going to be crucial information to
• 45:07
  Speaker 3: figure out what's actually going on deeper inside the planet.
• 45:10
  Speaker 3: Right our atmosphere on Earth is the way it is
• 45:13
  Speaker 3: because of interactions with the interior of the Earth, and
• 45:15
  Speaker 3: so we're going to be able to use information about
• 45:17
  Speaker 3: the atmospheres of these exoplanets to also tell us something
• 45:20
  Speaker 3: about the interior.
• 45:21
  Speaker 1: What do you mean by that? I know our atmosphere
• 45:23
  Speaker 1: is different because we have a magnetic field and because
• 45:25
  Speaker 1: of the surface gravity. What else does our atmosphere tell
• 45:29
  Speaker 1: us about what's inside the Earth.
• 45:30
  Speaker 3: Right, So if there was an alien flying by our
• 45:33
  Speaker 3: solar system, and all it could measure is kind of
• 45:36
  Speaker 3: the spectrum of our atmosphere, it would be able to
• 45:38
  Speaker 3: tell that there was life here most likely.
• 45:40
  Speaker 2: Right.
• 45:40
  Speaker 3: We've done things to our environment to make it very
• 45:43
  Speaker 3: obvious that there is industrial action happening on the surface.
• 45:47
  Speaker 2: Right.
• 45:47
  Speaker 3: But also, for example, a lot of the processes that
• 45:50
  Speaker 3: regulate some of the key species in our atmospheres, like
• 45:53
  Speaker 3: carbon dioxide. On Earth, there's the carbon cycle. The carbon
• 45:58
  Speaker 3: cycle not only involves the atmosphere, it involves the ocean,
• 46:01
  Speaker 3: the surface, and the deep interior. So carbon gets recycled
• 46:05
  Speaker 3: inside the Earth, and so we can actually learn about
• 46:09
  Speaker 3: how exchanges of materials happen with the interior and the
• 46:12
  Speaker 3: atmosphere by looking at how much carbon there is around,
• 46:15
  Speaker 3: for example, right. And so the same is true for
• 46:17
  Speaker 3: other element cycles, and so the same could be true
• 46:20
  Speaker 3: for exoplanets.
• 46:21
  Speaker 1: We had Professor Shields on the podcast recently, and she
• 46:24
  Speaker 1: does exoplanet climate simulations. We're basically building models of these
• 46:29
  Speaker 1: planets and then trying to make them consistent with what
• 46:32
  Speaker 1: we might understand from JWST. It sounds like you're talking
• 46:34
  Speaker 1: about doing something similar, but you're building models of the
• 46:37
  Speaker 1: internals of these planets to explain then the climate in
• 46:40
  Speaker 1: the atmosphere, which then tells us about the light we're
• 46:43
  Speaker 1: seeing from these planets. So it seems like quite a
• 46:45
  Speaker 1: few steps there from the photons we're getting in JWST
• 46:48
  Speaker 1: to our model of what's happening inside those planets. Incredible
• 46:51
  Speaker 1: that we could learn.
• 46:52
  Speaker 2: Anything, Yes, absolutely agree.
• 46:53
  Speaker 1: And what about future missions? I know there are space
• 46:56
  Speaker 1: telescopes that are going to be looking specifically for planets.
• 46:58
  Speaker 1: Are those going to have the toy to tell us
• 47:01
  Speaker 1: more about these planets or do we need to wait
• 47:03
  Speaker 1: until we can send landers to listen for exoplanet quakes.
• 47:07
  Speaker 3: What I'm most excited about for future exoplanet data has
• 47:12
  Speaker 3: to do with magnetic fields again, right, So if we
• 47:14
  Speaker 3: think Earth having a magnetic field is so important for
• 47:17
  Speaker 3: shielding life on the surface, then it might be nice
• 47:20
  Speaker 3: if we knew that exoplanets had magnetic fields. It maybe
• 47:22
  Speaker 3: it's something we should add to the conditions for a habitable.
• 47:25
  Speaker 2: Planet out there.
• 47:26
  Speaker 3: And there have been some signs, some evidence that we
• 47:29
  Speaker 3: might actually be able to measure magnetic fields of exoplanets
• 47:31
  Speaker 3: so there's hope that with even more measurements and so forth,
• 47:35
  Speaker 3: we might actually be able to tell in the future
• 47:38
  Speaker 3: if an exoplanet has a magnetic field.
• 47:40
  Speaker 1: Today, how would that be possible? Are you looking for
• 47:42
  Speaker 1: like the Northern lights equivalent on the planet, seeing the
• 47:45
  Speaker 1: effect of the magnetic field on the atmosphere.
• 47:47
  Speaker 3: So that's one way kind of so it's not the
• 47:49
  Speaker 3: Northern lights itself, but actually the way we found out
• 47:52
  Speaker 3: Jupiter had a magnetic field. We knew that Jupiter had
• 47:54
  Speaker 3: a magnet field in the nineteen sixties even though we'd
• 47:56
  Speaker 3: never been there, because electrons that spire roll along the
• 48:00
  Speaker 3: magnetic field lines of Jupiter get really close to the
• 48:03
  Speaker 3: poles into the atmosphere there right, and that causes aurora
• 48:06
  Speaker 3: on Jupiter as well. But it also causes a type
• 48:08
  Speaker 3: of radio emissions to come off of Jupiter, and those
• 48:12
  Speaker 3: radio emissions get beamed out into space and we could
• 48:14
  Speaker 3: actually measure them here on the surface of the Earth.
• 48:16
  Speaker 3: So we knew about Jupiter's magnetic field in the nineteen
• 48:18
  Speaker 3: sixties before we'd ever gone there, because we received these
• 48:21
  Speaker 3: radio emissions. Same is true for any other planet. Now,
• 48:25
  Speaker 3: it turns out that the intensity of those radio emissions
• 48:27
  Speaker 3: is really important, so you need really strong magnetic fields
• 48:30
  Speaker 3: in order to be able to measure them. On the
• 48:31
  Speaker 3: surface of the Earth. We have this horrible atmosphere on
• 48:33
  Speaker 3: Earth and it blocks a lot of radio emissions, which
• 48:35
  Speaker 3: is very frustrating, although kind of good for breathing. So
• 48:38
  Speaker 3: I guess, you know, let's say we put a radio
• 48:43
  Speaker 3: telescope on the far side of the Moon. That would
• 48:46
  Speaker 3: be great for helping to detect radio emissions from exoplanets.
• 48:49
  Speaker 3: So there's that method, but they're also what I would
• 48:52
  Speaker 3: call sneakier methods.
• 48:53
  Speaker 2: Right.
• 48:54
  Speaker 3: For example, if you look at the transit spectrum, so
• 48:57
  Speaker 3: if you look at a planet that's going in front
• 48:59
  Speaker 3: of a sign or a star and you see kind
• 49:03
  Speaker 3: of how wide the planet is. People can already kind
• 49:06
  Speaker 3: of tell if a planet has an atmosphere by the
• 49:08
  Speaker 3: fact that it could have different thicknesses or different radius
• 49:11
  Speaker 3: in different wavelengths, and that you know, sometimes the atmosphere
• 49:14
  Speaker 3: will let light through, whereas the planet itself won't, right,
• 49:18
  Speaker 3: And so that's how we can tell whether something has
• 49:20
  Speaker 3: an atmosphere, is what particular wavelengths of light get through
• 49:23
  Speaker 3: at different distances. The same can be true about a
• 49:25
  Speaker 3: magnetic field. Sometimes a magnetic field can cause certain light
• 49:28
  Speaker 3: spectra light frequencies to not get through, so we might
• 49:31
  Speaker 3: be actually able to measure a magnetosphere surrounding a planet
• 49:36
  Speaker 3: by looking at transit spectra. You can also maybe see
• 49:39
  Speaker 3: if a planet has like a tail, right, and so
• 49:42
  Speaker 3: sometimes if atmosphere is being blown off a planet, you
• 49:44
  Speaker 3: might be able to see that in a transit spectrum
• 49:46
  Speaker 3: or through other types of light detection. So there might
• 49:50
  Speaker 3: be some sneaky ways to look for magnet fields of
• 49:52
  Speaker 3: exoplanets as well.
• 49:53
  Speaker 1: Wonderful well, I expect that the next generation of scientists
• 49:56
  Speaker 1: will be even more creative about coming up with ways
• 49:58
  Speaker 1: to extract a me information from these tiny little blips
• 50:02
  Speaker 1: in our telescopes.
• 50:03
  Speaker 2: Yes, hopefully so.
• 50:04
  Speaker 1: Wonderful well. Thank you very much for coming on the
• 50:06
  Speaker 1: podcast and telling us so much about the mysteries that
• 50:08
  Speaker 1: are under our feet and the mysteries that are out
• 50:10
  Speaker 1: there in the universe.
• 50:11
  Speaker 2: Thanks so much.
• 50:12
  Speaker 1: This was fun, all right. That was my chat with
• 50:14
  Speaker 1: Professor Sabina Stanley again. She's the author of the book
• 50:17
  Speaker 1: What's Hidden Inside Plants, which you can get now at
• 50:20
  Speaker 1: all reputable booksellers. Thanks very much for listening. Tune in
• 50:24
  Speaker 1: next time. Thanks for listening, and remember that Daniel and
• 50:34
  Speaker 1: Jorge Explain the Universe is a production of iHeart Radio.
• 50:38
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• 50:43
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