Katherine de Kleer is a professor of Planetary Science and Astronomy at Caltech. Please support this podcast by checking out our sponsors:
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EPISODE LINKS:
Katherine's Website: http://web.gps.caltech.edu/~dekleer/

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OUTLINE:
0:00 - Introduction
1:27 - Pluto
6:35 - Kuiper belt
10:32 - How to study planets and moons
14:15 - Volcanoes on Io - moon of Jupiter
26:46 - Is there life in the oceans of Europa?
36:07 - How unlikely is life on Earth?
46:36 - Life on Venus
48:50 - Mars
55:37 - What is interesting about Earth as a planet?
1:06:15 - Weather patterns
1:11:25 - Asteroids
1:20:27 - Will an asteroid hit Earth soon?
1:29:10 - Oumuamua
1:44:20 - Book recommendations
1:50:58 - Advice for young people

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a conversation with Catherine DeCleer, a professor of planetary science and astronomy at Caltech.

Her research is on the surface environments, atmospheres, and thermochemical histories of the planets and moons in our solar system.

Quick mention of our sponsors, Fundrise, Blinkist, ExpressVPN, and Magic Spoon.

Check them out in the description to support this podcast.

As a side note, let me say that this conversation and a few others, quite big ones actually, that are coming up were filmed in a studio where I was trying to outsource some of the work.

Like all experiments, it was a learning experience for me.

Ultimately, I decided to return back to doing it the way I was doing before, but hopefully with a team who can help me out and work with me long term.

The point is, I will always keep challenging myself, trying stuff out, learning, growing, and hopefully improving over time.

My goal is to surround myself with people who love what they do, are amazing at it, and are obsessed with doing the best work of their lives.

To me, there's nothing more energizing and fun than that.

In fact, I'm currently hiring a few folks to work with me on very small projects.

If this is something of interest to you, go to lexfriedman.com slash hiring.

That's where I will always post opportunities for working with me.

This is the Lex Friedman Podcast, and here is my conversation with Catherine DeCleer.

Does this upset you, or has justice finally been served?

I think all planetary scientists get asked about Pluto, especially by kids who would just love for Pluto to still be a planet.

But the reality is when we first discovered Pluto, it was a unique object in the outer solar system, and we thought we were adding a planet to the inventory of planets that we had.

And then over time, it became clear that Pluto was not a unique large object in the outer solar system, that there were actually many of these.

And as we started discovering more and more of them, we realized that the concept of Pluto being a planet didn't make sense, unless maybe we added all the rest of them as planets.

So you could have imagined actually a different direction that this could have gone where all the other objects that were discovered in that belt, or at least all the ones let's say above a certain size, became planets instead of Pluto being declassified.

But we're now aware of many objects out there in the outer solar system and what's called the Kuiper Belt that are of the same size or in some cases even larger than Pluto.

So the declassification was really just a realization that it was not in the same category as the other planets in the solar system.

And we basically needed to refine our definition in such a way that took into account that there's this belt of debris out there in the outer solar system of things with a range of sizes.

Is there a hope for clear categorization of what is a planet and not?

When you study planets, when you study moons, satellites of those planets, is there lines that could be cleanly drawn or is it just a giant mess?

Is this all like a fluid, let's say not mess, but it's like fluid of what is a planet, what is a moon of a planet, what is debris, what is asteroids, all that kind of.

So there are technically clear definitions that were set down by the IAU, the International Astronomy Union.

So the parameters are that it has to orbit the Sun, which was essentially to rule out satellites.

Of course, this was a not very forward-thinking definition because it technically means that all extrasolar planets, according to that definition, are not planets.

It has to be large enough that its gravity has caused it to become spherical in shape, which also applies to satellites and also applies to Pluto.

The third part of the definition is the thing that really rules out everything else, which is that it has to have cleared out its orbital path.

And because Pluto orbits in a belt of material, it doesn't satisfy that stipulation.

Why didn't you clear out the path that's not big enough to knock everybody out of the way?

And this actually is not the first time it has happened.

So Ceres, when it was discovered, Ceres is the largest asteroid in the asteroid belt, and it was originally considered a planet when it was first discovered, and it went through exactly the same story, history, where people actually realized that it was just 1 of many asteroids in the asteroid belt region, and then it got declassified to an asteroid and now it's back to a dwarf planet.

So to me, as somebody who studies solar system objects, I just personally don't care.

My level of interest in something has nothing to do with what it's classified as.

So my favorite objects in the solar system are all moons.

And frequently when I talk about them, I refer to them as planets because to me they are planets.

They have volcanoes, they have geology, they have atmospheres, they're planet-like worlds.

And so the distinction is not super meaningful to me, but it is important just for having a general framework for understanding and talking about things to have a precise definition.

So you don't have a special romantic appreciation of a moon versus a planet versus an asteroid, it's just an object that flies out there and it doesn't really matter what the categorization is.

Because there's movies about asteroids and stuff.

And then there's movies about the moon, whatever, it's a really good movie.

You know, there's something about moons that's almost like an outlier.

Like, you think of a moon as a thing that's the secret part, and the planet is like the more like vanilla regular part.

None of that, you don't have any of that?

I really, satellites are, the moons are my favorite things in the solar system.

And I think part of what you're saying, I agree from maybe a slightly different perspective, which is from the perspective of exploration.

We've spent a lot of time sending spacecraft missions to planets.

We had a mission to Jupiter, we had a mission to Saturn.

We have plenty of missions to Mars and missions to Venus.

I think that exploration of the moons in the outer solar system is the next frontier of solar system exploration.

The belt of debris, just real quick, that's out there, is there something incredible to be discovered there?

Again, we tend to focus on the planets and the moons, but it feels like there's probably a lot of stuff out there and it probably, what is it?

It's like a garbage collector from outside of the solar system, isn't it?

Like, doesn't it protect from other objects that kind of fly in and what, it just feels like it's a cool, you know when you like walk along the beach and look for stuff and like look for sure, it feels like that's that kind of place where you can find cool weird things.

Or I guess in our conversation today, when we think about tools and what science is studying, is there something to be studied out there?

Or we just don't have maybe the tools yet, or there's nothing to be found?

So the material that's out there is remnant material from the formation of our solar system.

We don't think it comes from outside the solar system, at least not most of it.

But there are so many fascinating objects out there, and I think what you've hit on is exactly right, that we just don't have the tools to study them in detail.

But we can look out there and we can see there are different species of ice on their surface that tells us about the chemical composition of the disk that formed our solar system.

Some of these objects are way brighter than they should be, meaning they have some kind of geological activity.

People have hypothesized that some of these objects have subsurface oceans.

You could even stretch your imagination and say some of those oceans could be habitable.

But we can't get very detailed information about them because they're so far away.

And so I think if any of those objects were in the inner solar system, it would be studied intently and would be very interesting.

So would you be able to design a probe in that like very dense debris field, be able to like hop from 1 place to another?

Is that just outside of the realm of, like how would you even design devices or sensors that go out there and take pictures and land?

Do you have to land to truly understand a little piece of rock?

Or can you understand it from remotely, like fly up close and remotely observe?

You can learn quite a lot from just a flyby and that's all we're currently capable of doing in the outer solar system.

The New Horizons mission is a recent example which flew by Pluto and then they had searched for another object that was out there in the Kuiper Belt, any object that was basically somewhere that they could deflect their trajectory to actually fly by.

And so they did fly by another object out there in the Kuiper belt and they take pictures and they do what they can do.

And if you've seen the images from that mission of Pluto, you can see just how much detail we have compared to just the sort of reddish dot that we knew of before.

So you do get an amazing amount of information actually from just essentially a high-speed flyby.

It always makes me sad to think about flybys that we might be able to, we might fly by a piece of rock, take a picture, and think, oh, that looks pretty and cool and whatever, and that you could study certain like composition of the surface and so on.

But it's actually teeming with life and we won't be able to see it at first.

And it's sad, because you know, like when you're on a deserted island, you wave your hands and the thing flies by and you're trying to get their attention and they probably do the same, well, in their own way.

I don't know, some reason it makes me, it's the FOMO, it's fear of missing out.

It makes me sad that there might be life out there and we don't, we're not in touch with it.

A sad pause, Russian philosophical pause.

What are the tools available to us to study planets and their moons?

LS Oh my goodness, that is such a big question.

So, among the fields of astronomy, so planetary science broadly speaking, well, it falls kind of at the border of astronomy, geology, climate science, chemistry, and even biology.

So it's kind of on the border of many things, but part of it falls under the heading of astronomy.

And among the things that you can study with telescopes, like solar system moons and planets, The Solar System is really unique in that we can actually send spacecraft missions to the objects and study them in detail.

And so I think that's the kind of type of tool that people are most aware of, that's most popularized, these amazing NASA missions that either you fly by the object, you orbit the object, you land on the object, potentially you can talk about digging into it, drilling, trying to detect tectonic tremors on its surface.

The types of tools that I use are primarily telescopes.

And so I actually got into solar system science from astronomy, not from a childhood fascination with spacecraft missions, which is actually what a lot of planetary scientists became planetary scientists because of childhood fascination with spacecraft missions, which is kind of interesting for me to talk to people and see that trajectory.

I kind of came at it from the fascination with telescopes angle.

So you like telescopes, not rockets, or at least you were...

When I was a kid, it was looking at the stars and playing with telescopes that really fascinated me and that's how I got into this.

But telescopes, it's amazing how much detail and how much information you can get from telescopes today.

You can resolve individual cloud features and watch them kind of sheer out in the atmosphere of Titan.

You can literally watch volcanoes on Io change from day to day as the lava flows expand.

And then with spectroscopy, you get compositional information on all these things.

When I started doing solar system astronomy, I was surprised by how much detail and how much information you can get even from Earth and then as well as from orbit, like the Hubble Space Telescope or the James Webb.

So with the telescope, you can, I mean, how much information can you get about volcanoes, about storms, about sort of weather, just so we kind of get a sense, like what a resolution we're talking about?

Well, in terms of resolution, so on a given night, if I go and take a picture of Io and its volcanoes, you can sometimes see at least a dozen different volcanoes.

You can see the infrared emission coming off of them and resolve them, separate them from 1 another on the surface and actually watch how the heat coming off of them changes with time.

And I think this time variability aspect is 1 of the big advantages we get from telescopes.

So you send a spacecraft mission there and you get an incredible amount of information over a very short time period, but for some science questions, you need to observe something for 30 years,

Like let's say you want to look at the moon Titan, which has 1 of the most interesting atmospheres in the solar system.

Its orbital period is 29, 30 years, And so if you want to look at how its atmospheric seasons work, you have to observe it over that long of a time period.

And you're not going to do that with a spacecraft, but you can do it with telescopes.

Can we just zoom in on certain things like, let's talk about Io, which is the moon of Jupiter.

And you're sort of a scholar of many planets and moons, but that 1 kind of stood out to me.

For so many reasons, but Io is the most volcanically active object in the solar system.

It has hundreds of active volcanoes on it.

It has volcanic plumes that go hundreds of kilometers up above its surface.

It puts out more volume of magma per volcano than volcanoes on Earth today.

But I think to me the reason that it's most interesting is as a laboratory for understanding planetary processes.

So 1 of the broad goals of planetary science is to put together a sort of more general and coherent framework for how planets work in general.

Our current framework, you know, it started out very Earth-centric.

We start to understand how Earth volcanoes work.

But then when you try to transport that to somewhere like Io that doesn't have an atmosphere, which makes a...

Or has a very tenuous atmosphere, which makes a big difference for how the magma degasses.

For something that's really small, for something that has a different heat source, for something that's embedded in another object's magnetic field, the kind of intuition we have from Earth doesn't apply.

And so, broadly, planetary sciences is trying to broaden that framework so that you have a kind of narrative that all you can understand how each planet became different from every other planet.

When I say planet, I mean planets and moons.

Yeah, I actually already noticed that you didn't introduce Io as the moon of Jupiter.

You completely, you kind of ignored the fact that Jupiter exists.

Yeah, okay, so, and you also didn't mention Europa, which I think is the, is that the most famous moon of Jupiter?

Is that the 1 that gets attention because it might have life.

What's the difference between volcanoes on Io versus Earth?

So many of the moons in the outer solar system are heated from gravitationally by tidal heating.

So tidal heating is, if you want to understand and contextualize planets and moons, you have to understand their heat sources.

So for Earth, we have radioactive decay in our interior as well as residual heat of formation.

But for satellites, tidal heating plays a really significant role, and in particular, in driving geological activity on satellites and potentially making those subsurface oceans in places like Europa and Enceladus habitable.

And so the way that that works is if you have multiple moons and their orbital periods are integer multiples of 1 another, that means that they're always encountering each other at the same point in the orbit.

So if they were on just random orbits, they'd be encountering each other at random places and the gravitational effect between the 2 moons would be canceling out over time.

But because they're always meeting each other at the same point in the orbit, those gravitational interactions add up coherently And so that tweaks them into eccentric orbits.

So eccentric orbit or elliptical orbit, it just means non-circular, so a deviation from a circular orbit.

And that means that for Io or Europa, at some points in their orbit, they're closer to Jupiter, and at some points in their orbit, they're farther away.

And so, when they're closer, they're stretched out in a sense, but literally just not very stretched out, like a couple hundred meters, something like that.

And then when they're farthest away, they're less stretched out.

And so you actually have the shape of the object deforming over the course of the orbit.

And these orbits are like just a couple of days.

And so that in the case of Io, that is literally sufficient friction in its mantle to melt the rock of its mantle and that's what generates the magma.

Okay, so why is Europa is I thought there's like ice and oceans underneath kind of thing.

So why is Europa not getting the friction?

It is, it's just a little bit farther away from Jupiter.

And then Ganymede is also in the orbital resonance.

So it's a 3 object orbital resonance in the Jupiter system.

But we have these sorts of orbital resonances all over the solar system and also in exoplanets.

So for Europa, basically because it's farther from Jupiter, the effect is not as extreme, but you do still have heat generated in its interior in this way, and that could be driving hydrothermal activity at the base of its ocean, which obviously would be a really valuable thing for life.

So it's like heating up the ocean a little bit.

Heating up the ocean a little bit and specifically in these like hydrothermal vents where we see really interesting life evolve in the bottom of Earth's oceans.

So we know the source is this friction, but there's no atmosphere.

I'm trying to get a sense of what it's like if you and I were to visit Io.

Is this the entire thing covered in basically volcanoes?

So it's interesting because there's very little atmosphere.

The surface is actually really cold, very far below freezing on the surface when you're away from a volcano, but the volcanoes themselves are over a thousand degrees or the magma when it comes out is over a thousand degrees.

But it does come to the surface, the magma?

Like what is, it's rock, it's really cold rock.

And then you just have this like, what is that look?

What would that look like with no atmosphere?

Is just magma, like just red, yellow, like liquidy things?

Like think of the type of magma that you see in Hawaii.

So different types of magma flow in different ways, for example, so in somewhere like Io, the magma is really hot, and so it will flow out in sheets because it has really low viscosity.

And I think the lava flows that we've been having in Hawaii over the past couple of years are probably a decent analogy, although Io's magma's lavas are even more fluid and faster moving.

How fast, like what, how fast, like if you, by the way, Sarah, through the telescope, are you tracking at what time scale?

Like every frame is how far apart if you're looking through a telescope?

Are we talking about seconds, are we talking about days, months?

When you kind of track, try to get a picture of what the surface might look like, what's the frequency?

So It depends a little bit on what you want to do.

But you could take a frame every second and see how things are changing.

The problem with that is that for things to change on a one-second time scale, to actually see something change that fast, you have to have super high resolution.

The spatial resolution we have is a couple hundred kilometers, and so things are not changing on those scales over 1 second, unless you have something really crazy happening.

So if you get a telescope closer to Io, if you get a camera closer to Io, would you be able to understand something, is that something of interest to you?

Would you be able to understand something deeper about these volcanic eruptions and how magma flows and just the rate of the magmas or is it basically enough to have the kilometer resolution?

I mean, I don't wanna go there personally, but I wanna send a spacecraft mission there, absolutely.

I want to send a robot there to look at it though.

This is again, everybody's discriminating against robots.

But it's not hospitable to humans in any way, right?

The atmosphere is composed of sulfur dioxide, So

I mean, it's kind of all the same things you talk about.

The atmosphere is still a thousand times less dense than Mars is.

And the radiation environment is terrible because you're embedded deep within Jupiter's magnetic field.

And Jupiter's magnetic field is full of charged particles that have all come out of Io's volcanoes, actually.

So Jupiter's magnetic field strips all this material out of Io's atmosphere, And that populates its entire magnetosphere.

And then that material comes back around and hits Io and spreads throughout the system, actually.

It's just, it's like Io is the massive polluter of the Jupiter system.

So what does studying Io teach you about volcanoes on Earth or vice versa?

Is in the difference of the 2, what insights can you mine out That might be interesting in some way.

LS Yeah, it's we try to port the tools that we use to study Earth volcanism to IO and it works to some extent but it is challenging because the situations are so different And the compositions are really different when you talk about outgassing.

You know, earth volcanoes outgas primarily water and carbon dioxide, and then sulfur dioxide is the third most abundant gas.

And on Io, the water and carbon dioxide are not there.

Either it didn't form with them or it lost them, we don't know.

And so the chemistry of how the magma outgasses is completely different.

But the kind of 1, to me, most interesting analogy to Earth is that, so Io, as I've said, it has these really low viscosity magmas.

The lava spreads really quickly across its surface.

It can put out massive volumes of magma in relatively short periods of time.

And that sort of volcanism is not happening anywhere else in the solar system today, but literally every terrestrial planet and the moon had this, what we call very effusive volcanism early in their history.

Okay, so this is almost like a little glimpse into the early history of Earth.

Okay, cool, so what are the chances that a volcano on Earth destroys all of human civilization?

Maybe I wanted to sneak in that question.

Do you think about that kind of stuff when you just study volcanoes elsewhere?

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Katherine de Kleer: Planets, Moons, Asteroids & Life in Our Solar System | Lex Fridman Podcast #184