SPEAKER_1: Welcome to StarTalk, your place in the universe where science and pop culture collide.
SPEAKER_1: StarTalk begins right now.
SPEAKER_1: This is StarTalk.
SPEAKER_1: Neil deGrasse Tyson, your personal astrophysicist.
SPEAKER_1: Today, we're gonna talk about Ocean World.
SPEAKER_1: And we got with us a previous guest on StarTalk, Kevin Hand.
SPEAKER_1: Kevin, welcome back.
SPEAKER_2: Hey, my pleasure and welcome to JPL.
SPEAKER_1: Oh yeah, this is not my office, is it?
SPEAKER_2: You made a great trip out here.
SPEAKER_1: This is not my office.
SPEAKER_2: Yeah, yeah, yeah.
SPEAKER_1: Yeah, in your turf at Pasadena, California, the Jet Propulsion Labs.
SPEAKER_1: I don't ever presume that everyone knows what those three letters stand for, but you can take it for granted if you work here.
SPEAKER_1: Everybody knows.
SPEAKER_1: I don't think everybody knows.
SPEAKER_1: Jet Propulsion Labs and Water Worlds is your thing.
SPEAKER_2: It is.
SPEAKER_1: And my God, just at the dawn of COVID, you had a book by that title.
SPEAKER_2: That's right, Alien Oceans.
SPEAKER_1: Alien Oceans, there it is.
SPEAKER_1: Typically, when people think about an ocean world other than Earth, they go straight to Europa at the top of everybody's list.
SPEAKER_1: I don't know if it has a better PR agent, but if you abstract that idea and go to any place that might have sort of liquid in the world doing anything, that list goes up.
SPEAKER_2: It does, absolutely.
SPEAKER_2: And these ocean worlds, Europa is sort of the mother of ocean worlds.
SPEAKER_1: Europa, again, a moon of Jupiter, correct.
SPEAKER_2: And even back in the late 70s, we could see with the Voyager data that something curious was going on with Europa.
SPEAKER_2: And over the course of the past several decades, we've now come to learn and appreciate that the outer solar system has got a small fleet of ice-covered worlds.
SPEAKER_2: And beneath their icy shells, these moons of the outer solar system have liquid water oceans.
SPEAKER_2: And of course, the big picture for me is the search for life beyond Earth.
SPEAKER_1: That's your guiding star.
SPEAKER_2: Guiding star.
SPEAKER_2: I would love life on Mars, exoplanets, SETI, et cetera.
SPEAKER_2: But these ocean worlds like Europa and Enceladus and Titan, these are worlds where life could be alive to extant life.
SPEAKER_1: Oh, because when you're looking at Mars, no one really thinks anything's gonna be crawling around on its surface.
SPEAKER_1: Whatever might have been happening billions of years ago.
SPEAKER_1: But there's no active water activity on Mars.
SPEAKER_1: Well, at least not on the surface.
SPEAKER_2: Exactly.
SPEAKER_2: Not on the surface.
SPEAKER_2: There could be on the subsurface.
SPEAKER_2: Who knows?
SPEAKER_2: Maybe there's life in the subsurface on Mars.
SPEAKER_2: But our search for life on Mars is a search for past life.
SPEAKER_2: And the molecules of life don't last long.
SPEAKER_2: So like DNA, RNA, proteins, you know, the stuff that makes our biochemistry.
SPEAKER_1: But bones last pretty, pretty long.
SPEAKER_2: Well, bones do last long, you know, and it's not inconceivable.
SPEAKER_1: Lucy, that we didn't find life.
SPEAKER_1: Lucy would beg to differ.
SPEAKER_2: And as you appreciate, you know, back in the Viking days, even Carl Sagan wanted to leave, put some lights on the Viking lander.
SPEAKER_2: So what if there's a Martian mouse, right?
SPEAKER_2: So, you know, a Martian mouse would leave bones behind.
SPEAKER_2: Bones do last for a long time.
SPEAKER_2: But for the most part, we're talking about the search for microbial life.
SPEAKER_2: And microbes do actually leave behind minerals.
SPEAKER_1: By the way, if a microbe had bones, I don't want to meet it.
SPEAKER_1: I don't know what the hell that microbe is doing.
SPEAKER_2: Some of the most beautiful, you know, if you ever see, like, travertine or some of the beautiful rock structures that are used.
SPEAKER_1: Or the Burgess Shale.
SPEAKER_1: Yeah.
SPEAKER_1: Is that in Canada, I think?
SPEAKER_2: Yeah, Burgess Shale has got animals.
SPEAKER_2: But, you know, there are...
SPEAKER_1: Because that was after the Cambrian explosion, if I remember correctly, or during it.
SPEAKER_2: In that time frame.
SPEAKER_1: In that time.
SPEAKER_1: So they took on very interesting shapes.
SPEAKER_1: But they got preserved.
SPEAKER_1: That's my point of that, right?
SPEAKER_2: Yeah, exactly.
SPEAKER_2: Whereas microbes, microbes can mediate rock structures.
SPEAKER_2: And if we see sort of a weird wavy rock form, sometimes referred to as a microbial light or a stromatolite, that is a form of an inorganic biosignature for microbes.
SPEAKER_2: Kind of like bones for microbes in some ways.
SPEAKER_1: I like that analogy.
SPEAKER_2: It's more of a frozen apartment building for microbes.
SPEAKER_1: And you knew somebody lived there, because it's an apartment building.
SPEAKER_2: It's an apartment building, but you want to couple that observation of the strange rock structure with some detection of organic compounds or other things.
SPEAKER_2: But that's all for Mars, right?
SPEAKER_2: Looking at life in the past, billions of years ago on Mars, when it comes to a separate independent origin of life and a separate tree of life, we're going to be kind of constrained on Mars because those large biomolecules of if life on Mars utilize DNA, DNA only lasts like maybe 10 million or at best tens of millions of years in the rock record.
SPEAKER_2: So we're not going to get like Martian DNA from samples returned from Mars.
SPEAKER_2: On a world like Europa, on a world like Enceladus, these are worlds where if we find indications of life on the surface of the icy shells, that's most likely, I would argue, an indication that life is currently alive in the oceans below.
SPEAKER_2: And that's extraordinary because then we can actually study it and see, does it run on DNA, RNA and proteins or is there a different ballgame?
SPEAKER_1: Mechanism altogether.
SPEAKER_2: Yeah.
SPEAKER_2: You know, contingent versus convergent.
SPEAKER_1: That would completely transform everything we know of biology.
SPEAKER_2: Exactly.
SPEAKER_2: You know, contingent evolution versus convergent in terms of...
SPEAKER_1: What is contingent evolution?
SPEAKER_2: The impact that caused the dinosaurs to go extinct is perhaps a somewhat useful, though mildly flawed, contingent example.
SPEAKER_2: You could say that humans would not be here if it weren't for the impact that wiped out the dinosaurs.
SPEAKER_1: That is definitely the case.
SPEAKER_2: Well, but you might argue that at some point, something else would have wiped out the dinosaurs.
SPEAKER_2: But you get my point.
SPEAKER_1: It's definitely the case.
SPEAKER_1: I work at a Natural History Museum.
SPEAKER_1: We got bones everywhere.
SPEAKER_1: Okay, I'm telling you, here's the argument for that.
SPEAKER_1: Just hear me out if you didn't otherwise know this.
SPEAKER_1: Do you know when T rex went extinct 65 million years ago, do you realize more time had elapsed between the extinction of the Stegosaurus and T rex than the extinction of T rex and today?
SPEAKER_1: So dinosaurs thrived for hundreds of millions of years.
SPEAKER_1: If you say, well, something might have still taken them out in the last 65 million years, I don't think so, because it would have taken out a whole lot of other things and we would have known about it.
SPEAKER_1: Dinosaurs were a highly successful phenotype.
SPEAKER_1: Phenotype, is that the right word?
SPEAKER_1: No, a highly successful branch in the tree of life, the collective things we call dinosaurs.
SPEAKER_1: So I think they would have been here and we'd still be scurrying underfoot, not trying to get eaten as a snack by whatever the version of T rex is that survived today.
SPEAKER_2: Exactly, so I'll remove any nuance and say that that is contingent.
SPEAKER_2: And then convergent is something like eyes.
SPEAKER_1: Oh yeah, no, I got convergent.
SPEAKER_1: That one where a highly useful feature evolves completely independently and to serve the same purpose.
SPEAKER_2: Exactly.
SPEAKER_2: So something that I find fascinating is when it comes to the origin of life, is the polymerization of amino acids or nucleobases, et cetera, is that something that we're going to find is convergent, so life on Europa or Enceladus evolved to use DNA also.
SPEAKER_1: Is it inevitable?
SPEAKER_2: Right.
SPEAKER_2: Or is there some other way to get that biochemistry done?
SPEAKER_1: Now the best argument I've heard for DNA, it took me part of the way there, but I'm still skeptical, because of the complexity of a DNA molecule.
SPEAKER_1: A geologist said, look, when we go to other planets, the geology is familiar, right?
SPEAKER_1: A rock crystal of these atoms crystallizes the same way, given the right temperatures and pressures, here as in there.
SPEAKER_1: And so if the geology repeats itself, no matter what planet we're on, maybe biology will repeat itself.
SPEAKER_2: Exactly.
SPEAKER_1: And I thought, okay, I threw a bone to that.
SPEAKER_1: And I said, all right, let me hang with that for a bit.
SPEAKER_1: But speaking of bones, I got a bone to pick with you.
SPEAKER_1: You lumped Titan in with Enceladus and Europa.
SPEAKER_1: How dare you?
SPEAKER_2: Go on, go on.
SPEAKER_1: We, you're motivated by the search for life.
SPEAKER_1: Life on Earth everywhere has needs, uses liquid water.
SPEAKER_2: Yep.
SPEAKER_1: There's no liquid water on Titan.
SPEAKER_2: Well, to be clear, there is.
SPEAKER_2: We do think that beneath the ice shell of Titan, there is an ocean trapped beneath that thick ice shell.
SPEAKER_2: But I think you're referring to the fact that on the surface, we got these liquid methane and...
SPEAKER_1: If you have liquid methane, you don't have liquid water.
SPEAKER_2: That's right.
SPEAKER_1: Just to be clear about that, okay?
SPEAKER_1: But it's not just a given that every moon is gonna have a heated interior from tidal forces.
SPEAKER_1: Now, I didn't do my homework on Titan before this interview, but is it subject to the same title stressing of its physical body as Europa and as Enceladus?
SPEAKER_2: It's a bit of a more complicated story, specifically at Saturn, and this is...
SPEAKER_2: The story is complicated.
SPEAKER_1: Titan, the moon of Saturn.
SPEAKER_2: Right.
SPEAKER_2: So Titan and Enceladus and the moons of Saturn, when it comes to the tides and how much tidal energy they have now and have had in the past, it's a bit complicated because the various moons go through resonances, right?
SPEAKER_2: Kids on a swing set kind of pumping each other up to swing in harmony or out of phase, right?
SPEAKER_2: In the Jovian system with...
SPEAKER_1: Jupiter system.
SPEAKER_2: In the Jupiter system with Io, Europa and Ganymede, those three moons are right now in a beautiful resonance we call the Laplace resonance.
SPEAKER_2: So for every two times Io goes around Europa, Io goes around Jupiter, Europa goes around Jupiter once.
SPEAKER_2: For every two times Europa goes around Jupiter, Ganymede goes around Jupiter once.
SPEAKER_1: I did not know they were in resonance.
SPEAKER_2: Yeah, and so that's what keeps their orbits slightly...
SPEAKER_1: So the system evolves to that because the dynamical forces favor it.
SPEAKER_2: Exactly.
SPEAKER_2: So gradually the orbits widen out and then Io starts tugging on Europa and Europa on Ganymede.
SPEAKER_2: Perhaps someday Callisto will be part of the party, but right now it's not.
SPEAKER_1: So that would complete the big four.
SPEAKER_1: Io, Europa, Ganymede, Callisto, the four that Galileo discovered.
SPEAKER_2: That's right.
SPEAKER_1: Yeah, I think we'll call them Galilean moons.
SPEAKER_1: In fact, he called them stars, I think.
SPEAKER_2: That's right.
SPEAKER_1: The Medecian stars.
SPEAKER_2: He was no idiot.
SPEAKER_2: He knew where the paycheck was coming from.
SPEAKER_1: Because they were just points of light that moved around Jupiter.
SPEAKER_1: And I think it's a moon if it's just a dot of light.
SPEAKER_1: It looks like a star.
SPEAKER_2: So he started off really well with like naming the stars, the stars of Medeci, the Medeci family was all happy.
SPEAKER_2: And he was like, oh no, these things go around Jupiter.
SPEAKER_2: Next thing you know, he's under house arrest.
SPEAKER_1: What then, why not call IO an ocean world?
SPEAKER_2: Let's zoom out and think about kind of a Goldilocks scenario, right?
SPEAKER_2: In the early days of astronomy and planetary science, our conceptualization for habitability was kind of framed around this Goldilocks scenario, Venus, Earth and Mars.
SPEAKER_2: Venus is too hot, Mars is too cold, Earth is just right, and that's all mediated by the energy that the planets receive from the sun, from the central star.
SPEAKER_1: No, just that the energy that reaches the surface, because you can reflect away some energy and that doesn't participate in the energy equation.
SPEAKER_2: And so the thinking back then and still today is that in order to have an Earth-like habitable planet, you have to have, you have to be at that right star-planet distance so as to maintain and sustain liquid water on the surface of your world.
SPEAKER_2: Whereas, what these ocean worlds of the outer solar system are teaching us is that there's a new Goldilocks in town.
SPEAKER_2: It's a Goldilocks where the energy for maintaining and sustaining liquid water comes not through your parent star, but rather through the tug-and-pull and mechanical deformation and friction and internal heating of tides of getting stretched by Jupiter, which is some 318 times as massive as the Earth.
SPEAKER_2: And so, back to your question about Io.
SPEAKER_2: In this analogy with a new Goldilocks, Io is kind of like Venus.
SPEAKER_2: Billions of years ago, Io may have had water.
SPEAKER_2: But Io is the most volcanically active body in the solar system.
SPEAKER_2: And it has since lost any water that it perhaps had in the early days.
SPEAKER_1: Oh, you misunderstood my point.
SPEAKER_2: Go on.
SPEAKER_1: You misunderstood.
SPEAKER_1: No, I didn't make myself clear.
SPEAKER_1: Your book is titled Alien Oceans.
SPEAKER_1: You're talking about ocean worlds.
SPEAKER_1: You didn't specify water ocean.
SPEAKER_2: So you want to qualify a magma ocean.
SPEAKER_1: Magma ocean on Io.
SPEAKER_2: Well, I told you in the beginning.
SPEAKER_1: It was the most volcanically active object known.
SPEAKER_2: You find life forms in a magma ocean.
SPEAKER_2: And that's a, that's a...
SPEAKER_1: I don't know.
SPEAKER_2: Fair enough, fair enough.
SPEAKER_1: But you're right.
SPEAKER_1: If it's hot enough to melt rock, probably there's no life hanging out.
SPEAKER_2: Yeah.
SPEAKER_1: Doing a backstroke.
SPEAKER_2: But you are correct in that there have been some nice papers on a magma ocean in Io.
SPEAKER_2: Because that tidal energy dissipation is so extreme.
SPEAKER_1: Okay.
SPEAKER_2: From an habitability standpoint, it's got a game over.
SPEAKER_1: Okay.
SPEAKER_1: But also I wanted to think very freely, because you guys make me do this.
SPEAKER_1: If we go to Titan, where it has enough atmospheric pressure to sustain a liquid state of methane, because without pressure, then you lose your liquid, the range of temperatures where you can keep a liquid, right?
SPEAKER_1: So maybe life does not require liquid water.
SPEAKER_1: Maybe it just requires a liquid.
SPEAKER_1: Can you imagine a life form where it is liquid methane coursing through its veins or whatever circulatory system it has?
SPEAKER_2: Yeah.
SPEAKER_2: So I really hope that kind of weird life exists on Titan.
SPEAKER_2: The challenge is I actually have a bit of a hard time formulating an hypothesis that it could exist.
SPEAKER_2: So for example, Europa and Enceladus, we can say...
SPEAKER_1: Why should nature care what you have a hard time figuring out?
SPEAKER_1: Are you the metric of what exists in the universe?
SPEAKER_1: I know you wrote a book on it and everything.
SPEAKER_1: I get that, but still.
SPEAKER_2: But when we do experiments, obviously, with a scientific method, you formulate an hypothesis.
SPEAKER_2: And so I can formulate an hypothesis that life on Earth is based on liquid water, a suite of elements, and some energy to power life.
SPEAKER_2: I can then look at worlds like Mars and Europa and Enceladus and say, check, check, check.
SPEAKER_2: Now there's a fourth element there of time and stability that we can come back to.
SPEAKER_2: And there's some differentiation.
SPEAKER_2: But Mars, Europa and Enceladus, I think we can check the box on liquid water and the other keystones for life.
SPEAKER_2: With the liquid methane on Titan, it's hard for me to say, based on what I know of life on Earth, or even oil fields on Earth, that a hydrocarbon liquid could give rise to life.
SPEAKER_2: And here's the sort of key chemical difference.
SPEAKER_2: Liquid water is a polar solvent.
SPEAKER_2: So in liquid water, we can dissolve other polar compounds.
SPEAKER_1: That's the shape of the molecule, right?
SPEAKER_2: That's right.
SPEAKER_2: It gives a little plus-minus.
SPEAKER_1: Yeah.
SPEAKER_1: It's got hydrogen and...
SPEAKER_1: oxygen and two hydrogens coming off at an angle there.
SPEAKER_2: Yeah.
SPEAKER_2: And so we get the electrons get sort of preferentially positioned such that you end up with a plus and a minus with the water.
SPEAKER_1: So just correct my chemistry if I get it right.
SPEAKER_1: So if the two oxygens were sticking straight out on either side, then the molecule itself would have no polarity in that sense, correct?
SPEAKER_1: That is, there would be no difference between one orientation and another, and water would lose all of its really cool properties that we cherish.
SPEAKER_2: Well, the positive and negative actually comes a little more from the hydrogen and oxygen differentiation, right?
SPEAKER_1: So it's not the angle that they're coming down?
SPEAKER_2: The angle plays a little bit, but the...
SPEAKER_1: Okay, thanks for filling in my chemistry.
SPEAKER_2: Yeah, if you split it down the middle, like the oxygen is on one side of the V and the hydrogen is on the other.
SPEAKER_2: Yeah, and so if you flatten it out, you would definitely affect the charge distribution.
SPEAKER_1: It wouldn't be as effective at things we care about.
SPEAKER_2: Yeah, and certainly, when it comes to ice, you wouldn't get that beautiful hexagon that is in part due to the V shape of water.
SPEAKER_2: I think it's like 109 degrees and then 107, depending on liquid and solid form.
SPEAKER_2: But liquid water, great at dissolving other polar compounds.
SPEAKER_1: Universal solvent, we call it.
SPEAKER_2: Universal solvent for life on earth.
SPEAKER_2: But you go to Titan and now you've got these cold, by our standards, liquid methane lakes and seas.
SPEAKER_2: And liquid methane is non-polar.
SPEAKER_2: And so you're talking about life arising and thriving in a non-polar solvent.
SPEAKER_2: And that just makes me scratch my head.
SPEAKER_2: It's like, could that work?
SPEAKER_2: I sure hope it does.
SPEAKER_2: I sure hope Mother Nature is...
SPEAKER_1: I'm just saying, if you go back a hundred and whatever years, and when evolution was first a thing that people discussed, and in fact Darwin himself might have called for this, what we need is a 72 degree tide pool.
SPEAKER_1: So it's just right for life to form.
SPEAKER_1: And then the more we looked, it was like, no, you don't need that.
SPEAKER_1: You can do it this way.
SPEAKER_1: In fact, you don't even need sunlight.
SPEAKER_1: I'm old enough.
SPEAKER_1: I'm an old man here.
SPEAKER_1: My textbook said life requires sunlight.
SPEAKER_1: All right, that's before we had the undersea vents.
SPEAKER_2: Under thermal vents.
SPEAKER_1: Which got geochemical energy, thermal energy down there.
SPEAKER_1: And now even in modern astrophysics, the planetary astronomy, the Goldilocks zone is insufficient to get it all.
SPEAKER_1: All the places where you'd have liquid water.
SPEAKER_1: So this is an exercise in broadening any definition we previously laid down for what we'd expect of life.
SPEAKER_2: Yeah, and I think there's one thing, I'd be curious to hear your thoughts on this.
SPEAKER_2: Life is just, biology is a layer on top of geology, okay?
SPEAKER_2: And as such, what life does is...
SPEAKER_1: Wait, wait, just to be clear, we would later learn even that some significant fraction of Earth's biomass lives underground as a participant in the geology that's there.
SPEAKER_1: So it's not just life on Earth and then hand over to the geologist.
SPEAKER_1: There's this zone where the two have to make nice in the coffee lounge, right?
SPEAKER_2: And so life's job in the universe is to accelerate our production of entropy and heat, abiding by, if you will, the second law of thermodynamics.
SPEAKER_2: And so when it comes to Titan and say weird life on Titan in a non-polar solvent, yeah, I think as long as there is some energy that needs to be dissipated in some way, perhaps biology will fill that energetic niche, even if it requires going way out of the box of what we're able to conceive of.
SPEAKER_1: I'm reminded in the movie 2010, where we learn where the life form that made the monolith came from from 2001.
SPEAKER_1: And do you remember where it came from?
SPEAKER_2: Remind me.
SPEAKER_1: Is it Europa?
SPEAKER_2: Well, but the actual-
SPEAKER_1: But where it came from, but that was the solar system's outpost of this life, was Europa.
SPEAKER_2: That's right.
SPEAKER_1: And I think they found chlorophyll on the surface of Europa.
SPEAKER_2: Right, so back then, there was the thinking that, in the movie that I showed, the sort of a green underneath the ice.
SPEAKER_2: That would require a very thin ice shell at Europa.
SPEAKER_2: So yeah, that's where the sort of monolith stuff originates, but then it goes back to some distant place in the galaxy.
SPEAKER_2: Yeah, and 2001, 2010, some of my favorite movies, but I get no ending of people saying, attempt no landing on Europa, based on that movie.
SPEAKER_1: Are you sure?
SPEAKER_1: You don't have to say, are you authorized to divulge?
SPEAKER_1: We were not supposed to.
SPEAKER_1: Yeah, because-
SPEAKER_2: In the books.
SPEAKER_1: Wait, wait, dude, you're on a mission called Europa Clipper.
SPEAKER_1: You're going to Europa, no dipping over Europa, but you're not landing there.
SPEAKER_2: That's right, but doing beautiful flybys.
SPEAKER_1: But you're not landing there.
SPEAKER_1: You're heeding the warnings of the aliens in 2010.
SPEAKER_2: No, not at all.
SPEAKER_2: There's a cadence to-
SPEAKER_1: Of course, that's what you'd have to say.
SPEAKER_1: That's just what you should say.
SPEAKER_1: But let's talk about Europa Clipper.
SPEAKER_1: Six-year mission there.
SPEAKER_2: Six years to get there.
SPEAKER_1: Yeah, and then you hang out there a bit, orbiting Jupiter, but doing some close flybys of Europa.
SPEAKER_2: That's right.
SPEAKER_1: And it's very exciting.
SPEAKER_2: Oh, it's tremendously exciting.
SPEAKER_2: And when we say flybys, normally when we think about a spacecraft flying by a world, it's thousands of kilometers away.
SPEAKER_2: The engineers here at JPL, the pinball wizards, are able to get the Clipper spacecraft.
SPEAKER_1: But pinball wizards, because you have multiple...
SPEAKER_1: The gravity of all that.
SPEAKER_1: Europa Clipper is getting a gravity assist from what?
SPEAKER_2: From Earth and Mars.
SPEAKER_2: And then once it's in the Jovian system...
SPEAKER_1: Right, so this is a two-cushion pull shot to get to...
SPEAKER_2: To get to Jupiter.
SPEAKER_1: To get to Jupiter.
SPEAKER_2: But once it's at Jupiter, then we go off the cushions of Ganymede and Callisto a bit.
SPEAKER_1: Oh, so you get more gravity assist from the moons.
SPEAKER_2: That's right.
SPEAKER_1: Very cool.
SPEAKER_2: By that time, it's gravity assist to slow us down.
SPEAKER_1: Yeah, because people forget that you can gravity assist in either way for your energetics.
SPEAKER_1: Yeah.
SPEAKER_2: And so Ganymede and Callisto, it's a beautiful thing about the Jovian system, the Jupiter system, where those larger moons can actually help out the spacecraft engineers to get into all sorts of different orbits.
SPEAKER_2: And so we'll pinball around...
SPEAKER_1: Hence Pinball Wizards.
SPEAKER_2: Yeah, exactly.
SPEAKER_1: Great title for them.
SPEAKER_1: Wait, wait.
SPEAKER_1: Are they okay with the title?
SPEAKER_2: I use this endearingly with my engineering colleagues all the time, and they like it.
SPEAKER_1: They like it.
SPEAKER_2: Okay.
SPEAKER_2: And so we pinball around Jupiter, and then we start going into these roughly 14-day pedals orbiting Jupiter and making these close flybys of Europa.
SPEAKER_1: Like petals of a flower.
SPEAKER_2: Petals of a flower.
SPEAKER_2: Exactly.
SPEAKER_2: Or think about those Spirograph.
SPEAKER_1: I've had one, yeah.
SPEAKER_2: Spirograph.
SPEAKER_2: And so we'll orbit Jupiter but make these flybys of Europa, and the close approach is...
SPEAKER_1: How close are you going to get?
SPEAKER_2: 25 kilometers.
SPEAKER_2: What?
SPEAKER_2: That's one of the closest ones.
SPEAKER_1: That's as close as any object has ever swung by anything.
SPEAKER_2: It's going to be extraordinary.
SPEAKER_2: And the images, half a meter per pixel.
SPEAKER_1: What?
SPEAKER_2: And the Galileo images.
SPEAKER_2: So think about how extraordinary the images from Galileo...
SPEAKER_1: Galileo the Spacecraft.
SPEAKER_2: Yeah.
SPEAKER_1: Because he was an actual person.
SPEAKER_2: Not the astronomer.
SPEAKER_1: And he did have a telescope, and he did look at Jupiter.
SPEAKER_2: To make sure we're on the right...
SPEAKER_1: Galileo did not have half a meter per pixel resolution.
SPEAKER_2: So Galileo the Astronomer, point of light, Galileo the Spacecraft.
SPEAKER_2: We get beautiful pictures at kilometer scale.
SPEAKER_1: Suppose you could just tell Galileo what you're about to do.
SPEAKER_1: What a privilege that would be.
SPEAKER_2: Oh, absolutely.
SPEAKER_2: And that's 400 years ago, 400-plus years ago.
SPEAKER_1: That's nothing in the history of our species.
SPEAKER_2: Yeah.
SPEAKER_1: Just say, you know, one day we're going to go there.
SPEAKER_1: One of your Medetian moons.
SPEAKER_1: So, you're going to have a close view of the surface ice.
SPEAKER_1: But you're not looking at the water below, and that's what you really care about.
SPEAKER_2: Right.
SPEAKER_2: And so, what Clipper has on board are cameras to give us pictures of the surface, spectrometers to tell us about the surface composition.
SPEAKER_2: And by looking at the surface ice, we know from Galileo spacecraft, from telescopes, that...
SPEAKER_1: And Hubble helps out.
SPEAKER_2: Hubble, yep.
SPEAKER_2: And the ice of Europa serves as a window into the ocean below.
SPEAKER_2: So, using the spectrometers and looking at the ice, we will get a bit of a fingerprint of the ocean chemistry.
SPEAKER_1: But that's only because there are cracks that would might fill in with the water and then re-freeze.
SPEAKER_2: That's right.
SPEAKER_2: And subduction, subsumption, overturn.
SPEAKER_1: What is subsumption?
SPEAKER_1: It's...
SPEAKER_1: That shouldn't even be a word.
SPEAKER_1: Just my opinion here.
SPEAKER_1: Subsumption?
SPEAKER_2: Yeah, it's a term coined by some colleagues of mine.
SPEAKER_1: So you all just made up the word.
SPEAKER_2: As we do.
SPEAKER_1: Because I know there's subduction when a continental plate goes under.
SPEAKER_2: That's right.
SPEAKER_1: And then there's...
SPEAKER_2: Yeah, and so subsumption...
SPEAKER_1: Give me some other words here...
SPEAKER_2: .
SPEAKER_2: is kind of thinking about how that might occur on an icy shell.
SPEAKER_2: So for the most part, you can think about subsumption as subduction, but on an icy world with perhaps some other things mixed in.
SPEAKER_1: Did it really need another word?
SPEAKER_2: Yeah, debatable.
SPEAKER_2: But so with Clipper, we've got these cameras and spectrometers and then mass spectrometers that will allow us to taste any plume material coming out of Europa.
SPEAKER_2: We can taste any organic compounds, carbon compounds.
SPEAKER_1: So taste, you mean almost literally taste, because if you have the molecules and you have something to detect the molecule, you've basically tasted the molecule.
SPEAKER_2: That's right, exactly.
SPEAKER_2: And so I'm a co-investigator on the Suda instrument, which is a dust analyzer, mass spectrometer, surface analyzer for dust at Europa.
SPEAKER_2: We have acronyms these days there.
SPEAKER_1: Okay, well, I'll give you that.
SPEAKER_1: I'll give you a hall pass on that one.
SPEAKER_2: They don't necessarily go by the first letter of the word anymore.
SPEAKER_1: Okay, so that's more of a passive experiment, because you're not aiming for those.
SPEAKER_1: It has to sort of come to you if it happens to be spewed forth from the surface.
SPEAKER_2: Exactly.
SPEAKER_2: Think about a kid with a bucket running through a snowstorm.
SPEAKER_2: It's much more muted than that at Europa, but we will be getting those compounds into our bucket and passing them through the mass spectrum.
SPEAKER_1: And these aren't big plumes like you find on Enceladus, but there is certainly upward movement.
SPEAKER_2: Yeah, so I've been on a team that's used the Hubble Space Telescope and the James Webb Space Telescope to look for plumes on Europa.
SPEAKER_1: Isn't it great, we have telescopes that can see the edge of the universe, and then right in front of our nose as well.
SPEAKER_1: This is, we got good people.
SPEAKER_2: We can get amazing things done when we set our minds to it.
SPEAKER_1: People are good folks.
SPEAKER_1: Not just the astronomers, but of course the engineers that actually make it happen.
SPEAKER_1: Shout out to the engineers here, okay?
SPEAKER_2: They get the hard stuff done.
SPEAKER_2: So Enceladus is a tiny moon.
SPEAKER_2: It's only 500 kilometers in diameter and very low gravity, and so plumes on Enceladus go out for hundreds of kilometers.
SPEAKER_2: Europa is about the size of our moon, and Europa's gravity is about one-seventh of the Earth.
SPEAKER_1: So Europa is way bigger.
SPEAKER_2: Way bigger.
SPEAKER_2: 3,000 kilometers in diameter.
SPEAKER_2: I didn't even think about that.
SPEAKER_1: So 500 kilometers in American speak, that's like 300 miles across.
SPEAKER_1: All right.
SPEAKER_1: It's still a nice object, but it's not like Europa.
SPEAKER_2: Right.
SPEAKER_1: So what are the chances of you seeing sort of macroscopic life that might have bubbled up and landed on the surface, like fishes flopping?
SPEAKER_2: Are you asking if our bucket's going to catch a squid?
SPEAKER_1: And you reminded me, you advised on the movie, the sci-fi movie, low-budget, but still carefully conceived and executed movie, The Europa Report.
SPEAKER_2: That's correct.
SPEAKER_1: And I have a tiny cameo in there.
SPEAKER_1: A tiny little cameo.
SPEAKER_1: I think it was on CNN.
SPEAKER_1: They used actual footage of me on actual news, commenting.
SPEAKER_1: I said, I want to go ice fishing on Europa, cut a hole, lower submersible and see what's there.
SPEAKER_1: And they were expressing my enthusiasm for this.
SPEAKER_2: You and I, that's, if we could fish on Europa.
SPEAKER_1: Oh, man.
SPEAKER_1: So you were an advisor to that film.
SPEAKER_2: That's right.
SPEAKER_2: And they did a fantastic job.
SPEAKER_1: That's why it was so good.
SPEAKER_1: Not because I was in it, but because they thought about the science.
SPEAKER_2: Well, one of the really cool things, I've done some consulting on various movies and I was like, hey, team, if we're going to do Europa, we got to do Europa right.
SPEAKER_2: And so they didn't know that much about the radiation environment of Europa.
SPEAKER_1: From Jupiter.
SPEAKER_2: From Jupiter, exactly.
SPEAKER_2: And so that's factored into the movie and becomes sort of central to the story.
SPEAKER_2: And on Europa, that irradiation of the surface would kill an astronaut, but coming back to habitability, one of the things that we're looking for with Europa Clipper is how some of the radiation-driven chemistry on the surface of Europa could positively affect the chemistry of the ocean and the habitability of the ocean.
SPEAKER_2: Let me give you an example.
SPEAKER_2: Sulfur comes from volcanoes on Io.
SPEAKER_2: The eruptions on Io exude sulfur, and some of that sulfur actually lands on Europa.
SPEAKER_1: This is sulfur that has been spewed forth from volcanoes faster than the escape velocity of Io.
SPEAKER_2: That's right.
SPEAKER_1: Thereby contributing to the general orbital environment of Jupiter.
SPEAKER_2: That's right.
SPEAKER_2: It gets spun up in Jupiter's magnetic field.
SPEAKER_2: Next thing you know, that sulfur ion is slamming.
SPEAKER_1: Well, it's an ion, so it responds to the very strong magnetic field.
SPEAKER_2: That's right.
SPEAKER_2: But then some of that sulfur impacts Europa and then gets radiolytically processed into sulfate and other forms of sulfur, which then if mixed into the ocean...
SPEAKER_1: Sulfate.
SPEAKER_2: Sulfate.
SPEAKER_2: Microbes on earth, a lot of sulfate.
SPEAKER_2: And then get this.
SPEAKER_2: So what happens when you split apart H2O, water?
SPEAKER_2: You get OH and H.
SPEAKER_2: Some of that H escapes to space, some of the OH recombines with another OH, forming H2O2.
SPEAKER_2: H2O2 is hydrogen peroxide.
SPEAKER_2: We have observed...
SPEAKER_1: Which is the same thing as what anyone would call peroxide.
SPEAKER_2: Exactly.
SPEAKER_2: At the pharmacy.
SPEAKER_1: At the pharmacy, yes.
SPEAKER_2: Yeah.
SPEAKER_2: And so...
SPEAKER_1: That's that old joke.
SPEAKER_1: You know the old joke.
SPEAKER_2: What's that?
SPEAKER_1: Someone goes to the bar and says, I'd like some H2O.
SPEAKER_1: And then they hand him a glass of water.
SPEAKER_1: And then someone sees that and says, I want some H2O2.
SPEAKER_2: And so they go and get a glass of H2O2.
SPEAKER_1: And then they drink it and go...
SPEAKER_1: That'd be a very chemically literate bartender.
SPEAKER_2: And not a very tasty drink.
SPEAKER_2: But so get this.
SPEAKER_2: That radiation processing of the ice, of the water ice on Europa, leads to the formation of hydrogen peroxide, H2O2, which then that also gets radiolytically processed or decays to O2, oxygen.
SPEAKER_2: And telescopically, we see hydrogen peroxide and oxygen in the surface ice on Europa.
SPEAKER_1: You have to be very clever to go from one step to the other to see this through.
SPEAKER_1: A game of dominoes, and you don't know where the dominoes are, but you think you do, and maybe it is.
SPEAKER_1: And if it is, this leads to that, leads to that, and then you have what you need.
SPEAKER_2: Right.
SPEAKER_2: Except we actually observe it.
SPEAKER_2: So to be clear, we see condensed phase oxygen on the surface of your room.
SPEAKER_1: And you think that's how you get it?
SPEAKER_2: Right.
SPEAKER_2: We get it radio-lytically.
SPEAKER_2: I do that in my lab.
SPEAKER_1: I love when you say that.
SPEAKER_1: I do it in my lab.
SPEAKER_1: I need some of that in my lab.
SPEAKER_2: And that's the fun of like lab and spacecraft.
SPEAKER_2: I know, it's great.
SPEAKER_1: It's great.
SPEAKER_1: And they go hand in hand.
SPEAKER_2: Yeah, and so we can make predictions, and it's a lot of fun.
SPEAKER_2: But so, of course, we know that oxygen's very useful for life on Earth, not just for microbes, but for-
SPEAKER_1: Well, for our kind of life.
SPEAKER_2: For the macrophona.
SPEAKER_1: The anaerobic life does not like oxygen, to be clear.
SPEAKER_2: And they love sulfur and methane, all sorts of other things.
SPEAKER_2: But so here you are, the radiation environment on the surface of Europa could produce compounds, which then, if delivered to the ocean through subduction, subsumption, whatever you want to use, could help provide rich chemistry to the ocean to sustain a biosphere within Europa's ocean.
SPEAKER_1: And this will give you some of the chemical gradient you have described that you need.
SPEAKER_2: So you got hydrothermal vents on the bottom of the ocean spewing out things like methane and hydrogen and sulfide.
SPEAKER_2: And then from the ice shell, you might have things like oxygen and sulfate, so you can connect the battery, the biochemical battery.
SPEAKER_1: And that's how you make Godzilla.
SPEAKER_1: At least this is the recipe for Godzilla.
SPEAKER_1: So we got to wrap this up.
SPEAKER_1: Just one point, I care a lot about words and what they mean and how they're received.
SPEAKER_1: Europa has water underneath ice.
SPEAKER_1: Yet you named this mission Europa Clipper.
SPEAKER_1: A Clipper ship from the 19th century floats on water swiftly.
SPEAKER_1: So who came up with the word Clipper?
SPEAKER_1: I don't know.
SPEAKER_1: Because that's a little...
SPEAKER_1: You're not floating anywhere.
SPEAKER_2: Right, yeah, yeah.
SPEAKER_2: So in the early days, remember that during the gold rush, Clipper ships were used to very quickly get people from New York City to San Francisco.
SPEAKER_1: Yeah, they're some of the fastest ships made.
SPEAKER_1: They're narrower, a lot of sails, the wind can take you, before steamships, of course.
SPEAKER_2: And so...
SPEAKER_1: By the way, I think the phrase, let's get there on a good clip, I think it comes from Clipper ships.
SPEAKER_1: Oh, yeah, Clipper.
SPEAKER_1: Because swiftly, the Clipper ship gets you there fast.
SPEAKER_1: So I know you're getting there fast because you strip down the Falcon Heavy.
SPEAKER_1: The Falcon Heavy doesn't even have return stages because that uses weight that you could put in your payload.
SPEAKER_1: Right.
SPEAKER_1: So you strip it down, put it all in the payload, get it out there as fast as you can, get your two, get your two gravity assists, you're there in six years.
SPEAKER_2: That's right.
SPEAKER_1: So in that sense, it was a Clipper, but not in the sense that it's floating anywhere.
SPEAKER_1: I just got to make, I got to get that off my chest.
SPEAKER_2: 100%, yeah, and some of that Clipper terminology goes back to variation in launch vehicles and stuff.
SPEAKER_1: Okay, all right.
SPEAKER_1: Well, Kevin, great to have you back.
SPEAKER_2: Thanks so much, Neil, my pleasure, and great to see you, and it's an exciting time.
SPEAKER_1: So if something bad or good happens to the Clipper mission, we got to get you back on to talk about it.
SPEAKER_1: Okay.
SPEAKER_2: The laugh will cry.
SPEAKER_1: When all the good things happen, we got to get you back on.
SPEAKER_1: We won't do it while you're busily receiving the data, but if there's a break in there, you got to come back on.
SPEAKER_1: And we can find your book, Alien Oceans.
SPEAKER_2: Alien Oceans.
SPEAKER_1: I love the assonance there.
SPEAKER_1: Alien Oceans.
SPEAKER_2: The search for life in the depths of space.
SPEAKER_1: Yes.
SPEAKER_1: There you go.
SPEAKER_1: All right.
SPEAKER_1: Good luck with that.
SPEAKER_2: Thanks so much.
SPEAKER_1: For sure.
SPEAKER_1: This has been StarTalk, a JPL edition.
SPEAKER_1: Oh yeah.
SPEAKER_1: Neil deGrasse Tyson bidding you, as always, as they do here, to keep looking up.