Alien Oceans – with Kevin Hand
Join us in a conversation between planetary scientist Kevin Hand and astrophysicist Neil deGrasse Tyson, about “Alien Oceans”. The below is an abridged version of that conversation from the podcast “StarTalk“. To listen to the full episode, visit: https://www.startalkradio.net/show/cosmic-queries-alien-oceans/
NEIL: Today’s show is a StarTalk, Cosmic Queries Edition on The Search for Life in the Universe. So, while I carry some expertise in this, I carry nowhere near what is necessary to be the expert on this Cosmic Queries. We’ve got Kevin Hand, from the Jet Propulsion Laboratory in Pasadena, California, Director of the Ocean Worlds Lab. Welcome! So Kevin, you just published a book called, “Alien Oceans”. That’s audacious.
KEVIN: Thanks. Yeah, it’s an exciting topic. At least I’m passionate about it. And I’m excited to share it with everybody out there.
Neil: It’s got a big fat subtitle, “The Search for Life in the Depths of Space”. Love it. By Princeton Press. So we know it’s going to be sort of academically enlightening and plus, I just noticed that your Twitter handle is @Alienoceans. What is up with that?
KEVIN: It’s funny the way you can coordinate these things. So yeah, I’ve been working on the book for a long time and in the book we dive into our own alien ocean here on Earth, and then we go into our own backyard in the solar system and look at oceans that exist in the outer solar system that could harbor life.
NEIL: So, alien oceans, why not look for aliens in places other than oceans?
KEVIN: Well, we are and we should and I hope that we can pursue all of these different dimensions in places when it comes to exploration. But these moons of the outer solar system, these worlds like Europa, Enceladus, and Titan, these are worlds where liquid water could be today. And of course, if we’ve learned anything from our study of life on Earth, it’s that where you find the liquid water, you generally find life.
And so these worlds are incredibly compelling places to go. And potentially not just find life, but life that is alive today – life that we could study, and understand its fundamental biochemistry.
NEIL: So, you are using an Earth biased approach to the search for life elsewhere. Admit it.
KEVIN: As Carl Sagan used to say, you know, he’s a carbon chauvinist. And this is a really important point.
NEIL: But wait, it’s one thing to be made of carbon. Carbon is a pretty fertile molecule – an atom to make all kinds of molecules. But you’re going beyond just whether their life is made of carbon. You’re also asserting that it requires liquid water. So you’re not only a carbon chauvinist, you are a liquid water chauvinist.
KEVIN: That’s right. And so, in the book I there’s a whole chapter on speculating about a periodic table for life. Could there be many different modalities, different chemistries, et cetera? But there’s good reason to, at least initially, target our search for water and carbon based life.
And the reason for that is because of course, scientifically we need to frame an hypothesis. And so based on life on Earth and how life on Earth works, I can, we can put forth the hypothesis that if you bring together liquid water, carbon and a smattering of roughly 53 other elements from the periodic table, plus some energy, et cetera, to maybe get-
NEIL: Wait, wait, 53? That’s not a smattering. That’s half the elements.
KEVIN: Some of them are more important than others. I mean, it’s really carbon and nitrogen and you know, you got some phosphorus, maybe a little sulfur if you like.
Yeah. You know, the big five, six elements in there. But the key, back to the water and the carbon, is that we can formulate this hypothesis that if conditions are similar to what we find in habitable environments here on Earth and potentially in environments that we think were conducive to the origin of life. If those kinds of environments exist elsewhere in our solar system, then perhaps those environments, those alien oceans could have given rise to life. There could be a separate independent origin of life and those worlds could potentially be inhabited.
NEIL: I got a philosophical question for you. If you are only looking for life that you expect and you find it, won’t you be missing all the life that you don’t expect? And wouldn’t that life be way more interesting than life you expect to find?
KEVIN: Right. And so here’s the key, with any mission, with any spacecraft, mission, or frankly with any experiment that we do in a lab or here on Earth someplace, we have to design the experiment around an hypothesis, but also try to make sure that the experiment is well formulated, such that we can make discoveries that we did not expect to make.
NEIL: A serendipity mode.
KEVIN: A discovery mode, a serendipity mode. I think, yeah, that’s a nice way to put it.
NEIL: So we have collected questions from the internet, on this very subject. Let’s start off with a question from SveinbjÃ¶rn’s. “Will we have probes in the near future that will be able to take photos or videos beneath these water worlds”?
KEVIN: Well, it’s a great question and one that is very near and dear to my heart.
NEIL: Because you have to, you have to dig through the ice. The water is not surface water, right? It’s below, like a kilometer thick layer of ice. So you got your work cut out for you.
KEVIN: That’s right. And so, I believe it really depends on how you define near term.
This business is not for the faint of heart. I’ve been studying Europa and working towards trying to get missions out to Europa for 15 to 20 years now and we are a bit closer. So, NASA has committed to a flyby mission, a mission that will orbit Jupiter and fly by Europa some 45 plus times. And that’s called the Europa Clipper mission.
And I’m part of that mission, but I’m also working very hard to get a lander down to Europa’s surface. And hopefully that mission would hopefully land in the 2030s timeframe, but that’s highly uncertain. We have no commitment from NASA or the government, et cetera, to get that mission done so-
NEIL: Wait, so the 2030 mission does not yet go through the ice. It just lands and looks around, right?
KEVIN: Well, and it scoops in, we’ve got all sorts of novel drills and ways to sample the upper tens of centimeters, and that would help set the stage for a follow on mission that would drill or melt through the ice and then potentially get into the ocean.
NEIL: After you’re dead?
KEVIN: Well, here’s the thing, Neil-
NEIL: The answer to SveinbjÃ¶rn is no. That’s your answer.
KEVIN: Depending on how you define near term. Now, keep in mind it was 400 years ago, over 400 years ago that Galileo discovered these moons. And so as depressing as it can be to work on these missions that take so long, I do like to keep it in perspective in that for the first time in the history of humanity, we can actually get this exploration done.
It’s been 400 years since Galileo discovered these moons. I guess I sort of approach it like, you know, these spacecraft are our modern version of cathedrals. These are incredibly complex undertakings. They take generations, they take a long-term commitment, which obviously in this day and age of political whims, long-term commitments are hard to come by.
So, it’s frustrating, but at the same time, I feel fortunate that I get to be a part of even a little bit of this. Technologically, coming back to the main question, there is nothing, there are no magic wands that need to be invented to get us through the ice.
NEIL: That’s an important point, a very important point.
KEVIN: And you know, getting to the nearest star, if we were tasked with doing that within a hundred years, we’d have to invent some new fangled warp drive, and it’s a magic wand. There is no magic wand that needs to be invented in order to get through the ice of Europa and into the ocean.
If you could magically transport the Alvin submersible, one of our primary human submersibles that we use for the exploration of our ocean – if you could magically transport that to Europa’s ocean, it would do fine for at least the upper half of that ocean. Once it got to the lower half, the deeper half, the pressures would be a bit extreme, but nevertheless, most of our submersibles would work fine.
NEIL: Well, wait, wait, how deep are Europa’s oceans?
KEVIN: So, Europa’s ocean is about 100 kilometers or 60 miles in depth.
NEIL: And on earth, the deepest, is like five miles down?
KEVIN: 7 miles, 11 kilometers.
NEIL: 7, wow.
KEVIN: Just by a fun quirk of the solar system, Europa’s gravity is about a seventh of the Earth’s. And what that means is that even though the ocean is about 10 times as deep as the Earth’s, the pressure at the depth of Europa’s ocean, at the sea floor of Europa’s ocean is comparable to the pressure in the depth of the Mariana trench, the deepest region of our own ocean. And so the submersibles that go down to the Mariana trench would do well in Europa’s ocean if you could get them through the ice.
NEIL: You just have to fly it there and melt the ocean and melt the ice and then sink it.
NEIL: And doesn’t Alvin have somebody in it?
KEVIN: That’s right.
NEIL: And you have to send an astronaut to go.
KEVIN: Well, of course-
NEIL: Alright, we have another question from Dave W. “Given the high chance that life exists in the oceans of Enceladus, why isn’t Saturn included in the habitable zone of our solar system? Is the idea of a habitable zone even helpful for the search for extra terrestrial life?” Love that question! Kevin, go for it.
KEVIN: Yeah, that’s a great one, man. Two pieces I want to dive into there. First on the habitable zone, the question is spot on, and I go into this in the book. These alien oceans of the outer solar system are redefining the habitable zone. In the early days of astronomy and planetary science, there was this conception of the habitable zone where in order for a world to be habitable, you had to be at just the right distance from your parents’ star. In our case, it’s the sun, such that liquid water could be maintained and sustained on the surface. If you are too close like Venus, you were too hot. If you’re too far away like Mars, you were too cold. If you’re at the Earth-sun distance, you were in that kind of Goldilocks zone or the traditional habitable zone.
But what these worlds, like Europa and Enceladus are teaching us- is we’ve got this new Goldilocks in town, where the energy for maintaining and sustaining liquid water comes not from your parents’ star, but rather from the tidal tug and pull that these moons experience as they orbit their giant primaries. Europa orbits Jupiter, and Jupiter’s some 318 times as massive as the Earth. And Europa is about the size of our moon. And so as Europa is orbiting Jupiter, it’s getting tugged and stretched. And that internal mechanical energy is converted into heat, and that heat helps maintain the liquid water ocean beneath Europa’s icy shell. So it’s-
NEIL: It would otherwise be completely frozen, without…
KEVIN: That’s right. There would be some radiogenic decay, some heavier elements that might supply some heat that could maintain an ocean.
NEIL: Radiogenic decay, radioactivity?
KEVIN: That’s right. Exactly.
KEVIN: And so, the tides combined with the radioactivity provides some heat to maintain an ocean beneath the ice. So in this new habitable zone, I don’t want it to go unappreciated that another curious, beautiful fact of our universe is that ice floats. And if ice did not float, then even if you had the tidal energy for maintaining the liquid water in this kind of new, habitable zone of tides as opposed to solar energy, if ice did not float, you would not have a nice thermal barrier over these oceans, protecting these oceans from space. And so just like, you know, building an igloo or building a snow fort, where you crawl inside and all of a sudden you’re nice and warm. Ice and snow on Europa and Enceladus form a thermal blanket over the oceans that are being heated from within by the tides.
NEIL: So, what we’re saying is we can still think of a habitable zone, but not as some restricted place in the circumference of a star. That a habitable zone is any place you can have liquid water and that could be wherever there’s a source of heat.
KEVIN: That’s right. And so, these subsurface oceans, as I describe in the book, these Europas could be ubiquitous. And so when we think about habitable real estate in our universe, these subsurface liquid water oceans could be the predominant place where life resides.
NEIL: And especially since with so many of those such places that in our own backyard.
KEVIN: That’s right.
NEIL: I see.
KEVIN: Yeah. Now, what the questioner had at the beginning part of that question was, “since it’s likely that life exists within Enceladus”, I just want to pick that apart a little bit. We don’t know whether or not life is likely. We can put forth the hypothesis that the conditions within Enceladus and Europa and some of these other worlds might be conducive to life’s origins and habitability.
NEIL: Wait Kevin, Kevin. That’s the scientist’s way that gets written as a headline by the press saying “scientist found life on Enceladus”. You just said the conditions are such that it will possible, that we could have the likelihood of life, and then “Life Found on Enceladus”.
KEVIN: But as much as I would love to find life beyond Earth, as beautiful as that discovery would be, the non-discovery of life, if we were to go to many of these worlds – Europa, Enceladus, Mars – and find not a whiff of life, that also is a potentially equally profound discovery in terms of the rarity of life and the kind of biological singularity that that life on Earth might represent.
NEIL: Okay. Here’s one from Lee Daley from Facebook. He wonders, “Is the life in our own oceans not terrifying enough?” Shots fired, Lee.
KEVIN: Yeah. I don’t know quite how to interpret that. I would say I’ve gotten to make nine dives to the bottom of our ocean and also I’ve been a part of a number of expeditions to send robots down to our ocean. And it’s not, I wouldn’t qualify it as terrifying, it’s beautiful. It’s astonishing. It’s just jaw droppingly bizarre. On one of my dives, we encountered this two meter diameter space bagel, like creature, that was this undulating jellyfish.
And seeing life within our ocean and studying life within our ocean helps inform not only how our home planet works and the understanding the biological diversity of planet Earth, but it also just guides us and inspires us when we think about these deep, dark, distant oceans beyond Earth and in particular, life at the hydrothermal vents in our own ocean is really the kind of oasis in the deep ocean, that we look to when we think about what might exist in the regions where photosynthesis cannot operate in these ice covered oceans like Europa and Enceladus.
NEIL: Wait, so hydrothermal vents, that’s where the continents are separating and you’ve got heat? There’s a source of heat that’s not the sun?
KEVIN: That’s right.
NEIL: That’s so deep that the sun can’t reach it. So if you’re gonna have life there, it’s got to figure something out.
KEVIN: That’s right. So, traditionally we learned that the food chain, animals eat animals and plants and so on and so forth. And eventually you get down to photosynthesis. And photosynthesis serves as the base of the food chain. Well, when you go into the depths of our ocean, of course, sunlight doesn’t get there and so photosynthesis can’t form the base of the food chain.
But what microbiologists found back in the late 1970s is that these hot springs, these, these hydrothermal vents at the bottom of our ocean provide a tremendous menu of interesting compounds that microbes love to eat for lunch and dinner. And they then do chemosynthesis using the chemistry to synthesize the compounds they need. And then other organisms eat those microbes and so on and so forth. So you get this food chain that is fed off the chemistry of the vents.
And we think that kind of dynamic, that kind of ecosystem might be an interesting example for what could happen within these ice covered oceans of the outer solar system.
NEIL: That keeps you going.
NEIL: Very good. Laurie Mueller from Twitter wonders, do we have the ability to identify non-carbon based alien life or will our perspective prevent that? What’s NASA’s official criteria for identifying alien quote unquote life?
KEVIN: Yeah, this is a great question.
NEIL: In fact, Kevin, let me shape that a little differently to include our part of our earlier discussion. If you are looking for carbon based life, might you, does that preclude you from finding silicon-based life?
KEVIN: The short answer is no, as long as you bring the right tools with you. And I’ll give you a couple of different examples and again, there’s a whole chapter on this in the “Alien Oceans”. So, this is a great question, Laurie, and it’s one that has enlisted many PhDs, many grad students, many scientists, and it’s one that we debate in the community constantly. And there’s a thing called the latter of life that you can Google and you’ll find on NASA’s official astrobiology webpage, this sort of tier of what we call bio-signatures and the kind of the efficacy and fidelity of various bio-signatures leading up to claiming that you have actually detected life.
And so for example, if we sent a submersible down into Europa’s ocean and a Europan octopus came up and waved at the camera – Oh, that would be one heck of a bio- signature. We would have motility. We’d see this moving creature. We would potentially-
NEIL: And you wouldn’t care what the hell it was made of.
KEVIN: And to be clear, when we are talking about the search for life in our solar system, whether it’s Mars, Europa, Enceladus, Titan, we are largely talking about the search for even the tiniest of microbes. Such a discovery would revolutionize our understanding of biology and we would for the first time in human history, know that biology actually works beyond Earth. But, so-
NEIL: Just to be clear, just to be clear, Kevin. If the life you find on another planet is made of DNA, then it doesn’t revolutionize anything.
KEVIN: Ah, yes it could. So, let’s come back to that though, because that folds into the-
NEIL: I don’t mean to pick a fight or anything.
KEVIN: It’s a great one. So, to Lori’s question, there is this ladder of life and we’ve developed a bio- signature framework. In other words, that not just one measurement is enough. You have to make multiple complimentary and redundant measurements in order to have enough bio-signatures that you can then claim that you’ve detected the life. And you want to make sure that you have bio-signatures that are as universal as possible.
NEIL: Wait, wait Kevin, just, just to be clear, we have to alert our audience. This is an astrophysicist using the word universal to apply to the universe. Most people on Earth who have used the word universal mean all over Earth.
KEVIN: That’s right. Yes. We are talking universal bio-signatures being bio-signatures that could apply throughout the universe.
But think about it, a universal bio-signature, so think about if we were to use a DNA PCR machine or instrument in searching for life on Europa. PCR, polymerase chain reaction, that’s obviously what we’re using for looking for a lot of the COVID-19 virus. It’s used by a lot of companies doing genetic analysis. And that’s great but the, that kind of instrumentation, it’s contingent on that life using DNA. And so if we sent that kind of instrument to Europa or Enceladus or any of these other worlds, we could miss non-DNA based life.
NEIL: And, and your device doesn’t find DNA and so-
KEVIN: So we say, you know, game over. But an instrument like a mass spectrometer, I like to make the analogy to a mass spectrometer kind of being like a carpenter’s hammer. You’ll never go to a job site and find a carpenter without a hammer in their tool belt in someplace. And mass spectrometers are a great way of sorting and identifying the various compounds, be they carbon compounds, be they silicon compounds, be they nitrogen compounds, you name it, a mass spectrometer gives you that inventory of compounds. And what’s nice about that is that life, whether it’s carbon based life, silicon based life, you know, all sorts of other permutations that we can’t even imagine, life almost certainly needs to be specific in the compounds it uses. In other words, life will use a discrete set of subunit molecules to build the larger molecules of life. For life on Earth, it’s amino acids, building proteins, nucleoid basis, building DNA. So, a mass spectrometer would allow us to identify that kind of specificity in the building blocks.
NEIL: Are they included in these missions?
KEVIN: Yeah, on the Europa Lander model payload, prime instrument number one is bring something that can, without bias, give you the molecular inventory of what’s there. Now the DNA, to your question about DNA, which is, I love this one because it really is quite profound. If we go to Mars, and I love Mars, I’m doing some work on Mars 2020, it’s a, it’s a beautiful world.
If we were to go to Mars and find evidence of DNA based life, and this would have to be in the sub-surface of Mars, because our current search for life on Mars is in ancient rocks and DNA doesn’t last long in ancient rocks. But let’s imagine that we got into sub-surface of Mars and found some water and then we found DNA based life.
I would, and many of my colleagues would probably conclude that is evidence of a transfer of DNA life from Earth to Mars or Mars to Earth, at some point, billions of years ago. Just because Mars and the Earth are near neighbors and impact events, comets, asteroids, et cetera, hitting the Earth could have easily ejected material that then went to Mars or vice versa.
But with Europa, if we went out to Europa or Enceladus and we found DNA based life, it’s much harder for Earth to send microbiologically laden rocks out to Jupiter and once out there, it’s much harder for those rocks to actually hit Europa instead of Jupiter. And even if they hit Europa, they’re going to be coming in at something like 11 kilometers per second or faster.And, and then they annihilate themselves upon impact on the ice. And it’s just a lot harder for Earth rock to bring life to Europa or to Enceladus than it is to Mars. So if we found DNA based life on Europa, I would argue that is evidence of biochemical convergence towards DNA as a fundamental molecule for life.
NEIL: Analogous to, if you go to a Rocky moon, somewhere else, and you find quartz or-
NEIL: Or the geologic analog would be the same minerals are there that you find in the geology here on Earth.
KEVIN: Exactly. And just like on Earth, we’ve had eyes, eyes have evolved independently some 50 times. Maybe DNA is just kind of the convergent biochemical molecule that happens, or not.
NEIL: And we’re just too stupid to figure out how easy it is for nature to accomplish it.
KEVIN: But this is why the outer solar system is so compelling because there’s liquid water there. And so, these are places where large biomolecules, understanding the chemistry of the life could be done. We can actually examine whether or not DNA is the only game in town or there’s some other way to get the business of life done.
NEIL: So Kevin, great to have had you on StarTalk, Cosmic Queries talking about your book “Alien Oceans”. That’s just the coolest title of a book ever, and there should be a movie with that. I’m Neil deGrasse Tyson, and as always, bidding you to keep looking up.