Planetary Radio: Space Exploration, Astronomy and Science - Book Club Edition: Alien Oceans by Kevin Hand

Episode Date: September 18, 2026

Where are we most likely to find evidence of life, past or living, in the Solar System? Planetary scientist and author Kevin Hand looks to warm, salty ocean depths beneath protective layers of ice on worlds such as Europa and Enceladus. His enthralling book became a popular selection in The Planetary Society’s member book club. He recently joined the Society’s Mat Kaplan for a deep exploration of the best science. Kevin also shared tales of his own harrowing, revealing journeys through Earth’s undersea world. Discover more at: https://www.planetary.org/planetary-radio/book-club-kevin-handSee omnystudio.com/listener for privacy information.

What could be waiting for us in the warm, inviting seas of Europa and other ocean worlds? That's our topic this month on Planetary Radio Book Club Edition. Hello again, everyone. I'm Matt Kaplan of the Planetary Society with more of the human adventure across our solar system and beyond. The July 26th selection for the Planetary Society member book club is one of my all-time favorite books about space science and the search for life. In fact, it's one of my all-time favorite books of any genre. Alien Oceans, The Search for Life in the Depths of Space,

is still very much available from Princeton University Press and is very much recommended. Its author is our guest for the captivating conversation you're about to hear. Planetary Scientist Kevin Hand directs the Ocean World World World's lab at NASA's Jet Propulsion Laboratory just outside Pasadena, California. His research focuses on the origin, evolution, and distribution of life in the solar system with an emphasis on the icy worlds that hide those warm, salty seas. From 2011 to 2016, he served as deputy chief scientist for solar system exploration at JPL. He is the principal investigator of the

Sherlock spectrometer on the Mars Perseverance rover. Sherlock, that's the scanning, habitable environments with Raymond and luminescence for organics and chemicals. And it's all about finding signs of habitability and possible past life on Mars. He's also a co-investigator on the Europa Clipper mission that you'll hear us mention a couple of times today. Same status for the dragonfly mission to Saturn's Moon Titan. His work has brought him to the dry valleys of Antarctica, the sea ice near the North Pole, the deepest depths of the Earth's oceans, and the glaciers of Kilimanjaro.

He was selected as a National Geographic Explorer in 2011. Ladies and gentlemen, here is Dr. Kevin Hand, ace astrobiologist, a longtime researcher in this field who has been a part of many, many missions, including many that are still underway. And so, Kevin, it is a great pleasure to welcome you once again, because we've talked several times before. Good to see again, Matt, and thanks for the invite. And thanks to all the members, not just for taking an interest in my book, Alien Oceans, the Search for Life and the Depths of Space,

but also for all the work that you all do, whether it's on the hill or around your communities or so on and so forth, Obviously, anything we can do to advance critical thinking these days is much needed. And we should add to that. That you are speaking only for yourself today. That's right. I was just about to add that. I'll describe more of what I do and everything.

But this evening I am representing myself, only myself, and the brain on top of this head. Nobody else, no other organizations. Kevin, as I told you, a whole lot of people have already told us how much. much they enjoyed the book. I read it when it came out because we talked on planetary radio when it happened. I know I had a good reaction to it then. I am pretty sure I enjoyed it even more this time five years later. It's not just full of terrific information about our search for life across the solar system and beyond. It's simply really well written. And so it really is just a pleasure to read. Well, I appreciate that. And as you and folks out there listening,

well, no doubt recall. So my book came out in April of 2020, which was not a great time for a book to come out. I wasn't even excited about my book coming out because everybody was petrified about COVID and we had so many things going on in the country and the world. It was kind of sad because on small scale, something that I had worked so hard on, came out at such a challenging time. Thankfully, it has persisted, and folks have seemed to really enjoy it. And so it's music to my ears that you read it not just once, but a second time, and it held up. Yeah, it definitely does. And, of course, one of the reasons I wanted to bring you in to the book club is to follow up,

because a lot happens in planetary science and the search for life. And so hopefully that's some of what we will bring out over the next hour. I'm going to start with a quote from very close to the front of the book. And here it is. It's a good example of the good writing that you'll experience if you're one of those who's not quite gotten to the book yet. Here we go. Our brains have no way of processing the reality of the situation. Several thousand pounds of pressure per square inch.

A landscape revealed only by the limited lights on the sub. odd sounds and whirls of the machine that's protecting you from a gruesome, watery death. What an opening. I mean, because there you were, right, down in the very, very deep sea. Yeah, it's hard to believe that that was over 20, almost 25 years ago. That was back in, I think, 2003, I was on the Russian research vessel, the Keldish, which is now. been decommissioned, I believe, and we were diving in the two Russian submersibles and the mirrors and two other acrylic sphere submersibles. And that was all part of a James Cameron IMAX feature called Aliens of the Deep. And what an adventure. I was, you know, I was in grad school at

time and got a phone call from my friend George Whitesides, an amazing human being. And he was working for a startup company at the time that was looking at putting Landers on the moon. And he said, making an IMAX movie and they want to maybe connect the exploration of our ocean, of the deep ocean and hydrothermal vents to Europa. And they're looking for a young scientist to talk about Europa at the bottom of the ocean. So that was the story. That was the start of quite an astounding adventure where I got to make nine dives to the bottom of the ocean in the Atlantic and the Pacific combined going down to the hydrothermal vents. It just does something to your cortex.

Humans obviously are not programmed to be exposed to that amazing site. But it really comes to mind. I think I described this later in the book. There's a hydrothermal vent called Snake Pit and Beehive. It's just like Dr. Seuss down at the bottom of the ocean, just the various features and structures of the hydrothermal vents. So, yeah, that experience, Matt, and what I wrote at the beginning there about getting stuck at the bottom of the ocean.

Yeah. It was quite an introduction to my own experience with deep ocean exploration. The one time I got to interview James Cameron was because of this film when it was coming out on climax, Aliens of the Deep. And of course, it also featured, you know, Mrs. Whitesides, Loretta Hedong. Right, Loretta, dear friend. Yep. Yep. And, you know, as I mentioned to you yesterday, I'm one of the Uri's Knight founders.

And so I got to know George when he was a grad student still. And now, of course, it's Congressman White Sides. And so he's fantastic. He's done okay for himself. Just as an added no, I think, I'm not sure if this is still true, but I think aliens of the deep may well be Cameron's least financially successful movie. Oh, is that right? Okay. Yeah, all right.

Well, he's done okay. I mean, really. He's done okay otherwise. Yeah, really. And someday his passion for Europa will pay off. I hope this won't be a painful question to ask. We will get to science and the search for life. The Titan submersible disaster, it happened just to...

I just wonder if that maybe hit home more for you, someone who's been down there, which is, you know, a pretty small group of people who have ventured into that alien world, you know, knowing that these are folks who didn't make it back. Right. And obviously, a tragedy and very sad. I was contacted by the media to comment

on it as it was happening and I just stayed away from it had been exposed a little bit to what that company was doing but did not have deep knowledge you know there's something to be said for kind of trying to move fast and accept new risks

but what they were doing was in my opinion entirely unacceptable and it is a real tragedy that that folks who thought that they were signing on to something that had more technological and engineering rigor that they were kind of sold a

false bill of goods. And it was really interesting, whether it was the early 2000s expedition that I was on with the Russians, or in 2012 I was with Cameron and Rolex and National Geographic out at the Mariana Trench to go back down to the deepest steps in our ocean. In both of those, on both of those expeditions, I kick the tires on the submersibles and the safety, the redundancy, the belts and suspenders approach

that both the Russian mere submersibles and that Jim and his team had for the Deep Sea Challenger were just incredible. You know, and at the time, the Deep Sea Challenger was incredibly sporty. We were very nervous that Jim might not come back up. We knew that the sphere,

we knew that it wouldn't implode, but there's always going to be a risk that something happens. The release of ballast or so on and so forth might face some challenges. And I described some of this in the book, kind of the difference between going down in a submersible versus going up in a rocket. All you have to do is be heavier on the way down and lighter on the way up in a submersible. And thankfully, with the Deep Sea Challenger in 2012, it all worked beautifully. We did have some technical problems with the robotic arm and other stuff. But from a human safety standpoint, everything worked out well. This was his really, really innovative deep sea submersible, right?

That's right. You know, people often ask about the shape of it. It's designed. It's very elongated. It looks like a pickle or just a green torpedo. Vertical. Kawasaki Green. There was even a song that one of the engineers wrote about the Kawasaki Green used for the Deep Sea Challenger, and they used to play that song on the bow of the ship. Yeah, the reason it was designed to be so elongated was so that Jim could traverse the, you know, roughly seven miles, 11 kilometers of ocean water column faster than a traditional submersible, which is shaped more like a kind of large fish. If memory serves, I think Jim got down there in a little bit less than three hours, whereas a traditional submersible probably would have taken something like seven or eight. I may be wrong in those numbers, but it was basically a factor of two, I think, improvement. And it also reminds me, and you talked about kicking the tires, of the endless testing that takes place before JPL or other places worth their salt, what they do with the spacecraft before they leave the planet.

But it sounds like a good parallel. Well, yeah, and I get into that a bit in the book, now I'm very passionate about ocean exploration here on Earth and leveraging our lessons learned from space exploration to explore Earth Ocean and cryosphere. Right now, we actually have a robot up in Alaska, the buoyant rover for Under Ice Exploration, Brewery. You can Google that and check it out.

And we operated it remotely from JPL this past winter as it roved on the underside of the ice up in Alaska and returned data, just like a Mars rover would. But yeah, the sort of interesting things that I've seen is that deep ocean exploration inherited a lot of the sort of bigger as better mentality from the military and the Navy,

from kind of the genesis of where a lot of the submersible and ocean exploration stuff came from. Whereas obviously, in space exploration, every gram matters, every watt that you have matters. And so we are really incentivized to have small, low mass, incredibly capable and redundant systems. And it costs us a lot of money to build those things. But once they're, say, on the surface of Mars, they last for an incredibly long time and work very well. Whereas in deep ocean, exploration and this is changing. The trend is moving towards fast, light, redundant systems

that are low cost. Yeah, you know, think about the mere submersibles, the Alvin submersible, a lot of these large ROVs that require massive ships. Those ships are kind of the equivalent of a launch vehicle, of a rocket. And if you need a really large ship every time you want to explore the ocean, that's going to be your bottleneck. That's going to be your limiting factor. This is one of the things you talk about at the end of the book and that we need to change the focus because there is this dependence in many cases on retired military vessels. That's right. I think if I'm remembering correctly, the section's like you're going to need a bigger boat. I was doing a little playoff. That quote from Jaws. Pardon the pun, but were you already deep into considering the possibility of life in alien oceans when you.

you made that dive? Yeah, yeah. I got hooked on Europa in the late 90s. I studied physics and astronomy as an undergrad, also psychology, which had to do with the search for extraterrestrial intelligence. When I was in undergrad in the early to later 90s, that was right at the time when the first real confidence

in exoplanets was being published, when Mars exploration was the thing when it came to the search for life beyond Earth. But of course, later in that decade, we would have the failures of polar lander and climate orbiter, et cetera. But then the Galileo spacecraft started returning all that data from the Jovian system and Europa in particular. And so as an undergrad, I gave a presentation on the Galileo mission just to my interest. physics and astronomy colleagues in college and was very fortunate to go on and make a PhD out of it in the following decade and then make a career out of it for the past however many decades. Now, if you had asked me back then, where would we be in the exploration of Europa?

Some of your members may well remember this graphic, but in the post-Galileo days, JPL and NASA released that image of a melt probe coming through the other. and the hydrothermal vents, the sort of cartoon drawing. Goodness, do I wish we were at that stage. But at least we've got Clipper. Clipper is, we'll make a flyby of the Earth in December, and it'll be well on its way to Europa and arriving in 2030,

J-O-I, and then fly-bys in 20131. J-O-I, Jupiter Orbil In-Sertion. And then start all those fly-bys of Europa. That's going to be incredible. Yeah, and, you know, we're all hoping, that it smacks into something that looks like a fish without destroying the spacecraft. Well, it's not smacking into anything. We want it just to make those flybys nice and clean orbit Jupiter, once every two weeks,

make a close flyby and get close, but not too close. I'm so incredibly envious of this experience you had in the deep ocean here. There is a line that I think is a key line from the book. The scene through that porthole could be. what home looks like to most of the life in our universe. Most of the life, I mean, assuming that it's out there teeming across the universe waiting for us to find it, that you would expect we're going to maybe find it, be more likely to find it in these warm, salty water oceans than, you know, a place

like maybe a slightly warmer, wetter Mars. Right, right. And, you know, all bats are off. Our data is very limited. We've got a sample size of one with respect to our solar system and where habitable environments exist. And then we've got a sample size of one when it comes to actually having an inhabited planet that we know of, of course, the Earth.

And so I think as I mentioned in the book, I love to think about ubiquitous Europa's. Because when you do look at our solar system, the, these ice-covered ocean worlds with these alien oceans, they really may present the most habitable real estate by volume in our solar system. And if the origin of life can, with relative ease, huge asterisk on that, with relative ease arise in these oceans,

say around hydrothermal vents or in the ice shells, then it's off to the races. Having said that, if oceans on the surface of a planet in contact with an atmosphere, receiving sunlight from a star, and having tidal pools and continental activity and continental weathering, if that's kind of the only way to get the business of the origin of life done, then all that liquid water deep under Europa's ice shell and Enceladus's ice shell, and these other ice-covered ocean worlds, all that habitable real estate may just be going to waste. There's a terrific thing that you say in the book that your Ph.D. advisor told you once,

and he said, Earth is a bad place for life. What was he talking about? Chris Chiba, my PhD advisor, another incredible human being. Chris did a lot of his work, obviously, from those who know, with Carl Sagan. on comets and looking at where Earth's water came from. And so part of what he was referring to, or what he is referring to, what he makes that comment about the Earth being a bad place for life, is that if you just kind of looked from the exterior at our solar system,

they would say, oh, goodness, those rocky inner planets, they're probably cooked and don't have much water on them. You've got to go past the ice line. You've got to go far enough out in the solar system where ice condenses to then have water accrete and be in enough abundance to really provide the real estate for life. But of course, Mother Nature doesn't care what we think. And Earth does have quite a bit of water, not by mass, but at least in terms of surface coverage, it's plentiful. And certainly enough for our biosphere. That's what Chris was referring to as a sort of puzzle of Earth having more water than one might otherwise expect it to have.

Here's another quote from the book. Microbes and sea creatures that inhabit our ocean depths might do fine under the physical and chemical conditions thought to exist within the oceans of Europa and Celadus and Titan. Those are the big three, right? I mean, not the only ones, probably in our solar system, but the big three and the big three. the ones that you spend the most time talking about. Yeah, and that's just kind of an interesting quirk of the physics of our planet and of these alien oceans. It turns out that the pressure at the depths of our ocean in the Mariana Trench, if I'm remembering correctly, or somewhere in the range of like 120 megapascals at the bottom of Europa's ocean. If it's 100 kilometers deep and you do the math for one seventh gravity, if I recall,

I calculated it to be something like 150 megapascals. So a bit more than the 11 kilometer depth here on Earth. There, you're at 100 kilometers depth. But the difference in the gravity of each world compensates. And so, yeah, if you took life from Earth and just put it in Europa's ocean, the pressure of the ocean and the temperature of the ocean probably wouldn't be a problem, at least for those organisms that are adapted to the extreme pressures of Earth's ocean seafloor. Whether or not there's enough nutrients or if it's an octopus from Earth that requires oxygen, that's a different story. We can maybe get into a little bit of that later. But yeah, everything that we've learned about microbial life and even some of the

the multicellular macrophana in our ocean indicates that in some cases you might be able to have a similar type of organism in these distant alien oceans. There's something I did not remember from my first reading in the book, this amazing coincidence that it was almost simultaneous, the discovery of the hydrothermal vents, the kind that you explored, and that Europa almost certainly had this warm, salty ocean, which you go into tremendous and wonderful detail in the book explaining how we came to know that, but that both of these would happen at the same time just seems so serendipitous. Yeah.

We got a little caveat to that hydrothermal vents. That's the 70s. And in the late 70s, we had the Voyager flybys that. made those observations of Europa having this stunning surface of fractured ice, et cetera, and the mathematical predictions based on their eccentricity, et cetera, that Io, Europa and Ganymede would have quite a significant amount of tidal heating. With I.O., of course, that was validated by the volcanic eruptions that were observable, Ana Ayo. With Europa, the physics coupled with the imagery from Voyager provided key clues to there being a subsurface ocean.

But it really wasn't until the late 90s and early 2000s when the Galileo magnetometer data and additional imagery and spectroscopy helped really solidify the case that Europa must have a subsurface ocean, the gravity data also. And you explore this, how we came upon confirming this or as close as, as close as necessary to confirming it as the three easy pieces, which is a nice little cinema reference. The Rainbow Connection babysitting. It's also, it's both a cinema reference and also a Feynman reference. Oh, Richard. Oh, okay, right. He had six easy pieces. Yeah, I remember that.

I didn't even think of that. I wonder if that's where they got the title for the movie. We'll have somebody out there who will look it up for us. But you called it the three easy pieces, the rainbow connection, babysitting a spacecraft, learning to love airport security. That last one, I wish we had time to go through all of these, but if you read the book, you know what we're talking about. Airport security, you made that reference to it a moment ago because of the magnetometer

on Galileo, right? Because it was led, and this is kind of a sideline. But the wonderful Margaret Kivalson of UCLA, who was my guest not too long ago before I turned over planetary radio, I just saw that she is about to turn 98 years old. And you do a great job of talking about how this incredibly talented, brilliant woman had to fight to find her niche in science. And thank God she did because she helped deliver this evidence. Yeah, Margie's just an incredible woman and a mentor, and I believe she's up at Stanford now, and, you know, she's, she's, I saw her at a Galileo mission reunion not too long ago, and she is still clocking away new ideas and so excited about new discoveries and papers and everything, and just an incredible example and just an incredible human being. I love to hear that. There's something that you mention as well about Enceladus.

A small world surprised everybody because of those plumes and, you know, what is this little world doing, having a liquid water ocean? You speculate late in the book that a world like Enceladus with that low gravity might have these carbonate chimneys, basically the really tall, hydrothermal vents that form these big formations that at the bottom of our ocean, that they could be on Enceladus kilometers high, which is just amazing. I mean, that sounds like an image that belongs in one of Jim Cameron's Avatar movies.

For folks out there are listening, the way I structured the book, the first half is there's quite a bit of history, of science of space exploration, Earth Ocean exploration, some physics, as Matt referenced with the three easy pieces, et cetera. But as we move later in the book, I kind of gave myself license to get a little more speculative. And whether it's in that chapter, just thinking about what hydrothermal vents could potentially look like on Enceladus, how advanced could look like? life get on a world like Europa. That was a lot of fun for me. Just being able to get these

ideas out onto paper because these aren't part of what was great in writing a book and part of why I like writing popular science is that some of these ideas are not really fit to print in a scientific journal. I'm not going to write about an octopus using a hammer in a which was one of the chapter names, the octopus and hammer. I'm going to come back to that stuff because I love this speculation. But go on. That's great. So, yeah, putting it in a popular science book, totally doable, peer-reviewed journal, you know, I would never even try.

Time for a break. When we return with Kevin Hand, I'll ask him why the deadly radiation on the surface of Europa may have helped life far beneath that surface thrive. Hello, I'm George Ticay, and as you know, I'm very proud of my association with Star Trek. Star Trek was a show that looked to the future with optimism, boldly going where no one had gone before. I want you to know about a very special organization called the Planetary Society. They are working to make the future that Star Trek represents a reality. When you become a member of the Planetary Society, you join their mission to increase discoveries in our solar system, to elevate the search for life outside our planet, and decrease the risk of Earth being hit by an asteroid.

Co-founded by Carl Sagan, the Planetary Society exists for those who believe in space exploration to take action together. So join the Planetary Society and boldly go together to build our future. We know that, you know, the radiation up on the surface of Europa would not be a healthy place to be standing or even to put a spacecraft unless it's very well shielded. I mean, thank goodness Juno has shown us in its tremendous success that you can send a machine out there and have it swing through that radiation repeatedly. and continue to do okay. And I know that you folks with Europa Clipper learned a lot from, you know, that proof of concept. But you bring up this point

that the radiation pounding the surface could actually be very important, maybe even essential, to anything living down below the surface, those critters that live under that nice protective shield of ice, which is a wonderful sort of contrast. So to get into some of the physics and chemistry there, please. We've talked about hydrothermal vents and why are hydrothermal events exciting in the context of life and habitability?

Well, they may be a good place for the origin of life. That's a different component. But broadly speaking, the gases and chemicals coming out of hydrothermal vents are rich in electrons. They're kind of like the negative terminal of a battery. And the way that all life on Earth works, whether you are a Homo sapien or methanogen turning carbon dioxide into methane, all life on Earth works through the economy of electrons and electron transfer. and a measure of the energy extracted from the environment that can be used for metabolism and reproduction and cellular maintenance is what we call a negative change in Gibbs free energy named after the physicist Gibbs. Interestingly, I had a whole large chapter in the first draft of the book that got jettisoned because it got a little too technical. But suffice to say, when we think about habitable environments, we're looking for places where

electron donors, compounds that want to give away electrons like hydrogen sulfide and methane, come together with oxidants, the positive terminal of the sort of biochemical battery. And so here on Earth, obviously, we have got oxygen in the atmosphere, and that's good for the macro fauna, the large creatures, but microbes use all sorts of different oxidants. Sulfate, for example, is a great oxidant that the various microbes love to use. And they'll combine sulfate with any number of, you know, reduced iron minerals or various things. Microbes have got a mix and match of different kind of biogeochemical redox, reductant oxidant couplings that they can make.

Okay, so back to Europa or Enceladus for that matter. You could have an ocean that is plentiful with hydrothermal vents, but that just leads to a very reductant, rich ocean and no oxidant that provides the metabolic energy that life needs. And then it would just be game over. You'd have a really cool ocean, but you'd have insufficient chemical energy to help motivate and drive and power life. on Europa at least, the radiation that my engineering colleagues find so troublesome, I find very endearing and potentially very helpful from a Darwinian standpoint. And that's because Europa is embedded in Jupiter's magnetosphere, and these electrons and ions and charged particles are coming down,

hitting the water ice, the H2O, splitting apart that H2O, into H and OH. Some of the H escapes, some of the OH recombines with other OH forming H2O2, which is hydrogen peroxide, which in and of itself is an oxidant. But then maybe it gets hit by another proton or electron,

the H2 gets released, and now you're left with O2 in the ice of Europa. And we know from the Galileo spectroscopy and from ground-based telescope spectroscopy, that hydrogen peroxide and condensed phase molecular oxygen exist on the surface in the ice of Europa, along with things like sulfate and carbon dioxide. And I've done the math and the modeling. If Europa's ice shell cycles into the ocean on a timeline of once every 10 million years or so,

you could actually oxygenate Europa's ocean to a level where you start to reach the oxygen level found in the O2 minimo zones here on Earth. And in those O2 minimo zones, those regions of Earth's ocean that are depleted in oxygen, in those areas, you still find things like polychaet worms and other kind of curious small animals. So, yeah, the radiation on the surface

of Europa could well be helping to solve the problem of oxidants and oxidants supply in Europa's ocean. I have to compliment you because the substantial section explaining the chemistry of this and other phenomena in the book is absolutely terrific. It's kind of enthralling and very educational for a guy who didn't do more than high school chemistry. But that's true of other parts of the book as well. When I was a kid, I was completely baffled by why there was a high tide on both the side of the earth facing the moon and the other side. And you explain that. It's a very, very good explanation of times. Well, and these are things that like, I mean, it's just a way my brain works. And then, you know, there's that classic quote, goodness,

I'm not even going to try and attribute it because it's so ubiquitous. But, you know, if you can't, explain a hard concept in simple terms, you really don't understand it. And so throughout my education and career, I'm always kind of picking away at things, trying to really understand the details. And I think some of that comes through in the book. I also remember how you mentioned that you and Mike Brown, another friend of Planet. Yeah, trying to call it at Caltech, Yeah, right. The Mike Planet Pluto Killer Brown. But you and he did some, I guess it was fairly early work on getting, you know, spectral information back from the surface of Europa. And this is where you found some of these interesting compounds. Yeah. And that's a really great story about kind of the scientific process. And when I talk with students, I often go through that because rarely does science and hyper. hypothesis testing work out so cleanly and on the scale that we were able to do this hypothesis testing. Much of what I do in my lab, the Ocean World's lab, is this radiolidic processing, this recreation of Europa in my lab using ultra-high vacuum chambers.

And having a tiny, tiny, like, micron-thick piece of Europa ice that I irradiate and look at the oxygen. production, et cetera. And I can also put in other materials. And so back in like the 2012 timeframe, I was doing some experiments with various oceanic salts that I thought might be candidate for salts on Europa because we find them in Earth's ocean. And there had long been a debate about magnesium sulfate on Europa's surface. I won't go into detail on that, but I always kind of scratched my head on that because the dominant salt in Earth's ocean is sodium chloride

and there's good geophysical geochemical reasons for sodium chloride to be the dominant salt and if Europa's ocean is long lived it too should have sodium chloride as its dominant salt but everybody was talking about magnesium

sulfate well it turns out that part of the reason people weren't talking about sodium chloride is because sodium chloride, which is an alkali halide, alkaline, alkaline, halides do not, for the most part, have strong absorption features. Sodium chloride, potassium chloride, so on and so forth. These alkali halides are, as we say, spectroscopically flat.

And when you take sodium chloride table salt, which is white to the eye, and take a spectrum of it, it's just a flat line. So even if you wanted to search for sodium chloride, the thinking went, you wouldn't be able to find it on Europa's surface because there's no spectroscopic features to go after. Well, I said, I mean, I've got a chamber. Let's irradiate these salts and see what they look like under Europa conditions. Well, after irradiating them, I opened up the chamber, pulled out the irradiated sodium chloride. And it was this orangish, brownish, reddish color. and above this chamber, I've got a picture of Europa showing that sort of yellowish, orange, reddish region.

And my jaw just dropped. I was like, holy cow, irradiated sodium chloride looks like the color that we see on Europa. And so Bob Carlson, the PI of the Galileo NIMs spectrometer and an amazing mentor of mine. Sadly, he passed away a number of years ago. Bob and I published a paper a few years after that on the irradiated sodium chloride. And I went to Mike Brown, who obviously works with all sorts of telescopes on Earth and in space, and said, hey, Mike, can we figure out how to get some HST time or telescope time anywhere to look for these very distinct absorption features in the visible part of the wavelength spectrum

that correspond to the coloration of the sodium chloride. and his graduate student, Samantha Trumbo, took the ball and ran with it, and we got Hubble time. And when we got the Hubble Spectre down and Mike and Sam showed it to me, my jaw just dropped again because there was this absorption feature that beautifully matched what I saw in the lab. And so that data from the Hubble Space Telescope is the best indication that we have of oceanic salts on the surface of Europe. and that's really important because that indicates that ocean material is coming up to the surface. And so if salts are coming up, maybe if there's life in Europa's ocean, it's coming up there too. And so we have this pretty direct evidence of overturn of the ice shell and presentation of oceanic material on the surface. given the tidal energy dissipation, given sort of the analog to I.O. just inward of

Europa and all the volcanic activity there, I would be pretty surprised if Clipper gets out to Europa and does not see some sort of relatively recent geological activity and maybe even some plumes. Now, keep in mind that on its Pumns are easy to see. The gravity on Enceladus is barely over 1% out of the Earths. And Enceladus is just 500 kilometers in diameter. And so with the tidal fractures in the south pole of Enceladus ice shell, material that's escaping and ejected, it goes out for 500 kilometers because there's nothing pulling it back, really. On Europa, there we're talking about one-seventh of the Earth's gravity. Something

comparable, Europa's gravity is comparable to the moon's gravity. And so an eruption on Europa, a plume on Europa, may not actually get that far away from Europa. And that may explain part of why we still have these equivocal results from Hubble and JWS. etc. Now that's an ongoing investigation and something that Clipper will clear up pretty easily and I do think we'll probably find plumes and or new fractures.

I'm going to say... But that's a prediction. I understand. I'm going to make it a prayer, but you can stick to the prediction because you're a good scientist. A related question from Sheila that's pretty relevant. She's wondering about your thoughts on the recent discoveries of sugar molecules, even in deep space. Whether it's the samples returned from Benu

or what we're now seeing in the interstellar medium, the take-home message that the cosmos is telling us is that the raw materials are there. The building blocks for life are readily available. does that mean that you can then go from sugars or amino acids or nucleol bases or so on and so forth to having an assembled set of larger complex compounds that encode the information needed for an auto-catalytic self-sustaining system that we would call life and biology? that question still remains.

And that's where I just find our current age so exciting because this is the first time in the history of humanity when we have the tools and technology and the exploration capability to go out there and directly explore these worlds, whether it's Mars or Europa or Venus or Enceladus or Titan. or even a series, any or all of these worlds could have had life or may still have life

and will kind of help us answer that question of whether or not we're alone and how easy or hard the origin of life is. When you wrote the book, you said that your money was more on finding life, if we find it anywhere on Europa than Enceladus's ocean. Do you still feel that way? And what has happened? I mean, how much closer, if at all, are we to determining the habitability? I'm enamored by both worlds and I'm excited to explore both worlds. The one sort of key difference for me, though, when we think about the keystones for habitability, you need the liquid water. You need the elements that serve as the fundamental building blocks, whether it's carbon or nitrogen or

phosphorus, sulfur, so on and so forth. And then you need some form of energy, chemical energy or photolitic energy to get the business of life done. So those are like the three big keystones, but encased or encasing all of those is the question of time. How long have these keystones persisted together. You know, we don't know how long it takes for the origin of life to arise, but if I had to choose, I will pick the world where we think those habitable conditions have been around for longer. And we have good confidence that Europa has been around since the sort of early days

of the formation of the Jovian system. I thought at Saturn, there are a lot more unanswered questions about the origin of, and timing of the origin of Saturn's rings and the formation of many of its small and mid-sized moons, of which Enceladus is one. And so, you know, there are some who argue

that Enceladus might be in the range of 100 million years old, Now, 100 million years could be great for the origin of life, et cetera, et cetera. But if I've got a choice of 4 billion years versus 100 million years, I'll take the world that's got a 4 billion year timeline. Does that make sense? Absolutely, yeah. I mean, it makes perfect sense. I mean, it took what? About a billion or is it a billion and a half years as far as we know here on Earth?

And we don't really know, right? because maybe it arose rapidly, but that evidence got erased and it really is one of those, to some extent, unanswerable questions on Earth. But it's a question that does become answerable once we start exploring worlds like Europa and Enceladus and Mars for that matter. That's part of what's particularly exciting on PI on the Sherlock instrument on perseverance. And we had a few manuscripts come out this past year about evidence for past life in Noret Navalis, cutting through the Jesero crater wall. And if we can get those samples back, we'll get a better understanding on the timing and the age of those rocks and the veracity of those potential biosignatures. It's just killing so many of us.

I was going to bring up perseverance and Sherlock later, just because of the fantastic work that that spacecraft that rover is still doing. And the thought just killing so many of us that those little tubes, those once pristine tubes now loaded with bits of Mars, are just

sitting up there. They're in the belly and yes. So many tantalizing secrets just in the belly of perseverance right now. We've got to get those samples back down to Earth. It's not just astrobiology questions about potential biolus signatures and past life on Mars. It's also

questions of deep time and planetary formation and comparing some of the oldest rocks on Mars with some of the oldest rocks on Earth and better understanding that time period, the first half billion to billion years in our solar system. So yeah, I hope we can get those sample tubes back. I want to open the speculative side of this, I want to open that valve wide now and cut to some of the stuff at the end of the book. We already mentioned that you called Chapter 12, The Octopus and the Hammer. You opened it with this great hitchhiker's guide to the galaxy character, the designer of Fjords. For people who've read this series, we miss you, Doug. Slarty Bardfast, who said, imagine, never even thinking,

We are alone, simply because it has never occurred to you to think that there's any other way to be. And then you use that as the jumping off point for talking about, okay, what if there could be intelligent life down there in the dark under this thick ice? It made me think of, you ever hear of the, it was an old story, a classic by Isaac Asimov called Nightfall. And in this story, yeah, it's a civilization that is in a system with six suns, six stars, and they only have nighttime every couple of thousand years. And so civilization builds up. And then the astronomers figure out nights coming, and the civilization goes mad because suddenly they see the heavens. And so, I mean, your speculations about what this might mean to the culture, the mythology even, of an intelligent species living in permanent darkness under the ice is just mind-blowing. Oh, thanks.

You know, as you can tell from the writing in there. I mean, again, it was so much fun getting these ideas in my head down onto paper and having the opportunity to share them with readers. Because, I mean, think about it, if there did happen to be the equivalent of an intelligent octopus civilization that somehow develop tools and technology using hydrothermal vents or the ice shell or something, their mythology would potentially be centered around the cracking and creaking of this mysterious ice shell. Yes. And their gods would be, unbeknownst to them, kind of set by the 86-hour title cycle of Europa around Jupiter. And yeah, so just kind of trying to imagine what it would be like for a civilization to arise and how their imagination and curiosity and questions about the universe would arise. I love thinking about that stuff.

The other thing that I hope someday, maybe not in our lifetime, that's submersible that you and others, I mean, Britney Schmidt on the board of the planetary side also helping to help these robotic submersibles that are hopefully, you know, the grandparents of the ones that will someday descend through that ice, that one of them goes down there and finds these concentric circles surrounding a hydrothermal vent, which I'm. the equivalent of cornfields for a species that is, you know, plowing them and growing and, you know, maintaining its little farm down there in the deep black. Wow. And that was coming back to my dives to the hydrothermal vents. Part of the way that we would find the hydrothermal vents in the Atlantic in the Pacific is by following the vector of biology. So when you're up on the surface in the ship, you obviously have got GPS and you can set down these transponders to set up an acoustic grid based on GPS droppings. And then as you're descending and once you get to the bottom of the ocean, you can ping off those transponders to make

kind of a localized grid so you get your relative position. But you never really drop right on the hydrothermal vents, the kind of geographic position. positioning on the ocean floor is just insufficient in that capacity. So you end up kind of ticking back and forth. And that was one of my favorite parts about being in the submersible was looking out the tiny portal window and looking for, say, a Zawarsid fish or a deep ocean coral, and then following that trail of life and eventually finding a massive chimney. And so deep on Europa's ocean, as you mentioned, Matt, I love to envision that kind of the grand technological version of that would be this sort of agrarian deep ocean society that utilizes all of the chemistry

of the deep ocean. And there's all these wonderful, not just speculations, but actual history of life on earth and how important farming was to the development of tools and, you know, the tools that eventually have resulted in the spacecraft that we send out across the solar system. I'm wondering what you think of the cold scale, that confidence of life detection scale proposed by former NASA chief scientist Jim Green and others, because this whole idea of finding evidence that is so convincing that really there's not much other alternative than to believe that someday we will have found life elsewhere across the universe. Jim's fantastic.

I worked closely with him when he was at headquarters and he was just an incredible stalwart and advocate for astrobiology and getting missions off the ground. There are a number of different ladders of life and the cold scale and all that. And I think they are useful in perhaps the most pragmatic. way. They're a useful way for us to kind of help get the rest of the scientific community that is not deeply embedded in this stuff. It helps get them up to speed with how we are thinking about the extraordinary evidence needed to support extraordinary claims. Yeah. To use and Armstaganism. And so that cold scale is one way of thinking about it. And I think it captures

the complementary and redundancy of different potential biosignatures, you know, organics and complexity and inorganic biosignatures. For years, I led the effort to put a lander on the surface of Europa. And the Europa Lander Science Definition Team report, which came out in, what was that, 2016. You can still find that on the internet. And we go into all sorts of detail on exactly this kind of bar of evidence. And folks at headquarters like to refer to it as the sort of podium test. When do you send the president to the podium to make a really important announcement?

Right. Without embarrassing him sometime later. Yeah. Right, right. And no doubt you'll remember the clips of Bill Clinton that are in contact, and that goes back to ALH 8401. I don't like to get sort of overly critical. Science is a self-correcting process. And that announcement about the Martian meteorite was that perhaps made a little too early with too much confidence, maybe. But it was super exciting at the time and quite robust at the time. at least given the work that the folks had done. And it then catalyzed an incredible industry of digging deeper and trying to understand this stuff. You know, so ultimately the algorithm of science, the scientific process is self-correcting. And if we end up having some kind of fits and starts with the kind of the popular understanding of exactly what kind of confidence we have, that's unfortunate

but science does play out over time and what I don't want to see is too much trepidation because the pendulum can swing too far the other way where you have folks saying well unless and until we know exactly what to look for

and what measurements to make we should not bring any spacecraft to the launch pad to search for life we don't want to be in that position. And so I think we've got to find kind of a happy medium between strict hypothesis testing and discovery-driven science. I've mentioned before that when that announcement was made when those photos came out of ALH, Allen Hills 84001, I was driving up the Central Coast of California with my family, and it came on the radio, probably NPR. and I had to stop the car, get out, and do a little dance because I was so thrilled.

It was just so excited. I look forward to the next opportunity. And my hope is that on a world like Europa, where we might have living life, that the evidence will just be clear. Now, that's me dreaming a dream. Not praying or thinking with my gut, but dreaming a dream and, you know, having some confidence and a prediction of not just the habitability, but the hopeful inhabitants of a world like Europa. There is so much here that we simply don't have time to get to,

but there is one more great paragraph that I think is critical to understanding the search for life. This is right out of the book. This is not to say that there is something magical about life, but rather that life is more of a process than a tangible thing, air quotes, as microbiologist Lynn Margulis once said, life may be a noun, but it's really also a verb. Biology could simply be a collection of matter that is lifing.

And to me, that has profound things to say about both life and the search for life. Would you agree? 100%. Yeah, I love that phraseology and life. is a verb. Last question, I think. And then I'm going to ask you to read that last bit right at the end of the main text of the book. But first, we've already heard a few things on your wish list, like getting those samples back from Mars.

And maybe a Europa lander someday by somebody. What else do you most want to see while you're still in this profession? Or beyond being that. Well, we've got Clipper, we've got Dragonfly, those are on the books, and at least Clippers off the launch pad. Sample return. Hopefully we will return those samples, getting out to Enceladus with a flyby mission or even possibly a lander. And then getting down to the surface of Europa to scoop up some of that material, some of that salty ice that. that may well have other oceanic materials in it.

And then, of course, that dream of dreams coming back to where we started this conversation, that melt probe going through the ice and getting into the ocean and maybe even getting down to some hydrothermal vents or looking at microbial mats on the underside of the ice of Europa's ice shell. You know, that's the stuff I love to dream about under a clear night sky. We got an emphatic yes from member Christine a moment ago. If you could read that little close for us, it's a little bit of a long paragraph, but it's lovely, and I'd like to hear it. The discovery of life beyond Earth, or conversely, the discovery that it does not exist anywhere else is as profound a shift in our framework of the cosmos as is moving the Earth from the center of the universe to being.

just one of many planets, orbiting an average star in a universe full of stars. Perhaps we are the only ones. Perhaps the origin of life is hard and life is rare. Or perhaps we live in a universe teeming with life, a biological universe of incredible diversity across planets, moons, stars, and galaxies. Perhaps our tree of life, the same thing, the same thing, center of biology as we know it, is revealed to be but a tiny twig on a tiny branch, joined to a vast and grand tree of life, connecting the beauty of all life in the known universe. Looking up at the night sky, seeing Jupiter as a bright point of light above the horizon, I can't help but wonder whether our return to that beautiful planet and its magnificent moons

will once again catalyze a scientific revolution in our understanding of our place in the universe. Europa and the many alien oceans of our solar system await. So really, this is the thought that only just came to me. But hearing you read it, Carl Sagan came to mind. You're very kind. Praise doesn't come much higher. Thank you so much. Kevin, thank you so much.

This has been absolutely delightful, just as I knew it would be. I look forward to any other opportunity to talk. And I will remind folks, if you haven't read the book, you have great evidence now of why you should. It's alien oceans, the search for life in the depths of space. By our guest, Dr. Kevin Peter Hand. Kevin, thank you so much for joining us here in the Planetary Society Book Club. My pleasure, Matt, and thanks to all your members and listeners out there. That's it for this month's Planetary Radio Book Club edition.

I'll be back on October 16 with former astronaut and international space station commander Leroy Chow. We'll talk about his book, Dinner with an Astronaut. Sarah will be here much sooner with another great episode of the weekly show. Show your Plan Rad Love by wearing a planetary radio t-shirt. You can get one at planetary.org slash shop. Check out the other great space merch while you're there and help others discover the PBNJ, the passion, beauty, and joy of space science and exploration

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