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0:00:00 Sean Carroll: Hello everybody, welcome to the Mindscape Podcast, I’m your host, Sean Carroll. And today we’re gonna go looking for life elsewhere in the universe. I think that, with the discovery of many new planets around stars over the last few decades, the idea that there might be life elsewhere in the universe has become more and more of a scientific project. Of course, we’ve always been looking for it, we’ve been wondering, we’ve been doing the search for extra-terrestrial intelligence and so forth, but now we have a more focused idea of where we might look and a little, slightly more optimistic, perspective on how many places there are out there where life could be.

0:00:36 SC: We also talked, on this podcast previously, about the idea of the origin of life. If life only ever existed on earth then the search for it elsewhere would not be very helpful. But we talked to people, like Kate Adamala to Sara Imari Walker, about why life came to exist in the first place. Today, we’re gonna roll up our sleeves a little bit and think about looking for life. And it’s one thing to look for extra-terrestrial intelligence very, very far away. Today, we’re gonna talk about looking for actual living beings here in our solar system. People of a certain age, namely my age, came of age in the time when we were looking for life on the surface of Mars, with the Viking landers in the 1970s. It was very exciting but also a little bit inconclusive. We didn’t find any life. Mars is a pretty dry planet and these days we talk a lot about whether or not Mars might have had life in the past, less so about whether it has life now.

0:01:30 SC: But don’t get the wrong idea, because there’s other places here in the solar system, where life really could exist and we are actually going to go look for it. Today’s guest is Kevin Hand who is Deputy Chief Scientist for Solar System Exploration at the Jet Propulsion Laboratory here in Pasadena, California. Kevin is educated in physics and geology and biology and astronomy and planetary science and all of these things, mechanical engineering. He brings them together, both thinking about what life might be and how it might arise and how we might actually build something to go look for it. His special focus has been on Europa, the moon of Jupiter, but he also thinks about Enceladus and Triton and Titan and other places in the solar system, typically moons of giant planets, where you can get oceans underneath giant sheets of ice, which might be just the right conditions for life to form.

0:02:26 SC: Kevin has a new book out called Alien Oceans which is exactly about this topic, looking for life here in the solar system. Probably not technologically advanced life, don’t get too excited, but it’s very, very plausible that microscopic or primitive forms of life could exist elsewhere in our backyard. And it’s very exciting to think that we’re gonna go look for them. I wanted to mention very briefly that we have a Patreon here for the Mindscape Podcast. You can find links to it on the podcast webpage or just at patreon.com/seanmcaroll. But we also do, for the Patreon supporters, they get ad free versions of the podcast and also a monthly Ask Me Anything episode. And now, we’ve let the Ask Me Anything episodes go public. This was a vote taken by the Patreon supporters. So only Patreon supporters can actually ask questions but everyone can hear the answers.

0:03:20 SC: So I will put these on YouTube, and also the actual Patreon post where my answers… With the episode with my answers is put becomes public, a few days, for everybody, after I post it at the beginning of the month for the Patreon supporters. So check that out. Also check out the video series that I am doing called The Biggest Ideas in the Universe, where once a week I tackle a big idea, talk about it in hopefully a compelling, informal, chatty kind of way, then a couple of days later I’ll do a Q&A video about that. So a lot going on here at a time when many of us are locked down looking for things to do. We’re trying to provide content for everybody so your minds don’t atrophy. You gotta be thinking. You gotta be moving forward brain wise in this time of quarantine. And with that let’s go.

[music]

0:04:21 SC: Kevin Hand, welcome to the Mindscape Podcast.

0:04:23 Kevin Hand: Thank you, Sean. Good to see you.

0:04:24 SC: Now, I’ve heard that you just got back from Antarctica. And did you find life in Antarctica?

0:04:30 KH: Plenty of life.

0:04:32 SC: Not that hard, really. You’re not really giving yourself a challenge here.

0:04:34 KH: That’s right, that’s right.

0:04:35 SC: Why were you there?

0:04:37 KH: So our team was testing out and deploying this under ice robotic vehicle that is something that JPL has invested in as sort of a win-win robotic capability that can be used to study Earth’s ocean and Earth’s cryosphere, Earth’s ice, while simultaneously, building some of the capabilities that someday we hope to deploy beneath the ice of a world like Jupiter’s moon, Europa.

0:05:04 SC: Okay, so you’re there at a place where there is ice on top of water and sending it into the…

0:05:10 KH: That’s right, sea ice around Antarctica.

0:05:14 SC: Is this something where the thing you were dealing with had a capability of digging through the ice or did you [0:05:19] ____?

0:05:19 KH: No, we’re not there yet.

0:05:20 SC: Okay.

0:05:21 KH: Someday we will have this robot encased in another robot and that other robot will have the job of getting through the ice.

0:05:29 SC: Are you gonna put the whole thing on a rocket, send it to Europa?

0:05:32 KH: Send it to Europa. But doing… So doing what I just described, getting through ice, even thin ice… The ice that we were dealing with in Antarctica, down at the Australian Antarctic Division’s Casey Station… They were great partners. That ice is just about 160cm in thickness, at least when we were there.

0:05:54 SC: That’s nothing.

0:05:55 KH: Nothing, except to get through that ice and then deploy our robotic vehicle takes chain saws and ice clippers and all sorts of things. And projects that work to get through even thicker ice on Earth use hot water drills and just thousands upon thousands of kilograms to get through the ice, before you can even start to sample what’s beneath the ice. And so, as you can imagine, if our dream of dreams is to someday get through the ice of Europa, and directly study that ocean and whatever may be alive within it, we’ve got a long way go.

[chuckle]

0:06:36 KH: And so there’s this beautiful…

0:06:37 SC: How thick is the ice we think on Europa, roughly?

0:06:40 KH: Well that’s a huge debate. There are the thin shell-ists and the thick shell-ists. I happen to be on the thin shell side.

0:06:47 SC: But you kinda gotta plan for a thick shell if you’re sending up a spacecraft.

[chuckle]

0:06:52 KH: To be clear, by thin, I mean, about, let’s call it five kilometers in thickness.

0:06:57 SC: Right.

[chuckle]

0:06:57 KH: So it’s still pretty darn thick.

0:07:00 SC: More than 180 centimeters.

0:07:00 KH: Yeah, exactly, you’re not gonna chainsaw through that.

0:07:03 SC: Okay.

0:07:05 KH: So it’s, by Earth standards… So the Antarctic ice sheet above Lake Vostok, which is one of these sub-glacial lakes on the continent of Antarctica. The ice above Lake Vostok is about four kilometers in thickness.

0:07:18 SC: Okay.

0:07:20 KH: And that would be considered thin ice on Europa.

0:07:22 SC: Right.

0:07:23 KH: And we can’t even really access these sub-glacial lakes in Antarctica, easily, so…

0:07:29 SC: Even with all of our human capability of flying down there and having people and chainsaws… Yeah okay…

0:07:35 KH: Huge tractors full of devices to hot-water drill, etcetera.

0:07:39 SC: So this is depressing me. This is making me think that it’s less likely than I imagined to easily just dig down into Europa’s oceans.

[chuckle]

0:07:48 KH: Welcome to my world.

0:07:49 SC: Yeah, okay.

0:07:49 KH: That’s not for the faint of heart.

0:07:51 SC: So just, the audience here, we don’t presume they know anything at all, so we’ll get to what Europa is and why it’s interesting, but is there a mission planned to go do this or is this just planning for a future far off things?

0:08:04 KH: Well, so there is a mission that NASA has committed to call the Europa Clipper mission and that mission is a fly-by mission. It will orbit Jupiter and fly by Europa some 45 or more times… And with each fly-by, some of which may be fewer than 100 kilometers above Europa’s surface… With each fly-by it will collect incredible imagery, spectroscopy. It’s got an ice-penetrating radar instrument on it to essentially sound into the ice. And so it’s got all sorts of great ways of looking at Europa’s surface, looking into Europa’s interior, figuring out the surface chemistry, the surface geology and some of the interior geophysics. And that’s from a remote-sensing mission, a mission flying by.

0:09:00 SC: Right.

0:09:01 KH: That mission does not have any lander on it. I’m part of the Clipper mission, but much of what I focus on at JPL is the next step, trying to get a lander down to the surface of Europa or, for that matter, Enceladus a moon of Saturn, that is also incredibly compelling in the context of alien oceans beyond Earth and places where we could go to, not just find evidence of life, but find extant life, life that is alive today.

0:09:36 SC: Not just fossils.

0:09:37 KH: Not just fossils. And that’s incredibly important in terms of revolutionizing our understanding of biology.

0:09:45 SC: Sure. Do we know for sure that there are oceans beneath the ice on Europa’s surface?

0:09:50 KH: Well, you, of course, know that “for sure” needs to be in quotes. But, based on the available evidence, we can make the prediction that the best hypothesis to explain the available evidence is that Europa does have a salty, sub-surface liquid water ocean. And that evidence I like to kind of partition into three easy pieces.

0:10:16 SC: Okay.

0:10:16 KH: Kind of taking a page out of Feynman’s six easy pieces. Right?

[chuckle]

0:10:21 KH: And the first easy piece is use spectroscopy to figure out that the surface of Europa is covered in water ice.

0:10:28 SC: Uh-huh. Rather than methane or whatever…

0:10:32 KH: Or rocks or whatever right. Think about it. 1610, Galileo turns this military tool, the telescope, to the night sky. Looks at the moon, looks at Venus, looks at Jupiter and sees Jupiter and also sees these four little points of light. Which to him at the time, he thought were just stars…

0:10:56 SC: Stars, what else could they be?

0:10:57 KH: Right, yeah, and Galileo being a clever fellow named them the stars of Medici because, of course, that’s where his money was coming from and…

0:11:08 KH: You would name them the stars of NASA. ‘Cause that’s where your money’s coming from.

[chuckle]

0:11:12 KH: Right… So… But as we know, he mapped those little points of light around Jupiter night after night and discovered that they, in fact, revolve around Jupiter. Which at the time was heretical and got him in trouble with the Spanish Inquisition. But through his diligent observations, we came to appreciate that Jupiter has moons. Now, those little points of light stayed as points of light for some 350 years until astronomers like Kuiper and Vasilli Moroz, a Russian astronomer, used spectroscopy to figure out that the surface of Europa was made of water ice. So that’s the first easy piece. Okay, we go from a point of light to Europa having an icy surface.

0:12:07 SC: Right.

0:12:09 KH: The next easy piece. I like to make the analogy to baby-sitting a space craft.

0:12:15 SC: Okay.

0:12:16 KH: What do I mean by that?

0:12:16 SC: Something we’ve all done.

[chuckle]

0:12:19 KH: So baby-sitting a space craft. Well, here on earth we use the deep space network. This network of antennas, three of which are 70-meter antennas, to get the data back from spacecraft and to send commands up to spacecraft. The DSN is used for all missions. And along with collecting and transmitting data from the various spacecraft, the signals that are received can be used to look at the tiny red and blue shifts, the Doppler shifts, associated with those signals.

0:13:00 SC: Sure.

0:13:02 KH: And, phenomenally, this never ceases to amaze me, with the Galileo spacecraft, as it was flying by Europa, the beautiful little gravity well… And, you know, you’re the expert on all of that, and then the fabric of space and time.

[laughter]

0:13:19 KH: But Europa’s got its own little gravity well. And as the spacecraft flies by, Europa’s interior mass distribution and its rotation cause slight accelerations and deceleration, which appear as millimeter-per-second Doppler shifts in the signal being sent back to earth.

0:13:44 SC: So, Europa’s not a point mass. We can’t just…

0:13:47 KH: That’s right. And not only is it not a point mass, but by merit of looking at the gravity signal of Europa, in other words the Doppler shift as the Galileo spacecraft flew by, scientists on the Galileo mission were able to tease out the moment of inertia of Europa.

0:14:07 SC: Wait, sorry. We’re looking at the Doppler shift of the spacecrafts.

0:14:10 KH: Sending its transmission back to earth.

0:14:11 SC: Okay. But it’s influenced by Europa, and because Europa is not a point mass, it has a shape.

0:14:16 KH: That’s right, a shape.

0:14:16 SC: It is not a perfect sphere. That’s what you can look at.

0:14:18 KH: And non-uniform density.

0:14:20 SC: Right.

0:14:21 KH: Right. And so, the rotation, plus the non-uniform density, puts its fingerprint on the Doppler shift of the spacecraft as it flies by. And then you can invert that information about the gravity structure of Europa to get things like the moment of inertia, from which you can then build layered models.

0:14:47 SC: So you say such and such rock, such and such water, such and such ice.

0:14:50 KH: Exactly. So the second piece of the puzzle is that the gravity data, those Doppler shifts, necessitate that Europa, at least in kind of a three-layer model, has a dense core, iron or iron sulfur, a rocky silicate mantle, and then some outer layer of roughly 100 to possibly 200 kilometers in thickness of low density material. And in particular, the density that fits the gravity data well is something in the range of one gram per cubic centimeter.

0:15:28 SC: Also the density of the glasses of water in front of us right now.

0:15:31 KH: Exactly. Right. And so, the second piece of the puzzle follows on the first. The first says, you know, that Europa is covered in ice. The second piece of the puzzle tells you that water, in some phase, be it liquid or solid, extends down for 100 to 200 kilometers. Now the gravity data was not of sufficient sensitivity to differentiate between the density of water and the density of ice.

0:15:58 SC: Sure. It’s a miracle they could do anything at all. Astronomers are just geniuses at taking the tiniest bit of data and stringing a tale based on this.

0:16:08 KH: Oh, it’s remarkable.

0:16:08 SC: It’s remarkable. Yeah.

0:16:09 KH: But I always feel compelled to point out, we scientists often have the easy part of the job. Is the engineers who really make this possible. They make the data possible. Without their precision, you don’t get that millimeter per second velocity difference that you’re able to measure. So, that’s the second piece of the puzzle. We’re not yet at an ocean. That requires the third piece of the puzzle. A liquid water ocean, a salt water ocean.

0:16:41 SC: Right. Because given the first two pieces, it could just be all ice.

0:16:44 KH: That’s right. Exactly. So a third piece of the puzzle, I like to make the analogy to adhering to airport security.

0:16:53 SC: Okay.

0:16:53 KH: What the heck do I mean by that?

0:16:54 SC: What do you mean?

[chuckle]

0:16:56 KH: So, for the moment, disregard those big cylinders that we sometimes now have to walk in and, you know, we feel like we’re being zapped in a thousand ways. Go back to those doorways, the traditional metal detectors. When you’re at an airport and you’re walking through one of those doorway structures, you’re passing through a pulsating time-varying magnetic field. That time-varying magnetic field gives rise to electric currents in any conductor that you might have in your pocket or on your person. Those induced electric currents, as we know from Faraday and ENM, those induced electric currents give rise to induced magnetic fields. And within the little doorway, there are sensors to detect induced magnetic fields. So you walk through with a conductor in your pocket, that gives rise to induced electric currents, which gives rise to induced magnetic fields, and the alarm goes off.

0:18:01 SC: Yeah. We’ve all been there.

0:18:03 KH: All been there. Then you get the pat-down, you miss your flight. It’s a…

[laughter]

0:18:08 KH: So, with the Galileo spacecraft, the alarm went off. The Galileo spacecraft had on board a magnetometer. A fancy Compass. And as it flew by Europa, it detected an induced magnetic field. It had long been measuring Galileo… The Galileo spacecraft had long been measuring Jupiter’s magnetic field. And from that data, we knew that Jupiter’s magnetic field is tilted by nearly 10 degrees.

0:18:43 SC: From Jupiter’s rotational axis?

0:18:44 KH: Exactly. And so if you’re Europa, Jupiter’s magnetic field has a time-varying component. So the Galileo spacecraft had mapped that out reasonably well. And as it flew by Europa on a handful of occasions, it detected an induced magnetic field. What the heck could be giving rise to an induced magnetic field? Europa did not have a standard dipole the way the earth does. It did not have an intrinsic field. It had this induced field. Well, you could say maybe the time varying component of Jupiter’s magnetic field is interacting with Europa’s iron core. Iron’s a good conductor.

0:19:28 SC: Yep that makes sense, that will be my answer. Yeah.

0:19:30 KH: Sets off the alarm. Well, you do the math and the modeling. And I did a lot of this a number of years ago and tried to fit things. The core is just too small and too far away.

0:19:41 SC: Hmm.

0:19:42 KH: What about that rocky mantle? Turns out that rocks, silicon rocks, are not conductive enough to explain the data, but what fits the induced magnetic field data of Europa beautifully is a near-surface conducting layer. Now, from piece number one and piece number two, we know that that near-surface region of Europa is water in some phase.

0:20:07 SC: Right.

0:20:09 KH: And so the best answer to the induced magnetic field data at Europa is a salty, liquid water ocean. The salt provides the conductivity that explains…

0:20:20 SC: Water by itself would not work. But salty water would work.

0:20:23 KH: Water by itself… Exactly… Yeah.

0:20:25 SC: And liquid water is better than ice?

0:20:27 KH: That’s right, yeah. You can kind of play around with some mushy ice scenarios, but even in that you’re essentially at an ocean anyway.

0:20:38 SC: I mean, it’s both remarkable that we can say all that about a little dot in the sky, the Galileo looking in his telescope. It’s also very vivid that we could be wrong.

[chuckle]

0:20:50 SC: Right? Like you said, we never know for sure. There’s a lot of great evidence but presumably the Clipper will give us much more evidence.

0:20:57 KH: That’s right.

0:20:58 SC: What year is that coming?

0:21:00 KH: Well, so hopefully, the mission will get to the launch pad in the 2023 to 2025 time-frame.

0:21:07 SC: Okay.

0:21:09 KH: Either launch would hopefully get us out to JOI, Jupiter Orbit Insertion, and ultimately fly-bys of Europa in the late 2020s.

0:21:23 SC: Okay.

0:21:24 KH: And a lot of that uncertainty is in what launch vehicle we actually go on.

0:21:28 SC: But it could be roughly five years to get there?

0:21:30 KH: Yeah, on the low end, closer to three and a half, four. On the higher end, closer to six and a half, seven.

0:21:37 SC: Yeah. Okay, and then the lander, let’s say that everything works and you get the lander, you get the money, you get the launch date, when would that be arriving at Jupiter?

0:21:49 KH: Ahh.

0:21:49 SC: This is your baby right? This is your thing, you should know, you should have a quick snappy answer to this.

[chuckle]

0:21:54 KH: Sadly, sadly, there is no plan for a Europa landing right now.

0:21:58 SC: Okay. But 2030s, let’s say the 2030s.

0:22:00 KH: That’s right.

0:22:00 SC: Would be, okay.

0:22:02 KH: But yeah, we’re, we’re…

0:22:04 SC: And even that does not have a drill that’s gonna go through the ice that’s gonna land on the surface?

0:22:08 KH: That’s right. So the pathway is fly-by land and then get deeper into the sub-surface. Before we can do a melt probe or something that gets into the ocean directly, we need to do a lot of ground truth and directly get onto the surface of a world like Europa or Enceladus to see how hard that surface is, what it takes to drill or melt into it, how thick the ice truly is in the region of where we wanna someday go through. And I should say that, as great as the remote sensing will be, the Clipper mission is a habitability mission, we’ll be able to further constrain the ocean, the ocean chemistry, the ice shell chemistry and the geology. But unless Europa is extraordinarily generous with her evidence…

[chuckle]

0:23:01 SC: Which nature sometimes is not.

[chuckle]

0:23:04 KH: Right. We’re not going to find signs of life with a remote sensing mission.

0:23:09 SC: Sure.

0:23:10 KH: To detect bio-signatures you need to get on the surface.

0:23:14 SC: I mean there is a theory that at least some people have that you could detect really, really complex molecules, and even if you didn’t know that they had some particular biological function, you might say there’s no non-organic way of making them. Is that something that’s feasible with just the Clipper?

0:23:31 KH: That’s true, and so, Clipper has on board two very capable mass spectrometers, one of which I’m a co-investigator on, and these are really exciting instruments, and we hope to fly similar instruments through the Plumes of Enceladus someday. And in both case, whether it’s flying through the plumes of Enceladus or perhaps plume on Europa, instruments such as those mass spectrometers could give us an inventory of organic compounds, carbon compounds, that provide compelling evidence for a highly selective process that might point to biology.

0:24:17 SC: Mm-hmm.

0:24:18 KH: Because really at the end of the day, biology is selective and abiotic processes for generating carbon compounds is not. So you basically go from a Poisson distribution to a picket fence.

0:24:31 SC: Sorry, this is your fancy scientist way of saying, if it’s not organic, you get a lot of light tiny molecules…

0:24:36 KH: If it’s not biological.

0:24:37 SC: If it’s not biological, sorry I used organic in the casual way, but you scientists just mean carbon when you say organic I understand.

0:24:44 KH: Yeah.

0:24:44 SC: Carbon chemistry. So if it’s not biological…

0:24:46 KH: But there is a nuance there, ’cause carbon dioxide, of course, is carbon chemistry, and that’s not organic. So lots of…

0:24:51 SC: Yeah, okay hydro-carbon chemistry. These scientists man, this is why I don’t wanna have scientists on my podcast they’re just too picky. [chuckle] But anyway, you could imagine, lots of sort of random, crazy non-biological, chemical reactions that would occasionally spit out a long molecule, but only in the presence of many, many tiny molecules.

0:25:10 KH: Right.

0:25:11 SC: Whereas a truly biological thing might give you this anomalously large concentration of really long molecules.

0:25:16 KH: And coupled with that, so life as we know it… It’s really hard to pin down some of the fundamentals of life as we know. What do we think would be universal? For the most part, the community biologists, astrobiologist, etcetera, there’s a general convergence on biology, however you frame it, is selective, it will form larger molecules by utilizing a pool of smaller sub-units. In the case of life on Earth that is for proteins, amino acids.

0:26:00 SC: Proteins, RNA, DNA.

0:26:01 KH: Right, exactly. So…

0:26:04 SC: Not randomly chosen collections of carbon molecules, yeah. [laughter]

0:26:07 KH: Right. And so if you take RNA, DNA, proteins and just break them up, you’re going to see a pattern that has a fundamental unit based on, say, amino acids linked together one, two, three, so on and so forth, right? So it’s just not a random smatter.

0:26:28 SC: Yeah.

0:26:28 KH: Now back to the alien oceans and having missions that could fly through plumes on Europa or Enceladus, absolutely, there could be some incredibly compelling evidence, but even after that, you’re gonna wanna land. [chuckle] Yeah.

0:26:44 SC: Oh yeah, no, then you wanna land more than ever, right, that’s true.

0:26:48 KH: And with those chemical analyses, you’re not actually gonna see the life, you’re not gonna be able to put that under a microscope until you get down on the surface and grab a scoop of it. And one of the things that makes me nervous about depending on fly-by-missions for analyzing say plume material, is the small quantities that you actually get as you fly through a plume. And when we talk about flying through a plume on Enceladus or Europa, it’s not like flying through Old Faithful up in Yellowstone or even…

0:27:22 SC: Right. With the fires here in LA.

0:27:23 KH: Right or even a snow making machine at a ski resort. These plumes at the fly-by-altitudes, let’s say 50 kilometers or so, they’re very diffuse and so you’re collecting nano leaders to on a good day micro leaders of sample. Whereas if you’re on the surface, you’re collecting a full scoop worth of material.

0:27:48 SC: And it’s hard to know what you found. I mean I was a kid, you were a kid, when the Viking landers landed on Mars, and we all thought they were gonna tell us whether there was life and they did some chemistry experiments. And the answer is, “It’s maybe, there’s some hints, but we don’t know”.

0:28:04 KH: However, so the Viking was a phenomenal mission.

0:28:09 SC: In the ’70s, oh my goodness.

0:28:10 KH: In the ’70s. So I like to compare the Viking missions and the incredible achievement of the Viking missions, that’s the sort of robotic pioneering work that was done in the ’70s, that is analogous to putting humans on the moon.

0:28:29 SC: Yeah.

0:28:30 KH: Right. It’s a miracle that NASA did that back in the day. When it comes to Viking and life detection, there’s a really important nuance that often gets lost in the mix. And when I talk about Europa lander, Viking often gets thrown back at me from the naysayers who don’t like astrobiology or who don’t like the search for life. They say, “You don’t know what you’re looking for and the Viking failed and it killed the Mars program for decades.” That is a tremendously false read of history, for a number of different reasons. But scientifically, what’s really important to appreciate is that the Viking biology payload was largely designed to look for living microbes.

0:29:21 SC: Yeah.

0:29:22 KH: Microbes that were cooking along, living and breathing.

0:29:24 SC: Metabolising, eating and drinking, yeah.

0:29:26 KH: Metabolising. Exactly, right. And so the Viking Lander again, miraculously scooped up some sample poured it into a little agar plates, little sugar water essentially and did a host of different experiments, looking at consumption of gases, release of gases, some of the gases were isotropically labeled. But all of those results required microbes to actually be living and metabolising and as we know that’s hard to do even in the lab.

0:30:04 SC: Yeah.

0:30:04 KH: And so it was a tremendous achievement, but the way in which we search for biology now is to look for the chemistry of life, the structures of life. And on Viking, the measurement, the instrument that kind of put to rest some of the ambiguous results about the metabolic experiments, was the gas chromatograph mass spectrometer, which did not detect any organic compounds at the level of parts per billion. And so, the conventional wisdom is, if you ain’t got any carbon, you ain’t got life.

0:30:46 SC: Yeah.

0:30:47 KH: At least in terms of searching for life as we know it. And so, the GCMS results superseded any ambiguity on the biology result.

0:30:57 SC: But this gets into what I really wanted to use this opportunity for, is to talk about what life is or might be? I mean you’re looking for life in the solar system. We don’t know a lot about what it is, previously on the podcast, we’ve had Kate Adamala talking about making synthetic life in the lab, we had Sara Walker talking about what life is from the information theory perspective. Let’s get down and dirty with like the chemicals and what might be going on. So how do you conceptualize what life might be when you’re imagining what we should do to look for it?

0:31:22 KH: Yeah, that’s a great question, with a myriad of ways to answer it. And first and foremost, when it comes to searching for signs of life, be it on Mars, within alien oceans in the outer solar system, on Europa, Enceladus, Titan etcetera, or on extra-solar planets or with SETI signals. I think it’s really important to not get too precious about life. What do I mean by that? Well… The search for life comes under incredible scrutiny. Sometimes, very valuable scrutiny. But oftentimes, that scrutiny is disproportionate to the way in which other scientific questions come under scrutiny. And that’s in part because we, I think, imbue this question with a certain amount of preciousness.

0:32:33 SC: Yeah, well we take the answer seriously. But look, I’m certainly someone who thinks that both the investigation of how life started and our search for it is way underfunded and emphasized within the scientific community.

0:32:46 KH: Excellence, that’s… It’s… [chuckle]

0:32:48 SC: You’re preaching the conversion. There’s an official Mindscape position that we should spend more money and effort understanding where life came from.

0:32:49 KH: Right. Yeah, right. But let me give you an example. In geology, there’s the question, what is a mineral?

0:33:01 SC: Yeah, okay, but fine. Still, operationally, you’re building instruments.

0:33:04 KH: Right.

0:33:06 SC: You need an answer, even if it’s not the perfect answer.

0:33:07 KH: That’s right. So if we can remove sort of the precious layer of how we think about life and biology, then we get to some operational approaches. And fundamentally, life is a layer on top of geology. Life alleviates chemical disequilibrium in the environment to accelerate the increase in entropy. And I don’t need to tell you that. [chuckle]

0:33:36 SC: We love increasing entropy. It’s our favorite thing.

0:33:39 KH: But to that end, life does it in a very chemically specific way by harnessing the energy available in chemical systems to do work.

0:33:51 SC: The free energy, as we said.

0:33:53 KH: That Gibbs free energy, exactly.

0:33:54 SC: Yes, that’s right, yeah.

0:33:54 KH: And so, that’s…

0:33:56 SC: And that, sorry, you and I know what that means, but just to be clear, very roughly speaking, for those of you who’ve read “From Eternity to Here”, you know that if a system has energy, you can roughly divide it into useful energy and useless energy, right. The useless energy is just all entropy and temperature. The useful energy that you can do work with, that’s the free energy we’re talking about here.

0:34:16 KH: Right, and it gives free energy… So Josiah Willard Gibbs, huge fan. He’s one of these vastly underappreciated physicists.

0:34:25 SC: One of the first great American scientists, also.

0:34:28 KH: Oh, 100%. And can we divert into Gibbs for…

0:34:33 SC: Yeah. No one’s… These electrons are free.

0:34:36 KH: So yeah, Gibbs just vastly underappreciated. He’s incredibly humble and just lived a very simple life at Yale. None of the… As much as I love Einstein, Einstein sort of established the crazy physicist archetype, right?

0:34:54 SC: He did, yeah.

0:34:55 KH: And so, some of that persists and in order to be a genius and brilliant, you must have something weird about you. [laughter] If it’s not the crazy hair, you must have crazy tattoos, etcetera, etcetera. And to me, that’s so artificial. Gibbs was just an ordinary guy with great thoughts. And so, I find his… It’s very refreshing to read about Gibbs and…

0:35:23 SC: Well, and we’re still thinking about the significance of these concepts for ideas like the origin of life. So you can say…

0:35:28 KH: Yeah.

0:35:29 SC: And I will agree, that it makes sense that one of the things life does is turn this free energy into higher entropy energy. It’s not completely clear that there’s laws of… Law of physics that says that that should happen, or under what condition, it would happen, or is it probable? So that’s what we have to sort of empirically figure out.

0:35:46 KH: That’s right. And so, yeah, let’s dive into Gibbs free energy for a minute. So as you said, you can think about energy in a couple of different ways. The heat and change in entropy. Can’t get much done with that. [chuckle] And then there’s the work. And oftentimes, when we think about work, we think of PdV, pressure and change in volume, or…

0:36:08 SC: There’s a piston, we’re pushing it in there. It pushes back, we’re doing work, yeah.

0:36:11 KH: Yeah. Yeah, or to go to Physics 101, we can think of work as force times distance.

0:36:18 SC: Mm-hmm.

0:36:19 KH: And force, of course, is ma or mg in the case of planet earth. And so, when we think about the work done, we can think of mgh, mass times the gravitational acceleration times the height to which you hold something…

0:36:35 SC: Lift something, yeah.

0:36:37 KH: Drop it. Well, Gibbs had this great insight in that within chemical systems, there should be some chemical equivalent to mechanical work, and that chemical equivalent comes with something like chemical potential.

0:36:58 SC: Right.

0:37:00 KH: And that chemical potential times the change in mass of a given compound within a system yields you some of that energy available to do work.

0:37:09 SC: So can we think of this as if you have hydrogen and oxygen in a bottle, it has the ability to light on fire and do some work?

0:37:15 KH: That’s right. And so, Gibbs’ brilliance, so entropy is the… How do you think about aggregations? Where do things aggregate? And Gibbs obsessed over this. He was… Thankfully, so.

0:37:37 SC: Yeah, for us.

0:37:37 KH: Clausius and Boltzmann, etcetera, had preceded him. And so, he basically said, “Well, this aggregation and the pressure and volume changes, that’s missing a certain aspect of how we do the full-cost accounting for energy and changes in energy. And Gibbs said, “Well, you know what? If I have something like hydrogen and oxygen, these two parts,” and he loved to use this term, “new parts”. So, “There are these new parts that get created from old parts. So hydrogen and oxygen come together to make water. And so in any given system you might have the initial parts, some compounds, and then at the end you have new parts. And so his addition to the energy equation which folds into Gibbs free energy is that chemical potential for each compound, for each chemical in that system to then react with other compounds and to form new parts. So he really helped complete the full accounting for the conservation of energy.

0:38:47 SC: Okay, but we gotta get from here to life somehow. [chuckle]

0:38:49 KH: Okay, right so… So again…

0:38:51 SC: I gave you that digression. [chuckle]

0:38:54 KH: But it’s beautiful physics, isn’t it?

0:38:55 SC: Beautiful physics and I love it and I could go on but…

0:39:00 KH: Okay so back to life and why the heck life arises? And here I’m talking just about life as a chemical system.

0:39:10 SC: Yep.

0:39:11 KH: Certainly, there is life in silico. It’s all sorts of kind of broader ways, yeah.

0:39:16 SC: Artificial versions but…

0:39:18 KH: Yeah. But strictly speaking for life as a chemical process that we currently call biology I think it is, if you allow me to use a loaded term, I think it is motivated by that requirement of the universe to increase entropy and in so doing alleviate chemical disequilibrium in the environment.

0:39:51 SC: Yeah.

0:39:53 KH: And so any place where you’ve got Gibbs free energy available, enzymes which… And how you get to an enzyme is tricky, but enzymes allow you to overcome a bit of a hump, to then release that stored chemical energy.

0:40:09 SC: Right, metaphorically, it’s like the spark that could light the hydrogen and oxygen on fire, right?

0:40:12 KH: That’s right.

0:40:15 SC: There’s some ability for entropy to increase lurking there in the chemicals all around you, but you have to allow it to get there somehow and that kind of enzymatic process is what you’re saying leads to life? Is life, is life adjacent? [chuckle]

0:40:34 KH: That’s right, and so there are numerous hypotheses for the origin of life itself, but I think one of the most compelling suspects in the story of how life arose perhaps on earth and perhaps elsewhere is the reduction of carbon dioxide. How do you take carbon dioxide and pull off the oxygens and do something else with it?

0:41:02 SC: Mm-hmm.

0:41:02 KH: And sometimes this folds into the acetyl-CoA pathway that is part of modern biology.

0:41:09 SC: I’ll take your word for that. [chuckle]

0:41:14 KH: But early on minerals may have been the sort of first catalytic environment that where kind of the proto-enzymes that allowed for the reduction of things like carbon dioxide to then form organic compounds, and then to be a template for self-replication, and eventually the formation of vesicles that would some day be called cells.

0:41:51 SC: Yeah, I mean I don’t wanna get too deeply into this ’cause we gotta talk about various moons in the solar system.

0:41:56 KH: Right.

0:41:56 SC: But maybe the quick overview of metabolism, replication, compartmentalization. The most important ingredients for life.

0:42:05 KH: So. Well, so I’m a metabolism firster, and I think that… And that’s where Gibbs free energy comes into play. You need a motivation for the energy dynamics of life.

0:42:20 SC: Why don’t you tell us the opposing school of thought?

0:42:24 KH: Well, I don’t think it’s so much opposing. It’s just a lot of different camps are trying to figure out where the intersection of metabolism, information storage and current compartmentalization all come together.

0:42:45 SC: Everyone agrees you need these three things.

0:42:47 KH: Exactly.

0:42:47 SC: People put different emphases on what is the crucial step.

0:42:50 KH: Right, and…

0:42:52 SC: But replication and information seems to me from my reading of the community to be the thing that most people are focusing on whereas you’re saying you’re a metabolism kind of guy.

0:43:02 KH: Right, now, the information molecule side, what many of us like to call the top down side, it’s kind of low-hanging fruit. We have the information molecules.

0:43:14 SC: We know what RNA and DNA are, they’re in us now. Right?

0:43:16 KH: And so we can look at the RNA world, the idea that the earliest information molecule was some form of RNA or poly-nucleic acids, PNAs, etcetera, but the ladder down stops at those PNAs.

0:43:32 SC: To you mean down to simpler and simpler things going on?

0:43:35 KH: Right, right, so a top down approach, you can climb all the way down to poly-nucleic acids and variations there in. But how do you actually bootstrap from…

0:43:44 SC: Where do you get them from? Just from chemicals sloshing around in a warm small pond.

0:43:48 KH: Exactly. Right and so as much as I love the Miller-Urey experiments…

0:43:52 SC: Which were?

0:43:54 KH: Yeah. Getting amino acids and then some more complex compounds from a spark discharge experiment that had some pretty simple compounds like methane and water and ammonia in it. You then get amino acids and some of the building blocks of life. Amazing, right? Just mind blowing back in the ’50s.

0:44:11 SC: This is the ’50s and so, yeah, so as I recall, that was basically the conclusion is it’s not that hard to make amino acids out of random junk.

0:44:20 KH: Right.

0:44:21 SC: And they thought, “Well, yeah, tomorrow, we’ll do proteins and then we’ll do DNA, but that just turned out to be much…

0:44:25 KH: Further along a little mouse is gonna run out of the lab.

0:44:27 SC: Yeah. Exactly. Much harder.

0:44:31 KH: Right. And that it’s from that progression in the 1950s to now where of course we’ve had the genetic revolution. Leslie Orgel and others really spearheaded the RNA world, and that was phenomenal work. And then… In 1977, going back to Viking, right. So a year after Viking lands, hydrothermal vents are discovered.

0:45:00 SC: Here on Earth.

0:45:00 KH: Here on Earth.

0:45:00 SC: Not on the Mars. [chuckle]

0:45:01 KH: No. Right. [chuckle] More Europa for them, right?

0:45:05 SC: Yeah.

0:45:05 KH: But so much happened in the late 1970s. It’s just one of my favorite scientific periods, but… So hydrothermal vents are discovered.

0:45:13 SC: Under the oceans. Tell us what a hydrothermal vent is? Why we care.

0:45:15 KH: Right, so hot springs at the bottom of the ocean. New oceanic crusts is forming or fractures in the oceanic crust are allowing chemical reactions to proceed that drive hot water and all sorts of interesting chemistry. And so, part of what was exciting about the discovery of the hydrothermal vents is that along with the astonishing ecology, the biology that was found there, the tube worms, the zoarcid fish, the mussels, etcetera. These also started to become recognized as cauldrons for interesting mineralogical and potentially organic chemistry to serve as a place where processes, perhaps related to the origin of life could occur.

0:46:08 SC: And part of that is simply life is dynamical. You don’t want… You’re not gonna imagine the lifeforms in a… Something that’s just sitting there stationary. You need some shake-up, something that is knocking things around and hopefully, falling into good patterns.

0:46:21 KH: Right, and one of the things that I do like about the hydrothermal vents model for the origin of life is it’s motivated by a metabolism-first approach. You’ve got compounds coming out, the fluids are full of things like hydrogen and methane compounds that have electrons they just wanna give away.

0:46:46 SC: Energy.

0:46:46 KH: Energy, coming back to Gibbs free energy. And there are minerals that also want to give away electrons, and the ocean around it wants to accept those electrons. So there’s a lot of really compelling chemistry that occurs around hydrothermal vents. The downside and the argument that’s often put against hydrothermal vents is all that damn water.

[laughter]

0:47:13 SC: And water is not deadly.

0:47:13 KH: Right. Well, but it is to certain chemical reactions. So when you link two amino acids together, that process, that polymerization spits out a water molecule. So if you’re linking two amino acids together in a liquid water environment, you’re trying to introduce a new water molecule into a place that’s full of water molecules. That’s not particularly advantageous.

0:47:40 SC: Right.

0:47:40 KH: Chemistry doesn’t like to proceed in that direction.

0:47:42 SC: Yeah.

0:47:43 KH: And that’s where many of my colleagues who do brilliant work on like in warm tide pools on the flanks of some ancient continent where you can lap up some primordial soup, and then it gets baked in the sun and desiccated. That desiccation process, that’s a much better environment for concentrating things and linking things together.

0:48:08 SC: And they showed it on Star Trek that that was how life formed here on Earth.

0:48:11 KH: So it must be true.

0:48:12 SC: Yeah. [chuckle]

0:48:13 KH: Right. Now, so those are… There are different camps as far as information-first, metabolism-first, compartmentalization. And then layered on top of there is a Venn diagram of environments that we see here on Earth: Hydrothermal vents, tide pools, hot springs and other things. What I find so exciting about these alien oceans beyond Earth, these worlds like Europa, Enceladus and Titan is that we can just do this experiment.

0:48:47 SC: Yeah.

0:48:48 KH: Right?

0:48:49 SC: Well, we’ve done it a handful of times. Let’s put it that way, right?

0:48:50 KH: What do you mean we’ve done it, though?

0:48:51 SC: Indeed, the solar system has done it.

0:48:53 KH: Oh, exactly, right. So the solar system is running these experiments.

0:48:56 SC: Yeah.

0:48:57 KH: We can go into our own backyard, our own solar system backyard and just look in the ice and in the oceans of these ocean worlds of the outer solar system and say, “Hey, you got life? Life originate there?” And I do think these worlds are great places for second independent origins of life.

0:49:18 SC: So let me see if I have the picture. We know that certain things are necessary, the compartmentalization, the replication, the metabolism. We know they’re all necessary, but we don’t know the order or what led to what or anything like that, there’s various hypotheses. And part of the problem is even though we have a lot of life currently on earth, and even very simple organisms, it’s still a stretch to say what the first organisms were like, right?

0:49:41 KH: That’s right.

0:49:41 SC: We can’t definitely say that. So if we were able to look at other environments where there was also the possibility of these things going on, we could learn a lot.

0:49:50 KH: That’s right, and this is where… Oh, it’s just beautiful. We have a chance to look at what is contingent and what is convergent in biochemical evolution. Is DNA, RNA and protein chemistry the only game in town? If you run the clock again, does biochemistry converge on that solution?

0:50:15 SC: So what’s the answer?

0:50:17 KH: We gotta go to Europa.

0:50:17 SC: No, but what do you think? Do you think that DNA is necessary for life?

0:50:21 KH: So here’s what I can say with confidence, that… I love Mars. I love doing Mars exploration. It’s a beautiful world.

0:50:31 SC: But.

0:50:32 KH: But there are two things. First and foremost, our search for life on Mars is primarily a search for life in the past as preserved in the rock record. And large…

0:50:45 SC: Because there was running water on Mars, but there’s not now.

0:50:46 KH: Right, Mars had a wet and watery past and warmer past. And we think that Mars was definitely habitable. And I, for one, think that Mars, most likely, had life. Based on what I know of life on earth, I would predict that if the origin of life is easy…

0:51:05 SC: It’s a big if. Yeah, okay.

0:51:08 KH: Big if, right? But if you grant me that then Mars had life and there should be evidence of life on Mars.

0:51:13 SC: Yes. I would argue that we have strictly zero information about whether it was easy or hard.

0:51:17 KH: One hundred percent.

0:51:18 SC: Because our existence does not count.

0:51:20 KH: That’s right. But what’s the best way to turn that from zero to non-zero?

0:51:24 SC: Right. Look somewhere else for [0:51:25] ____.

0:51:26 KH: Exactly.

0:51:26 SC: That’s right. Okay. But you did you say you bet that Mars probably had life.

0:51:32 KH: Right.

0:51:32 SC: Do you think… We have a lot of evidence that it had the conditions.

0:51:35 KH: Right. Now the problem is that… Let’s say we go to Mars and we find some beautiful rocks and beautiful stromatolites, rocks that preserve the… Perhaps the microbial fabric or fossils. DNA, RNA, large information molecules do not last for a long time in the rock record. Now, in the subsurface of Mars there could be living life and I would be thrilled to go and explore Mars for that. But even if we found DNA based life on Mars, Occam’s razor would still tell me, “I can’t quite count on that as a second origin.” Because Earth and Mars…

0:52:18 SC: Too close.

0:52:18 KH: Too close. Neighbours, planetary buddies, just sending stuff back and forth.

0:52:22 SC: Swapping bodily fluids.

0:52:24 KH: Yep. Throwing the baseball, asteroid impacts, ejecting stuff.

0:52:29 SC: And in fact we have meteorites from Mars here on Earth and people look for evidence of life in them.

0:52:34 KH: Exactly. This isn’t just speculation, we actually have examples. The outer Solar System is much harder to say, contaminate with Earth rocks or Mars rocks. And so if we went to Europa or Enceladus or a Titan with a robotic vehicle and we found DNA based life, that to me would strongly point to a second independent origin with a convergent biochemical evolution towards DNA. And that is just… Would be phenomenal.

0:53:17 SC: Can you name at least one plausible alternative to DNA?

0:53:20 KH: No.

0:53:21 SC: No. Okay.

0:53:21 KH: I wish I could.

0:53:22 SC: But, we admit that that might just be our lack of imagination.

0:53:26 KH: That’s right. Now, Steve Benner in Florida has done some beautiful experiments on adding additional base pairs. So, there are some interesting synthetic biology experiments that have been done.

0:53:41 SC: I’ve heard about that. I think that Kate Adamala also talked about this. Yeah.

0:53:43 KH: Yeah.

0:53:43 SC: So the four… The GCTA might not be the whole alphabet?

0:53:47 KH: That’s right. It’s not the whole alphabet in terms of you can push, at least in the lab, the DNA molecule to have added base pairs. Is that biologically acceptable?

0:54:01 SC: Yeah.

0:54:02 KH: We don’t know those experiments. It hasn’t gone from cool chemistry to actual biology, but it’s really compelling.

0:54:10 SC: Okay. So we will at least have the ability to ask… So there’s one thing that we could learn. Obviously, the fact that if we learn that there’s life elsewhere, that’s the big thing. The second thing is it DNA, RNA similar kind of chemistry? I’m sure that some people in the audience are thinking, “Isn’t it too cold out there to have life way beyond the orbit of Mars?”

0:54:30 KH: Yeah, yeah, yeah.

0:54:31 SC: “Why are we even talking about these moons? They’re not in the Goldilocks Zone.”

0:54:35 KH: That’s right. So this comes back to the fundamental game changing aspect of these ocean worlds beyond Earth. Europa, Ganymede, Callisto, three moons of Jupiter. Titan and Enceladus, two moons of Saturn, and even Neptune’s curious moon Triton. These are worlds where liquid water is maintained and sustained in large part through tidal dissipation, tidal energy pumping and stretching and then heating these worlds from the interior.

0:55:13 SC: But these moons are orbiting gi-humongous planets.

0:55:16 KH: Exactly. So everybody knows and loves the tides on Earth. On Europa you’re dealing with a… Europa is about the size of our moon but Europa is orbiting Jupiter which is some 318 times as massive as the Earth. And Europa’s just getting tugged and squeezed like a ball of taffy. And the predictions are that if you stood on Europa you might rise and fall in the diurnal cycle, the daily up and down, which is equivalent to 3.55 Earth days. You might rise and fall with the tides about 30 meters or nearly 100 ft per Europan day.

0:56:00 SC: Alright, so take your Dramamine if you’re gonna visit Europa.

0:56:02 KH: Exactly. So…

0:56:03 SC: But that’s… Yeah, that’s injecting a lot of energy into the ice. It would almost crazy to think that some of it wouldn’t heat up and make a liquid water.

0:56:09 KH: That’s right. So the traditional habitable zone, the way we normally thought about planets in the early days of astronomy and planetary science was that the habitable zone is defined by the distance from your parent star, and habitability was conceived of as having a liquid water ocean on your planet surface, in contact with a nice atmosphere, and then you’re off to the races.

0:56:34 SC: Yeah.

0:56:35 KH: And in that kind of conception of the habitable zone, you had this, at least in our solar system, Goldilocks scenario, where Venus, Earth and Mars were kind of like those little bowls of porridge in the Goldilocks story. Venus is too close to the Sun, gets too much energy any water that it once had got baked out, it’s too hot. Mars, too far away, too cold, any water that it once had froze up. Now, the story of Venus and Mars, is much more complicated.

0:57:08 SC: It turned out to be more complicated. Atmosphere’s matter.

0:57:09 KH: You’re right. And they at points in the past did have liquid water. But at least in the modern epic, planet Earth is in that Goldilocks Zone where it has liquid water on the surface in contact with our nice thick atmosphere. And the reason we have that ocean, our ocean is because of energy from the sun, from our parent star.

0:57:34 KH: What these ocean worlds of the outer solar system are teaching us, is that there’s another way to get the business of maintaining and sustaining liquid water done. Tidal energy dissipation in part coupled with radiogenic decay in other words, the decay of heavy elements, uranium, thorium even potassium provide enough internal heat, so as to keep some liquid water liquid. And on Europa we think that the tidal energy dissipation could lead to an ocean, a global liquid water ocean of some 100 kilometers in depth, that’s 60 miles in depth, that’s 10 times the depth of the Mariana Trench, the deepest region in our own ocean. And so, that tidal energy is really changing the way we think about habitable environments in our own solar system.

0:58:38 SC: Would it almost always be the case that throughout the universe, not just the solar system as we know it, these kinds of oceans… So basically, there’s two possibilities, one is: You’re heated by the star, and you’re like the Earth, the other is you’re a satellite of a giant planet and regardless of what the star is doing you’re heated by these tidal stresses.

0:58:57 KH: Yeah.

0:58:58 SC: Would those, would that second option always come with an ice sheet around it?

0:59:03 KH: Yeah, so for the most part, and the answer is yes, I’ll get to Titan in a second ’cause Titan also has an atmosphere. But I do wanna give the heavy elements the credit that they’re due, and radiogenic decay can last for a long time. Pluto, and we’re still kinda understanding Pluto as this beautiful dynamic world, who cares if it’s a planet, or a dwarf planet or what have you. I just love it as a world. Pluto may well have a liquid water ocean, perhaps with some ammonia or other anti-freeze, mixed in, and if Pluto does, in fact, have a liquid water ocean, it is sustained through the trickling out of heat from the decay of these heavy radiogenic elements.

0:59:52 KH: Coupled with that there’s interesting thermal physics associated with ice shells, all of these ocean worlds rely on ice being a good insulator. Ice is a great blanket, but there are different kinds of ice, that serve as better blankets than others. So on Europa, Enceladus that’s ice one, ice that we can grab out of our freezer, the sort of traditional ice. And if you’ve ever built a snow fort or walked into an igloo or something like that you know that, you can actually stay pretty warm if you’re surrounded by frozen water.

1:00:37 SC: I’m told that it’s the snow that does the insulating not the ice.

1:00:40 KH: Well, yes, but even ice itself…

1:00:44 SC: My vast igloo experience coming in here.

1:00:47 KH: Yes, so snow, the porous material is definitely better, but even ice itself…

1:00:52 SC: Okay. Gotcha.

1:00:54 KH: Is not a tremendously good conductor of heat. But then there’s this other aspect, clathrates. So a kind of ice that reconfigures to trap various molecules. Clathrate means cage or to en-cage, and so on Pluto, the ice of Pluto, the water ice is mixed with nitrogen and methane and perhaps some ammonia and stuff, and that mixture may help Pluto have a better thermal insulation to keep its ocean from…

1:01:30 SC: There could be life on Pluto, is what you telling me?

1:01:32 KH: Well, so, okay…

1:01:33 SC: If we let ourselves dream a little bit.

[chuckle]

1:01:35 KH: Right, right, so the… No.

[chuckle]

1:01:40 SC: Cause I saw the ‘Rick and Morty’ episode, they’re very upset that they’ve been demoted from planet status.

[laughter]

1:01:43 KH: Ooh, I’ve not seen that. So, where Pluto kind of falls short is in… The way I like to frame this is, the keystones for life are you need liquid water, you need the elements to build life and to the best of our knowledge, life as we know it, at least needs a smattering of 54 elements from the periodic table. The most significant of which are the CHNOPS, the Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus and Sulfur, then you need iron and some heavy elements. Then the third key stone is you need some energy, and that comes back to Gibbs free energy, you need some chemical disequilibrium.

1:02:25 KH: Europa and Enceladus and perhaps even Titan I think, satisfy those three keystones. I think the oceans of Europa and Enceladus are mixing with a rocky sea floor, that rocky sea floor gives rise potentially to hydrothermal vents, which gives rise to the elements needed to build life and the energy needed to power life. Pluto might have a lot of the compounds and water needed for satisfying the liquid water keystone and potentially the energy keystone. Methane as I mentioned, is a good molecule and so life could eat or make that. But part of what I worry about with Pluto is whether or not it’s got enough of the heavy elements, whether or not it’s got enough…

1:03:12 SC: ‘Cause it’s so tiny.

1:03:13 KH: Yeah.

1:03:14 SC: Yeah.

1:03:14 KH: But its density is sufficient to indicate that there’s gotta be some rock for action.

1:03:19 SC: You seem to hint that Titan was a weirdo also.

1:03:22 KH: Titan is my favorite place to search for weird life.

1:03:27 SC: Weird life?

1:03:28 KH: Life, unlike life as we know…

1:03:30 SC: I wanna qualify any life that is not on Earth, as pretty weird, but you mean substantially different?

1:03:35 KH: That’s right. And here’s where coming back to an operational approach to searching for life, here’s where we can start to slice and dice things in a very pragmatic way. When I look out at Europa and Enceladus and… Titan also has a liquid water ocean beneath its icy shell. And that ocean may be mixing with rocks. I can generate an hypothesis about the prospects for carbon and water-based life out there in our solar system.

1:04:13 SC: Right.

1:04:14 KH: And that hypothesis is founded on observations of life here on earth. So, life on earth is water and carbon-based. Water is the solvent, carbon is the key building block. And we can look at all the extreme environments on earth, Antarctica, the hydrothermal vents, etcetera. And they’re saying, “Okay, water and carbon-based life is tenacious as… “

1:04:39 SC: There’s always a little bit of life everywhere. On Earth anyway.

[chuckle]

1:04:41 KH: Right.

1:04:43 SC: Whenever people say that, I feel like raising my hand and saying, “It’s not equally hospitable to life, all these different environments.” Right? I mean, there’s less life…

1:04:52 KH: That’s right.

1:04:53 SC: In the desert, in Antarctica than there is in the rain forest.

1:04:55 KH: One hundred percent.

1:04:56 SC: Okay. But there’s a little bit of life. There’s little microbial life everywhere.

1:05:00 KH: That’s right. And please be aware that oftentimes when I talk about the search for life and life on earth, as beautiful as the Penguins were in Antarctica, or the giraffes of the African savanna are, etcetera. Multi-cellular life, metazoans, these larger creatures, are boring as hell.

[laughter]

1:05:24 KH: And the reason for that is ’cause we all just represent the tiniest of twig on the vast genetic tree of life.

1:05:35 SC: Yeah. Not a lot of diversity within the metazoans.

1:05:38 KH: Right. For all of the shaped diversity, we all are heterotrophs, where we eat carbon compounds, and breathe oxygen to essentially do a fancy camp fire burn. From penguins, to sea slugs, to giraffes, we’re all doing the same metabolic process.

1:06:00 SC: Whereas microbes…

1:06:00 KH: Microbes, holy cow.

[laughter]

1:06:03 KH: It’s, they have figured out a way to eat anything and everything. From acids to bases, and doing it at high pressures, low pressures. You name it.

1:06:12 SC: Yeah. Which is extraordinarily reassuring for the search of life, for life elsewhere.

1:06:15 KH: Exactly. And so, when I talk about the diversity of life on earth and how we use our study of life on earth to provide a bridge for assessing habitable environments beyond earth, it’s in that microbial context.

1:06:29 SC: Okay. We’re not gonna find penguins on the ice shelf of Europa?

1:06:34 KH: Well, they’re birds. I mean, come on.

[laughter]

1:06:37 KH: I wouldn’t rule out octopi or things like that.

1:06:39 SC: Don’t distract from Titan. We’re going into the weird life.

1:06:45 KH: So we can make an hypothesis about water and carbon-based life on Europa, and Enceladus and even within the water ocean of Titan. And that water and carbon hypothesis is rooted in our understanding of how microbial life works on Earth. Those oceans. If you transported microbes on Earth to those worlds, the evidence that we have today would indicate that those microbes could survive. So we can design spacecraft to test that hypothesis of water and carbon-based life. Water is the solvent, carbon is the building block. Titan, along with having this deep ocean beneath its icy crust, also has this crazy methane cycle. The surface temperature and pressure of Titan. So the atmosphere is thick on Titan. It’s primarily, nitrogen. But the temperature and pressure of Titan is such that methane exists in all three phases. Solid, liquid and…

1:08:00 SC: Triple point.

1:08:00 KH: Triple point. Exactly. So solid, liquid and gas. Similar to where earth resides in terms of its surface being at the triple point of water. And so Titan’s got these seasonal cycles going on. And it’s raining down methane, and ethane, and potentially, larger organics. And on its surface, the Cassini spacecraft helped reveal all of these methane-dominated lakes and seas. And this is where things get weird.

[laughter]

1:08:31 SC: A lake of methane.

1:08:33 KH: A lake of methane.

1:08:33 SC: It’s already pretty weird. Yeah.

1:08:34 KH: Yeah. And so, could you have weird life on Titan where the solvent, the parts of life get mixed and combined on Earth. That’s water. Where the solvent is liquid methane? I don’t know the answer to that question. Nobody really does.

1:08:58 SC: No.

1:09:00 KH: Chemically, the difference between liquid methane and liquid water is that water is a polar solvent and methane is non-polar. Water molecules have a slight positive and negative charge on them due to the way in which the electrons arrange themselves in the two hydrogens and oxygen. Methane does not have that.

1:09:23 SC: Methane is like a perfect little tetrahedron.

1:09:25 KH: Yeah. And so, in chemistry, like dissolves like so water is very good at dissolving other polar compounds. That’s in part what allows the chemistry of our biology to work. And of course, as you know, from mixing oil and water, oil is, for the most part, non-polar, and it…

1:09:46 SC: Yeah, separates out.

1:09:46 KH: Separates, right.

1:09:47 SC: And that’s kind of useful.

1:09:48 KH: That’s kinda useful, right? Now, if you flip the tables and have a non-polar solvent like methane, could you get enough interesting chemistry done to really drive biochemistry?

1:10:02 SC: Yeah.

1:10:03 KH: There is water there.

1:10:03 SC: It would be different.

1:10:05 KH: It would be different. And thankfully, last year, last summer, if my memory serves, everything’s a blur. NASA selected a mission to get back out to Titan. It’s this phenomenally exciting mission called Dragonfly, PI’d by my friend Zibi Turtle and it’s out of the Applied Physics Laboratory in Maryland. This is a mission which hopefully will launch in the mid 2030s. I’m sorry, it’ll get out to Titan in the mid 2030s.

1:10:43 SC: Okay. I was gonna say that’s way out there. It’s hard to plan that far, but okay.

1:10:46 KH: Too many missions. So, it gets out to Titan in the mid 2030s, parachutes down through the atmosphere, gets rid of its heat shield and all that, and then starts turning on these rotors. So just like the quad drones that you see and somewhat annoyingly…

1:11:07 SC: Yeah, we’re sending a drone to Titan.

[chuckle]

1:11:08 KH: Right. So we’re sending a drone…

1:11:10 SC: We’re sending one to Mars, also I know.

1:11:13 KH: That’s right. Now, the Mars helicopter has got… It’s just got one set of rotors on it, the Titan Dragonfly mission is much larger, it’s the size of a dining room table. And along with looking at the geology and geochemistry of Titan, looking at the dunes and all of the interesting things that are happening in the world of Titan, we’re also going to be looking for signs of life.

1:11:44 SC: If it gets shot down by ornery locals that’ll be a great success, right?

1:11:47 KH: As long as we get a picture of them before they shoot us down.

1:11:49 SC: Is there a… Yeah, there’s a camera on the drone I hope, right?

1:11:51 KH: So… Yeah, so… It’s just a beautiful mission. And what’s fun about Titan, my friend and brilliant scientist and engineer Ralph Lorenz has done this calculation where… Now, if you could survive on Titan as a human, a lot of caveats there.

1:12:10 SC: Yeah.

1:12:11 KH: And have your own Icarus wings, you could fly.

1:12:15 SC: You could fly ’cause of low gravity, thick atmosphere.

1:12:17 KH: Exactly.

1:12:18 SC: I’m glad that calculation was done. Yeah, tax payer dollars at work.

1:12:21 KH: Yes.

[laughter]

1:12:23 KH: So, but that in part helped lead to the viability of doing a rotor craft mission that would land on Titan in search for signs of life.

1:12:34 SC: Wow.

1:12:34 KH: Now, primarily with that mission, and I’m a co-investigator on that mission, we’ll be looking for evidence of perhaps water-based life that has been erupted from below, but we’ll also have our eye towards the discovery driven aspect of science.

1:12:56 SC: Yeah. Who knows? Right.

1:12:57 KH: What if… Yeah, what if there is life that has originated and evolved in these methane-ethane rich lakes.

1:13:05 SC: Is the trick that we don’t even know how to look for that? So, we have to design an experiment that’s actually looking for certain chemicals.

1:13:13 KH: Right. And, here again we come back to that issue of specificity, life being very selective. We think that even if life is based on some chemistry, unlike life as we know it. Even if life is weird compared to the liquid water and carbon based life that we know, it will still have that selectivity and specificity where it is built on fundamental chemical units.

1:13:43 SC: It’ll like certain molecules more than others.

1:13:45 KH: Right. And so if you do an inventory with something like a gas chromatograph, mass spectrometer, you might see a pattern, even in weird life, that distinguishes it from the abiotic processes that are just random and link together atoms by atoms.

1:14:04 SC: I suppose we should put in a word for Enceladus, that’s the other place we should look.

1:14:08 KH: Enceladus is phenomenal.

1:14:10 SC: Yeah? When I hear people talk, there are more… There are certainly people who think that of all these Enceladus is the one that is the most likely to have life. I know you might not be in that, but there are Enceladus partisans. [laughter]

1:14:22 KH: 100%. And these worlds are all beautiful and meritorious of exploration.

1:14:31 SC: Like your children, yes. You love them all.

1:14:33 KH: Right. Enceladus, just to calibrate… Enceladus is the new kid on the block, the new shiny object. And so, the Cassini mission just ended and we have a lot of new data on Enceladus. And so, there’s a lot of excitement about Enceladus. And Enceladus was very generous.

[laughter]

1:14:57 KH: Wonderfully so. So Enceladus, coming back to Europa and the discovery of Europa’s ocean, that took that kind of detailed physics. The Galileo spacecraft did not observe any plumes erupting out of Europa’s ice shell. We now think we’ve got some curious evidence using the Hubble Space Telescope and some Galileo data for water rich plumes coming out of Europa. But when Cassini flew by Enceladus, bang, there it was. These plumes erupting out of the icy surface of Enceladus. Now initially, skeptics, myself among them, viewed those plumes as perhaps just a de-volatilization of the ice and clathrates perhaps and other things. We see jets of material elsewhere in our solar system, we see comets producing jets. So, early on, some of the evidence for Enceladus could have been explained by these plumes being analogous to cometary jets where something’s just causing the out gassing. But as the Cassini spacecraft flew by and tasted the plumes of water, it also revealed that the plumes have methane and carbon dioxide, a smattering of organics. And for me what really turned the tide was the discovery of salts.

1:16:38 SC: Okay. What’s the definition of a salt?

1:16:41 KH: So, a salt, something with cations and anions. Traditionally you think of salts as like sodium chloride, potassium chloride, magnesium chloride, magnesium sulphate, all sorts of stuff where you can take a positively charged cation and combine it with a negatively charged anion. So…

1:17:04 SC: So that means the life would be tasty.

1:17:06 KH: Well…

[laughter]

1:17:10 KH: No why are salts significant in terms of evidence for an ocean? On Enceladus if you just had water in the plumes of Enceladus, and water mixed with carbon dioxide and methane, and even small organics, those are all things that we see in comets.

1:17:34 SC: Okay. So no biggie, in some sense.

1:17:38 KH: No biggie, in some sense. Now, still very exciting.

1:17:40 SC: Still cool, but yeah.

1:17:41 KH: Right.

1:17:41 SC: But we see them in… There’s a trillion comets in the Oort cloud. [chuckle]

1:17:44 KH: Exactly. And comets, the way we get those compounds like methane and some of the organics is through the ice having things like methane and potentially ammonia, and then it gets photolytically processed. UV light from the sun processes it and produces these larger organic compounds. So at Enceladus, you could be very conservative and say, “No, this isn’t evidence of an ocean. This is just photochemistry combined with some de-volatilization of the ice shell.” But with salts, we don’t really see salts on comets.

1:18:18 SC: Right.

1:18:20 KH: Salts are a harbinger of water rock interaction, liquid water leaching through silicates.

1:18:26 SC: Right.

1:18:27 KH: So for me, when the Cosmic Dust Analyzer on Cassini returned evidence of salts, that was, “Okay, now… “

1:18:35 SC: So it’s sign of water not a sign of life, but once you have the water, then maybe it’s life appropriate.

1:18:39 KH: Right. And so, for me, the Cassini observation of the plumes and identifying that the plumes of Enceladus have salts, that gives me a large degree of confidence that we’re actually sampling plumes that are connected to a liquid water ocean below.

1:19:00 SC: And do we have evidence that there’s an icy crust on the top?

1:19:05 KH: Of Enceladus? Yeah, yeah, absolutely. That goes back to the first piece of the puzzle analogous to Europa. And I should, of course, mention that for both Europa and Enceladus, the geology of the icy surfaces point to very, very young ice.

1:19:24 SC: Which is good because…

1:19:25 KH: Right, something has to be resurfacing this material. Some sort of geological cycling of the ice with something below repaves the ice of Europa and the ice of Enceladus to give you a surface with no craters, at least.

1:19:42 SC: Right. So it’s not quiet.

1:19:44 KH: It’s not quiet, right. Now, at Enceladus, as the story would unfold from Cassini, additional evidence would corroborate the ocean hypothesis. The moving of the ice shell, a decoupled ice shell, a shell that is free-flowing and disconnected from a rocky interior. That was observed on Enceladus.

1:20:11 SC: Oh, okay, I didn’t know that. So that really clinches the deal, in some sense.

1:20:15 KH: Yeah, the elaborations in…

1:20:16 SC: There’s gotta be some liquid layer in between the ice and the rock.

1:20:18 KH: Right. And then there is also evidence of hydrogen and other things that actually point to potentially active hydrothermalism, active hydrothermal activity within Enceladus. Even things like silicon nanograins have been discovered.

1:20:38 SC: Okay. So the people who are very excited about Enceladus are not just whistling Dixie. There’s a lot of…

1:20:43 KH: Right, and I’m incredibly excited about Enceladus. Here’s the rub on Enceladus, though, if you do a one-for-one comparison with Europa. So…

1:21:00 SC: Keeping in mind, we’re talking to the PI of the Europa Lander. [chuckle]

1:21:02 KH: Well, not a PI ’cause the Europa Lander’s dead, so the…

1:21:07 SC: Oh, it’s dead?

1:21:08 KH: Well, it’s a technology development effort. It’s not…

1:21:10 SC: Well, okay.

1:21:11 KH: Planned to go to the launch pad. Yeah, in order to get it to be alive…

1:21:18 SC: But you’re a Europa guy?

1:21:19 KH: Yes, but I’m an Enceladus guy, too. I’ve published on Enceladus, not as much as Europa, but just doing a, again, a full calibration. Europa is 3,000 kilometers in diameter, that’s about the size of our moon. It’s a moon that we understand very well. We… I mean, very well, given the data available. We think that Europa has been around for the history of the solar system. We think it formed around Jupiter, as Jupiter was forming and we think that the ocean itself of Europa has been there for the history of the solar system.

1:22:07 SC: Billions of years, yeah.

1:22:08 KH: Yeah. Now, coupled with that, there’s some interesting chemistry that occurs within Europa’s ice shell and Europa’s ocean, and we’ll hopefully get to that. But Enceladus, when it comes to this issue of time, I mentioned the keystones for habitability, liquid water, elements, and energy. A fourth potentially fundamental keystone is time. “How long has that convergence of keystones been around?” Now, that may not be important, it may be that life arises very quickly, but if I were a betting man, I would…

1:22:48 SC: More time, the more chances, right? Yeah.

1:22:50 KH: Right. And so, Enceladus, there is a significant debate within the planetary science community right now about, first and foremost, “What makes Enceladus tick? What’s the full tidal energy evaluation for Enceladus and how long has Enceladus and its ocean been around?” And part of the thread that people have pulled on is the rings of Saturn. Rings are not particularly stable.

1:23:31 SC: Right.

1:23:32 KH: So the rings of Saturn, according to some again, this is a heavy debate, it’s a wonderful debate, it’s a beautiful debate, this is why we love doing what we do, but there’s a camp in the Saturn community that says the rings of Saturn tell us that something big happened not too long ago because otherwise those rings should have either collapsed, been pulled into Saturn, or been orbitally evolved out.

1:23:58 SC: Not too long ago might be millions of years, not…

1:24:00 KH: Tens of millions of years, a hundred million…

[chuckle]

1:24:02 SC: It’s not just a few decades ago.

[chuckle]

1:24:04 KH: That’s right, so the time scale is geologic and astronomic but so some of the hypotheses are that maybe the rings of Saturn were created 100 million years ago by a Kuiper Belt object, a Pluto sized object careening into Saturn and hitting a large moon breaking it up, creating the rings and a bunch of the small moons etcetera. And so there is a camp that says that the rings of Saturn are young and potentially some of the smaller moons, including Enceladus, could be quite young. And if Enceladus and its ocean are young then I kind of view Enceladus as this like fizzing Alka-Seltzer tablet that’s perhaps doing incredibly interesting chemistry but I kind of am a little more interested in a stable world like Europa that we know has been around for a long time.

1:25:09 SC: Yeah, has been. And this is good the issue of time because I would like to put everything in a bigger context here. I think that our listeners probably are happy to say that microbes are awesome but what they would really like is little aliens flying around in spaceships, and we’re not gonna find that in the solar system I think is most likely, but maybe elsewhere in the universe. So what can we learn from looking at these other places in the solar system that might tell us something about the likelihood of life, multi-cellular life, intelligent life, technological life, elsewhere in the world?

1:25:47 KH: Right, so this is a great question that actually folds into the second aspect of Europa and Enceladus. And some of the chemistry that I find very compelling about Europa that is potentially lacking on Enceladus, and this comes back to Gibbs free energy and Redox chemistry, the coupling of reductants with oxidants. And we touched on this earlier, a reductant is a compound that wants to give away an electron. An oxidant is a compound that wants to accept an electron. And the way I like to think of it… My background’s in physics and it’s just biochemical batteries and you connect the positive and negative terminal on [1:26:33] ____.

1:26:34 SC: Let the electrons flow.

1:26:36 KH: Exactly. So life alleviates chemical disequilibrium in the environment the same way that when you buy a battery at a corner store that battery will store energy for a long time and it’ll eventually trickle out, but you can put that battery in a flashlight, you can connect that battery to a circuit and allow those electrons to flow and in so doing you get work done. You get the work of shining light on something or running a little remote control car or what have you and the battery runs out a lot faster because you’ve completed the circuit. Biology does that in our environment, around Earth there are all sorts of geochemical batteries and the microbes tap into that.

1:27:26 SC: Who was the biologist who said that life is just an electron looking for a place to rest?

[chuckle]

1:27:29 KH: I don’t know but whoever it was was brilliant.

1:27:30 SC: That’s a good quote yeah, that was true. Yeah.

1:27:34 KH: My friend and colleague Everett Shock loves to say that the energy is being paid to eat a free lunch.

[chuckle]

1:27:44 KH: And so you’re getting energy out of this chemistry that’s available in the environment. And so why is this important and how does this tie back to your question of squid in Europa? Another aspect of what intrigues me about Europa potentially being a better place to search for life is the chemistry of Europa’s ocean. Hydro-thermal events, active sea floors are great places for reductants and we see that on planet Earth, hydrogen, methane, etcetera pump out of our sea floor and microbes love the reductants but if all you have is the reductant, if all you have is the negative terminal on the battery the circuit is not complete.

1:28:32 SC: Yeah. Nowhere for the electrons to go.

1:28:34 KH: Nowhere to go, right. So you need an oxidant, you need a source of oxidants and on Earth a lot of the oxidants are things like oxygen and sulfate etcetera, etcetera and we’ve got tons of oxidants. On Enceladus it’s not clear to me that it has a source of oxidants. So it could have an active sea floor pumping out the methane and hydrogen but if there’s no good source of oxidants then it might be kind of game over from a Gibbs free energy standpoint, from a what life can utilize standpoint. Europa has this beautiful but also somewhat frustrating surface environment where by merit of being embedded in Jupiter’s magnetic field, Europa’s icy surface is being bombarded by charged particle or radiation.

1:29:30 KH: Electrons, energetic electrons, tens of keV to tens of MeV electrons, ions, protons, etcetera, are careening into Europa’s surface ice. And that radiation chemistry, that radiolytic processing is splitting apart water in the simplest case, splitting apart H2O in the things like H + OH. Some of the H escapes, some of the hydrogen escapes and OH can combine with another OH to from H2O2. What is H2O2? Hydrogen peroxide, exactly the same stuff that you buy at a pharmacy to disinfect a cut.

1:30:19 KH: We know, thanks to Bob Carlson and colleagues and the Galileo Spectrometer, that hydrogen peroxide exists within the surface ice of Europa. Further to that, we also know that thanks to observations by John Spencer and Wendy Calvin using ground based telescopes, oxygen, O2, exists within the ice of Europa. And we know that things like sulfate and other very useful oxidants exist within the ice of Europa in large part from that radiation process. So if the ice of Europa is getting mixed into the ocean below, you now have this beautiful scenario where the radiation and the radiolytic processing in the surface ice creates that positive terminal of the biochemical battery. So if the oxygen, peroxide, sulphates, etcetera, get mixed into the ocean, they could be combined with reductants from the sea floor to help power life.

1:31:30 SC: Yep, okay.

1:31:30 KH: And so people often say, “Well, isn’t the radiation of Europa’s surface problematic? It can then destroy evidence for life. Is it gonna make landing there harder?” Yes and yes.

[chuckle]

1:31:41 KH: But the upshot of that radiation is that it could also be central to that third keystone of life, the energy component of life. And sulphate, microbes love sulphate, but as I mentioned oxygen is also present in Europa’s ice. Oxygen is critical to the emergence of large, multi-cellular life on Earth.

1:32:09 SC: Okay, wait, that was a big leap you just made there.

[chuckle]

1:32:11 KH: Yep, good, good. So…

[laughter]

1:32:11 SC: I mean, don’t we first need to make nuclear cells? Aren’t there…

1:32:19 KH: Right.

1:32:19 SC: On actual Earth life happened pretty quickly, multi-cellular life took forever.

1:32:23 KH: Well, I don’t know if it happened quickly. So we know that life arose… There’s debate about this, but some say that the first evidence for life is at the 3.8 billion years ago point in time, which would put it about 700 million years after the origin of the planet itself, 800 million years, somewhere in that range. More convincing evidence is available at 3.5 to 3.2 billion years ago. Then, multi-cellular life that utilizes oxygen, that doesn’t emerge until about 700 million years ago, 650 million years ago, 600 million years ago. And…

1:33:18 SC: Yeah. Took three billion years.

1:33:20 KH: Right. [chuckle] And so…

1:33:22 SC: Of little microbes bumping into each other, “Nah, I don’t wanna get together with you.”

1:33:26 KH: That’s right. And so there’s this long period of those early metabolisms and then the evolution of photosynthesis and the… People love to talk about life as Darwinian selection and survival of the fittest, etcetera, predator and prey and all that. That’s all well and good, but I also like to say that life is also largely about acquisitions and mergers.

[laughter]

1:33:57 SC: That was good. Okay.

1:33:58 KH: The symbiosis that took place, right?

1:34:00 SC: Okay, yeah.

1:34:00 KH: And it’s some what similar to economics.

1:34:04 SC: Could you say it’s about romance and love?

[chuckle]

1:34:09 KH: Go on.

[laughter]

1:34:09 SC: Swiping left and swiping right, you know?

1:34:13 KH: Love powers everything. [chuckle] So…

1:34:16 SC: But, sure, we can be capitalists about it. Good.

1:34:19 KH: Right. So acquisitions and mergers, what do I mean by that? Well, in the early days, horizontal gene transfer, there was all sorts of back and forth of like… Open source, life was open source. “You give me your code, I’ll give you my code.” Unix, Red Hat, etcetera. [chuckle] So horizontal gene transfer dominated in the early days. Then, once things really started to be…

1:34:46 SC: So, by which we mean, for those who don’t know, it’s not just that you’re a little microbe and you split and you duplicate your genes, and that’s the only thing that happens with the occasional mutation, but also literally you take in DNA from your neighbor or give DNA to your neighbor.

1:35:00 KH: That’s right, exactly.

1:35:01 SC: Which is crazy talk, but okay.

1:35:03 KH: So you’re looking at the biological GitHub and you’re…

1:35:06 SC: Yeah, forking and splitting and whatever it is you do, yeah. Merging…

1:35:11 KH: But then, as things got a little more complicated, you start to be more compartmentalized and less porous. And then instead of just grabbing genes, those early microbes started to subsume other microbes. Bacteria gobbled up other archaea or… Back then, who knows what they actually qualified as, but single-celled organisms engulfed other organisms. They acquired their capability, just like a Google would acquire a… What the heck is Google acquiring. Everything, right?

[laughter]

1:35:48 SC: Yeah, I don’t know. Some self-driving car, yeah.

[chuckle]

1:35:50 KH: So this acquisitions and mergers strategy is very true in the history of life on Earth.

1:36:00 SC: But when did that happen? When did that…

1:36:01 KH: So there’s a lot of debate about the time scales for when do mitochondria and organelle, which once upon a time was an independent microbe, when did that get incorporated? When do the cyanobacteria that really did the business of photosynthesis, when did they get incorporated into other cells and even the nucleus, there’s a lot of debate about that. And within the biology community, once upon a time, there were prokaryotes and eukaryotes, no nucleus and you’ve got a nucleus. But what the tree of life is telling us and what the study of life on Earth is telling us is that there’s a lot more to it.

1:36:55 SC: It’s not that simple. I know, yeah, it never is that simple, that’s why you should do physics instead of biology.

1:37:00 KH: F equals MA. [chuckle]

1:37:01 SC: Exactly, it’s all you need.

1:37:03 KH: But so, fast forward to the emergence of multi-cellular life, ’cause I wanna get to the squids on Europa.

1:37:10 SC: No, I know.

[chuckle]

1:37:12 KH: Thankfully, life on Earth began to utilize the energy from the sun, our apparent star and was able to start converting the CO2 to oxygen. And the initial stage of that pumping of oxygen into our atmosphere caused the ocean to rust out, essentially oxidizing a lot of the iron in our ocean, forming what we now see as banded iron formations, which are where we go to mine iron. And then once the ocean rusted out, we started building up oxygen in our atmosphere. And once oxygen levels got to a sufficient level, a few microbes started to realize that if they teamed up, they could collaboratively utilize the oxygen and some of the organics in solution to do the metabolism that we now know and love and depend upon, which is that heterotrophy of eating organics and burning them with oxygen.

1:38:21 SC: So you’re saying the transition to multi-cellularity was not just a bunch of random bumping into each other, but it was opportunistic?

1:38:28 KH: Totally opportunistic. Think about it like if we go back to the battery analogy, a lot of microbes have figured out ways to survive on the tiniest of watch battery. Methanogens and sulphate reducers operate with tens of kilojoules per mole of a negative change in Gibbs free energy. Compare that to the hundreds of kilojoules to thousands of kilojoules that are needed by larger organisms such as us. And so, yeah, it was an energetically opportunistic innovation to utilize the oxygen in the air as the oxidant and organics in the environment as the reductant.

1:39:17 SC: So Europa…

1:39:18 KH: So on Europa, this in my dream of dreams.

1:39:23 SC: Yeah, it’s late in the podcast we can dream a little bit. Let’s let our hair down here.

1:39:28 KH: So as I mentioned, the radiation processing produces oxygen in the ice and the ice of Europa is geologically young. The surface of Europa, globally, is tens of millions of years old. That’s a flash of a pan, geologically speaking. That’s comparable to the age of our oceanic crust here on Earth and those are some of the youngest rocks on Earth. So on Europa, if the ice is cycling into the ocean directly and that’s a significant if, we don’t know much about the conveyor belt type of motion of the ice and what may or may not be happening, subduction, subsumption all sorts of things like that. But if the ice is delivering oxygen to Europa’s ocean on a relatively short geological time scale, you could have enough oxygen in Europa’s ocean to support organisms on Earth. You could get those concentrations that are found in some of the O2 minimum zones in Earth’s ocean, and there you find polychaete worms and shrimp.

1:40:43 SC: So the motivation from multi-cellular life might be there on Europa.

1:40:45 KH: It could be there, even without the sunshine.

1:40:47 SC: Yeah. So we should tell the audience, you were a consultant on the movie Europa Report.

1:40:53 KH: Correct.

1:40:53 SC: And I’m not gonna give away anything, except that, yeah. They go to Europa and they find life.

1:40:58 KH: Yeah.

1:41:00 SC: Boy do they find life, yeah.

1:41:00 KH: Yeah. And if you haven’t seen the Europa Report the writing team, the production team, the actors, etcetera, that was a great project to be a part of, and you and I have worked on various movie consults together and had a lot of fun.

1:41:17 SC: That one was closer to the real science than most of the ones we’ve done.

1:41:20 KH: Well, so, you know, I think you and I worked on Thor together.

1:41:24 SC: Thor, yeah.

1:41:25 KH: With Kenneth Branagh and we can come to that. But for the most part, I don’t know what your opinion is, but we can add suggestions and try and guide the vector of where it will go but at the end of the day, it’s no big rub on us if they don’t actually take our advice. With the Europa Report, my colleague Steve Vance and I were like, “Oh well, this is really close to home.” And so… [chuckle]

1:41:51 SC: “We care a little bit more about what’s going on here than we do on Asgard.”

1:41:54 KH: “And so if you’re gonna do this, can you at least commit to us that you’re gonna try and get things right?” And they did. They were absolutely brilliant.

1:42:04 SC: Yeah, I love the movie. It was a low-budget movie that really did a very good job.

1:42:07 KH: Made for something like $8 million dollars the zero G stuff that they did in most large budget films.

1:42:16 SC: Some good movie magic.

1:42:17 KH: Use a Vomit Comet to get zero G. The brilliance of that team. They used green yoga balls and had the actors on their backs and on their stomachs rolling on green yoga balls in the little capsule to give the appearance of floating in space. I love that clever way of going about things.

1:42:42 SC: I hope that there are the squid in Europa, I think that would be very cool. But let’s sort of wrap things up with the lessons for beyond the solar system that we might get from the solar system. One obvious thing is, if we found… Let’s say that we really do a good job at looking at Europa, Enceladus, Titan, and we either find life on all of them or on none of them. How willing will you be to then extrapolate that to lessons for the rest of the universe?

1:43:12 KH: Right. This is a great and very important question. If we do a robust exploration of the alien oceans beyond Earth, Europa, Enceladus, Titan, Pluto, Triton, you name it, we will either find evidence of life or not. I think both answers are equally profound. So if we find life, then it’s kind of off to the races. The origin of life is easy. Life should arise wherever the conditions are right. Europa type worlds are potentially ubiquitous in our universe and we could live in a biological universe. Conversely, if we don’t find evidence of life on these worlds that gives us important information on hypotheses for the origin of life. That would tell me that, “Well, the origin of life most likely does not occur around hydro-thermal vents and it does not occur in icy environments.” And we didn’t talk much about origins and ice, but that’s a whole another thread.

1:44:25 SC: Or it just almost never occurs at all.

1:44:28 KH: Or it almost never occurs. But in the case of not finding life in these alien oceans beyond Earth, I would say then that the origin of life does require continents and the warm tide pools and the types of…

1:44:44 SC: Yeah, that would be evidence for that, yeah.

1:44:45 KH: Right. So Europa has no continents, there’s no rivers and tide pools. So we can add to the information content even with a null result. And granted, a null result would be hard to come by, you’d have to explore pretty thoroughly, but…

1:45:02 SC: But you’re willing to spend that money.

1:45:03 KH: Well, and the other thing is that Europa’s ocean, Enceladus’ ocean, these are global oceans and so if you sample in a few places, the ocean flows around and you can at least have some confidence in the connectivity. So then extrapolating to our galaxy and the universe more broadly, if we don’t find life in our own backyard, if we don’t find it on Mars or within these alien oceans, then I think we start to enter a realm where life on Earth is a biological singularity. It operates in the truest form of singularity where our evidence for life on Earth would say that it is a layer on top of biology and that Gibbs free energy, all these things should… The laws of physics.

1:46:00 SC: On top of chemistry… On top of geology, sorry you said on top of geology.

1:46:05 KH: Physics is the base, chemistry and geology are the layer there, and then biology is sort of a fancy layer.

1:46:12 SC: So you’re saying that we have enough other opportunities to find life in the solar system, that if we don’t, it really does suggest that maybe it’s not that ubiquitous.

1:46:20 KH: That’s right and that continents and Earth-like worlds are required for the origin of life. Now, Mars serves as a good template for that. If we do find evidence of life on Mars, it could be a standard bearer for life existing on another world. But coming back to what we talked about earlier, I would be reluctant to endow it with a second origin just because of…

1:46:52 SC: Yeah, that’d be tricky, especially if it were very similar.

1:46:54 KH: Exactly. And so, yeah. Then we get to this issue of biological singularity. The laws of physics as we know it, the laws of chemistry, geology, etcetera, lead to chemical disequilibrium, Gibbs free energy being a motivator for the metabolisms of life, and life being kind of a tool that the universe uses to increase entropy and to accelerate us to that entropic death. But if it arises only on Earth, perhaps something else is sparking the fire.

1:47:37 SC: So what is your… Final question. What is your favorite solution to the Fermi paradox of why we have not seen life elsewhere? We could imagine that life is rare, that multi-cellular life is rare, that technological life is rare, or that technological life is everywhere and they’re just not talking to us. Do you have a favorite one of these?

1:47:58 KH: Right. So I’ll answer this in two parts. First and foremost, and I worked at the SETI Institute many years ago and one of my favorite experiences as a young scientist was approaching Frank Drake after a seminar. And I was a young intern up at NASA Ames at the time and… “Dr. Drake?”

[laughter]

1:48:21 SC: Of the Drake Equation fame, yes.

1:48:24 KH: I said, “I’ve long been thinking about all this stuff and it’s a honor to meet you,” and all that stuff. And I said, “Well, what do you think would be the next intelligent species on planet Earth if you fast forward the time scales for what’s happening on planet Earth?” Without missing a beat he said, “Squirrels and raccoons.”

[laughter]

1:48:48 SC: Really? Okay.

1:48:50 KH: I thought he was gonna say dolphins and whales and all these things.

1:48:54 SC: Chimps or squid.

1:48:56 KH: Right, but squirrels and raccoons in part because they are living and surviving and developing in such close proximity to the intelligence that currently exists.

1:49:05 SC: So they’re being selected for cleverness.

1:49:07 KH: Right, right. And that’s why I love that answer. But with respect to the Fermi paradox, my primary answer is we just have not done enough searching. I think it’s a poorly framed paradox.

1:49:26 SC: Well Fermi, as I understand it, the original version of the paradox was if you could build self-replicating probes, they could fill the galaxy pretty quickly and we would notice that.

1:49:37 KH: Right. The Turing machines, etcetera. You could populate the galaxy quickly, would we see that? That is kind of… People kind of tuck that under the rug. So I happen to think that the center of the Milky Way Galaxy is like Manhattan. We’re eight and a half kilo parsecs out from the galactic bulge, we’re in the boon docks. We’re like in northern Canada trying to connect to the internet and we’re saying, “Why can’t we dial up?” Fermi paradox is like, “Why doesn’t the internet exist?” “Oh well, it does, you’re just not in the right place, you haven’t connected long enough.” And so I do think that…

1:50:34 SC: So it’s there, but we haven’t found it yet. That’s your favorite.

1:50:37 KH: Well, I think we haven’t searched in enough ways and in enough clever ways. And by clever, I mean we’ve gotta cover more of the radio spectrum but we also need to think about optical SETI, we need to think about ways in which advanced civilizations would communicate with each other. So answer A is we haven’t searched enough. Answer B comes to that, “Would we really see them?” And one of my favorite answers to this is the dark forest. If you read The Three-Body Problem, that trilogy of books that goes into contact with alien civilizations, etcetera. I highly recommend that trilogy. And I wanna talk about it, but I don’t wanna spoil it for people.

1:51:32 SC: Don’t spoil it. Don’t spoil it, but…

1:51:33 KH: Yeah. Won’t spoil it.

1:51:33 SC: It is worth reading, I agree.

1:51:36 KH: But basically, the point is…

1:51:38 SC: Cixin Liu?

1:51:40 KH: Correct. You probably have the pronunciation much better than I…

1:51:43 SC: Well, close anyway. Sorry.

1:51:44 KH: The basic point is, it’s not always advantageous to broadcast your existence. And so, we kind of take it for granted that of course if life’s out there it’s going to…

1:51:57 SC: It’ll wanna talk to us.

[chuckle]

1:51:58 KH: Right. So, that’s my part A and part B answer to the Fermi paradox.

1:52:04 SC: Good. Well, we’ll get some data once you get your spacecraft up there. And maybe around 2030, we’ll have you back on the podcast to talk about results from your lander.

1:52:14 KH: Potentially sooner than that. For the love of God, we’ve known each other for a long time. But listen, like think about it. The year you just mentioned 2030, 2035, 2040 even, how exciting is that?

1:52:29 SC: Oh, it’s very exciting. This could be the century.

1:52:29 KH: Within the next few decades, exactly. Whether it’s Dragonfly going to Titan, Clipper going to Europa, hopefully 