Can tardigrades survive on the Moon?

Daniel and Kelly talk about the extraordinary ability to tardigrades to survive extreme conditions, and ponder whether those abilities have kept them alive after a space craft carrying them crashed into the surface of the Moon. See omnystudio.com/listener https://omnystudio.com/listener for privacy information.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Daniel Whiteson?

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• 1:11Kelly Weinersmith?

  Water masts, moss piglets, tardigrades. They go by many names, but I think the one thing we can all agree on is that they're pretty much indestructible, right? I mean, these poor, teeny-tiny creatures have been exposed to all manner of unpleasant stimuli in the lab. They've been frozen to near absolute zero, heated up to way past boiling, irradiated, squeezed at pressures you'd experience 180 kilometers below Earth's surface, exposed to the vacuum of space, and shot into sandbags. If tardigrades ever become large and sentient and start looking for retribution, we're in a lot of trouble. But the good news for tardigrades is that they survive most of these experiences surprisingly

• 1:56Kelly Weinersmith?

  well. How do they do it? Well, that's what we're going to discuss today. And by the end of the episode, we'll answer a question that has no doubt kept you up at night. Are those tardigrades that crash-landed on the moon in 2019 still alive? Let's find out. Welcome to Daniel and Kelly's Extraordinary Universe.

• 2:28Daniel Whiteson?

  Hi, I'm Daniel. I'm a particle physicist and I don't like a lot of biology, but I do like hearing about critters that only poop when they molt.

• 2:36Kelly Weinersmith?

  Wait, wait, wait, wait, back up, back up. I'm Kelly Weinersmith, a biologist. Did you just say that you don't like a lot of biology?

• 2:43Daniel Whiteson?

  You know, there's a reason I'm in physics. The biology's all weird and messy. I mean, it's wonderful and fascinating, but sometimes I just feel like there aren't really any hard answers.

• 2:53Kelly Weinersmith?

  But you guys haven't reconciled quantum mechanics or general relativity yet. How dare you?

• 3:00Daniel Whiteson?

  But there is a hard answer. We don't have it yet, but I think one day eventually humans or some clever aliens will figure it out. Biology, I just don't even know if there's an answer.

• 3:11Kelly Weinersmith?

  I mean, I can't argue with that. I'm not sure there's an answer for a lot of this stuff either, but I still think that's exciting. And also, I will note that you said that they only poop when they molt. There are probably more than 1,300 species of tardigrades. I don't know that it's true that all of them only poop when they molt. I think some of them might just poop. Like the rest of us.

• 3:34Daniel Whiteson?

  All right. Well, I am fascinated. I want to hear more about it because I'm sure there's an answer to at least this question of when do tardigrades poop?

• 3:41Kelly Weinersmith?

  I mean, it's going to depend on the species, but yes. All right. So we had an amazing listener question. Let's go ahead and listen to that now.

• 3:50Speaker 04

  Hey, Daniel and Kelly. Question about tardigrades, those little water bears. Just curious, what is it about them that allows them to survive in basically any environment? I've heard that there's even some on the moon. And as far as I know, NASA hasn't engineered little space suits that small. So yeah, just curious, what is it about their physiology that allows them to survive? Thanks. Also, go Virginia.

• 4:17Kelly Weinersmith?

  Okay, so first off, I laughed out loud imagining NASA engineering tiny space suits for the tardigrades. That was amazing. Thank you for this question. And go Virginia.

• 4:28Daniel Whiteson?

  I'm sorry, this question is disqualified. I mean, obviously they have no credibility from the get-go.

• 4:33Kelly Weinersmith?

  Daniel, I did 10 hours of research for this episode. We are not dropping this episode.

• 4:37Daniel Whiteson?

  And did you discover that you have to be a tardigrade to enjoy the climate of Virginia?

• 4:41Kelly Weinersmith?

  Everybody enjoys the climate of Virginia. Tim and I agree on that at least. There was a little bit of snow falling the other day, and I felt highly festive. And I know that there are some places of California that have snow, but only some.

• 4:56Daniel Whiteson?

  Well, you know, tardigrades can live on the moon. They can live deep underwater. They can survive when it's dry. They can even survive Virginia winter.

• 5:04Kelly Weinersmith?

  Well, hold on, can they live on the moon?

• 5:06Daniel Whiteson?

  I don't know.

• 5:07Kelly Weinersmith?

  That's the whole point of this episode, trying to find the answer to that question. So should we dig in?

• 5:12Daniel Whiteson?

  Yes, Kelly, tell us, what are these tardigrades? What do they look like? Where do they stand in the context of all biology? And what do we know about where they can actually survive?

• 5:21Kelly Weinersmith?

  Okay, all right. Well, so it'll take me an hour or so to give you that answer. But let's start with reiterating that there are probably more than 1,300 species. In fact, it's under Kingdom Animalia, there's something like 30 phylum. And tardigrade, they're their own phylum.

• 5:37Daniel Whiteson?

  Whoa.

• 5:38Kelly Weinersmith?

  And so there's a lot of them, right? But usually you're like tardigrades do blah, blah, blah, as though there's just one species. But there's a lot more than just one species.

• 5:46Daniel Whiteson?

  And the fact that they're so high up in this tree of life, I mean, it's not just like, biologists like to organize things because they don't really understand them. It tells us something about like.

• 5:55Kelly Weinersmith?

  Wait, wait, wait. Let's listen to the particles episode and you're like, I don't know how we categorize these things. So anyway, a little hypocritical, but.

• 6:03Daniel Whiteson?

  No, seriously, I think when particle physics is failing is when it's just doing taxonomy. If we're just doing botany, then we don't really understand anything. It's when we're doing philosophy, when we're linking things together, we understand how they work underneath. And that's when I think we're really making progress. But what I want to ask you.

• 6:20Kelly Weinersmith?

  I think we need both, we'll move on.

• 6:22Daniel Whiteson?

  But what I want to ask you is how we should interpret where people have put tardigrades in this tree of life. The fact that they're so high up, does that mean that they're really their own kind of thing? They're so different from everything else? Or they have their own weird history or both?

• 6:35Kelly Weinersmith?

  Let's go with both and let's talk about why they're so unique.

• 6:38Daniel Whiteson?

  Awesome.

• 6:39Kelly Weinersmith?

  All right. So first of all, these are tiny little guys. They're multicellular, they got lots of cells. Big ones are about a millimeter long, so about the size of a period. They have this hard outer cuticle. And because it's hard, that doesn't grow with them. So they have to molt the way like nematodes and some insects will molt, the way snakes shed. Because snakes are awesome, let's get snakes in there. You probably don't even like snakes, do you, Daniel?

• 7:03Daniel Whiteson?

  You probably don't like snakes. Like, that's an outrageous thing, like, oh, yeah, snakes, rats and cockroaches. You don't like any of that, do you, Daniel?

• 7:12Kelly Weinersmith?

  Do you not like those things, Daniel?

• 7:14Daniel Whiteson?

  Well, I mean, I wouldn't want to like snuggle up with them, you know? It's not like if I see a bunch of them in my bed, I go, ooh, cozy. They're not in the same category as like kittens and bunnies, for sure.

• 7:24Kelly Weinersmith?

  All right, all right, I won't disagree with that, but I have seen some snuggly rats. But anyway, okay, hard outer cuticles, sometimes when they lose that cuticle, that is when they release the contents of their bowels that they've been holding on to for a while. That's also sometimes they'll release their eggs into that cuticle when they molt. And then the eggs sort of have this like protective little case that they're in for a while. And then when they hatch, they have to find like the holes in the cuticle to get back out.

• 7:46Daniel Whiteson?

  All right, so these things are really small. You're saying a millimeter is the biggest one. Can I see something with my naked eye that's just a millimeter? So like tardigrades, you could actually like, if you squint, see one of these things?

• 7:57Kelly Weinersmith?

  So it's about the size of like a period on a printed out sheet of paper. And so like, you know, maybe you could see some like flailing limbs. But like, if you had a dissecting scope, you could see them better. But again, a millimeter is about the size of like some of the bigger ones. And so a lot of them are even smaller. And so you'd be better off with like a compound microscope.

• 8:16Daniel Whiteson?

  And does everything that has this hard outer shell have to molt when it grows? Or are there some critters out there that can like gradually expand? Because like our skeleton gradually expands as we grow. Why can't you gradually expand your exoskeleton as you grow? Or is that a totally naive biology question?

• 8:33Kelly Weinersmith?

  Our skeletons are inside of us. And so they can like expand as our squishy outer parts sort of like accommodate that. But I think that if you have a particular kind of cuticle that's like super hard, that doesn't tend to grow and expand. I think you do usually need to lose those.

• 8:49Daniel Whiteson?

  All right, and so do all of these things look roughly the same? Even though some of them are a little bigger and some of them are smaller? Do they all roughly look like the same critter? Could like an individual, non-trained biologist tell them apart by eye?

• 9:01Kelly Weinersmith?

  They do have some definite characteristics that help you tell them apart. So my question for you is, I think when most people think of tardigrades, there is an animated video that they saw. Is something coming to mind for you? Or have you not seen this video?

• 9:13Daniel Whiteson?

  No, I definitely have a mental image of a tardigrade. I think the phrase water bear has also influenced me. So I'm imagining something that looks a little like a fat Caterpillar but with sort of claws and then a weird face with like a tube sticking out the front of it. So it's a little like a possum or something. I'm not sure exactly which animal it looks like. Maybe like a microscopic water possum.

• 9:35Kelly Weinersmith?

  Oh, I love possums. Okay, so there's this like famous video where they're pink and they've got that like almost a toilet paper roll on top of their face. And it kind of like goes into the face and out of the face over and over again as the tardigrades eight little legs furiously have it swim through this water. So I was listening to ologies and Ellie Ward was interviewing Dr. Paul Bartels and he was lamenting that that is like not what they look like at all.

• 10:00Daniel Whiteson?

  What? Popular science has led us astray, Kelly, really?

• 10:05Kelly Weinersmith?

  Hold on. I know. I know. It's amazing. Okay, so first of all, that toilet paper roll nose thing does not go out and in and out and in and out and in. That was a mistake because someone took a special kind of microscopic picture. They used a scanning electron microscope and the way the sample was prepared, one of the tardigrades had that thing sticking out like it usually does. And one of them, because of how it was prepared, it just kind of got like sucked into the face. But I don't think that usually happens. And so the nose thing isn't going in and out and in and out and in and out. I think someone just saw both of those photos and were like, oh, it must alternate between these two states as opposed to like the preparation process just kind of messes up specimens sometimes.

• 10:45Daniel Whiteson?

  Wow, it's like they saw two frames and just animated the interstitial. That's crazy.

• 10:50Kelly Weinersmith?

  Mm hmm. And then the other thing is they don't swim. They are what's called benthic. So they walk around on like the floor of things or like they crawl up vegetation, but they're not swimming. They're crawling along. And that video that most of us are, you know, perhaps imagining right now, it has eight legs that are all like in front of it. It's like a bear, but all of its legs have been multiplied by two. But what really happens is it has six legs and like the usual configuration. And then another two that go like straight out from its butt.

• 11:19Daniel Whiteson?

  Butt legs.

• 11:20Kelly Weinersmith?

  Butt legs. Yeah, how convenient.

• 11:24Kelly Weinersmith?

  So those butt legs hold on to stuff so that they like don't get washed away with the current or something. And some have claws and some don't have claws and they're not usually pink. A lot of them are clear or white, or if they've got color, a lot of times it's because they are clear, but you can see like the algae they ate. So they look green, or you can see their poop. So they look brown. And so some of them do have some colors, but they're not, even though they're moss piglets, they're not pink.

• 11:49Daniel Whiteson?

  Hmm. I see. So clear, like they're invisible, like you can see through them, they're like transparent?

• 11:55Kelly Weinersmith?

  If they are starved, some of them probably are transparent. But if they've eaten anything, you can see their digestive tract because they've got like green in it.

• 12:05Daniel Whiteson?

  Wow, that's crazy. So like little tardigrade children, when they've been sneaking cookies from the cookie jar, it's like, not a question. The parents are like, I see that cookie.

• 12:13Kelly Weinersmith?

  Exactly. Yes.

• 12:15Daniel Whiteson?

  Wow. What's the evolutionary advantage to being transparent? Is it like a form of camouflage? Or is it just totally incidental?

• 12:21Kelly Weinersmith?

  I really don't know. My first guess would be that it does help with camouflage. If like a predator just kind of sees through you. But then the other thing is that like creating pigmentation is often a process that requires some energy. And so maybe being clear is just easier than creating pigmentation. But if you're in an aquatic environment, probably being clear is a good way to hide and blend into stuff.

• 12:42Daniel Whiteson?

  Wow. All right. So we have totally the wrong mental image of a tardigrade. But it is still kind of cute.

• 12:48Kelly Weinersmith?

  Yeah.

• 12:48Daniel Whiteson?

  And it does have those fat little legs and a toilet paper snout. But we're setting the record straight here today.

• 12:53Kelly Weinersmith?

  Well, they don't all have the toilet paper snout. Again, there's over 1300 species. Some of them look like cute little salamanders, but instead of a tail, they've got like, you know, the two butt legs. There's some variability in how they look, but they do have that like general shape. There's also tons of variability in where you find them. Some are in lakes, some are in oceans, and some are living in like, when there's a little bit of water on lichens or moss, they live in that like little water film. And there's some that you find in like roof gutters. They're essentially anywhere where there is enough water to keep them from like desiccating, or they're in environments that dry out sometimes, and then water comes back. And this is what they're so well known for. They have a bunch of different strategies for surviving that dry out period.

• 13:35Daniel Whiteson?

  If you find them in large bodies of water, how come you never find like mega tardigrades? You know, like there are sharks and then there used to be like huge sharks. Was there ever a tardigrade that was like a meter long or like a hundred meter long? Or is that the next Michael Bay movie we're looking forward to?

• 13:52Kelly Weinersmith?

  There have been, I believe, a couple fossil tardigrades that have been found. And I don't think we've ever found a mega big one. So yeah, pass that idea on to Michael Bay. I think it's a winner because there are some that are carnivores. And including there are some that will eat other tardigrades. So I think that would make a great movie.

• 14:09Daniel Whiteson?

  Exactly. You thought they were cute and fuzzy until you saw the big one come for you.

• 14:14Kelly Weinersmith?

  Yum, yum, yum, yum, yum. Okay.

• 14:17Daniel Whiteson?

  But what limits them from growing? Like, why aren't there bigger ones? Is there something about their geometry which doesn't scale up? Or is it ecological thing? Like, they can't eat enough food to get that big? Or is there something which will eat them if they get too big? Or do we not know?

• 14:32Kelly Weinersmith?

  I don't think we know.

• 14:33Daniel Whiteson?

  Amazing.

• 14:33Kelly Weinersmith?

  Amazing that we don't know.

• 14:35Daniel Whiteson?

  Amazing how many things biologists don't understand.

• 14:38Kelly Weinersmith?

  Ah, I feel like that's a theme of the physics talks, but all right.

• 14:43Daniel Whiteson?

  Fair, fair.

• 14:44Kelly Weinersmith?

  All right, okay. Man, it's a battle between California and Virginia and physics and biology today. I appreciate when you and I are both anti-chemistry and we're on the same team. But I guess today we're doing battle. All right, so let's start with their abilities to survive desiccation, which means like drying out.

• 15:01Daniel Whiteson?

  So this is something you hear about a lot in popular science. Are you going to ruin this for us also, Kelly? Or is this something they really can do?

• 15:07Kelly Weinersmith?

  They really can. Well, not all of them. So again, many, many species, the ones that tend to live in like mosses and lichens and roof gutters, like places that are wet sometimes but dry other times. They're able to form this stage known as a tun state, where they essentially, it's like, almost go dormant. Some of them describe it as like, it's near death. So they're able to like, go into this like, super resistant form. And when they're in this super resistant form, this is when scientists have done all manner of horrible things to them, like dip them in liquid nitrogen, shoot them out of guns, just to see like, how much can they handle when they're in this state?

• 15:42Daniel Whiteson?

  So this is what they're famous for when it's not like a nice and cozy and damp time to be a tardigrade. You like, convert into this like, weird, long-lasting state where you're basically immortal. And then you can just like, unfurl and be a tardigrade again later? It's like, time traveling to the future?

• 15:57Kelly Weinersmith?

  So immortal, no. When they go into this state, they can survive for like years, maybe decades. But so one thing you might have heard is they can stay in this stage for hundreds of years. Actually, that seems to be possibly a misreading of a study. So there was like a museum specimen where we knew when it was collected. And 100 years later, it got taken out of like some drawer. And they found some tardigrades and they added some water. And it looked like part of an arm kind of moved a little. This was written in Italian, either Italian or French, in some romance language. And so it was like an arm moved a little, but then nothing else.

• 16:30Daniel Whiteson?

  Well, you know, in Italian, hand gestures are super duper important. So maybe that was interpreted as communication, you know?

• 16:36Kelly Weinersmith?

  That's right. It could be.

• 16:40Kelly Weinersmith?

  As a biologist, I've had to look at a lot of specimens where like, oops, the ethanol dried out. And now this animal is totally dried. And I'm going to try to like, get it back in its normal shape by adding like water or more ethanol. And when that happens, they often like move in response to the rehydrating. And it's not that they're alive, it's just the molecules responding to the presence of water. And if it did do a like, hello, guys, hand gesture, it died right afterwards. Maybe it's impressive, but probably it's just an artifact of it like rehydrating.

• 17:09Daniel Whiteson?

  Like if you poured water on a dried up leaf, it would change its shape also. And you might interpret that as motion, but it's definitely not alive.

• 17:15Kelly Weinersmith?

  Yes, exactly. And so that's a possible scenario. But there has been a specimen collected from Antarctica, where it was two tardigrades that had entered this dormant state and an egg that hadn't hatched yet. And the specimen was put in cold storage at, I think, negative 20 for 30 years and then removed. And they came out of their stunned state, became adults. One of them croaked, but the egg hatched. And then the two individuals who were still alive went on to like reproduce, I think more than once even. And so they were like, definitely alive, like not baby waved at you and then croaked. Like they're definitely alive. So decades.

• 17:52Daniel Whiteson?

  Now, the adult, that's really impressive, right? To freeze an adult and have it then reanimate and survive, that's amazing. Eggs are a different story, right? Because like human eggs, you can freeze, that's not such a big deal. But why is that? I've never really understood. Like I thought if you Freeze any cell, the water inside of it expands and bursts the cell membranes. And that's why it's like hard to freeze a cow and then like reanimate it. Why is it possible to do for eggs or sperm or stuff like that? Why doesn't that same physics apply?

• 18:20Kelly Weinersmith?

  Yeah, so I am not an expert on cryopreservation, but I think that it has something to do when you're freezing human eggs. If you freeze them really fast, the cells don't lice the same way. This is part of why, like, if you get meat, you don't want to, like, slowly freeze it and then defrost and do that over and over again because the cells lice and the meat tastes less good. I think something about freezing them really quick, but I don't know why it is that they can come back after that.

• 18:46Daniel Whiteson?

  Yeah, because even human embryos can do that, right? Even fertilized eggs, it's sort of amazing.

• 18:51Kelly Weinersmith?

  It is. We should have a whole episode on cryopreservation.

• 18:54Daniel Whiteson?

  Yes, let's do it. But it's definitely not something you can do to, like, a human adult, right?

• 18:59Kelly Weinersmith?

  Yeah.

• 19:00Daniel Whiteson?

  At least not yet. People are working on that, right? Preserving the brains of old baseball players for the future.

• 19:05Kelly Weinersmith?

  Ooh.

• 19:08Daniel Whiteson?

  All right, so you're telling us that this is real, that tardigrades really can't go into this crazy state and then survive insanely long exposure to really difficult conditions and then be alive again and reproduce and be happy. What's going on during that state? Like, are they alive? Are things paused? Like, is there some metabolism happening? Like, what's going on?

• 19:29Kelly Weinersmith?

  I'm going to tell you the answer to that, Daniel, after the break.

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• 21:24Kelly Weinersmith?

  OK, so you wanted to know what happens when the tardigrades go into this like semi-dormant state. So first of all, they like kind of squish up into a ball. And so they like pull their heads in, they pull their legs in, and they like expel and they lose almost all their water. By the end, they have something like 2% to 3% of the water they started with. Just to be clear, that would kill humans. Like we're like, what, 70% water or something? If we went down to 3%, we'd be goners. We'd be goners way before that. So as they lose that water, they start producing something called trehylus, which is a sugar. And it ends up forming kind of like a glass-like structure that holds everything together and gives it like structural integrity. And this has long been the explanation for why tardigrades

• 22:09Kelly Weinersmith?

  are able to survive such incredible conditions, including the explanation you gave five years ago on Daniel and Jorge Explaining the Universe when I listened to that episode.

• 22:17Daniel Whiteson?

  Oh, right. Doing some research.

• 22:19Kelly Weinersmith?

  Yeah, yeah, well, you know, I needed something to listen to while I was walking around the other day. But so here's the thing, though, about trehylus. Lots of tardigrade species, some of them make trehylus when they go into this tunneled state. Some of them make quantities so small that we're not actually sure that it can do the function. Of making this glass structure that protects the organism. And some of them don't appear to even have the equipment at all to make trehillos, which suggests maybe it's part of the picture for some species, but that's not like an across the board answer for how tardigrades are able to do this. So it's complicated and they make a bunch of other proteins. So cryptobiosis is a term. It means hidden life. And so it's another way for describing this tun state.

• 23:04Kelly Weinersmith?

  And I found a line in a 2017 paper that said, mechanisms that protect tardigrade cells during cryptobiosis are still poorly understood or completely unknown.

• 23:14Daniel Whiteson?

  Oh, that sounds like a fair description of all biology.

• 23:16Kelly Weinersmith?

  And physics and physics. And you guys only have like six questions you need to answer.

• 23:25Daniel Whiteson?

  Fair, fair.

• 23:26Kelly Weinersmith?

  Get to work on that, guys.

• 23:28Daniel Whiteson?

  And that's my favorite thing about the universe, that it's poorly understood or completely unknown, because otherwise it would be boring, right?

• 23:35Kelly Weinersmith?

  I feel the same way about biology, dude.

• 23:38Daniel Whiteson?

  All right, so some of these guys have these weird glass-like proteins called trehilloses, which maybe provide some internal scaffolding that like support the cell when it's all dried out. But some of them don't even have it, but they can still do this tun state weird survive for everything.

• 23:55Kelly Weinersmith?

  Yeah, right. And so we don't really know what's happening there. We felt like we had a handle on it and then we were like, oh, wait, some of these don't make that at all. So I don't know, back to the drawing board.

• 24:03Daniel Whiteson?

  Do you think that means that other tardigrades have different strategies? Or that this glass-like structure has no connection to their ability to survive?

• 24:12Kelly Weinersmith?

  I bet it's both. So it could depend a lot on the ecology of the animal. So some animals that are in these environments with no water for longer might need sort of more extreme solutions to this problem. And so it could be something about like, what kind of environment you tend to be in. Whereas if like, I don't know, maybe you're at the edge of a lake and you know, every once in a while you find yourself dry for five minutes, you can just kind of like get through that. And so it might depend on your ecology, how frequently you encounter these weird situations. Or it could be different solutions entirely. I don't think we know yet.

• 24:44Daniel Whiteson?

  All right. And then I have a basic biology question, which is like, in biology, how do you answer the question, this is how they're doing it, or that's how they're doing it? Do you have to develop an alternative where you like knocked out that capability and show that like, if they don't have this protein, then they can no longer do this thing? And that's how we know? Because biology is such a huge, complicated Rube Goldberg machine. How can you point to any one bit and say, this is the essential bit?

• 25:07Kelly Weinersmith?

  Yeah, so it's super complicated. So sometimes you can say like, you know, if trehyllos is produced by a gene or something, you could go in and turn that gene off and then put the tardigrade through a drying cycle and see how it does and measure like, okay, definitely it didn't make trehyllos anymore and it died.

• 25:27Daniel Whiteson?

  But even then, maybe trehyllos is just a precursor to something else, which is actually doing the crucial function, right? I mean, there's just such a complicated series of events. It seems to me hard to ever point to one and say, this is the explanation. Do you think it's just that we always want a simple explanation and there really aren't any? Or that sometimes there really are simple explanations and we can find them?

• 25:47Kelly Weinersmith?

  There are probably rarely simple explanations, but I think that's pretty rare. Like when we did the Human Genome Project, I think we expected we would like immediately understand the cause of cancer and a bunch of other diseases because now we have the whole genome and it's going to be super easy. But no, it depends on like how the genome is expressed. Lots of complicated extra bits. And you know, like for the trehyllos example, if you knocked out trehyllos and the tardigrades died, maybe it's because trehyllos does something else earlier, like even when it's not in desiccation mode and you've killed it in some way that has nothing to do with desiccation. So ideally, you try to address the question from a bunch of different angles and see what the picture you put together tells you. But usually the answer is like, it involves 5,000 different genes that are all upregulated

• 26:32Kelly Weinersmith?

  and different and then, you know, some of them are cell signaling genes. It's almost never like the answer is X. But you know, you guys have complicated answers too sometimes.

• 26:42Daniel Whiteson?

  Yeah, we do. Absolutely. And sometimes you look at a big complicated system and there is no simple story that you can tell or model that you can use to understand it. But sometimes you can, right? Like 10 to the 29 little molecules can all fly through the air together following F equals MA. It's a very simple story about a lot of complicated things that are all happening in concert and somehow simplicity emerges. So I was sort of wondering how often that happens in biology, that you can pull one strand of a story and say, this is the role this is playing, or if it's always just a huge chorus.

• 27:17Kelly Weinersmith?

  It never happens that it's one string.

• 27:20Kelly Weinersmith?

  I like to joke that in ecology, like, you know, the only quote unquote theory that we have is it depends.

• 27:27Daniel Whiteson?

  See, that's my problem with biology, exactly.

• 27:31Kelly Weinersmith?

  But, you know, if you don't try to figure out all the things it depends on, then you never cure cancer. Or, you know, you never save the endangered animals or whatever. So, you know, you gotta dig in anyway.

• 27:40Daniel Whiteson?

  No, exactly. Biology has no clear answers, but the questions are super duper important and interesting. And so they're worth going after anyway.

• 27:47Kelly Weinersmith?

  I appreciate the effort you're making to understand my perspective.

• 27:50Daniel Whiteson?

  I'm trying so hard.

• 27:51Kelly Weinersmith?

  You're doing a great job. You're doing a great job. Alright, so I forgot to answer a question that you had earlier, which was like, what is happening to metabolism and stuff when they're in this tense state? And the answer is-

• 28:01Daniel Whiteson?

  It depends, right?

• 28:05Kelly Weinersmith?

  This might be pretty straightforward.

• 28:08Daniel Whiteson?

  Alright, tell me.

• 28:09Kelly Weinersmith?

  They reduce their metabolism, they reduce their oxygen use, and it's almost like they're frozen in time. So they're not doing a lot of biological stuff when they're in this desiccated state.

• 28:18Daniel Whiteson?

  But to me, there's a difference between actually frozen, like, there's no motion, and very slow. Like, are they alive? Is there some consumption of energy? Are they gonna run out of energy at some point? Or is it really just paused?

• 28:33Kelly Weinersmith?

  I think it's gotta be the case, that there's still some consumption of energy. So, one, otherwise you'd expect that they could, like, live forever. And so I think at some point, they kind of run out of their stores. But of course, during that time, they're also, like, accumulating radiation damage and other sorts of problems of just being alive. They're amping it down, but I don't think it's completely zero.

• 28:51Daniel Whiteson?

  Yeah, amazing.

• 28:52Kelly Weinersmith?

  Yeah, and so because they're resistant to things like desiccation, actually, I wish I knew the history of the first time somebody was like, "Let's throw these guys in liquid nitrogen." It doesn't seem super nice, but they've got this sort of reputation for being super environmentally resistant. We've exposed them to pressures of seven and a half gigapascals, which is equivalent to being 180 kilometers below the surface of the earth. And this is an environment that I just can't imagine you would expect that selection would be preparing these organisms for, because it just doesn't come up. But they mostly did okay. At six hours, they were alive. And so here's the thing. You'll hear like a list of like, they can survive 7.5 gigapascals of pressure, blah, blah, blah. They can survive 7.5 gigapascals of pressure for six hours.

• 29:37Daniel Whiteson?

  That's pretty good, though. Six hours is a long time. Like, we're talking essentially like a hydraulic press. You know, like, this is serious stuff.

• 29:44Kelly Weinersmith?

  No, that's a good point. Like, so every once in a while, though, you'll see like a YouTube headline that's like, they're immortal. This is incredible. You're right. It's incredible. They can survive this. But they can't survive it for long. If they're exposed to it for 24 hours, they've kicked the bucket.

• 29:57Daniel Whiteson?

  All right. And I can understand why evolution wouldn't need them to like be able to survive 100 kilometers underground for 1,000 years. But it's not that hard to imagine why it would be useful to survive high pressure briefly, right? You can imagine some high pressure situation, comet impact, dinosaur steps on you. I don't know. Right? These things do happen. I suppose evolution can select for them. No? You're looking skeptical over there.

• 30:22Kelly Weinersmith?

  If you are a tardigrade living in the Marianas Trench, and I don't know if we have tardigrades in the Marianas Trench, then you would have experienced selection for being able to handle extreme pressures. But I don't know if like a once in many millions of years comet would still be exerting selection pressure now for 7.5 gigapascals of pressure.

• 30:45Daniel Whiteson?

  Well, if we had like lots of pianos dropping out of buildings on people's heads, the way I always thought we were gonna have when I was a kid, I thought that was like a feature of adult life, you know, quicksand, pianos and anvils dropping on people. If that was happening more often, then you would expect evolution to somehow select humans to be able to survive, you know, anvils and pianos and stuff like that. So, you know, there must be some biological equivalent to anvils and pianos.

• 31:06Kelly Weinersmith?

  First of all, I think Looney Tunes gave you a distorted view of adulthood, but.

• 31:10Daniel Whiteson?

  Fair, fair.

• 31:12Kelly Weinersmith?

  I feel like the strategy could just be like, you have eye spots that detect a shadow overhead. And when that happens, your brain is just like, piano, move. And you get out of the way. That seems like an easier path for selection to take than being able to withstand a piano dropping on your head.

• 31:27Daniel Whiteson?

  Also, it probably takes a while to get into this tun state. So it's not like tardigrade is swimming along, sees a comet coming down, and then like switches into tun state like a superhero. This is like, already happens to be in this state and then survives the impact, right?

• 31:41Kelly Weinersmith?

  Yep. Yes, exactly.

• 31:42Daniel Whiteson?

  Okay.

• 31:42Kelly Weinersmith?

  They can get into it like, I think, a couple hours, pretty quick, but not like immediately, not like snapping your fingers. It takes some work.

• 31:48Daniel Whiteson?

  A couple hours isn't great for our superhero movie plot.

• 31:50Kelly Weinersmith?

  Yeah, that's true. But you know, if Michael Bay contacts us, we can like change some biology stuff. Like, as we've talked about in the past, what's important is you're consistent. So, you know, we will consistently change their biology. Another incredible stressor they've been able to survive is a bunch of different kinds of radiation at levels that certainly would have killed people.

• 32:11Daniel Whiteson?

  Amazing.

• 32:12Kelly Weinersmith?

  And we think that we know partly how they do this one. So tardigrades produce a class of proteins called intrinsically disordered proteins. And you're like, why are you making me hear that multi-syllabic phrase?

• 32:26Daniel Whiteson?

  That is, in fact, exactly what was going through my mind.

• 32:28Kelly Weinersmith?

  Yes, I know. I've gotten to know you pretty well. But so the fact that they're disordered and like, kind of all over the place is important. And so if you think of this like blobby thing, this blobby protein is attracted to DNA. So your genetic material that codes for everything else, and it binds to the DNA like electrostatically. And because it's sort of like this blobby all over thing, and you know, I wish the listeners could see the beautiful things I'm doing with my arms right now.

• 32:55Daniel Whiteson?

  You're basically Italian right now.

• 32:57Kelly Weinersmith?

  I was just gonna say that. Yeah. You beat me to it. And so this blobby thing is able to just kind of like fall over the DNA like a coat. And then it appears to provide like a physical barrier to the radiation and protect the DNA from breaking. And in fact, they were able to get bacteria by like moving some genes around to produce these proteins. And then they mix them in to human cells. And these proteins bound to human DNA. And when you blasted the human DNA with radiation, they were protected by these disordered blobby kinds of proteins that were like coats for the DNA, radiation shielding for the DNA.

• 33:36Daniel Whiteson?

  Oh, my God. This is our superhero origin story. Bitten by a radioactive tardigrade, Kelly gained that critter's ability to withstand radiation.

• 33:46Kelly Weinersmith?

  It's gonna be amazing. Coming in fall 2025.

• 33:50Daniel Whiteson?

  Tarda Kelly.

• 33:52Daniel Whiteson?

  So let's remind our listeners exactly what radiation is and how it damages the cell, because we're talking about X-rays and ultraviolet light and gamma radiation. Those all sound like very different things, but they're all just photons. Talking about very high-energy photons. Photons like the ones emitted by your lamp or your screen or by the sun, just higher energy, so they like penetrate deeper. And the problem, of course, is that when these things penetrate into your cells, they can like blast open delicate stuff like your DNA, and that's how you get cancer, right? Or also, sometimes that's how your kids end up being like amazing cross-country runners, even though you have no athletic skills yourself, hypothetically speaking, right? Mutations are sometimes good and sometimes bad, you never know. But it's like going into computer code and just like randomly changing a few things

• 34:37Daniel Whiteson?

  and hoping that it gets better.

• 34:38Kelly Weinersmith?

  Yeah.

• 34:39Daniel Whiteson?

  Sometimes it gets worse. And so that's what we're protecting against, right?

• 34:42Kelly Weinersmith?

  That's right. And the study that I was reading, it was looking at breaks in the DNA. So DNA is like a double-stranded helix. It's almost like you took a ladder and then sort of twisted it so that it's like a spiral staircase. And they're looking at, do you get one break in the ladder or two breaks in the ladder? So does one of the like long poles break or both of them? And so they were able to find that you get fewer breaks overall when you have this like radiation coat protecting it.

• 35:08Daniel Whiteson?

  So why don't we all have this radiation coat? Is it like good to be susceptible to radiation because then you get these mutations? Or is this radiation coat like expensive in some other way that's usually not worth it?

• 35:19Kelly Weinersmith?

  I think it'll probably surprise some people to learn that usually when you get blasted with radiation, you get like cancer but not superpowers. You probably generally want to avoid it, but to be clear, we don't actually know the answer to this because we don't understand the system very well. But one hypothesis that I read about was that, you know, probably we don't all have these because if you've got something that's like a coat over your DNA, you know, like the way your DNA replicates is like stuff comes in and opens up the double strand and like there's machinery that starts replicating stuff. And if you've got like a big coat covering it, you can't do that stuff. It like gets in the way. And so it might be nice to protect you during a period where you're not doing a lot of replicating your DNA because you're just kind of hanging out waiting for the awful situation you find yourself into past.

• 36:02Daniel Whiteson?

  So it's sort of like you're locking down your DNA, but then you can't really use it. It's like when you freeze your credit and then you can't like open a new bank account because you protected yourself against yourself.

• 36:11Kelly Weinersmith?

  That's right. You shouldn't have sent your social security number to that person over email. Kelly from the past. Anyway, so they're surprisingly radiation resistant. Let's talk about what happens when you dip them in liquid nitrogen or expose them to the vacuum of space next.

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• 38:17Kelly Weinersmith?

  All right, we're back. We've talked about how tardigrades are amazingly resistant to high pressures, amazingly resistant to radiation, although not completely resistant. You can kill them eventually, but they're impressively resistant. Also, weirdly, we've been very interested in exposing them to temperature extremes. And so, Daniel, I have a question for you. There's this commonly made claim that you can expose tardigrades to very close to absolute zero, and they survive.

• 38:45Daniel Whiteson?

  Cool.

• 38:46Kelly Weinersmith?

  This was from a paper in the 1950s in a language I don't speak, and I couldn't find the original.

• 38:53Daniel Whiteson?

  Hmm.

• 38:54Kelly Weinersmith?

  How long have we been able to create temperatures close to absolute zero? Has it been since the 1950s?

• 39:00Daniel Whiteson?

  So the history is that colder earlier than you might expect. Like Faraday, Michael Faraday, who did so much amazing work on electromagnetism, he got stuff down to like negative 130 C, so that's 140 degrees above absolute zero. That was in 1845. And then a guy named Dour, after which the Dours are named, liquefied hydrogen down to 21 Kelvin in 1898, right? So this is already just 20 degrees above absolute zero in the 1800s. And then it was just 10 years later, we got down to 4 degrees Kelvin, won the Nobel Prize in 1913 for that one.

• 39:37Kelly Weinersmith?

  Oh, wow.

• 39:37Daniel Whiteson?

  And the current record, the closest we've ever gotten is 100 pico kelvins.

• 39:43Kelly Weinersmith?

  Whoa.

• 39:43Daniel Whiteson?

  That's 0.00000001 Kelvin. And there's an instrument on the International Space Station that's going to try to get to 1 pico Kelvin. It's called the Cold Atom Lab.

• 39:55Kelly Weinersmith?

  All right. Okay, so definitely by the 1950s, you could be testing how tardigrades survive to close to absolute zero. And Daniel, what is absolute zero? I believe that's the temperature at which molecular stuff just stops and everything's frozen in place. Is that right?

• 40:09Daniel Whiteson?

  Absolute zero is a theoretical limit we've never achieved and don't know if it's actually possible. And essentially, the argument is when things get colder, velocities internally slow down. It's a model of temperature that says things are Hot because the stuff inside it is moving fast or wiggling a lot. And so what happens when things get colder, they move slower, they wiggle less. Okay, make them colder. All right, they wiggle less. Is there a point at which all wiggling stops? And so sort of the way like when you learn calculus in high school, you could ever actually approach infinity. You like approach it and see what the tendencies are. In that same way, we estimate that absolute zero might be the place where everything stops. But that's extrapolating and it's all kind of classical physics.

• 40:51Daniel Whiteson?

  And quantum mechanics says you could never actually get there because there's a minimum energy to all the fields in the universe. So everything has to be buzzing. Because if anything was ever completely motionless, it would have no uncertainty. And there's a minimum uncertainty to the fabric of the universe. So we don't know if anything can ever get to absolute zero, if it's a real thing or not. But we've gotten pretty close.

• 41:12Kelly Weinersmith?

  Okay, and tardigrades were able to handle it for at least a little while, even though I couldn't find the original paper.

• 41:18Daniel Whiteson?

  Wow, so how cold did they get these tardigrades?

• 41:20Kelly Weinersmith?

  So the paper that I was able to find, both because it was online and in my native language. They dipped them in liquid nitrogen, so it's negative 196 degrees Celsius.

• 41:31Daniel Whiteson?

  Pretty cold?

• 41:32Kelly Weinersmith?

  Super cold and 90% of them survived.

• 41:36Daniel Whiteson?

  Wow.

• 41:36Kelly Weinersmith?

  Yeah, and it was for 15 minutes.

• 41:38Daniel Whiteson?

  I don't think many Californians would survive at that temperature for that long.

• 41:41Kelly Weinersmith?

  You know, even though Virginians are a hardy or bunch than you all Californians, I don't think we could have survived that either.

• 41:47Daniel Whiteson?

  That's because you have to wrap your heart in so many layers of protection that it's not available during normal use. See, that's why Californians are friendlier.

• 41:55Kelly Weinersmith?

  That doesn't make sense. No, no, no, no, no, that's not how this works. All right, but one point that I want to make here is that some of the tardigrades that were not in the TON state also survived. And that was also true during the radiation experiments too.

• 42:12Daniel Whiteson?

  Oh, wow.

• 42:13Kelly Weinersmith?

  And that makes us wonder, like those disordered proteins that we were talking about. Maybe they help, but maybe that's not the whole picture because you wouldn't expect the like active untunned individuals to be surviving if those proteins were the whole picture because they're not making a bunch of those when they're not in the TON state. So everything. Things complicated. Okay, but now let's get to the juicy stuff. Space. Some scientists have wanted to figure out if tardigrades can survive the super extreme environment of space. So first, we sent them up into spacecraft and exposed them to microgravity and some space radiation, but they were still like in this temperature controlled container thing.

• 42:54Kelly Weinersmith?

  They did pretty well in response to microgravity, like whereas humans, our bones and our muscles fall apart, in the TON state, they're just kind of chilling.

• 43:01Daniel Whiteson?

  And let's remind ourselves, what is the extreme environment of space? What's difficult about space? So there's high radiation because we don't have the magnetic field of Earth to bend those particles away, and we don't have the atmosphere to shield us. Then there's microgravity, but that's not so extreme. But then there could also be low temperatures if you're out in space, low pressure, and then of course, no oxygen.

• 43:21Kelly Weinersmith?

  Yes, and so this first experiment was replicating the microgravity problem. But they weren't exposed to the vacuum of space, they weren't experiencing full radiation, and they were in low Earth orbit, so they were still protected by the magnetosphere. And they weren't experiencing the kind of temperature extremes you usually experience in space. So another experiment or a set of experiments amped things up. They put them in a container that had holes in it, and then they had a variety of UV filters on top of the different containers. So some of the tardigrades were exposed to the vacuum of space while having their temperature controlled, but not being exposed to UV radiation. And then others experienced various kinds of UV radiation while being exposed to the vacuum of space,

• 44:04Kelly Weinersmith?

  while still having their temperatures controlled in a nice way. Does that all make sense? Vacuum of space, they rocked at, which, to be clear, would kill people.

• 44:14Daniel Whiteson?

  Right.

• 44:15Kelly Weinersmith?

  The three Soviet cosmonauts who were exposed to the vacuum of space did not survive the experience. And that's pretty much what you should expect for the rest of us, too.

• 44:24Daniel Whiteson?

  And the thing that first kills you there is what? Is it the low pressure? That like your eyeballs are boiling and your blood is boiling because you're used to being squeezed in by all the air?

• 44:32Kelly Weinersmith?

  I think what killed them in particular is that the nitrogen boiled out of their blood and it happened in their brains and they had a bunch of brain hemorrhaging.

• 44:39Daniel Whiteson?

  That does not sound good.

• 44:40Kelly Weinersmith?

  No, and so tardigrades don't have the same circular Military system, the internal goo that keeps these little guys going. It's not the same system as ours, so you might not have to worry about nitrogen bubbles. But also, they've gotten like, a bunch of the water out already. And so you're probably not going to have like, stuff that could bubble out. So they did great in the vacuum of space. But as soon as you opened those filters so that UV radiation could get them too, they started dying in droves. Like, I think-

• 45:05Daniel Whiteson?

  Oh, really?

• 45:06Kelly Weinersmith?

  Maybe four of the like, 60 survived- -that exposure. And that wasn't there like, a whole lifetime. I think it was like, one of the things that frustrates me about papers that are published in really high-impact journals is that they give you a short page limit. And so, important details get left out. And I couldn't figure out how long they were exposed. But, it couldn't have been more than 10 days because that's how long the entire mission lasted.

• 45:29Daniel Whiteson?

  Wait, so, we heard earlier that they can survive UV radiation on its own. And we heard just now that they can survive the vacuum of space. But you're saying if you combine them, then that snuffs them out? So they can't survive the combination?

• 45:41Kelly Weinersmith?

  So here's the problem. All these studies that we've been talking about-

• 45:44Daniel Whiteson?

  Yeah.

• 45:45Kelly Weinersmith?

  -all looking at different species of tardigrades. So because a tardigrade could survive some high radiation, doesn't mean that the next species that you expose it to could survive. And also, not all of these studies have the exact same experimental design. So it could be that a bunch of the tardigrades that were exposed to radiation were exposed to it for like, 5 minutes. But when you're exposed to it for 10 days, then you start dying. And so, you know, when you hear someone like, rattling off a list of all the extreme stuff that tardigrades can do, some species can do some of those things for some lengths of time. But it's not like all of them can do all of those amazing things indefinitely.

• 46:21Daniel Whiteson?

  So that's like saying, oh, polar bears can swim in cold water, and grizzly bears can run really fast. It doesn't mean that they can do both.

• 46:28Kelly Weinersmith?

  Yes, exactly. Or that they could do both, like, forever. Like, eventually the polar bear is gonna need to find land and stop swimming. So the space people don't invite me to their parties. The tardigrade people aren't gonna invite me to their parties. Anyway, it's alright, I'm a downer.

• 46:40Daniel Whiteson?

  Physicists will always invite you to their parties, Kelly. Because we don't have any.

• 46:44Kelly Weinersmith?

  Oh, oh. That's probably not true, maybe?

• 46:50Kelly Weinersmith?

  So here is the question everybody's been dying to know the answer to. In 2019, the Berisheet lunar lander crashed on the moon. It contained tardigrades, although the government officials who approved that launch did not know that because the company that had bought space on the lander did not disclose that they were sending biological specimens, which they are supposed to do.

• 47:13Daniel Whiteson?

  And why were they sending biological specimens? Was this some can tardigrade survive experiment? Or were they hoping to populate the moon?

• 47:20Kelly Weinersmith?

  I hope that it was a can tardigrade survive experiment. And also like that probably would have been a pretty cool PR move for their mission to be able to be like, oh, tardigrades in space, they really can survive everything. But for whatever reason, they decided to not disclose that it was happening. And I was not able to figure out what species they sent. I spent a long time asking. I asked Blue Sky, nobody knew. And if you know, let me know. But so part of figuring out whether or not they can survive involves knowing the tolerances for that species in particular.

• 47:52Daniel Whiteson?

  Right.

• 47:52Kelly Weinersmith?

  But I don't know what species it is.

• 47:54Daniel Whiteson?

  So the answer is it depends.

• 47:56Kelly Weinersmith?

  Well, we were talking about biology. So of course the answer is it depends. Biology doesn't disappoint, but I think probably not. And here's why. All right. So first, somebody decided to stick tardigrades in bullets and then shoot them at sandbags to try to figure out if they could survive the impact and the subsequent shock wave that would have been experienced when the lander crashed into the moon.

• 48:18Daniel Whiteson?

  This was an experiment done in response to the crash? Like just to answer this question, not an independently motivated experiment?

• 48:25Kelly Weinersmith?

  That's exactly right.

• 48:26Daniel Whiteson?

  Wow.

• 48:26Kelly Weinersmith?

  It doesn't say that in the paper, but I found a interview with the authors. It sounds like that's true. And so there's a sentence in the paper that says, accordingly, we have fired tardigrades at high speed in a gun onto sand targets, subjecting them to impact shocks and evaluating their survival. Actually, this paper was all about if something hit the earth and dislodged earth that had tardigrades, could the tardigrade survive space and survive so that they could land on like the moon or Mars or populate it? So it was a study about panspermia and the possibility of tardigrades becoming, you know, interplanetary before the rest of us. I found an interview where the author said, probably they wouldn't have survived because of the shock wave.

• 49:07Kelly Weinersmith?

  So it seems unlikely that they survived, but let's go ahead and assume that maybe they got lucky and they survived the initial shock wave.

• 49:16Daniel Whiteson?

  Because we don't know the speed of the descent of the lander, right? It depends on when it failed. If it fails just before it hits the surface, it's going to be a pretty gentle crash. If it fails really far away, then it's going to plummet towards the surface. But the moon's gravity is still not very strong, so it's not going to be going that fast, right? But still, it depends.

• 49:34Kelly Weinersmith?

  This paper that I read had a bunch of different impact speeds and shock waves that they looked at. And I looked on the internet to figure out what we think the impact speed was of the Bear Sheet lander. And based on their table, I think it's possible it survived. But then in an interview with the authors, they said, no, no, no, the shock wave, it wouldn't have survived. But then I found another paper that was like, no, it might have survived based on the info in the table. So, you know, it depends.

• 49:59Daniel Whiteson?

  Were any of these papers written by anonymous authors from the moon?

• 50:02Kelly Weinersmith?

  Oh, I don't know. Yeah, the tardigrades achieve sentience. I think we have to worry about them sending like moon rocks down at us as punishment for all the things that we've done to them in the lab.

• 50:12Daniel Whiteson?

  All right, so you think it's unlikely they survived the impact on the moon. Once they're on the moon, say they happen to survive, or if you do, then what did they have to put up with?

• 50:20Kelly Weinersmith?

  So now they've got to worry about radiation. So the moon doesn't have a strong planet-wide magnetosphere like Earth does, or a thick atmosphere. So they'd be exposed to all of the space radiation. And as we saw in those earlier studies, space radiation, solar radiation is bad for them. So that would kill them if they were exposed to it. But let's say, well, what if maybe when they crashed, the little container that was holding them ended up burying itself under the regolith? And so now the regolith is protecting them from radiation.

• 50:49Daniel Whiteson?

  Creative.

• 50:50Kelly Weinersmith?

  Let's imagine that. Okay, so now you got to deal with temperature. We know they can handle really cold temperatures. The moon at night has about a two-week period where it's negative 133 Celsius, which is negative 208 Fahrenheit. That's at the equator. We know that they survived negative 196 Celsius, which is more than that, but for 15 minutes. So we don't know if they could survive the long polar nights, which are the equivalent of two weeks on Earth. But I think the bigger problem is, one, temperature swings back and forth between extreme heat and extreme cold. But two, the fact that the moon does get really Hot. So without that atmosphere, things just heat up a lot. So without an atmosphere, things get really hot and really cold. There's nothing to sort of dampen the temperature swings.

• 51:35Kelly Weinersmith?

  And as we saw previously, tardigrades don't do great at really high temperatures. They do pretty well with cold temperatures, but with hot temperatures, they can't survive for super long. But let's imagine, hey, we said that they're underneath the regolith, they're protected from radiation. Underneath the regolith, you're also to some extent protected from temperature extremes. So maybe they're still alive there. But now you've got a problem with water. So in order to come out of their tun state, they need to be hydrated. And the lunar regolith is as wet as cement. So not super wet. So say it got hit by a comet that was bringing water. First of all, I think that impact and the like, heating up that happens when the comet

• 52:17Kelly Weinersmith?

  hits the surface could kill the tardigrades. But also, if you get water, you're only going to get it temporarily. And then it's going to like be lost to the vacuum of space. So I don't see them getting out of their tun state. And then the final big problem is food. If they did get out of their tun state, they don't have anything to eat. Like, I don't know what species this is, if this is the carnivorous ones, and there was enough of a size variability, maybe the big ones could eat the little ones, but eventually you're gonna run out of food. So I don't see the tardigrades permanently settling the moon.

• 52:47Daniel Whiteson?

  Hmm. So it's unlikely that the tardigrades are like water bearing around, being cute, and bouncing around the surface of the moon, living happily. But it's possible that some of them are in the tun state, survive the impact, are buried in the regolith, and don't need water or food because they're just basically paused for a long time, but maybe not forever.

• 53:08Kelly Weinersmith?

  I feel like that is a very low probability scenario, but it depends. I don't know that I can rule it out entirely. Maybe they're still in their tun state, we'll find them. I mean, we know that they can't be in that state for forever, and it's already been like five years. So I'm not super hopeful. Sorry.

• 53:24Daniel Whiteson?

  But if a huge impactor slams into the earth and like, completely demolishes it, so there's no record of life left on earth, there could still be on the moon, some basically like, frozen proof that there was once life on earth. So that aliens visiting in the deep future could be like, oh, look, there was something here once.

• 53:43Kelly Weinersmith?

  Maybe. Or those incredible temperature swings have killed them, and the bacteria that live in their guts have consumed them, and they've become liquid mush. Because biology's gross also.

• 53:54Daniel Whiteson?

  All right, well, I guess we're just gonna have to wait millions of years for a huge impact and alien arrival to find out the answer to that one.

• 54:00Kelly Weinersmith?

  Aw, and people say I'm the negative one.

• 54:03Daniel Whiteson?

  All right, well, thank you, Tim, for your really fun question. I think Kelly had a lot of fun digging into the research on tardigrades.

• 54:10Kelly Weinersmith?

  I did. It distracted me while I was sick and couldn't get out of bed. So thank you for this wonderful question. I had a blast.

• 54:15Daniel Whiteson?

  If you have a question about something in the universe that fascinates you, physics, biology, even, gasp, chemistry, write to us. We'd love to dig into it. We love hearing from all of you at [email protected].

• 54:36Kelly Weinersmith?

  Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We would love to hear from you.

• 54:41Daniel Whiteson?

  We really would. We want to know what questions you have about this extraordinary universe.

• 54:47Kelly Weinersmith?

  We want to know your thoughts on recent shows, suggestions for future shows. If you contact us, we will get back to you.

• 54:53Daniel Whiteson?

  We really mean it. We answer every message. Email us at [email protected].

• 55:00Kelly Weinersmith?

  You can find us on social media. We have accounts on X, Instagram, Blue Sky, and on all of those platforms, you can find us at D and K Universe.

• 55:09Daniel Whiteson?

  Don't be shy. Write to us.

• 55:15Kelly Weinersmith?

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• 57:21Daniel Whiteson?

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