The Hitchhiking Microbe’s Guide to the Galaxy

Summary

Unexplainable – "The Hitchhiking Microbe’s Guide to the Galaxy"

Date: April 15, 2026
Host: Bird Pinkerton (for Vox’s Unexplainable)
Guests: KT Ramesh (Johns Hopkins University), Lily Zhao

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Episode Overview

This episode delves into the scientific mystery of lithopanspermia — the idea that life might hitch a ride through space on rocks blasted off of planets by impacts, traveling between worlds and possibly seeding life elsewhere. Host Bird Pinkerton explores how plausible this scenario really is: could resilient microbes survive the violent journey embedded in meteorites? Researcher KT Ramesh and his team (notably Lily Zhao) put this to the test by subjecting bacteria to extreme pressures, seeking to discover the limits of what life can endure and expand our understanding of life's resilience on (and possibly beyond) Earth.

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Key Discussion Points and Insights

1. The Concept of Lithopanspermia (01:02 – 03:45)

• Definition and History:

  • Lithopanspermia posits life’s transfer between celestial bodies via rocks (e.g., meteorites).
  • The idea traces back to ancient Greece and resurged in the Victorian era with Lord Kelvin.
  • There are planetary protection policies to prevent contamination between Earth and other worlds, like Mars.
  • KT Ramesh: "So this is basically about rocks... the idea of being able to see life throughout the universe or throughout the solar system through rocks, through basically life being carried in rocks that move around inside the solar system." (01:42)

• Policy Implications:

  • Emphasis on avoiding cross-contamination: not sending Earth microbes to Mars, nor bringing Martian microbes to Earth.
  • Lighthearted reference to "Alien": precautions are to avoid inadvertently unleashing something dangerous (03:32).

2. The Gauntlet for Space-Faring Microbes (03:45 – 07:38)

• The Problems for Microbes:
  • Any hypothetical “hitchhiker” microbe must survive:
    • Catastrophic high-pressure shock of ejection (e.g., from an asteroid impact)
    • Immediate exposure to vacuum/cold/radiation of space
    • Heat of atmospheric reentry and subsequent impact on arrival
  • Researchers previously assumed these obstacles were insurmountable.
  • KT's skepticism: "Why would you even ask this question whether the answer is obviously no..." (04:49)

3. Extremophiles: Champions of Survival (07:38 – 09:03)

• Tough Microbes Already Exist:

  • Some microbes on Earth (extremophiles) have withstood severe cold, dryness, radiation, and pressure.
  • What helps them survive one extreme often helps with others.
  • KT Ramesh: "Organisms that can survive desiccation, organisms that can survive extreme cold, that can survive radiation. We call them extremophiles." (08:17)

• Still, the Pressure Problem Remained:

  • The unknown: could any microbe survive the supersonic, near-instant shock pressures experienced during meteorite ejection?

4. Shooting (At) Bacteria: Designing the Experiment (11:58 – 14:28)

• Engineering a Simulated Space Trauma:

  • KT and grad student Lily Zhao designed an experiment:
    • Bacterial cells ("Conan the Bacterium" — Deinococcus radiodurans) are sandwiched between steel plates.
    • The "sandwich" is placed in a vacuum and subjected to high-velocity impacts by a metal plate, mimicking the shock conditions of space rock ejection.
  • Lily Zhao: "He's like, what if we try to shoot some bacteria for alien research? And I was like, why not? Sure, I'll shoot some bacteria with you." (12:11)
  • KT Ramesh: "My lab is mostly about impact. I'm interested in impact problems." (14:14)

• Technical Details:

  • Multiple precise iterations to ensure the validity of methods and survival rates.

5. The Results: Microbes Under Pressure (15:33 – 19:47)

• Survival Under Extreme Shock:

  • At 1.4 GPa (12-13x Mariana Trench pressure): 95–97% survived.

    • KT Ramesh: "What I was expecting to hear was that there was nothing left, but instead..." (17:21)
    • Lily Zhao: "...we saw that it was, like, close to the control, like, 95% to 97% survival compared to the control." (17:26)

  • Repeated the experiment for accuracy, results held up.

  • Increased to 1.9 and then 2.4 GPa (up to 17x Mariana Trench); even at the highest pressure, ~60% survived.

    • Lily Zhao: "the screws of the metal plates were shearing open at 2.4 giga, but the microbes...survival that I found was around 60%." (19:33)

  • Key Finding: Microbial death rates were low even under massive, rapid shock pressures. The bacteria were stressed but recovered.

• Interpretations:

  • These toughness levels push the boundaries of what we thought possible for life.
  • Suggests that under some (not all) conditions, true panspermia is at least physically plausible.
  • KT Ramesh: "...if you start with enough cells to begin with...the possibility that some tiny fraction of cells might make it is not zero." (21:51)

6. Implications and Next Questions (20:49 – 23:33)

• Relevance for Panspermia:

  • The study strengthens the plausibility of lithopanspermia — at least in surviving the shock phase.
  • Still: real meteoritic pressures can be higher; more work remains.

• Broader Implications for Life on Earth:

  • Deep-sea microbes endure high pressures, but this experiment used sudden, impact-driven forces.

  • Potential to breed even tougher bacteria by repeating this process.

    • Lily Zhao: Efforts are ongoing to see if repeated selection can yield “super pressure resistant” strains.

  • KT Ramesh: Ongoing questions:

    • What traits grant this toughness?
    • Do other extremophiles or fungi share this kind of resilience?
    • Are features like cell wall structure critical?
    • KT Ramesh: "That's my current hypothesis, but so far every time I've tried something I've been wrong." (23:24)

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Notable Quotes and Memorable Moments

• KT Ramesh: "I have been wonderstruck by how much these things can take. It's just amazing." (20:49)
• Lily Zhao (on experiment design): “...like, a little sandwich with the little cells in the middle.” (12:44)
• KT and Lily’s surprise: The expectation was microbial annihilation; the reality was their practical invincibility.

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Important Timestamps

| Timestamp | Segment | Notes | |-----------|-----------------------------------------------|----------------------------------------------------------------------| | 01:02 | KT Ramesh introduction & interest in life | Sets up the episode’s central question | | 01:42 | Definition of lithopanspermia | Explains the literal meaning and scientific hypothesis | | 03:05 | Concerns over interplanetary contamination | “We have some policies that all countries...have agreed to” | | 04:49 | KT’s original skepticism | “Why would you even ask this question...” | | 07:38 | Extremophiles on Earth | “Organisms that can survive desiccation...extreme cold...radiation” | | 11:58 | “Shooting bacteria with a gun” experiment | KT and Lily begin their unique research methods | | 15:33 | Introduction of Deinococcus radiodurans | Description of a “super tough” bacterium (“Conan the Bacterium”) | | 17:21-17:26| Shock at survival rates | Expecting near-zero survival, got almost 100% | | 19:33 | Pushing pressures even higher | Screws fail before bacteria! | | 20:49 | Wonder at microbial resilience | “I have been wonderstruck...” | | 21:51 | Reassessment of panspermia plausibility | “...the possibility that some tiny fraction of cells might make it...”|

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Tone and Style

The episode maintains a sense of wonder, delight, and scientific curiosity—with moments of dry humor (Looney Tunes and Alien references) and respect for the resilience of even the smallest life forms. KT Ramesh and Lily Zhao both express surprise and humility at the unexpected toughness of their subjects, capturing the “edge of known science” spirit of Unexplainable.

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Further Exploration

• The team references related episodes (“Moon Poop” about the Apollo astronauts’ lunar leavings and the broader question of contamination; “Origins” trilogy about life’s beginnings on Earth).
• KT’s and Lily’s ongoing work continues to probe just how much more we can learn from life’s extremes—both for astrobiology and our basic understanding of biology.

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Summary Statement

This episode powerfully illustrates that even our most basic assumptions—about what can survive an anvil’s worth of pressure—are up for challenge. As KT puts it: we’ve gone from “improbable” to “possible” in our thinking about life's interplanetary journeys, and everywhere we look, the limits of survival get pushed a little further back. If panspermia ever occurred, it might just have been thanks to some truly hardy “Conan the Bacterium”-style hitchhikers—zooming through the solar system, bouncing back from cosmic shocks like microbial Looney Tunes.

Transcript

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[Bird Pinkerton]

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[KT Ramesh]

I think if you're interested in life, you're always interested in basic questions about life, where it comes from and what it can do.

[Bird Pinkerton]

KT Ramesh studies a lot of things.

[KT Ramesh]

I'm a professor of mechanical engineering and material science and earth and planetary sciences. At any given time, I'm not quite sure what I do, but one of those three.

[Bird Pinkerton]

But in the last few years, he's also been exploring questions of life. And specifically this kind of old idea that has a name that's somehow both technical and salacious at the same time. This thing called lithopanspermia.

[KT Ramesh]

So a good way to think about it is to just break that word up into three parts, right? So litho stone. So this is basically about rocks, pan everything, sperm meal, seeds. So the general idea is the idea of being able to see life throughout the universe or throughout the solar system through rocks, through basically life being carried in rocks that move around inside the solar system.

[Bird Pinkerton]

A version of this idea goes back as far as the 5th century BC when a Greek philosopher suggested that maybe life came to Earth as cosmic seeds. Later in the 1800s, Lord Calvin proposed that life might have come here on a meteorite, others put their own spin on this concept. And while people in more recent times have investigated the ways that life could have developed right here on Earth, no extraterrestrial sperm required. The lithopanspermia idea has lingered on. It has come up as people talk about space exploration. For example, people have asked, can life travel between planets or moons on rocks? Because they want to figure out where life might be in our solar system.

[KT Ramesh]

We have some policies that all countries that are involved in the space Program have agreed to one of those rules is that we'll be really careful about potentially contaminating another planet.

[Bird Pinkerton]

So far, we do not have definitive proof of life anywhere but Earth. But if we think there might be life on another planet or moon or asteroid, we would want to be extra careful to make sure we didn't contaminate that life with our own microbes.

[KT Ramesh]

You don't want to take Earth life and take it to Mars and let it loose, and now it's all over Mars. Right.

[Bird Pinkerton]

We also want to be really careful we don't bring something back to Earth from some other part of space.

[KT Ramesh]

We're clean.

[Bird Pinkerton]

Let us in. What happened to Caine? Something has attached itself to him.

[KT Ramesh]

We have to get him to the infirmary right away.

[Bird Pinkerton]

We don't want to accidentally reenact the movie Alien and contaminate ourselves. What kind of thing? I need a clear definition. An organism.

[KT Ramesh]

Open a hatch. So the way we do this is we define some bodies in the solar system as being restricted bodies, meaning these bodies you have to be really careful about because they may have life, right? Mars is one of those bodies. So if you go to Mars, you want to be really careful about sterilization. If you bring anything back from Mars, you want to be really careful about how you bring it back.

[Bird Pinkerton]

Wait a minute. If we let it in, the ship could be infected. You know the quarantine procedure.

[KT Ramesh]

24 hours for decontamination.

[Bird Pinkerton]

So restricting a place like Mars seems pretty obvious, but people have questions about other spots. Like, let's say there was life on Mars, right? And then an asteroid slammed into it at some point and sent little chunks of Mars debris flying through space. The question is, could life have traveled lithopanspermia style on those little bits of debris over to Amar's Moon, for example, and should we therefore be cautious about visiting Mars moons? When KT first encountered this question, he was skeptical.

[KT Ramesh]

Why would you even ask this question whether the answer is obviously no. That was my view of it.

[Bird Pinkerton]

But after several years and some more research, he thinks the answer is actually a little less obvious. This is unexplainable. I'm Bird Pinkerton, and today on the show, we're talking about lithopanspermia, but also we're talking about how researchers try to push life to its limits, try and figure out what the limits of life might be. Katie first got interested in the lithopanspermia hypothesis when the National Academy of Sciences approached him to work on a project about it. And he realized that in order for a cell to make it from one place to another place on a meteorite. It would have to overcome a truly wild series of obstacles, a kind of lithopinspermia gauntlet. So let's say there was some life out there, maybe on Mars first. Again, something like an asteroid would have to come and smash into the planet, and then lots of little bits of Mars would go whizzing off into space, giving us meteorites. Right. Hopefully with some life on them. But obviously, when one thing smashes into another thing, you can get very high pressures. And KT told me that the bits of rock that get flung up and out of space are not usually right underneath the incoming objects. They're usually kind of on the edges, but they're still probably experiencing a lot of pressure. And it's hitting all of a sudden, like an anvil dropping from the sky and then bouncing away.

[KT Ramesh]

So it's actually a shock. And one of the things we worry about is not just what the pressure is, but how fast it's put on. Because if I put the pressure on very slowly, maybe you adapt to it. And in fact, we know there are some bacteria that live way below the surface of the Earth. So there are bacteria that can adapt to high pressures. Maybe not this high, but high pressures.

[Bird Pinkerton]

And.

[KT Ramesh]

But if you do it as a shock, it happens really fast.

[Bird Pinkerton]

But let's say, just for the sake of argument, that some microbes do survive this shock of pressure, this takeoff period. Now they're on a meteorite hurtling through space. And for the lithopanspermia hypothesis to work, they also have to survive space travel.

[KT Ramesh]

They get really cold, and they get really dry. They get bombarded by radiation. And we know that you make things really cold. You can keep them from growing. You make them really dry, you can kill them. You put radiation on, you can kill them.

[Bird Pinkerton]

The meteorite might also have to travel through an atmosphere or move at really fast speeds. So the microbes are also probably getting hot for a while. They probably experience a bonk when the meteorite hits a surface somewhere. So, all in all, the likelihood of surviving this sort of panspermia gauntlet seems low. And yet, as KT was digging into the literature, he was also learning that life is pretty hardy. Like, for decades now, researchers have been turning up examples of life here on Earth that can withstand pretty intense conditions.

[KT Ramesh]

Organisms that can survive desiccation, organisms that can survive extreme cold, that can survive radiation. We call them extremophiles. They like extreme conditions sometimes.

[Bird Pinkerton]

What makes them good at surviving one thing can also help them survive other other things. So after he finished his reading, KT thought that maybe, just maybe, there was at least a chance that some microbes could survive the journey through space, despite all the radiation and the cold and the dryness. But he still wasn't sure that any microbes would even make it to that part of the journey, because he still wasn't sure if any microbes could even survive those initial pressures from the formation of the meteorite.

[KT Ramesh]

That question we did not have a good answer to.

[Bird Pinkerton]

Researchers had done a bunch of different experiments to try and work out if microbes could withstand huge pressures. And he respected the researchers who'd done these experiments a lot, but their results didn't give him a clear picture.

[KT Ramesh]

So that's how I got into this is I felt like the data wasn't really there to justify us saying one way or the other. And I figured that maybe I could do this a little more cleanly. So I took on this project of saying, maybe I can develop an experiment that would let me take bacteria and subject it to these really high pressures for very short times, just like a shock, and then measure how much of it survives. So I wrote a proposal to NASA saying, okay, let me go see if I can do that.

[Bird Pinkerton]

Which is how he wound up in his lab shooting bacteria with a gun. More on that after the break.

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[KT Ramesh]

Suddenly, and against all probability, a sperm whale had been called into existence several miles above the surface of an alien planet.

[Bird Pinkerton]

Before the break, I told you that KT Ramesh shot bacteria with a gun for an experiment. If I am being strictly accurate, though, he actually had one of his grad students do this, a mechanical engineer named Lily Zhao.

[Lily Zhao]

He's like, what if we try to shoot some bacteria for alien research? And I was like, why not? Sure, I'll shoot some bacteria with you.

[Bird Pinkerton]

KT and Lily were not the first people ever to shoot stuff at bacteria. But KT had a sort of new study design for this experiment that was a little bit different from the experiments that had come before. This technique that he thought would give him the clear answers he was looking for. The idea was to take some bacteria and then put them as a kind of layer between two steel plates, like

[Lily Zhao]

a little sandwich with the little cells in the middle.

[KT Ramesh]

And then you're going to take this sandwich of metal plates and put it inside a target chamber. So I have in my lab a giant gun, and inside that gun, I can launch projectiles at high velocity. So my sandwich containing my cells, is sitting inside the target chamber. I then close the target chamber, evacuate it. So I take all the atmosphere out, and then I launch my projectile. My projectile is carrying another metal plate. So I've got one metal plate hitting a sandwich of metal plates. And the sandwich of metal plates contains the bacteria.

[Bird Pinkerton]

So, I'm sorry, yeah, you have the sandwich of metal plates, and you are firing a massive gun gun at the plates. And the gun doesn't shoot like a bullet. It shoots another metal plate, essentially. And that slams into the sandwich.

[KT Ramesh]

Right. And what that does is sends waves into the metal plates, and those waves are like shockwaves, and they generate really high pressures inside the cell, and that's how we generate the high pressures for the experiment.

[Bird Pinkerton]

Why do you have, like, you just have a giant gun? Because you're firing things at things all the time or.

[KT Ramesh]

Right. So my lab is mostly about impact. I'm interested in impact problems. I do work for a bunch of places all of whom are interested in these impact conditions.

[Bird Pinkerton]

Do you ever use the massive gun for, like, silly things?

[KT Ramesh]

I will never admit to that.

[Bird Pinkerton]

Lily told me that it takes a long time, like almost an entire day to set up this gun. So the potential for silly things is somewhat limited. And also they had their hands full with this experiment, so they had their gun. But they also needed to put some actual bacteria in their steel sandwich. And several of the previous experiments on pressure and microbes had looked at E. Coli, which is like the bacterial equivalent of a lab rat, kind of. But E. Coli is not an extremophile. It's not able to withstand super intense conditions, and it's comparatively kind of puny.

[Lily Zhao]

I didn't say it. I didn't say it. E. Coli, don't get me sick. Don't come after me.

[Bird Pinkerton]

One of their collaborators, Jocelyn de Ruggiero, she suggested that they work with a more hardcore bacterium, one so tough that its nickname is Conan the Bacterium. But you can call it Deinococcus radiodurans.

[KT Ramesh]

And the name should tell you something. Radiodurans. To me that says radio. So radiation and durans is endurance is how I remember it. So this thing can handle a lot of radiation.

[Bird Pinkerton]

Deinococcus radiodurans is also good at being cold, it's good at being dry. Basically. It's good at a lot of the things you would want a bacterium to be good at if you were going to send it off into space and hope it would survive. So the team started to work with it, and the first tests they ran were relatively simple. They put some of these bacteria in the steel sandwich, they put the steel sandwich in the chamber with the gun, and then they left it there for a bit. Because even without the shock of pressure, it's just kind of stressful for a microbe to be living in a steel sandwich without an atmosphere around it. So they wanted to see how much stress in this experiment was coming just from that versus from the shock itself. But once they had that data, then

[KT Ramesh]

we shot it at the lowest velocity we could get, which ends up giving us a pressure of around 1.4 GPa.

[Bird Pinkerton]

In this case, 1.4 GPa or 1.4 GPa is somewhere between 12 and 13 times the pressure at the deepest spot in the Earth's ocean, so the bottom of the Mariana Trench. So imagine that you are a microbe minding your own business, and then out of nowhere, you are first slammed with many Mariana trenches worth of pressure. And then sort of just as suddenly, all that pressure disappears again. If this happened to you or me, we would be very dead. And that's kind of what Lilly and KT assumed would happen to most of these cells, too. After the gun firing, Lily did some microbiology work to figure out sort of what percentage of the cells had survived.

[KT Ramesh]

What I was expecting to hear was that there was nothing left, but instead,

[Lily Zhao]

we saw that it was, like, close to the control, like, 95% to 97% survival compared to the control configuration that we had.

[Bird Pinkerton]

So basically, it seemed like close to all the microbes had survived.

[KT Ramesh]

And I said, well, there's something wrong here. You know, it doesn't seem like this is right, because we were expecting 10 to the minus six, so one in a million, and this is now like one. So there's probably something not right in the experiment. And she said, yeah, I think there must be something going on.

[Lily Zhao]

Many things can go wrong along the way that could give you an incorrect result. So we wanted to make sure that the survival that we were seeing was absolutely correct.

[KT Ramesh]

So she started all over again and built the whole thing. And we did it again and again.

[Bird Pinkerton]

They got similar results. Only a small percentage of the bacteria seemed to be dying. And when Lily did more analysis, she found that the shocked bacteria were stressed out, but only about as stressed out as the control bacteria, the ones that had just gotten to hang out in the steel sandwich with no pressure involved. So it seemed like the pressure had not phased them much at all.

[KT Ramesh]

To me, this was really amazing, right? So the good thing about science is you have data, you repeat it, you get the same kinds of data. All right, now maybe there's something here.

[Bird Pinkerton]

And once you were sure, what was your reaction?

[Lily Zhao]

I mean, that was like, okay, let's go higher.

[Bird Pinkerton]

So they went higher. They upped the pressure to 1.9 gigapascals, which is roughly 17 times the pressure at the Mariana Trench. And when they checked the results, the bacteria still seemed relatively okay. So they went even higher than that to 2.4 gigapascals. For context, if you apply around 2.2 gigapascals of pressure to room temperature water, it changes into a kind of ice. In fact, at this pressure, their equipment was starting to fail.

[Lily Zhao]

So the screws of the metal plates were shearing open at 2.4 giga, but the microbes at 2.4 giga pa, the survival that I found was around 60%. So still pretty high.

[Bird Pinkerton]

They did find that the bacteria that had endured this higher pressure also seemed to be stressed out in a new way. So the researchers are careful about making grand conclusions from sort of limited data here, but they think what's happening is

[KT Ramesh]

that the Bacteria is now spending more time doing damage control. So it's seen a high stress and it's reacting to that stress and managing itself in various ways.

[Bird Pinkerton]

Eventually, though, the surviving microbes seemed to be able to pull themselves together again and be right back in that kinda stressed out because of the suboptimal steel sandwich state. To Lilly and to KT this was exciting. It's not the first time people have ever reported bacteria being resistant to pressure, even high pressure. But again, KT wanted to do this study because he wanted clarity. And the data here were pretty clear. These bacteria had a high survival rate even when they were subjected to high pressure.

[KT Ramesh]

I have been wonderstruck by how much these things can take. It's just amazing.

[Bird Pinkerton]

So what does all this mean for the Lithopanspermia hypothesis? This question about microbes traveling through space? My impression from talking to KT and to others is that this is a useful data point. Remember, this whole experiment tells us a bit about the takeoff part of the Lithopanspermia gauntlet. Could bacteria survive the immense pressures that occur as a meteorite is formed? There's still more follow up work to be done. These pressures are high to us, but still relatively low if you're talking about meteorite formation. But if KT once thought that it was totally obvious that no life could survive the Lithopanspermia gauntlet, he now thinks that if you start with enough cells to begin with, under some conditions, the possibility that some tiny fraction of cells might make it is not zero.

[KT Ramesh]

You go from saying this is improbable to well, it's possible. It's, it's still a low probability, but it is possible.

[Bird Pinkerton]

Beyond questions of Lithopanspermia though, I think it's just as interesting to look at the ways that this research contributes to our understanding of what life right here on Earth can do. Like we've known that microbes can live at high pressures deep in ocean mud, but those pressures are an order of magnitude less than these pressures and they're consistent, not sudden. Here it's a little like KT and Lily are telling us that Looney Tunes is a documentary that you really can smash something with an anvil. And in the next scene it'll be zooming around, ready to catch a roadrunner. It's something that understandably, both KT and Lily have further questions about. Lily's doing research to see essentially if she can breed like a super pressure resistant bacterium. So if she slams bacteria with a bunch of pressure and then takes the survivors and lets them grow? Will she get bacteria that are even more pressure resistant? And then kt, meanwhile, wants to figure out what makes these bacteria so pressure resistant. He wants to know if other extremophiles can also survive high pressures, or if fungi can. He wants to know if there's something special about Deinococcus radiodurans that helps them with pressure, like their cell walls.

[KT Ramesh]

That's my current hypothesis, but so far every time I've tried something I've been wrong. So we'll see what happens.

[Bird Pinkerton]

Ultimately, we may never know whether or not life has traveled around the solar system, but there are still plenty of questions about life right here on Earth for us to chase after. And maybe if we fire our Acme Science gun at enough organisms, we might even catch some answers. You want to hear more about microbes in space and other ideas about Panspermia besides life traveling around on meteorites, we have another episode all about the poop we left on the moon that you might really enjoy. It's called Moon Poop and we'll link to it in the transcript. Also, in my conversation with kt we were mostly focused on the idea of microbes traveling between something like Mars and a Mars moon. But for those of you who are Earth curious, we also have a three part series called Origins, all about how life might have developed right here on Earth. We will link to that as well. This episode was produced by by me Bird Pinkerton. It was edited by the wonderful Joanna Solotarov. Christian Ayala did the mixing and the sound design. Melissa Hirsch checked the facts, Noam Hassenfeld does our music, Jorge Just, Meredith Hadnot, Sally Helm and Amy Padula by the fact that octopuses have donut shaped brains. Thanks always to Brian Resnik for co creating the show with me and Noam. And a big thanks to Lily Zhao who has now defended her PhD and to KT Ramesh. Thanks also to their collaborator at Johns Hopkins, Jocelyn de Ruggiero, who helped me better understand biology here. And thanks to Paul Hazel at UNSW Canberra, Australia, Gareth Appleby Thomas at Cranfield University and Peter Dorn at Louisiana State University for helping me understand different aspects of this paper and of lithopanspermia. If you have thoughts about life in space or if you have subjects you think we should explore, please email us. We are@ unexplainablex.com I have been endlessly fascinated with microbes lately, so please send me weird microbiology stuff. I love reading through it. If you would like to support this show and the journalism that Vox does, we would love it very much if you would become a member. It's a very easy thing to do. Just go to vox.com/members and you will get access to all of Vox's journalism. But you also know that you're supporting all of Vox's journalism, including this show. And for those of you who have emailed us to let us know that you've signed up because of Unexplainable, thank you. I also want to thank the people who have left us a nice review and the people who have told people in their life about the show. All of you are, frankly, the best. Unexplainable is part of the Vox Media Podcast network, and we will be back very soon with another episode about everything that we do not yet know.