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It's Unexplainable. I'm Noam Hassenfeld. And this week, an enormous, apocalyptic unanswered question. I think it's the greatest question in planetary science. Robin George Andrews, volcanologist, journalist, obsessed with this question. I've been convinced of this by scientists just because it is kind of like a murder mystery. Yeah.
We know the victim, Venus, second planet from the sun. These days, it's a terrible volcanic hellscape. Venus is the worst place known to science. It is horrible, apocalyptic and awful in every possible way. But there's reason to believe that Venus was once a beautiful, habitable paradise.
It might have actually been the first habitable planet in our solar system. And it would have been a beautiful thing to see. Until at least a billion years ago, it was murdered.
Like some sort of cosmic deity had a really, really grumpy day and just went, "Nope, I'm going to ruin this planet!" We know the cause of death: out-of-control climate change. Average temperature of the planet shut up by something like several hundred degrees Fahrenheit. So it really sort of cooked itself to death. But we don't know what caused it to get so hot. And figuring out what killed Venus isn't just some historical curiosity.
Venus is a possible future for us, for Earth. Earth and Venus really like siblings. They would have been almost twins, really. They would have been born at the same time and made of the same stuff. Yet, Earth is a paradise. So why do we have a paradise next to a paradise lost? Whatever came for Venus could come for us next. What the hell happened to Venus that hasn't yet happened to Earth? Our senior reporter, Brian Resnick, spoke to Robin to try to unravel this mystery.
Just to start off here, how dead is Venus today? How bad is it over there? The state of Venus today is comically hellish. It's like if someone had to describe what hell would be like, Venus is probably not that far off. Venus is a sort of volcanic mishmash. It's covered in these sort of higgledy-piggledy, razor-sharp...
lava flows and these sort of really wide shield volcanoes and spider shaped volcanoes. It's actually incredibly hot and I mean like 900 degrees Fahrenheit hot, which is way hotter than it should be just by being like a tad closer to the sun. It's also got sulfuric acid clouds, good at eating up stuff, dissolving things. And the pressure on the surface is about 92 times that of sea level on Earth. So if you stood on the surface,
You would be pancaked and you would melt. So it's like being in a pressure oven a mile underwater. It's pretty horrible. This is why we don't hear of any billionaires wanting to colonize Venus. No. No, I imagine not, no. Okay, so it's a super harsh place. I'm not going there. Good call. My vacations are booked elsewhere. But you said this was a murder mystery. How do we know that Venus used to be alive?
So even though Venus today looks and is apocalyptic in every meaning of the word, probes have kind of looked at its atmosphere and found that there's a lot of something called heavy water in the atmosphere. Now, heavy water is one of those scientific terms where it is exactly what it sounds like. It's actually heavier water. The water we used to do, this classic H2O,
which is found commonly everywhere on Earth, is a more common type of water throughout the cosmos. Heavy water just kind of switches out that hydrogen for something called deuterium, which is like a heavier version of hydrogen. What does finding heavy water mean? Scientists know that there is a ratio between how much classic water there is to how much heavier water. So if you measure how much heavy water exists somewhere, you can make a reasonable guess as to how much
you know, classic water there is or was on that planet. So today, not much classic water in the skies of Venus, but it suggests that there once was a lot of classic water on Venus, like an abundance of it, at least an ocean's worth of water on Venus. If that water existed in liquid form, what are the odds that Venus was habitable at some point? You know, it's not unlikely, even though today it looks impossible. Could you imagine what this past Venus looked like?
Yeah, so it's almost like trying to reconstruct what happened after an all-consuming fire. You have these volcanoes and you have water oozing around it and gushing and cascading around it. There would have been great plateaus built of possibly volcanism and volcanoes standing up above these very shallow Great Lakes maybe of water kind of thing. I mean, it would have been a beautiful thing to see. How long ago must this have been, this habitable Venus?
That's one of the big queries, is actually how long ago did it become habitable in this sense, and how long did it last? There is a possibility that water was always steam, and it might have never been. But if it was liquid water, then it could have been habitable for billions of years. Maybe right up until the last billion years it was habitable. And there's kind of two leading theories as to what killed Venus.
You have me on the edge of my seat. What's the first option for what could have killed Venus? Option number one is the sun. From what we know of our sun and other stars, when they're kind of in their teenage years, they get quite hyper excitable and they kind of get hotter and brighter quite quickly. If the sun actually gets brighter and hotter too quickly, even though you might have that water just sitting on the surface, just doing its own thing, minding its own business, the sun can just sort of violently boil it off.
And that is a fate that lots of exoplanets are presumed to have gone through, lots of planets outside our galaxy. And once Venus loses this water, it gets blown away, it gets vaporized. Do we get this increased greenhouse gas? Yeah, yeah, because if you sort of
boil off its water into steam, that steam is a greenhouse gas, that would have just, you know, kicked up the greenhouse gas effect and then the carbon dioxide coming out of Venus's embryonic volcanoes would have just sealed the deal really. I mean, there was no chance, no chance that, and that could explain why we see Venus as it is today. So if this is true, so if this young, very excitable sun is what killed Venus, like,
The Earth would have been fine through this, right? Yeah, the Earth would have been fine. So it seems the Earth sort of spared the worst of it, yeah. Okay, so that's one suspect in our whodunit. What is the other suspect? Well, the other suspect just happened to be my favorite thing, and that's volcanoes. Yeah, so how could your fave volcanoes kill a planet? If you look back at Earth's history, every now and then you get these sort of volcanic eruptions happening.
Science has called large igneous provinces, but they're basically enormous prolonged outpourings of lava, like beyond the scale and time that anyone can really imagine. I can't imagine these sort of things.
When did this lava extravaganza happen on Earth? 252 million years ago, Earth experienced its worst mass extinction. Something called the Great Dying, which is a great name to give anything, I suppose, very dramatic. At least 90% of all life was wiped out. And the primary suspect as to what triggered this mass extinction were these sort of volcanic fissures that opened up in Siberia.
and it produced a continent-sized flood of lava that took about 2 million years to erupt. So it causes giant explosions that also unleashed all these greenhouse gases into the atmosphere. And it created a global warming effect that kind of raised the temperature by, you know, like a dozen degrees, which is quite a lot. And that caused 90% of all the life on Earth to die. You know, Earth had to kind of reset itself.
And the idea is, well, what if that happened on Venus, but worse? Okay, so like on Earth, there was one of these great dying eruptions and it didn't kill us. We're still here, but something could happen worse on Venus?
So you can't just have like a massive volcanic eruption on its own. You'd have to kill off plate tectonics. And plate tectonics is essentially a planet's thermostat. You have to kill off this kind of stabilizing thing. So plate tectonics, so that's what continents sit on and they kind of float around and smush into each other. How do those act like a thermostat? The temperature of a planet can go up and down for all kinds of reasons.
But carbon can get soaked up in the Venusian Ocean, for example, if there was an ocean. And that filters down to these tectonic plates. And if these tectonic plates dive down beneath each other, then you're burying this carbon. So if you have a way to break plate tectonics, that's how you can kind of kill a planet.
Okay, so plate tectonics here, they help regulate a planet's temperature because they take carbon dioxide and just shove it deep, deep down underground when they move? Yep. So if you dehydrate a planet and you break its plate tectonics, your thermostat's ruined. So scientists have been plugging this into models and like, how could you do this? How could you do this?
And it turns out that actually, maybe instead of just having one of these epic eruptions, you have two of them. Why not just have two at the same time? Two or three. So you now have an out of control inferno with no fire service to kind of put that fire out. You're kind of doomed already. If you break Lake Tetonix, you've broken the world.
So we have two suspects here. One, we have the sun. And then the other, we have massive eruptions on Venus that broke the planet. Which one should we sentence here? The volcanoes seem more likely because we can see how that's happened on Earth just to a slightly lesser extent. But if this was put into a court of law, they would both be presumed not guilty just because there isn't a...
Tell Talbot of Edmunds where you can think, yes, this is definitely how it happened. Not yet. So how do we solve this murder mystery? There's basically a fleet of missions that's going to unravel the geologic makeup of Venus today. And if it looks bone dry, and it was always bone dry, that may be the case, then maybe the sun did it because it's been dehydrated for a long time. But if it looks like there's still some dehydration going on, that means you still have water somewhere. Yeah.
So if Venus was still kind of soggy on the inside, and it's still kind of belching water out, the volcanoes probably killed Venus. Could the Earth pull a Venus one day? So it sounds like, you know, these planets started off the same or similar, and could Earth be turned to this hell? Yes!
Yeah, it could. A caveat, let's not panic. I mean, these sort of eruptions are like on millions of years of timescales, you know, hundreds of thousands of years, millions of years. So it's not like no one would see this coming and would instantly be doomed. Yeah, yeah. It's nice to have a little bit of like lead time before the apocalypse. But it could happen. And the question is like, is it normal for a planet to have just one of these really epic eruptions?
Game changer options at the wrong time? Or is it just a fluke? And the fact that no one knows the answer to this is weirdly perversely exciting to me that we don't know how often it is that volcanoes decide to trash the planets they're on. Which one is the exception? Is Venus the odd one out or is Earth the odd one out? If Earth is the odd one out, then not only does that mean it might be harder to find life out there,
But how lucky are we to exist? The Earth hasn't malfunctioned in that way. If Venus is the odd one out, then maybe we're not so special after all. So it's about all life, including us. Could we be the volcano in this scenario? Or likely not because the scales of carbon we're talking about are too big. Yeah, it's... I mean, the pace in which we're putting carbon dioxide into the sky is worse than what was happening during the Great Dying.
in terms of the amount of carbon per year type thing. So that is impressive in the worst possible way. I mean, that's kind of staggeringly horrible. But the rate in which we're putting carbon dioxide into the sky is probably not quite as bad as having multiple epic great dying eruptions at once. And what's happening now, hopefully, it's not going to keep happening for millions of years, right? Right.
This is weirdly reassuring that humans are unlikely to break the Earth completely. Yeah, weirdly, but, you know, if we want to pay homage to what happened to Venus, I think that would be a terrible idea. We shouldn't aspire to be volcanoes. We should not aspire to be volcanoes. Coming up after the break, what if this terrible, scorching hellscape isn't as dead as it seems? That's next.
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It's Unexplainable. We're back here with Brian. Hi. In the first part of the episode, we were talking about how Venus might have been killed either by the sun or volcanoes, which caused runaway climate change, turning it into this lifeless, uninhabitable, totally dead planet.
Yeah, yeah. But can I introduce a plot twist? Hit me. Now scientists are wondering, like, maybe it isn't so lifeless as we think? Like, maybe there's life on Venus? There seems to be a little crack in that door and some light peering through. So there was some big news back in 2020. A group of scientists published a paper in a big journal, Nature Astronomy, and
They had pointed a couple of telescopes at Venus, looking at its atmosphere, and they detected a certain gas in the clouds of Venus, a gas called phosphine. And what does that mean exactly? So phosphine is this gas that's just really strongly associated with life. So here on Earth, bacteria make it in swamps and in the intestines of animals.
There is some debate over whether volcanoes can make it too, but a lot of people just see phosphine as an exciting clue in the direction of life.
Huh. Okay, so we have essentially a possible sign of something made by life in the clouds of Venus. Does that mean there could be aliens on Venus? Well, maybe. Yeah. Okay. Yeah. I mean, other scientists have analyzed this data and say, like, they don't see the phosphene. You know, this is ongoing discussion, but it is tantalizing.
And it is leading some scientists to revisit some big ideas that Carl Sagan had. If there is life on Venus, it is probably of a type that we cannot now imagine. Can we try to imagine it, though? Like, we heard in the first half of the show just how terrible of a hellscape Venus is. I mean, how could life actually survive there? What kind of life would that be?
Yeah, so I love this question. And I asked Sarah Seeger. She's this planetary scientist who's a part of the team that first announced the phosphine in Venus's atmosphere. And she says there are basically three things that life needs to survive.
It requires a source of energy, like the sun. It requires some kind of liquid for chemical reactions to happen. And it requires the right temperature. And does Venus have those three things, like energy, liquid, and a good temperature?
Oh, it's got energy from the sun. Good old sun providing, you know, energy. It does actually have liquid, but the liquid is liquid sulfuric acid, which is really harsh stuff. Like, if there is life there, it'd have to be, like, really different and hardier than, like, life on Earth to survive living in liquid sulfuric acid.
But is that third thing, the temperature, that really provides a huge challenge here that makes thinking about life really difficult? Yeah, it's super hot.
The surface is too hot for life of any kind, that we know, because the temperature is so hot that we can't have complex molecules needed for life. So, like, the very proteins that make up life would, like, degrade and melt on the surface. But Venus does have these huge, thick layers of clouds. The whole entire planet is covered in clouds. And they're also very extensive vertically. They're, like, 20 kilometers deep.
So there's a lot of cloud material there. And the clouds, you know, they're not as hot. If you ever hike up a mountain, you know when you hike up and it gets colder and colder? So for Venus, far above the surface, at 50 kilometers or so above the surface, the temperature is actually just right for life. If there is life on Venus, it could be in those clouds. What kind of life lives in clouds? That's what I want to know.
I asked Sarah this, and she answered my question with another question. Did you know there's life in our clouds? No. We have bacteria that are swept up from the surface, and they spend about a week up in the clouds. Most of them are inside cloud droplets.
They can be transported over continental scales, and then they drop back down. So they just get swept up into the sky and live there for a little bit, and then come back down? Right, right. We imagine that if there is life on Venus, it's little kind of microbial-type life, like just little cells inside the cloud droplets. And they just stay up there in the clouds? They never fall back down? The main problem about life on Venus is it has to be able to stay in the atmosphere indefinitely.
But the problem there is these droplets collide and they grow over time. So they become bigger, but they also become heavier. And eventually the droplets will settle down like a kind of slow rain. And the problem is that if they go too far down,
then life will die from the high temperatures. Yeah. So you can't literally rain down to the surface or just annihilate itself. Right, right. So you can't have life aloft indefinitely if it's all raining out and getting heated until it's no longer alive. That's a really big inconsistency. And so I came up with the life cycle idea.
What's the life cycle idea? So life is inside the droplets, which can stay aloft for months or even years, depending on the size of the droplet. But as they start raining down slowly, they come to a layer where it's hot, so the liquid evaporates. But it's not too hot, so the life form could dry out into a spore, and they would stop sinking down.
And so spores like a dried out little husk of itself. Yes, like a dried out little husk of itself. Yes. And these spores would populate a layer just below the clouds. In fact, there's this layer of haze of unknown composition. So they would be in that layer and they could just be there all dried out for a long time.
and eventually be brought back up to the cloud layer. And you know, on Venus, winds blow over mountains and create ripples, like waves in the atmosphere. And the waves move upwards and they can nudge particles along. And then, like, to complete the cycle, once they get nudged upwards, they can, like, rehydrate or something? Yeah. Once these dried-out spores get transported up to the cloud layer, they can attract particles
liquid and rehydrate. And then maybe rain down again. Right. And then eventually, over time, they can live in the droplet and reproduce, and they will drop down again. This is a really... I don't know. I find that idea really pretty. It's like the cyclical kind of... If a snow kept falling and being recreated, but also being alive. Right, right. I'm glad you like it. And I'm wondering here, just thinking about...
what we were discussing on the first half of the show, that Venus was possibly this ocean world that was alive, this potential life you're talking about. Is this something that could have started in those oceans? Well, we do like the idea of Venus' life, if it has life, having started in the oceans. And as Venus got hotter and hotter and the oceans eventually evaporated, that life migrated to the clouds.
and found a way to evolve and survive in the clouds as they became more and more acidic. But this is all hypothetical, right? Yes. This is like a hypothetical drawing, like a sketch, if you will. How do we find out if there's life in Venus's clouds? Well, the great thing about Venus is it's not really too far away. We would like to go to Venus, capture some of the atmosphere and cloud particles, and bring them back to Earth so we can study them in extensive detail.
I know there are some missions that are being prepared to go to Venus. Are any of those going to look for life? These missions, they're not focused on the search for life. So we would need a...
specifically focused new mission to answer this question. But in the meantime, we can look for the gases that are far out of equilibrium, that don't have a chemical explanation. We can look for complex organic molecules. We can check the acidity of the droplets and see how acid they are. We can check the composition of what's in the droplets. We know there's some really unusual interesting chemistry on Venus.
There are several key mysteries. So if there's not life there, there's something else weird that's going on that we don't understand yet. And scientists love a puzzle. You know, like this conversation about Venus and it being such like a dynamic place, you know, potentially life there. Do you think too much attention has been paid to Mars and like all the searches for life there and all the rovers and all the missions that it's gotten?
Well, it sounds like you think so. Yeah, well, maybe. Maybe I've become convinced of that. Like we've ignored Venus. You know, I always, yeah, I think of Venus like the neglected sibling. What would it mean if there is life in the clouds? Like if something like this is real? Well, I think it would be incredibly awesome if there is life in the Venus clouds and we have a way to show that that life has an independent origin to our life on Earth. It means that life is common.
Because if life can form, you know, if it can originate and evolve and survive on two very different planets, surely it means that there's life everywhere. Anywhere life can form, it will form. This episode was reported by Brian Resnick and produced by me, Manning Nguyen.
We had editing from Meredith Hodnot, Katherine Wells, and Noam Hassenfeld, who also scored this episode. Richard Seema did the fact-checking, Christian Ayala did the mixing and the sound design, and Liz Kelley Nelson is the VP of Vox Audio. If you want to learn more about epic, world-transforming volcanoes, Robin Andrews has a new book out, and it's called Supervolcanoes, what they reveal about Earth and the worlds beyond. And in it, there's a chapter that goes into the volcanoes of Venus in more depth.
You can also email us at unexplainable at vox.com if you have any thoughts on the show, or, you know, if you feel like leaving us a nice review or rating on Apple Podcasts, I know we'd all really appreciate that. Unexplainable is part of the Vox Media Podcast Network, and we'll see you next Wednesday.