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What’s so bad about Venus, besides everything? How did it get so bad? And are we next? I discuss these questions and more in today’s Ask a Spaceman!

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Hosted by Paul M. Sutter, astrophysicist at The Ohio State University, and the one and only Agent to the Stars (http://www.pmsutter.com).

 

EPISODE TRANSCRIPTION (AUTO-GENERATED)

So Venus, what went wrong? What went wrong? Venus was so promising. I mean, 80% the mass of the Earth, 94% the radius of the Earth. Pretty much started with the exact same mix of elements of of oxygen and silicon and and carbon and nitrogen and water.

It was in the habitable zone. It still is in the habitable zone. You know, the the region around a star where it's not too close and too hot and it's not too far and too cold where all the water turns in ice. It's where you can have liquid water around the star. What went wrong?

What went wrong? We're pretty sure that billions of years ago, Venus was nice probably had liquid water oceans and blue skies and white fluffy clouds and rainbows and unicorns okay maybe not the unicorns but Venus was pretty nice and then something went wrong way wrong Venus isn't so pretty anymore, is it? Sometimes Venus has gotten the nickname of Earth's sister planet because it's so close in size and mass. One paper I read called Venus Earth's Twisted Sister, and, I mean, there's so much going wrong with Venus. It's where to start?

Can we start with the pressures? Can we start with the atmospheric pressure? At the surface of Venus, the atmospheric pressure is 90 times that of the Earth. 90. It's equivalent to one mile or one and a half kilometers below the surface of our oceans.

You go 10 feet underwater and your ears start to hurt, imagine going a mile down, that's the air pressure on Venus. It's almost entirely carbon dioxide, which means it's poison. It's chokingly thick. Its density is 6% that of water. The air surrounding you on the surface of Venus is 6% that of water.

You're practically swimming through it. And on top of this thick carbon dioxide haze are clouds made of sulfuric acid. You know, acid rain? The clouds are made of that. And these things are super highly reflective.

They're literally blindingly white. Like, if you're already close to Venus and actually look at it, it's so reflective, it hurts to look at. It's so reflective that only 2.5% of the radiation from the sun that reaches the cloud tops actually makes its way down to the surface. So if you're on the surface, you only vaguely know you are aware it's daytime versus nighttime. This atmosphere is so dense that you know how, like, nitrogen is, like, 90% of the Earth's atmosphere or 80%, one of those numbers?

Nitrogen for Venus is only three and a half percent of the atmosphere, but it's four times total the amount of nitrogen in the atmosphere of Venus than there is on the Earth. As for the climate, you know, what what's your weather for your your five day your weekday outlook gonna look like? Yeah. It's all hell all the time every day, every night, nonstop. The average temperature is 735 Kelvin.

How hot is that in Fahrenheit? It doesn't matter. It's hot. It's hot enough to melt lead, which is why our landers that go there don't last very long, and we kinda stopped doing that for a while. Also, this temperature of 735 Kelvin, keep in mind, only two and a half percent of the radiation from the sun that hits the cloud tots actually makes its way to the surface despite that.

Despite only a tiny fraction of sunlight actually making it to the surface, you still have this temperature of 735 Kelvin. The high temperature, there are variations in the temperature. So you can go to some hotter places and some colder places, you know, relatively. The hottest temperatures, the high temperatures are in the valleys, the deep valleys, and it's around six 765 Kelvin. That's hot enough for the ground to literally glow dull red.

Yeah. It's nasty. And the rotation, I mean, Venus is weird. Its day is half a year long, and it's in the wrong direction. The sun rises in the West and sets in the East.

And when it does that twice, you've orbited the sun. Let's talk about that backward rotation a little bit more. I think it deserves some, fleshing out. The word for backward rotation, by the way, is retrograde, as in why is her shirt on backwards because she's into retrograde fashion. I'm sorry.

If you want better jokes, you need to contribute to Patreon. That's patreon.com/pmsutter to learn how you can support the show. And maybe if I reach a certain threshold, I can write better jokes. Don't count on it, though, but please keep this show going. Did I mention it's this is my job.

Like, this is what I do. So anyway, rotates backwards retrograde, and it's so slow. Two days gives you a year. Earth rotation is around a thousand miles per hour, sixteen hundred kilometers per hour. Venus is at four miles per hour, six kilometers per hour.

You can walk faster than Venus rotates, which means you can keep the sun overhead if you felt like it, and you wouldn't even need to work hard. So Venus has a thick atmosphere, chokingly thick atmosphere, ridiculously high temperatures, highest temperatures in the solar system, hotter than Mercury, Mercury is closer to the sun. Doesn't matter. Venus is hotter. Weird, slow, backward rotation.

No evidence for plate tectonics. I mean, this is a planet as big as the Earth, which means it's still hot on the inside. It has a really hot core. There's no evidence for plate tectonics. There's no big rift valleys, no mountain chains, not a lot of volcanoes, if any.

Venus sucks. If there's an award for the least fun planet, Venus might win it. And yet it started off similar to the Earth. How did it get so bad? So we have three big mysteries.

Three big mysteries. The thick atmosphere, the slow rotation, the no tectonics. And when we see weird things or special cases in the universe, they kinda sorta demand explanations, so let's try to explain. I wonder if they're connected. I wonder if they're giving us a clue to how Venus went so wrong.

And the answer is, are you ready for this? We don't really know. The thick atmosphere, the slow rotation, the lack of flight tectonics may all be disconnected things, or they might be related. For example, maybe the backwards rotation is just caused by planets having all sorts of random rotations, or maybe it got struck early in its formation, maybe it had a moon for a while and lost it because it's too close to the sun, and the sun tugged gravitationally tugged on that moon and it lost it, so it could have all sorts of reasons. Maybe its atmosphere is just thick.

Sometimes planets have thick atmospheres, you know? We're not gonna judge. We're not gonna thick atmosphere shame a planet. If it's got it, then we'll fly. It's cool.

It's cool. That's just the way it goes. And Mercury and Mars don't have plate tectonics. We're watching Venus. I mean, sure, it's almost the same size as the Earth, but not quite.

Maybe it's just unlucky. Maybe there's a connection. Maybe these things are telling us not just that Venus sucks, but why it turned into the disaster that it is. And we think young Venus looked a lot like young Earth through modeling of the early solar system, through the fact that Venus is made of a lot of the same stuff as Earth, has a very similar composition, very similar size, and so it just naturally lends itself to the suggestion, and this is born out in simulations that, yeah, Venus was was wet and had liquid water oceans, and was was pretty great. So what killed Venus?

The sun killed Venus. The sun turned Venus from paradise into the inferno. You see, billions of years ago, our sun was a lot smaller and dimmer. As stars like our sun age, they steadily grow brighter and hotter. And the reason they do that is they're fusing hydrogen into helium in their cores, and this is leaving behind like a helium ash that just builds up in the core and it gunks up the works.

You know, makes makes it harder to do fusion reactions. But to maintain balance, if you if you add extra helium, if you add a bunch of ash to the core of the sun, that reduces the fusion rate for a little bit, which means the sun contracts a little bit. So there's a little bit more gravitational push, which actually amps up the fusion rates, which actually inflates and brightens the sun. So ironically, as you dump more and more ash, inert helium into the core, this actually increases the rate of fusion in order to maintain that steady state of the star and it will steadily grow brighter. So billions of years ago, Venus was well within the habitable zone of the sun, like right there.

But as the sun aged, it got brighter, it got hotter, and this habitable zone started to move. They are not fixed. They move. They steadily grow outwards with time. And so over the course of, like, a billion years, even though Venus started out just fine, the inner edge of the habitable zone, that inner, like, oh, watch out.

You're too hot now edge crept closer and closer to Venus, and Venus got too hot. The sun was getting hotter, started evaporating the oceans. More water vapor got in the atmosphere. With more water vapor in the atmosphere, the water vapor started to trap heat. Heat just couldn't escape out into space as efficiently.

So heat could come in from the sun, but now with the water vapor there, heat couldn't get back out, and the heat has to balance. And so in order to compensate for that, to kinda like power through that, the surface had to heat up to try and get more radiation out to get through all that water vapor. It was like a big old blanket. This is the greenhouse effect. But this just led to higher surface temperatures, which led to more ocean evaporation, which led to more water vapor, which led to more higher temperatures, and eventually the atmosphere was soaked with so much water that no radiation could escape at all.

And the temperatures on the planet Venus just spiraled out of control. This is called a runaway greenhouse effect, where there's so much water vapor that nothing can get out. Like, just radiation just can't get out. That's bad. Generally bad.

So now what? So now all the oceans are gone. Planets dried up. All the water is up in the atmosphere. We're pretty sure Venus used to have plate tectonics because why not?

It's hot in the core, similar composition of the Earth, it probably had plates. But once the oceans are gone, plate tectonics shut down. Because the oceans are important for plate tectonics, They keep the ocean plates, like, flexible and ductile, allow them to move, kind of, sort of lubricate them. Don't quote that to a geologist or they'll hate you forever because that's not right. But yeah, like, a a very loose visual metaphor.

The oceans help the process of plate tectonics. With no more oceans, the plates started to lock together. They couldn't move anymore. And plate tectonics play a role in regulating the amount of carbon dioxide in the mass atmosphere. Because at this time, there was probably a lot of nitrogen in Venus' atmosphere, but now there's a lot of water vapor.

How do they get all its carbon dioxide? Well, most of the carbon dioxide on the Earth is actually buried inside the Earth because carbon dioxide gets really friendly with silicates, which is, you know, dirt, and the dirt sinks down through plate tectonics. So the action of plate tectonics actually scrubs carbon dioxide out of our atmosphere. Now carbon dioxide gets into our atmosphere through volcanoes, through outgassing, through just carbon dioxide just randomly leaking out here and there. So it gets up in the atmosphere, but then the action of plate tectonics pulls it back down.

So it's constantly cycling cycling. So most of the carbon dioxide stays buried in the Earth and not in the atmosphere. But if you don't have plate tectonics, that scrubbing action shuts down. The filter turns off. And you still have volcanoes.

You still have outgassing. You still have leaking. And over the course of hundreds of millions of years, the amount of carbon dioxide in the atmosphere just goes up and up and up. The water vapor itself, over time, gets hit by sunlight and splits into hydrogen and oxygen. The hydrogen just floats away into space.

The oxygen hangs around. The volcanoes that are still going on in the early Venus this is, like, three billion years ago, by the way, when we think this all went down. The volcanoes are spewing out sulfur and nasty stuff. That sulfur finds oxygen. That's what makes the sulfuric acid.

So over the course of, like, a hundred million years or so, this nitrogen water vapor atmosphere is replaced with a carbon dioxide sulfuric acid atmosphere. We've done studies of the Earth of of how much carbon dioxide is buried inside of rocks, and, yeah, if you apply those numbers to Venus, that's about how much carbon dioxide is in the atmosphere. So Venus released all of its carbon dioxide into its atmosphere, unlike the Earth, which has kept its carbon dioxide buried. So now we've got our soaringly high temperatures that are now locked in place because of this thick atmosphere, and we do have this super thick carbon dioxide atmosphere. We've got plate tectonics shutting down.

And now that you have this thick atmosphere, it's gonna be unevenly heated. The side that's facing the sun is gonna be a lot hotter than the side that's facing away from the sun. And this is gonna cause a density difference because there'll be a temperature difference, and this will cause drag. Like, the atmosphere is so thick on Venus that it can drag on the dirt and the mountains in the volcanoes themselves and slow down the rotation of Venus. In this scenario, there are other ways to slow down Venus.

This is one possible way that might be due to the thick atmosphere itself dragging it. Did I mention that Venus has no magnetic field? Yeah. This gives us a clue of what's still happening underneath the surface. Because in order to make a magnetic field, you need a hot core, you need a cool surface, but you also need a lot of conduction.

You need flows of heat. Very efficient flows of heat. You need that heat to move around. You need the stuff, like the core and the mantle, all that. You need that to circulate.

It's the moving charges, electric charges that generate the magnetic field. So you need stuff to move. But there's no plate tectonics, so there's no way or no easy way for the heat in the core of Venus to make it out. We have our plate tectonics. Like, the plate tectonics are powered by the heat of the core of the Earth.

This is how the Earth is able to release its heat through grinding its plates together and moving them around. Venus doesn't get that, so all that heat just stays trapped. And the core Venus is still hot because it's a pretty big planet, and it's like the Earth, so it's blazing hot. How is this heat escaping? If it can't do it through plate tectonics, how does the heat in the core of Venus find a release mechanism?

And there's one clue, is that the surface of Venus only has about a thousand craters on it. Only has about a thousand craters. And if you if this if plate tectonics shut off billions of years ago, there should be a lot more than a thousand craters because the number of craters on a surface tells you how young or old a surface is. Look at Mercury or the Moon. Tons of craters, old surface.

Look at the Earth, Barely any craters at all because the arc surface is constantly changing. It's always young. Venus has a relatively young surface. There's a thousand craters, which is a lot, but, I mean, not a lot. This suggests that sometime within, like, the past few hundred million years, because that's how long you need to build up a thousand asteroid or comet impacts, get a thousand craters, that sometime within the past few hundred million years, there was a global resurfacing event, which sounds as horrible as it could possibly be.

This is how Venus releases its heat, not through slow and steady and gentle plate tectonics. I mean, yeah, we have earthquakes and stuff, but that's nothing to the entire surface of Venus flipping itself over at once as all that heat builds and builds and builds and finally reaches like, a critical threshold where it's like it blows its top. And Venus, you can imagine just the surface of Venus just coming apart at the seams, flipping itself over, being molten hot, you know, lava fields extending across the entire surface of the world and then cooling down now that all the heat is released, had a big outburst, now can cool down and solidify. That sucks. I mean, Venus is horrible.

Who wants to go to who wants Venus? Apparently, some people do. Some people have brought up the idea of colonizing Venus instead of Mars. Why? Well, it's it is bigger, more Earth like gravity, a little bit more familiar, which might be necessary.

It's a little bit closer to Mars, a little bit easier to get to. Okay. Okay. Mars is just a frozen desert, who wants that? But but Venus, obviously the surface isn't gonna be all that great with, you know, temperatures, in the mid seven hundreds, pressures 90 times that of the year.

That's not the greatest idea, but the atmosphere is interesting. Because it's made of carbon dioxide, just plain old nitrogen and oxygen are lighter than that, which makes the air we breathe, you could fill it with a balloon, and the balloon would float in Venus's atmosphere. And if you get about 50 kilometers up from the surface, the temperature is like room temperature, and the pressure is, you know, like room pressure. That's not too bad. Right?

Well, I mean, there is the carbon dioxide. There is the sulfuric acid. There's these incredibly fast winds that whip around at hundreds miles an hour. Kind of a problem. Could you have some sort of floating city in Venus?

Yeah. Maybe. Good luck. Seems like a pretty vicious engineering problem. I don't think anyone really wants to go to Venus, but, you know, we'll see.

Perhaps, though, the most tragic part of the tale of Venus, of how it used to be like the Earth and then it got too hot and it all fell apart, is that this is the Earth's future. Why? Because our sun isn't done aging. It's about halfway through its life. And our sun, like any other star, as it gets older, it gets hotter and brighter.

That didn't stop three billion years ago with Venus. The habitable zone in our solar system is still steadily creeping outwards, which means in as little as a hundred thirty million years, maybe as long as five hundred million years, we're gonna approach that inner edge or the inner edge is gonna approach us. And when it does, the temperatures will rise. The oceans will begin to evaporate. They'll dump water vapor in the atmosphere.

The water vapor in the atmosphere will trap heat, which will cause the oceans to evaporate even more. The Earth will go dry with all the water vapor in the atmosphere. The temperatures will skyrocket. Plate tectonics will shut down, and we'll look exactly like Venus. We currently live in a paradise.

Just like three billion years ago, Venus was a paradise. But just like Venus, us too will become an inferno. Thank you so much to at rostra on Twitter, Russell s on email, and at paper monster twelve on Twitter for the questions that led to today's episode. And, of course, thank you to all my Patreon contributors. It is your contributions that keep my excessively ridiculous lifestyle, not quite, going, but it keeps all this science communication stuff going.

Like, every science outreach thing I do is is is funded by you. Like, I can't thank you enough. I'd like to thank my top Patreon contributors, John, Matthew k, Helga b, Justin z, Matt w, Justin g, Kevin o, Doug and m, Corey d, Kirk b, Barbara k, Nuderdoo, Chrissy, Eric m, Steve c, and Digital Neo, plus all the others. That's patreon.com/pmsutter. Don't forget, I wrote a book and you can buy at your place in the universe.

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And you can ask questions. Go to askaspaceman.com, askaspacemangmail Com, hit me up, I'm at paulmattsonter on all the social channels. Send me questions, and I will see you next time for more complete knowledge of time and space.

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