Daniel and Kelly’s Extraordinary Universe - Does the Moon have an atmosphere?

Episode Date: November 29, 2022

Daniel and Kelly talk about what you might breathe if you opened your space-helmet on the surface of the Moon. See omnystudio.com/listener for privacy information.

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John Fogarty, Lil Wayne, LL Cool J, Mariah Carey, Maroon 5, Sammy Hagar, Tate McCrae, The Offsprin, Tim McGraw, tickets are on sale now at AXS.com. Get your tickets today. AXS.com. Hey, Kelly, how was your family trip? Oh, it was so much fun. Did you guys get to break out of your usual routines, experience something different? Yeah, and something that was unusual for our kids was eating at restaurants. We don't do a lot of that when we're at home, and we didn't do a lot of it because of COVID and stuff, so that was new. And what is it that your kids like about eating out at restaurants? Aren't you guys like super good cooks at home?

Well, we keep me out of the kitchen for everyone's sake. But Zach is a really good cook, so that's good. But I think for the kids, they mostly like the novelty of it, you know, the atmosphere. Well, that's exciting, but it doesn't actually bode very well for them as future space colonists. Nope, I'm not following. What do you mean? Well, I hear that restaurants on the moon have no atmosphere. Oh. Hi, I'm Daniel.

I'm a particle physicist and a professor at UC Irvine, and I'm always in the mood for a good space pun. I'm Kelly Wienersmith. I'm an adjunct assistant professor at Grace University, and I am also a fan of the puns, especially the moon-based ones. There's a lot of inappropriate moon-based puns that we could be. make right now. Yeah, sure. No, you and I are pretty good at that, but we're going to keep it clean. We are definitely going to keep it clean as we examine the deep, dark mysteries of the universe. And welcome to the podcast. Daniel and Jorge explain the universe in which we do exactly that. Ask the biggest, darkest, deepest questions about everything that's out there in

the universe. We don't want to sweep anything under the rug. We want to expose it all to the blinding glare of sunlight and make it all make sense to you. usual co-host Jorge can't be here today. So we are delighted to have one of our regular co-hosts, Kelly. Kelly, thank you very much for joining us today. I'm delighted to be back. Kelly, when you're on the podcast, we're often talking about space and about the wonders of the night sky, putting people out there mentally sort of at night, staring up in the stars, being amazed at everything that we are seeing. That's right. And then you turn it into something about how we're all going to die. But yes, we are usually looking up at the night sky and having a sense of all about it all. Because one of the things that I love about science is that it lifts us up away from our everyday lives. It forces us to turn our eyes skywards and think about what's out there in the universe. Usually that's something we do at night because during the day, the sun is so bright.

It keeps us from seeing everything that's out there that makes us wonder, that makes us ask deep questions about the very nature of the universe. But you know, everything that's out there is also out there during the daytime. And I remember that blew my mind when I was a kid and I first learned that. But yeah, it's all still out there. And sometimes you can see the moon during the day. It always feels sort of inappropriate, though. When you see the moon during the day, it feels like, you know, you've caught somebody like they're not supposed to be there, like they're tiptoeing to the fridge in the middle of the night and you spotted them. Yeah, or like they don't know their place, you know, like moon, your place is at night. You're stepping on the sun's toes.

And you know, it's not only the nighttime sky that's really fascinating. That's really amazing. that has a lot of physics in it. There's a lot we can learn about the nature of the universe and what's out there just by looking up at the daytime sky. Oh, well, what can we learn? Well, one common question from kids, of course, is why is the sky blue? You know, if the sun is just shining through space at us, what is it that makes the sky blue?

And so we've talked about it on the podcast a few times. It's a fascinating interaction between the sun's gas and the atmospheric gases. The light that comes directly from the sun is white. light. If you were out in space looking at the sun, it would mostly look white, maybe a little bit yellow. But not all of that light passes through our atmosphere equally well. When light hits gases in the atmosphere tends to scatter and it scatters more for the very high frequency light, the bluer light. That might make you think, oh, well, we should see everything but the blue light. The blue should get reflected back into space. And it does get reflected back into space,

but it also gets reflected down to the ground. So when you're standing on the surface of the earth and you're looking up at the sky, you're seeing light that doesn't come directly from the sun and sort of hidden atom and bounce down to your eyeballs. So the reason that our daytime sky is blue is because those gases bounce the blue light down to our eyeballs. And can we use this to figure out what the atmospheres of other planets are made of just by looking at the color that we see when we shine a telescope at them? We totally can. And we do exactly that. When exoplanets pass in front of their stars, the light goes through their atmosphere. And some of it bounces off and some of it passes through and some of it is absorbed.

It's a great way to understand what's in those exoplanet atmospheres. And so it's sort of like x-raying the atmosphere, passing light through it is a great way to figure out like what's there. How's it glow? What does it absorb or what does it reflect? I love the idea of seeing a sunrise on an exoplanet and using that to figure out what's in the sky. And you know, sunrises on different planets all look very different because different planets have different atmospheres. And so when I am looking up in the night sky recently, I've been seeing a big red dot. Is that Mars or is it Venus? And also, when I see those colors, is that the atmosphere I'm

seeing? Or is that something else that I'm seeing entirely? So if you look up in the night sky and you're seeing a red dot, that's probably Mars. And Mars is definitely red. If you were in a satellite orbiting Mars looking down, it would look red to your eyeballs. It's not just like a false color thing from satellite imagery that we take and then change the way like James Webb Space Telescope images are all false color. If your eyeballs were there where James Webb's space telescope was, you wouldn't be seeing those images because those images are all infrared. They're all too deep, too long wavelengths for your eyeball to even register. But if your eyeballs were orbiting Mars, hopefully with the rest of your body, you would see it as red. And the reason there is not actually

the atmosphere because Mars has almost no atmosphere. It's very, very thin atmosphere. It's because the surface of Mars itself is mostly red due to the iron and the oxidization. of it. So it's covered in this red dust. And it's sort of amazing that you can see it from the earth's surface, right? That this thing is so red that you can see it from your backyard. That's incredible. And then the fact that you, so you said that it has very little atmosphere, that makes me, I have a pop culture question to ask you. Someone told me that one of the things they didn't like about the Martian was that with a low atmosphere, if you had a big dust storm, it wouldn't be strong enough to like knock over a rocket

because low atmosphere means like far fewer molecules pushing against things even in a big windstorm. So is that not accurate about the Martian? This is important. This is absolutely vital stuff. Yeah, it's definitely true that the atmosphere on Mars is very, very low. It's like less than 1% of the Earth's atmosphere.

And that means that the wind don't apply as much pressure. So wind at the same velocity, for example, there just aren't as many molecules. bouncing off of you. But the velocity can get very high and there's also a lot of dust in the atmosphere on Mars. You definitely do have to worry about storms. A very high velocity windstorm on Mars can do a lot of damage because all the dust particles. You could basically sandblast you, right? I don't know if the velocities actually get high enough to knock things over. We'll have to get Andy Weir on the podcast and asking him that question. Well, you know, I loved that book in that

movie and you're making me feel better knowing that maybe that opening scene was feasible. I would hate to think it wasn't. But okay, all right, let's get back to the important stuff. But it does bring us to a really fascinating fact about Mars, which is if you're standing on the surface of Mars, and you look down, of course, it looks red, but also if you look up, it looks red. That is, the sky on Mars doesn't look blue like it does on Earth. That's because Earth has this atmosphere which scatters the blue light down to your eyeballs, but Mars doesn't. These atmosphere is so thin that it doesn't effectively scatter that light. So then why is it red instead of white from the sun.

It's because of all of the dust, right? Mars doesn't have much atmosphere, but the dust is up there. And that dust tends to absorb blue light. That's why it looks red. Remember, things that look a certain color, they're reflecting that color, and they're absorbing everything else.

So things that are yellow are things that reflect yellow because the yellow makes it to your eyeball and they absorb everything else. So it sounds weird to say that red dust absorbs blue light. You might think that makes it blue, Right? But actually, that's what makes it red. So when you look up in the sky during the daytime on Mars, you're seeing the red light reflected from that dust. I didn't realize that the dust never settled enough for the sky to not be red.

That's incredible. It is incredible. And if you're lucky enough to observe a sunset on Mars, then you'll see an amazing blue sunset, right? It's like totally reversed from Earth because this dust scatters the red light. And so if you're looking directly at the sun, sort of, then most of the red light is, been scattered away by the dust. And so the blue light is all that survives. So you see a blue sunset on Mars on a red sky. Oh, that's incredible. I hope within my lifetime we get photos of that taken by an astronaut that landed on the Martian surface. Blue sunset selfie. Wow, what an

Instagram pick. That'll be. Incredible. TikTok. And that makes you wonder like what it would be like to be on other planets, right? If the atmosphere of the planet is what determines what it looks like to be on the planet, the color of the daytime sky and atmospheres can be like, you know, anything, that opens the door to like having all sorts of crazy daytime colors. You know, can you have like a yellow sky or a purple sky or something with crazy stripes from atmospheric bands, right? I haven't yet seen that in a science fiction movie. You know, somebody living on Jupiter where the sky has like stripes of color. That would be really awesome. That would be epic. And there aren't many places in the solar system where we have had people take pictures, right? One of those, of course, is the moon.

And something that's striking about all of the pictures from the moon is that the sky, the backdrop, or if you look above the moon, it's always black. And why is that? Right. Because you associate black with the color of the night sky, right? But even during the moon sort of daytime, when the sun is shining right at you, there's nothing there to scatter the light. So from the point of view of somebody on the moon, the sun is just another star. So it's sort of like a perpetual night sky with one huge. very bright star in it half the time whoa also not very invited you wouldn't want to have a picnic under a black sky i feel like the regalith would get in my sandwich and would sort of mess up the overall feeling so the reason the night sky and the moon is black is because there isn't a strong enough atmosphere there on the moon to scatter it to make it blue or purple or yellow at

pink polka dots but it does raise an interesting question and the question of today's episode which is Does the moon have an atmosphere? So this is a fun question because it lets us dig into definitions and quibble about what it means to have an atmosphere. Yay for quibbling. Sometimes it feels to me like a big part of science is just like arguing about what a definition is. You know, like, is this really a mammal? I don't know, it lays egg.

What does that mean? Whereas really that interesting questions are like the questions behind that, you know, like, why does something with hair lay eggs anyway? Yeah, that was one of the most surprising things when I started college was like, wait a minute, we don't even know how to define a species. Really? And, yeah, of course, huge arguments over that. But, you know, it's because nature doesn't fit in the categories that humans would like it to.

Yeah, and sometimes those arguments are just a waste of time. People splitting hairs when there's nothing really to be learned. But sometimes it really is illuminating because we do try to describe the universe in terms of categories. These ways that we'd like to think about things are sort of our familiar basis. And in the end, that's what science is, is explaining everything we'd see in terms of things we understand. Physics is describing the unfamiliar in terms of the familiar. So the words we're using are sort of important. If we're going to communicate with each other about these ideas, we better at least know what the words mean. And I guess to be fair, I'm thinking that I don't exactly

know when an atmosphere starts and stops, because it seems like sort of a gradient. Like is, you know, At what point do you call it an atmosphere versus something else? And so I'm not sure that I know the answer. So let's see what your listeners think. Great idea. And so as usual, I went out there into the internet to ask people if they thought that the moon had an atmosphere. If you'd like to participate for future episodes of the podcast, please don't be shy. Write to me to questions at danielandhorpe.com and I will set you up.

It's free. It's fun. Your friends can hear your voice on the podcast. So before you hear these answers, think to yourself. Do you think the moon has an atmosphere? Here's what people had to say. Hi, so I don't think that our moon has an atmosphere, at least anything substantial enough to call it an atmosphere.

I did have a physics professor my first year of college who claimed to have a plan to give the moon atmosphere for 200 years by basically creating an orbital cannon that could help a smaller moon from either Jupiter or Titan that have like an escape velocity of 17 miles an hour to slingshot that into hours, vaporize it, and create an atmosphere, but it wasn't only for 200 years. So I think that implies temporary and nothing substantial enough. I don't think the moon has an atmosphere.

I mean, there might be some, like, low-density hydrogen or something floating around, but not enough to call it an atmosphere. I think it has some atmosphere only because I'm thinking that moon has a weak magnetic field that might be able to contain some kind of atmosphere. there are so not what Earth has, but still something. I would guess it probably does. I doubt it looks anything like ours does on Earth, but I would guess that if you're a body or an object in the sky

and you're large enough or dense enough that you probably attract some kind of atmosphere. The moon doesn't have an atmosphere. I think it's because its gravitational attraction is too weak weak to sort of hold the guesses around it to form an atmosphere. So what do you think of these answers, Kelly? A lot of skepticism here. A lot of folks feeling like the moon can't really have much of an atmosphere.

Yeah, but a lot of critical thinking also. A lot of folks trying to think through like, well, you know, I think the moon has a weak magnetic field so that wouldn't contain it. And yeah, so lots of good thinking through the problem. Absolutely. And I love seeing people apply their knowledge of physics to this question to come up with an answer that they think makes sense because if the answer is not the one that you expect, then there better be an explanation for it, right? That in the end is what physics is all about.

That's right. So how about we start by talking about where atmosphere has come from? How do you get an atmosphere? Well, you go to Amazon.com and you just type in whatever you'd like and you know they deliver it. I know so many space element advocates who are going to be so excited to know it's going to be so easy on the moon or Mars. It's surprising Bezos isn't. saying more about this. On Mars, isn't the plan to just like nuke the polar ice caps? Isn't that like step one in getting a Martian atmosphere? You know, that has been proposed, but I'm fairly certain the international community has mixed feelings about that proposal, so I'm not holding my breath. And also I think it makes it uninhabitable for quite a while. But you know, if we've got our

great grandkids in mind, maybe it's a good plan. Yeah, we have a whole episode on terraforming Mars and why that plan will not work. So we're lucky that we have such a nice atmosphere here on Earth. And I think you're right, it's a good idea to think about why Earth has an atmosphere and why the moon doesn't have at least the same atmosphere as we do. And the interesting thing is that the Earth sort of has had a few different atmospheres. The Earth got its first atmosphere when it was just forming. Remember that the whole solar system just comes from a big cloud of gas and dust and rock and little bits from other solar systems and stars that died. Most of it's just hydrogen left over from the Big Bang. But you have this big cloud of gas and dust in space. You have some blob

in it that are little denser than others, so they have stronger gravity, they are pulling everything together, and that's the formation of the solar system. Of course, in the very center is the sun, which gathers in most of the gas and the dust, but you also have other little blobs which eventually form planets, and they try to gather as much stuff as they can before the sun gobbles it all up. You know, it's funny, my intuition, and this is why I didn't become a physicist, my intuition, like it feels to me like gases shouldn't get pulled in by gravity, but of course, they are and they should, but the idea that gravity is holding our atmosphere on,

I don't know, it feels like the little molecule should be able to just pop out and escape, but I'm glad that I'm wrong about it. You're not actually wrong. A lot of them do escape, and the Earth is constantly boiling off its atmosphere into space. It's a tenuous balance, right? The Earth is pulling on those little guys,

but they are moving quickly. And the ones that have higher velocity and higher altitudes definitely do escape. And in the very early days of the solar system, the Earth had an atmosphere which came from these like primordial gases, the hydrogen, the helium, that was just sort of like around. But it didn't last for very long. It was not a very good atmosphere for having an atmosphere, I guess you could say, because first of all, the sun was gobbling up most of the hydrogen and the helium. And then once the sun formed, it was producing a lot of radiation,

which stripped the inner planets of their atmosphere. So like solar wind and heat from the sun basically blasted the Earth's atmosphere away. So it started off having a scoop of hydrogen and helium and stuff that could have made an atmosphere, but then it got blasted dry, basically, by the early sun. So is solar wind well-named? Is it like the sun is like, and the stuff just sort of blows away? Or is it more like the photons that come out from the sun? It's like a billiard table and it, like, knocks the hydrogen and the helium out of our

atmosphere when they, like, bounce into each other. I think it's pretty well-named because it's not just photons. It's protons, it's electrons, it's actual parts. So if you think about wind on Earth is like high moving particles that carry momentum and it can push stuff over, then the solar wind is really the same thing. It's stuff. It's matter particles carrying momentum and it could like push a solar sail and it definitely blasts things off of the moon and Mars and early Earth. Way to go, physicists. Good job naming that thing. And that's one reason why you have, for example, rocky planets in the interior of the solar system because that's the kind of stuff the sun couldn't blast off and like formed.

denser blobs and in the outer part of the solar system you have the gas giants because they were far enough away from the sun to get to gobble up some of their own gas and to hold on to it out there where the solar radiation is weaker so we got atmosphere very early on and so did the moon as the moon formed from whatever primordial blobs made it it also must have had some helium and some hydrogen but that also was blasted clean by the sun so we both started with an atmosphere and both lost our atmosphere very quickly. And we both, both of them lost it entirely, or did Earth retain some of it? Almost entirely. I mean, never completely dry. There must have been a little bit of hydrogen floating around. But compared to the densities we have today, basically zero. Okay, well, before we

get into what our second atmosphere was like, let's take a break. In the heat of battle, your squad relies on you. Don't let them down. Unlock Elite Gaming Tech at Lenovo.com. match with next level speed, seamless streaming, and performance that won't quit, and push your gameplay beyond limits with Intel Core Ultra processors. That's the power of Lenovo with Intel inside. Maximize your edge by shopping at Lenovo.com during their back-to-school sale. That's Lenovo.com.

The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal glass. The injured were being loaded into ambulances. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here. here to stay. Terrorism.

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This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating.

He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHart Radio app, Apple Podcasts, or wherever you get your podcast. Our IHeart Radio Music Festival, presented by Capital One, is coming back to Las Vegas.

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we had and we lost. But we know that we get to hold on to one atmosphere eventually. So what happens to the next atmosphere? This is like a Disney movie. You know there's a happy ending, right? So even when there's ups and downs, you can sort of hold on. Just like life. Right, but we're telling two stories simultaneously here.

We're interested in whether the moon has an atmosphere, and we're telling the story of the Earth and the Moon's atmospheres in parallel to see why they have different fates. So the Earth's got its atmosphere sort of rebooted from its interior. You had like volcanoes and all sorts of crazy stuff happening on the surface of the earth, which outgassed like water and CO2 and sulfur dioxide and nitrogen. So this is like the earth burping and giving itself an atmosphere just from those burps. That makes it like substantially less beautiful to watch the sunset. Oh, those are earth burps making those colors. Yeah, and you know, let's go with burps rather than any sort of other gaseous emission.

But it's incredible that there must have been so many volcanoes. so much sort of tectonic action in the early Earth that you could release vast quantities of gas, right? Did this happen on Mars too, or am I getting too far afield by asking that? Because Mars has volcanoes too, right? Yeah, we think it happened on a lot of these planets. And remember the scale, though, of the atmosphere, even though it seems vast to us and it seems dense, it's really a very, very thin layer on top of an enormous sphere. The atmosphere goes up like a few hundred kilometers, depending on how you define it. But the Earth's radius is 6,000.

kilometers. And so it's not that surprising that all of that stuff could bubble up enough gas to cover it with a very thin shell. It happened on Earth and it happened on Mars. And we also think it might have happened on the moon. The moon is not just like a lifeless inert frozen rock. It had volcanoes. We can see this on the surface of the moon. There are lava planes. Underneath the moon, there are these lava tubes, all sorts of crazy volcanic stuff that happened on the moon. How long ago did the volcanic activity end? We don't know. We don't think that there are any active volcanoes right now,

but we have measured moon quakes. Like you put these sensors on the surface of the moon, and there are moon quakes, right? And that suggests, yeah, that there's stuff going on inside the moon, that there's internal magma, there's stuff like swashing around in there, which might mean, you know,

future volcanic action. Probably not, though. The crust is probably now cooled and sealed, and all that stuff has sunk too far towards the center to ever crop up. Again. Will it cool and stop moon quaking at some point? Eventually, it probably will.

Yeah, the same sort of thing is happening on Mars. Mars and the moon, of course, much, much smaller than the Earth, and so they cool faster. And we think, for example, Mars still has some sort of liquid or at least fluid core, and there's stuff going on inside there because we've measured Mars quakes as well. But there isn't active volcanism on the moon or on Mars. Okay. And so did the moon lose its second atmosphere for the same reason that it lost? its first? Or did the volcanoes never give it an atmosphere to begin with? Yeah, it's a great question.

And so we have to understand not just how you get an atmosphere, but how you hold onto it, right? It's not enough to just produce the gases, either from the first scoop of solar system stuff or remaking it again from volcanoes. You got to hold onto it, right? Because as you say, there are things out there in the solar system that are trying to get rid of your atmosphere. And so the solar wind didn't stop, right? The solar wind was around in the early days. when things were forming, and it's still going on today. And so there are processes out there which remove atmospheres, which work against having an atmosphere on the Earth and on the moon and on Mars.

So this second atmosphere that the moon did have, unfortunately, did get blown away. Sorry, Moon. The story always seems so sad for the moon. But I think it's really interesting to understand sort of the balance between those effects. I like thinking about it microscopically the way you were. Like think about the atmosphere. individual particles of that gas, right? Because in the end, the atmosphere is not just like a huge blob of gas.

It really is made of individual particles. And the fate of those individual particles is what determines the fate of the atmosphere. And it's sort of weird to think about, but gravity does operate on like individual atoms of gas, right? Like the earth pulls on each of those nitrogen atoms and each of those oxygen atoms. It really is yanking and keeping a lot of them on the surface of the earth. And that's, of course, the biggest difference between the Earth and the Moon is that the Earth is bigger. It has more gravity.

And as a lot of our listeners said, the Moon just doesn't have the gravity to hold on to its atmosphere. Does the magnetosphere play a role, too, or is it mostly about gravity? That's a really interesting topic because the Earth's magnetic field does protect us from the solar wind, right? The solar wind are charged particles. These are protons. These are electrons. What happens when a charged particle hits a magnetic field is that it tends to bend. And so when charged particles from the sun hit our magnetic field, they don't immediately just like slam into our atmosphere. They spiral around these magnetic field lines and they go up to the North Pole or down to the South Pole.

And you finally see them as like the Northern Lights or the Southern Lights. That's what causes them this magnetic field. And so initially you think, oh, well, this must protect us. It's like a shield keeping our atmosphere in place. That's sort of the prevailing view that a big magnetic field will protect you like a shield. Other people feel like actually a magnetic field is sort of like a sail. It's going to capture a lot of solar wind and funnel it into the planet helping strip the atmosphere. And so like most things that involve like more than one particle, the story is complicated and people have differing opinions about it.

But in the case of the moon, there's very, very little magnetic field there. Like the moon we don't think has enough internal motion in its core to generate a strong magnetic field. There are magnetic rocks on the surface of the moon, but it has no like big overall magnetic field. to shield it or to act like a sail. Are those magnetic rocks big enough that you could try to address the question about whether magnetic fields help or hurt atmospheres or no, because there's just no atmosphere on the moon. So you can't compare like the area around magnetic rocks

versus the area around non-magnetic rocks. Yeah, in order to operate like a shield, I think you really do need to have a planet-sized magnetic field. And there just isn't a coherent one on the moon. I mean, if you map the moon's surface for magnetism, and they've done that, you do identify some spot. with more magnetic field or less, but it's more a probe of like what kind of metals are there just under the surface rather than telling you anything about the planet's atmosphere.

All right, so was that the end of our atmosphere story or is there a third phase? So the Earth's atmosphere did keep evolving, of course. Now we have oxygen in the Earth's atmosphere, which didn't come from those volcanoes, right? That actually mostly came from life. When little cells began to drink sunlight and do photosynthesis, they turned a lot of the atmosphere into oxygen. So surprisingly, it took a long time, right? You can't just pump oxygen into the atmosphere

and have it to stay there because oxygen is so reactive. Most of the oxygen that was produced by life actually got gobbled up by rocks because rocks like to get oxidized. So if you put oxygen in your atmosphere, it will weather the rocks or the surface of your planet will get like rusty, for example. And that gobbled up a lot of the oxygen.

So it took hundreds of millions of years of pumping oxygen into the atmosphere of the earth before it had like a measurable impact on what actually was in the atmosphere. And today, the Earth's atmosphere is mostly nitrogen, like 78%, it's like 20% oxygen, and then like 1% argon, 0.03% CO2 and rising, and then a bunch of other stuff. But the moon, of course, doesn't have life on it, and it didn't have, and it wasn't able to keep that atmosphere around. And so it didn't get to have the third act of its atmosphere.

And is there like a physics definition for when your atmosphere? ends? Is it like, you know, oh, at exactly 45 kilometers, the atmosphere ends, or is it like a gradient where you just have a little bit less and less as you go and there's no clear cutoff point? It's totally a gradient and there are definitions and they all disagree with each other. You know, some people say, oh, 100 kilometers. Some people say, no, the threshold should be 65 kilometers and people argue endlessly about it. And I'm not sure that we're really learning anything through that argument. There are some interesting distinctions. Like the Earth's atmosphere is mostly within 30 kilometers of the surface. It's like 97% of the mass of the atmosphere.

But you know, you could draw that threshold anywhere. You could say 99% or 99.9.9%. In order to get all of it, you have to go out like ridiculously far, you know, hundreds of thousands of kilometers to say this is the full envelope of the earth. But there is an interesting transition above a certain distance. The density is so low that the atoms don't really bump into each other. And so above what we call the atmosphere something called the exosphere, where the density is so low that atoms can travel for like hundreds of kilometers without bouncing into each other. So the dynamics of it are a little bit different. It's collisionless. So usually where we get to by the end of the episode is you telling me something awful. So now you've got me wondering, is Earth going to lose its

atmosphere? So can you tell me about the ways, like summarize for me the ways that atmosphere gets lost, and then is Earth going to lose the atmosphere? Because probably that's where this conversation is going, right? Your kids are going to be fine, Kelly. Now, their kids and their kids' kids, they're going to have to listen to the next generation of the podcast to find out. But I think it's really fascinating to think about the dynamic processes here, the things that are changing the solar system. We usually think of the solar system as so static. It's just like, this is the way it's been. It's been this way for thousands or millions or maybe billions of years. And so it probably has always been this way. And so it's always a little bit

shocking and surprising to discover that things are dynamic, that things are changing. And the atmosphere is definitely in that category because it is pretty tenuous. You know, it's not easy to hold onto these gases. And there are a lot of factors that are helped blowing it away. So we talked about the solar wind. You know, something that people don't really appreciate, I think, is that the solar wind comes in like a million miles per hour. These particles coming from the sun, yeah, they're zipping along, right? So like 0.15% of the speed of light, it sounds like a low value, but it's really, really high. And nobody wants to get shot at in the face with a proton at a million miles per hour. No, no, I'll pass.

And even if we didn't have the sun trying to strip us of our atmosphere, right? It does just boil away. The Earth's gravity is powerful, but at the upper edges of the atmosphere, there are fast-moving particles, and they can just achieve escape velocity. You know, you have a particle going fast enough, pointed in the right direction. It's just gone. You know, you don't have to launch it into outer space. It's just hot and fast moving and it's just taken off.

And so this definitely happens for every planet and it happens also for Earth. Now, heavier planets are going to lose less because the escape velocity is higher. But if you have lower mass gases like hydrogen and helium, then they just boil off. Does it get replenished? It doesn't really get replenished by new hydrogen or helium or oxygen, though we do get a lot of space dust every year. And so we get like tons of space dust, just like debris falling to Earth. And we're also losing our atmosphere. We lose three kilograms per second of hydrogen.

That sounds kind of scary. Okay. But we'll probably be fine. We're going to be fine for about a billion years until the sun, when it's going to be like 10% brighter than it is now, is going to make it hot enough on Earth for the oceans to boil, for water to break down into hydrogen and oxygen, and the Earth will probably lose a lot of that hydrogen. Time to invest in interstellar travel. All right. Well, you know, that news isn't as bad as some of the news that you've delivered to me, but I still think that we should take a break so that I

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That's Lenovo.com. Lenovo, Lenovo. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal, glass. The injured were being loaded into ambulances. Just a chaotic, chaotic scene.

In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system. is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly and now I'm seriously suspicious. Oh, wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's Back to School Week on the OK Storytime podcast, so we'll find out soon.

This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. And it's even more likely that they're cheating.

He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants. them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. Our IHeart Radio Music Festival, presented by Capital One, is coming back to Las Vegas.

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Recap for me what we know about the moon's atmosphere So we think that the moon probably did get a delivery of gas early on right from the primordial soup and then it may have also gotten a refreshing of its gas from volcanism but we don't think that there's much atmosphere there today and the reason is that it just doesn't have the mass to hold on to the stuff doesn't have the magnetic field so if you ordered a new atmosphere for the moon if you like went up there and pumped a bunch of oxygen and nitrogen and CO2 onto the moon most of it would get stripped away

by the sun or it would just drift away. Because remember that the moon is really pretty tiny. I mean, it looks impressive in the sky, but it's got like 1% of the mass of the Earth, and its surface gravity is very, very low. So the escape velocity of the moon is just much lower than it is here on Earth, which makes it easier for the stuff to boil away.

So I feel like I would have, you know, as someone who thinks about terraforming a little, I would have thought, well, maybe we can at great, great, great, great, great, great, great, great expense, give the moon a magnetic field to hold onto an atmosphere. But now what you've told me is that physics doesn't have that figured out yet, and a magnetic field may or may not help. So there's maybe nothing we can do about the moon not having an atmosphere?

Giving the moon an atmosphere is definitely a hopeless engineering project. I mean, you'd need to build like a containment vessel, right? You need to like put the whole moon inside a glass bulb or something crazy. Because it's not just that it doesn't have the gravity to hold onto that gas envelope on its own. It's a pretty harsh environment. I mean, the surface of the moon gets to like 250 Fahrenheit, 120 Celsius during the day, which makes it pretty easy to boil this stuff off. Because remember, it's a trade off between the temperature of the gas,

which means fast moving particles and the gravity of the object. If you have a small object, it's only hope for holding onto its gas is if that gas is very cold, meaning it's slow moving. But if the gas is hot and the object is small, then that stuff is just going to boil off into space. All right, I'm not investing in that project. And people have been wondering about a moon's atmosphere for a long time. It's not for a very long time that we've understood the source of the Earth's atmosphere. This is a very complex story.

It took us a long time to piece together. And so it wasn't until like the 1700s of people were speculating about whether the moon had an atmosphere. And people considered, oh my gosh, maybe the moon doesn't have any air on it. They just for a long time assumed that it would because the Earth did, right? But it's not actually that hard to tell, even from the Earth, that the Moon must not have any atmosphere. And that's using the same technique we talked about earlier. Remember, if we are studying exoplanets, one thing we can do is look at the light that passes through the atmosphere of those exoplanets to see that there is an atmosphere and what's in it. Well, you can do the same thing when you look at the moon.

You can look at sunlight that passes very, very close to the moon and see, is it absorbed? Is it getting reflected? Is it getting scattered? You can basically use the sun as a probe of what's right around the moon. But we've been there, so we don't have to rely on far off things. Did they try to measure an atmosphere when they got there? You're right, we have been there. And the Apollo missions have a long series of experiments trying to measure things on the moon, looking for trace atmosphere, and really finding almost nothing.

Apollo 17 saw a little bit of evidence for UV emitting gases. But there's another big clue about the moon's atmosphere from the fact that we did go there. You know, those footprints that people left on the moon, they're still there. You like write your name in the sand on the moon. and you could look at it 20 years later from the surface of the earth and read your own handwriting because there's basically no weather on the moon, right? There's no wind up there, like blow things around. And so it's sort of amazing that the rover tracks and the footprints, they're all still up there.

That's great. You know, I read that Pizza Hut was looking into the cost estimate for, like, lasering its name onto the moon. Oh, God, no, really? Yeah. It sounds like it would have been a good long-term investment because once it's up there, it's not going away, right? But I think they did determine it was probably not cost effective and actually might make people angry.

And in a million years, archaeologists are going to be like, what is a pizza and why did humans think to write about it on the moon? Right. And why are they keeping it in a hut? Yeah. Bad idea. Bad idea. So it seems like when you and I talk about something, the answer is never yes or no.

the answer is always something like yes but or yes well so is there a well is there something sort of like an atmosphere sometimes where's the well actually part to this this episode yeah there's definitely a well actually part to this episode otherwise it would have been very short and the answer is that the moon technically doesn't have an atmosphere but it does have an exosphere remember earlier we were talking about the earth having an exosphere up above the atmosphere there's a this point where there are gases, but they're very diffuse, a very low density. So they're not bumping into each other. The moon does have some gas particles and some other stuff floating around near it in this envelope that don't bump into each other. And so we can say the moon has an exosphere. And you might wonder like, well, how is it possible for it to hold onto its exosphere if it can't hold onto an atmosphere? And it's part of this fascinating dynamic story. Basically, it can't hold onto it, but it has sources of new material at the same time as it has sinks, ways to get rid of it. So it's constantly losing its exosphere and getting it replenished.

Oh, tell me more about where it comes from. So it's really a fun story. The moon's exosphere actually comes from itself, right? So things are constantly hitting the moon, like you have meteorites and then includes like really tiny little rocks that are hitting the surface of the moon. And we know this is happening because you look up at the moon and it's covered with craters, right? Which means that things are constantly impacting it. Well, what happens if you don't have very strong gravity and you get impacted with a meteorite is that it's it sprays a bunch of stuff up above the surface, then that stuff doesn't all immediately float back down. Some of it's pretty light. And it sort of like hangs out there a little bit, like these

cloud of dust particles. So when you say a little bit, do you mean like decades or like 30 minutes? That's a great question. I think that for an individual particle, it can vary a lot. Some of them might just stay on the moon for minutes. Some of them might float around for days or years or decades. I don't think that any of those things are going to last for more than decades, though. Okay, so it must be getting pounded pretty often then? Or does it have an exosphere sometimes, but not all the time? No, it has a constant exosphere, but I have to emphasize that this is very, very, very low density. We're talking about like a few hundred atoms per cubic centimeter. The Earth's atmosphere is like 10 to the 19 particles per cubic centimeter. So we're talking about something very, very, very, very

thin. You know, the ISS, the International Space Station, it flies through the Earth's exosphere, which is about as dense. So we're talking about the moon having an exosphere, which is similar to like what you would feel if you stuck your head out of the window and on the ISS, which I do not recommend. Do not recommend, yeah. So if you have like a dog on the moon in your rover, and maybe you've called your dog rover, don't encourage it to stick its head out because there's not really a lot there. But it is a really fascinating sort of physics because it's not just like comet fragments and meteorites, it's other processes as well. We talked about the sun blasting is free of an atmosphere. Well, that solar wind also helps generate new atmosphere because each of those particles hitting the surface of the surface kicks up stuff from the moon's surface, right? It like knock stuff off the surface, which then becomes part of the exosphere. Some of that again settles back down, but some of it doesn't. Some of it floats around for a while. before then getting like ionized by the sun and then floating off into space. Does it get like pushed in a certain direction by the wind or is it just sort of like floating off in all directions?

So there's an envelope surrounding the moon of all this stuff and is constantly getting blown away. You know how comets have a tail, right? They have a tail because the solar wind is pushing them away. You imagine a comet has a tail because it's like streaking through the sky and it's sort of like comic book wiggles or motion behind it. With the largest contribution for a comet's tail, comet's tail is actually the solar wind. And so the tail points away from the sun, not always away from the direction of its motion. And the same thing is true of the moon. It has this sort of short-lived envelope that's constantly being refreshed. And it also has a tail. We can now see it from Earth using special telescopes that we have to like block the light from the actual part of the

moon surface so we can see just around it like the corona of the moon. And they can see this envelope of sodium around the moon. And it has this tail that's getting blown. by the sun, away from the moon. That's so cool. I wish I could see that in real life. If you Google for it, there are these really cool videos where you can see the moon going around the earth. And when the moon is between the earth and the sun, the earth is in the moon's tail, right? We're like eating the moon's sodium dust. Do we retain any of it or does it just pass through?

We can retain it. You know, it just gets gathered by the earth. But again, these are very, very small amounts. It's the reason it took us a long time to even spot. It was like 1998 that we first saw the moon's like sodium envelope and this tail. It takes a long time. And one reason that they actually spotted it is really cool is because of the Leonid meteor shower. You know, when there's a meteor shower, it means like spectacular things happening in our atmosphere. It also means more things hitting the moon's surface, which kicks up more stuff, which enhances the moon's exosphere and its tail. So during the 1990 Leonid Meteor shower, the moon's exosphere was tripled in day.

Heavy stuff. Heavy stuff, exactly. So there's a lot of these processes going on, you know, like not just the solar wind and commentary impact, also just photons. This is fun process called desorption. We're used to the process of absorption where you can like gobble something up. But desorption is when a photon hits something and it kicks something off. Just like when a meteor hits a surface and kicks off a rock. Now we're talking about a photon hitting an atom and giving it the energy to like escape whatever bonds it was in. And it comes off the surface. And so the moon has all these various ways to replenish its exosphere and all these ways to lose it. So it's more like a flow, right? It's not just like a gaseous pool. It's like this stuff flowing off the moon and getting abraded by everything that's rounded. Does this mean that the other moons in the solar system might also have tails? Almost certainly every object in the solar system has an exosphere because they're not just alone, right? They're all in the solar wind. They're all getting constantly bombarded by little meteor fragments or big objects. So the solar system is a very dynamic place. And because of it, all these things are constantly

providing sources for their own exosphere and then also losing them constantly. So we think that, for example, in Salatus and Europa and Callisto and Ganymede and even dwarf planets like series in the asteroid belt probably have their own little exosphere, not quite an atmosphere, right, but a little exosphere of their own. Interesting. And, you know, as somebody who thinks about settlements, these exospheres will probably never be useful for anything. Because even if they were made out of useful stuff, it would be so hard to extract it. Yeah, exactly right. There's probably no economic benefit there.

But there is a lot of physics that you can learn. Because they're collision lists, they're not interacting with each other. They're mostly just flying along and doing their own dance. Each one tells you something different about a physics process that's going on. It helps us sort of like isolate the things and study them in detail. So we think that each of these solar system bodies probably have different sinks and different sources, right? Some of them, for example, are really cold on the surface, and that can be a sink. It can be like that it's so cold that it's like sticking your tongue to a flagpole that when those little molecules touch the surface, they stick on.

So the exospheres are a really cool way to learn a lot about the surface of these planets without even landing on them, right? You can pass your satellite near one of these objects and sample them and learn a lot about what's going on in the surface without actually. having to land. It's incredible. We can collect enough data from these very thin exosphere to learn this kind of stuff. Yeah, what you need is a mass spectrometer, one of these devices that tells you like, oh, you have 72 atoms of hydrogen or 16 atoms of sodium and tell you exactly what the composition is. And that gives you a lot of clues as to how these things formed and also what's going on on their surface right now. I spoke to one of my old friends from grad school who's now an expert in this. He's a he's a space geoscientist. And he said, any rocky

object in space gets bombarded by all sorts of crap that can liberate materials from the surface and form an exosphere. Is crap a technical term? I mean, he's speaking as a scientist. He's a professor. So now it is a technical term. Oh, fantastic. I didn't realize it was that easy. And I guess that means that, you know, even objects like the ISS, which are getting hit by the solar wind and getting hit by all sorts of stuff are also like liberating little bits, right? Spallation and abrasion are giving off little particles. And so even like an individual astronaut out there in space on an EVA must have their own little exosphere.

Whoa. Somehow I feel like that would make me feel even more important to know I had my own little exosphere. Exactly. And you don't even have to burp it out. That's right. It's one thing we have an advantage we have over Earth. And so recent studies of the moon suggests that, of course, there's sodium there.

We can see sodium pretty clearly because it's very rich. responsive in the UV, which is what these telescopes are good at looking at. But there's also helium there. There's neon, there's argon. There might even be like carbon-bearing species up there in the moon's exosphere. Oh, but there's not a lot of carbon on the moon. Where's the carbon coming from? There's definitely not a lot, but some of it could be coming from the asteroid impacts, right? Asteroids sometimes have silica in them. Sometimes they have carbon in them. They sometimes even have complex organic molecules. Interesting. So when you look up at the daytime sky you are seeing mostly the blue from our atmosphere but beyond that there's also

the earth's exosphere which is so dilute that you cannot see it it's black it's invisible but it's there it's doing something and everything else out there in the solar system the moon mercury all the other objects which are quote bombarded by all sorts of crap they also generate an exosphere and that tells you that the solar system is not a static thing it's a dance everybody is giving off gas and accepting photons and interacting with each other. So the solar system has an exciting future. You know, I usually think dances are better when they don't involve gas, but this one is beautiful.

This is sort of how objects in the solar system talk to each other and evolve. All right, thanks very much for joining us on this exploration of whether or not the moon has an atmosphere. To put a pin in it, I would say the moon does not have an atmosphere, but it definitely does have an exosphere. And thanks very much to our exosphere. host Kelly for joining us today. Thanks. I had a great time. I was going to say I had a gassy time,

but that just doesn't sound quite as good. I hope you didn't have gas, but I thought it was a pretty nice atmosphere. Agreed. That was a good pun. All right, thanks for joining us, everyone. Tune in next time. All right, that was fun. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. ultra-light, ultra-powerful, and built for serious productivity

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powered by Intel Core Ultra processors so you can work, create, and boost productivity all on one device. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal. Just a chaotic, chaotic scene.

In its wake, a new kind of enemy emerged. Terrorism. Listen to the new season of Law and Order Criminal Justice System. on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot.

He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone. Hold up. Isn't that against school policy? That seems inappropriate. Maybe find out how it ends by listening to the OK Storytime podcast and the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. This is an IHeart podcast.