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

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

0:08
Speaker 1: A Kelly, how was your family trip? Oh? It was
0:11
Speaker 1: so much fun. Did you guys get to break out
0:13
Speaker 1: of your usual routines experience something different? Yeah, And something
0:17
Speaker 1: that was unusual for our kids was eating at restaurants.
0:20
Speaker 1: We don't do a lot of that when we're at home,
0:22
Speaker 1: and you know, we didn't do a lot of it
0:24
Speaker 1: because of COVID and stuff. So that was new. And though,
0:26
Speaker 1: what is it that your kids like about eating out
0:29
Speaker 1: at restaurants? Aren't you guys like super good cooks at home? Well,
0:32
Speaker 1: we keep me out of the kitchen for everyone's sake,
0:34
Speaker 1: but that is a really good cook, so that's good.
0:37
Speaker 1: But I think for the kids, they mostly like the
0:39
Speaker 1: novelty of it, you know, the atmosphere. M Well, that's exciting,
0:43
Speaker 1: but it doesn't actually bode very well for them as
0:45
Speaker 1: future space colonists. No, I'm not following. What do you mean, Well,
0:49
Speaker 1: I hear that restaurants on the moon have no atmosphere. Oh. Hi,
1:11
Speaker 1: I'm Daniel. I'm a particle physicist and a professor at
1:14
Speaker 1: U C Irvine, and I'm always in the mood for
1:17
Speaker 1: a good space pun. I'm Kelly Weener Smith. I'm an
1:20
Speaker 1: adjunct assistant professor at Grace University, and I am also
1:24
Speaker 1: a fan of the puns, especially the moon based ones.
1:27
Speaker 1: There's a lot of inappropriate moon based puns that we
1:29
Speaker 1: can make right now. Yeah, sure, no, you and I
1:31
Speaker 1: are pretty good at that. But what we're going to
1:32
Speaker 1: keep it clean. We are definitely gonna keep it clean
1:35
Speaker 1: as we examine the deep dark mysteries of the universe.
1:39
Speaker 1: And welcome to the podcast. Daniel and Jorge explain the
1:43
Speaker 1: universe in which we do exactly that, ask the biggest, darkest,
1:47
Speaker 1: deepest questions about everything that's out there in the universe.
1:50
Speaker 1: We don't want to sweep anything under the rug. We
1:53
Speaker 1: want to expose it all to the blinding glare of
1:56
Speaker 1: sunlight and make it all makes sense to you. My
1:59
Speaker 1: usual host, Orgy can't be here today, so we are
2:02
Speaker 1: delighted to have one of our regular co hosts, Kelly. Kelly.
2:05
Speaker 1: Thank you very much for joining us today. I'm delighted
2:08
Speaker 1: to be back, Okelly. When you're on the podcast, we're
2:10
Speaker 1: often talking about space and about the wonders of the
2:13
Speaker 1: night sky, putting people out there mentally sort of at night,
2:17
Speaker 1: staring up in the stars, being amazed at everything that
2:20
Speaker 1: we are seeing that's right, and then you turn it
2:23
Speaker 1: into something about how we're all going to die. But yes,
2:25
Speaker 1: we are usually looking up at the night sky and
2:28
Speaker 1: having a sense of all about it all because one
2:31
Speaker 1: of the things that I love about science is that
2:33
Speaker 1: it lifts us up away from our everyday lives. It
2:35
Speaker 1: forces us to turn our eyes skywords and think about
2:40
Speaker 1: what's out there in the universe. Usually that's something we
2:43
Speaker 1: do at night because during the day the sun is
2:46
Speaker 1: so bright it keeps us from seeing everything that's out there.
2:49
Speaker 1: That makes us wonder, that makes us as deep questions
2:52
Speaker 1: about the very nature of the universe. But you know,
2:55
Speaker 1: everything that's out there is also out there during the daytime,
2:58
Speaker 1: and I remember that blew my mind when I was
3:00
Speaker 1: a kid and I first learned that. But yeah, it's
3:02
Speaker 1: all still out there, and sometimes you can see the
3:04
Speaker 1: moon during the day. It always feels sort of inappropriate, though.
3:06
Speaker 1: When you see the moon during the day, it feels
3:08
Speaker 1: like you know you've caught somebody, like they're not supposed
3:11
Speaker 1: to be there, Like they're tiptoeing to the fridge in
3:13
Speaker 1: the middle of the night and you spotted them, or
3:15
Speaker 1: like they don't know their place you know, like moon,
3:18
Speaker 1: your place is at night, you're stepping on the Sun's toes,
3:21
Speaker 1: and you know, it's not only the nighttime sky. That's
3:24
Speaker 1: really fascinating, that's really amazing. That has a lot of
3:27
Speaker 1: physics in it is what we can learn about the
3:29
Speaker 1: nature of the universe and what's out there just by
3:31
Speaker 1: looking up at the daytime sky. Oh well, what can
3:34
Speaker 1: we learn? Well, one common question from kids, of course,
3:37
Speaker 1: is why is the sky blue? You know, if the
3:41
Speaker 1: Sun is just shining through space at us, what is
3:44
Speaker 1: it that makes the sky blue? And so we've talked
3:47
Speaker 1: about on the podcast a few times. It's a fascinating
3:50
Speaker 1: interaction between the Sun's gas and the atmospheric gases. The
3:53
Speaker 1: light that comes directly from the Sun is white light.
3:56
Speaker 1: If you were out in space looking at the Sun,
3:58
Speaker 1: it would mostly look why it maybe a little bit yellow,
4:01
Speaker 1: but not all of that light passes through our atmosphere
4:04
Speaker 1: equally well, when light hits gases in the atmosphere tends
4:08
Speaker 1: to scatter, and it scatters more for the very high
4:11
Speaker 1: frequency light, the blue or light, and that might make
4:13
Speaker 1: you think, oh, well, we should see everything, but the
4:15
Speaker 1: blue light like the blue should get reflected back into space,
4:19
Speaker 1: and it does get reflected back into space, but it
4:21
Speaker 1: also gets reflected down to the ground. So when you're
4:24
Speaker 1: standing on the surface of the Earth and you're looking
4:26
Speaker 1: up at the sky, you're seeing light that doesn't come
4:29
Speaker 1: directly from the sun and sort of hid an atom
4:31
Speaker 1: and bounce down to your eyeballs. So the reason that
4:34
Speaker 1: our daytime sky is blue is because those gases bounce
4:38
Speaker 1: the blue light down to our eyeballs. And can we
4:41
Speaker 1: use this to figure out what the atmospheres of other
4:43
Speaker 1: planets are made up just by looking at the color
4:45
Speaker 1: that we see when we shine a telescope about them.
4:48
Speaker 1: We totally can and we do exactly that. When exo
4:51
Speaker 1: planets pass in front of their stars, the light goes
4:55
Speaker 1: through their atmosphere and some of it bounces off and
4:57
Speaker 1: some of it passes through, and some of it is absorbed.
5:00
Speaker 1: It's a great way to understand what's in those exo
5:03
Speaker 1: planet atmospheres. And so it's sort of like X raying
5:05
Speaker 1: the atmosphere. Passing light through it is a great way
5:08
Speaker 1: to figure out like what's there as a glow, what
5:10
Speaker 1: does it absorbed, what does it reflect? I love the
5:13
Speaker 1: idea of seeing a sunrise on an exo planet and
5:17
Speaker 1: using that to figure out what's in the sky. And
5:20
Speaker 1: you know, sunrise is on different planets all look very
5:23
Speaker 1: different because the different planets have different atmospheres. And so
5:27
Speaker 1: when I am looking up in the night sky recently,
5:30
Speaker 1: I've been seeing a big red dot. Is that Mars
5:33
Speaker 1: or is it Venus? And also when I see those colors,
5:35
Speaker 1: is that the atmosphere I'm seeing or is that something
5:37
Speaker 1: else that I'm seeing entirely, So, if you look up
5:39
Speaker 1: in the night sky and you're seeing a red dot,
5:41
Speaker 1: that's probably Mars, and Mars is definitely red. If you
5:44
Speaker 1: were in a satellite orbiting Mars looking down, it would
5:47
Speaker 1: look red to your eyeballs. It's not just like a
5:49
Speaker 1: false color thing from satellite imagery that we take and
5:52
Speaker 1: then change the way like James web Space Telescope images
5:55
Speaker 1: are all false color. If your eyeballs were there where
5:58
Speaker 1: James Webb Space Telescope is, you wouldn't be seeing those
6:01
Speaker 1: images because those images are all infrared. They're all too deep,
6:05
Speaker 1: too long wavelengths for your eyeball to even register. But
6:08
Speaker 1: if your eyeballs were orbiting Mars, hopefully with the rest
6:11
Speaker 1: of your body, you would see it as red. And
6:13
Speaker 1: the reason there is not actually the atmosphere, because Mars
6:16
Speaker 1: has almost no atmosphere. It's very very thin atmosphere. It's
6:20
Speaker 1: because the surface of Mars itself is mostly red due
6:23
Speaker 1: to the iron and the oxidization of it, so it's
6:26
Speaker 1: covered in this red dust. And it's sort of amazing
6:29
Speaker 1: that you can see it from the Earth's surface, right,
6:32
Speaker 1: that this thing is so red that you can see
6:34
Speaker 1: it from your backyard. That's incredible. And then the fact
6:37
Speaker 1: that you so you said that it has very little atmosphere,
6:40
Speaker 1: that makes me I have a pop culture question to
6:43
Speaker 1: ask you. Someone told me that one of the things
6:46
Speaker 1: they didn't like about the Martian was that with a
6:48
Speaker 1: low atmosphere, if you had a big dust storm, it
6:52
Speaker 1: wouldn't be strong enough to like knock over a rocket,
6:55
Speaker 1: because low atmosphere means like far fewer molecules pushing against
6:59
Speaker 1: things even in a big windstorm. So is that not
7:02
Speaker 1: accurate about the Martian? This is this is absolutely vital stuff. Yeah,
7:09
Speaker 1: it's definitely true that the atmosphere on Mars is very
7:11
Speaker 1: very low, like less than one percent of the Earth's atmosphere,
7:14
Speaker 1: and that means that the wind don't apply as much pressure,
7:18
Speaker 1: so whin did the same velocity. For example, there just
7:20
Speaker 1: aren't as many molecules bouncing off of you. But the
7:23
Speaker 1: velocity can get very high, and there's also a lot
7:26
Speaker 1: of dust in the atmosphere on Mars. You definitely do
7:29
Speaker 1: have to worry about storms. Very high velocity windstorm on
7:32
Speaker 1: Mars can do a lot of damage because all the
7:35
Speaker 1: dust particles you can basically sand blast you. Right, I
7:38
Speaker 1: don't know if the velocity is actually get high enough
7:40
Speaker 1: to knock things over. We'll have to get Andy Weir
7:43
Speaker 1: on the podcast and ask him that question. Well, you know,
7:45
Speaker 1: I loved that book in that movie, and you're making
7:47
Speaker 1: me feel better knowing that maybe that opening scene was feasible,
7:50
Speaker 1: because I would hate to think it wasn't. But okay,
7:52
Speaker 1: all right, let's let's get back to the important stuff.
7:55
Speaker 1: But it does bring us to a really fascinating fact
7:57
Speaker 1: about Mars, which is, if you're standing on the surface
7:59
Speaker 1: of Mars Mars and you look down, of course it
8:01
Speaker 1: looks red. But also if you look up, it looks red.
8:05
Speaker 1: That is, the sky on Mars doesn't look blue like
8:08
Speaker 1: it does on Earth. That's because Earth has this atmosphere
8:11
Speaker 1: which scatters the blue light down to your eyeballs. But
8:14
Speaker 1: Mars doesn't. This atmosphere is so thin that it doesn't
8:16
Speaker 1: effectively scatter that light. So then why is it red
8:19
Speaker 1: instead of like white from the sun. It's because of
8:22
Speaker 1: all of the dust. Right, Mars doesn't have much atmosphere,
8:25
Speaker 1: but the dust is up there, and that dust tends
8:28
Speaker 1: to absorb blue light. That's why it looks red. Remember,
8:31
Speaker 1: things that look a certain color, they're reflecting that color
8:35
Speaker 1: and they're absorbing everything else. So things that are yellow
8:38
Speaker 1: are things that reflect yellow because the yellow makes it
8:41
Speaker 1: to your eyeball and they absorb everything else. So it
8:44
Speaker 1: sounds weird to say that red dust absorbs blue light.
8:47
Speaker 1: You might think that makes it blue, right, but actually
8:50
Speaker 1: that's what makes it red. So when you look up
8:52
Speaker 1: in the sky during the daytime on Mars, you're seeing
8:55
Speaker 1: the red light reflected from that dust. I didn't realize
8:58
Speaker 1: that the dust never settled enough for the sky to
9:01
Speaker 1: not be red. That's incredible. It is incredible, And if
9:03
Speaker 1: you're lucky enough to observe a sunset on Mars, then
9:07
Speaker 1: you'll see an amazing blue sunset. Right. It's like totally
9:11
Speaker 1: reversed from Earth because this dust scatters the red light,
9:15
Speaker 1: and so if you're looking directly at the sun sort of,
9:18
Speaker 1: then most of the red light has been scattered away
9:20
Speaker 1: by the dust, and so the blue light is all
9:22
Speaker 1: that survives. So you see a blue sunset on Mars
9:25
Speaker 1: on a red sky. Oh, that's incredible. I hope within
9:29
Speaker 1: my lifetime we get photos of that taken by an
9:31
Speaker 1: astronaut that landed on the Martian surface. Blue sunset. Selfie,
9:36
Speaker 1: what an Instagram pick that will be in. And that
9:39
Speaker 1: makes you wonder, like what it would be like to
9:41
Speaker 1: be on other planets. Right, If the atmosphere of the
9:44
Speaker 1: planet is what determines what it looks like to be
9:47
Speaker 1: on the planet, the color of the daytime sky and
9:50
Speaker 1: atmospheres can be like, you know, anything that opens the
9:53
Speaker 1: door to like having all sorts of crazy daytime colors.
9:57
Speaker 1: You know, can you have like a yellow sky or
9:59
Speaker 1: a purple sky or something with crazy stripes from atmospheric bands? Right,
10:03
Speaker 1: I haven't yet seen that in a science fiction movie.
10:05
Speaker 1: You know, somebody living on Jupiter with the sky has
10:07
Speaker 1: like stripes of color. That would be really awesome. And
10:11
Speaker 1: there aren't many places in the solar system where we
10:13
Speaker 1: have had people take pictures, right. One of those, of course,
10:17
Speaker 1: is the moon. It's something that's striking about all of
10:19
Speaker 1: the pictures from the moon, is that the sky the
10:22
Speaker 1: backdrop or if you look above the moon, it's always black.
10:26
Speaker 1: And why is that right? Because you associated black with
10:29
Speaker 1: the color of the night sky, right, But even during
10:31
Speaker 1: the moon sort of daytime, when the sun is shining
10:35
Speaker 1: right at you, there's nothing there to scatter the light.
10:38
Speaker 1: So from the point of view of somebody on the moon,
10:40
Speaker 1: the sun is just another star. So it's sort of
10:44
Speaker 1: like a perpetual night sky with one huge, very bright
10:48
Speaker 1: star in it half the time. Also not very invited.
10:54
Speaker 1: You wouldn't want to have a picnic under a black sky.
10:57
Speaker 1: I feel like the regular would get in my sandwich
10:59
Speaker 1: and was sort of mess up the overall feeling. So
11:01
Speaker 1: the reason the night sky in the Moon is black
11:04
Speaker 1: is because there isn't a strong enough atmosphere there on
11:07
Speaker 1: the Moon to scatter it to make it blue or
11:09
Speaker 1: purple or yellow at pink polka dots. But it does
11:11
Speaker 1: raise an interesting question and the question of today's episode,
11:15
Speaker 1: which is does the moon have an atmosphere? So this
11:24
Speaker 1: is a fun question because it lets us dig into
11:26
Speaker 1: definitions and quibble about what it means to have an
11:30
Speaker 1: atmosphere for quibbling. Sometimes it feels to me like a
11:35
Speaker 1: big part of science is just like arguing about what
11:37
Speaker 1: a definition is, you know, like is this really a mammal?
11:40
Speaker 1: I don't know what lays egg? What does that mean?
11:42
Speaker 1: Whereas really that interesting questions are like the questions behind that,
11:45
Speaker 1: you know, like why does something with hair lay eggs? Anyway, Yeah,
11:49
Speaker 1: that was one of the most surprising things when I
11:51
Speaker 1: started college, was like, wait a minute, we don't even
11:53
Speaker 1: know how to define a species really and yeah, and
11:57
Speaker 1: of course huge arguments over that, but know it's because
12:00
Speaker 1: nature doesn't fit in the categories that humans would like
12:03
Speaker 1: it to. Yeah, And sometimes those arguments are just a
12:06
Speaker 1: waste of time, people splitting hairs where there's nothing really
12:08
Speaker 1: to be learned. But sometimes it really is illuminating because
12:12
Speaker 1: we do try to describe the universe in terms of categories.
12:15
Speaker 1: These ways that we like to think about things are
12:18
Speaker 1: sort of our familiar basis, and in the end, that's
12:21
Speaker 1: what science is, is explaining everything we'd see in terms
12:24
Speaker 1: of things we understand. Physics is describing the unfamiliar in
12:28
Speaker 1: terms of the familiar. So the words we're using are
12:31
Speaker 1: sort of important. If we're going to communicate with each
12:33
Speaker 1: other about these ideas, we better at least know what
12:35
Speaker 1: the words mean. And I guess, to be fair, I'm
12:37
Speaker 1: thinking that I don't exactly know what an atmosphere starts
12:40
Speaker 1: and stops, because it seems like sort of a gradient,
12:43
Speaker 1: like is you know at what point do you call
12:45
Speaker 1: it an atmosphere versus something else? And so I'm not
12:48
Speaker 1: sure that I know the answer. So let's let's see
12:50
Speaker 1: what your listeners think. Great idea, And so as usual,
12:53
Speaker 1: I went out there into the internet to ask people
12:55
Speaker 1: if they thought that the moon had an atmosphere. If
12:59
Speaker 1: you like the artists made for future episodes of the podcast,
13:02
Speaker 1: please don't be shy. Right to me two questions at
13:05
Speaker 1: Daniel I and Jorge dot com, and I will set
13:07
Speaker 1: you up. Is free. It's fun. Your friends can hear
13:10
Speaker 1: your voice on the podcast. So before you hear these answers,
13:13
Speaker 1: think to yourself, do you think the moon has an atmosphere?
13:18
Speaker 1: Here's what people had to say. All right, so I
13:20
Speaker 1: don't think that our moon has an atmosphere at least
13:23
Speaker 1: anything substantial enough to call it an atmosphere. UM. I
13:26
Speaker 1: did have a physics professor my first year of college
13:28
Speaker 1: who claimed to have a plan to give the Moon
13:31
Speaker 1: atmosphere for two hundred years by basically creating an orbital
13:34
Speaker 1: cannon that could help a smaller Moon from either Jupiter Titan.
13:38
Speaker 1: I have like an escape glossy of seventeen miles an
13:40
Speaker 1: hour UH to slingshot that into ours vaporize and create
13:44
Speaker 1: an atmosphere. But it wasn't only for two years, so
13:47
Speaker 1: I can get implaced temporary and nothing substantial enough. I
13:50
Speaker 1: don't think the Moon has an atmosphere. I mean there
13:52
Speaker 1: might be some like low density hydrogen or something floating around,
13:55
Speaker 1: but not enough to call it an atmosphere. I think
14:00
Speaker 1: has some atmosphere UM only because I'm thinking that Moon
14:07
Speaker 1: has a weak magnetic field that might be able to
14:11
Speaker 1: contain some kind of atmosphere. There are so not what
14:17
Speaker 1: Earth has, but still something. UM. I would guess it
14:21
Speaker 1: probably does. I doubt it looks anything like ours does
14:25
Speaker 1: on Earth, but I would guess that if you're a
14:27
Speaker 1: body or an object in the sky, and you're large
14:30
Speaker 1: enough or dense enough that you probably attract some kind
14:32
Speaker 1: of atmosphere. The Moon doesn't have an atmosphere. I think
14:36
Speaker 1: it's because it's gravitational attraction is too weak to um
14:43
Speaker 1: sort of hold the guesses around it to form an atmosphere.
14:46
Speaker 1: So what do you think of these answers? Kelly? A
14:48
Speaker 1: lot of skepticism here, a lot of folks feeling like
14:50
Speaker 1: the Moon can't really have much of an atmosphere. Yeah,
14:53
Speaker 1: but a lot of critical thinking also, a lot of
14:55
Speaker 1: folks trying to think through like, well, you know, I
14:58
Speaker 1: think the moon has a weak magnetic field old, so
15:00
Speaker 1: that wouldn't contain it. And yeah, so lots of good
15:04
Speaker 1: thinking through the problem. Absolutely, And I love seeing people
15:07
Speaker 1: apply their knowledge of physics to this question to come
15:09
Speaker 1: up with an answer that they think makes sense, because
15:12
Speaker 1: if the answer is not the one that you expect,
15:14
Speaker 1: then there better to be an explanation for it. Right, That,
15:17
Speaker 1: in the end, is what physics is all about. That's right.
15:20
Speaker 1: So how about we start by talking about where atmosphere
15:24
Speaker 1: has come from? How do you get an atmosphere? Well,
15:26
Speaker 1: you go to Amazon dot com and you just type
15:29
Speaker 1: in whatever you'd like, and you know, they deliver it.
15:32
Speaker 1: I know so many space space element advocates who are
15:34
Speaker 1: going to be so excited to know it's going to
15:36
Speaker 1: be so easy on the Moon or Mars. It's surprising, Bezos,
15:39
Speaker 1: isn't saying more about this on Mars. Isn't the plans
15:42
Speaker 1: just like nuke the polar ice caps? Isn't that like
15:45
Speaker 1: step one in getting a Martian atmosphere? You know that
15:47
Speaker 1: that has been proposed, but I'm fairly certain the international
15:50
Speaker 1: community has mixed feelings about that proposal, so I'm not
15:53
Speaker 1: holding my breath. And also I think it makes it
15:55
Speaker 1: uninhabitable for quite a while. But you know, if we've
15:58
Speaker 1: got our great grandkids in mind, maybe it's maybe it's
16:00
Speaker 1: a good plan. Yeah, we have a whole episode on
16:03
Speaker 1: terra forming Mars and why that plan will not work.
16:06
Speaker 1: So we're lucky we have such a nice atmosphere here
16:09
Speaker 1: on Earth. And I think you're right. It's a good
16:10
Speaker 1: idea to think about why Earth has an atmosphere and
16:13
Speaker 1: why the Moon doesn't have at least the same atmosphere
16:16
Speaker 1: as we do. And the interesting thing is that the
16:19
Speaker 1: Earth sort of has had a few different atmospheres. The
16:22
Speaker 1: Earth got its first atmosphere when it was just forming.
16:24
Speaker 1: Remember that the whole Solar system just comes from a
16:27
Speaker 1: big cloud of gas and dust and rock and little
16:30
Speaker 1: bits from other solar systems and stars that died. Most
16:33
Speaker 1: of it's just hydrogen left over from the Big Bang.
16:36
Speaker 1: But you have this big cloud of gas and dust
16:38
Speaker 1: in space, you have some blobs in it that are
16:40
Speaker 1: a little denser than others, so they have stronger gravity.
16:43
Speaker 1: They are pulling everything together, and that's the formation of
16:46
Speaker 1: the Solar system. Of course, in the very center is
16:49
Speaker 1: the Sun, which gathers in most of the gas and
16:51
Speaker 1: the dust. But you also have other little blobs which
16:54
Speaker 1: eventually formed planets, and they try to gather as much
16:57
Speaker 1: stuff as they can before the Sun gobbles it all up.
17:00
Speaker 1: You know. It's funny my intuition, and this is why
17:02
Speaker 1: I didn't become a physicist. My intuition, Like, it feels
17:05
Speaker 1: to me like gases shouldn't get pulled in by gravity,
17:09
Speaker 1: but of course they are, and they should. But the
17:12
Speaker 1: idea that gravity is holding our atmosphere on, I don't know.
17:15
Speaker 1: It feels like the little molecule should be able to
17:17
Speaker 1: just pop out in escape. But I'm glad that I'm
17:20
Speaker 1: wrong about it. You're not actually wrong A lot of
17:22
Speaker 1: them do escape, and the Earth is constantly boiling off
17:25
Speaker 1: its atmosphere into space. It's a tenuous balance, right, The
17:28
Speaker 1: Earth is pulling on those little guys, but they are
17:30
Speaker 1: moving quickly, and the ones that have higher velocity and
17:34
Speaker 1: higher altitudes definitely do escape. And in the very early
17:37
Speaker 1: days of the Solar System, the Earth had an atmosphere
17:40
Speaker 1: which came from these primordial gases, the hydrogen helium that
17:43
Speaker 1: was just sort of like around, but it didn't last
17:46
Speaker 1: for very long. It's not a very good atmosphere for
17:48
Speaker 1: having an atmosphere, I guess you could say, because first
17:51
Speaker 1: of all, the Sun was gobbling up most of the
17:52
Speaker 1: hydrogen and the helium, and then once the Sun formed,
17:55
Speaker 1: it was producing a lot of radiation which stripped the
17:58
Speaker 1: inner planets of theirmosphere. So like solar wind and heat
18:02
Speaker 1: from the Sun basically blasted the Earth's atmosphere away. So
18:06
Speaker 1: it started off having a scoop of hygen and helium
18:09
Speaker 1: and stuff that could have made an atmosphere, but then
18:11
Speaker 1: it got blasted dry basically by the early Sun. So
18:14
Speaker 1: is solar wind well named? Is it like the sun
18:18
Speaker 1: is like and the stuff just sort of blows away?
18:22
Speaker 1: Or is it more like the photons that come out
18:25
Speaker 1: from the Sun. It's like a billiard table, and it
18:27
Speaker 1: like knocks the hydrogen in the helium out of our
18:30
Speaker 1: atmosphere when they like bounce into each other. I think
18:32
Speaker 1: it's pretty well named because it's not just photons. It's protons,
18:37
Speaker 1: it's electrons, it's actual particles. So if you think about
18:40
Speaker 1: wind on Earth, it's like high moving particles that carry
18:43
Speaker 1: momentum and it can push stuff over, and the solar
18:46
Speaker 1: wind is really the same thing. It's stuff, it's matter
18:49
Speaker 1: particles carrying momentum, and it could like push a solar sail,
18:52
Speaker 1: and it definitely blasts things off of the Moon and
18:55
Speaker 1: Mars and early Earth. Way to go, phus. This good
18:58
Speaker 1: job name in that thing. And that's one reason why
19:01
Speaker 1: you have, for example, rocky planets in the interior of
19:03
Speaker 1: the Solar system, because that's the kind of stuff the
19:06
Speaker 1: Sun couldn't blast off and like formed dense or blobs.
19:10
Speaker 1: And in the outer part of the Solar system you
19:11
Speaker 1: have the gas giants because they were far enough away
19:14
Speaker 1: from the Sun to get to gobble up some of
19:16
Speaker 1: their own gas and to hold onto it out there
19:19
Speaker 1: where the solar radiation is weaker, So we got amosphere
19:22
Speaker 1: very early on, and so did the Moon. As the
19:24
Speaker 1: moon form from whatever primordial blobs made it. It also
19:28
Speaker 1: must have had some helium and some hydrogen, but that
19:31
Speaker 1: also was blasted clean by the Sun. So we both
19:34
Speaker 1: started with an atmosphere and both lost our atmosphere very quickly,
19:37
Speaker 1: and we both both of them lost it entirely or
19:40
Speaker 1: did Earth retain some of it almost entirely, I mean
19:43
Speaker 1: never completely dry. There must have been a little bit
19:45
Speaker 1: of hydrogen floating around, but compared to the densities we
19:48
Speaker 1: have today basically zero. Okay, Well, before we get into
19:51
Speaker 1: what our second atmosphere was, like, let's take a break. Okay,
20:08
Speaker 1: So the first atmosphere we had and we lost, but
20:12
Speaker 1: we know that we get to hold onto one atmosphere eventually,
20:15
Speaker 1: So what happens to the next atmosphere? This is like
20:18
Speaker 1: a Disney movie. You know, there's a happy ending, right,
20:20
Speaker 1: So even when there's ups and downs, you can sort
20:22
Speaker 1: of hold on, just like life. Right. But we're telling
20:26
Speaker 1: two stories simultaneously here. We're interested in whether the Moon
20:29
Speaker 1: has an atmosphere, and we're telling the story of the
20:31
Speaker 1: Earth and the Moon's atmosphere. Is in parallel to see
20:34
Speaker 1: why they have different fates. So the Earth's got its
20:37
Speaker 1: atmosphere is sort of rebooted from its interior. You had
20:40
Speaker 1: like volcanoes and all sorts of crazy stuff happening on
20:42
Speaker 1: the surface of the Earth which outgased like water and
20:46
Speaker 1: CEO two and sulfur dioxide and nitrogen. So this is
20:50
Speaker 1: like the Earth burping and giving itself an atmosphere just
20:53
Speaker 1: from those burps. That makes it like substantially less beautiful
20:58
Speaker 1: to watch the sunset. All those are Earth burps making
21:01
Speaker 1: those colors. Yeah, and you know, let's go with burps
21:04
Speaker 1: rather than any sort of other gaseous emission. But it's
21:06
Speaker 1: incredible that there must have been so many volcanoes, so
21:10
Speaker 1: much sort of tectonic action in the early Earth, that
21:12
Speaker 1: you could release vast quantities of gas. Right. Did this
21:16
Speaker 1: happen on Mars too? Or am I getting too far
21:18
Speaker 1: afield by asking that because Morris has volcanoes too, Right, Yeah,
21:21
Speaker 1: we think it happened on a lot of these planets.
21:23
Speaker 1: And remember the scale though of the atmosphere. Even though
21:26
Speaker 1: it seems vast to us and it seems dense, it's
21:28
Speaker 1: really a very very thin layer on top of an
21:31
Speaker 1: enormous sphere. Atmosphere goes up like a few hundred kilometers
21:35
Speaker 1: depending on how you define it. But the Earth's radius
21:38
Speaker 1: is six thousand kilometers, and so it's not that surprising
21:42
Speaker 1: that all of that stuff could bubble up enough gas
21:45
Speaker 1: to cover it with a very thin shell. It happened
21:48
Speaker 1: on Earth, and it happened on Mars, and we also
21:50
Speaker 1: think it might have happened on the Moon. The Moon
21:53
Speaker 1: is not just like a lifeless, inert, frozen rock. It
21:56
Speaker 1: had volcanoes. We can see this on the surface of
21:58
Speaker 1: the Moon. There are all lava planes underneath the Moon.
22:02
Speaker 1: There are these lava tubes, all sorts of crazy volcanic
22:05
Speaker 1: stuff that happened on the Moon. How long ago did
22:07
Speaker 1: the volcanic activity end, We don't know, and we don't
22:10
Speaker 1: think that there are any active volcanoes right now. But
22:13
Speaker 1: we have measured moon quakes, like you put these sensors
22:17
Speaker 1: on the surface of the Moon and there are moon quakes,
22:19
Speaker 1: right and that suggests, yeah, that there's stuff going on
22:23
Speaker 1: inside the Moon, that there's internal magma, this stuff like
22:25
Speaker 1: splashing around in there, which might mean you know, a
22:28
Speaker 1: future volcanic action. Probably not, though across is probably now
22:32
Speaker 1: cooled and sealed, and all that stuff is sunk too
22:34
Speaker 1: far towards the center to ever crop up again. Will
22:37
Speaker 1: it cool and stop moonquaking at some point? Eventually? Probably will. Yeah,
22:41
Speaker 1: the same sort of thing is happening on Mars. Mars
22:44
Speaker 1: and the Moon of course much much smaller than the Earth,
22:47
Speaker 1: and so they cool faster. And we think, for example,
22:49
Speaker 1: Mars still has some sort of liquid or at least
22:52
Speaker 1: fluid core, and there's stuff going on inside there, because
22:54
Speaker 1: we have measured Mars quakes as well. But there isn't
22:57
Speaker 1: active volcanism on the Moon or on Mars, okay. And
23:01
Speaker 1: so did the Moon lose its second atmosphere for the
23:05
Speaker 1: same reason that it lost its first, or did the
23:07
Speaker 1: volcanoes never give it an atmosphere to begin with? Yeah,
23:11
Speaker 1: it's a great question. And so we have to understand
23:13
Speaker 1: not just how you get an atmosphere, but how you
23:15
Speaker 1: hold onto it right. It's not enough to just produce
23:18
Speaker 1: the gases either from the first scoop of Solar system
23:21
Speaker 1: stuff or remaking it again from volcanoes. You gotta hold
23:25
Speaker 1: onto it right, because, as you say, there are things
23:28
Speaker 1: out there in the Solar System that are trying to
23:30
Speaker 1: get rid of your atmosphere, and so the solar wind
23:33
Speaker 1: didn't stop, right. The solar wind was around in the
23:35
Speaker 1: early days when things were forming, and it's still going
23:38
Speaker 1: on today. And so their processes out there which remove atmospheres,
23:42
Speaker 1: which work against having an atmosphere on the Earth and
23:46
Speaker 1: on the Moon and on Mars. So this second atmosphere
23:50
Speaker 1: that the Moon did have, unfortunately did get blown away. Sorry. Moon.
23:54
Speaker 1: The story always seems so sad for the Moon. But
23:58
Speaker 1: I think it's really interesting to understand sort of the
24:00
Speaker 1: balance between those effects. I like thinking about it microscopically
24:04
Speaker 1: the way you were. I think about the atmosphere and
24:06
Speaker 1: individual particles of that gas, right, because in the end,
24:10
Speaker 1: the atmosphere is not just like a huge blob of gas.
24:13
Speaker 1: It really is made of individual particles. And the fate
24:16
Speaker 1: of those individual particles is what determines the fade of
24:19
Speaker 1: the atmosphere. And it's sort of weird to think about,
24:21
Speaker 1: but gravity does operate on like individual atoms of gas, right,
24:26
Speaker 1: Like the Earth pulls on each of those nitrogen atoms
24:30
Speaker 1: and each of those oxygen atoms. It really is yanking
24:33
Speaker 1: and keeping a lot of them on the surface. Of
24:36
Speaker 1: the Earth, and that's of course, the biggest difference between
24:38
Speaker 1: the Earth and the Moon is that the Earth is bigger,
24:41
Speaker 1: it has more gravity, and it's a lot of our
24:44
Speaker 1: listeners said, the Moon just doesn't have the gravity to
24:47
Speaker 1: hold onto its atmosphere. Does the magnetosphere player roll too
24:50
Speaker 1: or is it mostly about gravity. That's a really interesting
24:53
Speaker 1: topic because the Earth's magnetic field does protect us from
24:56
Speaker 1: the solar wind. Right, the solar wind are charged particle,
25:00
Speaker 1: These are protons, these are electrons. What happens when a
25:03
Speaker 1: charge particle hits a magnetic field is that it tends
25:05
Speaker 1: to bend. And so when charge particles from the Sun
25:08
Speaker 1: hit our magnetic field, they don't immediately just like slam
25:11
Speaker 1: into our atmosphere. They spiral around these magnetic field lines,
25:15
Speaker 1: and they go up to the north pole or down
25:17
Speaker 1: to the south pole, and you finally see them as
25:20
Speaker 1: like the Northern lights or the Southern lights. That's what
25:22
Speaker 1: causes them, this magnetic field, and so initially you think, oh, well,
25:26
Speaker 1: this must protect us. It's like a shield keeping our
25:29
Speaker 1: atmosphere in place. That's sort of the prevailing view that
25:32
Speaker 1: a big magnetic field will protect you like a shield.
25:36
Speaker 1: But other people feel like, actually, a magnetic field is
25:39
Speaker 1: sort of like a sale. It's going to capture a
25:41
Speaker 1: lot of solar wind and funnel it into the planet,
25:44
Speaker 1: helping strip the atmosphere, and so, like most things that
25:47
Speaker 1: involved like more than one particle, the story is complicated
25:50
Speaker 1: and people have differing opinions about it. But in the
25:53
Speaker 1: case of the Moon, this very very little magnetic field there.
25:56
Speaker 1: Like the Moon, we don't think has enough internal motion
25:59
Speaker 1: in its core to generate a strong magnetic field. There
26:02
Speaker 1: are magnetic rocks on the surface of the Moon, but
26:04
Speaker 1: has no like big overall magnetic field to shield it
26:07
Speaker 1: or to act like a sale. Are those magnetic rocks
26:10
Speaker 1: big enough that you could try to address the question
26:13
Speaker 1: about whether magnetic fields help or hurt atmospheres or no,
26:16
Speaker 1: because there's just no atmosphere on the Moon, so you
26:18
Speaker 1: can't compare like the area around magnetic rocks versus the
26:21
Speaker 1: area around non magnetic rocks. Yeah, in order to operate
26:24
Speaker 1: like a shield, I think you really do need to
26:26
Speaker 1: have a planet sized magnetic field, um, and there just
26:30
Speaker 1: isn't a coherent one on the Moon. I mean, if
26:31
Speaker 1: you map the Moon's surface for magnetism, and they've done
26:35
Speaker 1: that you do identify some spots with more magnetic field
26:37
Speaker 1: or less. That's more probe of like what kind of
26:40
Speaker 1: metals are there just under the surface, rather than telling
26:43
Speaker 1: you anything about the planet's atmosphere. Arts was that the
26:46
Speaker 1: end of our atmosphere story? Or is there a third phase?
26:49
Speaker 1: So the Earth's atmosphere did keep evolving. Of course, now
26:52
Speaker 1: we have oxygen in the Earth's atmosphere, which didn't come
26:55
Speaker 1: from those volcanoes, right, That actually mostly came from life
26:58
Speaker 1: when little cells begin into drink sunlight and do photosynthesis.
27:02
Speaker 1: They turned a lot of the atmosphere into oxygen, though
27:05
Speaker 1: surprisingly it took a long time. Right, You can't just
27:08
Speaker 1: pump oxygen into the atmosphere and have it to stay
27:11
Speaker 1: there because oxygen is so reactive. Most of the oxygen
27:14
Speaker 1: that was produced by life actually got gobbled up by
27:17
Speaker 1: rocks because rocks like to get oxydized. So if you
27:21
Speaker 1: put oxygen in your atmosphere, it will weather. The rocks
27:25
Speaker 1: are the surface of your planet will get like rusty,
27:28
Speaker 1: for example, and that gobbles up a lot of the oxygen.
27:31
Speaker 1: So it took hundreds of millions of years of pumping
27:33
Speaker 1: oxygen into the atmosphere of the Earth before it had
27:35
Speaker 1: like a measurable impact on what actually was in the atmosphere.
27:39
Speaker 1: And today the Earth's atmosphere is mostly nitrogen. It's like oxygen,
27:45
Speaker 1: and then like one percent argon point oh three percent
27:48
Speaker 1: c O two and rising, and then a bunch of
27:51
Speaker 1: other stuff. But the Moon, of course doesn't have life
27:53
Speaker 1: on it, and it didn't have and it wasn't able
27:55
Speaker 1: to keep that atmosphere around, and so it didn't get
27:58
Speaker 1: to have the third act of its atmosphere. And is
28:00
Speaker 1: there like a physics definition for when your atmosphere ends?
28:06
Speaker 1: Is it like, you know, all what exactly kilometers the
28:10
Speaker 1: atmosphere ends, or is it like a gradient where you
28:12
Speaker 1: just have a little bit less and less as you
28:14
Speaker 1: go and there's no clear cut off point. It's totally
28:17
Speaker 1: a gradient. And there are definitions and they all disagree
28:20
Speaker 1: with each other. You know. Some people say, oh, a
28:22
Speaker 1: hundred kilometers, some people say no, the threshold should be
28:25
Speaker 1: sixty five kilometers, and people argue endlessly about it, and
28:28
Speaker 1: I'm not sure that we're really learning anything through that argument.
28:31
Speaker 1: There are some interesting distinctions, like the Earth's atmosphere is
28:34
Speaker 1: mostly within thirty kilometers of the surface, it's like of
28:38
Speaker 1: the mass of the atmosphere. But you know, you could
28:39
Speaker 1: draw that threshold anywhere, you could say nine or ninety
28:42
Speaker 1: nine nine percent. In order to get all of it,
28:44
Speaker 1: you have to go out like ridiculously far, you know,
28:47
Speaker 1: hundreds of thousands of kilometers to say this is the
28:50
Speaker 1: full envelope of the Earth. But there is an interesting
28:53
Speaker 1: transition above a certain distance, the density is so low
28:57
Speaker 1: that the atoms don't really bump into each other, and
28:59
Speaker 1: so above what we call the atmosphere something called the exosphere,
29:03
Speaker 1: where the density is so low that adams can travel
29:05
Speaker 1: for like hundreds of kilometers without bouncing into each other.
29:09
Speaker 1: So the dynamics of it are a little bit different.
29:11
Speaker 1: It's collision lists. So usually where we get to by
29:14
Speaker 1: the end of the episode, is you telling me something awful?
29:18
Speaker 1: So now you've got me wondering is Earth going to
29:22
Speaker 1: lose its atmosphere? So can you tell me about the ways,
29:26
Speaker 1: like summarized for me, the ways that atmosphere gets lost,
29:30
Speaker 1: and then is Earth gonna lose the atmosphere? Because probably
29:33
Speaker 1: that's where this conversation is going. Right, your kids are
29:37
Speaker 1: going to be fine, Kelly. Now, their kids and their
29:40
Speaker 1: kids kids. You know, they're gonna have to listen to
29:42
Speaker 1: the next generation of the podcast to find out. But
29:45
Speaker 1: I think it's really fascinating to think about the dynamic
29:48
Speaker 1: processes here and the things that are changing. The solar system.
29:51
Speaker 1: We usually think of the solar system is so static.
29:53
Speaker 1: It's just like this is the way it's been. It's
29:56
Speaker 1: been this way for thousands or millions or maybe billions
29:59
Speaker 1: of years, and so probably has always been this way,
30:02
Speaker 1: and so there's always a little bit shocking and surprising
30:04
Speaker 1: to discover that things are dynamic, that things are changing.
30:07
Speaker 1: And the atmosphere is definitely in that category because it
30:10
Speaker 1: is pretty tenuous. You know, it's not easy to hold
30:12
Speaker 1: onto these gases, and there are a lot of factors
30:15
Speaker 1: that are helped blowing it away. So we talked about
30:17
Speaker 1: the solar wind. You know, something that people don't really appreciate,
30:19
Speaker 1: I think is that the solar wind comes in like
30:22
Speaker 1: a million miles per hour, these particles coming from the Sun. Yeah,
30:26
Speaker 1: there's a bit along, right, and so like point one
30:30
Speaker 1: five percent of the speed of light. It sounds like
30:33
Speaker 1: a low value, but it's really really high. And nobody
30:35
Speaker 1: wants to get shot at in the face with a
30:37
Speaker 1: proton at a million miles per hour, I'll pass. And
30:41
Speaker 1: even if we didn't have the Sun trying to strip
30:43
Speaker 1: us of our atmosphere, right, it does just boil away.
30:46
Speaker 1: There's gravity is powerful, but at the upper edges of
30:49
Speaker 1: the atmosphere there are fast moving particles and they can
30:51
Speaker 1: just achieve escape velocity. You know, you have a particle
30:54
Speaker 1: going fast enough, pointed in the right direction, it's just gone.
30:58
Speaker 1: You know, you don't have to launch it into out
31:00
Speaker 1: of space. It's just hot and fast moving and it's
31:02
Speaker 1: just taken off. And so this definitely happens for every planet,
31:07
Speaker 1: and it happens also for Earth. No heavier planets is
31:09
Speaker 1: gonna lose less because the escape velocity is higher. But
31:12
Speaker 1: if you have lower mass gases like hydrogen and helium,
31:16
Speaker 1: then they just boil off. Does it get replenished. It
31:19
Speaker 1: doesn't really get replenished by new hydrogen or helium or oxygen.
31:23
Speaker 1: That we do get a lot of space dust every year,
31:26
Speaker 1: and so we get like tons of space dust, just
31:29
Speaker 1: like debris falling to Earth, and we're also losing our atmosphere.
31:33
Speaker 1: We lose three kilograms per second of hydrogen. That sounds
31:37
Speaker 1: kind of scary, Okay, but we'll probably be fine. We're
31:41
Speaker 1: gonna be fine for about a billion years until the Sun,
31:45
Speaker 1: when it's gonna be like ten brighter than it is now,
31:48
Speaker 1: is going to make it hot enough on Earth for
31:50
Speaker 1: the oceans to boil, for water to break down into
31:52
Speaker 1: hydrogen oxygen, and the Earth will probably lose a lot
31:55
Speaker 1: of that hydrogen. Time to invest in interstellar travel, all right.
32:00
Speaker 1: You know that news isn't as bad as some of
32:02
Speaker 1: the news that you've delivered to me, But I still
32:04
Speaker 1: think that we should take a break so that I
32:06
Speaker 1: can recover for a moment. We'll be back soon. Okay,
32:21
Speaker 1: we're back. Recap for me what we know about the
32:24
Speaker 1: Moon's atmosphere. So we think that the Moon probably did
32:28
Speaker 1: get a delivery of gas early on, right from the
32:31
Speaker 1: primordial soup, and then it may have also gotten the
32:34
Speaker 1: refreshing of its gas from volcanism. But we don't think
32:38
Speaker 1: that there's much atmosphere there today, and the reason is
32:41
Speaker 1: that it just doesn't have the mass to hold onto.
32:44
Speaker 1: The stuff doesn't have the magnetic feel. So if you
32:47
Speaker 1: ordered a new atmosphere for the Moon, if you like
32:50
Speaker 1: went up there and pumped a bunch of oxygen and
32:53
Speaker 1: nitrogen and c O two onto the Moon. Most of
32:55
Speaker 1: it would get stripped away by the Sun or it
32:57
Speaker 1: would just drift away because remember remember that the Moon
33:00
Speaker 1: is really pretty tiny. I mean, it looks impressive in
33:03
Speaker 1: the sky, but it's got like one percent of the
33:06
Speaker 1: mass of the Earth, and its surface gravity is very,
33:09
Speaker 1: very low, and so the escape velossity of the Moon
33:11
Speaker 1: is just much lower than it is here on Earth,
33:13
Speaker 1: which makes it easier for the stuff to boil away.
33:16
Speaker 1: So I feel like I would have, you know, as
33:18
Speaker 1: someone who thinks about terror forming a little, I would
33:21
Speaker 1: have thought, well, maybe we can, at great, great, great, great, great,
33:24
Speaker 1: great great great expense, give the Moon a magnetic field
33:28
Speaker 1: to hold onto an atmosphere. But now what you've told
33:30
Speaker 1: me is that physics doesn't have that figured out yet,
33:33
Speaker 1: and a magnetic field may or may not help, So
33:35
Speaker 1: there's maybe nothing we can do about the Moon not
33:37
Speaker 1: having an atmosphere. Giving the Moon an atmosphere is definitely
33:40
Speaker 1: a hopeless engineering project. I mean, you need to build
33:42
Speaker 1: like a containment vessel, right, You need to like put
33:45
Speaker 1: the whole Moon inside a glass bulb or something crazy.
33:48
Speaker 1: Because it's not just that it doesn't have the gravity
33:51
Speaker 1: to hold onto that gas envelope on its own. It's
33:54
Speaker 1: a pretty harsh environment. I mean, the surface of the
33:56
Speaker 1: Moon gets to like two hundred and fifty fahrenheit a
33:59
Speaker 1: hundred and twenty cell see us during the day, which
34:01
Speaker 1: makes it pretty easy to boil this stuff off, because remember,
34:04
Speaker 1: it's a trade off between the temperature of the gas,
34:07
Speaker 1: which means fast moving particles, and the gravity of the object.
34:10
Speaker 1: If you have a small object, it's only hope for
34:13
Speaker 1: holding onto its gas is if that gas is very cold,
34:16
Speaker 1: meaning it's slow moving. But if the gas is hot
34:19
Speaker 1: and the object is small, then that stuff is just
34:22
Speaker 1: going to boil off into space. All right. I'm not
34:24
Speaker 1: investing in that project. And people have been wondering about
34:26
Speaker 1: the Moon's atmosphere for a long time. It's not for
34:29
Speaker 1: a very long time that we've understood the source of
34:31
Speaker 1: the Earth's atmosphere. This is a very complex story. It
34:34
Speaker 1: took us a long time to piece together, and so
34:36
Speaker 1: it wasn't until like the seventeen hundreds of people were
34:38
Speaker 1: speculating about whether the Moon had an atmosphere, and people considered,
34:41
Speaker 1: oh my gosh, maybe the Moon doesn't have any air
34:44
Speaker 1: on it. They just for a long time assumed that
34:46
Speaker 1: it would because the Earth did right, But it's not
34:48
Speaker 1: actually that hard to tell even from the Earth that
34:51
Speaker 1: the Moon must not have any atmosphere, and it's using
34:54
Speaker 1: the same technique we talked about earlier. Remember, if we
34:56
Speaker 1: are studying exoplanet, one thing we can do is look
34:59
Speaker 1: at the light that passes through the atmosphere of those
35:02
Speaker 1: exoplanets to see that there is an atmosphere and what's
35:05
Speaker 1: in it. But you can do the same thing when
35:06
Speaker 1: you look at the Moon. You can look at sunlight
35:09
Speaker 1: that passes very very close to the Moon and see
35:11
Speaker 1: is it absorbed, is it getting reflected, is it getting scattered.
35:15
Speaker 1: You can basically use the sun as a probe of
35:18
Speaker 1: what's right around the Moon. But we've been there, so
35:20
Speaker 1: we don't have to rely on far off things. Didn't
35:23
Speaker 1: they try to measure an atmosphere when they got there,
35:26
Speaker 1: You're right, we have been there, and the Apollo missians
35:28
Speaker 1: have a long series of experiments trying to measure things
35:31
Speaker 1: on the Moon, looking for trace atmosphere and really finding
35:34
Speaker 1: almost nothing. A Poulost seventeen saw a little bit of
35:38
Speaker 1: evidence for UV emitting gases, but there's another big clue
35:42
Speaker 1: about the Moon's atmosphere from the fact that we did
35:45
Speaker 1: go there. You know, those footprints that people left on
35:47
Speaker 1: the moon, they're still there. You like, write your name
35:51
Speaker 1: in the sand on the Moon, and you could look
35:54
Speaker 1: at it twenty years later from the surface of the
35:56
Speaker 1: Earth and read your own handwriting, because there's basically no
35:59
Speaker 1: whether on the moon, right, there's no wind of their
36:01
Speaker 1: like blow things around, and so it's sort of amazing
36:04
Speaker 1: that the rover tracks and the footprints they're all still
36:07
Speaker 1: up there. You know, I've read that pizza hut was
36:09
Speaker 1: looking into the cost estimate for like lasering its name
36:13
Speaker 1: onto the moon. Yeah, it sounds like it would have
36:19
Speaker 1: been a good long term investment because once it's up there,
36:21
Speaker 1: it's not going away, right, But I think they did
36:24
Speaker 1: determine it was probably not cost effective and actually might
36:29
Speaker 1: make people angry, And in a million years archaeologists are
36:33
Speaker 1: gonna be like, what is a pizza and why did
36:35
Speaker 1: humans think to write about it on the moon? Right?
36:39
Speaker 1: And why are they keeping it in a hut? Yeah?
36:43
Speaker 1: Bad idea, bad idea. So it seems like when you
36:45
Speaker 1: and I talk about something, the answer is never yes
36:49
Speaker 1: or no. The answer is always something like yes but
36:54
Speaker 1: or yes, well, so is is there a will? Is
36:58
Speaker 1: there something sort of like an atmosphere? Sometimes where's the
37:01
Speaker 1: well actually parked to this this episode? Yeah, there's definitely
37:05
Speaker 1: a well actually varked to this episode, otherwise it would
37:08
Speaker 1: have been very short. And the answer is that the
37:10
Speaker 1: Moon technically doesn't have an atmosphere, but it does have
37:14
Speaker 1: an exosphere. Remember earlier we were talking about the Earth
37:17
Speaker 1: having an exosphere. Up above the atmosphere, there's this point
37:20
Speaker 1: where there are gases, but they're very diffuse and very
37:23
Speaker 1: low density, so they're not bumping into each other. The
37:25
Speaker 1: Moon does have some gas particles and some other stuff
37:29
Speaker 1: floating around near it in this envelope that don't bump
37:32
Speaker 1: into each other. And so we can say the Moon
37:34
Speaker 1: has an exosphere, and you might wonder, like, well, how
37:37
Speaker 1: is it possible for it to hold onto its exosphere
37:39
Speaker 1: if it can't hold onto an atmosphere, and it's part
37:42
Speaker 1: of this fascinating dynamic story. Basically, it can't hold onto it,
37:45
Speaker 1: but it has sources of new material at the same
37:48
Speaker 1: time as it has sinks ways to get rid of it,
37:51
Speaker 1: so it's constantly losing its exosphere and getting it replenished
37:56
Speaker 1: tell me more about where it comes from. So it's
37:57
Speaker 1: really a fun story. The Moon's exosphere actually comes from itself, right,
38:02
Speaker 1: So things are constantly hitting the Moon, like you have
38:05
Speaker 1: meteorites and then includes like really tiny little rocks that
38:08
Speaker 1: are hitting the surface of the Moon. And we know
38:10
Speaker 1: this is happening because you look up at the Moon
38:12
Speaker 1: and it's covered with craters, right, which means that things
38:14
Speaker 1: are constantly impacting it. Well, what happens if you don't
38:17
Speaker 1: have very strong gravity and you get impacted with the
38:19
Speaker 1: meteorite is that it sprays a bunch of stuff up
38:21
Speaker 1: above the surface, and that stuff doesn't all immediately float
38:25
Speaker 1: back down. Some of it's pretty light, and it's sort
38:27
Speaker 1: of like hangs out there a little bit, like this
38:30
Speaker 1: cloud of dust particles. So when when you say a
38:34
Speaker 1: little bit, do you mean like decades or like that's
38:39
Speaker 1: a great question. I think that for an individual particle,
38:41
Speaker 1: it can vary a lot. Some of them might just
38:43
Speaker 1: stay in the moon for minutes, some of them might
38:45
Speaker 1: float around for days or years or decades. I don't
38:49
Speaker 1: think that any of those things are going to last
38:51
Speaker 1: for more than decades though, Okay, so it must be
38:53
Speaker 1: getting pounded pretty often then, or does it have an
38:56
Speaker 1: exosphere sometimes but not all the time. It has a
39:00
Speaker 1: constant exosphere. But I have to emphasize that this is
39:03
Speaker 1: very very low density. We're talking about like a few
39:06
Speaker 1: hundred atoms per cubic centimeter. The Earth's atmosphere is like
39:10
Speaker 1: ten to the nineteen particles per cubic centimeter, so we're
39:14
Speaker 1: talking about something very very very very thin. You know,
39:18
Speaker 1: the I S S the International Space Station, it flies
39:21
Speaker 1: through the Earth's exosphere, which is about as dense. So
39:25
Speaker 1: we're talking about the Moon having an exosphere which is
39:28
Speaker 1: similar to like what you would feel if you stuck
39:30
Speaker 1: your head out of the window and on the I.
39:32
Speaker 1: S S, which I do not recommend remend you. So
39:37
Speaker 1: if you have like a dog on the Moon in
39:39
Speaker 1: your rover, and maybe you've called your dog rover, don't
39:42
Speaker 1: encourage it to stick its head out because there's not
39:45
Speaker 1: really a lot there. But it is really fascinating sort
39:47
Speaker 1: of physics because it's not just like common fragments and meteorites.
39:51
Speaker 1: It's other processes as well. We talked about the sun
39:54
Speaker 1: blasting is free of an atmosphere, Well, that solar wind
39:57
Speaker 1: also helps generate new atmosphere because each of those particles
40:01
Speaker 1: hitting the surface of the Moon kicks up stuff from
40:05
Speaker 1: the Moon's surface, right like knock stuff off the surface,
40:08
Speaker 1: which then becomes part of the exosphere. Some of that
40:10
Speaker 1: again settles back down, but some of it doesn't. Some
40:13
Speaker 1: of it floats around for a while before then getting
40:16
Speaker 1: like ionized by the Sun and then floating off into space.
40:19
Speaker 1: Does it get like pushed in a certain direction by
40:24
Speaker 1: the wind or is it just sort of like floating
40:26
Speaker 1: off in all directions. So there's an envelope surrounding the
40:30
Speaker 1: Moon of all of this stuff, and it's constantly getting
40:32
Speaker 1: blown away. You know how commets have a tail, right,
40:35
Speaker 1: They have a tail because the solar wind is pushing
40:37
Speaker 1: them away. You imagine a comet has a tail because
40:39
Speaker 1: it's like streaking through the sky and it's sort of
40:41
Speaker 1: like comic book wiggles or motion behind it. With the
40:43
Speaker 1: largest contribution for a comet's tail is actually the solar wind,
40:46
Speaker 1: and so the tail points away from the Sun, not
40:49
Speaker 1: always away from the direction of its motion. And the
40:52
Speaker 1: same thing is true of the Moon. It has this
40:54
Speaker 1: sort of short lived envelope that's constantly being refreshed, and
40:58
Speaker 1: it also has a tail. We can now see it
41:01
Speaker 1: from Earth using special telescopes that we have to like
41:03
Speaker 1: block the light from the actual part of the Moon's surface,
41:06
Speaker 1: so we can see just around it, like the corona
41:08
Speaker 1: of the Moon. And they can see this envelope of
41:11
Speaker 1: sodium around the Moon, and it has this tail that's
41:14
Speaker 1: getting blown by the Sun away from the Moon. That's
41:17
Speaker 1: so cool. I wish I could see that in real life.
41:20
Speaker 1: If you google for it, there are these really cool
41:22
Speaker 1: videos where you can see the Moon going around the
41:24
Speaker 1: Earth and when the Moon is between the Earth and
41:27
Speaker 1: the Sun, the Earth is in the Moon's tail. Right,
41:30
Speaker 1: we're like eating the Moon's sodium dust is do we
41:35
Speaker 1: retain any of it or does it just pass through?
41:38
Speaker 1: We can retain it, you know, it just gets gathered
41:39
Speaker 1: by the Earth. But again these are very very small amounts.
41:42
Speaker 1: Is the reason it took us a long time to
41:44
Speaker 1: even spot it. It was like that we first saw
41:47
Speaker 1: the Moon's like sodium envelope and this tail. It takes
41:50
Speaker 1: a long time. And one reason that they actually spotted
41:53
Speaker 1: it is really cool is because of the landed meteor shower.
41:56
Speaker 1: You know, when there's a meteor shower. It means like
41:58
Speaker 1: spectacular things happening in our atmosphere. It also means more
42:02
Speaker 1: things hitting the Moon's surface, which kicks up more stuff,
42:06
Speaker 1: which enhances the Moon's exosphere and its tail. So during
42:09
Speaker 1: the Leanded meteor shower, the Moon's exosphere was tripled in density,
42:15
Speaker 1: heavy stuff, heavy stuff exactly. So there's a lot of
42:18
Speaker 1: these processes going on, you know, like not just the
42:21
Speaker 1: solar wind and commentary impact, also just photons. This is
42:25
Speaker 1: fun process called desorption. You know, we're used to the
42:29
Speaker 1: process of absorption where you can like gobble something up,
42:33
Speaker 1: but desorption is when a photon hits something and it
42:36
Speaker 1: kicks something off, just like when a meteor hits the
42:38
Speaker 1: surface and kicks off a rock. Now we're talking about
42:40
Speaker 1: a photon hitting an atom and giving it the energy
42:42
Speaker 1: to like escape whatever bonds it was in and it
42:44
Speaker 1: comes off the surface. And so the Moon has all
42:47
Speaker 1: these various ways to replenish its exosphere and all these
42:51
Speaker 1: ways to lose it. So it's like more like a flow, right,
42:54
Speaker 1: It's not just like a gaseous pool. It's like the
42:57
Speaker 1: stuff flowing off the Moon and getting a braid and
43:00
Speaker 1: by everything that's around it. Does this mean that that
43:02
Speaker 1: the other moons in the Solar System might also have tails?
43:07
Speaker 1: Almost certainly every object in the Solar System has an
43:10
Speaker 1: exo sphere because they're not just alone, right, They're all
43:13
Speaker 1: in the Solar wind. They're all getting constantly bombarded by
43:16
Speaker 1: little meteor fragments or big objects. So the Solar System
43:19
Speaker 1: is a very dynamic place. And because of it, all
43:22
Speaker 1: these things are constantly providing sources for their own exosphere
43:26
Speaker 1: and then also losing them constantly. So we think that
43:28
Speaker 1: for example, and slate Us in Europa, and Callisto and
43:32
Speaker 1: Ganymede and even dwarf planets like Ceres in the Asteroid
43:36
Speaker 1: Belt probably have their own little exosphere. Not quite an atmosphere, right,
43:41
Speaker 1: but a little exosphere of their own. Interesting. And then,
43:44
Speaker 1: and you know, as somebod who thinks about settlements, these
43:46
Speaker 1: exo spheres will probably never be useful for anything, because
43:49
Speaker 1: even if they were made out of useful stuff, it's
43:51
Speaker 1: so it would be so hard to extract it. Yeah,
43:53
Speaker 1: exactly right. There's probably no economic benefit there, But there
43:56
Speaker 1: is a lot of physics that you can learn because
43:59
Speaker 1: their collision list they're not interacting with each other, mostly
44:02
Speaker 1: just flying along and doing their own dance. Each one
44:04
Speaker 1: tells you something different about a physics process that's going on.
44:08
Speaker 1: It helps to sort of like isolate the things and
44:10
Speaker 1: study them in detail. So we think that each of
44:12
Speaker 1: these Solar System bodies probably have different sinks and different sources. Right.
44:17
Speaker 1: Some of them, for example, are really cold on the surface,
44:20
Speaker 1: and that can be a sink. It can be like
44:22
Speaker 1: that there's so it's so cold that it's like sticking
44:24
Speaker 1: your tongue to a flagpole, that when those little molecules
44:27
Speaker 1: touch the surface they stick on. So the exospheres are
44:30
Speaker 1: a really cool way to learn a lot about the
44:31
Speaker 1: surface of these planets without even landing on them. Right,
44:34
Speaker 1: You can pass your satellite near one of these objects
44:37
Speaker 1: and sample them and learn a lot about what's going
44:39
Speaker 1: on in the surface without actually having to land. It's incredible.
44:42
Speaker 1: We can collect enough data from these very thin exospheres
44:46
Speaker 1: to learn this kind of stuff. Yeah, which you need
44:48
Speaker 1: is a mass spectrometer. One of these devices that tells
44:50
Speaker 1: you like, oh, you have seventy two atoms of hydrogen
44:54
Speaker 1: or sixteen atoms of sodium. Can tell you exactly what
44:57
Speaker 1: the composition is, and that gives you a lot of
44:59
Speaker 1: clues to how these things formed and also what's going
45:02
Speaker 1: on on their surface right now. I spoke to one
45:04
Speaker 1: of my old friends from grad school who's now an
45:06
Speaker 1: expert in this. He's a he's a space geoscientist, and
45:09
Speaker 1: he said, any rocky object in space gets bombarded by
45:13
Speaker 1: all sorts of crap that can liberate materials from the
45:16
Speaker 1: surface and form an exo sphere is crap a technical term.
45:20
Speaker 1: I mean he's speaking as a scientist, he's a professor,
45:23
Speaker 1: So now it is a technical term. Fantastic. I didn't
45:26
Speaker 1: realize it was that easy, And I guess that means that,
45:28
Speaker 1: you know, even objects like the I s s, which
45:31
Speaker 1: are getting hit by the solar wind and getting hit
45:33
Speaker 1: by all sorts of stuff, are also like liberating little bits, right,
45:36
Speaker 1: Spellation and abration are giving off little particles. And so
45:40
Speaker 1: even like an individual astronaut out there in space on
45:45
Speaker 1: an e v A must have their own little exo sphere. Somehow,
45:50
Speaker 1: I feel like that would make me feel even more
45:51
Speaker 1: important to know I had my own little exo sphere exactly,
45:55
Speaker 1: and you don't even have to burp it out. That's right.
45:58
Speaker 1: It's one thing we have advantage we have over Earth,
46:01
Speaker 1: and so recent studies of the Moon suggests that, of
46:04
Speaker 1: course there's sodium there. We can see sodium pretty clearly
46:07
Speaker 1: because it's very responsive in the UV, which is what
46:10
Speaker 1: these telescopes are good at looking at. But there's also
46:12
Speaker 1: helium there, there's neon, there's argon. There might even be
46:16
Speaker 1: like carbon burying species up there in the Moon's exosphere.
46:21
Speaker 1: But there's not a lot of carbon on the Moon.
46:24
Speaker 1: Where's the carbon coming from. There's definitely not a lot,
46:27
Speaker 1: but some of it could be coming from the asteroid impacts, right.
46:29
Speaker 1: Asteroids sometimes are have silica in them, sometimes they have
46:32
Speaker 1: carbon in them. They sometimes even have complex organic molecules. Interesting.
46:37
Speaker 1: So when you look up at the daytime sky, you're
46:39
Speaker 1: seeing mostly the blue from our atmosphere, but beyond that
46:43
Speaker 1: there's also the Earth's exosphere, which is so dilute that
46:46
Speaker 1: you cannot see it. It's black, it's invisible, but it's there.
46:50
Speaker 1: It's doing something. And everything else out there in the
46:53
Speaker 1: Solar system, the Moon, mercury, all the other objects which
46:57
Speaker 1: are quote bombarded by all sorts of crap, they also
47:00
Speaker 1: generate an exo sphere, and that tells you that the
47:03
Speaker 1: Solar System is not a static thing. It's a dance.
47:06
Speaker 1: Everybody is giving off gas and accepting photons and interacting
47:10
Speaker 1: with each other. So the Solar system has an exciting future.
47:14
Speaker 1: You know, I usually think dances are better when they
47:16
Speaker 1: don't involve gas, but but but this one is beautiful.
47:20
Speaker 1: This is sort of how objects in the Solar System
47:22
Speaker 1: talk to each other and evolve. All right, Thanks very
47:25
Speaker 1: much for joining us on this exploration of whether or
47:28
Speaker 1: not the Moon has an atmosphere. To put a pin
47:31
Speaker 1: in it, I would say the Moon does not have
47:33
Speaker 1: an atmosphere, but it definitely does have an exo sphere.
47:36
Speaker 1: And thanks very much to our exo host Kelly for
47:39
Speaker 1: joining us today. Thanks. I had a great time. I
47:42
Speaker 1: was gonna say I had gas e time, but that
47:45
Speaker 1: just doesn't sound what. It's good. I hope you didn't
47:47
Speaker 1: have gas, but I thought it was a pretty nice atmosphere. Agreed,
47:51
Speaker 1: that was a good punt. All right, Thanks for joining us.
47:53
Speaker 1: Everyone tune in next time. All right, that was fun.
48:04
Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain
48:07
Speaker 1: the Universe is a production of I Heart Radio. For
48:10
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