Apollo, the God of Dust - EWTS #008

Joe: Hello and welcome to Enough with the Science, I'm Joe.

Senan: And I am Senan, and this week we are blowing the dust off a fascinating topic.

Joe: Another fascinating topic. For anybody who is new to our podcast, Senan is a bit of a science nut, and I'm not really, but I like listening to you, Senan, talk about science and then try and distract him by talking about anything except science. And asking him weird questions that come into my head.

Senan: You wouldn't believe how easily I am distracted.

Joe: Yeah, well here we go. Let's see can we get completely off topic. Now, when was the first time you realized you wanted to be an astronaut?

Senan: That was just now actually. [laughter] I think I'll just wait until space travel becomes just that little bit more... luxurious.

Joe: Luxurious. You want just like...

Senan: No, I mean more routine, commonplace, everything, all the kinks have been worked out. Anyway, Joe, I want to cast your mind back about 50 years ago.

Joe: That's easier for you than me. I wasn't around 50 years ago.

Senan: Well, almost. When you were in kindergarten or whatever they called it, kindergarten in your neck of the woods. Imagine you were one of the Apollo astronauts on your way to the moon. Millions, literally, of people in your country have spent almost a decade toiling away trying to provide you with the technology necessary to get you to the moon and beat the Soviets in the process. What kind of things would have been keeping you up at night? What would you have been worrying about?

Joe: Peeing. Where would you pee? That would be a big thing for me now, at my age. Just like...

Senan: I imagine they probably thought of that.

Joe: Yeah. But I imagine it's not probably the most comfortable or natural way of doing it. Also...

Senan: One of the problems might be that it wouldn't flow downwards, it would just go everywhere in little droplets.

Joe: Yeah. Well, that can happen sometimes anyway. So that would be primary. But you would just start thinking about, obviously there was a budget for this, and a lot of these things that they're building went out to the kind of contractor with the lowest bid. You're wondering, did anyone come in kind of a Monday morning feeling a little bit rough and go, "Yeah, I really need to make that as well as I usually do," and is that stuck on the outside of your rocket?

Senan: Yeah. Actually, it's funny you should say that. There was one particular component of the Apollo rocket that we're gone off away completely from what we were supposed to be talking about... anyway! There was one particular component of the rocket, which was the ascent engine. That's the engine that gets them off the moon surface on the way home. For technical reasons I won't go into now, that could not be tested in advance. So they had to push the button and hope that it was plugged in, properly assembled, you know, nobody had put a tube on backwards, etc. Because if nothing happened when they pushed that button, that's it. They'd be still there today.

Joe: Wow. Yeah, see stuff like that. That would keep me awake at night. Little things like that. Have they tested everything? Is everything working?

Senan: But I bet you one thing that would not have been keeping you awake would have been problems that might be caused by moon dust.

Joe: No. And I do believe it causes a lot of problems.

Senan: Moon dust? This is dust on the moon.

Joe: Yes, not any other illicit substance. [laughter]

Senan: Okay. Yeah, so that's the topic of today's podcast because moon dust turned out to be a very problematic thing altogether. So much so that for future moon missions, which the Americans are hoping to go back to the moon in the next few years, they'll have to put a lot of thought into how they cope.

Joe: The Chinese have been there already, haven't they?

Senan: Not in person, no. Just robots. No, there hasn't been any people on the moon since the last Apollo flight which was 1971, I think.

Joe: Oh really? Okay.

Senan: Yeah. I mean there's been a couple of robots sent in the meantime but no, nothing with a beating heart in it.

Joe: Okay.

Senan: So yeah, some of the problems. First of all, it got absolutely everywhere because of static.

Joe: Hold on, moon dust. So we're talking about, like, because obviously nobody has dusted the moon in a long time, there's a lot of dust about the place. So it's like sand?

Senan: It is. It's not like terrestrial dust which is like skin cells and dead bits of dead insects and God knows what else.

Joe: Dead aliens. Dead alien skin cells.

Senan: No, we're talking about sand and pulverized sand that's smaller than your average sand grain. So yeah, it's all basically pulverized rock.

Joe: Okay.

Senan: But it turns out it has a really strong static charge and it clings to things. So when they went out on a moonwalk, it got all over their suits and stuck to their suits. And then they came back inside into the spaceship and it spread into the air inside in the cabin and on their equipment in the cabin and so on. It got everywhere.

Joe: And they knew it wasn't poisonous?

Senan: Well... they didn't. And it is.

Joe: See, this would be another thing that kept me awake at night. Like, what's out there? Did anybody check this?

Senan: Yeah, people were worried about little green men, not little grains of dust.

Joe: No, but I do believe it causes a lot of problems.

Senan: Yeah, it's very abrasive. So it's got really, really, it's essentially like little shards of glass. Imagine millions of miniature, miniature shards of glass. Because the edges of it are much sharper than the edges of the dust here on Earth, or the sand here on Earth. That's mainly because here we've got wind and water which abrades, you know, there's erosion on the dust and that softens all the sharp edges and rounds, makes the dust particles round more or less. Whereas on the moon that didn't happen. There's no wind and water to do that. So they have these sharp edges.

Joe: Can you imagine that kind of painful getting into your space shorts? Or space sandwiches?

Senan: Yeah. Can you imagine that stuff in your sandwiches and in between your teeth and your gums?

Joe: I imagine it would be dangerous, I imagine, to be chewing down on that, maybe?

Senan: Absolutely. Dangerous apart from the physical aspect of the sharp edges, there's also the fact that because it has this static charge, it stays, it sticks, it doesn't fall off. So it continues to be dangerous for a long time. But also for reasons we'll come to later, chemically it tended to react with any moisture or oxygen that it came into contact with. So the results of those reactions could also have been irritants or poisonous or whatever. So yeah, it was a real humdinger.

Joe: Again, no sleep for the astronauts. None. Like any night before this was happening it was just like, the amount of things that can go wrong.

Senan: And the dust was probably the last thing in their mind until they went on a spacewalk and brought it back into the capsule. But some of it is like really fine-grained. And you know, some of their equipment had very fine tolerances. So you're talking about two moving parts that have a very slight little gap between them and they're supposed to be able to slide past each other. Suddenly this sharp, sticky, static-charged dust gets in there and they're not sliding past each other smoothly anymore. Stuff was getting clogged. It was, like, things were getting abraded by it. You know, like sandpaper rubbing off something.

Joe: Imagine the guys who didn't bother testing the engine, what was it called, the ascent engine?

Senan: The ascent engine, yeah.

Joe: The boys who just decided, "Feck it, we tried when were up there, it's all grand, it'll be grand."

Senan: "Didn't bother" might not be a fair reflection of the situation. The boys who just decided, "Feck it, we tried when were up there, it's all grand, it'll be grand."

Joe: But then of course the final coup de grâce was it smelt awful.

Senan: So obviously they only realized this inside the capsule.

Joe: Nobody had ever smelt moon dust before... before Neil Armstrong and... lived.

Senan: Yeah. And came back, you know, before Neil and Buzz came back in from their spacewalk and took off their helmets and filled back up the capsule with air. And suddenly they smelt this stuff that was something like burnt toast and gunpowder and burnt metal all mixed together.

Joe: See, there would be my first concern there wouldn't be "Is that the moon dust?" I'd be like, "Is something on fire?" There would be a smell of gunpowder, burnt toast... we're in a spaceship, like, 250,000 miles away from Earth and something is burning. This is not good.

Senan: "Buzz, did you leave that machine gun at home?"

Joe: Oh yeah. Well, I mean, or maybe someone's cooking marshmallows. Maybe your man lost his mind, the guy who was left in the capsule...

Senan: Oh no, you're talking about Mike Collins. He wasn't down on the ground. He was up in space orbiting the moon.

Joe: Ah, okay. So there was no one sitting in the capsule waiting?

Senan: No, I mean the two, the two guys that were in the capsule, we're talking about the first moon mission, were Buzz Aldrin and Neil Armstrong. Both of them went out.

Joe: They were very trusting really that no one was going to rob it. Like kind of both the lads outside.

Senan: Well they would have been famous of course for discovering alien life.

Joe: Would it be worth it to be stranded? So kind of... "Your first mission to the moon and someone steals your lunar lander."

Senan: And would anybody believe you if you came over the radio to tell Mission Control that you'd lost your spaceship? Would anybody believe you?

Joe: The guy who was left in orbit would probably notice somebody heading off in the wrong direction in the lunar lander.

Senan: Yeah, he'd probably gone after them thinking that you've lost your marbles and he's trying to retrieve you. But yeah, so it is... future moon missions, there's a lot of planning for future moon missions is going to involve mitigating all those dust problems.

Joe: So they obviously brought enough back to be experimenting away with it now?

Senan: Some has come back and also they kind of have a good idea of its constituents now in terms of what the components of it are. So they can kind of make simulated moon dust as well. It mightn't behave exactly the same.

Joe: Fake moon dust. Oh yeah. Or for selling it to people.

Senan: But it's interesting, a lot of these problems are caused by the fact that the moon has no atmosphere. Because the solar radiation is able to bombard the surface of the moon in a way that it cannot bombard the surface of the Earth, 'cause we've got a nice blanket of an atmosphere protecting us from all that high energy stuff that's coming out of the sun. So millions of years of this stuff hitting the moon dust unimpeded has given it a static charge. So essentially the solar radiation, high energy electrons give some of it a negative charge and then UV light gives some bits of it a positive charge. So there's like a mixture of negative and positive going on there. So if your suit is negatively charged, the positive stuff is going to stick to you and vice versa. So it's hard to avoid it, you know?

Joe: Weirdly, dry cleaning. That's a job for a specialist dry cleaner when they got back, obviously.

Senan: Well, and that brings us nicely onto the whole subject of how they're going to mitigate all this problem. You don't want this dust inside in your spaceship because apart from the problems with the equipment that it causes, it's also caused problems with the health of the people. Some of it's so fine-grained it gets up into the air, people breathe it in and it irritates the insides of their lungs. Gives them kind of hay fever symptoms.

Joe: And then death. Death as it cuts through all the internal organs.

Senan: Well, death might not be an immediate worry.

Joe: But eventually. Eventually death.

Senan: I mean if you keep breathing it, potentially you could get a thing called silicosis which was an old disease involved with, where fine irritable particles got lodged in people's lungs... miners were one group that often suffered from it because of all the dust in the mines. The stuff built up inside in their lungs and eventually caused permanent lung damage. So you could have something like that for long-term exposure.

Joe: Astronaut's Lung.

Senan: "Astro Lung." We have a new disease, I wonder can we get that one classified? So it's just irritation to your skin. Apart from the fact that this abrasive stuff is on your skin and scratching your skin or in your eyes or in your nose...

Joe: Ow. I didn't think of that. Ow.

Senan: Anywhere there's damp mucus membranes it's going to stick to and irritate. And that's just the physical aspect. And as I said before, it's also chemically quite reactive which is where the smell comes from. Those chemicals that are on the surface of the dust get into your mucus membranes, your eyes, your mouth, your nose, your sinuses...

Joe: I knew I was right to be worried about the peeing. I knew it. I knew that should be at the top.

Senan: Yeah, well true enough, yeah, you don't want it in any of that department either. But yeah, so it's a real nasty bugger. But you're probably aware of, you know if you've got a synthetic shirt on and you take it off in the dark and you can hear the crackles of static electricity and somebody's looking at you in that dark room they might see the little sparks. Have you ever experienced that?

Joe: I don't know how you spend your Saturday nights but this is just like... I think there's a little too much information for listeners and definitely for me.

Senan: Okay well...

Joe: People looking at you taking off your shirt in a darkened room? I can't really roll back on that story now, can I?

Senan: It's recorded for posterity. This will be part of the court case.

Joe: Anyway, the same kind of thing can spontaneously happen with moon dust on space suits. You can get tiny little sparks of static electricity happening. So small that probably the human eye might not notice them unless it's very dark. But those space suits are advanced pieces of technology with electronics in them doing this, that and the other, and the little sparks could actually upset the electronics as well. So there's all kinds of stuff.

Joe: Definitely upset like kind of the fumes of whatever fuel they were using to power the ships if a little static...

Senan: Oh yeah, yeah, if it gets into the... hopefully it won't get into the fuel tanks with any luck.

Joe: Probably have a bigger problem if there's dust getting into the fuel tanks than the possibility of an explosion killing everybody? What would the bigger problem than that be, Senan?

Senan: Okay fair enough, I'll give you that one, I'll give you that one. Anyway, how are they going to stop that stuff from getting inside the ship? Any ideas?

Joe: Yeah. Don't go to the moon.

Senan: Actually that is probably the most effective strategy.

Joe: And go to the moon. But we're trying to put you off going to... Like I don't think really if anybody's sitting at home planning to go to the moon, I don't think the whole moon dust thing is going to really... you know, if you have someone passionately sitting at home designing...

Senan: Well they might have to hear this show.

Joe: Well yeah, there's time left. You can switch off now. If you have any young ears who want to be astronauts...

Senan: So maybe they'll... Do you know those old British country mansions? They all had a boot room. This was a special room where, you know, when you come in from deer stalking or shooting partridge or whatever the hell you've spent your days doing... This was where you took off your muddy boots and your muddy jodhpurs and so on before you got into your nice clean clothes and went back into the house. So this was a room where all the dirty stuff happened.

Joe: No euphemism required. I'm just going to let you dig. Keep digging. Keep digging. I'm not even needed. I'm not even needed here anymore.

Senan: It sounds like the kind of room where Jilly Cooper would have based her novels. Anyway, they might use that strategy in for the next moon missions where there's like a separate outdoor room where they take off their space suit and all that gear before they come inside into the inner part.

Joe: Some sort of power hose.

Senan: Well, if you're talking about water, I mean it's going to come out as chunks of ice on the moon because it's so cold up there.

Joe: Okay. Heated power hose.

Senan: They have tested various different strategies for trying to deal with this and some of the things... they blasted suits with liquid nitrogen or ionized argon gas. Both of those tests were fairly successful at removing the moon dust.

Joe: But killed the astronaut stone dead.

Senan: Where do you get a large supply of liquid nitrogen or ionized argon when you're up on the moon? It's a bit of a tricky one that.

Joe: That was another thing that used to keep me awake at night when I was thinking about being an astronaut.

Senan: When you were not thinking about being an astronaut. So they've done tests with space suit material that they can change the... they can flip the polarity of the static charge. So it's like there's some kind of wire matrix in the suit and they can flick a switch that changes the charging of that from negative to positive to kind of negate the charge of the dust.

Joe: And they have absolutely no idea what effect that'll have on an astronaut.

Senan: Yeah, well... I don't know. Suddenly he'll feel positive, then he'll feel negative, and then he'll feel positive, and then he'll feel negative. Decontamination wands. This is for the Harry Potter aficionados. So that's like an electric stick that has a charge and you wave it near the suit and it attracts the charged dust onto itself off the suit.

Joe: Just a really, really expensive dust magnet.

Senan: A really expensive feather duster, essentially. What else have they done? Now, look, the fact is no matter what you do, some dust is going to get inside into the station even if it's only small amounts. So they also are working on more efficient air filters that can remove that dust. So you remember in a spaceship you need to keep the air circulating so there's fans running the whole time to keep the air moving around. Because if you don't, what's going to happen is you're going to have some parts of the spaceship where carbon dioxide from people's lungs builds up and if you try to breathe the air in that part of the spaceship you could well pass out because you're not getting enough oxygen. So there's fans going the whole time there to circulate the air in the spaceship. Those fans can push the air through these filters which hopefully will take out the bad particles out of the air. So there's all kinds of things like that. Lots of different experiments going on. You know, there's been loads of different strategies tried to see what's the most efficient way of dealing with this problem. Because ultimately if we send people back to the moon they are going to have to go and walk around outside on the moon surface. So we need to deal with the problem.

Joe: And I mean, they were there for a few days. They could put up with a bit of hay fever for a couple of days. They could put up with skin irritation.

Senan: They were there for a few days, yeah. Each mission was only there for a couple of days.

Joe: Oh yeah. Oh no, I mean I just thought they kind of went down, had a walk around, quick look about and hopped back in the ship. They were there for a few days?

Senan: I think they were there for a couple of days, yeah, each mission.

Joe: Oh. Okay.

Senan: I mean they had a couple of the missions had a car, a moon rover they called it, that they drove several kilometers away from the ship and explored things and came back.

Joe: Yeah, still just I don't know why, just in my head it was kind of like a day trip. It was like, "Right, we land, we have a look around, have a picnic, back in the ship, let's go, let's get home." But no, they were there for a few days. Wow.

Senan: So yeah, it's an interesting problem. It's gas how small little things like that... can snooker a space mission. Things that like, you could plan for a hundred different contingencies and never think once of the dust.

Joe: Yeah. That would be terrible now if you had like all of this years and years and years of engineering genius and sacrifice and then nobody thought of the dust. It's like... and all they needed was a little Hoover.

Senan: Yeah. But anyway, what is good about the dust? Well, for the starters, one thing that's really cool about it is that it levitates. We'll come back to that in a minute because that's an interesting one.

Joe: But all dust kind of levitates a bit, doesn't it?

Senan: Not the way this dust does.

Joe: Do you know when sunlight shines through the window and you have... is it motes? Is that the word? Dust motes?

Senan: The dust isn't really levitating under its own power there. I mean that's convection that you're seeing there. So there's warm and cool patches in the air in the room and that's causing the air currents to rise.

Joe: What if I just simply chose to believe it was levitating?

Senan: Well, I mean it probably is levitating but it's not under its own power. But you can choose to believe that if you like.

Joe: So the dust on the moon is under its own power?

Senan: There's a new scientific mission for you now. Think up some kind of experiment that you can prove that it's under its own power levitating here on Earth.

Joe: Why would I want to do that? God, I don't have enough time in the day as it is. What are you doing Joe? Well, actually I'm trying to figure out whether this dust is levitating under its own power.

Senan: So you're happy just to leave the hypothesis there standalone.

Joe: Well I mean I just, because I haven't seen dust in a vacuum, so I don't know.

Senan: Okay, moving rapidly along. We're going to come back to the levitation in a minute. There's rust in that there dust.

Joe: Okay.

Senan: So a significant... rust is of course iron oxide which is a compound of iron and oxygen. And there is a significant proportion of that of the component of the dust is actually rust, iron oxide. And we... as when I say "we" I mean astronauts on the moon.

Joe: I'm glad you just... you're part of that fraternity. We're very lucky to have you.

Senan: Well I'm imagining I might be one day. Not that I've any chance of ever getting accepted into any astronaut program anyway. Those who go to the moon might be able to bake the oxygen back out of that rust. And essentially harvest oxygen out of it so that they can use it to breathe.

Joe: And there would be enough of it there to do that?

Senan: Oh yeah, there's plenty of it there. Now whether they can come up with a process that's feasible, that's not too energy intensive and that can produce oxygen at a sufficiently high rate is another matter. But yeah, it is in theory at least feasible to generate oxygen from that rust. To essentially reverse the reaction where the oxygen and the iron has combined.

Joe: Did the rust happen on the moon? I mean was it iron... like the meteorites hit and it was iron and then...

Senan: Yeah, good question. An awful lot of the meteorites that are flying around our solar system are iron.

Joe: Okay.

Senan: So a lot of this stuff that has been delivered there by meteorite impacts. Which is something actually we should have touched on a bit more earlier. If you look at any close-up picture of the moon you see all these circles on the surface. Like thousands of them. All mixed in together. And those are all evidence of meteorites that have bashed into the moon at very high speed and caused large explosions. And that's how this dust gets created. Because over millennia, over millions of years, there's just constant bombardment of asteroids hitting the surface of the moon. We're protected by our atmosphere. So unless, on the very rare occasion when a really big one hits us, it doesn't burn up in the atmosphere and it reaches the ground. But the vast, vast majority of the meteorites that hit Earth are burnt up in the atmosphere. So it protects us. But the moon does not have that atmosphere so they just hit the ground and we see all the evidence of it on the surface.

Joe: So if most of them are iron, right? They're iron.

Senan: Well a lot of them are, maybe not most.

Joe: Okay. There's iron. There's iron in some of them.

Senan: Yeah.

Joe: And they hit the moon. And the iron gets smashed into the moon. Where does the oxygen come from?

Senan: Yeah, good question. I don't know the answer to that. I don't know was the oxygen on the moon already or did they rust before they hit the moon? I'm not sure to be honest with you.

Senan: Apologies, I don't have that answer for you.

Senan: Every week he finds a question I don't have the answer for. And he waits until we're recording. Rather than having the manners to say it to me beforehand. Like beforehand I could Google it. No, no, he waits until we're recording.

Joe: I don't script. I don't script. These things just come to me. They're the best type of questions.

Senan: Anyway, what else is good about the moon dust? We could maybe melt it. Or "fuse" it is a fancy term for melting it. With lasers or microwaves or even concentrating sunlight with magnifying glasses. If we can melt it into a kind of a glass, we could make bricks or road slabs that will be the surface of roads etc. So that's another potential good use for it. Certain amount of sulfur in that dust and potentially if you can purify that sulfur and then mix it back into the dust you can make a kind of space cement. So that's another potential building material. And finally, one of the big problems for the same reason we've been harping on about for the whole program practically at this stage... is that there's no atmosphere to protect the astronauts from radiation. So there's a lot of radiation coming from the sun mostly, but also coming from other places in space. But primarily from the sun in that area. And if we build a base, a house for our astronauts on the moon, we don't want them if they're going to be there for like six months, we do not want them exposed to radiation for all that amount of time. So potentially we could pile thick layers of moon dust up on top of their houses to act as a barrier to protect them from the radiation. So the moon dust potentially is a useful thing.

Joe: I think I prefer Moon Base than Moon House. Moon Base sounds a bit better.

Senan: Do you remember that... Do you remember a program called Space 1999?

Joe: Yeah, there's something twinkling in the vast recesses of my brain.

Senan: They lived in... that was astronauts living on the moon... and they lived in something called Moon Base Alpha.

Joe: All right. Yeah.

Senan: The plot of that one was... I can't remember what happened but some catastrophic event caused the moon to leave Earth's orbit. So the moon was wandering through space encountering various alien civilizations with these astronauts stranded on it.

Joe: Oh. Wow. That would be a great way to actually travel through space on an actual planet. And have all the resources that you need and kind of...

Senan: All the resources except air or food.

Joe: Air or food. But never mind. Once you have laughter and music.

Senan: So we'll just touch on... we've covered an awful lot of ground here, dusty ground at that. But we'll briefly go back to the levitating moon dust and what's going on there.

Joe: I love the way you said "very briefly" there. I like when you do that.

Senan: You realize I'm not going to follow up on the briefly bit don't you?

Joe: I'm just going to unplug this.

Senan: So, the moon has a tail. And it's a tail we can't see but it's a tail we can detect with scientific instruments. So what's going on? Again it's our friend the lack of an atmosphere is the cause of what's going on here. This happens around sunrise and sunset on the moon. So during the daytime you get UV radiation from the sunlight hitting the moon dust and it builds up a positive charge. It changes the structure of the atoms in a way that builds up, makes them positively charged. And then during the lunar night, you have no UV radiation but you still have high energy electrons which are part of the solar wind, part of the constant stream of particles that are coming out of the sun. Those are able to find their way down to the moon surface at nighttime even though it's not in direct sunlight. And they have the opposite effect. They negatively charge. So you have a situation where daytime positive charge, nighttime negative charge. And then you've got this crazy changeover, this really messy changeover at sunrise and sunset. And what you end up with is some areas are still positive, other areas nearby are negative. So you've got this crazy mixture of positive and negative layers of dust just around that sunrise, sunset period. And some of it gets, some of the finer particles then just get repelled off the surface of the moon by this mad mixture of different charges. And the real fine ones can go up like ten kilometers up.

Joe: All right. Okay. So it's not just like kind of a couple of feet there.

Senan: No, no, no. And I mean the astronauts observed... the astronauts that were orbiting the moon in their capsule before or after they landed... they observed this glow on the horizon above...

Joe: And they had no idea what it was.

Senan: Not at the time, no. Not at the time.

Joe: See, another thing to keep me awake at night. Like kind of those sort of things. Like what is it? Is it an alien civilization advancing towards us?

Senan: Yeah. So it was one of the many mysteries they observed. And it takes, could take a couple of hours for that mishmash to settle down. So there's a period of chaos for a couple of hours at the terminator, that's the line between day and night, is passing over each area.

Joe: I love that name. I didn't know that. Until you said it. It's called the Terminator, yeah?

Senan: Yeah, yeah. And it's a very apt name, you know, because the other Terminator, the former governor of California, one of his famous phrases was "I'll be back." And it's very apt of course because the terminator does come back every day.

Joe: That is the worst link in the history of podcasting.

Senan: We cannot have an episode without a decent Arnie reference.

Joe: Yes we can. But we won't. But we can.

Senan: "Hasta la vista, baby." But how come they just don't float off?

Joe: Gravity pulls them back.

Senan: Gravity pulls them back, yeah, yeah eventually. So very briefly, there's another effect caused by the same thing by the solar wind and it's...

Joe: I'm just going to unplug this. Really I am.

Senan: Again, you've got these high energy UV ultraviolet radiation coming from the sun. You've got high energy particles that are part of the solar wind also coming from the sun. And you have micrometeorites. So those are like tiny pebbles, space pebbles that are travelling at thousands of kilometers an hour. Hundreds of them smash into the moon every day. And all those things are impacting on the surface. And they drive sometimes, they have enough energy to drive sodium atoms out of the moon dust. So some of the constituents of the moon dust is sodium atoms. Sodium is a particularly light weight atom. So it's easy enough to drive it off, it doesn't take a lot of energy. So you literally get these sodium atoms being kicked off the surface of the moon. And the gravity is so weak on the moon, it's only one-sixth of Earth, that they rise away from the surface of the moon and then the solar wind grabs them and stretches them out into a tail off into space. And the tail we believe is over 100,000 kilometers long. That's a very tenuous, it's just this wispy, almost invisible set of sodium atoms drifting off into space away from the moon.

Joe: But is it like, are they just... they don't come back? They just keep going?

Senan: So it's a mixture. Some of 'em go on a large ballistic trajectory where they get launched way out into space in an arc but eventually the gravity of the moon gets hold of them and pulls them back. So it could be a couple of days before they come back. But others, depending on the trajectory and the amount of force that they were driven off with in the first place, some of them just keep going off into space.

Joe: Free forever. Free the sodium.

Senan: We should probably keep going off into space at this point now because we've been at it for half an hour.

Joe: Have we?

Senan: We have.

Joe: That didn't seem like half an hour. There was an awful lot of information in there for listeners now today.

Senan: Yeah.

Joe: I think there was a lot of stuff that people didn't know. There was some stuff that I didn't know. And there was some stuff that you didn't know. So everybody's on the same boat.

Senan: We should rename this podcast "Stuff Nobody Knows."

Joe: What? Stuff nobody really cares about.

Senan: But mind you if you do care about it, please think about subscribing to us or maybe even leave us a review on Apple Podcasts.

Joe: Oh yeah. I have no idea how to do that. Maybe one of the listeners could show us.

Senan: You could write in. On the back of a postcard.

Joe: Yeah. Or...

Senan: Care of Senan and Joe, PO Box 6000.

Joe: Or you could just write it in the review how to write the review. It's like an existential description of writing a review.

Senan: It's reviews all the way down, sonny.

Joe: That's it. Okay. Look, listen, thanks for listening this week.

Senan: Yeah, I'm Senan and we'll see you again soon.

Joe: I'm Joe, take it easy.