What is the electrical charge of the moon?

00:00:08
Speaker 1: Hey, Daniel, what's your feeling about the Moon?

00:00:11
Speaker 2: I guess I don't have that many strong feelings. Does anyone Do you like it? Do you dislike it? I mean, I guess I'm generally pro moon, although if it's made out of white chocolate, I'm not going to be very happy about it.

00:00:21
Speaker 1: Oh what if it was would you want to nuke it out of the sky?

00:00:25
Speaker 2: Oh? Man, that sounds like a disaster. It would cause a shower of molten white chocolate all over the earth.

00:00:31
Speaker 1: Yeah, a lot of people would be happy.

00:00:33
Speaker 2: That sounds like a disaster movie.

00:00:35
Speaker 1: To me, it sounds like you have really charged feelings about the moon and white.

00:00:38
Speaker 2: Chocolate, both positive and negative.

00:00:56
Speaker 1: Hi am Jorhemy Cartoonist'm the author of Oliver's Great Big Universe.

00:01:00
Speaker 2: Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine. And you couldn't pay me enough white chocolate to take a trip to the moon.

00:01:07
Speaker 1: Can we pay you some money to eat white chocolate?

00:01:09
Speaker 2: I guess it depends on the amount of white chocolate and the amount of money.

00:01:12
Speaker 1: Wait, you would have wanted to go to the moon? Why not?

00:01:14
Speaker 2: I mean, I don't take trips to Antarctica, and I'm pretty sure the Moon is like less cozy than Antarctica.

00:01:21
Speaker 1: It's not about coziness, It's about the adventure, you know, excitement being someplace interesting.

00:01:26
Speaker 2: Yeah again, still don't take a lot of trips to Antarctica for the same reason.

00:01:30
Speaker 1: Have you been to Antarctica? How do you know you won't like it.

00:01:32
Speaker 2: I've never been to Antarctica, but I've been to some places that are sort of Antarctica adjacent, and I wasn't a fan.

00:01:38
Speaker 1: I've been to the Arctics Circle that was pretty exciting. I've been on a glacier.

00:01:42
Speaker 2: I know. I'm trying to hook you up with a trip to Antarctica to visit the physics experiments there, but no luck yet.

00:01:47
Speaker 1: M Are you just trying to get rid of me? Are you hoping that some sort of a freak accident will happen while I'm there.

00:01:55
Speaker 2: I think that's a conversation you should have with your therapist about your paranoia. I thought you wanted to visit the South Pole. I don't know.

00:02:00
Speaker 1: There's all very suspicious, Daniel. I mean, of all the places you could send me to Hawaii, Fiji, do you want to send me to the most remote place on Earth.

00:02:08
Speaker 2: There's also an awesome physics experiment in the south of France. Maybe you want to visit that one.

00:02:12
Speaker 1: Yeah, let's do it. I'll take it. Is a podcast paying.

00:02:16
Speaker 2: Everybody chip in crowdsource Jorgees trip to the South of France. We'll see how many contributions we get.

00:02:20
Speaker 1: There you go, We'll kickstarted. But anyways, welcome to our podcast. Daniel and Jorge Explain the Universe, a production of iHeartRadio.

00:02:27
Speaker 2: In which we get all charged up about the mysteries of the universe. We are very positive about the idea that humans can understand the nature of the universe that we live in, and not just a few humans operating on the forefront of science. Everybody. We love taking these crazy ideas that scientists have developed and explaining all of them to you.

00:02:45
Speaker 1: It's right because we are attracted to the deep mysteries of the universe, and we are also repelled by our deep ignorance of the things. We don't know about how things work.

00:02:53
Speaker 2: But what we definitely do know is that the universe is controlled by forces. There are pushes, there are pulls, there are tugs. Everything that happens out there in the universe is the result of forces in balance and out of balance.

00:03:06
Speaker 1: Wait, are you sure about that? I mean, I feel like we need for a long time about the force of gravity, but now I hear that there's no just a thing as the gravitational force.

00:03:14
Speaker 2: You're right, of course, that gravity is not a force. It's just the curvature of space time, which gives the illusion of a force if you're not aware that space is curved in front of you and causing things to move in a way you might not expect. We can still actually describe a lot of that in terms of pseudo forces. So for the spirit of today's conversation about pushes and pulls and what's tugging on the moon and what's not, doesn't really make a difference if gravity is a force or the curvature of space time.

00:03:41
Speaker 1: I wonder it could it be that we eventually find out that the other forces in nature are also just distortions of space and time or are we pretty sure those are forces forces?

00:03:50
Speaker 2: No, you're absolutely right, and that is an active idea people are working on. Einstein spent many, many years trying to explain electromagnetism in terms of additional curvature of space time. He thought maybe that force is actually also a pseudo force, just the result of space being curved in additional ways. He never made it work, and one reason is that he didn't understand the weak force, which is crucially related to electromagnetism, So he sort of didn't have the whole picture. But there are people working on that right now. They just haven't succeeded yet.

00:04:19
Speaker 1: I guess Einstein felt he was kind of forcing it at some point. He didn't want to push it.

00:04:23
Speaker 2: I think he went around the wrong curve.

00:04:25
Speaker 1: He felt like he couldn't pull it off.

00:04:28
Speaker 2: It wasn't a grave enough matter.

00:04:29
Speaker 1: But it does seem like in our everyday lives, like things are governed by these laws of nature that seem to pull and push on things. And that's kind of what physics it's all about, right, the push and pull of the universe.

00:04:39
Speaker 2: That's right. And the universe as we see it is shaped by lots of different forces. Stuff in the universe is mostly built out of the more powerful forces, the strong force, electromagnetism. But the overall shape of the universe, the way the Solar System is, the shape of the Earth, the structure of the galaxy and beyond is mostly dominated by the weakest force, gravity.

00:05:00
Speaker 1: As our gravity is what gives the universe its structure. If it wasn't for gravity, we wouldn't have planets, right, or suns or galaxies, and we wouldn't be here. I mean, be nice to be lighter than what we are, but without gravity, we and none of us would exist.

00:05:14
Speaker 2: That's right. It's gravity that causes the Sun to burn because it squeezes all that gas together, giving it the high temperature and density needed to ignite fusion. It's gravity that forms the structure of the Earth. It's gravity that's formed the Moon. It's gravity that's formed everything that we see out there in the universe. But that doesn't mean that gravity is the only force at play in our Solar system.

00:05:35
Speaker 1: Yeah, there are other forces, some of which play an equally important role in our existence. If it wasn't for the electromagnetic force, like, none of our atoms would hold together, and so we also wouldn't be here.

00:05:47
Speaker 2: That's right. You're basically built out of the electromagnetic force. All of your atoms and molecules are bonded together using electrons and electromagnetism. So basically every structure you're familiar with, is an electromagnetic structure.

00:05:59
Speaker 1: I feel like we're saying we're basically everything. Everything is everything made out of everything, due to everything.

00:06:05
Speaker 2: It is an incredible balance of all those forces.

00:06:08
Speaker 1: Yeah, and sometimes that force pulls and pushes on things in ways that you don't quite expect.

00:06:13
Speaker 2: And so we think that gravity is the dominant force remaining in the solar system, but that's not always the case.

00:06:19
Speaker 1: And so on the podcast, we'll be tackling the question what's the electrical charge of the moon? Interesting question, like the moon has as a plug in it?

00:06:38
Speaker 2: Is the Moon a battery? And if we travel there, can we use it to recharge our phone?

00:06:42
Speaker 1: There you go, that'd be important. Does it have a USBC connector a USB connector lightning port, the USB Moon connector Yeah, that's what I want to know before you send me to the Moon.

00:06:54
Speaker 2: You know, the way it is with USB, there's always some new shape you've never seen before.

00:06:58
Speaker 1: Yeah, Well, hopefully the Moon has a stand under plug. But this is an interesting question to ask about the moon, like the idea that the moon has a charge at all.

00:07:07
Speaker 2: Yeah, because we're very familiar with the Moon having a mass, which is sort of like a gravitational charge. You you're thinking about gravity as a force and a Newtonian sense, but it's weird to think about the Moon having like an electric charge, like it being overall positive or negative.

00:07:21
Speaker 1: Hmm. Well, I'm positive we'll get to the bottom of this, but as usual, we were wondering how many people out there had thought about the Moon having a charge or what that charge could be.

00:07:31
Speaker 2: Thanks very much to everybody who volunteers for this fun segment of the podcast. One of my favorites. I love hearing your voices. Please join the group right to meet at questions at Danielanjorge dot com.

00:07:41
Speaker 1: So think about it for a second. Do you think the Moon has a charge? Here's what people had to say.

00:07:46
Speaker 3: I would think planets and moons get their charge from their cores, you know. In Earth's case, I think the iron core gives it a magnetic field. But then again, I guess the charges would cancel out and make it neutral.

00:07:58
Speaker 2: So I don't know.

00:08:00
Speaker 3: I don't think the Moon has a core or an electric field as far as I know, so I guess maybe you can call that neutral too.

00:08:04
Speaker 4: I feel like the Moon should have a total electrical charge of zero. It's probably different locally depending on what's getting hit by the solar wind and being ionized at the dust particular level, but that's probably a zero overall.

00:08:19
Speaker 5: I'm not sure about the electric charge of the Moon because it doesn't have more to love in it, I think, but since it's spinning, it might have a really small, undetectable amount. But I'm not sure about it.

00:08:37
Speaker 6: Otherwise, I would have guessed that the electrical charge of the Moon would be zero because I thought that all electrical charge balanced out. But you're asking the question, so I'm guessing it's not zero. I'm not sure though. Maybe it has something to do with the Earth's magnetic field. But I'm really not sure. I'm not too sure what the charge of the Moon would be, but I imagine it has the same charge as the Earth.

00:09:05
Speaker 1: I believe that the electrical charge of the Moon is zero, just us on Earth. All the positive and negative charges should balance, all right, some charge answers here.

00:09:16
Speaker 2: Consensus seems to be a zero charge for the Moon.

00:09:19
Speaker 1: Well, it's not positive or negative. It's just kind of there.

00:09:23
Speaker 2: The Moon just neutral. Just kind of me.

00:09:29
Speaker 1: Just kind of mad, as the kids say these days. But the moon is a pretty interesting object out in our night sky. It's big, it's about the quarter of the size and diameter.

00:09:41
Speaker 2: Of the Earth, right, Yeah, I think that sounds right.

00:09:44
Speaker 1: Yeah, And it's out there in orbit around the Earth. And so the question is does it have an electrical charge? Why would it have an electrical charge? Or should it have an electrical charge?

00:09:52
Speaker 2: I think the listeners had the right spirit. That ended up mostly getting the wrong answer because a simple model of the solar system suggests that it shouldn't have any charge, that it should be basically neutral.

00:10:04
Speaker 1: Well, maybe let's take a step back and talk about the charge of things in general, Like do I have a charge? An overall charge me like my body? Or I guess where does a charge come from? Do I have to add up all my electrons and then add up all my protons and if there's an imbalance, then I have an overall charge? Is that kind of what having a charge means?

00:10:23
Speaker 2: Yeah, You're made out of charged objects, the quarks, the electrons that are in your body. They all have electric charges, and some of them are positive and some of them are negative, and so you add them all up. It's like a big accounting and if you have more positives the negatives. Then you're positively charged, and you're made up of charged out of the molecules. Sometimes you have ions inside your body which have electrical charges, but the electromagnetic force is very, very powerful, and so it tends to try to neutralize things.

00:10:50
Speaker 1: But would you say that's an overall way to define my charge or define the charge of something like if it has more electrons than protons, which are made out of quarks, then it has a negative charge.

00:11:02
Speaker 2: Yeah. That's the definition of the charge of an object is the sum of all the charges of its particles.

00:11:08
Speaker 1: So if I have excess electrons somehow inside of me, then I'm going to be negative charge, which means that if you put me in front of a whole bunch of electrons, am I going to be repelled by those electrons?

00:11:17
Speaker 2: Yeah? Exactly. If you're negatively charged and then like a cloud of electrons comes by, you're going to be repelled from those electrons and they will be repelled by you. Or if a cloud of protons comes by, you would be attracted to those protons and they would be attracted to you. And that's sort of the reason why most stuff in the universe is very close to electrically neutral, because electromagnetism is very strong, and if you do have an overall charge, it tends to cancel itself out by slurping up the opposite charge.

00:11:45
Speaker 1: Right Like, if I have just a whole bunch of electrons floating in space, I guess, first of all, they would repel each other and fly away from each other. But second of all, they would probably attract protons from around them, and then they would quickly become neutral in terms of charge exactly.

00:11:58
Speaker 2: And that's just what happened in our universe when things cooled down very early on. There were protons and there were electrons, and they were all flying around. The whole universe was charged. It was a plasma, which is just a gas of charged particles. We think overall it was neutral, but like individual electrons and protons of course had charge, but they also had a lot of energy, were moving really really fast, too fast for electromagnetism to sort of capture them. But then when the universe cooled down, eventually they were captured by each other, and protons electrons came together to make neutral hydrogen. Then the whole universe was filled with neutral gas.

00:12:34
Speaker 1: Oh, that's an interesting question. Is the universe overall charge? Like, is the total number of universal electrons the same as a number of protons?

00:12:43
Speaker 2: Yeah, great question. We don't know. We think that charge is concerned in the universe, meaning it can't change. So when the universe was born, there was a number which is a total charge and that hasn't ever changed. We think probably that was zero just due to symmetry arguments, but the whole thing is very fuzzy.

00:12:59
Speaker 1: And poorly now probably zero. Interesting.

00:13:02
Speaker 2: Yeah, in the same way that we think like matter and antimatter were made at the same rates in the very early universe, although now we have a lot more matter than antimatter, which is not something we understand. We think that positrons and electrons were made at the same rate in the early universe, that we started overall with zero charge and created equal amounts of positive and negative charge particles.

00:13:22
Speaker 1: All right, So now let's get to the moon. And now the question we're asking today is is the moon positively or negatively charge overall? And you said that the simple model of the moon says that it should be neutral, So why is that?

00:13:34
Speaker 2: Well, go back to our simple history of the universe. The universe is filled with neutral gas. And what happened after that is gravity took over. Right, Electromagnetism is neutralized out, it's not really pushing and pulling on everything anymore. And now gravity, the weakest force by huge amount, right, like trillions and trillions of times weaker than electromagnetism, finally has a chance to influence things. And it takes millions and billions of years, but it pulls together planets and stars and moons and forms the structure of the universe. The weird thing about gravity is that it can't get canceled out. There's only one charge for gravity. There's positive mass, there's no negative mass, and so gravity forms this structure and it's still the thing that dominates the universe because it's still around. Unlike electromagnetism, it doesn't get neutralized or canceled out. So the simple model of the universe is everything neutralizes and then gravity takes over, and it's basically just the gravity of neutral objects. So the Earth, the Moon, everything should be basically neutral.

00:14:32
Speaker 1: M I think you're saying that the Moon was basically formed out of rocks, and way before those rocks formed the Moon, those rocks were already electrically neutral.

00:14:41
Speaker 2: Mmmmm exactly. And if the Moon had like a really big positive charge and the Earth had a really big negative charge, what would happen is that they would slur particles off of each other and neutralize that.

00:14:52
Speaker 1: Wait wait, wait, do you mean slur particles like pull the electrons out of their rocks?

00:14:56
Speaker 2: I mean you would hear this giant sucking sound like whew. Quite literally.

00:15:01
Speaker 1: I thought there was no sound in space. What kind of misinformation are you giving out of here?

00:15:06
Speaker 2: There is sound on Earth. And if the Moon was sucking electrons off the Earth, we would hear it. Yeah, the Moon was positively charged and the Earth was very negatively charged, then the Moon would suck electrons off the Earth until it was roughly in balance. Because electromagnetism is very powerful.

00:15:22
Speaker 1: Why would the Moon give up its electrons whatever they're like embedded inside of their atoms.

00:15:26
Speaker 2: I'm saying, if somehow the Moon was positively charged, like I had a bunch of protons that didn't have electrons to match it. They were hanging out on the Moon, and the Earth had an excess of electrons like hanging out in the atmosphere, then those electrons would get sucked off the Earth to the Moon. The protons might also get sucked off towards the Earth, but electrons are lighter, so they would move further than the protons.

00:15:49
Speaker 1: But I guess we're sticking to the model where the Moon and the Earth were made out of neutral rocks, and so that's what you're saying. That's a simple model of how things got to be.

00:15:58
Speaker 2: Yeah, so that simple model tells you that the Moon should either be totally neutral or very close to neutral, because anything else would have gotten balanced out early on, and any large deviation from that later on would be balanced out.

00:16:11
Speaker 1: All right, Well, that's the first approximation. But as usual, we know that physics and nature likes to surprise this. So let's find out if that's really the case. Is the Moon charged or not? Dig into that, But first let's take a quick break. Right. We're asking the question is the moon charged? Like is it amped up?

00:16:39
Speaker 2: What else is going on with the moon to give it positive or negative charges?

00:16:44
Speaker 1: M All right, Well you said that the simple bottle is that the Moon is made out of rocks, and by the time those rocks got made, they were pretty electrically neutral. Because that's kind of how the universe works, and so what makes us think that maybe the universe is not neutral.

00:16:58
Speaker 2: Well, I think probably the whole universe is neutral. But the Moon, it turns out, is more complex because that simple story we told where you have like just a bunch of gravitational rocks floating in space is not everything that's happening in the Solar system. There's a lot more going on, and specifically, the Sun is pumping out a huge amount of positive and negatively charged particles. The solar wind, which is essentially a stream of plasma flowing through the Solar system, has big impact on everything.

00:17:26
Speaker 1: You mean, we're all getting kind of showered by sun rays, which not only include light, but also little tiny particles, right like little quarks and electrons.

00:17:34
Speaker 2: Exactly, mostly protons and electrons. A few positrons are also created, and the Moon is going through this essentially soup of electrons and protons, and that has a big effect on the charge of the Moon.

00:17:46
Speaker 1: But what isn't the Sun throwing out both positive and negative charges. So basically the solar wind is neutral too, isn't it.

00:17:55
Speaker 2: The solar wind is overall neutral, But fascinatingly, the backside of the moon tends to attract electrons more. Electrons stick to the backside of the Moon more than protons do because electrons are lighter and faster.

00:18:10
Speaker 1: Wait wait, wait, wait, go back a little bit. What does that mean. What do you mean electrons are different?

00:18:13
Speaker 2: Well, electrons and protons have opposite charges, but they don't have the same mass. Protons are much much more massive than electrons are, right, and so that affects their velocity. They come out of the Sun with the same energy, but they have a lot more mass, so they're moving much more slowly and it takes a bigger force to accelerate them. And so electrons come out of the Sun moving faster, and so there's just like a greater flux of them hitting the Moon than the.

00:18:38
Speaker 1: Protons, a greater flux.

00:18:40
Speaker 2: So there's like more electrons per second per square meter hitting the Moon than there are protons.

00:18:47
Speaker 1: So wouldn't that mean that the Sun is making more electrons than protons.

00:18:50
Speaker 2: It's making the same number. But because the electrons are faster, more of than are getting out to the moon. Like, the protons don't have as much energy, so they don't always get out to the moon, and they certainly don't get out as rapidly.

00:19:01
Speaker 1: Wait wait, wait, so you're saying that, what do you mean, like some of the protons don't make it out to the moon, like they get stuck somewhere.

00:19:06
Speaker 2: Some of them get stuck. They just like exist in the outer layers of the Sun.

00:19:10
Speaker 1: Like the Sun is punet electrons and protons. But some of the protons that don't get very far they maybe get stuck back into the Sun you're saying, or they get it's trapped into orbit with the Sun.

00:19:20
Speaker 2: Yeah, exactly. And there are electrons and protons that do make it out there by the Moon. But again the electrons are moving faster and so they just tend to hit the Moon more.

00:19:29
Speaker 1: But then what would that mean that the center of the solar system it has a positive charge, if you know, if there's more electrons leaving it than protons, that.

00:19:37
Speaker 2: Does tend to make the Sun more positive than negative. There's a lot of other processes happening at the same time that affect the overall charge. For example, the streams of electrons end up creating a positive charge at the core of the solar system, but that in turn makes an electric field that tends to accelerate positive charges away from the Sun, which ends up helping to balance that out. So you see how electromagnetic effects tend to neutralize themselves. The key takeaway is not that the Sun is throwing out electrons which are hitting the Moon, but just more generally, that the Sun fills the solar system with charged particles which are then around to interact with the Moon. So that's a whole other topic we can dig into, like what is the electrical charge of the Sun. Turns out to be much more complicated even than the electrical charge of the moon.

00:20:25
Speaker 1: Hmmm. But I guess it does have a positive charge because you know, the Sun is so sunny all the time.

00:20:33
Speaker 2: I've never seen the Sun be negative. That's true.

00:20:36
Speaker 1: There you go, all right. So then the idea is that the Sun is positive and negative charges in the solar wind, but more electrons make it out to where we are, and so are basically weed the Earth and the Moon are getting showered by more electrons than protons.

00:20:51
Speaker 3: Mm hmm.

00:20:52
Speaker 2: But this turns out to be a dominant effect only on the back side of the Moon. The backside of the Moon, you have this like sheath of plasma, these protons and these electrons that have come along from the solar wind and they're hanging out there and more the electrons end up on the Moon than the protons. So the backside of the Moon is negative. But there's a very different process that dominates on the other side of the Moon, on the sun facing side of the moon.

00:21:16
Speaker 1: Wait wait, wait, so okay, so I'm the Moon and I'm facing the Sun and I'm getting showered by electrons and a little bit of protons. Now what you're saying that the electrons stick to my backside, why would that be?

00:21:28
Speaker 2: The electrons will also stick to your front side. But there's another process on your front side that's even more powerful. That's forcing the front side to become positively charged, and that's the photoelectric effect. Photons from the Sun, really high energy particles hit the Moon and they eject electrons. This is the same experiment that Einstein wather bo fries for explaining if you shine light on a piece of metal, you'll give energy to electrons and eject electrons from the metal, making it overall positively charged. The same thing happens on the sun facing side of the mo Moon, making that side positive and the backside ends up negative.

00:22:04
Speaker 1: Okay, So I'm the Moon and I'm getting hit by sun rays. So forget the electrons for now, I'm just getting hit by sunlight, which are photons. And you're saying it's kicking off the electrons off of the rocks facing the sun. But where are those electrons going? Are you saying they're flying off into space?

00:22:20
Speaker 2: They're flying off into space exactly. The Moon doesn't have a significant atmosphere as what they call an exosphere we talked about once on the podcast, so they don't like run into other particles. It's basically collisionless, so they just fly out into space.

00:22:33
Speaker 1: Yeah, okay, Well what's kicking them off into space?

00:22:36
Speaker 2: The photons, right, Photons are coming in hitting those rocks, giving those electrons a boost so they have enough energy to leave the rocks and also leave the Moon.

00:22:44
Speaker 1: Okay. So you're saying, like the moon's getting a little bit of a sunburn, and the sunburn basically makes the surface of the Moon facing the sun positively charge. Okay, so now my sun facing side is positively charge. And you're saying, now I'm getting a shower of electrons from the Sun.

00:23:03
Speaker 2: That's right. At the same time, you have a shower of electrons from the sun, and your backside tends to attract those electrons. Those electrons end up in this plasma sheath that's around you. Plasma member is just a mix of protons and electrons.

00:23:16
Speaker 1: So it would in the front facing side, which is positively charged, wouldn't that attract the electrons hitting me and make them stick to me more?

00:23:23
Speaker 2: It does do that, Yeah, and that limits the overall positive charge of the front side. Right. The more positively charged she gets, the more it pulls electrons back out of the solar wind and out of this plasma. So this isn't a huge effect. It's self limiting. As we talked about, electromagnetism can be neutralized, and anytime you build up a big charge, it tends to limit itself. But there's a constant process here. You're constant getting bombarded by more and more photons where it's generating more of a positive charge, so it sort of comes into balance.

00:23:52
Speaker 1: Oh, I see, so getting electrons knocked up into space by the sunlight, but I'm also getting showered by electrons from the sun. But maybe those two are not the same amounts, and so overall I have a little you're saying overall, I'm still left with a little bit of a positive charge in my sun facing side.

00:24:09
Speaker 2: Yes, exactly, your sunburn side is positively charged.

00:24:12
Speaker 1: Okay, so then what happens.

00:24:14
Speaker 2: And on the backside, as we talked about, you're negatively charged. Wait, why so the front side gets charged because it's being hit by these photons, right, that doesn't happen on the backside. The backside of the Moon is dark. Photons don't make it there, right, and so there's no photons to drive it positively charged. All you have are the protons and the electrons floating around in this plasma. And the electrons are much higher velocity and they tend to hit the Moon's surface and stick more.

00:24:39
Speaker 1: Wait, I thought that this is not facing the Sun, and most of this stuff is coming from the Sun to where is my backside of the moon catching all this stuff?

00:24:48
Speaker 2: There's a gravitational effect here, right, You have this like solar wind that's washing over the Moon, and then some of the protons and the electrons get pulled around on the backside, and you have this plasma of electrons and proto hanging out on the backside because of gravity. And then the electrons get pulled down to the Moon more than the protons because electrons are faster moving and lighter.

00:25:10
Speaker 1: So you're saying the backside of my moon sucks electrons in through gravity.

00:25:15
Speaker 2: Yeah, And also the electrons are moving faster and they end up hitting the backside of the moon.

00:25:20
Speaker 1: M all right. So then and more electrical than positive because that's just what the solar wind is made out of it.

00:25:26
Speaker 2: And because electrons are lighter, right, they are easier to pull down, And so you end up with this positive charge on one side and this negative charge on the other side. And then there's this threshold, this terminator region right at the edge of darkness and light where it's totally neutral between the positive and the negative. So this is like a ring of neutrality on the Moon between the positive these charged sun facing side and the negatively charged dark side.

00:25:53
Speaker 1: Hmmm, that's super interesting. But I wonder, like, isn't the Moon rotating with respect to the Sun, so r and d these surfaces and positive negative surfaces rotating all the time and changing.

00:26:05
Speaker 2: Yes. Absolutely. As the moon rotates, a different part of it comes into contact with the photons, and so a different part of the moon becomes positive and negatively charged. This charging and discharging times are very very quick, and so like fractions of a second, so there's not like a lag between the charge of the moon and which part the Sun is hitting.

00:26:26
Speaker 1: So when I look at the moon, whether it's like full moon or half moon, basically when I see it, I should imagine that the part that we can see, the light side, is positively charged and the dark side is negatively charge no matter what phase of the moon it is in.

00:26:39
Speaker 2: Exactly, if you can see half of the moon and half of it is lit, then that side is positive and the dark half is negative. Then as it rotates, those charges change. So if you're just standing on the surface of the moon, the surface you're standing on goes from being positively to negatively charged from daytime to nighttime.

00:26:57
Speaker 1: Hmmm, that sounds super interesting. See what do you want experience that yourself? I mean, you talk so excitedly about it. Wouldn't it be great to be there?

00:27:08
Speaker 2: I think it's super fascinating, But I think it could also be unpleasant. I mean we're talking about like up to forty five hundred volts of static electricity.

00:27:16
Speaker 1: Wait what, yeah? That much?

00:27:19
Speaker 2: Yes, it's so powerful that it causes like dust to levitate on the surface of the Moon. If your dust develops a charge, it can repel the surface of the moon. You have like electromagnetic levitation happening on the surface of the moon.

00:27:33
Speaker 1: That just makes it sound more exciting, Daniel, I.

00:27:37
Speaker 2: Think it's exciting for other people to go and take pictures and tell me all about it while I stay in the comfort of southern California.

00:27:44
Speaker 1: I see charge neutral on your couch.

00:27:47
Speaker 2: The astronaut saw this. You can see dust levitating like a meter off of the Moon's surface if you go for a.

00:27:54
Speaker 1: Walk, meaning that there is like if you're in the light side, there's just a lot of it's just a lot of electrons floating and things. Everything's negative charge, which makes the dust repel the rest of the dust which makes it float.

00:28:06
Speaker 2: Yeah, it can repel the surface. So if you're standing on the surface of the moon and it's daytime, so you're in the lift part, the surface is positively charged. So if you can have a rock be also positively charged, then it will repel the surface of the moon. You just got to like rub the rock and brust some electrons off of it, just that hard. You can do that with like a rag then it will be positive and it can float. It's not something we experienced like down here on Earth very often, like unless you're in a magnetically levitating train.

00:28:32
Speaker 1: M And I guess the same would happen in the dark side too, right, I mean, the same effect would happen in the dark side, like you might see dust floating, but for the opposite reason.

00:28:40
Speaker 2: Yeah, exactly. And so if you plan to like have your house plants levitate, then you have to switch from positive to negative charge as the day goes into night.

00:28:48
Speaker 1: Mmm. Right, like a dawn and a dust things would fall to the ground.

00:28:53
Speaker 2: Sounds like a good problem for the engineers.

00:28:55
Speaker 1: Yeah exactly, or just you know, a handy man with a hammer and a nail. All right, Well, it sounds like the moon has at all times a positively charged side and a negatively charged side at all times. But maybe the question is does it overall have a positive or negative charge? So let's dig into that. But first let's take another quick break. All right, we're asking charge questions about the moon. Does the moon have a charge? And it sort of does? I guess it depends on which side of the moon you're in. If you're in the light side being hit by sunlight, then things are positively charged where you are, and if you're in the dark side, things are negatively charged by a lot. You said about forty five hundred volts.

00:29:50
Speaker 2: It can be up to that. Yeah, that's the largest that they've measured.

00:29:53
Speaker 1: Wow, So why doesn't it just act like a giant battery? And you see these you know, sparks or currents going through the moon.

00:29:59
Speaker 2: You don't get lightning storms on the moon, right, There isn't like another layer there to discharge from. And I think it depends also on the distance over which you have this voltage, but it can potentially be dangerous for stuff on the moon if you have like electrical equipment up there. That's very sensitive.

00:30:13
Speaker 1: M But I guess if the light side and the darks are so differently charged, why doesn't the charge equalize, Like why don't you get a whole bunch of electrons from the backside rushing to the front side.

00:30:24
Speaker 2: Some of that does happen, right, This is self limiting, and so this is like the result of a balance of all these processes. If you turned off the solar wind, for example, then eventually the moon would just neutralize. But the solar wind is constantly making this happen, and really interestingly, when the solar wind is stronger, like when you have solar storms, these effects grow more dramatic. Then the moon is more charged, or when the moon passes through like the magnetic tail of the Earth, which tends to focus the solar wind, then it also gets more powerful. So it sort of depends on the solar weather.

00:30:54
Speaker 5: Mmm.

00:30:55
Speaker 1: Interesting, Okay, so then the light side is positively charged and dark side is maked charged. But does it have a charge overall or does it all balance out to zero for the whole mood?

00:31:05
Speaker 2: So this is really interesting question, like philosophically, like do you really mean exactly zero? Because I think that's pretty unlikely for the number of protons and the number of electrons to be exactly matched to each other. It's like flipping a billion coins and getting fifty percent heads exactly. I think it's unlikely. So I'm sure the moon has some overall charge, but I bet it's very very close to zero because it's mostly made of neutral stuff, and then the surfaces are a little bit charged, but one's positive, one's negative, So I think overall it's going to be very close to zero.

00:31:35
Speaker 1: But here, you're just speculating, or yes.

00:31:40
Speaker 2: I'd be pretty confident that if you added up every single particle on the Moon, it would not come out to a perfect balance of zero.

00:31:47
Speaker 1: Right, But I guess would it be negative or positive? What do you think it would be?

00:31:51
Speaker 2: If I had to guess, I'd probably lean negative because I think the effects of the sun light probably taper off more quickly near the terminator region as the sun sort of gets low in the Moon's sky, So overall that might be a little bit weaker than the effects on the negative side. But I'm really not sure.

00:32:07
Speaker 5: Hmm.

00:32:08
Speaker 1: I see, like, if the sunlight effect kicking off electrons off of the rocks is not as strong as like the idea of being showered by a whole bunch of electrons from the sun, then overall it would have a negative charge. Yeah, exactly, But it's not quite clear, right, Like, maybe maybe the sunlight does kick off more electrons than get absorbed from the silver wind.

00:32:27
Speaker 2: Mm, And this is not something we know the answer to. There are folks who study the charge of the Moon, and they make some measurements from things orbiting the Moon, but mostly they have models that describe like these plasmachines and on these processes we talked about the photo electric effect, and they try to match them up with a few measurements they make. But we don't have a whole lot of measurements on the surface of the Moon, and we have some measurements from Apollo astronauts. We're not sure that they were always working in like typical conditions, and as we know, this is like constantly changing throughout the day.

00:33:00
Speaker 1: Throughout the seasons as well, right like as it interacts with the Earth.

00:33:03
Speaker 2: Maybe also yeah, and it's probably not a coincidence, but most of the Apollo astronauts tend to visit the Moon under pretty normal solar conditions, Like if there's going to be a big solar storm, then you're probably not going to launch your astronauts up to the Moon. And so we tend to have measurements during intervals of less extreme space weather.

00:33:22
Speaker 1: But I wonder if you could measure some other charge of the Moon from a distance, could you? Or you mentioned earlier, some signists are trying to do that. How are they doing that and what kind of effect are they using to measure this?

00:33:32
Speaker 2: What they're doing is basically measuring the particles that come off of the moon. Like you have something orbiting the moon. You can collect particles, you can count, like how many electrons are being pushed off of the positive side, how many electrons are being lost on the negative side. Basically, where are the particles and where are they going? And then compare that to the model you have of what's going on on the surface, and try to constrain it and say, by measuring this many protons per second per square centimeter up here, then how many are actually being attracted to the moon or being pushed off of the moon.

00:34:03
Speaker 1: Or I guess maybe to bring it down to Earth. Like if I had an apple in front of me, how would I measure whether it has a positive or negative charge?

00:34:09
Speaker 2: So the overall charge you can measure quite easily from a distance. Right, you just have a test particle, You put an electron near it, and you see the force on that electron, and that will tell you the charge of the apple.

00:34:20
Speaker 1: What do you mean you test the force of an electron.

00:34:23
Speaker 2: So if the apple is charged, it will create an electric field, and that electric field would push or pull on other charged particles. So if you want to measure the charge of the apple, you basically need to measure the strength of the field that it creates, and you can do that by putting another particle in that field. So if you have an electron, for example, and you drop it near some object and you watch that electron move, it'll tell you what the strength of the field is moving through is because you'll see it bend or accelerate or whatever, and that'll tell you the charge of the object that made that field.

00:34:52
Speaker 1: Could you do that with the Moon? Also? Like could we not just like drop an electron near the Moon and then figure out if it's positively or negatively?

00:35:00
Speaker 2: Yeah, it's a cool question, and you could do that if like there was a total vacuum, right, But everywhere around the moon is a plasma. There's lots of positive negative particles, So you can't just like isolate the moon. And it comes down a little bit too like definition, Like what do you mean by the moon? Do you mean just the rocks that are made up you mean also the exosphere? Do you mean this plasma sheet that surrounds it as well?

00:35:21
Speaker 1: Yes, to all of it. I mean I mean just like if you stand away from the Moon a good distance away, is it is it does overall have a negative or positive charge. I mean, I thought that's kind of what we're asking in this episode.

00:35:33
Speaker 2: Yeah, I don't know if anybody's actually tried to measure the overall charge of the Moon in that way. I'm pretty sure it's close to zero. And we've measured the charges on various sides of it and these processes and understood that pretty well, and that all comes together to tell you the story that the Moon is very likely overall zero. But I don't know about an actual direct measurement, Like we're talking about here dropping electrons somewhere near the Moon and seeing what happens to them.

00:35:58
Speaker 1: It sounds like somebody needs to go there, I know.

00:36:01
Speaker 2: All right, everybody chip in for Jorges trip to the Moon.

00:36:04
Speaker 1: Yeah, there you go, I'll pay for the electrons, now go drop them off. All right. Well, what does this mean about the Moon in general in kind of how things are going in our solar system?

00:36:16
Speaker 2: Well, it makes the Moon an even less pleasant place to visit, because all the dust on there is very very charged up, and it makes it really a pain, like the dust tends to stick to everything. All the experiments they did on the Moon and all the equipment they brought came back like coded with this terrible regolith dust. Everything on the Moon tends to stick because it all gets charged up and it's a big mess.

00:36:39
Speaker 1: Wait, why would dust stick if it's negatively charged? Wouldn't be repelled by something neutral? Or would he care about something neutral like my clothes?

00:36:48
Speaker 2: For the same reason that like a balloon will stick to your hair if you rub it enough. You know, you are effectively shedding charges, and so you're building up an overall electromagnetic force. And so the same thing happens on the Moon all the time.

00:37:01
Speaker 1: I see. So it's not easy to get rid of this dust.

00:37:04
Speaker 2: Yeah, exactly, But there are some positive sides. The fact that the moon surface can be positively or negatively charged might help us develop technology to explore or live on the Moon. Is a group trying to build a levitating glider. They're like, Hey, if dust can float on the Moon using electromagnetism, why can't we build a device that like floats on the moon, basically flying cars on the Moon? Mmm?

00:37:29
Speaker 1: Like, use the fact that the surface of the Moon is very charged, you know, positively on the light side, negatively on the dark side, to maybe do like a mac left train.

00:37:38
Speaker 2: Yeah, except in this case would be like electro lev I suppose the idea is to use an ion engine. An ion engine is where you take like a neutral atom, you know, a proton and an electron, you break them down, you accelerate one of them and shoot them out the back of the engine. So say, for example, you shoot the electrons out the back of the engine. That's like you're propellant. So you have a little rocket that's shooting electrons the back and it gives you a little bit of thrust. That's an ion engine. Well, one consequence of throwing electrons out the back of your engine is now your engine becomes positively charged. So if you're trying to levitate over a positively charged surface, that gives you an extra little boost. So you run your little engines, but they don't have to be as powerful as normal because now they're getting positively charged, so they're getting repelled by the surface. So if you're going to build a little glider to explore the Moon, you can take advantage of this effect.

00:38:26
Speaker 1: I see, figure out how to get rid of all your electrons so that your car is positively charged, which would make it float a little bit above the positively charged moon.

00:38:39
Speaker 2: Floor exactly, But then you're like Cinderella and you have to watch out for the sunset because then your car is going to slam into the surface.

00:38:45
Speaker 1: When you get to the dark side, then the whole surrounding floor turns negative exactly.

00:38:51
Speaker 2: But then you just got to flip your ion engines the other way and shoot the protons out of it instead of the electrons, so it can work on either side.

00:38:58
Speaker 1: But would that be enough gosh, I know the gravity is lower on the Moon, but would it be enough to actually make something flow?

00:39:06
Speaker 2: Potentially? They're working on the technology and they've tested one on Earth where they have like a one kilogram object who was able to levitate a centimeter above the surface, and they speculate that on future missions to very low mass moons, very small moons, you might want a flyer instead of a rover because rovers get stuck on surface effects, and helicopters can be pretty tricky if there isn't enough atmosphere. So they're thinking about developing these electrically levitating gliders for exploring future small moons. We might want to figure out if there's like alien life on or just figure out what's on them.

00:39:40
Speaker 1: I see, just to get around, because I guess wheels can only get you so far.

00:39:44
Speaker 2: Yeah, exactly. The glider doesn't get stuck in a crevass, then it's easier to get over hills. You know. We have these cool helicopter on Mars now and they're developing one to fly on some of the moons of Jupiter. But those are really good in higher atmosphere environments, and this would work in a very low atmosphere environment moon.

00:40:00
Speaker 1: All right, Well, it sounds like the answer to our question today what's the electrical charge of the moon, is that it depends on what side of the Moon you're in. If you're in the light side, the charge is positive. You're in dark side, it's negative. If you're in the dusks or twilight zone, then things are neutral. But overall it sounds like it's still kind of a mystery what the charge of the whole moon is.

00:40:21
Speaker 2: We think it's probably pretty close to zero, but we don't have direct measurement using jorgees.

00:40:27
Speaker 1: Electron right, right, and by we Daniel means Daniel.

00:40:30
Speaker 2: That's right. I've not yet sent jorget to measure the charge of the moon, so I don't have that data. Nobody knows the exact charge of the.

00:40:37
Speaker 1: Moon right now, all right, but I think it's another interesting example of how complex things can get in the universe. You know, you might think that something like the Doing is just floating out there in space and it's made out of neutral rocks, and so it must have a neutral charge. But you know, there's so much going on in the Solar system with the solar wind and gravity and light and the photo electric effect, that things can I get complicated and a little bit charged up.

00:40:59
Speaker 2: Yeah, there's a lot more going on than just gravity that shapes our solar system and our galaxy. These winds affect our solar system, but there are also galactic winds radiation from the center of the galaxy that shape the structure of the galaxy and the star formation. So electromagnetism still has things to say about the structure of the universe.

00:41:18
Speaker 1: All right, Well, we hope you enjoyed that. Thanks for joining us. See you next time.

00:41:27
Speaker 2: For more science and curiosity. Come find us on social media where we answer questions and post videos. We're on Twitter, this word instant and now TikTok. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.