< Where did Earth's moon come from? And other moon mysteries

EMILY KWONG: You're listening to Short Wave from NPR. Hey, Short Wavers, Emily Kwong here.

REGINA BARBER: And me, Regina Barber. And Em, all summer long, we've been on this, like, 10-episode odyssey through our changing universe. We've covered planets, stars, living in space, and even, like, how it's all going to end. But there's one big set of objects in space that we've totally skipped over. We're going to take care of that in this episode, where we bring our Space Camp series back to our solar system.

KWONG: With a very special guest, a maestro of mayhem just like us-- Latif Nasser, co-host of the Radiolab podcast from WNYC. Hey.

LATIF NASSER: Thank you for having me. I'm like-- I feel so honored to be at Space Camp.

KWONG: Aw.

NASSER: This is the space camp I never got to go to.

BARBER: Yeah, us either.

KWONG: Yeah.

BARBER: You are welcome, Latif.

KWONG: OK, so about a year and a half ago, Latif, you were solving a space mystery. It all started with this one poster. What happened?

NASSER: Yeah, I was putting my kid to bed. We had a solar system poster we bought from the internet on his wall. Out of the corner of my eye, I saw that Venus had a moon, which was so weird. I was like, I don't remember learning that in school, that Venus had a moon. Not only that, though, the Venus moon on this poster, it had a name. And the name was Z-O-O-Z-V-E.

KWONG: How do you say that?

NASSER: "Zooz-vay"? I don't know. I know as well as you do. So first of all, I googled, "Does Venus have a moon?" First result is from NASA, saying Venus does not have a moon. And the second thing I did is google this word, "Zoozve"-- no English results. Like, how often does that happen on Google?

BARBER: Never!

NASSER: Never, right?

KWONG: Right.

NASSER: So I was like, what is happening? I called a friend of mine. Her name is Liz Landau. She works at NASA. And she fields questions from reporters about space. I was like, she must have heard of this before. I'm like, OK, what's Zoozve? And she's like, I have no idea. I've never heard of that. Venus definitely doesn't have a moon. I have no idea what you're talking about.

KWONG: Weird. So what happened then?

NASSER: She texted me after we talked. And she was like, I cracked it. It's not "Zoozve." It's 2002 VE. The Z's were actually 2's.

BARBER: Oh, my--

NASSER: The zeros--

BARBER: Oh, my gosh.

NASSER: --were actually O's. The O's were actually zeros.

KWONG: It's Twos-ve.

NASSER: It's Twos-ve. It actually is a thing. And it is a thing near Venus that's up there. But then the question became, OK, so wait, what is this thing? And is it a moon of Venus or is it not a moon of Venus? And the answer is that it's kind of both. It turns out it's called a "quasi-satellite" or a "quasi-moon."

KWONG: Quasi-satellite, quasi-moon. Gina, have you heard of these things before?

BARBER: Yeah, so they go by multiple names. One of my planetary scientist friends calls these things "near-earth asteroids." And--

NASSER: Right.

BARBER: --it's interesting to think about how, like, these are not making the moon cut because what scientists do call moons already spans, like, a very wide spectrum.

KWONG: OK.

BARBER: You've got, like, our moon, which actually was made in this, like, spectacular way. And it's unlike moons around other planets in our solar system. Our moon is also, like, nothing like the moons of Jupiter and Saturn, these gas giants, because their moons are more like Earth.

KWONG: It's like moon diversity. I love it.

BARBER: Yeah.

KWONG: You know, why we wanted to bring you on, Latif, is because you determined basically that Venus does have a quasi-moon. And you went through a formal process with the International Astronomical Union to officially rename 2002 VE. It's officially Zoozve. You did it.

BARBER: [LAUGHS]

KWONG: And now, Radiolab has launched a contest to invite anyone to name a different quasi-moon closer to Earth, right?

NASSER: Yeah. It was so much fun. I want everyone to have the fun. Because-- so we partnered-- Radiolab partnered with the IAU to launch a month-long global naming contest for one of Earth's quasi-moons, which means if you are listening to this podcast right now, you could be the next person to name one.

KWONG: So today on the show, a moon tour with Regina and Latif, starting with the surprising history of our very own moon. You are listening to Short Wave, the science podcast from NPR.

KWONG: All right. So before we get into the contest and quasi-moons, let's start with some moon fundamentals--

BARBER: OK.

KWONG: --like our moon, the royal moon. Gina, tell me about the moon near Earth.

BARBER: Yeah.

KWONG: Does it have a special name?

BARBER: No.

KWONG: [LAUGHS]

BARBER: Well, it's called the Moon.

NASSER: It's like we got the generic brand moon.

KWONG: That's right. [INAUDIBLE]

BARBER: I mean, we got it because we named it before we found all the other ones, right? So, like, it was the OG, right? And it's the brightest thing in the sky. And it's a natural satellite, satellite being something that orbits, you know, a larger body in space.

KWONG: OK. But for a long time, did scientists even know how ours got there?

BARBER: Yeah, so scientists really had these theories about how we got our own moon. And one of them is, like, that the moon was captured.

NASSER: It's a hostage.

BARBER: Was it just like, floating this asteroid or something. And we just, like, grabbed it. The other one was, like, it formed with the same stuff within this planetary disk as Earth? The other hypothesis was maybe Earth was spinning so fast when it was being created, it kind of, like--

KWONG: Wow.

BARBER: --pooped it out, like--

KWONG: A planet turd.

BARBER: Yeah.

NASSER: Yeah.

BARBER: Yeah, I like it. And the last one is that there was this giant collision with some other object. And it broke pieces off of Earth and created the moon.

NASSER: Wow, that's kind of the most dramatic one.

KWONG: Well, which one is right?

BARBER: Yeah, so the leading theory now is that giant collision, that our moon used to be part of Earth. And scientists think that when the early solar system was forming, something the size of, like, Mars collided with this proto-Earth, probably, like, 4.5 billion years ago. Here's Jorge Núnez. He's a planetary scientist at Johns Hopkins that I talked to.

JORGE NUNEZ: And so, as a result of this sort of combined collision of, you know, cataclysmic proportions, the Earth came to being. But that remnant material that got kicked out coalesced and started orbiting around the Earth. And what formed became the moon.

KWONG: So the moon could be the debris of this cataclysmic collision that is now, like, held in place by Earth's gravity?

BARBER: Yeah, it's not even "could" at this point. The debate was pretty much settled when scientists were able to study lunar samples brought back by NASA's Apollo missions. This was, like, 1969, early '70s.

NUNEZ: They were able to compare, sort of, the elements and the isotopes. And they were able to determine that, oh, hey, the isotopes, the minerals on the moon are very similar, almost exactly the same as the Earth's.

BARBER: And these rock samples also showed that the moon had been, like, molten when it formed--

NASSER: Wow.

BARBER: --and was covered with an ocean of magma, which only could have been possible after this, like, giant impact.

NASSER: Wow. It's fun when, like, history turns out to be the most dramatic version of itself.

BARBER: Yes.

NASSER: We've discovered other moons in our solar system. Like, how many are we talking?

BARBER: Like, hundreds. So according to NASA's solar system dynamics team, the total number of moons orbiting planets in our solar system is, like, 293.

NASSER: Huh.

BARBER: You know, Earth's got our one. Mars has two. Saturn has, like, 146 moons.

NASSER: Wow.

BARBER: But then there are these moons that are orbiting other moons, which, Latif, a while ago, you told me, are called--

NASSER: Moonmoons.

BARBER: Yeah, moonmoons. Scientists have documented over 470 of those. And, like, NASA is continually finding just moons upon moons.

KWONG: So you got all of these orbital bodies up there kicking around. There's moons. There's also moonmoons, apparently.

BARBER: Mm-hmm.

KWONG: Some of these moons, though, are so interesting to us that they're sites of active scientific inquiry.

BARBER: Yeah.

KWONG: Regina, tell us about the moon that NASA is planning on visiting soon.

BARBER: Yeah, so this is actually Jorge's, like, area of expertise, like, Titan. It's Saturn's largest moon. And its surface is, like, obscured because it has this, like, really dense atmosphere. It's one of the only objects in our solar system that actually has a thick atmosphere.

NASSER: Wow.

BARBER: And Titan's thick atmosphere is mostly made of nitrogen, like Earth.

NUNEZ: And that's in part why Titan just looks so hazy. It's because, basically, it has smog. So if you think back of, like, the 1980s, right, LA, 1980s or early '90s, that it's very smoggy. You barely see the mountains from the city. That's kind of imagine how, sort of, Titan looks like.

KWONG: So cool. OK, so you've got, like, this smoggy LA in the '90s era atmosphere. What else is going on on Titan?

BARBER: Liquid.

KWONG: Oh.

BARBER: Like, this place has lakes and rivers and oceans.

KWONG: Wow.

BARBER: They're not made of water. They're made of liquid hydrocarbons like methane and ethane. And they're hundreds of feet deep, hundreds of miles wide. And they're really, really, really cold because, you know, Saturn is so far away from the Sun. So, because it's cold, there's this, like, layer of frozen water. And underneath that frozen water is actually liquid water and ammonia.

KWONG: Hmm.

BARBER: And maybe there, there could be some sort of life.

KWONG: Gina, everything you're describing, I mean, it's so sci-fi. It's so cool. It sounds completely non-safe for humans. So how is NASA planning to, like, study Titan?

BARBER: So there's this mission called Dragonfly, and it's scheduled for 2028. And it's basically going to be, like, this craft that's going to fly around Titan. And it's going to examine these, like, various locations on that moon.

NASSER: Wow.

NUNEZ: And so Titan is kind of this laboratory of sort of what happens when you have all these sort of ingredients that are important for life, right? Like methane, liquid water, organic materials. And you have a laboratory that's--

NASSER: Wow.

NUNEZ: --you know, running experiments for billions of years.

NASSER: Wow, OK. And this is all just literally all of everything we've been talking about is on one moon. And there's just-- there's so many moons out there.

BARBER: Yeah, so I actually looked this up. And the International Astronomical Union says that there are so many moons, they no longer, like, name the smallest moon unless there's, like, significant scientific interest. So there's, like, probably thousands out there.

NASSER: When I was talking to the guy who discovered Zoozve, Brian Skiff, he told me that a lot of scientists, they have naming fatigue because they name so many-- they've discovered so many things. And they just, like, have run out of names for them, basically.

KWONG: Wow. Latif, you've been focusing on, like, quasi-moons as a legitimate moon that we should be naming in light of this fatigue. I mean--

NASSER: Right.

KWONG: --Zoozve could have easily just fallen by the wayside, but not for you and, like, not for Radiolab, which is super cool.

BARBER: Making a difference.

KWONG: There we go. How is a quasi-moon, though, different from a regular moon?

NASSER: So Emily and Gina-- OK, so everything you just heard about moons, just throw that out the window, because none of that applies to quasi-moons.

KWONG: OK.

NASSER: OK, so think about it this way. So, OK. So a moon orbits, you know, a planet or another large object, right? A quasi-moon, it actually orbits the star. It orbits the Sun. And, sort of, while it's orbiting the Sun, it does so, so close and at the same rate as a planet that it's sort of gravitationally influenced by that planet. So it's almost like Zoozve is orbiting the Sun. 99% of its-- sort of where it's going is influenced by the pull of the Sun, the Sun, you know, whipping it around. But 1% is influenced by Venus and 'cause it's sort of close enough to Venus that Venus has this little toehold on it.

BARBER: Yeah, so basically, Zoozve isn't, like, gravitationally bound to Venus. It's mostly kind of bound within our solar system, like the planets are around the Sun. So this is totally different from the Earth, right? Like, Earth and the moon, they are totally gravitationally bound. Like, that's why we have tides.

KWONG: But Zoozve is far more free-form, is what you're saying?

BARBER: Yeah, it's loosey-goosey.

NASSER: Yeah, it's actually-- it's so complicated. And that's one of the reasons why I really dig it, because you just-- I feel like we all grew up looking at that solar system poster. And you just imagine everything going in those ovals, right, on those tracks. But Zoozve is kind of different because it's doing this kind of three--way dance with the Sun and with Venus. And in a few hundred years from now, it's not going to be with Venus anymore. This Finnish scientist I talked to--

SEPPO MIKKOLA: In Finland, my name is pronounced Seppo Mikkola.

NASSER: --he told me that it's so complicated, you just cannot calculate where it's going to go after that.

MIKKOLA: Mathematically, it's impossible to follow it exactly.

NASSER: Hmm.

MIKKOLA: But there are no equations telling how the bodies will move.

KWONG: So Latif, you and your colleagues-- I mean, you had so much fun learning about Zoozve and naming Zoozve that you wanted to give the general public a chance to name a different quasi-moon. Now, this quasi-moon is near Earth, like our Earth. What is it called, and what are the rules for renaming it?

NASSER: It has the very sexy name of 164207 right now.

KWONG: Oh.

NASSER: So-- yeah, right? So it doesn't really have a name. That's why we want to name it. And the other kind of key rule is that it has to be a mythological inspired name.

KWONG: Well, the polls are open, folks. You can make celestial history. If you've ever wanted to name an orbital body, now is, like, truly your chance. Go to radiolab.org/moon. We have the link in our episode notes, as well as the Zoozve episodes. You can hear the long and winding journey to how Latif got to this place, as well as more reporting from our Space Camp series.

BARBER: Woo.

KWONG: Latif and Gina, thanks so much for hanging out with me.

NASSER: Oh, man, what a pleasure.

BARBER: Thank you. I love talking about moons.

KWONG: This episode was produced by Hannah Chinn. And it was edited by Rebecca Ramirez. It was fact-checked by Regina, Hannah, and me.

BARBER: Maggie Luthar was the audio engineer. Julia Carney is our Space Camp project manager. Beth Donovan is our senior director. And Collin Campbell is our senior vice president of podcasting strategy.

KWONG: Special thanks to our friends at the US Space and Rocket Center, home of Space Camp. I'm Emily Kwong.

BARBER: And I'm Regina Barber.

KWONG: Thank you for listening to Short Wave from NPR.

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