Short Wave - Every Moon, Ranked

Episode Date: April 16, 2020

Science writer Jennifer Leman did it. She ranked all 158 moons in our solar system. The criteria? Interviews with NASA scientists, astronomers, and her own moonpinions. She talks to host Maddie Sofia about some of her favorites. Here's her full list for Popular Mechanics. Email the show at [e-mail]. See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. I don't know how many moons I thought there were in our solar system, but it was not 158. I mean, there are a lot of incredible moons. We made some really tough decisions. Science writer Jennifer Lehman, in a piece for popular mechanics, ranked them all. I did spend a lot of weekends at a coffee shop.

All the moons. The baristas at that coffee. shop, we're so kind because I would always, you know, go up, grab my coffee and then tell them a moon fact and then, like, go back to my seat. Now, before any moonsplainers out there get started, we want to say at the outset that while Jennifer talked to a lot of experts, big deal, planetary scientists, people at NASA, this list well, is entirely subjective. The ranking is based on the moon pinions that I collected at the American Geo, Physical Union Conference,

It's based on interviews. And really, it's based on kind of which moons I thought were coolest. So it is highly subjective. I want to answer a question. It's based on my moon pinions one day. This episode, one small look at a few amazing moons, one giant leap for moons. I'm Betty Safaya.

And this is Shortwave, the Daily Science Podcast from NPR. Two small notes before we hit you with some hot moon takes. One, obviously we're not talking about all 158 moons. We picked a handful from the top 10. And then we'll do a lightning round on some others. All of these bodies meet the technical definition of a moon, meaning they orbit an asteroid or a planet, not the sun. Second note.

Jennifer's list also includes a few of what NASA calls provisional moons. These are bodies that are kind of. of, let's say, unofficial, maybe haven't been studied that well or confirmed yet. Yeah. And so even still, I want to add that the scientists that I spoke to, they said that there are probably way more moons out there that we haven't even discovered yet. Wow. So cool.

Okay. All right. So number 10, on your list. Diddy moon? Yes. Is that how I say it? Yes. Where is Diddy moon?

So Diddy moon, it's not circling a planet. It is actually circling an asteroid. It is very tiny. It's about 524 feet in diameter, and it's orbiting the asteroid Diddy Most. And it's kind of part of a very cool future NASA mission, right? Yeah, so Diddy Moon is part of a really important mission, the Ida mission. And the Ida mission is like this cosmic dress rehearsal. Basically, NASA wants to send a spacecraft to slam into Diddy Moon. and knock it off course. Now, I know what you're thinking.

It sounds pretty familiar. And yes, it is essentially the plot of Armageddon, but mine is Steve Bouchemmy. But it's a really, really important mission. And it's going to help us test one of the ways that we think we might be able to potentially deflect a hazardous object that might be hurtling towards Earth. So cool. Okay. Number six, called by one expert you talked to, the most underrated, moon in the solar system, orbiting Jupiter, Ganymede.

Yeah, Ganymede. Ganymed is such a fascinating world. Ganymed is the largest moon in our solar system. It's actually larger than Mercury. Ganymede is also the only moon that we've known to have a magnetosphere. Cool. Earth has a magnetosphere. And it's essentially this covering, this kind of magnetic shell that we have of charged particles.

And what it does is it actually protects us from harmful radiation. So there's tons of radiation that's generated by the sun and from interstellar space. And that magnetosphere protects us. It's potentially allowed life to form. Can I tell you that I am horrified to report that I thought Ganymed was a made-up moon on the sci-fi show, The Expans. Oh, yes. On that show, they like farm on Ganymed. And I'm like, that's a fun made-up place. I love that shout out to the expanse. It's a great show. Yeah, no, Ganymede is just so fascinating. So number four on your list, orbiting Neptune.

Triton. Yeah, so Triton is an absolute misfit. First of all, I will say, it looks just like a cantaloupe if you, you know, look at the pictures. Okay, how I see why it was ranked so high. Keep going. I mean, that is, of course, the important feature. But really, what's cool about Triton is that it's essentially this kind of Pluto-sized object that we believe has been captured by Neptune. and now orbits the planet.

And temperatures on Triton, and we know this thanks to the Voyager 2 spacecraft, but temperatures on Triton have dipped as low as minus 391 degrees Fahrenheit. Nope, nope, nope, nope, no thanks, no thanks. But it's partially because it's got like this ice-covered surface, right, and that reflects a ton of the light that it receives. Is that its vibe? Yeah, absolutely. And that's another really weird thing about Triton.

It has what's called an incredibly high albedo. So that's basically a measurement of how much light a body reflects. And Tritons is actually really high. It reflects about 70% of the sunlight it receives. I'm liking Triton. I'm going to be honest with you. Ganymede's got a good run at it, but I'm liking Triton right now. All right.

Okay. Time for the top three, Jennifer. Are you prepared? I think so. Okay. Bronze medal orbiting Saturn, a moon that contains the big, four ingredients for life, hydrogen, carbon, nitrogen, and oxygen, Enceladus. Yeah, so Enceladus is an absolutely fascinating moon.

So the Cassini mission, when it arrived to observe Saturn's moons, it noticed that there were jets spewing out of Enceladus. Right. So they actually took a detour and had Cassini swing through those jets to collect samples of that liquid, and it turned out to be. liquid water. Right. I remember when that happened. That was wild. That was like a big deal. Yes, absolutely. And so it really spurred a lot of interest in Enceladus. Of course, we love Europa. But Enceladus is really this kind of new and exciting moon. And, you know, as you mentioned,

it has the big four ingredients for life. That's really just an incredible sign that this might be one of the places where we find life. Okay. Number two on the list, orbiting Jupiter, a lot of volcanoes, and some lightning, Iyo. Yes. So I will admit that I have some volcanic biases. I really love volcanoes. Thank you for disclosing that conflict of interest, Jennifer. I have to be honest.

Anyone who knows me knows that I absolutely love volcanoes. So naturally, Iyo, which is the most volcanically active body in our solar system, would have to take second. There are over 400 volcanoes on the surface of I.O. And they spew jets of lava hundreds of miles into space. It's really incredible. Okay. So this is the wildest thing about Io to me is that IO can generate like an electric current? Yeah.

So of all of the Galilean moons of Jupiter, IO is actually the closest to Jupiter. And so it sweeps through its magnetic field. And that causes it to create this electric current. And it can generate as much as 3 million amperes. and actually this jolt of electricity is then shot back to Jupiter, and it creates lightning in the planet's upper atmosphere. I mean, that's cooler than the volcano's. Some people would say that, yes. Okay.

Your number one moon, Jennifer, orbiting Saturn, a moon I could walk on with potentially nothing more than an oxygen mask. Titan. Yeah, so Titan actually is the only other point. place that we've observed so far that has a thick substantial atmosphere. So our atmosphere, of course, is critical for life here on Earth. And Titan, it has a similar, it has a sort of similar atmosphere. It's also mostly composed of nitrogen, but the second most common gas in the atmosphere is actually methane. So. Right, right. So instead of like us having oxygen, the next most abundant compound in that moon's atmosphere, in Titan's atmosphere, is methane.

Yeah, absolutely. And if you think about Earth, we have water on Earth. We have all three phases of water on Earth. So there's liquid and gas and ice. But on Titan, you have liquid methane on the surface, which is really, really incredible. It's the only other body in the solar system that we've observed to have liquid on its surface. And these are rivers and lakes and seas of methane and ethane. Is that part of the reason why it's got this like orange goopy haze around the moon? Yeah, so the ethane, the methane, those hydrocarbons that kind of creates, it's really this, I feel like it's really beautiful.

It's this kind of soft, orangish glow. So it looks a little bit fuzzy, whereas other moons that don't have an atmosphere, they look very sharp. But this is very, it's a very muted moon. It's, yeah. Very beautiful, I think. Yeah. So before we go, Jennifer, we had to leave out a lot of sweet moons. So we're going to do a lightning round.

I'm going to mention a moon from your list, and you give us one moon fact. These are not moon pinions, but moon facts. Perfect. That sounds great. Okay. Number 41, Jupiter's moon, Amalthia. Yeah, so Amalthia is actually the reddest object in our solar system, and we aren't 100% sure why. Beautiful. Red's my favorite color. It's promoted to 31. Okay. Number 20, Jupiter's moon Calisto.

So, Callisto is thought to have the oldest surface in the entire solar system. Pretty sweet. Okay. Number 18 and 19 combined, also Saturn moons, Atlas and Pan. Atlas and Pan look like giant Ravioli with material around their equator. I really like that. I'm having so much fun. Number 13, one of the two moons around Mars, Phobos. So Phobos is a giant rubble pile on track to either fling itself into Mars or split apart in orbit. Some missions have actually proposed a pit stop on the tiny moon on our way to the red planet. Love it.

Okay. Number 11, Miranda, orbiting Uranus. So Miranda is home to Verona Roops. It's the tallest cliff in the solar system. If you fell off its edge, you would have time to read the newspaper before you hit the ground. Okay, that's it for the lightning round. Jennifer Lehman, thank you for this massive and important scientific undertaking. I'm excited for our listeners to hear the other 84 parts of this series.

Looking forward to it. Jennifer Lehman is more than happy to argue with you about moons, including our own, which she calls Moon Moon, number eight, by the way, on the list. Check out her entire list for popular mechanics. There's a link in our episode notes. This one was produced by Brett Bachman, who we captured up like Triton,

edited by Viet Le, the planet to our many moons, and fact-checked by Emily Vaughn, who's got that old soul, Colisto vibe, for sure. I'm Maddie Safaya, back tomorrow with more shortwave from NPR.