Why Experts Are Racing To Learn About This Interstellar Comet

The comet 3I/ATLAS is taking a long holiday journey this year. It’s visiting from another solar system altogether. Those interstellar origins have the Internet rumor mill questioning whether 3I/ATLAS came from aliens. Co-hosts Emily Kwong https://www.npr.org/people/767284140/emily-kwong and Regina G. Barber https://www.npr.org/people/1082526815/regina-g-barber dive into that, plus what it and other interstellar comets can tell us about planets beyond our solar system. Read more https://www.npr.org/2025/10/30/nx-s1-5591378/3i-atlas-comet-nickel-space of NPR’s coverage of 3I/ATLAS. Also, if you liked this episode, check out our episodes on: - the physics in the film Interstellar https://www.npr.org/2025/09/09/nx-s1-5534348/interstellar-wormhole-black-hole-space-time-movie - why Pluto is still helpful for learning how our solar system formed https://www.npr.org/2024/06/22/g-s1-5023/pluto-dwarf-planet-solar-system-ceres Interested in more space science? Email us your question at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://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 https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:17Emily Kwong?

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• 1:46Emily Kwong?

  Hey, ShortWavers. Emily Kwong here with my favorite astrophysicist. You know her, you love her, you hear her a lot. Her name is Regina Barber.

• 1:55Regina Barber?

  Aw, Emily, thank you for reading that so well. I wrote that for you.

• 1:58Emily Kwong?

  Oh, my God. Don't out me. Gina, you are here to tell us about 3I Atlas.

• 2:04Regina Barber?

  Yes.

• 2:05Emily Kwong?

  I keep hearing about this comet, but why are people so obsessed?

• 2:08Regina Barber?

  So, Em, this comet isn't from here. Like, she doesn't even go here. Okay, that's my Mean Girls reference. Do you like it?

• 2:15Emily Kwong?

  I do.

• 2:16Regina Barber?

  Okay. So, it's a piece of ice and gas and rock, like most comets are, but it's from another solar system. It's interstellar. But we know it's from our own galaxy. We know it was created around another star, not our sun. And we get to see it once and then never again.

• 2:31Emily Kwong?

  So, wait, it's not like Halley's Comet? Which comes, what, every 70-something years?

• 2:37Regina Barber?

  76 years, yeah.

• 2:38Emily Kwong?

  This is just one and done?

• 2:39Regina Barber?

  Yeah.

• 2:39Emily Kwong?

  How do we even know it's a comet?

• 2:41Regina Barber?

  Yeah.

• 2:41Emily Kwong?

  And not like an asteroid?

• 2:42Regina Barber?

  Yeah, so astronomers have been studying 3I Atlas since July of this year. We know it's a comet because it has this icy nucleus. It has a bright cloud of gas and dust. Astronomers can see this through their telescopes. They also see that it has a tiny tail. And most comets we see from Earth, they orbit our sun. And they're made during the formation of our solar system. But this one, this comet, 3I Atlas, it came from somewhere else. It's going to come in, then it's going to leave.

• 3:07Emily Kwong?

  And she'll scream, "Get in, loser, we're going shopping," on the way by.

• 3:11Regina Barber?

  Yes.

• 3:12Emily Kwong?

  Okay. So, why are astronomers so invested in studying her?

• 3:16Regina Barber?

  Because 3I Atlas tells us something about planets around other stars, which we definitely care about.

• 3:21Speaker 03

  It's the only way we're ever going to get material from another solar system. I mean, certainly within our lifetimes.

• 3:28Regina Barber?

  That's John Tonry, an astronomer who was part of a team that created the NASA-funded Asteroid Terrestrial Impact Last Alert System, or ATLAS. And they were responsible for finding this comet, and it was the third ever detected interstellar comet.

• 3:42Emily Kwong?

  Oh, that's why it's 3I.

• 3:44Regina Barber?

  Yes. I stands for interstellar. Yeah. And Atlas, by the way, they do a lot. They survey the entire sky several times a night. And they also look for objects that may collide with Earth.

• 3:56Speaker 03

  After all, if something's going to hit us, just before it hits us, it gets really bright and really big. And so, it's not hard to find. You just have to be looking in the right place at the right time.

• 4:06Regina Barber?

  Although, this comet, to be clear, is not going to impact Earth.

• 4:10Emily Kwong?

  That's good. Okay. What else are people saying about 3I Atlas?

• 4:14Regina Barber?

  So, like the first interstellar comet, that one was found in 2017, there's this internet rumor mill. And it's going on about... How 3I Atlas could be alien technology. But John says, no way.

• 4:27Speaker 03

  I'll bet you my house at 50/50 odds that it's natural. And I'll take you to the bank every day. There's just not a chance that I would, I'd be worried about that bet.

• 4:37Regina Barber?

  He sounds fun. Yeah, he is fun. I didn't know this until like, I started researching this story, but he is my PhD advisor's PhD advisor. So he is my academic grandfather.

• 4:49Emily Kwong?

  Respect.

• 4:50Regina Barber?

  But just because this isn't aliens does not mean that this interstellar comet isn't exciting.

• 4:57Regina Barber?

  So today on the show, we go interstellar with the Comet 3I Atlas. What it can tell us about another part of the galaxy, far, far away. And what was so interesting about the first interstellar comet found, Amuamua. I'm Regina Barber.

• 5:12Emily Kwong?

  And I'm Emily Kwong, and you're listening to Short Wave, the science podcast from NPR.

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• 6:50Emily Kwong?

  Okay Gina, before we get into this new interstellar comet, why is everyone so obsessed with them?

• 6:55Regina Barber?

  Why are you so obsessed with me? Isn't that a Mean Girls line too?

• 6:58Emily Kwong?

  Oh no! Why are people so into this topic?

• 7:01Regina Barber?

  Because they're really, really rare. So I talked to Teddy Coretta. He's a planetary astronomer at Villanova University.

• 7:07Speaker 05

  When the first one of these objects, 1I, "umuamua," from the Hawaiian word for scout, was discovered in October of 2017, I'd only been a graduate student for about two months. And I really kind of thought, oh, this is the one we're ever gonna find. Right? You know, I am so out of luck.

• 7:24Emily Kwong?

  But we clearly found another one.

• 7:26Regina Barber?

  Yeah, yeah. And he was actually part of the team that studied the second one. This was in 2019, 2I Borisov. And then he's also studying this new one, 3I Atlas.

• 7:36Emily Kwong?

  Oh, I remember covering Borisov on Short Wave.

• 7:39Regina Barber?

  Yeah.

• 7:39Emily Kwong?

  Our show had just started around that time. So it seems like from the very beginning, though, people have been baffled by these objects.

• 7:46Regina Barber?

  Yeah.

• 7:46Emily Kwong?

  "Umuamua" also raised allegations that it came from alien tech. Why?

• 7:53Regina Barber?

  Yeah, it didn't have a tail. And most comets do.

• 7:58Emily Kwong?

  A comet without a tail.

• 7:59Regina Barber?

  Yeah. And when, you know, comets move irregularly, like, you know, like something's pushing it or something's coming out of it like a rocket.

• 8:07Emily Kwong?

  It looks suspicious.

• 8:08Regina Barber?

  Right. So here's my PhD grandfather again, John Tonneri, and I talking about this controversy.

• 8:13Speaker 03

  As soon as we discovered it, we sort of jumped in and did a bunch of kind of back-of-the-envelope things like, well, could it be an alien spacecraft if it were? Blah, blah, blah, blah, blah. You know, all that sort of stuff.

• 8:23Regina Barber?

  Yeah.

• 8:24Speaker 03

  That's fun. Fun to think about.

• 8:26Regina Barber?

  It gets the students engaged.

• 8:28Speaker 03

  But there's basically no reason to think that it's anything other than a physical object. But when you come down to, how come it's dry? Most of the things we'd expect to be ejected from Um, other stars or our own are just loaded with volatile molecules like water and CO2 and CO and so forth and so on. And so that's kind of strange.

• 8:53Regina Barber?

  So when astronomers say volatiles, they mean like stuff like ice, you know? So when it gets hot, it turns into gas. And when it comes to comets, you know, some of that can make a tail.

• 9:03Emily Kwong?

  Okay, so Amuamua had no tail, was kind of dry, moved in a weird way.

• 9:08Regina Barber?

  Yeah, but what really got a lot of people excited about Amuamua was that weird movement I mentioned earlier, like it moved as if something was pushing or pulling it. Gravity from a planet or a moon or a sun as it passes by is really the only thing that does that in space. But it was moving like it had exhaust, maybe from volatiles, but we couldn't see those volatiles.

• 9:30Speaker 03

  There was a little bit, just a teeny weeny weeny bit of extra acceleration that was ascertained as it was moving away. And people got very excited about that. And there have been lots of theories about what it could have been. Maybe the most realistic ones are just nitrogen or hydrogen pockets of

• 9:52Regina Barber?

  Right.

• 9:53Speaker 03

  those molecules that got boiled off.

• 9:56Regina Barber?

  And you wouldn't necessarily be able to see that.

• 9:57Speaker 03

  You wouldn't be able to see it because they wouldn't get excited, so they wouldn't emit any light, and so you just wouldn't know it.

• 10:02Emily Kwong?

  So it'd be like invisible comet farts.

• 10:04Regina Barber?

  Yes.

• 10:05Emily Kwong?

  Were causing little like bops in the movement or something?

• 10:07Regina Barber?

  Yeah, I mean, and we also didn't see it for very long. It was only here for a couple of weeks.

• 10:11Emily Kwong?

  Yeah.

• 10:12Regina Barber?

  But Teddy pointed out.

• 10:13Speaker 05

  While there was never by any means a really large fraction of scientists who were, let's say, willing to entertain or really that interested in this idea that maybe this object was artificial, it had been constructed, it was some way related to aliens, that's not to say that we had an easy time explaining many of its properties quickly.

• 10:32Emily Kwong?

  What a baffling little interstellar visitor. We're so glad that she came by. But it's, and it sounds like scientists did come to the consensus that One I Amuamua was not made by aliens.

• 10:43Regina Barber?

  No.

• 10:44Emily Kwong?

  It was made by nature.

• 10:44Regina Barber?

  No aliens.

• 10:45Emily Kwong?

  Okay. Let's talk about this new interstellar visitor, 3I Atlas.

• 10:50Emily Kwong?

  Will it tell us something about other solar systems if scientists manage to truly study it when it comes to see us?

• 10:56Regina Barber?

  Yeah, that's the goal. So like interstellar comets, like I said, they formed around another star

• 11:01Emily Kwong?

  Yeah.

• 11:01Regina Barber?

  in our galaxy with the same material that probably that star's planets formed.

• 11:08Emily Kwong?

  Yeah.

• 11:09Regina Barber?

  So.

• 11:09Emily Kwong?

  So they carry chemical clues from like distant worlds?

• 11:13Regina Barber?

  Yeah. So if we determine what the interstellar comet is made out of, we can compare them to comets in our own solar system and we can figure out, is our solar system normal? Is it unique?

• 11:24Emily Kwong?

  Yeah. But how do scientists figure out like the chemical ingredients of a comet? You can't catch it.

• 11:29Regina Barber?

  Yeah. So what we do is we actually look at the light. Like most astronomers, all we can do is look at light. Unless we have advanced notice, then we can actually send a spacecraft out. We've done this before. We've sent it to asteroids and brought back material.

• 11:42Emily Kwong?

  Right, like Benu. Yeah.

• 11:43Regina Barber?

  Yeah, but this one, we're not going to like send a spacecraft to. We're going to look at its light and how it's reflected off this comet. And what that looks like can tell us about the comet's composition. Ice is pretty reflective, so we can look and we can see maybe there's ice. We can also look at the color.

• 12:01Speaker 05

  When you see a comet with your naked eye and you notice it looks a smidgen green, that's because diatomic carbon, carbon bonded to carbon is glowing in the sunlight and changing the way it looks to you.

• 12:11Emily Kwong?

  Do we know what color Three Eye Atlas is?

• 12:14Regina Barber?

  So this is actually pretty complicated because a comet's color can change over time. So when it was found, it looked a bit reddish and now it looks a little greenish blue, more like the comets in our solar system. And it all depends also on like what telescopes are looking at it, like what filters, but also what's happening to the comet, right? So if it gets hotter, it's maybe like boiling off different stuff when it gets closer to the sun, you know, so it depends on what's actually happening to the comet. Here's Teddy again, talking about what scientists are looking at.

• 12:47Speaker 05

  So we can sort out not just what kinds of gases are being emitted by the comet based on the way that they glow in the sunlight, but we can determine the ratios of them, too. We can start to group them together, ask if two comets look the same. Even if one is a lot closer, a lot brighter, we can compare. Oh, well, it has more of this kind of molecule than this other one. Maybe it's like this class of comet.

• 13:10Emily Kwong?

  I'm happy for Teddy, though, because it sounds like he went from thinking, I'm never going to see one of these interstellar comets, to seeing three in his lifetime, studying two.

• 13:18Regina Barber?

  Yeah.

• 13:19Emily Kwong?

  Why does he think, I don't know, science has been able to find so many interstellar comets recently?

• 13:24Regina Barber?

  Yeah, I definitely asked him that. I was like, is it new technology? But he speculates that scientists now just know what to look for.

• 13:33Speaker 05

  As NASA and the other space agencies have funded and supported searches for near-Earth asteroids, dangerous comets, things that get close by, it's not just a question that we're scanning more of the sky, and we are. It also is that the teams who do it are getting better at finding fainter kinds of sources in their data.

• 13:51Emily Kwong?

  Yeah, I mean, this matters for science, and it also matters for, like, security, because we don't want one of these comets hitting us.

• 13:56Regina Barber?

  Unless you're my academic grandfather, John, he told me about an asteroid that Atlas found called YR4.

• 14:03Speaker 03

  Oh, it could have been so good. It was so perfect. It very likely could have hit the Earth in 2032, maybe over the South Atlantic with about 100 megaton explosion. It would have been a big explosion.

• 14:18Emily Kwong?

  But we would have been fine. People would have been fine.

• 14:20Speaker 03

  Probably. We now know it's not going to hit in 2032, so it was a big disappointment.

• 14:27Emily Kwong?

  Why is it a disappointment? Did you want to be like the one to be like, I found it, we can make preparations?

• 14:31Speaker 03

  Yes.

• 14:32Emily Kwong?

  Got it, got it. Let's just be clear here, you're not a monster.

• 14:34Speaker 03

  That's right. That's right. That's right. We have a purpose in life, which is to give you warning on a civil defense time scale.

• 14:41Emily Kwong?

  You want to be able to give warnings.

• 14:42Speaker 03

  And if I'd been able to say, there, if you hadn't funded us, you would have been sorry. That would have been great. So it's still conceivable it might hit the moon in 2032.

• 14:52Emily Kwong?

  Well, OK, moon, something might still be coming for you yet.

• 14:55Regina Barber?

  Yeah.

• 14:56Emily Kwong?

  Gina Barber, thank you so much for coming on to talk about interstellar comets and why they are not aliens.

• 15:01Regina Barber?

  You're welcome. You're welcome. This is our beat now, interstellar. Interstellar forever.

• 15:04Emily Kwong?

  Interstellar buddies.

• 15:05Regina Barber?

  Yeah.

• 15:08Emily Kwong?

  If you liked this episode, check out our show on the physics of the film Interstellar, or our episode on how Pluto, despite not being a planet, is still helpful for learning how our solar system formed. We'll link both of these masterpieces in our episode notes.

• 15:24Regina Barber?

  Also, NPR's first ever Pod Club Awards are coming up, and you can crown the winner of the People's Choice Award. Vote for us at npr.org/People'sChoice.

• 15:35Emily Kwong?

  This episode was produced by Rachel Carlson. It was edited by our showrunner, Rebecca Ramirez. Tyler Jones checked the facts.

• 15:42Regina Barber?

  Quacey Lee was the audio engineer. Beth Donovan is our vice president for podcasting. And I'm Regina Barber.

• 15:47Emily Kwong?

  And I'm Emily Kwong. Thank you for listening to Short Wave from NPR.

• 16:01Speaker 00

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