B (2:34)

76 years. Yeah.

A (2:35)

This is just one and done.

B (2:37)

Yeah.

A (2:37)

How do we even know it's a comet? Yeah. So not like an asteroid.

B (2:40)

Yeah. So astronomers have been studying three Eye 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, 3A Atlas, it came from somewhere else. It's gonna come in, then it's gonna.

A (3:05)

Leave and she'll scream, get in, loser. We're going shopping on the way by.

B (3:09)

Yes.

A (3:09)

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

B (3:14)

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

C (3:19)

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

B (3:26)

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.

A (3:39)

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

B (3:42)

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

C (3:54)

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.

B (4:04)

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

A (4:07)

That's good. Okay, what else are people saying about 3i Atlas?

B (4:11)

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 three Eye Atlas could be alien technology. But John says, no way.

C (4:24)

I'll bet you my house at 5050 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.

A (4:35)

He sounds fun.

B (4:36)

Yeah, 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.

A (4:47)

Respect.

B (4:47)

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

A (4:54)

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.

B (5:04)

And what was so interesting about the first interstellar comet found? Oumuamua. I'm Regina Barber.

A (5:10)

And I'm Emily Kwong. And you're listening to Shortwave, the science podcast from npr.

D (5:25)

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A (6:12)

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A (6:24)

Visit solventum.com okay, Gina, before we get into this new interstellar comet, why is everyone so obsessed with them? Why are you so obsessed with me? Isn't that a mean girls line too?

B (6:34)

Yes.

A (6:35)

Oh no. Why are people so into this topic?

B (6:38)

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

E (6:44)

When the first one of these objects, One Eye Oumuamua, from the Hawaiian word for scout, was discovered In October of 2017, I had only been a graduate student for about two months. And I really kind of thought, oh, this is the one we're ever going to find.

A (6:58)

Right.

E (6:58)

You know, I am so out of.

A (7:00)

Luck, but we clearly found another one.

B (7:02)

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

A (7:13)

Oh, I remember covering Borisov on Short wave. Yeah, our show had just started around that time. So it seems like from the very beginning, though, people have been baffled by these objects. Amua Mua also raised allegations that it came from Alien Tech. Why?

B (7:30)

Yeah, it didn't have a tail. And most comets do. 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, it looks suspicious. Right. So here's my PhD grandfather again, John Thomas Connery and I, talking about this controversy.

C (7:49)

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 that's fun. Fun to think about.

B (8:02)

It gets the students engaged.

C (8:04)

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 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.

B (8:30)

So when astronomers say volatiles, they mean 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.

A (8:39)

Okay, so Oumuamua had no tail, was kind of dry, Moved in a weird way.

B (8:44)

Yeah. But what really got a lot of people excited about Oumuamua 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.

C (9:07)

There was a little bit, just a teeny weeny weeny bit of extra acceleration. And 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 those molecules that got boiled off.

B (9:32)

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

C (9:34)

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.

A (9:39)

So it'd be like invisible comet farts.

B (9:41)

Yes.

A (9:42)

Were causing little, like, bops in the movement or something.

B (9:44)

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

A (9:48)

Yeah.

B (9:49)

But Teddy pointed out, while there was.

E (9:51)

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.

A (10:08)

What a baffling little interstellar visitor. We're glad that she came by. And it sounds like scientists did Come to the consensus that one Aya Muamua was not made by aliens.

B (10:20)

No, it was made by nature. No aliens.

A (10:22)

Okay, let's talk about this new interstellar visitor, three EYE Atlas. Will it tell us something about other solar systems? If scientists manage to truly study it when it comes to see us?

B (10:33)

Yeah, that's the goal. So, like, interstellar comets, like I said, they formed around another star in our galaxy with the same material that. That probably that star's planets formed. Yeah, so.

A (10:46)

So they carry chemical clues from, like, distant worlds.

B (10:50)

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?

A (11:00)

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

B (11:06)

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.

A (11:19)

Right, like Bennu.

B (11:20)

Yeah, yeah. But this one we're not gonna, like, send a spacecraft to. We're gonna 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.

E (11:38)

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.

A (11:48)

Do we know what color 3i atlas is?

B (11:51)

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.

E (12:24)

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. 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 classic comet.

A (12:47)

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

B (13:01)

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

E (13:08)

Know what to look 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.

A (13:28)

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.

B (13:33)

Unless you're my academic grandfather, John. He told me about an asteroid that Atlas found called why Are four?

C (13:40)

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.

B (13:55)

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

C (13:57)

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

B (14:03)

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

C (14:08)

Yes.

B (14:09)

Got it. Got it. Let's just be clear here. You're not a monster.

C (14:11)

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

B (14:17)

We want to be able to give warning.

C (14:19)

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.

A (14:29)

Well, okay, moon, something might still be coming for you yet. Yeah. Gina Barber, thank you so much for coming on to talk about interstellar comets and why they are not aliens.

B (14:38)

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

A (14:41)

Interstellar buddies. Yeah. 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.

B (15:01)

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@npr.org PeoplesChoice this episode was.

A (15:12)

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

B (15:18)

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

A (15:24)

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

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