Science Friday - Why Astronomers Are Excited About Comet 3I/ATLAS’ Close Approach

Episode Date: December 19, 2025

This year, comet 3I/Atlas broke into our solar system, but also the zeitgeist. This dirty snowball is a visitor from another solar system, and it’s only the third interstellar object we’ve ever spotted. And today, it's closer to us than ever before—just 170 million miles away.Astronomy experts Stefanie Milam and Hakeem Oluseyi join Host Flora Lichtman to dish about 3I/ATLAS and how it captured the spotlight in a way that maybe no other big hunk of rock ever has.Plus, the sun is setting on the ISS, and the plan is to eventually crash it  into the ocean. But wouldn’t it be cooler to send it into deep space instead? A listener pleads his case.Guests: Dr. Stefanie Milam is an astrochemist at NASA and a project scientist for the James Webb Space Telescope. She studies comets and interstellar objects.Dr. Hakeem Oluseyi is an astrophysicist and CEO of the Astronomical Society of the Pacific.Transcripts for each episode are available within 1-3 days at sciencefriday.com.  Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

Hey, I'm Flor Lickman, and you're listening to Science Friday. Today in the show, an attention-hogging larger-than-life celebrity that everyone, and I mean everyone, seems to be talking about. Comet 3-E-A, Atlas. This dirty snowball is a visitor from another solar system, and it's only the third interstellar object we've ever found. And today, today, it's closer to us than ever before, a mere 100,000. 170 million miles away. So naturally, space nerds like my next guest and me are really excited about this, but 3i has permeated the astrophysicist bubble and captured the spotlight in a way that I think maybe no other big hunk of rock ever has. We will talk about that too. Here to dish about this

interstellar luminary are my guests, Dr. Stephanie Milam and astrochemist at NASA who studies comets and interstellar objects, and Dr. Hakeem Olu-Shei, an astrophysicist who runs the Astronomical Society of the Pacific. Stephanie, Hakeem, welcome back to Science Friday. Thanks for having me. Yes, thank you. Stephanie, I know interstellar objects are your jam. How pumped are you right now?

Super excited. This has been a whirlwind of a year since the discovery in July, and we are getting amazing data from telescopes on this object. and learning more and more each and every day about its origins, where it's from, and comparing that to objects in our own solar system. I want to drill into that in a second, but Hekim, I know you're a space, more of a space generalist. Does this rise to the same level of excitement for you? Oh, it definitely does.

And, you know, I'm just impressed with the field, right? It just keeps giving from images of supermassive black holes at the cores of galaxies to gravitational waves of black holes colliding to now, you know, interstellar objects coming into the solar system, you know, it just doesn't stop. It's awesome. Can't stop, won't stop. Stephanie, what answers are you trying to get while 3i is closest to us? We're mostly studying the composition of this object right now. We want to know what it's made of and what clues we can get about where it came from based on that composition. So we're seeing what different molecules are there and what abundances they have, which tells us a little bit about the chemistry of the

planetary system that it was formed from. But we're also looking at things like isotope ratios, which are the heavier forms of any given atom, because those are actually from either the primordial Big Bang or are formed in stars of different masses and ages. And that actually tells us about where in the galaxy some of these molecules could have formed and how that has then been preserved in this interstellar object. Hekeem, what do you want to know about this object? Well, you know, what really excites me about these interstellar objects is the fact that we're getting samples of other star systems.

You know, when a star forms, it forms as a part of this, you know, more massive structure that has a star at the core and a disk that will eventually form planets. And in that process, you build up these commentary bodies. You end up with asteroid-like objects. And, you know, every star has a different history. And every cloud that they form from, you know, they have different chemical abundances. So when a person like Stephanie and her team, they look at the light and figure out what this common is made of, we're getting an understanding of the variations that can exist in these various forming planetary systems.

The diversity of solar systems, it sounds like. Exactly. Stephanie, I know we're trying to get James Webb to take a look at this. What can go wrong? So good news. We are looking at it with the James Webb Space Telescope. We got new data just yesterday with one of our instruments on board. And we're expecting to have more data next week.

So hopefully I get a good Christmas present. The challenges. that we have right now for observing this object with the James Webb Space Telescope is we have to know precisely where in the sky this object is to point the telescope at the exact position that it's at. This is challenging because it's moving. It's flying across our solar system. It just passed the sun, so it's nice and, you know, ramped up and its activity. And that makes it very challenging for us to see where exactly it is. in the sky with respect to known stars so that we can take the James Webb Space Telescope, which is designed to look at the farthest galaxies of our universe.

So it has this really tiny little window that we can actually peek through. And we have to make that little tiny window fit right on top of this interstellar object. So we've been using telescopes all over the world to try to really hone in on where it is in the sky so that we can make sure we don't miss it with the James Webb Space Telescope. This sounds stressful. I'm stressed. Yeah. Lots. We are, my entire team is on the edge of our seats. We've reached out to all of our colleagues at every telescope asking them,

begging them to get as much data as they possibly can to help us refine this orbit. And make sure that we can actually do the observations that we really want to do next week and can really, you know, put the beacon on this object in the way that we want to. We have to talk about aliens because there have been all these alien theories about 3i Atlas. I'll ask you both. But in your view, what are the chances that this is an alien craft? This looks like a comet. There is no evidence that we've seen to date that there is anything atypical about the composition, the activity, or any other phenomenon.

So far, nothing has come up as an extreme. that can't be explained by our regular physical processes that we see in comets in our own solar system. Yeah, there's nothing that says that this is alien. But I'll say this. You know, there are aliens and there are aliens, right? So as astrobiologists study the origin of life and where life could possibly be in various niches in the universe, one idea, which is wild and, you know, highly unlikely, but it is still, you know, not complete. ridiculous is that, you know, comets could possibly hold microscopic life forms, right? We've already

found a lot of complex biological molecules on comets. So, you know, if you're talking about microbial life, hey, there's a tiny probability that there might be something like that. But if you're talking about the Klingons or the Ferengi or, you know, an alien civilization, I think the probability is vanishingly small. Hakeem, is there any teeny tiny little part of you that feels disappointed? No. Not even the smallest corner of your heart. Well, so to be disappointed, the expectation has to be there, right?

And I never had the expectation in terms of an alien craft. Because, you know, there are a lot assumptions that go into that. Anytime you see an alien depicted in fiction, you know, and they're kind of human-like, That means that they were a primate that evolved in a canopy of trees somewhere, right? What's the probability of that? That's not, you know, it's not happening. It just seems, you know, that is what humans would do. And my general smell test for anything that is said to be alien is how similar is it to humans?

And if it's similar in any way, then it's projection. You're not letting the data tell you the story. you're projecting your hopes and dreams onto it. I think Hakeem's right. We want to find life out there. We want to know if we're alone. We want to know how did we get here. We're trying to find the ingredients for biology.

So we want to know are there structures like RNA or DNA out in space? We're getting close. We're finding amino acids. We're finding sugars. We're finding molecules that we find that, that life is comprised of. And so that's very intriguing. We're pushing as hard as we can and technology is taking us one step closer every time we have a new observatory or a new facility that's enabling us to look even harder. Look, on a philosophical level, this is what I want your take on.

We know that science is about challenging assumptions, being open to outside the box answers. why does the questioning around this being alien craft rile up the scientific community? Oh, man. You know, there are cultural issues. You know, I think, you know, we're best when we are open-minded skeptics. I do think we do have to keep an open mind. I've seen a lot of cases over the duration of my own career where you have some new observatory and someone makes an observation or an experiment. and they report their results. And the scientific community says, hey, even though they've never observed this phenomenon, they say, hey, we know how this really works.

We've calculated it. And what you observe does not match. Therefore, there's something wrong with your observatory or your experiment. Right. Right. This goes against conventional wisdom, and thus it is wrong.

Exactly. Exactly. So, no, I'm completely open-minded. I listen to the craziest people. but I bring my rigor, my scientific rigor, and skepticism along. So do I think that there is life out there? I think it's probably almost certain. But when you get to the level of civilization and technology, that's when the probabilities

absolutely plummet. So that is not what I'm expecting, but I am expecting life. But not necessarily in this comment. You know, setting aside the alien theories for a second. Yes. This comet has gone viral, which I think is awesome personally. You know, I love to see it. And I'm wondering if you take any meaning from that.

Oh, I do. I think that the sizzle around this comet, even if it's about aliens, is a good thing. I think that it is bringing more curious minds to wondering about nature. And, you know, personally, I, my. on ramp to being a scientist, you know, in my youth, included exploring the paranormal, exploring, you know, ghost stories and Bigfoot and those sort of idea. They live in a similar part of the soul and mind, right? That part of curiosity, exploring the unknown, going for that, which is really weird and different. And I think that the attention that astronomy is able to generate,

which leads to people, right, becoming a part of this. enterprise, and this is the on-ramp that gets us there. So I'm all for it. Well, Bon Voyage, 3-Eightlas, and good luck, Stephanie. We can't wait to hear what you find out. Dr. Stephanie Milam is an astrochemist at NASA who studies comets and interstellar objects. Thank you for being with us today. Thank you so much for having me. Hakeem, can I hold on to you for one more second? Yes. We have a listener with a space question, and I'm wondering if you can help.

I'll try. We're going to hear it right after this short break. Don't go away. Hey, it's Flora, just reminding you that Science Friday has a dollar-for-dollar donation match right now, meaning that if you make a donation today through December 31st, it will be doubled. So now is the time to head over to sciencefriday.com slash support and make a gift. Our 2026 programming depends on your support. That's science friday.com slash support. And thank you.

Okay, here's some of that conversation. My name's Michael, and I'm calling from St. Louis. my question is why has the United States and the other countries involved decided to simply throw away the International Space Station by letting it crash into the Pacific Ocean when there are so many imaginative things that might happen if we did something else like turn the thing loose into deep space there's so many thrusters on that thing that they could shoot it off into the great unknown and just let it go to just throw it away like you're putting it in the recycling bin, you know, it just doesn't make sense. What do you see as the advantage of letting it go into the final frontier? If some other civilization, you know, if they find it and investigate things about it, questions like, where's this from?

Why is it uninhabited? You know, what was its purpose? And was it intentionally set free from somewhere? or did it escape or did someone lose a war or what? Forget the golden record. We have a whole home we can send into space. Exactly, exactly. You see this as an act of generosity to aliens.

I suppose it is. But I was thinking of it more of an act of a gift to the artists and musicians and poets of the world who would think about this thing just cruising off into whoever knows where. The poets on earth, the earthlings, the earthlings. The earthling poets. Right, right, right. This is a gift to our imagination, actually, is what you're saying.

Yes, to our imagination. Yes, yes. And to the scientists of the foreign universes and galaxies yet to be discovered. Okay. Well, I want to look into that, if that's okay. I'm with you. Why don't I do some work and then report back? That would be delightful.

Hakeem. Okay, I am sure that there are a million and one reasons not to send the ISS out into the Great Unknown. But can we at least agree that listener Michael has a point here, that this is a romantic option? Oh, if it were only so simple, it is a romantic option. And you know what's also a romantic option? Just leaving it where it is in orbit. But even that is far too expensive and dangerous. Walk me through it.

What are the practical reasons for crashing it into the sea as opposed to leaving it out in space or sending it into the Great Unknown? You have three options, really, right? So there are what are called graveyard orbits. You boost it up to a higher orbit and it pretty much just stays there orbiting. And even that is too expensive. it's a lot of mass to move, and because of that, you know, it just is prohibitive. And then once you get there, it becomes a debris risk.

Another option is doing nothing. And in that case, it's going to deorbit naturally, right? Anything in low Earth orbit tends to come down for various reasons. And in that case, it could land on someone. It can land on a crowd of people. You don't want to have an uncontrolled deorbiting. So the third option is a controlled deorbiting. And that is the option that NASA has selected.

That's the least expensive and the safest, right? It's balancing all things. Is Michael Wright technologically that you just, it has thrusters on it? You just turn them on and let them go for as long as they go. And then it's out and out on its way. No, that is not, I mean, there are thrusters, but they aren't designed to move the entire space station as it is currently assembled. And it wasn't designed to even last this long, right? And it certainly wasn't

designed to last indefinitely. And a de-orbit, you know, acceleration kick as a complete body, you know, it's big. So you have to get fueled to it. You got to slap rockets on it. You would have to model that mechanically to understand how to do it. And that's going to cost you millions of dollars. Then when you get to the point of actually trying to do it, that's going to cost you. It's going to cost you definitely billions, if not hundreds of billions of dollars. And then you're going to have astronauts and potentially cosmonauts involved. So you're putting human lives at risk. So there is no really compelling reason to send it out.

It would be nice if, you know, if we had infinite money and infinite resources, oh, yeah, let's undertake this massive, you know, task of making that happen. You know, it's worse than building a pyramid. You know, it's really, really challenging. So you're telling me there's a chance. Well, here's the thing. If we get that asteroid psyche that is made up of all the precious metal and is worth more than a quintillion dollars, yeah, maybe we can make it happen. Dr. Hakeem O'Lushay is an astrophysicist and CEO of the Astronomical Society of the Pacific.

And if you, like Michael, have a burning question for us, or maybe an outside-the-box idea, we want to hear it. Leave us a voicemail at 877. for SciFri. And we'll look into it. This episode was produced by Russia Auretti. Thank you so much for listening. Happy Friday. I'm Florida Lixman.