Hello, and welcome to the Physics World Stories podcast. I'm Andrew Blester. And in this episode, we're going to be exploring comet three I ATLAS. High above the orbital plane of our solar system, the comet is currently screaming past us at 58 kilometers per second. It started its journey, if the latest data is correct, thirteen billion years ago in the thick dust of the young Milky Way is a relic of the cosmic noon, a time capsule from an era before our sun even existed.
It was first spotted in July 2025, and the internet did what it does best it speculated. With the velocity nearly double that of the first interstellar visitor we knew about Oumuamua and a trajectory that seemed to defy easy tracking from earth based telescopes the alien probe headlines practically wrote themselves. But as physicists, we know that the natural truth is far
more profound than the science fiction. Today on the Physics World Stories podcast, we're looking at three I atmos through a more sensible scientific lens, and I would argue a more fascinating one. We're joined by doctor Tracy Becker, a lead on the team that has used the sensors of the Europa Clipper mission to observe the comet from a unique perspective. We're also talking to Michelle Quippus from the
European Space Agency. Michelle is a key figure in the comet interceptor mission, a daring project designed to park a spacecraft deep in space and wait for a comet to arrive. We'll hear about that mission later in the podcast, but first to doctor Tracy Becker. I'm a planetary scientist at the Southwest Research Institute, which is located in San Antonio, Texas. And, primarily, I study icy small bodies like, Europa, which is one of the moons of Jupiter, and, asteroids and,
planetary rings. So rings around Saturn, Uranus, Neptune. So that's really awesome, and I feel like that's what we should be talking to you about. But we're actually talking to you about three I Atlas. How have you come into this story? So it's actually really exciting because when, we first heard about the interstellar object, it was back in July. It was, like, July 4 weekend, just before that when it was first discovered. And I was in a meeting with the with some of the Europa Clipper team,
and I said, wow. Wouldn't it be so cool if we could observe it? But that was like a throwaway sentence. I didn't know anything about the geometry of where the where the object was versus where Europa Clipper was or anything like that. And then and then it was the holiday, so everyone
kinda forgot about it. But somehow over the weekend, that the lead of the mission, the project scientist, Bob Papalardo, reached out to the UVS team, which is the instrument that I work on, Europa UVS, and asked, you know, would we be able to observe it? And we
were like, absolutely. They sent us, one of the other scientists on the team had put together a little diagram with the geometry of where is the spacecraft, where is the comet gonna be on closest approach, and, where is the sun and all of that geometry. And when we looked at it, we're like, this is an incredible opportunity to observe this object with
our with our spacecraft. And so, we were excited and got busy right away because we only had a couple of weeks to plan the observations and get the commanding of the instrument onboard the spacecraft, in time for the observations that were gonna happen, in early November. So it it so it's Europa Clipper. Right? It's it's going tell us a bit about what it's going to do because I want to ask you next, how easy is it is to essentially turn it? I I do you have to
turn it? How do you repurpose it all? That's a great question. So Europa Clipper was launched in October 2024, and it's on its way to, the Jupiter system to study Europa, which is this really interesting moon of Jupiter that is mostly an ice shell made out of water ice as we know it here on Earth, water ice. But underneath that icy shell is liquid is an ocean of liquid water, and there's more liquid water there than in all of Earth's oceans combined
times two. And so if there's anywhere in the solar system to look for life, or the signs of the, habitability, that's the place to go and check. And so that mission is really designed with the goal of habitability in mind. It's it's meant to understand the conditions of of Europa, the the geology, the interior ocean. You know? Is the temperature? Is the salinity, sufficient to support life as we know it? We're not necessarily trying to say, yes. Life
is there or not. But certainly understanding that first step of are the conditions there even favorable for the existence of life. That's insanely exciting. Yes. Very. I know. 2001. Right? And then 2010, those science fiction books. Hands off, Europa. That's ever since then, I've wanted to get my hands on Europa, and you're actually doing it. Yeah. That's insane. Oh, yeah. When somebody says, you know, don't go there. That's where we're gonna go.
And we do have a we have a monolith at every one of our, team meetings to, you know, commemorate where we're going. What sorry. When's it getting there? When's it when's it gonna arrive? Yeah. So it's it's on a on a six year journey. And, actually, the spacecraft will be doing a flyby of the Earth and the moon to get a gravity assist later this year in 2026. And then, and then it will be a direct shot out to the Jupiter system and is planned to arrive in 2030.
Okay. And then the data will get to you when? Well, we'll start collecting data as soon as we get there, and, it takes just the time of the speed of light. So depending on where Jupiter is compared to the distance of Earth anywhere between a half hour and two hours or something like that to get start getting some of those bits down. When you say the data, has it also got cameras on it? Oh, yeah. There's a full suite
of instruments. This is a considered to be a NASA flagship mission, so it's kind of got all the things we could possibly fit on board and still launch the spacecraft. So it has a really powerful camera. We're gonna get images that are completely mind blowing compared to the images that we have from, for example, the Galileo spacecraft. We're gonna get some really, really beautiful
shots. We have a magnetometer on board because that's one of the best ways to sense, the ocean underneath is to actually understand the magnetic field and how how Europa's induced magnetic field due to its ocean deflects the magnetic field of Jupiter. So that's actually one of the main ways we know about that ocean. So we have a magnetometer. We have a plasma instrument that also helps measure those kinda interactions with magnetic field.
There's a radar, a ground penetrating radar to try to pierce through the ice and maybe hit where that, ocean deck starts and, an infrared spectrometer to understand the composition of Europa's ice. Because while it's mostly water ice, we see these really interesting discolorations that we think, are generally they kind of fall line along these lines of cracks and and breakups of the ice that we see.
So that might indicate that that water is coming from underneath that ocean up to the surface and refreezing. And so if we can understand the composition of those discolorations, maybe we can say something about the materials that are in that ocean underneath. Let's see. I don't wanna miss any oh, and then and then the instrument that I work on, of course, is the UV instrument, ultraviolet studies of Europa that are mostly focused on the atmosphere, the very thin atmosphere of
Europa. And then we have two in situ instruments. One, one is a dust collector, and one is a gas sniffer, a mass spectrometer. And so from those, we can actually collect the dust the dust and collect the gas and analyze them on board and send that data back down. And that's a way to basically taste and sniff the the composition of whatever material might be up in the atmosphere of Europa. Oh, amazing. Listen.
Can we make a promise that if I'm still making this podcast in 2030, you talk to me again about it then? Absolutely. Awesome. Let's do that. But you what you have done is and you and your team have turned, Europa Clipper. Did you turn it? It's going to do that. But while we're there, on the way, let's look at this comet. Yeah. So, on this as a scientist on the scientist side, we just kind of say, hey. We wanna look at it. Right? And and then the engineers have to go and figure out how to do it.
But, yeah, the spacecraft was not necessarily meant to be pointing that direction. So they do have to take into a lot of they have to take a lot of things into account when turning the spacecraft. Things like where are the solar panels going to be pointing because we have these huge solar panels on board, but you don't want to point them away from the sun all of a sudden and then lose power. And so it is it's a very big spacecraft, and it's slow. It takes a while to slew.
But we're kinda just, you know, on this journey out to Jupiter, and there's not much else not too much else going on, I would say. And so, it was feasible in that sense. We were in the middle of doing a lot of our calibrations. And so one of the things that actually worked out was that in our for our instrument in particular, we weren't going to be able to understand how, an object other than a star kind of what that data would look like in our detector. And so a star is a point
source. It's very kinda sharp, clean signal, but we have this very narrow slit. And so Europa, when we get there, it's gonna be bigger than our slit size. And the effects of that on the detector are appreciable. And so we wouldn't be able to understand those until we already were at Europa already taking data.
And so this actually presented an opportunity for what we call a calibration where we could look at an object that had an angular size, that would fill the slit and, use that as a way to start to already get a sense of how does our detector work when we're looking at a a big object other than a star. And so
that kinda worked together. So we actually were able to move around some of our other planned calibrations and replace it with this with this special observation and still use it for calibration, but also get really, really cool science. Okay. So what have you seen by looking at it then? That's a good question, and we're still figuring it out. So we we the UV instrument, it's interesting, right, because it's designed to look
at Europa, but mostly Europa's atmosphere. And so one of the things that it's meant to do is understand how, molecules in in the gas form kind of break up, and they they send out a signal. When when you have a breakdown of any kind of compound or or, yeah, elemental material,
it releases light at a certain wavelength. And so, for example, if you have o two, two oxygen molecules, and they break up, they're gonna send out a signal at a very, very specific wavelength, and that is a very strong signal at at UV wavelengths. Lengths. And so that's what we're planning to do at Europa. It happens to work out nicely for a comet where comets are also constantly getting interactions with the sunlight, and that's kind of breaking apart some of the molecules
that are making up its gas coma. And so as those molecules break apart, they send out these signals to us. Well, they just send out the signals, and we can capture those with our cameras and understand basically what what that composition is. So it's really a way of understanding what the comet is made out of. And so it works really well as a as a comet instrument
too. And, in fact, there are UV instruments, that are orbiting Mars and UV instruments on, the the Lunar Reconnaissance Orbiter around the moon that also tried to look at, at, at three I Atlas, and I'm not sure what all of those results are yet. But they and then in Hubble Hubble data and Swift data. So everything was kind of looking in the UV. It's really actually a a a perfect wavelength to be looking at and studying comets. And so what did we see so far? So we saw some really interesting
signatures. The the main one is that we we definitely see lots and lots of hydrogen, which was not unexpected by any stretch. And we also see a lot of oxygen. Both of those are coming from the central coma, that gas that's kind of sublimated off of the main comet and kinda hangs around the comet.
That part is completely expected. We also definitely see other signatures of materials, but we're still trying to understand our detector because, remember, we were still in the calibration phase where we're understanding exactly how the detector works and what, the signal the signal's coming in, exactly what wavelengths they are, and then seeing how much of that might be carbon or might be, sulfur or argon or whatever other materials might
be there. And so we are still in that process of figuring it out, but we do think we see a a bit of carbon and, probably a few other things. The other main thing that we see definitely in the data itself is sort of the scattered light coming from
the from probably from the tail. So we think that the the dust tail that kind of gets, trails off of the edge of the the comet, that those different dust particles are basically scattering sunlight into our into our detector, and we're measuring those as well. The intriguing things that we're seeing is that we definitely see what's known as the tail, the ion tail, which is usually when the gas, sublimates when it when it comes off of the the comet,
then it interacts with the sun. You have this pressure from the solar wind, and that usually makes an anti sunward tail. We see that one. That one kinda lines up with kind of all of the expectations. But we also see some tail structure going towards the sun, and we're not the only ones. Other people have seen sort of this anti they call it the anti tail even though it's the tail that's going towards the sun.
They're seeing other other instruments are seeing that as well, but we're still trying to figure the way we're seeing it out. We're seeing it from a very different perspective than most of the other spacecrafts that have looked at this object have seen it. They are you know, most of the objects most of the telescopes, the observations have come from, from Earth based telescopes. Right? It's from Hubble or from JWST or from ground based telescopes. Where we were, we're actually looking at the
night side of the comet. So we're actually looking the comet is kind of in between us and the sun, more or less. And so we're getting it from a very different angle. And and so far, what we're seeing on that sunward facing tail and maybe that dust tail, is not lining up exactly with what would be predicted. And so we're trying to figure
out, is it how we're viewing it? Is it geometry, or is it something that we're able to see that the other ones can't because of that unique lighting geometry that we have? Okay. I mean but that doesn't mean it's aliens. Right? No. It definitely does not mean it's aliens. I would expect something way more fun than just a just a a a tail that's in the wrong direction if it were aliens. I would hope it would spill out something or make it pretty drawing or something like
that. Oh, hey. That would be cool, wouldn't it? Like, hello. That sort of thing. I've or maybe they wouldn't choose English. Who knows? But, well, I mean, it doesn't make a lot of sense, does it, that that there'd be a tail going that way? Yeah. I don't know. As a not comet person, as someone who's meant to be studying Europa, I think it's not completely unheard of to see some of these sunward facing
tails, but they're yeah. And it's hard to say how much of what we're seeing is coming from the dust, how much of it is coming from a gas tail that somehow sunward facing. I don't know. I mean, it's it's fun to get to play with it, though, and try to figure out this mystery. I think that's probably the best part about it. So when you say what you've seen so far, does that mean because you're going through the data or you're gonna make more observations? We cannot make any more observations, so it
really is about processing. It's really still trying to figure out how our detector is inter is collecting the data and what that means, in terms of the exact wavelengths. And, yeah, there's just a lot of data there. We did some really cool different types of studies of it. So we purposefully lined up our slit, which is very, very narrow slit, but it's long. It's seven and a half degrees long by point one degree wide.
And we purposefully lined that up to be, where the long part was kind of in that sun, comet, anti sun tail direction so that we could capture that tail. It turns out the tail was even longer than we expected, and the coma was even bigger than we expected. But what we did was that so because it was narrow, that means we're only kinda getting a sliver of that sort of region of space that's the the comet and the tail and the anti tail.
But then we took the instrument, well, we took the spacecraft, and and the the NASA team did a fantastic job planning this somewhat complicated movement of the spacecraft where they they moved our slit down off the target and then all the way back up over the target. And we did that a couple of times. So we actually have sort of different time domain data. We have different, different sort of views of different parts of
the sky with that data. And so, yeah, there's still just a lot of data to play with and try to interpret, and then changes that we might be seeing over the couple of hours that we were pointing because I think we took observations over about eight hours. So any kind of changes in the emission rates of the gases, would be a little bit more subtle, and we have to kind of do the analysis a little bit more carefully.
And while Europa Clipper isn't going to be collecting more data, we do have actually really cool data from the JUICE mission. The JUICE mission is a European Space Agency mission, and we have a sister instrument, another UV instrument, onboard that mission called Juice UVS. And so that telescope is actually observing, observed at the same time as the UV data from Europa Clipper. And more fast like, what's gonna be super cool about that data, we don't have that
data yet. So there is still analysis to be done. That data, because of the geometry of where Juice is right now, it can't send back a lot of data just yet. So we're expecting that data, in the coming months to to come down, and then we can analyze it. But what's super cool about that is that JUICE was kind of positioned closer to the sun. So it's looking at the comet
from the perspective of the sun. So it's gonna see sort of some of that reflected light as well as the light that's, still being emitted in that auroral fashion. And then Europa Clipper was looking at it almost completely from the night side. So they're from two totally different angles we're gonna be able to collect that data. And that's really important because things like dust, for example, if it's big
chunks of dust, reflect light. But when you have, like, little tiny dust particles, they backscatter light. So just like when you're kind of in your kitchen or in your bedroom and you get that beautiful, like, sunbeam in and suddenly you realize, wow, my room's really dusty. Like, there's dust floating around everywhere. That's because those dust particles are backscattering light. You're not
ever standing in the sunbeam. You're looking at the sun and the sunbeam, and that those dust particles get highlighted in that way. That's what Europa Clipper will be seeing, those smallest particles from that perspective. But Juice, looking at it from the other perspective, will see a different set of particle sizes,
because it's got this different observing geometry. So that's one of the things that makes it really cool is looking at one thing from multiple angles gets us a lot more information. And so we will be able to do a even better analysis of the CLIPr data when we can also see what happened with the JUICE data. You said there was carbon in it. Would you expect to see that in comments? Yeah. So from my understanding is that this object in particular has actually shown way more carbon.
It's had a higher carbon to water ratio than any than most or all, comets that have been observed from our own solar system. And that could be indicative of sort of what the chemical makeup of the solar system that this thing formed in is. Like, is it just a more carbon rich solar system? Is that the norm, or is ours the norm?
We don't know. And so we, we're not surprised to see carbon in general, but some of the observations have shown a really high percentage of carbon to oxygen or carbon to water. And I don't think our data is showing it to be quite that much, but we're also a lot closer to the sun now. So a lot of those observations started, when the comet was still pretty far out. It was out by the orbit of Jupiter.
And so that's what's made this object so exciting is that we've known about it for a long time before we got to its, before it got close to the sun, and we were able to then see it start sublimating different materials, pretty early on in it on its pathway towards the sun. And even that part has been unique for it. Like, the fact that it started sublimating and being detectable that far out might be a sign that this object, has never been close to a star before.
So this object could have been been formed pretty far out from its host star and launched out of the solar system before it ever had a chance to get close to it. And that might be why it started sublimating so early as it came into our solar system. And so it's a really unique opportunity to see some of the, like, primitive ices and volatiles that were on this object. Basically, some of the the most natural formed materials from its solar system as it comes
into ours. And so that's a very rare, very cool opportunity for setting this object. Do you know, do people know do you know if if because of the trajectory it's come from, whereabouts in space it's coming? Not me personally. But, yeah, there is an there there have been studies on basically, its trajectory points to it being from a a pretty old portion of our galaxy.
And so it's probably been traveling for billions and billions of years and probably came from a solar system that that was forget the exact age now, but much, much older than our own solar system. And so that's also very cool because that could indicate, you know, the way that we get a lot of the materials spread through the solar system is through supernova that kind of has some of that material. They burn the material. They create the next level
up. Like, they burn the hydrogen and the oxygen the hydrogen and and, the helium, and then they can make the higher, the heavier, quote, unquote, elements like oxygen and carbons and and everything else that we have all comes from sort of you know, we're all made out of stardust. Right? And so that those
materials are formed inside the star. So if this is a more ancient solar system, it may lack some of those, the or at least lack the, the same ratio or abundances that we have in our solar system, which is a more a younger, hipper
solar system, so to speak. And so understanding those ratios even from just this one opportunity to see this semi pristine object, is a really cool opportunity to understand how other solar systems form and what's the genetic makeup of those solar systems compared to ours. So you say pristine, but it's it's traveled a long way through space. Right? So that's
changed. That's a very good point. Yes. So it is being exposed to constant, cosmic ray radiation, and some of the observations have shown that that probably affects the outer parts of the, of the comet itself as it's been traveling. And so there is definitely some alteration. It's not not oh, unfortunately, after billions of years, nothing's very, very pristine anywhere.
But, but, yeah, it hasn't been from what we think, at least, it probably hasn't been heated the to the level that most of the comets that have kind of been on multiple journeys around our sun have or, like, the asteroids, for example, that are super overly heated. And so you really do lose some of those initial, compositions that were kind of frozen in in time, and can stay frozen if they don't get too too hot.
And so it's very fast moving. Does that make it difficult to observe, or is it does that not make a difference? It does make a difference. Yeah. So it depends on your spacecraft or your telescope. The ones on Earth can track things pretty easily, I think, because, we have the mechanics to just keep, you know, track we just say track, and it and it tracks. Engineering's a wonderful thing. But some for some spacecraft,
moving targets are hard to do. For example, JWST was designed to study astrophysical objects. They're not supposed to move very fast. But I think it's gotten some incredible data of this target, so I don't think this one was moving too fast for it. But there are some, objects, for example, that would be moving too fast for Hubble or JWST or even for Europa Clipper. But we were able to,
to hold on to it perfectly. Again, the the spacecraft team, the engineering team on Europa Clipper was able to set up this observation within two and a half months and figure out how to track it, and everything worked really, really well. So our observations are are beautiful. Europa, right, completely full of waters. Do I is it possible that that water came from comets?
It's possible that some of the water there are contributions from comets, but the the place where Europa formed, it's actually just an area where water could be stable. And so water is very abundant across our solar system, and the reason we don't think Earth's water is sort of from the beginning is just that we're much closer to the sun. And so it should have all kind of heated off at some point in the in the multiple processes that the Earth underwent.
Certainly, some of those major impacts, including the one that may have formed the moon. And so we don't think we could have held on to the sort of initial inventory of water that would have been in the solar system. But Europa is further out. It's past what we call the snow line, which is where, liquid or solid water ice could kind of still stay stable. And so Europa probably formed with most of the water that it has.
And then, certainly, it's probably been bombarded by other objects, asteroids that are water rich or comets that may contribute and change, its overall water con like, water amount or, style of water too because it can have different sort of what we call d to h ratio, the different kind of, levels of hydrogen, types of hydrogen that make up the h two o. So, yeah, I mean, it it can be, but most of it's water. It's it's a natural comet in that sense.
I've spoken to, scientists involved in in in sort of distant space missions over the years, and I don't think I've ever spoken to somebody who's kind of, you know, done this. Or they're on the way somewhere, and then they've just thought, yeah, we could look at that. So let's see if we can. Is is it normal, this kind of behavior? It can be. So I think it's more we don't usually get surprise visitors or that we know about at least. So that part's been really exciting.
There is often the opportunity to observe maybe an asteroid that we're passing close to on our way out. So there have been observations of asteroids in the main belt, or even near Earth asteroids as a spacecraft is kind of on its main journey. But, again, it makes such a good opportunity to test out how all the instruments work when you can observe something two years before you get to your main target. Once we get to Europa, it's gonna be rapid fire. We're gonna be doing, 50 flybys
within three and a half years. And so we're gonna be getting data, looking at the data. As soon as we get the data, we were gonna wanna figure out how we wanna, you know, set up our detector for the next observation. And it's gonna be so, so fast that we're not gonna have that much time to sit and work and fully understand how the detector itself is. You know, all of these detectors have little quirks, and, they're complicated. Right? You're they're not just your
cell phone camera. And even your cell phone camera has a lot of calibration that goes into it before it ends up in your cell phone. And so you have to figure it out. It's these are all custom designed specifically for the missions that they're on. And so, yeah, we will it it's much better when you can get one of these kinda surprise or or fortuitous opportunities to observe on your way to the target rather than waiting until you get there.
So it's been done before, but I don't know of one where it's like, oh, surprise. We just found found the object. One, actually, one I'll take that back. So one other example would be, in some ways, is the New Horizons mission, which I also work on. But, you know, that one was destined to go to Pluto and then to go and explore the Kuiper Belt, but it wasn't guaranteed that there would be an object for it
to do a second flyby of. Once it got past Pluto, there wasn't a guarantee of finding something else that it could look at. And then, fortunately, through lots of, observations and surveys of the Kuiper Belt, then they were able to find, Arrokoth, which ended up being the next flyby target, for New Horizons. So that one may be less of a surprise in that sense. Like, they wanted to do that anyway, but they had to look for it before they
could. Is it all solar powered? Have you used some of the battery that you'd be able to use elsewhere, or is it all solar powered? Yeah. Europa Clipper has these huge solar panels that are when when you fold them all the way out, they're the size of a basketball court. So it's a massive spacecraft, massive solar panels. That's where, most of the power is coming from. We don't have anything like, RTGs that have been on some of the more deep space missions.
There's also some forms of propellant on there, I think. But, the majority of the powering of the of the spacecraft comes from the solar power generated power. Right. So just quickly on the horizon because it can't not. Amazing images of Pluto that came from that. That's kind of the thing that caught the public attention particularly after that sort of thing. Does that you know, as a UV specialist, do you do you want people to be more focused on the UV?
I think any interest in a planetary body is a good thing to have. I do try to talk up the UV. I think people don't think about the world in the UV. Right? I mean, our eyes see in the visible, so it makes sense to want to see those visible color images. But one of the powers of the UV is that it is seeing, you know, information that our eyes and our regular visible cameras can't see, especially when it comes to those kind of elemental materials like I was saying in the in the atmospheres.
One of the main ways we study in the UV these bodies, not so much Pluto, but Europa has an atmosphere. The comet is obviously emitting light. It's it's those auroral emissions. So you're actually seeing the aurora in many ways with the UV of of these different bodies. And so, and the aurora that you see in the UV is gonna be slightly different, than the aurora that you would see in the visible.
And so it could tell you either you can kinda get, you know, oxygen has a rural emissions in both UV and in oxygen, but you can understand more about how much oxygen must be there if you're depending on the ratio you see in the UV versus the visible. But then there are other materials that won't have a rural emissions in the visible that do in the UV
and vice versa. And so you kind of want to look at everything, from as many different eyes and eye styles as you can to get the full picture of what's going on with any object in the solar system. So we don't see the UV, but there are, creatures on Earth that do. Right? Yeah. I think bees and probably some other ones, but these are the ones that I know. But it's cool. Yeah. Because and I don't know the extent of what bees can see.
Like, do they see the UV and all of the colors that we see, or does, like, their eyes cut off at, green? I I don't know. But it could be. And so, yeah, and some animals can see into the infrared, which is also a really powerful part of the of of the spectrum for understanding, like, mineralogy
of of rocks and and materials. Because it's it's tempting to think of the visual from our perspective as being the world as it is, but, you know, there are literally things flying around us that that see the UV that you're studying. It's brilliant. Yeah. And it makes sense for humans' eyes to be focused on the visible because the UV is very hard. We don't get a lot of UV light through our atmosphere. Our atmosphere absorbs most of the sunlight that's coming in
the UV. The stuff that does get through, of course, burns our skin and things like that, so we have to be careful. But we can't do UV observations from Earth based telescopes, which is also why you don't hear about, UV data as often, I think, because the only way to collect UV data is from space. You have to be up above the atmosphere.
And so, assets like the Hubble Space Telescope observing the UV and then all of these spacecraft observing the UV, but you can't go to, like, a a nice telescope at the top of a mountain and get UV data. It's harder to get. It's rarer to get, but it's still extremely powerful. We'll hear more from Michelle later in the podcast. But I wanted to know more about this fascinating mission, comet interceptor, one of the most audacious wait and see projects in the history of space exploration.
With the famous Rosetta mission to 67 p, we had years, even decades to study the target from afar. We know the orbit, the size. But the thing with those comets is that they are short period comets. They've been around the sun many times, and therefore, they're weathered, heat blasted, and altered. And that's why scientists really want the sort of comet that they'd be able to catch with comet interceptor.
If a comet that had spent a long time in deep freeze in space, perhaps somewhere in the Oort Cloud got nudged out and towards us, then lying in wait will be comet interceptor. Now in this conversation, you'll hear the term
Lagrange points. They're named after the mathematician, Joseph Louis Lagrange, and they are gravitational sweet spots in space where something like a small satellite or indeed the comet interceptor project spacecraft can stay in a fixed position relative to the Earth and the sun, enabling the spacecraft to effectively hover in space using very little
fuel. Here's ESA scientist, Michel Kuepes. I'm working on the comet interceptor mission, which is an ESA mission incorporation with JAXA, the Japanese aerospace agency, and it's currently being built. Launch is foreseen in late twenty eight or early twenty nine, and Comet interceptor will be parked in the L two Lagrange point behind the Earth as seen from the sun, roughly a million and a half kilometers behind the Earth as seen from the sun, and they'll wait on its target.
And, essentially, then where, when it's time to to to leave to to encounter the target, leave L two and be transferred to the target, which it will meet most likely at the point where the target comet causes a eclipse. Okay. What l s l s s Oh, sorry. LSST is a legacy survey in space and time, and it's essentially the the Vera Rubens telescope, a new eight meter survey telescope that's currently starting to operate in in Chile, and it will image the sky visible from roughly once every three days.
And the last I heard is actually that the survey will that the survey will start mid mid this month. I'll get an update actually today or tomorrow on that, but the survey is now going to to start very soon. Now the sparking is done because for those comets are typically detected only a couple of months or a year before they
before they before they perihelion. Now comet interceptor relies that with LSST, this time increases to several years, but even several years is not enough to def to to to define, design, build, and fly a space mission. Therefore, comet interceptor is being built now and waits in l two. And then with a typical transfer time of one or two years, it's feasible to fly by a reachable comet if it's detected on time by by LSSD. You've got your spacecraft parked at Lagrange 0.2. There's a comet coming.
If it was three I Atlas, would you have been able to use interceptor on that? No. It's, it's it's would not have been reachable with a fuel available on Comet Interceptor, and it's still a little bit far out. So the Comet Interceptor spacecraft is able to to encounter targets, well, which can be reached with the fuel and also has to be relatively close to Earth's orbit, ideally between point nine and one point two AU.
There is maybe a little bit of margin of it, but, see, I was already too far out from that. And the other aspect is comet interceptor is designed against flyby velocities of up to 70 kilometers per second. And ATLAS, I don't know what's the hypothetical velocity. Flyby velocity would have been as kind of worst case in terms of flyby velocity as an interstellar object with a very high eccentricity and on a nearly retrograde orbit. So most likely, also, the flyby velocity would have been too high.
Okay. But it so you're looking at comets which are, within our solar system, born in our solar system. So Yes. And, so have you got particular targets that you're looking at? No. We do not. I mean, the target still has to be detected. In the unlikely case that no comet will be found that can be encountered in the up to six years in space for comet interceptor, We have a list of short period comets as backup targets.
So for for for each launch, yeah, we we we have, depending on the exact launch date, we have two or three backup targets that could be reached in case we do not find a a long period, Comet. Okay. Fair enough. And so when, when you do get your target, you fly your spacecraft to it. What happens then? Okay. So comet interceptor, actually, three spacecraft.
So the main comet interceptor spacecraft and two small spacecraft that we call probes b one and b two, with probe b one contributed by YAXA and probe b two by ESA. And one one to two days before the flyby, the probes will separate and approach the nucleus a bit closer than the main spacecraft. And then the actual science mission out as a prime science mission is is is essentially only a few minutes when the spacecraft are close to the close to the comet.
And space the main spacecraft will fly by at a nominal distance of 1,000 kilometers, which may be a little bit modified based on comet activity. And based on the flyby velocity, it may get a bit closer. And we'll essentially collect all the data. It can in the time of the closest approach and afterwards use up to half a year for the downlink of the data. The small sats will go closer with a nominal distance of, 400 kilometers for one of them and around 800 for the other.
We'll do the same. We'll take all the data they can in the hours before closest approach and during closest approach and send the data back to the main spacecraft through an inter satellite link. And then everything will be downloaded from the main spacecraft to Earth. What does the having the three different spacecraft bring? One thing is, that we get multipoint observations.
So we sample different areas of the coma at the same time with the three spacecraft, and we also get some stereo view on the nucleus. And the other aspect is with the small satellites, we are willing to take a little bit more of a risk and to get closer to the nucleus of the comet. Bit more disposable. Yeah. More disposable in a sense. Yeah. Imagine that you could use, interceptor to look at three I Atlas. What, what would it what extra information would it give us? Yes. One
thing is we would get high resolution. High resolution, meaning a couple a couple of meters per pixel images of the nucleus. We would also get a much more detailed coma composition mainly because comet interceptor is flying a mass spectrometer that's similar to receptor. So to reset up, can get many observations at the same time. Many molecules at the same time. Sorry.
And we get some some the soft also infrared spectra that show the the variation of composition over the surface that shows the thermal properties, some, yeah, some physical properties of the surface. And, we we get a lot of information also about the the plasma environment and the and the outer commas who the who the spacecraft observing at at the same time between the case of an interstellar object may not be the highest priority.
Just talking about this, there's there's there's there's there's been three interstellar objects. I presumably, there have been many more interstellar objects. And the reason we've seen three is because we now have the instrumentation, whatever it is, to to be able to detect Indeed. There are many more of them, and we only detect, let's say, the brighter ones and the ones that come in close.
And, yeah, as I already indicate, also, the reason that all three have been detected in the last ten years is simply because of more of more advanced instrumentation. And with LSST, we get we hope to get get more. Maybe, I don't know, maybe 10 or 100 more. It's really very difficult to predict on the small statistics and objects we are having. Yeah. Yeah. I mean, I was gonna ask you a silly question.
But, like, do you do you think that Oumuamua, for example, is is actually common, relatively common, or do you think that was really a a one off? I mean, we don't know right now. Is that what? Sorry. Oumuamua. Yeah. Was it I don't know. No. I mean, with with I mean, it was its properties were unexpected. And, of course, based on the discovery of one object and the total of three, it's very hard to say if it's. So so my guess is as good as yours.
It's it sounds like to me that this is going to become, the it's it's a very exciting area of science. If you're interested in in space, which I certainly am, then this is a very interesting area of science. You know? Interstellar, objects coming through our solar system, comets within our solar system, flying spacecraft to comets within our solar system. It sounds like it's an area of science which is developing more and more. If we've only found three so far, it's a bit like exoplanets.
Right? There was a time when we thought they were going to be exoplanets, and now there's thousands and thousands that we know of. Yeah. In a sense, it's maybe like exoplanets since the nineteen nineties. Obviously, ESA had the Rosetta mission that go into a comet ten years ago. Why do we need comet interceptor as well on top of that? The other thing is we had comet 67 p, which is a small period comet that orbits the sun every six years.
And did and and and and, yeah, observed it and its evolution in very much detail. But the interesting thing is for some of the large structures like the the supposed layers, the two there's a two bodies, the the kind of by contact binary structures, the big, the the big holes that we have seen. There are still a discussion ongoing for many of those things to which extent they are primordial.
They are remnants of the formation and to which extent they have been created by the many orbits around the sun and the many warming up, periods in the sun. And they are a mission that gets at least those large structures also on a on a on a new comet that comes into the inner solar system for the very first time will help to distinguish which of those structures have been, yeah, are there as well. And if they're on the new comet as well, they are indeed primordial.
If they are not there, they may be they may be a consequence of the of the evolution due to the formations for the inner solar system of a comet like 67 b. So in those sense, those missions are complementary, and comet interceptor may also help with an with the analysis or reanalysis of the of the of the results from Rosetta.
Now I did mention at the start of this podcast, and you'll no doubt be aware, there is speculation in the press that maybe three I Atlas is some sort of alien spacecraft or something to do with alien technology, which has been sent to our solar system. Now we don't want to get into conspiracy theories here on the Physics World Stories podcast. Of course, we're far more interested in the universe as it actually is.
But from a science communication point of view, it's something that I wanted to talk to Tracy Becker about. Because doctor Tracy Becker was the winner of the Carl Sagan Award for the Public Appreciation of Science in 2023.
And I wondered what her take was on this story of fascinating story of an interstellar comet being mixed up in the media, in some cases inspired by comments from scientists who, for whatever reason, seem to say that anything that is slightly peculiar might well be alien technology.
My feelings can be mixed. I mean, I think that anything that gets people excited and talking about space and focused on space and understanding that there's all these really cool phenomena happening all the time around us and and focusing on the science, that's all exciting. So I'm, in some ways, glad to have so much interest generated in this object. We don't get a lot of interest generally just from a an average comet passing by.
This object, of course, is spectacular in the sense that it's only the third time we've ever known about an interstellar visitor. Right? This is an object that came from outside of our solar system, and it's in our solar system. And so it rightfully deserves a lot of talk and a lot of press. And so from that perspective, it's good to see,
so much interest in it. What I hope that the public does is take that initial, you know, a little bit of bait, I guess, in terms of of what is this thing and and then go look at it more carefully and see, wow. This is really cool even though the bait was this kind of alien thing that people like to throw out there. But the the actual science behind it is interesting. The part that I waiver on a little bit is that, you know, the public we want the public to trust scientists.
There's already a lot of, erosion of trust in scientists and science in general in multiple fields. And so experts kind of throw out claims that are not backed by empirical evidence, can further tarnish and further hurt sort of that goal of making sure we're communicating, good science and making sure that that people understand the science and trust the science and trust the scientists. I hope that people use it as a
launching point of saying, what? Aliens? Oh, no. That's it's not aliens, but this is cool. And not the other way, which could be, oh, it's aliens. Oh, wait. No. All these other scientists are saying no. I guess science never can con can come to a conclusion on anything, and now I don't believe any of it. You know? That's a harmful, response to it. So, yeah, I think a mix. But, hopefully, again, people just appreciate how how
cool this is. And I think the images that, Hubble and other telescopes have been producing and the results that hopefully we'll be publishing with Europa UBS and other spacecraft will keep that interest alive, and just show how cool it is to be able to have this fleet of spacecraft all be able to turn and point at this one really special, interstellar object that serendipitously came through our solar
system at the right time. Stay tuned for whatever for the results that we do publish with this instrument and with the various other spacecraft and, telescope ground based telescope observations that are happening because I think we're just scratching the surface. We just kind of are taking images right now and and getting some of that initial data out there, but this is our first real opportunity to understand and kind of put into context what our solar system is. You know?
When we look at we can look at planets now. We can see these exoplanets around other stars, which is fantastic. But it's hard to get any compositional information about those, and and even then, it's some of the usually the biggest ones. It's hard to get information about comets in our own solar system that don't come close to the Earth, or come close to the sun, let alone
comets from other solar systems. So this is really one of those extremely rare opportunities to potentially understand sort of that reservoir of materials that form the the basic building blocks of another solar system and ask those questions. You know? How unique is our solar system, or how common is it? And are we the weird ones? Is that solar system the weird one? We won't know that until we start getting more and
more of these objects. And I think what's really exciting is that we do have these powerful telescopes like Vera Rubin and others coming online where we're gonna be able to see and detect some of these objects way earlier out. You know, this is the third one we've known about, but it's certainly not the third one that's ever come through our solar system.
But having the opportunity to detect them in advance and seeing the results of and the the power of having gotten these observations and working together across all these missions, and across the ground based telescope network to study it, I think that we're gonna see this more and more and more, and that's something exciting. We're on the precipice of understanding other solar systems in a way that we
weren't really expecting to do. Right? We're trying to understand you know, build a bigger telescope so that we can, see further further and further out. But this is an opportunity to make sure we're also ready to see the things that come come into our backyard and actually get to play with a little bit. I'd like to thank Tracy and Michelle for talking to me for this episode of the
Physics World Stories podcast. Don't forget that physicsworld.com is an excellent resource for everything to sate your desire for the latest and greatest of astronomy and space news. I hope 2026 has been treating you well so far, and we'll be back next month with something else from this wonderful world of physics. And thank you very much for listening.