3I/ATLAS: The third interstellar object ever found

Sarah Al-Ahmed: A rare cometary visitor from beyond our solar system. This week on Planetary Radio, I'm Sarah Al-Ahmed of The Planetary Society. With more of the human adventure across our solar system and beyond. We've spotted only three known interstellar objects, cometary bodies passing briefly through our solar system after long journeys between the stars. Bryce Bolin, a research scientist at Eureka Scientific Incorporated, has been part of the scientific teams that have studied all three of these objects. He joins us to share the story of 3I/ATLAS, the newest interstellar object, and how studying these fleeting visitors helps us learn about planetary systems beyond our own. 

Later in the show, Bruce Betts, our chief scientist, drops by for What's Up. He'll tell us about Comet Interceptor, a mission from the European Space Agency and the Japanese Aerospace Exploration Agency designed to wait patiently in space and then chase down a pristine comet or maybe even one of these interstellar wanderers. If you love Planetary Radio and want to stay informed about the latest space discoveries, make sure you hit that subscribe button on your favorite podcasting platform. By subscribing, you'll never miss an episode filled with new and awe-inspiring ways to know the cosmos and our place within it. 

Before we dive in, I want to take a moment to ask for your help with an upcoming episode of Planetary Radio. Right now, I'm putting together a show focused on how cuts to grant funding are impacting students, researchers, and faculty in the space science community. While these budget decisions are happening in the United States, their effects are being felt around the world, especially by people that come to the United States to study or conduct research in space science and exploration. If you've been affected by these funding cuts, whether you're facing uncertainty, loss support, or you've seen your work disrupted, I'd like to hear your story. You're welcome to share a one-minute audio or video clip describing your experience, which I may share on the show. You can introduce yourself or stay completely anonymous if you prefer. Just email your clip to [email protected]. Your story matters, and together we can help others understand the real human impact behind these decisions. 

Now for our main topic of the day, 3I/ATLAS. For only the third time in history, astronomers have identified a macroscopic object from another star system traveling through our cosmic neighborhood. These rare visitors that are called interstellar objects aren't born around our sun, but they're flung out of distant planetary systems before finding their way to us. The first one, 1I/'Oumuamua, arrived in 2017. I will never forget how exciting that was. The second one, 2I//Borisov followed in 2019. Now we welcome 3I/ATLAS, discovered on July 1st, 2025, by the Asteroid Terrestrial-impact Last Alert system or ATLAS. This new interstellar comet is visibly active, trailing dust as it flies into our solar system. Its reddish hue and extended coma tell us a complex story, one that hints at how it may differ from its predecessors. 3I/ATLAS is moving fast and growing more active as it nears the sun. 

So observers all around the world are trying to get a glimpse of it. To learn more, I spoke with Dr. Bryce Bolin, a research scientist at Eureka Scientific Incorporated, and the lead author on a new study describing the discovery and the physical characteristics of this interstellar comet. Bryce is one of only a few astronomers in the world who have studied all three known interstellar objects. His early work on 'Oumuamua helped characterize its elongated cigar-like shape. He later co-authored papers on 2I//Borisov, including studies on its rotation and chemical composition. 

Now with 3I/ATLAS, he and his team are back at the forefront. Their paper titled Interstellar Comet 3I/ATLAS Discovery and Physical Description was published on July 18th, 2025, in the Monthly Notices of the Royal Astronomical Society Letters. During the conversation, you're going to hear him refer to some of the images that are in that paper. I'm going to link to the images that he references, along with the actual paper, on this web page for this episode of Planetary Radio. You can find that at planetary.org/radio. Hey Bryce, thanks for joining me.

Bryce Bolin: Hey, it's great to be here. Thank you for having me.

Sarah Al-Ahmed: So you've had this really rare opportunity, which is that you've gotten to observe all three known interstellar objects during your career. What initially drew you to studying small bodies and then ultimately these interstellar objects?

Bryce Bolin: Yeah, it's kind of a strange, I don't know, I guess you could say it's a calling because I originally started out in physics, not wanting to do anything to do with astronomy. I was going to do high energy physics, particle physics at the time when I was finishing up my undergrad, CERN was starting to pop off with the Large Hadron Collider and that was the big excitement thinking, oh yeah, we're going to see all these crazy new particles with the LHC and this is relevant for why I got to astronomy. I went to grad school, didn't go to grad school for high-energy physics because it was the height of the financial meltdown of 2008, and it was very hard to get into grad school. I barely got in, but where I wound up was not focused at all on high-energy physics, which was a disappointment for me. 

So I went to a school in Florida. Florida has this weird rule. Only one school in the state university system can have an astronomy program, but they had a program that was specialized in planetary science. So I was like, okay, I'm not doing the particle physics stuff, so why not try planets? I didn't even know that was a topic you could study. So I was unofficially working with some of the planetary science faculty there, and through that connection, I got to go to France to a planetary science conference, and it was there that I actually got set up with my first astronomy job. I met someone who was an associate with people at where I did my master's, who just happened to be looking for a research assistant for this new project that they were building in Hawaii called Pan-STARRS. And Pan-STARRS is this all-sky survey on Mt. Haleakalā that looks for asteroids, and it was also doing an all-sky survey, like early Rubin Observatory kind of stuff to look at galaxies and the other stars and other phenomenon. 

But the person who I linked up with for this job was specialized in asteroids, and it also turns out this goes well back to the grad school days. This person was also a former particle physicist, so it was really the connection with particle physics, because I didn't want to do asteroids and comets, because I thought they were boring. Like, oh, they're rocks, right? So what got me into it was really this particle physics connection with Robert Jedicke at the University of Hawaii where he came up with a way to parameterize the problem of using observations of asteroids and calculating the observational selection effects that go into the observations, which gives you an estimate of the inherent population before you have all these observational selection effects go into play. 

They do that in particle physics, and he found a way to apply this to asteroid observations from ground-based telescopes, and it just, wow, it was so fascinating for me, and I was at the University of Hawaii working for three years. Actually, I was also working with Larry Denneau, who is the guy who discovered the 3I/ATLAS, the third interstellar object. I was working almost every day with Larry Denneau and Robert Jedicke, and others at the University of Hawaii, doing the discovery of near-Earth asteroids, potentially dangerous asteroids if they were to hit the earth.

Sarah Al-Ahmed: So how did you end up becoming parts of the teams that did the first observations on the first two interstellar objects?

Bryce Bolin: That's an interesting story. That was also an accident kind of thing. After Hawaii, I went to France where I did my PhD, which was another three years, and then when I finished that, I wound up at the University of Washington, which is where a lot of the Rubin Observatory work that is being done, the director Zeljko Ivezic is a professor there, the lead of the solar system processing teams. Mario Jurić is also a professor there, and Mario was my supervisor while I was there and at that time, the idea was that we were going to develop all these interesting tools to study asteroids at the Rubin Observatory and then when Rubin comes on to use those tools to study the asteroids, but while I was there, there was also an opportunity to use this telescope in Apache Point called the ARC, the Astrophysical Research Consortium, three and a half meter telescope. 

Just on a side note, Apache Point is also where the Sloan Digital Sky Survey is hosted, and so there's a lot of collaboration between University of Washington Sloan Digital Sky Survey. So they have access to this three-and-a-half-meter there, and it was right after I started in the fall of 2017 at the University of Washington that this 'Oumuamua first interstellar object, was just discovered. And at the time I'd never really, I'd worked on survey detections of asteroids, and my PhD was on more dynamics of asteroids in the main belt. I'd never really done a case study focused on one object study with ground-based telescopes kind of project before, but I had just this weird feeling. It's like, wow, this is really cool. When the announcement of 'Oumuamua, the discovery of 'Oumuamua, came out, I couldn't believe it because I discussed interstellar objects with Robert Jedicke at the University of Hawaii. 

He was one of the first people to study these things. He did the theoretical calculations to estimate how often you would see one based on actual data from Pan-STARRS, using his expertise in synthesizing survey data to come up with an estimate of what the expected population is, but this is one real bonafide thing. I could hardly believe it had eccentricity of 1.17 or 1.19 might have to correct me there, but it was significantly above one. And for an asteroid to be bound to the sun, it has to have an eccentricity less than one. And we've seen comets that are kind of weakly bound just a little bit above one like hyperbolic 1.01, 1.05, but they usually have an encounter with a gas giant, and so we know they come from our solar system they were just perturbed, which made them a little bit hyperbolic, but seeing something with a 1.2, like 20% higher than one, that was just mind blowing. 

It was really startling, and it was like, wow, we talked about these things, and there were some estimates that it would take five, 10 years with Pan-STARRS and full power mode to see these things, but now we're actually seeing one. We see one, it's on our doorstep, it's here, and it's just like, wow, I just couldn't believe it. A body that formed into another star system coming into our system, it just was absolutely incredible. And we didn't know at the time it was an asteroid or a comet, is it like something we would see from the outer part of our solar system, versus something that's formed maybe more closer to the terrestrial planets or their equivalent in exoplanetary systems. So we didn't know it was a huge mystery box. So I talked about it with Rob, and I thought, are people looking to study this thing? 

He's like, "Yeah, well, they're trying to hop on all the telescopes to look at it." And I was like, "All right." So I went home. I remember lying down in the afternoon to take a nap, and I just couldn't get it out of my mind. I was like, wow, this an interstellar object. This is pretty incredible. So I wrote to the director or the assistant director of the Apache Point, who was a professor at the University of Washington, to say, "Hey, do y'all have any telescopes that we could use to study these things? Seems like it would be pretty important to try and study this object. It seems pretty interesting." And he was like, "Yeah, well, you can maybe try to work with Apache 3.5 meter. I think we can probably get you some time for that, but you're going to have to work with this team from John Hopkins University." And it turns out one of the members of the team was the professor I worked with at University of Central Florida. His name is Yan Fernandez, and the other guy was this guy named Casey Lisse, who was a longtime collaborator of Yan Fernandez studying comets. And it was Hal Weaver, senior professor at I think Duke University and studying comets. So we had collaborated and observed on observing the first interstellar object [inaudible 00:12:53] with this three-and-half-meter telescope, and the conditions were pretty good. We got pretty good data, and we were the first ones to assemble a complete light curve of this object and to see it over its full eight-hour rotation to have this very large light curve amplitude of about two magnitudes, where we were able to estimate the rotation period and the parameters of the light curve. It implies that this very elongated shape, very large axial ratio, our calculations were six to one because we came up with a way to kind of correct for geometric effects and shadowing effects on the asteroid. 

You would basically, if you assume without those effects, you'd get an axial ratio of 10 to one, but we were more like six to one after you do this correction. So it was so bizarre that not only was it the first one coming from another star also had some peculiar properties we put out. We constructed this paper quite nicely, and it was pretty, I think, well-received. So that was my first observational paper, and it was not bad. We talked about these things before, but we never thought, oh, it could be real. It was so surreal.

Sarah Al-Ahmed: But really though, I mean we know that these objects must exist and that they must come through our solar system at some point, but we're only now beginning to have the technologies to discover these things, and I think we're about to potentially discover a lot more because of tools like the Vera Rubin Observatory, just objectively, even someone who has no understanding of what's going on in planetary science. I think this is one of those stories that just lights the imagination on fire. This, as you said, is one of our only opportunities to be able to really observe material coming into our solar system from somewhere else entirely, and I think people are right to be really excited about this.

Bryce Bolin: Yeah. It's just mind-blowing. You have all these theories about how many of these things exist out there and what their properties could be like, but the difference between theory and what we actually observe can be quite large. So for 'Oumuamua, we think it's most likely a comet because it has large non-gravitational perturbations like a comet. Have you heard the Queen song "Don't Stop Me Now"? But there's a really great line. There's a lot of astronomical references in that song, by the way. Talks something about I'm on a rocket ship to Mars or something, or-

Sarah Al-Ahmed: On a collision course, defy the laws of gravity.

Bryce Bolin: So that line defying the laws of gravity is very scientifically based because astronomers in the 19th century were observing Halley's Comet, and they noticed that its predicted position from gravity only was very different from its true position in the sky. When they ran the calculations using Newton's laws and Kepler's laws to figure out where the comet would arrive next, it was off, and they were like, oh, it's defying the laws of gravity. They didn't know why exactly. Right? But that line defying the laws of gravity that was in the Queen song comes from the study of Halley's Comet. It comes from the observation using a model where you only have gravity, only the laws of gravity is not sufficient to explain the full physics of what's going on with the comet, which results in it having a position very different from where you would predict using only the laws of gravity. 

So defying the laws of gravity is what 'Oumuamua did as well. Comets defy the laws of gravity, and they emit gases, which has a non-negligible momentum on their impulse, on their trajectory. And so 'Oumuamua did this, and so there's some interesting discussion about that, but that kind of let's say eased some tension there because we weren't sure if 'Oumuamua was an asteroid or a comet. And because we think that comets outnumbered the asteroids by quite a lot in our star system and star systems extrasolar we think they should as well. You'd think that what's going to be ejected into space and seen by some other people in the star system somewhere else in the galaxy is going to be a comet, but we didn't know. 

And so when 'Oumuamua was defying the laws of gravity, that kind of gave us a sigh of relief. The other two interstellar objects, 2I//Borisov, 3I/ATLAS, are clearly comets. They have a very active appearance, a tail, and some peculiar quality. You see, with that, they're both very different from each other in that respect, but they are comets. So it seems that so far all the interstellar objects they're comet-like material, which kind of chucks with our expectations of planet formation and what we think the material around other stars should be like, but we're in exciting times. We could see something astroidal at some point, and because these are comets, they are basically hiding the nuclei of 2I and 3I are hiding inside this envelope of dust.

Sarah Al-Ahmed: What kind of things have you been studying during the limited amount of time that we've known about the subject?

Bryce Bolin: Yeah, so for 3I/ATLAS, our first look at it was using broadband colors, getting optical wavelength colors. Also observed it with Keck, Keck Telescope. We got near infrared colors and near infrared spectra. We want to understand the surface properties, well, not really the surface properties, [inaudible 00:18:32], but kind of the bulk like scattering cross-section properties as a function of wavelength. And that tells us a number of things. We can see possibly the emission of cometary gases. In the visible in the near UV, you emit gases like cyanogen and diatomic carbon, triatomic carbon, and this can be indicative of the devolatilization of the comet. You are producing these molecules that are first originating as ices in the comet, and then the heat from the sun is causing the ices to sublimate, and then they're undergoing these complex reactions while they're in the coma of the comet, and breaking down one of those products can be cyanogen as well as the triatomic carbon. 

We're going to be getting some James Webb observations of these objects. I'm not formally a part of that team, but James Webb is going to be able to observe the comet in wavelengths well beyond the visible and near infrared. They go into the wavelengths into the three to five micron range, where we can start to see the emission of cometary gases directly from the ball to species that we see are most common among comets in our solar systems, such as water, carbon dioxide, and carbon monoxide. And so we can do the direct detection of these gases using the James Webb. With Borisov, the second interstellar object we saw, we did detect carbon monoxide using ground-based AMOE observations as well as the Hubble Space Telescope using the near UV instrumentation on the Hubble Space Telescope. But now we have James Webb with Borisov, and we did not have James Webb, but now we have James Webb, and it has this great capability to study the [inaudible 00:20:14] of comets. So that's going to be potentially pretty huge, and they should be happening in a few days. We'll see if they get the comet.

Sarah Al-Ahmed: As with anything that's moving within our solar system, it's always tricky at a distance to try to actually capture that thing. But I mean, those observations are going to be really wild. I mean, I don't know what the images themselves are going to look like, but the spectra of this object from a completely different system could be pivotal, especially given that we don't know where this thing came from. But some of other things I've seen online suggest that this object could be much older than even things in our own solar system. What do we know about where this object came from and potentially its origins based on that?

Bryce Bolin: Well, this is a very interesting topic and something that I've thought a bit about, what people are doing with interstellar objects, 1I, 2I, 3Is. They're basically estimating their kinematic ages in the galaxy, basically how, let's say, heated up or excited, the orbits of these objects are, and the timescale in which it takes for them to get to this level of excitation. And they're saying that that can occur; it would take billions of years for that to occur. If they were more recent ejections from the star systems, they would have orbits that aren't as heated up with respect to the galaxy. But my understanding is that this is actually pretty difficult to do. I mean, I'm not a galactic dynamics expert. With the discovery of 'Oumuamua, it became an open question: okay, we're studying hyperbolic orbit with respect to the sun, but what is this thing doing out there in the galaxy? 

And it turns out that the galaxy is, well, I think everyone knows this, it's quite complicated. It's a lot more difficult problem than asteroids orbiting our sun in the sense that it's not like you have all the stars in the galaxy orbiting Sagittarius a star or a supermassive black hole. I mean, they do in a way, but the gravitational potential is quite variable in the galaxy because it's huge, and it can vary quite a bit because you have irregularities, you have molecular clouds, you have spiral arms, we have stellar clusters. And so the way that this affects the orbits of stars and interstellar objects that they float around in the galaxy is quite difficult to understand. So when you're talking about things that are old, I think I saw some papers, some results saying, "Oh, these are billions of years old object." One orbit of the galaxy is like what, 500,000 years for the sun? 

And so, just in that time period, you can encounter spiral arms and all sorts of things that can really throw off your trajectory of the galaxy. And so I think it's really hard to say anything more than that past maybe one or two galactic orbits. So I think people who are trying to backwards integrate these orbits to see, okay, when they were close to some star, they must have come from some star. It's a good idea. It's a first-order of curiosity thing to try and do, but it turns out the dynamics in the galaxy prevent you from doing this accurately.

Sarah Al-Ahmed: Yeah, everything's moving out there, and everything's moving inside our solar system. I do want to say to people though, who might be worried about this, that this new object 3I/ATLAS is not going to come close enough to earth, that we have to worry about it hitting us even though it was discovered by ATLAS, which predominantly looks for these kinds of things that might be a danger to us. Do we have a general idea of the way that this thing might be passing through our solar system?

Bryce Bolin: Yeah. So I have a picture of the orbit of this object. So this is our paper that was published in the Monthly Notices of the Royal Astronomical Society, where we described the orbit of this object. Now, this is not the best orbital diagram in the world. I'm sure there is much more fancy ones out there that are animated and so on, but this is showing the orbits of planets in our solar system. The orbit of 3I/ATLAS is this black line right here, and Jupiter is this khaki green line, and Mars is red, and the Earth is green, and Venus is blue, and Mercury is pink. So this was at the time the object was discovered on July 1st of this year. So the Earth is going to be rotating counterclockwise like this, whereas 3I/ATLAS is going to be going along this trajectory in this kind of bottom-to-top direction right here. 

So what's going to happen is 3I/ATLAS is going this direction, but the Earth is going to be rotating around this direction right here. So as you can see, it's 3I/ATLAS is actually going to get quite close to the orbit of Mars. So it could actually pass pretty close to Mars, which could be an interesting opportunity for spacecraft in Mars to try and observe this thing. I'm a fan of it. I think they should give it a try. 3I/ATLAS will be observable up until the end of August, early September-ish, and then it goes into solar conjunction because as it's getting closer to the sun, the Earth is going to be rotating around the Sun, and the Sun's at the center of this plot right here. The sun is going to be blocking the view of 3I/ATLAS from the Earth. So when it passes through perihelion, it will be in what we call solar conjunction. But when the earth gets around the other side of the sun, 3I/ATLAS will be going here. So we'll be able to see it again after it goes through perihelion.

Sarah Al-Ahmed: And for people who are listening to this, since you can't see the plot, I will be sharing the paper and an image of this plot on the web page for this episode at planetary.org/radio, so you can see. But it is very clear by looking at this diagram that this thing is on a wild trajectory, that it's just going to careen right out of the solar system. But also, I think what you've pointed out about the fact that we are limited in our ability and time to see this object from Earth is really interesting. And I love the idea of some spacecraft around Mars or maybe even, I don't know, the JUICE mission or other ones that are out there right now, maybe even Psyche to maybe if they can turn their cameras on this thing and see if they can get a look at it during the times that we can't observe,

Bryce Bolin: That would be really interesting.

Sarah Al-Ahmed: And since there's so much stuff coming out of this, it's got to be hard to figure out exactly what size the nucleus is on this thing. Do we have any size estimates?

Bryce Bolin: So there's two ways of doing that. So at the present brightness of the comet, it's about 18th magnitude, 17th magnitude, and located about three or four astronomical units from the sun. Kind of can give us an estimate of the nucleus where we can compare that to other interstellar objects when they were observed at route the same time, they're not really the same because they have different amounts of dust in the proximity of the sun. But at the similar distance from the sun, 2I//Borisov had a brightness that was a couple of magnitudes fainter, and we didn't detect the nucleus of Borisov; it was too small, but we think it's somewhere in the order of 500 meters, a few hundred meters. So when you have two orders of magnitude difference, that implies a size of about a kilometer for a 3I/ATLAS. The other way of doing this is with high-resolution imaging. 

So David Jewitt at the University of California Los Angeles observed this object with the Hubble Space Telescope. The great thing about Hubble is that you have near-diffraction-limited observations from space that aren't affected by the smearing of the Earth's atmosphere. So from the ground, typical seeing is about one arc second, but in space from Hubble, the resolution is about 0.04 arc seconds. So we're talking much, much finer resolution there. Now, the reason why that's important for comets is because comets are resolved objects. So, a point source viewed from the ground with an arc second to resolution is going to be one arc second. When viewed from space, it's going to be the size is going to be 0.04 arc seconds, but for comets, because of their extended sources, the angular size from the ground for this case of 3I/ATLAS is about two arc seconds wide. 

And in space, it's also two arc seconds wide. The key differences is in the nucleus region, because the nucleus is unresolved, the tail and the coma of the comet are resolved, but the nucleus is unresolved. So when you look at the comet from the ground, you're seeing a mishmash of the nucleus and the unresolved nucleus with the resolved tail. So they're combined on top of each other, and the scale of the mishmash for the comet nucleus is about an arc second wide. But in space, the tail is two arc seconds wide because it's a resolved object, but the mishmash with the nucleus is much, much smaller. And the cross-sectional area difference between 0.04 arc seconds from space versus one arc second from the ground is a factor of 600. 

So what that lets you do is lets you observe much closer in the nucleus to the comet by a factor of about 600, and the reason why that's important is because you can basically measure the light from the nucleus with much less contamination from the dust, and it's a factor of 600 difference level in contamination. So when you're looking at a comet, it's like looking at a fuzzy cat. Have you ever seen a big fluffy cat after it goes to the groomer and it gets a buzz cut?

Sarah Al-Ahmed: Yes.

Bryce Bolin: So it's kind of a similar thing with comets. When I was a kid, we had a Persian cat, and my mom had allergies, so he would have to get a haircut. This big fluffy cat, and you'd get the lion cut, it got a buzz cut. It's a lot smaller. It's way smaller in cross-section. And so using the Hubble Space Telescope to estimate the size of the cap or the comet versus the ground base is a difference between just getting a light haircut, removing just a little bit of the fur from the ground would be like the ground observation. You just give the cat a little bit of a trim here. But when you use the Hubble Space Telescope, you're getting the buzz cut, you're moving a lot of the hair, so you can get a much better estimate of the size of the cat. You need a higher resolution to shave most of the fur off and get a much accurate estimate of the size.

Sarah Al-Ahmed: I'm just never going to think of a Hubble Space Telescope the same way ever again now. Thank you.

Bryce Bolin: Yeah, yeah. It's like the cat groomer of space for cat comets. It's the ultimate space grooming tool.

Sarah Al-Ahmed: We'll be right back with the rest of my interview with Bryce Bolin after the short break.

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Sarah Al-Ahmed: There's a lot of complexity to the way that comet tails behave. What's going on with the tail or tails on this object?

Bryce Bolin: The 3I/ATLAS is quite interesting in the sense that the tail is going in a strange direction. So here is the Hubble data of 2I//Borisov and it has this extended tail that goes in the anti-solar direction. So in this plot, I showed the direction of the sun as well as the direction of the comet in its orbit but the really important one is the direction of the sun. So the sun is going this southeast direction, and the comet tail's in the opposite direction of that. It goes out into space into kind of the northwest. So that's the key idea is that comet dust, when it gets ejected in space, is blown in the direction opposite from the sun due to solar radiation pressure. But curiously, this is not what we see for 3I/ATLAS. So I'll show you my data here. 

There's much better data taken from the Hubble Space Telescope, but this is with a Palomar 200-inch over here. The key thing here is the sun. The sun direction is going off into the northwest direction. Curiously, the tail of this comet, it's blobby and it's preferentially going into the direction of the sun. It's going in the solar direction. So I discussed this in my paper. The interpretation is that you have large dust particles that are being ejected into space, and they could be larger, large-ish. They could be say hundreds of microns across. They're too heavy due to their size. They're too heavy to be blown in the opposite direction from solar radiation pressure. So I think what's happening is that the sun-facing side of the comet is heating up, and that is where the [inaudible 00:34:37] are coming off, and the solar wind is blowing in the opposite direction, but the dust particles. 

They're leaving the comet nucleus, they're going into space towards the direction of the sun, but the solar radiation pressure isn't strong enough to blow them around and go into the opposite direction again. So it's giving the comet a little bit of a distended directionality towards the sun's direction. And the Hubble data shows this really well because the Hubble data are really, really nicely resolved. And based on this information in my paper, we think that dust is leaving the comet at very slow speed, about a meter per second, very, very low velocity. It seems to suggest that maybe the comet is weakly active right now. It's a little bit further from the sun. It's starting to become active, it's starting to become more active. It's not something like whoa, unexplainable, but it's just not the typical thing that we see for a comet.

Sarah Al-Ahmed: And all the more reason why we need to get as many observations of this thing while we can before it goes behind the sun from our perspective, do you have any recommendations for people who might want to pull out their telescopes or maybe if they're asteroid hunters, what can they do to try and help in the effort to understand this object?

Bryce Bolin: Yeah, so I would recommend that they try to observe the comets in the morning hours before it goes into the solar conjunction. It'll be available in the evening around end of August, as well as when it comes out of solar conjunction early December or mid mid-November. It's predicted to be quite bright around 12th magnitude. So that's within the range of smaller telescopes. It might be difficult to see with the human eye if you're looking through an eyepiece, but if you have a CCD camera or a CMOS camera, I think it should be quite doable. I'm looking for ways to collaborate with the community. We're putting together an observing campaign for this. Some people contacted me who have interest in working and studying this object. So if any listeners or people out there want to get involved, don't be shy. You can reach out to me and let me know, and we can see what we can do.

Sarah Al-Ahmed: Yeah, we only have limited time on this one, but they seemingly happen to come through our solar system on enough of a regular cadence that we're getting these opportunities every few years. And now with the Rubin Observatory and its ability to find objects, I was speaking with Stephanie Deppe from their communications team just a few weeks ago, and we were having this conversation literally days before this object was found. So I think people are going to have way more opportunities. But I mean, what does that feel like to you as someone who's stumbled or random walked your way into a career full of these objects?

Bryce Bolin: So I think we're living in some really exciting times here, and it's interesting that 3I/ATLAS was discovered by a half-meter telescope in Chile, not more than 10 miles away from where Rubin Observatory is. So I think it's a pretty interesting sign here that things are accelerating towards more discovery of these types of objects. We had a little bit of a wait there because between the first interstellar object and second interstellar object, we only had a two-year period, and we had to wait six, seven years for this other one right here, almost. 

I think with the Rubin Observatory, we can expect to find more, increase the search volume for these things, and it's going to be a wild time because we have to figure out how we're going to study these things in the Rubin era, because Rubin is going to be detecting them much fainter. So 3I/ATLAS is very bright, its seven to eight feet magnitude is found by half-meter telescope by the ATLAS telescope, but Rubin is a six-meter equivalent telescope and detecting things much fainter than that, detecting things 23, 24th magnitude, that is going to be well outside the range of most telescopes. 

So far with this telescope, I've characterized it with, I use Keck Telescope, which 10-meter telescope, but a lot of the characterization so far has come from smaller telescopes, even for eight-meter telescope, 23, 24th magnitude object is going to be difficult to characterize. They'll require photometry, spectroscopy will be basically almost impossible. I think the majority will have to be getting photometry from the ground and then relying on space-based telescopes like James Webb to get the spectra, which is going to make James Webb more in demand for studying these types of objects. There'll be very interesting times. I think we'll see more discoveries, and I hope that the astronomical community will respond by accommodating more requests for the characterization of these objects. And I mean looking very far to the future with the ELTs, like the Extremely Large Telescope, Rubin is projected to have a 10-year operational lifetime, but if there's some overlap between the Extremely Large Telescopes, and Rubin will be great for the characterization of these objects.

Sarah Al-Ahmed: Between ELT and the Magellan Telescope, we spoke about a few weeks ago. There's so many cool opportunities that are coming up, and I love that you've gotten to be at the crux of this new form of discovery. These objects are so cool and can teach us so much, and potentially someday we'll be able to rendezvous with these and learn even more, but that's even further in the future.

Bryce Bolin: So that's the dream. There's a mission called the Comet Interceptor, which has that as a goal. I don't know exactly when they're going to go into space, when they're going to launch, but I think it's within three to four years. But I'm thinking it's going to accelerate because of the discovery of 3I. I think it's going to accelerate that process, and I think there will be overlap between Comet Interceptor and Rubin Observatory. So I think you can expect... No guarantees, of course, but I think it's very realistic that we will have a Comet Interceptor rendezvous with interstellar object within the lifetime of Rubin. I think that's very viable.

Sarah Al-Ahmed: Well, sometime when I bring you back on to talk about the next interstellar object you're studying, we'll see whether or not that's true. We'll play this clip and see what happens.

Bryce Bolin: It could be very soon. It could be two months from now. You never know. It could be a year from now, it could be five years from now, but I think we can expect 4I the fourth interstellar object to be in the not too distant future, I would say within a year or so.

Sarah Al-Ahmed: Awesome. Well, I want to thank you for taking the time to do this. I know that you're currently at a Rubin workshop doing a bunch of work, but also I understand that after this object was detected, you spent something like 35 hours straight working on this, and that is some dedication. I've had some long observing nights, but that is a long time.

Bryce Bolin: Yeah. Oh my gosh. Yeah, that was wild and nerd alert here. I was playing Magic: The Gathering when I saw in the email that this was starting to come out. And so I was already organizing, making phone calls to try an observing effort to get telescope time on this thing. So we got time on it very quickly. July second, when we got time on it was discovered on July 1st, so we got it on July 2nd with the Kottamia telescope near Cairo. And July 3rd we observed it with a Palomar 200 inch and July 6th we observed it with the Apache to point a three and a half meter. A day later, we submitted our paper. And so yeah, we were working around the clock on this, and not only my paper is about photometry, but there's a student I worked with at Caltech by the name of Matthew Beiley. 

He was doing this spectroscopy, so we got photometry from imaging as well as spectroscopy, and so I was working on the photometry. He was working on the spectroscopy, and he has a paper, well, it's a research note of the American Astronomical Society, and he was working on a peer review publication in WAS Journals to be submitted soon. But yeah, that was a very intense few days there. I was at one point sleeping for just a few hours on some chair in the office there. But yeah, it was a race in these cases, it is with the Interstellar objects. 

The 'Oumuamua was a mad dash as well. When the discovery was made, it was around Halloween of 2017, and we jumped on it and got observations of it in early November, and submitted our paper a week later, the second week of November and posted it on the archive. And yeah, it's just every astronomer in the world who studies asteroids and comets is going to want to look at this thing. There's going to be big telescopes, grand Telescope Canarias is one that's 10-meter telescope in the Canary Islands. You have the Keck Telescope, you've got Gemini North, Gemini South, these eight-meter telescopes, you have the VLT. There's a lot of really good observers out there who want to pounce on these things immediately. And so if you want to survive in this kind of environment, you have to be very quick.

Sarah Al-Ahmed: But seriously, may the coffee and the Magic: The Gathering be with you as you do all of this work. I think a lot of people sometimes think that astronomy is really chill, very long scales between discoveries, especially in planetary science. It can be a long time before you can go back to another world and get a whole new set of data, but there are realms of planetary science and astronomy that are really, you make a discovery and everyone's on it in a hot second, and you are right at the crux of that. So I appreciate you putting in all the work because I know how tiring that can be. But here we are learning all these amazing things about the third interstellar object we've ever discovered, ever. It's crazy that we can even say that.

Bryce Bolin: Yeah, well, it's just really exciting, and it's like, yeah, it's tiring, right? But it's the excitement and the adrenaline rush just keeps you going, and a lot of excitement to be out there and try to be the first one to publish something on this. I don't know, I just couldn't stop until, just like the first interstellar object I was telling you about how I wanted to take a nap, but I couldn't until I did something about it. It's kind of similar for me. I just want to figure it out, and it's more exciting if you're the first person.

Sarah Al-Ahmed: For a just brief moment there, you and the people on your team and the people observing this object around the world were the only people to know something deeper about an object that may have been traveling through our galaxy for ages. It's a fascinating thing to think about and a special place to be, and that you have a really cool career, and I really appreciate you taking the time to come on and share more about this, and seriously, when 4I happens, I'm calling you.

Bryce Bolin: Oh, sure thing.

Sarah Al-Ahmed: Well, thanks so much, Bryce.

Bryce Bolin: Oh, thank you.

Sarah Al-Ahmed: Now it's time for What's Up with Dr. Bruce Betts, our chief scientist at The Planetary Society. Hey Bruce.

Bruce Betts: Hey there, Sarah.

Sarah Al-Ahmed: Right into the nerdy element.

Bruce Betts: Hey, I'm ready for ready to go. Let's do a show. Okay, I'm done.

Sarah Al-Ahmed: Nerd adjacent. So I was talking with our guest this week, Bryce, and he told me that the moment that he learned that this new interstellar comet existed, he was literally in the middle of a game of Magic: The Gathering. I love that so much.

Bruce Betts: What action did he take?

Sarah Al-Ahmed: Who knows? I mean, I'm sure as soon as he found out, he just flipped the table.

Bruce Betts: Yeah. Flip the table. People love it when you do that.

Sarah Al-Ahmed: But it was the perfect opportunity. I've been playing that game since high school, and it was funny to me because on the day that we were having that conversation, it was literally the release of the first fully space set of Magic: The Gathering Edge of Eternities, excluding Unfinity and all of the commander decks that are space themed. So we got to have a fun nerdy conversation about that, and I wanted to ask, have you ever played Magic: The Gathering before?

Bruce Betts: I did, but it was many, many years ago with my sons when they were not adults, and we did play, and it was fun, but I haven't stuck with it like you have, obviously.

Sarah Al-Ahmed: Wow, that's a really great way to teach math skills to the younglings. I mean, there's a lot of math there. Man, the number of counters and tokens and compounding factors.

Bruce Betts: I see. Magically gathering with compounding interest.

Sarah Al-Ahmed: But if you are a fan of space games and you haven't played that card game before, I just want to shout out the beautiful space art on those cards. It's absolutely phenomenal, but another thing that came up in my conversation with Bryce was the European Space Agency's Comet Interceptor mission, and we didn't get to talk a whole lot about it in our conversation. Clearly, it's not launched yet; it's launching in 2029. But since I have you here, can you tell us a little bit about their mission?

Bruce Betts: Sure. It's a really cool concept because they're basically going to try in 2029 to launch a mission that will go out and just hang out until a comet's coming in that hasn't been to the inner solar system before. So it's coming from way out in the [inaudible 00:48:22] cloud, and they have a spacecraft ready to go, and then when they find one that they can reach with the fuel they've got, they go after it. So they put it at Earth-Sun L2, so a million and a half kilometers away from Earth from the sun, and it hangs out there in some type of halo orbit, probably. And then it goes off to try to encounter either a long-period comet or one of our interstellar visitors, which would be even trickier since there are fewer of them, but either would be super cool and super different since even the long-period comets have never presumably been altered by coming by the sun yet. 

So it gives a new opportunity. So it's a neat mission, and they actually even have three spacecraft, although they all travel as one until they get closer to the object. They've got a couple others besides the main one to do observations from other angles, and they will be visiting something new, whether it's from outside the solar system or just way out into the solar system, and I should say it's ESA in collaboration with JAXA, the Japanese Space Agency who's providing portions of it as well. 

So they basically have a good flyby type spacecraft, and they have the wherewithal to put it out there without an active target when they launch. And that actually will be very beneficial for trying to get to one of these things that there's no way we could just... Well, there's no way, but there's no current technology easily done way to go hunt them once they come flying through, and you've found them. Also, we find things farther out now as the telescopes and the search gets better, so there's more time to go after these things, either type of object than there ever was before. Okay, shall we move into a [inaudible 00:50:18].

Sarah Al-Ahmed: Let's do it.

Bruce Betts: Lunar football one, a very amusing concept for a game that would be impossible to organize. Two, a nickname for the Apollo Lunar Rock 61016, which also has the nickname Big Muley, which, oddly enough, is the more official nickname. And Big Muley is the largest single rock and the most massive single rock returned by the Apollo astronauts, and it is roughly the size of an NFL football.

Sarah Al-Ahmed: Wow.

Bruce Betts: Lunar football, it is 11.7 kilograms, which on Earth is 26 pounds, and one-sixth of that on the moon. It's a thing. I'll also mention the next two in size. We've got Great Scott and Big Bertha.

Sarah Al-Ahmed: Great Scott.

Bruce Betts: Great Scott, which, presumably, I assume it was named after Dave Scott, the Apollo 15 astronaut. Big Bertha is just a thing. Oh, I should say Muley, it was named after someone with a longer name, abbreviated to that, who is leading some of the geology activities on Apollo 16 and 17. Muley is hanging out with most of the lunar rocks in the curatorial facility at NASA Johnson Space Center, being kept all happy and pristine. I mean, as much as you can, so that researchers can keep applying new technologies to studying these things.

Sarah Al-Ahmed: I've seen some smaller moon rocks, but just being that close to a piece of the moon, I mean, I know we get little pieces of the moon every now and again coming in as lunar meteorites and things like that, but it hits different when you're right next to one of those Apollo rocks.

Bruce Betts: Yeah, it's pretty trippy. A little-known fact: I did infrared spectroscopy of some lunar regolith way back in the past, so I was hanging out with lunar dust. That's what made me so crazy. All right, everybody, go out there, look up at the night sky, and think about gel cats, whatever that is. Thank you and good night.

Sarah Al-Ahmed: We've reached the end of this week's episode of Planetary Radio, but we'll be back next week with even more space science and exploration. If you love the show, you can get Planetary Radio T-shirts at planetary.org/shop, along with lots of other cool spacey merchandise. Help others discover the passion, beauty, and joy of space science and exploration by leaving your review or a rating on platforms like Apple Podcasts and Spotify. Your feedback not only brightens our day but helps other curious minds find their place in space through Planetary Radio. You can also send us your space thoughts, questions, and poetry at our email [email protected]. Or if you're a Planetary Society member, leave a comment in the Planetary Radio space and our member community app. Planetary Radio is produced by The Planetary Society in Pasadena, California, and is made possible by our members. 

You can us as we work together to support the space science community around the world at planetary.org/join. Mark Hilverda and Rae Paoletta are our associate producers. Casey Dreier is the host of our monthly space policy edition, and Mat Kaplan hosts our monthly book club edition. Andrew Lucas is our audio editor, Josh Doyle composed our theme, which is arranged and performed by Pieter Schlosser. My name is Sarah Al-Ahmed, the host and producer of Planetary Radio, and until next week, ad astra.