#763: Interstellar Comets

Transcript

Fraser Cain: AstronomyCast, Episode 763 Interstellar Comets. Welcome to AstronomyCast, your weekly facts-based journey through the Cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, I’m the Publisher of Universe Today.

With me, as always, is Dr. Pam LeGay, a Senior Scientist for the Planetary Science Institute and the Director of Cosmocosm. Hey Pam, how are you doing?

Dr. Pamela Gay: I am doing well. I figured out roughly our recording schedule for the year, and it looks like Episode 800 is going to either be the last episode of this year, or the first episode of next year.

Fraser Cain: It depends on what happens.

Dr. Pamela Gay: Yeah, we’re so close, and this is Season 19.

Fraser Cain: It is Season 19, okay, because I just lost track, I don’t even care anymore what season this is.

Dr. Pamela Gay: Yeah.

Fraser Cain: Yeah.

Dr. Pamela Gay: It’s more than five.

Fraser Cain: Season 19, wow.

Dr. Pamela Gay: And have you seen all the new features that Patreon rolled out last week? So it’s just sort of like, new season, new us, and so I’m super excited. I am working on rolling out all the new features, and wow, I’m going to be busy this week.

Fraser Cain: Yeah, we’ve leaned hard into Patreon for Universe Today. Essentially, I’m pushing all of the content there, all of our RSS feeds, the public feed goes there, the private feed goes there. It makes me a little nervous, but it’s such a better existence.

Since we made the change over to no ads on Universe Today, switching completely supported by Patreon, I’ve just, I’ve never felt calmer. I’m in this sort of monk-like existence where I’m just in this state of eternal bliss, choosing what to do today, as opposed to feeling anxiety and panic over the rise of AI slop and the decreasing amount of ad rates and the brutal search engine optimization mouse wheel and all of that. It’s all just bliss now.

So yeah, if you haven’t already, come support us on Patreon if you want this content. That is the way. Patreon.com slash astronomycast, or patreon.com slash universe today.

Dr. Pamela Gay: Or patreon.com slash CosmoQuestX.

Fraser Cain: Yeah, and so you can support all of that work that we do. And for those of you who already subscribe, I mean, the hope is that we’ll make this an even more valuable experience because we’re just, you know, we’re all in. And then for those of you who are like, I’m on the fence, I don’t know, are there benefits?

Oh, there are benefits and you will appreciate them. So definitely go and check out what we’re doing. Okay, well, during our summer hiatus, the third interstellar object was discovered, Comet 3i Atlas.

So now we have three different interstellar interlopers to compare and contrast. What are we starting to learn about other star systems from this small sample size, and how will our detection get even better? And we will talk about it in a second, but it’s time for our break.

And we’re back. Do you like the timing on this? The discovery of 3i Atlas was July 1st, I think?

Dr. Pamela Gay: It was July 1st, and we had just finished recording our last episode. I don’t think it had quite come out yet. And it was like, we just missed it.

But I mean, what would we have said at that point? There’s a fast moving object that we know has a coma-ish around it.

Fraser Cain: Yeah, it’s out by Jupiter or is out by Saturn.

Dr. Pamela Gay: It was out by Jupiter at that point, yeah.

Fraser Cain: So now it is much closer. Every major telescope, space and ground has been pointed at it. And we are getting, I mean, every week when I do my news update, it’s just like, here’s the latest news on 3i Atlas, and it just gets better and better and better.

So yeah, this has been a fun one. And so we’re just going to plant our flag now and let you know what we know about it and just what we’re learning about interstellar objects and continue this conversation. So I guess, what do we know about 3i Atlas?

Dr. Pamela Gay: All right. So on July 1st, it was recognized that there was something moving at an absurdly high velocity through the outer solar system. And we’re talking at that point, they were trying to figure out exactly what it was, but it was like 60 to 90, depending on which set of images you used.

And when you say 60 to 90, kilometers per second, sorry, units matter. And that is obscenely fast for a solar system object. And in fact, you cannot be tied into our sun at that distance and not be on an escape velocity at that velocity.

Fraser Cain: This is way faster than Oumuamua. This is way faster than Borisov. And yet we are super fortunate that we’re catching it inbound and not outbound.

Dr. Pamela Gay: Yes. And unfortunately, this is the most annoyingly timed comet that ever could exist. If you run one of the simulators that allows you to see, it’s almost straight line, both through the solar system compared to the orbits of Earth, Mars, Jupiter.

There is pretty much a straight line through I3 Atlas, the sun and Earth when it is closest to the sun. So we’re going to be like in the worst of all possible places when it is in the most interesting of all possible places.

Fraser Cain: Right. So perihelion, when it’s going to be experiencing the maximum amount of radiation pressure from the sun, it should have the best tail, should be throwing out as much of its material as we can hope for to get a really good glimpse of what it’s made out of. That is the time when we’re not going to be able to see it.

And then it’s going to be lost in the glare of the sun before and after. And so yeah, it is terrible, terrible timing.

Dr. Pamela Gay: But next Christmas, as we come around the other side of the sun, we should be able to watch it on its way out. It won’t have made it too much further at that point. So unfortunately, the place that would have the absolute best view of this is Mars.

And we just don’t have a big telescope at Mars.

Fraser Cain: We have a pretty good telescope at Mars. So it’s going to be coming within, I forget the exact number, but like in between one and two AU of the sun. So farther than Earth.

So it’s not going to get that close in early October. But it is going to do a flyby of Mars and get within point two AU?

Dr. Pamela Gay: That sounds about right.

Fraser Cain: Of Mars. Yeah. So it’s going to get, it’s going to get very close to Mars.

And we do have a bunch of spacecraft there, including the Mars Reconnaissance Orbiter, which has pretty much the largest telescope that is not in orbit around the Earth or at the, you know, at the LaGrange point. So I think, what is it? I forget the size of the telescope.

Several, several centimeters. Anyway, it’s, it’s relatively large and that’s what gives us those great images of the, of the surface of, of Mars. So it’s going to be able to take some pictures, but you know, does it, is it better to have James Webb take a shot from farther away with dramatically more power?

You know, we use everything. We’ll throw the kitchen sink at it.

Dr. Pamela Gay: Yeah. And, and I mean, the, the sad part is just, we want to see it when, when it’s closest to the sun, because as you said, that’s, that’s when we’re going to have the most outgassing. It’s when it’s having the most outgassing that we can measure its composition the best.

But we’re still getting really good data already because we do have that many meter across James Webb Space Telescope that’s able to capture it in the infrared. And that’s where it’s most interesting right now. And Rubin Observatory is coming online, which is going to allow us to get a study stream of images of it.

And I’m betting that we’re just going to be systematically bouncing back and forth between Gemini says, Hey, we saw JWST says, Hey, we saw, and this is what’s happening right now is director’s discretionary time is getting used on all these different instruments. And one of the most glorious things to, to eat popcorn while watching this summer was the astronomical community on blue sky, which is where they all move to basically responding to the spattering of papers, claiming that it is aliens by just going hard in publicizing their data fast and early. And so irritation is causing people to be motivated to work fast.

And the fact that this is an interstellar object that looks like nothing in our solar system is then spurning us to keep working fast. All right.

Fraser Cain: We’re going to talk about what makes this thing different in a second, but it is time for another break. And we’re back. All right.

So we’ve got all these telescopes. As you said, Gemini, Subaru, James Webb, Hubble Space Telescope, many more grounded space based telescopes have turned on it in different wavelengths. What have we learned so far?

Dr. Pamela Gay: First of all, it does not have the same composition of what we expect of comets in our own solar system. And in our own solar system, we’re usually like starting to worry about things like what are the isotopic ratios of different comets because they’re that similar. Yeah.

Some will have sulfur, some will have there, there are differences, but in the grand scheme of things, our sun brought together gas and dust that was more or less uniform as a function of distance from the sun. And so the differences we’re seeing are just differences of being at a different point in the solar system during formation. Well, this sucker comes from a different star’s cloud that came from a different combination of supernovae giving up their materials to feed into this particular system.

And so what we’re finding is the carbon dioxide to water ratio is eight to one, which is the highest ratio ever seen.

Fraser Cain: And I know that in addition to that, normally you see carbon dioxide and carbon monoxide going hand in hand with their ratios to water and its ratios are not linking up the way comets normally do either.

Dr. Pamela Gay: And so we’re seeing folks saying things, and here I’m going to read a quote from one of the research papers, a low coma water gas abundance may be implied, continuing on, due to inhibited heat penetration into the nucleus, there could be a suppression of water sublimation rate relative to carbon dioxide and carbon monoxide. So we already have the theorists involved saying it’s got a different composition. It’s gone through these different things.

It’s behaving differently. And this is where everyone’s going to have their eyes peeled to watch how it evolves as it passes through the solar system. We already know that we can expect slightly different evolution of a comet that is on its one and only passage through the inner solar system compared to one that’s on its nth of many passages through the solar system.

Well, in this case, we don’t know how long this object has been out between the stars, just sitting there doing things that you do when you’re cold. And there’s different molecular chemistry that we’ve learned happens very, very, very slowly in very, very cold situations. And so we’re going to see the results of these different chemical processes.

Fraser Cain: Do we have a sense of the age of this comet?

Dr. Pamela Gay: So there are folks saying it is old and it could come from the thick disk of the galaxy. I’m waiting for there to be more data. I’m waiting for there to be high resolution spectroscopy and being able to start catching radioisotopes that give us something.

And the reason for that is simple. Its current trajectory demonstrates that it is currently on a vector that when you work it backwards has it coming on a line that carries it out to the thick disk. It’s not confined to the plane of our galaxy.

It’s on a slope. Now, the thing is, there’s a whole lot of stuff between us and the edge of the galaxy, a whole lot of stuff between us and the thick disk. And so, one, assuming its velocity has never been changed by an encounter with some other mass, it could have come from anywhere along that line.

And in order for something to get flinged at one heck of an amazing velocity out of a solar system, it probably underwent some sort of a three-body problem that would have changed its velocity, changed its vector. And we don’t know what it’s encountered since it was jettisoned from its home solar system.

Fraser Cain: Right, right. But, like, space is big and those flybys are uncommon and difficult to coordinate. And so, if it does come from the thick disk, where that makes it interesting is that those are old stars.

Dr. Pamela Gay: Exactly.

Fraser Cain: That would mean that it is many billions of time, many billion years older than the solar system, which is really interesting because we still don’t really understand how the metals came together for earlier generations of stars. And so, you’ve got the universe hurling samples right at us. We just have to catch them, at least with our telescopes, but ideally get samples and bring them home.

Dr. Pamela Gay: Yeah, that’s not happening.

Fraser Cain: I know. I know. I know.

I know. Make a dream. But we will be examining other star systems if we can get our hands on samples.

Dr. Pamela Gay: And this, I think, is further fodder for the idea that it does benefit us to keep the occasional space probe in a parking orbit ready to zip off in this direction or that to run down these objects.

Fraser Cain: Yeah.

Dr. Pamela Gay: And that’s the future I want.

Fraser Cain:  Yeah. Well, I mean, that future is in the works. So, the European Space Agency is working on a mission called the Comet Interceptor.

It originally was expected to launch with Ariel. I don’t know if it’s still on schedule to do that. That was going to be 2028.

It would go to the Earth-Sun L1 Lagrange point and then just loiter. L2. L2.

for either an interesting or cloud comet or, ideally, an interstellar object that is within its fuel capability. And then it will fire its rockets and go and try and make an intercept trajectory to give us close-up pictures, fly through the tail, try to do some kind of spectroscopy on the object itself. That’s still a long way from bringing a sample home, but it’s a great first step.

Imagine if we could get close-up pictures of a comet or asteroid that came from another star system.

Dr. Pamela Gay: Exactly. And there’s nothing to stop us in the future from designing things that may not be bringing the samples home, which has a whole lot of slightly concerning things going on. But if we can start lifting things that carry better scientific suites on board, where they start being able to do chemistry similar to what Curiosity has been capable of doing, we have a future where, as we look at heavy-lift rocket after heavy-lift rocket being under development, we can start imagining heavy-mass ships capable of grabbing a sample and doing in-situ laboratory science.

Fraser Cain: Yeah. I mean, I’ve reported on every version of this. So, I’ve reported on in-situ analysis by probes to places like Enceladus.

And it’s kind of the same technology, that you fly through the plumes on Enceladus and then you taste it, and then you analyze what it is that you picked up. Same thing, fly through a comet tail and analyze it locally. But the dream is to bring back a sample return.

And there’s some really interesting mission ideas where you could even theoretically bring samples back home. You know, as you said, honking big rocket. But then there are ion thruster, essentially an ion thruster connected to a nuclear reactor, or even an ion thruster connected to an RTG, like the kind of power system that’s on Curiosity and Perseverance, but with no other craft.

And so, it’s just engine and power with a tiny little sample return capsule. Then you could fly through the tail and then head for home. And these things can give you like delta Vs in the range that would actually be able to retrieve a sample.

Maybe not from Trialis, it’s going so fast, but maybe a slower one. So, there’s some, you know, now that we know these things are out there, people are starting to go, oh, how do we get some of this home? Which is great.

All right, we’re going to continue talking about this, but it’s time for another break. And we’re back. All right, so now we’ve got some sense of what’s happening with Trialis, so now do we have some larger context?

I mean, we know about Borisov, we know about Oumuamua, and now we know about Trialis. Are we getting a sense of how many of these things are out there? How many are passing through the Solar System?

Is there anything in common among them?

Dr. Pamela Gay: Well, saying there’s something in common, at what level do you want to look at them? They’re all objects that grew comas as they passed through our Solar System. Now, what’s important to realize is we actually have for a long time had a sense that there should be comets from other Solar Systems.

We just haven’t had the survey instrumentation capable of finding things on the regular. But as we build system after system, as our software gets faster and faster and able to process for what changed more efficiently, it’s thought that we’re going to be able to start detecting, depending on which paper you read, six per year to a dozen per year of these objects that should be out there. And so it’s not that we didn’t think they were out there, it was that we didn’t really have the capacity to see them.

And one of the things that I’ve been kicking myself for is all of us as undergrads who became astronomers learned conic sections in both our physics classes, our calculus classes, and our astronomy classes in connection to comets, where we were learning comets have hyperbolic, parabolic, and elliptical orbits. Well, only elliptical orbits keep them in our Solar System. And none of us thought to ask, as struggling undergraduates, or at least no one in any of my classes thought to ask as struggling undergraduates, wait, these parabolic and hyperbolic, we’re flinging those, right?

So that means we’re ditching this number of comets. That means other Solar Systems, if they’re out there, are also ditching comets. As soon as you start thinking about what fraction of our comets have parabolic and hyperbolic orbits, it becomes natural to start asking what percentage of other Solar Systems.

Now, when I was an undergrad, we didn’t know exoplanets existed yet. You and I are old. But now we do.

And now we also know exocomets are visiting. And it is amazing. And I want high-resolution spectroscopy.

And you can’t do that from a spacecraft. Because it takes the entire basement of an observatory to build a high-resolution spectrograph. So you’re needing something bigger than several ISS units to do it.

But it will get closer. We’ll be able to see it better. And I am excited.

Fraser Cain: Yeah, people have been saying, why did we never notice this before? Why are they just happening now? Well, it’s because our ability to detect them has finally come online.

We are in the era of these all-sky surveys. The Zooki Transient Facility, the Atlas. When you look at the names of comets and asteroids, they’re often named after the observatory.

And so there’s a bunch of these now that are operating. But the mother of all sky surveys is now in its final commissioning phase. And that is Vera Rubin.

And so our ability to detect these kinds of things, to identify them quickly and start to study them, will go up orders of magnitude thanks to Vera Rubin, which is now just a couple of months away. It’s crazy how soon we are to the beginning of that operation. And then it’s just going to be a firehose of these things.

And asteroids and comets and planet nines and supernovae and all of this is all going to come online because of all-sky rapid time domain surveys. So, I mean, what I find really interesting about Oumuamua and Borisov and 3i Atlas is that they are very different from each other. Borisov is the least weird of the bunch.

It has a very comet-like, like it feels like it didn’t come up.

Dr. Pamela Gay: It was a comet as comets should be.

Fraser Cain: It felt like it came out of the Oort cloud, but it didn’t. But it had very similar characteristics to a comet, grew a comet, grew a tail. The chemicals in it were relatively similar.

But Oumuamua, as we saw, had this really strange length to height ratio, which was super unusual. It outgassed in a different way than a comet normally would. And so people are still on the fence about whether it’s an asteroid, whether it’s a comet, or whether it’s like a weird iceberg of frozen hydrogen.

There’s some really out there ideas. I mean, not to mention that people think that they’re spacecraft, but prove it. And then Atlas, as we talked about, has different ratios of carbon dioxide to water, different ratios of carbon monoxide to water, ratios of even the metals that we’re starting to see in them.

It’s again. And so now I want 10, I want 100. I want to see, because then we can completely reset our perspective on what solar systems are made of.

Like right now here in the solar system, we have different classifications for asteroids.

Dr. Pamela Gay: Yeah.

Fraser Cain: There’s the metal ones. There’s the carbonaceous chondrites. But there’s a ton of different flavors of them even.

And I’m sure we’ll get to this place, maybe 10 years down the road, 20 years down the road, where it’s like, oh, it’s another hydrogen iceberg. Oh, it’s another, you know, titanium asteroid, right?

Dr. Pamela Gay: The question is going to be, why doesn’t our solar system form hydrogen icebergs? Or is it simply that we haven’t discovered them yet? Because they’re so far out in the Oort cloud.

And we’re learning more and more about how violent star forming regions are. My favorite story of the year so far is a baby star in a star forming region about 440 light years away, spun up jets, as baby stars do, and ignited a nearby cloud of gas and basically slapped itself in the face with the shockwave from this. And it distorted the disk.

And so you have these remarkably violent things that are happening to stars and by stars to themselves, apparently.

Fraser Cain: Yeah, planets to planets, stars to planets, planets to stars.

Dr. Pamela Gay: Yeah. Yeah. World’s getting ripped off.

Fraser Cain: Yeah. The universe is throwing all this stuff at us. Yeah.

And now we just have to spot it and study it. It’s awesome. Yeah.

Yeah. Who needs interstellar spacecraft now? We don’t even need to go to another star system.

Everything we could ever want is being hurled in our direction. We just have to pay attention. Very cool.

Thanks, Pamela. And I’m sure this is good. We’re going to do probably another update when it’s on its way out and we’ve sort of learned all we can.

We’ll do a proper, okay, what did we learn about 3i Atlas? But for now, hopefully this whets everybody’s appetite and you’ll continue to watch Slackjawed as we learn more about this interstellar interloper. Thanks, Pamela.

Dr. Pamela Gay: Thank you, Fraser. And thank you to all our patrons. I completely have not downloaded your names because I’ve been working on setting up the site.

So what’s going to happen is I am going to read your names. And having looked at how Fraser does this to try and learn lessons from him, I am going to come back and read your names with the names going down the screen so that the pronunciation is destroyed but the actual words are there. So this will be recorded later.

And we’re going to improve how we do this. Changes are coming to Patreon. Please go check out everything.

I’ve been posting a bunch of free posts over there talking about what we have planned. We’re going to be learning how to take advantage of that Go Live feature. And there is a new, I have to math that, Q&A coming that is distinctly different from what Fraser does because it’s literally going to be me taking the questions you ask that require math and working the math on camera.

Fraser Cain: That’s amazing.

Dr. Pamela Gay: All right. Thanks, Pamela. Thank you.

Fraser Cain: We’ll see you next week.

Dr. Pamela Gay:  All right. Bye-bye, everyone.

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