Astronomers Stunned by a Tiny World With an Atmosphere

0:00And now a word from our sponsor South by Southwest London. Imagine a future where things just make sense. In the 1700s, we had canals. In the 1800s, the railways. Then telecom, fibre optic. And now? In a world that's more unsure than ever before, we need the answers. South by Southwest London presents over 900 speakers, 200 music artists, and 100 films in one location in June. To find out how they merge together and shape the future in person, visit southbysouthwestlondon.com. That's S-X-S-W-LON-DON dot com Sometimes it's good to leave it all behind So for this episode we're going far away all the way to an object in the Kuiper Belt It's as far away as Pluto in the outer solar system and astronomers have been studying one of the rocks out there It's a big rock but it's not a planet and they've been stunned to find that it has an atmosphere Can I go there now actually for a short break?

0:54Yeah, this is a tiny thing It's only 500 kilometres in diameter and things that small are not supposed to be able to hold on to an atmosphere. So that's the mystery. That's the big mystery we're going to get into today on The World, The Universe and Us. I'm Dr. Rowan Hooper. And I'm Dr. Penny Sarchet. We're joined by editor Jacob Aaron and reporter James Woodford. Jacob, we're going to come to you in a minute when we get into the great Pluto debate, of course. But James, first, let's start with this object. Does it have a name and what's its story? It has a very prosaic name. So at the moment it's called 612-533-2002-XV93.

1:36And so if you want to give it a nickname, 2002-XV93. We can still work on that nickname a bit, can't we? But it is actually, I think the cutest name is it's called a Plutino. Oh, that is cute. I'll go for that. So Plutino is a group of objects that are in the Kuiper Belt. Yeah, so a Plutino is an object that's out at the same kind of distance as Pluto and in a stable orbit. And what they do is that for every two orbits that Neptune does, a Plutino does three. And what's special? Tell us about what's special about this particular Plutino. Well, the really special thing is that, you know, it was discovered in 2002.

2:21And at the time, really nothing much was thought about it. And so it's kind of like just one of those objects that's right out in the... Loads of them. Loads of them. They're right out in the edges of the solar system. But in 2024, there was... Japanese researchers realized that there was going to be an occultation, which is kind of like an eclipse. that was going to happen. And so they set up four different stations around Japan to observe this occultation. And they got data from three. And what they were expecting is that when this kind of eclipse happened, that when the distant star went behind this object, that it would very, very quickly, instantly blink back in again.

3:12But instead what happened was there was a 1.5 second delay. And the only explanation for this is that it means that there must be some kind of an atmosphere. That was dulling out the light slightly as it went through. So we know that Pluto has a very thin atmosphere. So Pluto is much bigger than this Plutino. Pluto is like 2 ,300 odd kilometers in diameter. and all the other sort of dwarf planets, they're sometimes called like Pluto, these planetoids, they also, the ones that we know of, don't have atmosphere. So there's Eris, Haumea, Makemake, and there's a candidate planetoid as well. They don't have atmospheres, but they're bigger than this new one, 2002 XV93.

4:05So what's going on? Okay, so I think first of all, we should understand what an atmosphere is. So an atmosphere is all the kind of molecules, the aerosols, the gases, and the various particles like in Earth's atmosphere, it's things like dust that are held close to the body by gravity. And an atmosphere is really important because without an atmosphere, life is extremely difficult. And so an atmosphere allows organisms to breathe, It protects us from radiation. It has so many different important aspects to it. And so that is why an atmosphere is so important to have been found in this situation.

4:51So gravity is important there for holding the sort of cloud around. So does a planet or small planet-like thing need a certain amount of mass, a certain minimum size to be able to have an atmosphere? Well, and that was what had been previously thought, that an object like this would be just too small to be able to hold an atmosphere. So it's kind of forcing astronomers to rethink how many of these distant objects may actually have an atmosphere. I think it's really important to keep in mind that the atmosphere we're talking about is extremely thin. So we're talking about an atmosphere that's 50 to 100 times thinner than Pluto's atmosphere and 5 million to 10 million times thinner than Earth's atmosphere.

5:42So you are not going to go to this planet and take a big, deep breath of fresh air. Yeah, so the big question then is where it's coming from. Because, you know, a few years ago, the New Horizons spacecraft went past Pluto, did some amazing measurements, photos from there. We saw all this ice on the surface of Pluto, and that was methane, ice made of methane, carbon monoxide and nitrogen. It's so cold, all those things are frozen. But they vaporise slightly and make this thin atmosphere on Pluto. but this planetino doesn't have any ice on it. So where is this very tenuous thin atmosphere coming from?

6:23Okay, so the very first question is whether the atmosphere was just there at that day when... I mean, that would be very lucky, wouldn't it? It just happened to be there. Yeah, so the thing is, how long has the atmosphere been there? Was it just there on that particular day? If it is an atmosphere that this object holds permanently, then the researchers put forward two main ideas for where the atmosphere has come from. The first is that there must be some kind of volcanic activity, which is emitting gases.

7:01But it's such a small object. And then the other possibility is that something has hit the object and then the small gravity of that body is holding it in place. It does seem amazing that it's either an amazing stroke of luck that it's clung onto it just at that moment or somehow there's something coming from the planet to replenish it. And so that it's stable for some decent period of time. Let's talk about Pluto now. should we bring Jacob in because I know he has some strong feelings about it does anyone, do you have a mnemonic when you were a kid to remind you of the names of the solar system I never did, not to brag but I can remember eight things in order or nine as it was my very excited mother just served us nine pizzas I don't remember pizza being involved and then now it's my very excited mother just served us nachos because we don't get the pizza anymore.

8:05No pizza. Pluto's gone, ends with Neptune. No one goes to Hank's for his spreadsheets. They go for a darn good pizza. Lately, though, the shop's been quiet, so Hank decides to bring back the$1 slice. He asks Copilot in Microsoft Excel to look at his sales and costs to help him see if he can afford it. Copilot shows Hank where the money's going and which little extras make the dollar slice work. Now Hank's has a line out the door. Hank makes the pizza. Copilot handles the spreadsheets. Learn more at m365copilot.com slash work. So look, Pluto was demoted in 2006, Jacob. It caused anguish. Take us through what happened and why the anguish still lingers.

8:50Yeah, so in the early 2000s, astronomers started seeing new objects in the Kuiper belt beyond Neptune, similar to Pluto. So in fact, like this one, which was discovered in 2002 that we've been talking about today. And as more and more of these cropped up, people started saying, well, hang on, if Pluto is a planet, what about all these other objects? How should we be classifying them? Coincidentally, NASA launched its New Horizons probe in 2006 to go to Pluto. A few months later, the International Astronomical Union, which is kind of the big, big astronomy body in the world, had a vote about what to do about all these Pluto-like bodies.

9:33And they decided to demote Pluto to a dwarf planet. So NASA had already launched this mission. And then suddenly the target was somewhat diminished. And the definition that the IAU voted on is worth discussing. So I'll read it out in full. It's a celestial body that A, is in orbit around the sun, B, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium shape. Basically, it's round. And C, it's cleared the neighborhood around its orbit. Yeah, that's the big one, isn't it? C is where Pluto falls down. So, you know, as we said, there's all these other objects that got resonances with Neptune.

10:14Pluto is just too small to clear them out and dominate its orbit. And that's why it gets demoted to dwarf planet status. And now this debate has raged on and on, but it's sort of bubbling up again because the current NASA administrator, Jared Isaacman, has said that they're looking at whether they can make Pluto a planet again. Is that a populist move? well you know i think it definitely appeals to to certain quarters of the internet um but it's uh it's not really in nasa's remit to determine what is or is not a planet and a lot of scientists are quite unhappy that nasa is going to be devoting any time to this at all given that the nasa science budget has been massively massively cut so even pro-pluto planet scientists are not really happy that the debate is coming up again but yeah here we are and I think it's one that people just feel really really passionate about but there is there is a divide within scientists as to whether the IAU definition was correct so it's really a divide between astronomers who we can think about you know they're sort of looking at planets from very very far away using telescopes like this team did and planetary scientists who want to get up close and treat them as, you know, sort of geological objects in the same way that you would with Earth.

11:40I remember when I was reporting on the New Horizons mission, when it arrived at Pluto in 2015, you know, we saw these amazing pictures. Alan Stern, who's the leader of the New Horizons, said he used the Star Trek test to determine whether something was a planet. And, you know, if Captain Kerr is going to look out the window of the Enterprise and see a planet, then he knows what a planet is. And it was, you know, it was so apparent as soon as those Pluto pictures came, you got this big round thing, all these amazing features to deny it as a planet just because it's not cleared out its orbit. It seems like nonsense to me.

12:15So Jacob, if we were to bring Pluto back into the fold on a scientific basis rather than a nostalgia basis, does that mean we'd also have to call loads of other things planets as well? Because there's a lot more out there now and we know it. Exactly. So there's this feeling of, oh, we'd have to have thousands and thousands of planets. And I sort of go, great, we'd have thousands and thousands of planets. It doesn't seem like it's a problem to me. But this is the line that astronomers have drawn. You can't have a tiny lump of rock and say it's a planet. It happens to be spherical. There must be loads and loads of objects in the Kuiper Belt that then would qualify.

12:56So Ceres, which is the largest asteroid in the solar system, so it orbits in the asteroid belt between Mars and Jupiter, it was first discovered in 1801. And at the time it was called a planet. They said, you know, we found a planet. We didn't know about Pluto at the time. I think possibly we didn't know about Neptune. I'd have to check that. But, you know, they discovered what looked like a planet and said, yep, it's a planet. and it was only a few decades later as more and more asteroids started being discovered that astronomers said okay maybe we'll downgrade it to an asteroid so there is precedent for things being sort of moved in and out of this this planet bucket and the the fact is there isn't really a proper scientific definition even returning to the IAU's definition so the first part is that it's an orbit around the sun that means that all exoplanets are not planets scientifically because they don't orbit the sun it's a technicality but you know it is the case i say i say let's make pluto great again oh god see i told you it's populist i i i'm actually a planet maximalist so not only do i think uh pluto and all the plutino should be planets i think there's a whole bunch of moons that should be planets as well.

14:14So you look at Titan. How can a moon be a planet? It's a moon. Well, if Titan was in orbit around the sun, you would call it a planet. But it's not. It's in orbit around a giant planet. But the question is, is it the characteristics of the object that matters or is it the thing that it happens to be orbiting about? You know, if we magically were able to pluck Titan up, put it in orbit around the sun, you would just say it's a planet. And so it seems to me the the more scientific thing is to look at what the object actually is than where it is it does feel like this is this is not a mainstream view no it's not but it does feel like you know it's been we've been blinded almost by what we could see for a long time with the telescopes we had on earth and and our imagination we love learning the nine now eight planets naming them after great mythological gods and that kind of thing and it does seem potentially that stopped us from thinking okay there's thousands of these things and and we don't want to have to grapple with that because we like our solar system feels much more knowable if we just know like the eight main players i don't know i mean i just think it's getting a bit mad if we start calling titan a planet and moon's a planet but what really changes if we adopt that point well how does that really change anything because then what are moons moons can't be planets of course moons can be planets What?

15:36I mean, Mars' moons are asteroids. Mars' moons are asteroids. So is our moon an actual asteroid, not a planet? Is our moon an asteroid? No. Our moon is a moon. Mars' moons are captured asteroids, we're fairly certain. Right. So that's, you know, an object was in one location, and then it changed location, and now we've changed the label that applies to it. Well, so you're talking historically now that our moon was once part of what is now Earth and got broken into two. So you're going to go hardline. That's what a moon is. Well, I don't know. Anything else is just a rock. I like Jacob's definition from Star Trek.

16:19You know one when you see one. Yeah. There's other things that's been said about, hasn't there? Yeah. Look, let's park this for now. I do think what this is really interesting about is that the Kuiper Belt, it's really remarkable quite how recent it's been that we even, so it was predicted its existence, but its hardcore detection is really recent. How recent? Like in the 90s. Right, okay. And then like only until 2010 did we start seeing like actually there's thousands of these objects in the Kuiper Belt and maybe now hundreds of thousands. And we're still learning loads about them. They think that they're...

17:02So we now know that there's an atmosphere on one of them or a couple of them because Pluto as well. Someone, I read someone saying that there's been... The building blocks of life have been detected out there. And I don't quite know what that means because I don't know if we've directly detected them. I know we have on some of the meteors that are closer by, Bennu and Vyugu asteroids. We've detected the nuclear bases of RNA and DNA on those. But maybe they are referring to those. But it's bringing our cosmic ecosystem. We're kind of learning more about it. And it does interact with us, right? So that's how it was predicted, the existence of the Kuiper bug, because comets would be coming in from the outer solar system, coming past us, and people thought, where are they coming from?

17:51So I do like the idea that we're starting to learn more about our local cosmic ecosystem. And I found it really fascinating as well because I was asking the researcher, do you think you'd actually be able to see this atmosphere? And I was fully expecting the answer would be no. But he actually said to me that it is quite possible that we could see a little smudge. So I think the extraordinary thing is... You mean if you were standing on the surface and looking up? If you were close enough to be able to observe it. And so he's not ruling out the fact that you'd actually be able to see this atmosphere.

18:25And so this is very far away. It's 30 to 50 astronomical units away. That's the distance between us and the sun. So it's 30 to 50 times as far out as we are, which is at least 5 billion kilometers away. So the idea of being able to actually see an atmosphere there is quite incredible. You know what? I think if an object has an atmosphere, that's a good... I always call that a planet. I guess. Allow it. You're changing your tune. Titan has an atmosphere. Yeah, well, I do have a fondness for Titan. I might make an exception. Well, Jacob, what about Planet Nine or these other sort of mysterious planets we think might exist somewhere out there in the solar system?

19:01Yeah, so the fact is by looking at the Kuiper Belt, there are a few collection of objects that don't seem to be quite where we would expect them to be. It's difficult to piece together, but it seems that there's potentially something gravitationally disturbing these objects out there. And so then this is this theoretical Planet Nine. It would have a very large mass, I think possibly two times the mass of Earth. This idea has been around for a while now. We've still, you know, despite many, many attempts to find it, we've not found one. Can't be there. I don't think it's been completely ruled out.

19:43And, you know, this disturbance in the Kuypah-Vell objects is still there and unresolved to some extent. So I don't think we can stay either way yet. But yes, I mean, certainly if we were to discover Planet Nine, that feels like that's going to open up a whole new can of worms about what gets called a planet. And meanwhile, the Vera Rubin Observatory, which I think it just opened this year, didn't it? It just became active. that's going to be looking a lot more closely at all these objects we're going to learn a lot more about these Kuiper Belt objects soon, very soon We'll leave it there Thanks to our guests Jacob Aaron and James Woodford and thanks to you for listening Do subscribe wherever you get your podcasts YouTube, Spotify, anywhere Subscribe Thanks, bye Bye