Are there comets in the asteroid belt?

00:00:08
Speaker 1: Hey, Daniel, what's the difference between a physicist and an astronomer?

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Speaker 2: Oh? I feel like this is a trap.

00:00:17
Speaker 1: It seems like a simple question.

00:00:19
Speaker 2: It's a constant debate we have in faculty meetings in the Department of Physics and Astronomy. Where do we draw the arbitrary dotted line?

00:00:27
Speaker 3: Like?

00:00:28
Speaker 1: Are all astronomers physicists or are some physicists astronomers? How does it work?

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Speaker 2: I feel like any answer I give here is can generate a lot of angry.

00:00:37
Speaker 1: Emails physicists or astronomers.

00:00:39
Speaker 2: A lot of astronomers think of themselves as physicists first applied to questions of astronomy, but also a lot of astronomers think of themselves as a very different breed of scientists who tackle problems differently and think about things differently than physicists do.

00:00:54
Speaker 1: All right, that wasn't so hard.

00:00:56
Speaker 2: It was my best non answer.

00:00:58
Speaker 1: All Right? May I actually just ask non questions in the future.

00:01:01
Speaker 2: Welcome to our non podcast.

00:01:18
Speaker 1: I am Jorge. I'm a cartoonist and the author of Oliver's Great Big Universe.

00:01:22
Speaker 2: Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine. Though I'm no longer sure what those categories even mean.

00:01:29
Speaker 1: You don't know what you are? Are you having like an identity crisis?

00:01:32
Speaker 2: Yes? Yes, and yes. I mean if everything's particles, then isn't everybody a particle physicist?

00:01:39
Speaker 3: Well?

00:01:39
Speaker 1: Not everything's a particle, right, then we're.

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Speaker 2: All field physicists.

00:01:43
Speaker 1: I suppose, like what's dark energy? Dark energy is not necessarily a particle.

00:01:47
Speaker 2: Yet nobody knows. Maybe dark energy is a particle we don't know.

00:01:50
Speaker 1: In fact, isn't particles in arbitrary name or term? Like, isn't everything just energy? In the end, maybe you should just all be energiest.

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Speaker 2: Yeah, if you ask ten particle physicists what is a particle? You'll get ten different answers.

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Speaker 1: Well, if you guys can't even agree, then you know what's the point.

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Speaker 2: The point is that names and words are how we communicate, though it's probably best if we do assign meaning to them first.

00:02:15
Speaker 1: Maybe should just all do science with sign language.

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Speaker 2: Or like charades, Let's just give up on language and use math. Right, that's just so much more crisp.

00:02:25
Speaker 1: I think charades is not just more fun, but also maybe a little bit easier. You would have a whole conferences where the presentations are just signists getting up there and and miming their papers.

00:02:38
Speaker 2: Is that supposed to increase clarity or just hilarity?

00:02:42
Speaker 1: Well, hopefully it'll increase clarity and also hilarity. But anyways, welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.

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Speaker 2: A podcast that does try to pump both clarity and hilarity into your brain. We hope that the universe is one that we can understand, that we could take it up hard into little bits that follow some fundamental rules. Then we can weave it back together into all the amazing and beautiful emergent phenomena that we enjoy from ourselves, to our planets, to our solar system, to everything beyond, and explain all of it to you with a little bit of Dad Joe hilarity sprinkled on top.

00:03:17
Speaker 1: Yeah, Because whether you're a physicist and astronomer, a cartoonists and energists, or a dad, we all live in this universe and we all look out there and we wonder how things work, why are things the way they are? And can you cerade math?

00:03:32
Speaker 2: Nobody wonders that man, Nobody wonders that that's done in the top one thousand questions. Humans ask, how do you know?

00:03:39
Speaker 1: Nobody wonders that, Daniel, do you have scientific proof or data to back up your claim.

00:03:44
Speaker 2: I do have some data. Yes, I cannot rule it out entirely. But over the many tens of thousands of questions I get from listeners, I've never gotten that one, which means it's not in the top one thousand questions. I can confidently say that.

00:03:57
Speaker 1: I see, But you can't say that nobody wonders that.

00:03:59
Speaker 2: No, right, that was too strong. You wonder that, apparently, and your people, So the exception proves the rule.

00:04:07
Speaker 1: I'm sure the situation has come up, like somewhere in the history of math, at some point some people needed to communicate some calculation or result and they couldn't talk for some reason.

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Speaker 2: Maybe in Italian universities, you know, hand gestures are much more important in communicating these abstract ideas.

00:04:24
Speaker 1: Maybe that's why their equations have so much possess.

00:04:26
Speaker 2: Yes, exactly, whether we're Italian or not, or using charades or symbols or language, we are trying to make sense of the universe, and part of that involves categorizing it, saying this is one kind of thing. This is another kind of thing, whether that means distinguishing between particles and fields, or between living things and not living things, or planets and dwarf planets. Putting things in boxes is just one way the humans make sense of the universe, defining kinds of things and applying those labels.

00:04:56
Speaker 1: Willy nilly, yeah, And we are trying to make sense of the whole universe, not just the little things that we're made out of, then that things are made out of, but everything, all the huge amazing phenomena that are happening out there, the flying planets, the swirling galaxies, and the ginormous galaxy clusters.

00:05:13
Speaker 2: And we'd love to study all that in great detail, but most of it is very far away, and so far our technological eyeballs aren't powerful enough to really resolve all the details. So if we want to get down to the astronomical nitty gritty, we're best off studying our own backyard, looking in our solar system to understand how did it form, what's in it, what kinds of stuff are out there swirling around in our neighborhood. And over the last few hundred years, we've come to a pretty good understanding of what's there and where it's going.

00:05:41
Speaker 1: Yeah, we live in a pretty busy neighborhood full of planets, asteroid comets, raining satellites from failed rockets, and so there's a lot for us to see in our very near vicinity.

00:05:54
Speaker 2: And while the truth is that the Solar system is fills with a huge spectrum of stuff, from tiny cosmic dust to huge we asked giants to the Sun itself, we do like to impose categories on it. And as the decades and centuries go by, we keep discovering things that lie at the edge of those boundaries that challenge our definitions for what is what, Pluto of course being a famous example. But as our telescopes get more powerful, we keep discovering things in the wrong places or at the edge of these definitions that make us wonder, really, where do we draw these dotted lines?

00:06:24
Speaker 1: And so to be on the podcast, we will be tackling the question are there comments in the asteroid belt?

00:06:35
Speaker 4: Now?

00:06:35
Speaker 1: How many people do you think wonder about this question? Of your tens of thousands of emails, how many have asked this particular question.

00:06:43
Speaker 2: This particular question in this phrasing.

00:06:45
Speaker 1: Zero So you're saying the same amount of people that wonder if there are commets in the astert belt. Also probably perhaps wonder if you can cherate.

00:06:55
Speaker 2: Now if that was your metric. Yes, but there are a lot of questions in the vicinity of this, wondering about like what's the difference between comments and asteroids? Or why do we have comments out there and asteroids over here? And so I think people are curious about, like what's out there in the solar system? Why do we give them these labels? And is it really so neat and crisp?

00:07:14
Speaker 1: This is an interesting question, and so let's dig into it. And as usually, we were wondering how many out there had thought about this question of whether there are comets in the asteroid belt.

00:07:22
Speaker 2: Thanks very much to everybody who contributes their voice to this segment of the podcast. Really appreciate your responses. If you'd like to hear yourself on a future episode, please don't be shy or write to me too questions at Danielandjorge dot com.

00:07:36
Speaker 1: So think about it for a second, cast your mind out there into the far reaches of our solar system and wonder if there are comets in the asteroid belt. Here's what people had to say.

00:07:46
Speaker 4: I mean, sure, why not. Maybe they also pass through the asteroid belt from time to time. And I always thought asteroid belt was what's mainly in that reage, not what's the only thing in that region.

00:07:59
Speaker 5: I don't have very good idea of the definition of a comet versus an asteroid, but I think it has to do with amount of ice in the structure. So if that is the definition, I can imagine sure there might be something that falls under that definition in the asteroid belt.

00:08:14
Speaker 2: No comment in the asteroid belt, just asteroids. Comments are out a lot further.

00:08:19
Speaker 6: I think another sort of way to distinguish commets from asteroids is that asteroids are well in the asteroid belt, and comets can come from a couple different places. Long period comets come from the Oort Cloud, but then there are shorter period.

00:08:31
Speaker 2: Comets than that.

00:08:32
Speaker 6: Now, if we have a dirty snowball in the asteroid belt, which I believe there are. Some of these bodies that have been discovered, are they correctly labeled as comets?

00:08:41
Speaker 2: Are not commets? I'm always heard made up ice. I think if they were that close, they probably melt.

00:08:46
Speaker 7: I think comets coming in at a high rate of speed from the Oort cloud are unlikely to get caught up in the asteroid belt.

00:08:53
Speaker 1: Comments might be more about composition than trajectory. I mean that if it has more ice than rock, it might be a comet.

00:09:01
Speaker 3: I can never remember the difference between asteroids and comets. I mean, surely there's a good acronym or something out there to remember the difference. But I have to say that there's no comets in the asteroid belt because asteroids become comets after they and through the atmosphere.

00:09:13
Speaker 8: So there are short period comets, and I think there are some that operate closer to the Sun kind of in that asteroid belt range, but being within the ice line like most of its quote unquote life, I don't really see how they can be long lived.

00:09:26
Speaker 9: I think comets heavenly bodies which have eccentric orbits around the Sun, so they don't fit in nicely with the other better behaved inhabitants of the Solar System. So although comets may pass through the asteroid belt, I don't think they can remain there permanently.

00:09:43
Speaker 10: I think that the asteroid belt is far enough out so that comets could remain frozen, and I guess the asteroid belt does have a lot of its own gravity, so it could capture comets if it was lucky.

00:09:54
Speaker 7: I think there might be a few transient comets in the asteroid belt, but I don't think that there would much chance for comets to persist in that kind of orbit because of exposure to the Solar wind and the interaction of the gravity of Jupiter disrupting either the orbit or the structure of those comets.

00:10:14
Speaker 8: Guess there could be comets, but yeah, usually commas have a large orbit, a very large orbit in detail.

00:10:19
Speaker 2: That wouldn't be the case if it was found in the asteroid belt.

00:10:22
Speaker 1: So yeah, pretty wide range of answers here. I guess there's only two options, yes or no.

00:10:28
Speaker 2: Or there could be this is a trick question, or let's answer in charades, right.

00:10:35
Speaker 1: What made you think of this question? Why are there comets in the asteroid belt? Is this something that astromers have been wondering about.

00:10:41
Speaker 2: I've been thinking about this kind of question for a while because I find the whole labeling of stuff in the Solar System to be kind of ridiculous and arbitrary. You know, we're just humans putting dotted lines on a smooth spectrum of different kind of stuff that's out there. But also it is interesting because when you invent categories, then you can wonder about this in the boundaries or things across the boundaries. And then I read a paper about people who were finding weird stuff in the asteroid belt that didn't belong there.

00:11:08
Speaker 1: All right, well, let's dig into it, Daniel, I guess the question is, but comets and asteroids, what's the difference between the two?

00:11:15
Speaker 2: Yes, so these are two human constructed, arbitrary definitions that are mostly historical and don't really represent like our best understanding of what's out there in the Solar System. If you were going to start today, you probably wouldn't come up with the same definitions. But you know, science is a human endeavor, which means we need to understand the words scientists use when they talk to each other, even if it's imprecise or historical or ridiculous. So what do we mean by an asteroid and what do we mean by a comet? So an asteroid is basically like a mini planet. Right, there's this complicated definition of a planet as an object in the Solar System that's orbiting the Sun is big enough to be mostly round and has cleared its own path. An asteroid is like that, except that it's not necessarily big enough to be round, and it hasn't cleared its own path. So it's like a mini chunky, funky shaped planet that doesn't have its own parking space.

00:12:09
Speaker 1: But is there like a size a range, like can you have an asteroid size of a marble? Or or does that count of something else?

00:12:19
Speaker 2: Technically there's no minimum size for an asteroid, so like a dust grain, technically is an asteroid. Practically that's very, very difficult to see those things, you know, of course, unless they land on Earth, in which case they're no longer an asteroid. We can't really detect them in the asteroid belt unless they're very shiny or large, or some combination of them. So the range of asteroids that we've discovered, like in the asteroid belt goes from things like down to one meter across all the way up to things like five hundred kilometers across. So there's an incredible range of stuff in the asteroid belt that we call asteroids. We give them all the same name.

00:12:55
Speaker 1: But I guess there's one common threat, which is that it needs to be some kind of solidial, right, Like a cloud of gas doesn't count as an asteroid, right.

00:13:04
Speaker 2: Yeah, that's right, needs to hold itself together.

00:13:07
Speaker 1: So it has to be solid and it has to be in space. Is that about the definition of an asteroid? Something solid floating in space that's not round.

00:13:14
Speaker 2: And it has to be orbiting the Sun. It's a rocky object that orbits the Sun and doesn't qualify as being a planet or a comet.

00:13:22
Speaker 1: But I guess why does it need to be orbiting the Sun? Can't you have an asteroid other than space by itself? Like, what do you call those?

00:13:29
Speaker 2: Well, if it's not orbiting the Sun and it's orbiting like the Earth, then you'd call it a moon. If it's not orbiting the Sun and it's not really orbiting anything, it's just like floating in the galaxy, then it's not an asteroid. It's just a rock.

00:13:43
Speaker 1: Is that the official astronomy definition? It's just a space rock? Are you sure we don't want to anger any astronomers.

00:13:51
Speaker 2: Now, it's definitely don't. And you know, I'm in a department of physics and astronomy, and that doesn't make me an astronomer, even though I'm technically a professor of physics and astronomy. And I don't want to speak for the astronomers, but that is my understanding. If it's out there in interstellar space, you could call it an interstellar asteroid. I suppose the problem is we haven't like discovered or seen many of those. You know, we have had a couple of interstellar objects come, but those who think are interstellar comets not interstellar asteroids. So yeah, that's a whole new frontier.

00:14:22
Speaker 1: Yeah, like like in Star Wars when they run into like an asteroid field, are they takenly not calling it the right thing?

00:14:28
Speaker 2: Well? I think those are usually near a stars. There probably are orbiting a star.

00:14:33
Speaker 1: I don't know, they never show the star.

00:14:36
Speaker 2: That's what I'm always thinking about when they're dodging asteroids. Where's the star that makes us an asteroid and not a rock?

00:14:42
Speaker 1: Excuse me? Excuse me, I don't see the sun actually, all right, So an asteroid is by definition a rock that's orbiting the sun. Basically, Yeah, that has to be solid, right, or like a solid object that's orbiting the Sun.

00:14:59
Speaker 2: Yeah, and your point about it being solid as crucial. Asteroids are rocky objects, meaning they're made of rock and metal and this kind of stuff, and that's going to help us distinguish them from their cousin the comet.

00:15:11
Speaker 1: Gosh, well, how do you define a rock?

00:15:13
Speaker 2: A rock is something made it mostly out of silica? You know, the chemical composition of these things tells you what it is. If it's a blob of iron, then it's metal, you know, if it's a This is all chemistry. Man, it's well beyond me. Don't ask me to do chemistry.

00:15:26
Speaker 1: Joined the Department of physic Astronomy and chemistry.

00:15:29
Speaker 2: No, never, never, My son is into chemistry.

00:15:33
Speaker 1: Yeah, I guess. I guess all those professors just don't have the chemistry.

00:15:37
Speaker 2: I don't have chemistry with those professors, that's for sure. No. I respect chemistry, I respect chemists, but I'm not that in the history of asteroids is kind of fascinating because, you know, we use these words, but for a long time, people didn't really distinguish between planets and asteroids, and the word planet was used very broadly, Like the moon was a planet for a while before we invented the concept of a moon. So these things change with time. It's possible to redefine what is a planet or an asteroid maybe in five hundred years astronomers will have totally different words for these things, or use the same words in a different way. Who knows.

00:16:11
Speaker 1: Yeah, or maybe they'll use the same like charade gesture.

00:16:15
Speaker 2: That's exactly when we transition fully to charade science.

00:16:19
Speaker 1: Then we're I wonder if in the future we transition to like telepathy, you know, then you don't need words, you can just transfer thoughts.

00:16:26
Speaker 2: All right, Well, if we're playing charades and your clue was asteroid, what motions would you use to describe it?

00:16:33
Speaker 1: Oh, that's totally easy, Dan, I would do this, so he totally conveys what asteroid means.

00:16:40
Speaker 2: Okay, that's a funny way to duck the question. But seriously, can you describe what an asteroid gesture would be?

00:16:46
Speaker 1: I just did, all right, but I feel like we're getting a little bit uh deilled.

00:16:54
Speaker 2: Well, then let's go back to the history of asteroids, because I also think it's fascinating when we knew there were lots of asteroids, Like, as our technology developed to be able to see these things, right, we can see smaller and smaller ones. Then we discovered more, and it's this incredible sort of explosion of discovery.

00:17:11
Speaker 1: But how do we see them? Like you sort of can't see asteroids with the naked eye, can you? Or sometimes if they catch the sun.

00:17:18
Speaker 2: Technically, I don't see why you couldn't have photons hit an asteroid and then hit your eye, but enough of them for you to spot it and identify it seems very challenging. So asteroids are usually seen through telescopes just because you know, the aperture is larger and you're gathering more light and so it's basically a bigger eyeball.

00:17:37
Speaker 1: So is that how they discover them? Like they were looking through a telescope and they saw a bunch of these They probably looked like pinpoint stars, but they were probably moving faster than the regular stars.

00:17:47
Speaker 2: Exactly the same way that planets move across the field of the stars, which is how you know that they're closer, right, And that's why sort of planets and asteroids were called the same thing for a long time before we distinguished between them somewhat arbitrarly. And you know, until one hundred and fifty years ago, we thought there were six ish planets, and we thought there were about ten asteroids. Like eighteen forty nine, we knew about ten different asteroids, and then as technology improved, that number grew to be one hundred twenty years later to a thousand about one hundred years ago. And now we know about more than a million individual asteroids that can be tracked, and we have these telescopes that look at these things, of course, because we're concerned about whether one of them might eventually hit the Earth. And NASA is tracking all of these things. And as you say, they don't glow, but they do reflect the sun, and so when the conditions line up for like photons from the Sun to hit the asteroid and then reflect back into the telescope aperture, that's when we see it. But a lot of these things are invisible for long fractions of their flight around the Sun.

00:18:50
Speaker 1: Now, what was the technological advance that it allows us to see so many Like you just we just got bigger telescopes and we're more sensitive. They could see dimmer things, or we could maybe zoom with more presitionion into certain parts of the sky.

00:19:06
Speaker 2: Yeah, it's a combination of more telescopes and bigger telescopes. So a lot of this is limited by glass technology. Can you make lenses that are big and smooth and free of aberrations and so like Galileo's original telescopes are pretty bad, right, and limited by the size of the telescope you could make, because the glass you could grind and have it to be smooth and not create distortions was pretty small. But then people got a lot better about that about one hundred and fifty years ago, and things exploded from there, and then we also just built more of them, and now of course we have dedicated space telescopes just out there looking for these things.

00:19:43
Speaker 1: Meli Nastas, that's pretty wild. I mean, if you could see the way these telescopes could see, you would see the night sky basically like shifting all the time, right, moving, swirling, spinning.

00:19:54
Speaker 2: Yeah, it's much more dynamic than you imagine. There's a lot of stuff out there. There's also inflection point in sort of the history of astronomy in the mid nineties when Jupiter was hit by a comet. Comet shoemaker Levee broke up as it entered the inner Solar system, whipped around the Sun, and then each of the twenty six or so pieces slammed into Jupiter, creating huge fireballs the size of the Earth and that's made people wake up to the idea that like, wow, you know, asteroids of comets really could hit the Earth. This is potentially an existential threat, and NASA has really been investing in tracking near Earth objects ever since that moment comet shoemaker levee. That's one reason why we went from like seeing some of the asteroids to like, let's be serious about this, folks and make a solid catalog of all the biggest ones.

00:20:42
Speaker 1: Okay, so that's asteroids, and most asteroids are in the asteroid belt, right, or there's a couple of belts around the Solar System.

00:20:48
Speaker 2: Yeah, asteroids are mostly in the asteroid belt, which is between Mars and Jupiter. And that's not an accident, right. The reason we have asteroids is basically because of Jupiter. Jupiter has a huge, huge fraction of the mass of the Solar System that's not in the Sun. Like the Sun is ninety nine percent of the mass of the Solar System, and Jupiter is almost three times the mass of everything else in the Solar System combined, including like Saturn and Neptune and Urinous. So it's a big massive thing and it's gravity.

00:21:18
Speaker 1: Wait what so like seventy five percent of the non sun mass in the Solar system is Jupiter.

00:21:24
Speaker 2: Yeah, Jupiter is a big hog.

00:21:26
Speaker 1: You know, I'm not sure we should be shaming Jupiter, Daniel.

00:21:31
Speaker 2: You're taking big hog to be pejorative. I meant it as a compliment, like, hey, good job, Jupiter, congrats.

00:21:38
Speaker 1: I don't know. I guess it was your tone.

00:21:40
Speaker 2: Okay, Hey, Jupiter is a big hog. Has that. But you know, this is gravitational runaway effect at work. You have a huge cloud of gas and dust that forms the Solar system. Somewhere in there is an initial density that causes the collapse that's going to turn into the Sun, but it's somewhere else in that nearby cloud also has a little spot of density. Then it can form its own little runaway effect to gobble up some of that gas and dust before it falls into the Sun. And that's what Jupiter did.

00:22:11
Speaker 1: Now, Jupiter is mostly made out of gas. So I wonder why got so much of the gas in the Solar system, Like, did it some of it just blow away when the Sun ignited or what and it just happened to gather around Jupiter.

00:22:22
Speaker 2: Yeah, there's a lot of controversy about that where gas giants form. Do they mostly form in the outer Solar System and then transition inward? Do they form in the inner Solar System? We see a lot of gas giants in exoplanet systems that are near their Sun, but we think probably these gas giants form farther away because further away from the Sun. Number one, the gas isn't being blown away by the radiation of the Sun. And number two, there's ice there, which helps these planets to crete more quickly. There's like more stuff to gather. So we think that Jupiter became so big because it's so close to that snow line, you know, where ice and frozen vapor can still exis. It helps these planets accrete quickly. And then we think it's probably a complicated history of Jupiter moving in towards the Sun and then getting pulled back out by a now missing gas giant which was ejected in that interaction. So the whole formation of Jupiter is a really fascinating and complex topic.

00:23:18
Speaker 1: All right, Well, let's dig into where else in the Solar System you might find asteroids, and then we'll dig into comets and whether there are any in the asteroid belt. So we'll get to that But first, let's take a quick break. All right, we're talking about asteroids, comets and belts and the fact that Jupiter needs a really big built and the question is are there comets in the asteroid belt? So we've been talking about asteroids what they are, and you said they're mostly in the asteroid build but can you find them anywhere else in the Solar System?

00:24:00
Speaker 2: You can find them also in Jupiter's orbit. So there's a big blob of asteroids ahead of Jupiter in its orbit and another one behind Jupiter in its orbit. They're like bleeding and trailing Jupiter. These are called the Greeks and the Trojans, and these are just like big clumps of rock that are in Jupiter's orbit. So you know, technically, did Jupiter really clear its orbit? Is Jupiter even a planet?

00:24:25
Speaker 1: Well? I mean is if these things are orbiting Jupiter, then they're not asteroids, right, No, these.

00:24:29
Speaker 2: Things are orbiting the Sun in the same orbit as Jupiter. Oh yeah, and all of this is just dominated by Jupiter's gravity. Like why don't the rocks in the asteroid belt come together to make another planet the way they did for Earth or for Mercury, or even for Mars. The answer is Jupiter's gravity distorts it. It pulls it apart, it shreds things. These are all tidal forces. Jupiter's gravity is so strong that if you try to pull these things together, It's gravity would tug on one side harder than the tug's on the other side and pull it apart. So it's sort of like mixes it up. It's I got a big spoon, and it keeps stirring up the asteroid belt and keeping it from coalescing into something.

00:25:09
Speaker 1: Whoa, It just disrupts the formation of any planets in that sort of neighborhood exactly. Do we have any asteroids out there beyond the gas giants?

00:25:20
Speaker 2: There are definitely rocks further out in the Solar System, because remember any big rocky object that's not a planet or a dwarf planet is technically an asteroid. There's some fuzziness there because past Neptune there's a huge number of these objects were called dwarf planets, which are like sort of larger enough to be called a planet maybe but haven't cleared their own path right like Pluto and Shareon for example. And so the distinction between dwarf planet and asteroid out there, and the edges of the Solar system is pretty fuzzy. You'd have to ask an astronomer.

00:25:53
Speaker 1: Okay. So then the question was are there commets in the asteroid belt? So now, how do you define what a comet is?

00:26:00
Speaker 2: So your comment earlier about asteroids that they have to be solid was really on point because one of the crucial ways we define a comet is very similar to the way we define an asteroid. An asteroid is a rocky object that orbits the sun. A comet is an icy and dusty object that orbits the sun.

00:26:20
Speaker 1: Icy. So it's made out of ice. But isn't ice technically a mineral, which means it's a rock? Right?

00:26:27
Speaker 2: Yeah, there's a distinction here. Ice is not like a silicate, right, It doesn't have the same chemical composition as these things we call it rocks.

00:26:35
Speaker 1: Excuse me, Daniel, excuse me. I believe. I believe that the definition of a rock is like a composite of minerals, right, and ice is a mineral. So wouldn't ice be a rock? Or is this something that would be have to be decided in a death match between geologists and astronomer Yeah?

00:26:53
Speaker 2: And I think some chemistsy to be involved in that conversation. But in terms of the Solar System, we distinguish between ice and other kinds of rock or rocks, depending on whether you're gonna call ice.

00:27:05
Speaker 1: A rock and so ice. How do you define ice? Does it need to be water or can it be other liquids?

00:27:09
Speaker 2: There's several categories there. First of all, water ice has lots of different chemical forms, so it's not just the kind of ice that we see on Earth. There's like ice and ice three, and ice seven and ice nine, all sorts of complicated water chemistry to give you solid forms of ice that we don't often see on Earth because it's a very different pressure environment out there in the outer Solar system. But also you know things like methane. If that's frozen, they call that ice. A lot of the ice that's out there is water ice, but there are also other kinds of ices.

00:27:39
Speaker 1: Gosh, I have so many nitpicky questions, Daniel. I mean, like, if you heat up a rock, it'll melt, so it's liquid. So really a rock is just frozen liquid rock.

00:27:49
Speaker 2: Yes, a rock is frozen liquid rock, But lots of solids are frozen liquids, right.

00:27:54
Speaker 1: How do you define what an ice is?

00:27:56
Speaker 2: There's an arbitrary dotted line, you know, it's just historical crystals we call ices, some crystals we call rocks. And that's, frankly, is my whole problem with chemistry. All of chemistry is like this, just like draw dotted lines between stuff because some dude one hundred and fifty years ago thought that made sense. We're sticking to it.

00:28:13
Speaker 1: Well, it sounds like it's not just chemistry, it's physics. And it's proud of me too. Why are you trying chemist under the bus.

00:28:18
Speaker 2: We're definitely guilty of that in physics and in astronomy, and especially in this situation naming things in the Solar system. But and I'm really going to catch a lot of flak from the chemists out there. I feel like all of chemistry is just built on that. Like, if you took that away from chemistry, what do you have left?

00:28:33
Speaker 9: Man?

00:28:34
Speaker 2: It's all just exceptions.

00:28:36
Speaker 1: Oh man, he just lost is a bunch of chemists listeners?

00:28:40
Speaker 2: No, man, they're all going to write to me and they're gonna listen carefully through all the next episodes to see if I slight chemistry.

00:28:45
Speaker 1: I see they're gonna hate listen. That's the kind of fan that we want. Look, as long as they sit through the ads, then we don't care why.

00:28:53
Speaker 2: They're love listen or hate listen.

00:28:54
Speaker 1: We love you, all right. But so then what does that leave with about the definition of a comet.

00:29:02
Speaker 2: So, according to the arbitrary distinction between ices and rocks, comets are made out of ice and asteroids are made out of rocks. And one important difference is that if you bring something made out of ice into the Inner Solar System, it tends to vaporize, Like the Sun is capable of turning those ices into vapor, and it's not capable of doing that with rock. So probably there's some distinction there about like the melting point or the vapor point of these substances.

00:29:28
Speaker 1: Oh, I see, all right, now we're getting somewhere. It's the sort of scientific If it melts under the light of the sun, then you might call it a comet. That's basically the only distinction.

00:29:38
Speaker 2: That yeah, yeah, And when you bring these things into the inner Solar System, like comets traditionally originate in the Kuiper Belt or in the Oort Cloud, which are kind of like bands of rocks in the more distant parts of the Solar System, much further out than the asteroid belt. When you bring them into the inner Solar System, they develop tails because the Sun is beginning to vaporize them. They get a coma, they have like a little envelope of gas around them, and then as they move in towards the Solar System, they get tails. And so that's really what distinguishes comets from asteroids. Asteroids are just rocks, and comets have these little gas clouds and tails because they're made out of ices.

00:30:17
Speaker 1: All right, and they mostly hang out on the outside of the Solar System.

00:30:21
Speaker 2: Right, Yeah, they originate in the Kuiper Belts, which is this big collection of rocks, billions and billions of snowballs in the distant Solar system, and this is probably the origin of short period comets, like you know, years up to tens of years. And then we think there's a collection of them also much much further out in the Ort Cloud, which is like very far out there, much further than Pluto. And it's also technically theoretical because we've never actually seen the Orc Cloud. We've just like deduced its existence from various gravitational calculations and models. And we also think that it's a source of long period comets, comets with periods, you know, again longer than tens or hundreds of years, and they could take a very long time to fall into the inner Solar System. And out there there could be trillions of these snowballs.

00:31:09
Speaker 1: And that's in the or cloud. So what's the Kuiper belt? Is it asteroids or comets?

00:31:14
Speaker 2: The Kuiper Belt is snowballs, and when they fall into the Inner Solar System you call them comets. I think you still call them comets when they're in the Kuiper Belt before they've fallen in, because technically they are icy objects out in the Solar System orbiting the Sun.

00:31:27
Speaker 1: Because they would melt if they got closer to the Sun. But doesn't everything melt if you get close enough to the Sun?

00:31:32
Speaker 2: Yeah, exactly, And so this distinction between asteroids and comets is also a little bit fuzzy. I found a comet from an astronomer or the University of Arizona who said, quote, everything is a comet. If you brought my couch close enough to the Sun, it would start melting and have a coma. So like it's just a question of how close you get to the Sun. Because you bring an asteroid close enough to the Sun, it's going to get vaporized, even if it's like a hunk of iron.

00:31:56
Speaker 1: What if it's a hunk of like diamond.

00:31:58
Speaker 2: If you dropped a huge diamond into the Sun, it would definitely get vaporized.

00:32:02
Speaker 1: Yeah, into the Sun.

00:32:04
Speaker 2: If you had a huge diamond and you dropped it from the outer Solar system and it fell in towards the Sun, there at some point at which it would reach its melting point, and you would melt that.

00:32:12
Speaker 1: Diamond and become a diamond commet.

00:32:15
Speaker 2: A diamond, commet with a cloud of carbon.

00:32:17
Speaker 1: And leave a trail of sparkly melted diamonds.

00:32:21
Speaker 2: Yeah. I think melted diamond is just carbon though, because it's only diamond because of the arrangement of those carbon atoms, and so once you melted it could it's the same as like melted coal. I guess.

00:32:31
Speaker 1: Oh, man, now we're getting really confusing.

00:32:33
Speaker 2: Turn chemistry is a mess.

00:32:36
Speaker 1: Is melted chocolate just carbon?

00:32:38
Speaker 3: Then?

00:32:38
Speaker 1: Oh no, amre I just eating coal when I when I'm drinking my hot coco.

00:32:45
Speaker 2: That's why putting these names on things is such a mess, and we should just use math or charades.

00:32:50
Speaker 1: That's why would you just use charades or speed up the telepathy idea.

00:32:57
Speaker 2: And then to make things even more confusing, there's another counter glory of stuff that's sort of like a hybrid, these things that are actually brilliantly named. They call them centaurs. You know, centaurs are like half horse, half human. These things have characteristics of asteroids and characteristics of comets. So they're sort of like a comet because they have long elliptical orbits the way comets do, and some of them have dust comas. But they're kind of like asteroids in that they're really large and they're mostly metallic. But they're not like asteroids because they leave the asteroid belts and they sort of traverse the Solar system the way comets do. So these centaurs are sort of like a weird thing in the Solar system that blurs the line between asteroid and.

00:33:42
Speaker 1: Comet, meaning like it's a mix of rocks and ice.

00:33:46
Speaker 2: Yeah, exactly, And it sort of moves like a comet, and it's the size of an asteroid. These things tend to be typically bigger.

00:33:52
Speaker 1: Wait, what do you mean it moves like a comet? You never said motion was part of the definition.

00:33:57
Speaker 2: Yeah, it's not technically part of the definition, right, But comets tend to have these longer elliptical orbits just because of where they come from in the Solar System. They come from further out, and so they have these longer orbits that traverse the path of the giant planets, whereas asteroids typically hanging out in the asteroid belt and sometimes fall in and so they don't traverse the giant planets. So if you have like an asteroid like rock that also has a long elliptical orbit, you're like, hmm, it's a little comedy. It's a little asteroid y. You know. It's sort of like chocolate and peanut.

00:34:27
Speaker 1: Butter, which we all know. If you melt it just becomes carbon.

00:34:31
Speaker 2: And if you squeeze it hard enough, it becomes a diamond.

00:34:34
Speaker 1: Yeah, technically a chunky diamond or a smooth diamond.

00:34:38
Speaker 2: Yeah, maybe a creamy diamond.

00:34:39
Speaker 1: Yeah, or me a carrot diamond.

00:34:40
Speaker 2: I like my diamonds nicely salted.

00:34:42
Speaker 1: So these centers are pretty interesting. How big can they get?

00:34:45
Speaker 2: Some of them are pretty big, Like the largest one is two hundred and seventy kilometers across and Actually it's so big that it has its own rings, like a little group of dust and tiny rocks orbiting this centaur.

00:34:59
Speaker 1: Well, and where is that it orbits in.

00:35:00
Speaker 2: The Solar system out there between Saturn and Urinus. So it's a big blob out there, and it's sort of weird to be that far out. Why isn't it in the asteroid belt? Or if it's that far out, why doesn't that have more ice? You know? You might ask also, well why do all the objects and what we call the asteroid belt, why are they mostly rocks and metal and the stuff out there in what we call the Kuyper belt in the or cloud, why do they have more ices? And that's just distance from the sun. If you're further from the Sun, then the sun is not bright enough, not hot enough to vaporize all that stuff, so you get these ices. And that's why comets when they form out there, are icy and asteroids are not. The way the Earth is not mostly icy, right, and so it's weird to have an object that's out there beyond the snow line that doesn't have as much snow or ice as everything else.

00:35:50
Speaker 1: And how do we know it's a scenter? Does it have a tail.

00:35:53
Speaker 2: This one is big enough that it might have its own like little atmosphere, right, things that are boiling off of it. But we don't know the compassation of it that well, it's sort of far enough away that it's difficult to study. But we do see that has its own ring systems, so we have some information about it. But these things are really fascinating because they paint sort of a picture of the history of the solar system. A lot of this stuff is interesting in the context of like, hey, how did we get here? How did our solar system end up the way that it is? All these things are clues that let us like back out that story and figure out how it all got arranged to be this way.

00:36:28
Speaker 1: So can we tell what it's made out of?

00:36:30
Speaker 2: With our telescopes, we can tell a little bit because of the color, Like some of these things are a little bluer and some of these things are a little redder. That gives us a clue as to what they are, because what they are determines you know, what they're reflecting and what they're absorbing. So we have some clues about their chemical composition. But that's also sort of a mystery, Like some of these centaurs are bluer, and some of these are redder. Some of them look more like asteroids, some of them look less like asteroids. That's sort of one of the central mysteries of centaurs. But none of these things have been like foot Graft up close. A lot of Solar System objects have been visited by probes, like we recently had up close pictures of Pluto, which is awesome, and most of the moons of Saturn and Jupiter have been visited. But nobody's ever done a close flyby of a centaur to take like crisp photos of its surface and see what it's made out of and what that surface looks like. It'd be really fascinating.

00:37:22
Speaker 1: But wait, how do we know what they're made out of?

00:37:24
Speaker 2: Then we don't know for sure. It's just really guesses based on the spectrometry looking at the wavelength of light that bounces off of it. So we have ideas.

00:37:32
Speaker 1: How do you assume that it has I in it?

00:37:34
Speaker 2: Because they look different from the asteroids, right, they have different reflections than asteroids do m All.

00:37:40
Speaker 1: Right, Well, let's get to the question of the episode, which is are there comments in the asteroid belt So let's tackle that. But first let's take another quick break. All right, we're talking about comets, asteroids, and centaurs and also a charades.

00:38:09
Speaker 2: So in your house, who typically wins the games of charades?

00:38:12
Speaker 1: We never play charades.

00:38:14
Speaker 2: What you're such a big proponent on the podcast, but you don't practice that at home.

00:38:18
Speaker 1: That's what I'm trying to see, Daniel, is bring more charates into everyone's homes. So we're tackling today the question are there comments in the asteroid belt? Now, Daniel? Is the answer yes or no?

00:38:28
Speaker 2: The answer is that there's some weird stuff in the asteroid belt that we don't understand. In nineteen ninety six, people saw something in the asteroid belt that had a coma, Like it has this gas and envelope in it, so it looks like it's melting in the presence of the sun.

00:38:45
Speaker 10: Wait.

00:38:46
Speaker 1: Wait, so that the tail of a comet, you call it a coma.

00:38:48
Speaker 2: The tail is when it's moving, a coma is like the envelope that surrounds It's sort of like a little atmosphere, but it's not really an atmosphere because it's not holding onto it gravitationally. It's just sort of like off gassing. It's like melting the vapor that's coming off as the sun is melting it.

00:39:02
Speaker 1: That's the coma, like an ara or like a cloud of a vapor around it.

00:39:07
Speaker 2: Yeah, exactly. And then if it's in motion, it's going to leave that behind because it's not gravitationally holding on to it and generated a tail. So coma and a tail are characteristic signatures of a comet rather than asteroid. And in nineteen ninety six people were looking at stuff in the asteroid belt and it's like, what's out there, what's weird? And they found this one that had a coma and a tail, and people were like, well, that's weird. But you know, one example is never anything, because you can always find one weird thing just necessarily tell you anything. But then a few years later they did a systematic study this Isaac Newton telescope in the Canary Islands. They were watching five hundred and thirty four asteroids specifically looking for like a gassy shell around them or whether they had a tail, and they found like twenty more of these things in the asteroid belt that have comas and tails.

00:39:58
Speaker 1: Well, so does that I mean their comments or centaurs.

00:40:01
Speaker 2: It means we don't know what to name these things, and maybe we're all wrong about these definitions. After all, it means that we don't really understand like how they got there, you know. I think question number one is like, why is there something in the asteroid belt that's still melting? You put something there and it's melting, it's gonna shrink, so it can't last for very long. But we think a lot of these asteroids have been there for like billions of years, and so how long have these things been in the asteroid belt? And if it's only and if it's a recent event, then where do they come from? And if it's not a recent event, then how they lasted so long? So it's weird to see something that you know has got to be short lived. So it's weird to see so many things that you know have to be short lived, because there's got to be some explanation there.

00:40:46
Speaker 1: You're saying they saw a coma or a shell or a cloud or a tail, because you can see it with the telescope.

00:40:53
Speaker 2: As it passes in front of the sun, for example, you could see the gas around it affecting the light as it transits, or you can see the way it reflects light differently.

00:41:01
Speaker 1: These are pretty firmly in the asteroid belt or are they maybe just cruising through the asteroid belt?

00:41:06
Speaker 2: Oh yeah, great question. Now these are things that are part of the asteroid belt, and as they watch them, they have stable orbits that can make them be part of the asteroid belt. They're not just like happened to be comets that were captured on their way into the inner Solar System. These things are not transients. They're there in the asteroid belt basically to stay. But we don't understand where they came from. And these are deep and important questions because we want to understand, like where is the water in the Solar System? How did it get spread out the way that it did? For example, where did Earth's water come from? We know that all the ice and all the water that originally was involved in the formation of our planet got boiled off by the Sun in the early history of the Solar System, and so it's still an open question of like where did the water that's on the surface of the Earth. Now, Like where did our oceans come from? Did it come from comets hitting the Earth? Did it come from the water that's still trapped inside the Earth. These are important questions and to answer them, we're gonna have to understand like where's the water now and what is it? All of its history. It's a deep question about our origins and the whole history of the Solar System. And so whenever you see something weird.

00:42:12
Speaker 1: Like wait, are you saying that maybe, like some of these weird objects in the asteroid belt, they came from the outer Solar System and then maybe they crashed into the asteroid belt.

00:42:23
Speaker 2: It could be absolutely it could be that they were comets and they were coming into the asteroid belt and they like interfered with something. And people think of the asteroid belt the way you described like Star Wars earlier, like oh it's hard, you got to dodge the asteroids, it's very dense. In reality, the asteroid belt is very dilute, Like if you flew through the asteroid belt, it'd be hard to hit an asteroid. So a random comet flying through the asteroid belt is not going to have a problem making it through. But you know, maybe occasionally these things do get disturbed, or they get deflected by Jupiter or captured effectively somehow, And so it could be that these are comets that got waylaid and ended up in the asteroid belt. But then you'd need a continuous stream of them to keep it populated because they're not going to last very long in the asteroid belt, like the Sun is.

00:43:06
Speaker 1: Going to fry them even with they're that far away.

00:43:08
Speaker 2: Yeah, I mean, the fact that they have a gassy shell means that they are actively outgassing because they can't hold onto that gas. And if you're actively outgassing, you're literally melting, you're shrinking. That's not going to last very long. They might have like a rocky core and that might be left over when the Sun is done frying all of their ices, but they're definitely not going to look like this for that long. We're talking, you know, millions of years, but in the history of the Solar System, that's just a blink of an eye.

00:43:37
Speaker 1: I wonder if it could be just like the Earth when the Earth got formed, they had water trapped inside of it in the rock. Could these asteroids also have water inside of them that's maybe sweating out.

00:43:47
Speaker 2: They certainly might have water inside of them the way the Earth does. And you know, if you think about water inside the Earth, it's not like there's literally an ocean you can go swimming in. It's like the chemical composition of the rock includes a lot of water, and so in a similar way, you might have water infused into the metals and the rocks at the heart of these asteroids. But any water ice that the sun is capable of frying off got fried off a long time ago, because these asteroids have been there for billions of years, and so these guys would have to be new, right, these new, weird things they spotted in the asteroid belt should have arrived fairly recently, if that makes any.

00:44:21
Speaker 1: Sense, all right, Well, so I guess the answer is maybe are there comets in the asteroid There could be There are definitely things that are comedy, right, or that have ice in them.

00:44:32
Speaker 2: There's definitely something in the asteroid build that has ice because it's melting. We don't understand what they are, where they came from, or what it means about where our drinking water came from.

00:44:41
Speaker 1: Or would you say, maybe the answer is that some of the things in the asteroid belt are comets or could be classified as sort of comets.

00:44:50
Speaker 2: Yeah, by our definition, where comets are things that have ice in them, they're icy and dusty. Then, yeah, there are definitely some icy, dusty things in the asteroid belt. The asteroid belt is not just asteroid anymore where.

00:45:00
Speaker 1: I guess if you go by your definition of a comment, then everything is a comment.

00:45:06
Speaker 2: That's right, You're a comment. Right, we tossed you into the sun, you would melt and vaporize as well.

00:45:11
Speaker 1: So yeah, yeah, yeah, of course I'd be you know, trying to communicate with charades all the way down hoping someone picks me up. Good luck with that, all right? Well, another interesting exploration into our solar system, it's history and the mysteries that are still out there waiting to be discovered.

00:45:31
Speaker 2: There's so many missing chapters to the history of our solar system, so many things about our own backyard we still don't understand. And every time we look more carefully the things we thought we understood, we find weird things that defy our explanation, that tell us there's a lot more to this story to be revealed.

00:45:48
Speaker 1: Yeah, to be revealed by astronomers or physicists or both, or perhaps chemists. We're all just people, No, we're all just comments.

00:45:59
Speaker 2: That's right, what is it? Comed?

00:46:01
Speaker 1: Yeah? Thank you? We all have tales in Komas. All right, well, we hope you enjoyed that. Thanks for joining us, See you next time.

00:46:13
Speaker 2: For more science and curiosity, come find us on social media, where we answer questions and post videos. We're on Twitter, Discord, Insta, and now TikTok. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.