Several of the planets and moons in the Solar System are in orbital resonance, orbiting in a geometric lockstep. And not just the Solar System, astronomers have found the same resonances in other star systems.

(This is an automatically generated transcript)

Fraser Cain [00:01:19] Astronomy Cast episode 714 Orbital Resonance. Welcome to Astronomy Cast, 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 Doctor Pamela Guay, a senior scientist for the Planetary Science Institute and the director of Cosmic Quest. Hey, Pam, how are you doing? 

Pamela Gay [00:01:39] I am doing well. If you are watching this live, or perhaps even in recording, and things aren’t going entirely the way you would like, the audio will be perfect. There is something screwy going on with the internet right now. Apologies if the video and audio and everything is a little bit glitchy. 

Fraser Cain [00:01:59] We recorded a local version completely separate, and it gets edited and processed and it sounds beautiful and you should be experiencing these things via podcast. That way you can be out on a walk or a bike ride or, or gardening or doing the dishes. Yeah, yeah. 

Pamela Gay [00:02:15] Get out today outside. 

Fraser Cain [00:02:17] Right. Don’t don’t sit in front of a computer screen on a tiny phone watching us. No, let’s do a podcast. And then you can increase the speed to like 1.5 and one. We’re talking really quickly. 

Pamela Gay [00:02:29] Yeah. I’m not all those people. 

Fraser Cain [00:02:30] I’m more I’m totally one of those people. I listen to all my podcast super fast. Who has time for this? My brain can handle it at top speed. I watch all my YouTube videos at double speed. I review my own videos at triple speed because like, I don’t want to take 30 minutes to sit through my video. Yeah, then I know what I’m really just looking to catch mistakes as opposed to engaging with the content. But who knows? Who knows, maybe they’re just living in in some sort of fast forward future. Right. So some of the planets and moons in the solar system are in orbital resonance, orbiting in a geometric lockstep and not just the solar system. Astronomers have found the same resonance at other star systems. All right. So before we get into all of the crazy examples of where this happens, I want to just like just understand what is orbital residence, what’s going on here? 

Pamela Gay [00:03:24] The idea is compared to the stars, two or more objects will go around so that the alignment between the thing they’re orbiting them and the thing they’re in resonance with will in an integer number of orbits repeatedly line up with the stars so that you get object being orbited object or orbiting object orbiting stars lined up perfectly integer number of orbits. 

Fraser Cain [00:03:55] And so like, how do these integer numbers tend to fall like is it always the same number or does it differ. 

Pamela Gay [00:04:02] So it it can be all over the map. And different kinds of things can be in resonance for different reasons. So the the example that everyone starts out learning is the orbits of the Galilean moons, which even Galileo was like, oh, that’s weird. Where it where what we see is, Ganymede is the furthest out and Ganymede will go around once, and, Europa will go around twice, io will go around four times. And, so you have with, with these three worlds, this, this resonance in how they go around Callisto. Callisto decides it’s it’s not going to play any part in these memory games. Right. But with the other three. Yeah, yeah. Ganymede, Europa and innermost io have this integer resonance, which is really cool to look at top down in terms of you, you have just this periodic alignment of all three of them in Jupiter in a line. And when this occurs, you end up with more gravity affecting tidally pulling apart the worlds. And then when you have them most apart, you have the least tidal tugging. And this constant change on the forces on the worlds are what are driving Io’s volcanism are what is driving, we believe Europa’s crust slowly migrating, spiraling, changing. All of these forces generate heat inside the worlds, and it also has the ability in other cases to move things around. Now these worlds are locked in place. They’re going to stay in orbital resonance. But sometimes when objects sneak into orbital resonance. For instance, with the asteroid belt that repeated tug that they get every time they line back up with that other world. If it’s a significantly different size, for instance, if they end up in resonance with Jupiter, that’s going to actually change their orbits, and you can end up with either bands inside the rings of Saturn, you can end up with bands inside the asteroid belt where fewer objects are able to accumulate. 

Fraser Cain [00:06:37] That’s that’s really interesting, and I definitely want to get to that. But I but I kind of want to go back and get a sense of, of what is the mechanism that’s going on here. I mean, I think when we think about the, the interior, how io is this volcanic moon and how Europa has its liquid water and that we know that they’re being heated this tidal heating. The moons are playing a big part in this tidal heating. But what is, I guess, what is causing if you see, IO goes around once and Europa goes around. Oh, sorry. Yeah. So Ganymede goes around once. Yes. Goes around, goes around twice, and io goes around four times. Yes, but what is what is like causing them to lock up into this residence? Like they didn’t start out that way? Probably. 

Pamela Gay [00:07:25] Probably. It’s, you know, that that is kind of weird to think about. Now, if things like this don’t happen accidentally, they happen. Because if you’re very close to lining up, you’re going to get pulled forward as you get closer to that other object you’re in orbit with. If you’re a little bit ahead, you’re going to get slowed down so the forces will actually cause the objects to want to line up like this icy. And so over time, this, this torquing that occurs on the orbits will force them into alignment. It’s it’s very similar to the kinds of situations that happen that cause worlds to get tidally locked. In this case, instead of locking the rotation, it’s locking the orbit. And you can actually and I’m sure we’ll get to it, have a combination of the rotation and the orbit get locked together. There’s all different ways to fall into resonance. 

Fraser Cain [00:08:25] Right? Right. I mean, we think about the moon being tidally locked to the Earth. I guess that’s a form of residence. 

Pamela Gay [00:08:33] It’s we don’t usually talk about that as being a resonance. But for instance, if you look at the planet Mercury, we had thought for decades that it would probably be tidally locked to the sun. And then back in the 1960s when they finally did radar observations of it. And it’s not perfectly round this works. They were able to see that for every two times it goes around the sun, it spins three times. Right. And this particular spin orbit resonance is super rare. We think there is only a 26% probability that this could happen. But I’ve read this really cool paper preparing for this show. It’s it’s a paper in Mercury from 2011 by Mark White Sturrock that talks about how it’s possible. And we’re going to be able to figure out if this is true, probably from the BAP of Colombo data, that Mercury was once tidally locked, high probability event, and then got the bejesus smacked out of it by some sort of an impacting event, and that knocked it into the 3 to 2 resonance that we see today. And if that’s true, we will see differences in the two sides of it, how they appear. And this may explain some of the features that we’ve already been able to make out. We just need more data. We always need more data. 

Fraser Cain [00:10:06] All right. So we’ve looked at the famous moons of Jupiter and this really interesting situation of Mercury’s spin versus its orbital resonance. What other what are some other examples of things inside the solar system that have some kind of orbital resonance there? 

Pamela Gay [00:10:28] There are so many different moons orbiting so many different worlds that it seems like it’s just kind of ultimately, when you have multiple moons going around an object, you’re going to end up with this kind of a thing. We have cases of asteroids. We have moons of pretty much every world that do this. So there there are moons in residence scattered all. Throughout our our solar system. And there’s also worlds in resonance. Earth and Venus have an 8 to 13 resonance. Venus to Mercury has a 9 to 23 resonance. Yeah. 

Fraser Cain [00:11:23] That’s amazing. So? So sorry. What were the numbers for Venus again? 

Pamela Gay [00:11:28] Earth to Venus is 8 to 13. 

Fraser Cain [00:11:31] So for every 13 times of Venus goes around the sun, Earth goes eight times around the sun. Yeah. That’s bonkers. 

Pamela Gay [00:11:39] Yeah. So? So there’s all of these different things going on. Deimos and Phobos are a 1 to 4 resonance. And. Then the Jupiter versus asteroids like Jupiter versus the really large asteroid Pallas is a 7 to 18 resonance. And I figured there must be some one out there. Now that just runs software. Every time a new world is discovered to find that, the resonances. 

Fraser Cain [00:12:11] Find the resonances. Yeah. That’s interesting. 

Pamela Gay [00:12:14] But once upon a time, it was people doing all of this by hand, trying to figure out what exactly is and isn’t in resonance. And we see all sorts of different resonances with your Uranus’s satellites, with Neptune satellites. And it just seems to be the talks will naturally, if worlds are left alone, allow resonances to occur. Even Pluto, with all of its little satellites, Styx and Sharon or one, two, three Nix and Sharon is 1 to 4. Kerberos and Sharon is 1 to 5. Hydra and Sharon is 1 to 6. 

Fraser Cain [00:12:54] I think. But but the Pluto to Neptune one is really interesting. People always ask like, why is it if if Neptune hasn’t cleared its orbit? I’m sorry if Pluto hasn’t cleared its orbit, right. If, if if it crosses orbit with Neptune every I forget some number of years. Why does it sometimes crash into Neptune? But in fact Neptune in Pluto or any two three orbital resonance. So? So they never can. They are always orbiting in their exact way, so that the paths of Neptune and Pluto never cross and they will never collide because of this orbital resonance. 

Pamela Gay [00:13:35] And these are the things that allow us to say, yeah, our solar system has been around in the form it’s in currently long enough to allow all of these resonances to accumulate. And that’s one of the cool things to think about is when solar systems form, you have mass chaos. You have things that form in all sorts of different orbits. You have things that form in elliptical orbits and go off and smash into other things. And over the fullness of time, worlds get captured by bigger worlds. Things evolve into resonance, things rotate into resonance, and it’s simply the gravity wins. Gravity always wins, including in forming resonances. 

Fraser Cain [00:14:26] That’s interesting if you think about this. I mean, I like this idea that you find a new object, and then it’s this question of finding it’s, you know, once you’ve calculated its orbit, try to figure out what the influence is. And eventually it may turn out to be some integer. Oh, what do you know? This newly discovered dwarf planet has a 364 to, I don’t know, 197 orbital resonance with some other object that that these objects have been orbiting each other and the sun for billions of years. They have made millions, tens of thousands. Or even billions of orbits. And those tiny perturbations just add up over time. Everything wants to settle into the most stable residence that it can. So you brought up Saturn’s rings earlier in the night? Yeah. Brutally cut you off. So can you continue that thought? What do we see in terms of residence in the rings of Saturn? 

Pamela Gay [00:15:29] So? So with with both the asteroid ring and the, rings of Saturn, there are times where larger moons are able to fling objects out of gaps. And, Saturn’s rings and Jupiter’s able to fling things out of certain orbits in the asteroid belt. And this is simply a matter of the thing that you’re in resonance with, is significantly larger than you are. And and so it’s able to simply move you about at its whim and whimsy until you, cease to be there. 

Fraser Cain [00:16:11] Really interesting. So astronomers don’t just see resonance here in the solar system. I mean, obviously, if everything is in resonance, then you would expect to see resonance wherever you look across, you know, across the cosmos. Yeah. So we but but it’s one thing to propose. Of course, this is everywhere. The. But finding it. Astronomers have made some incredible examples of finding resonance out there around other star systems. So can you show me some examples of that? 

Pamela Gay [00:16:39] I think the one that people talk about most is a six planet system that is, given the license plate address, HD 11 0067. And this world is basically designed like it feels like musical strings. The innermost world to the next is a 3 to 2 ratio. That one and the one furthest out is a 3 to 2 ratio. That one and the one further out is a 3 to 2 ratio. So we have three 3 to 2 ratios in a row. And then we have two 4 to 3 ratios. And and so it’s this really cool set of three things that are identical sort of two things that are identical and six different worlds. They’re not all that hugely different in size. And of course they’ve done all sorts of cool infographics showing what are basically spiral graphs of the motions of this system. It’s called a resonant six top list of sub Neptune’s that are all orbiting one star. 

Fraser Cain [00:17:51] Wow. And in fact, a pretty big percentage of multi planetary systems are in resonance. I mean, I think it’s something, you know, it’s like it’s above 10% of just all of the, you know, whenever they find a system that has at least two planets in it, there’s a pretty good chance that they’re going to be in residence again, A12. Yeah. So they’re everywhere. 

Pamela Gay [00:18:16] And and so we see it again. The Trappist system of seven planets has resonances. And there’s been some really cool. Sonia Graf is the wrong word. 

Fraser Cain [00:18:27] Like to like to hear it? 

Pamela Gay [00:18:28] Yeah. What’s the name of the thing where they make it to the. Here? 

Fraser Cain [00:18:31] It’s on a fram. Yeah, I know what you mean. It’s like an acoustic version where they give a different musical note to each planet, and then they play them at the cadence that they’re going around. And it sounds kind of like music. Yeah. 

Pamela Gay [00:18:45] And so with Trappist one, seven worlds, this is totally what they are finding. 

Fraser Cain [00:18:52] So, you know, we’ve talked about planets, we’ve talked about moons. But then do we get other things like if we had a multi star system. Yeah. Would we get some kind of residence going on. 

Pamela Gay [00:19:04] Yes. And we have seen stars and multi multi stellar resonances. The trick is with stars the most likely thing that’s going to end up happening is you end up with two in the center going around each other, and a third going around the inner to or some version of that. You might end up with one in the center and then the other two going around it. So you really have to start to get to the four star systems where it’s not two binaries. But it is possible. So it’s, it’s all a matter of how do they go around. But to get resonance the vast you have large mass in the center, things of similar mass going around. If you have large thing in the center, small thing, big thing, big thing, remove small thing. Gas in Saturn’s rings. Gap in orbit. Right. If you have things of similar size like this, set six to split of sub Neptune’s. I cannot say that fast, but is my challenge to all of you. 

Fraser Cain [00:20:10] Six couple of separate tunes. 

Pamela Gay [00:20:12] Okay. All you then you start to see more and more of these resonances occurring. And so it is. It is a matter of what is the ratio of masses? How long have they been there to get to move each other around? And, given the fullness of time. Resonances will occur where the masses allow it. 

Fraser Cain [00:20:39] And then I wonder if you have even weirder things. I mean, could you have three black holes in some kind of of interaction where or even. 

Pamela Gay [00:20:51] No, because they’re you’re looking at three equal mass objects. So with star. 

Fraser Cain [00:20:55] No. Well let’s say they’re not. No. Like say you’ve got one supermassive black hole and it’s being orbited by two other smaller black holes. And they’re destined to merge in the future. 

Pamela Gay [00:21:03] Yes. Then you can get a resonance. 

Fraser Cain [00:21:05] Yeah. Like, would you see the residents like, right now we see the resonance in that we we can can track them. But imagine if you could see that resonance in the gravitational waves as opposed to tracking them then visually. And it should all just at the end you’ll get the same numbers, but with black holes they don’t have. Yeah, things that they don’t have gravitational handles in the same way. And so I wonder if black holes would, would end up with the same kinds of resonances that, that objects that are not perfectly mathematically, I guess oblate. 

Pamela Gay [00:21:41] There’s no reason that that can’t occur, but I can’t see why we would be able to detect it in the gravitational waves with current technology. That’s where it gets tricky. Story is we generally see currently the the waves only at that last moment of of collision. But technology will change over time and who knows what will be possible. Although it does sound rather like a low probability kind of thing. 

Fraser Cain [00:22:14] Yeah. And then I guess, should we also see that the larger scales, when you imagine galaxies orbiting around galaxy clusters, I mean, I guess they’re getting torn apart by tidal forces because they’re not. But I wonder. 

Pamela Gay [00:22:28] So there you have the added force of drag, which we don’t really have within the solar system. So yeah, orbital resonances can occur because of that. Orbit is defined by by GMM over r squared. Then it’s getting affected by that larger mass that it’s also in orbit with. But no drag is being involved. Once you add in drag, that changes all of the physics. 

Fraser Cain [00:23:00] Right. And can you think of anything else like. Where this could be useful for science. In terms of like, are there interesting ways that they can use or like, I know, for example, they use orbital resonance to try to predict the existence of other worlds in the solar system, dwarf planet, planet nine, things like that. Right? That you’re you’re seeing what should be an orbital resonance, and that allows you to infer that there must be some object affecting gravitationally. Yes. 

Pamela Gay [00:23:34] And so we can assume that the best places to go looking for things is where the resonance points are. We can look at slightly elliptical orbits and say what kind of a resonance would create that ellipticity? Things are extremely complicated. So. That doesn’t always help. We are learning with the search for Planet nine or whatever you wish to number it. I leave the numbering up to you. I’m going to be agnostic. 

Fraser Cain [00:24:11] But you’re right. This Alan Stern gives this a strongly worded email. 

Pamela Gay [00:24:15] Yeah, yeah. Yeah. It’s so there are so many interesting explanations for why there isn’t a Planet Nine out there. There are so many interesting explanations for why there must be. And this is why we haven’t found it. We need to have an observatory to do Lsst survey as quickly as possible. And yes, I know the word survey is in the acronym Lsst, but it sounds stupid to just say Alice s t. 

Fraser Cain [00:24:43] All right. Very interesting. 

Pamela Gay [00:24:45] Thanks, Pamela. Thank you, Fraser, and thank you to any of you who made it through all of our internet difficulties. As I see, we are now streaming live once again. Apologies for all the chaos my computer and Chrome’s desire to spawn AI is causing us this week. 

Fraser Cain [00:25:04] Well, the podcast listeners don’t have a problem with that. Don’t listen to the nicely edited version. Listen to the podcast. 

Pamela Gay [00:25:11] It’s true. Listen to the podcast. And, all of you, whether you know it or not, are extremely grateful to these people and many others who are our patrons. These folks have joined our. Pamela will mispronounce my name here and we are grateful. This week I would like to thank Cooper, Benjamin Mueller, Peter Don Mundus, Aaron Zagreb, Philip Grand, Cami Ross, Ian James, Roger, Sean Matz, Sam Brooks and his mom Nate Detweiler, Dean, Jeff Wilson, Kimberly Reck, disaster. Cheena, Tim Gerrish, John Drake, Philip Walker, Paul de Disney, Janelle aka Veronica Cure, Michelle Cullen, Benjamin. Davies, Dwight. Ilke, Brian. Kilby, Sydney. Walker, David. Bogard, Robert. Cordova, Justin S, Maxim Levitt, Howe McKinney. Bebop. Apocalypse Ruben McCarthy, Larry. Dots, Frank. Stewart, Jason. Caduceus, Gordon. Turner, Christiane. Golding, Bob. Czapski, Ron. Thorson, Daniel. Donaldson. Thank you all so very much. 

Fraser Cain [00:26:23] Thanks, everyone, and we’ll see you next week. 

Pamela Gay [00:26:26] And I’m going to stop the recording and save. And then they saved and then they saved and then they saved and then they saved and then they saved and then they saved and then they saved. And be safe. 

Fraser Cain [00:26:52] And they saved. 

Pamela Gay [00:26:54] All right. And then they saved. 

Fraser Cain [00:26:57] And then they saved. Our dogs are really losing their minds. 

Pamela Gay [00:27:02] I don’t know what’s going on. I’m sorry. We’re just gonna have to pause for a moment. There’s howling and barking and more howling. I don’t understand it. This normally is what happens when someone comes over, but I don’t think anyone’s coming over today. Astronomy cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy cast is released under a Creative Commons Attribution license. So love it, share it, and remix it, but please credit it to our hosts, Fraser Cain and Doctor Pamela Gay. You can get more information on today’s show topic on our website. Astronomy. Cars.com. This episode was brought to you. Thanks to our generous patrons on Patreon. If you want to help keep the show going, please consider joining our community at Patreon.com Slash Astronomy Cast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox and invites to online events. We are so grateful to all of you who have joined our Patreon community already. Anyways, keep looking up. This has been Astronomy Cast. 

Orbital resonance (Wikipedia entry)

What is orbital resonance? A dance between heavenly bodies (EarthSky)

Orbital Resonance: Planets Have a Gravitational Dance With Aligning Orbits (Discover Magazine, Chris Impey of University of Arizona)

Resonant Effects (NASA Science)

ESA’s Cheops helps unlock rare six-planet system (ESA)

Found super-Earth and mini-Neptune in orbital resonance (Universe Magazine)

Astronomers from the University of Liège discover a key planetary system to understand the formation mechanism of the mysterious ‘super-Earths’ (University of Liège ExoTIC)

Mercury’s spin–orbit resonance explained by initial retrograde and subsequent synchronous rotation (Nature Geoscience)

Orbital resonance in the solar system (S. J. Peale, University of California Santa Barbara; archived by NASA ADS)

Orbital resonances in planetary systems (Preprint) (Renu Malhotra, Lunar and Planetary Laboratory, University of Arizona)

Wherever we find liquid water on Earth, we find life, so it makes sense to search for water across the Universe, and hopefully we can find evidence of life. But what about worlds which are completely covered in water, oceans hundreds of kilometers deep. Can there be too much water?

(This is an automatically generated transcript)

Fraser Cain [00:01:50] Astronomy Cast. Episode 705 Waterworld. Looking for life beyond Earth. Welcome to Astronomy Cast, a 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 Doctor Pamela K, a senior scientist for the Planetary Science Institute and the director of Cosmic Quest. Hey, Padma, how are you doing? 

Pamela Gay [00:02:13] I am doing well. I just want to alert all of our listeners. We’re going to take a completely random week in January off. Yes, because next week I’m going to be in Orlando for the ship Podcast Conference and Sonic Bloom Awards. Astronomy Cast is nominated for a People’s Choice Award. All of the voting occurred while we were on hiatus, so Lord knows how that’s going to work. Yeah, yeah. But, yeah, I will I will be away next week, and I’m actually going to take a couple of days off. My colleague in crime, Annie Wilson, she and I are going to reprise our is the save rocket travels through Disney and Universal. 

Fraser Cain [00:02:57] That sounds great. Wherever we find liquid water on Earth, we find life. So it makes sense to search for water across the universe. And hopefully we can find evidence of life. But what about worlds which are completely covered in water? Oceans hundreds of kilometers deep? Can there be too much water? So this idea of water worlds. I mean, we learned everything we needed to know from that Kevin Costner movie, right? 

Pamela Gay [00:03:21] No. Now, one of the things that that I was thinking about preparing for this show is just how magnificently wrong in pretty much every way that movie appears to have been, except from a climate change perspective. And really, if you want one thing to be wrong, you want it to be the climate change part that’s wrong. 

Fraser Cain [00:03:44] So yeah, but climate change causes sea levels to rise by a couple of hundred feet in the worst case scenario, right? 

Pamela Gay [00:03:52] No. That’s true. It won’t eat the entire planet. It will still be soil. 

Fraser Cain [00:03:55] The coastlines will be roughly where they were, especially in places that are very mountainous. So, you know, won’t be hard where you’re trying to find evidence of violence. No, no, but this idea of water worlds, these we know they exist here in the solar system, and we’re starting to we assume that they’re out there. So. So give us sort of like an idea. What is the quintessential water world here in the solar system? 

Pamela Gay [00:04:22] So within, our system, we’re looking at the more moon like definition of world, where we have things like Europa and Solidus and potentially things I personally would never have expected 20 years ago, like Ganymede, these these are worlds that have what appeared to be solid surfaces. And from all of our data and the occasional observation of geysers. It looks like there are massive liquid oceans beneath these seemingly solid surfaces. 

Fraser Cain [00:04:59] Yeah. I mean, we’re looking at like, you see Ganymede, we’ve got Pluto. Sharon said. Yeah. Eris. Homer. Triton. Like probably there are dozens, if not maybe a hundred objects in the solar system that could be sort of in that classification of a water world. And so when we think about the kinds of worlds that are out there, they are the, the vast majority of the kinds of habitable environments. But, of course, you know, we have to sort of change our definition of what, of what habitable is. So, so let’s imagine then that we are starting to look for exoplanets. Yeah. What are some kinds of water world exoplanets that we might be able to find out there? 

Pamela Gay [00:05:49] Well, there has been for a while now theoretical models that there should be these super Earth sub Neptune mass objects with rocky cores, massive complete oceans, and hydrogen atmospheres. I have apparently been mispronouncing these worlds since the first time I read about them, because the word looks like it should be pronounced piscean, but it’s actually a portmanteau, which is where you smash two words together to get a new word like portmanteau. I don’t do French. I’m sorry. 

Fraser Cain [00:06:30] Apartment okay. Apartment. Okay, I oh, you do know. 

Pamela Gay [00:06:38] Sorry. But anyways, ignoring my inability to pronounce words. Podcast is an example where where, we’re broadcasting these pods of information essentially. 

Fraser Cain [00:06:55] To iPods, to Apple iPods. 

Pamela Gay [00:06:57] Yeah, yeah. 

Fraser Cain [00:06:58] Is the the historical. What’s an iPod, grandpa? 

Pamela Gay [00:07:02] I know, I know. But, it’s a combination of the words hydrogen and ocean. And when you combine hydrogen and ocean, you do not get high. Seein which I’m sure each of us will say at least. 

Fraser Cain [00:07:18] What I’m going to say. From here on out, I’m not. I’m not changing. 

Pamela Gay [00:07:22] All right. Yeah. The correct pronunciation for the people who came up with the word is apparently Haitian. 

Fraser Cain [00:07:28] Yep. Not doing it. 

Pamela Gay [00:07:30] We’re moving on. I can’t. All right. All right, that’s fine. So these, as I said, these are super Earth sub Neptune sized objects. Mass objects with rocky core, massive oceans and hydrogen atmosphere. And we have started finding them. 

Fraser Cain [00:07:46] Right. And I guess so. I’m sort of imagining a world like we’ve got a planet, like maybe Earth or a little bigger than Earth. It’s got ocean and it’s got this thick atmosphere that is majority hydrogen. And so is it like a warm ice giant. I mean, I think about a one in the interior of, say, Neptune. Right. You’ve got an atmosphere and then it’s got a lot of hydrogen and it’s got various ices and water and stuff inside of it. It’s just close to the sun. 

Pamela Gay [00:08:23] So. So you can’t make assumptions on temperature since these things can be moved around inside their solar system. It comes down to do they have enough gravity to hold on to the hydrogen. And do they have enough heat in their cores to maintain a liquid ocean at some point. And the fraction of liquid ocean to icy surface is going to vary with age of the system, distance from the sun kind of star, all that sort of craziness that makes making any assumptions about anything in our universe very difficult. 

Fraser Cain [00:09:04] Well, and the thing that is really exciting about these worlds is that, hydrogen is a really good insulator. Yeah, it’s a very potent greenhouse gas. And so you get a much wider habitable zone in a star system for where you can maintain a liquid water underneath that atmosphere. So here Venus is on the very inside of the habitable zone. Mars is on the very outside of the habitable zone. But you can have a habitable zone that is from Venus all the way out to the asteroid belt and still have liquid water on the surface of your planet. And so now what is a habitable zone is now has to be redefined. And that’s going to require, you know, if we can find some of these high C in worlds out there, Asian worlds out there. See, I did it. Then. Then and you find them, say, out of the orbit of Mars, beyond the over to Mars, the asteroid belt on the way to Jupiter. Ish. Suddenly the rules have changed. 

Pamela Gay [00:10:11] And and what I’m loving is the propensity for liquid water to exist beneath shells means the volume of space available for life has gone up significantly. There’s been some really cool work looking at Pluto and modeling the energy transport necessary to go from the heart on one side to the chaotic terrain on the other side. And, just what kind of density profile would allow that to happen? A a researcher, a Denton, has, has done all of this, and it’s amazing work that she’s done. And if you run the math on if from here to here is liquid ocean inside of Pluto. Calculate the volume and then compare that volume to the volume produced. If you take everything within plus or -two kilometers of sea level here on Earth, you end up with a greater volume available for for life in Pluto than on Earth. 

Fraser Cain [00:11:26] Wow. All right, we’re gonna talk about this some more, but it’s time for another break. 

Pamela Gay [00:11:32] This episode is sponsored by Factor Meals. A lot of us have New Year’s resolutions to eat better. No matter your reason to change your ways, factor has the meals to help you reach your goals and do it in the best way possible. Factors ready to eat meal delivery takes the stress out of meal planning. Skip the grocery stores, prep work and cooking fatigue instead. Get chef created, dietitian approved meals delivered right to your door, with over 35 meals to choose from per week, including options like keto, calorie, smart, vegan plus, veggie, and more. They’ve got you covered. My goals are just to eat more coherently and stop calling random handfuls of crackers and chunks of cheese. Lunch with two minute meals. I can have a real meal by factor in the time it takes water to boil to make my tea. Factor has everything I need for a week of flavorful, nutritious eats. In addition to ready to eat meals, they have cold pressed juices, smoothies, energy bites, extra protein, veggie sides, and more to keep me energized during frantic times. I am admittedly my own worst enemy when it comes to a healthy diet. And factor has become the ally I need to overcome my lazy grazing habits. Factors. No prep, no mass. Meals are easier than ordering takeout, and I can order everything for the week with just a few clicks. Need your own ally in the war to eat better? Head to factor meal Scoutmaster A50 and use code Aster 50 to get 50% off. That’s code Astro 50 at factor meals.com/astro 50 to get 50% off. 

Fraser Cain [00:13:25] And we’re back. So I actually interviewed the guy who came up with the name and was sort of pioneering these, these worlds, and we were talking about just how wide ranging these. Haitian. Ask so hard. These Haitian worlds are. And. And, you know, as I said, you know, the habitable zone is much wider that even the like rogue planets are back on the table because you could have, like, say, a brown dwarf star with one of these worlds orbiting around it. And if you get this tidal interactions, then it’s enough heat that it could keep the surface of this planet liquid, even though it is doesn’t have a star per se. 

Pamela Gay [00:14:12] In the fullness of time, it will cool off. But you’ve got a lot of times. 

Fraser Cain [00:14:17] Yeah, they got a lock. They got you got to stop. You know, you got to have multiple, multiple planets orbiting this brown dwarf so that you’ve got those resonances in there interacting with each other. Yeah. But yeah, eventually and eventually it will lock. But but again, like, suddenly what you thought was like the only place for us to look for life is in these terrestrial planets orbiting around sun like stars will. Now everything is as we note. So, so that’s like one type of of Waterworld. But let’s talk about like a more traditional one that we’re thinking about, like one that is more like Earth doesn’t have that thick hydrogen atmosphere is within the temperate zone. What is you know, what sort of what are our options there. 

Pamela Gay [00:15:02] I mean technically that makes us the quintessential example. We are a world that we have a high density core surrounded by liquid water and a splash of land and. As we look around the the nearby star systems trying to find Earthlike worlds, we keep finding things with different densities for their given size. And it seems like if you can imagine it, the universe will create it. So we can expect there to be, through collisions and other natural interactions, as well as from formation, a suite of worlds with the entire distribution from tiny core, lots of water, nitrogen atmosphere to massive core oceans and crust with more crust than we have. Wow. And and it’s going to be a continuum. And this is what I’m loving. We’re finding just looking around our solar system, more and more evidence for massive collisions happening during planetary formation as, instruments like, the Atacama Large Millimeter and submillimeter Array and Meerkat look at planetary forming disks are starting to find evidence for, increased, collisions in other solar systems while they form. And every collision offers a new opportunity for weird planets to exist. 

Fraser Cain [00:16:44] Yeah. And so I’m sort of imagining, like, like, let’s take Earth as the standard planet, which of course, is is ridiculous to say. But, you know, we have maybe, whatever, ten, approximately ten kilometers deep at the deepest part of the ocean. I don’t know what the average depth is. A couple of kilometers across the Earth is. Yeah, 70 something percent water. But that’s just, you know, Europa has more water than Earth does. And so, yes, you could imagine a world that maybe has no land that it has. Yeah. That oceans that are not that are maybe 100km deep or more. 

Pamela Gay [00:17:23] Yes. And and the one thing that we do seem to be seeing consistently is due to the distribution of materials out there and how gravity works, you are going to end up with dust grains colliding to form, planetesimals colliding to form bigger and bigger cores. And it is these cores that are able to attract in the volatile elements. So the gases and ultimately water in the early solar system, and then it appears to be through collisional processes that water gets delivered later. So you’re imagining solar systems that built up this core have sufficient gravity to hold on to their atmosphere, and then got the bejesus pounded out of them by things carrying water to them, or they’re orbiting a star that didn’t blast them dry early in their solar system, because they either migrated from farther out inwards towards their star, or there’s a mechanism we just don’t understand yet. And I mean both. Yeah, seems to always be the universe’s answer. 

Fraser Cain [00:18:35] Well, and it’s funny. Yeah, I think both sounds great because we are it’s funny. Like we’re posting stories on Universe Today, I would say every couple of weeks, which are some variation of where did Earth get its water from? And it is always the Earth is too close to the sun, it’s within the frost line and so water shouldn’t be stable. It should be blasted away by the radiation and sun. Just look at the moon and you hear that sounds of water. So where did that water come from? Like, did it form in place or was it delivered later by comets, as you said. And and they are finding that and there and in fact, astronomers have found with James Webb evidence of water in the dust grains of newly forming planetary systems. And so it really both sounds exactly right, that you had this water present in the early material that formed the planet, and if the planet had enough gravity, then it could hold on to the water, it could keep it safe inside its interior, and then at the same time, it could have that stuff delivered. And then if some mechanism that stopped it from, from, you know, that that allowed it to keep all this water out on the surface, then then who knows where you’re going to get. And so I think you’re 100% right that in the end it’s going to end up with all of it. C all of the above. Right. 

Pamela Gay [00:19:51] Well, and what I’m loving is we actually don’t know how common or uncommon it is for life to form. So everything has its own probability. There. There is the the probability. I’m going to somehow manage to make it through an entire week without getting coffee on my counter. While making coffee in the morning, the probability of that happening is close to zero. There is the probability of getting through an entire. Higher week, without going to bed before midnight, the probability of that happening is close to 100%. There’s so many things that are in between. And if life has even a 30% chance of forming under a water nutrient temperature gradient, kind of. This has the potential to support life environment. We will find life in our solar system on one of these icy worlds, in fossil relics, on a worlds like Mars. Potentially even living on the surface and really small, not very intelligent formats on Titan. And and so within our solar system, we have the potential to figure out what is the probability of life finding a way. And as we look out at other worlds, we’re already starting to see with Kepler K2 18 b, a world that has a biosignature that doesn’t have to be a biosignature, but could be a biosignature. And this is an ocean world. And if we find out. Maybe it’s being argued. 

Fraser Cain [00:21:39] Yeah. Yeah. 

Pamela Gay [00:21:40] There’s dimethyl sulfide. It’s made by algae here. 

Fraser Cain [00:21:43] Maybe. 

Pamela Gay [00:21:45] All right. I looked at. Go ahead, tell us more. I simply looked at the spectra and went, yes, that looks like a spectra. Okay. 

Fraser Cain [00:21:53] Yeah, I know what you’re talking about. And there’s been quite a lot of, of people talking about sort of. And there was this original hydrogen world and there was the discovery of a potential. But but like just the amount of segments are just too low. So yeah. So the the presence of the biosignature is very weak evidence. And it’s a big claim. It’s a big, bold claim to say, we’ve found a we found a chemical in the atmosphere of a plane that can only be formed by life there for life. 

Pamela Gay [00:22:22] That is I would I wouldn’t say the second half. So so what I’m comfortable saying is molecules are messy, molecules are hard to detect. There is a spectra from the James Webb Space Telescope that one way to interpret the spectra is the overlapping patterns of carbon dioxide, methane and dimethyl sulfide overlapping, making it really hard to figure out how much any of these things, what proportions they exist in. And it is a non-unique signature. I’m not willing to say dimethyl sulfide. Sulfide, that gas, that gas is only made by life. I mean, the universe is more creative than we are. But it’s an intriguing spectrum that needs replicated. We just don’t have a bigger telescope to replicate it with. 

Fraser Cain [00:23:17] Well, more time with with Webb to pull it off. But but yeah, like, I’ve been obsessing about Exoplanetary atmosphere observations for the last couple of months, and I’ve probably done 4 or 5 interviews in the last in this time with people who specialize in this. And. And and there I mean, they’re really good at what they do. And the message keeps coming back loud and clear, which is that we are not ready to recognize the signal, a biosignature that the scientists haven’t even agreed on. What is a potential biosignature. They argue about Venus as a potential biosignature. We’re so far away from that, and so weirdly, I can’t believe this is coming from me, but I think it is premature for people to be saying that a biosignature it’s getting found on this planet. We actually did another article in Universe Today about how it’s actually really hard to tell the difference between a planet where one half of it is covered in lava and one half of it is covered in water, that in fact they give off a very similar signal, produce a very similar chemical trace in the atmosphere. Because if all you’re doing is measuring the chemicals, you don’t know whether it’s farting bacteria or farting volcanoes. And so true. Yeah. And so we’re just so there was one to the last thing I really wanted to talk about, which was just this idea. Like, if you do have an ocean that is hundreds of kilometers deep. Is that a problem for life? 

Pamela Gay [00:24:52] I was giving this a good hard think the other day because at the bottom of the ocean you’re dealing with extremes in temperature, you’re dealing with extremes in pressure, and there is not the same. Kinds of life found at the bottom of the ocean that we find at more moderate depths, because they do have to find a way to not go squish. 

Fraser Cain [00:25:24] Yeah. 

Pamela Gay [00:25:27] But. Just as we’ve talked so often about the possibility for, balloon based studies, Venus, where you’re working at reasonable pressures and what you have at the surface of the world, you can imagine there being the kinds of thermodynamic mixing that allow there to be a depth that is amenable for life. But the question then becomes, how can it form? We don’t fully understand formation of life on Earth by any means. There are folks arguing that it started in clays, that it started in ice, that it started in hydrothermal springs. It’s possible it did all three. There is debating arguments over whether or not life emerged once or multiple times. It’s looking like, we can’t say how many times singular cellular life emerged. But multicellular life tried to spring forth in a many tentacled version, died off, spring forth with more solid bodies later. So when we can’t even answer with our own question, how did life form? How many times did life initialize, the zero to life versus the single cellular to multicellular level? I don’t think I’m comfortable saying what limits we need to place on other planets. 

Fraser Cain [00:26:59] Yeah. So there so there’s a couple of, like, interesting papers on on this one is that. Yeah. When you have that much water, as you said, you know, reaching intense pressures and. Yeah, and, and temperatures that in fact, you’re starting to approach the kinds of ice that you find inside worlds like Uranus and Neptune, that you’re actually the stuff is moving away from just liquid water and starting to turn into more exotic forms of, of water, like high pressure water. 

Pamela Gay [00:27:27] We did an entire episode. 

Fraser Cain [00:27:28] Yeah, yeah, yeah. And so you get to a certain point and now this stuff is no longer just water. It is now slushy. 

Pamela Gay [00:27:36] Chaotic environments of molecules that aren’t crystalline. Exactly. 

Fraser Cain [00:27:40] That’s the first thing. And then the second thing is, is that there might not be any mechanism for nutrients to get from the mantle, from the from the crust up. Yeah. The up the water column up to a place where it could then be able to provide for life. And so you’ve got the bottom of the ocean is uninhabitable because it’s just not it’s not liquid water. The topic would be habitable, but there’s no source of nutrients that’s able to come up for life to be able to work with. And then if. 

Pamela Gay [00:28:07] There’s an icy saw, if there’s an icy, surface, the nutrients from. So. So, yeah. Yeah. Raining down on nutrients from space. There’s some cool papers on that. Totally. 

Fraser Cain [00:28:18] Yeah. So you get, like a slight trickle of I mean, here on Earth, we get a little bit of 100 tons of dust a day. Yeah. And so that would be landing on. And so you can imagine the life really quickly scooping that stuff out and trying to incorporate it. Yeah. And but any time anything dies and sinks to the bottom of the ocean, then those nutrients lose ones. Yeah, yeah, yeah. So it’s like it just upends our idea. And we have these naive assumptions about what these places are going to be like. And yet nature tends to make it more complicated, as you said earlier on. And, and so it’s it feels like the vast majority of the worlds out there that we’re going to find are going to be some variation of water worlds, right? Maybe by a factor of 101. But how habitable are they? That’s still the question. 

Pamela Gay [00:29:09] And and I’m I hate this. Reaching the point in our lives where we have to start asking, will they answer these questions while I still care? Well, you still care. It’s like. It’s like, hurry up, humans. 

Fraser Cain [00:29:25] Do you mean like, while you’re still alive? Or do you expect there’s going to be time when you won’t care anymore? 

Pamela Gay [00:29:30] Well, I mean, there’s always multiple ways to approach the end of life. Asymptotically or directly. Yeah. So. Yeah. 

Fraser Cain [00:29:40] Yeah. 

Pamela Gay [00:29:40] That’s a darker topic for a different day. 

Fraser Cain [00:29:43] Yeah. But yeah, it’s a it’s an exciting time and it’s such a time of flux, like, like I can imagine a more exciting time than where we’re at now because we have the tools. We have a mission. The Europa Clipper is on its way to Europa soon. We’ve got the the Juice mission. We’ve got the Titan Dragonfly that’s going to be flying at Titan. We’ve got telescopes like James Webb and the upcoming Habitable Worlds Observatory. There’s the ground based telescopes like the Extremely Large Telescope. 

Pamela Gay [00:30:11] Like we have got to name things better. 

Fraser Cain [00:30:13] The pieces are all in place to finally be able to answer these questions. But but everyone’s gonna have to be patient while this work gets done and water worlds are on the list. 

Pamela Gay [00:30:27] And please name telescopes better. I know we’re writing stories last week. There is now the Large telescope array being built, the Extremely Large telescope being built. There is already a very large telescope, a very long bearing array. Yes. We need to do a better. 

Fraser Cain [00:30:44] No, this is purely the European Southern Observatory and that’s their style. So they named it the Very Large Telescope. And then they named it the Extremely Large Telescope. And the other telescope. It’s going to be called the Overwhelmingly Large Telescope. 

Pamela Gay [00:30:58] I approve. I love it one. 

Fraser Cain [00:31:00] Yeah. 

Pamela Gay [00:31:00] And that one went away. We need to bring the owl back. 

Fraser Cain [00:31:03] Yes. So, no, I think more power. Keep going. But. But with more ridiculously large names for their telescopes. I love it, every part of it. 

Pamela Gay [00:31:13] Yes, yes. 

Fraser Cain [00:31:14] Thank you, Pamela. 

Pamela Gay [00:31:15] And thank you, Fraser. And and thank you so much to to all of our patrons out there. I’m wearing my Patreon hoodie because it’s really warm and comfy. And thank you. This week I would like to thank in particular Joel Stein, Richard Drum, les Howard, Gordon doers, Adam and these Brown, Alexis Wanderer and 101 Kim Baron Felix good Astro sets William Andreas gold, Roland Vermeer, Dharma, Jeff Collins, Simon Parton, Stuart. Mills, Jeremy. Cohen, Kellyanne and David Parker, Harold. Burden, Hagen, Alex. Cohen, Claudia mastroianni. Conception, Fiona. Go and Esau, Matt Rucker, MH, w 1961 Supersymmetric Call. Mark Steven Resnick shares some, Abraham Cottrell, Paul L Hayden, Andrew Stevenson, Alex Rain, Benjamin Carrier, Bart Flaherty, the Lonely Sand Person, Daniel Loosely, and Jim Schooler. Thank you all so very much. 

Fraser Cain [00:32:16] Thanks, everyone, and we’ll see you next week. No. In two. 

Pamela Gay [00:32:19] Weeks. No. In two weeks. Yes. Bye bye. Astronomy cast is a joint product of the Universe Today and the Planetary Science Institute. Astronomy cast is released under a Creative Commons Attribution license. So love it, share it, and remix it. But please credit it to our hosts, Fraser Cain and Doctor Pamela Gay. You can get more information on today’s show topic on our website. Astronomy. Cars.com. This episode was brought to you. Thanks to our generous patrons on Patreon. If you want to help keep the show going, please consider joining our community at Patreon.com Slash Astronomy Cast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox and invites to online events. We are so grateful to all of you who have joined our Patreon community already. Anyways, keep looking up. This has been Astronomy Cast. 

Show Notes

Hycean planet (Wikipedia entry)

Webb Discovers Methane, Carbon Dioxide in Atmosphere of K2-18 b (NASA Webb Telescope Team)

Hycean planets might be habitable ocean worlds (Paul Scott Anderson, Earth Sky)

‘Hycean’ exoplanets may not be able to support life after all (Paul Sutter, Space.com)

‘Mini-Neptunes’ beyond solar system may soon yield signs of life (Nicola Davis, The Guardian)

Evidence for the volatile-rich composition of a 1.5-Earth-radius planet (Piaulet, C., Benneke, B., Almenara, J.M. et al, Nature Astronomy 7, 206–222 (2023))

Habitability and Biosignatures of Hycean Worlds (Nikku Madhusudhan et al, 2021, The Astrophysical Journal, 918 1)

The Runaway Greenhouse on Sub-Neptune Waterworlds (Raymond T. Pierrehumbert, 2023, The Astrophysical Journal, 944 20)

Validation and atmospheric exploration of the sub-Neptune TOI-2136b around a nearby M3 dwarf (K. Kawauchi, 2022, Astronomy and Astrophysics, 666)

Okay sci-fi writers, today we’re going to give you a guided tour of building planets. How they form, how they grow, and how things can go horribly horribly wrong.

(This is an automatically generated transcript)

Fraser Cain [00:01:19] Astronomy Cast. Episode 678. World Building. Planet formation, growth and ejection. Welcome to Astronomy Cast for weekly facts based on 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, the publisher of Universe Today. With me is Doctor Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Causal Quest. Hey, how you doing? 

Pamela Gay [00:01:41] I am doing well, but sleepy like you. And not even quite as extreme as you. We got up to attempt to watch a giant rocket. Yeah, go up and hopefully come back down. And it did not. But we we are still paying the sleep penalty for it. 

Fraser Cain [00:02:02] So we’ve like even though the weather is just horrible here, we’ve been getting a lot of really interesting wildlife things. The swallows just showed up for us for the first time this year. The daffodils have opened up for the first time this year where I live. And sandhill cranes. So I’m on the flight path for sandhill cranes that go from their summer to their winter homes. And it’s just amazing. Like you hear them when they’re over the horizon, and then you go outside and you wait, and then and then it’s just this giant formation of sandhill cranes that say overhead hundreds and hundreds and hundreds of them giant birds, like, as big as anything. Any other bird that you’ll ever see and like, think like pink flamingos size like the big. Yeah, yeah. And they, they fly overhead and they make this great sound. And we have these ponds in like a little marshy area. You know, I’m out there and I’m like, wave them. Come on down here. Like spend the night like I will, I will offer you great facilities. But they just keep flying overhead. So so so far we have yet to convince a, a a wing of sandhill cranes to come and land our property and enjoy an evening on our palatial estate. 

Pamela Gay [00:03:28] That would be amazing. 

Fraser Cain [00:03:29] It would really be amazing. Yeah. Yeah, I’m really excited. Hopefully. Apparently around here, they do. So. So various places. They’ll stop for the night. And it’s just like, cacophony just sounds wonderful. 

Pamela Gay [00:03:43] That’s. Yeah, that’s. We just have lake barred owls being very loud this time of year. Yeah. And they sound like monkeys. And it’s really disturbing to wake up at two in the morning to what sounds like monkeys going between the trees, but it’s just the owls. 

Fraser Cain [00:04:02] Yeah. All right, sci fi writers, today we’re going to give you a guided tour of building planets, how they form, how they grow and how things can go horribly, horribly wrong. All right. So how do you want to approach this? I mean, we’ve got. How do you get this is how you get planets, I guess. How do you get planets? 

Pamela Gay [00:04:24] Well, when when a large enough, stellar nebula gets knocked by a shockwave of some kind, it might collapse. And while collapsing, sometimes, if you’re very lucky, you can end up with a blob of matter glob ING on gravitationally to other blobs of matter until they form a planet. 

Fraser Cain [00:04:52] All right. That’s too simplified. I even use a more complicated word. Like I get the analogy you’re trying to run with here. When have Mommy Planet lost? Anyway. How so? Like, what is the. I mean, how do we get these planets? 

Pamela Gay [00:05:13] So. So basically when when you have a star forming, you have a cloud that is majority hydrogen, helium. And then in addition to that are going to be heavier elements in a variety of different proportions depending on how many different supernovae and other things like stellar mass loss through solar winds have occurred in that vicinity. 

Fraser Cain [00:05:39] So like how polluted you’re still in tabular is by previous generations of stars. 

Pamela Gay [00:05:44] Exactly. And if you have those heavier materials as everything comes in. Angular momentum is is the great deterrent of so many things in this universe, as a material tries to fall in towards that forming star. It ends up forming a disk. And within that disk you have the potential for these atoms to form molecules, to, form dust grains for dust grains to then collide together and through electrostatic forces, begin to build larger and larger things until they start to get big enough that gravitationally, they start pulling in the material around them. 

Fraser Cain [00:06:31] On top of that, for one, for one second. Sorry. Yeah. So, I mean, and this is something that always sort of confused me. Was that you if you have these little pieces of dust? 

Pamela Gay [00:06:40] Yeah. 

Fraser Cain [00:06:41] They’re so small and have so little gravity that they’re not going to cling to each other gravitationally when the interactions and perturbations from the rest of the source are just going to keep tearing them apart. And I’m assuming this was a mystery in astronomy for the longest time to. 

Pamela Gay [00:06:59] I don’t know how long it was a mystery. I have to admit. That’s that’s one of those things that I don’t know the history of. But as professors all deal with chalk dust, we are all fully aware that when you you erase that chalkboard, you get this fine particulate of dust just about everywhere. But in the chalk tray beneath the chalk board, you can end up with growing globs of whoa, chalky grossness. 

Fraser Cain [00:07:29] Really? 

Pamela Gay [00:07:30] And and this is usually because humidity in the air, someone spills something and you get chemical reactions. And these chemical reactions can allow the chalk. Chalk and the chalk dust tray. It’s not gravitationally holding itself together. It’s chemically holding itself together. And and so once you’ve seen that, it’s easy to go from. Well, if dust in my classroom is capable of growing over time through the interplay of room conditions and dust, it’s easy to imagine that in the universe itself, you have things chemically coming together and growing as well. 

Fraser Cain [00:08:16] But what you said is that it’s electrostatic coming together. 

Pamela Gay [00:08:21] And if you think about it, if you have two charged particles they come together or if you have two particles where one I guess electrostatic is the wrong word. Electro mechanics electrochemical. If you have two atoms that have energy shells for their electrons that allow them to share electrons back and forth, you can get molecules forming. You can get these molecules then glomming on to other molecules. This is where I prove I’m truly an astronomer who understands hydrogen, helium and everything else is a metal. But you can get these molecules binding together through either charges or chemical reactions to form larger and larger things. And eventually this is this is how you start getting blobs. Does that get big enough to gravitationally Lamont one another? And I just like the word glum. 

Fraser Cain [00:09:23] Right? Yeah, that is the scientific term is glomming. Yes. So you get these little planet nuggets? Yes. 

Pamela Gay [00:09:31] How many cosmos. 

Fraser Cain [00:09:32] Planetesimals like, how big are these things before other forces start to take over a gravity? Like, are they asteroid sized or are they pebble sized? Are they sort of mash together, breaking each other up? 

Pamela Gay [00:09:47] Well, and the reason I’m staring off into the distance is we now know that you have objects like Bennu and Rio Goo that are gravitationally held together, but are made of shattered minerals. And so you have this situation where you have things coming together loosely, and they have to get big enough that they gravitationally crush themselves in the minerals before you can really start having anything more than fluffy dust balls in space, which is rather unsatisfying. Exactly what size that’s going to happen is going to depend on. Are they truly fluffy or are we looking at ice crystals growing? What is the composition? Things further away from that baby star where you’re going to get a lot more ice production, are going to start forming solid objects that are interesting at smaller sizes than I, where you’re dealing with more of that fluffy dust. 

Fraser Cain [00:10:56] So we’ve got these fluffy dust particles. Yes. Ice crystals forming. Things are becoming larger and larger. What happens next? 

Pamela Gay [00:11:10] As as they get larger and larger, they start to go from sticking together because they literally stuck together like two snowballs colliding to they start to be able to gravitationally pull material toward them out of the surrounding cloud. 

Fraser Cain [00:11:29] And have you seen that picture of some of the Shepherd moons orbiting satellites? And you can see this. These things aren’t big. They’re like a kilometer across, but you can see this little spirally winding trail of material that’s coming from the ring being distorted by this moon, and then returning to the ring on the other side and leaving these little wakes. It’s beautiful. Yeah. And it’s just this tiny little thing, these tiny little shepherd moons. You could see the gravitational influence, even just from them. Give that process millions of years. You see what happens. 

Pamela Gay [00:12:08] And and in this case, instead of looking at these pictures of Saturn’s rings, systems start looking instead at the Atacama Large Millimeter Array images that we have of the planetary disks, protoplanetary disks around young stars. And you can start to see the gaps in the disk that are created in the places where planets are starting to come into existence. And and now, instead of having so much a shepherd moon, you have a hungry planet eating out that material, and it’s kind of awesome. 

Fraser Cain [00:12:51] Yeah. So now I guess the larger dynamics of the solar system start to, to take over because these things are now clearing out their orbits. So what happens next? 

Pamela Gay [00:13:05] Now you start to get into this competition of who can grow fastest and keep the most material. And it’s also a battle against the light from the star at this point. So you have two different processes going on. You have the planets gravitationally trying to grab the material within their sphere of influence, which they carry around with them as they orbit in orbits in orbit. You have the light pressure and the solar wind coming off of the young star. Then that is also blasting material outwards. So you have the planets trying to grab material from their surroundings at the same time that you have the star lighting up and trying to blast the material out of its surroundings. And this leads to, we thought initially a model where you would consistently get rocky worlds forming right next to their parent planet, and you’d end up with gas giants in the outer solar system. And right now, we’re not actually sure where and how things form. We just know that they do. And. Once they form, we start having these weird gravitational puzzles work out as the worlds don’t start out necessarily in stable orbits. They’re just forming and grabbing whatever they can gravitationally. And this includes grabbing onto each other gravitationally, and you can end up with the worlds flinging each other into new orbits. And in our own solar system, we think at one point we ended up with Jupiter and Saturn in a resonance, so that they were going around in an integer number so that they could both end up on one side of the sun at the same time. And by repeatedly adding their gravities together, they were able to rearrange the other objects in our solar system, including flinging Uranus and Neptune out to much greater distances from where they probably formed. 

Fraser Cain [00:15:17] And we’ve done a whole episode on planetary migration, but this idea that that all of the large planets started out a lot closer to the sun, and then through their interactions between their gravity, they all shifted outward and hurled Uranus and Neptune even farther, and Uranus and Neptune switched places. 

Pamela Gay [00:15:41] Yeah, yeah. It’s wild. And and now, as we look out at other solar systems, we’re seeing that there are gas giants snuggled up next to their stars, losing their atmospheres. And given the fullness of time, these could become little, tiny, rocky worlds that are, in reality, nothing more than the core of a former ice giant or gas giant. And so we can’t necessarily know because we don’t know where planets initially started in our solar system, just how big an atmosphere different worlds had, what was their original state compared to what they are now. And and that is one of those things that I find fabulously intriguing. Now we know that things changed quickly. So what whatever was was over within probably half a billion years. But that that period of complete chaos continued for, for a period of time as everything rearranged. We just don’t fully understand how it started. 

Fraser Cain [00:16:56] Like when we’re talking about this period of mayhem, like we’re even beyond earlier than the Late Heavy Bombardment, like even rocky surfaces. Yet you just got planetoids crashing into planet like, can you just imagine? Like, yeah, there would be dozens of planetoids all attempting to clear out their orbits, attempting to create material there. They’re interacting with one another gravitationally. Three orbits later, they crash into each other. They form a bigger object. That object pulls in other objects. Like there must have just been mayhem in it, and only when most of it had cleared out did you then get the time when asteroid strikes could happen all over the rocky planets. 

Pamela Gay [00:17:45] And we don’t fully know how many worlds there were. What we do know is Earth was struck by something the size of Mars and ended up forming the Earth-Moon system. We know that Jupiter was struck by something big enough to make its core fluffy. We know that Uranus somehow got knocked over onto its side. Venus somehow got flipped over. So that. 

Fraser Cain [00:18:09] Right. 

Pamela Gay [00:18:10] It it is just wrong in every kinematic way of looking at it. There were other worlds than these, and we ate some of them. Some of them left our solar system. Some probably dove into the sun. Right? It’s just wild. 

Fraser Cain [00:18:30] So, like, thanks to the revolution of these large radio telescopes like Alma, right. The large Atacama Millimeter. 

Pamela Gay [00:18:40] A large millimeter submillimeter array. 

Fraser Cain [00:18:42] Yeah, that we’re seeing other star systems that are forming. What clues are we getting? I mean, are we seeing them in those times when these things are crashing into each other and and making a mess? 

Pamela Gay [00:18:57] So, no, because what we’re seeing is the dusty disk where planetesimals are just starting to coalesce out of the desk. The period of of great chaos would have come after the disk had mostly been used up and blasted away by. That central star. So we’re seeing the earlier period of time. But. It’s still cool because it gives us the sense of just how big solar systems are when they’re first forming. 

Fraser Cain [00:19:34] I mean, I know that we have seen a couple of examples of planets that recently collided. 

Pamela Gay [00:19:40] Yes, but but that’s different from seeing the full on complete chaos space. 

Fraser Cain [00:19:46] But I mean, from our perspective as human beings, when we live, say, 100 years at the most this year, this period is hundreds of thousands of years long, millions of years long. 

Pamela Gay [00:20:00] It’s thought that the initial stage is probably measured in the hundreds of thousands, and then the settling down into orbits is in the tens of millions. 

Fraser Cain [00:20:11] And so we wouldn’t see this bonkers, planetary collision happening nonstop. We would see the end, I guess, as you said. Right. Like, like when you’ve got this giant star system that’s forming with tons of dust, it’s the perfect wavelength for all my to observe this incredible dust structure. But after the star has ignited, blown away all that dust, and now you’re just left with a zillion planetoids. Yeah, they’re not easy to spot. And so we do see them when they collide with each other. And you get this, this puff of dust created from the shrapnel from these collisions. And I know, like like I said, we’ve reported on several of these on Universe Today. Yeah. That are happening in those first tens of millions of years. Now, you mentioned though like some go into the star, some get ejected out. So let’s talk about some of the like, what are the forces that are going to push those planets out of their star system? 

Pamela Gay [00:21:18] It’s the three body interactions are the worst man. It’s just that simple. So you you end up with, for instance, that situation of Jupiter and Saturn, and then they can just keep pumping energy into the things around them and either fling them inwards or fling them outwards. And this dichotomy of options means sun or leave the solar system. And. And then you also have. There. There are we. We haven’t seen them yet. And that’s pauses every time I say the sentence. We haven’t seen them yet. You have read some papers that I haven’t yet. So you’re just. 

Fraser Cain [00:22:07] Waiting for me to tell you where we’ve seen this. 

Pamela Gay [00:22:10] This thing. 

Fraser Cain [00:22:11] To describe. Okay, okay. I’m ready, I’m ready. 

Pamela Gay [00:22:13] So, so there is that potential for there to be a double planet system that manages to grab on to a third planet and fling it outwards. So you can imagine we have the Pluto Sharan system, and then Himalaya gets a little too close and gravitationally gets flung away. 

Fraser Cain [00:22:35] I do not know of any examples of rogue planets on escape trajectories where we can trace where they came from. No. 

Pamela Gay [00:22:45] So. So we have SUVs, we have seen rogue planets, but they have been of the gas giant variety, where it is probably this energy pumping of of that things getting into synchronization and the resonance just flings things away. 

Fraser Cain [00:23:06] And we’re detecting it through methods like, gravitational microlensing is the method for finding these rogue planets. And I don’t think you get a lot of really good information about the velocity of the planet and maybe what its origins were. It sounds like a big ask for us to be able to see that kind of thing. 

Pamela Gay [00:23:26] And one to say there was a a planet on its way away from its star that was spotted by the Hubble Space Telescope in the early 2000 of the late 90s, where it was one of those. Is it a gas giant or a brown dwarf? 

Fraser Cain [00:23:43] Right? Yeah. I mean, there have definitely been some brown dwarfs seen at high velocities moving through the interstellar medium. 

Pamela Gay [00:23:50] Yeah. 

Fraser Cain [00:23:51] So then, I mean, one of the theories right now is that there are as many rogue planets in the Milky Way as there are stars. Yeah. So is it then just generally believed that each solar system kicks out at least one big planet? 

Pamela Gay [00:24:15] So how it would have to be more than that. Because if you think about it, not all of the stars have planets because you have the low metallicity ones. Stars in general are quite often found in multiples. So you’re looking at systems that have planets are likely to evict more than one planet on average. 

Fraser Cain [00:24:40] Yeah. 

Pamela Gay [00:24:40] And that’s just kind of amazing to think about. 

Fraser Cain [00:24:43] Yeah I mean, the most extreme estimate that I had heard for that was that there could be like ten planets for every star, rogue planets, ten rogue planets for every star out there, that there are so many of those three body interactions that kick out material, that there’s just mountains of it out there drifting through the cosmos. 

Pamela Gay [00:25:04] And where we really struggle is we have the capacity through gravitational lensing to see foreground high mass objects, gravitationally land background stars. And these are often, dramatic enough to draw attention such that we also see when a planets, that is orbiting that star also microlensing but star. But we aren’t seeing just random blips of light from planets. Microlensing things left and right and right. Those are going to be lost and a lot of the noise, unfortunately. 

Fraser Cain [00:25:52] So mean we’re going to it’s going to give us eventually like the machine is really going to do. This is the Nancy Grace Roman Telescope. It’s going to be looking for microlensing at the largest scale. It’s going to be watching huge chunks of the sky, watching the brightness of the stars, checking to see if any of them dim. And we should get an upper boundary on the number of planets that are out there, even a sense of how many rogue black holes there are zipping around the cosmos. So Niantic is where we can’t come soon. Soon enough. 

Pamela Gay [00:26:27] It’s true. And honestly, Lsst as well, because it’s it’s going to be able to spot more of the these background stars getting lensed as well with it’s constant night after night cadence and all of the software that’s being developed to specifically look for anything that changes in brightness. So here’s to hoping. 

Fraser Cain [00:26:50] It’s at a different time scale, like variety is going to be taking a picture and then coming back three days later and noting the supernova that went off. Well, that’s Chris Roman will be watching a field of view, slicing it up in time and noting for any variations in brightness of any of the objects in that field of view. So they’re just they’re kind of two different ways to two approaches, hopefully overlapping. But yes. But yeah. So it’s it’s kind of amazing the how you just go from gas dust and the corpses of other stars into the desiccated corpses of other stars into new planets, life and chaos. Thank you Palmer. 

Pamela Gay [00:27:31] Thank you Fraser, and thank you everyone out there who supports the show. And as a reminder, our patrons get ad free versions of every episode through Patreon. 

Fraser Cain [00:27:43] No ads. No just sounds so civilized. 

Pamela Gay [00:27:47] It really, really does. So if you don’t want to hear me reading ads, join our Patreon! This week I would like to, thank a subset of our donors, and you can find out how much you have to give to hear me mispronounce your name over on Patreon.com slash Astronomy Cast. I really don’t mean to mispronounce your names, but here goes. I’m gonna try one more time. This week I would like to thank Kenneth Ryan, Benjamin Mueller, Paul de Disney, Omar dahl, Riviera, Janelle Rucker, Aaron segev, Michelle Cullen, Peter Scott briggs, Mark h. Whittock, Mark Steven Rusnak, Philip Grand, Bruce. Amazing, Don Mundus, Abraham. Cattell, Jim McGeehan. Anna. Tour. And I saw Michael Regan, Dean McDaniel, Ninja neck, J. Alex Anderson, father Proxmire, some Frodo Tenenbaum, James Ruger, Roger Dwight Elk, and Paul L Hayden. Thank you. 

Fraser Cain [00:29:00] Thank you everyone, and we’ll see you next week. 

Pamela Gay [00:29:02] Bye bye. Astronomy cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy cast is released under a Creative Commons Attribution license. So love it, share it, and remix it, but please credit it to our hosts, Fraser Cain and Doctor Pamela Gay. You can get more information on today’s show topic on our website. Astronomy. Cars.com. This episode was brought to you. Thanks to our generous patrons on Patreon. If you want to help keep the show going, please consider joining our community at Patreon.com Slash Astronomy Cast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox and invites to online events. We are so grateful to all of you who have joined our Patreon community already. Anyways, keep looking up. This has been Astronomy Cast.

We’ve spent a lot of time gushing about Saturn’s rings, but there are other places with ring systems. And not just Jupiter and the ice giants, but asteroids, dwarf planets, centaurs and even exoplanets. Today we’ll gush about them.

Show Notes | Transcript

Rings (NASA)

Uranian Rings (Smithsonian)

Ring detected around a dwarf planet (Nature)

Neptune’s Rings (NASA)

What is an occultation in astronomy? (BBC Sky at Night)

Introduction to Photometry (Las Cumbres Observatory)

European Space Agency

Cheops (ESA)

Quaoar (NASA)

ESA’s Cheops finds an unexpected ring around dwarf planet Quaoar (ESA)

A dense ring of the trans-Neptunian object Quaoar outside its Roche limit (Nature)

10199 Chariklo (NASA)

Possible ring material around centaur (2060) Chiron (Astronomy & Astrophysics)

Centaurs (Swinburne University)

Main Asteroid Belt (Swinburne University)

What are Trojan asteroids? (Asteroid Day)

PODCAST: Ep. 675: Exotic Forms of Ice (Astronomy Cast)

The Nancy Grace Roman Space Telescope (NASA JPL)

Rubin Observatory

Super-Saturn: astronomers find a massive ring system around an exoplanet (NASA)

Could we have already imaged a ringed exoplanet? (Ars Technica)

Phobos Might Only Have 10 Million Years to Live (Universe Today)

Here’s What Earth Might Look Like With a Ring System (Futurism)

Witch Head Nebula (NASA)

Back to Top

Transcriptions provided by GMR Transcription Services

This episode is brought to you by Hello Fresh. Go to HelloFresh.com/Astro50 and use code Astro 50 for 50% off, plus your first box ships free.

Fraser Cain:                 Astronomy Cast Episode 676, Other Things with Rings. Welcome to Astronomy Cast, our 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 am Fraser Cain, the publisher of Universe Today. With me is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Cosmo Quest. Hey, Pamela, how you doing?

Dr. Pamela Gay:         I am doing well, and I want to share news for folks who may not have stayed around for the very end of the episode. I am super pleased to say that we’ve had Better Help as a sponsor for months now and we just added Hello Fresh as an advertiser, and this means that we can afford to produce content for all of you out there who can’t afford to become members of Patreon or just don’t pay for content, there’s folks like that out there.

Fraser Cain:                 Yeah.

Dr. Pamela Gay:         But if you’re out there going, hey, I’m a Patreon, well, we have an ad-free feed through Patreon just for you. So, if you are someone who is also thinking I would pay to get rid of these ads because I would pay to get rid of ads.

Fraser Cain:                 I pay to get rid of ads all the time. Yeah, I can’t stand ads.

Dr. Pamela Gay:         Yeah. Just join our Patreon, $1.00 and up, ads go away. And as you add larger amounts, like at $10.00, those are the names I read out at the end of the show. We love all of you equally but we have to give you things to differentiate because that’s how Patreon works, and we get it, we love all of you and if you want to get rid of the ads and never hear why I’ve used Better Help ever again, this is your opportunity.

Fraser Cain:                 Right. Sounds good. Now, we’ve spent a lot of time gushing about Saturn’s rings but there are other places with ring systems and not just Jupiter and the ice giants but asteroids, dwarf planets, centaurs and even exoplanets. Today, let’s gush about them. All right. My recommendations for telescopes really boiled down to get Saturn and its rings into your eyeballs, into your brain.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                 The whole reason to buy a telescope is to see Saturn with your own eyes and to see that magnificent ring system. Everything else is secondary, like science, seeing Jupiter.

Dr. Pamela Gay:         You do need to be able to lift it. I add the caveat, buy a telescope that will let you see Saturn and that you can carry.

Fraser Cain:                 Yes, sure, yeah, yeah. No, but all I’m saying is that the primary purpose of telescope technology, really since telescopes were first invented, was for people to be able to see Saturn’s rings and then everything else is secondary. Like if you’re going to discover the age of the universe that’s fine but have you seen Saturn’s rings first?

Dr. Pamela Gay:         It’s true, it’s true.

Fraser Cain:                 Yeah, yeah. Yeah, I don’t think anyone can argue with this. And we’ve know that there are rings in Jupiter, there’s rings at Neptune, but there are other places with rings. So, where do we want to start?

Dr. Pamela Gay:         How we detect them because –.

Fraser Cain:                 Sure, yeah, how do we find rings?

Dr. Pamela Gay:         Yeah, that was the thing that perplexed me.

Fraser Cain:                 We looked through our telescope, right? We looked through our telescope at Saturn’s rings and then just – that’s how we see rings.

Dr. Pamela Gay:         Yeah. So, it turns out that like Saturn’s rings were the first to ever be discovered, those were found by Galileo, and then it wasn’t until the 1900s that we found rings somewhere else and it was Uranus where they were found next because Uranus is the second largest set of rings in our solar system. And with these two sets of rings, it’s very much a point and expose, expose, expose, expose, expose, expose, expose, expose if you want to see the rings at Uranus.

                                    But that doesn’t work if you’re trying to find the rings around itty-bitty little tiny objects, especially the objects that are out beyond Jupiter and Saturn in our solar system. And it turns out, we found rings around objects in our solar system, as far away as like Haumea, which is one of the dwarf planets that’s out in the Kuiper Belt, and to do that, it hasn’t been on purpose and I love this.

Fraser Cain:                 Yes. Okay. So, we learned about Saturn’s rings from Galileo.

Dr. Pamela Gay:         We looked, yeah.

Fraser Cain:                 We looked. We learned about Uranus from looking. We learned about Jupiter, Neptune from looking.

Dr. Pamela Gay:         Looking with closer satellites.

Fraser Cain:                 So, the Voyagers helped us find them.

Dr. Pamela Gay:         Yeah, yeah.

Fraser Cain:                 Right, okay. So, then, so what is the technique then? Let’s say that you want to find out if an object out there has rings, what, I guess, what is the accident, the happy accident that you’re trying to encourage?

Dr. Pamela Gay:         It’s called observing occultations. This is where an object, be it an asteroid, a planet, whatever is seen to pass in front of a distant bright object. So, the moon occults other planets on a regular basis where you get these fabulous images of planet going behind the moon and we can actually start to see mountains based on when the planet disappears.

Fraser Cain:                 Yeah.

Dr. Pamela Gay:         Well, if you have an asteroid that’s going in front of a distant star, different observers on the planet will actually be able to see a slightly different alignment between how that asteroid and how that star pass together and this tiny difference in geometry can allow us to measure the width of the asteroid at different points along the asteroid’s body. We’ve talked about this on other episodes.

Fraser Cain:                 Yeah. I mean this idea of occultation shows you how precise astronomy really is because you have to be – like the occultation is gonna happen at a specific time that the –.

Dr. Pamela Gay:         Yes.

Fraser Cain:                 That the asteroid is gonna pass directly in front of the star, but it also has to happen in a specific place. There is this cone or some range on Earth where you are going to be lined up and if you’re in that range then you will actually see the occultation, and if you’re not then it will be partial or you’ll miss it completely. So, I mean there’s times when like the moon will occult Saturn or Mars but it’s only visible to people who are in certain parts of the world. So, this one is visible in South America, this one’s visible in Chile, right.

Dr. Pamela Gay:         And the way to think about it is, when you’re on an airplane you can look down and be like, huh, that town you can actively see the clouds pass over it, and each different house in the town will sample the shadow of a different part of that cloud.

Fraser Cain:                 Oh, that’s such a great analogy.

Dr. Pamela Gay:         And so this is the you are under the shadow of the asteroid as cast by that star.

Fraser Cain:                 Right. And so how did you see the shadow come onto your house? How quickly did it darken for you under that cloud as you were standing there looking at the sky? That’s a great analogy. And so, you get the shape of the asteroid purely through the occultation.

Dr. Pamela Gay:         And it’s just like you can get the shape of the cloud by combining with your neighbors all of the times that you saw the shadow start and the shadow end. And you and your neighbors are probably not gonna do that because let’s face it, you have better things to do in your life. But with asteroids – well, there’s a dog to walk or something.

Fraser Cain:                 All right, okay.

Dr. Pamela Gay:         But with asteroids, this is the only way we can measure their shape if they’re not close enough to bounce a radar off of. And while measuring the shapes of asteroids at a whole variety of different locations throughout our solar systems, there have been a handful of times where they’ve gotten on object early because they are diligent and well-behaved scientists.

Fraser Cain:                 Right.

Dr. Pamela Gay:         And they’ve seen this little dip that didn’t go down far enough for it to actually be the asteroid unless they misplaced it, and I can just imagine that more than once this has led to an observer going, did I calculate something wrong.

Fraser Cain:                 Right.

Dr. Pamela Gay:         And then the actual dip occurs, which is what you are waiting for, star totally goes away, okay, confirmation life is fine. But then wait a half-beat and then there is another dip, and what they’ve been able to figure out is these dips correspond to rings around the objects. And this has gotten us a whole new reason to be excited to go outside and do high-speed photometry of distant objects moving in front of more distant stars.

Fraser Cain:                 And I mean this is one of those fields that amateurs get involved in all the time.

Dr. Pamela Gay:         Yes.

Fraser Cain:                 Like if you want to participate in science and you have – it doesn’t have to be a very big telescope, like an eight-inch telescope, as long as you’ve got the right detector system on your telescope you can, at the appointed time, watch the occultation, measure the brightness of the star and then pass along the data to the scientists and they will use that to help figure out the shape, figure out whether it has rings, figure out whether it has moons and learn a lot more about the solar system purely through how the brightness of an asteroid dims or how the brightness of a star dims momentarily. It’s astonishing. All right, we’re gonna talk about this some more but it’s time for a break.

Fraser Cain:                 And we’re back. All right. So, now we understand the technique, this is how astronomers find things with rings.

Dr. Pamela Gay:         Yes.

Fraser Cain:                 So, let’s talk about some of the actual discoveries that have been made.

Dr. Pamela Gay:         So, the first one that caught my attention, and this is like where the rabbit hole begins, was ESA’s Cheops mission found a ring around the dwarf planet Quaoar, which is one of the first objects to really start the discussion on displacing Pluto as a planet. This is a dwarf planet that is on a highly elliptical orbit. It was discovered in the early, early 2000s and while watching it they found a ring at a distance of about seven and a half of the radius of Quaoar, which means how did the find stuff that didn’t either coalesce into being a moon, dissipate away because it’s not held so tightly and smashing of the objects amongst themselves can make it go away or fall to the surface of the world?

                                    And once I saw this story, I started digging further into this and it turns out that we have found Haumea has a ring and we’ve found centaurs. And there is a strangely large number of objects that begin with the letter C, I don’t know why, this is just weird reality.

Fraser Cain:                 If you want something to have rings give it the name C and then just wait and someone will find rings.

Dr. Pamela Gay:         Exactly.

Fraser Cain:                 Yeah.

Dr. Pamela Gay:         This is how it works. And each of these discoveries within our solar system has over and over been a case of watching these occultations. And there have been times that we were like, okay, so what if we aren’t seeing the rings because of some limitation, and for a long time the abundance of tiny moons around Pluto had folks really worried that there could be a ring around Pluto that was going to attempt to eat the New Horizon spacecraft.

Fraser Cain:                 Right, yeah.

Dr. Pamela Gay:         And as New Horizons got closer and closer, the realization was made, no, no rings at Pluto, we got this right. And so it turns out we have an exceptional ability to spot rings and when we don’t spot rings, we are actually not spotting rings.

Fraser Cain:                 One of the things that I find really exciting about the Quaoar discovery, well, there’s kinda two parts to it. One is that it was done with Cheops, which is not a ring finding mission, its job is to confirm exoplanet discoveries. And so, it’s sort of going through the list of known exoplanets or candidate exoplanets and confirming whether or not they actually exist. But I guess they got this opportunity where an occultation was gonna be visible to the spacecraft and they go, well, why not, let’s take a look and see what we see.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                 And then the other part that’s kind of amazing is that the size of the ring system is so much bigger than what anyone thought, and maybe even what anyone thought should be possible around an object. That it’s like seven times the radius away from the object itself and that’s really impressive that it’s a dwarf planet but it’s holding on to this ring system quite far away from where it is. And that makes you wonder, like how did it happen because you would expect it to be a lot closer. If it tore up a moon it should be very close and yet it’s actually quite far away. Why?

Dr. Pamela Gay:         And they had the same thing come up with observations of, and today is the day where I mispronounce objects, I am so sorry, everyone, Chiron and Chariklo, which are two more centaurs, they also found rings in these extraordinarily large orbits. And it looks like the objects that are in these rings may be having what’s called elastic collisions. So, when things come together you can have an inelastic collision, this is like when two cars crash together and merge into a single very destroyed new object,

                                    You can also have inelastic collisions which is what we experience playing pools, where objects come together and they bounce off of each other and energy is just transformed between objects, but pool balls don’t shatter into a million pieces. Which is another thing that can happen when you have these collisions, is they can collide and energy gets turned into – turning them into multiple objects flying in all directions.

Fraser Cain:                 Right.

Dr. Pamela Gay:         So, if you have just the right kind of inelastic collision they just bounce off of each other like the particles in our atmosphere, and just like our atmosphere doesn’t settle to the floor of our house for many reasons, but one of those reasons is the motion of the particles that has this constant inelastic collisions going on allows the air to support itself, pressure, it’s our friend and it could be these rings’ friends.

Fraser Cain:                 Right. And the Chiron and Chariklo are centaurs. So, for people who aren’t familiar with that term, what are the centaurs?

Dr. Pamela Gay:         So, we have main belt asteroids that are located between Mars and Jupiter and then we have centaurs which have a variety of different orbits that are beyond Jupiter and just to make things confusing, there are the Trojans that share the orbit with Jupiter but in two blocks that we’re sending Lucy to.

                                    So, these centaurs, which are further out, are in temporary orbits being so close to Jupiter and Saturn their location isn’t entirely stable. They have got there by something knocking them out of their happy existence in either the Kuiper Belt or the Oort Cloud. They have migrated inwards. They are eventually going to either migrate further in become comets, migrate further out, do whatever things do when they migrate further out.

But these are really cool objects that we like to look at because related to last week’s episode, we sometimes see them having outbursts of activity where they suddenly get much more reflective because they expel clouds of dust and ice just like a comet would but at a distance that isn’t melting like a comet from the sun. But is, instead, triggered either by landslides or this transition from amorphous ice to crystalline ice. So, looking at them, watching them in detail, super interesting to look for these outbursts, and in the process we have found rings, and I love when there is ancillary science nobody expected.

Fraser Cain:                 Yeah, yeah. But I mean at this point now, with four objects beyond the planets that contain rings, it just means that there’s gonna be lots and lots more of them, it’s just a matter of timing of those occultations. And when I think about upcoming missions or telescopes like Nancy Grace Roman, like Vera Rubin, you’ve got spacecrafts that are designed to watch for changes in brightness, we should get a lot more found. And I’m sure there is just gonna be some amazing ones, like a comet, like a long-period comet that’s coming in and bringing a ring system with it will be really neat.

                                    All right. So, we’ve talked about stuff that’s in the solar system but when you think about science fiction, there are always these planets with ring systems, as if like there should be Saturns everywhere. So, do we have any evidence that there are ring systems out there across the Milky Way?

Dr. Pamela Gay:         Yes, yes. There is, in fact, a super Saturn found orbiting the star J1407. It was found back in 2007. And this is a world that as it transits in front of its star you get this really cool, complex dip that is from having a good old, happy, not quite ice giant bigger than ice giant but not a hot Jupiter. I don’t know what we’re calling those anymore, and then this massive ring system that absolutely dwarfs what Saturn has.

                                    The ring system itself was found in 2012, and it consists of about 30 rings that are millions of kilometers in diameter, and just imagine sitting there at the telescope watching the data come in and it’s just like, okay, we’re gonna have to wait a while before this thing comes back around to confirm that but, dang.

Fraser Cain:                 Yeah.

Dr. Pamela Gay:         It’s really cool.

Fraser Cain:                 Like your watching the flickering light of the planet or the flickering light of the star as the planet with this gigantic ring system is passing in front. Yeah, I remember, it’s like 200 times bigger than Saturn’s rings.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                 Like maybe that is the real purpose of the telescope is to look at this planet with its rings, that is the real reason the telescope was invented. And I’m sure the people who live at that star system are correct, like they win in a ring down.

Dr. Pamela Gay:         There is this fabulous quote from Matthew Kenworthy who is a researcher at Leiden, who was one of the ones that made this discovery and he writes the details that we see in the light curve, that’s how the light goes up and down, are incredible. The eclipse lasted for several weeks but you can see rapid changes on time scales of 10s of minutes as a result of fine structure in the rings.

Fraser Cain:                 Wow.

Dr. Pamela Gay:         The star is much too far away to observe the rings directly but we could make a detailed model based on the rapid brightness variations in the star light passing through the ring system. If we could replace Saturn’s rings with the rings of J1407B they would easily be visible at night and many times larger than the full moon. I want that ring system.

Fraser Cain:                 Yes.

Dr. Pamela Gay:         I want to live there.

Fraser Cain:                 Then the telescope would never even need to be invented because you could just look up with your eyeballs and see this enormous ring system, bigger than the moon.

Dr. Pamela Gay:         I need a space artist who is not me because I am really bad at doing rings. I need a space artist to like do what the sky would look like with like that hanging out near a crescent moon.

Fraser Cain:                 Well, people have done that. Like have you seen simulations where people have put various moons in the sky?

Dr. Pamela Gay:         Yeah.

Fraser Cain:                 And if the moon was Jupiter or if the moon was Saturn?

Dr. Pamela Gay:         Oh, yeah.

Fraser Cain:                 And you just see how ridiculous it would be as the thing rises up at the distance of the moon. Yeah, no, that would be very impressive. Yes, please. So, what will it take for us to find more ring systems around exoplanets? Like this one is clearly bonkers extreme, so –.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                 So, what would we be expecting to see? What’s the best spacecraft that we have right now to find something like that?

Dr. Pamela Gay:         So, we can get lucky if there is a ring system that is somehow able to stay stable on a planet on a small orbit around one of the hottish Jupiters out there. I don’t think dynamically a hot Jupiter can actually have rings.

Fraser Cain:                 Yeah.

Dr. Pamela Gay:         And it would have to be on a much faster orbit than what we’re seeing with this J1407B, and that’s because missions like tests don’t just linger for weeks on one field. They’re like, okay, we’re gonna sit here for a bit then we’re gonna come back. We’re gonna sit here for a bit and then we’re gonna come back. And so, like how do you differentiate between it being a variable star that’s having a really weird dust explosion and a planet without having this extremely long duration light?

Fraser Cain:                 Right.

Dr. Pamela Gay:         And this is where I’m really looking forward to the day that we have cheaper 24-inch telescopes for amateurs. Like I want tomorrow’s 24-inch telescopes to cost what the eight-inch telescopes cost when I was in high school.

Fraser Cain:                 Sure. Yes, please.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                 But I can see that the irony is that the planets that are easiest to find are the hot Jupiters, are the ones that are close to their star. And when you’re close to the star, I mean like here in the solar system, the frostline extends out halfway to the asteroid belt, so beyond Mars. So, you’re not just finding exo-Earths, you’re not just finding exo-Mars, you’re finding exo-Jupiters, exo-Saturns, and those, when you think about how long it takes for Jupiter to make one pass, it’s like five years, Saturn is like 11 years.

Dr. Pamela Gay:         Right.

Fraser Cain:                 And so you’re having to wait a long time. So, we just don’t have the timescales to find regular sized gas giants with ring systems yet. We just haven’t been watching long enough and caught them.

Dr. Pamela Gay:         Yeah. And the ring system that we see at Saturn is largely the kind of ring system you get from ice, and to get a ring system closer in you have to have something that is rock. So, you’re looking at a moon that was disrupted, Mars is gonna have that in its future, it’s going to temporarily have a ring. You are looking at materials splashed up during a collision. We temporarily had a ring after getting nailed by a Mars-sized object when the solar system was young.

                                    Yeah, if you want to see something like this, you have to look at the distance objects, and this is where I want every amateur astronomer to have a 24-inch telescope that after they’re done taking their stunning astrophotography or –.

Fraser Cain:                 Of Saturn.

Dr. Pamela Gay:         May there be exoplanets –. Well, I mean imagine this. You have someone out there who is doing 300 hours on the Witch Head Nebula and there happens to be a star in that system that is undergoing this kind of a slow transit where they’re able to catch in the starlight while getting their gorgeous astrophotography image.

Fraser Cain:                 Right. So, they can feed the photometric data of all of the stars to the astronomers and let them dig through it.

Dr. Pamela Gay:         Yeah.

Fraser Cain:                 Yeah, that would be something. Yeah, so.

Dr. Pamela Gay:         I want that future.

Fraser Cain:                 Okay, all right. That sounds fun. All right. Well, thanks, Pamela, that was great.

Dr. Pamela Gay:         And thank you, everyone out in the audience. I am more than a little excited about anything that varies in brightness and you have now shared my enthusiasm. And in particular, I would like to thank our patrons who are at the $10.00 and up level, David Everson, Michael Prochoda, John Theys, Burry Gowen, Stephen Veit, Jordan Young, Jeanette Wink, nanoFlipps, Andrew Poelstra, Venkatesh Chary, Brian Cagle, David Truog, Gerhard Schwarzer, David, Buzz Parsec, Laura Kittleson, Robert Palsma, Les Howard, Jack Mudge, Joe Hollstein, Alexis, Gordon Dewis, Richard Drumm, Adam Annis-Brown, Frank Tippin, Greg David, William Andrews, and Gold. And if you too would like to get episodes without ads, join our Patreon at the $1.00 or up level. Thank you so much.

Fraser Cain:                 Thanks, everyone, and we will see you next week.

Dr. Pamela Gay:         Bye-bye.

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Moons orbit planets, planets orbit stars, stars orbit within galaxies. It’s orbits all the way down. But occasionally objects can receive a powerful kick that sends them off on a journey, never to return.

PART II

PART III

Show Notes | Transcript

Superman (DC Comics)

Iron Man (Tony Stark) (Marvel)

Conic Sections (Math is Fun)

Parabola (Math is Fun)

Hyperbola (Math is Fun)

Ellipse (Math is Fun)

Ballistic Trajectory (Universe Today)

FAQ – Earth (Planetary Science Institute)

Escape Velocity (Let’s Talk Science)

Spitzer (Caltech)

The Three-Body Problem (Scientific American)

PODCAST: Ep 102: Gravity (Astronomy Cast)

In Depth | Oort Cloud (NASA)

Overview | Comets (NASA)

Types of Comet (CometWatch)

In Depth | Oumuamua (NASA)

Ukrainian Astronomers Discover ‘Exocomets’ around Another Star (Scientific American)

The Solar System may have lost the original “Planet Nine” (Inverse)

Slingshot Star? (Science Magazine)

JOURNAL: A search for runaway stars in 12 Galactic supernova remnants (Astronomical Notes)

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Transcriptions provided by GMR Transcription Services

Fraser: Astronomy Cast episode 660, Runaways. Welcome to Astronomy Cast, 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. I’ve been a space and astronomy journalist for over 20 years. With me is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey, Pamela. How you doing?

Pamela: I am doing well. If I don’t sound the way I normally sound or look the way I normally look, I still haven’t recovered where all my stuff is after I was in Vegas for Annie Wilson’s wedding [inaudible] [00:01:29] one of our community members and one of my good friends. Unfortunately, during the travels, several people got COVID, so there was a come home, dump all belongings, get the phone call that people had tested positive, quarantine, and then chaos ensued.

Fraser: But you didn’t.

Pamela: I did not get sick. I had a random sore throat, which I’m gonna blame on things I was allergic to. I escaped.

Fraser: Good.

Pamela: So, folks, wear your masks. I wore my K95 like my life depended on it because it probably did. Yeah, so I managed to stay safe. I just haven’t found my microphone or my webcam. But congratulations to the beautiful couple. It was a fabulous ceremony. And everyone is now home.

Fraser: Good. Well, hopefully by next week, you will have started to put your life back together.

Pamela: That’s the goal.

Fraser: Moons orbit planets. Planets orbit stars. Stars orbit within galaxies. It’s orbits all the way down. But occasionally, objects can receive a powerful kick that sends them on a journey never to return. So, let’s talk about orbits first. Let’s say that you are on the surface of Earth and Superman is going to punch you really hard. Describe the —

Pamela: That would be so bad.

Fraser: Yes, it would. Now, describe the trajectories, here, that we could be looking at if Superman gives you a punch.

Pamela: The pause here is the structural integrity of the human body is such that I’m not sure there’d so much be a trajectory –

Fraser: He’s punching another Superman.

Pamela: He’s punching Iron Man with the suits. Let’s go with –

Fraser: Yeah, he’s punching the Hulk.

Pamela: Let’s go with Iron Man because I have faith in that steel suit.

Fraser: Okay, sure. Superman’s punching Iron Man.

Pamela: So, Iron man is going to travel on what’s called a comic section. So, imagine, if you will, a round cone, like good old-fashioned ice cream cone, and you can cut a plane through that and in a bunch of different ways. If you cut it just right, you’ll get a perfect circle. And depending on how you do it, you may end up with a not entirely closed surface. So, you can end up with what are called a parabola, a hyperbola, or an ellipse. Now, if –

Fraser: Or a circle, which is, I guess, a type of ellipse.

Pamela: Is a type of ellipse. So, ellipses are defined as a nice closed shape that has two foci that, if you tie a string to both of them and you move that string around the foci, you’ll end up with the ellipse. And depending on how far apart the foci are, you get a flatter and flatter ellipse. And if those two foci are in the exact same point, you get a circle. 

Fraser: Isn’t it foci? Maybe it’s foci, hmm. Right. So, maybe it’s Canadian just versus American English. So, Superman gives him a punch. Not very hard. Just a light tap. He goes up. He comes back down.

Pamela: So, that’s a ballistic trajectory. Now –

Fraser: And it is a parabola?

Pamela: Well, you don’t really have enough information to tell because he collided with the surface of the object. Now, it’s entirely possible to have a perfectly healthy elliptical orbit that just happens to intersect the surface of a planet, which would be unfortunate. Except, in this case, Iron Man gets to keep breathing air that doesn’t have to come from his suit. So, that’s ballistic.

Fraser: Right. I guess you chose Iran Man for a reason here. And we know that to go into orbit around the Earth is 7.6 kilometers per second, 20,000 kilometers per hour. If Superman punched –

Pamela: Mostly sideways.

Fraser: Yes. If Superman punched Iron Man that fast, he still wouldn’t be in orbit.

Pamela: Yeah, it all depends on the exact angle of the punch. So, if Superman punches him straight up so that there is a line through the center of mass of the Earth that extends straight through the surface of the planet, through Superman’s fist, and sends Iron Man straight up, that kind of a punch is going to lead to a very skinny ellipse, so skinny, in fact, that it is a straight line and, again, a ballistic trajectory. And Iron Man is going to hit the surface of the planet on his way back down –

Fraser: Right. He’s gonna go up.

Pamela: – hitting Super Man if Super Man doesn’t move.

Fraser: He’s gonna come back down. Even though he’s punched him into orbital velocity speed, he’s not gonna be able to go into orbital velocity. Even if he punches him at an angle, he’s just always gonna be taking these parabolic ballistic trajectories and coming back down to the surface. So, how can Superman make sure that Iron Man doesn’t return to hitting the Earth again?

Pamela: He has to hit him sideways. So, if he hits him so that you have the surface of the planet, you have Iron Man on the pedestal off the surface of the planet, and –

Fraser: No, he’s on the surface. He’s just standing on the surface. Just comes up and punches him.

Pamela: Okay, so if he just plain punches him, he’s going to have to hit him hard enough that he goes into an elliptical orbit that has him going off the surface, coming back, grazing the surface of the planet – may there not be mountains on the other side – and then coming back, and he hits Super Man again. So, no –

Fraser: But if he punches him a million kilometers an hour, he’s just gonna escape velocity. He’s not coming back. That’s where I’m going with this.

Pamela: Okay, yes. He can escape if he hits him hard enough, yes.

Fraser: Right. So, you’re gonna have all of these various punches that are gonna lead to various kinds of ballistic trajectories. He won’t go into orbit.

Pamela: Iron Man is fine.

Fraser: Right. Iron Man’s fine. He’s fine. He can’t go into orbit from these punches, right? He can only either return to hit the Earth again or escape the Earth entirely. So, now, Superman punches him and then flies up, because he can, and punches him again when he’s in space. What could he do with him now?

Pamela: So, with that double firing, it is possible to put Iron Man in orbit. So, the trick is you need Iron Man to get to a certain height and then stay at that height or at least stay away from the surface. And this is where I started to say had him on a pedestal because, if you had him on a pedestal, you could just punch and he continues going around the planet at the height of the pedestal if you have exactly the right punch. If you don’t have that pedestal, you have to go up from the surface, and then you have to turn, and that turn is what allows you to keep going around the planet instead of falling back down to the surface.

Fraser: Right. And so now that you are in orbit – Iron Man is in orbit. He’s fine. At every point, he’s perfectly fine. They’re just having fun. He’s got all kinds of inertial dampeners on board. He can handle this an infinite amount. Every time Superman gives him a punch, it’s going to change his orbit around the Earth, but it’s not going to cause him to, say, spiral outwards or spiral inward unless he goes back to that –

Pamela: He could.

Fraser: How could it be a spiral with one hit?

Pamela: No, it’s gonna have to be repeated hits to be a spiral.

Fraser: Right. Yes, yeah. It’s gonna have to be repeated hits. All right. So, then, Iron Man is orbiting around the Earth. Superman comes up, punches him in the direction opposite to his orbit. What happens to him?

Pamela: So, if you decelerate, you’re going to – this is where it gets [inaudible] [00:11:00], and the astronauts –

Fraser: Let’s say the exact amount of his orbital velocity.

Pamela: The exact amount of his orbital velocity, then he’s going to go plunging back down to the surface of the planet.

Fraser: And if he is able to punch him in the direction of his orbit another, say, 20 kilometers per second, what happens to him?

Pamela: That will ultimately end up changing the shape of the orbit and making it more and more elliptical unless it’s at the exact right point in the orbit that the punch occurs and it was already elliptical, in which case, you can make it circular. So, you’re going to change the shape of the orbit.

Fraser: Right. But at a certain point, he’s putting him into orbit around the sun and no longer into orbit around the Earth.

Pamela: Yes. And this is something we’ve done with the Spitzer Space Telescope. 

Fraser: Yes. Remember when Superman punched the Spitzer Space Telescope into orbit around the sun. Yeah, I remember that.

Pamela: All right, yes.

Fraser: Yeah, no, I understand. This analogy is starting to get a little tortured, so we’ll shift gears and actually talk about actual objects. So, the setup, really – and I think it’s really important to understand this. There are objects on escaped trajectories that are leaving the solar system, that are leaving the Milky Way. How is this possible? What did it take to get these things into these new runaway trajectories?

Pamela: Well, we assume that it wasn’t Superman punching them. We don’t actually have evidence that it wasn’t Superman punching them, but we’re pretty sure that –

Fraser: I think it’s safe to say.

Pamela: – wasn’t the case. And so, quite often, with the things that we believe are escaping our solar system or have escaped other solar systems, it’s due to interactions with two other objects. There’s what’s called the three-body problem, and we did an entire episode on it long, long, long ago. And there are certain systems of three bodies that can end up ejecting one of the bodies, quite violently, outta the system. This quite often happens when you have two similarly massed objects and then a little one gets involved. And if that little one isn’t in a dead locked-in orbit around one or the other of the objects, if it’s shared between the two of them, it can just get flat-out ejected in all sorts of wild and crazy ways.

Fraser: Now, you say fairly violent, but it doesn’t actually have to be because, when you’ve got, say, the Oort Cloud surrounding the sun, the objects that are out in the Oort Cloud have almost no additional escaped velocity that’s required. They’re teetering right on the edge, and almost any amount of three-body interaction will kick them over the edge and cause them to drift away from the sun.

Pamela: And this is where I have to admit I’m thinking of stars and globular clusters as my baseline for this at all times. 

Fraser: You could have a star come relatively close and the three-body interaction between the star and the sun, and the Oort Cloud object causes it to drift away from the solar system. And now, it’s gone interstellar. So, it doesn’t have to be catastrophic. And you could have a situation where a comet falls into the inner solar system. And it should return back out to the Oort Cloud, but it interacts Jupiter on its way through, goes near Ganymede, gets a kick, and now, it’s over the – it, now, has enough speed, on the way back out again, that it will overcome the sun’s escaped velocity, and away it goes, again, into the larger galaxy.

Pamela: And this is one of the really awesome things to think about where we have these comets that we see coming in, on hyperbolic or parabolic orbits where we know they’re leaving our solar system. And so we know that objects that have passed near our sun, have been influenced by our sun, weathered by our sun are, now, going to go and eventually make their way into another solar system out there. We also know that, if there are objects that are getting flung inwards, there’s objects that are getting flung outwards. So, there are also icy bodies that have never interacted with our sun that are getting flung outwards. And if we’re flinging things outward, there must be other solar systems doing the exact same thing. And now, we have observed that occurring with ‘Oumuamua. It’s a trading of icy bodies all over the galaxy.

Fraser: Yeah. I’ve read a couple of papers on this. It’s estimated that there are thousands, maybe even tens of thousands, of objects of these transferred Oort Cloud objects from other star systems passing through the solar system at any time. And so tens of thousands of our objects have left the solar system. 

It’s mind-bending when you think about that, and then you think about the age of the Milky Way, how long – or the age of the sun – this process has been happening and how much material is getting from star system to star system. Now, you were sort of getting a little more violent, and so let’s kick that back up a notch and talk about how planets can leave on a hurry, very rapidly. So, what can cause a planet to leave a solar system very quickly?

Pamela: Well, a planet can leave the solar system if there is some kind of a three-body interaction between it and a couple of other planets in the solar system. It is thought that our solar system may have had many more planets than what it currently has, depending on your value of planet. And three-body interactions between Saturn, Jupiter, and those objects led to them getting flung not just further out in the solar system, but out of the solar system entirely. It’s kinda cool to think that there may be these isolated planets that got stuff from the early Earth, stuff from the early Mars flung on to them and are now carrying those samples away to other places in our galaxy.

Fraser: And this idea of rogue planets, I mean, a few have now been found through gravitational microlensing. It’s estimated that there could be as many rogue planets in the Milky Way as there are regular planets. That’s probably a high estimate, but still, they’re gonna be in the hundreds of millions or billions. So, we’ve talked about planets and how they can, either through three-body interactions of within the system or – you could obviously have a black hole or a star get very close and kick a bunch of planets out into space as well. So, I wanna talk about stars that are on an escaped trajectory. All right, let’s talk about stars. So, what can cause a star to go on a runaway trajectory?

Pamela: So, three-body problems are still a thing. There’s research that shows that globular clusters somewhat beat like a heart because they will condense down, over time, getting more and more combined systems. But then, as those systems get towards the core, they’ll undergo interactions that fling things out into much larger orbits, so they’ll expand back out. And so you have these star-star interactions that will fling an additional star. But the thing that is new, once we get to the stellar level of interactions, is you can also get things flung out during supernovae. And this is one of the things where we’ve seen many different runaway stars.

And what is thought to happen is you have the giant star. You have its companion, and the bigger of them evolves first. Evolves, evolves, gets big, and hits the point where it’s no longer generating energy in its core, collapses down, and the collapse drives nuclear explosion, essentially. And the force of this can fling that companion star at a runaway velocity. You can also end up with asymmetric supernovae that just fling stars on their own.

Fraser: So, the blast of the supernova is hurling the star out? Because my assumption was that it was like a slingshot. You’ve got the star going around this other star, and then, suddenly, the star is no longer there. And now, the star is on a slingshot trajectory.

Pamela: So, to say it’s not still there depends on the kind of supernova. So, it is this combination of –

Fraser: Oh, that’s a great point, yeah. Right, because you could have it either completely disappear or end up with a neutron star or black hole.

Pamela: Exactly. So, you have the leftover relic. You have the explosion outward is going to exert force on things, and you have the change in the distribution of mass that’s going to change the interaction of things. End of the day, that companion star is, in many cases, gone. Not all cases. It’s deeply confusing that we keep finding systems that have an advanced star and a companion star and we know supernovae have occurred, but they’re still together. So, we’re still figuring out all of the dynamics here. But sometimes, you end up just with a supernova remnant and nothing inside, in which case the runaway object is running away from itself, which we all understand at a fundamental level.

Fraser: Yeah, possibly. So, the supernova goes off, and it’s not equal, and so it’s almost like it fires off thruster.

Pamela: Exactly. Yes. 

Fraser: Wow.

Pamela: And so that asymmetric supernova explosion will leave you with your supernova remnant and the stars running away from it. And I just love the conceptual idea of this where the supernova basically makes a giant mess, explodes all over the place, and runs away from the mess it made.

Fraser: So, with stars, we can get this situation where you’ve got – the supernova is symmetrical or not symmetrical, and so the star is given a giant thrust. You can have the situation where the star goes off and it blasts away its companion star with enormous explosion. You can have a situation where the star vaporizes completely. And now, the star is on a slingshot trajectory and in all cases. There’s one last scenario that I think is interesting is with a supermassive black hole. You can have a situation where a supermassive black hole could be kicked out on an escaped velocity, right?

Pamela: So, this is another multibody problem where, in this case, it’s the two galaxies coming in to merge that is leading to this situation, and so you have these two supermassive black holes. And instead of orbiting and merging, the collision and all the physics involved, as they pass to and fro, can end up flinging one of the black holes entirely away. And we think this is what explains the fact that there are a lot of merged systems out there that don’t have evidence for two supermassive black holes in their centers.

Fraser: So, the supermassive black hole just bounces off the other one and is off.

Pamela: I wouldn’t use the word bounce.

Fraser: I don’t know if bounce is the right word, but instead of it – if it’s not large enough, then it doesn’t merge. It just gets kicked out when it gets too close. 

Pamela: It’s all of the multiple passes and gravitational tugs to and fro and everything else that is going on can just fling it away.

Fraser: That’s crazy. All right, thank you, Pamela.

Pamela: Thank you, Fraser. And thank you to all of our patrons out there. This week, I would like to thank, in particular, Matthew Horstman, Alex Cohen, Phillip Walker, David Gates, Claudia Mastroianni, Matthias Heyden, Kseniya Panfilenko, Justin Procter, Jim Schooler, Scott Bieber, Scott Kohn, Daniel Loosli, Gregory Singleton, Disasterina, Jeff Wilson, Tim McMackin, Kenneth Ryan, Cooper, Omar Del Rivero, Omar Del Rivero, Allan Mohn, Eran Segev, NinjaNick, Steven Shewalter, Paul D Disney, Don Mundis, Janelle aka Veronica_Cure, Michelle Cullen, Micheal Regan, Benjamin Müller, J. AlexAnderson, Dean McDaniel, Matt Rucker, Scott Briggs, Anitusar, Frode Tennebø, schercm, Bruce Amazeen, Benjamin Carryer, Peter, Moose and Deer, Jim McGihon, Philip Grand, Mark Steven Rasnake, Father Prax, Brent Kreinop, Dustin A Ruoff, Abraham Cottrill. Thank you, all, so very much for everything you do. To all our editors who have their work cut out for them today to be paid and to keep our show going, thank you.

Fraser: Thanks, everyone.

Pamela: Buh-bye. Astronomy Cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy Cast is released under a creative comments attribution license. So, love it, share it, and remix it, but please credit it to our hosts, Fraser Cain and Dr. Pamela Gay. You can get more information on today’s show topic on our website, astronomycast.com. 

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