Did the Earth ever have a ring?

Daniel and Kelly talk about whether the Universe ever put a ring on the Earth See omnystudio.com/listener https://omnystudio.com/listener for privacy information.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Daniel Whiteson?

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• 1:40Daniel Whiteson?

  The message you often hear about space is that it's vast and empty. The Earth and even the Sun are these tiny dots in a huge ocean of black space. That's all true, but it gives you the wrong idea about our cosmic neighborhood. It suggests that the Earth is isolated, alone, not affected by our neighbors, not in danger. The truth is actually the opposite. Space is vast, but gravity is also very patient. There are a lot of big, dark rocks out there that could get tugged by gravity towards Towards the earth and then dramatically affect our way of life, both positively or negatively. They could, of course, smash into us and cause an extinction event, but then they could also create new snazzy bling around our planet.

• 2:23Daniel Whiteson?

  So today, we're going to dig deep into the history of earth within our cosmic neighborhood, understand the gravitational dance between all of these objects, and ask the question about whether there was ever a time when the universe put a ring on the earth. So just in time for Valentine's Day, we're getting cosmically romantic and asking, did earth ever have a ring? Welcome to Daniel and Kelly's Extraordinary Universe.

• 3:02Speaker 04

  Hello, I'm Kelly Wiener Smith. I'm a parasitologist and I stopped wearing rings because I got fish guts stuck in my ring too many times and decided it was too gross.

• 3:13Daniel Whiteson?

  Oh, isn't that romantic, though?

• 3:16Speaker 04

  Fish guts in a ring? You got a weird sense of romance, Daniel.

• 3:22Daniel Whiteson?

  I'm trying to resonate with the biology. Hi, I'm Daniel. I'm a particle physicist and I bought my wedding rings for $2 on Telegraph Avenue in Berkeley.

• 3:32Speaker 04

  I was going to ask you, are you and Katrina ring people or not ring people?

• 3:37Daniel Whiteson?

  We have rings, which we feel sentimental about, but we're not people who are into expensive, fancy stuff. So like, her engagement ring has a piece of amber in it and I designed the ring myself. There's no like crazy diamond in there and we didn't want to spend a lot of money on crazy rings. So we just walked down Telegraph Avenue and found a guy who made silver rings and bought them for a couple of bucks.

• 3:58Speaker 04

  You designed a ring with amber and got it for $2?

• 4:01Daniel Whiteson?

  Oh no, the engagement ring I had a friend make. So that was more than $2, but yes, I designed it myself. It has a bunch of Danish runes in it and stuff and a piece of amber in the middle.

• 4:12Kelly Weinersmith?

  Oh, that's great.

• 4:13Daniel Whiteson?

  How about you? What's your guy's ring story?

• 4:14Kelly Weinersmith?

  Can I tell you about our engagement story really quick?

• 4:16Daniel Whiteson?

  Oh, yes. Does it involve fish guts?

• 4:18Kelly Weinersmith?

  No, no, the rest of our life involves fish guts. But no, our engagement story. So Zach is like not a super sentimental guy. And so like a couple of months earlier, I had said to him like, hey, you know, we've been together for a year. Do you think you could ever see yourself marrying me? Because if so, let's keep going. But if not, let's like cut our losses and just be like, this was fun. And so his response, and this is amazing, his response was, I think you're really nice.

• 4:43Daniel Whiteson?

  Wow.

• 4:44Kelly Weinersmith?

  Which I thought was him being like, I don't want to answer this question because it's going to be uncomfortable. But like, that's not what I was looking for, right? And so I thought to myself like, okay, in a couple more months, I'm going to ask him this again. And if I don't get a better answer, it's over. But so Zach thought, well, you marry the person who you think is really nice. So he thought he had said like, yeah, I could marry you one day. And he thought after that conversation that it was locked in and that he didn't even really need to ask.

• 5:10Daniel Whiteson?

  That was like the most positive thing he could think of saying, I think you're really nice.

• 5:14Kelly Weinersmith?

  No, he's not a super sentimental guy. So it was pie day, March 14th. And he gave me a little card with a pie on it that said, don't open until, what are the extended digits of pie? So 314 is the date and then it's

• 5:27Daniel Whiteson?

  159.

• 5:28Kelly Weinersmith?

  159. Okay. Yeah. So don't open until 159. And I thought it was going to be a poem about how like I eat too much pie because he writes like weird poems. And I forgot about it. And so later in the day, it was like 4pm and he was in the restroom and I reached into my pocket and I was like, oh, I've got this card in my pocket. And it's after 159, so I can open it. And it said something to the effect of like, you get frustrated because I forgot our anniversary, but if we got engaged on pie day, that's a date I'd always remember.

• 5:55Daniel Whiteson?

  Oh, my gosh.

• 5:56Kelly Weinersmith?

  And so he came out of the bathroom and I was like, are you asking me to marry you? And so I'll note that he forgot when 159 passed. So he wasn't worried about the answer. He knew what the answer was going to be.

• 6:06Daniel Whiteson?

  And I love that there's a bathroom visit in the middle of this story. That's very Kelly and Zach.

• 6:12Kelly Weinersmith?

  Exactly. Very scatological. And so I was like, wait, so are we engaged now? And all he said was, well, you weren't supposed to read it while I was on the

• 6:23Kelly Weinersmith?

  Anyway, he didn't have a ring. He didn't have anything. We're not very sentimental. So anyway, we went out, we got a ring. I got fish guts in it. So I stopped wearing it because while I was doing dissections, it kept getting in the way. I got him a ring. And when we were walking around Rice University, our daughter was playing with it. And I was like, Zach. And she was like, two. I was like, Zach, she's gonna drop it. You're gonna lose your wedding ring. You probably shouldn't let her play with it. And we got back into the car and he sat down and he goes, uh oh.

• 6:52Kelly Weinersmith?

  Anyway, so he lost his ring and I don't wear mine because of fish guts. And we are not super sentimental, but we know it's been almost 20 years since we've been together. So it's working out.

• 7:01Daniel Whiteson?

  So Zach's ring is somewhere on the campus of Rice University?

• 7:04Kelly Weinersmith?

  Or some undergrad plays drinking games with it or something. I don't know. I don't know where it ended up. We never found it.

• 7:11Daniel Whiteson?

  All right, Rice students, if you see a ring on campus, send it to Kelly.

• 7:16Kelly Weinersmith?

  Yeah, I'll take all the random rings that get lost on campus. All right. Well, I've gotten us off topic. Your story was lovely. Mine was hopefully good for a laugh, but today we're talking about whether or not Earth ever had a ring, which is a fun question to think about.

• 7:30Daniel Whiteson?

  It's fun to think about because it makes us think about the deep past and how we think of the earth as a certain way and having the moon and the sky looks a certain way. And the solar system's arranged a certain way. And we imagine it's always been that way or for zillions of years. But it turns out that on a cosmic time scale, the solar system has a very chaotic history and things used to look quite a bit different. So it's really fun for me to like, go deep into the past and learn about how the solar system used to be quite different, how life on Earth could have been different. You could have looked up at the sky and seen different stuff out there.

• 8:05Kelly Weinersmith?

  And I gotta say, when you sent me this idea for a podcast episode topic, it had not been on my radar at all that Earth could have ever had a ring. So I'm excited about hearing the answer to this.

• 8:17Daniel Whiteson?

  So I was wondering if folks out there had considered the possibility of whether Earth had ever had a ring. So I sent this question to our intrepid volunteers. Thank you very much to everybody who plays along. If you would like to hear your voice answering questions on the podcast, please don't be shy. We would love to have you as part of the chorus. Write to us to questions at daniel and kelly.org and we will set you up. In the meantime, think about it for a minute. Do you think Earth could have ever had a ring? Here's what our listeners had to say.

• 8:47Kelly Weinersmith?

  A big meteorite smashed into the earth. All the debris shot up into into space. The earth did have a ring with the material that eventually coalesced into

• 8:57Speaker 06

  the moon. Yes, it did have a ring and it still does. Maybe it did like with all the rocks flying around it right at the beginning when it was being formed, it might have had like a ring of rocks around it. And maybe when the ice age happens, then there could have been a ring of ice around it when there was the ice age. I don't really think that could have happened. I'd say yes, that earth probably had a ring when the moon was born. As bodies coalesced and started to form into planetoids and eventually planets, there would have been rings.

• 9:31Daniel Whiteson?

  Earth might have had a ring after the collision with Theta. If you're referring to a persistent ring system akin to Saturn's, then that's more of a complex question open to interpretation. The ejecta from that collision temporarily formed a ring. There is a chance that there be some sort of ring during its creation. It no longer has a ring because it is divorced. Middle Earth did, and it was a big freaking deal. Is that one of the theories or hypotheses behind where the moon came from? When a Mars sized object collided with Earth.

• 10:05Speaker 07

  Do bears poop in the woods? Do tacos taste better on Tuesdays? Does Tom Cruise love to sprint like a maniac in every one of his movies? Yes. Yes, the earth had a ring. But I'll do know that Liberace had rings. During the formation of the moon?

• 10:19Speaker 01

  No, I mean Saturn offered, but long distance relationships just never work out.

• 10:24Speaker 07

  When a protoplanet hit it to form the moon. While the the moon was being formed. Uh, I really don't know, but I imagine not since the moon has been there.

• 10:34Kelly Weinersmith?

  That was an amazing mix of like, serious good answers and some really clever not answers.

• 10:41Daniel Whiteson?

  I think Tom Cruise does sprint in every movie he's in. I think that's true.

• 10:46Kelly Weinersmith?

  Every movie I can think of. Did he sprint in Jerry Maguire? He must have. There must have been a reason to sprint.

• 10:52Daniel Whiteson?

  Somebody check the footage.

• 10:53Kelly Weinersmith?

  Okay, let us know.

• 10:55Daniel Whiteson?

  And I was a little surprised though, I guess I shouldn't have been, that most people went to the sort of early formation of the earth. The impact with the protoplanet that formed the moon and thinking about how that might have been a ring as well. And that's a totally reasonable answer. But it's not what I was going for, for today's episode.

• 11:12Kelly Weinersmith?

  Well, I think probably it would help to know how rings are formed in general. So I'm guessing you're going to tell us that today, but let's start even earlier. So like, what are rings? I guess I realized, well, I was thinking about this question, like, you know, the moon orbits in a ring, but that's not a ring. How continuous does the line need to be before you have a satellite versus a ring?

• 11:33Daniel Whiteson?

  Yeah. So it's astronomy, which means we're going to do our best to draw arbitrary dotted lines between continuous concepts that really exist on a spectrum. But you know, some things we call moons, some things we call rings. What's the difference? How many tiny moons does it take before you start calling it a ring? Typically, we call something a ring if it's composed of solid materials such as dust or moonlit. But it's not in one single object. So, you know, basically there's a spectrum between like, you have one single object, you call that a moon. If you break that moon up into little rocks, you could call those moonlit. Or you could say if they're fine enough, you could call it a ring.

• 12:14Kelly Weinersmith?

  What if you had two objects as big as the moon that somehow didn't run into each other? Would that be a ring? Does Mars have a ring? Or does it just have two moons?

• 12:23Daniel Whiteson?

  Mars has two moons. So I think there isn't a very crisp distinction. I couldn't find a crisp distinction online. I don't think like the astronomers have had a meeting arguing about this yet.

• 12:35Kelly Weinersmith?

  Nature doesn't care about our criteria and our categories.

• 12:38Daniel Whiteson?

  But I think one thing that is important. For a ring is that it's basically in a plane. So you know, a swarm of objects surrounding a planet, you wouldn't call that a ring if it's like in a sphere. If it's orbiting in every direction and completely surrounding the planet with little rocks, that isn't a ring. One distinguishing feature of a ring is that it does orbit in a plane, right? That like the vertical motion relative to the ring is small compared to the motion around the planet.

• 13:04Kelly Weinersmith?

  Does it happen that you get junk like all around a planet? Or does it always end up in the same plane as a ring?

• 13:11Daniel Whiteson?

  Yeah, great question. You can get junk around a planet, but that's sort of temporary. That's not a very stable situation because gravity will eventually pull it down together into a plane. There's a reason that planets have rings and not swarms of stuff. And there's a reason that moons typically form in a single plane around a planet, which aligns with the planet's spin usually. And it's the same reason why the planets all spin in the same plane as their motion around the sun, which aligns with the rotation of the sun. And the reason is angular momentum. Gravity would like to pull everything down together into a little dot. What resists that? Well, sometimes it's like structural integrity. The earth doesn't collapse into a black hole because it's solid, right?

• 13:56Daniel Whiteson?

  And the rocks resist being crushed. But there's another factor there, which is the earth is spinning. And the spinning of the earth sort of fluffs it up a little bit and makes it larger. So like the earth's radius from the core to the surface is larger at the equator because it's spinning. And if the earth was softer like pizza dough, it would get flatter and flatter as that spinning resists gravity.

• 14:18Kelly Weinersmith?

  Yeah.

• 14:18Daniel Whiteson?

  But the spinning only resists gravity along the plane, right? So if you have like the earth spin axis, the spinning helps resist gravity, helps keep earth fluffed out along the plane of that spin, right? So the axis is perpendicular to the plane, but it doesn't prevent things from collapsing to the plane. So now imagine you have a big swarm of stuff that's swirling around the earth. Gravity can pull it down into that plane, making a disk. But the spinning keeps gravity from pulling it down into the earth necessarily. Why a big swarm of stuff would collapse into a plane. And it's the same reason why the whole solar system has collapsed into a plane. The original blob of gas and dust that formed our solar system collapsed due to gravity,

• 15:03Daniel Whiteson?

  but didn't collapse as far along that plane because everything is spinning. It keeps stuff from falling all the way in.

• 15:11Kelly Weinersmith?

  So if you had a speck around the earth, not around like the plane where you get the ring, would it get thrown out or pulled in or either?

• 15:23Daniel Whiteson?

  Yeah, so say, for example, earth has a big ring. And now you add a rock in a random orientation to the earth. What's going to happen to it? Well, it has a lot of velocity, so it's not going to fall to the earth. It's going to be in orbit, but it's going to get gravitated towards the ring. The ring is going to pull it in. And so while it's going to maintain an orbit because of its speed, that orbit's going to shift until it joins the ring. The ring, because of its gravity, is going to pull that new rock into it. So gravity pulls things together, but it can't overcome angular momentum.

• 15:55Kelly Weinersmith?

  Okay, and are rings always at the equator of the thing that they're orbiting around? And if the thing is at a tilt, that's why it doesn't look like it's straight around? So like Saturn is at a tilt and that's why its rings are kind of tilty?

• 16:09Daniel Whiteson?

  Yes, great question, and it depends a little bit on the formation. And this is actually a question people have about how rings form. Like if the ring formed from the original blob of stuff that made the planet. And one of the theories for how rings formed is you have a big blob of stuff and some of it collapses into a planet and some of it doesn't because it's moving too fast and it stays outside and forms a ring. Then it all comes from the initial blob of stuff that's spinning. And then you expect it to have the same spin on the same plane and basically be around the equator of the planet. But another theory is that these rings come from the outside. You have a planet that forms, it's already spinning and hard and compact. And now some material comes from the outside and is captured by the planet into a ring.

• 16:51Daniel Whiteson?

  That will collapse on its own, but its axis doesn't have to align with the axis of the planet. Gravity will pull it down into a single ring and it will orbit. Around its own spin axis. It doesn't have to align with the planet. There's nothing the planet can do to change its spin axis. Because angular momentum is conserved.

• 17:09Kelly Weinersmith?

  All right. Is there anything else we need to know about how rings are formed? Are we all now experts?

• 17:14Daniel Whiteson?

  Another thing to think about is the difference between the formation of moons and rings. Like, why do some planets have rings and some of them have moons and some of them have both? You know, why doesn't gravity always pull a ring together into a moon, right? You could imagine like a string of little moonlets orbiting together in a circle around a planet. Why doesn't gravity always pull those together? It can do that without violating angular momentum. And the answer there is tidal forces. Usually when we think about the solar system, we're thinking about gravity as just like here you have a rock and there you have a rock. And there's gravity between them and they're pulling on each other. But gravity is a little bit more complex than that. If your rocks are not just point objects, if they're just points, then yeah, you can just think about the gravity on the objects.

• 17:59Daniel Whiteson?

  But if it's big, then you have one side that's closer and another side that's further. And gravity depends on distance. So gravity is going to pull on the closer part harder than it's pulling on the further part. And that's true always. So for example, if you're an astronaut and you're in space and you're doing, you know, an EV or whatever. The earth is pulling on your feet harder than it's pulling on your head. And you might think, no big deal, but those are relative forces. You can think of it as pulling on your feet harder than your head, or equivalently, you can think the earth is trying to pull your head off of your body. Because that's really what it's doing, right? It's pulling on one side harder than the other side. It's trying to tear you apart. And normally your neck is strong enough that the earth's not going to decapitate you.

• 18:43Daniel Whiteson?

  But if you were close to a very powerful body like a black hole, then those tidal forces are powerful enough to pull you apart. That's what spaghettification is. And so planets pull on things. The earth, for example, is tugging on the moon. It's trying to squeeze the moon into a football. It's trying to pull rocks off the surface of the moon that's closer to it.

• 19:02Kelly Weinersmith?

  I can imagine how that pulling over time would start to like pull off pieces and result in a ring. So does that mean that a lot of the rings around planets are moons that just got kind of crushed? And then why didn't our moon end up succumbing to that?

• 19:15Daniel Whiteson?

  Hmm. It depends on distance. It also depends on structural integrity, what your moon is made out of. But basically, if a moon gets too close to a planet, the tidal forces will pull it apart. If the moon is far enough away, then the structural integrity of the moon is more powerful than the tidal forces. It'll stay together. So if you look at all the planets in the solar system, you notice that it's usually rings on the inside and moons on the outside. And you can calculate this sort of dividing line. It's called the Roche limit. Things that are closer than the Roche limit, the tidal forces will probably pull it apart. Things that are further, things will coalesce into a moon. The self-gravity will pull it together, and then the structural forces will hold it.

• 19:53Kelly Weinersmith?

  Is it an interplay between distance and size? Or is it just size? Or distance, size, and what you're made out of? Like a chunk of metal would be harder to pull apart than something else?

• 20:05Daniel Whiteson?

  Yeah. It's mostly distance from the planet and what you're made out of. So for example, there's a different Roche limit for a blob of water than there is for like a moon made of diamond, which would be much harder to pull apart. But for like a typical rock, you can calculate these distances. For the moon, for example, if it came within 10,000 kilometers of the surface of the earth, it would be pulled apart. Its orbit is safely outside that. It's like 390,000 kilometers. So it's well past the Roche limit. And you know, the sun has a Roche limit. If a planet gets too close to the sun, it would get pulled apart by its tidal forces. So for example, if the earth came within almost a million kilometers of the sun, it would get pulled apart. We're like 150 million kilometers,

• 20:46Daniel Whiteson?

  so we're in no danger. But this is the distinguishing feature between rings and moons. Basically, how far you are from the surface of the planet.

• 20:53Kelly Weinersmith?

  You know, now, anytime we discuss something that's named after someone, and I'm guessing the Roche limit is named after Roche, I find myself wanting to have Kathy Johnson back. Because I want to be like, Kathy, did Roche really come up with this? Or who was he building on? What were people thinking at the time? She should just always give us the Background on everything because she's wonderful.

• 21:10Daniel Whiteson?

  Mm hmm. Yeah. And science is a human story, which means that every time you learn a little bit of knowledge, there's a fascinating, probably tortured history for how we figure that out and how it was named after this person and whether that person was actually a jerk and if their paper was full of mistakes and whether they deserve the credit for that or not. Human history is always fascinating. Every time you lift up the rug, you find really interesting stuff under there.

• 21:34Kelly Weinersmith?

  Everyone should check out, if you missed it, our episode on Maxwell's equation to hear Kathy's amazing history and also to make you feel better if you're not good at math.

• 21:43Daniel Whiteson?

  Because neither was Faraday.

• 21:45Kelly Weinersmith?

  Or Maxwell, apparently.

• 21:46Daniel Whiteson?

  Maxwell was good at math. He just wasn't good at keeping track of minus signs. But hey, who is?

• 21:51Kelly Weinersmith?

  He got away with a lot of mistakes. Yes. All right.

• 21:54Daniel Whiteson?

  That's true. I have fewer published math errors than Maxwell.

• 21:58Kelly Weinersmith?

  There you go. You should feel good about that. You should get a plaque to put over your desk.

• 22:02Daniel Whiteson?

  Maybe just a T-shirt.

• 22:03Kelly Weinersmith?

  There you go. That's right. Fewer mistakes than Maxwell. It's got to be a pretty niche audience for that T-shirt. Okay.

• 22:11Kelly Weinersmith?

  All right. Well, we're all missing Kathy right now, but there's nothing we can do about it at the moment. So let's take a break to think about how great Kathy is. And when we come back, we'll talk about what those rings tend to be made of.

• 22:30Kelly Weinersmith?

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• 22:57Speaker 03

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• 23:40Kelly Weinersmith?

  All right, so based on our earlier conversation, I'm guessing that a lot of rings are made out of, you know, like moons that got crushed. So probably, you know, rocks and metal and stuff. What else do we get out there?

• 23:51Daniel Whiteson?

  Yeah, so the rings tend to be made out of the same stuff that the solar system is made out of. So the inner solar system, it's mostly rocky because, you know, the solar system, well, it starts out mostly gas, but all that gas gets gobbled up by the sun. And any gas left over in the inner solar system got blasted out of it by the sun's radiation. So you don't have a whole lot of gas left in the inner solar system. The rings closer to the sun are going to be rockier. Further out, you're more distant from the sun, so you can have things like water crystals. And out past what we call the frost line, where water isn't vaporized by the sun, you have ice. And so, for example, beyond Jupiter, there's a lot of ice in those rings.

• 24:31Kelly Weinersmith?

  So you don't get any ice in rings between the sun and Jupiter? But Jupiter outwards, you can get ice in rings?

• 24:38Daniel Whiteson?

  Yeah, exactly. And so we have some pretty spectacular ring systems in the solar system, right? And one of the first ever to be seen was Saturn's. This is one of the first things, actually, that Galileo saw through his telescope on those cold Italian nights in the early 1600s are the rings of Saturn, which, you know, anybody who's used a telescope in their backyard knows that this is an amazing thing to see.

• 25:00Kelly Weinersmith?

  I can't imagine being the first one to see that must have been just absolutely mind blowing.

• 25:04Daniel Whiteson?

  Right, right? To me, it's always exciting when you can resolve any feature on these objects in the night sky. Like you look at the moon and you can see things on the surface. That's super cool because it's not just like a point. And seeing the rings of Saturn is the same way. You're like, I'm seeing something that's really out there. I don't know about you, but when I look at the night sky, it's just too easy to think of it as like a screen with dots on it. But when you can resolve features. On something, then suddenly I'm transported to this mode where I understand I'm looking across an incredibly vast ocean of nothingness to huge objects that are incredibly distant. You know, it's so difficult for your mind to really put yourself in that vast 3D space. But on a clear night, when you can see the rings of Saturn or the moons of Jupiter,

• 25:50Daniel Whiteson?

  I feel like it's easier to visualize yourself in this vast space rather than thinking of it as a screen.

• 25:56Kelly Weinersmith?

  Well, part of me feels like this is cheating, but I love those apps on my iPhone where you look up at the night sky and it tells you like, that's Saturn, that's Venus. And like, to me, I get all philosophical when I get that extra detail. It makes me feel like I'm more of a small speck than if I just look out. It's like you said, it's almost like you've got a sheet with little pinpricks in it and lights coming through. It's like easy to not think about it as a vast expanse out there. But anyway, yay for technology. There's an app for that.

• 26:25Daniel Whiteson?

  Well, the rings of Saturn are really incredible because they're so varied. There are a bunch of different rings. They're separated and NASA has given them really creative names. There's the A ring, the B ring, the C ring, you know, goes out to the G ring and the E ring, which are sort of harder to see with your naked eye. Some of these things have like a lot of dark organic compounds, so they're not as easy to see. The inner ones have more ice, like they're just basically a bunch of icy particles spread out in these vast, very flat rings.

• 26:55Kelly Weinersmith?

  Who should be naming these, right? You know, so NASA clearly shouldn't be allowed to name things because they're not doing a good job. But you know, like if you let the internet name them, it would have been like Ringy McRingface. What is the right solution here for these amazing celestial objects? I think they should be renamed. That's what I think.

• 27:11Daniel Whiteson?

  Yeah, absolutely. I think they should not be named by scientists. Maybe we should have Jorge on the podcast to suggest names. He was always good at that.

• 27:18Kelly Weinersmith?

  Sounds good.

• 27:18Daniel Whiteson?

  But there are these fascinating gaps between the rings, like there's the A ring and the B ring. And we've known about these gaps forever. It was Cassini in like the late 1600s who first saw these gaps. And that's why we call that spacecraft that visited Saturn, the Cassini spacecraft, because he was the first one to see them. And these gaps in the rings come from Actually, the interactions of the ring material with little moons. You know, so we talked about how like their only moons out past the rings. But if you're small enough, you can avoid those tidal forces. You're like basically a big chunk of rock within the ring. Is it really part of the ring? Is it a moonlit? Now we're getting into that murky territory where the dotted lines don't make any sense. But these rings sometimes are called shepherd rings, shepherd moons.

• 28:03Daniel Whiteson?

  Because they orbit near the edges of these rings. And they can like help keep the material in place. There's these fascinating gravitational interactions between the ring and the moon.

• 28:14Kelly Weinersmith?

  Huh, and okay, so the moon is countering Saturn's gravity to keep some of the stuff in the ring in its place. How is the moon clearing its own orbit? Is its gravity pulling anything else that might have been in a ring in that location? It's pulling it into itself?

• 28:27Daniel Whiteson?

  Yeah, essentially, it's acting like a little shepherd. It helps keep the edge of the ring sharply defined. Because anything that gets too close gets accreted onto the moon. Or it can make a near miss and can like get accelerated by the moon and then deflected back away from the moon. Like a slingshot back into the ring. That's how it keeps its own like little lane. That's why you get these gaps in the rings. It's really fascinating that these rings are really, really broad, right? They're like 70,000 kilometers wide, the rings of Saturn. And they're only 20 meters thick. That's meters, not kilometers.

• 29:03Kelly Weinersmith?

  Oh, wow.

• 29:03Daniel Whiteson?

  Yeah, it's the scale of like, if you had a sheet of paper, the sheet of paper would be like a kilometer wide. Right, it's incredibly thin compared to the breadth of it. And that's due to angular momentum and gravity. Gravity has done its work to collapse it down to a thin sheet. But it can't do it in the sort of plane of rotation because of angular momentum.

• 29:23Kelly Weinersmith?

  It's kind of amazing that we can see anything that thin from all the way here on Earth.

• 29:26Daniel Whiteson?

  It's because it's reflective. It's the icy particles that make it possible to see it.

• 29:30Kelly Weinersmith?

  Oh, okay. All right, so then where did Saturn get this ring in the first place? Was Jupiter feeling amar? At some point.

• 29:38Daniel Whiteson?

  You know, the story of Saturn's rings is interesting history. It used to be that people thought this was probably left over from formation of Saturn because it does orbit in the plane of Saturn. And it seemed like, wow, this must have been here for a long time. But Cassini's visits revealed that the rings are quite low mass. You know, there's like, less stuff in there than we thought. And it's still very sharp and bright, like the edges of these ice crystals are still very sharp, which isn't consistent with like, being there a long time. You know, things tend to get rounded and collisions tend to soften stuff. A more recent theory is that some moons of Saturn might have collided and left a huge spray of debris, which basically formed into a ring, which might mean that

• 30:20Daniel Whiteson?

  these rings themselves are temporary. It might be that Saturn gathers them back together into moons. We don't quite know, because the Roche limit is a little bit fuzzy, you know, the structural integrity, if those rings will be there in 100 million years.

• 30:35Kelly Weinersmith?

  Oh, man, and we're not going to be around to know.

• 30:37Daniel Whiteson?

  How do you know? Come on, we're gonna have great, great, great, great, great grandkids making non sentimental marriage proposals to each other, using ice from the rings of Saturn.

• 30:47Kelly Weinersmith?

  Wait, your grandkids are going to, are we getting into incestuous stuff? Oh, you might.

• 30:51Daniel Whiteson?

  I mean humanities descendants. I couldn't say enough great, great, greats to get us 100 million years. But are you not optimistic that people will be living in the solar system in 100 million years?

• 31:00Kelly Weinersmith?

  I know I'm optimistic.

• 31:02Daniel Whiteson?

  All right. Somebody will be here to see the new moons of Saturn and to give them a creative name.

• 31:07Kelly Weinersmith?

  I hope somebody gets on that much sooner. I don't want to wait for that to happen.

• 31:14Daniel Whiteson?

  And other planets in the solar system have fascinating histories with rings. Like, astronomers think that Mars has gone through several cycles of having rings and moons and rings and moons.

• 31:24Kelly Weinersmith?

  Wait, so does that mean that like, Phobos and Deimos have broken up and come back together multiple times? Or?

• 31:30Daniel Whiteson?

  Well, we don't know how long Phobos and Deimos will last, but we think that Phobos and Deimos formed from a ring that was created from a giant impact. So like, something hit Mars and then ejected a huge amount of stuff, like 10 to the 20. 3 kilograms of stuff into orbit and left this huge debris cloud around Mars, which then collapsed into a ring, which then got gathered together into these small moons.

• 31:56Kelly Weinersmith?

  So is it possible to look at a moon and figure out if it's gathered up ring? Or not like that's got to be hard.

• 32:06Daniel Whiteson?

  It's not always possible to tell the history, but you can get some clues. Like, for example, Phobos and Deimos have very circular orbits, which suggests that you have like a lot of stuff which formed a ring and then gathered together, rather than being single objects that were like captured as they floated near Mars, which would tend to be like more elliptical orbits and not necessarily in the same plane as Mars. So that suggests that it formed from a ring. Also, you could look at the composition of the stuff. And Phobos and Deimos are made of the same stuff as Mars is, which suggests like our moon, that it formed due to a giant impact, rather than like was captured. Sometimes moons can be captured. Some of the moons of Saturn and Jupiter,

• 32:48Daniel Whiteson?

  we think are just like big rocks that floated too close and got gobbled up into the gravitational system of those planets, not yet torn apart.

• 32:56Kelly Weinersmith?

  But hit the cosmic lottery and didn't get pulled into the center.

• 33:02Daniel Whiteson?

  Exactly. And if these things form moons and then they're too close to the planet, like they'll drag. If there's an atmosphere there, they'll drag and then eventually just fall into the planet. And so then you can lose your moon. So there's evidence on Mars of several of these cycles, like impact, forms a cloud, makes a ring, then makes a little moon and that moon gets dragged down into the planet and lost and you start again. So Mars is like a really kind of checkered history with its moons. It's kind of like a bunch of X's that it's gobbled up.

• 33:31Kelly Weinersmith?

  Oh, man. Yet one more reason to not go to Mars. As if I needed one. So it sounds like these transitions. are very chaotic and would be dangerous if humans were living on the surface at the time.

• 33:42Daniel Whiteson?

  Oh, yeah. No, you don't want to be around during one of these transitions. You don't want to be around when you have like a huge dust cloud around your planet either, because it's going to block a lot of light. So, you know, the temperature probably plummets on the planet when you have a situation like that. In general, it's probably really fun to watch from far away, but not fun to watch from the surface.

• 34:01Kelly Weinersmith?

  And the connection with the dust cloud is because when something plummets, it kicks up a bunch of dust. Is that right?

• 34:05Daniel Whiteson?

  Yeah, a lot of these are formed from an impact. So either you have something that comes nearby and is torn apart, and then you get a cloud of debris, or you get an actual impact on the planet, which kicks up huge piles of stuff from the planet, which then coalesces into a ring and then a moon. And so we used to think that Saturn was the only planet in the solar system that had rings. But now we've discovered that rings are much more common. So, for example, Jupiter has rings, but we've only known that since 1979, when Voyager went to visit. These things are so faint that you either need to send a probe to see them or have a very powerful space telescope. Like Hubble can see the rings of Jupiter now, but otherwise we couldn't see them from Earth.

• 34:45Kelly Weinersmith?

  And what are they named? One, two?

• 34:51Kelly Weinersmith?

  I hope we've done better with Jupiter's rings.

• 34:55Daniel Whiteson?

  Maybe alpha, beta, gamma, delta. Yeah, that's a good question. But these rings around Jupiter are very faint, because they mostly consist of these little dust particles that come from like tiny meteors hitting the planet's moons and then being vaporized. But this dust also doesn't last very long in the Jovian system, because Jupiter is crazy. It has really powerful magnetic fields. And these basically pull these rings apart and shepherd them up to the poles. And so a piece of dust can only last in these rings for like a few hundred years or a few thousand years, which means that Jupiter's rings are constantly being degraded and replenished. Like micrometeors are hitting the moons, which then get vaporized,

• 35:39Daniel Whiteson?

  and then they join the ring. But there's also an outflow. So it's not like a constant structure. It's more like a river of dust that's moving through this sort of like dust cycle around Jupiter.

• 35:49Kelly Weinersmith?

  It's probably nice to get some new bling from time to time, you know? Out with the old, in with the new ring.

• 35:56Daniel Whiteson?

  Yeah, maybe you and Zach should get new rings sometime.

• 35:58Kelly Weinersmith?

  Yeah, no, he'd just lose them and I would get bug guts in them and it would just not, it wouldn't work for us. It's all right.

• 36:04Daniel Whiteson?

  Yeah, you know, I'm the same way. I lose stuff. I put stuff down. I can't remember it. So I've always been terrified I was gonna lose my ring. So I just never, ever, ever take it off. Like, that's my rule. Not in the shower. I never take it off because I'm afraid I'll lose it. Same with my glasses. Like, I wear glasses all the time. I actually only need them for reading.

• 36:22Kelly Weinersmith?

  Really?

• 36:22Daniel Whiteson?

  But if I ever took them off, they would be gone within a day. So I just wear them all the time because I can't manage it otherwise.

• 36:29Kelly Weinersmith?

  I'm just totally blind without mine, so I never take mine off. But lately, my kids think it's funny to try to pull them off. And I do not think that's funny at all. So we're working on that.

• 36:42Daniel Whiteson?

  You think it's hilarious when mom bumps into stuff in the kitchen?

• 36:45Kelly Weinersmith?

  I mean, yeah, I guess so. But then I remind them, like, oh, I can't drive you to go get ice cream. And then they're like, oh, we found your glasses. Like, oh, that was easy.

• 36:54Daniel Whiteson?

  Isn't it wonderful as your kids grow up to be real people?

• 36:57Kelly Weinersmith?

  Yeah, I know. They're growing up to be bullies.

• 37:01Kelly Weinersmith?

  I'll do better. All right. So we've talked about how Mars maybe had rings. Jupiter, Saturn definitely have rings. How about Uranus? She says with glee.

• 37:11Daniel Whiteson?

  You're just desperate to talk about rings around Uranus.

• 37:13Kelly Weinersmith?

  I mean, what would an episode be without it?

• 37:17Daniel Whiteson?

  So there are actually Uranian rings. The individual particles in these rings are jet black, like lumps of coal. And we haven't visited close enough or been able to study these enough to know exactly what they're made out of. But they seem like some kind of carbon or hydrocarbon compounds. They're not very well understood because they're so far out and they're so hard to see because they're black. Like, remember, we can only see stuff that reflects light unless we go and visit. And so jet black stuff out there in the deep, dark solar system, it's very hard to study.

• 37:49Kelly Weinersmith?

  I would have so much fun naming things on a Uranus mission, rings and all that. Okay, let's take a break. You think of what you would name Uranus rings if you discovered them. And when we get back, let's talk about whether or not Earth ever had a ring.

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• 39:23Kelly Weinersmith?

  All right, so I am going to hope that Earth never has another ring because I think that would probably result in something catastrophic for the humans living on the planet. And actually, have you ever read Seven Eves by, I think it's Neal Stephenson?

• 39:36Daniel Whiteson?

  I have read Seven Eves and greatly enjoyed it. It's a fun book. I really wanted to know more about what blows up the ring in that book. It's not a spoiler because it happens in like chapter one. And I thought, oh, this book is going to be about understanding the mystery of what destroyed the moon. But he just basically moves on to like what it's like to live in that system, never answers the question like, was it an alien attack? Was it a random impactor? I found that very unsatisfying. I mean, it's a great book otherwise.

• 40:03Kelly Weinersmith?

  I kind of appreciated that. I felt like, you know, there's just a lot of things we don't know the answer to. And probably like in a situation like that where you think humanity is in peril, that probably goes to the bottom of your to-do list, like figuring out the answer to that. But I had some questions about the evolutionary biology stuff there.

• 40:21Daniel Whiteson?

  No, we're science people. We're curious. You can't like give us a huge mystery and then leave it unsolved. That's the point of these books is to inflame your curiosity itch and then scratch it. You can't just inflame it. That's really unfair.

• 40:32Kelly Weinersmith?

  I mean, there was a lot of other hard science in that book.

• 40:34Daniel Whiteson?

  No, there definitely was. Yeah.

• 40:36Kelly Weinersmith?

  If anyone knows Mr. Stevenson, we would love to talk to him on the show. Let us know.

• 40:40Daniel Whiteson?

  Yes, absolutely. Please, Mr. Stevenson, come, talk to us. We will be very nice.

• 40:44Kelly Weinersmith?

  We'll be huge nerds. All right. So let's hope that Earth never has a ring into the future. But let's look into our past. When might we have had a ring?

• 40:52Daniel Whiteson?

  So a lot of the answers from listeners were really insightful. They were thinking about the early formation of the moon and how that probably got gathered together from a big cloud of stuff, which probably initially formed into a ring. And that's a very insightful answer. I think my only quibble with that would be like, was the Earth really formed at that time? You know, we had the Proto-Earth, which then got collided with Thea and formed a huge swirling system which coalesced into the Earth and the moon simultaneously. So like, I don't know if that counts as the Earth having a ring, because the Earth itself was still forming. But it's true that the moon was likely a ring of material before it formed a moon.

• 41:31Kelly Weinersmith?

  Oh, interesting.

• 41:33Daniel Whiteson?

  But that was over 4 billion years ago, very, very early in the solar system. There was actually another period, much more recently, only 466 million years ago, when scientists think the Earth might have temporarily had a ring system.

• 41:46Kelly Weinersmith?

  Oh, man. All right. What catastrophic thing happened to make that happen?

• 41:49Daniel Whiteson?

  So what we do know and has been well established is that around 466 million years ago, there was a time of heavy bombardment. It's the Ordovician period of the Earth. And we know from fossil records and from other crazy pieces of evidence we have, that there was just a lot of impacts on Earth. Like, there are these quarries in Sweden where you like dig down to get limestone. Each layer is older and older. And there's a layer that corresponds to this time period with all these fossil meteorites in it. Like, they found these weird green rocks down there. They're like, what is this? And you find them in this one particular strand, and they dug into them and discovered these are meteorites. You can tell. Like chemically and also from the shape of these things that they're meteorites and

• 42:31Daniel Whiteson?

  not just like rocks from Earth. And then they found similar impact sites in other places around the Earth. That tells us like, wow, there was a period here where like the weather was bad on Earth.

• 42:41Kelly Weinersmith?

  So is the idea then that there was something that got within the Roche limit and it got broken up into a ring and then it fell all over the planet and that's why there's a lot of it?

• 42:53Daniel Whiteson?

  Yes. So the theory used to be that there was probably some impact between asteroids out in the asteroid belt or near Jupiter or something that created a lot of shrapnel. And then the Earth basically flew through a cloud of this shrapnel. That was the original idea. So we know that there was a lot of impacts. You see them all over the planet. There's even evidence of like enhanced seismic and tsunami activity from all this time ago. It's incredible what you can learn from geology, from like seeing these fragments of rock that got broken up and stuck back together in ways you only get from like really cataclysmic tsunamis and seismic events. Anyway, the theory used to be, okay, there's a cloud of stuff that's created far from Earth and the Earth flies through this cloud,

• 43:35Daniel Whiteson?

  which creates all these impacts, right? But a recent study, they analyzed where on the surface these craters were, and they discovered that they were suspiciously all along the equator. That suggested there was time for this thing to form into a ring around the Earth. And probably your description was more accurate, that some big thing came pretty close to the Earth within its Roche limit, was then torn apart into bits, which orbited for a while, formed a ring before the atmosphere dragged it down into impacts on Earth.

• 44:08Kelly Weinersmith?

  Oh, my gosh. And so was there an extinction that happened concurrent with this?

• 44:12Daniel Whiteson?

  There is a moment called the Great Ordovician Biodiversification Event, and there was definitely a change in the Earth's temperature. If you look at the temperature records, they call this a global ice house. It's like a big dip in the history of the temperature on Earth. And so this paper suggests, oh, this could explain that as well, because if you have a huge ring that forms over the equator, it's going to significantly shade the planet. And this is a really hard study to do. Because if you want to think about where these things land on the earth, you have to know where that land was at the time, right? Continents move. And you might be thinking, hold on, didn't Daniel say there were a bunch of fossil meteors that landed in Sweden and Sweden isn't close to the equator?

• 44:53Daniel Whiteson?

  Yeah, it isn't today, but 466 million years ago, it actually was. So what they had to do was figure out where are all these craters that you can associate with this time period, which isn't always easy because sometimes you can date these things very well, sometimes you can't because of the layers they're in. Then they had to rewind the history of the earth to understand where were these craters when the impact actually happened. And so they computed this amazing word, I love this, the paleolatitude, right? Like where on the earth was this when it happened? I love that.

• 45:26Kelly Weinersmith?

  That's a good word. So those people should be in charge of naming the rings. We found the people.

• 45:32Daniel Whiteson?

  Exactly. Right? Sometimes you hear a word in science, you're like, okay, that's well done.

• 45:36Kelly Weinersmith?

  That's right.

• 45:37Daniel Whiteson?

  Nice. That's nice.

• 45:41Daniel Whiteson?

  And so they did this calculation, they found all these things. But you know, we're talking about a handful of things, not like millions of examples. They have like a couple of dozen, maybe three dozen craters that they can definitively pinpoint are from the Ordovician period. And so you might wonder like, well, how do you really know these are within the equator? It's not like they all line up perfectly on the equator. They're sort of like loosely associated with the equator. Their paleolatitude tends to be less than 30 degrees. And so they did a pretty robust statistical analysis. I read this paper carefully because honestly, I'm kind of skeptical about the ability of lots of folks out there to do statistics in a robust way because not that many people really understand statistics.

• 46:23Daniel Whiteson?

  And I've been shocked to read papers in other fields, especially biology.

• 46:27Kelly Weinersmith?

  Yeah.

• 46:28Daniel Whiteson?

  And be like, mm, I'm pretty sure that statistical analysis is totally wrong.

• 46:31Kelly Weinersmith?

  Yeah.

• 46:32Daniel Whiteson?

  But.

• 46:33Kelly Weinersmith?

  I'll give you that.

• 46:35Daniel Whiteson?

  But I read this paper, I thought they did a great job. They thought about like, what are the chances of getting this kind of distribution of paleolatitudes? If things actually were evenly spread and they did some. Good calculations and some good simulations. They look, for example, at the distribution of modern impacts and show that they're much more broadly distributed than these. So they calculate it's very unlikely that these things by random chance just happen to fall along the equator. And that suggests that they probably were in a ring above the earth for a while. This is 466 million years ago. They also looked at some of these rocks, these actual fossil meteors, and they can study the

• 47:15Daniel Whiteson?

  chemical composition of these things and understand how much space radiation they were exposed to.

• 47:21Kelly Weinersmith?

  What?

• 47:22Daniel Whiteson?

  This is super awesome. Yeah. Because, you know, there's a lot more radiation out in space than there is here on earth because out in space you don't have the benefit of our atmosphere protecting you. And so like there are all these high speed particles, cosmic rays and solar wind constantly penetrating it, and that changes the chemical composition of stuff, right? It smashes into the rocks, it degrades some of those isotopes. So you can basically count how long something has been in space by looking at the chemical makeup of a rock. And it looks like these rocks were not exposed to space for very long, only like a few tens of thousands of years, not millions. And that means that probably they were like on the inside of some large asteroid for many,

• 48:05Daniel Whiteson?

  many, many millions or billions of years, basically protected from the radiation of space, then torn apart by the earth's tidal forces into a bunch of little rocks, which were not protected by the radiation of space, but only for a few tens of thousands of years before they fell to the surface of the earth and then protected again. So, you know, they were near the surface of an asteroid out in space, exposed to radiation for only a few tens of thousands of years. So that's also suggestive. None of this is completely conclusive, but you know, this is like solving a mystery. You have a few clues, you're trying to piece together a story. All this is very circumstantial, but it all points in the same direction.

• 48:43Kelly Weinersmith?

  You mentioned that there was like a Shrapnel theory. Wouldn't the Shrapnel theory also have something big where most of it was protected by space radiation and then it got broken into pieces and those pieces were exposed to space radiation for a short period of time before earth hit it? How would you tell the difference between those two options?

• 49:00Daniel Whiteson?

  Yes, a short period of time, but longer. Like if there was a collision out in the asteroid belt that created all this shrapnel, it would take much longer to get to Earth, probably millions of years, not just 10,000. And so that's how they can tell the difference.

• 49:14Kelly Weinersmith?

  Got it. That's very cool. Who was the first author in this study? Let's give him some credit. This sounds awesome. And scientists who understand statistics.

• 49:21Daniel Whiteson?

  Yeah, so this is Andrew Tompkins, Aaron Martin, and Peter Kaywood in a paper in Earth and Planetary Studies in November 2024. It's really quite readable, even for somebody outside their field. So congrats on the exciting result and the nicely written paper.

• 49:37Kelly Weinersmith?

  And where did you come across this? How did we come to talk about this today?

• 49:41Daniel Whiteson?

  I think a bunch of listeners might have heard press releases about it and sent me an email asking me to explain it. So I put it on my list and eventually I actually do get to everything on my list, as I promised. But we got a long backlog, so it might take me a while. But if you are curious about something you've heard about in the news and you'd like for us to break it down and explain it to you, for Kelly to ask me hard questions, for me to ask Kelly naive biology questions, then please send us your questions. We'd love to dig into something you'd like to hear more about.

• 50:11Kelly Weinersmith?

  So write us at question. Oh, I always forget our email address. What's our email address, Daniel?

• 50:15Daniel Whiteson?

  [email protected]. You can write to us and ask us, like, what is our email address?

• 50:21Kelly Weinersmith?

  Yes, you're probably not going to be super successful on that one. But good luck and we hope to hear from you.

• 50:26Daniel Whiteson?

  Until next time, put a ring on it.

• 50:28Kelly Weinersmith?

  That's right.

• 50:31Kelly Weinersmith?

  My daughter would be absolutely appalled if I say it. So anyway, thanks, everyone.

• 50:35Daniel Whiteson?

  Tune in next time.

• 50:43Kelly Weinersmith?

  Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We would love to hear from you.

• 50:48Daniel Whiteson?

  We really would. We want to know what questions you have about this extraordinary universe.

• 50:54Kelly Weinersmith?

  We want to know your thoughts on recent shows, suggestions for future shows. If you contact us, we will get back to you.

• 51:01Daniel Whiteson?

  We really mean it. We answer every message. Email us at [email protected].

• 51:07Kelly Weinersmith?

  Or you can find us on social media. We have accounts on X, Instagram, Blue Sky. And on all of those platforms, you can find us at D and K Universe.

• 51:17Daniel Whiteson?

  Don't be shy. Write to us.

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  Cool fall nights always make me want to entertain more. A few friends around the table, maybe a fire outside when the sun goes down. Before everyone comes over, I stop at Total Wine & More. Right now, there's a cranberry flavored wine, a crisp apple wine, even a pumpkin spice cream that's perfect in coffee after dinner. And with the lowest prices, I can bring home a few different fall flavors for everyone to try. Find your favorite fall flavors at the lowest prices at Total Wine & More. Spirits are not sold in Virginia and North Carolina. Drink responsibly, must be 21.

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