Planetary Radio: Space Exploration, Astronomy and Science - The disappearing act of Saturn's young rings

Episode Date: June 21, 2023

Saturn's rings are so young that they may have formed when dinosaurs walked the Earth. Richard Durisen, a Professor Emeritus of Astronomy from Indiana University Bloomington, and Paul Estrada, a Research Scientist at NASA Ames Research Center, join Planetary Radio to discuss their research on the surprisingly recent formation of Saturn's rings and why they are disappearing over time. Then Bruce Betts and host Sarah Al-Ahmed share what's in the upcoming night sky and chat about creepy-crawly constellations. Discover more at: https://www.planetary.org/planetary-radio/2023-saturn-young-ringsSee omnystudio.com/listener for privacy information.

Saturn's rings are younger than humans initially thought. This week on Planetary Radio. I'm Sarah Al-Ahmed of the Planetary Society with more of the human adventure across our solar system and beyond. Richard Duresen and Paul Estrada joined me this week to talk about their research about Saturn's rings. Their findings show that the ring system didn't form with the planet. The event that created them happened much more recently, cosmically speaking. Not just that, but the rings are disappearing over time. We'll get into all of the details. Then Bruce Betts and I will share what's going to happen in the upcoming night sky and talk about bug constellations. And if you enjoy shiny space nail polishes and fun facts, you'll want to stick around for our space trivia contest. We got some cool findings from the James Webb Space Telescope

last week, but that thing just keeps cranking out the hits. JWST has imaged the faintest galaxy ever detected. The ultra-faint galaxy, which is called JD-1, is thought to be one of the universe's earliest galaxies. It was formed during a time called the Epoch of Reionization. That's when light first began to permeate through the fog of hydrogen in the early universe. Back on Earth, the United States Federal Aviation Administration and the Commerce Department are working to manage space traffic and debris. A new bill from the U.S. House of Representatives tasked the FAA with tracking objects in orbit that might reenter the atmosphere and could pose a threat to aircraft. The Commerce Department is also responsible for managing orbital traffic, so they could potentially duplicate the FAA's efforts. And if you enjoy pictures from Mars rovers, we've got a new and beautiful one that you'll

want to check out. Day in and day out, the Curiosity rover lives on Mars, and while it was stationary for a day, the NASA rover captured two views of Marker Band Valley in the foothills of Mount Sharp. One of the pictures was taken in the morning, and the other one was taken in the afternoon. The photos were originally captured in black and white, but by merging and enhancing the colors, this picture gives the morning view on the left side in a yellowish tint and the afternoon view on the right in a bluish hue. It's really beautiful. We share the photo and more stories from space in the June 16th edition of our weekly newsletter, The Downlink. Read it or subscribe to have it

sent to your inbox for free every Friday at planetary.org slash downlink. You'll also find a link in it to the web version of our quarterly magazine called The Planetary Report. The latest issue focuses on the OSIRIS-REx mission, which is going to be returning samples from the asteroid Bennu to Earth in September. We explore why the mission matters and what we hope to learn from the samples it returns. Planetary Society members are going to get a physical copy of the magazine sent to them in the mail, but everyone else can read it for free online. Today we'll be diving into the fascinating history of Saturn's rings. We have two special guests with decades of experience studying Saturn and so many other topics. Paul Estrada is a research scientist from NASA Ames Research Center, and Richard Durson is a professor emeritus of

astronomy at Indiana University Bloomington. You may hear his friend Paul call him Dick during the interview. They've recently published two studies on Saturn's rings in the scientific journal Icarus. We'll discuss a major finding in our understanding of Saturn's iconic rings. The development was only made possible thanks to the wealth of data returned by NASA's Cassini spacecraft. During the mission's grand finale in 2017, the spacecraft made 22 orbits through the gap between Saturn and its rings, which left us with a trove of invaluable information. After that, Cassini plunged into the planet and ended its mission. R.I.P. Cassini. Richard Paul and their colleagues have delved into this data, combining it with computer modeling. They've uncovered some surprisingly

cool things about the ongoing drama around Saturn's rings. Their findings not only show that the rings are much younger than the planet, but that micrometeoroids from the distant Kuiper Belt out where Pluto lives are smashing into Saturn's rings and causing these iconic structures to dissipate over time. Let's learn more. Hi, Richard and Paul. Thanks for joining me. Hi.

Oh, thanks for having us. I'm so glad to have you both here to talk about this, because let's face it, if you walk up to a random person on the street and you ask them what their favorite planet is, I mean, other than Earth, obviously, because that is obviously the best planet, but they're all going to say Saturn, and they're going to say it's Saturn because of the rings. And you've both spent decades studying a wide variety of subjects, but you both keep kind of coming back to Saturn's rings at some point. What led you both to conduct this research? Well, I can blame Jeff Cussey, who's also a research scientist at NASA Ames.

When I was there as a postdoctoral fellow many years ago before Indiana University, he came into my office and he said, you're a dynamicist. How is it that Saturn has an oblique rotation axis just like the Earth and the planet processes? So why do the rings stay in the equatorial plane? So that was the first scientific question I was posed about Saturn. And we worked on that for a few years, dragged in other people. And then in part because of Jeff, then that connection made the Voyager data in particular excited me. And I found out about the idea of erosion producing gas and dust particles flying around as a halo kind of around the rings I just

decided to work on the transport of those particles not the gas so much but the particles that are blasted off the rings by meteoroid impacts. And I worked on that with Jeff in the 80s and 90s, and then Paul joined the effort and didn't leave. Dick has been working on this problem for quite some time. And the reason why I got dragged in is because I came in as an undergrad working with Jeff Cussey here at NASA Ames. And the first project that he put me on was more looking at photometry of the rings, looking at trying to determine what the spectral color of the rings were. We knew they were mostly icy. That goes way back to 1990 even. But I got dragged into this problem and eventually it just sort of escalated

as I moved into grad school, studying the physics of this process and the throwing around of material and polluting the rings from these bombarding meteoroids and doing models, complementary models to what Dick had been doing for years of this process, but Dick was doing it more from a dynamical standpoint of, you know, how the rings were evolving structurally. But we, Jeff and I, did it from a compositional standpoint. So we were actually looking at how the composition of the rings changes over time and how material can get thrown around. Then Cassini came along and there was this always underpinning idea that the rings are young and that goes back to Voyager. We really never thought about specifically the long-term evolution of the rings and what it means for their age and how long they last. There was enough exciting work just in the compositional evolution and the structural

evolution, but I think Cassini changed that picture. And so we started to realize that, well, you know, the rings are young. We had said that before in the 90s, but now we had this sort of added extra detail that the rings are going away. So that sort of led us to this point where we are now. There were some crucial pieces of information that were missing, and one of them was the meteoroid influx to Saturn. Cassini helped clarify that. The mass of the rings was somewhat uncertain. It was information like that and confirmation that the rings were icy all the way through, not just on the surface, that really started fleshing out the story. I mean, I had worried about structural features in the rings.

Even Voyager had shown that there were these weird structures at the inner edges of the A-ring and the B-ring. And there's no other explanation for them but ballistic transport. And I'm convinced that that's what causes them. And that implied that the meteoroid bombardment was significant. And actually, it could produce those features on a short time. That alone made me think the rings were young. And then the pollution work

that Paul and Jeff did, that was pretty suggested that the rings are young. But Cassini really helped us nail it down. Yeah, it's a testament to what one dedicated mission can really do for our understanding of a planet. Because having Voyager fly by, that's awesome. But it's not until you can really get up close and personal, and particularly with those ring dives, get enough information to do this kind of science. Let's start at the beginning. How old do we think Saturn's rings are now? And how long are they still going to be with us? After teaching 100-level astronomy for decades, I like to keep round numbers rather than the kind of specific

numbers you'll find in papers, because there's still some uncertainty. But it looks like the rings are less than a few hundred million years old and will only live less than a few hundred million years more. A few hundred million years sounds like a long time. It's enough to take us back to the dinosaurs if you go back in time. But that's relatively recent when you think about the planet itself and the planet and solar system being basically four and a half billion years old. Most people decades ago thought the rings formed when the planet formed. thought the rings formed when the planet formed. I feel like what's interesting about this is there have been so many little clues here and there over the years that Saturn's rings are young. But the first time that I saw an article that actually said not only are they young, but they're disappearing, I had this influx of mixed emotions because that's really cool to know. But also, it's kind of sad to think that Saturn's rings won't always be around with us. And I'm curious, do you have any kind of words of wisdom or any kind of happiness that you

can share with people that might be feeling a little melancholy about the fact that Saturn's rings are going to go away? My feeling is, is that if we look at other planetary ring systems, like the Uranian or Neptunian ring systems, you know, they're still around, but they're kind of very sparse. They're not going to completely go away because I think eventually the process of the bombardment, you know, as you get punier and end up in these annuli of rings, it becomes less efficient. And then other processes can probably hold the rings in place. So I don't think they'll completely go away, but I think it's just because they're so majestic right now and so massive. And I think that's what captures everybody. But I think that that is just maybe not a normal circumstance. I think it's possible that all of those planets, you know, even Jupiter,

It's possible that all of those planets, you know, even Jupiter, Jupiter's ring is nothing but a bunch of small micron-sized dust now. They were maybe much more massive when the planets formed. And there's reason to think that that would be the case because these moons might have formed from those massive rings, you know, because they can't be too massive because then they will go away and they kind of spread viscously like molasses you know so you could actually make all these moons out of these rings the idea that they're constantly being impacted by this dirt coming from in this particular case mostly is coming from kuiper belt but you know leftovers of formation of the solar system it's just kind of natural that they're just going to get eroded i think we maybe we were all sort of had the blinders on. You know, on the surface, when you step back and think about it, it kind of makes sense. A slightly different way of looking at it.

One, we're impermanent, but we enjoy being here, right? Okay, so Saturn's rings may be impermanent, but everything's impermanent on some level. impermanent, but everything's impermanent on some level. And I think the wonderful thing is that it's a great lesson in how dynamic the whole universe is, that when you have a complicated system of interacting stuff, you get unique behaviors, unusual behaviors. And a system can sit there rather quietly for billions of years and then do something dramatic. We have the Cambrian explosion of life evolution on the earth happened in a very short period of time, half a billion years ago. But life was around for billions of years before that. These things happen in complex systems, and it's one of the beautiful things about the place we live. Maybe we are, in fact,

very lucky to live during a time when Saturn's rings are so big and beautiful, but you're right, things change over time, and that makes, to me, that makes it even more special that they're as awesome as they are now and one more thing think about eclipses yes solar eclipses that's another coincidence you know we happen to be around at a time when the moon just about covers the face of the sun so we get to see the chromosphere prominences and the corona every once in a while and uh Bloomington, Indiana, where I live, is going to be right in the middle of totality next April. That's so lucky. Might even come up there.

Really, though, I remember after seeing the last major solar eclipse in the United States, I believe that was 2017. I remember thinking that if I had the capacity to go from planet to planet across the universe, the thing I would chase would be solar eclipses because that's just such a wild, awesome situation to have the size of the sun and the moon just happen to be just right for that to happen. That's really special. And I don't think people fully understand or comprehend what that's all about i'm sure we'll get into talking a lot about that in the future when we let everyone know how awesome this next solar eclipse is going to be if the rings around saturn were much older than they are now how would that present itself how would we know that they were older what would they look

like and how would they be different from what we see? The thing that we showed is they can't be. Rings like that have an asymptotic lifetime. They can only be so old before meteoroid bombardment cuts them off and makes them disappear. That's the work on the paper that Paul is the first author on. That's where we do these solar system age kind of evolutions. They cannot be as old as the planet, not a bright, massive ring system like Saturn. It doesn't work. If they were old, they might look like the rings of Uranus and Neptune. In that paper, I mean, we kind of do these models where we just kind of look at this sort of traditional view, as I mentioned earlier, about how the rings evolve

viscously. You know, they spread. If they start massive, they spread and the mass goes into the planet and some of it goes outside of the Roche limit, which is just that radial distance where bodies can accrete into moons and won't be broken up by Saturn's tides. If you just sort of did things that way and then just let the micrometeoroids pollute the rings, they would look much darker. I mean, that's kind of the implication for the Uranian or Neptunian rings. You know, they would look darker. And I think in that paper, I do some models like that where it's considerably darker than they look now. So that isn't the case. And then on top of that, there's this dynamical evolutionary

aspect of this process of bombarding the rings and the impacts, throwing out all of this ejected material from, you could think of them as a little cratering impacts on the ring particles. And that's the ballistic transport part where they just, all of those little grains get, you know, transported to different locations in the ring. And, you know, ultimately it's all this kind of an angular momentum transferring angular momentum all over the place. The rings, it's almost like a classic accretion disk material, you know, angular momentum outward and the mass flows inward. So eventually you would just lose the material. accretion disk material you know angular momentum outward and the mass flows inwards so eventually you would just lose the material i guess you could say well maybe there this bombarding material doesn't always happen it's not a constant flux of material and if say if you turned it off then

in such a situation sure the ring could be as old as the solar system, even though there are other processes going on in the rings that could change their structure. But it's actually not a very good argument. As you go back in time, it's going to be worse, the amount of material flowing around. And if you sort of go with that idea, it's like, well, that time when the solar system formed and all the planets formed and the rings maybe were massive, there's all this leftover debris and material and things are colliding and the flux of material coming into the saturn system is going to be much higher and so if you take that into account then the rings would last even less time you know because there's such a stronger erosion rate going on that they would just go

away so i go back to what dick says it's just it's just we just find that it's not really possible. That would be the conclusion. It's just not that they can't be that old. They just can't. We'd have to have a very clean planetary system. We'd have to have not a lot of leftover junk to produce interplanetary meteoroids. But we do. And probably other solar systems will too but surely there's a

clean solar system out there somewhere i'm not sure i think it's probably pretty common just that that's just the leftover stuff you know other systems have kuiper belts and uh you know cloud comets and and even the irregular satellites in these planetary systems like Saturn and Jupiter, there's collisions and impacts. And there's just dust gets produced, you know, one way or another. You know, it's just it's there. Are we assuming that these micrometeoroids are coming from the Kuiper Belt just because that's where there's so much leftover material? Or is there something about their composition that suggests their origin? there's so much leftover material, or is there something about their composition that suggests their origin? Well, there's a measurement, and that's the key thing. There was a measurement

of the influx of interplanetary meteoroids into the Saturn's system. That was really key. That actually held up our papers for a few years. That's the third paper in this triumvirate that's being talked about, and that's the paper on the cosmic dust analyzer. And Paul is actually on that paper, I'm not, so maybe he wants to address that a little bit. So we know that number, and that really helped. And the cosmic dust analyzer is an instrument aboard Cassini, correct? Yes, that's correct. That's some work we did with Sasha Kemp at UC Boulder. He was the PI on the CD8 instrument. So the CD8 instrument basically is just a dust collector and it measures the impact on a sensor and tabulates all of these impactors. As it's flying around, it's got an

open dish and occasionally a particle come in and boom, it hits and it gives off a charge and you can measure. Depending on the orientation, you can determine its dynamical origin and also a sense of what the material is. So just to kind of put it into perspective, let me just back up. You know, so this instrument was on for over 12 years of the Cassini mission. That was its job was to measure these dust particles. And so it logged, I think, well over 2 million impacts over the 12-plus years of observations. But only 163 of those 2 million are considered micrometeorites of extrinsic origin coming from outside the system. So that just shows

you most of them are actually little particles from the E ring due to Enceladus and then you have to filter all those things out. In fact, if you flew through the E ring, it didn't even, we didn't even bother to check whether any of those particles were, there's just too much going on there that we just wouldn't even look for it. there's only 163 and we had you know the trajectories and we did models and you sort of back up their trajectories and you come up with a dynamical character that is consistent with the kyber belt so these are basically things that are making their way for millions of years from the kyber belt due to collisions and eventually come into the saturn system at relatively low speeds as they enter the gravitational influence of the Saturnian system.

And then they get sped up, you know, they get focused onto the rings because they come in so slow and then my focus system on the rings. And then this just enhances this effect of because the surface area of the rings are so huge. I mean, the number is actually very small when you look at it, what that micrometeoroid flux is. You know, you look at the number and it's like 10 to the minus 16 kilograms per square meter per second.

You know, it's a small number, but it adds up. And the surface area of the rings is so huge. If you were to put it all into a moon smaller than Mimas, the surface area of the rings is like 10 to 100,000 times the surface area of that moon. So that's how you sort of can appreciate that even though that number is so small, it really is consequential for this process. I'm not sure a lot of people really understand the fact that these rings are so bright and shiny does not indicate that there's like a bunch of material in the rings. In fact, they're actually kind of thin and we didn't really know how thin they were until Cassini got there and particularly

during those ring dives to see just how thin they are. Can you give people an understanding of the structure of Saturn's rings and how surprisingly thin they are? I've got an analogy I used in my 100-level classes, and that's if you made a scale model of Saturn's ring and plopped them down, say, made them the size of my local county or central Indiana, they would be as thin as a sheet of paper. That's how thin they are. In fact, one of the puzzles for a long time was given that they are so thin, and it took time for us to realize that. I was involved a little bit with Jeff Cousy again on how thick or thin the rings are. One of the neat things that Cassini clarified is why the rings don't disappear completely when they're edge-on. Twice a Saturn orbit, we see the rings in an edge-on orientation, and they have a residual brightness. It turns out that there are bending waves,

brightness. It turns out that there are bending waves, that some of the external moons produce bending waves in the rings that flip them up, like folding the piece of paper up. And they fold it up kilometers in size in a very narrow region. And so when you look at the rings edge on, you're seeing the light reflected from this bent, this twisted surface of the rings. And there are wonderful Cassini images of that, of some of those edges. One of the wonderful things about Saturn's rings is that it's a system that lives on the edge of so many different processes. It's marginally, gravitationally unstable. It's got rings, it's got waves being produced in it by external moons. It's borderline collisional. I mean, some parts of the rings, you get multiple collisions per orbit. Sometimes you get about

one per orbit or less between the particles themselves. It lives in a place where most physical systems we study are extremely to one side or the other. But in Saturn's rings, it's always on the edge. It's always in a marginal condition, which makes them very hard to model, actually. It's a theoretical problem. That brings up a question for me because the way that you did this research was by taking data from Cassini and then putting it through computer models that allowed you to understand more about their age and how they're going away over time. But did this computer model just spit out a really clear answer or was there kind of a range of answers that could explain this? And how does

that help us narrow down how old the rings actually are? Like, we can't actually say they were created on this date by this thing, but how close can we get to knowing that answer? Well, I mean, of course, you know, any model is only good as what you put into it. I should point out that that's a process that Dick and I have modeled for many years is actually pretty complicated. The models that actually take into account the throwing around of material and redistribution and material, it's actually quite complicated. It was not possible to do that for these models because the overhead is too high. And so Dick has a paper that I'm the co-author on where we sort of distill things down into the inflow rates and basically the transport part of these equations,

not the structural evolution parts. So there's a magnitude of these things that depends on the micrometeoroid flux and it depends on the mass of the rings and the velocity at which things might get ejected and whatnot. From that standpoint, I'd say that the models are a little bit simpler, but the model is complicated just doing the viscous evolution of the rings and you're just adding these features to the rings. And so there, of course, can be some variation in parameters, but it's not in such that unless the flux is completely wrong, you know, which we measured, there's not really a whole lot of wiggle room. It's giving you not an exact answer, of course, because there can be some variation. But I think

it's roughly consistent with this idea that they can only be a few hundred million years old. But the main point is, it's not four and a half billion years old. And it's kind of a diminishing return. I don't know if that's the right expression here. Because if they are as old as the solar system, that's one thing. If it's 100 million years old or 500 million years old, you are in trouble because there's no model really out there that applies to rings that young. It's just that they're all kind of fit into this category that requires lots of stuff, big stuff floating around the solar system, which no longer is the case anymore. Right. So it's all that stuff's been cleared out.

Where you're getting to now is the idea that, well, how did the rings form? Now that we know they're young, how did they form? And people have tried to work the numbers on how likely it is that, say, some big object, big enough to create the rings, came into the Saturn system from outside and was broken apart by tidal forces of Saturn and settled into an equatorial orbit around Saturn. And the numbers don't work. There are people, at least as far as we know, there aren't enough big objects. The probability of seeing a rain system like that is pretty low based on an object coming in from the outside. That leads us to what I was saying before about complex systems. The Saturnian moon satellite system is actually pretty complicated.

Moon satellite system is actually pretty complicated. And if you look at it closely, there are things that are a little hard to understand. I mean, some of these moons have been melted. Some of them have hot oceans underneath the surface. So what's that all about? I mean, they're in orbit resonances now, some of them, but it's hard to make that effect strong enough to produce the kind of surfaces on these moons that we see or explain Enceladus' hot ocean. But if something dramatic happened, some sort of billiard game happened due to a simmering instability, say, of the orbits of this complicated satellite system, all hell might have broken

loose a few hundred million years ago. And that's why it looks the way it does now. And as part of that game, somebody got shoved into too close to Saturn and broke apart. That is pure speculation on my part. But there are some people who are thinking about how that might have happened. They're kind of subtle dynamics. And I like it because it's an example of what I was saying before, that this complicated system can sit around for billions of years and rather abruptly do something really kind of extravagant

and amazing. That's happening all the time in the universe on different scales. We'll be right back with the rest of my interview with Richard Durson and Paul Estrada after this short break. Greetings, planetary defenders. Bill Nye here. At the Planetary Society, we work to prevent the Earth from getting hit with an asteroid or comet. Such an impact would have devastating effects, but we can keep it from happening. The Planetary Society supports near-earth object research through our Shoemaker-Neo grants. These grants provide funding for astronomers around the world to upgrade their observational facilities. Right now, there are astronomers out there finding, tracking, and characterizing potentially

dangerous asteroids. Our grant winners really make a difference by providing lots of observations of the asteroid so we can figure out if it's going to hit Earth. Asteroids big enough to destroy entire cities still go completely undetected, which is why the work that these astronomers are doing is so critical. Your support could directly prevent us from getting hit with an asteroid. Right now, your gift in support of our grant program will be matched dollar for dollar up to $25,000. With your support, working together, we can save the world. Thank you.

We know that at least the E-ring is just mostly water that's just being cranked out by Enceladus. But the rest of Saturn's rings, do we think that it comes from this one single common origin, one object that might have broken up? Or might it be more than one? And how could we be able to tell the differences there between those scenarios? be able to tell the differences there between those scenarios? You know, going back to this idea that these kind of systems, remember, are teetering on the edge of stability in many ways. You know, you've got all these moons that are deep in the gravitational well, and, you know, if it were early on in the solar system, they would be really in peril of being hit by stuff coming in. You know, they could have been, you know been blown apart and remade early on, but not

anymore. As Dick's saying, there's not really much stuff flying around. You know, the implication from the rings being young is there has to be some other mechanism to make them that is not like the traditional origin scenario. And that's why I'm pointing to what something happened in the system. And there's lots of evidence, I think, that says, like Enceladus, for example, how does it have such a high heat flow? Why does it have an ocean? It's spewing out all this stuff. It doesn't look old. And there are other things in the system that look strange. For example, old. And there are other things in the system that look strange. For example, the moons, you know, if you, I don't know how much you know about cratering, but typically if you look at the Uranian moons, for example, or even the Jovian ones, you know, the cratering

is associated with bodies that come from orbiting the sun. They have these populations and they fit it to them and they say, well, you know, all of these things look predominantly what we call from heliocentric bodies. But in the Saturnian system, strangely enough, you have a different population of impactors on many of these moons. And some of the surfaces are a little bit saturated, but they are consistent with planetocentric origin. So it's almost like, so this is like another piece of saying, well, there must have been all of this stuff floating around in the system that impacted all these moons more equatorially. You know, this is actually a very hot subject with the cratering people.

And then there are things that would tighten, tighten. It's like, what, why does Titan have an atmosphere? It's kind of weird because there are physical reasons to think that it shouldn't. It doesn't even have a global magnetic field. Like, what is even going on there? Exactly. So it's like, well, why is that the case? And so going back to the rings, it's like, well, can one body do it?

I don't know. Maybe not. it's like well it can can one body do it i don't know maybe not so we have a paper in review right now where we present our model and we as present as the smoking gun of something happening this is something it's based on some work of a colleague at seti matia chuk who you know was studies a dynamicist and studied the system and he basically uh he discovered some things that basically implied that the system doesn't appear to be as old as the age of the solar system and one of these is this idea that rhea you know which is the outermost moon of the sort of quintet of icy moons, you know, from Mimas out to Rhea. Rhea's the outermost one. These moons tidally evolve outwards, you know, just like our moon is tidally evolving outwards.

So Rhea had to cross, there's a, what's called an eviction resonance just inside Rhea's orbit. Now, eviction resonance is basically, it's where if you were to put a moon at that location and it's precessing, its precessional period around the planet is the same as the orbit period of Saturn around the sun. So the sun is perturbing that body. So what happens? Well, that moon had to tidally be evolving outwards

and it encounters this resonance and through all these you know sophisticated dynamical modeling showed that this thing gets excited and will eventually collide with a moon say protodion that's evolving outwards as well that's evolving outwards as well. And so they collide and they get disrupted. And this actually can lead to a cascade because then, you know, they get disrupted and then there's all this material that enlarged chunks and things from the one body that is kind of on an eccentric orbit and then could hit the moon interior to it.

But the smoking gun is that that well did this moon survive crossing this residence and because it's now located outside of the residence so it must have crossed it and you can estimate within the last 100 200 million years it had to have crossed it so the issue is is that if it survives crossing it its inclination gets perturbed as well as its eccentricity. And so it all of a sudden will become much more inclined than it currently is now. And it's really hard to damp inclination. So once it has that high inclination, it's not going to lose it in that time period. So right now, Rhea's inclination is very small.

So that suggests that it must have formed outside this resonance. So it got disrupted, and then the material got repelled. It's a complicated process. I won't go into the details, but the material gets repelled, and it can reform a new moon. But this whole process could lead to this chain reaction. But in this paper, we showed that even from that one impact, you can, depending on, you know, the impact parameter and how they hit each other and whatnot, I mean, there's some variation. You can deliver a significant amount of material with periopsies inside the Roche limit,

very close to the planet. But they're also, even though they're on very eccentric orbits, if once they sort of damp into circular orbits, much of that material actually have circular orbits inside the Roche limit. So they could form rings. It's not the entire mass of the rings. It's hard to get the entire mass from that one impact. But interestingly, it's all ice because it comes from the mantle of the moons. So it's the mantle material that gets thrown around the most, right? The rocky material kind of sticks around and stays in larger chunks and could impact other moons or reaccrete into new moons. So I would say, at least based on that,

probably it's going to take more than one event, but it all falls within this kind of billiard ball scenario that dick's talking about it does look like it could work of course it's going to require much more sophisticated modeling than we've always done as modeled it's more like a proof of concept it's like here we've done this very sophisticated collisional simulation to show that wow all of this stuff gets thrown out, not just inwards, but also outwards. So that also might have implications for Titan, because a lot of this stuff is probably going to impact Titan as well. And so what does that mean for the surface of Titan? What does that mean for, you know, how much mass, how much does that stir

up the surface of Titan? That is the kind of thing that I can't help but wonder, given what we know and given how perturbed the Saturn system looks. Some of the moons, they're not cratered as heavily as they should be. It's just weird. I think if something like that happened, there were probably a lot of events that could have thrown material into near enough to Saturn to produce the rings. Even maybe one moon that's not there anymore got thrown in. Yeah. I mean, that's true because the implication, of course, is that the system we see now was not the system before. So there was a pre-existing system. I mean, I think there's

good reason to think that it wasn't totally unlike. It probably has to be similar mass, more or less, maybe a little more. Just the idea of how we understand how moons form, whether it's from massive ring or if they formed in the disk of gas around the planet itself, they tend to form multiple moons. And there probably was some other system there, and now it's a new system. It may have happened more than once. Saturn may have originated with a tight enough satellite that 200 million years ago wasn't the first time that things went crazy. That's something for science fiction, I guess.

Well, there's so many satellites in that system. I mean, at this point, what, we think there's 124 moons of Saturn that we know of? There's got to be all kinds of interesting shenanigans going on there. This makes me wonder something about Enceladus, which has been kind of sitting in the back of my brain for a while. That thing's just been geysering water into space for what seems like a while, but at some point you would imagine if it'd been doing it for billions of years, it would run out of water to do so, which always made me wonder if it's only a recent development that it's been kind of geysering this much material into space. And this would explain that for me. Maybe there was some kind of event that finally allowed Enceladus to get to this point. And that's wild to think about all on its own. It's not inconsistent. I mean, like,

the state of Enceladus is strange. You know, there's clearly really high heat flow in the southern equator. I mean, it's like, yeah, something knocked the crap out of that thing or reformed. Other moons like Tethys, they're almost pure ice. It's almost like you've redistributed material. And it's like, why is Tethys pure ice for the most part? Because eventually, when things settle down, all this stuff is going to crater the surfaces of these moons as you clean it out. There are a lot of strange things in this. And Saturn itself, its interior is very strange so

teetering on stability i think is kind of a good way to think about it these kind of systems any little thing can push it one way or the other and something happens and all hell breaks loose there's so many questions i mean why does titan have this large eccentricity i mean it has a relatively large eccentricity it's like there's so many things so of course we would love to go back to saturn i mean thankfully maybe we'll get like the Enceladus life finder mission at some point fingers crossed but there are so many mysteries that remain here that really just beg for more observation we've kind of established that there's all these interesting things going on with all these moons and these

micrometeorites that are crashing through the rings but how much material is actually raining down from this ring on to saturn what is the sheer volume of this, that's actually a measurement that was made by Cassini as it was diving between Saturn's atmosphere and the rings, the grand finale. There's a paper that claims that there's a lot of stuff falling into Saturn, and it's been detected by different methods. But the deep dive grand finale orbits, people have estimated that about a few to dozens of metric tons of material fall onto Saturn every second from a region at latitudes that are sort of concentrated toward the equator, presumably coming from the rings. That's part of the story of these two papers that Paul and I wrote. I was sitting at the last Cassini conference, which was held in Colorado in 2018.

On the last day, I admit that like a lot of people, I don't always go to the last session, but I decided to stay along with the scattering of other people. And this talk mentioned this flow rate. I was like, wait a minute, I can explain that. And that's what led me to write the one paper showing that when the meteoroids hit the ring particles, they tend to hit the front of the ring particle. And so when there's a little cratering event that produces a whole bunch of ejecta coming out of that crater, they fly forward. So most of the ejected material from an impact by a meteoroid onto a ring particle, and by the way, they think snowballs or the big balls that a snowman is made out of, that's kind of what a ring particle looks like. kind of what a ring particle looks like. Throwing material forward like that, it causes everybody,

the whole ring system, to kind of drift inward over time. Angulon gets moved outward for the physics people in your audience, and mass gets moved inward. And if I know the rate of mass coming in from meteoroids, put all that in, you get a flow of material through the B-ring and the C-ring onto Saturn. That's, well, guess what? It's a few metric tons per second or maybe larger. Obviously, you can see that the measurement, it was not very precise. I mean, it's uncertain by a factor of 10 at least. So within plausible ranges of parameters, that's the amount of material you would expect the inflow of meteoroids and the meteoroid bombardment to cause to flow into Saturn. Unfortunately, we didn't predict that, but we could have. It was listed in the papers that we were writing in the 90s but we didn't ever say that in particular that well if you put a spacecraft between the rings and saturn you would see this

flow of material it's unfortunate you know you could claim that that was your idea yeah we missed a chance there it's funny because this like sparks this very futuristic sci-fi thought in my brain but maybe someday hundreds of years in the future when we have the ability to just go around the solar system we might have people going to saturn just to go see the ring rain here on earth we get these beautiful meteor showers anytime earth plows through the trail left behind by a comet something like that i wonder if there are just beautiful meteor showers underneath the rings of saturn at all times that's unclear i mean cassini did make it through so there can't be a lot of big particles yeah they're really kind of on the order of nanometers and uh they're they're pretty tiny but it's hard to say because it's you know we can say

that there's a mass inflow going in but something is transporting it into the but it's hard to say because it's, you know, we can say that there's a mass inflow going in, but something is transporting it into the planet. It's causing it to go in as ions and nanoparticles and it's a whole slew of things. And the ring rain in particular could be a combination of nanoparticles and vapor. nanoparticles and vapor and as dick said there are multiple measurements that were sort of not just in the equatorial plane that in the context of our papers would be the basically the everything you know that's like that's telling you how much inflow is being caused by this bombardment but there were other measurements at higher latitudes that shows that there are probably some charged particles that are coming from the rings, and those are also ring rain, and those are ending up in the atmosphere too. And clearly there's water in these things because there's emission from the atmosphere

that requires a certain amount of water per second, kilograms per second, to be deposited there to keep these patterns of emission that you see in saturn's atmosphere so it's all going in there i'm not sure it would be as it would be great if it was like some beautiful process here but i mean i i don't know i think they're probably a little bit too small and fortunately because uh know, that was one of the worries about sending the Cassini spacecraft through that region between the D-ring and the atmosphere, which is, you know, only a couple thousand kilometers. You know, it's like, is it really empty?

You know, what happens? That's why we save it for the last part of the mission. Yeah, you don't want to take Cassini out before it's time. No. Were you able to actually go to one of the parties for the end of the Cassini mission? Oh, yeah. I was there for the end at Caltech. It was, well, how can I forget it?

September 15th of 2017. So, yep, we were there, we watched it. They had a big screen set up with the JPL command center and just waiting for the signal to sort of go away as it entered the atmosphere. Tears were shed and, you know, hugs were given. It was, you know, an emotional moment. I still remember that day and that date and will live in in for me, I guess is what they say. But I mean, it was it was hard to see it finally go. It was. I'm glad that the people that got to work on that mission were at least able to be with other people who cared so deeply. I was one of those people that literally got out of bed early and just sat at my computer by myself, just kind of feeling all the feelings.

and just sat at my computer by myself, just kind of feeling all the feelings. It was, yeah. Missions of that length, you know, people are working together for so long. It just becomes sort of a part of the daily ritual and routine. And that's the amazing thing, though, about Cassini was that it's amazing that you keep getting surprised all the way to the end. It's amazing that you keep getting surprised all the way to the end. Blows your mind. And even to the last, you know, Cassini left us with this amazing realization that all this stuff is flowing into the planet.

Just astounding. And so, yes, I don't want to get too emotional. It's okay. I think a lot of people in the audience get emotional over Cassini, so you're in good company. If we were going to design another mission to go to Saturn, specifically to learn more about the age of the rings and their origin, what would you want on that mission? And what would you hope it would do while it was at Saturn in order to actually get these readings? One idea that's been kicked around is a ring skimmer, a mission where the probe would go into orbit above the rings. Now you might, if you think about it, say, wait a minute, it's got to orbit the center of Saturn. So yeah, it would have thrusters that would keep it up above the rings and it could look down and also even change its orbit radius.

That would tell us an awful lot about the rings. And there are a lot of features in the rings that we can get from a mission like Cassini, that it's hard to know why do we see those kind of striations in the rings, or why is that region bright and, you know, a neighboring band is not. There's just a lot of funny structure there that is not explained by these bending waves and spiral waves produced by the moons or they're the plateaus paul and i have banged our heads on the plateaus a few times these funny looking bands in the searing and right now we don't have an explanation for those i have an idea, but I'm retired. I like that, the idea of a mission like

that, but Paul may know more being at NASA and a little more attached to the observers. A lot of these missions would be challenging, but you know, you could just think right off how cool something hovering above the rings would be because as dick said at the resolution of cassini you know you're never close enough to the rings to see like little individual ring particles i mean even the ones that are as big as uh you know a truck or a house you know we're just never that close it still looks like a flat plane of material you know or it's hard hard to distinguish but those kind of missions where you could essentially even sit above a particular point in the ring, you know, and just watch the particles

flow by, you know, and interact with each other. To me, that would be very cool. There is also a skimmer, which actually flies above the rings repeatedly and, you know, can also get that kind of resolution of imagery, you know, to see, wow, look, we got all of this data from Cassini and occultations and why does, you know, look at these textures in the rings and why do they look that way? And, but of course, if you could get close enough, then it might all start to make sense. It's like, well, that's what's going on there. You want to be close enough to the rings to be in that layer of ejecta that is getting thrown around all over the place from these impacts. Because once you embed yourself in that layer, now you're collecting these particles that are coming essentially from the source you know impact it just got thrown off maybe you could determine exactly where what part of the ring it

came from or you could uh look at what they're made of this you're directly sampling the ring material uh those kind of things i think would help to really nail home this process. But, you know, right now it's a bike dream. I mean, we'd have to get another mission that be willing to do that. I think from a public standpoint, I mean, if you've got really cool, close pictures of the rings, I mean, that would be very cool stuff. However, I think even I would say that going to Enceladus or going to titan would be higher

priority i'd like a mission that put a drone boat or a drone submarine on one of the mare on titan one of the methane seas and just find out what's going on there there are a lot of a lot of interesting possibilities. There are, and I'm so looking forward to the Dragonfly mission to Titan. It's not going to do something cool like bob around in the seas, but having a quadcopter, just to tell us anything about it. The Huygens probe showed us that clearly we need to know more about this. I can't tell you how excited I am about Dragonfly.

I could go off. No, I totally agree. That just a warranting another flagship mission. But of course, you know, NASA is going to have its priorities and, you know, there's only a limited pot of money. So. We can't always get what we want, but, you know, if we all work together and advocate for these missions, maybe we can increase NASA's budget enough that we can do all this amazing science because I don't want to wait until it's decades and decades and then I'm gone and we won't know anything about these questions. I want to know right now, but that's just me being selfish and impatient. Well, thank you both for joining me and for sharing so much about Saturn. I've

actually learned a lot just listening to all the interesting details about moons and rings that I hadn't even considered. And I'm looking forward to that paper that's not out yet. I'm definitely going to read that. Hopefully soon, yes. I want to thank the audience for being interested in this. And I want to thank the Planetary Society and you, Sarah, personally, for following through and making this happen. Happy to do it. And always happy to share more Saturnian science. Same sentiment for me as well.

It's been a lot of fun. Thanks so much. Thankfully, now is a really great time of year to go out and spot Saturn in the night sky. And if you have a telescope, 10 out of 10 recommend checking out its rings. Let's check in with Bruce Betts, the chief scientist of the Planetary Society for What's Up. Hey, Bruce. Hey, Sarah. How are you doing? Space stuff, you know. Space stuff. There's still space stuff going on. Always. Did you know there's still things in the sky?

There are a lot of stars you can look at, and in the night sky, you can check out Venus. Super bright over in the evening in the west. Still looking very cool. Mars getting closer to it through July 1st, and then they'll be three and a half degrees apart, so a little ways, but still fairly close. Mars

much dimmer and reddish. If you're picking this up right when it comes out, you may be able to go out and look in the evening of the 21st and check out the crescent moon hanging out with Venus and Mars. Otherwise, the moon, it'll still be there, but it'll be somewhere different the next night, the way that pesky moon does things. And the pre-dawn sky, Saturn's just cooking its way up higher in the sky. So, it's coming up a couple hours before dawn and right before dawn is high in the east or southeast. Then you got Jupiter looking really bright down low, but getting higher and higher as we go along. So, all in all, a good collection of planets still.

Yeah, I was out the other night and I caught one of my neighbors just staring up at Venus in the sky, you know, kind of like, what is that? I never know whether or not to, like, stop and answer the question I see in their eyes. Like, that's Venus. Just yell Venus at them and keep going. That's a great way to make friends.

Just, Venus! Okay, I didn't know you wanted to make friends. Then, yeah, probably not the right way we move on speaking of not jokes but the one of the greatest missions in the history of the world launched this week four years ago light sail to the planetary society's demonstration of cubesat solar sailing for the first time in history launched on a SpaceX Falcon Heavy four years ago now. And we were up for about three and a half years, then dragged down by the atmosphere and burned up. And we're still analyzing and working on the data. And that

happened. Gosh, I can't believe it was four years ago. Yeah. Things have changed. But I'm sure that's even weirder for you because you were so deeply involved in that project it's like your your spaceship child you know yeah i mean i i adopted it a fair way and although i was there for the anyway that that analogy is getting too weird too fast um i was just talking about light sail remotely for a uh solar sailing conference so it's fresh in my head and we're working on science papers to report the technical aspects of the mission so it's still living pretty strongly in my life at the moment even if it's not flying around yeah and light sail will always be in our hearts i literally have a necklace with

little light sail on it than i wear when I think about Little Light Sail, you know. And this is a great minute to pitch, too, because if anybody doesn't know anything about the Light Sail mission, well, we could talk about how awesome it is, but we have a whole documentary. So if anybody wants to know more, you can go to the Planetary Society YouTube channel and look up Sailing the Light. Just make sure you have tissues or something, because I can't get through it without crying. I know that's me, but I think that might be everyone. You can also get our general webpage, sail.planetary.org, and there are links to pictures and history and more on that page. And if you're really into it, there are also links to the

currently existing technical papers and presentations. so all sorts of good stuff on the web there and there will continue to be more as we turn out more of what we learned all right let's move on to so i was thinking we just had the nba basketball championship and the stanley cup nhl hockey championship so what if you combine those two in some kind of fact well i did if saturn were the size of a basketball earth's diameter would be about the height of a hockey puck so picture basketball with a hockey puck sitting next to it and earth's about the height of the hockey puck. So picture a basketball with a hockey puck sitting next to it and Earth's about the height of the hockey puck. There you go. That's not counting the rings.

All right, let's slam dunk and check into the next segment of trivia. Yeah, that was smooth. I asked you to name only all the constellations named for insects, and that was to use the IAU officially approved 88 constellations. How'd we do? This is actually really funny because I've never seen so many people get a space trivia question wrong. You managed to completely throw people for a loop on this one. Should have done some biology classification beforehand.

Exactly, right? I mean, if you're one of the people that got this question wrong, don't feel bad. A lot of people, the majority, were there with you, which is fun. We're all going to learn something today. So, first off, the answer is not Scorpio the scorpion. Scorpions are arachnids, like spiders. So, they're not insects. Too many legs. And the answer is also not cancer the crab, because crabs are crustaceans. They are pinchy, but they are not insects. Insects not defined by pinchiness. But you know, like, I get it. That totally makes sense in my brain that scorpions and

crustaceans would pop up in people's minds here. Oh, yeah, definitely. Six legs. Got to be looking for six legs. No more, no less. And the answer is the constellation Musca, the fly. And I think, too, that it makes sense that our winner this week is from Australia. Oh, yeah. Because you have to be in the southern hemisphere in order to see this thing.

And I think of all the groups on Earth, the ones that are most likely to know their bugs are probably the Aussies. Well, congratulations. And who is that winner? Our winner this week is John Gweeton from Sanford Valley, Australia. Cool. And you'll be winning a goodnight oppie thermal mug. It's one of my last ones. But, you know, it'll be a good opportunity to think about the rover and drink some nice warm tea and consider how many bugs are nearby you, John, at any given moment.

This was cool. We always get some beautiful poetry in, and forgive me, because this one's a little long, but I loved it. This is from Gene Lewin, who wrote in, Amidst the lofty company of constellations far and wide, four stars make up a creature which navigators use to guide. Observed by two explorers, the East Indies was their aim. And being from the Netherlands, De Vlieg became the name. At one time, it was known as Apis, but with a chameleon right nearby, it was later changed to Musca, what in English is the fly. There's also a scorpion that may evoke a shrug, and it's not classified as an insect, and it's definitely not a bug. So, if insects are the goal here,

and depending on your source, there is only one insect, unless you count a flying horse. And we don't, by the way. And we don't. That was super clever. That was. That was great. And this other comment was actually about your trivia question from last week, which was about who was the first person to fall asleep in space. And Joseph Caliputre from New Jersey, USA wrote in to ask what you would count in space when you're trying to go to sleep. Like, would it be spaceship or speep? Speep. All right. what's our next trivia question? Short and sweet. What is the closest

nebula to Earth? Go to planetary.org slash radio contest. And you have until Wednesday, June 28th at 8am Pacific time to get us your answer. I don't think I know the answer to this one off the top of my head. That's really fun. Yeah, I thought so. I didn't know myself. I thought, what is the closest nebulator?

So we'll see. Hopefully there's not too much disagreement. I think it's a clear answer, but I usually do. Yeah, and I like this prize this week because I was really lucky. I got to do a collaboration with this nail polish company called Orly that teamed up with NASA to make a whole line of NASA nail polishes and the JWST nail stickers. I loved it. So we were filming recently and I got a lot of cool extra nail polishes and stuff. Whoever gets this question correct, you're going to be getting a copy of their JWST nail polish called The View from L2. And I'll send some cool Korean and Nebula stickers along with it. And for those that don't wear nail polish, this makes an excellent gift for people who love space and sparkly stuff.

So highly recommend. I am obsessed. Cool. So let me do your nails all sparkly. It looks like space. I'm wearing the nail polish right now, actually. Did you just offer to do my nails? Yeah. Fun bonding activities, Bruce.

I'll do your dog's nails. They'd love it. Yeah, well, the big guy's got nails about the size of a bear's claws. Perfect. They're black. So no base coat. It's perfect. All right, everybody go out there, look up the night sky and think about the fact that you should never paint the nails of a dog. Thank you. Good night.

We've reached the end of this week's episode of planetary radio, but we'll be back next week with some awesome results about the Sun from the Parker Solar Probe. Planetary Radio is produced by the Planetary Society in Pasadena, California, and is made possible by our Saturn-loving members. If you want to help make a future where we have even more missions to the ring planet, you can join us at planetary.org. Mark Hilverda and Ray pauletta are our associate producers andrew lucas is our audio editor josh joyle composed our theme which is arranged and performed by peter schlosser and until next week ad astra