Astronomy Cast

Ep. 539: Weird Issues: Why We Don’t Know the Age of Saturn’s Rings

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How old are Saturn’s rings? They could be brand new, or they could be as ancient as the Solar System itself. Planetary scientists thought they knew the answer thanks to new data from Cassini, but new ideas are calling even that into question. 

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Fraser:                         Welcome to Astronomy Cast for a weekly facts-based journey through the cosmos where we hope you understand not only what we know but how we know what we know. I’m Fraser Cain, publisher of Universe Today and with me as always, Dr. Pamela Gay, senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hi Pamela, how you doing?

Pamela:                        I’m doing well, although I kinda think that today’s tagline should be more like how we know what we don’t know about the universe, because today’s topic is all about how we totally, totally don’t know –

Fraser:                         Know anything for certain.

Pamela:                        Right.

Fraser:                         Well, so before we get into that, I want to just quickly give a shout out to a couple of interesting upcoming interviews that I’m going to be having over on my channel on Open Space.

                                    So on Monday, I’ve got Dr. David Kipping from the Cool Worlds lab at Columbia. We’re going to be talking about exomoons and his idea to turn the entire planet into a telescope.

                                    Next Friday, two hours before Astronomy Cast, I’m going to be interviewing Robert Zubrin live, writer of The Case for Mars, and then the Monday after that, I’m going to be interviewing Sean Carroll for talking about quantum mechanics. So, I’ve got three really fascinating interviews coming up over the course of a week. So, stay tuned.

Pamela:                        And I also have things to plug this week. So, I – no big deal. International Observe the Moon Night is coming up. It is that first awesome Saturday in October, and I’m going to be at the Flandrau Center in Tucson, Arizona putting on a live presentation.

                                    You can check all of this out over on the their website. Look for their International Observe the Moon Night event and go. Be there with me. I’ll live stream if I can, but really, I’m therefore the live human beings.

                                    And if all the content we’re reproducing isn’t enough for you, if Astronomy Cast, The Guide to Space, Open Science, Weekly Space Hangout, is not enough well, we have more. You can check out the Daily Space Podcast, which is our new podcast that brings you a quick rundown of all that is new in space and astronomy we are in. All your favorite podcast directors, check out the Daily Space.

                                    And if you’d rather read it than look at it, well, we have everything over on DailySpace.org, and we link out a lot to longer reads over on Universe Today.

Fraser:                         Wonderful. How old are Saturn’s rings? They could be brand-new or they could be as ancient as a solar system itself. Planetary scientists thought they knew the answer thanks to new data from Cassini, but new ideas are calling even that into question.

                                    Pamela, this is an episode – I mean I don’t know if it’s like cut and dry, but this is an episode where we are probably going to have to reevaluate an episode that we had a couple of – maybe about a year ago or so where we were quite excited about new data coming from Cassini that now we know that Saturn’s rings are young and might not last long, and now we’ve learned this week that in fact, they’re probably – they could be old. How do we know anything ever at all anymore?

Pamela:                        So, I think this episode might end up being the beginning of a new series on those things that we regularly get press releases about that we keep thinking we now finally understand, and we keep thinking wrong, because we don’t actually understand anything.

Fraser:                         John Snow.

Pamela:                        Yeah.  I think it’s safe to say with Saturn’s ring, we know they are there.

Fraser:                         Can confirm.

Pamela:                        We can confirm they exist. We can tell you that they are made up of chunks of ice and snow and debris that ranges in size from dust to ranch-style house in size, semi truck in size, but how they got there and how long they’ve been there is basically a matter of massive debate with multiple teams looking at the same data coming from the same spacecraft and putting out press-release-triggering paper after press-release-triggering paper causing all sorts of really well written we-understand-it-now papers to be written.

Fraser:                         All right. So, let’s hit the scene here. Let’s go back maybe four years or so, and if we – and in fact, people probably even can. They can go back to some old episode of Astronomy Cast, I’m sure someone’s going to dig it up, and probably the conversation went something like this. Hey Pamela, how old are Saturn’s rings? And the answer was we don’t know.

Pamela:                        And then –

Fraser:                         They might be old and they might be new. So, let’s pretend. Let’s go back to four years ago and if I had asked you that question, what would you have said?

Pamela:                        Well, so four years ago, I would’ve said they were young. Eight years ago I would’ve said they were old. A few months ago, I would’ve said they were young. Yesterday I would’ve said well, maybe they’re old. The answer is really – let’s just look at all the data side-by-side and agree to disagree.

Fraser:                         All right. So, why did we used to be – like I said, let’s unravel the history of our thinking about the age of Saturn’s rings. So, four years ago before Cassini took its deep dive, if you asked a planetary scientist studying Saturn, how old? What would be their explanation for why we don’t really know the age of Saturn’s rings?

Pamela:                        Well, I think a lot of planetary scientists would’ve wanted to claim one side or the other of the debate.

Fraser:                         Yeah. They would’ve come one way or the other.

Pamela:                        Yeah. And so you would’ve had one school of thought that was well, you can have old rings, because over time, they’re going to hit each other, their orbits are going to decay, and the rings are just going to basically fall apart and go away, and it’s not possible to have ancient rings that had enough mass to leave behind what we see today. So, people would’ve argued that their young.

                                    But then you would’ve also seen people who were like wait, wait, wait, hold on. But if you take a massive moon and you shatter it out and you look to see how long it takes to relax out into the organized structure we see today, the amount of time that it takes to get the rings in place makes them ancient.

                                    So, on one hand you have one group of people who are just like dynamically they must be young. And you have another group of people who are like dynamically they must be old.

                                    And then comes the shiny people. And these are the people who are looking at the rings and saying well, we need to study their color. And if the rings are pristine white, which we think they are, then they must be young, because –

Fraser:                         Right, because otherwise they’d be covered with dust.

Pamela:                        Exactly. And now we have a paper that is arguing that –

Fraser:                         Well hold on. Hold on. Hold on. You’re going right to the conclusion.

Pamela:                        Sorry.

Fraser:                         There’s one other piece of news that came out about this time last year –

Pamela:                        The moons.

Fraser:                         – with Cassini, the final deep dive that Cassini did into the inner rings, it was able to see the width of the rings and make an estimate on how quickly the rings are probably disappearing. And we got young. We get very young, that the rings are only a couple of 100 million years old at the most, and they are rapidly falling into Saturn and disappearing, and they’re only going to be here for another 50 million years or so.

Pamela:                        And another argument that also came out from looking at data from Cassini is that when you look at the orbits of the innermost big moons of Saturn’s rings, these orbits should be migrating over time as they’re getting gravitationally affected by the tides of Saturn and the effects of all of these rings, but if they were moving around, then we wouldn’t have the rings that we see, and so the rings must be young, because otherwise the moons wouldn’t be able to be there.

Fraser:                         Right.

Pamela:                        So many arguments. So many arguments.

Fraser:                         And then the one that you are going at with the moons replenishing.

Pamela:                        Right. And so then you also have the argument that because the moons are shiny white, because the moons like Enceladus are blowing material out there – there’s two arguments for replenishing. I’m doing the old argument first. In order to have the moons in the rings and everything shiny white created at the same time, which can actually be done in a model, you can explain everything in one model, you end up with rings and moons that are only 10 to 100 million years old.

                                    But then, but wait, there’s more, you can also argue that because you have moons like Enceladus that are just like I shall blast everything with snow, all of this material that’s getting ejected can make things look shiny and white, and they are dynamical conveyor belts where all of these different motions are moving material through the rings so that yes, there’s material falling on Saturn, but that material falling on Saturn is material that should have fallen on the ring material making it darker. And since that material is not falling on the ring material and it is not making it darker, then the rings must be old.

Fraser:                         Right. And I’m going to completely totally side tangent here two things very quickly. One is it turns out there was a gigantic asteroid that smashed up about 350 million years ago and was the cause – you know, out in the asteroid belt, and was the cause for one of the earth’s ice ages, but one third of the meteorites that still hit the earth now came from that impact.

                                    So, if you measure all the meteorites hitting the earth, a third of them. So, this stuff gets around. But the other piece of news – this came from actually the same conference, this European conference, was that Enceladus now looks like it is snow blowing onto the other moons of the Saturnian system. And I guess as you said –

Pamela:                        Mimas and Theus. These are the outermost moons, but yeah.

Fraser:                         Right. Right. That it has actually been Enceladus is helping make all of the other moons very reflective, very icy and reflective, because in fact it’s just snow blowing them with its cryovolcanos, which is – this is just like brand-new news that came out just two days ago, so I thought I’d just throw it into the Astronomy Cast.

                                    It’s kind of tangentially related to what were talking about. All right. So, now everyone is completely confused. Nobody knows. New world, and now last week, we’ve got the next piece of compelling evidence.

Pamela:                        And this is that evidence that it looks like you can dynamically say if you have a massive event that occurred roughly 4 billion years ago, which is the same period of time that something hit Jupiter so hard it ended up with a fluffy core, and yes the word fluffy was used in the paper. It is the same period of time that the moon was getting hit with all of the impactors that created the basins that allow us to now see what you view as either the old man in the moon, the rabbit in the moon, or whatever else, all those dark seas.

Fraser:                         Right. The late heavy bombardment.

Pamela:                        And so during this late heavy bombardment, we know that the collisions got real. And so, the idea that at the same period in our solar system’s history, something happened that put so much material in the outer area around Saturn, these rings and moonless could coalesce out of that whatever was, is consistent with the dynamics of our solar system.

                                    But when you go to instead say that the rings are only 10 million, 100 million years old – Wikipedia says 101 million years, very accurate.

Fraser:                         But I think they’re basing that on the press releases that came out last year saying that they were young. And now, it could build again.

Pamela:                        And the thing about having a young set of Saturn’s rings is, as was pointed out in an article on the SETI Institute website, this would’ve placed that incident in the age of the dinosaurs. So, dinosaurs that happened to be observing Saturn, because we all know the dinosaurs had amazing astronomical skills –

Fraser:                         Yeah. They loved Saturn.

Pamela:                        – they would’ve been able to see the formation of these rings. And we know, because we no longer have dinosaurs, that there was still large stuff hanging around waiting to collide with worlds in our solar system.

                                    But the probabilities of this kind of massive impact happening appeared to have been much higher at the 4 billion-ish-year-old age.

Fraser:                         Right. When there were lots more debris in the solar system.

Pamela:                        So, we have a whole lot of conflicting information. We have no clear answers. And this is why scientists love their jobs, because we don’t always know the answers, and sometimes were not the ones trying to find the answers, and we get to watch other people struggle.

                                    Because I’m really enjoying watching all of the Saturn people duke it out trying to figure out the age of Saturn’s rings. They’re not literally duking it out. That has happened in the past. We’re a little bit more civilized today, but there’re so many different lines of evidence, and the question is, how do you put it all together using all the data we have in one paper.

                                    And so, what we’re seeing right now is a lot of work that, because programs have to make assumptions, because computer software takes a long time to run, because we don’t always understand everything, people are not cherry picking, but they’re making choices on I’m going to incorporate this data and this data and see what the outcome is, or I’m going to use this data and this data, or I’m going to make these assumptions in my dynamical models, we don’t have yet one model that cleanly puts together in a three-dimensional framework the dust motions, the tidal forces – we don’t even know how long it takes Saturn to rotate – that puts together the orbits of the moons, the residences over time, the influx of material that continues to come in, the – we don’t know just how much mass Enceladus is pushing out through its geysers.

                                    We can make estimates, but how long has it been doing that? How is it not hollow with the amount of stuff it’s spewing out?

Fraser:                         Well, so I think –

Pamela:                        It’s hard.

Fraser:                         – and I think this kinda gets to the heart of it, right, which is that the whole point of this is that we’re watching the science get figured out in real time. And for many of the various scientific controversies, why do we – what is an infection? Why does food go bad? Why do we have such variations of life here on earth? How does the sun work?

                                    There are these questions that for the longest time people didn’t know the answers to these. And then they figured out through the scientific method, and here we are on the other side of that with our cell phones and televisions and lasers and enjoying this discovery that happened in this process, and for a lot of people, I think they find this frustrating. Like there’s dark matter, and we don’t know what it is, and we don’t know if Saturn’s rings are young or old.

                                    And so, I would love to hear from your perspective, especially someone who has sat on some of the planning committees, like I think about this process where you’ve got okay, we’ve got all these questions, new questions. We’ve argued, we’ve got the data from casino, we’ve got all these questions, the next step is to try to really zone in on what are the specific things that we need to answer next.

                                    So, how would that work? How would people figure out how to get to the bottom of this question?

Pamela:                        Well, so with Saturn’s rings, I really think that it’s going to take getting all the people together and as has been done with other questions, not as often as I should’ve been, but as has been done in the past, get everyone together in one place – quite often it’s in Colorado in a mountain resort – sit them down an say let’s talk through this. Let’s figure out how we put together a model that synthesizes all of these ideas.

                                    And the data that we are using is crazy in its diversity. The way that they were able to measure the mass of Saturn and its rings is by looking at the delays in radio signals they came from the interactions between the radio signals and the gravity of Saturn and its rings. That’s wild.

                                    And so we have all this diversity of data in everything from gravity data to light-based data to grabbing particles out of space and sampling what those particles are, and we need to have all these different experts, who may not usually talk to one another, sit down and talk to one another.

                                    And this is hard, and how do you write the grants that pays for all of the people to do this and get everyone to commit and recognize that no, no one is probably going to get an award for whatever result comes out of this, so you’re just going to have to suck it up and share the credit.

                                    So much ego goes into science that sometimes that gets in the way of. So much money isn’t going into science that lack of funds get in the way, and so we need to look past these problems and get everyone together.

Fraser:                         But I imagine this process where you’ve got all of these different conflicting papers that are proposing different ideas, and you’re looking for what are the sort of core pieces of data and what are the unknowns, the foundation that they’re basing this on.

                                    And to then turn around and say okay, if we are going to send a new mission back to Saturn, or we’re going to add new instruments to say James Webb, what kind of instrument would reduce the uncertainty, would answer the question, would get us – and that feeds into the next round of instruments and missions and experiments like as part of the Decadal survey and all this, right, like that’s got to be – hopefully if they’re working and they are really, you know, the scientists are in a room, and they’re going you think this, we think that, how could we agree on what it really is? What would it take?

Pamela:                        And this is one of the things that we’re starting to see happen where you get a pair of scientists who are on opposite sides of a what-is-the-answer debate to say okay, we’re going in together to propose for telescope time on this spacecraft, and this is going to decide the answer.

                                    And we need to make the sacrifices necessary in some cases saying well, we need to put all of our financial eggs in one basket and pay what it costs to launch JWST.

                                    We need to do all the things that are hard to try to figure out what the heck dark energy is, including admitting that right now, we don’t even know if it’s an energy, a force, in our universe, out of our universe, leaking into our universe, and the Decadal surveys are actually really good at doing this kind of thing, because they start from let’s allow everyone in the community to submit their ideas.

                                    And then they have panels of experts that go through and codify what is in all of the proposals that look for trends and suggestions, that look for those creative new ideas that deserve a chance.

                                    The hard part is often corralling the government to fund those things that we want to do.

Fraser:                         Or for the actual –

Pamela:                        This whole manned mission to the moon.

Fraser:                         – experiment or the instrument or the mission to be developed on time and on budget, cough-James Webb, so these all come together. But then you can look at many missions like TESS which came together quickly, launched on time, on budget, and are working hard.

Pamela:                        Yeah. And then there’s the missions that refuse to stop working. And so it more or less balances out, but it all comes down to all of us just listening a little bit better.

                                    Science is always done in collaboration. Papers are not always published in collaboration, but science itself is always done in collaboration.

Fraser:                         So, do you think that the media does – is it media’s fault on this one? Because I as a member of the media think about how we do this reporting, and we are following the lead from the press officers, and the press officers are trying to turn the latest research it to something that will be chum to us sharks, and I think that we – I mean we’re careful and Universe Today. We try to not get overblown about which way this goes, and we enjoy the – you thought it was this, but now it’s that, and try to sort of show the – not the controversy exactly, but just the journey.

Pamela:                        The nature of science.

Fraser:                         Yeah. Yeah. It is the nature of science and the answer to that are involved. I mean I think that if there’s one thing that I’ve learned over the years that I’ve been doing this is to be more nuanced about how I present these kinds of scientific investigations and what we know and what does it mean to be certain about something.

Pamela:                        I think a lot of the problem that we have in taking stories that should be, we think this, other people think this other thing, let’s compare the evidence and in that we don’t know the answer.

                                    I think the reason that those stories become new research now shows with certainty that this thing is true. But the way that we get between those two points comes down to a failure to allow uncertainty and no results.

                                    When we have an NSF grant, I have to every single time after I get that grant for five years when I’m seeking new funding say with the funding you gave me before, I proved these things definitively.

Fraser:                         Right. Or as opposed to I found nothing.

Pamela:                        Right. That’s not allowed.

Fraser:                         That’s not allowed, and yet to find nothing is what’s expected.

Pamela:                        Sometimes.

Fraser:                         I mean you should find nothing more often than you find something.

Pamela:                        And when we build our careers on how many papers can you publish showing amazing results where a minimum number decides whether or not you’re allowed to keep your job if you’re a tenure track professor, you have to have results. When getting your next grant requires your current grant to have results, well then you start saying the result is, and you try to add the given these constraints, we feel that, but then your press officer who really just wants to see how many news articles they can get, because that press officer’s job, they’re getting promotion, they’re getting kept based on how many news stories come out of those press releases.

                                    So now our press officers are basically being judged by how well they search engine optimize their press releases and how many news releases come out of it. And so now everyone – it’s turtles all the way down, and everyone is getting judged by saying definitively something that catches the eyes of the next person down that totem pole.

Fraser:                         So are Saturn’s rings young or old?

Pamela:                        We don’t know, and that’s amazing.

Fraser:                         And that’s fun. Thanks, Pamela. Do you have any people to think this week?

Pamela:                        I do. As a reminder, we are brought to you by you. This show allows us to pay Susie who does our audio editing, who maintains our website, who herds cats, because Fraser and I are totally cats. So, thank you.

                                    And if you want to see more things happening around here and you aren’t already contributing, go contribute. Just a buck will let us bring you new cool stuff and will help us pay Susie. Let us pay Susie better.

                                    Anyways, the people we want to thank this week are Jason Szymanski, Andrew Stephenson, Benjamin Davies, Dustin A. Roof, Jay Wilkinson, Chad Callippe, William Layer, Omar Del Riviera, Jay Alex Anderson, Jeremy Kerwin, Mark Stephen Raznaki, Brandon Wolverton, Brent Kernop, Jack, William Andrews, Joshua Pearson, Nuder dude, Brian Kilby, Arthur Latshall, Claudia Mastroianni, Frederick Schlag, and Jessica Felts.

Fraser:                         Thank you, everybody. Thank you, Pamela. We’ll see you next week.

Pamela:                        Sounds good. Bye-bye.

Susie:                           Thank you for listening to Astronomy Cast, a nonprofit resource provided by the Planetary Science Institute, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at Astronomy Cast. You can email us at info@AstronomyCast.com, Tweet us at Astronomy Cast, like us on Facebook, and watch us on YouTube.

                                    We record our show live on YouTube every Friday at 3:00 p.m. Eastern, 12:00 p.m. Pacific, or 1900 UTC. Our intro music was provided by David Joseph Wesley, the outro music is by Travis Suro, and the show was edited by Susan Murph.

[End of Audio]

Duration: 30 minutes

 

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