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We’ve spent a lot of time gushing about Saturn’s rings, but there are other places with ring systems. And not just Jupiter and the ice giants, but asteroids, dwarf planets, centaurs and even exoplanets. Today we’ll gush about them.
Download MP3 | Show Notes | Transcript
Show Notes
Rings (NASA)
Uranian Rings (Smithsonian)
Ring detected around a dwarf planet (Nature)
Neptune’s Rings (NASA)
What is an occultation in astronomy? (BBC Sky at Night)
Introduction to Photometry (Las Cumbres Observatory)
Cheops (ESA)
Quaoar (NASA)
ESA’s Cheops finds an unexpected ring around dwarf planet Quaoar (ESA)
A dense ring of the trans-Neptunian object Quaoar outside its Roche limit (Nature)
10199 Chariklo (NASA)
Possible ring material around centaur (2060) Chiron (Astronomy & Astrophysics)
Centaurs (Swinburne University)
Main Asteroid Belt (Swinburne University)
What are Trojan asteroids? (Asteroid Day)
PODCAST: Ep. 675: Exotic Forms of Ice (Astronomy Cast)
The Nancy Grace Roman Space Telescope (NASA JPL)
Super-Saturn: astronomers find a massive ring system around an exoplanet (NASA)
Could we have already imaged a ringed exoplanet? (Ars Technica)
Phobos Might Only Have 10 Million Years to Live (Universe Today)
Here’s What Earth Might Look Like With a Ring System (Futurism)
Witch Head Nebula (NASA)
Transcript
Transcriptions provided by GMR Transcription Services
This episode is brought to you by Hello Fresh. Go to HelloFresh.com/Astro50 and use code Astro 50 for 50% off, plus your first box ships free.
Fraser Cain: Astronomy Cast Episode 676, Other Things with Rings. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know but how we know what we know. I am Fraser Cain, the publisher of Universe Today. With me is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Cosmo Quest. Hey, Pamela, how you doing?
Dr. Pamela Gay: I am doing well, and I want to share news for folks who may not have stayed around for the very end of the episode. I am super pleased to say that we’ve had Better Help as a sponsor for months now and we just added Hello Fresh as an advertiser, and this means that we can afford to produce content for all of you out there who can’t afford to become members of Patreon or just don’t pay for content, there’s folks like that out there.
Fraser Cain: Yeah.
Dr. Pamela Gay: But if you’re out there going, hey, I’m a Patreon, well, we have an ad-free feed through Patreon just for you. So, if you are someone who is also thinking I would pay to get rid of these ads because I would pay to get rid of ads.
Fraser Cain: I pay to get rid of ads all the time. Yeah, I can’t stand ads.
Dr. Pamela Gay: Yeah. Just join our Patreon, $1.00 and up, ads go away. And as you add larger amounts, like at $10.00, those are the names I read out at the end of the show. We love all of you equally but we have to give you things to differentiate because that’s how Patreon works, and we get it, we love all of you and if you want to get rid of the ads and never hear why I’ve used Better Help ever again, this is your opportunity.
Fraser Cain: Right. Sounds good. Now, we’ve spent a lot of time gushing about Saturn’s rings but there are other places with ring systems and not just Jupiter and the ice giants but asteroids, dwarf planets, centaurs and even exoplanets. Today, let’s gush about them. All right. My recommendations for telescopes really boiled down to get Saturn and its rings into your eyeballs, into your brain.
Dr. Pamela Gay: Yeah.
Fraser Cain: The whole reason to buy a telescope is to see Saturn with your own eyes and to see that magnificent ring system. Everything else is secondary, like science, seeing Jupiter.
Dr. Pamela Gay: You do need to be able to lift it. I add the caveat, buy a telescope that will let you see Saturn and that you can carry.
Fraser Cain: Yes, sure, yeah, yeah. No, but all I’m saying is that the primary purpose of telescope technology, really since telescopes were first invented, was for people to be able to see Saturn’s rings and then everything else is secondary. Like if you’re going to discover the age of the universe that’s fine but have you seen Saturn’s rings first?
Dr. Pamela Gay: It’s true, it’s true.
Fraser Cain: Yeah, yeah. Yeah, I don’t think anyone can argue with this. And we’ve know that there are rings in Jupiter, there’s rings at Neptune, but there are other places with rings. So, where do we want to start?
Dr. Pamela Gay: How we detect them because –.
Fraser Cain: Sure, yeah, how do we find rings?
Dr. Pamela Gay: Yeah, that was the thing that perplexed me.
Fraser Cain: We looked through our telescope, right? We looked through our telescope at Saturn’s rings and then just – that’s how we see rings.
Dr. Pamela Gay: Yeah. So, it turns out that like Saturn’s rings were the first to ever be discovered, those were found by Galileo, and then it wasn’t until the 1900s that we found rings somewhere else and it was Uranus where they were found next because Uranus is the second largest set of rings in our solar system. And with these two sets of rings, it’s very much a point and expose, expose, expose, expose, expose, expose, expose, expose if you want to see the rings at Uranus.
But that doesn’t work if you’re trying to find the rings around itty-bitty little tiny objects, especially the objects that are out beyond Jupiter and Saturn in our solar system. And it turns out, we found rings around objects in our solar system, as far away as like Haumea, which is one of the dwarf planets that’s out in the Kuiper Belt, and to do that, it hasn’t been on purpose and I love this.
Fraser Cain: Yes. Okay. So, we learned about Saturn’s rings from Galileo.
Dr. Pamela Gay: We looked, yeah.
Fraser Cain: We looked. We learned about Uranus from looking. We learned about Jupiter, Neptune from looking.
Dr. Pamela Gay: Looking with closer satellites.
Fraser Cain: So, the Voyagers helped us find them.
Dr. Pamela Gay: Yeah, yeah.
Fraser Cain: Right, okay. So, then, so what is the technique then? Let’s say that you want to find out if an object out there has rings, what, I guess, what is the accident, the happy accident that you’re trying to encourage?
Dr. Pamela Gay: It’s called observing occultations. This is where an object, be it an asteroid, a planet, whatever is seen to pass in front of a distant bright object. So, the moon occults other planets on a regular basis where you get these fabulous images of planet going behind the moon and we can actually start to see mountains based on when the planet disappears.
Fraser Cain: Yeah.
Dr. Pamela Gay: Well, if you have an asteroid that’s going in front of a distant star, different observers on the planet will actually be able to see a slightly different alignment between how that asteroid and how that star pass together and this tiny difference in geometry can allow us to measure the width of the asteroid at different points along the asteroid’s body. We’ve talked about this on other episodes.
Fraser Cain: Yeah. I mean this idea of occultation shows you how precise astronomy really is because you have to be – like the occultation is gonna happen at a specific time that the –.
Dr. Pamela Gay: Yes.
Fraser Cain: That the asteroid is gonna pass directly in front of the star, but it also has to happen in a specific place. There is this cone or some range on Earth where you are going to be lined up and if you’re in that range then you will actually see the occultation, and if you’re not then it will be partial or you’ll miss it completely. So, I mean there’s times when like the moon will occult Saturn or Mars but it’s only visible to people who are in certain parts of the world. So, this one is visible in South America, this one’s visible in Chile, right.
Dr. Pamela Gay: And the way to think about it is, when you’re on an airplane you can look down and be like, huh, that town you can actively see the clouds pass over it, and each different house in the town will sample the shadow of a different part of that cloud.
Fraser Cain: Oh, that’s such a great analogy.
Dr. Pamela Gay: And so this is the you are under the shadow of the asteroid as cast by that star.
Fraser Cain: Right. And so how did you see the shadow come onto your house? How quickly did it darken for you under that cloud as you were standing there looking at the sky? That’s a great analogy. And so, you get the shape of the asteroid purely through the occultation.
Dr. Pamela Gay: And it’s just like you can get the shape of the cloud by combining with your neighbors all of the times that you saw the shadow start and the shadow end. And you and your neighbors are probably not gonna do that because let’s face it, you have better things to do in your life. But with asteroids – well, there’s a dog to walk or something.
Fraser Cain: All right, okay.
Dr. Pamela Gay: But with asteroids, this is the only way we can measure their shape if they’re not close enough to bounce a radar off of. And while measuring the shapes of asteroids at a whole variety of different locations throughout our solar systems, there have been a handful of times where they’ve gotten on object early because they are diligent and well-behaved scientists.
Fraser Cain: Right.
Dr. Pamela Gay: And they’ve seen this little dip that didn’t go down far enough for it to actually be the asteroid unless they misplaced it, and I can just imagine that more than once this has led to an observer going, did I calculate something wrong.
Fraser Cain: Right.
Dr. Pamela Gay: And then the actual dip occurs, which is what you are waiting for, star totally goes away, okay, confirmation life is fine. But then wait a half-beat and then there is another dip, and what they’ve been able to figure out is these dips correspond to rings around the objects. And this has gotten us a whole new reason to be excited to go outside and do high-speed photometry of distant objects moving in front of more distant stars.
Fraser Cain: And I mean this is one of those fields that amateurs get involved in all the time.
Dr. Pamela Gay: Yes.
Fraser Cain: Like if you want to participate in science and you have – it doesn’t have to be a very big telescope, like an eight-inch telescope, as long as you’ve got the right detector system on your telescope you can, at the appointed time, watch the occultation, measure the brightness of the star and then pass along the data to the scientists and they will use that to help figure out the shape, figure out whether it has rings, figure out whether it has moons and learn a lot more about the solar system purely through how the brightness of an asteroid dims or how the brightness of a star dims momentarily. It’s astonishing. All right, we’re gonna talk about this some more but it’s time for a break.
Fraser Cain: And we’re back. All right. So, now we understand the technique, this is how astronomers find things with rings.
Dr. Pamela Gay: Yes.
Fraser Cain: So, let’s talk about some of the actual discoveries that have been made.
Dr. Pamela Gay: So, the first one that caught my attention, and this is like where the rabbit hole begins, was ESA’s Cheops mission found a ring around the dwarf planet Quaoar, which is one of the first objects to really start the discussion on displacing Pluto as a planet. This is a dwarf planet that is on a highly elliptical orbit. It was discovered in the early, early 2000s and while watching it they found a ring at a distance of about seven and a half of the radius of Quaoar, which means how did the find stuff that didn’t either coalesce into being a moon, dissipate away because it’s not held so tightly and smashing of the objects amongst themselves can make it go away or fall to the surface of the world?
And once I saw this story, I started digging further into this and it turns out that we have found Haumea has a ring and we’ve found centaurs. And there is a strangely large number of objects that begin with the letter C, I don’t know why, this is just weird reality.
Fraser Cain: If you want something to have rings give it the name C and then just wait and someone will find rings.
Dr. Pamela Gay: Exactly.
Fraser Cain: Yeah.
Dr. Pamela Gay: This is how it works. And each of these discoveries within our solar system has over and over been a case of watching these occultations. And there have been times that we were like, okay, so what if we aren’t seeing the rings because of some limitation, and for a long time the abundance of tiny moons around Pluto had folks really worried that there could be a ring around Pluto that was going to attempt to eat the New Horizon spacecraft.
Fraser Cain: Right, yeah.
Dr. Pamela Gay: And as New Horizons got closer and closer, the realization was made, no, no rings at Pluto, we got this right. And so it turns out we have an exceptional ability to spot rings and when we don’t spot rings, we are actually not spotting rings.
Fraser Cain: One of the things that I find really exciting about the Quaoar discovery, well, there’s kinda two parts to it. One is that it was done with Cheops, which is not a ring finding mission, its job is to confirm exoplanet discoveries. And so, it’s sort of going through the list of known exoplanets or candidate exoplanets and confirming whether or not they actually exist. But I guess they got this opportunity where an occultation was gonna be visible to the spacecraft and they go, well, why not, let’s take a look and see what we see.
Dr. Pamela Gay: Yeah.
Fraser Cain: And then the other part that’s kind of amazing is that the size of the ring system is so much bigger than what anyone thought, and maybe even what anyone thought should be possible around an object. That it’s like seven times the radius away from the object itself and that’s really impressive that it’s a dwarf planet but it’s holding on to this ring system quite far away from where it is. And that makes you wonder, like how did it happen because you would expect it to be a lot closer. If it tore up a moon it should be very close and yet it’s actually quite far away. Why?
Dr. Pamela Gay: And they had the same thing come up with observations of, and today is the day where I mispronounce objects, I am so sorry, everyone, Chiron and Chariklo, which are two more centaurs, they also found rings in these extraordinarily large orbits. And it looks like the objects that are in these rings may be having what’s called elastic collisions. So, when things come together you can have an inelastic collision, this is like when two cars crash together and merge into a single very destroyed new object,
You can also have inelastic collisions which is what we experience playing pools, where objects come together and they bounce off of each other and energy is just transformed between objects, but pool balls don’t shatter into a million pieces. Which is another thing that can happen when you have these collisions, is they can collide and energy gets turned into – turning them into multiple objects flying in all directions.
Fraser Cain: Right.
Dr. Pamela Gay: So, if you have just the right kind of inelastic collision they just bounce off of each other like the particles in our atmosphere, and just like our atmosphere doesn’t settle to the floor of our house for many reasons, but one of those reasons is the motion of the particles that has this constant inelastic collisions going on allows the air to support itself, pressure, it’s our friend and it could be these rings’ friends.
Fraser Cain: Right. And the Chiron and Chariklo are centaurs. So, for people who aren’t familiar with that term, what are the centaurs?
Dr. Pamela Gay: So, we have main belt asteroids that are located between Mars and Jupiter and then we have centaurs which have a variety of different orbits that are beyond Jupiter and just to make things confusing, there are the Trojans that share the orbit with Jupiter but in two blocks that we’re sending Lucy to.
So, these centaurs, which are further out, are in temporary orbits being so close to Jupiter and Saturn their location isn’t entirely stable. They have got there by something knocking them out of their happy existence in either the Kuiper Belt or the Oort Cloud. They have migrated inwards. They are eventually going to either migrate further in become comets, migrate further out, do whatever things do when they migrate further out.
But these are really cool objects that we like to look at because related to last week’s episode, we sometimes see them having outbursts of activity where they suddenly get much more reflective because they expel clouds of dust and ice just like a comet would but at a distance that isn’t melting like a comet from the sun. But is, instead, triggered either by landslides or this transition from amorphous ice to crystalline ice. So, looking at them, watching them in detail, super interesting to look for these outbursts, and in the process we have found rings, and I love when there is ancillary science nobody expected.
Fraser Cain: Yeah, yeah. But I mean at this point now, with four objects beyond the planets that contain rings, it just means that there’s gonna be lots and lots more of them, it’s just a matter of timing of those occultations. And when I think about upcoming missions or telescopes like Nancy Grace Roman, like Vera Rubin, you’ve got spacecrafts that are designed to watch for changes in brightness, we should get a lot more found. And I’m sure there is just gonna be some amazing ones, like a comet, like a long-period comet that’s coming in and bringing a ring system with it will be really neat.
All right. So, we’ve talked about stuff that’s in the solar system but when you think about science fiction, there are always these planets with ring systems, as if like there should be Saturns everywhere. So, do we have any evidence that there are ring systems out there across the Milky Way?
Dr. Pamela Gay: Yes, yes. There is, in fact, a super Saturn found orbiting the star J1407. It was found back in 2007. And this is a world that as it transits in front of its star you get this really cool, complex dip that is from having a good old, happy, not quite ice giant bigger than ice giant but not a hot Jupiter. I don’t know what we’re calling those anymore, and then this massive ring system that absolutely dwarfs what Saturn has.
The ring system itself was found in 2012, and it consists of about 30 rings that are millions of kilometers in diameter, and just imagine sitting there at the telescope watching the data come in and it’s just like, okay, we’re gonna have to wait a while before this thing comes back around to confirm that but, dang.
Fraser Cain: Yeah.
Dr. Pamela Gay: It’s really cool.
Fraser Cain: Like your watching the flickering light of the planet or the flickering light of the star as the planet with this gigantic ring system is passing in front. Yeah, I remember, it’s like 200 times bigger than Saturn’s rings.
Dr. Pamela Gay: Yeah.
Fraser Cain: Like maybe that is the real purpose of the telescope is to look at this planet with its rings, that is the real reason the telescope was invented. And I’m sure the people who live at that star system are correct, like they win in a ring down.
Dr. Pamela Gay: There is this fabulous quote from Matthew Kenworthy who is a researcher at Leiden, who was one of the ones that made this discovery and he writes the details that we see in the light curve, that’s how the light goes up and down, are incredible. The eclipse lasted for several weeks but you can see rapid changes on time scales of 10s of minutes as a result of fine structure in the rings.
Fraser Cain: Wow.
Dr. Pamela Gay: The star is much too far away to observe the rings directly but we could make a detailed model based on the rapid brightness variations in the star light passing through the ring system. If we could replace Saturn’s rings with the rings of J1407B they would easily be visible at night and many times larger than the full moon. I want that ring system.
Fraser Cain: Yes.
Dr. Pamela Gay: I want to live there.
Fraser Cain: Then the telescope would never even need to be invented because you could just look up with your eyeballs and see this enormous ring system, bigger than the moon.
Dr. Pamela Gay: I need a space artist who is not me because I am really bad at doing rings. I need a space artist to like do what the sky would look like with like that hanging out near a crescent moon.
Fraser Cain: Well, people have done that. Like have you seen simulations where people have put various moons in the sky?
Dr. Pamela Gay: Yeah.
Fraser Cain: And if the moon was Jupiter or if the moon was Saturn?
Dr. Pamela Gay: Oh, yeah.
Fraser Cain: And you just see how ridiculous it would be as the thing rises up at the distance of the moon. Yeah, no, that would be very impressive. Yes, please. So, what will it take for us to find more ring systems around exoplanets? Like this one is clearly bonkers extreme, so –.
Dr. Pamela Gay: Yeah.
Fraser Cain: So, what would we be expecting to see? What’s the best spacecraft that we have right now to find something like that?
Dr. Pamela Gay: So, we can get lucky if there is a ring system that is somehow able to stay stable on a planet on a small orbit around one of the hottish Jupiters out there. I don’t think dynamically a hot Jupiter can actually have rings.
Fraser Cain: Yeah.
Dr. Pamela Gay: And it would have to be on a much faster orbit than what we’re seeing with this J1407B, and that’s because missions like tests don’t just linger for weeks on one field. They’re like, okay, we’re gonna sit here for a bit then we’re gonna come back. We’re gonna sit here for a bit and then we’re gonna come back. And so, like how do you differentiate between it being a variable star that’s having a really weird dust explosion and a planet without having this extremely long duration light?
Fraser Cain: Right.
Dr. Pamela Gay: And this is where I’m really looking forward to the day that we have cheaper 24-inch telescopes for amateurs. Like I want tomorrow’s 24-inch telescopes to cost what the eight-inch telescopes cost when I was in high school.
Fraser Cain: Sure. Yes, please.
Dr. Pamela Gay: Yeah.
Fraser Cain: But I can see that the irony is that the planets that are easiest to find are the hot Jupiters, are the ones that are close to their star. And when you’re close to the star, I mean like here in the solar system, the frostline extends out halfway to the asteroid belt, so beyond Mars. So, you’re not just finding exo-Earths, you’re not just finding exo-Mars, you’re finding exo-Jupiters, exo-Saturns, and those, when you think about how long it takes for Jupiter to make one pass, it’s like five years, Saturn is like 11 years.
Dr. Pamela Gay: Right.
Fraser Cain: And so you’re having to wait a long time. So, we just don’t have the timescales to find regular sized gas giants with ring systems yet. We just haven’t been watching long enough and caught them.
Dr. Pamela Gay: Yeah. And the ring system that we see at Saturn is largely the kind of ring system you get from ice, and to get a ring system closer in you have to have something that is rock. So, you’re looking at a moon that was disrupted, Mars is gonna have that in its future, it’s going to temporarily have a ring. You are looking at materials splashed up during a collision. We temporarily had a ring after getting nailed by a Mars-sized object when the solar system was young.
Yeah, if you want to see something like this, you have to look at the distance objects, and this is where I want every amateur astronomer to have a 24-inch telescope that after they’re done taking their stunning astrophotography or –.
Fraser Cain: Of Saturn.
Dr. Pamela Gay: May there be exoplanets –. Well, I mean imagine this. You have someone out there who is doing 300 hours on the Witch Head Nebula and there happens to be a star in that system that is undergoing this kind of a slow transit where they’re able to catch in the starlight while getting their gorgeous astrophotography image.
Fraser Cain: Right. So, they can feed the photometric data of all of the stars to the astronomers and let them dig through it.
Dr. Pamela Gay: Yeah.
Fraser Cain: Yeah, that would be something. Yeah, so.
Dr. Pamela Gay: I want that future.
Fraser Cain: Okay, all right. That sounds fun. All right. Well, thanks, Pamela, that was great.
Dr. Pamela Gay: And thank you, everyone out in the audience. I am more than a little excited about anything that varies in brightness and you have now shared my enthusiasm. And in particular, I would like to thank our patrons who are at the $10.00 and up level, David Everson, Michael Prochoda, John Theys, Burry Gowen, Stephen Veit, Jordan Young, Jeanette Wink, nanoFlipps, Andrew Poelstra, Venkatesh Chary, Brian Cagle, David Truog, Gerhard Schwarzer, David, Buzz Parsec, Laura Kittleson, Robert Palsma, Les Howard, Jack Mudge, Joe Hollstein, Alexis, Gordon Dewis, Richard Drumm, Adam Annis-Brown, Frank Tippin, Greg David, William Andrews, and Gold. And if you too would like to get episodes without ads, join our Patreon at the $1.00 or up level. Thank you so much.
Fraser Cain: Thanks, everyone, and we will see you next week.
Dr. Pamela Gay: Bye-bye.