Extrasolar Planets | Astronomy Cast: Recent Episodes
Extrasolar Planets | Astronomy Cast
Several of the planets and moons in the Solar System are in orbital resonance, orbiting in a geometric lockstep. And not just the Solar System, astronomers have found the same resonances in other star systems.
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Wherever we find liquid water on Earth, we find life, so it makes sense to search for water across the Universe, and hopefully we can find evidence of life. But what about worlds which are completely covered in water, oceans hundreds of kilometers deep. Can there be too much water?
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Okay sci-fi writers, today we’re going to give you a guided tour of building planets. How they form, how they grow, and how things can go horribly horribly wrong.
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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.
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Show NotesRings (NASA)
Uranian Rings (Smithsonian)
Ring detected around a dwarf planet (Nature)
Neptune’s Rings (NASA)
What is an occultation in astronomy? (BBC Sky at Night)
Introduction to Photometry (Las Cumbres Observatory)
European Space Agency
Cheops (ESA)
Quaoar (NASA)
ESA’s Cheops finds an unexpected ring around dwarf planet Quaoar (ESA)
A dense ring of the trans-Neptunian object Quaoar outside its Roche limit (Nature)
10199 Chariklo (NASA)
Possible ring material around centaur (2060) Chiron (Astronomy & Astrophysics)
Centaurs (Swinburne University)
Main Asteroid Belt (Swinburne University)
What are Trojan asteroids? (Asteroid Day)
PODCAST: Ep. 675: Exotic Forms of Ice (Astronomy Cast)
The Nancy Grace Roman Space Telescope (NASA JPL)
Rubin Observatory
Super-Saturn: astronomers find a massive ring system around an exoplanet (NASA)
Could we have already imaged a ringed exoplanet? (Ars Technica)
Phobos Might Only Have 10 Million Years to Live (Universe Today)
Here’s What Earth Might Look Like With a Ring System (Futurism)
Witch Head Nebula (NASA)
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TranscriptTranscriptions provided by GMR Transcription Services
This episode is brought to you by Hello Fresh. Go to HelloFresh.com/Astro50 and use code Astro 50 for 50% off, plus your first box ships free.
Fraser Cain: Astronomy Cast Episode 676, Other Things with Rings. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know but how we know what we know. I am Fraser Cain, the publisher of Universe Today. With me is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Cosmo Quest. Hey, Pamela, how you doing?
Dr. Pamela Gay: I am doing well, and I want to share news for folks who may not have stayed around for the very end of the episode. I am super pleased to say that we’ve had Better Help as a sponsor for months now and we just added Hello Fresh as an advertiser, and this means that we can afford to produce content for all of you out there who can’t afford to become members of Patreon or just don’t pay for content, there’s folks like that out there.
Fraser Cain: Yeah.
Dr. Pamela Gay: But if you’re out there going, hey, I’m a Patreon, well, we have an ad-free feed through Patreon just for you. So, if you are someone who is also thinking I would pay to get rid of these ads because I would pay to get rid of ads.
Fraser Cain: I pay to get rid of ads all the time. Yeah, I can’t stand ads.
Dr. Pamela Gay: Yeah. Just join our Patreon, $1.00 and up, ads go away. And as you add larger amounts, like at $10.00, those are the names I read out at the end of the show. We love all of you equally but we have to give you things to differentiate because that’s how Patreon works, and we get it, we love all of you and if you want to get rid of the ads and never hear why I’ve used Better Help ever again, this is your opportunity.
Fraser Cain: Right. Sounds good. Now, we’ve spent a lot of time gushing about Saturn’s rings but there are other places with ring systems and not just Jupiter and the ice giants but asteroids, dwarf planets, centaurs and even exoplanets. Today, let’s gush about them. All right. My recommendations for telescopes really boiled down to get Saturn and its rings into your eyeballs, into your brain.
Dr. Pamela Gay: Yeah.
Fraser Cain: The whole reason to buy a telescope is to see Saturn with your own eyes and to see that magnificent ring system. Everything else is secondary, like science, seeing Jupiter.
Dr. Pamela Gay: You do need to be able to lift it. I add the caveat, buy a telescope that will let you see Saturn and that you can carry.
Fraser Cain: Yes, sure, yeah, yeah. No, but all I’m saying is that the primary purpose of telescope technology, really since telescopes were first invented, was for people to be able to see Saturn’s rings and then everything else is secondary. Like if you’re going to discover the age of the universe that’s fine but have you seen Saturn’s rings first?
Dr. Pamela Gay: It’s true, it’s true.
Fraser Cain: Yeah, yeah. Yeah, I don’t think anyone can argue with this. And we’ve know that there are rings in Jupiter, there’s rings at Neptune, but there are other places with rings. So, where do we want to start?
Dr. Pamela Gay: How we detect them because –.
Fraser Cain: Sure, yeah, how do we find rings?
Dr. Pamela Gay: Yeah, that was the thing that perplexed me.
Fraser Cain: We looked through our telescope, right? We looked through our telescope at Saturn’s rings and then just – that’s how we see rings.
Dr. Pamela Gay: Yeah. So, it turns out that like Saturn’s rings were the first to ever be discovered, those were found by Galileo, and then it wasn’t until the 1900s that we found rings somewhere else and it was Uranus where they were found next because Uranus is the second largest set of rings in our solar system. And with these two sets of rings, it’s very much a point and expose, expose, expose, expose, expose, expose, expose, expose if you want to see the rings at Uranus.
But that doesn’t work if you’re trying to find the rings around itty-bitty little tiny objects, especially the objects that are out beyond Jupiter and Saturn in our solar system. And it turns out, we found rings around objects in our solar system, as far away as like Haumea, which is one of the dwarf planets that’s out in the Kuiper Belt, and to do that, it hasn’t been on purpose and I love this.
Fraser Cain: Yes. Okay. So, we learned about Saturn’s rings from Galileo.
Dr. Pamela Gay: We looked, yeah.
Fraser Cain: We looked. We learned about Uranus from looking. We learned about Jupiter, Neptune from looking.
Dr. Pamela Gay: Looking with closer satellites.
Fraser Cain: So, the Voyagers helped us find them.
Dr. Pamela Gay: Yeah, yeah.
Fraser Cain: Right, okay. So, then, so what is the technique then? Let’s say that you want to find out if an object out there has rings, what, I guess, what is the accident, the happy accident that you’re trying to encourage?
Dr. Pamela Gay: It’s called observing occultations. This is where an object, be it an asteroid, a planet, whatever is seen to pass in front of a distant bright object. So, the moon occults other planets on a regular basis where you get these fabulous images of planet going behind the moon and we can actually start to see mountains based on when the planet disappears.
Fraser Cain: Yeah.
Dr. Pamela Gay: Well, if you have an asteroid that’s going in front of a distant star, different observers on the planet will actually be able to see a slightly different alignment between how that asteroid and how that star pass together and this tiny difference in geometry can allow us to measure the width of the asteroid at different points along the asteroid’s body. We’ve talked about this on other episodes.
Fraser Cain: Yeah. I mean this idea of occultation shows you how precise astronomy really is because you have to be – like the occultation is gonna happen at a specific time that the –.
Dr. Pamela Gay: Yes.
Fraser Cain: That the asteroid is gonna pass directly in front of the star, but it also has to happen in a specific place. There is this cone or some range on Earth where you are going to be lined up and if you’re in that range then you will actually see the occultation, and if you’re not then it will be partial or you’ll miss it completely. So, I mean there’s times when like the moon will occult Saturn or Mars but it’s only visible to people who are in certain parts of the world. So, this one is visible in South America, this one’s visible in Chile, right.
Dr. Pamela Gay: And the way to think about it is, when you’re on an airplane you can look down and be like, huh, that town you can actively see the clouds pass over it, and each different house in the town will sample the shadow of a different part of that cloud.
Fraser Cain: Oh, that’s such a great analogy.
Dr. Pamela Gay: And so this is the you are under the shadow of the asteroid as cast by that star.
Fraser Cain: Right. And so how did you see the shadow come onto your house? How quickly did it darken for you under that cloud as you were standing there looking at the sky? That’s a great analogy. And so, you get the shape of the asteroid purely through the occultation.
Dr. Pamela Gay: And it’s just like you can get the shape of the cloud by combining with your neighbors all of the times that you saw the shadow start and the shadow end. And you and your neighbors are probably not gonna do that because let’s face it, you have better things to do in your life. But with asteroids – well, there’s a dog to walk or something.
Fraser Cain: All right, okay.
Dr. Pamela Gay: But with asteroids, this is the only way we can measure their shape if they’re not close enough to bounce a radar off of. And while measuring the shapes of asteroids at a whole variety of different locations throughout our solar systems, there have been a handful of times where they’ve gotten on object early because they are diligent and well-behaved scientists.
Fraser Cain: Right.
Dr. Pamela Gay: And they’ve seen this little dip that didn’t go down far enough for it to actually be the asteroid unless they misplaced it, and I can just imagine that more than once this has led to an observer going, did I calculate something wrong.
Fraser Cain: Right.
Dr. Pamela Gay: And then the actual dip occurs, which is what you are waiting for, star totally goes away, okay, confirmation life is fine. But then wait a half-beat and then there is another dip, and what they’ve been able to figure out is these dips correspond to rings around the objects. And this has gotten us a whole new reason to be excited to go outside and do high-speed photometry of distant objects moving in front of more distant stars.
Fraser Cain: And I mean this is one of those fields that amateurs get involved in all the time.
Dr. Pamela Gay: Yes.
Fraser Cain: Like if you want to participate in science and you have – it doesn’t have to be a very big telescope, like an eight-inch telescope, as long as you’ve got the right detector system on your telescope you can, at the appointed time, watch the occultation, measure the brightness of the star and then pass along the data to the scientists and they will use that to help figure out the shape, figure out whether it has rings, figure out whether it has moons and learn a lot more about the solar system purely through how the brightness of an asteroid dims or how the brightness of a star dims momentarily. It’s astonishing. All right, we’re gonna talk about this some more but it’s time for a break.
Fraser Cain: And we’re back. All right. So, now we understand the technique, this is how astronomers find things with rings.
Dr. Pamela Gay: Yes.
Fraser Cain: So, let’s talk about some of the actual discoveries that have been made.
Dr. Pamela Gay: So, the first one that caught my attention, and this is like where the rabbit hole begins, was ESA’s Cheops mission found a ring around the dwarf planet Quaoar, which is one of the first objects to really start the discussion on displacing Pluto as a planet. This is a dwarf planet that is on a highly elliptical orbit. It was discovered in the early, early 2000s and while watching it they found a ring at a distance of about seven and a half of the radius of Quaoar, which means how did the find stuff that didn’t either coalesce into being a moon, dissipate away because it’s not held so tightly and smashing of the objects amongst themselves can make it go away or fall to the surface of the world?
And once I saw this story, I started digging further into this and it turns out that we have found Haumea has a ring and we’ve found centaurs. And there is a strangely large number of objects that begin with the letter C, I don’t know why, this is just weird reality.
Fraser Cain: If you want something to have rings give it the name C and then just wait and someone will find rings.
Dr. Pamela Gay: Exactly.
Fraser Cain: Yeah.
Dr. Pamela Gay: This is how it works. And each of these discoveries within our solar system has over and over been a case of watching these occultations. And there have been times that we were like, okay, so what if we aren’t seeing the rings because of some limitation, and for a long time the abundance of tiny moons around Pluto had folks really worried that there could be a ring around Pluto that was going to attempt to eat the New Horizon spacecraft.
Fraser Cain: Right, yeah.
Dr. Pamela Gay: And as New Horizons got closer and closer, the realization was made, no, no rings at Pluto, we got this right. And so it turns out we have an exceptional ability to spot rings and when we don’t spot rings, we are actually not spotting rings.
Fraser Cain: One of the things that I find really exciting about the Quaoar discovery, well, there’s kinda two parts to it. One is that it was done with Cheops, which is not a ring finding mission, its job is to confirm exoplanet discoveries. And so, it’s sort of going through the list of known exoplanets or candidate exoplanets and confirming whether or not they actually exist. But I guess they got this opportunity where an occultation was gonna be visible to the spacecraft and they go, well, why not, let’s take a look and see what we see.
Dr. Pamela Gay: Yeah.
Fraser Cain: And then the other part that’s kind of amazing is that the size of the ring system is so much bigger than what anyone thought, and maybe even what anyone thought should be possible around an object. That it’s like seven times the radius away from the object itself and that’s really impressive that it’s a dwarf planet but it’s holding on to this ring system quite far away from where it is. And that makes you wonder, like how did it happen because you would expect it to be a lot closer. If it tore up a moon it should be very close and yet it’s actually quite far away. Why?
Dr. Pamela Gay: And they had the same thing come up with observations of, and today is the day where I mispronounce objects, I am so sorry, everyone, Chiron and Chariklo, which are two more centaurs, they also found rings in these extraordinarily large orbits. And it looks like the objects that are in these rings may be having what’s called elastic collisions. So, when things come together you can have an inelastic collision, this is like when two cars crash together and merge into a single very destroyed new object,
You can also have inelastic collisions which is what we experience playing pools, where objects come together and they bounce off of each other and energy is just transformed between objects, but pool balls don’t shatter into a million pieces. Which is another thing that can happen when you have these collisions, is they can collide and energy gets turned into – turning them into multiple objects flying in all directions.
Fraser Cain: Right.
Dr. Pamela Gay: So, if you have just the right kind of inelastic collision they just bounce off of each other like the particles in our atmosphere, and just like our atmosphere doesn’t settle to the floor of our house for many reasons, but one of those reasons is the motion of the particles that has this constant inelastic collisions going on allows the air to support itself, pressure, it’s our friend and it could be these rings’ friends.
Fraser Cain: Right. And the Chiron and Chariklo are centaurs. So, for people who aren’t familiar with that term, what are the centaurs?
Dr. Pamela Gay: So, we have main belt asteroids that are located between Mars and Jupiter and then we have centaurs which have a variety of different orbits that are beyond Jupiter and just to make things confusing, there are the Trojans that share the orbit with Jupiter but in two blocks that we’re sending Lucy to.
So, these centaurs, which are further out, are in temporary orbits being so close to Jupiter and Saturn their location isn’t entirely stable. They have got there by something knocking them out of their happy existence in either the Kuiper Belt or the Oort Cloud. They have migrated inwards. They are eventually going to either migrate further in become comets, migrate further out, do whatever things do when they migrate further out.
But these are really cool objects that we like to look at because related to last week’s episode, we sometimes see them having outbursts of activity where they suddenly get much more reflective because they expel clouds of dust and ice just like a comet would but at a distance that isn’t melting like a comet from the sun. But is, instead, triggered either by landslides or this transition from amorphous ice to crystalline ice. So, looking at them, watching them in detail, super interesting to look for these outbursts, and in the process we have found rings, and I love when there is ancillary science nobody expected.
Fraser Cain: Yeah, yeah. But I mean at this point now, with four objects beyond the planets that contain rings, it just means that there’s gonna be lots and lots more of them, it’s just a matter of timing of those occultations. And when I think about upcoming missions or telescopes like Nancy Grace Roman, like Vera Rubin, you’ve got spacecrafts that are designed to watch for changes in brightness, we should get a lot more found. And I’m sure there is just gonna be some amazing ones, like a comet, like a long-period comet that’s coming in and bringing a ring system with it will be really neat.
All right. So, we’ve talked about stuff that’s in the solar system but when you think about science fiction, there are always these planets with ring systems, as if like there should be Saturns everywhere. So, do we have any evidence that there are ring systems out there across the Milky Way?
Dr. Pamela Gay: Yes, yes. There is, in fact, a super Saturn found orbiting the star J1407. It was found back in 2007. And this is a world that as it transits in front of its star you get this really cool, complex dip that is from having a good old, happy, not quite ice giant bigger than ice giant but not a hot Jupiter. I don’t know what we’re calling those anymore, and then this massive ring system that absolutely dwarfs what Saturn has.
The ring system itself was found in 2012, and it consists of about 30 rings that are millions of kilometers in diameter, and just imagine sitting there at the telescope watching the data come in and it’s just like, okay, we’re gonna have to wait a while before this thing comes back around to confirm that but, dang.
Fraser Cain: Yeah.
Dr. Pamela Gay: It’s really cool.
Fraser Cain: Like your watching the flickering light of the planet or the flickering light of the star as the planet with this gigantic ring system is passing in front. Yeah, I remember, it’s like 200 times bigger than Saturn’s rings.
Dr. Pamela Gay: Yeah.
Fraser Cain: Like maybe that is the real purpose of the telescope is to look at this planet with its rings, that is the real reason the telescope was invented. And I’m sure the people who live at that star system are correct, like they win in a ring down.
Dr. Pamela Gay: There is this fabulous quote from Matthew Kenworthy who is a researcher at Leiden, who was one of the ones that made this discovery and he writes the details that we see in the light curve, that’s how the light goes up and down, are incredible. The eclipse lasted for several weeks but you can see rapid changes on time scales of 10s of minutes as a result of fine structure in the rings.
Fraser Cain: Wow.
Dr. Pamela Gay: The star is much too far away to observe the rings directly but we could make a detailed model based on the rapid brightness variations in the star light passing through the ring system. If we could replace Saturn’s rings with the rings of J1407B they would easily be visible at night and many times larger than the full moon. I want that ring system.
Fraser Cain: Yes.
Dr. Pamela Gay: I want to live there.
Fraser Cain: Then the telescope would never even need to be invented because you could just look up with your eyeballs and see this enormous ring system, bigger than the moon.
Dr. Pamela Gay: I need a space artist who is not me because I am really bad at doing rings. I need a space artist to like do what the sky would look like with like that hanging out near a crescent moon.
Fraser Cain: Well, people have done that. Like have you seen simulations where people have put various moons in the sky?
Dr. Pamela Gay: Yeah.
Fraser Cain: And if the moon was Jupiter or if the moon was Saturn?
Dr. Pamela Gay: Oh, yeah.
Fraser Cain: And you just see how ridiculous it would be as the thing rises up at the distance of the moon. Yeah, no, that would be very impressive. Yes, please. So, what will it take for us to find more ring systems around exoplanets? Like this one is clearly bonkers extreme, so –.
Dr. Pamela Gay: Yeah.
Fraser Cain: So, what would we be expecting to see? What’s the best spacecraft that we have right now to find something like that?
Dr. Pamela Gay: So, we can get lucky if there is a ring system that is somehow able to stay stable on a planet on a small orbit around one of the hottish Jupiters out there. I don’t think dynamically a hot Jupiter can actually have rings.
Fraser Cain: Yeah.
Dr. Pamela Gay: And it would have to be on a much faster orbit than what we’re seeing with this J1407B, and that’s because missions like tests don’t just linger for weeks on one field. They’re like, okay, we’re gonna sit here for a bit then we’re gonna come back. We’re gonna sit here for a bit and then we’re gonna come back. And so, like how do you differentiate between it being a variable star that’s having a really weird dust explosion and a planet without having this extremely long duration light?
Fraser Cain: Right.
Dr. Pamela Gay: And this is where I’m really looking forward to the day that we have cheaper 24-inch telescopes for amateurs. Like I want tomorrow’s 24-inch telescopes to cost what the eight-inch telescopes cost when I was in high school.
Fraser Cain: Sure. Yes, please.
Dr. Pamela Gay: Yeah.
Fraser Cain: But I can see that the irony is that the planets that are easiest to find are the hot Jupiters, are the ones that are close to their star. And when you’re close to the star, I mean like here in the solar system, the frostline extends out halfway to the asteroid belt, so beyond Mars. So, you’re not just finding exo-Earths, you’re not just finding exo-Mars, you’re finding exo-Jupiters, exo-Saturns, and those, when you think about how long it takes for Jupiter to make one pass, it’s like five years, Saturn is like 11 years.
Dr. Pamela Gay: Right.
Fraser Cain: And so you’re having to wait a long time. So, we just don’t have the timescales to find regular sized gas giants with ring systems yet. We just haven’t been watching long enough and caught them.
Dr. Pamela Gay: Yeah. And the ring system that we see at Saturn is largely the kind of ring system you get from ice, and to get a ring system closer in you have to have something that is rock. So, you’re looking at a moon that was disrupted, Mars is gonna have that in its future, it’s going to temporarily have a ring. You are looking at materials splashed up during a collision. We temporarily had a ring after getting nailed by a Mars-sized object when the solar system was young.
Yeah, if you want to see something like this, you have to look at the distance objects, and this is where I want every amateur astronomer to have a 24-inch telescope that after they’re done taking their stunning astrophotography or –.
Fraser Cain: Of Saturn.
Dr. Pamela Gay: May there be exoplanets –. Well, I mean imagine this. You have someone out there who is doing 300 hours on the Witch Head Nebula and there happens to be a star in that system that is undergoing this kind of a slow transit where they’re able to catch in the starlight while getting their gorgeous astrophotography image.
Fraser Cain: Right. So, they can feed the photometric data of all of the stars to the astronomers and let them dig through it.
Dr. Pamela Gay: Yeah.
Fraser Cain: Yeah, that would be something. Yeah, so.
Dr. Pamela Gay: I want that future.
Fraser Cain: Okay, all right. That sounds fun. All right. Well, thanks, Pamela, that was great.
Dr. Pamela Gay: And thank you, everyone out in the audience. I am more than a little excited about anything that varies in brightness and you have now shared my enthusiasm. And in particular, I would like to thank our patrons who are at the $10.00 and up level, David Everson, Michael Prochoda, John Theys, Burry Gowen, Stephen Veit, Jordan Young, Jeanette Wink, nanoFlipps, Andrew Poelstra, Venkatesh Chary, Brian Cagle, David Truog, Gerhard Schwarzer, David, Buzz Parsec, Laura Kittleson, Robert Palsma, Les Howard, Jack Mudge, Joe Hollstein, Alexis, Gordon Dewis, Richard Drumm, Adam Annis-Brown, Frank Tippin, Greg David, William Andrews, and Gold. And if you too would like to get episodes without ads, join our Patreon at the $1.00 or up level. Thank you so much.
Fraser Cain: Thanks, everyone, and we will see you next week.
Dr. Pamela Gay: Bye-bye.
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Moons orbit planets, planets orbit stars, stars orbit within galaxies. It’s orbits all the way down. But occasionally objects can receive a powerful kick that sends them off on a journey, never to return.
PART II
PART III
Download MP3 | Show Notes | Transcript
Show NotesSuperman (DC Comics)
Iron Man (Tony Stark) (Marvel)
Conic Sections (Math is Fun)
Parabola (Math is Fun)
Hyperbola (Math is Fun)
Ellipse (Math is Fun)
Ballistic Trajectory (Universe Today)
FAQ – Earth (Planetary Science Institute)
Escape Velocity (Let’s Talk Science)
Spitzer (Caltech)
The Three-Body Problem (Scientific American)
PODCAST: Ep 102: Gravity (Astronomy Cast)
In Depth | Oort Cloud (NASA)
Overview | Comets (NASA)
Types of Comet (CometWatch)
In Depth | Oumuamua (NASA)
Ukrainian Astronomers Discover ‘Exocomets’ around Another Star (Scientific American)
The Solar System may have lost the original “Planet Nine” (Inverse)
Slingshot Star? (Science Magazine)
JOURNAL: A search for runaway stars in 12 Galactic supernova remnants (Astronomical Notes)
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TranscriptTranscriptions provided by GMR Transcription Services
Fraser: Astronomy Cast episode 660, Runaways. Welcome to Astronomy Cast, your weekly facts-based journey through the cosmos where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain. I’m the publisher of Universe Today. I’ve been a space and astronomy journalist for over 20 years. With me is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey, Pamela. How you doing?
Pamela: I am doing well. If I don’t sound the way I normally sound or look the way I normally look, I still haven’t recovered where all my stuff is after I was in Vegas for Annie Wilson’s wedding [inaudible] [00:01:29] one of our community members and one of my good friends. Unfortunately, during the travels, several people got COVID, so there was a come home, dump all belongings, get the phone call that people had tested positive, quarantine, and then chaos ensued.
Fraser: But you didn’t.
Pamela: I did not get sick. I had a random sore throat, which I’m gonna blame on things I was allergic to. I escaped.
Fraser: Good.
Pamela: So, folks, wear your masks. I wore my K95 like my life depended on it because it probably did. Yeah, so I managed to stay safe. I just haven’t found my microphone or my webcam. But congratulations to the beautiful couple. It was a fabulous ceremony. And everyone is now home.
Fraser: Good. Well, hopefully by next week, you will have started to put your life back together.
Pamela: That’s the goal.
Fraser: Moons orbit planets. Planets orbit stars. Stars orbit within galaxies. It’s orbits all the way down. But occasionally, objects can receive a powerful kick that sends them on a journey never to return. So, let’s talk about orbits first. Let’s say that you are on the surface of Earth and Superman is going to punch you really hard. Describe the —
Pamela: That would be so bad.
Fraser: Yes, it would. Now, describe the trajectories, here, that we could be looking at if Superman gives you a punch.
Pamela: The pause here is the structural integrity of the human body is such that I’m not sure there’d so much be a trajectory –
Fraser: He’s punching another Superman.
Pamela: He’s punching Iron Man with the suits. Let’s go with –
Fraser: Yeah, he’s punching the Hulk.
Pamela: Let’s go with Iron Man because I have faith in that steel suit.
Fraser: Okay, sure. Superman’s punching Iron Man.
Pamela: So, Iron man is going to travel on what’s called a comic section. So, imagine, if you will, a round cone, like good old-fashioned ice cream cone, and you can cut a plane through that and in a bunch of different ways. If you cut it just right, you’ll get a perfect circle. And depending on how you do it, you may end up with a not entirely closed surface. So, you can end up with what are called a parabola, a hyperbola, or an ellipse. Now, if –
Fraser: Or a circle, which is, I guess, a type of ellipse.
Pamela: Is a type of ellipse. So, ellipses are defined as a nice closed shape that has two foci that, if you tie a string to both of them and you move that string around the foci, you’ll end up with the ellipse. And depending on how far apart the foci are, you get a flatter and flatter ellipse. And if those two foci are in the exact same point, you get a circle.
Fraser: Isn’t it foci? Maybe it’s foci, hmm. Right. So, maybe it’s Canadian just versus American English. So, Superman gives him a punch. Not very hard. Just a light tap. He goes up. He comes back down.
Pamela: So, that’s a ballistic trajectory. Now –
Fraser: And it is a parabola?
Pamela: Well, you don’t really have enough information to tell because he collided with the surface of the object. Now, it’s entirely possible to have a perfectly healthy elliptical orbit that just happens to intersect the surface of a planet, which would be unfortunate. Except, in this case, Iron Man gets to keep breathing air that doesn’t have to come from his suit. So, that’s ballistic.
Fraser: Right. I guess you chose Iran Man for a reason here. And we know that to go into orbit around the Earth is 7.6 kilometers per second, 20,000 kilometers per hour. If Superman punched –
Pamela: Mostly sideways.
Fraser: Yes. If Superman punched Iron Man that fast, he still wouldn’t be in orbit.
Pamela: Yeah, it all depends on the exact angle of the punch. So, if Superman punches him straight up so that there is a line through the center of mass of the Earth that extends straight through the surface of the planet, through Superman’s fist, and sends Iron Man straight up, that kind of a punch is going to lead to a very skinny ellipse, so skinny, in fact, that it is a straight line and, again, a ballistic trajectory. And Iron Man is going to hit the surface of the planet on his way back down –
Fraser: Right. He’s gonna go up.
Pamela: – hitting Super Man if Super Man doesn’t move.
Fraser: He’s gonna come back down. Even though he’s punched him into orbital velocity speed, he’s not gonna be able to go into orbital velocity. Even if he punches him at an angle, he’s just always gonna be taking these parabolic ballistic trajectories and coming back down to the surface. So, how can Superman make sure that Iron Man doesn’t return to hitting the Earth again?
Pamela: He has to hit him sideways. So, if he hits him so that you have the surface of the planet, you have Iron Man on the pedestal off the surface of the planet, and –
Fraser: No, he’s on the surface. He’s just standing on the surface. Just comes up and punches him.
Pamela: Okay, so if he just plain punches him, he’s going to have to hit him hard enough that he goes into an elliptical orbit that has him going off the surface, coming back, grazing the surface of the planet – may there not be mountains on the other side – and then coming back, and he hits Super Man again. So, no –
Fraser: But if he punches him a million kilometers an hour, he’s just gonna escape velocity. He’s not coming back. That’s where I’m going with this.
Pamela: Okay, yes. He can escape if he hits him hard enough, yes.
Fraser: Right. So, you’re gonna have all of these various punches that are gonna lead to various kinds of ballistic trajectories. He won’t go into orbit.
Pamela: Iron Man is fine.
Fraser: Right. Iron Man’s fine. He’s fine. He can’t go into orbit from these punches, right? He can only either return to hit the Earth again or escape the Earth entirely. So, now, Superman punches him and then flies up, because he can, and punches him again when he’s in space. What could he do with him now?
Pamela: So, with that double firing, it is possible to put Iron Man in orbit. So, the trick is you need Iron Man to get to a certain height and then stay at that height or at least stay away from the surface. And this is where I started to say had him on a pedestal because, if you had him on a pedestal, you could just punch and he continues going around the planet at the height of the pedestal if you have exactly the right punch. If you don’t have that pedestal, you have to go up from the surface, and then you have to turn, and that turn is what allows you to keep going around the planet instead of falling back down to the surface.
Fraser: Right. And so now that you are in orbit – Iron Man is in orbit. He’s fine. At every point, he’s perfectly fine. They’re just having fun. He’s got all kinds of inertial dampeners on board. He can handle this an infinite amount. Every time Superman gives him a punch, it’s going to change his orbit around the Earth, but it’s not going to cause him to, say, spiral outwards or spiral inward unless he goes back to that –
Pamela: He could.
Fraser: How could it be a spiral with one hit?
Pamela: No, it’s gonna have to be repeated hits to be a spiral.
Fraser: Right. Yes, yeah. It’s gonna have to be repeated hits. All right. So, then, Iron Man is orbiting around the Earth. Superman comes up, punches him in the direction opposite to his orbit. What happens to him?
Pamela: So, if you decelerate, you’re going to – this is where it gets [inaudible] [00:11:00], and the astronauts –
Fraser: Let’s say the exact amount of his orbital velocity.
Pamela: The exact amount of his orbital velocity, then he’s going to go plunging back down to the surface of the planet.
Fraser: And if he is able to punch him in the direction of his orbit another, say, 20 kilometers per second, what happens to him?
Pamela: That will ultimately end up changing the shape of the orbit and making it more and more elliptical unless it’s at the exact right point in the orbit that the punch occurs and it was already elliptical, in which case, you can make it circular. So, you’re going to change the shape of the orbit.
Fraser: Right. But at a certain point, he’s putting him into orbit around the sun and no longer into orbit around the Earth.
Pamela: Yes. And this is something we’ve done with the Spitzer Space Telescope.
Fraser: Yes. Remember when Superman punched the Spitzer Space Telescope into orbit around the sun. Yeah, I remember that.
Pamela: All right, yes.
Fraser: Yeah, no, I understand. This analogy is starting to get a little tortured, so we’ll shift gears and actually talk about actual objects. So, the setup, really – and I think it’s really important to understand this. There are objects on escaped trajectories that are leaving the solar system, that are leaving the Milky Way. How is this possible? What did it take to get these things into these new runaway trajectories?
Pamela: Well, we assume that it wasn’t Superman punching them. We don’t actually have evidence that it wasn’t Superman punching them, but we’re pretty sure that –
Fraser: I think it’s safe to say.
Pamela: – wasn’t the case. And so, quite often, with the things that we believe are escaping our solar system or have escaped other solar systems, it’s due to interactions with two other objects. There’s what’s called the three-body problem, and we did an entire episode on it long, long, long ago. And there are certain systems of three bodies that can end up ejecting one of the bodies, quite violently, outta the system. This quite often happens when you have two similarly massed objects and then a little one gets involved. And if that little one isn’t in a dead locked-in orbit around one or the other of the objects, if it’s shared between the two of them, it can just get flat-out ejected in all sorts of wild and crazy ways.
Fraser: Now, you say fairly violent, but it doesn’t actually have to be because, when you’ve got, say, the Oort Cloud surrounding the sun, the objects that are out in the Oort Cloud have almost no additional escaped velocity that’s required. They’re teetering right on the edge, and almost any amount of three-body interaction will kick them over the edge and cause them to drift away from the sun.
Pamela: And this is where I have to admit I’m thinking of stars and globular clusters as my baseline for this at all times.
Fraser: You could have a star come relatively close and the three-body interaction between the star and the sun, and the Oort Cloud object causes it to drift away from the solar system. And now, it’s gone interstellar. So, it doesn’t have to be catastrophic. And you could have a situation where a comet falls into the inner solar system. And it should return back out to the Oort Cloud, but it interacts Jupiter on its way through, goes near Ganymede, gets a kick, and now, it’s over the – it, now, has enough speed, on the way back out again, that it will overcome the sun’s escaped velocity, and away it goes, again, into the larger galaxy.
Pamela: And this is one of the really awesome things to think about where we have these comets that we see coming in, on hyperbolic or parabolic orbits where we know they’re leaving our solar system. And so we know that objects that have passed near our sun, have been influenced by our sun, weathered by our sun are, now, going to go and eventually make their way into another solar system out there. We also know that, if there are objects that are getting flung inwards, there’s objects that are getting flung outwards. So, there are also icy bodies that have never interacted with our sun that are getting flung outwards. And if we’re flinging things outward, there must be other solar systems doing the exact same thing. And now, we have observed that occurring with ‘Oumuamua. It’s a trading of icy bodies all over the galaxy.
Fraser: Yeah. I’ve read a couple of papers on this. It’s estimated that there are thousands, maybe even tens of thousands, of objects of these transferred Oort Cloud objects from other star systems passing through the solar system at any time. And so tens of thousands of our objects have left the solar system.
It’s mind-bending when you think about that, and then you think about the age of the Milky Way, how long – or the age of the sun – this process has been happening and how much material is getting from star system to star system. Now, you were sort of getting a little more violent, and so let’s kick that back up a notch and talk about how planets can leave on a hurry, very rapidly. So, what can cause a planet to leave a solar system very quickly?
Pamela: Well, a planet can leave the solar system if there is some kind of a three-body interaction between it and a couple of other planets in the solar system. It is thought that our solar system may have had many more planets than what it currently has, depending on your value of planet. And three-body interactions between Saturn, Jupiter, and those objects led to them getting flung not just further out in the solar system, but out of the solar system entirely. It’s kinda cool to think that there may be these isolated planets that got stuff from the early Earth, stuff from the early Mars flung on to them and are now carrying those samples away to other places in our galaxy.
Fraser: And this idea of rogue planets, I mean, a few have now been found through gravitational microlensing. It’s estimated that there could be as many rogue planets in the Milky Way as there are regular planets. That’s probably a high estimate, but still, they’re gonna be in the hundreds of millions or billions. So, we’ve talked about planets and how they can, either through three-body interactions of within the system or – you could obviously have a black hole or a star get very close and kick a bunch of planets out into space as well. So, I wanna talk about stars that are on an escaped trajectory. All right, let’s talk about stars. So, what can cause a star to go on a runaway trajectory?
Pamela: So, three-body problems are still a thing. There’s research that shows that globular clusters somewhat beat like a heart because they will condense down, over time, getting more and more combined systems. But then, as those systems get towards the core, they’ll undergo interactions that fling things out into much larger orbits, so they’ll expand back out. And so you have these star-star interactions that will fling an additional star. But the thing that is new, once we get to the stellar level of interactions, is you can also get things flung out during supernovae. And this is one of the things where we’ve seen many different runaway stars.
And what is thought to happen is you have the giant star. You have its companion, and the bigger of them evolves first. Evolves, evolves, gets big, and hits the point where it’s no longer generating energy in its core, collapses down, and the collapse drives nuclear explosion, essentially. And the force of this can fling that companion star at a runaway velocity. You can also end up with asymmetric supernovae that just fling stars on their own.
Fraser: So, the blast of the supernova is hurling the star out? Because my assumption was that it was like a slingshot. You’ve got the star going around this other star, and then, suddenly, the star is no longer there. And now, the star is on a slingshot trajectory.
Pamela: So, to say it’s not still there depends on the kind of supernova. So, it is this combination of –
Fraser: Oh, that’s a great point, yeah. Right, because you could have it either completely disappear or end up with a neutron star or black hole.
Pamela: Exactly. So, you have the leftover relic. You have the explosion outward is going to exert force on things, and you have the change in the distribution of mass that’s going to change the interaction of things. End of the day, that companion star is, in many cases, gone. Not all cases. It’s deeply confusing that we keep finding systems that have an advanced star and a companion star and we know supernovae have occurred, but they’re still together. So, we’re still figuring out all of the dynamics here. But sometimes, you end up just with a supernova remnant and nothing inside, in which case the runaway object is running away from itself, which we all understand at a fundamental level.
Fraser: Yeah, possibly. So, the supernova goes off, and it’s not equal, and so it’s almost like it fires off thruster.
Pamela: Exactly. Yes.
Fraser: Wow.
Pamela: And so that asymmetric supernova explosion will leave you with your supernova remnant and the stars running away from it. And I just love the conceptual idea of this where the supernova basically makes a giant mess, explodes all over the place, and runs away from the mess it made.
Fraser: So, with stars, we can get this situation where you’ve got – the supernova is symmetrical or not symmetrical, and so the star is given a giant thrust. You can have the situation where the star goes off and it blasts away its companion star with enormous explosion. You can have a situation where the star vaporizes completely. And now, the star is on a slingshot trajectory and in all cases. There’s one last scenario that I think is interesting is with a supermassive black hole. You can have a situation where a supermassive black hole could be kicked out on an escaped velocity, right?
Pamela: So, this is another multibody problem where, in this case, it’s the two galaxies coming in to merge that is leading to this situation, and so you have these two supermassive black holes. And instead of orbiting and merging, the collision and all the physics involved, as they pass to and fro, can end up flinging one of the black holes entirely away. And we think this is what explains the fact that there are a lot of merged systems out there that don’t have evidence for two supermassive black holes in their centers.
Fraser: So, the supermassive black hole just bounces off the other one and is off.
Pamela: I wouldn’t use the word bounce.
Fraser: I don’t know if bounce is the right word, but instead of it – if it’s not large enough, then it doesn’t merge. It just gets kicked out when it gets too close.
Pamela: It’s all of the multiple passes and gravitational tugs to and fro and everything else that is going on can just fling it away.
Fraser: That’s crazy. All right, thank you, Pamela.
Pamela: Thank you, Fraser. And thank you to all of our patrons out there. This week, I would like to thank, in particular, Matthew Horstman, Alex Cohen, Phillip Walker, David Gates, Claudia Mastroianni, Matthias Heyden, Kseniya Panfilenko, Justin Procter, Jim Schooler, Scott Bieber, Scott Kohn, Daniel Loosli, Gregory Singleton, Disasterina, Jeff Wilson, Tim McMackin, Kenneth Ryan, Cooper, Omar Del Rivero, Omar Del Rivero, Allan Mohn, Eran Segev, NinjaNick, Steven Shewalter, Paul D Disney, Don Mundis, Janelle aka Veronica_Cure, Michelle Cullen, Micheal Regan, Benjamin Müller, J. AlexAnderson, Dean McDaniel, Matt Rucker, Scott Briggs, Anitusar, Frode Tennebø, schercm, Bruce Amazeen, Benjamin Carryer, Peter, Moose and Deer, Jim McGihon, Philip Grand, Mark Steven Rasnake, Father Prax, Brent Kreinop, Dustin A Ruoff, Abraham Cottrill. Thank you, all, so very much for everything you do. To all our editors who have their work cut out for them today to be paid and to keep our show going, thank you.
Fraser: Thanks, everyone.
Pamela: Buh-bye. Astronomy Cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy Cast is released under a creative comments attribution license. So, love it, share it, and remix it, but please credit it to our hosts, Fraser Cain and Dr. Pamela Gay. You can get more information on today’s show topic on our website, astronomycast.com.
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Space is a big place, with a lot of galaxies, stars, planets and moons, and that means a lot of names. How do astronomers name stuff, like comets, asteroids, exoplanets, craters?
Download MP3 | Show Notes | Transcript
Show NotesThanksgiving Day in Canada (Timeanddate)
How did all the planets with their moons get their names? (Astronomy Magazine)
Ancient African Skies (Space.com)
PAPER: Origins of the ancient constellations: I. The Mesopotamian traditions (Journal of the British Astronomical Association)
Whose stars? Our heritage of Arabian astronomy (The Planetary Society)
Division C WG Star Names (IAU)
Maori Astronomy (New Zealand Astronomy)
Stellarium
The moons of Jupiter (Universe Today via Phys.org)
The Shakespearean Moons of Uranus (Folger Shakespeare Library)
List of geological features on Europa – Chaos Terrain (Wikipedia)
6 Mars craters that are named after PH towns (Manila Bulletin)
International Astronomical Union
United Nations
Mike Brown (Caltech)
Pluto and the Solar System (IAU)
Naming of Astronomical Objects (IAU)
Naming of Astronomical Objects – Comets (IAU)
Pan-STARRS1 data archive (Space Telescope Science Institute)
Asteroid numbers and names (ESA)
Asteroid (158092) Frasercain (RASC)
Announcing Asteroid 158092 Frasercain (Universe Today)
How do exoplanets get their names? (NASA)
The Interactive NGC Catalog Online (SEDS)
Smithsonian Astrophysical Observatory Star Catalog (SAO)
The Abell catalog of planetary nebulae (In The Sky)
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TranscriptTranscriptions provided by GMR Transcription Services
Fraser: Astronomy Cast episode 657: astronomy naming schemes. 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’m Fraser Cain, the publisher of Universe Today.
I’ve been a space and astronomy journalist for over 20 years, and with me is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey Pamela, how you doing?
Pamela: I am doing well. How are you doing?
Fraser: Good. Happy Thanksgiving.
Pamela: Happy Canadian Thanksgiving.
Fraser: Yeah. Every year, we record on a Canadian Thanksgiving because we record on Mondays and it’s always on Mondays, and I always lord over you how much superior Canadian Thanksgiving is to US Thanksgiving for one reason.
Pamela: Go ahead.
Fraser: Weather. That.
Pamela: It’s true.
Fraser: We hold our Thanksgiving a month earlier –
Pamela: Yes.
Fraser: – and that means that the weather is going to be better. And so, if people are flying, it is less mayhem –just because you’re just gonna have milder weather. And so, people can make the journey without it just being horrible snowstorms and such. And once again, we’re having a draught here in western Canada, so if anybody wanted to fly, it’d be easy flying to get out here to western Canada.
But yeah. So, happy Thanksgiving. I guess we’ll take off US Thanksgiving, but we’ll work through Canadian Thanksgiving.
Pamela: But I still think they’re gonna launch SLS on American Thanksgiving, which means we will be working.
Fraser: Right.
Pamela: At least, I’ll be working.
Fraser: Right, of course. They absolutely will be launching SLS on some kinda holiday.
Space is a big place with lots of galaxies, stars, planets, moons, and that means a lot of names. So, how do astronomers name stuff? Like comets, asteroids, exoplanets, craters? All right, everything’s got a name. So, I guess let’s start with the easy stuff – the stuff that we’ve known the names of for antiquity. Where do we get those names from?
Pamela: So, do you mean things like planets?
Fraser: Yeah, the planets, bright stars –the moon –the sun – Right? These things have names. Where did they come from?
Pamela: So, the original names for the planets that we use in the English language – they simply come basically from the Greek and Roman names for them. And so, we have – Saturn is a Roman god, we have – Jupiter is a Roman god, but these are the Romanized versions of the Greek gods’ names. So, we basically just fell back on the names the Romans stole and changed and kept them for ourselves.
Fraser: But what about names like “the moon” or “the sun”?
Pamela: Well –
Fraser: “The earth.”
Pamela: Yeah. That is, again, just ancient language where I am not the kind of anthropologist that can explain these truly ancient words that –
Fraser: Right.
Pamela: Yeah. I mean, earth is the dirt under our feet. The fact that it’s a planet that we stand upon – that one took a hot minute to figure out.
Fraser: But I think it’s funny, right? I get emails all the time from people saying like, “What is the name of the moon?” and I say, “It’s the moon.” And then, someone will comment like, “No, no, no; it’s Luna.” But that’s not true. That’s just another language –
Pamela: That’s just the name in another language.
Fraser: In another language.
Pamela: Yeah.
Fraser: Yeah. Yeah, the sun – you know, “Soleil” – whatever you wanna call it – earth, “Terra” – just another –word in – and the reason is because we didn’t know there were others.
Pamela: Right.
Fraser: And so, it’s just like, of course it’s “the moon” – it’s a name for the thing that’s in the sky. You don’t realize that it’s actually a classification of objects. Antiquity, they just thought it was the thing.
Pamela: Yeah.
Fraser: So –yeah, I find that really funny.
Pamela: Well, and what gets really amazing is when we start looking at stars, there are some stars whose names linguists think are so old that they go back to like –pre-distribution-of-humans-all-over-the-planets times.
Fraser: Wow.
Pamela: And –
Fraser: That’s really interesting.
Pamela: – the idea that there are stellar names that go back prior to –homo sapiens’ diaspora from Africa – Like, that’s a phrase I never thought I would be saying, but the stars have just been an integral part of our lives for that long.
Fraser: But there are – I mean, in the west, a lot of our names come from Arabic astronomers –
Pamela: Yes.
Fraser: –as well as like Sumerian and – Again, just cultures that are thousands of years old in some cases, we still use those names. And in some cases, just lost to antiquity. And then, every society – I mean, people in China have names for the different stars that they have, again, from antiquity. And probably –you know, I’m sure the Aztecs had their names for everything as well.
Pamela: And luckily, there were only a few thousands of naked-eye stars for astronomers, or astrologers, or whatever they were in whatever culture – magi – there were only 1,500 to 2,000 stars that could be seen and catalogued by the naked eye, and not all of those had common names.
So, we have a few stars like Betelgeuse, Sirius that have these names that are words –and everything else luckily just got catalogued.
Fraser: I wish we could kinda go back and look at the names that every culture has given the same star and then be able to present them as like a menu and go like, “I like this one the best.” I’m sure there are some really cool names that the aboriginals in Australia came up with for stars and things like that. It’d be great to sort of have the whole list. Wonder if anyone’s built a cross-cultural list.
Pamela: Yes. Yes. I’m like exploding with vibrations here waiting to say yes. The International –
Fraser: Anyway, I guess we’ll never know. Go ahead.
Pamela: So, the International Astronomical Union has a committee on stellar names that is working to collect the names from various cultures around the world so that we don’t lose these names, and in places like New Zealand where they’re working so hard to commemorate the people whose land that they stay on who are still alive and still there, you can actually go to museums and by star charts that have the Maori peoples’ names for stuff. They are working to keep this information that could so easily have been lost, and software like Stellarium will even let you turn on and off the constellations of different cultures.
Fraser: Oh, that’s cool. Okay. Yeah, I mean, there’s gonna be some badass names for some of the objects in the sky, and I think we should be able to settle in on a cross-cultural collection that is only the coolest names.
Pamela: Yes.
Fraser: Anyway, so, then, objects that have been discovered in modern times –
Pamela: Yes.
Fraser: I’m thinking about the extra planets, the moons, and etcetera. How does that naming scheme work?
Pamela: Well, those are a couple of very different time periods that these rules ended up coming from, so what we have – for Jupiter – initially, Jupiter – it was the wives of Jupiter, and mistresses as well that the names were drawn from. So, Jupiter is literally being circled by mistresses, which just amuses me to no end, but as they got further and further down, they did eventually run out of mistress’s names to use.
So, these are all names that are drawn from mythology. With Saturn, you have Shakespearian names kick in at a certain point. And so, each world has its own slightly different sets of rules, and with worlds that have surfaces that we can define features on, it gets kinda crazy.
So, for Europa, you have the chaos terrain that is named after Celtic myths. You have craters that are named after Celtic gods and heroes – ring features are named after Celtic stone circles. So, you see how astronomers latch on a theme and go down the rabbit hole.
Fraser: Right. The mythology rabbit hole –features very strongly across the naming schemes for the solar system.
Pamela: And sometimes, it’s not just mythology. With Mars, one of my favorite details is small craters are named after places on earth with a population less than 100,000.
Fraser: Hm. I wonder if there’s a Courtney crater out there, then.
Pamela: There could be. Or, you could go name one. Or, propose to the IAU the name of one.
Fraser: I guess so. Yeah. Yeah. All right, we’re gonna talk about this some more, but it’s time for a break.
Fraser: Now, you’ve said this is the name for that, and those are the names for these, and they’re getting the official names, so who decides what the names are?
Pamela: There are a variety of different committees within the International Astronomical Union, which is a global union of scientists that works in collaboration with the United Nations, actually, in a lot of different things.
And there’s the Planetary Naming Conventions Group, there’s the Asteroid or Minor Planet Naming Conventions Group, there’s the Stars Naming Group, and the fact that these are all separate committees under different –parts of the IAU sort of –came to a nasty head in 2006 because –Michael Brown had discovered a new large object out in the Kuiper belt that was potentially larger than Pluto, and the question was “Does it get to be named by the IC Objects Minor Planet Naming Committee, or does it get to be named by the Planetary Naming Committee?”
Fraser: Whoa.
Pamela: And –
Fraser: You’re talking about Eris here?
Pamela: Yeah.
Fraser: Yeah.
Pamela: And it comes down to –they had to have a definition of what a planet is so they knew which committee got to approve the name.
Fraser: That’s crazy! Is that real? Is that –?
Pamela: Lovely. It’s real.
Fraser: So, the reason why whether or not Pluto is a planet had to come to a vote was because they needed to decide who got to name Eris?
Pamela: Well, it’s slightly more complex. It was the –
Fraser: No, no, no. It feels as simple as that.
Pamela: It was the realization that we don’t have a definition of what makes a planet, and both groups wanted –dominance over these objects.
Fraser: Yeah. Right. And so, they forced a vote.
Pamela: And so, basically – Yeah, they forced a vote. And they came up with a terrible definition.
Fraser: Why did you never tell me this before?
Pamela: I’m sure I did at some point!
Fraser: No. No, no, no, no, no. No, we talked…
Pamela: I failed. I failed you.
Fraser: It’s not that you failed, but it’s just like, you buried the lead. Like, this is the chain of events: Mike Brown finds an object. The object is Pluto-sized – therefore, theoretically, it’s planet-sized.
Pamela: Yeah.
Fraser: Who gets to name it? The two groups – because it falls somewhere between those two groups, they had to decide whether it was a planet or not, and if it’s a planet or not, then Pluto’s a planet or not, and –
Pamela: Right.
Fraser: Wow. Anyway –
Pamela: Isn’t that –delicious?
Fraser: Yeah. Yeah. Yes. Yeah. I’m sure there are certain members of the “I love Pluto” community that are just raging right now –
Pamela: I refer to it as “Pluto: Planet Classic.”
Fraser: Yeah. Me, as having absolutely no dog in this fight, don’t care at all. My emotion neither rises nor falls with any mention of Pluto’s pro- or non-planethood.
Pamela: I’m just amused.
Fraser: But I do find it funny that this is the story.
Pamela: Yes.
Fraser: So, I mean – but the names – like Makemake, Eris – Those were suggested by Brown – by Mike Brown.
Pamela: So, the way it works is the people who find the objects get to propose names, but they don’t get to –say outright “These are the names.” They have to propose the names, fill out paperwork, submit the paperwork, the committee has to meet, the committee has to approve, and thus, you get a world that has been named.
Fraser: All right. All right, let’s move on, then. Let’s talk about comets. How do comets get their name?
Pamela: So, comets are fairly straightforward. They get the name of the humans that found them, the year that they were discovered, and depending on which nomenclature you’re looking at, you may see additional letters and numbers that have to do with “Are they periodic or non-periodic comments?”
One of the problems we run into is comet nomenclature as well as minor-planet-naming nomenclature got revised. And so, if you’re looking at something from like the 1980s or if you’re looking at something from the 2000s, you’re gonna see different ways of stating the nomenclature.
Fraser: So, take any example comet, and break it down for me.
Pamela: Comet Halley – named strictly after Halley.
Fraser: Right. But Comet Halley, for example, is a bad example because Halley didn’t find it – it had been known for 100’s of years, and it had been coming back again and again. So, I think that’s a bad example. Like, it shoulda been Comet “That Comet We’ve All Seen for a Long Time and Talked about, and No One Ever Really Put a Name to It.”
Pamela: So, the thing is we didn’t know what comets were before Halley put –one in many together and got an orbit.
Fraser: Right.
Pamela: Halley looked through history and found that every 70-something years, this bright-tailed object streaked through the sky –
Fraser: But that’s just accounting. That’s not like noticing a comet for the first – I’m saying – Halley should lose his naming rights for the comet. It should be stripped.
Pamela: But we don’t know who the first pre-diaspora human to notice the comet was.
Fraser: That’s the historians’ problem. It’s not my problem. Not my problem.
Pamela: I’m just gonna keep saying “diaspora” today.
Fraser: Yeah. Yeah. So, that is a historian’s problem. I’m just saying that Halley getting the comet named after him is illegitimate and should be stripped. But I’ll let the IAU have that fight. I’m ready. I’m ready to present my case.
But a modern comet, like Hyakutake or Hale-Bopp. Now, those are brand new comets that nobody’s ever seen before.
Pamela: Right. Those are, again, from some of the earlier nomenclature where they’re named after the discoverer. It gets more chaotic with modern comets, but since PAN-STARRS is finding most of them, we are glad for the chaos.
Fraser: Right.
Pamela: So, for instance, there is Comet/2017 K2 (PAN-STARRS).
Fraser: Perfect. Okay. So, that’s a jumble of information. What does that mean?
Pamela: Yes. So, that means it was found in 2017. The K2 starts to give you information on the where in a given month and which number in a given month it is that it was found, and PAN-STARRS is the discoverer. So, in this case, it’s just a telescope survey.
Fraser: It’s a robot.
Pamela: Yeah. Yeah, it’s kinda boring.
Fraser: Right. Beep-boop. Right. So, robots. So, would you say that accurately, the comets are named after robots?
Pamela: Yes. And I am okay with this.
Fraser: Yeah, I’m all right with that. That’s fine. I mean, this really should smooth over the rise of the robots. Like, when they come to dismantle us for our atomic parts, we’ll say, “But, well, we named all these comets after you,” and they’d be like, “You humans. Aw, shucks. All right. No matrix for you. No termination. We’ll live in peace and harmony until the end of time.”
Pamela: I don’t think it’s gonna work that simply, but I hope you are right.
Fraser: It’s worth a shot. It’s worth a shot.
Pamela: It’s worth a shot.
Fraser: Yeah. All right. So, now, for the best part. We’ve talked about comets. Let’s talk about asteroids. How do asteroids get their name?
Pamela: My dog just sighed as well.
Fraser: Good.
Pamela: So, asteroids get their name basically in the order they have been found. So, it’s asteroid one, two, three, four, and then, sometimes –if they’re a lucky asteroid –someone decides to grant them a name.
Fraser: Yeah.
Pamela: And again, the name has to be approved of by an International Astronomical Union committee, but in the past, we didn’t have this committee. So, you can go and look up the earliest discovered asteroids, and they have the number, and the name, and the IAU was not involved – Ceres, Vesta – they were just names.
Fraser: But that’s interesting. So, when you see 4 Vesta, or 1 Ceres, or whatever – when you see the number, you know that it is –
Pamela: What order it was found in.
Fraser: What order it was found in. And so, for example, Asteroid, I don’t know – 158,092 – That was –
Pamela: We haven’t got that high yet, but continue.
Fraser: Yes we have. We absolutely have.
Pamela: We have? Oh, geez.
Fraser: Yeah. Yeah, asteroid 158,092 – Asteroid Frasercain – was the 158,092nd asteroid that was discovered.
Pamela: All right. All right. Fair. Fair enough.
Fraser: So, yeah. How did it get the Fraser Cain part of its name?
Pamela: So, either the person who discovered it –or, if it got ignored long enough, someone who noticed that it had been ignored long enough submitted to the IAU that this asteroid deserves a name. And this name I am proposing commemorates someone who is good and noble, and had done excellent things, and has a name that is absolutely not controversial.
Fraser: Right. And so, in this case, Jeff Metcalf – the blue-collar scientist who passed away –
Pamela: In 2008.
Fraser: 15 years ago? Yeah.
Pamela: Yeah.
Fraser: –was a prolific asteroid discoverer and named asteroids after a whole bunch of people in the science and science communication community.
Pamela: Yeah. Yeah, You and Phil Plait got your names at the same time.
[Crosstalk]
Fraser: Got me, got Phil, Emily Lakdawalla, but missed you, and we’re always sorry. So, if anyone’s listening to this and you discover asteroids, throw a bone to Pamela. Come on. She could really use an asteroid named after her.
Pamela: Well –yeah.
Fraser: So, the point being: Jeff discovered the asteroid, got to provide the name, and it was – Like, it’s not that he got to suggest the name to the community. It was more like if he had said something trolling or hateful, then they could’ve stripped it, but that was gonna be the name because I guess there are so many asteroids being discovered all the time.
Pamela: Yeah.
Fraser: Yeah. That’s really cool. Now, what about exoplanets?
Pamela: So, exoplanets – we haven’t started giving them other than occasionally, a research team will bestow a name upon something they find, but those I don’t believe are considered official anywhere.
They get names that are lowercase A, B, C, D, E according to their distance or their discovery order from their main star. So, if we end up finding something later that is closer in then things get to be a jumbled mess, luckily, it’s usually easiest to find the thing that’s innermost. So –
Fraser: But there is no “A”. The A is the star –right?
Pamela: Right.
Fraser: Right. So, say you have Pegasi 51 – the first planet every discovered…
Pamela: Actually, I’m gonna factcheck that one because this is a lowercase and there’s [inaudible] [00:26:41]
Fraser: Okay. Because my understanding – like, you’ve got 51 Peg B, and that was really the first planet orbiting a sunlike star that was ever found – in 1995 – and that’s the B. And so, the first one found is the letter, but if you find a bunch at the same time, then, they typically will to them from the inside out.
But the category – like, the actual name – like Gliza, the Trappist – Kepler – like, those are coming from the telescope. So, essentially, the telescope is the first part of the name – Gliza –whatever. The star catalogue. Then, it is the designation in the catalogue – so, 5,781-whatever, and then, it is the letter designation, which is the planet, and whether it’s closest to the star or first discovered –
Because –there are probably more planets in, say, the 51 Peg system than the one that we know of – the hot Jupiter that we know of – but they’re just too feint to see. And so, do you shift everything if you find more? No. You just – you find a closer one; now it’s C. And then, [inaudible] [00:28:09] D, and then, the one in between those two – that’ll be E.
So, it’s really in the order that they’re found. But if you’re gonna find a bunch at the time –
Pamela: Yes.
Fraser: –then you just – like the Trappist planets – then you put them all in a row nicely.
Pamela: You are entirely correct, and the reason I had to take a moment to be confused is multi-star systems. So –
Fraser: Right. It’s capital though, right?
Pamela: Yeah. And this is where the capital versus the lowercase comes into play. So, back in my Slacker Astronomy days, we took great delight in the discovery of a planet in the Tau Boötissystem orbiting the primary star, which is A. So, it is legitimate to either say “Tau Boötis, capital ‘A,’ lowercase ‘b’,” or to simply say “Tau Boötis B,” but you really always just abbreviate it. So, it’s Tau Boö B, and I’m apparently an eight-year-old and still take delight in that.
So, if it’s the primary star of a binary system, you can omit the letter. If it’s a secondary, tertiary, whatever star in a multi-star system, it would be the star designator – so, that’s usually a number – and then, for bright stars. So, Bayesian number, the constellation name, the capital letter of the star and the multi-star system when the letter is not A –followed by the lowercase letter.
Fraser: Right. And then, you’re also gonna see the names of stars, galaxies, pulsars – things like that, and it’s gonna be a jumble of numbers and letters. That just comes from some star catalogue.
Pamela: But they have a meaning. Those have meaning.
Fraser: Sure. Two mass – Yes. The HD – Yeah, they do have meaning. They’re named after the catalogue that they’re stored in.
Pamela: But the license plate that follows the catalogue actually has meaning.
Fraser: Right.
Pamela: So, the NGC numbers don’t so much have meaning. Those are just kind of the order they got listed and more discovered, and those go all the way back to like –when Herschel – all three of them were cataloguing things. So, William Herschel, his younger sister Caroline Herschel, his son John Herschel – they all helped contribute to the new general catalogue. That’s how old the new general catalogue is.
Fraser: Right.
Pamela: But modern catalogues – so, for instance, if you’re looking at a Abell galaxy cluster, you have the Abell number, which is the order in which it was found, and if there’s an S in front of it, that means it’s a southern hemisphere system –ID. So, it’s Abell – no letter means northern hemisphere; S in front of it means southern hemisphere –
But Abell, for instance, SO295 is also catalogued as XRCJ0245.45302 –
Fraser: Right.
Pamela: And that means that it is the object that was found in the Chandra mapping of the region that has that particular Julian date – so, J2000, a coordinate describing where it is. And they usually only give the RA part of that license plate, but if you go to the actual catalogue, it will then have either a plus or a minus and give you the [inaudible] [00:31:56] as well.
Fraser: And so, you can see the name of the object and know where to find it in the sky. As opposed to having to look up a catalogue, find the location of the object, you can just find it there in the name. But what if they drift overtime? That’s a terrible naming scheme.
Pamela: No, no, no. So, the reason that they have that J in front or they have a B – which means the 1950’s coordinate system – that letter that you have in front tells you when that position is good for. And so, we know when it has a J in front of it, those coordinates are completely right for 2000 on the specific date that the calendar is set to zero on. And it’s the same for the 1950.
Fraser: Yeah, you can just modify based on the clock. All right. We could do this all day. The point being: if you see a great big jumble of letters and numbers after some object, that is the astronomers attempting to communicate important information about the object’s location right there in the name, which is smart, but also incomprehensible for the rest of us attempting to read it.
Pamela: True.
Fraser: All right. Thank you, Pamela.
Pamela: Thank you, Fraser. And thank you to everyone out there who helped support this show this week.
I would like to thank Alexis, William Baker, WandererM101, Zero Chill, Felix Gutt, Astrosetz, William Andrews, Gold, Roland Warmerdam, Jeff Collins, Simon Parton, Kellianne and David Parker, Jeremy Kerwin, Stuart Mills, Rob Cuffe, Harald Bardenhagen, Phillip Walker, Daniel Loosli, Matthew Horstman, Alex Cohen, marco iarossi, David Gates, Scott Bieber, Rando, Disasterina, Scott Kohn, Kseniya Panfilenko, Jim Schooler, and Justin Proctor. Thank you all so much for all you to do help support our show. Thank you.
Fraser: And we’ll see you all next week.
Pamela: Bye-bye, everyone.
Astronomy Cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy Cast is released under a Creative Commons attribution license. So, love it, share it, and remix it, but please, credit it to our hosts, Fraser Cain and Dr. Pamela Gay.
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Download MP3| Download Raw Show with Q&A| Show Notes | Jump to Transcript or Download
Show Notes * Red dwarfs (Wikipedia) * Red Dwarf (Cosmos) * Red dwarf star (Britannica) * Red Dwarf Stars (Universe Today) * Formation and evolution of the Solar System (Wikipedia) * Planetary formation and migration (Scholarpedia) * Hot Jupiters (NASA) * Investigating the Mystery of Migrating ‘Hot Jupiters’ (NASA Spitzer Telescope) * What are Hot Jupiters? (Universe Today)
Transcript
Transcriptions provided by GMR Transcription Services
Astronomy Cast, Episode 546
Weird Issues: Planetary Migration
Fraser: Welcome to Astronomy Cast, our weekly fact-based journey through the cosmos where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me, as always, Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the Director of CosmoQuest. Hey Pamela. How you doing?
Pamela: I’m doing well. How are you doing?
Fraser: Great. For anyone listening, it’s been a week since you’ve heard our dulcet tones, but for us, it’s been scarcely 10 minutes. So, here we are with our next episode on our weird series – weird issue series. And Pamela is traveling, so we had to bunch them up. But I don’t think the science will change dramatically in a week or so, but I could be wrong.
Pamela: It’s true.
Fraser: Yeah. Now, before we discovered other planets, our solar system seemed like a perfectly reasonable template for everywhere. But now, we seem to have some planets closer to the stars, which leads you to the question how does it all get there? Do the planets form in place or do they migrate around? All right, Pamela. You put this in the docket. You had a much more complicated title when you originally put this in. It was something to the gist of, which I just put as that last sentence, did everything form in place or did it all migrate around?
Pamela: I’m not allowed to name things. I am an astronomer, but the one precludes the other. We’ve discussed this before. You were here to name this.
Fraser: You are either too poetic or –
Pamela: Wordy. Let’s just go with wordy.
Fraser: Too wordy. Yeah, yeah. And I’m like “I’m all about the clickbait, man, so keep it short.” But, no. So, again as always, each time we kinda go back and think about the days of yore, and what did we think about planetary formation and the locations of the planets back in old timey land?
Pamela: Well, back when we only had one solar system to study in detail –
Fraser: Right. There was only one.
Pamela: We came up with this beautiful solar nebula model, which the big pieces are still generally thought to be true, but the details, oh my goodness, were wrong. So, the picture that we had before is that solar systems form and the light pressure of the sun pushes most of the gases outward, leaving rocky worlds forming. Internal – the gas gets gathered up, forms usually one giant gas giant. Outer – in the outer solar system, you can end up with some ice giants, maybe a smaller gas giant, and things form in a nice and ordered way. And you may end up with resonances between those massive worlds that push things out further and send rocks cascading in.
But in general, where we see things is where they formed, which means that when we look at things like the asteroid belt, which is located at that place in the solar system where the heat from the sun either baked things dry or left them moist, those asteroids that formed there are still representative of that solar nebula and the distribution on the trail within it. That’s what we thought.
Fraser: Right, right. And in fact, the distribution – I forget the exact rules on this, but if you looked at the locations of all the planets in the solar system, there was a really straightforward, almost mathematical position to each one of the planets. As long as you assumed the asteroid belt is a planet –
Pamela: It was a beautiful set of ratios that led people to think that that was where they had to be.
Fraser: Right. There was a beautiful set of ratios. Yes. And so, we assumed that everywhere we looked, we would see the exact same thing. Did we?
Pamela: No.
Fraser: What did we find?
Pamela: So, one of the first things that we found was gas giants don’t always exist far away from their stars. They tend to be found snuggled up next to their stars periodically. And we’d also assumed that they’d have to be in circular orbits because angular momentum issues. But then, we find them in these highly elliptical orbits. And we assumed that there would only be one gas giant, truly giant, Jupiter-like planet per star, and we sometimes find more than one. And so, basically, all the rules we came up with were wrong.
Fraser: Right. And so, now, if we were to look out into the universe and try to make some rules about how planets – where you’ll find planets in other star systems, what are the rules?
Pamela: I think that depends on who you talk to and what they ate for breakfast that day.
Fraser: So, is it bordering on no rules?
Pamela: It’s bordering on new rules appear to come out every week.
Fraser: Right. But there are no – there have been star systems found with, as you mentioned, giant planets orbiting close to their stars, multiple giant planets, planets that are small, located close, in between, planets are on red dwarfs – it’s a mess. It’s chaos out there.
Pamela: If the solar system could do something, it has done something.
Fraser: Right.
Pamela: And this is kind of awesome. And what’s fun is watching the theorists play catch up. And one of my favorite examples of this –
Fraser: Poor theorists.
Pamela: Yes. One of my favorite examples of this is a new paper that came out in the astrophysical journal that had as lead author, graduate student, Renata Ferlich, and this young woman did this amazing work where she ran a myriad of hundreds of simulations of solar systems where she started out each solar system with 10 worlds. And she started out each solar system with a different amount of mass, and let the mass fall as it would to the different planets, and she allowed her models to have multiple, massive gas giants. And this was new. Like this wasn’t a thing people had been doing before because solar systems are not supposed to have multiple, massive gas giants.
Fraser: Don’t we have two?
Pamela: Well, Saturn’s not that big. So, they’re allowing two Jupiter or larger size.
Fraser: Two Jupiters – okay – or more.
Pamela: And so, the models that she did were able to explain all of these crazy Jupiters we’re finding as what happens when you allow a solar system to evolve for 20 million years, and notice that worlds collide. And the fact that worlds collide seems to be something that we have to keep re-realizing. And this is one of my favorite things, as someone who does not do this research, to sit back and watch as a spectator. Because first there is this realization of “oh, expletive.
One of the best ways to get at the Earth having a moon is to assume that a Mars-sized object hit the proto-Earth; they collided; they splashed up the light materials; the light materials re-coalesced; we ended up with a moon that’s lower density than the Earth. We even named the prior object Theia.
Fraser: Right. And so, I’m just imaging the cognitive dissonance here, right? You’re saying planets don’t move, but also a planet moved and crashed into the Earth. But ultimately, planets don’t move except for that time that they did, which they don’t.
Pamela: Right, right. And so, the fact that other collisions may have occurred, people talk about, especially when we look at things like Uranus, which has its pole pointed into the plane of the suns; when we look at Venus, which seems to be flipped all the way over. Well, maybe that could’ve occurred via some sort of a collision, but there’s always that modeler out there trying to figure out how to do this using nothing more than tidal forces so that no collisions are required. Because we keep assuming that collisions have to be rare.
But then, there was a recent paper that was able to explain that the reason Jupiter isn’t as dense in the core as we had previously expected, as measured from its angular moment of inertia, is it appears that Jupiter got smacked by a massive protoplanet many times the size of our Earth when it was young. So, we now have in our solar system alone, Earth moon – result of a collision; Jupiter’s fluffy core, and they did use the word fluffy to describe this explained with a massive collision.
Fraser: A super-Earth.
Pamela: A super-Earth.
Fraser: Yeah. We used to have a super-Earth, and then Jupiter ate it.
Pamela: Or it committed suicide. I don’t know who was on the elliptical orbit that drove this collision.
Fraser: Right. So, then this idea then that a planet crashed into the Earth. A planet was gobbled up by Jupiter, or threw itself into Jupiter. Uranus is flipped over on its side and is in the wrong position in the orbit compared to Neptune in the solar system. It looks like they’ve been flipped. This started to lead astronomers to the possibility that, in fact, maybe planets shift around. Maybe they do shift around in a solar system.
Pamela: And once you start thinking about that, you start looking at the data in a completely different way. So, initially when we were trying to figure out how the heck do you get a Jupiter snuggled in next to its sun, everyone was blaming frictional effects, drag effects. The early Jupiter was inside the disk of material, the protoplanetary disk, and it kept consuming things at smaller and smaller orbits until it had migrated in to where there was the hollow spot in the disk, and it stopped there. Well now, by instead looking at this as “oh no, it simply got smacked around through collisions with other objects and got pushed in.”
Perhaps it ended up on a highly elliptical orbit, and highly elliptical orbits do, over time, get tidally made more circular. This is a completely different and, in many ways, easier way to explain what we see, and tidal forces do still play a role. Don’t get me wrong. This is how things like when you look at Mars, it’s inner moon, Deimos, will eventually become it’s inner broken band of rocky rubble, Deimos –
Fraser: Phobos.
Pamela: Phobos. Yes, sorry.
Fraser: Yeah. Phobos is going in. Deimos is going out.
Pamela: Deimos is fine. So, it looks like you can also have tidally locked worlds migrate in as well. And so, you have collisions that are driving it, you have frictional effects that are driving I, and the newest result that we’re looking at is planets have now been found near late-type stars that had previously been much bigger red giants.
Fraser: Yes. I saw this.
Pamela: The planets are being found in locations that used to include where the star was.
Fraser: Right. So, we’ve got stars – we’ve got planets that were able to withstand their stars – They were inside their star for a while.
Pamela: So, they actually figured out how to explain them without having to have them inside the star, which seemed like a really bad way to be a planet.
Fraser: Yeah.
Pamela: So, the way they figured out how to explain this is you have massive star and the planets turned out to be in much further out orbits. So, the planets weren’t actually consumed initially. Star expands out. Its rotation rate changes as it expands and contracts. The planets are asymmetric. As the star collapses back down, the same effects that are causing the inner moon of Mars to spiral inwards towards Mars are causing these planets to spiral inwards towards their star. So, they were tidally dragged in towards their star as it shrank.
Fraser: Wow. That’s really cool. Yeah. And this is brand new. This is like today, yesterday.
Pamela: Last week.
Fraser: Yeah. So, then let’s run the clock back now to think about the early solar system. What did it look like?
Pamela: It was probably – and here again, this is what we’re thinking today. Tomorrow could be different. There is some consensus, but I wouldn’t say there’s great consensus on our understanding right now. We believe that things started out with all of the outer planets closer into the sun, so our solar system was initially much more compact. The Oort cloud may or may not have been there. The Kuiper belt may or may not have been there. The asteroids may or may not have been there.
Over time, gravitational interactions between the most massive worlds in our solar system redistributed everything leading to the asteroids in the resonant places that they are – and they aren’t in the asteroid belt – leading to the centaurs grouping up where they are and where they’re gonna stay for 1000 years at a time before they get flung in a new direction, leading toward Uranus and Neptune perhaps even switching locations according to some models.
Fraser: Yep. And rolling Uranus over on its side, although that could’ve happened with a crash.
Pamela: Through an impact. And so, the best that we can say is everything moved, and we luckily ended up on a world that stayed in the habitable zone for the surface of our world.
Fraser: Crazy. So, then this idea – how does this help us better explain the other star systems that we see out there in the universe? As we said, we’re now seeing all of this complexity. Why does this knowledge that planets migrate around – how does that help us better understand what we see?
Pamela: So, the two big questions that we’re finally able to answer are it’s through this planetary migration that we see so many collisions taking place. And if your initial solar nebula is only able to form one fairly significant Jupiter-sized world, and then things like Saturn, Neptune, and Uranus – if those Saturn, Neptune, and Uranus-type things decide they’re gonna collide together, this is how you start ending up with these truly massive worlds. So, what we’ve been finding is truly massive worlds in highly elliptical orbits, and these new models also explain this highly elliptical orbits. Because the high ellipticity, that’s not natural.
The easy way for things to form is a nice, circular orbits that some resonances can knock things slightly out of the round, but in general, round is how orbits want to be. But when you have collisions and you have separate masses doing it, you end up with a single, much larger object, or moons and a central large object – Earth-moon system. And if it happens just right, you end up with the high ellipiticity systems that we are seeing.
Fraser: I mean, I guess when you see a planet – like a hot Jupiter – and you see this planet that is located really close to the star, that shouldn’t be possible.
Pamela: Right.
Fraser: Like it shouldn’t be there. It couldn’t have formed there, therefore it had to move there. And the fact that it had to move there means that planets move –
Pamela: But how?
Fraser: But how? And how. So, what are those mechanisms that are causing those planets to shift around?
Pamela: So, we’re looking at three main mechanisms for shifting the worlds around. One is when we still have that young solar nebula with a whole bunch of debris in it, you have an object that forms with a gap outside of it relative to its star, and a whole bunch of material internal to it around its star. And it starts gobbling up the material inside of it, and this changes its angular momentum and causes it to migrate slowly inwards depending on how this occurs. And it’s through this consumption from the drag and through the conservation of angular momentum that you get this very complex and hard to math out migration inwards in an early solar system.
Fraser: And I’ve heard this process might actually happen very rapidly.
Pamela: Yes.
Fraser: Like you’ve got these disks of material. The planet is embedded inside of it, and you’ve got these tidal tails that are coming from the disks that are feeding into the planet. And the closest analogy is you can see structures that are kind of like this with the shepherd moons that are orbiting within the rings of Saturn. You can see these lines of material that are coming to these little shepherd moons because of their gravity, and that in fact these movements could have happened in hundreds of thousands of years, the low millions of years at the most. It was not a slow process. It was fast.
Pamela: Right. So, primary planetary formation probably only took a few hundred thousand years.
Fraser: Wow.
Pamela: And it was during that next billion years that all chaos broke out with things moving each other around. And so, you do have this frictional migration.
Fraser: You mentioned three mechanisms, right?
Pamela: Right. So, the next way that we look at things is you have that next phase of the solar systems – the era of heavy bombardment that we saw within our own solar system. This is where you have massive collisions taking place where you start off with way more worlds than you eventually end up with. And it is through the collision of Earth, Mars, and bigger sized objects that you can grow massive Jupiters. You can grow massive terrestrial worlds.
Fraser: So, I kind of imagine this. You’ve got these planets that are on these fast tracks that are moving around inside this disk of material, but potentially at different speeds, and then you’ve got planets crashing into each other as they enter each other’s orbits.
Pamela: And what allows this to take place is as things form, they don’t necessarily have the long-term stability that they need. They still have all of these resonances that can put them on short time scales, much more elliptical orbits that cause these collisions to take place. Now over time, the orbits do circularize. But even once they’re circular, you can still have resonances that slowly move things. And if this slow migration ends up with things in just the wrong or right, depending on your perspective, kind of alignment, you can end up with what we had, which is Jupiter and Saturn going around such that for every two times Jupiter goes around the sun, Saturn goes around once.
And gravitationally, anything that hadn’t already been flung somewhere is now gonna get flung somewhere.
Fraser: Yeah, and I think you’ve mentioned in the past that there’s still a chance that some of the planets will get thrown out by Jupiter.
Pamela: And this is the long-term, slow effects that we model over the course of thousands and millions of years in our computers where we can see how the processing of our own Earth’s orbit, which isn’t a perfect circle, and the procession of all the other not quite circular orbits leads to different alignments over time. We see the Martian pole wandering over time because it doesn’t have a giant moon like we have.
Very few things are in any permanent kind of an alignment, and I don’t think anything in our solar system except for maybe the sun, and even it is only on like millions of years, fairly permanent – nothing has a permanent alignment. Because all of these slight shifts, all of these slight processions can lead to new resonances building up and flinging something hither and yon.
Fraser: Is that the end of the story? You talk about there can still be some interactions, some slight instabilities that build up over time and Jupiter throws Mercury out of the solar system, for example.
Pamela: That’s not going to happen.
Fraser: But could there be – I mean, are there more mechanisms in play? As the sun dies and it loses its mass, will we see another round of this?
Pamela: Yes. So, our sun is constantly losing mass. And this means that very gradually over time, everything is migrating outwards a little bit. Now, eventually, it’s going to also expand out as it undergoes a change in the kinds of a nuclear burning that are going on in its core. And this change and this massive expansion coupled with the mass loss that is going to predate this is going to eat some of the planets in the solar system, is going to move some the other planets in the solar system. And this redistribution will, of course, change what resonances are possible as everything moves.
Now, you also have the continued possibility of things, like well there are 60 km objects in the centaur belt which are not entirely stable and could get flung in our direction. And that’s not necessarily going to change our orbit that much, but who knows what else it could hit along the way and change its orbit.
Fraser: Right.
Pamela: And so, all sorts of collisions are possible, and you never know when we’re going to be affected by another solar system. We orbit our Milky Way.
Fraser: So, do you think that we will eventually have a single model? With things like James Webb, they’re gonna be able to see newly forming planetary systems and watch those little gaps moving around. Will we end up eventually with some unified model of being able to calculate how planets moved around and where they are likely to end up, and finally know what a planetary system should look like based on all the factors?
Pamela: Well, I think what we’re eventually gonna end up with is a better understanding of all the things that need to go into our computer models, and quantum computers and the ability to say “here is all the stuff that can happen. Universe – go.” And then we’re gonna realize the universe is still finding stuff we didn’t include in our models. I really think that this is going to stay one of those things where the universe remains more creative than we are in all of the diversity that is actually created. There is gonna be multiple ways for the same situation to arise.
And since humans are short-lived, we’re always gonna have to say “well, here are all the different ways you can get that,” and we still may be missing something in our understanding of the universe.
Fraser: I can’t wait for us to discover the weirdness and we’ll make another weird issues episode. Pamela, do you have some names for us this week?
Pamela: I do. As always, our show is supported through the generous contributions of people on Patreon. If you would like to support our show, this is how we pay for our servers, our software, and Susie, Susie being the most important of those three. You can support all of these things by going to patreon.com/astronomycast. This week, we would like to thank Sciaran Svar, Ed Steven Shewater, Gordon Dewey, Bill Hamilton, Frank Tippen, George Thorwald, Richard Riviera, Alexis Thomas Upstrup, Sylvan Wesby, Jeff Collins, John Drake, Arctic Fox, Marek Videry, Nate Detweiler, James Platt, and Ron Thorson. Thank you.
Fraser: Thank you, Pamela, and we’ll see you next week.
Pamela: Bye-bye everyone.
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 information@astronomycast.com, tweet us @astronomycast, 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 Searle, and the show was edited by Susie Murph.
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Duration: 29 minutes
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