Speaker 1: Hey, org, did you share a room with siblings when
Speaker 1: you were a kid?
Speaker 2: I did. I shared a room with my brother.
Speaker 1: Ooh, And was that like cozy and fun for the
Speaker 1: two of you? Or did you get on each other's nerves?
Speaker 3: It was pretty fun. We get along pretty good. How
Speaker 3: about you?
Speaker 1: I shared a room with two brothers and there was
Speaker 1: not a whole lot of coziness there. We got on
Speaker 1: each other's nerves a lot.
Speaker 2: Yikes. Sounds intense.
Speaker 1: Yeah, I remember after one argument my mom telling us
Speaker 1: if we couldn't get along, we'd have to live outside. Intense.
Speaker 3: WHOA, sounds intense? But is that why you like camping
Speaker 3: so much? Because you did end up outside in the tent?
Speaker 3: That's that where your love of the stars came from.
Speaker 3: This is your origin story. It's all because of your brother,
Speaker 3: your nemesis or nemesi.
Speaker 1: Is how I extracted something beautiful from a difficult story.
Speaker 3: Sounds like a hallmark. We we know how you overcame,
Speaker 3: sibling Riberry.
Speaker 1: Depends on whether it ends well or not.
Speaker 2: I guess only ends and one of you dies.
Speaker 3: Hi am Jorhemick, cartoonist and the author of Oliver's Great
Speaker 3: Big Universe.
Speaker 1: Hi, I'm Daniel, I'm a particle physicist and a professor
Speaker 1: at u C Irvine, and I've been totally eclipsed by
Speaker 1: my younger brother.
Speaker 3: Oh boy, is he a more shiny star or something.
Speaker 1: He's taller than me, he's a professor at a fancier
Speaker 1: university than I am. What else is there?
Speaker 2: But does he have a podcast?
Speaker 1: There you go. I don't know if he wants a podcast,
Speaker 1: but yeah, that's a good point. I'm going to bring
Speaker 1: that up at Thanksgiving.
Speaker 3: Thanks You know, it's super hard to do a podcast,
Speaker 3: or at least the start one. There's a high bar
Speaker 3: for putting things on the internet. They don't just let
Speaker 3: anyone post things on the internet, you know.
Speaker 1: I guess we'll find out if he listens to the
Speaker 1: if he responds to this.
Speaker 2: Oh boy one.
Speaker 3: In case you're listening, Hello, Daniel's brother. It sounds like
Speaker 3: we should have you on a podcast and break it
Speaker 3: down Oprah style.
Speaker 1: He's been on the podcast once before when we talked
Speaker 1: about artificial intelligence because he's a machine learning professor.
Speaker 3: Oh I thought you were going to say he's a
Speaker 3: machine that too. But anyways, welcome to our podcast. Daniel
Speaker 3: and Jorge explain the Universe a production of our Heart
Speaker 3: Radio in.
Speaker 1: Which we try not to eclipse your knowledge of the universe.
Speaker 1: We try to shine a light on it. We think
Speaker 1: everybody should be cozy with the physics of the universe,
Speaker 1: snuggling up to a deep understanding of what's going on
Speaker 1: out there, how it all works, how it started, and
Speaker 1: what story it tells us about where we live and
Speaker 1: where we will live in the future.
Speaker 2: That's right.
Speaker 3: We tried to be your big brother in terms of
Speaker 3: telling you how the universe works and what we've learned
Speaker 3: from our mistakes and our discoveries so that you can
Speaker 3: navigate this fantastic universe with a little bit more ease
Speaker 3: and a little bit more confidence.
Speaker 1: I'm not sure Big Brother has the meditations we're looking for.
Speaker 1: You know, it's a little bit overwhelminging, isn't it.
Speaker 3: M not necessarily Isn't there like a Big Brother program
Speaker 3: where you mentor kids.
Speaker 2: That's a positive thing too.
Speaker 1: Yeah, there you go. We're not telling you what to
Speaker 1: think of what not to think. We're just teaching you
Speaker 1: about the universe.
Speaker 2: That's right.
Speaker 3: And there is a lot to know about the universe
Speaker 3: and to discover and to find out because it is
Speaker 3: pretty interesting, pretty complex, pretty vast, and also microscopic in
Speaker 3: the way that it reveals its secrets.
Speaker 1: And one surefire way to figure out how the universe
Speaker 1: works is to ask basic questions about it. To look
Speaker 1: up at the night sky and ask why does this
Speaker 1: do this? And why does this not do that? How
Speaker 1: can we see this happening and not some other thing happening.
Speaker 1: What are the rules of the universe that allow us
Speaker 1: to have huge planets like Jupiter but not other situations
Speaker 1: like planets shaped like a pretzel.
Speaker 3: Yeah, because I guess you can look around and wonder like,
Speaker 3: are we a result of the rules of the universe
Speaker 3: or are we like an exception to the rules of
Speaker 3: the universe.
Speaker 1: Well, we definitely a results of the rules of the universe,
Speaker 1: if you believe the universe has rules and it follows them.
Speaker 1: But there might be weird outcomes and there might be
Speaker 1: standard outcomes like it. It could be that our solar system
Speaker 1: is very unusual as an example of things in the galaxy,
Speaker 1: or it could be that were totally vanilla.
Speaker 3: Yeah, because as humans here on planet Earth, we only
Speaker 3: really have one view of one planet that we can
Speaker 3: study up close so far, and so it makes you
Speaker 3: wonder if other planets are the same, or if humans
Speaker 3: could have lived in other planets, could things have been
Speaker 3: different in our history?
Speaker 1: That's true, and there are other planets nearby that we
Speaker 1: can study, though not quite as up close, to try
Speaker 1: to get more insight into what a planet can be, like,
Speaker 1: what are the various possibilities how planets can turn out?
Speaker 3: And do they get along as siblings? Or have any
Speaker 3: siblings been kicked out of the Solar System and are
Speaker 3: living in intents by the asteroid build That's right.
Speaker 1: We talked recently about those really fun theories that there
Speaker 1: was once an ice giant in the outer Solar System
Speaker 1: that was ejected during a period of chaos.
Speaker 3: WHOA, so you think it just couldn't get along with
Speaker 3: the other planets.
Speaker 1: I'm wondering who the parent is this analogy? Like, is
Speaker 1: it really the Sun's fault that it didn't work out?
Speaker 4: Yeah?
Speaker 3: And how responsible is it to kick your children outside
Speaker 3: and live outside?
Speaker 2: Yeah? Yeah, somebody should call it you universal child services.
Speaker 1: But one thing we do notice about our Solar System
Speaker 1: is that the planets all seem to have their own orbits.
Speaker 1: Jupiter's got an orbit, or Earth has an orbit, Mars
Speaker 1: has an orbit. It's sort of like everybody's got their
Speaker 1: own room.
Speaker 2: They all have their own lane.
Speaker 1: You mean, yeah, exactly.
Speaker 3: Like there's no other Earth on the other side of
Speaker 3: our orbit, right, or didn't scientists think for a while,
Speaker 3: or maybe there was?
Speaker 1: It sounds like a pretty cool science fiction story, right,
Speaker 1: a second Earth on the other side of the Sun.
Speaker 2: Planet X. Wasn't it called Planet X?
Speaker 1: I think planet X is an idea for a tenth
Speaker 1: or now ninth planet that might be out there tugging
Speaker 1: on distant planets, but wouldn't necessarily share an orbit with ours.
Speaker 3: But it's technically is it possible that there's like another
Speaker 3: Earth on the other side of the Sun? Weich just
Speaker 3: have never seen it because it's on the other side
Speaker 3: of the Sun.
Speaker 1: We wouldn't be able to see it directly from Earth.
Speaker 1: But of course we've had probes go all over the
Speaker 1: Solar System. We would have seen it, and we would
Speaker 1: have noticed its gravitational effects on Mars and Venus and
Speaker 1: other stuff in the Solar System.
Speaker 3: So I guess each planet does have its own orbit,
Speaker 3: its own lane.
Speaker 1: In our Solar System, each planet mostly does have its
Speaker 1: own lane. But of course the question is why is
Speaker 1: that and is that typical? So today on the podcast,
Speaker 1: we'll be tackling the question why don't planet share an orbit?
Speaker 1: Is it because they couldn't get along? Yeah?
Speaker 2: And are we the little the younger sibling or are
Speaker 2: we the more accomplished sibling.
Speaker 1: I think the younger sibling is often motivated to eclipse
Speaker 1: the older siblings.
Speaker 2: Boy, it sounds like a lot to impact there in
Speaker 2: your family.
Speaker 1: I'm nothing but proud of my younger brother.
Speaker 3: Let's stick to physics maybe, but yeah, it's an interesting question.
Speaker 3: I guess the implied fact is that no planets in
Speaker 3: our Solar system share an orbit, meaning they're not going
Speaker 3: around the Sun at the same distance.
Speaker 1: Yeah, although you could quibble about that in the case
Speaker 1: of Jupiter. There is some stuff in Jupiter's orbit, not
Speaker 1: another planet, but it does share its orbit with some
Speaker 1: other chunks.
Speaker 3: And I guess the other implied fact is that all
Speaker 3: the orbits don't overlap. I guess right, because most of
Speaker 3: the orbits are pretty much circular, right, They're not like
Speaker 3: ellipses that kind of overlap with each other.
Speaker 1: You mean, like if they intersect, Yeah.
Speaker 3: Like they intersect, or if you look at them from
Speaker 3: the top they're maybe like the two ellipsoids are overlapped.
Speaker 1: Yeah, I think two ellipsoids that overlap and have different
Speaker 1: periods would eventually collide. So I don't think you could
Speaker 1: have that situation for very long.
Speaker 3: But it's true that most of the orbits are pretty
Speaker 3: much circular, right.
Speaker 1: They're all a little bit eccentric. None of them are
Speaker 1: exactly circular, kind of.
Speaker 3: Like you and your brothers. They're all a little eccentric
Speaker 3: as well. I think a little is kind of generous there.
Speaker 3: We're all quite eccentric. Actually called professors or something.
Speaker 1: Exactly how does that happen? But in the case of
Speaker 1: the Solar system, none of the orbits are perfectly circular.
Speaker 1: They're all at least a little bit eccentric. But yeah,
Speaker 1: none of them are overlapping. They basically all have their
Speaker 1: own lanes.
Speaker 3: So the question is why don't two planets have the
Speaker 3: same orbit? So, as usually'll be ever wondering how many
Speaker 3: people out there had thought about this question.
Speaker 1: Thanks very much to our group of volunteers. We'd love
Speaker 1: if you joined them. Right to me two questions at
Speaker 1: Daniel and Jorge dot com, and I'll send the questions
Speaker 1: on over.
Speaker 3: So think about it for a second. Why do you
Speaker 3: think no two planets share an orbit. Here's what people
Speaker 3: had to say.
Speaker 5: I think planets don't share orbits because the center of
Speaker 5: gravity would have to be absolutely stationary, or it'd oscillate
Speaker 5: and shake itself out of sync.
Speaker 2: But I think they actually do. It's just very unlikely
Speaker 2: because it'd be a major coincidence.
Speaker 4: So I'm under the impression that planet's by definition or
Speaker 4: celestial objects orbiting stars that have cleared their orbital path
Speaker 4: of competing debris like asteroids, and that as a planet forms,
Speaker 4: it's gravity gets stronger and it sucks up other objects
Speaker 4: in that orbital path. And that's one of the reasons
Speaker 4: that objects like series are not considered true planets because
Speaker 4: they share their orbit with a number of other large
Speaker 4: asteroids and other computing debris.
Speaker 6: Planets don't share orbits because of the way closters get together.
Speaker 6: If there is a clumpup matter very close to another
Speaker 6: glombal matter, they will make a planet, and the things
Speaker 6: that are fought up are they will make another planet.
Speaker 3: All right, some interesting answers. Some people think it's maybe
Speaker 3: unlikely because there would be a big coincidence.
Speaker 1: Or that gravity just doesn't work that way, that it
Speaker 1: can't pull things together into two planets.
Speaker 3: Oh interesting, but I guess you know, thinking about it,
Speaker 3: like the asteroid built has a whole bunch of mini
Speaker 3: planets and they're all kind of in the same orbit.
Speaker 1: Mm hmm, yeah, absolutely, I.
Speaker 3: Guess we'll dig into that. So first of all, Daniel,
Speaker 3: let's maybe start with the basics. What is a planet
Speaker 3: or what do you define as a planet?
Speaker 1: So a planet famously has a fairly legalistic definition of
Speaker 1: what it is. And remember this is just a rooms
Speaker 1: giving names to things, Like there's stuff out there in
Speaker 1: the universe. The rocks don't care whether you call them
Speaker 1: a rock or an asteroid or a planet or a planetismal,
Speaker 1: They're still out there and doing the physics. This is
Speaker 1: just humans applying like our framework of categorization to the stuff,
Speaker 1: and different humans on a different planet, or aliens whatever
Speaker 1: it might come up with a totally different categorization. It's
Speaker 1: mostly historical. It doesn't really reflect deep underlying physics. But
Speaker 1: it's language and we should all agree what the meanings
Speaker 1: of words are. And so in the case of a planet,
Speaker 1: there are three requirements. One that it's mostly spherical, This
Speaker 1: is basically isn't big enough, because anything that's big enough
Speaker 1: is going to be mostly as fear due to gravity.
Speaker 1: Requirement Number two is that it orbits the Sun and
Speaker 1: not some other object like a planet, otherwise the Moon
Speaker 1: would be a candidate for a planet. And then the
Speaker 1: last one is that it's cleared its path of planetismals
Speaker 1: and other big objects, basically that of all the stuff
Speaker 1: in its lane, it's gathered up all the bits into
Speaker 1: one object.
Speaker 3: Well, it sounds like by definition then a planet cannot
Speaker 3: share an orbit, because a planet in your definition, is
Speaker 3: something that is by itself in an orbit exactly.
Speaker 1: So technically speaking, like the legal answer is no, because
Speaker 1: then it wouldn't be a planet. But really we're asking, like,
Speaker 1: could you have two Jupiters on opposite sides of the
Speaker 1: Sun orbiting in the same orbit. That would be really fascinating.
Speaker 1: Now astronomers from this committee would say, well, technically those
Speaker 1: aren't planets, and we say like, well, we don't really care.
Speaker 1: It's fascinating that they're doing this thing, whether or not
Speaker 1: you call them planets.
Speaker 3: I mean, if there was another Earth orbiting in our orbit,
Speaker 3: just on the other side of the Sun, we wouldn't
Speaker 3: be like, that's not a planet. We would still call
Speaker 3: it a planet, and you'd just be forced to change
Speaker 3: the definition of a planet.
Speaker 1: Yeah. Maybe, Or we'd have t shirts saying like Earth
Speaker 1: isn't a planet, or Earth is a planet, or I'm
Speaker 1: on Team Earth or whatever. It'd be a whole ridiculous
Speaker 1: battle really just over names. You know, where do you
Speaker 1: draw the dotted line?
Speaker 3: But I guess maybe the question is like, why is
Speaker 3: that part of the definition? Why is it important for
Speaker 3: astronomers it a planet? It quote unquote has its own orbit.
Speaker 1: It's a good question, and I don't think the answer
Speaker 1: is just scientific. I think it's historical. You know, we
Speaker 1: try to sometimes reverse engineer these definitions to reflect the
Speaker 1: decisions we've been making historically. We've been calling these things planets,
Speaker 1: and we sort of want to have a definition that
Speaker 1: aligns with the decisions we've already made, even if they
Speaker 1: aren't the decisions we would have made if we knew
Speaker 1: better at the time. You know, early on, when we
Speaker 1: started talking about planets, we didn't understand everything that was
Speaker 1: out there in the Solar System, all the smaller rocks
Speaker 1: that were invisible to us. We didn't realize that there
Speaker 1: was like a full spectrum from tiny rocks to planetisimals,
Speaker 1: to dwarf planets to real planets.
Speaker 3: But I guess maybe the idea that this is part
Speaker 3: of the definition maybe tells me that there are things
Speaker 3: out there that are spherical that orbit the Sun but
Speaker 3: that don't have cleared its path of planetesimals, that are
Speaker 3: maybe as big as some of the things we do
Speaker 3: call planets.
Speaker 2: Is that true?
Speaker 1: Well, basically that's Pluto, right. Pluto got rejected as a
Speaker 1: planet because it was judged to have not sufficiently cleared
Speaker 1: the neighborhood around its orbit of other stuff. Basically, if
Speaker 1: you look in Pluto's orbit, you find other pretty big
Speaker 1: rocks that are roughly the size of Pluto. Pluto is
Speaker 1: just one of an example of lots of we call
Speaker 1: them dwarf planets that far out in the Solar System.
Speaker 1: They have not gathered together sufficiently to say there's one
Speaker 1: really dominant object and nothing else out there.
Speaker 2: Wait wait, wait, wait wait, this was the rule that.
Speaker 3: They kicked Pluto out because of you mean it's not
Speaker 3: because of its size. I always thought it was because
Speaker 3: of its size.
Speaker 1: It's sort of indirectly because of its size. I mean,
Speaker 1: if everything else out there in Pluto's orbit was just
Speaker 1: dust and tiny grains, then they would have said, okay,
Speaker 1: it's a planet. But because there are chunks of rock
Speaker 1: out there that are sort of too big to ignore,
Speaker 1: then you say Pluto hasn't really cleared its orbit. I mean, really,
Speaker 1: technically speaking, nothing has cleared its orbit, because you know
Speaker 1: there's dust and all sorts of other rocks in Earth's
Speaker 1: orbit certainly, right, It's not like it's perfectly empty space
Speaker 1: in Earth's orbit, So you can ask like, well, what
Speaker 1: does it mean to clear its orbit? Even that definition
Speaker 1: gets a little bit fuzzy, but that's the reason why
Speaker 1: Pluto was demoted.
Speaker 2: WHOA, I'm a little bit outraged.
Speaker 3: I feel like this is such a weird technicality to
Speaker 3: have kick Pluto for.
Speaker 1: Well, this is the problem with creating categories, right, You're
Speaker 1: always going to find something on the edge of the category,
Speaker 1: and then you're going to have to try to crisply
Speaker 1: define the category, and then you discover the category is
Speaker 1: just artificial. You're just really drawing dotted lines between a
Speaker 1: smooth spectrum of stuff. Like I remember when we talked
Speaker 1: about space centaurs, the things that are so kind of
Speaker 1: comets and kind of asteroids, And what you discover is
Speaker 1: really the two things are part of a larger community.
Speaker 1: And you've drawn a dotted line between comets and asteroids,
Speaker 1: and it doesn't really make sense to distinguish between them.
Speaker 1: This is just a problem of humans creating categories that
Speaker 1: don't really work.
Speaker 3: But there was sort of like a voter, there was
Speaker 3: a lot of discussion about Pluto. So what is it
Speaker 3: about not having anything in its path that is so
Speaker 3: important to scientists to kick go, you know, change science
Speaker 3: books basically for everybody. You know, why is that important
Speaker 3: whether or not it has little chunks of rocks in
Speaker 3: its path or not.
Speaker 1: I think it's just sociological, Like we look at Earth
Speaker 1: and Jupiter and Mars and Venus and we say this
Speaker 1: is one kind of thing, and Pluto is sort of
Speaker 1: a different kind of thing because it's different in this way.
Speaker 1: Is just one example of many big chunks of rock
Speaker 1: out there in the Pluto orbit. So I think there
Speaker 1: is a distinction to be made between these two different
Speaker 1: categories of objects. Then again, it's sort of fuzzy.
Speaker 3: Meaning like the fact that it has chunks in its
Speaker 3: path is maybe the only thing that sits it apart
Speaker 3: from the others, like none of the other things that
Speaker 3: we call planets have things in its path, and so
Speaker 3: they're using this as an excuse to kick Pluto out exactly.
Speaker 1: And when we talk about the history of the formation
Speaker 1: of the Solar System, you see that it's sort of
Speaker 1: like one step, you know, the Solar System. You have
Speaker 1: the planetary disk, and it gathers into rocks and those
Speaker 1: become planetesimals, and then in some cases they form big
Speaker 1: planets and other cases they just stay a big spread
Speaker 1: of planet isimals, they don't really form planets. So in
Speaker 1: that sense, planets really are sort of like the next
Speaker 1: step in the formation of an object in the Solar System,
Speaker 1: and you've got to respect that or reflect it, or
Speaker 1: at least, you know, describe it.
Speaker 6: You know.
Speaker 3: I guess it would make sense if there were a
Speaker 3: lot of Pluto like planets that look like Pluto or
Speaker 3: the size of Pluto, but didn't clear its path, and
Speaker 3: then maybe I could see like, Okay, if you let
Speaker 3: Pluto in, you have to let all these other things in.
Speaker 3: But is that the case, or is Pluto just like
Speaker 3: a loan border case.
Speaker 1: Well, Pluto is maybe the thing closest to the edge.
Speaker 1: But there are a lot of things out there, you know,
Speaker 1: there aren't a lot of these dwarf planets that you
Speaker 1: might call planets. You know, Series, for example, is a
Speaker 1: dwarf planet, but it's part of the asteroid belt, and
Speaker 1: there's lots of other stuff in the asteroid belt. So
Speaker 1: you can't say that Series really is a planet because
Speaker 1: it didn't gather together all the other bits. So I
Speaker 1: think that is true that once you open the door
Speaker 1: to Pluto, you have to let in lots of other folks.
Speaker 1: I don't know why that's the problem. Like, let's have
Speaker 1: a solar system with hundreds of planets. That sounds awesome
Speaker 1: to be big party.
Speaker 2: Yeah, more savings to fight with.
Speaker 1: But there is something of a distinction here between objects
Speaker 1: that are basically alone in their orbit and objects that
Speaker 1: are not. And I do think it's really interesting to wonder, like,
Speaker 1: could you have two planet like objects orbiting the Sun
Speaker 1: in the same orbit. Why don't we see that in
Speaker 1: our solar system? Is that something you might see in
Speaker 1: other solar systems, et cetera.
Speaker 3: I see, you want to sort of pivot to the
Speaker 3: question of like what would happen if two planets did
Speaker 3: share an orbit, or two large objects like the Earth
Speaker 3: share it an orbit.
Speaker 1: Could that situation be stable? Why don't we see it?
Speaker 1: Could that form at all? I think those are really
Speaker 1: interesting sort of physics questions instead of like category legalistic questions.
Speaker 3: That sounds like something siblings would argue about for no
Speaker 3: good reason. All right, well let's dig into these interesting questions.
Speaker 3: But first let's take a quick break. All right, we're
Speaker 3: asking the question here today why don't planets share an orbit?
Speaker 3: And we just went through a defined print to find
Speaker 3: out that astronomers call a planet something that doesn't share
Speaker 3: an orbit, So technically planets cannot share an orbit. But
Speaker 3: now we're going to pivot a little bit and ask
Speaker 3: the question, well, what would happen if something like the
Speaker 3: Earth share it an orbit with another big thing like
Speaker 3: the Earth. Well, first of all, you would get kicked
Speaker 3: out of the planet category, right.
Speaker 1: Yeah, that's right. If you built an earth sized death
Speaker 1: star and put it in orbit on the other side
Speaker 1: of the Sun, then Earth would no longer be a planet.
Speaker 3: Would you say, maybe the Moon is still something that
Speaker 3: we haven't cleared.
Speaker 1: Well, but the Moon is orbiting the Earth, right, so
Speaker 1: mm hmmm, Oh, I see what you mean. Does the
Speaker 1: Moon disqualify the Earth because we haven't absorbed it into
Speaker 1: the Earth? Oh yeah, these are complicated legal questions.
Speaker 3: That sounds like we need a lawyer. Is the brother
Speaker 3: a lawyer, also an accomplished lawyer.
Speaker 1: Probably he's arguing in front of the Astronomy Supreme Court
Speaker 1: right now.
Speaker 2: Yeah. No, he just broken a machine to do it
Speaker 2: for it.
Speaker 3: But yeah, so I guess we're asking more of a
Speaker 3: physics question, not a technical definition question like could you
Speaker 3: have two giant Earth or to jupiters kind of circling
Speaker 3: each other maybe opposite sides of the Sun or maybe not.
Speaker 2: I don't know. That's kind of the question now, right, Yeah, I.
Speaker 1: Think that's the interesting physics question. You know, is that possible?
Speaker 1: Is there some law physics that prevents that from happening,
Speaker 1: either to stop it from forming or to break it
Speaker 1: up if it did somehow randomly land that way?
Speaker 3: Because I guess the question is have we seen that
Speaker 3: We haven't seen that in our Solar system or have
Speaker 3: we maybe like Pluto has it and anti Pluto out there.
Speaker 1: So we don't have examples of Earth sized objects with
Speaker 1: other Earth sized objects in their orbits. But we do
Speaker 1: have in our Solar system some sort of edge cases,
Speaker 1: Like Jupiter has a whole collection of asteroids that are
Speaker 1: not in the asteroid belt per se, the one you
Speaker 1: think about between Mars and Jupiter, but are actually in
Speaker 1: its orbit. There's two different groups of asteroids that are
Speaker 1: orbiting with jupil Wait.
Speaker 3: Wait, wait, Like on the opposite side of Jupiter from
Speaker 3: the Sun, there's a whole bunch of debris.
Speaker 1: So not on the opposite side of Jupiter. It's sort
Speaker 1: of thirty degrees trailing and thirty degrees ahead of it.
Speaker 1: Because there are several stable points around Jupiter where you
Speaker 1: can balance the gravity of Jupiter and the gravity of
Speaker 1: the Sun, so they cancel out. These are called the
Speaker 1: lagrange points, And in the fourth and fifth Lagrange points
Speaker 1: in front of Jupiter and behind Jupiter in its orbit,
Speaker 1: there's a whole collection of asteroids that are sort of
Speaker 1: hanging out there.
Speaker 2: Whoa Well, does that mean Jupiter is not a planet?
Speaker 1: I know exactly right, Like, has Jupiter really cleared its orbit? Well,
Speaker 1: it's so much bigger than these rocks that I guess
Speaker 1: you can say so. But like if I were Pluto's lawyers,
Speaker 1: I would have raised that example, right right.
Speaker 3: Why didn't anybody raise that example? Was nobody advocating for
Speaker 3: Pluto or four science books in general and not confusing
Speaker 3: the entire human population.
Speaker 1: I'm not going to make the mistake of trying to
Speaker 1: defend any of these definitions, because to me, they're all
Speaker 1: just arbitrary, and they all break down under some scenario.
Speaker 1: And this is an example, you know, and Earth even
Speaker 1: has one of these. Earth has an object like this
Speaker 1: that's in its orbit. That orbit's in one of its
Speaker 1: lagrange points. It's a pretty big rock.
Speaker 3: Wait, what really? How big is it? It's not that big.
Speaker 3: It's like five kilometers in diameter. We've only known about
Speaker 3: it since like nineteen eighty six when it was first spotted.
Speaker 3: It's got this terrible name I won't even try to pronounce,
Speaker 3: but it's spelled c r ui, thh and E. Maybe
Speaker 3: you can pronounce it, maybe, yeah, but not on air apparently.
Speaker 1: Anyway, It's the sort of feature of gravity. You know,
Speaker 1: there are places you can be where you can be
Speaker 1: in a stable orbit, like the James Web Space Telescope
Speaker 1: is in one of these lagrange points relative to the
Speaker 1: Earth and the Sun.
Speaker 3: Well, I think what you mean by stable orbit points
Speaker 3: meaning that it has the same location relative to the
Speaker 3: Earth and it goes around the Sun at the same rate,
Speaker 3: like it takes the same amount of time to go
Speaker 3: around the Sun. That's what you mean by like being
Speaker 3: in a stable position.
Speaker 1: Well, there's two different things there. One is being in
Speaker 1: the same orbit, and that means following the same path,
Speaker 1: taking the same amount of time to go around the Sun.
Speaker 1: The second thing is whether you're stable, and stability beings
Speaker 1: like if you get a little push, do you return
Speaker 1: back to the path you are on or does that
Speaker 1: cause like a cascade where it creates a bigger push
Speaker 1: and then a bigger push, and then a bigger push
Speaker 1: and then you fall away, sort of the way like
Speaker 1: a pencil balanced on its tip is unstable. The tin
Speaker 1: is little push and it will fall over. But like
Speaker 1: a ball in the bottom of a glass is stable.
Speaker 1: You give it a little push, gravity restores it back to
Speaker 1: where it was. So some configurations are stable, meaning that
Speaker 1: gravity will push them back to that configuration if they
Speaker 1: get pushed by a little rock or hit by the
Speaker 1: solar wind or whatever. And if you have two objects
Speaker 1: like the Sun and the Earth, there are five points
Speaker 1: are called the garage points that are stable. Three of
Speaker 1: them are in your orbit, and two of them are.
Speaker 3: Not right, meaning three of them are in the same
Speaker 3: circle that the Earth traces around the Sun, and two
Speaker 3: of them are like one of them a little bit
Speaker 3: further the circle and the other one closer to the Sun.
Speaker 3: And if you're at those positions going at the right speed,
Speaker 3: then you're going to trace a circle kind of along with.
Speaker 1: The Earth exactly. The simplest one to understand is that
Speaker 1: there's a point between the Earth and the Sun where
Speaker 1: the gravity cancels up because the Sun is pulling in
Speaker 1: one way and the Earth is pulling another way. And
Speaker 1: if you're just the right point, it's not halfway between
Speaker 1: the Earth and the Sun, because the Sun is obviously
Speaker 1: more massive and has more gravity, But there is a
Speaker 1: point there where the Earth and the Sun gravity balances out,
Speaker 1: and if you're right there, there's effectively no gravity and
Speaker 1: you could just move with the same period though not
Speaker 1: the same velocity as the Earth and stay there.
Speaker 3: Meaning like you'll go around the Sun in exactly a year,
Speaker 3: just like the Earth.
Speaker 1: Mm hmm, exactly.
Speaker 3: That's what it means to kind of share an orbit
Speaker 3: in that case, you would have a different radius, so
Speaker 3: you'd have the same period, but it wouldn't really be
Speaker 3: the same orbit. But there are three of these points
Speaker 3: that are actually in the same orbit, meaning you're following
Speaker 3: the same path. One of them is on the other
Speaker 3: side of the Sun from the Earth, as you said,
Speaker 3: And that's very intuitive, right, and because you're like exactly
Speaker 3: balancing the Earth, and so you could just be like
Speaker 3: constantly a hundred eighty degrees out of phase with the Earth.
Speaker 3: And then there are two points thirty degrees behind and
Speaker 3: thirty degrees ahead of the Earth that also have this
Speaker 3: special gravitational balance where the Sun and the Earth effectively
Speaker 3: neutralize each other's gravity.
Speaker 2: And does it depend on how big you are or
Speaker 2: how heavy you are.
Speaker 1: So the location of some of these points do depend
Speaker 1: on the mass ratios, but the other ones are just geometric.
Speaker 1: So Jupiter has them, Earth has them. All the planets
Speaker 1: have these lagrange points, and that's why, for example, Jupiter
Speaker 1: has this collection of asteroids behind it and ahead of it,
Speaker 1: because they're hanging out at one of these lagrange points.
Speaker 3: Okay, so I think what we're trying to say here
Speaker 3: is that each planet has an orbit and each orbit
Speaker 3: sort of has these spots where you could maybe put
Speaker 3: in another planet and it would still be stable, and
Speaker 3: both of them keep going around the Sun, like it's possible.
Speaker 1: It's possible. One tiny little wrinkle there is that some
Speaker 1: of these logrange points are stable, some of them are unstable.
Speaker 1: There are all locations where the gravity balance is out
Speaker 1: and if you're exactly at the right spot, you can
Speaker 1: stay there for ever. But some of them are unstable,
Speaker 1: meaning if you deviate a tiny little bit, it's like
Speaker 1: a pencil leaning over on the table. It's going to
Speaker 1: fall over and you're not going to return. Where some
Speaker 1: of them are stable, meaning that if you deviate a
Speaker 1: little bit, you'll come back. So the fourth and fifth
Speaker 1: le Graunge points, so one ahead and behind you in
Speaker 1: the orbit, are actually stable locations. So yeah, and principle,
Speaker 1: you could have another Earth that's not on the other
Speaker 1: side of the Sun, but just like thirty degrees behind
Speaker 1: us in our orbit, and it could be there and
Speaker 1: be stable gravitationally.
Speaker 3: But didn't you say it sort of depends on the mass,
Speaker 3: like and you can imagine if I put a James
Speaker 3: Web telescope, it'll be stable there, or maybe a small
Speaker 3: asteroid or five kilometer rock. But if I put a
Speaker 3: whole Earth, wouldn't it just destabilize the whole thing? Or
Speaker 3: wouldn't it be totally a different point?
Speaker 1: If you put another Earth there, it would be stable,
Speaker 1: Like the situation is symmetric and they could both survive there.
Speaker 1: There are mass limitations, like if you put a star
Speaker 1: there that's much more massive than the Earth I think
Speaker 1: is like a limit of like twenty five times the
Speaker 1: mass of the Earth, then make some assumptions it doesn't
Speaker 1: work anymore. But you could put a pretty massive planet
Speaker 1: there and it would be stable.
Speaker 3: Interesting. But then now the question is why isn't there
Speaker 3: something there? Because I'm sure at the beginning of the
Speaker 3: Solar system they're asteroids everywhere, there are rocks everywhere. Why
Speaker 3: didn't those two points start to gather things? And why
Speaker 3: don't we have a little twin Earth.
Speaker 1: The answer to that is that we don't really know.
Speaker 1: I mean, we think that in the formation of a
Speaker 1: Solar system, it's possible for it to happen. Remember the
Speaker 1: story we told earlier. We start from a big cloud
Speaker 1: of gas and dust and leftover bits from other solar
Speaker 1: systems that have died and that collapses most of it
Speaker 1: into the star, but like one percent of it stays
Speaker 1: in this proto planetary disc, a bunch of heavy metals
Speaker 1: and gas and dust and ice that is moving too
Speaker 1: fast to fall into the stars. The star gobbles up
Speaker 1: mostly gas and leaves behind this protoplanetary disc. And then
Speaker 1: gravity does this thing. It starts from little seeding locations there,
Speaker 1: little dots of heavy metal or little gravitational spots that
Speaker 1: have over densities. Starts to cluster together other stuff, and
Speaker 1: you get the string of rocks. So now instead of
Speaker 1: having like a disc, you have a bunch of rings,
Speaker 1: rings of these rocks of various sizes, which then gather
Speaker 1: together and form stuff. And so one option is that
Speaker 1: you know it forms into a planet. There's like one
Speaker 1: dominant thing that pulls out all together into a planet.
Speaker 1: Another option is that it just sort of stays a
Speaker 1: ring of rocks because of tidal forces from neighboring planets
Speaker 1: that prevent it from gathering together. But there's nothing that
Speaker 1: says in physics that you couldn't have two objects coalescing.
Speaker 1: You know that two things couldn't have pulled together sort
Speaker 1: of an each other's lagrange points and ended up being
Speaker 1: what looks like two planets, although you know the astronomers
Speaker 1: would have said neither of them are planets.
Speaker 3: Well, I feel like maybe we skipped the step there.
Speaker 3: So you're saying, like the early Solar system was a
Speaker 3: flat disc and then the stuff that was orbiting the
Speaker 3: Sun or the new Sun kind of arrange itself into rings,
Speaker 3: sort of like maybe Saturn's rings. So you can imagine
Speaker 3: the Sun in the middle a bunch of rings, just
Speaker 3: like Saturn has rings of rocks, and then those rings
Speaker 3: eventually collapse into planets. Now, what's the process for that, Like,
Speaker 3: what causes a ring of rocks to suddenly collapse into
Speaker 3: a giant ball on one specific spot.
Speaker 1: Well, that's gravity. Also, you know you have one spot
Speaker 1: along the ring that's denser than another, and so it's
Speaker 1: going to pull on stuff nearby, stuff that's ahead of it,
Speaker 1: it's going to pull closer. The stuff that's behind it,
Speaker 1: it's going to pull closer. And then as it gathers
Speaker 1: more stuff, it's going to have more gravity. It's gonna
Speaker 1: be able to reach further along that ring and essentially
Speaker 1: grab that stuff together.
Speaker 3: But I can see that for gathering the things around
Speaker 3: it but what about the things that we're on, like
Speaker 3: on the opposite side.
Speaker 1: Of the ring. I think the answer is that we
Speaker 1: aren't one hundred percent sure how that happens. We don't
Speaker 1: know for example, if you can really form stuff on
Speaker 1: the other side of the Solar System that stays there,
Speaker 1: like for example, Jupiter's asteroids. Did those form? There is
Speaker 1: an example of exactly what you're talking about, stuff forming
Speaker 1: along that same ring and not getting absorbed into the
Speaker 1: planet basically resisting because it's in a lagrange point and
Speaker 1: it's gravity is to totally balanced. Or is that stuff
Speaker 1: that came later? Did Jupiter actually clear its own path,
Speaker 1: use up all the stuff in the ring, and then
Speaker 1: later on stuff fell into Jupiter's legrange points. We just
Speaker 1: don't know the answer to that. If stuff really can
Speaker 1: form stably at the same time as a planet, that's
Speaker 1: what you're asking, right.
Speaker 3: Well, I think i'm asking like it once we had
Speaker 3: a ring of rocks sort of like Saturn has rings.
Speaker 3: Is it the case that each ring could only clasp
Speaker 3: into one planet because of the bath Basically like the
Speaker 3: math doesn't let you make more than one big planet
Speaker 3: because anything else would be unstable.
Speaker 1: No, the math would let you imagine a perfectly symmetric ring,
Speaker 1: and then imagine like ten or twelve or fifty tiny
Speaker 1: points perfectly spaced around that ring that are a little
Speaker 1: bit heavier. Those would gather up all the stuff around them.
Speaker 1: You'd end up with like ten or twelve or fifty
Speaker 1: or whatever identically sized objects in an orbit around the Sun.
Speaker 1: Physically and mathematically, it is nothing preventing that from happening.
Speaker 1: I think the reason why it's not likely to happen
Speaker 1: is that it requires a lot of symmetry balance for
Speaker 1: that arrangement to get set up. It's much more likely
Speaker 1: that one of them is bigger and one of them
Speaker 1: is smaller, and then the bigger when it eats the
Speaker 1: smaller one.
Speaker 3: But I feel like you told me that before that
Speaker 3: there's only like two stable spots around and stable orbit
Speaker 3: where other things can be. You know, if I form
Speaker 3: four miniplanets along the Earth's orbit, that wouldn't like some
Speaker 3: of them be unstable.
Speaker 1: It gets much more complicated as soon as you add
Speaker 1: more than two objects. But no, you could have that
Speaker 1: stable arrangement. You could have like a thousand planets in
Speaker 1: a stable orbit around the Sun, as long as they're
Speaker 1: perfectly equally spaced in equal mass. That's also allowed. Earlier,
Speaker 1: we were just talking about the two planets around the Sun.
Speaker 1: But if you allow them for more than two planets,
Speaker 1: there's a lot more configurations you could have, but they're
Speaker 1: also much more unstable, like they need to be perfectly
Speaker 1: balanced in mass. In fact, I found some guy on
Speaker 1: the web who's done a bunch of simulations of like
Speaker 1: crazy solar systems.
Speaker 2: You know, we have to say, some guy on the web, Yeah,
Speaker 2: what this is? Okay?
Speaker 6: Mm hmm.
Speaker 1: I found some guy in the web who posted a
Speaker 1: blog about simulations he had done about crazy solar systems
Speaker 1: where you have like sixty jubiters in orbit around the
Speaker 1: Sun and it's stable, Like if you arrange them perfectly,
Speaker 1: sixty jupiters can stay in orbit around the Sun if
Speaker 1: you set them up perfectly.
Speaker 3: I see, I see. But how do you know he's right?
Speaker 3: I mean, no offence. But if I told you that
Speaker 3: some guy in the internet it's only something, would you
Speaker 3: assume it's true?
Speaker 1: No, But this one makes sense. I mean, just from
Speaker 1: symmetry arguments, a ring could collapse and do a bunch
Speaker 1: of objects as long as it does it symmetrically, then
Speaker 1: it's still stable. Every one of those objects is the
Speaker 1: same as any other objects, so it feels the same
Speaker 1: gravity from all the other ones. They all cancel out essentially.
Speaker 2: But I wonder how true that is. I don't know.
Speaker 3: I mean not that I don't trust your guy on
Speaker 3: the internet, but you know, at some point, maybe, like
Speaker 3: if you have four things going around the Sun, maybe
Speaker 3: the angles and the way they interact with each other,
Speaker 3: and depending on how big they are, maybe it would
Speaker 3: make it un.
Speaker 1: I think it's a pretty simple extension of the argument
Speaker 1: for why you don't feel gravity from anything that orbits
Speaker 1: the Sun at like the same radius as you or
Speaker 1: larger or for example, as you dig into the Earth,
Speaker 1: you're not feeling gravity from layers of the Earth that
Speaker 1: are larger than you because they all add up to
Speaker 1: cancel out. There are fewer that are closer to you
Speaker 1: and more that are further and they all balance out.
Speaker 1: It's basically the same argument. It's like gravitational shell argument.
Speaker 1: If you have a whole string of earths in orbit
Speaker 1: with you, all of their gravity will cancel out.
Speaker 2: All right.
Speaker 3: Well, it sounds like we have a big mystery, which
Speaker 3: is that it sounds like it's possible for two planets
Speaker 3: to share an orbit definitions notwithstanding, But we don't really
Speaker 3: see that in our solar system or maybe in other
Speaker 3: solar systems out there in space. So let's dig a
Speaker 3: little bit more into that mystery. But first, let's take
Speaker 3: a quick break. All right, we're asking the question why
Speaker 3: can't planets share? What's going on? Why are they so selfish?
Speaker 1: It's the parent's fault.
Speaker 3: It's always the parent's fault. But yeah, the planets like
Speaker 3: to be loners. They don't like to share an orbit.
Speaker 3: And we sort of know that mostly from what we
Speaker 3: can see, right, because it sounds like theoretically it is
Speaker 3: possible to have like two Earth orbiting or maybe for
Speaker 3: Earth orbiting the same circle around the Sun. But we
Speaker 3: just don't see that, and so the question is like
Speaker 3: why not?
Speaker 1: Yeah, I think that mathematically it's possible. If you set
Speaker 1: up a solar system that way, you're like a solar
Speaker 1: system builder, and you bring into Jupiter's and you align
Speaker 1: them perfectly, you could build a solar system like that
Speaker 1: which would be stable and last a long time.
Speaker 6: You know.
Speaker 1: The other question is would a solar system like that
Speaker 1: form naturally? I think they're. The answer is that it's
Speaker 1: most likely for things to collapse into one big planet,
Speaker 1: or for things to not really collapse at all, like
Speaker 1: Pluto or the asteroid belt because of tidal forces, or
Speaker 1: they're just two distant gravity. And for things to collapse
Speaker 1: into two really big or three big objects would require
Speaker 1: a sort of a perfect symmetry where they like divide
Speaker 1: up the mass budget into two or three portions and
Speaker 1: each of them gather it up themselves. I think that
Speaker 1: just requires a lot of balance for it to happen.
Speaker 3: Like it basically a big coincidence you're saying. But I
Speaker 3: guess maybe paint the scenario for us. So we have
Speaker 3: initially around the young Sun sort of a ring of rocks.
Speaker 3: Let's say, like there's a ring of rocks around where
Speaker 3: Earth goes around the Sun in the Earth's orbit, and
Speaker 3: maybe there's a little bit more more rocks in one spot,
Speaker 3: and so that one starts to gather more things. But
Speaker 3: there's a whole bunch of things all around the circle.
Speaker 3: Does that mean like the things on the other side
Speaker 3: of the orbit somehow speed up in order to catch
Speaker 3: up to the Earth or slow down. What causes those
Speaker 3: things to slow down or speed up, and if they did,
Speaker 3: wouldn't they change orbits?
Speaker 1: No, you're right, something on the other side of the Earth,
Speaker 1: like perfectly opposed to the Earth feels no gravitational tug. Right,
Speaker 1: the Earth cannot pull that thing into itself because it's
Speaker 1: at a labraange point, right, So something that's there will
Speaker 1: stay there. But that's a really tiny spot, the actual
Speaker 1: exact lagrange point. Anything slightly ahead of it or slightly
Speaker 1: behind it will feel a gravitational tug from the Earth,
Speaker 1: and eventually the Earth will pull it into itself.
Speaker 3: But it has to go all the way around the circle,
Speaker 3: meaning like it speeds up in the orbit.
Speaker 2: But if it speeds up, wouldn't it change orbits?
Speaker 1: Yeah, that's possible. Also, the Earth could tug it, not
Speaker 1: so that it ends up in the Earth, but that
Speaker 1: it falls into another orbit or falls into the Sun. Right.
Speaker 1: And remember that this is a very simplified way of
Speaker 1: thinking about the Solar System, just one planet and the
Speaker 1: Sun and one rock. In reality, there's lots of other
Speaker 1: things going on there, so lots of chaotic tugs from
Speaker 1: Jupiter and Mars as it passes by, so all sorts
Speaker 1: of stuff disrupting this pile of rocks, some of them
Speaker 1: falling out of this orbit and landing on Venus or
Speaker 1: landing on Mars, or some of them ending up on Earth.
Speaker 1: That's why Earth has rocks from all over the Solar
Speaker 1: System that are landing on it, not just things from
Speaker 1: our orbit.
Speaker 3: Oh I see you're saying, like maybe the picture I
Speaker 3: had of how planet's form is not quite correct, Like
Speaker 3: you know, maybe to go from the equivalent of Saturn's
Speaker 3: rings around the Sun to a planet, it doesn't mean
Speaker 3: like a ring of rocks is kind of collapsed into
Speaker 3: a planet, like Earth might be made out of the.
Speaker 2: Rocks from different rings.
Speaker 1: Absolutely it is.
Speaker 2: Other planets might be made from rocks from other rings.
Speaker 1: Absolutely, Yeah, there is is not just made from rocks
Speaker 1: from one specific range of radii. Definitely, stuff has contributed
Speaker 1: from the inner Solar System and from further out. Absolutely
Speaker 1: there's a big mix.
Speaker 2: Oh I see.
Speaker 3: So like the history of the Solar System is that
Speaker 3: it pour into a disc then rings. Then it was
Speaker 3: a free for all or all the siblings for fighting
Speaker 3: over who gets which toys and which rocks, and then
Speaker 3: and then whoever was left victorious, whoever it was bigger
Speaker 3: one exactly yeah, and whoever, I couldn't get along sleeping
Speaker 3: outside in the tent.
Speaker 1: And that's mostly the story. And to understand whether that's
Speaker 1: the story the Solar system, we look around if there's
Speaker 1: like weird stuff happening, you know, we'd love to have
Speaker 1: seen two planets in the same orbit so we could
Speaker 1: try to understand how that happened. There are some really
Speaker 1: fascinating and interesting counter examples to this that we see
Speaker 1: even in our own Solar system, like the moons of Saturn.
Speaker 2: What do you mean, what's going on with the moons
Speaker 2: of Saturn.
Speaker 1: So Saturn's got lots of moons, and there's two in
Speaker 1: particular that swap orbits. So there's the moon Janus and
Speaker 1: then there's the moon Epimetheus, and these two swap orbits
Speaker 1: every four years. Like Janus is on the outside and
Speaker 1: Epimetheus is on the inside, which has a short orbit
Speaker 1: and it comes really close to Janus and tugs on it,
Speaker 1: and the gravitational interaction means that they end up swapping.
Speaker 1: So now Genus is on the inside and Epimetheus is
Speaker 1: on the outside.
Speaker 3: Well, well do they swap orbits or it's just that
Speaker 3: they both have really complicated orbits that overlap each other.
Speaker 1: Well, there's two different radii and for four years, one
Speaker 1: of them has the inner one and the other one
Speaker 1: has the outer one, and then they swap. So you
Speaker 1: can think about it two ways, like one is they
Speaker 1: have different lanes and they're changing lanes, or you could
Speaker 1: think about it in the more general sense, like each
Speaker 1: moon does four laps on the outer one and then
Speaker 1: four laps on the inner one, and they're perfectly synced
Speaker 1: to never be on top of each other.
Speaker 3: And the reason they change lanes is from the where
Speaker 3: they interact with each other, or just the way they
Speaker 3: interact with Saturn, the.
Speaker 1: Way they interact with each other, like the one on
Speaker 1: the inner lane catches up to the one on the
Speaker 1: outer lane and tugs on it, pulling it in, and
Speaker 1: the gravitational interaction pushes the one from the inner lane out.
Speaker 3: Well, meaning sort of like a younger sibling who's motivated
Speaker 3: to catch up to its older sibling and then or
Speaker 3: takes it for four years.
Speaker 1: What else motivates younger siblings If not that, I mean
Speaker 1: that's basically it, right.
Speaker 3: Wait, are you trying to take credit for your brother's accomplishments?
Speaker 3: Is this what this is all about.
Speaker 1: That's right?
Speaker 3: Is this why this whole episode is just the far
Speaker 3: you to take some of your brother's glory.
Speaker 1: My entire life is just nothing but setting the stage
Speaker 1: to take credit from a younger brother.
Speaker 3: That's all right, Yeah, okay, you're trying to overtake him
Speaker 3: and steal his orbit.
Speaker 1: Yeah. The whole thing is a fifty year long con man.
Speaker 2: The whole thing is a therapy session.
Speaker 1: I feel like, Oh, in the end, you know, you're
Speaker 1: defined by the circumstances in which you're born, just like
Speaker 1: Saturn and Janus and Epimetheus doomed to do this dance forever.
Speaker 1: But it's really fascinating to see this like every four years.
Speaker 1: And it's a funny story because when these moons were discovered,
Speaker 1: they didn't realize there were actually two moons there basically
Speaker 1: in the same orbit. They saw one, and then somebody
Speaker 1: else was looking at that moon and realizing, huh, this
Speaker 1: doesn't look like the same moon that was previously reported,
Speaker 1: but it's in the right orbit. What's going on? And
Speaker 1: took people a while to figure out, actually the two
Speaker 1: moons here that are swapping orbits?
Speaker 3: Whoa and does the swapping happen like really fast or
Speaker 3: over years as well.
Speaker 1: The swapping happens pretty fast. I mean it's every four
Speaker 1: years that happens, but the swap itself doesn't take years.
Speaker 3: And could something like that happen elsewhere or is this
Speaker 3: like a super duper bizarre circumstance.
Speaker 1: It's a pretty bizarre sir cumstance. You need exactly the
Speaker 1: right radii and exactly the right masses. We also don't
Speaker 1: know how long it can go on for. You know,
Speaker 1: it's pretty chaotic, and so it seems like something else
Speaker 1: passing nearby gives just the right tug and one of
Speaker 1: these things just plummets into Jupiter. But it's an example
Speaker 1: of how really weird, rare stuff can happen in the
Speaker 1: Solar system. And it might mean that even if two
Speaker 1: big planets forming in the same orbit seems unlikely because
Speaker 1: you need just the right balance, it might happen. It
Speaker 1: might happen in other solar systems. It might happen more
Speaker 1: than we even expect.
Speaker 3: Well, it sounds like it might happen just from how
Speaker 3: random and chaotic the you know, young Solar system is, right, Like,
Speaker 3: you know, maybe you wouldn't get two plants from the
Speaker 3: same ring of rocks. But maybe, you know, you could
Speaker 3: get the Earth and then something like Mars drifts into
Speaker 3: our orbit or something, or we swap orbits with Mars,
Speaker 3: just like these two moons. That's totally possible, right.
Speaker 1: It's totally possible, And some people think that something like
Speaker 1: that might have been a cause for the collision actually
Speaker 1: between the proto Moon and the proto Earth. The theory
Speaker 1: of the Moon's formation is that there were two proto
Speaker 1: planets that slammed into each other that formed the Earth
Speaker 1: in the Moon, and it could have been like two
Speaker 1: planets that formed separately and then got too close to
Speaker 1: each other, or maybe they were in each one of
Speaker 1: each other's lagrange points for a while, but it wasn't
Speaker 1: stable and then it ended up colliding.
Speaker 3: And it sounds like it could still happen maybe in
Speaker 3: our Solar system, Like you know, those meteors that are
Speaker 3: orbiting with Jupiter ahead and behind it, those could kind
Speaker 3: of maybe cluster together into something that might look like
Speaker 3: a planet, couldn't they.
Speaker 1: Yeah, eventually they might unionize and work together and form
Speaker 1: their own planet, and then they could protest Jupiter and
Speaker 1: they could get Jupiter demoted from being a planet or
Speaker 1: Pluto upgraded. You never know once you start an astronomical
Speaker 1: lawsuit what happens.
Speaker 3: Right, it might be like a planetary conspiracy and they
Speaker 3: all get you know, sued together.
Speaker 1: Maybe we just get rid of this whole name for
Speaker 1: a planet. We just stuff out there, man.
Speaker 3: Unless you just call them, yeah, rocks, big floating rocks,
Speaker 3: unless they're made out of gas.
Speaker 1: Oh no, there's big planets the size of the.
Speaker 3: Balls, just calling balls if it's circular, and as southern space,
Speaker 3: just call space balls.
Speaker 1: I know. And they even require these things to be spherical,
Speaker 1: and none of them actually are sphericle, right, even the
Speaker 1: Earth is not technically spherical.
Speaker 3: Oh boy, so it's a lawsuit waiting to happen. Well,
Speaker 3: how about out there beyond our Solar system? You know
Speaker 3: now we can see with our telescopes really far away
Speaker 3: distant stars and distant planets. Have we seen two planets
Speaker 3: share in orbit out there in the wider universe?
Speaker 1: We have not yet seen it, and we've looked. You know,
Speaker 1: we are pretty good at seeing planets around stars in
Speaker 1: other solar systems in some scenarios. And we can tell
Speaker 1: because those planets like orbit the star and eclipse it,
Speaker 1: or they tug on the star, and we can tell
Speaker 1: about the change and the light from the star. And
Speaker 1: so it's looking for the wobble in the star and
Speaker 1: dips in its brightness that give us clues. And from
Speaker 1: those dips or from those wobbles, we can get a
Speaker 1: sensul like the period of the planet. And so far
Speaker 1: we've never seen like two waters or dips with the
Speaker 1: same period that would indicate like co orbiting planets. So
Speaker 1: so far we haven't seen anything like that.
Speaker 3: I feel like maybe there's something else going on here,
Speaker 3: maybe something that physicists haven't thought about, because it seems possible,
Speaker 3: it seems sort of not impossible. And given so many
Speaker 3: planets and asteroids and things out there floating in space
Speaker 3: in our Solar system, and also all of the trillions
Speaker 3: of Solar systems we can see out there that we
Speaker 3: haven't seen one, it seems like there's something going on.
Speaker 1: There's a conspiracy. Remember that we've looked at only several
Speaker 1: thousand stars to see if there are planets around them,
Speaker 1: and there's billions and billions of stars in the galaxy.
Speaker 1: That might mean that it's unlikely and not that common,
Speaker 1: but it doesn't mean it doesn't happen. In fact, there
Speaker 1: are astronomers that used a radio array in Chile to
Speaker 1: look at a planetary system that's still forming. There's a
Speaker 1: young star like three hundred and seventy light years from Earth,
Speaker 1: and it's not done making its planets, like they see
Speaker 1: exoplanets forming around it, but it's still got a really
Speaker 1: big disc of protoplanetary stuff. And when they studied this system,
Speaker 1: they found a big blob of dust in one of
Speaker 1: the lagrange points near that exoplanet. So that might be
Speaker 1: like a coplanet that's forming, or it could be that
Speaker 1: whatever this conspiracy is, you know, breaks that up before.
Speaker 3: It can happen, Like maybe it's not as stable as
Speaker 3: you think it is or something. That's what you're saying.
Speaker 1: Right, Maybe it's technically possible, but this requires such ridiculous
Speaker 1: balance between all the factors that's never practically achieved in
Speaker 1: the universe.
Speaker 3: All right, well, it sounds like maybe the answer to
Speaker 3: the question of why don't you have two planets sharing
Speaker 3: in orbit. The answers that are like, we don't know.
Speaker 3: It seems possible, but we just haven't seen it yet.
Speaker 1: Yeah, it seems possible. It might just require a very
Speaker 1: very special set of circumstances that we just haven't had
Speaker 1: a chance to see yet. But as you look deeper
Speaker 1: into the universe, everything that's possible, everything that's weird, I
Speaker 1: think eventually.
Speaker 3: You will see, like two brothers that get along statistically,
Speaker 3: it might happen two.
Speaker 1: Brothers that are professors at exactly the same level of
Speaker 1: prestigious university.
Speaker 2: There you go.
Speaker 3: Make it all depends on their intent. All right, Well,
Speaker 3: we hope you enjoyed that. Thanks for joining us. See
Speaker 3: you next time.
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