Speaker 1: Hey, Daniel, what pets do you have these days?
Speaker 2: Oh, we just have our rescue dog, Peppito.
Speaker 1: Haven't you had other pets in the past, like rodents.
Speaker 2: We did have rats for a time, and we actually
Speaker 2: had cats before that.
Speaker 1: Oh what happened Pepito?
Speaker 2: Ate them? No, we've never had a pet eat another pet.
Speaker 2: We've only lost them to old age.
Speaker 1: Old age. All that dark chocolate and big goods in
Speaker 1: your house just did them in with the heart attack.
Speaker 2: We don't feed dark chocolate at the dog, but everybody
Speaker 2: does eat pretty well at our house.
Speaker 1: Unless you like white chocolate, then your starved.
Speaker 2: You know. If that's the reason you run away from home,
Speaker 2: then maybe you never were really a white sun.
Speaker 1: Wait, if you don't like white chocolate, you're not a
Speaker 1: white son. It sounds like a white lie.
Speaker 2: I have a dark secret. Hi.
Speaker 1: I am Poor hammy cartoonists and the author of Oliver's
Speaker 1: Great Big Universe.
Speaker 2: Hi. I'm Daniel. I'm a particle physicist and a professor
Speaker 2: at UC Irvine, and I will not waiver in my
Speaker 2: campaign for dark.
Speaker 1: Chocolate, Dark chocolate, dark matter. You're just a very dark physicist.
Speaker 2: I'm trying to bring light to the world at the
Speaker 2: same time as exposed all the dark secrets of the universe.
Speaker 1: Oh, you're trying to expose dark matter. I thought you
Speaker 1: were all about letting the universe.
Speaker 2: Be Absolutely not. I do not believe in universe privacy.
Speaker 1: You're like the universe paparazzi.
Speaker 2: That's exactly right, except I'm not selling it to the
Speaker 2: national inquirer. I'm just publishing papers.
Speaker 1: Well, your buyer is the cosmological inquirer, the human inquirer.
Speaker 2: Inquiring brains want to know.
Speaker 1: Yeah, do you stand outside their home, like, Hey, dark
Speaker 1: matter over here, over here snapping pictures?
Speaker 2: If I knew where dark matter lived, I would definitely
Speaker 2: go there with my dark matter camera.
Speaker 1: I thought dark matter was all around us. It lives
Speaker 1: in us and within us. It surrounds us and binds
Speaker 1: the galaxy together.
Speaker 2: You're absolutely right, it's everywhere. We just don't know how
Speaker 2: to take a picture of it.
Speaker 1: But anyways, welcome to our podcast, Daniel and Jorge Explain
Speaker 1: the Universe, a production of iHeartRadio.
Speaker 2: In which we join our inquiring minds with yours to
Speaker 2: wonder together about the nature of the universe, to think
Speaker 2: deeply about how everything comes together to make the cosmos
Speaker 2: and the night sky that we appreciate to think about
Speaker 2: how the tiniest little particles and the most massive black
Speaker 2: holes shape the very world we live in, and whether
Speaker 2: it has always looked this way.
Speaker 1: That's right. We satisfy our curiosity for stars and what
Speaker 1: they're doing with their lives, and we take pictures and
Speaker 1: also sound recordings of what's out there in the universe
Speaker 1: and what's going on to maybe get a clue about
Speaker 1: how it all works.
Speaker 2: We'd like to figure out the fundamental nature of the
Speaker 2: universal laws that everything follows. But I also like to
Speaker 2: know the story of the universe. What happened, How did
Speaker 2: we end up where we are? How long have things
Speaker 2: looked this way for? How long can we rely on
Speaker 2: things to look this way? Do we live in a
Speaker 2: momentary blip of the universe or is this a long
Speaker 2: term trend?
Speaker 1: Yeah, looking at our past is a way to look
Speaker 1: into our future. We can try to deduce. But the
Speaker 1: rules of the universe are and what they might mean
Speaker 1: for us in the deep future? What is going to
Speaker 1: be the future of humanity here in our solar system?
Speaker 1: Can we call this our home for the next few
Speaker 1: billion years?
Speaker 2: Are you not planning to move out of that house
Speaker 2: for a few billion years, so your kids can always
Speaker 2: come home and their kids and their kids and their kids.
Speaker 1: Well, we're kind of just squatting in this solar system,
Speaker 1: right like we just popped in here, started living here.
Speaker 1: We didn't ask if anyone owned these planets. What if
Speaker 1: the real owners come back when they they're like, what
Speaker 1: is going on here? Call pest control.
Speaker 2: Don't we have some sort of like solar B and
Speaker 2: B contract squatter rights. Maybe exactly after one hundred million years,
Speaker 2: we're officially allowed to call ourselves the owners. It's a
Speaker 2: good question how long things have looked this way. When
Speaker 2: you look by the night guy, you expect to see
Speaker 2: basically the same stars as you did a year ago,
Speaker 2: and you know that you're looking at roughly the same
Speaker 2: stars that Newton looked at, and the Egyptians looked at
Speaker 2: and the Sumerians looked at thousands of years ago. But
Speaker 2: the Solar system operates on a very different kind of
Speaker 2: timescale than your life or even human civilization. And in
Speaker 2: fast forward things don't seem so stable. They seem quite
Speaker 2: chaotic and dynamic.
Speaker 1: Yeah, when we were all kids, we learned in school
Speaker 1: about the different planets in our solar system and how
Speaker 1: many of there are. And that's basically the same story
Speaker 1: that our kids are learning in school as well, right, Like,
Speaker 1: it hasn't really changed so much, except maybe for Pluto.
Speaker 2: We of course change what we mean by a planet
Speaker 2: and make up new categories all the time. But you're right,
Speaker 2: the stuff that's out there that we're seeing, whatever name
Speaker 2: we give it, hasn't changed in our lifetime or in
Speaker 2: our grandparents' lifetime.
Speaker 1: Yeah, And so I guess you kind of get the
Speaker 1: sense that maybe it will never change, you know, you
Speaker 1: sort of memorize these facts and these things and think
Speaker 1: that maybe it's going to be like that forever. But actually,
Speaker 1: if you look at the grand scale of the Solar
Speaker 1: System and the universe in or galaxy, things are rapidly changing.
Speaker 1: If you look at it from that point of view.
Speaker 2: If the Solar system changes, do you think we all
Speaker 2: have to go back to elementary school to learn a
Speaker 2: new mnemonic?
Speaker 1: Oh, there's a mnemonic. I didn't grow up yours. I
Speaker 1: don't know what do you use? Obviously the mnemonic did
Speaker 1: it work because you don't remember it.
Speaker 2: There's a lot of mnemonics to help you memorize the
Speaker 2: order of the planets. One of them is my very
Speaker 2: easy method just speeds up nothing. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Urinus, Neptune.
Speaker 1: Whoa, that is so not kit friendly. How many kids
Speaker 1: use methods and have methods?
Speaker 2: The history of them is actually really funny. There's ones
Speaker 2: from the fifties that go like men very easily make jugs,
Speaker 2: serve useful needs.
Speaker 1: Perhaps, Oh man, I wonder why we'd stopped using that one.
Speaker 2: And then a more recent one says, my very energetic
Speaker 2: mother jumps skateboards under nana's patio.
Speaker 1: Oh, there you go. That's a pretty good one, and
Speaker 1: true as well for some people.
Speaker 2: I'm sure my very educated mother just served us notches.
Speaker 1: Oh that's an even tastier.
Speaker 2: One, exactly. But the point is that though these things
Speaker 2: have seemed stable for a long time, it's not necessarily
Speaker 2: true that they always will be.
Speaker 1: Yeah, things are always changing, And in fact, you can
Speaker 1: ask the question of whether our solar SYSM had more
Speaker 1: planets in the past.
Speaker 2: It might be that the planets we know today are
Speaker 2: not all the planets that have ever orbited our star.
Speaker 1: And if we had more, what happened to them? So
Speaker 1: today on the podcast will be tackling the question has
Speaker 1: our Solar System lost any planets? That just seems kind
Speaker 1: of irresponsible there. How can you lose a whole planet?
Speaker 2: I mean I had it in my hands and then
Speaker 2: I put my keys down and the last place.
Speaker 1: Remember having that planet was on top of the dog.
Speaker 2: Blamed the dog. Huh, that's the first thing.
Speaker 1: The dog ate my planet. Classic excuse.
Speaker 2: Or maybe it just went rogue because it needed to
Speaker 2: find a white chocolate friendly Solar system. You know, maybe
Speaker 2: it just didn't fit in here.
Speaker 1: It just rebelled against your tyranny of trying to dictate
Speaker 1: what kind of chocolate people should eat or feel good
Speaker 1: about eating. Doctor, Why.
Speaker 2: You call it tyranny, I call it wisdom. Let's call
Speaker 2: the whole thing off.
Speaker 1: Yeah, that's what I'll tyrn say at two. Yeah, So
Speaker 1: it's been an interesting story of the Solar System. You
Speaker 1: got to wonder if maybef we had more than nine
Speaker 1: or eight planets in the past. Well, we definitely had
Speaker 1: more planets to pay in the past before Pluto got downgraded.
Speaker 1: But that's a separate story and a separate reason.
Speaker 3: Right.
Speaker 2: Yeah, Pluto is still there, it's just not called the
Speaker 2: planet anymore. It's called a dwarf planet.
Speaker 1: Right, But we can ask the question of whether our
Speaker 1: solar system did really have other giant planets like Jupiter
Speaker 1: or Mars or Venus, but maybe they decided they didn't
Speaker 1: like it here.
Speaker 2: It's really fun to dig into the history of the
Speaker 2: Solar system and understand how we got here, how it
Speaker 2: might have been different, and give us a sense for
Speaker 2: what other solar systems out there are likely to look like.
Speaker 1: So, as usual, we were wondering how many people had
Speaker 1: thought about the question of whether our solar system lost
Speaker 1: any planets, or at least misplaced them temporarily. Maybe, So,
Speaker 1: as usual, Daniel went out there into the internet to
Speaker 1: ask people has our Solar system lost any planets?
Speaker 2: Thanks very much to our group of volunteers. We greatly
Speaker 2: appreciate them, but we also would like to add you
Speaker 2: to their ranks. Please don't be shy write to me
Speaker 2: two questions at Danielanjorge dot com.
Speaker 1: What do people get I know if they sign up.
Speaker 2: The satisfaction of hearing their voice on the podcast and
Speaker 2: a weekly injection of hard physics questions.
Speaker 1: And also a monthly supply of white chocolate that gets
Speaker 1: kicked out of your house.
Speaker 2: I will send you exactly zero grams of white chocolate.
Speaker 1: Well, think about it for a second. Do you think
Speaker 1: our Solar System has lost any planets? Here's what people
Speaker 1: had to say.
Speaker 3: I don't know if we can know for sure, maybe
Speaker 3: by the orbits of current planets, but I'd have to
Speaker 3: assume given the five billion years or so that or
Speaker 3: some spent around, that at least one planet has come
Speaker 3: in and been kicked out. But maybe it depends on
Speaker 3: if we consider those objects planets.
Speaker 4: So I think that there have been planets knocked out
Speaker 4: of the Solar System, especially since when the Solar System
Speaker 4: was first created there would have been loads of rocks
Speaker 4: flying around to form planets. So then there would have
Speaker 4: been planets formed and then hit by maybe another planet
Speaker 4: which knocked them out of the system.
Speaker 5: Nothing that I know of, they're all accounted for. Some
Speaker 5: of them have lost the designation planet, like Pluto. I
Speaker 5: think regularly objects get flung out of Solar systems due
Speaker 5: to gravitational interactions with.
Speaker 2: Other own jobjects.
Speaker 5: So I can imagine Jupiter getting tired of somesome little
Speaker 5: planet and flinging it out. Maybe when we were forming
Speaker 5: all the planets performing them. Some of them were close
Speaker 5: to the Sun and got gabbled up. I'm curious to
Speaker 5: know if there's any record of planets that we're here
Speaker 5: in now or not.
Speaker 6: Apart from the reclassification of Pluto as a dwarf planet,
Speaker 6: meaning that we've effectively lost one planet, I have heard
Speaker 6: rumors about a tenth planet, which would now be a
Speaker 6: ninth planet, that potentially all within our inn a soda
Speaker 6: system and then could have collided with Earth and created
Speaker 6: the Moon and then spun off out into an orbit
Speaker 6: way out in our outer Soder system. Other than that,
Speaker 6: I'm unaware of any lost planets.
Speaker 1: Interesting answers. It seems to be all over the place.
Speaker 1: Some people say yes, some people say no, not really,
Speaker 1: some people say poor Pluto.
Speaker 2: There does generally seem to be an appreciation of the
Speaker 2: fact that the Solar System might not have always been
Speaker 2: an orderly, stately placed that there might have been primordial chaos.
Speaker 1: That's right. It was a big party here in the
Speaker 1: Solar System, where we're kind of in the after party
Speaker 1: of the Solar System, right.
Speaker 2: We're waking up the next morning going, man, what happened?
Speaker 2: And has anybody seen a dog?
Speaker 1: Yeah? Well, why am I waking up next to Venus here?
Speaker 1: How did that happen?
Speaker 2: And why is the hot tub filled with white chocolate?
Speaker 1: Yeah, so let's start with the basics, Daniel, is it
Speaker 1: even possible for Solar system to lose the planet? I
Speaker 1: thought that, you know, once you form, things are kind
Speaker 1: of stuck to you gravitationally in orbits, or that at
Speaker 1: least that it's hard to escape the gravitational field of
Speaker 1: like Sun or all these planets. Wouldn't they either fall
Speaker 1: in or go into a stable orbit.
Speaker 2: I think the key idea is the word you used, form, Like,
Speaker 2: when do you consider the Solar System to have formed?
Speaker 2: The Solar system? Formation is a slow and gradual, constant process.
Speaker 2: It's basically always changing. And so you can go all
Speaker 2: the way back to the very beginning of the Solar
Speaker 2: system to understand the chaos of that formation and understand
Speaker 2: that that formation is a constant process, that things are
Speaker 2: always potentially bumping into each other and disturbing each other.
Speaker 1: Wait, are you saying that if we leave the window
Speaker 1: open for the fact that maybe the Solar System is
Speaker 1: still forming, does that mean we technically haven't lost any planets? Like?
Speaker 1: Can I use it in my real life.
Speaker 2: No, it just means that during the formation, planets could
Speaker 2: form and be lost. There is no final form to
Speaker 2: the Solar System. It's a constantly evolving thing. It's not
Speaker 2: like at some point somebody says, Okay, the Solar System
Speaker 2: is finished, let's package it and ship it and move
Speaker 2: on to the next project. I see.
Speaker 1: It's like a Pokemon, is what you're saying. It's always evolving,
Speaker 1: it's looking for its final form.
Speaker 2: I don't know enough about Pokemon to know whether that
Speaker 2: analogy holds, So I'm just gonna.
Speaker 1: Trust you on that. I don't know either. To be honest,
Speaker 1: I just heard final form and it made me think
Speaker 1: of Pokemon.
Speaker 2: Well, it's sort of in the same way that animals
Speaker 2: never have a final form. Evolution is a constant process.
Speaker 2: Things are always changing in response to the environment.
Speaker 1: Except for crocodiles and sharks, they're pretty settled there.
Speaker 2: In the plateau. Yeah that's true.
Speaker 1: Yeah, but let me take us through to some of
Speaker 1: the early history of the Solar System. How do we
Speaker 1: get planets in the first place.
Speaker 2: So planetary formation is a super fascinating topic, and it
Speaker 2: helps us understand like the formation of the Solar System
Speaker 2: as a whole. Remember that the Solar system forms from
Speaker 2: the collapse of a huge cloud of like gas and dust.
Speaker 2: It's mostly hydrogen, which is made in the Big Bang,
Speaker 2: and it's also interspersed with a bunch of other heavier
Speaker 2: stuff that's made from other solarss where the stars have
Speaker 2: already fused heavier elements out of that hydrogen. So you
Speaker 2: have this big cloud of mostly hydrogen with a few
Speaker 2: heavier bits in it, and it collapses into stars. You
Speaker 2: don't just get one solar system. You typically get several
Speaker 2: made at the same time. In one of these stellar nurseries,
Speaker 2: we have a big blob of this stuff and it
Speaker 2: collapses and most of the stuff goes into the center
Speaker 2: to make a star, like ninety nine percent of the
Speaker 2: stuff goes in to make the star. But you typically
Speaker 2: have a disc of gas and dust that's orbiting that star.
Speaker 2: It's spinning too fast to collapse in the way the
Speaker 2: Moon is orbiting the Earth without falling into the Earth,
Speaker 2: and so you get this protoplanetary disc around this new star,
Speaker 2: and that disc then coalesces into larger stuff. Gravity is
Speaker 2: doing the work there to pull the gas and dust
Speaker 2: in the disk into heavier things. And where you have
Speaker 2: like little spots of iron or little spots of heavier metals,
Speaker 2: those things will use their gravity to form larger objects.
Speaker 1: But I think the Solar System formed into a disc first,
Speaker 1: and then the star kind of ignited.
Speaker 2: Right. Moment of ignition depends a little bit on the
Speaker 2: mass of the star. I mean, in some cases you
Speaker 2: don't even get ignition if there isn't enough mass there.
Speaker 2: You have like a subcritical brown dwarf, but it's definitely
Speaker 2: collapsing into a disc as it forms. Right, a big
Speaker 2: amorphous blob is going to collapse, and it's going to
Speaker 2: collapse into a disc shape because of its angular rotation.
Speaker 2: So the two things can sort of happen simultaneously, And
Speaker 2: when ignition happens depends on the mass of the star.
Speaker 1: Right, And there's also kind of an intermediate step there
Speaker 1: where the disc kind of turns into rings for a while.
Speaker 1: Right before you get the planets.
Speaker 2: Exactly, you get the seeding of structure and they pull
Speaker 2: together into larger and larger objects, and rings are basically
Speaker 2: just clusters of larger objects. So you get these gaps emerging,
Speaker 2: and then you get those things formed together into planets
Speaker 2: or not, depending on the tidal forces. A large object
Speaker 2: can form and sort of gather up a lot of
Speaker 2: the gas and dust near it, and then it can
Speaker 2: also distort the other stuff nearby, preventing it from forming.
Speaker 2: So it's a bit of a chaotic process in the beginning,
Speaker 2: and it also depends a little bit on your distance
Speaker 2: from the st There's a point it's called the snow line,
Speaker 2: after which water tends to be ice, tends to be
Speaker 2: a solid, and before which it tends to be vapor.
Speaker 2: Like if you're close enough to the star, it's warm
Speaker 2: enough that the water is vapor and if you're further
Speaker 2: from that point, the water is frozen. That helps form
Speaker 2: giant planets. So you tend to have these large planets
Speaker 2: with ice and rock seeding structure on the outer part
Speaker 2: of the Solar System past the snow line, and then
Speaker 2: less ice so smaller planets before the snow line in
Speaker 2: the inner Solar system.
Speaker 1: Right in the inner Solar system, you get all the
Speaker 1: rocky planets.
Speaker 2: Right exactly because the gas there is blown away by
Speaker 2: the radiation from the ignition of the Sun. In the
Speaker 2: very beginning of the Solar system, the Sun is pumping
Speaker 2: out a huge amount of ultraviolet, very high energy photons,
Speaker 2: which tends to blast the inner planets clean, which is why,
Speaker 2: like our initial atmosphere on Earth was blown off by
Speaker 2: this stellar wind in the very early years of the
Speaker 2: Solar System. So you get the rocky planets in the core,
Speaker 2: and then you get the gas and ice giants out
Speaker 2: past the snow line.
Speaker 1: Right, And I think the process is like, yep, these
Speaker 1: rings kind of like Saturn has rings right now, and
Speaker 1: the rings eventually little by little collapse into planets or
Speaker 1: first planet tesimals first, right.
Speaker 2: Yeah, planet testimals a super fun word. They sound like
Speaker 2: many cute little planets where they're basically like building blocks
Speaker 2: of planets, and they don't always form, right, which is
Speaker 2: why you have like the asteroid belt and the Kuiper Belt.
Speaker 2: It depends on the tidal forces of the nearby stuff,
Speaker 2: so it's not happening in isolation. This is complicated interplay
Speaker 2: between all of the objects.
Speaker 1: Right, But it's kind of a bit of a runaway process.
Speaker 1: Like once you seed a planet or once more you know,
Speaker 1: some planet tesimals moush together, then that becomes kind of
Speaker 1: a center of gravity and more and more stuff falls
Speaker 1: into it, and that's kind of how you get a planet.
Speaker 2: Right, Yeah, that's kind of how you get a planet exactly.
Speaker 2: And in this initial picture, everything forms very orderly, like
Speaker 2: they tend to be mostly in the same plane, and
Speaker 2: it be mostly circular because you have this big disc
Speaker 2: as we say, that collapses in the rings and then
Speaker 2: planet ismals and then planets. But once you have these
Speaker 2: large objects formed with their own significant gravity, then they
Speaker 2: can start to hug on each other pretty hard, and
Speaker 2: you can get instabilities, you can get chaos, you can
Speaker 2: get resonances, and that's how planets can migrate, and they
Speaker 2: can tug on each other and you might even lose.
Speaker 1: One, right, because I guess there's no guarantee that your
Speaker 1: orbit is going to be stable. I mean, it's such
Speaker 1: a complex and you know, there's so many things moving
Speaker 1: around that there's no guarantee that even if you're orbiting
Speaker 1: around the Sun, you're going to be there forever, because
Speaker 1: something else might come around and knock you off your
Speaker 1: orbit or pull you away from your orbit, right.
Speaker 2: And that can be things from outside the Solar System,
Speaker 2: like a passing star can nudge something and perturb the
Speaker 2: otherwise stable orbits of the Solar System like even just
Speaker 2: a little nudge from a star that's coming nearby, it's
Speaker 2: not like it has to pass right through the Solar
Speaker 2: system can cause a cascade effect of instabilities. But also,
Speaker 2: just like the planetismals and the Kuyper Belt or the
Speaker 2: asteroid belt can tug on stuff, and enough of that
Speaker 2: happening can cause things to go.
Speaker 1: Wonky and wonky. They might have gone in our Solar system,
Speaker 1: perhaps wonky enough to lose a couple of planets here
Speaker 1: and there. Let's get into that idea and whether or
Speaker 1: not we did misplace a couple of planets in our history.
Speaker 1: But first let's take a quick break. All right, we're
Speaker 1: talking about whether our Solar system has lost any planets.
Speaker 1: I feel like that sounds very irresponsible of the Solar system.
Speaker 1: Can would you say, like, have any planets escaped our
Speaker 1: Solar system?
Speaker 2: Maybe we've grown up and graduated planets. They're like off
Speaker 2: into the universe living their best lives.
Speaker 1: Yeah, there you go. You don't want it to live
Speaker 1: at home forever.
Speaker 2: Exactly when your kid graduates and goes to college, you
Speaker 2: don't consider that you've lost them.
Speaker 1: Yeah, there you go. So have we shepherded planets out
Speaker 1: into the larger cosmos is the question of the day.
Speaker 2: Yeah, in this scenario, they would like come back and
Speaker 2: visit with their own little moons or something that we
Speaker 2: could coop over. Oh look, how cute.
Speaker 1: Oh yeah, yeah, except we already turned their bedroom into
Speaker 1: like a workout room or a craft and so now
Speaker 1: there's no room for them.
Speaker 2: Sorry about that, your orbits being used?
Speaker 1: Yes, sorry, you'll have to airbnb a nearby apartment or something.
Speaker 1: But yeah, So it's possible in the early chaos of
Speaker 1: a solar system to lose a planet, right because things
Speaker 1: aren't quite settled. Even though we're all bound gravitationally to
Speaker 1: the central star, things can get kind of wonky and
Speaker 1: maybe wank enough to actually fling a planet out into space.
Speaker 2: Exactly and when this happens is sort of the most
Speaker 2: recent question people have been struggling with. There's a classic
Speaker 2: model of the formation of the Solar system and how
Speaker 2: the planets move around that we'll talk about. It's called
Speaker 2: the Nice model because it was developed by researchers in Nice, France,
Speaker 2: that has a bit of an issue with when exactly
Speaker 2: all this chaos happened that might be solved by a
Speaker 2: more recent model with a different picture for how these
Speaker 2: instabilities might have been triggered.
Speaker 1: Well, now, I wonder if some listeners out there might
Speaker 1: be confused about how you can lose a planet, Like,
Speaker 1: there isn't that much around us, right in terms of
Speaker 1: other Solar systems or any large stars or galaxy or
Speaker 1: you know, very heavy objects. So even if something gets
Speaker 1: flung into space, wouldn't it eventually come back?
Speaker 2: You're right that space near the Solar System is pretty empty.
Speaker 2: I mean, the closest star is light years away, and
Speaker 2: so its gravitational pull is pretty weak. But you can
Speaker 2: still have an escape velocity. If you throw something hard
Speaker 2: enough off the Earth, it will leave the Earth and
Speaker 2: never return. If you throw something out of the Solar
Speaker 2: System with enough velocity enough to escape the gravitational well
Speaker 2: of the Solar System, then it will not return.
Speaker 1: Mmmmm yeah, I think we talked about that in an
Speaker 1: other episode. It's kind of a weird kind of math, right,
Speaker 1: Like you need to have enough velocity so that as
Speaker 1: you get further and further, the pool of gravity pulling
Speaker 1: your back gets weaker and weaker, and so actually you
Speaker 1: kind of outrun the pool of gravity exactly.
Speaker 2: It seemed confusing because you know that gravity has an
Speaker 2: infinite extent, like no matter how far away you are,
Speaker 2: and the Sun is always pulling on you. But just
Speaker 2: because there are infinite number of contributions doesn't mean it
Speaker 2: adds up to an infinite force. It's just like any
Speaker 2: integral or converging series. It can add to a finite
Speaker 2: amount of energy. So as long as you have more
Speaker 2: energy than the sum of all the tugs the Sun
Speaker 2: will ever pull on you, you can escape the Solar System.
Speaker 2: So if, for example, you have a planet that gets
Speaker 2: a push from another planet and gets flung out into
Speaker 2: the deep dark space, it might never return.
Speaker 1: Yeah, I guess sort of like we've done with spacecraft
Speaker 1: that we sent out into space right like it left
Speaker 1: Earth eventually, it was going so fast it left the
Speaker 1: gravity of Earth and through the gravity of maybe other planets.
Speaker 1: And now we have some that are going out of
Speaker 1: the Solar System exactly.
Speaker 2: That can be a little bit more complicated because they
Speaker 2: can have rockets and they can use gravitational assists from
Speaker 2: other planets, but the principle is the same. Like Voyager
Speaker 2: and Pioneer, they have enough velocity that they're leaving the
Speaker 2: Solar System without any more rocket burns or gravitational assists.
Speaker 2: It's definitely possible to leave home.
Speaker 1: All right. Well, now the question here today is have
Speaker 1: we actually lost any planets? Did the Solar System have
Speaker 1: more planets than the eight that we have now, and
Speaker 1: have we missed or have any left home?
Speaker 2: But if you look at the pattern of the planets
Speaker 2: that we have now and you try to tell a
Speaker 2: story about how we got there, it's a hard thing
Speaker 2: to do without another planet. The patterns that we see
Speaker 2: in the eccentricities of the planets and the structure of
Speaker 2: the Kuiper Belt and the asteroids is much easier to
Speaker 2: explain if there was at one point another ice giant
Speaker 2: like Neptune that was flung out of the Solar System.
Speaker 1: I mean, you sort of look at how the planets
Speaker 1: are moving now and their orbits, and you basically hit
Speaker 1: the rewind button, kind of like you use math and
Speaker 1: a computer to backtrack what the Solar System was doing
Speaker 1: millions and millions of years ago, and you're saying that
Speaker 1: it doesn't make sense or what.
Speaker 2: It actually usually works. In the forward direction, like you
Speaker 2: start from the Protosolar System and try to evolve forward
Speaker 2: and see if it matches what we see today. Conceptually
Speaker 2: it's the same as backtracking, but the way the simulations
Speaker 2: actually work is forwards. You know, we model physics equations
Speaker 2: forwards in time, and we try to see if we
Speaker 2: can get to the current Solar system and explain everything
Speaker 2: we see. And what we find is that doesn't really
Speaker 2: work without another planet.
Speaker 1: But are there like a million things that could have
Speaker 1: happened in between? Absolutely, how do you make it match
Speaker 1: what we have now? Like, what do you start with?
Speaker 1: And if you can make it match, how do you
Speaker 1: know it's not just you're making it error?
Speaker 2: Absolutely, it's not definitive, right, it's statistical. It's totally possible
Speaker 2: that our solar system could have arisen without another planet.
Speaker 2: But it's just a question of what's more likely. Like
Speaker 2: when you run the simulations of our solar system, how
Speaker 2: many times do you get to something like what we
Speaker 2: have now with a lost planet and without a lost planet?
Speaker 2: And so is it just easier to make this arrangement
Speaker 2: with a lost planet or without? It's totally possible to
Speaker 2: do it without, but it's just less likely. It happens
Speaker 2: in fewer of those simulations.
Speaker 1: And by like what we have now, you don't mean
Speaker 1: like exactly what we have now just kind of like
Speaker 1: sort of like what we have now.
Speaker 2: If you run enough simulations, you can get essentially a
Speaker 2: sense for what's more likely and what's less likely under
Speaker 2: various hypotheses. And if you have another planet in your system,
Speaker 2: then you get more simulations that are similar to ours. Yeah,
Speaker 2: so more like probability gets clustered in the kind of
Speaker 2: arrangement that we have now. And the cool thing about
Speaker 2: that is that it tells the story. You can look
Speaker 2: at those simulations and you can see, oh, what happened
Speaker 2: in the inner what happened in the early days of
Speaker 2: the Solar System? How did this happen?
Speaker 1: Okay, So then scientists have been running these simulations and
Speaker 1: it's kind of hard to get what we have now
Speaker 1: without some mystery planet that moved away from the Solar System.
Speaker 1: How did scientists think that happen?
Speaker 2: So the original models, called the NIE model, basically blames
Speaker 2: it on the Kuiper Belt. So in the original Solar system,
Speaker 2: you have Jupiter, Saturn, Urinus, Neptune, all formed in very nice,
Speaker 2: neat circular orbits like we talked about, in fairly closely
Speaker 2: spaced to each other. But then you have these planetismals
Speaker 2: out in the Kuiper Belt that haven't formed into planets,
Speaker 2: but they're tugging on Neptune, they're tugging on Urinus, they're
Speaker 2: tugging on Saturn, and they get pulled into the inner
Speaker 2: Solar System. And when that happens, these big planets get
Speaker 2: pushed out a little bit, and then the planetismal falls
Speaker 2: further into the Solar System until it reaches Jupiter, and
Speaker 2: then Jupiter actually pushes it back out and Jupiter gets
Speaker 2: pushed in. The effect of these little planetismals, these little
Speaker 2: tugs is to pull out Neptune, Saturn, Uriness and to
Speaker 2: push Jupiter in a little bit. So they're disturbing the
Speaker 2: Solar System. And you might think, well, what can one
Speaker 2: little rock do? And the key is that there's lots
Speaker 2: of these rocks, and so over time this can really
Speaker 2: have an effect on the orbit of the.
Speaker 1: Planets because we know that at around that space, that
Speaker 1: ring of the Solar System, you had a lot of
Speaker 1: big rocks, and maybe you have a lot of big
Speaker 1: rocks right now exactly.
Speaker 2: The Kuiper Belt is huge. There could be like trillions
Speaker 2: of objects out there. We think today it's the source
Speaker 2: of comets that fall into the Solar System, the short
Speaker 2: period comets. There's an even bigger blob of stuff out
Speaker 2: in the Oort Cloud. It might be the source of
Speaker 2: long term comments, but it's an enormous, massive stuff out there,
Speaker 2: and each of those little bits as they interact with
Speaker 2: the Solar System can give a little tug. You have
Speaker 2: these nice circular orbits that were formed initially, but now
Speaker 2: they're getting perturbed by these tugs from all these rocks
Speaker 2: in the Kuiper Belt. Mmm.
Speaker 1: Okay, scientist think that maybe these rocks from the Kuyper
Speaker 1: berl maybe cause some planet that we had before to
Speaker 1: exit the Solar System.
Speaker 2: Well, essentially leads to some instability because you're pushing Jupiter in,
Speaker 2: you're pushing Neptune, Saturn, Urinus out, and then those planets
Speaker 2: start to interact like they used to be in a nice,
Speaker 2: happy orbit. But now you get instabilities and resonances from
Speaker 2: those planets themselves. Jupiter starts to drift inwards, and then
Speaker 2: Saturn pulls on Jupiter, and Jupiter pulls on Saturn. You
Speaker 2: start to get a regular orbits, and Saturn actually pulling
Speaker 2: on Jupiter is what saves it. Saturn pulls on Jupiter
Speaker 2: and changes its direction so it migrates back out away
Speaker 2: from the Sun. Without Saturn there, it might have been
Speaker 2: that Jupiter would have just like plummeted into the Sun
Speaker 2: thanks to the influence of the Kuiper Belt.
Speaker 1: You know, it all sounds kind of complicated, So I
Speaker 1: wonder why do scientist think that making it more complicated
Speaker 1: by adding another planet makes it easier to understand? Like
Speaker 1: it's all really complex dynamics, right, Like, so then how
Speaker 1: does adding another planet make it easier to predict, like
Speaker 1: what's the missing thing that we currently have? That missing
Speaker 1: planet would help with.
Speaker 2: Some of the features of our Solar system that we
Speaker 2: see today are difficult to explain without adding another planet,
Speaker 2: you know, like the irregular orbits of Jupiter and Saturn.
Speaker 2: They're not perfect circles. There are sort of ellipses that
Speaker 2: have like a five percent eccentricity, And there's this structure
Speaker 2: in the material of the Kuiper Belt. A lot of
Speaker 2: it seems to have been lost, and a lot of
Speaker 2: the rest of it is in resonance with Neptune. And
Speaker 2: these things aren't like smoking guns that say like, oh, look,
Speaker 2: there has to be another planet here. But when you
Speaker 2: run the simulations, you get these kind of features more
Speaker 2: often when you add another planet. If you put another
Speaker 2: ice giant in around the size of Neptune between Saturn
Speaker 2: and Urinus, then the story you get when you run
Speaker 2: these simulations more closely resembles the Solar System we have today.
Speaker 1: And I guess scientists just throw this mystery planet in
Speaker 1: and all kinds of velocities in all kinds of sizes,
Speaker 1: and you sort of see overall, like, hey, it does
Speaker 1: kind of shape the Solar System more into what we
Speaker 1: have now.
Speaker 2: Yeah. Another way to say it is like they were
Speaker 2: running the simulations with just the planets and they were
Speaker 2: noticing that they pretty rarely ended up describing the situation
Speaker 2: that we see today, Like it was very unlikely to
Speaker 2: get Jupiter and Saturn to have these eccentricities, and to
Speaker 2: have these asteroid belts along Jupiter's orbit, the Trojans and
Speaker 2: the Greek camp of asteroid belts, those things were pretty
Speaker 2: rare to get in a Solar system without this additional planet.
Speaker 2: But when you put that new planet in, it started
Speaker 2: to be less unlikely. It started to be like, oh,
Speaker 2: this kind of thing happens pretty frequently, and so it's
Speaker 2: just a question of like, how do you explain it.
Speaker 2: It's not the only possible story, right, Maybe there are
Speaker 2: two other planets. Maybe something else happened that could explain this,
Speaker 2: but it does make the story more likely.
Speaker 1: Maybe the planet had a big fight with Jupiter, stormed
Speaker 1: out of the house with all their bags, left to
Speaker 1: go live with their aunt or their niece. This is
Speaker 1: the Nice model, right, This.
Speaker 2: Is the Nie model exactly. They went to live with
Speaker 2: their aunt in France.
Speaker 1: So then that's one model you're seeing. One model says
Speaker 1: and maybe it was all these big rocks from the
Speaker 1: Kuiper Belt that maybe caused a lot of instability out
Speaker 1: there in the icy planets, and then maybe it caused
Speaker 1: a planet that we used to have to flyway exactly.
Speaker 2: And one of the nice things about this model until
Speaker 2: recently was that it lined up with other pieces of
Speaker 2: evidence for when this instability happened. And in the Nice model,
Speaker 2: this happens like about a billion years after the Solar
Speaker 2: system is formed, so you get like the ignition of
Speaker 2: the Sun, you get the formation and the gas planets
Speaker 2: and the rocky planets. Things cycle around for a little while,
Speaker 2: and it takes time for the Kuyper Belt to sort
Speaker 2: of drive this because these are tiny little rocks. This
Speaker 2: sort of lines up with another piece of evidence from
Speaker 2: looking at our Moon. Our moon is a great record
Speaker 2: for impacts in the Solar System, like when rocks have
Speaker 2: been raining down in the inner Solar System. And when
Speaker 2: the astronauts in the Apollo mission went to the Moon,
Speaker 2: they gathered a bunch of samples to study, like the
Speaker 2: craters and the impacts, to try to get a sense
Speaker 2: for like what is the history of the Solar system.
Speaker 2: One of them been sort of more or less impacts
Speaker 2: when it's been like bad weather and good weather, and
Speaker 2: for a long time, there was this evidence for what
Speaker 2: we call a late heavy bombardment, that there's this period
Speaker 2: of billion years after the Solar system formed when a
Speaker 2: lot of rocks were raining down in the the Solar system,
Speaker 2: And that kind of lines up with the story of
Speaker 2: the nice model that like all these rocks from the
Speaker 2: Kuiper Belt were coming in and making trouble and maybe
Speaker 2: also some of them were landing on the Moon. So
Speaker 2: that was sort of a nice story.
Speaker 1: For a while, meaning like there's a lot of activity
Speaker 1: from the Kuiper Bell which may have contributed to us
Speaker 1: kicking out an icy planet.
Speaker 2: Exactly, and until a few years ago that all seemed
Speaker 2: to kind of hang together. But then there was a
Speaker 2: reanalysis of this data from the Moon and it turns
Speaker 2: out that it may have been a mistake.
Speaker 1: Well, we lost the theory the dog at theory.
Speaker 2: It turns out of the way the astronauts gathered the
Speaker 2: data that may have basically only collected data from one
Speaker 2: big impact. So what we thought was a bunch of
Speaker 2: impacts that all happened at the same time, like three
Speaker 2: and a half billion years ago, might have actually just
Speaker 2: been one big impact that the astronauts gathered from. So
Speaker 2: it could have been like essentially just a statistical anomaly
Speaker 2: in the data that made it look like there was
Speaker 2: really bad weather for like a few hundred million years
Speaker 2: three and a half billion years ago, But it was
Speaker 2: really just one bad day that the astronauts happened to
Speaker 2: elect data from.
Speaker 1: Wait what, so we didn't we just had one sample.
Speaker 1: We didn't take some samples from all over the Moon
Speaker 1: or analyze the craters visually through telescopes, so.
Speaker 2: We don't have samples from all over the Moon. And
Speaker 2: they definitely collected a bunch of samples from different locations,
Speaker 2: and that's why they thought maybe this was like a
Speaker 2: fair sample from everywhere on the Moon. But a reanalysis
Speaker 2: of it suggests that a single impact site Imbrium might
Speaker 2: be responsible for basically all of the evidence that the
Speaker 2: astronauts gathered. I don't know if the astronauts are being
Speaker 2: lazy and not following instructions or if it was not
Speaker 2: a well organized study, but more recent analysis suggests there
Speaker 2: may have been no late heavy bombardment. There may just
Speaker 2: be like a gradual decline in the number of impacts
Speaker 2: over time.
Speaker 1: And so maybe this idea that kyper Berl maybe caused
Speaker 1: us to lose an icy planet maybe didn't really happen,
Speaker 1: or could it still have happened without this late heavy bombardment.
Speaker 2: This really causes us to doubt that model. And there's
Speaker 2: been another lingering problem with this Nie model that has
Speaker 2: never really been answered, which is why the terrestrial planets
Speaker 2: kind of survived it. If you have these gas giants
Speaker 2: doing this dance a billion years after the Solar System
Speaker 2: is formed, when Earth and Mars are also already formed,
Speaker 2: then how did the Earth and Mars and Venus survive
Speaker 2: all these gravitational tugs. If Jupiter comes into the inner
Speaker 2: Solar System basically turns around at the asteroid belt, how
Speaker 2: does Mars stay in orbit? How does Earth stay where
Speaker 2: it is? So one concerned about the Nie model has
Speaker 2: always been how did the terrestrial planets not get disrupted
Speaker 2: by the giants. So now there's a news story about
Speaker 2: when this instability happened and what the cause was that
Speaker 2: doesn't rely on this late heavy bombardment and places the
Speaker 2: blame on the instability somewhere else.
Speaker 1: But I guess why do we assume that there was
Speaker 1: an instability because we think that maybe we did lose
Speaker 1: a planet.
Speaker 2: Because we can't explain the orbits and the eccentricities and
Speaker 2: the structure of the Kyper Belt without some kind of
Speaker 2: motion of these planets. We know the planets moved around,
Speaker 2: we know there was interaction. We know that they did
Speaker 2: not form in the order that we see them today.
Speaker 1: All right, So then what's this new model? Not so nice,
Speaker 1: the less nice model exactly, not the Nie model, the
Speaker 1: Nephew model.
Speaker 2: The nibbling model. So this model is called the rebound model,
Speaker 2: and it suggests that this instability happened much much earlier. Actually,
Speaker 2: while the rocky planets were forming, or maybe even before
Speaker 2: they formed, that was basically an early instability.
Speaker 1: Well, that's a big difference in timescale, But don't your
Speaker 1: simulations as a solar system sort of help you pinpoint
Speaker 1: when it happened.
Speaker 2: It turns out that the simulations can come in to
Speaker 2: either an early instability or a later instability, like the
Speaker 2: instability for in the nice model, like a billion years
Speaker 2: after the formation of the Solar system, can explain the
Speaker 2: orbits that we got if there, in fact was a
Speaker 2: bunch of interactions from the Kuiper Belt. But you could
Speaker 2: also have an instability much earlier on that could reproduce
Speaker 2: the orbits and the eccentricities that we see today.
Speaker 1: All right, so then what does this model say? What
Speaker 1: happened according to this model? So this is called the
Speaker 1: rebound model, and essentially the instability trigger here, the thing
Speaker 1: that can kicked off all this bouncing around was the
Speaker 1: interaction of the planets with this gas. Imagine the formation
Speaker 1: of the Solar system, as we talked about earlier. You
Speaker 1: have these planets forming and they're pulling their stuff together,
Speaker 1: but you still have something of a protoplanetary disk. You
Speaker 1: still have a bunch of gas sort of in between
Speaker 1: the planets. Now we don't have that today, and the
Speaker 1: reason is that the Sun has effectively blown all that out.
Speaker 1: As the Sun triggered and the ignited and its radiation
Speaker 1: grew and grew, it blew out all that gas from
Speaker 1: the Solar system. So in the first ten million years
Speaker 1: or so, that gas disc is sort of moving out
Speaker 1: through the Solar System and it affects the orbits of
Speaker 1: those planets. If the planets are passing through the gas,
Speaker 1: it slows them down, and if that gas is getting
Speaker 1: pushed out by the star, it actually carries those planets
Speaker 1: with them a little bit. So as this gas disc
Speaker 1: is getting pushed out of the Solar System, it passes
Speaker 1: through all of these orbits and it gives them all
Speaker 1: a little tweak. So this rebound model suggests that the
Speaker 1: interaction of the planets with this gas disc as it's
Speaker 1: getting blown out of the Solar System and trigger these
Speaker 1: same instabilities and can explain all the features we see
Speaker 1: in the Solar system today. But couldn't you kind of
Speaker 1: make the same argument as before with the other model,
Speaker 1: like Wooden Huck How is it then that we'd the
Speaker 1: Earth and Mars and Venus have such a nice even
Speaker 1: orbits if we were disturbed and blown out.
Speaker 2: Yeah, great question. It's because this happened much earlier, and
Speaker 2: so essentially this happened before those terrestrial planets even form.
Speaker 2: The terrestrial planets we think formed after the gas giants.
Speaker 2: M how come the gas giants have a lot of
Speaker 2: advantages over the rocky planets in the inner solar systems.
Speaker 2: Number one, there's ice out there, which is like a
Speaker 2: solid that can help seed the formation of planets. To
Speaker 2: there's a lot more gas out there because the Sun
Speaker 2: hasn't gobbled it up, and you don't have this proto
Speaker 2: star messing everything up and heating things. So it's much colder,
Speaker 2: which makes it easier for gravity to pull things together.
Speaker 2: So the outer Solar system is a much easier place
Speaker 2: to form planets. So we think that gas planets formed
Speaker 2: before the gas disc actually evaporated, sometimes in like the
Speaker 2: two to ten million year range. But rocky planets take
Speaker 2: longer because the inner Solar system is much hotter and messier,
Speaker 2: is less gas available to form planets and no ice whatsoever,
Speaker 2: So those take like thirty to one hundred million years
Speaker 2: to form.
Speaker 1: Okay, so I think what you're saying is that this
Speaker 1: new model, this rebound model, is saying that we kicked
Speaker 1: off a gassy icy planet a long time ago, before
Speaker 1: we even had Earth and Venus and Mars and the
Speaker 1: rocky planets inside, and that it was due to a
Speaker 1: lot of this gas being blown out of the center.
Speaker 2: Exactly, and as the sort of inner radius of that
Speaker 2: gas passes through these early ice giants and gas planets,
Speaker 2: it triggered that instability. They did their crazy dance with
Speaker 2: Jupiter moving in and the other planets moving out and
Speaker 2: ejected an ice giant planet that left the Solar System,
Speaker 2: And all that happened even before the Earth and Mars
Speaker 2: were formed, so they didn't mess up the formation of
Speaker 2: the Earth and Mars because it was already done by then.
Speaker 1: All right, well, those are both great stories. Now the
Speaker 1: question is can we see the planet that we kicked out?
Speaker 1: Are there lonely dejected planets floating out there in space
Speaker 1: that we can see and maybe identify and track to
Speaker 1: perhaps our Solar System? So let's stick into that, But
Speaker 1: first let's take another quick break. All right, we're asking
Speaker 1: the question, did our Solar system lose a planet or
Speaker 1: I guess shepherd it out peacefully into the cosmos.
Speaker 2: That's the niser model. If anything happened, it sounds like
Speaker 2: we can blame it on the gas giants, Like we
Speaker 2: weren't even around when all of this went down. It's
Speaker 2: just the drama we heard about when we showed up.
Speaker 2: Oh I see.
Speaker 1: It's like, yeah, it's like you're the younger sibling and
Speaker 1: there's all this drama before you were even born.
Speaker 2: Exactly, Like why is everybody so mad? And who is
Speaker 2: this missing sibling everybody's talking about you never met?
Speaker 1: Oh wow, this is just god, this is just turned
Speaker 1: into a Korean drama. I feel like super complicated.
Speaker 2: But it is sort of the story. I mean, what
Speaker 2: we learned from this is that these unstable giant planets,
Speaker 2: the ice giants and the gas basically sculpted the inner
Speaker 2: Solar system. I mean, it didn't disrupt the already formed
Speaker 2: Earth in Mars and Venus, but it created the gravitational
Speaker 2: context for them to form and probably changed how they
Speaker 2: did form, the way younger siblings arrive, and family dramas
Speaker 2: that have existed for years.
Speaker 1: But again, I guess this is just kind of a model, right,
Speaker 1: or sort of a guess to maybe explain some of
Speaker 1: what we see. We don't quite know for sure, right.
Speaker 2: We definitely don't know for sure. We've quibbled before about
Speaker 2: what a guess means. Scientifically, I think we have a model,
Speaker 2: we have some evidence for it, we're never exactly sure.
Speaker 2: I mean, we have not identified a planet and said
Speaker 2: that's our lost planet. It's just easier to explain what
Speaker 2: we see in the universe when you add this to
Speaker 2: the story. But that happens for lots of things, like
Speaker 2: we don't witness the early years of the Earth's formation,
Speaker 2: but we have a pretty detailed story about the formation
Speaker 2: of the Earth based on the patterns of evidence that
Speaker 2: we see in the rocks beneath our feet. And so
Speaker 2: that's a big part of science, is developing a story
Speaker 2: to explain the data, even if you don't directly witness
Speaker 2: all of those events, right, right.
Speaker 1: But I guess what I'm trying to say is that
Speaker 1: we had a pretty good story that seemed to check
Speaker 1: out and make sense before, but then it turned out
Speaker 1: to be not quite correct.
Speaker 2: Yeah, that's true. These stories are always evolving in they're
Speaker 2: getting better, Like we like the nice model, but there
Speaker 2: were some dangling questions about how the Earth and Mars
Speaker 2: survived it. And now we like this new model, the
Speaker 2: rebound model, But there's always going to be dangling questions,
Speaker 2: and somebody's going to come along with a better model
Speaker 2: and maybe tell a different story in five years. It's
Speaker 2: a constantly evolving story.
Speaker 1: I guess. But I wonder if maybe like a smoking
Speaker 1: gun or something to definitely be able to say, like, hey,
Speaker 1: there used to be a planet here in the Solar
Speaker 1: System that we don't have anymore, is to actually maybe
Speaker 1: see this planet that we kicked out or that left
Speaker 1: Liane its own out there in space. Isn't it possible
Speaker 1: that we could see a planet like and track it
Speaker 1: to our Solar system out there beyond our Solar System?
Speaker 2: I suppose it's possible, But we're talking about events that
Speaker 2: happened four billion or more years ago, so that planet
Speaker 2: is pretty far gone by now. If it did leave,
Speaker 2: we can do so of more indirect discoveries, though. We
Speaker 2: can look out and say, are there any rogue planets?
Speaker 2: If this is happening in our Solar System, it should
Speaker 2: be happening in other Solar systems. Shouldn't space be filled
Speaker 2: with these ejected ice giants when it happened in other families,
Speaker 2: not just ours, and we can go and look for those.
Speaker 1: Yeah, we had a whole episode on rogue planets. There
Speaker 1: might be a billions of them out there right exactly.
Speaker 2: We can actually spot some of these using what we
Speaker 2: call micro lensing. If one of these planets out there
Speaker 2: floating between stars, passes in front of a star, like
Speaker 2: a little eclipse, then it'll blink out and actually change
Speaker 2: the way that light bends around the planet. So we
Speaker 2: can use these micro lensing techniques to try to spot them.
Speaker 2: We also have infrared telescopes like the Wise telescope that
Speaker 2: can try to directly image them. These planets don't glow
Speaker 2: in the visible light, but they do have some temperature,
Speaker 2: and everything with the temperature glows in some frequency. These
Speaker 2: would low in infrared, and so it's possible to see them.
Speaker 2: So we have seen a bunch of these rogue planets,
Speaker 2: and so we can estimate that there's like one of
Speaker 2: these things for every star in the galaxy.
Speaker 1: Well, I mean there's ae hundred billion of them right
Speaker 1: in our galaxy.
Speaker 2: Exactly, and we've only spotted a few of them. And
Speaker 2: so the calculation of like how many there are is
Speaker 2: very uncertain. There's a huge extrapolation there, which means a
Speaker 2: huge uncertainty, but we know it's a pretty big number.
Speaker 2: We know it's not just like ten in the galaxy.
Speaker 2: There's lots of these things out there, and that lends
Speaker 2: credence to this story that, like when solar systems form,
Speaker 2: there's a period of instability when big planets can get
Speaker 2: thrown out.
Speaker 1: So we've actually seen these like if you look at
Speaker 1: a picture of the nice guy in the infrared, you
Speaker 1: can see these thoughts moving across the sky.
Speaker 2: We can actually see these planets, and we have seen
Speaker 2: with direct imaging some of these rogue planets. Again, not
Speaker 2: very many, and so we're extrapolating from a handful up
Speaker 2: to a big number. We've definitely seen non zero and
Speaker 2: very recently James Webb saw some really crazy stuff out there.
Speaker 2: They found these Jupiter mass binary objects. They call them jumbos.
Speaker 2: These are pairs of planets floating out there in the
Speaker 2: galaxy with no star near by.
Speaker 1: Wait what, well, first of all, James Webb, you mean
Speaker 1: the telescope right, Yes, not James web from Erie, Pennsylvania.
Speaker 2: We did not exhume the previous NASA administrator and ask
Speaker 2: him to look at the night sky and then write
Speaker 2: down with what he said. Though that would make a
Speaker 2: pretty cool graphic novel. Yeah.
Speaker 1: Yeah, Well, I just don't want to assume everyone knows
Speaker 1: what James Webb is.
Speaker 2: No, you're exactly right. The James web Space Telescope a
Speaker 2: very powerful device that we launched a couple of years
Speaker 2: ago and is an infrared telescope capable of seeing things
Speaker 2: that are pretty cold. Spotted forty two pairs of jumbos.
Speaker 1: WHOA and so is there? Is it weird that they're
Speaker 1: in pairs? Or does it feel normal that they're in pairs? Meaning?
Speaker 1: Does that mean that they were ejective from their Solar
Speaker 1: system in pairs like they left together.
Speaker 2: It's a great question. We don't know the answer to that.
Speaker 2: Simulations suggest that it's unlikely for big planets to leave
Speaker 2: the Solar system together, right. They would have to be
Speaker 2: like bound together and then leave together, which means that
Speaker 2: their fragile orbits around each other would have survived very
Speaker 2: chaotic period. Seems very unlikely. So these are rogue planets
Speaker 2: that are out there without their star, but they don't
Speaker 2: seem to have been ejected from solar systems. So it
Speaker 2: just sort of like adds to the murkiness of what's
Speaker 2: going on with rogue planets.
Speaker 1: Whoa wait, wait, so maybe they were ejected and then
Speaker 1: they met up with another jumbo out there in space.
Speaker 2: We actually don't have a great story to explain how
Speaker 2: these even exist. Like that seems very unlikely for all
Speaker 2: these jupiters to like start dancing around each other just
Speaker 2: in space.
Speaker 1: Well, maybe they have like a planet dating app or something.
Speaker 2: Maybe they're speed dating there, or they're square dancing or something.
Speaker 2: They're all changing partners.
Speaker 1: That's right, they have jumpler under phones.
Speaker 2: Some people suggested maybe they just formed independently, like you
Speaker 2: had a solar system and it didn't have enough stuff
Speaker 2: to actually have a star. You just got a couple
Speaker 2: of jupiters. But we think that there's like a minimum
Speaker 2: amount of mass you need to get like your own
Speaker 2: solar system, otherwise you just get slurped up in like
Speaker 2: a neighboring solar system when that huge stellar nurseries breaking
Speaker 2: up into chunks that form solar systems. So we think
Speaker 2: that these things are probably too small to have seeded
Speaker 2: their own structure and be their own solar system. We
Speaker 2: don't think they could have been ejected from other solar systems.
Speaker 2: So it's something of a question of where these came from,
Speaker 2: you know, just to paint the picture that like, there's
Speaker 2: a lot we still don't know. There's a lot of
Speaker 2: guessing going on.
Speaker 1: But I guess if they didn't come from a solar system,
Speaker 1: then that doesn't really tell us anything about this idea
Speaker 1: of how often solar systems kick out planets exactly.
Speaker 2: But it adds doubt to the argument that because we
Speaker 2: see a bunch of rogue planets out there that suggest
Speaker 2: that planets are lost from solar systems, because there are
Speaker 2: planets out there whose formations we just don't understand and
Speaker 2: we think don't come from having been lost by a
Speaker 2: solar system.
Speaker 1: All right, well, I guess to answer the question of
Speaker 1: the episode, has our solar system lost any planets? The
Speaker 1: answer is maybe, we guess. So we guess. Maybe we
Speaker 1: used to have a brother, an older brother, but now
Speaker 1: nobody likes to talk about him or her, and it's
Speaker 1: very awkward. It makes all the models break, all the
Speaker 1: pets are uncomfortable.
Speaker 2: Almost all of the models we use to explain the
Speaker 2: solar system do have an additional planet. It's not absolutely required.
Speaker 2: It's possible to explain the Solar System without an additional
Speaker 2: planet that got ejected during one of these early instabilities.
Speaker 2: But it just makes the story come together more crisply.
Speaker 2: It makes our Solar system seem less unlikely.
Speaker 1: Now, how does this match up with I know there
Speaker 1: are scientists that think that we have maybe a ninth
Speaker 1: planet in our Solar system. We just can see it
Speaker 1: planet X, right.
Speaker 2: Yeah, there are some people who look at like gravitational
Speaker 2: aberrations in the orbits of our planet to see if
Speaker 2: there's something else out there tugging on it. But there's
Speaker 2: no conclusive evidence for that. It's like very very gentle,
Speaker 2: and there's a lot of disagreement about whether it's just
Speaker 2: noise or has other explanations.
Speaker 1: It's almost sort of the same, right, They use simulations
Speaker 1: and try to figure out what would best explain what
Speaker 1: we have now.
Speaker 2: Yeah, exactly, but the data there are not conclusive.
Speaker 1: All right. Well, another interesting lesson to keep track of
Speaker 1: your planets. Don't lose them because once they're gone, they're
Speaker 1: gone forever.
Speaker 2: And try to understand where you came from and what's
Speaker 2: your contact is, what happened before you showed up on
Speaker 2: the scene.
Speaker 1: Yeah, well, not that we have much influence over what happens,
Speaker 1: but it's interesting to think about what might happen in
Speaker 1: the future, Like, is it possible that the Earth might
Speaker 1: get kicked out of the Solar System right in the
Speaker 1: future exactly?
Speaker 2: The difference between these models tells a very different story.
Speaker 2: If it really is lots of gentle tugs from planet Esimals, well,
Speaker 2: that could still happen in the future. We have the
Speaker 2: Orc Cloud, we have the Kuyper Belt. There's still tugging
Speaker 2: going on. But if it was something that only happened
Speaker 2: in the very early formation of the Solar System itself,
Speaker 2: as this gas was pushed out, that's not something that's
Speaker 2: likely to be reproduced, and so that level of instability
Speaker 2: is probably not going to happen again.
Speaker 1: Now, Daniel, if we did have an icy gas planet before,
Speaker 1: but it was filled with white chocolate, are you happy
Speaker 1: that it's gone or are you sad that we don't
Speaker 1: have anymore?
Speaker 2: No, it's bittersweet. I wish it's the best.
Speaker 1: No, it's not bitter, it's sweet. It's white chocolate. That's
Speaker 1: the whole point of white chocolate.
Speaker 2: It's oversweetened. That's the problem.
Speaker 1: But maybe it'd be good for you because it would
Speaker 1: make all the white chocolate lovers go to this planet
Speaker 1: and leave ours exactly.
Speaker 2: Let's arrange transit to the frozen planet of white chocolate.
Speaker 1: Well call it white.
Speaker 2: No son of mine?
Speaker 1: All right, Well, we hope you enjoyed that. Thanks for
Speaker 1: joining us, See you next time.
Speaker 2: For more science and curiosity, come find us on social media,
Speaker 2: where we answer questions and post videos. We're on Twitter, Discord, Instant,
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Speaker 2: and Jorge Explain the Universe is a production of iHeartRadio.
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