Speaker 1: Hey, Kelly, I have a controversial question for you.
Speaker 2: Oh boy, coming from you that makes me particularly nervous.
Speaker 2: Is this another episode I'm gonna have to make sure
Speaker 2: my kids don't listen.
Speaker 1: To no, but it might cause some other kind of
Speaker 1: family drama.
Speaker 2: Okay, now you have my attention.
Speaker 1: Well, you know, since you're married to a cartoonist, I'm
Speaker 1: wondering if I'm allowed to ask you whether you're a
Speaker 1: fan of a different cartoon.
Speaker 2: Well, that depends if it's a rival cartoon or not.
Speaker 1: So I'm wondering if you have a favorite cartoon from
Speaker 1: the Far Side.
Speaker 2: Oh, I mean he hasn't updated for a while, right,
Speaker 2: I mean, I suppose he's still competition. But anyway, all right,
Speaker 2: let's see, let's see. Oh, so hard to pick so
Speaker 2: many favorites. So there's one where there's a slide, you know,
Speaker 2: like a kid's playground, and some spiders have built a
Speaker 2: net or a web along the bottom, and one spider
Speaker 2: is saying something like, if we can pull this off,
Speaker 2: we'll never be hungry again, nor something like that, And I,
Speaker 2: as an invert person, just thought that that was amazing.
Speaker 2: And of course I liked the like School for the
Speaker 2: Gifted the one that was on T shirts when I
Speaker 2: was a kid. What about you, Well, I have.
Speaker 1: To ask you. Do you see that Spider's eating a
Speaker 1: baby cartoon differently now that you're a parent?
Speaker 2: No, still hilarious.
Speaker 3: Us.
Speaker 1: I think your children should be terrified if they listen
Speaker 1: to this episode.
Speaker 2: Probably. Oh my gosh, poor kid won. The other day,
Speaker 2: I told her to go get a bowl in my office,
Speaker 2: and she thought it was going to have something like
Speaker 2: candy in it, but she accidentally picked up the bowl
Speaker 2: of dead insects that I found in the in the
Speaker 2: barn that I was thinking of pinning at some point,
Speaker 2: and they were all over my office, so she must
Speaker 2: have seen it and thrown it up in the air
Speaker 2: and they went all over. My kids are going to
Speaker 2: have very high therapy bills at some point, but I
Speaker 2: love them very much.
Speaker 1: I think that living in your house must be even
Speaker 1: weirder than the Far Side cartoon, almost certain. Hi. I'm Daniel.
Speaker 1: I'm a particle physicist and a professor at UC Irvine,
Speaker 1: and I don't think I've yet traumatized my children with insects.
Speaker 2: Hi. I'm Kelly Wiener Smith, and I study creepy crawley
Speaker 2: things at race university, and I'm traumatizing kids all the time.
Speaker 1: Education through trauma is set your strategy.
Speaker 2: That's a good way to make people remember stuff.
Speaker 1: Where you live out on the farm, but there's lots
Speaker 1: of access to creepy crawley weird things, and so I
Speaker 1: hope your kids are become ver acclimatized.
Speaker 2: To that I'm making them because it.
Speaker 1: Takes a brave soul to explore the nature of the universe,
Speaker 1: or even just your backyard, depending on what's slithering out there.
Speaker 1: So whether or not you turn your eyes down to
Speaker 1: the ground or up to the skies, there's a whole
Speaker 1: lot of stuff to wonder about, and so welcome to
Speaker 1: the podcast. Daniel and Jorge explain the universe in which
Speaker 1: we do all of that wondering. We think about everything
Speaker 1: that's between your toes and everything that your eyes can
Speaker 1: gather as you look up into the night sky. We
Speaker 1: think about what's on the moon, what's on the backside
Speaker 1: of the moon, and what's in the deepest, darkest depths
Speaker 1: of the universe. We chew all of it up and
Speaker 1: try to digest it and explain.
Speaker 2: It to you, and it's not always pretty.
Speaker 1: Sometimes the truth is just gross. My typical co host
Speaker 1: and friend, Jorge Champ can't be here today, so I'm
Speaker 1: very glad to have one of our regular guest hosts, Kelly. Kelly,
Speaker 1: thanks very much for joining us again and terrifying your children.
Speaker 2: Yeah, well, I hope I could terrify some people today too.
Speaker 2: Thanks for having me back.
Speaker 1: But today we're not talking about the weird, creepy crawley
Speaker 1: bits that are inside Kelly's pantry, strange as that might be.
Speaker 1: We are turning our eyes to the sky tonight. We
Speaker 1: are thinking about what's out there in the universe, and
Speaker 1: what we can see and what we can't see, and
Speaker 1: how the gravitational forces that have built the structure of
Speaker 1: our universe also limit what we can see out there.
Speaker 1: If you were a kid like me, then you spent
Speaker 1: a lot of time looking up at the night sky,
Speaker 1: not just absorbing the stars, but also gazing on the
Speaker 1: closest object that's out there, the biggest, fattest thing in
Speaker 1: the night sky, and that's, of course our moon. It
Speaker 1: has so many fascinating features to it, but one of
Speaker 1: the most interesting features is that you always see the
Speaker 1: same features. Cally, do you remember understanding this as a kid,
Speaker 1: or wondering about why you're always seeing the same bits
Speaker 1: on the moon.
Speaker 2: You know, I really wish you hadn't asked me that,
Speaker 2: because the answer is, when I was a kid, I
Speaker 2: didn't realize I was always seeing the same side of
Speaker 2: the moon. That hadn't really hit me until I think, baby,
Speaker 2: I was in college, and then I was like, wait
Speaker 2: a minute, and I guess it just wasn't I was
Speaker 2: looking down at the salamanders and not up at the sky.
Speaker 2: But so, no, that is not a question I had
Speaker 2: when I was a kid, but it should be. When
Speaker 2: did you learn this?
Speaker 1: I remember learning about it, I think when I was
Speaker 1: seven or eight, But you know, my dad was pretty
Speaker 1: into astronomy and into science, and so we talked about
Speaker 1: this kind of stuff. Something I'm still curious about, though,
Speaker 1: is when humanity understood that, or when humanity understood it
Speaker 1: was an interesting question, like did ancient Chinese astronomers, who
Speaker 1: spend a lot of time looking up at the moon
Speaker 1: and predicting its eclipses, did they figure out that the
Speaker 1: moon was a sphere and that it was rotating and
Speaker 1: that it was weird that we always saw the same
Speaker 1: side of it? Or is this just something they overlooked.
Speaker 2: Do you know the answer to that question.
Speaker 1: I don't know the answer to that question. I've been
Speaker 1: digging through the history of astronomy a little bit, and
Speaker 1: I know that Newton understood it because of his ideas
Speaker 1: of gravitation, But digging deeper into history, it's not really
Speaker 1: discussed very much. And I sort of wonder if people
Speaker 1: suspected that it was just a coincidence that the Moon
Speaker 1: rotates at this perfect rate just so that we can
Speaker 1: only see one side of it, because you know, there
Speaker 1: are other fascinating coincidences about the moon. For example, the
Speaker 1: moon and the Sun happen to be the same size
Speaker 1: in our sky, right, the Sun is much much bigger,
Speaker 1: but much much further away, and those two numbers line
Speaker 1: up perfectly. So the Sun and the Moon appear to
Speaker 1: be the same size, which is why we can get
Speaker 1: so many fascinating eclipse effects. And that, of course, is
Speaker 1: just a coincidence. There's no like deep reason for that.
Speaker 1: It just happens to be. These two numbers just kind
Speaker 1: of line up in our.
Speaker 2: Universe, and humans are notoriously tripped up by coincidences.
Speaker 1: Exactly, And so I think ancient astronomers must have wondered
Speaker 1: about that size, and I wonder if they also wondered
Speaker 1: about the rotation of the moon, if they understood that. Now,
Speaker 1: I do know that ancient Chinese astronomers had a little
Speaker 1: bit of a disadvantage compared to, for example, ancient Greek astronomers,
Speaker 1: because they didn't have geometry. Right, we think about the
Speaker 1: universe in terms of geometry. You imagine how clips has happened,
Speaker 1: and you think, probably in your head, you have a
Speaker 1: mental picture of all these things happening and to explain it.
Speaker 1: But Chinese astronomers didn't develop geometry, so they didn't have
Speaker 1: the same sort of geometrical thinking that we're all very
Speaker 1: familiar with. Instead, they had like tables of numbers, and
Speaker 1: they had arithmetic, and they could manipulate these numbers to
Speaker 1: do their predictions. So I think they must have thought
Speaker 1: about these things very differently than we did.
Speaker 2: Interesting, it's nice to have our modern tools.
Speaker 1: Thank you to those folks who invented geometry. It turns
Speaker 1: out to be pretty.
Speaker 2: Useful quote unquote modern.
Speaker 3: Yeah.
Speaker 1: Right, And so we have been looking up in the
Speaker 1: night sky and looking at the moon and seeing the
Speaker 1: same side of it for thousands and thousands of years,
Speaker 1: and now, of course we understand why. And so today
Speaker 1: on the podcast, we're going to be digging into the
Speaker 1: physics of the far side of the Moon and many
Speaker 1: other objects in our solar system that exhibit the same behavior.
Speaker 1: On today's episode, well, I answer the question what is
Speaker 1: tidal locking?
Speaker 2: And this is another thing that connects us to the dinosaurs, right,
Speaker 2: because they also would have seen the same side.
Speaker 1: Of the moon. If dinosaur geometers had figured that out, boy,
Speaker 1: they could have written a paper and got a lot
Speaker 1: of citations.
Speaker 2: They really could have, and then maybe they could have
Speaker 2: started a you know, NASA and had an asteroid deflection program.
Speaker 2: Everything could have been different.
Speaker 1: You sound like you're kind of hoping for that, but
Speaker 1: you know, in that scenario, we don't exist.
Speaker 2: Oh, good point.
Speaker 1: We're rooting for the asteroid on that one.
Speaker 2: That's right, we sure are.
Speaker 1: I'm sorry dinosaurs, which puts us on the anti math
Speaker 1: Education for Dinosaurs committee as well.
Speaker 2: It's an uncomfortable place to be, but no, it doesn't
Speaker 2: feel very good, but I'm firmly in this position. Yeah.
Speaker 1: So this is a topic that affects our Moon, and
Speaker 1: affects our planet, and affects a lot of things in
Speaker 1: the Solar system and in other Solar system. It's a
Speaker 1: fascinating little bit of physics. So I was curious what
Speaker 1: people knew about the topic of title locking and if
Speaker 1: they understood the physics of it. So I went out
Speaker 1: there into the internet to ask folks if they understood this.
Speaker 1: Thanks very much to those of you who participate in
Speaker 1: this segment of the podcast to let us know what
Speaker 1: people think about the topic of the day. If you'd
Speaker 1: like to hear your voice for a future episode, please
Speaker 1: don't be shy. Write to me two questions at Danielandjorge
Speaker 1: dot com. So think about it for a minute. Do
Speaker 1: you understand the physics of title locking? Here's what some
Speaker 1: listeners had to say.
Speaker 4: So, I believe that title locking is when, say, a
Speaker 4: planet has a moon that's locked in orbit at a
Speaker 4: certain distance, so the tides are always the same. So
Speaker 4: I guess you could say that we're in title locking
Speaker 4: because day in and day out, our tides go the
Speaker 4: same because.
Speaker 1: The moon's in a fixed orbit.
Speaker 2: Title locking is just like our moon. We see the
Speaker 2: same face of it at all times.
Speaker 4: It has no spin, and the dark side of the
Speaker 4: moon is facing outward.
Speaker 2: It is the deformation that a celestial body so first
Speaker 2: when it's orbiting or is orbited by another massive celestial body.
Speaker 3: Title locking is when a lower mass body is orbiting
Speaker 3: a much higher mass body and the the same side
Speaker 3: always faces it, so I know that we always see
Speaker 3: the same side of the Moon means tidally locked to
Speaker 3: the Earth.
Speaker 2: I was impressed that none of the listeners seemed totally
Speaker 2: stumped by this, because I feel like tidle locking is
Speaker 2: not necessarily something that you hear, like that at least
Speaker 2: there's a phrase I don't hear very often, and so like,
Speaker 2: it seems like some people knew exactly what you were
Speaker 2: asking about, and none of them were like me when
Speaker 2: I was a kid, and we're just totally unaware that
Speaker 2: this is a thing that was happening.
Speaker 1: Yeah, we got some pretty well educated listeners. The word title,
Speaker 1: I think makes some people think of tides, which is
Speaker 1: connected of course to tidal forces, you know, like the
Speaker 1: Moon pulls on the Earth and squishes its oceans and
Speaker 1: makes us have higher tides in some places and lower
Speaker 1: tides and other places. But that's not what we mean
Speaker 1: by title locking. Tidle locking is actually a different phenomena
Speaker 1: we're going to dig into today. But thank you very
Speaker 1: much to all of our volunteers. We really cherish your thoughts.
Speaker 2: Yeah, you have a smarter than average audience, I think,
Speaker 2: or smarter than Kelly average. I'm always impressed by the answers.
Speaker 1: They're smart and they're good looking too.
Speaker 2: That's right. I think that's called the halo effect. You
Speaker 2: know one good thing about them, and you assume you
Speaker 2: know all the good things about them.
Speaker 1: So let's dig into the physics of tidal locking. What
Speaker 1: it is, what's going on and why I play such
Speaker 1: a big role in what we see in our night sky.
Speaker 1: And I think the first thing to understand is just
Speaker 1: like the geometry of what's going on. Obviously, the Moon
Speaker 1: is orbiting the Earth, and the Earth is spinning, and
Speaker 1: the Moon is spinning around the Earth, and the Moon
Speaker 1: is also spinning on its axis. So there's sort of
Speaker 1: a lot of spinning going on. But you got to
Speaker 1: get all that spinning in your head to understand, like
Speaker 1: why we only see one side of the moon.
Speaker 2: Yes, so I am staring directly ahead trying to picture everything,
Speaker 2: So go ahead, what should I be imagining?
Speaker 1: So first, just put yourself on the Earth and forget
Speaker 1: the fact that the Earth is spinning, and just move
Speaker 1: the Moon around the Earth in your mind and imagine
Speaker 1: the Moon is like a shoe or something. If the
Speaker 1: Moon is not spinning, it's just orbiting the Earth, then
Speaker 1: the Earth is going to see different sides of the shoe.
Speaker 1: It's going to see the back of the shoe, it's
Speaker 1: going to see the front of the shoe, because as
Speaker 1: the shoe moves around the Earth, different sides of it
Speaker 1: are going to be closer to the Earth or closer
Speaker 1: to outer space.
Speaker 2: So the shoe is not rotating either.
Speaker 1: That's right. So first the shoe is not rotating, and
Speaker 1: so we see one side of it, and then we
Speaker 1: see the other side of it. So if the shoe
Speaker 1: or the moon or whatever is not spinning, then you
Speaker 1: would see different sides of it. Right now, the moon,
Speaker 1: of course, is spinning. It's spinning on its axis. But
Speaker 1: if it was spinning at some random rate, like really
Speaker 1: really fast or really really slow, you would still see
Speaker 1: both sides of it, because eventually it would spin in
Speaker 1: a way that revealed every part of the moon. The
Speaker 1: only way for us to not be able to see
Speaker 1: part of the moon is for its spin to be
Speaker 1: perfectly syncd up with its orbit, so that as it
Speaker 1: goes around the Earth, it turns just the right a
Speaker 1: mount every second, so the same side of it is
Speaker 1: always facing the Earth, like if the back side of
Speaker 1: the shoe is always fa the Earth, because the shoe
Speaker 1: itself is spinning at just the right rate as it
Speaker 1: goes around the Earth.
Speaker 2: And everyone on every part of the Earth is always
Speaker 2: seeing the same side of the Moon. Right, It's not
Speaker 2: like you know, in the US you see one side
Speaker 2: and in China you see the other side, or right,
Speaker 2: You're always seeing the same side.
Speaker 1: That's right. The same side of the Moon is always
Speaker 1: closer to the Earth, and the other side of the
Speaker 1: Moon that we call the far side, which I assume
Speaker 1: is the origin of the name of the far side
Speaker 1: and comic, it is always facing outer space. And this
Speaker 1: is the sort of coincidence we were talking about. Like these
Speaker 1: two numbers, the rate at which the Moon goes around
Speaker 1: the Earth and the rate at which the Moon spins
Speaker 1: around its axis have to be perfectly synced up to
Speaker 1: get this effect.
Speaker 2: And why are they perfectly syncd up? Is this one
Speaker 2: of the few instances in which we have something special
Speaker 2: going on and they just happen to sync up. Or
Speaker 2: are we just like every other moon because this happens
Speaker 2: all the time.
Speaker 1: So it's not that special and it's not a coincidence,
Speaker 1: but it's not something that's always happened. Like, to get
Speaker 1: into it, you have to understand the history of the
Speaker 1: formation of the Moon, like how did it get made,
Speaker 1: how was it spinning originally, and then how has that changed?
Speaker 1: You know, our moon is not just like some object
Speaker 1: that we captured as it was flying by. We think
Speaker 1: that the Moon actually comes from a huge collision something
Speaker 1: like one hundred million years after the Earth was formed,
Speaker 1: so we're talking like four point four billion years ago.
Speaker 1: You have some like very hot proto Earth. It got
Speaker 1: slammed into by some giant Mars sized planet they called Fea,
Speaker 1: And so you're talking about a huge collision like Earth
Speaker 1: versus Mars in space and both objects are essentially vaporized.
Speaker 2: But we still have thirst in the moon.
Speaker 1: You're like, how do that to current reality? You know,
Speaker 1: you're exactly right, it got vaporized, but then it coalesced. Right.
Speaker 1: Gravity is very very patient, and so even though all
Speaker 1: of its original work in the first one hundred million
Speaker 1: years was ruined by this collision. It got back to
Speaker 1: work and it pulled those blobs together and it made
Speaker 1: two new blobs, one that formed the Earth, and then
Speaker 1: a big ring around the Earth, like a ring of
Speaker 1: debris that was spinning sort of too fast around the
Speaker 1: Earth to fall into the central clump, which formed this
Speaker 1: like huge spray of material.
Speaker 2: All right, So, and that's why the Moon's made out
Speaker 2: of the same stuff the Earth is made out of.
Speaker 1: Exactly when we visited the Earth first and we sampled it,
Speaker 1: people were surprised to discover that it's basically the same
Speaker 1: mixture of stuff as the Earth. It's not like a
Speaker 1: different Solar System body that was formed in another place,
Speaker 1: and so it has a different mixture of like ices
Speaker 1: and rocks and different isotopes and stuff. It's basically made
Speaker 1: out of the same stuff as the Earth. And that's
Speaker 1: because it comes from the same mixture of those two planets.
Speaker 1: Like it was the same vaporized blob of stuff, and
Speaker 1: some of it fell in towards the Earth, and the
Speaker 1: stuff that was spinning around sort of too fast ended
Speaker 1: up in this big debris ring. But then gravity pulled
Speaker 1: that together into a moon.
Speaker 2: Did we have this hypothesis before we went to the
Speaker 2: Moon and found what it was made of, or did
Speaker 2: going to the Moon and physically collecting samples give us
Speaker 2: this hypothesis when we were like, whoa, it's the same stuff.
Speaker 1: This hypothesis has been around for a while, but it
Speaker 1: really became the favorite once we went to the Moon,
Speaker 1: and also once we understood something about the Moon's inner core.
Speaker 1: The Moon has sort of a small iron core, smaller
Speaker 1: than you would expect, and the hypothesis is that a
Speaker 1: lot of that iron was probably lost from when the
Speaker 1: impactor hit the proto Earth, and some of that was
Speaker 1: like melted and vaporized, and so it would have a
Speaker 1: bigger iron core otherwise. This became a much more popular
Speaker 1: hypothesis after we went to the Moon and visited and
Speaker 1: understood what it was made out of. And there's a
Speaker 1: lot of really interesting physics there that's relevant to it,
Speaker 1: Like why doesn't it all just collapse into a planet, right,
Speaker 1: Why doesn't it all just become one huge giant planet.
Speaker 1: How come part of it ended up as a ring?
Speaker 1: And that's just because you know, the whole thing is
Speaker 1: spinning and a lot of it has angular momentum, and
Speaker 1: so some stuff was just moving too fast to fall
Speaker 1: in the way, like the moon now is moving too
Speaker 1: fast to fall into the Earth. It's all about that.
Speaker 1: And then when that stuff gathered together into a moon,
Speaker 1: that stuff was spinning. So the moon had some original spin, right,
Speaker 1: that came from the spinning motion of all of that
Speaker 1: stuff after the vaporization. And we think that spin rate
Speaker 1: originally was much much higher than it is today. So
Speaker 1: the Moon used to be spinning faster than it is now.
Speaker 2: Was there this is maybe an unfair question. Was there
Speaker 2: anything alive on Earth when it was spinning fast enough
Speaker 2: that sometimes you'd see what is now the far side
Speaker 2: of the moon. So like dinosaurs probably never saw the
Speaker 2: far side of the moon, but did like the first
Speaker 2: bacteria see the far side of the Moon. I mean,
Speaker 2: I'm sure they don't see anything that far away, but
Speaker 2: you know, could they have.
Speaker 1: Yeah, it's possible. We don't really know exactly how old
Speaker 1: life is on Earth, but it stretches back billions of years, right,
Speaker 1: And so it's possible that there are critters that have
Speaker 1: lived on Earth that have seen other parts of the Moon.
Speaker 1: That's a very cool thought. Because the Earth has been
Speaker 1: gradually slowing down the Moon's spin little by a little
Speaker 1: every year, and the opposite is also true. But you know,
Speaker 1: until nineteen fifty nine, no human had ever seen the
Speaker 1: backside of the Moon. It was this like dark spot
Speaker 1: in our vision that we just couldn't see, no matter
Speaker 1: how many thousands of years we've been staring up at
Speaker 1: the Moon. Nobody had ever laid eyes on the backside
Speaker 1: until nineteen fifty nine, which feels really recent.
Speaker 2: Right, And the Soviets did.
Speaker 1: It, right, Yeah, they certainly did.
Speaker 2: Yeah, they beat us there with the lunar program. Their
Speaker 2: third one made it there. I think the first two
Speaker 2: maybe blew up. That was a thing that happened a
Speaker 2: lot for the Soviets. But anyway, so.
Speaker 1: Sorry, no, there's a really fun set of stories there.
Speaker 1: Maybe you know about because of your book research, that
Speaker 1: the Soviets were there first, and so they got to
Speaker 1: name a lot of stuff on the far side of
Speaker 1: the Moon first. So they have all these Russian names
Speaker 1: and that like really annoyed the Americans at the time.
Speaker 1: And then you know, later this International Astronomical Union took
Speaker 1: over the naming, so it wasn't all just you know,
Speaker 1: named after kinds of vodka or whatever.
Speaker 2: All now that's an unfair stereotype. Did the IAU change
Speaker 2: any of the names that the Soviet program had put
Speaker 2: in place, or they just like stopped the Soviets from
Speaker 2: doing any more naming.
Speaker 1: I think they just stopped them. And there's a lot
Speaker 1: of respect, I think for the people who discover something
Speaker 1: to name it. But then I think that the Soviets
Speaker 1: were so far ahead that they didn't want them to
Speaker 1: just like name the whole thing after their favorite Soviet
Speaker 1: flower or whatever.
Speaker 2: Thank, yes, there we go. That's good. That's good. I
Speaker 2: think there is like a Gagarian and seas or something
Speaker 2: like them. All Right, so we're gonna take a quick
Speaker 2: break and then we'll talk about what they found on
Speaker 2: the far side of the moon. The first time we
Speaker 2: got to see the far side of the moon was
Speaker 2: nineteen fifty nine. Not too long after that, the Apollo
Speaker 2: astronauts were flying around the Moon and got to see
Speaker 2: the far side. What kinds of things were on the
Speaker 2: far side to see, Daniel.
Speaker 1: Well, you know, in research, it's always exciting to see
Speaker 1: something nobody's ever seen before because you don't know what's
Speaker 1: going to be there. Right, Maybe it's like a crashed
Speaker 1: alien battleship or some weird new geological formation. Right, your
Speaker 1: imagination goes crazy when you're first landing on a spot
Speaker 1: and seeing something no human has ever seen before. But
Speaker 1: you know, in research, discoveries never guaranteed. Just because you
Speaker 1: land on new shores doesn't mean you find something fascinating.
Speaker 1: And in this case, basically we found that the far
Speaker 1: side of the Moon has more rocks and more dust,
Speaker 1: and it's not even very different from the front side
Speaker 1: of the Moon. I mean there are more craters, there
Speaker 1: are fewer of these like seas, these lunar lava flows,
Speaker 1: but all in all, it's not that exciting.
Speaker 2: Yeah, that's the moon, good old, dependable Moon.
Speaker 1: And the first time anybody actually landed there was twenty nineteen,
Speaker 1: like just a few years ago the Chinese put a
Speaker 1: lander down and started to do a bunch of experiments.
Speaker 1: So it's only recently we started to explore it in detail.
Speaker 1: So you know, there's still hope to find that crashed
Speaker 1: alien battleship or.
Speaker 2: The aliens might be living in a lavatude. We could
Speaker 2: find something even more exciting than what you've imagined.
Speaker 1: Yeah, maybe so, Or maybe we could build something that
Speaker 1: future aliens could land and discover for themselves, like people
Speaker 1: are proposing building radio telescopes on the far side of
Speaker 1: the moon looking out into space, because then you'd have
Speaker 1: the whole moon to shield you from the noise of
Speaker 1: the Earth.
Speaker 2: From my perspective, that's an interesting prospect geopolitically, because if
Speaker 2: you built one of those radio telescopes, it wouldn't work
Speaker 2: as well if people put other stuff on that side
Speaker 2: of the moon. So now there's like competition for that space.
Speaker 2: And can you tell someone they can't use the far
Speaker 2: side of the moon because your radio telescope is there. Anyway,
Speaker 2: These things are complicated, but yes, it would be a
Speaker 2: good place for a radio telescope.
Speaker 1: Sounds like the kind of things a bunch of lawyers
Speaker 1: in a conference room are going to hash out one day.
Speaker 1: So the far side of the Moon is not that
Speaker 1: exciting on its own, but it is fascinating to understand
Speaker 1: why there is a far side of the moon. Before
Speaker 1: we dig into that, I just want to clarify something
Speaker 1: that's a common misunderstanding, which the difference between the far
Speaker 1: side of the Moon and the dark side of the moon.
Speaker 1: Also the Pink Floyd album.
Speaker 2: I don't think anyone needs clarification. We all know about that,
Speaker 2: and we've all probably seen the light show if we're
Speaker 2: around forty years old.
Speaker 1: So some people imagine that the far side of the
Speaker 1: moon is also the dark side of the moon, that like,
Speaker 1: this part of the moon never sees sunlight, which is
Speaker 1: definitely not true. The dark side of the moon is
Speaker 1: the side of the moon facing away from the Sun.
Speaker 1: The far side of the moon is the side facing
Speaker 1: away from the Earth, and those two often don't agree.
Speaker 1: So when we have a full moon, the sun is
Speaker 1: illuminating the entire side of the Moon that we are
Speaker 1: seeing because the Sun is sort of behind us in space.
Speaker 1: Then the back side of the moon, the far side
Speaker 1: that we don't see, is also dark. But the opposite
Speaker 1: scenario when the moon is totally dark when we see
Speaker 1: a new moon, and that's because the far side of
Speaker 1: the moon is totally lit up by the sun. Right
Speaker 1: half of the moon is always lit up, it's just
Speaker 1: sometimes not the side that we're seeing, So the far
Speaker 1: side and the dark side are different. It would be
Speaker 1: like a Gary Larsen Pink Floyd crossover event when they meet.
Speaker 2: I'm pretty sure if you play Dark Side of the
Speaker 2: Moon backwards it explains that.
Speaker 1: That's how you understand the far side cartoons, right, you
Speaker 1: have to listen to the dark side of the moon backwards.
Speaker 2: Yeah, there was a lot of cross talk between the
Speaker 2: arts back then. Okay, so how is this happening. The
Speaker 2: moon was going faster, you said, and it's been slowing down.
Speaker 2: Why has it slowed down to be exactly the same
Speaker 2: rotation rate and stuff? What's going on?
Speaker 1: So it's not a coincidence, right. Physics seems to like
Speaker 1: this scenario, and it's called tidal locking because it's connected
Speaker 1: to the concept of tidal forces, which are in effect
Speaker 1: we see all the time in gravity. And it sounds complicated,
Speaker 1: but it's really pretty simple. The only thing you really
Speaker 1: have to understand is that gravity gets weaker as distances
Speaker 1: get longer. So if you're further away from the Sun,
Speaker 1: it's gravity is less powerful. As you get closer to
Speaker 1: the Sun, it's gravity is more powerful. That makes sense.
Speaker 1: But now imagine you're a pretty big object. Part of
Speaker 1: you is closer to the Sun than another part, then
Speaker 1: part of you is going to feel stronger gravity than
Speaker 1: the other part. And this happens all the time, Like
Speaker 1: if you are standing on the surface of the Earth,
Speaker 1: then the Earth is pulling on your legs harder than
Speaker 1: it's pulling on your head, right, and so that's a
Speaker 1: tidal force because there's a difference there. You can actually
Speaker 1: think about the Earth is sort of like trying to
Speaker 1: pull your head off of your body.
Speaker 2: Is this like many spaghetification?
Speaker 1: Yes, exactly, when it's very powerful. When it's more powerful,
Speaker 1: then the force is holding an object together, that's spaghetification.
Speaker 1: And so when you get near a black hole, for example,
Speaker 1: gravity is super powerful, and the difference between the gravity
Speaker 1: at your feet and your head is much more dramatic
Speaker 1: and much more powerful than the force is holding your
Speaker 1: head on your body, and so it's effectively natural decapitation
Speaker 1: or spaghetification.
Speaker 2: But lucky for us, instead of death, we get.
Speaker 1: The tie exactly, so you don't have to worry about that,
Speaker 1: because the difference of the force of gravity on your
Speaker 1: feet and on your head is very gentle, and your
Speaker 1: neck is very powerful in comparison. But the moon is
Speaker 1: pretty big, and so the difference between the gravitational force
Speaker 1: on one side of the moon and on the other
Speaker 1: is much stronger. And so what happens is that the
Speaker 1: Earth basically turns the Moon a little bit into a football.
Speaker 1: It like makes it a little bit all blong, because
Speaker 1: it pulls on the closer bits more powerfully, and it
Speaker 1: pulls on the further bits more gently, and has the
Speaker 1: effect of sort of like stretching it out, making it
Speaker 1: longer like a football instead of like a sphere.
Speaker 2: This is another one of those things I'm surprised we
Speaker 2: ever figured out, because when I look at the Moon,
Speaker 2: I would not think football.
Speaker 1: It's a subtle effect, right, It looks like a sphere,
Speaker 1: but is slightly distorted by the gravity of the Earth,
Speaker 1: and that has a big impact on how it spins,
Speaker 1: because now it has a gravitational preference to be aligned
Speaker 1: a certain way with the Earth. If it was a
Speaker 1: perfect sphere, then the gravity on the object wouldn't change
Speaker 1: as it spins. But if it has a bulge, then
Speaker 1: gravity prefers that bulge to be aligned with the object,
Speaker 1: sort of like gravity has a handle now on the
Speaker 1: Moon to pull that bulge, so one point is towards
Speaker 1: the Earth and one point is away from the Earth.
Speaker 1: That's like gravitationally less energetic a configuration than having the
Speaker 1: whole thing spin.
Speaker 2: All right, Okay, so I'm trying to wrap my head
Speaker 2: around this, and picturing things in my head is not
Speaker 2: one of my stronger suits. But here we go. Okay,
Speaker 2: so we prefer to have a grip on the handle.
Speaker 2: Does the moon spin at a not constant speed where
Speaker 2: like we hold on to the handle for a little longer.
Speaker 2: I don't think that's what you're saying, And so what
Speaker 2: am I missing?
Speaker 1: So what happened initially is that the Earth started to
Speaker 1: form these bulges on the Moon, and then the Moon
Speaker 1: was spinning, and so these bulges were like ripples through
Speaker 1: the surface of the Moon. There were like these waves
Speaker 1: that pass through the Moon. But Earth is also pulling
Speaker 1: on those bulges, right Like, if the Moon has a bulge,
Speaker 1: it's like a football, and then it starts to spin
Speaker 1: away from the Earth. The Earth is going to pull
Speaker 1: on that nearest point a little bit and try to
Speaker 1: pull it back, and that effectively moves the bulge through
Speaker 1: the surface of the Moon a little bit, and so
Speaker 1: that slows down the rotation of the Moon a little bit,
Speaker 1: because the Earth is like tugging trying to pull that
Speaker 1: point back towards it, and so that slows the moon
Speaker 1: down a little bit. And eventually the Moon settles into
Speaker 1: a pattern where these waves the bulge doesn't travel over
Speaker 1: its surface anymore, like settles into one location. And that's
Speaker 1: what the Earth prefers.
Speaker 2: Gravitationally, Okay, I'm with you.
Speaker 1: And so that's how gravity makes the Moon a little
Speaker 1: bit pointy and also slows down its spin. It's like
Speaker 1: stealing some of its energy a little bit to slow
Speaker 1: down its spin.
Speaker 2: But why does its spin get slowed down to exactly
Speaker 2: the right amount, Like it seems like that should just
Speaker 2: slow things down in general.
Speaker 1: It does. It slows things down in general, but at
Speaker 1: some point it starts spinning at just the right speed
Speaker 1: so that the pointy bit is always pointing towards the Earth.
Speaker 1: And then the Earth is happy, and the gravity of
Speaker 1: the Earth no longer wants to slow down the spin
Speaker 1: of the Moon because the point to bit is always
Speaker 1: facing the Earth, and so gravity is happy, because it's
Speaker 1: sort of like a ball rolling to the bottom of
Speaker 1: a valley, happy when it's settled in the bottom of
Speaker 1: the valley. So this is sort of like, you know,
Speaker 1: you let a marble go at the top of a
Speaker 1: hill and it's gonna roll down. It's gonna awesantly pass
Speaker 1: the minimum, but eventually friction and everything it's gonna settle
Speaker 1: down in the minimum, and the same thing happens. There's
Speaker 1: like friction inside the Moon, and the Moon gets heated
Speaker 1: up a little bit by this, and the Moon also
Speaker 1: speeds up in its orbit because there's like conservation of
Speaker 1: angular momentum. So you've slowed down the Moon's spin a
Speaker 1: little bit, and you've sped up its orbit a little bit,
Speaker 1: which is why the Moon's orbital radius is increasing a
Speaker 1: little bit.
Speaker 2: And so how rare is this? Like if Earth were
Speaker 2: a little bit smaller, would this not happen? If there was,
Speaker 2: like if Mars was a little closer, would this not happen?
Speaker 1: Like?
Speaker 2: How lucky are we that it worked out this way?
Speaker 1: We're not that lucky. It's sort of the eventual fate
Speaker 1: of almost every pair of bodies that orbit each other
Speaker 1: for long enough. And in fact, we've done it to
Speaker 1: the Moon, and eventually the Moon will do it to
Speaker 1: the Earth. It's just a slower process.
Speaker 2: Whoa like, how slow? Like are we gonna swallowed up
Speaker 2: by the Sun before it happens? Or is my you know,
Speaker 2: kid gonna see it before they turn eighty.
Speaker 1: Yeah, so the Earth's rotation has already been significantly slowed
Speaker 1: by this effect from the Moon. Over the four billion
Speaker 1: years since the Earth and the Moon were formed, the
Speaker 1: length of an Earth day has lengthened from six hours
Speaker 1: to twenty four hours. So the Moon has made our
Speaker 1: days four times longer. It's slowed down the Earth spin
Speaker 1: by a big factor. And eventually, because the Moon keeps
Speaker 1: tugging on the Earth and making it a little bit
Speaker 1: longer than tugging on that handle as it passes, eventually
Speaker 1: it's gonna make the Earth take forty seven days to spin.
Speaker 1: And at that point, the Earth and the Moon will
Speaker 1: both be tidally locked to each other, and the Moon
Speaker 1: will only ever see the same face of the Earth.
Speaker 2: I don't think that's very nice of the bit. I
Speaker 2: like having days. Ah, so I'm glad that's not gonna
Speaker 2: happen in my lifetime.
Speaker 1: That would be fascinating, right because it would mean that
Speaker 1: half of the Earth would see the Moon and the
Speaker 1: other would never see it. If life evolved in that planet,
Speaker 1: then like half of life wouldn't even know there was
Speaker 1: a moon.
Speaker 2: WHOA, I bet we'd have all sorts of different like
Speaker 2: creation stories. If some of us had moons and some
Speaker 2: of us didn't. That would be that would be fascinating.
Speaker 1: Or imagine being an explorer and like settling around the
Speaker 1: world and then discovering this huge thing floating in your sky.
Speaker 1: You're like, what, that would be crazy, that would be
Speaker 1: super amazing. But you're right, it's going to take a
Speaker 1: long time. And well, before that happens, the Earth is
Speaker 1: going to be eaten by the Sun, which is going
Speaker 1: to end its life cycle in about five billion years,
Speaker 1: turn into a red giant and absorb the Earth. So
Speaker 1: the Moon is not powerful enough to make that happen
Speaker 1: anytime soon.
Speaker 2: Well, on the upbeat topic of the end of our planets,
Speaker 2: let's take a break, and when we come back, you
Speaker 2: can tell us if the other moons on the other
Speaker 2: planets are doing this as well. If I live on Mars,
Speaker 2: am i gonna see all of Phobos or not? Okay,
Speaker 2: we're back. So, Daniel, the question that everybody wants to
Speaker 2: know when we move to Mars, are we going to
Speaker 2: see the far side of Phobos and Demos or what?
Speaker 1: So this is a process that happens all over the
Speaker 1: Solar System and all over the universe. Eventually, gravity will
Speaker 1: do its bit and distort objects from spheres into like
Speaker 1: gentle little footballs. It'll grab on those handles and it
Speaker 1: will hidly lock stuff. And so as we look around
Speaker 1: the Solar System, we notice that all of the big moons,
Speaker 1: all of the twenty round moons that exist around planets,
Speaker 1: are all tidally locked to their planet.
Speaker 2: Only the round moons. And what causes the Moon to
Speaker 2: be round, It's that it needs to be a certain size,
Speaker 2: Is that right?
Speaker 1: Yeah, If you're big enough, then gravity is going to
Speaker 1: be powerful enough to pull down any big features, which
Speaker 1: is why, for example, like neutron stars have no features
Speaker 1: on them that are highiher than one millimeter. And the
Speaker 1: larger the gravity, the harder it is to keep a
Speaker 1: stack of stuff from falling down. And so if you're
Speaker 1: a pretty small object, you don't have to be very
Speaker 1: spherical because your gravity's pretty weak. If you're a big
Speaker 1: object like the Moon or the Earth, then you're going
Speaker 1: to end up as a sphere because stuff falls down basically,
Speaker 1: and stuff falls down more when you have more gravity.
Speaker 1: And so these round moons are technically not actually round, right,
Speaker 1: They're a little bit footballish and they're all tidally locked
Speaker 1: to their planet. Most of these also orbit pretty closely
Speaker 1: and so their gravity is pretty powerful. And then example,
Speaker 1: you raise like Phobos and Demos on Mars. These are
Speaker 1: little moons and they're not very large, they're not very round,
Speaker 1: and they're actually spending really really fast. And so while
Speaker 1: Mars is doing its job to try to tidly lock them, Phobos,
Speaker 1: for example, is not yet tidally locked, but it will be.
Speaker 1: It will be eventually. It's going to happen to everybody.
Speaker 2: So we've been talking about moon planets. Has it happened
Speaker 2: to any sun and planets or planets yet?
Speaker 1: Absolutely? It has absolutely will Right, the Sun is the
Speaker 1: most powerful source of gravity in the Solar System, and
Speaker 1: so it's not going to be left out of this party.
Speaker 1: And it has mercury tidly locked in its grasp. But
Speaker 1: it's actually fascinating. It's not quite the same way as
Speaker 1: with the Earth and the Moon because mercury doesn't have
Speaker 1: as circular an orbit. It's much more elliptical. The mercury
Speaker 1: is tightly locked in this weird way. Instead of spinning
Speaker 1: once every time it goes around the Sun, it spins
Speaker 1: three times for every two revolutions around the Sun. And
Speaker 1: this is not something we understood for a while because
Speaker 1: we can't always see Mercury because it's so close to
Speaker 1: the Sun. There's a few spots in its orbit when
Speaker 1: it's like easy to see mercury, and so when people
Speaker 1: were observing Mercury, they were always seeing the same side
Speaker 1: of it, so they thought, oh, it must have been
Speaker 1: a one to one tide locking. And it's only later
Speaker 1: when we got more observations in Mercury did we notice, Oh, no,
Speaker 1: it's doing this even weirder thing. That's because the orbit
Speaker 1: is not circular, and so it can do another little
Speaker 1: bit of spin as it gets further away, and then
Speaker 1: it comes back around, but still it settles into this
Speaker 1: really cool pattern, this three two tidal locking.
Speaker 2: All right, So let's see, my very elderly mother. We're
Speaker 2: on v I'm guessing Mercury is tidally locked in part
Speaker 2: because it's so close to the Sun. So is Venus
Speaker 2: the next closest to being tidally locked or is is
Speaker 2: it tidally locked?
Speaker 1: Also, Venus is next on the list to getting tidly locked.
Speaker 1: It's not yet tidly locked. In fact, Venus has a
Speaker 1: really weird orbit and spin. It takes five hundred and
Speaker 1: eighty three days to go around the Sun, but it
Speaker 1: takes two hundred and twenty four Earth days to rotate.
Speaker 1: So like a Venus year only has one point nine
Speaker 1: Venus days. Like you only see two sunrises and two
Speaker 1: sunsets in a Venus year.
Speaker 2: Huh, But that wouldn't bother you, because Venus would have
Speaker 2: killed you in four or five different ways long before
Speaker 2: you cared about whether the sunrise was coming.
Speaker 1: That's right. But Venus is sot again there right, Like
Speaker 1: it's spin is similar to its orbital period. We actually
Speaker 1: think that's because of a collision that Venus was like
Speaker 1: smacked into by something which really changed its spin. We
Speaker 1: don't think there's been enough time for it to be
Speaker 1: like almost tighly locked by the Sun. It takes a
Speaker 1: much longer time because Venus is so far away from
Speaker 1: the Sun and so small relative to the Sun.
Speaker 2: All right, So we've done moon and planets. We've done
Speaker 2: comparisons between the Sun and the planets. Is there any
Speaker 2: other combination of tidally locked things for us to think about?
Speaker 2: Can asteroids get tidly locked? For example?
Speaker 1: They could, but it's much harder because their gravity is
Speaker 1: so weak. Another really fascinating thing to look at are
Speaker 1: things that have similar masses, like dwarf planets and their moons. So,
Speaker 1: for example, Pluto no longer a planet, but it's still
Speaker 1: a dwarf planet. It's got a pretty big moon, Sharon,
Speaker 1: and these two things are mutually tightly locked already. So
Speaker 1: if you're like on Pluto and you look up, you
Speaker 1: always see the same side of the Moon. And if
Speaker 1: you're on Moon and you look up, you always see
Speaker 1: the same side of Pluto.
Speaker 4: Oh.
Speaker 2: Interesting to how many moons does Pluto have.
Speaker 1: Oh, Pluto's got a bunch of moons, but most of
Speaker 1: them rotate chaotically. They're too small to have been tidly
Speaker 1: locked so far. But it's sort of beautiful to see
Speaker 1: these things like orbiting their center of mass and facing
Speaker 1: each other. It's kind of like a dance.
Speaker 2: Yeah, that's awesome. It's beautiful.
Speaker 1: And that's not the only example of a dwarf planet.
Speaker 1: There's another one out there, a trans Neptunian object called Eris,
Speaker 1: which is also a dwarf planet, and it's got a
Speaker 1: pretty big moon called Dyspnomia, which happens to be the
Speaker 1: second largest dwarf planet moon after Pluto's moon, and these
Speaker 1: two are also tidly locked with each other.
Speaker 2: That sounds like it's a pretty common thing for dwarf
Speaker 2: planets to have moons, that know, because how many dwarf
Speaker 2: planets are there.
Speaker 1: There's a lot of dwarf planets out there. That's one
Speaker 1: reason why Pluto isn't really a planet anymore, because we
Speaker 1: discovered there's kind of a lot of them out there.
Speaker 1: And if we call Pluto a planet, we've got to
Speaker 1: call them all planets, and then we're going to have
Speaker 1: a lot of planet and so you know, astronomers have
Speaker 1: big arguments about where to draw the line, but there's
Speaker 1: a lot of dwarf planets.
Speaker 2: Out there, right, and like, how are we going to
Speaker 2: have naemonic if there's twenty of one or something like?
Speaker 2: We just no way, no way, all right. So that's
Speaker 2: our solar system. This sounds like a fundamental physics thing.
Speaker 2: So I'm guessing that when we look at other solar systems,
Speaker 2: they've got the same thing going on.
Speaker 1: Yes, exactly. We expect that the same thing will happen
Speaker 1: to planets around other stars and to moons around those planets,
Speaker 1: and because of sort of the way that we can
Speaker 1: discover those exoplanets. We expect a lot of the ones
Speaker 1: we've seen so far have been tidly locked. Like the
Speaker 1: way that we discover these planets is by seeing their
Speaker 1: impact on their star. Either they pass in front of
Speaker 1: their stars, so they give like a little mini planetary
Speaker 1: eclipse which dims the star a little bit, or they
Speaker 1: wiggle the star because of the gravity of the planet
Speaker 1: pulling on the star. So in both cases they have
Speaker 1: to be pretty close to the star for us to
Speaker 1: see it, which means that of all the planets out
Speaker 1: there in the galaxy orbiting their stars, we're best at
Speaker 1: seeing the ones that are closest to their stars, which
Speaker 1: also means we're best at seeing the ones that are
Speaker 1: probably tidally locked. And so astronomers have done a bunch
Speaker 1: of calculations to understand the orbits of these things and
Speaker 1: the masses and predict their tidle locking, and they expect
Speaker 1: that a lot of these planets are tidly locked, maybe
Speaker 1: one to one, maybe like three to two the way
Speaker 1: Mercury is, or maybe like five to two. It depends
Speaker 1: a lot on the eccentricity of the orbit. Wh's the
Speaker 1: sort of gravitationally most preferred arrangement.
Speaker 2: Would it be fair to say that it's too far
Speaker 2: away for us to have been able outside of our
Speaker 2: solar system to see planets and their moons being tidally locked,
Speaker 2: and so the only thing we've been able to look
Speaker 2: at so far is tidal locking with suns and planets.
Speaker 1: Yeah, that's exactly right. Exo moons is a brand new
Speaker 1: area of study. People looking for these moons around exo
Speaker 1: planets super exciting and in the next few years, as
Speaker 1: we turn on more and more space telescopes, we're going
Speaker 1: to get more information about these planets and their moons
Speaker 1: and we can start to measure their spin and to
Speaker 1: understand this and to figure out like whether these planets
Speaker 1: out there a lot more of them are tidly locked
Speaker 1: or a lot less. You know, a question we always
Speaker 1: have is is our solar system weird or is it typical?
Speaker 1: Like in most cases, is it just the first couple
Speaker 1: of planets closest to the Sun that are tidally locked,
Speaker 1: which would align with our understanding and tell us that
Speaker 1: our solar systems not that weird, or maybe would be surprised,
Speaker 1: and we'll discover Oh my gosh, all those solar systems
Speaker 1: out there, they're all tidly locked. What's going on. Something
Speaker 1: is different from what we expect. You never know when
Speaker 1: you go out in the universe and ask these questions
Speaker 1: and look for the first time, if you're just going
Speaker 1: to see like more dust and rubbel or something really
Speaker 1: really exciting.
Speaker 2: The universe is good at providing job security in the
Speaker 2: form of new questions.
Speaker 1: And it's not just stars and planets we can study.
Speaker 1: We can also look at pairs of stars. We're used
Speaker 1: to thinking about stars as like individual and you have
Speaker 1: a solar system with one star at its core and
Speaker 1: a bunch of planets, But actually there's lots of binary
Speaker 1: star systems out there. And the reason is that stars,
Speaker 1: when they're formed, it's a big cloud of gas and
Speaker 1: dust which collapses, and typically you get multiple stars from
Speaker 1: a big cloud of gas and dust. You have like
Speaker 1: little gravitational seeds that start this runaway gravitational effect, and
Speaker 1: you don't just have one seed, you have a bunch
Speaker 1: of them, so you get like an stellar nursery makes
Speaker 1: lots and lots of stars. So we have a whole
Speaker 1: podcast episode about binary star systems and even like trinary
Speaker 1: star systems. But the point is that lots of stars
Speaker 1: out there have brothers and sisters they were born with
Speaker 1: like twins, and so they're pretty close to another star,
Speaker 1: which means that you can have pairs of stars that
Speaker 1: are tidly locked to each other.
Speaker 2: That's awesome.
Speaker 1: Or if you have a really big planet, you could
Speaker 1: have a planet and a star that are tidly locked
Speaker 1: to each other, so the planet is always seeing the
Speaker 1: same side of the star. Right, that could be weird.
Speaker 2: Yeah, but we haven't seen that yet, Right.
Speaker 1: We have not seen that yet. There's a star out
Speaker 1: there Tao Buddhists, which we suspect is tidly locked to
Speaker 1: its planet, but we're not one hundred percent sure of that.
Speaker 1: But you know, this kind of stuff makes a difference
Speaker 1: because it really changes the experience of being on a planet.
Speaker 1: Like if Earth was tidly locked to the sun, we'd
Speaker 1: have half of the Earth at sunshine all day, and
Speaker 1: half of the Earth would be the dark side of
Speaker 1: the Earth. The far side of the Earth would be
Speaker 1: the dark side, you know where Pink Floyd plays concerts
Speaker 1: and Gary Larson draws his cartoons, And that would be
Speaker 1: the very very cold side of the Earth, right dead side,
Speaker 1: the oh, the dead side exactly. And then you'd have
Speaker 1: this ring around the middle of the Earth that was
Speaker 1: like right on the edge, you'd be like permanent sunrise,
Speaker 1: and that might be the only place on the planet
Speaker 1: you could live because one side would be too hot
Speaker 1: and one side would be too cold. And then you'd
Speaker 1: have this like goldilocks ring around the planet that might
Speaker 1: be hospitable.
Speaker 2: Location, location, location.
Speaker 1: Exactly. And so if that's the case on some of
Speaker 1: these exoplanets, that means it'd be a lot harder for
Speaker 1: life to form. Either they'd have to evolve to survive
Speaker 1: very hot conditions or very cold conditions, or there'd only
Speaker 1: be a thin strip of their planet that they could
Speaker 1: live on, and you know, then there wouldn't be seasons.
Speaker 1: In the same way, it would make for a very
Speaker 1: different kind of biology.
Speaker 2: It would make it easy to study extremophiles, though, because
Speaker 2: you know exactly where you needed to go, just you know,
Speaker 2: the cold ones are over there and the hot ones
Speaker 2: are over there. But there probably wouldn't be a lot
Speaker 2: of funding for science in a world like that.
Speaker 1: You never know, right, and we have all these expectations
Speaker 1: for what life would be like on these planets, because
Speaker 1: we imagine what our life would be like on those planets.
Speaker 1: But of course, if you evolve on those planets, you'd
Speaker 1: think that's the normal way to live, and they would
Speaker 1: think it's super duper weird for like your planet to
Speaker 1: spin and get constantly bathed in sunlight, or for you
Speaker 1: to have no control over whether you're seeing the sun
Speaker 1: or not. Because on tidly locked planets, right, you don't
Speaker 1: want sun, you just move to the backside. You want sun,
Speaker 1: you move to the front side, totally up to you,
Speaker 1: whereas here we're like at the mercy of celestial objects,
Speaker 1: spin rates to determine when we see sun and when
Speaker 1: we don't.
Speaker 2: Yeah, I guess you get used to what you grew
Speaker 2: up with. It sure seems like it's nice to have
Speaker 2: a more moderate in between.
Speaker 1: It certainly does. But in the end, the universe prefers
Speaker 1: tidal luck, and given enough time gravity, it's going to
Speaker 1: do its business, make everything round and then make it
Speaker 1: a little bit footballish, and it's going to tug on
Speaker 1: those gravitational handles until everything is tidly locked, unless, of course,
Speaker 1: your son explodes and eats you before it can even happen,
Speaker 1: but it's sort of the gravitational destiny of every other
Speaker 1: kind of object.
Speaker 2: And there's the ending that'll keep from listening.
Speaker 1: And hopefully inspire a lot of crazy music and silly cartoons. Yes,
Speaker 1: all right, Thanks very much everybody for exploring the physics
Speaker 1: of tidal locking with us. It turns out to play
Speaker 1: a big role in what it's like to live on
Speaker 1: our planet, what it's like to look up at disguise
Speaker 1: and understand the universe or wonder at its mysteries, and
Speaker 1: it will continue to play a big role in life
Speaker 1: on Earth.
Speaker 2: Huzza.
Speaker 1: Thanks for listening. Tune in next time. Thanks for listening,
Speaker 1: and remember that Daniel and Jorge Explain the Universe is
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