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Transcript

What is tidal locking? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: Hey, Kelly, I have a controversial question for you.
0:11
Speaker 2: Oh boy, coming from you that makes me particularly nervous.
0:15
Speaker 2: Is this another episode I'm gonna have to make sure
0:17
Speaker 2: my kids don't listen.
0:18
Speaker 1: To no, but it might cause some other kind of
0:21
Speaker 1: family drama.
0:22
Speaker 2: Okay, now you have my attention.
0:25
Speaker 1: Well, you know, since you're married to a cartoonist, I'm
0:27
Speaker 1: wondering if I'm allowed to ask you whether you're a
0:30
Speaker 1: fan of a different cartoon.
0:32
Speaker 2: Well, that depends if it's a rival cartoon or not.
0:38
Speaker 1: So I'm wondering if you have a favorite cartoon from
0:42
Speaker 1: the Far Side.
0:43
Speaker 2: Oh, I mean he hasn't updated for a while, right,
0:46
Speaker 2: I mean, I suppose he's still competition. But anyway, all right,
0:48
Speaker 2: let's see, let's see. Oh, so hard to pick so
0:50
Speaker 2: many favorites. So there's one where there's a slide, you know,
0:54
Speaker 2: like a kid's playground, and some spiders have built a
0:57
Speaker 2: net or a web along the bottom, and one spider
1:02
Speaker 2: is saying something like, if we can pull this off,
1:06
Speaker 2: we'll never be hungry again, nor something like that, And I,
1:10
Speaker 2: as an invert person, just thought that that was amazing.
1:13
Speaker 2: And of course I liked the like School for the
1:14
Speaker 2: Gifted the one that was on T shirts when I
1:18
Speaker 2: was a kid. What about you, Well, I have.
1:20
Speaker 1: To ask you. Do you see that Spider's eating a
1:22
Speaker 1: baby cartoon differently now that you're a parent?
1:24
Speaker 2: No, still hilarious.
1:28
Speaker 3: Us.
1:28
Speaker 1: I think your children should be terrified if they listen
1:30
Speaker 1: to this episode.
1:31
Speaker 2: Probably. Oh my gosh, poor kid won. The other day,
1:35
Speaker 2: I told her to go get a bowl in my office,
1:38
Speaker 2: and she thought it was going to have something like
1:40
Speaker 2: candy in it, but she accidentally picked up the bowl
1:43
Speaker 2: of dead insects that I found in the in the
1:46
Speaker 2: barn that I was thinking of pinning at some point,
1:48
Speaker 2: and they were all over my office, so she must
1:51
Speaker 2: have seen it and thrown it up in the air
1:53
Speaker 2: and they went all over. My kids are going to
1:56
Speaker 2: have very high therapy bills at some point, but I
1:58
Speaker 2: love them very much.
1:59
Speaker 1: I think that living in your house must be even
2:01
Speaker 1: weirder than the Far Side cartoon, almost certain. Hi. I'm Daniel.
2:21
Speaker 1: I'm a particle physicist and a professor at UC Irvine,
2:25
Speaker 1: and I don't think I've yet traumatized my children with insects.
2:28
Speaker 2: Hi. I'm Kelly Wiener Smith, and I study creepy crawley
2:32
Speaker 2: things at race university, and I'm traumatizing kids all the time.
2:36
Speaker 1: Education through trauma is set your strategy.
2:38
Speaker 2: That's a good way to make people remember stuff.
2:43
Speaker 1: Where you live out on the farm, but there's lots
2:45
Speaker 1: of access to creepy crawley weird things, and so I
2:48
Speaker 1: hope your kids are become ver acclimatized.
2:50
Speaker 2: To that I'm making them because it.
2:52
Speaker 1: Takes a brave soul to explore the nature of the universe,
2:56
Speaker 1: or even just your backyard, depending on what's slithering out there.
3:00
Speaker 1: So whether or not you turn your eyes down to
3:02
Speaker 1: the ground or up to the skies, there's a whole
3:04
Speaker 1: lot of stuff to wonder about, and so welcome to
3:07
Speaker 1: the podcast. Daniel and Jorge explain the universe in which
3:10
Speaker 1: we do all of that wondering. We think about everything
3:12
Speaker 1: that's between your toes and everything that your eyes can
3:15
Speaker 1: gather as you look up into the night sky. We
3:18
Speaker 1: think about what's on the moon, what's on the backside
3:20
Speaker 1: of the moon, and what's in the deepest, darkest depths
3:22
Speaker 1: of the universe. We chew all of it up and
3:25
Speaker 1: try to digest it and explain.
3:26
Speaker 2: It to you, and it's not always pretty.
3:31
Speaker 1: Sometimes the truth is just gross. My typical co host
3:34
Speaker 1: and friend, Jorge Champ can't be here today, so I'm
3:36
Speaker 1: very glad to have one of our regular guest hosts, Kelly. Kelly,
3:39
Speaker 1: thanks very much for joining us again and terrifying your children.
3:42
Speaker 2: Yeah, well, I hope I could terrify some people today too.
3:45
Speaker 2: Thanks for having me back.
3:47
Speaker 1: But today we're not talking about the weird, creepy crawley
3:50
Speaker 1: bits that are inside Kelly's pantry, strange as that might be.
3:55
Speaker 1: We are turning our eyes to the sky tonight. We
3:58
Speaker 1: are thinking about what's out there in the universe, and
4:01
Speaker 1: what we can see and what we can't see, and
4:04
Speaker 1: how the gravitational forces that have built the structure of
4:07
Speaker 1: our universe also limit what we can see out there.
4:11
Speaker 1: If you were a kid like me, then you spent
4:12
Speaker 1: a lot of time looking up at the night sky,
4:14
Speaker 1: not just absorbing the stars, but also gazing on the
4:17
Speaker 1: closest object that's out there, the biggest, fattest thing in
4:21
Speaker 1: the night sky, and that's, of course our moon. It
4:24
Speaker 1: has so many fascinating features to it, but one of
4:26
Speaker 1: the most interesting features is that you always see the
4:29
Speaker 1: same features. Cally, do you remember understanding this as a kid,
4:33
Speaker 1: or wondering about why you're always seeing the same bits
4:36
Speaker 1: on the moon.
4:37
Speaker 2: You know, I really wish you hadn't asked me that,
4:40
Speaker 2: because the answer is, when I was a kid, I
4:43
Speaker 2: didn't realize I was always seeing the same side of
4:46
Speaker 2: the moon. That hadn't really hit me until I think, baby,
4:49
Speaker 2: I was in college, and then I was like, wait
4:51
Speaker 2: a minute, and I guess it just wasn't I was
4:53
Speaker 2: looking down at the salamanders and not up at the sky.
4:58
Speaker 2: But so, no, that is not a question I had
5:00
Speaker 2: when I was a kid, but it should be. When
5:03
Speaker 2: did you learn this?
5:04
Speaker 1: I remember learning about it, I think when I was
5:06
Speaker 1: seven or eight, But you know, my dad was pretty
5:08
Speaker 1: into astronomy and into science, and so we talked about
5:11
Speaker 1: this kind of stuff. Something I'm still curious about, though,
5:14
Speaker 1: is when humanity understood that, or when humanity understood it
5:17
Speaker 1: was an interesting question, like did ancient Chinese astronomers, who
5:22
Speaker 1: spend a lot of time looking up at the moon
5:24
Speaker 1: and predicting its eclipses, did they figure out that the
5:27
Speaker 1: moon was a sphere and that it was rotating and
5:29
Speaker 1: that it was weird that we always saw the same
5:32
Speaker 1: side of it? Or is this just something they overlooked.
5:34
Speaker 2: Do you know the answer to that question.
5:36
Speaker 1: I don't know the answer to that question. I've been
5:38
Speaker 1: digging through the history of astronomy a little bit, and
5:41
Speaker 1: I know that Newton understood it because of his ideas
5:44
Speaker 1: of gravitation, But digging deeper into history, it's not really
5:48
Speaker 1: discussed very much. And I sort of wonder if people
5:51
Speaker 1: suspected that it was just a coincidence that the Moon
5:54
Speaker 1: rotates at this perfect rate just so that we can
5:57
Speaker 1: only see one side of it, because you know, there
5:59
Speaker 1: are other fascinating coincidences about the moon. For example, the
6:03
Speaker 1: moon and the Sun happen to be the same size
6:06
Speaker 1: in our sky, right, the Sun is much much bigger,
6:09
Speaker 1: but much much further away, and those two numbers line
6:13
Speaker 1: up perfectly. So the Sun and the Moon appear to
6:15
Speaker 1: be the same size, which is why we can get
6:17
Speaker 1: so many fascinating eclipse effects. And that, of course, is
6:21
Speaker 1: just a coincidence. There's no like deep reason for that.
6:24
Speaker 1: It just happens to be. These two numbers just kind
6:26
Speaker 1: of line up in our.
6:27
Speaker 2: Universe, and humans are notoriously tripped up by coincidences.
6:32
Speaker 1: Exactly, And so I think ancient astronomers must have wondered
6:35
Speaker 1: about that size, and I wonder if they also wondered
6:38
Speaker 1: about the rotation of the moon, if they understood that. Now,
6:41
Speaker 1: I do know that ancient Chinese astronomers had a little
6:44
Speaker 1: bit of a disadvantage compared to, for example, ancient Greek astronomers,
6:48
Speaker 1: because they didn't have geometry. Right, we think about the
6:51
Speaker 1: universe in terms of geometry. You imagine how clips has happened,
6:54
Speaker 1: and you think, probably in your head, you have a
6:56
Speaker 1: mental picture of all these things happening and to explain it.
7:00
Speaker 1: But Chinese astronomers didn't develop geometry, so they didn't have
7:03
Speaker 1: the same sort of geometrical thinking that we're all very
7:06
Speaker 1: familiar with. Instead, they had like tables of numbers, and
7:09
Speaker 1: they had arithmetic, and they could manipulate these numbers to
7:12
Speaker 1: do their predictions. So I think they must have thought
7:14
Speaker 1: about these things very differently than we did.
7:16
Speaker 2: Interesting, it's nice to have our modern tools.
7:20
Speaker 1: Thank you to those folks who invented geometry. It turns
7:22
Speaker 1: out to be pretty.
7:23
Speaker 2: Useful quote unquote modern.
7:25
Speaker 3: Yeah.
7:26
Speaker 1: Right, And so we have been looking up in the
7:28
Speaker 1: night sky and looking at the moon and seeing the
7:30
Speaker 1: same side of it for thousands and thousands of years,
7:34
Speaker 1: and now, of course we understand why. And so today
7:37
Speaker 1: on the podcast, we're going to be digging into the
7:39
Speaker 1: physics of the far side of the Moon and many
7:42
Speaker 1: other objects in our solar system that exhibit the same behavior.
7:46
Speaker 1: On today's episode, well, I answer the question what is
7:54
Speaker 1: tidal locking?
7:56
Speaker 2: And this is another thing that connects us to the dinosaurs, right,
7:59
Speaker 2: because they also would have seen the same side.
8:00
Speaker 1: Of the moon. If dinosaur geometers had figured that out, boy,
8:06
Speaker 1: they could have written a paper and got a lot
8:07
Speaker 1: of citations.
8:08
Speaker 2: They really could have, and then maybe they could have
8:10
Speaker 2: started a you know, NASA and had an asteroid deflection program.
8:13
Speaker 2: Everything could have been different.
8:15
Speaker 1: You sound like you're kind of hoping for that, but
8:17
Speaker 1: you know, in that scenario, we don't exist.
8:20
Speaker 2: Oh, good point.
8:22
Speaker 1: We're rooting for the asteroid on that one.
8:23
Speaker 2: That's right, we sure are.
8:25
Speaker 1: I'm sorry dinosaurs, which puts us on the anti math
8:28
Speaker 1: Education for Dinosaurs committee as well.
8:30
Speaker 2: It's an uncomfortable place to be, but no, it doesn't
8:33
Speaker 2: feel very good, but I'm firmly in this position. Yeah.
8:36
Speaker 1: So this is a topic that affects our Moon, and
8:38
Speaker 1: affects our planet, and affects a lot of things in
8:41
Speaker 1: the Solar system and in other Solar system. It's a
8:43
Speaker 1: fascinating little bit of physics. So I was curious what
8:46
Speaker 1: people knew about the topic of title locking and if
8:50
Speaker 1: they understood the physics of it. So I went out
8:52
Speaker 1: there into the internet to ask folks if they understood this.
8:55
Speaker 1: Thanks very much to those of you who participate in
8:57
Speaker 1: this segment of the podcast to let us know what
9:00
Speaker 1: people think about the topic of the day. If you'd
9:02
Speaker 1: like to hear your voice for a future episode, please
9:05
Speaker 1: don't be shy. Write to me two questions at Danielandjorge
9:09
Speaker 1: dot com. So think about it for a minute. Do
9:11
Speaker 1: you understand the physics of title locking? Here's what some
9:14
Speaker 1: listeners had to say.
9:16
Speaker 4: So, I believe that title locking is when, say, a
9:20
Speaker 4: planet has a moon that's locked in orbit at a
9:23
Speaker 4: certain distance, so the tides are always the same. So
9:26
Speaker 4: I guess you could say that we're in title locking
9:29
Speaker 4: because day in and day out, our tides go the
9:32
Speaker 4: same because.
9:33
Speaker 1: The moon's in a fixed orbit.
9:34
Speaker 2: Title locking is just like our moon. We see the
9:37
Speaker 2: same face of it at all times.
9:40
Speaker 4: It has no spin, and the dark side of the
9:42
Speaker 4: moon is facing outward.
9:43
Speaker 2: It is the deformation that a celestial body so first
9:47
Speaker 2: when it's orbiting or is orbited by another massive celestial body.
9:52
Speaker 3: Title locking is when a lower mass body is orbiting
9:57
Speaker 3: a much higher mass body and the the same side
10:00
Speaker 3: always faces it, so I know that we always see
10:03
Speaker 3: the same side of the Moon means tidally locked to
10:06
Speaker 3: the Earth.
10:07
Speaker 2: I was impressed that none of the listeners seemed totally
10:10
Speaker 2: stumped by this, because I feel like tidle locking is
10:13
Speaker 2: not necessarily something that you hear, like that at least
10:17
Speaker 2: there's a phrase I don't hear very often, and so like,
10:20
Speaker 2: it seems like some people knew exactly what you were
10:23
Speaker 2: asking about, and none of them were like me when
10:25
Speaker 2: I was a kid, and we're just totally unaware that
10:27
Speaker 2: this is a thing that was happening.
10:29
Speaker 1: Yeah, we got some pretty well educated listeners. The word title,
10:33
Speaker 1: I think makes some people think of tides, which is
10:36
Speaker 1: connected of course to tidal forces, you know, like the
10:39
Speaker 1: Moon pulls on the Earth and squishes its oceans and
10:43
Speaker 1: makes us have higher tides in some places and lower
10:45
Speaker 1: tides and other places. But that's not what we mean
10:48
Speaker 1: by title locking. Tidle locking is actually a different phenomena
10:51
Speaker 1: we're going to dig into today. But thank you very
10:54
Speaker 1: much to all of our volunteers. We really cherish your thoughts.
10:57
Speaker 2: Yeah, you have a smarter than average audience, I think,
11:00
Speaker 2: or smarter than Kelly average. I'm always impressed by the answers.
11:06
Speaker 1: They're smart and they're good looking too.
11:08
Speaker 2: That's right. I think that's called the halo effect. You
11:12
Speaker 2: know one good thing about them, and you assume you
11:13
Speaker 2: know all the good things about them.
11:15
Speaker 1: So let's dig into the physics of tidal locking. What
11:18
Speaker 1: it is, what's going on and why I play such
11:20
Speaker 1: a big role in what we see in our night sky.
11:23
Speaker 1: And I think the first thing to understand is just
11:25
Speaker 1: like the geometry of what's going on. Obviously, the Moon
11:28
Speaker 1: is orbiting the Earth, and the Earth is spinning, and
11:32
Speaker 1: the Moon is spinning around the Earth, and the Moon
11:34
Speaker 1: is also spinning on its axis. So there's sort of
11:37
Speaker 1: a lot of spinning going on. But you got to
11:39
Speaker 1: get all that spinning in your head to understand, like
11:41
Speaker 1: why we only see one side of the moon.
11:44
Speaker 2: Yes, so I am staring directly ahead trying to picture everything,
11:48
Speaker 2: So go ahead, what should I be imagining?
11:51
Speaker 1: So first, just put yourself on the Earth and forget
11:54
Speaker 1: the fact that the Earth is spinning, and just move
11:56
Speaker 1: the Moon around the Earth in your mind and imagine
11:59
Speaker 1: the Moon is like a shoe or something. If the
12:01
Speaker 1: Moon is not spinning, it's just orbiting the Earth, then
12:04
Speaker 1: the Earth is going to see different sides of the shoe.
12:06
Speaker 1: It's going to see the back of the shoe, it's
12:07
Speaker 1: going to see the front of the shoe, because as
12:09
Speaker 1: the shoe moves around the Earth, different sides of it
12:12
Speaker 1: are going to be closer to the Earth or closer
12:15
Speaker 1: to outer space.
12:16
Speaker 2: So the shoe is not rotating either.
12:17
Speaker 1: That's right. So first the shoe is not rotating, and
12:20
Speaker 1: so we see one side of it, and then we
12:21
Speaker 1: see the other side of it. So if the shoe
12:23
Speaker 1: or the moon or whatever is not spinning, then you
12:25
Speaker 1: would see different sides of it. Right now, the moon,
12:28
Speaker 1: of course, is spinning. It's spinning on its axis. But
12:31
Speaker 1: if it was spinning at some random rate, like really
12:33
Speaker 1: really fast or really really slow, you would still see
12:36
Speaker 1: both sides of it, because eventually it would spin in
12:38
Speaker 1: a way that revealed every part of the moon. The
12:41
Speaker 1: only way for us to not be able to see
12:44
Speaker 1: part of the moon is for its spin to be
12:46
Speaker 1: perfectly syncd up with its orbit, so that as it
12:49
Speaker 1: goes around the Earth, it turns just the right a
12:52
Speaker 1: mount every second, so the same side of it is
12:55
Speaker 1: always facing the Earth, like if the back side of
12:58
Speaker 1: the shoe is always fa the Earth, because the shoe
13:01
Speaker 1: itself is spinning at just the right rate as it
13:03
Speaker 1: goes around the Earth.
13:04
Speaker 2: And everyone on every part of the Earth is always
13:07
Speaker 2: seeing the same side of the Moon. Right, It's not
13:09
Speaker 2: like you know, in the US you see one side
13:11
Speaker 2: and in China you see the other side, or right,
13:13
Speaker 2: You're always seeing the same side.
13:15
Speaker 1: That's right. The same side of the Moon is always
13:17
Speaker 1: closer to the Earth, and the other side of the
13:19
Speaker 1: Moon that we call the far side, which I assume
13:22
Speaker 1: is the origin of the name of the far side
13:24
Speaker 1: and comic, it is always facing outer space. And this
13:28
Speaker 1: is the sort of coincidence we were talking about. Like these
13:31
Speaker 1: two numbers, the rate at which the Moon goes around
13:34
Speaker 1: the Earth and the rate at which the Moon spins
13:36
Speaker 1: around its axis have to be perfectly synced up to
13:40
Speaker 1: get this effect.
13:41
Speaker 2: And why are they perfectly syncd up? Is this one
13:44
Speaker 2: of the few instances in which we have something special
13:46
Speaker 2: going on and they just happen to sync up. Or
13:49
Speaker 2: are we just like every other moon because this happens
13:52
Speaker 2: all the time.
13:54
Speaker 1: So it's not that special and it's not a coincidence,
13:57
Speaker 1: but it's not something that's always happened. Like, to get
14:00
Speaker 1: into it, you have to understand the history of the
14:02
Speaker 1: formation of the Moon, like how did it get made,
14:05
Speaker 1: how was it spinning originally, and then how has that changed?
14:08
Speaker 1: You know, our moon is not just like some object
14:10
Speaker 1: that we captured as it was flying by. We think
14:13
Speaker 1: that the Moon actually comes from a huge collision something
14:17
Speaker 1: like one hundred million years after the Earth was formed,
14:20
Speaker 1: so we're talking like four point four billion years ago.
14:24
Speaker 1: You have some like very hot proto Earth. It got
14:27
Speaker 1: slammed into by some giant Mars sized planet they called Fea,
14:32
Speaker 1: And so you're talking about a huge collision like Earth
14:35
Speaker 1: versus Mars in space and both objects are essentially vaporized.
14:40
Speaker 2: But we still have thirst in the moon.
14:43
Speaker 1: You're like, how do that to current reality? You know,
14:47
Speaker 1: you're exactly right, it got vaporized, but then it coalesced. Right.
14:51
Speaker 1: Gravity is very very patient, and so even though all
14:54
Speaker 1: of its original work in the first one hundred million
14:56
Speaker 1: years was ruined by this collision. It got back to
14:59
Speaker 1: work and it pulled those blobs together and it made
15:02
Speaker 1: two new blobs, one that formed the Earth, and then
15:04
Speaker 1: a big ring around the Earth, like a ring of
15:07
Speaker 1: debris that was spinning sort of too fast around the
15:10
Speaker 1: Earth to fall into the central clump, which formed this
15:13
Speaker 1: like huge spray of material.
15:15
Speaker 2: All right, So, and that's why the Moon's made out
15:17
Speaker 2: of the same stuff the Earth is made out of.
15:19
Speaker 1: Exactly when we visited the Earth first and we sampled it,
15:22
Speaker 1: people were surprised to discover that it's basically the same
15:25
Speaker 1: mixture of stuff as the Earth. It's not like a
15:28
Speaker 1: different Solar System body that was formed in another place,
15:31
Speaker 1: and so it has a different mixture of like ices
15:33
Speaker 1: and rocks and different isotopes and stuff. It's basically made
15:36
Speaker 1: out of the same stuff as the Earth. And that's
15:38
Speaker 1: because it comes from the same mixture of those two planets.
15:42
Speaker 1: Like it was the same vaporized blob of stuff, and
15:45
Speaker 1: some of it fell in towards the Earth, and the
15:46
Speaker 1: stuff that was spinning around sort of too fast ended
15:49
Speaker 1: up in this big debris ring. But then gravity pulled
15:52
Speaker 1: that together into a moon.
15:54
Speaker 2: Did we have this hypothesis before we went to the
15:56
Speaker 2: Moon and found what it was made of, or did
15:58
Speaker 2: going to the Moon and physically collecting samples give us
16:02
Speaker 2: this hypothesis when we were like, whoa, it's the same stuff.
16:06
Speaker 1: This hypothesis has been around for a while, but it
16:08
Speaker 1: really became the favorite once we went to the Moon,
16:11
Speaker 1: and also once we understood something about the Moon's inner core.
16:14
Speaker 1: The Moon has sort of a small iron core, smaller
16:17
Speaker 1: than you would expect, and the hypothesis is that a
16:20
Speaker 1: lot of that iron was probably lost from when the
16:23
Speaker 1: impactor hit the proto Earth, and some of that was
16:26
Speaker 1: like melted and vaporized, and so it would have a
16:28
Speaker 1: bigger iron core otherwise. This became a much more popular
16:31
Speaker 1: hypothesis after we went to the Moon and visited and
16:34
Speaker 1: understood what it was made out of. And there's a
16:36
Speaker 1: lot of really interesting physics there that's relevant to it,
16:38
Speaker 1: Like why doesn't it all just collapse into a planet, right,
16:41
Speaker 1: Why doesn't it all just become one huge giant planet.
16:44
Speaker 1: How come part of it ended up as a ring?
16:46
Speaker 1: And that's just because you know, the whole thing is
16:49
Speaker 1: spinning and a lot of it has angular momentum, and
16:51
Speaker 1: so some stuff was just moving too fast to fall
16:54
Speaker 1: in the way, like the moon now is moving too
16:57
Speaker 1: fast to fall into the Earth. It's all about that.
17:00
Speaker 1: And then when that stuff gathered together into a moon,
17:03
Speaker 1: that stuff was spinning. So the moon had some original spin, right,
17:07
Speaker 1: that came from the spinning motion of all of that
17:10
Speaker 1: stuff after the vaporization. And we think that spin rate
17:14
Speaker 1: originally was much much higher than it is today. So
17:17
Speaker 1: the Moon used to be spinning faster than it is now.
17:20
Speaker 2: Was there this is maybe an unfair question. Was there
17:23
Speaker 2: anything alive on Earth when it was spinning fast enough
17:27
Speaker 2: that sometimes you'd see what is now the far side
17:29
Speaker 2: of the moon. So like dinosaurs probably never saw the
17:32
Speaker 2: far side of the moon, but did like the first
17:34
Speaker 2: bacteria see the far side of the Moon. I mean,
17:36
Speaker 2: I'm sure they don't see anything that far away, but
17:39
Speaker 2: you know, could they have.
17:40
Speaker 1: Yeah, it's possible. We don't really know exactly how old
17:43
Speaker 1: life is on Earth, but it stretches back billions of years, right,
17:47
Speaker 1: And so it's possible that there are critters that have
17:49
Speaker 1: lived on Earth that have seen other parts of the Moon.
17:52
Speaker 1: That's a very cool thought. Because the Earth has been
17:55
Speaker 1: gradually slowing down the Moon's spin little by a little
17:59
Speaker 1: every year, and the opposite is also true. But you know,
18:03
Speaker 1: until nineteen fifty nine, no human had ever seen the
18:08
Speaker 1: backside of the Moon. It was this like dark spot
18:10
Speaker 1: in our vision that we just couldn't see, no matter
18:13
Speaker 1: how many thousands of years we've been staring up at
18:15
Speaker 1: the Moon. Nobody had ever laid eyes on the backside
18:18
Speaker 1: until nineteen fifty nine, which feels really recent.
18:21
Speaker 2: Right, And the Soviets did.
18:23
Speaker 1: It, right, Yeah, they certainly did.
18:25
Speaker 2: Yeah, they beat us there with the lunar program. Their
18:27
Speaker 2: third one made it there. I think the first two
18:30
Speaker 2: maybe blew up. That was a thing that happened a
18:32
Speaker 2: lot for the Soviets. But anyway, so.
18:36
Speaker 1: Sorry, no, there's a really fun set of stories there.
18:39
Speaker 1: Maybe you know about because of your book research, that
18:41
Speaker 1: the Soviets were there first, and so they got to
18:43
Speaker 1: name a lot of stuff on the far side of
18:45
Speaker 1: the Moon first. So they have all these Russian names
18:48
Speaker 1: and that like really annoyed the Americans at the time.
18:51
Speaker 1: And then you know, later this International Astronomical Union took
18:54
Speaker 1: over the naming, so it wasn't all just you know,
18:57
Speaker 1: named after kinds of vodka or whatever.
18:59
Speaker 2: All now that's an unfair stereotype. Did the IAU change
19:05
Speaker 2: any of the names that the Soviet program had put
19:07
Speaker 2: in place, or they just like stopped the Soviets from
19:10
Speaker 2: doing any more naming.
19:11
Speaker 1: I think they just stopped them. And there's a lot
19:13
Speaker 1: of respect, I think for the people who discover something
19:16
Speaker 1: to name it. But then I think that the Soviets
19:18
Speaker 1: were so far ahead that they didn't want them to
19:20
Speaker 1: just like name the whole thing after their favorite Soviet
19:23
Speaker 1: flower or whatever.
19:24
Speaker 2: Thank, yes, there we go. That's good. That's good. I
19:28
Speaker 2: think there is like a Gagarian and seas or something
19:30
Speaker 2: like them. All Right, so we're gonna take a quick
19:33
Speaker 2: break and then we'll talk about what they found on
19:34
Speaker 2: the far side of the moon. The first time we
19:49
Speaker 2: got to see the far side of the moon was
19:50
Speaker 2: nineteen fifty nine. Not too long after that, the Apollo
19:54
Speaker 2: astronauts were flying around the Moon and got to see
19:57
Speaker 2: the far side. What kinds of things were on the
20:00
Speaker 2: far side to see, Daniel.
20:01
Speaker 1: Well, you know, in research, it's always exciting to see
20:04
Speaker 1: something nobody's ever seen before because you don't know what's
20:07
Speaker 1: going to be there. Right, Maybe it's like a crashed
20:09
Speaker 1: alien battleship or some weird new geological formation. Right, your
20:13
Speaker 1: imagination goes crazy when you're first landing on a spot
20:16
Speaker 1: and seeing something no human has ever seen before. But
20:19
Speaker 1: you know, in research, discoveries never guaranteed. Just because you
20:22
Speaker 1: land on new shores doesn't mean you find something fascinating.
20:25
Speaker 1: And in this case, basically we found that the far
20:28
Speaker 1: side of the Moon has more rocks and more dust,
20:30
Speaker 1: and it's not even very different from the front side
20:33
Speaker 1: of the Moon. I mean there are more craters, there
20:35
Speaker 1: are fewer of these like seas, these lunar lava flows,
20:38
Speaker 1: but all in all, it's not that exciting.
20:41
Speaker 2: Yeah, that's the moon, good old, dependable Moon.
20:46
Speaker 1: And the first time anybody actually landed there was twenty nineteen,
20:49
Speaker 1: like just a few years ago the Chinese put a
20:52
Speaker 1: lander down and started to do a bunch of experiments.
20:55
Speaker 1: So it's only recently we started to explore it in detail.
20:57
Speaker 1: So you know, there's still hope to find that crashed
21:00
Speaker 1: alien battleship or.
21:01
Speaker 2: The aliens might be living in a lavatude. We could
21:04
Speaker 2: find something even more exciting than what you've imagined.
21:06
Speaker 1: Yeah, maybe so, Or maybe we could build something that
21:09
Speaker 1: future aliens could land and discover for themselves, like people
21:13
Speaker 1: are proposing building radio telescopes on the far side of
21:17
Speaker 1: the moon looking out into space, because then you'd have
21:20
Speaker 1: the whole moon to shield you from the noise of
21:23
Speaker 1: the Earth.
21:24
Speaker 2: From my perspective, that's an interesting prospect geopolitically, because if
21:28
Speaker 2: you built one of those radio telescopes, it wouldn't work
21:30
Speaker 2: as well if people put other stuff on that side
21:32
Speaker 2: of the moon. So now there's like competition for that space.
21:36
Speaker 2: And can you tell someone they can't use the far
21:39
Speaker 2: side of the moon because your radio telescope is there. Anyway,
21:41
Speaker 2: These things are complicated, but yes, it would be a
21:43
Speaker 2: good place for a radio telescope.
21:45
Speaker 1: Sounds like the kind of things a bunch of lawyers
21:46
Speaker 1: in a conference room are going to hash out one day.
21:48
Speaker 1: So the far side of the Moon is not that
21:50
Speaker 1: exciting on its own, but it is fascinating to understand
21:53
Speaker 1: why there is a far side of the moon. Before
21:56
Speaker 1: we dig into that, I just want to clarify something
21:57
Speaker 1: that's a common misunderstanding, which the difference between the far
22:01
Speaker 1: side of the Moon and the dark side of the moon.
22:04
Speaker 1: Also the Pink Floyd album.
22:05
Speaker 2: I don't think anyone needs clarification. We all know about that,
22:09
Speaker 2: and we've all probably seen the light show if we're
22:11
Speaker 2: around forty years old.
22:13
Speaker 1: So some people imagine that the far side of the
22:16
Speaker 1: moon is also the dark side of the moon, that like,
22:18
Speaker 1: this part of the moon never sees sunlight, which is
22:21
Speaker 1: definitely not true. The dark side of the moon is
22:23
Speaker 1: the side of the moon facing away from the Sun.
22:26
Speaker 1: The far side of the moon is the side facing
22:28
Speaker 1: away from the Earth, and those two often don't agree.
22:31
Speaker 1: So when we have a full moon, the sun is
22:33
Speaker 1: illuminating the entire side of the Moon that we are
22:36
Speaker 1: seeing because the Sun is sort of behind us in space.
22:40
Speaker 1: Then the back side of the moon, the far side
22:42
Speaker 1: that we don't see, is also dark. But the opposite
22:44
Speaker 1: scenario when the moon is totally dark when we see
22:47
Speaker 1: a new moon, and that's because the far side of
22:50
Speaker 1: the moon is totally lit up by the sun. Right
22:52
Speaker 1: half of the moon is always lit up, it's just
22:55
Speaker 1: sometimes not the side that we're seeing, So the far
22:58
Speaker 1: side and the dark side are different. It would be
23:00
Speaker 1: like a Gary Larsen Pink Floyd crossover event when they meet.
23:03
Speaker 2: I'm pretty sure if you play Dark Side of the
23:05
Speaker 2: Moon backwards it explains that.
23:09
Speaker 1: That's how you understand the far side cartoons, right, you
23:12
Speaker 1: have to listen to the dark side of the moon backwards.
23:14
Speaker 2: Yeah, there was a lot of cross talk between the
23:17
Speaker 2: arts back then. Okay, so how is this happening. The
23:22
Speaker 2: moon was going faster, you said, and it's been slowing down.
23:25
Speaker 2: Why has it slowed down to be exactly the same
23:29
Speaker 2: rotation rate and stuff? What's going on?
23:31
Speaker 1: So it's not a coincidence, right. Physics seems to like
23:34
Speaker 1: this scenario, and it's called tidal locking because it's connected
23:38
Speaker 1: to the concept of tidal forces, which are in effect
23:41
Speaker 1: we see all the time in gravity. And it sounds complicated,
23:44
Speaker 1: but it's really pretty simple. The only thing you really
23:46
Speaker 1: have to understand is that gravity gets weaker as distances
23:50
Speaker 1: get longer. So if you're further away from the Sun,
23:52
Speaker 1: it's gravity is less powerful. As you get closer to
23:54
Speaker 1: the Sun, it's gravity is more powerful. That makes sense.
23:57
Speaker 1: But now imagine you're a pretty big object. Part of
24:00
Speaker 1: you is closer to the Sun than another part, then
24:03
Speaker 1: part of you is going to feel stronger gravity than
24:06
Speaker 1: the other part. And this happens all the time, Like
24:08
Speaker 1: if you are standing on the surface of the Earth,
24:10
Speaker 1: then the Earth is pulling on your legs harder than
24:13
Speaker 1: it's pulling on your head, right, and so that's a
24:16
Speaker 1: tidal force because there's a difference there. You can actually
24:19
Speaker 1: think about the Earth is sort of like trying to
24:21
Speaker 1: pull your head off of your body.
24:23
Speaker 2: Is this like many spaghetification?
24:26
Speaker 1: Yes, exactly, when it's very powerful. When it's more powerful,
24:30
Speaker 1: then the force is holding an object together, that's spaghetification.
24:33
Speaker 1: And so when you get near a black hole, for example,
24:36
Speaker 1: gravity is super powerful, and the difference between the gravity
24:39
Speaker 1: at your feet and your head is much more dramatic
24:42
Speaker 1: and much more powerful than the force is holding your
24:45
Speaker 1: head on your body, and so it's effectively natural decapitation
24:48
Speaker 1: or spaghetification.
24:49
Speaker 2: But lucky for us, instead of death, we get.
24:52
Speaker 1: The tie exactly, so you don't have to worry about that,
24:56
Speaker 1: because the difference of the force of gravity on your
24:58
Speaker 1: feet and on your head is very gentle, and your
25:01
Speaker 1: neck is very powerful in comparison. But the moon is
25:04
Speaker 1: pretty big, and so the difference between the gravitational force
25:07
Speaker 1: on one side of the moon and on the other
25:10
Speaker 1: is much stronger. And so what happens is that the
25:12
Speaker 1: Earth basically turns the Moon a little bit into a football.
25:16
Speaker 1: It like makes it a little bit all blong, because
25:18
Speaker 1: it pulls on the closer bits more powerfully, and it
25:21
Speaker 1: pulls on the further bits more gently, and has the
25:23
Speaker 1: effect of sort of like stretching it out, making it
25:26
Speaker 1: longer like a football instead of like a sphere.
25:28
Speaker 2: This is another one of those things I'm surprised we
25:30
Speaker 2: ever figured out, because when I look at the Moon,
25:32
Speaker 2: I would not think football.
25:34
Speaker 1: It's a subtle effect, right, It looks like a sphere,
25:36
Speaker 1: but is slightly distorted by the gravity of the Earth,
25:39
Speaker 1: and that has a big impact on how it spins,
25:41
Speaker 1: because now it has a gravitational preference to be aligned
25:44
Speaker 1: a certain way with the Earth. If it was a
25:47
Speaker 1: perfect sphere, then the gravity on the object wouldn't change
25:49
Speaker 1: as it spins. But if it has a bulge, then
25:52
Speaker 1: gravity prefers that bulge to be aligned with the object,
25:56
Speaker 1: sort of like gravity has a handle now on the
25:59
Speaker 1: Moon to pull that bulge, so one point is towards
26:02
Speaker 1: the Earth and one point is away from the Earth.
26:04
Speaker 1: That's like gravitationally less energetic a configuration than having the
26:08
Speaker 1: whole thing spin.
26:10
Speaker 2: All right, Okay, so I'm trying to wrap my head
26:12
Speaker 2: around this, and picturing things in my head is not
26:15
Speaker 2: one of my stronger suits. But here we go. Okay,
26:17
Speaker 2: so we prefer to have a grip on the handle.
26:19
Speaker 2: Does the moon spin at a not constant speed where
26:23
Speaker 2: like we hold on to the handle for a little longer.
26:26
Speaker 2: I don't think that's what you're saying, And so what
26:28
Speaker 2: am I missing?
26:29
Speaker 1: So what happened initially is that the Earth started to
26:31
Speaker 1: form these bulges on the Moon, and then the Moon
26:34
Speaker 1: was spinning, and so these bulges were like ripples through
26:37
Speaker 1: the surface of the Moon. There were like these waves
26:40
Speaker 1: that pass through the Moon. But Earth is also pulling
26:43
Speaker 1: on those bulges, right Like, if the Moon has a bulge,
26:46
Speaker 1: it's like a football, and then it starts to spin
26:48
Speaker 1: away from the Earth. The Earth is going to pull
26:51
Speaker 1: on that nearest point a little bit and try to
26:53
Speaker 1: pull it back, and that effectively moves the bulge through
26:56
Speaker 1: the surface of the Moon a little bit, and so
26:58
Speaker 1: that slows down the rotation of the Moon a little bit,
27:01
Speaker 1: because the Earth is like tugging trying to pull that
27:03
Speaker 1: point back towards it, and so that slows the moon
27:06
Speaker 1: down a little bit. And eventually the Moon settles into
27:09
Speaker 1: a pattern where these waves the bulge doesn't travel over
27:13
Speaker 1: its surface anymore, like settles into one location. And that's
27:17
Speaker 1: what the Earth prefers.
27:18
Speaker 2: Gravitationally, Okay, I'm with you.
27:20
Speaker 1: And so that's how gravity makes the Moon a little
27:23
Speaker 1: bit pointy and also slows down its spin. It's like
27:26
Speaker 1: stealing some of its energy a little bit to slow
27:29
Speaker 1: down its spin.
27:31
Speaker 2: But why does its spin get slowed down to exactly
27:35
Speaker 2: the right amount, Like it seems like that should just
27:37
Speaker 2: slow things down in general.
27:39
Speaker 1: It does. It slows things down in general, but at
27:41
Speaker 1: some point it starts spinning at just the right speed
27:44
Speaker 1: so that the pointy bit is always pointing towards the Earth.
27:47
Speaker 1: And then the Earth is happy, and the gravity of
27:49
Speaker 1: the Earth no longer wants to slow down the spin
27:52
Speaker 1: of the Moon because the point to bit is always
27:54
Speaker 1: facing the Earth, and so gravity is happy, because it's
27:56
Speaker 1: sort of like a ball rolling to the bottom of
27:59
Speaker 1: a valley, happy when it's settled in the bottom of
28:02
Speaker 1: the valley. So this is sort of like, you know,
28:03
Speaker 1: you let a marble go at the top of a
28:05
Speaker 1: hill and it's gonna roll down. It's gonna awesantly pass
28:08
Speaker 1: the minimum, but eventually friction and everything it's gonna settle
28:11
Speaker 1: down in the minimum, and the same thing happens. There's
28:13
Speaker 1: like friction inside the Moon, and the Moon gets heated
28:16
Speaker 1: up a little bit by this, and the Moon also
28:18
Speaker 1: speeds up in its orbit because there's like conservation of
28:21
Speaker 1: angular momentum. So you've slowed down the Moon's spin a
28:24
Speaker 1: little bit, and you've sped up its orbit a little bit,
28:27
Speaker 1: which is why the Moon's orbital radius is increasing a
28:29
Speaker 1: little bit.
28:30
Speaker 2: And so how rare is this? Like if Earth were
28:33
Speaker 2: a little bit smaller, would this not happen? If there was,
28:37
Speaker 2: like if Mars was a little closer, would this not happen?
28:41
Speaker 1: Like?
28:41
Speaker 2: How lucky are we that it worked out this way?
28:43
Speaker 1: We're not that lucky. It's sort of the eventual fate
28:45
Speaker 1: of almost every pair of bodies that orbit each other
28:49
Speaker 1: for long enough. And in fact, we've done it to
28:51
Speaker 1: the Moon, and eventually the Moon will do it to
28:54
Speaker 1: the Earth. It's just a slower process.
28:57
Speaker 2: Whoa like, how slow? Like are we gonna swallowed up
29:00
Speaker 2: by the Sun before it happens? Or is my you know,
29:04
Speaker 2: kid gonna see it before they turn eighty.
29:07
Speaker 1: Yeah, so the Earth's rotation has already been significantly slowed
29:11
Speaker 1: by this effect from the Moon. Over the four billion
29:14
Speaker 1: years since the Earth and the Moon were formed, the
29:16
Speaker 1: length of an Earth day has lengthened from six hours
29:20
Speaker 1: to twenty four hours. So the Moon has made our
29:23
Speaker 1: days four times longer. It's slowed down the Earth spin
29:26
Speaker 1: by a big factor. And eventually, because the Moon keeps
29:29
Speaker 1: tugging on the Earth and making it a little bit
29:31
Speaker 1: longer than tugging on that handle as it passes, eventually
29:34
Speaker 1: it's gonna make the Earth take forty seven days to spin.
29:39
Speaker 1: And at that point, the Earth and the Moon will
29:41
Speaker 1: both be tidally locked to each other, and the Moon
29:44
Speaker 1: will only ever see the same face of the Earth.
29:47
Speaker 2: I don't think that's very nice of the bit. I
29:51
Speaker 2: like having days. Ah, so I'm glad that's not gonna
29:54
Speaker 2: happen in my lifetime.
29:55
Speaker 1: That would be fascinating, right because it would mean that
29:57
Speaker 1: half of the Earth would see the Moon and the
29:59
Speaker 1: other would never see it. If life evolved in that planet,
30:02
Speaker 1: then like half of life wouldn't even know there was
30:04
Speaker 1: a moon.
30:05
Speaker 2: WHOA, I bet we'd have all sorts of different like
30:07
Speaker 2: creation stories. If some of us had moons and some
30:10
Speaker 2: of us didn't. That would be that would be fascinating.
30:13
Speaker 1: Or imagine being an explorer and like settling around the
30:16
Speaker 1: world and then discovering this huge thing floating in your sky.
30:19
Speaker 1: You're like, what, that would be crazy, that would be
30:24
Speaker 1: super amazing. But you're right, it's going to take a
30:26
Speaker 1: long time. And well, before that happens, the Earth is
30:30
Speaker 1: going to be eaten by the Sun, which is going
30:32
Speaker 1: to end its life cycle in about five billion years,
30:35
Speaker 1: turn into a red giant and absorb the Earth. So
30:38
Speaker 1: the Moon is not powerful enough to make that happen
30:41
Speaker 1: anytime soon.
30:42
Speaker 2: Well, on the upbeat topic of the end of our planets,
30:45
Speaker 2: let's take a break, and when we come back, you
30:48
Speaker 2: can tell us if the other moons on the other
30:50
Speaker 2: planets are doing this as well. If I live on Mars,
30:53
Speaker 2: am i gonna see all of Phobos or not? Okay,
31:09
Speaker 2: we're back. So, Daniel, the question that everybody wants to
31:12
Speaker 2: know when we move to Mars, are we going to
31:16
Speaker 2: see the far side of Phobos and Demos or what?
31:19
Speaker 1: So this is a process that happens all over the
31:21
Speaker 1: Solar System and all over the universe. Eventually, gravity will
31:24
Speaker 1: do its bit and distort objects from spheres into like
31:27
Speaker 1: gentle little footballs. It'll grab on those handles and it
31:31
Speaker 1: will hidly lock stuff. And so as we look around
31:33
Speaker 1: the Solar System, we notice that all of the big moons,
31:36
Speaker 1: all of the twenty round moons that exist around planets,
31:40
Speaker 1: are all tidally locked to their planet.
31:44
Speaker 2: Only the round moons. And what causes the Moon to
31:47
Speaker 2: be round, It's that it needs to be a certain size,
31:50
Speaker 2: Is that right?
31:51
Speaker 1: Yeah, If you're big enough, then gravity is going to
31:53
Speaker 1: be powerful enough to pull down any big features, which
31:56
Speaker 1: is why, for example, like neutron stars have no features
31:59
Speaker 1: on them that are highiher than one millimeter. And the
32:01
Speaker 1: larger the gravity, the harder it is to keep a
32:04
Speaker 1: stack of stuff from falling down. And so if you're
32:07
Speaker 1: a pretty small object, you don't have to be very
32:09
Speaker 1: spherical because your gravity's pretty weak. If you're a big
32:11
Speaker 1: object like the Moon or the Earth, then you're going
32:14
Speaker 1: to end up as a sphere because stuff falls down basically,
32:17
Speaker 1: and stuff falls down more when you have more gravity.
32:20
Speaker 1: And so these round moons are technically not actually round, right,
32:23
Speaker 1: They're a little bit footballish and they're all tidally locked
32:27
Speaker 1: to their planet. Most of these also orbit pretty closely
32:30
Speaker 1: and so their gravity is pretty powerful. And then example,
32:32
Speaker 1: you raise like Phobos and Demos on Mars. These are
32:35
Speaker 1: little moons and they're not very large, they're not very round,
32:39
Speaker 1: and they're actually spending really really fast. And so while
32:41
Speaker 1: Mars is doing its job to try to tidly lock them, Phobos,
32:45
Speaker 1: for example, is not yet tidally locked, but it will be.
32:48
Speaker 1: It will be eventually. It's going to happen to everybody.
32:51
Speaker 2: So we've been talking about moon planets. Has it happened
32:54
Speaker 2: to any sun and planets or planets yet?
32:58
Speaker 1: Absolutely? It has absolutely will Right, the Sun is the
33:01
Speaker 1: most powerful source of gravity in the Solar System, and
33:03
Speaker 1: so it's not going to be left out of this party.
33:06
Speaker 1: And it has mercury tidly locked in its grasp. But
33:09
Speaker 1: it's actually fascinating. It's not quite the same way as
33:13
Speaker 1: with the Earth and the Moon because mercury doesn't have
33:16
Speaker 1: as circular an orbit. It's much more elliptical. The mercury
33:19
Speaker 1: is tightly locked in this weird way. Instead of spinning
33:23
Speaker 1: once every time it goes around the Sun, it spins
33:25
Speaker 1: three times for every two revolutions around the Sun. And
33:29
Speaker 1: this is not something we understood for a while because
33:32
Speaker 1: we can't always see Mercury because it's so close to
33:34
Speaker 1: the Sun. There's a few spots in its orbit when
33:37
Speaker 1: it's like easy to see mercury, and so when people
33:39
Speaker 1: were observing Mercury, they were always seeing the same side
33:42
Speaker 1: of it, so they thought, oh, it must have been
33:43
Speaker 1: a one to one tide locking. And it's only later
33:46
Speaker 1: when we got more observations in Mercury did we notice, Oh, no,
33:49
Speaker 1: it's doing this even weirder thing. That's because the orbit
33:52
Speaker 1: is not circular, and so it can do another little
33:54
Speaker 1: bit of spin as it gets further away, and then
33:56
Speaker 1: it comes back around, but still it settles into this
34:00
Speaker 1: really cool pattern, this three two tidal locking.
34:03
Speaker 2: All right, So let's see, my very elderly mother. We're
34:05
Speaker 2: on v I'm guessing Mercury is tidally locked in part
34:09
Speaker 2: because it's so close to the Sun. So is Venus
34:13
Speaker 2: the next closest to being tidally locked or is is
34:16
Speaker 2: it tidally locked?
34:17
Speaker 1: Also, Venus is next on the list to getting tidly locked.
34:21
Speaker 1: It's not yet tidly locked. In fact, Venus has a
34:23
Speaker 1: really weird orbit and spin. It takes five hundred and
34:27
Speaker 1: eighty three days to go around the Sun, but it
34:30
Speaker 1: takes two hundred and twenty four Earth days to rotate.
34:34
Speaker 1: So like a Venus year only has one point nine
34:38
Speaker 1: Venus days. Like you only see two sunrises and two
34:42
Speaker 1: sunsets in a Venus year.
34:44
Speaker 2: Huh, But that wouldn't bother you, because Venus would have
34:46
Speaker 2: killed you in four or five different ways long before
34:50
Speaker 2: you cared about whether the sunrise was coming.
34:53
Speaker 1: That's right. But Venus is sot again there right, Like
34:55
Speaker 1: it's spin is similar to its orbital period. We actually
34:59
Speaker 1: think that's because of a collision that Venus was like
35:01
Speaker 1: smacked into by something which really changed its spin. We
35:05
Speaker 1: don't think there's been enough time for it to be
35:06
Speaker 1: like almost tighly locked by the Sun. It takes a
35:09
Speaker 1: much longer time because Venus is so far away from
35:11
Speaker 1: the Sun and so small relative to the Sun.
35:14
Speaker 2: All right, So we've done moon and planets. We've done
35:20
Speaker 2: comparisons between the Sun and the planets. Is there any
35:26
Speaker 2: other combination of tidally locked things for us to think about?
35:29
Speaker 2: Can asteroids get tidly locked? For example?
35:32
Speaker 1: They could, but it's much harder because their gravity is
35:35
Speaker 1: so weak. Another really fascinating thing to look at are
35:38
Speaker 1: things that have similar masses, like dwarf planets and their moons. So,
35:43
Speaker 1: for example, Pluto no longer a planet, but it's still
35:46
Speaker 1: a dwarf planet. It's got a pretty big moon, Sharon,
35:50
Speaker 1: and these two things are mutually tightly locked already. So
35:54
Speaker 1: if you're like on Pluto and you look up, you
35:56
Speaker 1: always see the same side of the Moon. And if
35:59
Speaker 1: you're on Moon and you look up, you always see
36:02
Speaker 1: the same side of Pluto.
36:04
Speaker 4: Oh.
36:04
Speaker 2: Interesting to how many moons does Pluto have.
36:06
Speaker 1: Oh, Pluto's got a bunch of moons, but most of
36:08
Speaker 1: them rotate chaotically. They're too small to have been tidly
36:11
Speaker 1: locked so far. But it's sort of beautiful to see
36:14
Speaker 1: these things like orbiting their center of mass and facing
36:16
Speaker 1: each other. It's kind of like a dance.
36:18
Speaker 2: Yeah, that's awesome. It's beautiful.
36:20
Speaker 1: And that's not the only example of a dwarf planet.
36:23
Speaker 1: There's another one out there, a trans Neptunian object called Eris,
36:26
Speaker 1: which is also a dwarf planet, and it's got a
36:28
Speaker 1: pretty big moon called Dyspnomia, which happens to be the
36:32
Speaker 1: second largest dwarf planet moon after Pluto's moon, and these
36:36
Speaker 1: two are also tidly locked with each other.
36:39
Speaker 2: That sounds like it's a pretty common thing for dwarf
36:42
Speaker 2: planets to have moons, that know, because how many dwarf
36:44
Speaker 2: planets are there.
36:45
Speaker 1: There's a lot of dwarf planets out there. That's one
36:47
Speaker 1: reason why Pluto isn't really a planet anymore, because we
36:49
Speaker 1: discovered there's kind of a lot of them out there.
36:52
Speaker 1: And if we call Pluto a planet, we've got to
36:53
Speaker 1: call them all planets, and then we're going to have
36:56
Speaker 1: a lot of planet and so you know, astronomers have
36:58
Speaker 1: big arguments about where to draw the line, but there's
37:00
Speaker 1: a lot of dwarf planets.
37:01
Speaker 2: Out there, right, and like, how are we going to
37:03
Speaker 2: have naemonic if there's twenty of one or something like?
37:05
Speaker 2: We just no way, no way, all right. So that's
37:08
Speaker 2: our solar system. This sounds like a fundamental physics thing.
37:12
Speaker 2: So I'm guessing that when we look at other solar systems,
37:14
Speaker 2: they've got the same thing going on.
37:16
Speaker 1: Yes, exactly. We expect that the same thing will happen
37:19
Speaker 1: to planets around other stars and to moons around those planets,
37:23
Speaker 1: and because of sort of the way that we can
37:25
Speaker 1: discover those exoplanets. We expect a lot of the ones
37:29
Speaker 1: we've seen so far have been tidly locked. Like the
37:33
Speaker 1: way that we discover these planets is by seeing their
37:36
Speaker 1: impact on their star. Either they pass in front of
37:39
Speaker 1: their stars, so they give like a little mini planetary
37:41
Speaker 1: eclipse which dims the star a little bit, or they
37:45
Speaker 1: wiggle the star because of the gravity of the planet
37:47
Speaker 1: pulling on the star. So in both cases they have
37:50
Speaker 1: to be pretty close to the star for us to
37:52
Speaker 1: see it, which means that of all the planets out
37:55
Speaker 1: there in the galaxy orbiting their stars, we're best at
37:57
Speaker 1: seeing the ones that are closest to their stars, which
38:00
Speaker 1: also means we're best at seeing the ones that are
38:03
Speaker 1: probably tidally locked. And so astronomers have done a bunch
38:07
Speaker 1: of calculations to understand the orbits of these things and
38:09
Speaker 1: the masses and predict their tidle locking, and they expect
38:12
Speaker 1: that a lot of these planets are tidly locked, maybe
38:16
Speaker 1: one to one, maybe like three to two the way
38:18
Speaker 1: Mercury is, or maybe like five to two. It depends
38:21
Speaker 1: a lot on the eccentricity of the orbit. Wh's the
38:24
Speaker 1: sort of gravitationally most preferred arrangement.
38:27
Speaker 2: Would it be fair to say that it's too far
38:29
Speaker 2: away for us to have been able outside of our
38:32
Speaker 2: solar system to see planets and their moons being tidally locked,
38:36
Speaker 2: and so the only thing we've been able to look
38:37
Speaker 2: at so far is tidal locking with suns and planets.
38:40
Speaker 1: Yeah, that's exactly right. Exo moons is a brand new
38:44
Speaker 1: area of study. People looking for these moons around exo
38:47
Speaker 1: planets super exciting and in the next few years, as
38:50
Speaker 1: we turn on more and more space telescopes, we're going
38:53
Speaker 1: to get more information about these planets and their moons
38:56
Speaker 1: and we can start to measure their spin and to
38:58
Speaker 1: understand this and to figure out like whether these planets
39:01
Speaker 1: out there a lot more of them are tidly locked
39:04
Speaker 1: or a lot less. You know, a question we always
39:06
Speaker 1: have is is our solar system weird or is it typical?
39:11
Speaker 1: Like in most cases, is it just the first couple
39:13
Speaker 1: of planets closest to the Sun that are tidally locked,
39:16
Speaker 1: which would align with our understanding and tell us that
39:18
Speaker 1: our solar systems not that weird, or maybe would be surprised,
39:21
Speaker 1: and we'll discover Oh my gosh, all those solar systems
39:23
Speaker 1: out there, they're all tidly locked. What's going on. Something
39:26
Speaker 1: is different from what we expect. You never know when
39:29
Speaker 1: you go out in the universe and ask these questions
39:31
Speaker 1: and look for the first time, if you're just going
39:33
Speaker 1: to see like more dust and rubbel or something really
39:36
Speaker 1: really exciting.
39:36
Speaker 2: The universe is good at providing job security in the
39:39
Speaker 2: form of new questions.
39:40
Speaker 1: And it's not just stars and planets we can study.
39:43
Speaker 1: We can also look at pairs of stars. We're used
39:47
Speaker 1: to thinking about stars as like individual and you have
39:50
Speaker 1: a solar system with one star at its core and
39:52
Speaker 1: a bunch of planets, But actually there's lots of binary
39:55
Speaker 1: star systems out there. And the reason is that stars,
39:58
Speaker 1: when they're formed, it's a big cloud of gas and
40:01
Speaker 1: dust which collapses, and typically you get multiple stars from
40:04
Speaker 1: a big cloud of gas and dust. You have like
40:06
Speaker 1: little gravitational seeds that start this runaway gravitational effect, and
40:11
Speaker 1: you don't just have one seed, you have a bunch
40:12
Speaker 1: of them, so you get like an stellar nursery makes
40:15
Speaker 1: lots and lots of stars. So we have a whole
40:17
Speaker 1: podcast episode about binary star systems and even like trinary
40:21
Speaker 1: star systems. But the point is that lots of stars
40:24
Speaker 1: out there have brothers and sisters they were born with
40:27
Speaker 1: like twins, and so they're pretty close to another star,
40:30
Speaker 1: which means that you can have pairs of stars that
40:33
Speaker 1: are tidly locked to each other.
40:35
Speaker 2: That's awesome.
40:36
Speaker 1: Or if you have a really big planet, you could
40:39
Speaker 1: have a planet and a star that are tidly locked
40:41
Speaker 1: to each other, so the planet is always seeing the
40:44
Speaker 1: same side of the star. Right, that could be weird.
40:47
Speaker 2: Yeah, but we haven't seen that yet, Right.
40:49
Speaker 1: We have not seen that yet. There's a star out
40:51
Speaker 1: there Tao Buddhists, which we suspect is tidly locked to
40:55
Speaker 1: its planet, but we're not one hundred percent sure of that.
40:58
Speaker 1: But you know, this kind of stuff makes a difference
41:00
Speaker 1: because it really changes the experience of being on a planet.
41:03
Speaker 1: Like if Earth was tidly locked to the sun, we'd
41:06
Speaker 1: have half of the Earth at sunshine all day, and
41:08
Speaker 1: half of the Earth would be the dark side of
41:10
Speaker 1: the Earth. The far side of the Earth would be
41:12
Speaker 1: the dark side, you know where Pink Floyd plays concerts
41:15
Speaker 1: and Gary Larson draws his cartoons, And that would be
41:18
Speaker 1: the very very cold side of the Earth, right dead side,
41:22
Speaker 1: the oh, the dead side exactly. And then you'd have
41:24
Speaker 1: this ring around the middle of the Earth that was
41:26
Speaker 1: like right on the edge, you'd be like permanent sunrise,
41:30
Speaker 1: and that might be the only place on the planet
41:32
Speaker 1: you could live because one side would be too hot
41:34
Speaker 1: and one side would be too cold. And then you'd
41:36
Speaker 1: have this like goldilocks ring around the planet that might
41:39
Speaker 1: be hospitable.
41:40
Speaker 2: Location, location, location.
41:44
Speaker 1: Exactly. And so if that's the case on some of
41:46
Speaker 1: these exoplanets, that means it'd be a lot harder for
41:49
Speaker 1: life to form. Either they'd have to evolve to survive
41:52
Speaker 1: very hot conditions or very cold conditions, or there'd only
41:56
Speaker 1: be a thin strip of their planet that they could
41:58
Speaker 1: live on, and you know, then there wouldn't be seasons.
42:00
Speaker 1: In the same way, it would make for a very
42:02
Speaker 1: different kind of biology.
42:04
Speaker 2: It would make it easy to study extremophiles, though, because
42:07
Speaker 2: you know exactly where you needed to go, just you know,
42:10
Speaker 2: the cold ones are over there and the hot ones
42:11
Speaker 2: are over there. But there probably wouldn't be a lot
42:13
Speaker 2: of funding for science in a world like that.
42:16
Speaker 1: You never know, right, and we have all these expectations
42:18
Speaker 1: for what life would be like on these planets, because
42:21
Speaker 1: we imagine what our life would be like on those planets.
42:23
Speaker 1: But of course, if you evolve on those planets, you'd
42:26
Speaker 1: think that's the normal way to live, and they would
42:28
Speaker 1: think it's super duper weird for like your planet to
42:31
Speaker 1: spin and get constantly bathed in sunlight, or for you
42:34
Speaker 1: to have no control over whether you're seeing the sun
42:37
Speaker 1: or not. Because on tidly locked planets, right, you don't
42:40
Speaker 1: want sun, you just move to the backside. You want sun,
42:43
Speaker 1: you move to the front side, totally up to you,
42:45
Speaker 1: whereas here we're like at the mercy of celestial objects,
42:48
Speaker 1: spin rates to determine when we see sun and when
42:51
Speaker 1: we don't.
42:51
Speaker 2: Yeah, I guess you get used to what you grew
42:53
Speaker 2: up with. It sure seems like it's nice to have
42:56
Speaker 2: a more moderate in between.
42:58
Speaker 1: It certainly does. But in the end, the universe prefers
43:01
Speaker 1: tidal luck, and given enough time gravity, it's going to
43:04
Speaker 1: do its business, make everything round and then make it
43:06
Speaker 1: a little bit footballish, and it's going to tug on
43:09
Speaker 1: those gravitational handles until everything is tidly locked, unless, of course,
43:14
Speaker 1: your son explodes and eats you before it can even happen,
43:17
Speaker 1: but it's sort of the gravitational destiny of every other
43:20
Speaker 1: kind of object.
43:21
Speaker 2: And there's the ending that'll keep from listening.
43:26
Speaker 1: And hopefully inspire a lot of crazy music and silly cartoons. Yes,
43:31
Speaker 1: all right, Thanks very much everybody for exploring the physics
43:34
Speaker 1: of tidal locking with us. It turns out to play
43:36
Speaker 1: a big role in what it's like to live on
43:38
Speaker 1: our planet, what it's like to look up at disguise
43:40
Speaker 1: and understand the universe or wonder at its mysteries, and
43:44
Speaker 1: it will continue to play a big role in life
43:47
Speaker 1: on Earth.
43:47
Speaker 2: Huzza.
43:48
Speaker 1: Thanks for listening. Tune in next time. Thanks for listening,
43:58
Speaker 1: and remember that Daniel and Jorge Explain the Universe is
44:01
Speaker 1: a production of iHeartRadio. For more podcasts from iHeartRadio, visit
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Speaker 1: your favorite shows.