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Speaker 1: Hey, do you ever wish that we had more moons

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Speaker 1: in our night sky?

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Speaker 2: Hmmm? I think the universe as moon does enough times.

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Speaker 1: Actually, well, I like the moons, and I sometimes wish

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Speaker 1: we had more going on in the night sky, like

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Speaker 1: lots of little moons.

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Speaker 2: But then I wonder if we had the same line

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Speaker 2: in Star Wars, you know, where he says that's no moon.

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Speaker 2: That wouldn't work.

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Speaker 1: Maybe instead of the Death Star, they would have had

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Speaker 1: the death constellation.

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Speaker 2: Or that song when the moon hits your eye like

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Speaker 2: a big pizza pie. That wouldn't work with a lot

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Speaker 2: of little moons. I guess it would work with lots

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Speaker 2: of mini pizzas.

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Speaker 1: The personal pan pizza would have been invented earlier.

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Speaker 2: Hi am Horehea, ma cartoonist and the creator of PhD comics.

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Speaker 1: Hi I'm Daniel. I'm a particle physicist and a professor

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Speaker 1: at UC Irvine, and I'd never really been a fan

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Speaker 1: of the pan pizza, of.

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Speaker 2: The pan or the pizza or just a combination of

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Speaker 2: the two.

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Speaker 1: The pizza in the pan. Definitely a thin crust kind

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Speaker 1: of guy over here, not.

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Speaker 2: A bread fan trying to curb your carbs.

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Speaker 1: I like tomato sauce. But I don't like the kiddie

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Speaker 1: pool of marinera that they call pizza in Chicago.

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Speaker 2: I feel like there's a thin line between a pan

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Speaker 2: pizza and like a casserole or like a pot pie.

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Speaker 1: It's really just a Midwestern hot dish.

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Speaker 2: There you go, But anyways, welcome to our podcast, Daniel

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Speaker 2: and Jorge Explain the Universe, a production of iHeartRadio.

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Speaker 1: Where we love everything about the universe, the thick ready

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Speaker 1: questions and the thin crunchy ones we wonder about how

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Speaker 1: everything out there in the universe works. We take a

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Speaker 1: big curiosity motivated by it, of the universe and try

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Speaker 1: to chew through all of it for you.

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Speaker 2: That's right, because the universe is a deep dish of

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Speaker 2: amazing facts and incredible things happening in it, full of

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Speaker 2: mysteries and wonderful conundrums for us to try to figure out.

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Speaker 1: And while physics has made incredible progress in understanding the

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Speaker 1: way the world works, we're still answering the kinds of

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Speaker 1: questions we've been asking basically forever, just looking around us,

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Speaker 1: seeing how the world is and wondering like, why is

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Speaker 1: it this way? How did it get to be this way?

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Speaker 2: Why does Deep Dish Pizza exist? Fundamental questions? That's what

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Speaker 2: we ask here on the podcast, and why doesn't Daniel

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Speaker 2: like them?

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Speaker 1: We know why Deep Dish Pizza exist for the same

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Speaker 1: reason vanilla ice cream exists, because you know, there's a

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Speaker 1: whole spectrum of people out there and everybody loves different things.

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Speaker 2: Are you saying the universe is kind of cheesy? I

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Speaker 2: guess it will definitely give you a heart attack as well.

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Speaker 2: There's no topping that joke, but yeah, we like to

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Speaker 2: think about the universe and all of the perfecting things

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Speaker 2: in it, like how did things come to be the

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Speaker 2: way they are? Why are we here? And where are

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Speaker 2: we in the universe?

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Speaker 1: And what is One of the real, simple but enduring

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Speaker 1: joys of being a curious person is just looking up

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Speaker 1: at the night sky. Not just being amazed at it's

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Speaker 1: beauty and odd at the depth of the view that

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Speaker 1: you were looking at, but this shared feeling through time

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Speaker 1: that humans one hundred years ago, a thousand years ago,

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Speaker 1: twenty five thousand years ago probably looked up at almost

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Speaker 1: the same night sky and wondered what was up there

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Speaker 1: and why it looked the way it did, and whether

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Speaker 1: it could have been different.

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Speaker 2: Yeah, you're looking at the exact same sky that our

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Speaker 2: ancestors did, full of stars, comments, and even a moon.

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Speaker 2: And they probably asked the same question that maybe a

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Speaker 2: lot of you have out there, which is, why do

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Speaker 2: we have a moon? And is it made out of cheese?

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Speaker 2: Is it just a big, flat, giant, floating deep dish

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Speaker 2: of cheese.

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Speaker 1: It's a spherical pizza. In the end, I have my

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Speaker 1: spherical pizza theory of the moon.

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Speaker 2: Do you do tell? Give us a slice of that

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Speaker 2: knowledge there?

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Speaker 1: All right? You called my bluff.

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Speaker 2: I got nothing and it was a crusty joke. But yeah,

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Speaker 2: sometimes we look out into the universe, into the night sky,

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Speaker 2: and we wonder why are things there, and how did

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Speaker 2: they come to be the way they are? What's going on?

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Speaker 2: And it wasn't just our ancestors that looked up at

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Speaker 2: the moon. It's like all of the planet that is

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Speaker 2: looking up at the moon, right, it's feeling its facts

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Speaker 2: and howling at it and rolling with the tides that

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Speaker 2: go along with the moon. The moon has. It makes

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Speaker 2: a big difference here on this planet.

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Speaker 1: Yeah, and these are not just questions asked by amateur astronomers,

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Speaker 1: but planet heiogeologist at the cunning edge are still trying

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Speaker 1: to figure out the details of how everything came to

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Speaker 1: be in our night sky.

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Speaker 2: So to the other podcast, we'll be tackling the question

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Speaker 2: how the planets get their moon or moons. Some planets

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Speaker 2: have lots of moons, right.

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Speaker 1: Yeah, that's right. It turns out our planet is quite

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Speaker 1: unusual in having approximately one moon.

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Speaker 2: So you do believe in the moon. The moon does exist, right.

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Speaker 1: I can see the moon. I know it's there, But.

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Speaker 2: How you know it's round? It always looks the same.

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Speaker 1: Well, we've been to the moon, so we can see

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Speaker 1: all around it, and you can tell that is round. Also,

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Speaker 1: the curved edge between the bright side and the dark

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Speaker 1: side of the moon tell us that it's going to

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Speaker 1: be round.

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Speaker 2: Oh right, you get sort of like the shadow of

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Speaker 2: it tells you it's round.

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Speaker 1: Exactly?

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Speaker 2: Is it perfectly round? Is the Moon perfectly round? Or

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Speaker 2: is it kind of an ellipsoid like the Earth.

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Speaker 1: Nothing in the universe is perfectly round. There are no

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Speaker 1: actual circles out there, maybe even not the event horizons

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Speaker 1: of black holes due to quantum effects. So the Moon

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Speaker 1: is definitely not perfectly round, and it's also pulled into

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Speaker 1: something of a football shape thanks to the Earth's gravity.

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Speaker 1: Tidal forces on the Moon by the Earth make it

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Speaker 1: a little bit oblong.

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Speaker 2: Whoa, I guess it's not spinning in the way that

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Speaker 2: the Earth is so that you get this centropical force.

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Speaker 2: But you're saying that the fact that the Earth is

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Speaker 2: pulling on it kind of stretches it out.

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Speaker 1: Yeah, it is spinning. It's just spinning at exactly the

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Speaker 1: right rate so that the same side of it is

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Speaker 1: always facing the Earth. This is called a tidal locking. Eventually,

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Speaker 1: the Earth pulls on the Moon to make it oblong,

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Speaker 1: and then they get stuck in this stable equilibrium where

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Speaker 1: that long bit is always pointing towards the Earth because

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Speaker 1: gravity on that long bit is a little stronger, so

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Speaker 1: it's sort of like a pendulum dangling towards the Earth.

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Speaker 2: Well, it is cool that we have a moon. I

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Speaker 2: guess it would to inspire all of these songs and

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Speaker 2: all these stories and legends about the moon.

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Speaker 1: It is nice to have a moon. It lights up

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Speaker 1: otherwise very dark nights, and it's something very close by

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Speaker 1: to look at, right, So much of the rest of

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Speaker 1: the night sky are just dots. They're so far away

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Speaker 1: they look like pinpricks. But the Moon has features on it.

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Speaker 1: I remember as a kid looking up at it and

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Speaker 1: studying those and like wondering what it would be like

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Speaker 1: to walk across it and to be on it, or

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Speaker 1: to look at the Earth from the moon. It's cool

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Speaker 1: that it's both in the night sky and kind of

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Speaker 1: close by.

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Speaker 2: Yeah, I guess it's kind of scary to think about it. Actually,

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Speaker 2: it's just kind of swinging around the Earth. It's constantly

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Speaker 2: falling around the Earth. That's what the Moon is doing.

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Speaker 2: And it's big, Like you don't want to mess with

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Speaker 2: the moon either.

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Speaker 1: Yeah, the Moon is pretty massive. And not only is

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Speaker 1: the Earth tugging on the Moon and forcing it to

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Speaker 1: face us the same way, but the Moon is doing

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Speaker 1: the same thing to Earth. Eventually, the Earth of the

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Speaker 1: Moon will both be tidally locked to each other.

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Speaker 2: Mmmmm, wait what does that mean? That means that we

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Speaker 2: will be going around the moon.

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Speaker 1: It means that, given enough time, the Moon will stay

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Speaker 1: on the same side of the Earth. The Earth's spin

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Speaker 1: and the Moon's spin will balance so that only one

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Speaker 1: side of the Earth ever sees the Moon the same way,

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Speaker 1: only one side of the Moon ever sees the Earth.

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Speaker 2: Wait, what for real. When is that going to happen.

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Speaker 1: It's not going to be for billions of years, but

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Speaker 1: it has already had an impact, Like the rate that

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Speaker 1: the Earth is spinning has slowed down to twenty four

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Speaker 1: hours per spin over the last four billion years. Four

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Speaker 1: billion years ago, it took about six hours for the

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Speaker 1: Earth to spin, So the Moon is slowing down the

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Speaker 1: spin of the Earth. Eventually, it will take about forty

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Speaker 1: seven of our current days to spin the Earth. That

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Speaker 1: will match the Moon's orbital period, and the Earth and

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Speaker 1: the Sun will be tidally locked to each other. But

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Speaker 1: that wouldn't be for billions of years, and that would

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Speaker 1: be assuming that the Sun doesn't gobble the Earth first.

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Speaker 2: Yeah, we would have bigger problems in the Moon at

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Speaker 2: that point.

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Speaker 1: But it would be kind of amazing if you could

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Speaker 1: only see the Moon from one half of the Earth.

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Speaker 1: It would mean you could grow up your whole life

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Speaker 1: and not see the Moon, and then travel to another

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Speaker 1: part of the Earth and see the Moon for the

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Speaker 1: first time. That would be incredible.

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Speaker 2: Whoa which sid gets to have the moon? Can they

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Speaker 2: predict that? Or we even have the same We probably

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Speaker 2: won't even have the same continents.

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Speaker 1: Right, Yeah, not in billions of years exactly.

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Speaker 2: I guess we have the moon to thank for having

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Speaker 2: more time in our day. Then without the moon that

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Speaker 2: things will be a lot more hectic.

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Speaker 1: Yeah, that's true. Those of you who like to work

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Speaker 1: late at night would have much shorter nights to get

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Speaker 1: stuff done.

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Speaker 2: I think the people during the day would also have

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Speaker 2: a shorter time, right, But it is an interesting question

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Speaker 2: how did we get this moon? Like how do planets

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Speaker 2: get moons at all? And why do we only have

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Speaker 2: one moon versus having lots of moons like other planets

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Speaker 2: which have up to eighty four moons.

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Speaker 1: It is really fun, fascinating question, and the answer tells

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Speaker 1: us a lot about how solar systems form, whether our

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Speaker 1: planet is weird, and maybe whether our solar system itself

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Speaker 1: is kind of weird.

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Speaker 2: Well, you can get all that from the moon.

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Speaker 1: You can learn a lot just by asking questions.

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Speaker 2: Well, as usual, we were wondering how many people out there?

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Speaker 2: I thought about the question of where moons come from

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Speaker 2: and how are they form? How do we get ours?

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Speaker 2: So as usual Daniel went out there into the internet

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Speaker 2: to ask people how do moons form?

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Speaker 1: Thanks very much to everybody who participates in this segment

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Speaker 1: of the podcast. If you've been listening for a while

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Speaker 1: and thinking about participating, please let me encourage you. It's fun,

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Speaker 1: it's easy. Everybody enjoys it. Write to me two questions

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Speaker 1: at Danielandjorge dot com.

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Speaker 2: So think about it for a second. How do you

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Speaker 2: think planets get their moons? Here's what people had to say.

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Speaker 3: I think that most moons form from cloud discs around planets,

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Speaker 3: and that Satan's rings are a picture of that process

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Speaker 3: going on.

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Speaker 4: Moons on form? How planet form? So they're small rocks

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Speaker 4: and then they hit each other and create bigger ones.

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Speaker 4: So when a planet is created, maybe when it gets created,

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Speaker 4: some debris goes out and then creates like a miniature

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Speaker 4: planet aka a moon.

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Speaker 2: Maybe I suppose the moon is just a small planet.

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Speaker 2: It's kind of just a planet that gets trapped by

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Speaker 2: another planet. Right, they're just rocks.

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Speaker 5: There's got to be like at least six ways moon forms.

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Speaker 5: I don't know, like things crashing together. Apparently we might

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Speaker 5: have stolen the Moon from Venus. Maybe probably a bunch

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Speaker 5: of other ways they could form too.

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Speaker 6: I think Moon's form either just sort of alongside they're

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Speaker 6: planet like Lucky, or from collisions like our own moon

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Speaker 6: came from an impact. Those are, I guess, the only

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Speaker 6: two I really know.

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Speaker 7: I would say that this is a collisions between among

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Speaker 7: asteroids planets, and then you have planet that has been

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Speaker 7: hit by an asteroid, and a small chunk of this

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Speaker 7: planet would be placed in a sort of an orbit,

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Speaker 7: and then you get the Moon.

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Speaker 8: I think it's when space dust is orbiting a planet

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Speaker 8: and then it clumps together into the Moon eventually, or if,

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Speaker 8: like an asteroid, is caught in the gravitational pool of

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Speaker 8: a planet and falls into its orbit.

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Speaker 1: I think Moon's form from asteroids and other bits of

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Speaker 1: space debris that get trapped in a planet's orbit.

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Speaker 9: I think that moon's form around planets the same way

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Speaker 9: that planets form around stars. I think that basically there's

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Speaker 9: a bunch of junk floating around the planet that aggregates

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Speaker 9: into a moon or moons.

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Speaker 2: All right, a lot of interesting answers here. Somebody said

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Speaker 2: at least six ways, that's all they said, But only

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Speaker 2: at least six he or she had six ways in mind.

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Speaker 1: M reminds me that Paul Simon's song just get on

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Speaker 1: the bus, gus don't need to discuss much. Yeah, there

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Speaker 1: must be six ways to get a moon.

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Speaker 2: Sounds like clickbait. Six ways so we can get a moon.

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Speaker 2: The sixth one will totally amaze you. Maybe we should

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Speaker 2: be learning from this listener and how to title our

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Speaker 2: podcast episodes. Although that you hear BuzzFeed is going down,

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Speaker 2: it's going out of business or BuzzFeed news.

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Speaker 1: Do you think there's a lesson there for us podcasters?

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Speaker 2: Yeah, I think there are six amazing lessons. The sixth

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Speaker 2: one will totally astound you.

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Speaker 1: I can't wait to hear.

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Speaker 2: But yeah, a lot of interesting theories here from people.

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Speaker 2: Some people think it happens from like a collision. Some

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Speaker 2: people think we stole it from another planet? Is that true?

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Speaker 1: The truth is that there are lots of different ways

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Speaker 1: to get moons, and we'll dig into several of them today.

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Speaker 2: M The sixth one will amaze you.

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Speaker 1: If we get there.

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Speaker 2: If we get that right, know for sure we'll get there.

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Speaker 2: Question is how long before we get there? Will we

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Speaker 2: do it before the hour is up? Towards a close call?

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Speaker 2: All right, Well, let's start with the basics, Daniel, how

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Speaker 2: would you define a moon? Like what is a moon?

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Speaker 2: And what's the difference between a moon and like a

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Speaker 2: satellite or an asteroid or just a space jump.

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Speaker 1: Yeah, this is an interesting question in astronomy. We have

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Speaker 1: all these categories we've invented to describe the kinds of

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Speaker 1: things we've seen out there, and then we find things

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Speaker 1: that break those categories, and it turns out there are

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Speaker 1: no real hard divisions and bright lines between stuff. It's

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Speaker 1: just sort of like where humans like to draw a

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Speaker 1: dotted line between things, and so it's kind of a

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Speaker 1: mess what a moon is signs. Originally they called these

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Speaker 1: things natural satellites, Like when you look at Jupiter and

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Speaker 1: you see things going around it, you call those satellites

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Speaker 1: of Jupiter. And for a long time, like before the

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Speaker 1: space age, the word moon just referred to the moon

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Speaker 1: of the Earth, which is the name of our moon.

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Speaker 1: But then we started launching artificial satellites, and so when

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Speaker 1: Sputnik went up, people called it an artificial satellite. But

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Speaker 1: that's sort of awkward and a mouthful, so people didn't

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Speaker 1: like saying artificial satellite. They just start calling it satellite,

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Speaker 1: and so that makes natural satellite kind of awkward.

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Speaker 2: To say organic satellite exactly, or farm raised satellites.

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Speaker 1: But natural satellite is kind of a mouthful, and so

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Speaker 1: now people, even scientists, sometimes say moons. Technically, we have

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Speaker 1: artificial satellites, things we have launched in due space, and

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Speaker 1: then we have natural satellites, things that are in orbit anyway,

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Speaker 1: naturally without the influence of humans.

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Speaker 2: But wait, wait, I think I've seen NASA call the

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Speaker 2: moons of Jupiter the moons of Jupiter. They never say

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Speaker 2: the satellites of Jupiter.

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Speaker 1: That's right. So technically we have artificial satellite and we

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Speaker 1: have natural satellite, though typically we just say satellite for

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Speaker 1: artificial satellite, and now we say moon for natural satellite,

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Speaker 1: even in scientific publications and like official press releases. So

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Speaker 1: now moon has come to mean natural satellite.

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Speaker 2: I see. But I guess if you put the in

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Speaker 2: front of it, then it's our moon. Like the moon

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Speaker 2: is our moon, but then other moons are just moons.

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Speaker 1: Yeah, exactly, the moon is our moon or Luna if

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Speaker 1: you prefer. And moon with a lowercase M means any

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Speaker 1: kind of natural satellite.

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Speaker 2: I guess you can have rocks, and you can have

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Speaker 2: the rock.

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Speaker 1: Exactly. We have lots of rocks in orbit, but I

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Speaker 1: don't think we have the rock in orbit yet, though

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Speaker 1: I haven't seen fast and Furious twenty seven or whichever

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Speaker 1: one has space.

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Speaker 2: I'm assureing the next one there, they'll you know, speed

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Speaker 2: up a ramp and somehow make it up to space

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Speaker 2: and crash into a space station. While he jumps and

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Speaker 2: also launches a rocket launcher.

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Speaker 1: He's got to flex his muscles at some point. Another

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Speaker 1: question is size, Like, is every object that's orbiting the

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Speaker 1: Earth a moon? Every tiny little rock is at a

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Speaker 1: moon of the Earth. Officially, there's no lower limit, right,

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Speaker 1: Like every natural object with an orbit around the planet,

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Speaker 1: technically you could call it a moon.

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Speaker 2: Wait what I mean? No, at some point, it's just

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Speaker 2: the rock, right.

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Speaker 1: The moon is just a rock. Also makes the Moon

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Speaker 1: different from other rocks orbiting the planet is just the size,

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Speaker 1: and there is no official lower limit to the size

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Speaker 1: of a moon. You could have a moon of any size,

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Speaker 1: and any limit you place is going to be totally ourary, right.

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Speaker 2: I wonder if the definition also has to do with

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Speaker 2: how stable its orbit is. Like, if I just throw

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Speaker 2: a rock and into space, it's kind of orbiting the

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Speaker 2: Earth for a little bit, does that mean it's a.

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Speaker 1: Moon that's not really in orbit? Right? I don't know

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Speaker 1: how strong you are. Recently haven't seen you in a while,

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Speaker 1: But I don't think you could throw a rock and

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Speaker 1: actually get it into orbit. It has to be in orbit.

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Speaker 2: Oh yeah, do you want to make that bet? I'll

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Speaker 2: bet you a billion dollars because with a billion dollars

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Speaker 2: I can come into space and throw the rock.

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Speaker 1: If you get a rock orbiting the Earth, I will

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Speaker 1: campaign NASA to let you name it officially.

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Speaker 2: Well, if you get me on a rocket ship into

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Speaker 2: space to throw a rock, we'll start the whole process.

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Speaker 1: But we can look at the typical sizes of these things,

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Speaker 1: and like in our Solar system there are a few

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Speaker 1: hundred of these moons. There's six planets that have moons,

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Speaker 1: for a total of two hundred and twenty six moons,

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Speaker 1: and typically the planet to moon mass ratio is at

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Speaker 1: least ten thousand to one, so moons typically have a

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Speaker 1: much smaller mass than the planet they orbit.

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Speaker 2: Wait, there are six planets in our Solar system with moons.

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Speaker 2: Who doesn't have a moon?

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Speaker 1: Neither Mercury nor Venus have moons. That's probably because they're

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Speaker 1: too close to the Sun and so tidal disruption basically

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Speaker 1: pulls those moons away.

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Speaker 2: Oh interesting, and I just figured out that's probably what

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Speaker 2: the listener meant when they said at least six ways.

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Speaker 1: Oh nice. Probably every moon has a unique story, m

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Speaker 1: they have their own origin story. Of course, our moon

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Speaker 1: is a big exception to this ten thousand to one rule, right,

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Speaker 1: because the mass of the Moon is about one eightieth

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Speaker 1: of the mass of the Earth. It's like more than

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Speaker 1: one percent of the mass of the Earth. So it's

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Speaker 1: a big honk and moon it's very unusual.

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Speaker 2: So most of the moons in the Solar System, some

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Speaker 2: of them are as big as our moon, but you're

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Speaker 2: saying that the ratio compared to their planet, most of

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Speaker 2: them are small.

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Speaker 1: Most of them are small exactly. And then there's the case,

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Speaker 1: for example, of Pluto. Pluto has a moon which is Sharon,

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Speaker 1: which is one eighth of its mass, and so like

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Speaker 1: we call Pluto a dwarf planet, and we call Sharon

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Speaker 1: a moon of Pluto. But you know, you could also

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Speaker 1: argue that it's really like a dwarf planet binary system,

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Speaker 1: which one is a planet and which one is the moon?

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Speaker 1: It all gets kind of fuzzy.

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Speaker 2: Whoa, it's like a double planet.

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Speaker 7: Man.

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Speaker 1: One way to distinguish the two scenarios, like having a

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Speaker 1: double planet or a planet with a moon. Is whether

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Speaker 1: the center of mass of the system is within the

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Speaker 1: surface of one of them. If you find the point

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Speaker 1: that averages where all the mass is, the point around

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Speaker 1: which the two objects really are orbiting, if that is

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Speaker 1: underground one of the two objects, and you call the

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Speaker 1: more massive one a planet and the other one a moon.

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Speaker 1: Otherwise you call it a binary system. Again, that's still

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Speaker 1: kind of arbitrary, right, We're just like giving these things

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Speaker 1: names and drawing lines between them. Really, there's just a

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Speaker 1: bunch of different rocks out there in the universe orbiting

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Speaker 1: each other.

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Speaker 2: Except also, Pluto is not a planet, So can you

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Speaker 2: have a moon around something that's not planet? Like can

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Speaker 2: you can moon or can a moon have a moon?

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Speaker 1: You can have a moon around a dwarf planet, though

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Speaker 1: maybe you would want to call it a dwarf moon.

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Speaker 1: I don't know. And it's possible in principle to have

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Speaker 1: moons around moons. There are asteroids that have moons.

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Speaker 2: Wait what, and you still call them moons, not master moons.

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Speaker 1: Some people want to call them moonlits or moon moons

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Speaker 1: like the moon of a.

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Speaker 2: Moon or moony's or mini moons.

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Speaker 1: And there are even some moons, like Rhea has its

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Speaker 1: own ring system Saturn's moon Rhea.

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Speaker 2: Wait what some moons can have rings? Yeah, because they

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Speaker 2: have so many mini moons.

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Speaker 1: If you're big enough that you dominate the gravitational environment nearby,

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Speaker 1: then yeah, you can have your own rings.

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Speaker 2: I mean, I guess technically anything can have a satellite, right,

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Speaker 2: Like I can take a baseball, put in into space

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Speaker 2: and then knock a you know, a speck of dust

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Speaker 2: in orbit around it.

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Speaker 1: Right, yeah, exactly. That wouldn't be a planet or even

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Speaker 1: a dwarf planet, but it would have an orbiting object.

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Speaker 1: Is that a natural satellite? I'm not quite sure.

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Speaker 2: A what else do we know about moons?

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Speaker 1: If you try to dig into the ancient history of moons,

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Speaker 1: it gets quite confusing to read about because until Copernicus,

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Speaker 1: moons were actually called planets, like the Moon itself was

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Speaker 1: referred to as a planet. Like when you talked about

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Speaker 1: astronomy in the fifteen hundreds, you said the planet Mars,

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Speaker 1: the planet Venus, the planet Luna. And it wasn't until Kepler,

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Speaker 1: who was thinking about how these things orbit each other,

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Speaker 1: who had a better understanding of these orbits, that we

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Speaker 1: started calling the moon a satellite of the Earth, and

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Speaker 1: then the satellites of Jupiter are of course the moons

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Speaker 1: of Jupiter. So there's a really fun interesting history to

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Speaker 1: these words.

442
00:20:34,960 --> 00:20:37,359
Speaker 2: Wait, really, so like, for a moment in human history,

443
00:20:37,400 --> 00:20:41,000
Speaker 2: we thought the Moon was another planet orbiting the Solar System.

444
00:20:41,240 --> 00:20:42,920
Speaker 2: Technically it is orbiting the Sun.

445
00:20:43,200 --> 00:20:45,240
Speaker 1: Yeah, it is orbiting the Sun, and it is orbiting

446
00:20:45,240 --> 00:20:47,440
Speaker 1: the Earth. Right, it's not that we thought the Moon

447
00:20:47,560 --> 00:20:50,119
Speaker 1: was a planet like Mars. It's just that we categorized

448
00:20:50,160 --> 00:20:52,320
Speaker 1: all these things the same way. All these words are

449
00:20:52,359 --> 00:20:54,680
Speaker 1: just buckets, right, and they're just like grab a bunch

450
00:20:54,760 --> 00:20:56,600
Speaker 1: of the stuff that's out there and gather it all

451
00:20:56,640 --> 00:20:59,600
Speaker 1: into a conceptual bucket. And where the lines between these

452
00:20:59,640 --> 00:21:02,160
Speaker 1: buckets is a little bit arbitrary. And so it used

453
00:21:02,160 --> 00:21:04,360
Speaker 1: to be that we lumped the moon in with the planets.

454
00:21:04,680 --> 00:21:07,240
Speaker 1: Now we have a separate category for things that orbit

455
00:21:07,280 --> 00:21:08,320
Speaker 1: the planets.

456
00:21:09,280 --> 00:21:11,639
Speaker 2: Shoot for the Moon. I guess when you're naming things,

457
00:21:11,760 --> 00:21:14,159
Speaker 2: all right, well, let's get a little deeper into where

458
00:21:14,200 --> 00:21:16,920
Speaker 2: the Moon came from, Where do moons in general come from,

459
00:21:16,960 --> 00:21:19,480
Speaker 2: how do other planets get their moons, and what does

460
00:21:19,520 --> 00:21:22,399
Speaker 2: it all mean about the history of the Solar System.

461
00:21:22,560 --> 00:21:37,479
Speaker 2: But first let's take a quick break, all right, we're

462
00:21:37,520 --> 00:21:40,840
Speaker 2: getting a little looney here talking about the moon and

463
00:21:40,880 --> 00:21:43,399
Speaker 2: how we got it and how do planets get their moons.

464
00:21:43,560 --> 00:21:46,320
Speaker 1: It is really fun in ancient question to wonder why

465
00:21:46,359 --> 00:21:48,560
Speaker 1: that thing is in our sky and why Jupiter has

466
00:21:48,600 --> 00:21:51,359
Speaker 1: more moons than we do. And if history had been different,

467
00:21:51,440 --> 00:21:53,320
Speaker 1: would we have had a bunch of moons? What would

468
00:21:53,359 --> 00:21:55,919
Speaker 1: it be like to live in that scenario? Could we

469
00:21:56,080 --> 00:21:59,240
Speaker 1: sail as well? If the ties were crazy and complicated

470
00:21:59,359 --> 00:22:02,080
Speaker 1: from having like fifteen different little moons? Hmmm?

471
00:22:02,400 --> 00:22:05,440
Speaker 2: Interesting? Yeah, that would affect the tides, right, But that

472
00:22:05,440 --> 00:22:06,919
Speaker 2: wouldn't affect navigation, would it.

473
00:22:06,920 --> 00:22:09,000
Speaker 1: It wouldn't affect navigation, but it would affect when it's

474
00:22:09,040 --> 00:22:11,359
Speaker 1: easy to launch your ships or not, and so it

475
00:22:11,400 --> 00:22:13,800
Speaker 1: might affect lots of industries and exploration.

476
00:22:14,160 --> 00:22:16,199
Speaker 2: M Also, if you're a were wolf, it would be

477
00:22:16,240 --> 00:22:19,840
Speaker 2: pretty complicated, right, probably, just you know, just the planet ahead.

478
00:22:20,760 --> 00:22:22,840
Speaker 1: Maybe you change into one kind of wolf for one

479
00:22:22,880 --> 00:22:24,879
Speaker 1: moon and another kind of wolf for another moon, and

480
00:22:24,920 --> 00:22:27,440
Speaker 1: like a Pomeranian for the little moon or a shitsu.

481
00:22:29,040 --> 00:22:31,840
Speaker 2: Yeah, there you go, different moons for different breeds.

482
00:22:31,600 --> 00:22:33,600
Speaker 1: Two moons up in the sky. Then you're a hybrid, right,

483
00:22:33,800 --> 00:22:35,520
Speaker 1: This sounds like a fun science fiction story.

484
00:22:35,600 --> 00:22:37,200
Speaker 2: It sounds like a great Ya novel.

485
00:22:39,080 --> 00:22:40,159
Speaker 1: So many spin offs.

486
00:22:40,200 --> 00:22:42,560
Speaker 2: All right, we talked about the word moon is kind

487
00:22:42,560 --> 00:22:45,879
Speaker 2: of flexible and it's not quite super well defined, but

488
00:22:46,040 --> 00:22:48,200
Speaker 2: basically it just kind of means like a big rock

489
00:22:48,280 --> 00:22:50,800
Speaker 2: circling around a bigger rock. Right, that's right.

490
00:22:50,840 --> 00:22:53,320
Speaker 1: It's a big rock orbiting another big rock.

491
00:22:53,520 --> 00:22:55,760
Speaker 2: And as you said, six of the planets in our

492
00:22:55,800 --> 00:22:59,280
Speaker 2: Solar system have them. Venus and Mercury don't because I

493
00:22:59,280 --> 00:23:01,879
Speaker 2: guess they're too hot, you said. And if they had moons,

494
00:23:01,880 --> 00:23:04,840
Speaker 2: then the Sun would have disrupted its orbit and probably

495
00:23:04,920 --> 00:23:06,960
Speaker 2: made it crash into the planet, right or fly away.

496
00:23:07,080 --> 00:23:08,879
Speaker 1: Yeah, it's all about the tidal forces. It makes it

497
00:23:08,920 --> 00:23:12,240
Speaker 1: basically impossible for Mercury or Venus to have moons and

498
00:23:12,280 --> 00:23:14,560
Speaker 1: to keep them. It's because they're so close to the Sun.

499
00:23:14,600 --> 00:23:18,080
Speaker 1: It's not their actual temperature, it's the gravitational tidal forces

500
00:23:18,080 --> 00:23:18,640
Speaker 1: from the Sun.

501
00:23:18,880 --> 00:23:21,399
Speaker 2: All right, Well, what do we know about where moons

502
00:23:21,400 --> 00:23:22,440
Speaker 2: come from and how they're form?

503
00:23:22,640 --> 00:23:24,280
Speaker 1: So you can tell a lot about where a moon

504
00:23:24,320 --> 00:23:26,679
Speaker 1: came from based on what it's made out of and

505
00:23:26,760 --> 00:23:29,439
Speaker 1: how it's orbiting. If a moon is mostly in a

506
00:23:29,600 --> 00:23:32,800
Speaker 1: circular orbit, and the circular orbit follows the tilt of

507
00:23:32,840 --> 00:23:36,600
Speaker 1: the planet, so for example, it's orbiting around the equator

508
00:23:36,680 --> 00:23:39,399
Speaker 1: in mostly a circle. Then it's very likely that that

509
00:23:39,520 --> 00:23:43,000
Speaker 1: moon came from the same stuff that formed the planet.

510
00:23:43,280 --> 00:23:45,560
Speaker 1: Remember how planets form in the beginning, it's a big

511
00:23:45,640 --> 00:23:48,679
Speaker 1: cloud of gas and dust that forms the whole Solar System.

512
00:23:48,800 --> 00:23:50,680
Speaker 1: Most of the gas is gobbled up by the star

513
00:23:50,760 --> 00:23:53,240
Speaker 1: as it forms, and our Sun has ninety ninety percent

514
00:23:53,480 --> 00:23:55,359
Speaker 1: of the mass of the Solar System. But if you

515
00:23:55,400 --> 00:23:57,719
Speaker 1: get a little isolated pocket of heavy stuff that has

516
00:23:57,760 --> 00:24:00,439
Speaker 1: its own gravity and can gather itself together, then you

517
00:24:00,440 --> 00:24:02,600
Speaker 1: can get a planet. So a planet sort of forms

518
00:24:02,640 --> 00:24:05,200
Speaker 1: the same way the Solar System does. It's the gravitational

519
00:24:05,280 --> 00:24:06,800
Speaker 1: collapse of a big blob of.

520
00:24:06,760 --> 00:24:09,280
Speaker 2: Stuff, right, And initially it's just kind of like a

521
00:24:09,320 --> 00:24:13,000
Speaker 2: big cloud of rocks and dust that's spinning or has

522
00:24:13,080 --> 00:24:14,160
Speaker 2: kind of an overall spin.

523
00:24:14,800 --> 00:24:17,240
Speaker 1: Exactly. The reason you get moons around planets is the

524
00:24:17,280 --> 00:24:20,280
Speaker 1: same reason you get planets around stars. Right. You don't

525
00:24:20,320 --> 00:24:22,480
Speaker 1: just get all the mass of the Solar System collapsing

526
00:24:22,560 --> 00:24:24,560
Speaker 1: into the Sun. You get these little pockets that have

527
00:24:24,640 --> 00:24:27,040
Speaker 1: enough gravity to form themselves together and then are moving

528
00:24:27,080 --> 00:24:30,040
Speaker 1: at high enough speed that they can resist falling into

529
00:24:30,119 --> 00:24:33,080
Speaker 1: the Sun. Now, around those planets, of course, you also

530
00:24:33,160 --> 00:24:35,679
Speaker 1: have little clouds of gas and dust. Some of it

531
00:24:35,720 --> 00:24:38,199
Speaker 1: collapses into the planet, most of it, but some of

532
00:24:38,240 --> 00:24:41,680
Speaker 1: it pulls itself together and has enough velocity to avoid

533
00:24:42,119 --> 00:24:45,320
Speaker 1: falling into the planet. And so if you have enough

534
00:24:45,359 --> 00:24:47,600
Speaker 1: velocity and you can pull yourself together, then you can

535
00:24:47,600 --> 00:24:50,439
Speaker 1: form like a little planet's planet, a little miniature system

536
00:24:50,480 --> 00:24:52,680
Speaker 1: around the planet, the same way the planet is going

537
00:24:52,720 --> 00:24:53,320
Speaker 1: around the Sun.

538
00:24:53,560 --> 00:24:56,360
Speaker 2: Right, because I guess gravity. That's how gravity works, right,

539
00:24:56,400 --> 00:24:59,600
Speaker 2: Like everything is attracted to everything else. It's not just

540
00:24:59,640 --> 00:25:01,960
Speaker 2: like we're attract it to the Sun or juice attracted

541
00:25:02,200 --> 00:25:06,159
Speaker 2: to the planet Earth. It's like I'm attracted to my

542
00:25:06,320 --> 00:25:08,800
Speaker 2: car and to this base bomb, the base will attracted

543
00:25:08,840 --> 00:25:10,520
Speaker 2: to me. And so if we were out in space,

544
00:25:11,160 --> 00:25:13,040
Speaker 2: we would both be falling towards the Earth, but then

545
00:25:13,080 --> 00:25:15,040
Speaker 2: we would there would also be an attraction between us.

546
00:25:15,080 --> 00:25:18,000
Speaker 2: And sometimes I think what you're saying is that if

547
00:25:18,200 --> 00:25:21,520
Speaker 2: a clump of dirt and rocks when the planet is forming,

548
00:25:21,560 --> 00:25:24,040
Speaker 2: it's kind of far enough out there, it will clump

549
00:25:24,080 --> 00:25:25,879
Speaker 2: together before it clumps with the Earth.

550
00:25:26,040 --> 00:25:28,680
Speaker 1: Yeah, that's exactly right. And there's sort of two steps there.

551
00:25:29,119 --> 00:25:32,760
Speaker 1: One is have enough velocity, like are you spinning fast

552
00:25:32,840 --> 00:25:35,880
Speaker 1: enough that you can basically get in orbit around the planet,

553
00:25:35,960 --> 00:25:38,560
Speaker 1: And that's how you get like a protoplanetary disc. The

554
00:25:38,600 --> 00:25:41,240
Speaker 1: planet forms and have some stuff out there that hasn't

555
00:25:41,280 --> 00:25:43,920
Speaker 1: fallen into the planet. So initially it's like a disc

556
00:25:44,280 --> 00:25:47,120
Speaker 1: and that can pull itself together using gravity into a ring.

557
00:25:47,359 --> 00:25:49,280
Speaker 1: And then there's a question of whether that ring can

558
00:25:49,320 --> 00:25:52,439
Speaker 1: pull itself together into a moon or not. Sometimes it

559
00:25:52,480 --> 00:25:55,800
Speaker 1: stays a ring and sometimes it forms a moon, and

560
00:25:55,840 --> 00:25:58,879
Speaker 1: that depends on how close you are to that planet.

561
00:25:59,119 --> 00:26:01,680
Speaker 1: If you're really really close to that planet, close to

562
00:26:01,720 --> 00:26:04,159
Speaker 1: than what we call the Roche limit, then tile forces

563
00:26:04,160 --> 00:26:05,879
Speaker 1: from the planet are too strong. If you try to

564
00:26:05,880 --> 00:26:08,280
Speaker 1: form a moon, the tile forces will tear it apart.

565
00:26:08,560 --> 00:26:11,720
Speaker 1: If you're outpast the Roche limit, then the tidle forces

566
00:26:11,720 --> 00:26:14,240
Speaker 1: are weak and you can gather together into a moon.

567
00:26:14,440 --> 00:26:16,879
Speaker 1: So you have to have enough velocity to avoid falling

568
00:26:16,920 --> 00:26:19,200
Speaker 1: into the planet, and then you have to be out

569
00:26:19,280 --> 00:26:22,119
Speaker 1: past the Roche limit to have a ring get turned

570
00:26:22,160 --> 00:26:22,840
Speaker 1: into a moon.

571
00:26:23,880 --> 00:26:26,760
Speaker 2: Because I think, as we've talked about before, gravity kind

572
00:26:26,800 --> 00:26:29,439
Speaker 2: of depends on the distance between two things. Right. So

573
00:26:29,840 --> 00:26:32,560
Speaker 2: if you're really close to the Earth, then like the

574
00:26:32,560 --> 00:26:34,560
Speaker 2: difference between one side of the Moon and the other

575
00:26:34,600 --> 00:26:38,040
Speaker 2: side of the Moon is they experience very different gravitational forces.

576
00:26:38,080 --> 00:26:40,960
Speaker 2: But maybe if you're far out and beyond this limit,

577
00:26:41,040 --> 00:26:44,560
Speaker 2: then you don't see this difference in pull from the

578
00:26:44,600 --> 00:26:48,119
Speaker 2: Earth between one and and the other, which kind of

579
00:26:48,200 --> 00:26:49,040
Speaker 2: lets you clump together.

580
00:26:49,680 --> 00:26:52,119
Speaker 1: You'll still always feel that difference, right, and like the

581
00:26:52,160 --> 00:26:55,280
Speaker 1: Moon does feel that difference. That's why we talked about earlier.

582
00:26:55,359 --> 00:26:58,199
Speaker 1: The Moon is a football. It is being pulled by

583
00:26:58,200 --> 00:27:00,560
Speaker 1: the Earth's tidal forces, but it's far and away that

584
00:27:00,640 --> 00:27:03,320
Speaker 1: those tidle forces are not strong enough to tear it apart.

585
00:27:03,440 --> 00:27:06,520
Speaker 1: The roach limit for the Earth is around ten thousand kilometers.

586
00:27:06,680 --> 00:27:08,840
Speaker 1: The Moon is like three hundred and eighty five thousand

587
00:27:08,880 --> 00:27:11,880
Speaker 1: kilometers away, so it's well past the roach limit. If

588
00:27:11,920 --> 00:27:14,000
Speaker 1: the Moon was much much closer, if it was like

589
00:27:14,119 --> 00:27:16,720
Speaker 1: less than ten thousand kilometers from the surface of the Earth,

590
00:27:17,000 --> 00:27:19,640
Speaker 1: the Earth would tear it apart with those tidal forces

591
00:27:19,680 --> 00:27:22,000
Speaker 1: into a massive ring system instead.

592
00:27:21,920 --> 00:27:23,800
Speaker 2: Where some of the rocks in that ring are going

593
00:27:23,840 --> 00:27:24,600
Speaker 2: at different speeds.

594
00:27:24,640 --> 00:27:26,320
Speaker 1: Right, it would be pretty cool to see the Moon

595
00:27:26,440 --> 00:27:28,840
Speaker 1: get torn up into rocks. Not all of them would

596
00:27:28,960 --> 00:27:31,760
Speaker 1: have the same velocity originally as the Moon. I'm sure

597
00:27:31,800 --> 00:27:34,159
Speaker 1: it would be somewhat destructive and chaotic. Some of them

598
00:27:34,160 --> 00:27:35,600
Speaker 1: would end up falling to the Earth, some of them

599
00:27:35,640 --> 00:27:37,199
Speaker 1: would get lost, and some of them would end up

600
00:27:37,200 --> 00:27:37,680
Speaker 1: in orbit.

601
00:27:37,880 --> 00:27:40,400
Speaker 2: Cool And I think that, as you said, also applies

602
00:27:40,400 --> 00:27:42,000
Speaker 2: to planets, right like you kind of have to be

603
00:27:42,040 --> 00:27:44,280
Speaker 2: a certain distance away from the Sun just to form

604
00:27:44,320 --> 00:27:44,920
Speaker 2: a planet, too.

605
00:27:45,200 --> 00:27:47,439
Speaker 1: Exactly, if you're too close to the Sun, then the

606
00:27:47,480 --> 00:27:51,640
Speaker 1: Sun's tidal forces, which are very powerful, will pull you apart.

607
00:27:51,800 --> 00:27:53,760
Speaker 1: So the roche limit for the Sun is like seven

608
00:27:53,840 --> 00:27:56,520
Speaker 1: hundred and fifty thousand kilometers. So if the Earth was

609
00:27:56,600 --> 00:27:59,200
Speaker 1: that close to the Sun, not only will we be fried,

610
00:27:59,240 --> 00:28:01,240
Speaker 1: of course, but the Sun would pull us apart with

611
00:28:01,359 --> 00:28:05,120
Speaker 1: its tidal forces. As you said, the gravitational force depends

612
00:28:05,160 --> 00:28:07,719
Speaker 1: on the distance, and so the Sun's gravit on the

613
00:28:07,760 --> 00:28:09,720
Speaker 1: near side of the Earth would be so much more

614
00:28:09,760 --> 00:28:11,879
Speaker 1: powerful than the Sun's gravity in the far side of

615
00:28:11,880 --> 00:28:14,520
Speaker 1: the Earth. It's effectively pulling us apart, and the Earth

616
00:28:14,880 --> 00:28:17,439
Speaker 1: is not strong enough to survive if it's closer than

617
00:28:17,480 --> 00:28:20,879
Speaker 1: seven hundred and fifty thousand kilometers. Fortunately, we're like one

618
00:28:20,960 --> 00:28:24,120
Speaker 1: hundred and fifty million kilometers from the Sun, so we're

619
00:28:24,119 --> 00:28:27,360
Speaker 1: nowhere near the Roche limit. And this isn't like an exact,

620
00:28:27,440 --> 00:28:29,840
Speaker 1: hard and fast number, it's like approximate. It depends on

621
00:28:29,880 --> 00:28:32,119
Speaker 1: the mass of the object, and it depends on structural

622
00:28:32,119 --> 00:28:34,080
Speaker 1: features of it, Like if you had a planet made

623
00:28:34,080 --> 00:28:36,520
Speaker 1: out of diamond, it could get closer to the Sun

624
00:28:36,680 --> 00:28:38,080
Speaker 1: than a planet made out of gravel.

625
00:28:39,360 --> 00:28:41,920
Speaker 2: But I guess generally speaking, it depends on the size

626
00:28:41,960 --> 00:28:44,080
Speaker 2: of the thing in the middle, Like the Sun has

627
00:28:44,120 --> 00:28:47,200
Speaker 2: a very big roach limit and the Earth as a

628
00:28:47,200 --> 00:28:47,719
Speaker 2: smaller one.

629
00:28:47,800 --> 00:28:49,920
Speaker 1: Yeah, that's true. You can get closer to the Earth,

630
00:28:50,160 --> 00:28:51,960
Speaker 1: then you can get to the Sun. But if you

631
00:28:51,960 --> 00:28:54,560
Speaker 1: see a moon around a planet and it's orbiting in

632
00:28:54,640 --> 00:28:58,040
Speaker 1: a circular orbit and it mostly has the same angle

633
00:28:58,080 --> 00:29:01,120
Speaker 1: or momentum as the planet, then you suspect that probably

634
00:29:01,280 --> 00:29:03,800
Speaker 1: came from the same stuff that made the planet, and

635
00:29:03,840 --> 00:29:06,360
Speaker 1: when that planet coalesced into stuff, not all of it

636
00:29:06,400 --> 00:29:08,920
Speaker 1: got turned into the planet, some of it got left

637
00:29:08,960 --> 00:29:12,320
Speaker 1: over and turned into a moon. So circular orbits with

638
00:29:12,400 --> 00:29:16,960
Speaker 1: the same anglermentum probably came from the same protoplanetary disk

639
00:29:17,320 --> 00:29:18,280
Speaker 1: that formed the planet.

640
00:29:19,800 --> 00:29:22,880
Speaker 2: Okay, So then if a moon is orbiting a planet

641
00:29:23,080 --> 00:29:26,800
Speaker 2: kind of in the same plane as the planet is spinning,

642
00:29:27,560 --> 00:29:30,280
Speaker 2: then most likely they're like siblings, kind of like they

643
00:29:30,320 --> 00:29:33,000
Speaker 2: were born at the same time from the same stuff.

644
00:29:33,680 --> 00:29:36,360
Speaker 1: Yeah, I suppose you could say so though, sort of

645
00:29:36,360 --> 00:29:38,520
Speaker 1: the scenario where like one twin is really big and

646
00:29:38,560 --> 00:29:39,440
Speaker 1: the other one is tiny.

647
00:29:39,560 --> 00:29:41,280
Speaker 2: Yeah, they're fraternal twins.

648
00:29:42,280 --> 00:29:44,960
Speaker 1: Exactly, and probably one it's pretty grumpy about not getting.

649
00:29:44,760 --> 00:29:46,600
Speaker 2: As much of dinner, all right. So that's one way

650
00:29:46,600 --> 00:29:49,200
Speaker 2: that maybe a moon can form, which is like it's

651
00:29:49,240 --> 00:29:51,320
Speaker 2: borne along with the planet, and you can sort of

652
00:29:51,320 --> 00:29:53,880
Speaker 2: tell which ones those are, Which of those do we

653
00:29:53,920 --> 00:29:56,120
Speaker 2: have in our Solar system, Like, is our moon one

654
00:29:56,120 --> 00:29:56,400
Speaker 2: of them?

655
00:29:56,480 --> 00:29:58,760
Speaker 1: Our moon is not one of those. Our moon is

656
00:29:58,760 --> 00:30:01,200
Speaker 1: actually a very weird case. Most of the moons in

657
00:30:01,200 --> 00:30:03,680
Speaker 1: the Solar System do not have nice circular orbits that

658
00:30:03,720 --> 00:30:05,880
Speaker 1: are orbiting with the planets. In fact, most of them

659
00:30:06,200 --> 00:30:09,600
Speaker 1: have elliptical orbits that have weird tilts. And that suggests

660
00:30:09,600 --> 00:30:11,280
Speaker 1: a completely different history for how.

661
00:30:11,160 --> 00:30:14,520
Speaker 2: That moon formed, necessarily, because like I wonder if maybe

662
00:30:14,720 --> 00:30:16,560
Speaker 2: the moon was formed as a sibling, but then it

663
00:30:16,640 --> 00:30:21,320
Speaker 2: got not by something and then it got a skewed orbit.

664
00:30:21,400 --> 00:30:24,040
Speaker 1: Yeah, that's certainly possible, but we think that most of

665
00:30:24,080 --> 00:30:27,240
Speaker 1: the ones with skewed orbits, that with tilted orbits that precess,

666
00:30:27,280 --> 00:30:31,480
Speaker 1: for example, are probably captured objects, things that came nearby

667
00:30:31,600 --> 00:30:34,479
Speaker 1: and were grabbed onto by the gravity of that planet.

668
00:30:34,560 --> 00:30:36,560
Speaker 1: You're right, it's possible for moon to be formed with

669
00:30:36,560 --> 00:30:38,760
Speaker 1: a planet and then get tilted through a collision. You

670
00:30:38,760 --> 00:30:40,680
Speaker 1: can tell the difference by looking at what that moon

671
00:30:40,760 --> 00:30:42,600
Speaker 1: is made out of. Is it made out of basically

672
00:30:42,600 --> 00:30:45,280
Speaker 1: the same stuff that formed the planet, or is it

673
00:30:45,320 --> 00:30:47,800
Speaker 1: made out of something totally weird and different. So that's

674
00:30:47,800 --> 00:30:50,640
Speaker 1: sort of like the key piece of information for distinguishing.

675
00:30:50,240 --> 00:30:53,160
Speaker 2: Like a DNA test prove of your siblings or not.

676
00:30:54,120 --> 00:30:56,800
Speaker 2: All right, well, then what does not having a circular

677
00:30:56,920 --> 00:30:58,480
Speaker 2: orbit tell you about the moon.

678
00:30:58,560 --> 00:31:01,120
Speaker 1: It tells you that probably it was captured, that the

679
00:31:01,160 --> 00:31:04,000
Speaker 1: planet is formed, and the moon comes from somewhere else.

680
00:31:04,040 --> 00:31:07,000
Speaker 1: It's like an asteroid or a dwarf planet or something

681
00:31:07,280 --> 00:31:09,640
Speaker 1: that was floating around and just came too close to

682
00:31:09,680 --> 00:31:12,560
Speaker 1: this massive object and its gravity took over. There's a

683
00:31:12,640 --> 00:31:15,360
Speaker 1: vicinity of a massive object we called the hill sphere,

684
00:31:15,360 --> 00:31:18,320
Speaker 1: which is the region sort of where its gravity dominates,

685
00:31:18,320 --> 00:31:21,520
Speaker 1: where everything else that's far away can basically be neglected,

686
00:31:21,560 --> 00:31:23,960
Speaker 1: and if an object passes within the hillsphere, it's a

687
00:31:24,000 --> 00:31:25,840
Speaker 1: candidate for getting captured.

688
00:31:26,000 --> 00:31:28,520
Speaker 2: But isn't that kind of weird? Or isn't it kind

689
00:31:28,520 --> 00:31:30,840
Speaker 2: of unlikely that you'll just kind of catch a big

690
00:31:30,960 --> 00:31:33,120
Speaker 2: rock out there and it'll have just the right speed

691
00:31:33,160 --> 00:31:35,960
Speaker 2: and distance to fall into a stable orbit, Like, aren't

692
00:31:35,960 --> 00:31:38,320
Speaker 2: stable orbits kind of hard to get into?

693
00:31:38,560 --> 00:31:40,840
Speaker 1: It is unlikely and it is weird. You're right. You

694
00:31:40,840 --> 00:31:43,520
Speaker 1: have to match the radius and the velocity. Like the

695
00:31:43,600 --> 00:31:46,080
Speaker 1: reason the Earth is in a stable orbit is because

696
00:31:46,120 --> 00:31:48,720
Speaker 1: it has the right velocity for our radius. You have

697
00:31:48,720 --> 00:31:51,560
Speaker 1: to be moving in a certain velocity at a given radius.

698
00:31:51,280 --> 00:31:53,240
Speaker 2: Like if we slowed down at all in our orbit,

699
00:31:53,280 --> 00:31:55,480
Speaker 2: we would start to spiral into the Sun. Right.

700
00:31:55,600 --> 00:31:58,600
Speaker 1: First orbit is actually quasi stable. So if we slowed

701
00:31:58,640 --> 00:32:01,640
Speaker 1: down a little bit, gravitational forces what actually pushes back

702
00:32:01,680 --> 00:32:03,920
Speaker 1: towards our orbit? But that's a whole other topic.

703
00:32:04,280 --> 00:32:05,920
Speaker 2: Like if you slow down a lot, though.

704
00:32:06,000 --> 00:32:07,720
Speaker 1: Yes, if we slowed down a lot, we would fall

705
00:32:07,760 --> 00:32:09,480
Speaker 1: in towards the Sun. If we sped up a bunch,

706
00:32:09,640 --> 00:32:12,360
Speaker 1: we would be ejected from the Solar system. And so

707
00:32:12,440 --> 00:32:14,920
Speaker 1: you have to have this match between these two quantities,

708
00:32:15,320 --> 00:32:17,680
Speaker 1: and it's not trivial for that to happen. Not only

709
00:32:17,680 --> 00:32:19,080
Speaker 1: do you have to have the right velocity and the

710
00:32:19,160 --> 00:32:21,719
Speaker 1: right radius, but you also have to lose energy in

711
00:32:21,800 --> 00:32:24,080
Speaker 1: order to fall into an orbit. Any object that falls

712
00:32:24,120 --> 00:32:27,400
Speaker 1: into the Solar System by definition has enough energy to

713
00:32:27,560 --> 00:32:30,560
Speaker 1: escape because it came from outside the Solar System. And

714
00:32:30,600 --> 00:32:33,440
Speaker 1: so if it just passes through on like a hyperbolic trajectory,

715
00:32:33,800 --> 00:32:36,440
Speaker 1: you know it has enough kinetic energy to climb out

716
00:32:36,440 --> 00:32:38,920
Speaker 1: of the gravitational well of the Solar System because it

717
00:32:38,960 --> 00:32:41,560
Speaker 1: came from outside the gravitational well. So in order to

718
00:32:41,600 --> 00:32:43,360
Speaker 1: get captured it not only does it have to come

719
00:32:43,400 --> 00:32:45,760
Speaker 1: in at the right radius and the right velocity, got

720
00:32:45,800 --> 00:32:48,280
Speaker 1: to lose a little bit of energy so that no

721
00:32:48,360 --> 00:32:50,840
Speaker 1: longer has the energy to escape. That can happen if

722
00:32:50,840 --> 00:32:53,560
Speaker 1: you like drag on the atmosphere the planet a little bit,

723
00:32:53,600 --> 00:32:55,720
Speaker 1: which gives you a little bit of friction, or maybe

724
00:32:55,720 --> 00:32:58,800
Speaker 1: another moon steals a little bit of your energy. So like,

725
00:32:58,840 --> 00:33:01,440
Speaker 1: the more moons you have and the puffier your atmosphere,

726
00:33:01,560 --> 00:33:03,920
Speaker 1: the more likely you are to be able to capture

727
00:33:03,960 --> 00:33:05,440
Speaker 1: an object that comes near you.

728
00:33:06,120 --> 00:33:09,080
Speaker 2: M it's kind of interesting to think of this idea

729
00:33:09,160 --> 00:33:11,719
Speaker 2: that planets like the Earth has a kind of a

730
00:33:11,720 --> 00:33:14,240
Speaker 2: halo kind of right, like a big sphere around it.

731
00:33:14,240 --> 00:33:17,640
Speaker 2: It's basically like a giant net. Like whatever falls into it,

732
00:33:17,640 --> 00:33:19,040
Speaker 2: it's gonna get sucked in.

733
00:33:19,400 --> 00:33:21,200
Speaker 1: Yeah, exactly. And if you fall in too far and

734
00:33:21,240 --> 00:33:23,000
Speaker 1: you slow don too far, then of course you're going

735
00:33:23,040 --> 00:33:25,600
Speaker 1: to burn up as you enter the atmosphere. So it's

736
00:33:25,600 --> 00:33:28,520
Speaker 1: a delicate operation. This is also think that sometimes a

737
00:33:28,560 --> 00:33:31,400
Speaker 1: pair of objects that are orbiting each other can fall

738
00:33:31,440 --> 00:33:33,920
Speaker 1: in the hillsphere and then one of them can get

739
00:33:33,960 --> 00:33:36,400
Speaker 1: captured and the other one can get ejected. So all

740
00:33:36,440 --> 00:33:38,800
Speaker 1: these sort of complicated things have to go just right

741
00:33:39,240 --> 00:33:41,360
Speaker 1: in order for a planet to capture a moon.

742
00:33:42,200 --> 00:33:45,520
Speaker 2: And by capturing, that's a nice word for stealing, right right,

743
00:33:45,560 --> 00:33:46,920
Speaker 2: I guess you're like trapping.

744
00:33:48,560 --> 00:33:50,720
Speaker 1: You're dancing, you're dancing with them, have of that?

745
00:33:50,880 --> 00:33:51,800
Speaker 2: Oh I see see?

746
00:33:52,160 --> 00:33:52,360
Speaker 3: Is that?

747
00:33:52,400 --> 00:33:55,480
Speaker 2: Where our that listener who mentioned earlier that maybe we

748
00:33:55,560 --> 00:33:57,840
Speaker 2: got our moon by stealing it from Venus? Is that?

749
00:33:58,120 --> 00:33:59,080
Speaker 2: Is there some truth to that?

750
00:34:00,080 --> 00:34:02,880
Speaker 1: We don't think that our moon was stolen from Venus,

751
00:34:02,880 --> 00:34:04,400
Speaker 1: but we do think that lots of the moons of

752
00:34:04,480 --> 00:34:06,920
Speaker 1: Jupiter and Saturn, for example, and these guys have like

753
00:34:07,000 --> 00:34:10,839
Speaker 1: dozens of moons come from scattered objects in the early

754
00:34:10,920 --> 00:34:14,240
Speaker 1: Solar system. Remember that very early on things were forming.

755
00:34:14,400 --> 00:34:16,560
Speaker 1: There may even have been more planets than the ones

756
00:34:16,600 --> 00:34:20,080
Speaker 1: we have now, and everything was quite chaotic. So now

757
00:34:20,080 --> 00:34:22,560
Speaker 1: we have sort of an orderly solar system where everything

758
00:34:22,640 --> 00:34:25,280
Speaker 1: is in place because it's been in place for so long,

759
00:34:25,719 --> 00:34:27,960
Speaker 1: and things that were not in place have been lost

760
00:34:28,040 --> 00:34:30,279
Speaker 1: or captured or fallen into the Sun. But in the

761
00:34:30,320 --> 00:34:32,279
Speaker 1: early days there were a lot of things going in

762
00:34:32,320 --> 00:34:35,480
Speaker 1: crazy orbits and crazy trajectories, and so Jupiter and Saturn

763
00:34:35,600 --> 00:34:37,279
Speaker 1: sort of like hoovered up a bunch of them.

764
00:34:37,560 --> 00:34:39,520
Speaker 2: So like, if you look at the moons of Jupiter,

765
00:34:39,560 --> 00:34:41,600
Speaker 2: for example, they're not all going to be like lined

766
00:34:41,640 --> 00:34:44,240
Speaker 2: up in a plane like our solar system. They probably

767
00:34:44,280 --> 00:34:46,680
Speaker 2: all have like crazy orbits around Jupiter.

768
00:34:46,760 --> 00:34:49,000
Speaker 1: Right, Yeah, that's exactly right, and that's why we think

769
00:34:49,000 --> 00:34:51,360
Speaker 1: that most of these were captured. Also, in the cases

770
00:34:51,360 --> 00:34:53,200
Speaker 1: that we've been able to try to study what these

771
00:34:53,239 --> 00:34:55,239
Speaker 1: moons are made out of, they're all made out of

772
00:34:55,280 --> 00:34:57,360
Speaker 1: totally different things, and so it doesn't look like they

773
00:34:57,480 --> 00:34:59,920
Speaker 1: formed from the same sort of scoop of solar systems

774
00:35:00,120 --> 00:35:01,879
Speaker 1: off that Jupiter did.

775
00:35:02,320 --> 00:35:03,960
Speaker 2: That's what you were saying, like you can check the

776
00:35:04,040 --> 00:35:06,720
Speaker 2: DNA basically the DNA of the moon and the planet

777
00:35:06,800 --> 00:35:08,600
Speaker 2: to see if they came from the same stuff, and

778
00:35:08,640 --> 00:35:10,080
Speaker 2: sometimes they don't, right.

779
00:35:10,640 --> 00:35:13,080
Speaker 1: Yeah, exactly. That's still tricky to do because we haven't

780
00:35:13,200 --> 00:35:15,840
Speaker 1: landed on those moons and like really taken samples that

781
00:35:15,880 --> 00:35:18,600
Speaker 1: we can study. But we can like do spectroscopy, we

782
00:35:18,600 --> 00:35:20,640
Speaker 1: can see the light that bounces off of them, we

783
00:35:20,640 --> 00:35:23,239
Speaker 1: can see what they emit, these kind of things. We

784
00:35:23,320 --> 00:35:25,640
Speaker 1: have done some flybys, and so we have ideas for

785
00:35:25,719 --> 00:35:27,719
Speaker 1: what these moons are probably made out of.

786
00:35:29,120 --> 00:35:31,520
Speaker 2: And in the early Solar system, like you said, things

787
00:35:31,560 --> 00:35:34,400
Speaker 2: were like there were probably like rock giant rocks flying

788
00:35:34,400 --> 00:35:37,279
Speaker 2: all over the place, and so it wouldn't be that

789
00:35:37,360 --> 00:35:40,360
Speaker 2: weird for some of them to fall into orbit around

790
00:35:40,600 --> 00:35:42,960
Speaker 2: like a passing Jupiter or Centurn. So is that how

791
00:35:43,000 --> 00:35:45,000
Speaker 2: we got our moon? Did we capture it or steal

792
00:35:45,000 --> 00:35:45,640
Speaker 2: it from somebody?

793
00:35:45,719 --> 00:35:47,600
Speaker 1: So we think our moon is unusual because it doesn't

794
00:35:47,640 --> 00:35:50,719
Speaker 1: fall into either of these categories. We don't think that

795
00:35:50,719 --> 00:35:53,080
Speaker 1: the Moon was formed with the Earth. We also don't

796
00:35:53,080 --> 00:35:56,800
Speaker 1: think that a wholly formed moon was captured by the Earth. Instead,

797
00:35:56,840 --> 00:35:59,239
Speaker 1: we think it comes from a collision. We think that

798
00:35:59,280 --> 00:36:02,480
Speaker 1: there was the proto Earth, this early planet, and then

799
00:36:02,480 --> 00:36:05,680
Speaker 1: there was another Mars like planet that came by and

800
00:36:05,760 --> 00:36:09,480
Speaker 1: smashed into the Earth, and there was this incredible collision

801
00:36:09,680 --> 00:36:12,440
Speaker 1: where essentially these two planets merged, but they left a

802
00:36:12,600 --> 00:36:16,360
Speaker 1: huge debris ring, and then that debris ring pulled together

803
00:36:16,680 --> 00:36:17,479
Speaker 1: and made the Moon.

804
00:36:17,719 --> 00:36:20,759
Speaker 2: Does our moon have an orbit that's around our equator

805
00:36:20,920 --> 00:36:21,640
Speaker 2: or is it tilted?

806
00:36:21,760 --> 00:36:24,360
Speaker 1: The Moon doesn't have a totally random orbit relatively angular

807
00:36:24,400 --> 00:36:27,120
Speaker 1: momentum of the Earth, because the two objects are essentially

808
00:36:27,160 --> 00:36:30,799
Speaker 1: formed by the combined angularmentum of this collision. So you

809
00:36:30,840 --> 00:36:33,200
Speaker 1: get this collision and basically you start from scratch. You

810
00:36:33,239 --> 00:36:35,600
Speaker 1: have a new blob of stuff which is then going

811
00:36:35,640 --> 00:36:38,480
Speaker 1: to coalesce again into a planet and a moon. And

812
00:36:38,520 --> 00:36:40,960
Speaker 1: so there is a relationship of course between the Earth's

813
00:36:40,960 --> 00:36:43,719
Speaker 1: spin and the Moon's orbit, and that's because they come

814
00:36:43,760 --> 00:36:46,800
Speaker 1: from this combined blob from this collision.

815
00:36:46,840 --> 00:36:49,040
Speaker 2: It's pretty dramatic. I think you can look up videos

816
00:36:49,040 --> 00:36:51,920
Speaker 2: of simulations of it online. It's like the Earth, the

817
00:36:51,960 --> 00:36:54,600
Speaker 2: proto Earth before Earth was just hanging out and then

818
00:36:54,640 --> 00:36:57,640
Speaker 2: this giant rock just slams into it. It all sort

819
00:36:57,640 --> 00:37:00,880
Speaker 2: of explodes together, but then gravity pulls it together into

820
00:37:01,200 --> 00:37:02,320
Speaker 2: Earth and the Moon.

821
00:37:02,239 --> 00:37:04,640
Speaker 1: Exactly, and the early Moon, we think, was much much

822
00:37:04,760 --> 00:37:07,480
Speaker 1: closer to the Earth, something like a tenth of its

823
00:37:07,520 --> 00:37:11,080
Speaker 1: current orbit, and then over time it spirals out and

824
00:37:11,200 --> 00:37:13,800
Speaker 1: ends up becoming tightly locked to the Earth. One reason

825
00:37:13,840 --> 00:37:15,399
Speaker 1: we think this is that we've been to the Moon

826
00:37:15,440 --> 00:37:17,480
Speaker 1: and we've been able to land on it and study

827
00:37:17,480 --> 00:37:19,680
Speaker 1: what it's made out of, and we see that it's

828
00:37:19,719 --> 00:37:21,480
Speaker 1: made out of a lot of stuff that's very very

829
00:37:21,520 --> 00:37:23,719
Speaker 1: similar to what the Earth is made out of, which

830
00:37:23,760 --> 00:37:26,200
Speaker 1: suggests that they do have some sort of common origin.

831
00:37:27,320 --> 00:37:30,400
Speaker 2: And does the Earth also sort of have moon like

832
00:37:30,840 --> 00:37:32,920
Speaker 2: materials in it that are not like the rest of

833
00:37:32,960 --> 00:37:33,360
Speaker 2: the Earth.

834
00:37:33,440 --> 00:37:34,920
Speaker 1: Well, we see that the Earth and the Moon have

835
00:37:34,960 --> 00:37:37,279
Speaker 1: a lot of very similar elements, which sugg they all

836
00:37:37,320 --> 00:37:39,920
Speaker 1: came from the same stuff, But the Moon has fewer

837
00:37:39,920 --> 00:37:42,960
Speaker 1: of like volatile elements things that vaporize at low temperatures

838
00:37:43,040 --> 00:37:45,920
Speaker 1: we're probably lost in this high energy event, and the

839
00:37:45,960 --> 00:37:48,480
Speaker 1: Moon has smaller gravity and so it's not able to

840
00:37:48,680 --> 00:37:50,719
Speaker 1: recapture these things the way the Earth did, so the

841
00:37:50,760 --> 00:37:53,360
Speaker 1: Earth and the Moon don't have exactly the same kinds

842
00:37:53,400 --> 00:37:55,680
Speaker 1: of stuff. The Moon also has a sort of surprisingly

843
00:37:55,840 --> 00:37:59,800
Speaker 1: small iron core which overall makes the Moon have lower density.

844
00:38:00,080 --> 00:38:02,560
Speaker 1: Simulations confirmed that this is what you would expect from

845
00:38:02,560 --> 00:38:05,200
Speaker 1: this kind of collision, that the Moon was formed more

846
00:38:05,280 --> 00:38:07,479
Speaker 1: out of the sort of external debris and the Earth

847
00:38:07,560 --> 00:38:10,320
Speaker 1: sort of got a bigger sampling of the core stuff.

848
00:38:11,280 --> 00:38:13,440
Speaker 2: I guess the Moon is also smaller, so it doesn't

849
00:38:13,440 --> 00:38:17,560
Speaker 2: have as much gravity compressing it, right, making it denser exactly.

850
00:38:17,960 --> 00:38:19,839
Speaker 1: And when they study like what's inside the Moon, they

851
00:38:19,880 --> 00:38:23,000
Speaker 1: find samples that suggest the Moon was molten down to

852
00:38:23,080 --> 00:38:26,240
Speaker 1: like a surprising depth. And you don't expect the small

853
00:38:26,280 --> 00:38:29,120
Speaker 1: body like the Moon to have the gravitational pressure to

854
00:38:29,320 --> 00:38:31,880
Speaker 1: like melt its inerts the way the Earth does. So

855
00:38:31,920 --> 00:38:34,040
Speaker 1: they think that the Moon was probably molten because of

856
00:38:34,080 --> 00:38:36,760
Speaker 1: this collision, not because of its like gravitational pressure.

857
00:38:37,120 --> 00:38:37,440
Speaker 4: Hmm.

858
00:38:37,640 --> 00:38:40,640
Speaker 2: Interesting. And I think they also found like the same

859
00:38:40,880 --> 00:38:43,600
Speaker 2: cheese inside of the Moon as some of the cheese

860
00:38:43,680 --> 00:38:47,000
Speaker 2: we have on Earth too, Right, that's part of the theory.

861
00:38:49,000 --> 00:38:51,560
Speaker 1: Yeah, they found pan pizzas rejected on the surface of

862
00:38:51,560 --> 00:38:52,840
Speaker 1: the Moon that nobody could eat.

863
00:38:53,000 --> 00:38:56,520
Speaker 2: That's right, the same mozzarella, cheese, the same cows, even

864
00:38:57,280 --> 00:39:00,399
Speaker 2: space cows. All right, well, that's the origin of our moon.

865
00:39:00,520 --> 00:39:03,360
Speaker 2: Let's get a little bit into what that means about

866
00:39:03,400 --> 00:39:07,279
Speaker 2: the formation of all moons and the formation of our

867
00:39:07,320 --> 00:39:10,279
Speaker 2: whole Solar system, why we're here, and why are things

868
00:39:10,320 --> 00:39:12,880
Speaker 2: the way they are. But first, let's take another quick break.

869
00:39:25,600 --> 00:39:27,799
Speaker 2: All right, we are coming face to face with the

870
00:39:28,000 --> 00:39:31,440
Speaker 2: lunacy here in the podcast talking about the origin of

871
00:39:31,520 --> 00:39:35,440
Speaker 2: moons and in particular our moon. You're saying, it's interesting because,

872
00:39:35,719 --> 00:39:37,839
Speaker 2: like our moon is sort of a combination of how

873
00:39:37,920 --> 00:39:40,520
Speaker 2: some of these other moons can form. Right, Like, we

874
00:39:40,600 --> 00:39:43,040
Speaker 2: had a proto planet Earth, and when there was a

875
00:39:43,160 --> 00:39:47,080
Speaker 2: visitor that was flying around came near us, it sort

876
00:39:47,080 --> 00:39:49,400
Speaker 2: of got captured or collided with our Earth, and then

877
00:39:49,440 --> 00:39:51,680
Speaker 2: it all became a big mess. And out of that mess,

878
00:39:52,280 --> 00:39:54,360
Speaker 2: you know, the Earth and the Moon forms sort of

879
00:39:54,400 --> 00:39:58,400
Speaker 2: a siblings, but also not siblings, because there was it

880
00:39:58,480 --> 00:40:01,000
Speaker 2: came from a different planet. The stuff.

881
00:40:01,120 --> 00:40:03,799
Speaker 1: There was a big fight early on, and we were left

882
00:40:03,800 --> 00:40:06,279
Speaker 1: over cleaning up the mess. Yeah, it is really fascinating,

883
00:40:06,320 --> 00:40:09,000
Speaker 1: and I love this sort of archaeology, this like detective

884
00:40:09,040 --> 00:40:13,280
Speaker 1: story figuring out what happened billions of years ago, reconstructing

885
00:40:13,280 --> 00:40:15,279
Speaker 1: the story from the clues that are left behind, these

886
00:40:15,320 --> 00:40:17,919
Speaker 1: really subtle hints. You know, why does the Moon seem

887
00:40:17,960 --> 00:40:19,560
Speaker 1: to be made of the same stuff as the Earth,

888
00:40:19,560 --> 00:40:22,040
Speaker 1: but it doesn't have sort of a close circular orbit

889
00:40:22,040 --> 00:40:24,480
Speaker 1: the way you would expect. Why exactly is it so big?

890
00:40:24,719 --> 00:40:27,719
Speaker 1: These stories are really fascinating because we missed so much

891
00:40:27,760 --> 00:40:29,960
Speaker 1: of the Solar System history. You know, like billions of

892
00:40:30,120 --> 00:40:33,440
Speaker 1: years happened with crazy fireworks in the sky and we

893
00:40:33,440 --> 00:40:35,520
Speaker 1: weren't here to look at it. But we can still

894
00:40:35,520 --> 00:40:36,840
Speaker 1: get hints about what happened.

895
00:40:37,040 --> 00:40:39,759
Speaker 2: Hmmm, do you think that's an official job title out there,

896
00:40:39,760 --> 00:40:42,000
Speaker 2: like space archaeologists.

897
00:40:42,760 --> 00:40:46,000
Speaker 1: Space murder mystery, you know, exactly.

898
00:40:45,800 --> 00:40:49,400
Speaker 2: Give me like Indiana solo a combination of Indiana Jones

899
00:40:49,480 --> 00:40:50,240
Speaker 2: and Hands solo.

900
00:40:51,600 --> 00:40:54,359
Speaker 1: And you know, we're still learning stuff about moons, like

901
00:40:54,560 --> 00:40:57,719
Speaker 1: Mars has some funny moons, Phobos and Demos, And the

902
00:40:57,800 --> 00:41:01,319
Speaker 1: smaller of those two moons, Demos, is really tiny. It's

903
00:41:01,360 --> 00:41:04,800
Speaker 1: only like nine miles across, has a really weird shorwt

904
00:41:04,800 --> 00:41:07,160
Speaker 1: of blobby shape to it, and for a long time

905
00:41:07,160 --> 00:41:10,239
Speaker 1: people thought it was probably a captured asteroid because of

906
00:41:10,280 --> 00:41:13,359
Speaker 1: its orbit, but they recently send an orbiter very very

907
00:41:13,360 --> 00:41:16,160
Speaker 1: close to it, super close approach by this spacecraft from

908
00:41:16,160 --> 00:41:18,839
Speaker 1: the UA Emirates. Actually it's called Hope, and they were

909
00:41:18,840 --> 00:41:21,240
Speaker 1: able to study what it's made out of and discover

910
00:41:21,400 --> 00:41:24,440
Speaker 1: that it has sort of the same carbon and organics

911
00:41:24,480 --> 00:41:27,680
Speaker 1: that Mars does, unlike the asteroids, sort of like the

912
00:41:27,800 --> 00:41:30,640
Speaker 1: DNA test you were saying before, which means that Demos

913
00:41:30,680 --> 00:41:34,600
Speaker 1: probably is a chunk of Mars that got blown off

914
00:41:34,719 --> 00:41:36,480
Speaker 1: in some sort of prehistoric collision.

915
00:41:36,600 --> 00:41:38,400
Speaker 2: Isn't that also kind of the theey of how we

916
00:41:38,440 --> 00:41:41,360
Speaker 2: got life on Earth, like a possible way that maybe

917
00:41:41,400 --> 00:41:43,480
Speaker 2: Mars got hit by something. It threw a bunch of

918
00:41:43,600 --> 00:41:46,279
Speaker 2: rocks out into space. Some of them became Demos, the

919
00:41:46,320 --> 00:41:48,360
Speaker 2: moon of Mars, and maybe some of them came to

920
00:41:48,400 --> 00:41:50,240
Speaker 2: Earth bringing like little bacteria.

921
00:41:50,280 --> 00:41:53,880
Speaker 1: Perhaps we're very sure that rocks from Mars have landed

922
00:41:53,920 --> 00:41:56,320
Speaker 1: on Earth. We have found them and their geology matches

923
00:41:56,360 --> 00:41:59,160
Speaker 1: Mars and doesn't match Earth. So there's no controversy about

924
00:41:59,160 --> 00:42:03,000
Speaker 1: whether visions from asteroids on planets can knock stuff off

925
00:42:03,000 --> 00:42:05,320
Speaker 1: into outer space and have it land on other planets.

926
00:42:05,440 --> 00:42:08,120
Speaker 1: Whether there's life in those rocks that then seeded life

927
00:42:08,160 --> 00:42:12,120
Speaker 1: on Earth totally open question. There was this famous misdiscovery

928
00:42:12,400 --> 00:42:14,959
Speaker 1: about twenty years ago when they found these weird little

929
00:42:15,000 --> 00:42:18,000
Speaker 1: shapes inside a Martian rock on Earth, and they made

930
00:42:18,000 --> 00:42:20,319
Speaker 1: this announcement that they were certain that there was life

931
00:42:20,320 --> 00:42:23,000
Speaker 1: in them, that these shapes could only be made by life.

932
00:42:23,160 --> 00:42:25,960
Speaker 1: But then later analysis demonstrated that you could make those

933
00:42:25,960 --> 00:42:29,399
Speaker 1: things without life. So there's no concrete proof that life

934
00:42:29,440 --> 00:42:32,840
Speaker 1: has traveled between planets on an asteroid, but it's totally

935
00:42:32,920 --> 00:42:35,799
Speaker 1: possible for it to happen. And Demos definitely is a

936
00:42:35,920 --> 00:42:38,680
Speaker 1: chunk of Mars floating in space. Sort of like if

937
00:42:38,680 --> 00:42:40,960
Speaker 1: you went out into space and you found like Manhattan

938
00:42:41,239 --> 00:42:43,759
Speaker 1: floating out in space, you'd be like, whoa, Where'd this

939
00:42:43,800 --> 00:42:44,280
Speaker 1: come from?

940
00:42:44,520 --> 00:42:45,920
Speaker 2: Yeah, well people wonder about that.

941
00:42:46,640 --> 00:42:50,879
Speaker 1: Now, what's the story? How did Manhattan get so weird?

942
00:42:50,880 --> 00:42:53,799
Speaker 2: Where did New Yorkers come from their lunatics?

943
00:42:53,880 --> 00:42:56,319
Speaker 1: But they have the best pizza, right, so I don't

944
00:42:56,360 --> 00:42:57,560
Speaker 1: want to have to go out of space to get

945
00:42:57,600 --> 00:42:59,480
Speaker 1: my pizza.

946
00:43:00,200 --> 00:43:02,839
Speaker 2: You just insulted everyone in Chicago. He lost a big

947
00:43:02,920 --> 00:43:03,960
Speaker 2: chunk of our listenership.

948
00:43:04,080 --> 00:43:06,520
Speaker 1: I love Chicago, I love Chicago wins, and I love

949
00:43:06,560 --> 00:43:09,239
Speaker 1: the Chicagoans love Chicago pizza. That's all fine with me.

950
00:43:09,480 --> 00:43:11,640
Speaker 2: All right, Well, what does all of this tells about

951
00:43:11,680 --> 00:43:14,319
Speaker 2: the formation of the Solar System and how we ended

952
00:43:14,400 --> 00:43:16,200
Speaker 2: up where we are and how we are.

953
00:43:16,440 --> 00:43:18,320
Speaker 1: It's a story that we are still unraveling.

954
00:43:18,400 --> 00:43:18,520
Speaker 5: Right.

955
00:43:18,560 --> 00:43:21,080
Speaker 1: We're still learning about our moon, We're still learning about

956
00:43:21,080 --> 00:43:25,520
Speaker 1: our neighbor's moons. We're still discovering moons. Right. Saturn recently

957
00:43:25,560 --> 00:43:28,160
Speaker 1: past Jupiter. I think in the number of moons that

958
00:43:28,239 --> 00:43:30,799
Speaker 1: it has, each one tells us a little bit of

959
00:43:30,840 --> 00:43:33,160
Speaker 1: the story of the Solar system, and what we're looking

960
00:43:33,200 --> 00:43:35,799
Speaker 1: for now are like more details for that story. As

961
00:43:35,840 --> 00:43:39,560
Speaker 1: you said earlier, we're asking questions like can moons have moons?

962
00:43:39,800 --> 00:43:42,120
Speaker 1: A lot of people think that it's impossible for the

963
00:43:42,120 --> 00:43:44,600
Speaker 1: same reason that like Mercury and Venus don't have moons

964
00:43:44,719 --> 00:43:47,600
Speaker 1: from the tidal forces of the Sun, that Jupiter's moons

965
00:43:47,640 --> 00:43:50,120
Speaker 1: probably can't have their own moons because of the tidal

966
00:43:50,200 --> 00:43:53,840
Speaker 1: forces of Jupiter. But you know, Saturn's moon Rhea probably

967
00:43:53,840 --> 00:43:57,640
Speaker 1: has rings which even though they're disrupted by the title forces,

968
00:43:57,719 --> 00:44:00,479
Speaker 1: they can still be in orbit around Rhea. And there's

969
00:44:00,560 --> 00:44:03,560
Speaker 1: like hundreds of minor planets deep out there in the

970
00:44:03,560 --> 00:44:06,440
Speaker 1: Solar system that do have their own moons, like Pluto.

971
00:44:06,600 --> 00:44:09,280
Speaker 1: But beyond that, we're also looking into other solar systems

972
00:44:09,320 --> 00:44:11,480
Speaker 1: to try to understand whether the moons that we have

973
00:44:11,800 --> 00:44:15,359
Speaker 1: are weird or typical? Right, Like, we only so far

974
00:44:15,520 --> 00:44:18,000
Speaker 1: have this one solar system to study at this level

975
00:44:18,040 --> 00:44:20,160
Speaker 1: of detail. Twenty years ago, we were able to see

976
00:44:20,200 --> 00:44:22,759
Speaker 1: planets around other stars, which tells us a lot about

977
00:44:22,760 --> 00:44:25,560
Speaker 1: whether the planets in our solar systems are weird. Now

978
00:44:25,560 --> 00:44:28,160
Speaker 1: we're pushing those boundaries to try to look for moons

979
00:44:28,280 --> 00:44:32,480
Speaker 1: in other solar systems. This thing we call exo moons

980
00:44:32,520 --> 00:44:34,800
Speaker 1: to try to discover if the distribution of moons that

981
00:44:34,840 --> 00:44:38,440
Speaker 1: we have is strange or pretty typical in the universe.

982
00:44:38,520 --> 00:44:40,640
Speaker 2: Well, that's wild. How are we seeing moons and other

983
00:44:40,680 --> 00:44:43,839
Speaker 2: planets outside of our solar system? Can we see them

984
00:44:43,920 --> 00:44:46,280
Speaker 2: or do we have to infer them from the gravity.

985
00:44:46,560 --> 00:44:48,840
Speaker 1: So there's a few ways that we discover planets, and

986
00:44:48,880 --> 00:44:51,680
Speaker 1: we can try to apply those ways to discover moons.

987
00:44:51,960 --> 00:44:54,839
Speaker 1: One of the early ways we discovered planets around other

988
00:44:54,880 --> 00:44:58,640
Speaker 1: stars was seeing their gravitational impact on the star, and

989
00:44:58,680 --> 00:45:01,280
Speaker 1: that would wiggle the star and cause like a change

990
00:45:01,320 --> 00:45:04,080
Speaker 1: in the frequency of the light, this Doppler shift, and

991
00:45:04,120 --> 00:45:06,160
Speaker 1: so we could discover that there was something pulling on

992
00:45:06,239 --> 00:45:08,480
Speaker 1: that star. We don't think that method will work for

993
00:45:08,600 --> 00:45:11,480
Speaker 1: discovering moons because it's really hard to distinguish the gravitational

994
00:45:11,520 --> 00:45:13,560
Speaker 1: effect of a little moon around a planet from the

995
00:45:13,560 --> 00:45:16,120
Speaker 1: planet itself. What we do think is possible is the

996
00:45:16,200 --> 00:45:20,000
Speaker 1: transit method, this eclipse method, where a planet passes in

997
00:45:20,000 --> 00:45:22,000
Speaker 1: front of a star and dips the light that comes

998
00:45:22,040 --> 00:45:24,239
Speaker 1: from it, And if that happens in a regular way,

999
00:45:24,320 --> 00:45:27,600
Speaker 1: we can tell that these little microeclipses come from a planet. Well,

1000
00:45:27,600 --> 00:45:29,960
Speaker 1: if those eclipses have their own little dips in them,

1001
00:45:30,280 --> 00:45:33,719
Speaker 1: because the moon going around the planet sometimes blocks this

1002
00:45:33,880 --> 00:45:36,480
Speaker 1: life from the star and sometimes doesn't, then you can

1003
00:45:36,520 --> 00:45:42,000
Speaker 1: discover moons around those planets. So like microeclipses within microeclipses.

1004
00:45:42,120 --> 00:45:45,200
Speaker 2: Wow, exo eclipses exo exo moon eclipses.

1005
00:45:45,320 --> 00:45:47,919
Speaker 1: Yeah, they're like eclipses squared. And we don't have any

1006
00:45:47,960 --> 00:45:50,680
Speaker 1: confirmed exo moons yet, though there are a couple of

1007
00:45:50,719 --> 00:45:54,480
Speaker 1: candidates from the Kepler telescope that look promising, but people

1008
00:45:54,480 --> 00:45:58,279
Speaker 1: can't yet agree whether that actually is the discovery of

1009
00:45:58,320 --> 00:46:01,920
Speaker 1: a moon. And more recently, we've developed this incredible technology

1010
00:46:01,960 --> 00:46:05,280
Speaker 1: to do direct imaging of exoplanets, like telescopes that actually

1011
00:46:05,360 --> 00:46:09,440
Speaker 1: take pictures of planets around other stars. Blows my mind.

1012
00:46:09,480 --> 00:46:11,560
Speaker 1: I never thought that would be possible. A lot of

1013
00:46:11,560 --> 00:46:13,960
Speaker 1: it involves like blocking out the light from the star

1014
00:46:14,040 --> 00:46:16,440
Speaker 1: itself so you can see the ring around it. And

1015
00:46:16,480 --> 00:46:19,799
Speaker 1: sometimes that lets us see planets being formed. So we

1016
00:46:19,800 --> 00:46:22,439
Speaker 1: can see, for example, a star with a planetary disc

1017
00:46:22,560 --> 00:46:24,960
Speaker 1: around it. And in one case we have a direct

1018
00:46:25,040 --> 00:46:28,520
Speaker 1: image of a protoplanetary disc which seems to have a

1019
00:46:28,560 --> 00:46:31,520
Speaker 1: planet with its own disc around it. So like you

1020
00:46:31,520 --> 00:46:33,480
Speaker 1: can see the planet and it's got like a bunch

1021
00:46:33,480 --> 00:46:36,040
Speaker 1: of stuff around it, and maybe that stuff will form

1022
00:46:36,080 --> 00:46:36,680
Speaker 1: into a moon.

1023
00:46:37,920 --> 00:46:39,040
Speaker 2: You can see the rings in it.

1024
00:46:39,239 --> 00:46:41,520
Speaker 1: Yeah, exactly. You can see this disc that's going to

1025
00:46:41,640 --> 00:46:44,200
Speaker 1: form it either into rings or moons or something.

1026
00:46:44,280 --> 00:46:46,359
Speaker 2: Yeah, it's pretty mind blowing because I wonder like if

1027
00:46:46,360 --> 00:46:48,040
Speaker 2: a lot of people know that you can actually see

1028
00:46:48,040 --> 00:46:50,279
Speaker 2: the moons of Jupiter kind of with your naked eye,

1029
00:46:50,360 --> 00:46:52,319
Speaker 2: or at least with a small telescope. You don't need

1030
00:46:52,360 --> 00:46:54,399
Speaker 2: like a super amazing telescope. You can just use something

1031
00:46:54,400 --> 00:46:55,839
Speaker 2: you can buy for your house and you can see

1032
00:46:55,840 --> 00:46:56,640
Speaker 2: the moons of Jupiter.

1033
00:46:56,719 --> 00:46:58,960
Speaker 1: Yeah, it doesn't take a fancy telescope. It was one

1034
00:46:59,000 --> 00:47:01,040
Speaker 1: of the first things that Galla saw when he pointed

1035
00:47:01,040 --> 00:47:02,799
Speaker 1: a telescope at the sky. It was one of the

1036
00:47:02,800 --> 00:47:04,560
Speaker 1: first people to ever do this, and he saw the

1037
00:47:04,640 --> 00:47:06,640
Speaker 1: moons of Jupiter. It's not hard. You can do it,

1038
00:47:06,640 --> 00:47:09,520
Speaker 1: and it's pretty exciting to see Jupiter expand from this

1039
00:47:09,640 --> 00:47:11,799
Speaker 1: tiny dot you can see with the naked eye to

1040
00:47:11,920 --> 00:47:14,480
Speaker 1: this whole orbital system with its own dynamics.

1041
00:47:14,840 --> 00:47:18,200
Speaker 2: H pretty cool. All right. Well, one thing that's day

1042
00:47:18,200 --> 00:47:20,560
Speaker 2: announced recently is that we're sending more people to the Moon.

1043
00:47:20,719 --> 00:47:22,960
Speaker 1: That's right, if Elon Musk ever gets that starship off

1044
00:47:23,000 --> 00:47:23,400
Speaker 1: the ground.

1045
00:47:23,520 --> 00:47:26,319
Speaker 2: No, the new artem is missions right, It isn't one

1046
00:47:26,360 --> 00:47:27,920
Speaker 2: of the plants to send more people to the moon.

1047
00:47:28,040 --> 00:47:30,040
Speaker 1: Yeah, that's exciting. It'd be cool to go back to

1048
00:47:30,080 --> 00:47:32,279
Speaker 1: the Moon. With all of our advanced technology, we can

1049
00:47:32,440 --> 00:47:35,360
Speaker 1: take more detailed measurements. We can map its magnetic field,

1050
00:47:35,400 --> 00:47:38,399
Speaker 1: we can understand its geology and its history even better. Yeah.

1051
00:47:38,440 --> 00:47:40,200
Speaker 2: I wonder why kind of pizza they would eat there though?

1052
00:47:40,880 --> 00:47:43,520
Speaker 2: It's a deep dish because there's not much that much gravity.

1053
00:47:43,560 --> 00:47:45,160
Speaker 2: So can you have a deep dish pizza?

1054
00:47:46,000 --> 00:47:48,279
Speaker 1: Probably every pizza would rise a lot more because there

1055
00:47:48,280 --> 00:47:49,400
Speaker 1: isn't gravity, right.

1056
00:47:49,320 --> 00:47:51,480
Speaker 2: Oh, my goodness. In space, every pizza is a deep

1057
00:47:51,520 --> 00:47:53,719
Speaker 2: dish pizza. That's why you're not going to Earth.

1058
00:47:53,840 --> 00:47:57,080
Speaker 1: Danu or maybe astronaut pizza is just freeze dried and

1059
00:47:57,120 --> 00:48:00,880
Speaker 1: gross no matter where it comes from.

1060
00:48:01,239 --> 00:48:03,239
Speaker 2: I guess there's something one way to find out to

1061
00:48:03,280 --> 00:48:06,799
Speaker 2: take the podcast to space. All right, Well that kind

1062
00:48:06,800 --> 00:48:09,480
Speaker 2: of answers our question. How the Moon's form basically two

1063
00:48:09,520 --> 00:48:13,360
Speaker 2: main ways, right, They either capture something flying by in space,

1064
00:48:13,600 --> 00:48:16,480
Speaker 2: or they form together with the planet, or some combination

1065
00:48:16,560 --> 00:48:20,319
Speaker 2: of the tube where something comes from space crashes into you,

1066
00:48:20,560 --> 00:48:22,880
Speaker 2: creates a big mess, and then you both sort of

1067
00:48:22,920 --> 00:48:24,640
Speaker 2: form together or reform together.

1068
00:48:24,800 --> 00:48:26,880
Speaker 1: And the incredible thing is that by looking at the

1069
00:48:26,880 --> 00:48:29,840
Speaker 1: Moon today we can mostly figure out how that happened,

1070
00:48:29,840 --> 00:48:32,160
Speaker 1: how this huge space rock ended up in orbit around

1071
00:48:32,200 --> 00:48:33,160
Speaker 1: the planet. Yeah.

1072
00:48:33,160 --> 00:48:34,680
Speaker 2: And the cool thing is that you can see the

1073
00:48:34,719 --> 00:48:37,000
Speaker 2: Moon almost every night. Every night you step outside of

1074
00:48:37,000 --> 00:48:39,840
Speaker 2: your house, you can see this giant rock floating in

1075
00:48:39,920 --> 00:48:43,319
Speaker 2: space there for us to see, pretty shiny, pretty bright.

1076
00:48:44,560 --> 00:48:47,240
Speaker 1: It's nice to have one big, fat moon. I agree.

1077
00:48:47,480 --> 00:48:49,799
Speaker 2: All right, Well, we hope you enjoyed that. Thanks for

1078
00:48:49,880 --> 00:48:51,680
Speaker 2: joining us, See you next time.

1079
00:48:59,480 --> 00:49:02,360
Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain

1080
00:49:02,400 --> 00:49:06,399
Speaker 1: the Universe is a production of iHeartRadio. For more podcasts

1081
00:49:06,400 --> 00:49:11,080
Speaker 1: from iHeartRadio, visit the iHeartRadio, app, Apple podcasts, or wherever

1082
00:49:11,120 --> 00:49:12,840
Speaker 1: you listen to your favorite shows.