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Speaker 6: Good job.

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Speaker 1: Thanks, Hey, hey, do you ever wish that we had

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Speaker 1: more moons in our night sky?

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Speaker 7: Hmmm?

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Speaker 5: 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 5: But then I wonder if we had the same line

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Speaker 5: in Star Wars, you know, where he says that's no moon.

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Speaker 5: 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 5: Or that song when the moon hits your eye like

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Speaker 5: a big pizza pie. That wouldn't work with a lot

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Speaker 5: of little moons. I guess it would work with lots

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Speaker 5: of mini pizzas.

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

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Speaker 5: I am Horehem, a 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 Irvin and I've never really been a fan

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Speaker 1: of the pan pizza, of.

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Speaker 5: The pan or the pizza, but just a combination of

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Speaker 5: 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.

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Speaker 5: Not 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 5: I feel like there's a thin line between a pan

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Speaker 5: 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 5: There you go, But anyways, welcome to our podcast, Daniel

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Speaker 5: 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 5: That's right, because the universe is a deep dish of

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Speaker 5: amazing facts and incredible things happening in it, full of

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Speaker 5: mysteries and wonderful conundrums for us to try to figure out.

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Speaker 1: And while physics has made incredible progress and understand 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 5: Why does deep dish pizza exist? Fundamental questions, that's what

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Speaker 5: we ask here on the podcast, and why doesn't Daniel

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Speaker 5: 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 5: Are you saying the universe is kind of cheesy? I

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Speaker 5: guess it will definitely give you a heart attack as well.

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Speaker 1: There's no topping that joke.

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Speaker 5: But yeah, we like to think about the universe and

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Speaker 5: all of the perfecting things in it, like how did

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Speaker 5: things come to be the way they are? Why are

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Speaker 5: we here? And where are we in the universe? And

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Speaker 5: what is around us?

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Speaker 1: One of the real, simple but enduring joys of being

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Speaker 1: a curious person is just looking up at the night sky.

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Speaker 1: Not just being amazed at it's beauty and odd at

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Speaker 1: the depth of the view that you were looking at,

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Speaker 1: but this shared feeling through time that humans one hundred

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Speaker 1: years ago, a thousand years ago, twenty five thousand years

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Speaker 1: ago probably looked up at almost the same night sky

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Speaker 1: and wondered what was up there and why it looked

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Speaker 1: the way it did, and whether it could have been different.

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Speaker 5: Yeah, you're looking at the exact same sky that our

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Speaker 5: ancestors did, full of stars, comments, and even a moon.

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Speaker 5: And they probably asked the same question that maybe a

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Speaker 5: lot of you have out there, which is, why do

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Speaker 5: we have a moon? And is it made out of cheese?

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Speaker 5: Is it just a big, fat, giant, floating, deep dish

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Speaker 5: 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 5: Do you do tell? Give us a slice of that

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Speaker 5: knowledge there?

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Speaker 1: All right? He called my bluff I got nothing.

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Speaker 5: And it was a crusty joke. But yeah, sometimes we

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Speaker 5: look out into the universe, into the night sky, and

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Speaker 5: we wonder why are things there, and how did they

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Speaker 5: come to be the way they are? What's going on?

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Speaker 5: And it wasn't just our ancestors. I'd looked up at

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Speaker 5: the Moon. It's like all of the planet that is

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Speaker 5: looking up at the moon, right, it's feeling its facts

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Speaker 5: and howling at it and rolling with the tides that

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Speaker 5: go along with the moon. The moon has. It makes

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Speaker 5: 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 heygologist 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 5: So to the other podcast, we'll be tackling the question

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Speaker 5: how the planets get their moon or moons. Some planets

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Speaker 5: 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 5: 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 how.

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Speaker 5: You know it's round? It always looks the same.

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Speaker 1: Well, we've been to the Moon. Obviously 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 got to

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Speaker 1: be round.

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Speaker 5: Oh right, you get sort of like the shadow of

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Speaker 5: it tells you it's round. M exactly is it perfectly round?

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Speaker 5: Is the Moon perfectly round or is it kind of

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Speaker 5: 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 5: Whoa, I guess it's not spinning in the way that

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Speaker 5: the Earth is, so that you get this centropical force.

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Speaker 5: But you're saying that the fact that the Earth is

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Speaker 5: 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 5: Well, it is cool that we have a moon. I

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Speaker 5: guess it to inspire all of these songs and all

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Speaker 5: these stories and legends about.

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

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Speaker 5: it's just kind of swinging around the Earth. It's constantly

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Speaker 5: falling around the Earth. That's what the moon is doing.

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Speaker 5: And it's big, like you don't want to mess with

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Speaker 5: 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 7: Mmmm.

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Speaker 5: Wait, what does that mean? That means that we will

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Speaker 5: 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

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

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Speaker 5: 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'll take about forty seven

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

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

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

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

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

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Speaker 5: Yeah, we would have bigger problems in the moon at

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Speaker 5: 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 a 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 5: Whoa which SI gets to have the moon? Can they

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Speaker 5: predict that? Or we even have the same We probably

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Speaker 5: 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 5: I guess we have the moon to thank for having

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Speaker 5: more time in our day. Then without the moon, things

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Speaker 5: 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 5: I think the people during the day would also have

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Speaker 5: a shorter time, right. But it is an interesting question

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Speaker 5: how did we get this moon? Like how do planets

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Speaker 5: get moons at all? And why do we only have

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Speaker 5: one moon versus having lots of moons like other planets

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Speaker 5: which have up to eighty four moons.

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

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

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

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Speaker 1: itself is kind of weird.

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Speaker 5: 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 5: Well, as you sure, we were wondering how many people

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Speaker 5: out there, I thought about the question of where moons

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Speaker 5: come from and how are they form? How do we

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Speaker 5: get ours? So as usual Daniel went out there into

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Speaker 5: the internet 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 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. Right to me. Two questions

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Speaker 1: at Danielandjorge dot com.

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Speaker 5: So think about it for a second. How do you

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Speaker 5: think planets get their moons? Here's what people had to say.

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Speaker 6: I think that most moons form from cloud discs around planets,

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Speaker 6: and that Satan's rings are a picture of that process

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Speaker 6: going on.

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Speaker 8: Moons form, how planets form, So there's small rocks and

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Speaker 8: then they hit each other and create bigger ones. So

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Speaker 8: when a planet is created, maybe when it gets created,

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Speaker 8: some debris goes out and then creates like a miniature

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Speaker 8: planet aka and Moon.

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Speaker 5: Maybe I suppose the Moon is just a small planet.

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Speaker 5: It's kind of just a planet that gets tripped by

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Speaker 5: another planet. Right, They're just rocks.

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Speaker 7: There's got to be like at least six ways moon forms.

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Speaker 7: I don't know, like things crashing together. Apparently we might

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Speaker 7: have stolen the Moon from Venus. Maybe probably a bunch

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Speaker 7: of other ways they could form too.

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Speaker 9: I think Moon's form either just sort of alongside they're

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Speaker 9: planet like Lucky, or from collisions like our own Moon

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Speaker 9: came from an impact. Those are, I guess the only

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Speaker 9: two I really know.

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Speaker 6: I would say that this is a collisions between among

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Speaker 6: asceoids planets.

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Speaker 1: And then you have a planet that has been.

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Speaker 10: Hit by an asteroid and a small chunk of this

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Speaker 10: planet would be placed in a sort of an orbit,

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Speaker 10: and then you get the Moon.

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Speaker 11: I think it's when space dust is orbiting a planet

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Speaker 11: and then it clumps together into Moon eventually, or if

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Speaker 11: like an asteroid is caught in the gravitational pool of

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Speaker 11: a planet and falls into its orbit.

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Speaker 2: I think moon's form from asteroids and other bits of

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Speaker 2: space debris that get trapped in a planet's orbit.

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Speaker 12: I think that moon's form around planets the same way

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Speaker 12: that planets form around stars. I think that basically there's

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Speaker 12: a bunch of junk floating around the planet that aggregates

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Speaker 12: into a moon or moons.

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Speaker 5: All right, a lot of interesting answers here. Somebody said

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Speaker 5: at least six ways, that's all they said, But only

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Speaker 5: at least six he or she had six ways in mind.

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Speaker 1: Mm 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 5: Sounds like clickbait. Six ways that we can get a moon.

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Speaker 5: The six one will totally amaze you. Maybe we should

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Speaker 5: be learning from this listener to title our podcast episodes.

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Speaker 5: Although that you hear BuzzFeed is going down, it's going

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Speaker 5: out of business or BuzzFeed news.

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

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Speaker 5: I think there are six amazing lessons. The sixth one

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Speaker 5: will totally astound you.

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Speaker 1: I can't wait to hear.

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Speaker 5: But yeah, a lot of interesting theories here. From people.

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Speaker 5: Some people think it happens from like a collision. Some

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Speaker 5: 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. Hmmm.

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Speaker 5: The sixth one will amaze.

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Speaker 1: You if we get there.

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Speaker 5: If we get that right, know for here, we'll get there.

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Speaker 5: Question is how long before we get there? Will we

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Speaker 5: do it before the hour is up? So it's a

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Speaker 5: close call. All right, Well, let's start with the basics, Daniel,

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Speaker 5: how would you define a moon? Like what is a moon?

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Speaker 5: And what's the difference between a moon and like a

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Speaker 5: 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 category 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 5: To say, sort of like organic satellite exactly, or farm

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Speaker 5: 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 satell lights, things that are in

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Speaker 1: orbit anyway, naturally without the influence of humans.

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Speaker 5: But wait, wait, I think I've seen NASA call the

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Speaker 5: moons of Jupiter the moons of Jupiter. They never say

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Speaker 5: 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 5: I see. But I guess if you put the in

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Speaker 5: front of it, then it's our moon. Like the moon

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Speaker 5: 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 5: I guess you can have rocks, and you can have the.

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Speaker 1: Rock exactly, and we have lots of rocks in orbit,

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

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Speaker 1: though I haven't seen Fast and Furious twenty seven or whichever.

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Speaker 5: I'm assuing. The next one, the you know, speed up

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Speaker 5: a ramp and somehow make it up to space and

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Speaker 5: crash into a space station while he jumps and also

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Speaker 5: 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, Like,

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

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Speaker 1: you could call it a moon.

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Speaker 5: Wait, what I mean. No, I mean at some point

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Speaker 5: it's just 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

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

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

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Speaker 1: anti size and any limit you place is going to

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Speaker 1: be totally arbitrary. Right.

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Speaker 5: I wonder if the definition also has to do with

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Speaker 5: how stable its orbit is. Like, if I just throw

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Speaker 5: a rock into space, it's going to be orbiting the

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Speaker 5: Earth for a little bit. Does that mean it's a

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Speaker 5: moon that's not really in orbit?

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Speaker 1: Right? I don't know how strong you are recent I

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Speaker 1: haven't seen you in a while, but I don't think

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Speaker 1: you could throw a rock and actually get it into orbit.

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Speaker 1: It has to be in orbit.

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Speaker 5: Oh yeah, do you want to make that bet? I'll

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Speaker 5: bet you a billion dollars because with a billion dollars

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Speaker 5: I can throw the rock.

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Speaker 1: If you get a rock orbit in the Earth, I

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

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Speaker 5: Well, if you get me on a rocket ship into

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Speaker 5: 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 5: Wait, there are six planets in our Solar system with moons.

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Speaker 5: 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 5: Oh interesting, and I just figured it out. That's probably

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Speaker 5: what 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 5: So most of the moons in the Solar system, some

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Speaker 5: of them are as big as our moon. But you're

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Speaker 5: saying that the ratio compared to their planet. Most of

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Speaker 5: 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 the planet and which one is the moon.

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Speaker 1: It all gets kind of fuzzy.

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Speaker 5: Whoa, it's like a double planet.

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Speaker 9: 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 and the point

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

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

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

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Speaker 1: a moon. Otherwise you call it a binary system. Again,

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Speaker 1: that's still kind of arbitrary, right, We're just like giving

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Speaker 1: these things names and drawing lines between them. Really, there's

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Speaker 1: just a bunch of different rocks out there in the

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Speaker 1: universe orbiting each other.

443
00:20:40,119 --> 00:20:42,439
Speaker 5: Except also, Pluto is not a planet, So can you

444
00:20:42,480 --> 00:20:45,080
Speaker 5: have a moon around something that's not a planet? That

445
00:20:45,160 --> 00:20:46,840
Speaker 5: can you can a moon or can a moon have

446
00:20:46,880 --> 00:20:47,200
Speaker 5: a moon.

447
00:20:48,119 --> 00:20:50,200
Speaker 1: You can have a moon around a dwarf planet, though

448
00:20:50,240 --> 00:20:52,040
Speaker 1: maybe you would want to call it a dwarf moon.

449
00:20:52,200 --> 00:20:55,960
Speaker 1: I don't know. And it's possible in principle to have

450
00:20:56,119 --> 00:20:59,760
Speaker 1: moons around moons. There are asteroids that have moons.

451
00:21:00,560 --> 00:21:03,359
Speaker 5: And you still call them moons, not master moons.

452
00:21:03,440 --> 00:21:06,200
Speaker 1: Some people want to call them moonlits or moon moons

453
00:21:06,680 --> 00:21:07,400
Speaker 1: like the moon of a.

454
00:21:07,359 --> 00:21:10,359
Speaker 5: Moon or moony's or mini moons.

455
00:21:10,480 --> 00:21:12,560
Speaker 1: And there are even some moons like Rhea has its

456
00:21:12,560 --> 00:21:14,920
Speaker 1: own ring system Saturn's moon Rhea.

457
00:21:15,080 --> 00:21:18,919
Speaker 5: Wait what some moons can have rings? Yeah, because they

458
00:21:18,960 --> 00:21:20,760
Speaker 5: have so many mini moons.

459
00:21:20,880 --> 00:21:23,919
Speaker 1: If you're big enough that you dominate the gravitational environment nearby,

460
00:21:24,000 --> 00:21:25,600
Speaker 1: then yeah, you can have your own rings.

461
00:21:25,640 --> 00:21:28,440
Speaker 5: I mean, I guess technically anything can have a satellite, right,

462
00:21:28,440 --> 00:21:30,760
Speaker 5: Like I can take a baseball put in into space

463
00:21:30,840 --> 00:21:34,000
Speaker 5: and then knock a you know, a speck of dust

464
00:21:34,000 --> 00:21:35,280
Speaker 5: in orbit around it, right.

465
00:21:35,560 --> 00:21:37,520
Speaker 1: Yeah, exactly. That wouldn't be a planet or even a

466
00:21:37,640 --> 00:21:41,359
Speaker 1: dwarf planet, but they would have an orbiting object. Is

467
00:21:41,359 --> 00:21:43,600
Speaker 1: that a natural satellite? I'm not quite sure.

468
00:21:44,119 --> 00:21:45,720
Speaker 5: All right, what else do we know about moons?

469
00:21:45,840 --> 00:21:48,199
Speaker 1: If you try to dig into the ancient history of moons,

470
00:21:48,240 --> 00:21:52,000
Speaker 1: it gets quite confusing to read about because until Copernicus,

471
00:21:52,200 --> 00:21:55,000
Speaker 1: moons were actually called planets, like the Moon itself was

472
00:21:55,040 --> 00:21:57,560
Speaker 1: referred to as a planet, like when you talked about

473
00:21:57,560 --> 00:22:01,439
Speaker 1: astronomy in the fifteen hundreds, the Mars, the planet of Venus,

474
00:22:01,520 --> 00:22:05,119
Speaker 1: the planet Luna. And it wasn't until Kepler, who was

475
00:22:05,119 --> 00:22:07,199
Speaker 1: thinking about how these things orbit each other, who had

476
00:22:07,200 --> 00:22:10,359
Speaker 1: a better understanding of these orbits, that we started calling

477
00:22:10,359 --> 00:22:13,199
Speaker 1: the Moon a satellite of the Earth. And then the

478
00:22:13,240 --> 00:22:16,040
Speaker 1: satellites of Jupiter are of course the moons of Jupiter.

479
00:22:16,240 --> 00:22:19,080
Speaker 1: So there's a really fun interesting history to these words.

480
00:22:19,280 --> 00:22:21,680
Speaker 5: Wait, really, so like, for a moment in human history,

481
00:22:21,720 --> 00:22:25,320
Speaker 5: we thought the Moon was another planet orbiting the Solar System.

482
00:22:25,560 --> 00:22:27,280
Speaker 5: Technically it is orbiting the Sun.

483
00:22:27,520 --> 00:22:29,560
Speaker 1: Yeah, it is orbiting the Sun, and it is orbiting

484
00:22:29,560 --> 00:22:31,760
Speaker 1: the Earth. Right, It's not that we thought the Moon

485
00:22:31,880 --> 00:22:34,439
Speaker 1: was a planet like Mars. It's just that we categorized

486
00:22:34,480 --> 00:22:36,640
Speaker 1: all these things the same way. All these words are

487
00:22:36,680 --> 00:22:39,000
Speaker 1: just buckets, right, and they're just like, grab a bunch

488
00:22:39,080 --> 00:22:40,920
Speaker 1: of the stuff that's out there and gather it all

489
00:22:40,960 --> 00:22:44,000
Speaker 1: into a conceptual bucket. And where the lines between these

490
00:22:44,000 --> 00:22:46,199
Speaker 1: buckets are is a little bit arbitrary. And so it

491
00:22:46,320 --> 00:22:48,080
Speaker 1: used to be that we lumped the moon in with

492
00:22:48,119 --> 00:22:51,000
Speaker 1: the planets. Now we have a separate category for things

493
00:22:51,000 --> 00:22:52,640
Speaker 1: that orbit the planets.

494
00:22:53,600 --> 00:22:56,560
Speaker 5: Shoot for the moon. I guess when you're naming things right, Well,

495
00:22:56,640 --> 00:22:59,480
Speaker 5: let's get a little deeper into where the moon came from.

496
00:22:59,560 --> 00:23:01,800
Speaker 5: Where do moons in general come from, how do other

497
00:23:01,840 --> 00:23:04,320
Speaker 5: planets get their moons, and what does it all mean

498
00:23:04,359 --> 00:23:07,600
Speaker 5: about the history of the Solar system. But first, let's

499
00:23:07,640 --> 00:23:08,639
Speaker 5: take a quick break.

500
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551
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560
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566
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568
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Speaker 5: All right, we're getting a little looney here talking about

569
00:26:53,160 --> 00:26:55,399
Speaker 5: the moon and how we got it and how do

570
00:26:55,520 --> 00:26:56,840
Speaker 5: planets get their moons.

571
00:26:56,960 --> 00:26:59,720
Speaker 1: It is really fun in ancient question to wonder why

572
00:26:59,760 --> 00:27:02,240
Speaker 1: that's is in our sky and why Jupiter has more

573
00:27:02,280 --> 00:27:04,800
Speaker 1: moons than we do. And if history had been different,

574
00:27:04,840 --> 00:27:06,760
Speaker 1: would we have had a bunch of moons? What would

575
00:27:06,760 --> 00:27:09,320
Speaker 1: it be like to live in that scenario? Could we

576
00:27:09,480 --> 00:27:12,680
Speaker 1: sail as well? If the tides were crazy and complicated

577
00:27:12,800 --> 00:27:14,760
Speaker 1: from having like fifteen different little moons?

578
00:27:15,240 --> 00:27:18,800
Speaker 5: Hmmm? Interesting? Yeah, that would affect the tides, right, But

579
00:27:18,840 --> 00:27:20,359
Speaker 5: that wouldn't affect navigation, would it.

580
00:27:20,240 --> 00:27:22,480
Speaker 1: It wouldn't affect navigation, but it would affect when it's

581
00:27:22,480 --> 00:27:24,760
Speaker 1: easy to launch your ships or not, and so it

582
00:27:24,840 --> 00:27:27,240
Speaker 1: might affect lots of industries and exploration.

583
00:27:27,600 --> 00:27:31,320
Speaker 5: M Also, if your were wolf would be pretty complicated, right, probably,

584
00:27:31,840 --> 00:27:33,600
Speaker 5: just you know, just to plant ahead.

585
00:27:34,200 --> 00:27:36,280
Speaker 1: Maybe you changed into one kind of wolf for one

586
00:27:36,320 --> 00:27:38,280
Speaker 1: moon and another kind of wolf for another moon, and

587
00:27:38,359 --> 00:27:40,800
Speaker 1: like a Pomeranian for the little moon or a shit.

588
00:27:40,720 --> 00:27:45,280
Speaker 5: Sou for Yeah, there you go, different moons for different breeds.

589
00:27:45,000 --> 00:27:47,040
Speaker 1: Two moons up in the sky. Then you're a hybrid. Right,

590
00:27:47,240 --> 00:27:49,440
Speaker 1: this sounds like a fun science fiction story. It sounds

591
00:27:49,440 --> 00:27:53,600
Speaker 1: like a great Ya novel, so many spin offs.

592
00:27:53,640 --> 00:27:55,959
Speaker 5: All right, we talked about the word moon is kind

593
00:27:56,000 --> 00:27:59,240
Speaker 5: of flexible and it's not quite super well defined, but

594
00:27:59,440 --> 00:28:01,640
Speaker 5: basically it just kind of means like a big rock

595
00:28:01,720 --> 00:28:04,239
Speaker 5: circling around a bigger rock. Right, that's right.

596
00:28:04,240 --> 00:28:06,720
Speaker 1: It's a big rock orbiting another big rock.

597
00:28:06,960 --> 00:28:09,199
Speaker 5: And as you said, six of the planets in our

598
00:28:09,240 --> 00:28:12,720
Speaker 5: Solar system have them. Venus and Mercury don't because I

599
00:28:12,760 --> 00:28:15,320
Speaker 5: guess they're too hot, you said. And if they had moons,

600
00:28:15,320 --> 00:28:18,320
Speaker 5: then the Sun would have disrupted its orbit and probably

601
00:28:18,359 --> 00:28:20,440
Speaker 5: made it crash into the planet, right or fly away.

602
00:28:20,520 --> 00:28:22,320
Speaker 1: Yeah, it's all about the tidal forces. It makes it

603
00:28:22,359 --> 00:28:25,679
Speaker 1: basically impossible for Mercury or Venus to have moons and

604
00:28:25,720 --> 00:28:28,000
Speaker 1: to keep them. It's because they're so close to the Sun.

605
00:28:28,000 --> 00:28:31,520
Speaker 1: It's not their actual temperature, it's the gravitational tidal forces

606
00:28:31,520 --> 00:28:32,080
Speaker 1: from the Sun.

607
00:28:32,320 --> 00:28:34,800
Speaker 5: All right, Well, what do we know about where moons

608
00:28:34,840 --> 00:28:35,960
Speaker 5: come from and how they're formed?

609
00:28:36,080 --> 00:28:37,680
Speaker 1: So you can tell a lot about where a moon

610
00:28:37,760 --> 00:28:40,120
Speaker 1: came from based on what it's made out of and

611
00:28:40,160 --> 00:28:42,880
Speaker 1: how it's orbiting. If a moon is mostly in a

612
00:28:43,040 --> 00:28:46,240
Speaker 1: circular orbit, and the circular orbit follows the tilt of

613
00:28:46,280 --> 00:28:50,040
Speaker 1: the planet, so for example, it's orbiting around the equator

614
00:28:50,120 --> 00:28:52,840
Speaker 1: in mostly a circle. Then it's very likely that that

615
00:28:52,960 --> 00:28:56,480
Speaker 1: moon came from the same stuff that formed the planet.

616
00:28:56,720 --> 00:28:59,000
Speaker 1: Remember how planets form in the beginning, it's a big

617
00:28:59,080 --> 00:29:01,440
Speaker 1: cloud of gas, gas, and dust that forms the whole

618
00:29:01,440 --> 00:29:03,760
Speaker 1: Solar System. Most of the gas is gobbled up by

619
00:29:03,800 --> 00:29:06,040
Speaker 1: the star as it forms, and our Sun has ninety

620
00:29:06,120 --> 00:29:08,520
Speaker 1: ninety percent of the mass of the Solar System. But

621
00:29:08,560 --> 00:29:10,920
Speaker 1: if you get a little isolated pocket of heavy stuff

622
00:29:10,920 --> 00:29:13,440
Speaker 1: that has its own gravity and can gather itself together,

623
00:29:13,600 --> 00:29:15,600
Speaker 1: then you can get a planet. So a planet sort

624
00:29:15,640 --> 00:29:17,720
Speaker 1: of forms the same way the Solar System does. It's

625
00:29:17,720 --> 00:29:20,240
Speaker 1: the gravitational collapse of a big blob of.

626
00:29:20,200 --> 00:29:22,720
Speaker 5: Stuff, right, And initially it's just kind of like a

627
00:29:22,720 --> 00:29:26,400
Speaker 5: big cloud of rocks and dust that's spinning or has

628
00:29:26,520 --> 00:29:27,600
Speaker 5: kind of an overall spin.

629
00:29:28,240 --> 00:29:30,680
Speaker 1: Exactly. The reason you get moons around planets is the

630
00:29:30,720 --> 00:29:33,720
Speaker 1: same reason you get planets around stars. Right. You don't

631
00:29:33,760 --> 00:29:35,920
Speaker 1: just get all the mass of the Solar System collapsing

632
00:29:35,960 --> 00:29:38,000
Speaker 1: into the Sun. You get these little pockets that have

633
00:29:38,080 --> 00:29:40,480
Speaker 1: enough gravity to form themselves together. And then are moving

634
00:29:40,480 --> 00:29:43,520
Speaker 1: at high enough speed that they can resist falling into

635
00:29:43,560 --> 00:29:46,520
Speaker 1: the Sun. Now, around those planets, of course, you also

636
00:29:46,600 --> 00:29:49,080
Speaker 1: have little clouds of gas and dust. Some of it

637
00:29:49,160 --> 00:29:51,640
Speaker 1: collapses into the planet, most of it, but some of

638
00:29:51,680 --> 00:29:55,120
Speaker 1: it pulls itself together and has enough velocity to avoid

639
00:29:55,560 --> 00:29:58,760
Speaker 1: falling into the planet. And so if you have enough

640
00:29:58,800 --> 00:30:00,800
Speaker 1: velocity and you can pull yourself to together, then you

641
00:30:00,840 --> 00:30:03,520
Speaker 1: can form like a little planet's planet, a little miniature

642
00:30:03,520 --> 00:30:05,880
Speaker 1: system around the planet, the same way the planet is

643
00:30:05,920 --> 00:30:06,760
Speaker 1: going around the Sun.

644
00:30:06,960 --> 00:30:09,800
Speaker 5: Right, because I guess gravity. That's how gravity works, right,

645
00:30:09,840 --> 00:30:13,080
Speaker 5: Like everything is attracted to everything else. It's not just

646
00:30:13,080 --> 00:30:15,719
Speaker 5: like we're attracted to the Sun or just attracted to

647
00:30:15,840 --> 00:30:20,040
Speaker 5: the planet Earth. It's like I'm attracted to my car

648
00:30:20,160 --> 00:30:22,440
Speaker 5: and to this base bomb. The base will attracted to me.

649
00:30:22,480 --> 00:30:24,920
Speaker 5: And so if we were out in space, we would

650
00:30:24,960 --> 00:30:26,800
Speaker 5: both be falling towards the Earth, but then we would

651
00:30:26,800 --> 00:30:29,280
Speaker 5: there would also be an attraction between us. And sometimes

652
00:30:29,480 --> 00:30:32,040
Speaker 5: I think what you're saying is that if a clump

653
00:30:32,120 --> 00:30:35,160
Speaker 5: of dirt and rocks when the planet is formed, it's

654
00:30:35,280 --> 00:30:37,840
Speaker 5: kind of far enough out there, it will clump together

655
00:30:37,960 --> 00:30:39,320
Speaker 5: before it comps with the Earth.

656
00:30:39,480 --> 00:30:42,120
Speaker 1: Yeah, that's exactly right, And there's sort of two steps there.

657
00:30:42,560 --> 00:30:46,200
Speaker 1: One is have enough velocity, like are you spinning fast

658
00:30:46,280 --> 00:30:49,320
Speaker 1: enough that you can basically get in orbit around the planet,

659
00:30:49,360 --> 00:30:52,000
Speaker 1: And that's how you get like a protoplanetary disc. The

660
00:30:52,040 --> 00:30:54,680
Speaker 1: planet forms and have some stuff out there that hasn't

661
00:30:54,720 --> 00:30:57,360
Speaker 1: fallen into the planet. So initially it's like a disc

662
00:30:57,720 --> 00:31:00,560
Speaker 1: and that can pull itself together using gravity into a ring.

663
00:31:00,760 --> 00:31:02,719
Speaker 1: And then there's the question of whether that ring can

664
00:31:02,760 --> 00:31:05,840
Speaker 1: pull itself together into a moon or not. Sometimes it

665
00:31:05,920 --> 00:31:09,239
Speaker 1: stays a ring and sometimes it forms a moon, and

666
00:31:09,280 --> 00:31:12,320
Speaker 1: that depends on how close you are to that planet.

667
00:31:12,560 --> 00:31:15,280
Speaker 1: If you're really really close to that planet, closer than

668
00:31:15,280 --> 00:31:17,760
Speaker 1: what we call the Roche limit, then tidle forces from

669
00:31:17,760 --> 00:31:19,520
Speaker 1: the planet are too strong. If you try to form

670
00:31:19,560 --> 00:31:22,120
Speaker 1: a moon, the tile forces will tear it apart. If

671
00:31:22,160 --> 00:31:25,320
Speaker 1: you're outpast the Roche limit, then the tile forces are

672
00:31:25,320 --> 00:31:27,959
Speaker 1: weak and you can gather together into a moon. So

673
00:31:28,000 --> 00:31:30,600
Speaker 1: you have to have enough velocity to avoid falling into

674
00:31:30,600 --> 00:31:33,000
Speaker 1: the planet, and then you have to be out past

675
00:31:33,080 --> 00:31:35,840
Speaker 1: the Roche limit to have a ring get turned into

676
00:31:35,880 --> 00:31:36,280
Speaker 1: a moon.

677
00:31:37,320 --> 00:31:40,240
Speaker 5: Because I think, as we've talked about before, gravity kind

678
00:31:40,240 --> 00:31:42,880
Speaker 5: of depends on the distance between two things. Right, So

679
00:31:43,280 --> 00:31:45,960
Speaker 5: if you're really close to the Earth, then like the

680
00:31:46,000 --> 00:31:48,000
Speaker 5: difference between one side of the Moon and the other

681
00:31:48,040 --> 00:31:51,479
Speaker 5: side of the Moon is they experience very different gravitational forces.

682
00:31:51,520 --> 00:31:54,360
Speaker 5: But maybe if you're far out in it, beyond this limit,

683
00:31:54,480 --> 00:31:58,000
Speaker 5: then you don't see this difference in pull from the

684
00:31:58,040 --> 00:32:01,800
Speaker 5: Earth between one and the other, which kind of lets

685
00:32:01,840 --> 00:32:02,520
Speaker 5: you clump together.

686
00:32:03,120 --> 00:32:05,560
Speaker 1: You'll still always feel that difference, right, and like the

687
00:32:05,600 --> 00:32:08,760
Speaker 1: Moon does feel that difference. That's why we talked about earlier.

688
00:32:08,800 --> 00:32:11,600
Speaker 1: The Moon is a football. It is being pulled by

689
00:32:11,640 --> 00:32:14,000
Speaker 1: the Earth's tidal forces, but it's far enough away that

690
00:32:14,080 --> 00:32:16,760
Speaker 1: those tidal forces are not strong enough to tear it apart.

691
00:32:16,880 --> 00:32:19,960
Speaker 1: The roach limit for the Earth is around ten thousand kilometers.

692
00:32:20,080 --> 00:32:22,280
Speaker 1: The Moon is like three hundred and eighty five thousand

693
00:32:22,320 --> 00:32:25,320
Speaker 1: kilometers away, so it's well past the Roche limit. If

694
00:32:25,360 --> 00:32:27,440
Speaker 1: the Moon was much much closer, if it was like

695
00:32:27,560 --> 00:32:30,160
Speaker 1: less than ten thousand kilometers from the surface of the Earth,

696
00:32:30,440 --> 00:32:33,080
Speaker 1: the Earth would tear it apart with those tidal forces

697
00:32:33,080 --> 00:32:35,160
Speaker 1: into a massive ring system.

698
00:32:34,720 --> 00:32:37,040
Speaker 5: Instead, where some of the rocks in that ring are

699
00:32:37,080 --> 00:32:38,040
Speaker 5: going at different speeds.

700
00:32:38,080 --> 00:32:39,760
Speaker 1: Right, it would be pretty cool to see the Moon

701
00:32:39,880 --> 00:32:42,280
Speaker 1: get torn up into rocks. Not all of them would

702
00:32:42,360 --> 00:32:45,200
Speaker 1: have the same velocity originally as the Moon. I'm sure

703
00:32:45,240 --> 00:32:47,600
Speaker 1: it would be somewhat destructive and chaotic. Some of them

704
00:32:47,600 --> 00:32:49,040
Speaker 1: would end up falling to the Earth, some of them

705
00:32:49,080 --> 00:32:50,640
Speaker 1: would get lost, and some of them would end up

706
00:32:50,640 --> 00:32:51,120
Speaker 1: in orbit.

707
00:32:51,280 --> 00:32:53,800
Speaker 5: Cool And I think that, as you said, also applies

708
00:32:53,840 --> 00:32:55,440
Speaker 5: to planets, right like you kind of have to be

709
00:32:55,480 --> 00:32:57,720
Speaker 5: a certain distance away from the Sun just to form

710
00:32:57,760 --> 00:32:58,360
Speaker 5: a planet, too.

711
00:32:58,640 --> 00:33:00,880
Speaker 1: Exactly, if you're too close to the Sun, then the

712
00:33:00,920 --> 00:33:04,920
Speaker 1: Sun's tidal forces, which are very powerful, will pull you apart.

713
00:33:05,240 --> 00:33:07,200
Speaker 1: So the roche limit for the Sun is like seven

714
00:33:07,280 --> 00:33:10,000
Speaker 1: hundred and fifty thousand kilometers. So if the Earth whereas

715
00:33:10,040 --> 00:33:12,640
Speaker 1: that close to the Sun, not only will we be fried,

716
00:33:12,680 --> 00:33:14,680
Speaker 1: of course, but the Sun would pull us apart with

717
00:33:14,800 --> 00:33:18,560
Speaker 1: its tidal forces. As you said, the gravitational force depends

718
00:33:18,600 --> 00:33:21,160
Speaker 1: on the distance, and so the Sun's gravit on the

719
00:33:21,200 --> 00:33:23,160
Speaker 1: near side of the Earth would be so much more

720
00:33:23,200 --> 00:33:25,280
Speaker 1: powerful than the Sun's gravity on the far side of

721
00:33:25,320 --> 00:33:28,040
Speaker 1: the Earth. It's effectively pulling us apart, and the Earth

722
00:33:28,320 --> 00:33:30,880
Speaker 1: is not strong enough to survive if it's closer than

723
00:33:30,920 --> 00:33:34,320
Speaker 1: seven hundred and fifty thousand kilometers. Fortunately, we're like one

724
00:33:34,400 --> 00:33:37,560
Speaker 1: hundred and fifty million kilometers from the Sun, so we're

725
00:33:37,560 --> 00:33:40,800
Speaker 1: nowhere near the Roche limit. And this isn't like an exact,

726
00:33:40,880 --> 00:33:43,240
Speaker 1: hard and fast number, it's like approximate. It depends on

727
00:33:43,280 --> 00:33:45,560
Speaker 1: the mass of the object, and it depends on structural

728
00:33:45,560 --> 00:33:47,480
Speaker 1: features of it, Like if you had a planet made

729
00:33:47,520 --> 00:33:49,960
Speaker 1: out of diamond, it could get closer to the Sun

730
00:33:50,120 --> 00:33:51,520
Speaker 1: than a planet made out of gravel.

731
00:33:52,760 --> 00:33:55,360
Speaker 5: But I guess generally speaking, it depends on the size

732
00:33:55,400 --> 00:33:57,520
Speaker 5: of the thing in the middle, Like the Sun has

733
00:33:57,520 --> 00:34:00,640
Speaker 5: a very big roach limit and the Earth as a

734
00:34:00,640 --> 00:34:01,160
Speaker 5: smaller one.

735
00:34:01,240 --> 00:34:03,320
Speaker 1: Yeah, that's true. You can get closer to the Earth

736
00:34:03,600 --> 00:34:05,360
Speaker 1: than you can get to the Sun. But if you

737
00:34:05,400 --> 00:34:08,000
Speaker 1: see a moon around a planet and it's orbiting in

738
00:34:08,080 --> 00:34:11,560
Speaker 1: a circular orbit and it mostly has the same angular

739
00:34:11,640 --> 00:34:14,680
Speaker 1: momentum as the planet, then you suspect that probably it

740
00:34:14,719 --> 00:34:17,239
Speaker 1: came from the same stuff that made the planet, and

741
00:34:17,280 --> 00:34:19,799
Speaker 1: when that planet coalesced into stuff, not all of it

742
00:34:19,840 --> 00:34:22,360
Speaker 1: got turned into the planet, some of it got left

743
00:34:22,400 --> 00:34:25,759
Speaker 1: over and turned into a moon. So circular orbits with

744
00:34:25,840 --> 00:34:30,400
Speaker 1: the same anglarmentum probably came from the same protoplanetary disk

745
00:34:30,760 --> 00:34:31,720
Speaker 1: that formed the planet.

746
00:34:33,239 --> 00:34:36,320
Speaker 5: Okay, so then if a moon is orbiting a planet

747
00:34:36,520 --> 00:34:40,240
Speaker 5: kind of in the same plane as the planet is spinning,

748
00:34:41,000 --> 00:34:43,600
Speaker 5: then most likely they are like siblings, kind of like

749
00:34:43,600 --> 00:34:46,440
Speaker 5: they were born at the same time from the same stuff.

750
00:34:47,080 --> 00:34:49,680
Speaker 1: Yeah, I suppose you could say so, though it's sort

751
00:34:49,719 --> 00:34:51,839
Speaker 1: of the scenario where like one twin is really big

752
00:34:51,880 --> 00:34:52,880
Speaker 1: and the other one is tiny.

753
00:34:53,000 --> 00:34:54,640
Speaker 5: Yeah, they're fraternal twins.

754
00:34:55,719 --> 00:34:58,279
Speaker 1: Exactly, and probably one's pretty grumpy about not getting as

755
00:34:58,360 --> 00:34:59,200
Speaker 1: much of dinner.

756
00:34:59,000 --> 00:35:01,480
Speaker 5: All right, So that's one way maybe a moon can form,

757
00:35:01,719 --> 00:35:04,120
Speaker 5: which is like it's borne along with the planet, and

758
00:35:04,200 --> 00:35:06,480
Speaker 5: you can sort of tell which ones those are, Which

759
00:35:06,520 --> 00:35:08,680
Speaker 5: of those do we have in our Solar system, Like,

760
00:35:08,800 --> 00:35:09,839
Speaker 5: is our moon one of them?

761
00:35:09,920 --> 00:35:12,200
Speaker 1: Our moon is not one of those. Our moon is

762
00:35:12,200 --> 00:35:14,640
Speaker 1: actually a very weird case. Most of the moons in

763
00:35:14,640 --> 00:35:17,120
Speaker 1: the Solar System do not have nice circular orbits that

764
00:35:17,160 --> 00:35:19,279
Speaker 1: are orbiting with the planets. In fact, most of them

765
00:35:19,600 --> 00:35:23,040
Speaker 1: have elliptical orbits that have weird tilts, And that suggests

766
00:35:23,040 --> 00:35:24,720
Speaker 1: a completely different history for how.

767
00:35:24,600 --> 00:35:27,960
Speaker 5: That moon formed, necessarily, because like I wonder if maybe

768
00:35:28,160 --> 00:35:30,000
Speaker 5: the moon was formed as a sibling, but then it

769
00:35:30,080 --> 00:35:34,759
Speaker 5: got not by something and then it got a skewed orbit.

770
00:35:34,840 --> 00:35:37,480
Speaker 1: Yeah, that's certainly possible, but we think that most of

771
00:35:37,520 --> 00:35:40,680
Speaker 1: the ones with skewed orbits, that with tilted orbits that precess,

772
00:35:40,719 --> 00:35:44,920
Speaker 1: for example, are probably captured objects, things that came nearby

773
00:35:45,040 --> 00:35:47,880
Speaker 1: and were grabbed onto by the gravity of that planet.

774
00:35:48,000 --> 00:35:50,000
Speaker 1: You're right, it's possible for moon to be formed with

775
00:35:50,000 --> 00:35:52,160
Speaker 1: the planet and then get tilted through a collision. You

776
00:35:52,200 --> 00:35:54,120
Speaker 1: can tell the difference by looking at what that moon

777
00:35:54,200 --> 00:35:56,040
Speaker 1: is made out of. Is it made out of basically

778
00:35:56,040 --> 00:35:58,719
Speaker 1: the same stuff that formed the planet, or is it

779
00:35:58,719 --> 00:36:01,239
Speaker 1: made out of something totally weird and different. So that's

780
00:36:01,239 --> 00:36:04,080
Speaker 1: sort of like the key piece of information for distinguishing.

781
00:36:03,680 --> 00:36:06,600
Speaker 5: Like a DNA test prove of your siblings are not

782
00:36:07,520 --> 00:36:10,240
Speaker 5: all right. Well, then what does not having a circular

783
00:36:10,360 --> 00:36:11,839
Speaker 5: orbit tell you about the moon.

784
00:36:12,000 --> 00:36:14,560
Speaker 1: It tells you that probably it was captured that the

785
00:36:14,600 --> 00:36:17,640
Speaker 1: planet formed, and the Moon comes from somewhere else. It's

786
00:36:17,680 --> 00:36:20,879
Speaker 1: like an asteroid or a dwarf planet or something that

787
00:36:20,960 --> 00:36:23,200
Speaker 1: was floating around and just came too close to this

788
00:36:23,280 --> 00:36:26,600
Speaker 1: massive object and its gravity took over. There's a vicinity

789
00:36:26,640 --> 00:36:29,000
Speaker 1: of a massive object we call the hill sphere, which

790
00:36:29,040 --> 00:36:31,920
Speaker 1: is the region sort of where its gravity dominates where

791
00:36:31,960 --> 00:36:35,040
Speaker 1: everything else that's far away can basically be neglected, and

792
00:36:35,080 --> 00:36:37,960
Speaker 1: if an object passes within the hillsphere, it's a candidate

793
00:36:38,160 --> 00:36:39,280
Speaker 1: for getting captured.

794
00:36:39,440 --> 00:36:41,960
Speaker 5: But isn't that kind of weird? Or isn't it kind

795
00:36:41,960 --> 00:36:44,279
Speaker 5: of unlikely that you'll just kind of catch a big

796
00:36:44,400 --> 00:36:46,560
Speaker 5: rock out there and it'll have just the right speed

797
00:36:46,600 --> 00:36:49,359
Speaker 5: and distance to fall into a stable orbit, Like, aren't

798
00:36:49,400 --> 00:36:51,759
Speaker 5: stable orbits kind of hard to get into?

799
00:36:52,000 --> 00:36:54,279
Speaker 1: It is unlikely and it is weird. You're right. You

800
00:36:54,280 --> 00:36:56,960
Speaker 1: have to match the radius and the velocity. Like the

801
00:36:57,040 --> 00:36:59,520
Speaker 1: reason the Earth is in a stable orbit is because

802
00:36:59,560 --> 00:37:02,160
Speaker 1: it has the right velocity for our radius. You have

803
00:37:02,160 --> 00:37:04,600
Speaker 1: to be moving in a certain velocity at a given radius.

804
00:37:04,719 --> 00:37:06,680
Speaker 5: Like if we slowed down at all in our orbit,

805
00:37:06,719 --> 00:37:08,600
Speaker 5: we would start to spiral into the Sun.

806
00:37:08,719 --> 00:37:11,640
Speaker 1: Right first orbit is actually quasi stable, so if we

807
00:37:11,719 --> 00:37:14,680
Speaker 1: slowed down a little bit, gravitational forces would actually push

808
00:37:14,760 --> 00:37:17,360
Speaker 1: us back towards our orbit. But that's a whole other topic.

809
00:37:17,719 --> 00:37:20,000
Speaker 5: Like if you slow down a lot, though, yes.

810
00:37:19,800 --> 00:37:21,239
Speaker 1: If we slow down a lot, we would fall in

811
00:37:21,239 --> 00:37:23,160
Speaker 1: towards the Sun. If we sped up a bunch, we

812
00:37:23,200 --> 00:37:25,920
Speaker 1: would be ejected from the Solar system. And so you

813
00:37:26,040 --> 00:37:28,880
Speaker 1: have to have this match between these two quantities, and

814
00:37:29,080 --> 00:37:31,200
Speaker 1: it's not trivial for that to happen. Not only do

815
00:37:31,280 --> 00:37:33,160
Speaker 1: you have to have the right velocity and the right radius,

816
00:37:33,200 --> 00:37:35,480
Speaker 1: but you also have to lose energy in order to

817
00:37:35,480 --> 00:37:37,920
Speaker 1: fall into an orbit. Any object that falls into the

818
00:37:37,960 --> 00:37:41,680
Speaker 1: Solar System by definition has enough energy to escape because

819
00:37:41,719 --> 00:37:44,239
Speaker 1: it came from outside the Solar System. And so if

820
00:37:44,239 --> 00:37:47,319
Speaker 1: it just passes through on like a hyperbolic trajectory, you

821
00:37:47,480 --> 00:37:49,960
Speaker 1: know it has enough kinetic energy to climb out of

822
00:37:49,960 --> 00:37:52,600
Speaker 1: the gravitational well of the Solar System because it came

823
00:37:52,840 --> 00:37:55,560
Speaker 1: from outside the gravitational well. So in order to get captured,

824
00:37:55,600 --> 00:37:57,040
Speaker 1: it not only does it have to come in at

825
00:37:57,040 --> 00:37:59,600
Speaker 1: the right radius and the right velocity, got to lose

826
00:37:59,640 --> 00:38:02,359
Speaker 1: a little bit of energy so that no longer has

827
00:38:02,400 --> 00:38:04,560
Speaker 1: the energy to escape. That can happen if you like

828
00:38:04,880 --> 00:38:07,239
Speaker 1: drag on the atmosphere the planet a little bit, which

829
00:38:07,320 --> 00:38:09,520
Speaker 1: gives you a little bit of friction, or maybe another

830
00:38:09,600 --> 00:38:12,200
Speaker 1: moon steals a little bit of your energy. So like,

831
00:38:12,280 --> 00:38:14,879
Speaker 1: the more moons you have and the puffier your atmosphere,

832
00:38:15,000 --> 00:38:17,360
Speaker 1: the more likely you are to be able to capture

833
00:38:17,400 --> 00:38:18,880
Speaker 1: an object that comes near you.

834
00:38:20,360 --> 00:38:23,320
Speaker 5: It's kind of interesting to think of this idea the planets,

835
00:38:23,360 --> 00:38:25,839
Speaker 5: like the Earth has a kind of a halo, kind

836
00:38:25,840 --> 00:38:28,320
Speaker 5: of right, like a big sphere around it. It's basically

837
00:38:28,360 --> 00:38:31,080
Speaker 5: like a giant net like it. Whatever falls into it,

838
00:38:31,080 --> 00:38:32,680
Speaker 5: it's gonna get sucked in.

839
00:38:32,840 --> 00:38:34,640
Speaker 1: Yeah, exactly. And if you fall in too far and

840
00:38:34,640 --> 00:38:36,400
Speaker 1: you slow don too far, then of course you're going

841
00:38:36,480 --> 00:38:39,000
Speaker 1: to burn up as you enter the atmosphere. So it's

842
00:38:39,040 --> 00:38:42,280
Speaker 1: a delicate operation. Physicists also think that sometimes a pair

843
00:38:42,320 --> 00:38:44,920
Speaker 1: of objects that are orbiting each other can fall in

844
00:38:44,960 --> 00:38:47,359
Speaker 1: the hill sphere and then one of them can get

845
00:38:47,360 --> 00:38:49,839
Speaker 1: captured and the other one can get ejected. So all

846
00:38:49,840 --> 00:38:52,239
Speaker 1: these sort of complicated things have to go just right

847
00:38:52,640 --> 00:38:54,799
Speaker 1: in order for a planet to capture a moon.

848
00:38:55,640 --> 00:38:58,960
Speaker 5: And by capturing, that's a nice word for stealing, right right,

849
00:38:59,480 --> 00:38:59,920
Speaker 5: you're like.

850
00:39:01,960 --> 00:39:04,160
Speaker 1: You're dancing, you're dancing with them. How of that?

851
00:39:04,320 --> 00:39:07,399
Speaker 5: Oh, I see see? Is that where that listener who

852
00:39:07,760 --> 00:39:10,120
Speaker 5: mentioned earlier that maybe we got our moon by stealing

853
00:39:10,200 --> 00:39:12,600
Speaker 5: it from Venus? Is that? Is there some truth to that?

854
00:39:13,400 --> 00:39:16,320
Speaker 1: We don't think that our moon was stolen from Venus,

855
00:39:16,320 --> 00:39:17,800
Speaker 1: but we do think that lots of the moons of

856
00:39:17,920 --> 00:39:20,360
Speaker 1: Jupiter and Saturn, for example, and these guys have like

857
00:39:20,440 --> 00:39:24,279
Speaker 1: dozens of moons come from scattered objects in the early

858
00:39:24,320 --> 00:39:27,640
Speaker 1: Solar system. Remember that very early on things were forming.

859
00:39:27,840 --> 00:39:30,000
Speaker 1: There may even have been more planets than the ones

860
00:39:30,040 --> 00:39:33,520
Speaker 1: we have now, and everything was quite chaotic. So now

861
00:39:33,520 --> 00:39:36,000
Speaker 1: we have sort of an orderly solar system where everything

862
00:39:36,080 --> 00:39:38,720
Speaker 1: is in place because it's been in place for so long,

863
00:39:39,160 --> 00:39:41,400
Speaker 1: and things that were not in place have been lost

864
00:39:41,480 --> 00:39:43,719
Speaker 1: or captured or fallen into the Sun. But in the

865
00:39:43,760 --> 00:39:45,680
Speaker 1: early days there were a lot of things going in

866
00:39:45,760 --> 00:39:48,920
Speaker 1: crazy orbits and crazy trajectories, and so Jupiter and Saturn

867
00:39:49,040 --> 00:39:50,719
Speaker 1: sort of like hoovered up a bunch of them.

868
00:39:51,000 --> 00:39:52,960
Speaker 5: So like, if you look at the moons of Jupiter,

869
00:39:53,000 --> 00:39:55,000
Speaker 5: for example, they're not all going to be like lined

870
00:39:55,080 --> 00:39:57,640
Speaker 5: up in a plane like our solar system. They probably

871
00:39:57,680 --> 00:40:00,000
Speaker 5: all have like crazy orbits around Jupiter.

872
00:40:00,160 --> 00:40:02,440
Speaker 1: Right, Yeah, that's exactly right, And that's why we think

873
00:40:02,440 --> 00:40:04,800
Speaker 1: that most of these were captured. Also, in the cases

874
00:40:04,800 --> 00:40:06,640
Speaker 1: that we've been able to try to study what these

875
00:40:06,680 --> 00:40:08,680
Speaker 1: moons are made out of, they're all made out of

876
00:40:08,719 --> 00:40:10,799
Speaker 1: totally different things, and so it doesn't look like they

877
00:40:10,920 --> 00:40:13,320
Speaker 1: formed from the same sort of scoop of Solar system

878
00:40:13,360 --> 00:40:15,319
Speaker 1: stuff that Jupiter did.

879
00:40:15,760 --> 00:40:17,360
Speaker 5: That's what you were saying, Like you can check the

880
00:40:17,440 --> 00:40:20,160
Speaker 5: DNA basically the DNA of the moon and the planet

881
00:40:20,200 --> 00:40:22,000
Speaker 5: to see if they came from the same stuff, and

882
00:40:22,080 --> 00:40:23,520
Speaker 5: sometimes they don't, right.

883
00:40:24,080 --> 00:40:26,520
Speaker 1: Yeah, exactly. That's still tricky to do because we haven't

884
00:40:26,640 --> 00:40:29,279
Speaker 1: landed on those moons and like really taken samples that

885
00:40:29,280 --> 00:40:32,040
Speaker 1: we can study. But we can like do spectroscopy. We

886
00:40:32,040 --> 00:40:34,040
Speaker 1: can see the light that bounces off of them, we

887
00:40:34,080 --> 00:40:36,680
Speaker 1: can see what they emit these kind of things. We

888
00:40:36,719 --> 00:40:39,080
Speaker 1: have done some flybys, and so we have ideas for

889
00:40:39,160 --> 00:40:41,160
Speaker 1: what these moons are probably made out of.

890
00:40:42,520 --> 00:40:44,960
Speaker 5: And in the early Solar System, like you said, things

891
00:40:45,000 --> 00:40:47,799
Speaker 5: were like there were probably like rock giant rocks flying

892
00:40:47,840 --> 00:40:50,719
Speaker 5: all over the place, and so it wouldn't be that

893
00:40:50,800 --> 00:40:53,840
Speaker 5: weird for some of them to fall into orbit around

894
00:40:54,040 --> 00:40:56,399
Speaker 5: like a passing Jupiter or Center. So is that how

895
00:40:56,440 --> 00:40:58,440
Speaker 5: we got our moon? Did we capture it or steal

896
00:40:58,440 --> 00:40:59,080
Speaker 5: it from somebody?

897
00:40:59,120 --> 00:41:01,040
Speaker 1: So we think our moon is unusual because it doesn't

898
00:41:01,080 --> 00:41:04,120
Speaker 1: fall into either of these categories. We don't think that

899
00:41:04,160 --> 00:41:06,480
Speaker 1: the Moon was formed with the Earth. We also don't

900
00:41:06,520 --> 00:41:10,200
Speaker 1: think that a wholly formed moon was captured by the Earth. Instead,

901
00:41:10,280 --> 00:41:12,680
Speaker 1: we think it comes from a collision. We think that

902
00:41:12,719 --> 00:41:15,920
Speaker 1: there was the proto Earth, this early planet, and then

903
00:41:15,920 --> 00:41:19,080
Speaker 1: there was another Mars like planet that came by and

904
00:41:19,200 --> 00:41:22,920
Speaker 1: smashed into the Earth, and there was this incredible collision

905
00:41:23,120 --> 00:41:25,880
Speaker 1: where essentially these two planets merged, but they left a

906
00:41:26,000 --> 00:41:29,800
Speaker 1: huge debris ring, and then that debris ring pulled together

907
00:41:30,080 --> 00:41:30,919
Speaker 1: and made the Moon.

908
00:41:31,160 --> 00:41:34,160
Speaker 5: Does our moon have an orbit that's around our equator

909
00:41:34,320 --> 00:41:35,080
Speaker 5: or is it tilted?

910
00:41:35,200 --> 00:41:37,440
Speaker 1: The Moon doesn't have a totally random orbit relative to

911
00:41:37,440 --> 00:41:40,000
Speaker 1: the angular momentum of the Earth, because the two objects

912
00:41:40,040 --> 00:41:43,280
Speaker 1: are essentially formed by the combined angular momentum of this collision.

913
00:41:43,840 --> 00:41:46,520
Speaker 1: So you get this collision and basically you start from scratch.

914
00:41:46,560 --> 00:41:48,839
Speaker 1: You have a new blob of stuff which is then

915
00:41:48,920 --> 00:41:51,799
Speaker 1: going to coalesce again into a planet and a moon.

916
00:41:51,840 --> 00:41:54,040
Speaker 1: And so there is a relationship of course between the

917
00:41:54,080 --> 00:41:56,960
Speaker 1: Earth's spin and the Moon's orbit, and that's because they

918
00:41:56,960 --> 00:41:59,960
Speaker 1: come from this combined blob from this colison.

919
00:42:00,280 --> 00:42:02,440
Speaker 5: It's pretty dramatic. I think you can look up videos

920
00:42:02,440 --> 00:42:05,360
Speaker 5: of simulations of it online. It's like the Earth, the

921
00:42:05,400 --> 00:42:07,880
Speaker 5: pro too Earth before Earth was just hanging out and

922
00:42:07,920 --> 00:42:10,640
Speaker 5: then this giant rock just slams into it. It all

923
00:42:10,880 --> 00:42:13,960
Speaker 5: sort of explodes together, but then gravity pulls it back together.

924
00:42:14,040 --> 00:42:16,120
Speaker 5: Into Earth and the Moon exactly.

925
00:42:16,160 --> 00:42:18,600
Speaker 1: And the early Moon, we think, was much much closer

926
00:42:18,600 --> 00:42:21,600
Speaker 1: to the Earth, something like a tenth of its current orbit,

927
00:42:21,960 --> 00:42:24,960
Speaker 1: and then over time it spirals out and ends up

928
00:42:25,000 --> 00:42:27,520
Speaker 1: becoming tightly locked to the Earth. One reason we think

929
00:42:27,560 --> 00:42:29,120
Speaker 1: this is that we've been to the Moon and we've

930
00:42:29,120 --> 00:42:31,239
Speaker 1: been able to land on it and study what it's

931
00:42:31,280 --> 00:42:33,560
Speaker 1: made out of, and we see that it's made out

932
00:42:33,560 --> 00:42:35,480
Speaker 1: of a lot of stuff that's very very similar to

933
00:42:35,520 --> 00:42:37,640
Speaker 1: what the Earth is made out of, which suggests that

934
00:42:37,680 --> 00:42:39,640
Speaker 1: they do have some sort of common origin.

935
00:42:40,719 --> 00:42:43,800
Speaker 5: And does the Earth also sort of have moon like

936
00:42:44,280 --> 00:42:46,360
Speaker 5: materials in it that are not like the rest of

937
00:42:46,400 --> 00:42:46,719
Speaker 5: the Earth.

938
00:42:46,840 --> 00:42:48,360
Speaker 1: Well, we see that the Earth and the Moon have

939
00:42:48,400 --> 00:42:50,719
Speaker 1: a lot of very similar elements, which suggests they all

940
00:42:50,719 --> 00:42:53,320
Speaker 1: came from the same stuff, But the Moon has fewer

941
00:42:53,360 --> 00:42:56,400
Speaker 1: of like volatile elements. Things that vaporize at low temperatures

942
00:42:56,440 --> 00:42:59,359
Speaker 1: were probably lost in this high energy event, and the

943
00:42:59,360 --> 00:43:01,799
Speaker 1: Moon has small or gravity, and so it's not able

944
00:43:01,800 --> 00:43:04,040
Speaker 1: to recapture these things the way the Earth did, so

945
00:43:04,080 --> 00:43:06,359
Speaker 1: the Earth and the Moon don't have exactly the same

946
00:43:06,480 --> 00:43:08,400
Speaker 1: kinds of stuff. The Moon also has a sort of

947
00:43:08,400 --> 00:43:12,319
Speaker 1: surprisingly small iron core, which overall makes the Moon have

948
00:43:12,440 --> 00:43:15,160
Speaker 1: lower density, and simulations confirm that this is what you

949
00:43:15,160 --> 00:43:17,640
Speaker 1: would expect from this kind of collision, that the Moon

950
00:43:17,760 --> 00:43:20,440
Speaker 1: was formed more out of the sort of external debris

951
00:43:20,480 --> 00:43:22,839
Speaker 1: and the Earth sort of got a bigger sampling of

952
00:43:22,880 --> 00:43:23,760
Speaker 1: the core stuff.

953
00:43:24,719 --> 00:43:26,880
Speaker 5: I guess the Moon is also smaller, so it doesn't

954
00:43:26,880 --> 00:43:31,000
Speaker 5: have as much gravity compressing it, right, making it denser exactly.

955
00:43:31,400 --> 00:43:33,279
Speaker 1: And when they study like what's inside the Moon, they

956
00:43:33,320 --> 00:43:36,440
Speaker 1: find samples that suggest the Moon was molten down to

957
00:43:36,520 --> 00:43:39,640
Speaker 1: like a surprising depth. And you don't expect the small

958
00:43:39,719 --> 00:43:42,560
Speaker 1: body like the Moon to have the gravitational pressure to

959
00:43:42,760 --> 00:43:45,319
Speaker 1: like melt its inerts the way the Earth does. So

960
00:43:45,360 --> 00:43:47,480
Speaker 1: they think that the Moon was probably molten because of

961
00:43:47,520 --> 00:43:50,160
Speaker 1: this collision, not because of its like gravitational pressure.

962
00:43:50,560 --> 00:43:50,920
Speaker 4: Hmm.

963
00:43:51,080 --> 00:43:54,080
Speaker 5: Interesting. And I think they also found like the same

964
00:43:54,320 --> 00:43:57,080
Speaker 5: cheese inside of the Moon as some of the cheese

965
00:43:57,080 --> 00:44:01,480
Speaker 5: we have on Earth too, right, that's part of the.

966
00:44:02,440 --> 00:44:04,960
Speaker 1: Yeah, they found pan pizzas rejected on the surface of

967
00:44:05,000 --> 00:44:06,240
Speaker 1: the Moon that nobody could.

968
00:44:06,000 --> 00:44:09,600
Speaker 5: Eat, that's right, the same mozzarella, cheese, the same cows,

969
00:44:09,680 --> 00:44:13,400
Speaker 5: even space cows. All right, well, that's the origin of

970
00:44:13,440 --> 00:44:16,040
Speaker 5: our moon. Let's get a little bit into what that

971
00:44:16,160 --> 00:44:20,440
Speaker 5: means about the formation of all moons and the formation

972
00:44:20,520 --> 00:44:23,399
Speaker 5: of our whole solar system. Why we're here and why

973
00:44:23,440 --> 00:44:25,680
Speaker 5: are things the way they are. First, let's take another

974
00:44:25,800 --> 00:44:26,280
Speaker 5: quick break.

975
00:44:30,440 --> 00:44:32,239
Speaker 1: When you pop a piece of cheese into your mouth

976
00:44:32,360 --> 00:44:35,480
Speaker 1: or enjoy a rich spoonful of Greek yogurt, you're probably

977
00:44:35,560 --> 00:44:39,560
Speaker 1: not thinking about the environmental impact of each and every bite,

978
00:44:39,640 --> 00:44:42,240
Speaker 1: But the people in the dairy industry are. US Dairy

979
00:44:42,280 --> 00:44:46,560
Speaker 1: has set themselves some ambitious sustainability goals, including being greenhouse

980
00:44:46,600 --> 00:44:49,160
Speaker 1: gas neutral by twenty to fifty That's why they're working

981
00:44:49,200 --> 00:44:51,520
Speaker 1: hard every day to find new ways to reduce waste,

982
00:44:51,600 --> 00:44:55,839
Speaker 1: conserve natural resources, and drive down greenhouse gas emissions. Take water,

983
00:44:55,880 --> 00:44:59,440
Speaker 1: for example, most dairy farms reuse water up to four times.

984
00:44:59,520 --> 00:45:02,880
Speaker 1: The same water cools the milk, cleans equipment, washes the barn,

985
00:45:03,000 --> 00:45:06,720
Speaker 1: and irrigates the crops. How is US dairy tackling greenhouse gases?

986
00:45:06,760 --> 00:45:09,759
Speaker 1: Many farms use anaerobic digestors that turn the methane from

987
00:45:09,760 --> 00:45:13,160
Speaker 1: maneuver into renewable energy that can power farms, towns, and

988
00:45:13,200 --> 00:45:15,439
Speaker 1: electric cars. So the next time you grab a slice

989
00:45:15,440 --> 00:45:17,320
Speaker 1: of pizza or lick an ice cream cone, know that

990
00:45:17,400 --> 00:45:20,080
Speaker 1: dairy farmers and processors around the country are using the

991
00:45:20,160 --> 00:45:23,920
Speaker 1: latest practices and innovations to provide the nutrient dense dairy

992
00:45:23,920 --> 00:45:26,600
Speaker 1: products we love with less of an impact. Visit us

993
00:45:26,680 --> 00:45:29,200
Speaker 1: dairy dot com slash sustainability to learn more.

994
00:45:30,239 --> 00:45:33,760
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995
00:45:33,760 --> 00:45:36,160
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996
00:45:36,200 --> 00:45:36,960
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997
00:45:36,920 --> 00:45:37,720
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998
00:45:37,920 --> 00:45:40,880
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999
00:45:41,000 --> 00:45:44,880
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1000
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1035
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Speaker 5: All Right, we are coming face to face with the

1036
00:47:39,440 --> 00:47:43,360
Speaker 5: lunacy here in the podcast talking about the origin of moons,

1037
00:47:43,880 --> 00:47:46,880
Speaker 5: and in particular our moon. You're saying, it's interesting because,

1038
00:47:47,160 --> 00:47:49,279
Speaker 5: like our moon is sort of a combination of how

1039
00:47:49,360 --> 00:47:51,960
Speaker 5: some of these other moons can form. Right, Like, we

1040
00:47:52,000 --> 00:47:54,480
Speaker 5: had a proto planet Earth, and when there was a

1041
00:47:54,560 --> 00:47:58,600
Speaker 5: visitor that was flying around came neros, it sort of

1042
00:47:58,640 --> 00:48:00,920
Speaker 5: got captured or collide with our Earth, and then it

1043
00:48:00,960 --> 00:48:03,080
Speaker 5: all became a big mess. And out of that mess,

1044
00:48:03,719 --> 00:48:05,800
Speaker 5: you know, the Earth and the Moon form sort of

1045
00:48:05,800 --> 00:48:09,839
Speaker 5: a siblings, but also not siblings, because there was it

1046
00:48:09,880 --> 00:48:12,440
Speaker 5: came from a different planet. The stuff.

1047
00:48:12,560 --> 00:48:14,920
Speaker 1: There was a big fight early on, and we were

1048
00:48:15,000 --> 00:48:17,719
Speaker 1: left over cleaning up the mess. Yeah, it is really fascinating,

1049
00:48:17,760 --> 00:48:20,800
Speaker 1: and I love this sort of archaeology, this like detective story,

1050
00:48:20,840 --> 00:48:24,759
Speaker 1: figuring out what happened billions of years ago, reconstructing the

1051
00:48:24,840 --> 00:48:27,040
Speaker 1: story from the clues that are left behind, These really

1052
00:48:27,080 --> 00:48:29,440
Speaker 1: subtle hints. You know, why does the Moon seem to

1053
00:48:29,520 --> 00:48:31,080
Speaker 1: be made of the same stuff as the Earth, but

1054
00:48:31,120 --> 00:48:33,560
Speaker 1: it doesn't have sort of a close circular orbit the

1055
00:48:33,560 --> 00:48:35,920
Speaker 1: way you would expect. Why exactly is it so big?

1056
00:48:36,160 --> 00:48:39,160
Speaker 1: These stories are really fascinating because we missed so much

1057
00:48:39,160 --> 00:48:41,440
Speaker 1: of the Solar System history. You know, like billions of

1058
00:48:41,560 --> 00:48:44,879
Speaker 1: years happened with crazy fireworks in the sky and we

1059
00:48:44,880 --> 00:48:46,959
Speaker 1: weren't here to look at it. But we can still

1060
00:48:46,960 --> 00:48:48,240
Speaker 1: get hints about what happened.

1061
00:48:48,480 --> 00:48:48,800
Speaker 9: Mmm.

1062
00:48:49,160 --> 00:48:51,160
Speaker 5: Do you think that's an official job title out there,

1063
00:48:51,200 --> 00:48:53,360
Speaker 5: like space archaeologists.

1064
00:48:54,200 --> 00:48:57,520
Speaker 1: Space murder mystery, you know, exactly.

1065
00:48:57,200 --> 00:49:01,000
Speaker 5: Give me like Indiana solo combination of Janna Jones and

1066
00:49:01,080 --> 00:49:01,640
Speaker 5: hand solo.

1067
00:49:03,040 --> 00:49:05,759
Speaker 1: And you know, we're still learning stuff about moons, like

1068
00:49:06,000 --> 00:49:09,160
Speaker 1: Mars has some funny moons, Phobos and Demos, and the

1069
00:49:09,200 --> 00:49:12,759
Speaker 1: smaller of those two moons, Demos, is really tiny. It's

1070
00:49:12,800 --> 00:49:16,240
Speaker 1: only like nine miles across, has a really weird short

1071
00:49:16,239 --> 00:49:18,560
Speaker 1: of blobby shape to it, and for a long time

1072
00:49:18,600 --> 00:49:21,680
Speaker 1: people thought it was probably a captured asteroid because of

1073
00:49:21,719 --> 00:49:24,799
Speaker 1: its orbit, but they recently send an orbiter very very

1074
00:49:24,800 --> 00:49:27,600
Speaker 1: close to it, super close approach by this spacecraft from

1075
00:49:27,600 --> 00:49:30,239
Speaker 1: the UA Emirates. Actually it's called Hope, and they were

1076
00:49:30,280 --> 00:49:32,680
Speaker 1: able to study what it's made out of and discover

1077
00:49:32,840 --> 00:49:35,839
Speaker 1: that it has sort of the same carbon and organics

1078
00:49:35,880 --> 00:49:39,120
Speaker 1: that Mars does, unlike the asteroids, sort of like the

1079
00:49:39,239 --> 00:49:42,040
Speaker 1: DNA test you were saying before, which means that Demos

1080
00:49:42,120 --> 00:49:46,040
Speaker 1: probably is a chunk of Mars that got blown off

1081
00:49:46,160 --> 00:49:47,920
Speaker 1: in some sort of prehistoric collision.

1082
00:49:48,040 --> 00:49:49,840
Speaker 5: Isn't that also kind of the theory of how we

1083
00:49:49,880 --> 00:49:52,800
Speaker 5: got life on Earth like a possible way, and maybe

1084
00:49:52,840 --> 00:49:54,960
Speaker 5: Mars got hit by something. It threw a bunch of

1085
00:49:55,040 --> 00:49:57,719
Speaker 5: rocks out into space. Some of them became Demos, the

1086
00:49:57,760 --> 00:49:59,759
Speaker 5: moon of Mars, and maybe some of them came to

1087
00:49:59,800 --> 00:50:01,680
Speaker 5: Earth bringing like little bacteria.

1088
00:50:01,719 --> 00:50:05,320
Speaker 1: Perhaps we're very sure that rocks from Mars have landed

1089
00:50:05,320 --> 00:50:07,720
Speaker 1: on Earth. We have found them and their geology matches

1090
00:50:07,800 --> 00:50:10,560
Speaker 1: Mars and doesn't match Earth. So there's no controversy about

1091
00:50:10,600 --> 00:50:14,399
Speaker 1: whether collisions from asteroids on planets can knock stuff off

1092
00:50:14,440 --> 00:50:16,760
Speaker 1: into outer space and have it land on other planets.

1093
00:50:16,840 --> 00:50:19,520
Speaker 1: Whether there's life in those rocks that then seeded life

1094
00:50:19,600 --> 00:50:23,560
Speaker 1: on Earth totally open question. There was this famous misdiscovery

1095
00:50:23,840 --> 00:50:26,399
Speaker 1: about twenty years ago when they found these weird little

1096
00:50:26,440 --> 00:50:29,399
Speaker 1: shapes inside a Martian rock on Earth, and they made

1097
00:50:29,400 --> 00:50:31,759
Speaker 1: this announcement that they were certain that there was life

1098
00:50:31,760 --> 00:50:34,480
Speaker 1: in them that these shapes could only be made by life,

1099
00:50:34,600 --> 00:50:37,359
Speaker 1: But then later analysis demonstrated that you could make those

1100
00:50:37,400 --> 00:50:40,839
Speaker 1: things without life. So there's no concrete proof that life

1101
00:50:40,880 --> 00:50:44,320
Speaker 1: has traveled between planets on an asteroid, but it's totally

1102
00:50:44,360 --> 00:50:47,239
Speaker 1: possible for it to happen. And Demos definitely is a

1103
00:50:47,360 --> 00:50:50,080
Speaker 1: chunk of Mars floating in space. Sort of like if

1104
00:50:50,120 --> 00:50:52,400
Speaker 1: you went out into space and you found like Manhattan

1105
00:50:52,680 --> 00:50:55,160
Speaker 1: floating out in space, you'd be like, WHOA, where'd this

1106
00:50:55,239 --> 00:50:55,680
Speaker 1: come from?

1107
00:50:55,960 --> 00:50:57,360
Speaker 5: Yeah? Well people wonder about that.

1108
00:50:58,040 --> 00:51:02,319
Speaker 1: Now, what's theory? How to Manhattan get so weird?

1109
00:51:02,320 --> 00:51:05,239
Speaker 5: Where did New Yorkers come from their lunatics?

1110
00:51:05,320 --> 00:51:07,759
Speaker 1: But they have the best pizza, right, so I don't

1111
00:51:07,800 --> 00:51:08,960
Speaker 1: want to have to go out of space to get

1112
00:51:09,000 --> 00:51:10,920
Speaker 1: my pizza.

1113
00:51:11,600 --> 00:51:14,279
Speaker 5: You just insulted everyone in Chicago. You lost a big

1114
00:51:14,360 --> 00:51:15,400
Speaker 5: chunk of our listenership.

1115
00:51:15,520 --> 00:51:17,960
Speaker 1: I love Chicago. I love Chicago Wins, and I love

1116
00:51:18,000 --> 00:51:20,640
Speaker 1: the Chicago Wins, love Chicago pizza. That's all fine with me,

1117
00:51:20,880 --> 00:51:21,239
Speaker 1: all right?

1118
00:51:21,280 --> 00:51:23,640
Speaker 5: Well, what does all of this tells about the formation

1119
00:51:23,760 --> 00:51:25,920
Speaker 5: of the Solar System and like how we ended up

1120
00:51:26,160 --> 00:51:27,640
Speaker 5: where we are and how we are.

1121
00:51:27,880 --> 00:51:30,120
Speaker 1: It's a story that we are still unraveling, right, we're

1122
00:51:30,160 --> 00:51:32,640
Speaker 1: still learning about our moon, We're still learning about our

1123
00:51:32,680 --> 00:51:37,720
Speaker 1: neighbors moons. We're still discovering moons. Right, Saturn recently past Jupiter.

1124
00:51:37,800 --> 00:51:40,200
Speaker 1: I think in the number of moons that it has,

1125
00:51:40,520 --> 00:51:42,840
Speaker 1: each one tells us a little bit of the story

1126
00:51:43,000 --> 00:51:44,920
Speaker 1: of the Solar system, and what we're looking for now

1127
00:51:44,960 --> 00:51:47,920
Speaker 1: are like more details for that story. As you said earlier,

1128
00:51:47,960 --> 00:51:51,480
Speaker 1: we're asking questions like can moons have moons? A lot

1129
00:51:51,520 --> 00:51:54,120
Speaker 1: of people think that it's impossible for the same reason

1130
00:51:54,120 --> 00:51:56,440
Speaker 1: that like Mercury and Venus don't have moons from the

1131
00:51:56,480 --> 00:51:59,640
Speaker 1: tidal forces of the Sun, that Jupiter's moons probably can't

1132
00:51:59,680 --> 00:52:02,120
Speaker 1: have their our own moons because of the tidal forces

1133
00:52:02,160 --> 00:52:05,440
Speaker 1: of Jupiter. But you know, Saturn's moon Rhea probably has

1134
00:52:05,560 --> 00:52:09,040
Speaker 1: rings which even though they're disrupted by the tidle forces,

1135
00:52:09,160 --> 00:52:11,919
Speaker 1: they can still be in orbit around Rhea. And there's

1136
00:52:11,960 --> 00:52:15,000
Speaker 1: like hundreds of minor planets deep out there in the

1137
00:52:15,000 --> 00:52:17,880
Speaker 1: Solar system that do have their own moons, like Pluto.

1138
00:52:18,040 --> 00:52:20,760
Speaker 1: But beyond that, we're also looking into other solar systems

1139
00:52:20,760 --> 00:52:22,880
Speaker 1: to try to understand whether the moons that we have

1140
00:52:23,239 --> 00:52:26,799
Speaker 1: are weird or typical. Right, Like, we only so far

1141
00:52:26,960 --> 00:52:29,440
Speaker 1: have this one solar system to study at this level

1142
00:52:29,480 --> 00:52:31,600
Speaker 1: of detail. Twenty years ago, we were able to see

1143
00:52:31,640 --> 00:52:34,200
Speaker 1: planets around other stars, which tells us a lot about

1144
00:52:34,200 --> 00:52:37,000
Speaker 1: whether the planets in our solar systems are weird. Now

1145
00:52:37,000 --> 00:52:39,600
Speaker 1: we're pushing those boundaries to try to look for moons

1146
00:52:39,719 --> 00:52:43,920
Speaker 1: in other solar systems. This thing we call exo moons

1147
00:52:43,960 --> 00:52:46,239
Speaker 1: to try to discover if the distribution of moons that

1148
00:52:46,280 --> 00:52:49,360
Speaker 1: we have is strange or pretty typical in the universe.

1149
00:52:49,960 --> 00:52:52,080
Speaker 5: Well, that's wild. How are we seeing moons and other

1150
00:52:52,120 --> 00:52:55,239
Speaker 5: planets outside of our solar system? Can we see them

1151
00:52:55,360 --> 00:52:57,719
Speaker 5: or do we have to infer them from the gravity.

1152
00:52:58,000 --> 00:53:00,319
Speaker 1: So there's a few ways that we discover planet. Then

1153
00:53:00,320 --> 00:53:03,120
Speaker 1: we can try to apply those ways to discover moons.

1154
00:53:03,360 --> 00:53:06,239
Speaker 1: One of the early ways we discovered planets around other

1155
00:53:06,280 --> 00:53:10,080
Speaker 1: stars was seeing their gravitational impact on the star, and

1156
00:53:10,080 --> 00:53:12,720
Speaker 1: that would wiggle the star and cause like a change

1157
00:53:12,719 --> 00:53:15,520
Speaker 1: in the frequency of the light, this Doppler shift, and

1158
00:53:15,560 --> 00:53:17,600
Speaker 1: so we could discover that there was something pulling on

1159
00:53:17,680 --> 00:53:19,920
Speaker 1: that star. We don't think that method will work for

1160
00:53:20,000 --> 00:53:22,440
Speaker 1: discovering moons because it's really hard to distinguish. It's the

1161
00:53:22,480 --> 00:53:24,880
Speaker 1: gravitational effect of a little moon around a planet from

1162
00:53:24,920 --> 00:53:27,400
Speaker 1: the planet itself. What we do think is possible is

1163
00:53:27,440 --> 00:53:31,320
Speaker 1: the transit method is eclipse method where a planet passes

1164
00:53:31,360 --> 00:53:33,120
Speaker 1: in front of a star and dips the light that

1165
00:53:33,200 --> 00:53:35,680
Speaker 1: comes from it, And if that happens in a regular way,

1166
00:53:35,760 --> 00:53:39,040
Speaker 1: we can tell that these little microeclipses come from a planet. Well,

1167
00:53:39,040 --> 00:53:41,359
Speaker 1: if those eclipses have their own little dips in them,

1168
00:53:41,719 --> 00:53:45,160
Speaker 1: because the moon going around the planet sometimes blocks this

1169
00:53:45,320 --> 00:53:47,920
Speaker 1: life from the star and sometimes doesn't, then you can

1170
00:53:47,960 --> 00:53:54,400
Speaker 1: discover moons around those planets. So like microeclipses within microeclipses.

1171
00:53:53,560 --> 00:53:56,600
Speaker 5: Whoa exo eclipses exo exo moon eclipses.

1172
00:53:56,719 --> 00:53:59,319
Speaker 1: Yeah, they're like eclipses squared. And we don't have any

1173
00:53:59,400 --> 00:54:03,080
Speaker 1: confirm exomoons yet though there are a couple of candidates

1174
00:54:03,120 --> 00:54:06,120
Speaker 1: from the Kepler telescopes that look promising, but people can't

1175
00:54:06,200 --> 00:54:10,160
Speaker 1: yet agree whether that actually is the discovery of a moon.

1176
00:54:10,440 --> 00:54:13,600
Speaker 1: And more recently we've developed this incredible technology to do

1177
00:54:13,719 --> 00:54:17,640
Speaker 1: direct imaging of exoplanets, like telescopes that actually take pictures

1178
00:54:17,680 --> 00:54:21,239
Speaker 1: of planets around other stars. Blows my mind. I never

1179
00:54:21,239 --> 00:54:23,640
Speaker 1: thought that would be possible. A lot of it involves

1180
00:54:23,680 --> 00:54:26,239
Speaker 1: like blocking out the light from the star itself, so

1181
00:54:26,280 --> 00:54:28,480
Speaker 1: you can see the ring around it. And sometimes that

1182
00:54:28,600 --> 00:54:31,560
Speaker 1: lets us see planets being formed. So we can see,

1183
00:54:31,560 --> 00:54:34,480
Speaker 1: for example, a star with a planetary disc around it.

1184
00:54:34,600 --> 00:54:37,040
Speaker 1: And in one case we have a direct image of

1185
00:54:37,040 --> 00:54:40,560
Speaker 1: a protoplanetary disc which seems to have a planet with

1186
00:54:40,640 --> 00:54:43,359
Speaker 1: its own disc around it. So like you can see

1187
00:54:43,360 --> 00:54:45,360
Speaker 1: the planet and it's got like a bunch of stuff

1188
00:54:45,400 --> 00:54:48,120
Speaker 1: around it, and maybe that stuff will form into a moon.

1189
00:54:49,320 --> 00:54:50,520
Speaker 5: You can see the rings in it.

1190
00:54:50,680 --> 00:54:52,960
Speaker 1: Yeah, exactly, you can see this disc that's going to

1191
00:54:53,080 --> 00:54:55,640
Speaker 1: form it either into rings or moons or something.

1192
00:54:55,719 --> 00:54:57,759
Speaker 5: Yeah, it's pretty mind blowing because I wonder like if

1193
00:54:57,800 --> 00:54:59,479
Speaker 5: a lot of people know that you can actually see

1194
00:54:59,480 --> 00:55:01,719
Speaker 5: the moons of Jupiter kind of with your naked eye,

1195
00:55:01,800 --> 00:55:03,719
Speaker 5: or at least with a small telescope. You don't need

1196
00:55:03,800 --> 00:55:05,799
Speaker 5: like a super amazing telescope. You can just use something

1197
00:55:05,840 --> 00:55:07,239
Speaker 5: you can buy for your house and you can see

1198
00:55:07,280 --> 00:55:08,080
Speaker 5: the moons of Jupiter.

1199
00:55:08,160 --> 00:55:10,400
Speaker 1: Yeah, it doesn't take a fancy telescope. It was one

1200
00:55:10,440 --> 00:55:12,440
Speaker 1: of the first things that Galleys saw when he pointed

1201
00:55:12,480 --> 00:55:14,239
Speaker 1: a telescope with the sky. It was one of the

1202
00:55:14,239 --> 00:55:16,040
Speaker 1: first people to ever do this, and he saw the

1203
00:55:16,080 --> 00:55:18,080
Speaker 1: moons of Jupiter. It's not hard. You can do it,

1204
00:55:18,080 --> 00:55:20,960
Speaker 1: and it's pretty exciting to see Jupiter expand from this

1205
00:55:21,080 --> 00:55:23,239
Speaker 1: tiny dot you can see with the naked eye to

1206
00:55:23,320 --> 00:55:25,920
Speaker 1: this whole orbital system with its own dynamics.

1207
00:55:26,280 --> 00:55:29,600
Speaker 5: Hmm, pretty cool. All right. Well, one thing that's day

1208
00:55:29,640 --> 00:55:32,000
Speaker 5: announced recently is that we're sending more people to the Moon.

1209
00:55:32,160 --> 00:55:34,440
Speaker 1: That's right, if Elon Musk ever gets that starship off

1210
00:55:34,440 --> 00:55:34,840
Speaker 1: the ground.

1211
00:55:34,960 --> 00:55:37,759
Speaker 5: No, the new artem is missions right, It isn't one

1212
00:55:37,800 --> 00:55:39,359
Speaker 5: of the plants to send more people to the Moon.

1213
00:55:39,480 --> 00:55:41,480
Speaker 1: Yeah, that's exciting. It'd be cool to go back to

1214
00:55:41,480 --> 00:55:43,719
Speaker 1: the Moon. With all of our advanced technology, we can

1215
00:55:43,880 --> 00:55:46,800
Speaker 1: take more detailed measurements. We can map its magnetic field,

1216
00:55:46,840 --> 00:55:49,839
Speaker 1: we can understand its geology and its history even better. Yeah.

1217
00:55:49,840 --> 00:55:51,640
Speaker 5: I wonder why kind of pizza they would eat there though?

1218
00:55:52,320 --> 00:55:54,239
Speaker 5: It's a deep dish because but there's not much that

1219
00:55:54,320 --> 00:55:56,640
Speaker 5: much gravity, So can you have a deep dish pizza?

1220
00:55:57,400 --> 00:55:59,640
Speaker 1: Probably every pizza would rise a lot more because there

1221
00:55:59,640 --> 00:56:00,160
Speaker 1: isn't great.

1222
00:56:00,760 --> 00:56:02,879
Speaker 5: Oh my goodness, in space. Every pizza is a deep

1223
00:56:02,920 --> 00:56:05,879
Speaker 5: dish pizza. That's why you're not going to Earth Dannel.

1224
00:56:06,160 --> 00:56:09,000
Speaker 1: Or maybe astronaut pizzas just freeze dried and gross no

1225
00:56:09,040 --> 00:56:12,480
Speaker 1: matter where it comes from.

1226
00:56:12,680 --> 00:56:14,680
Speaker 5: I guess there's something one way to find out to

1227
00:56:14,719 --> 00:56:18,239
Speaker 5: take the podcast to space. All right, Well that kind

1228
00:56:18,239 --> 00:56:20,919
Speaker 5: of answers our question. How the Moon's form basically two

1229
00:56:20,960 --> 00:56:24,800
Speaker 5: main ways, right, They either capture something flying by in space,

1230
00:56:25,040 --> 00:56:27,920
Speaker 5: or they form together with the planet, or some combination

1231
00:56:28,000 --> 00:56:31,759
Speaker 5: of the tube where something comes from space crashes into you,

1232
00:56:32,000 --> 00:56:34,279
Speaker 5: creates a big mess, and then you both sort of

1233
00:56:34,320 --> 00:56:36,040
Speaker 5: form together or reform together.

1234
00:56:36,239 --> 00:56:38,319
Speaker 1: And the incredible thing is that by looking at the

1235
00:56:38,320 --> 00:56:41,240
Speaker 1: Moon today we can mostly figure out how that happened,

1236
00:56:41,280 --> 00:56:43,640
Speaker 1: how this huge space rock ended up in orbit around

1237
00:56:43,640 --> 00:56:44,560
Speaker 1: the planet. Yeah.

1238
00:56:44,600 --> 00:56:46,120
Speaker 5: And the cool thing is that you can see the

1239
00:56:46,160 --> 00:56:48,400
Speaker 5: Moon almost every night. Every night you step outside of

1240
00:56:48,440 --> 00:56:51,279
Speaker 5: your house, you can see this giant rock floating in

1241
00:56:51,320 --> 00:56:54,759
Speaker 5: space there for us to see, pretty shiny, pretty bright.

1242
00:56:56,000 --> 00:56:58,680
Speaker 1: It's nice to have one big, fat moon. I agree.

1243
00:56:58,920 --> 00:57:01,200
Speaker 5: All right, Well, we hope you enjoy with Thanks for

1244
00:57:01,280 --> 00:57:03,080
Speaker 5: joining us, see you next time.

1245
00:57:10,960 --> 00:57:13,760
Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain

1246
00:57:13,840 --> 00:57:17,840
Speaker 1: the Universe is a production of iHeartRadio. For more podcasts

1247
00:57:17,840 --> 00:57:22,480
Speaker 1: from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever

1248
00:57:22,560 --> 00:57:36,080
Speaker 1: you listen to your favorite shows. When you pop a

1249
00:57:36,080 --> 00:57:38,400
Speaker 1: piece of cheese into your mouth, you're probably not thinking

1250
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1251
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