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How do planets get their moons? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, do you ever wish that we had more moons
• 0:12
  Speaker 1: in our night sky?
• 0:14
  Speaker 2: Hmmm? I think the universe as moon does enough times.
• 0:18
  Speaker 1: Actually, well, I like the moons, and I sometimes wish
• 0:23
  Speaker 1: we had more going on in the night sky, like
• 0:25
  Speaker 1: lots of little moons.
• 0:28
  Speaker 2: But then I wonder if we had the same line
• 0:31
  Speaker 2: in Star Wars, you know, where he says that's no moon.
• 0:34
  Speaker 2: That wouldn't work.
• 0:36
  Speaker 1: Maybe instead of the Death Star, they would have had
• 0:38
  Speaker 1: the death constellation.
• 0:40
  Speaker 2: Or that song when the moon hits your eye like
• 0:42
  Speaker 2: a big pizza pie. That wouldn't work with a lot
• 0:44
  Speaker 2: of little moons. I guess it would work with lots
• 0:47
  Speaker 2: of mini pizzas.
• 0:50
  Speaker 1: The personal pan pizza would have been invented earlier.
• 1:08
  Speaker 2: Hi am Horehea, ma cartoonist and the creator of PhD comics.
• 1:11
  Speaker 1: Hi I'm Daniel. I'm a particle physicist and a professor
• 1:14
  Speaker 1: at UC Irvine, and I'd never really been a fan
• 1:17
  Speaker 1: of the pan pizza, of.
• 1:19
  Speaker 2: The pan or the pizza or just a combination of
• 1:21
  Speaker 2: the two.
• 1:22
  Speaker 1: The pizza in the pan. Definitely a thin crust kind
• 1:24
  Speaker 1: of guy over here, not.
• 1:26
  Speaker 2: A bread fan trying to curb your carbs.
• 1:30
  Speaker 1: I like tomato sauce. But I don't like the kiddie
• 1:31
  Speaker 1: pool of marinera that they call pizza in Chicago.
• 1:34
  Speaker 2: I feel like there's a thin line between a pan
• 1:37
  Speaker 2: pizza and like a casserole or like a pot pie.
• 1:40
  Speaker 1: It's really just a Midwestern hot dish.
• 1:42
  Speaker 2: There you go, But anyways, welcome to our podcast, Daniel
• 1:45
  Speaker 2: and Jorge Explain the Universe, a production of iHeartRadio.
• 1:48
  Speaker 1: Where we love everything about the universe, the thick ready
• 1:51
  Speaker 1: questions and the thin crunchy ones we wonder about how
• 1:54
  Speaker 1: everything out there in the universe works. We take a
• 1:57
  Speaker 1: big curiosity motivated by it, of the universe and try
• 2:00
  Speaker 1: to chew through all of it for you.
• 2:02
  Speaker 2: That's right, because the universe is a deep dish of
• 2:05
  Speaker 2: amazing facts and incredible things happening in it, full of
• 2:09
  Speaker 2: mysteries and wonderful conundrums for us to try to figure out.
• 2:12
  Speaker 1: And while physics has made incredible progress in understanding the
• 2:15
  Speaker 1: way the world works, we're still answering the kinds of
• 2:18
  Speaker 1: questions we've been asking basically forever, just looking around us,
• 2:23
  Speaker 1: seeing how the world is and wondering like, why is
• 2:25
  Speaker 1: it this way? How did it get to be this way?
• 2:28
  Speaker 2: Why does Deep Dish Pizza exist? Fundamental questions? That's what
• 2:33
  Speaker 2: we ask here on the podcast, and why doesn't Daniel
• 2:36
  Speaker 2: like them?
• 2:36
  Speaker 1: We know why Deep Dish Pizza exist for the same
• 2:38
  Speaker 1: reason vanilla ice cream exists, because you know, there's a
• 2:41
  Speaker 1: whole spectrum of people out there and everybody loves different things.
• 2:44
  Speaker 2: Are you saying the universe is kind of cheesy? I
• 2:47
  Speaker 2: guess it will definitely give you a heart attack as well.
• 2:50
  Speaker 2: There's no topping that joke, but yeah, we like to
• 2:51
  Speaker 2: think about the universe and all of the perfecting things
• 2:54
  Speaker 2: in it, like how did things come to be the
• 2:56
  Speaker 2: way they are? Why are we here? And where are
• 2:58
  Speaker 2: we in the universe?
• 2:59
  Speaker 1: And what is One of the real, simple but enduring
• 3:02
  Speaker 1: joys of being a curious person is just looking up
• 3:05
  Speaker 1: at the night sky. Not just being amazed at it's
• 3:08
  Speaker 1: beauty and odd at the depth of the view that
• 3:10
  Speaker 1: you were looking at, but this shared feeling through time
• 3:13
  Speaker 1: that humans one hundred years ago, a thousand years ago,
• 3:17
  Speaker 1: twenty five thousand years ago probably looked up at almost
• 3:20
  Speaker 1: the same night sky and wondered what was up there
• 3:23
  Speaker 1: and why it looked the way it did, and whether
• 3:25
  Speaker 1: it could have been different.
• 3:27
  Speaker 2: Yeah, you're looking at the exact same sky that our
• 3:30
  Speaker 2: ancestors did, full of stars, comments, and even a moon.
• 3:34
  Speaker 2: And they probably asked the same question that maybe a
• 3:36
  Speaker 2: lot of you have out there, which is, why do
• 3:39
  Speaker 2: we have a moon? And is it made out of cheese?
• 3:42
  Speaker 2: Is it just a big, flat, giant, floating deep dish
• 3:45
  Speaker 2: of cheese.
• 3:47
  Speaker 1: It's a spherical pizza. In the end, I have my
• 3:49
  Speaker 1: spherical pizza theory of the moon.
• 3:51
  Speaker 2: Do you do tell? Give us a slice of that
• 3:55
  Speaker 2: knowledge there?
• 3:57
  Speaker 1: All right? You called my bluff.
• 3:58
  Speaker 2: I got nothing and it was a crusty joke. But yeah,
• 4:02
  Speaker 2: sometimes we look out into the universe, into the night sky,
• 4:05
  Speaker 2: and we wonder why are things there, and how did
• 4:08
  Speaker 2: they come to be the way they are? What's going on?
• 4:10
  Speaker 2: And it wasn't just our ancestors that looked up at
• 4:12
  Speaker 2: the moon. It's like all of the planet that is
• 4:15
  Speaker 2: looking up at the moon, right, it's feeling its facts
• 4:17
  Speaker 2: and howling at it and rolling with the tides that
• 4:20
  Speaker 2: go along with the moon. The moon has. It makes
• 4:22
  Speaker 2: a big difference here on this planet.
• 4:23
  Speaker 1: Yeah, and these are not just questions asked by amateur astronomers,
• 4:27
  Speaker 1: but planet heiogeologist at the cunning edge are still trying
• 4:30
  Speaker 1: to figure out the details of how everything came to
• 4:32
  Speaker 1: be in our night sky.
• 4:34
  Speaker 2: So to the other podcast, we'll be tackling the question
• 4:41
  Speaker 2: how the planets get their moon or moons. Some planets
• 4:44
  Speaker 2: have lots of moons, right.
• 4:45
  Speaker 1: Yeah, that's right. It turns out our planet is quite
• 4:47
  Speaker 1: unusual in having approximately one moon.
• 4:50
  Speaker 2: So you do believe in the moon. The moon does exist, right.
• 4:54
  Speaker 1: I can see the moon. I know it's there, But.
• 4:56
  Speaker 2: How you know it's round? It always looks the same.
• 4:58
  Speaker 1: Well, we've been to the moon, so we can see
• 5:01
  Speaker 1: all around it, and you can tell that is round. Also,
• 5:04
  Speaker 1: the curved edge between the bright side and the dark
• 5:06
  Speaker 1: side of the moon tell us that it's going to
• 5:08
  Speaker 1: be round.
• 5:09
  Speaker 2: Oh right, you get sort of like the shadow of
• 5:12
  Speaker 2: it tells you it's round.
• 5:13
  Speaker 1: Exactly?
• 5:14
  Speaker 2: Is it perfectly round? Is the Moon perfectly round? Or
• 5:16
  Speaker 2: is it kind of an ellipsoid like the Earth.
• 5:18
  Speaker 1: Nothing in the universe is perfectly round. There are no
• 5:21
  Speaker 1: actual circles out there, maybe even not the event horizons
• 5:25
  Speaker 1: of black holes due to quantum effects. So the Moon
• 5:28
  Speaker 1: is definitely not perfectly round, and it's also pulled into
• 5:31
  Speaker 1: something of a football shape thanks to the Earth's gravity.
• 5:34
  Speaker 1: Tidal forces on the Moon by the Earth make it
• 5:37
  Speaker 1: a little bit oblong.
• 5:39
  Speaker 2: Whoa, I guess it's not spinning in the way that
• 5:41
  Speaker 2: the Earth is so that you get this centropical force.
• 5:44
  Speaker 2: But you're saying that the fact that the Earth is
• 5:46
  Speaker 2: pulling on it kind of stretches it out.
• 5:48
  Speaker 1: Yeah, it is spinning. It's just spinning at exactly the
• 5:50
  Speaker 1: right rate so that the same side of it is
• 5:52
  Speaker 1: always facing the Earth. This is called a tidal locking. Eventually,
• 5:56
  Speaker 1: the Earth pulls on the Moon to make it oblong,
• 5:59
  Speaker 1: and then they get stuck in this stable equilibrium where
• 6:01
  Speaker 1: that long bit is always pointing towards the Earth because
• 6:04
  Speaker 1: gravity on that long bit is a little stronger, so
• 6:07
  Speaker 1: it's sort of like a pendulum dangling towards the Earth.
• 6:10
  Speaker 2: Well, it is cool that we have a moon. I
• 6:11
  Speaker 2: guess it would to inspire all of these songs and
• 6:14
  Speaker 2: all these stories and legends about the moon.
• 6:16
  Speaker 1: It is nice to have a moon. It lights up
• 6:18
  Speaker 1: otherwise very dark nights, and it's something very close by
• 6:21
  Speaker 1: to look at, right, So much of the rest of
• 6:23
  Speaker 1: the night sky are just dots. They're so far away
• 6:26
  Speaker 1: they look like pinpricks. But the Moon has features on it.
• 6:29
  Speaker 1: I remember as a kid looking up at it and
• 6:31
  Speaker 1: studying those and like wondering what it would be like
• 6:33
  Speaker 1: to walk across it and to be on it, or
• 6:36
  Speaker 1: to look at the Earth from the moon. It's cool
• 6:38
  Speaker 1: that it's both in the night sky and kind of
• 6:40
  Speaker 1: close by.
• 6:41
  Speaker 2: Yeah, I guess it's kind of scary to think about it. Actually,
• 6:44
  Speaker 2: it's just kind of swinging around the Earth. It's constantly
• 6:47
  Speaker 2: falling around the Earth. That's what the Moon is doing.
• 6:50
  Speaker 2: And it's big, Like you don't want to mess with
• 6:52
  Speaker 2: the moon either.
• 6:53
  Speaker 1: Yeah, the Moon is pretty massive. And not only is
• 6:57
  Speaker 1: the Earth tugging on the Moon and forcing it to
• 7:00
  Speaker 1: face us the same way, but the Moon is doing
• 7:02
  Speaker 1: the same thing to Earth. Eventually, the Earth of the
• 7:05
  Speaker 1: Moon will both be tidally locked to each other.
• 7:07
  Speaker 2: Mmmmm, wait what does that mean? That means that we
• 7:12
  Speaker 2: will be going around the moon.
• 7:14
  Speaker 1: It means that, given enough time, the Moon will stay
• 7:17
  Speaker 1: on the same side of the Earth. The Earth's spin
• 7:19
  Speaker 1: and the Moon's spin will balance so that only one
• 7:23
  Speaker 1: side of the Earth ever sees the Moon the same way,
• 7:26
  Speaker 1: only one side of the Moon ever sees the Earth.
• 7:29
  Speaker 2: Wait, what for real. When is that going to happen.
• 7:31
  Speaker 1: It's not going to be for billions of years, but
• 7:33
  Speaker 1: it has already had an impact, Like the rate that
• 7:36
  Speaker 1: the Earth is spinning has slowed down to twenty four
• 7:40
  Speaker 1: hours per spin over the last four billion years. Four
• 7:43
  Speaker 1: billion years ago, it took about six hours for the
• 7:46
  Speaker 1: Earth to spin, So the Moon is slowing down the
• 7:49
  Speaker 1: spin of the Earth. Eventually, it will take about forty
• 7:52
  Speaker 1: seven of our current days to spin the Earth. That
• 7:55
  Speaker 1: will match the Moon's orbital period, and the Earth and
• 7:57
  Speaker 1: the Sun will be tidally locked to each other. But
• 8:00
  Speaker 1: that wouldn't be for billions of years, and that would
• 8:02
  Speaker 1: be assuming that the Sun doesn't gobble the Earth first.
• 8:05
  Speaker 2: Yeah, we would have bigger problems in the Moon at
• 8:08
  Speaker 2: that point.
• 8:09
  Speaker 1: But it would be kind of amazing if you could
• 8:11
  Speaker 1: only see the Moon from one half of the Earth.
• 8:13
  Speaker 1: It would mean you could grow up your whole life
• 8:15
  Speaker 1: and not see the Moon, and then travel to another
• 8:17
  Speaker 1: part of the Earth and see the Moon for the
• 8:19
  Speaker 1: first time. That would be incredible.
• 8:21
  Speaker 2: Whoa which sid gets to have the moon? Can they
• 8:24
  Speaker 2: predict that? Or we even have the same We probably
• 8:26
  Speaker 2: won't even have the same continents.
• 8:27
  Speaker 1: Right, Yeah, not in billions of years exactly.
• 8:31
  Speaker 2: I guess we have the moon to thank for having
• 8:33
  Speaker 2: more time in our day. Then without the moon that
• 8:35
  Speaker 2: things will be a lot more hectic.
• 8:37
  Speaker 1: Yeah, that's true. Those of you who like to work
• 8:38
  Speaker 1: late at night would have much shorter nights to get
• 8:41
  Speaker 1: stuff done.
• 8:42
  Speaker 2: I think the people during the day would also have
• 8:44
  Speaker 2: a shorter time, right, But it is an interesting question
• 8:49
  Speaker 2: how did we get this moon? Like how do planets
• 8:52
  Speaker 2: get moons at all? And why do we only have
• 8:54
  Speaker 2: one moon versus having lots of moons like other planets
• 8:56
  Speaker 2: which have up to eighty four moons.
• 8:59
  Speaker 1: It is really fun, fascinating question, and the answer tells
• 9:01
  Speaker 1: us a lot about how solar systems form, whether our
• 9:04
  Speaker 1: planet is weird, and maybe whether our solar system itself
• 9:08
  Speaker 1: is kind of weird.
• 9:09
  Speaker 2: Well, you can get all that from the moon.
• 9:12
  Speaker 1: You can learn a lot just by asking questions.
• 9:14
  Speaker 2: Well, as usual, we were wondering how many people out there?
• 9:16
  Speaker 2: I thought about the question of where moons come from
• 9:19
  Speaker 2: and how are they form? How do we get ours?
• 9:22
  Speaker 2: So as usual Daniel went out there into the internet
• 9:25
  Speaker 2: to ask people how do moons form?
• 9:27
  Speaker 1: Thanks very much to everybody who participates in this segment
• 9:30
  Speaker 1: of the podcast. If you've been listening for a while
• 9:32
  Speaker 1: and thinking about participating, please let me encourage you. It's fun,
• 9:36
  Speaker 1: it's easy. Everybody enjoys it. Write to me two questions
• 9:39
  Speaker 1: at Danielandjorge dot com.
• 9:42
  Speaker 2: So think about it for a second. How do you
• 9:43
  Speaker 2: think planets get their moons? Here's what people had to say.
• 9:47
  Speaker 3: I think that most moons form from cloud discs around planets,
• 9:53
  Speaker 3: and that Satan's rings are a picture of that process
• 9:57
  Speaker 3: going on.
• 9:58
  Speaker 4: Moons on form? How planet form? So they're small rocks
• 10:02
  Speaker 4: and then they hit each other and create bigger ones.
• 10:05
  Speaker 4: So when a planet is created, maybe when it gets created,
• 10:08
  Speaker 4: some debris goes out and then creates like a miniature
• 10:10
  Speaker 4: planet aka a moon.
• 10:12
  Speaker 2: Maybe I suppose the moon is just a small planet.
• 10:16
  Speaker 2: It's kind of just a planet that gets trapped by
• 10:19
  Speaker 2: another planet. Right, they're just rocks.
• 10:22
  Speaker 5: There's got to be like at least six ways moon forms.
• 10:25
  Speaker 5: I don't know, like things crashing together. Apparently we might
• 10:29
  Speaker 5: have stolen the Moon from Venus. Maybe probably a bunch
• 10:33
  Speaker 5: of other ways they could form too.
• 10:35
  Speaker 6: I think Moon's form either just sort of alongside they're
• 10:40
  Speaker 6: planet like Lucky, or from collisions like our own moon
• 10:47
  Speaker 6: came from an impact. Those are, I guess, the only
• 10:51
  Speaker 6: two I really know.
• 10:52
  Speaker 7: I would say that this is a collisions between among
• 10:57
  Speaker 7: asteroids planets, and then you have planet that has been
• 11:01
  Speaker 7: hit by an asteroid, and a small chunk of this
• 11:04
  Speaker 7: planet would be placed in a sort of an orbit,
• 11:07
  Speaker 7: and then you get the Moon.
• 11:08
  Speaker 8: I think it's when space dust is orbiting a planet
• 11:11
  Speaker 8: and then it clumps together into the Moon eventually, or if,
• 11:15
  Speaker 8: like an asteroid, is caught in the gravitational pool of
• 11:21
  Speaker 8: a planet and falls into its orbit.
• 11:24
  Speaker 1: I think Moon's form from asteroids and other bits of
• 11:28
  Speaker 1: space debris that get trapped in a planet's orbit.
• 11:31
  Speaker 9: I think that moon's form around planets the same way
• 11:34
  Speaker 9: that planets form around stars. I think that basically there's
• 11:37
  Speaker 9: a bunch of junk floating around the planet that aggregates
• 11:40
  Speaker 9: into a moon or moons.
• 11:42
  Speaker 2: All right, a lot of interesting answers here. Somebody said
• 11:46
  Speaker 2: at least six ways, that's all they said, But only
• 11:50
  Speaker 2: at least six he or she had six ways in mind.
• 11:55
  Speaker 1: M reminds me that Paul Simon's song just get on
• 11:57
  Speaker 1: the bus, gus don't need to discuss much. Yeah, there
• 12:01
  Speaker 1: must be six ways to get a moon.
• 12:04
  Speaker 2: Sounds like clickbait. Six ways so we can get a moon.
• 12:07
  Speaker 2: The sixth one will totally amaze you. Maybe we should
• 12:11
  Speaker 2: be learning from this listener and how to title our
• 12:14
  Speaker 2: podcast episodes. Although that you hear BuzzFeed is going down,
• 12:17
  Speaker 2: it's going out of business or BuzzFeed news.
• 12:20
  Speaker 1: Do you think there's a lesson there for us podcasters?
• 12:22
  Speaker 2: Yeah, I think there are six amazing lessons. The sixth
• 12:25
  Speaker 2: one will totally astound you.
• 12:27
  Speaker 1: I can't wait to hear.
• 12:28
  Speaker 2: But yeah, a lot of interesting theories here from people.
• 12:30
  Speaker 2: Some people think it happens from like a collision. Some
• 12:33
  Speaker 2: people think we stole it from another planet? Is that true?
• 12:37
  Speaker 1: The truth is that there are lots of different ways
• 12:39
  Speaker 1: to get moons, and we'll dig into several of them today.
• 12:42
  Speaker 2: M The sixth one will amaze you.
• 12:46
  Speaker 1: If we get there.
• 12:47
  Speaker 2: If we get that right, know for sure we'll get there.
• 12:50
  Speaker 2: Question is how long before we get there? Will we
• 12:54
  Speaker 2: do it before the hour is up? Towards a close call?
• 12:57
  Speaker 2: All right, Well, let's start with the basics, Daniel, how
• 12:59
  Speaker 2: would you define a moon? Like what is a moon?
• 13:01
  Speaker 2: And what's the difference between a moon and like a
• 13:03
  Speaker 2: satellite or an asteroid or just a space jump.
• 13:06
  Speaker 1: Yeah, this is an interesting question in astronomy. We have
• 13:08
  Speaker 1: all these categories we've invented to describe the kinds of
• 13:12
  Speaker 1: things we've seen out there, and then we find things
• 13:14
  Speaker 1: that break those categories, and it turns out there are
• 13:17
  Speaker 1: no real hard divisions and bright lines between stuff. It's
• 13:20
  Speaker 1: just sort of like where humans like to draw a
• 13:23
  Speaker 1: dotted line between things, and so it's kind of a
• 13:25
  Speaker 1: mess what a moon is signs. Originally they called these
• 13:29
  Speaker 1: things natural satellites, Like when you look at Jupiter and
• 13:32
  Speaker 1: you see things going around it, you call those satellites
• 13:34
  Speaker 1: of Jupiter. And for a long time, like before the
• 13:36
  Speaker 1: space age, the word moon just referred to the moon
• 13:40
  Speaker 1: of the Earth, which is the name of our moon.
• 13:42
  Speaker 1: But then we started launching artificial satellites, and so when
• 13:46
  Speaker 1: Sputnik went up, people called it an artificial satellite. But
• 13:49
  Speaker 1: that's sort of awkward and a mouthful, so people didn't
• 13:52
  Speaker 1: like saying artificial satellite. They just start calling it satellite,
• 13:55
  Speaker 1: and so that makes natural satellite kind of awkward.
• 13:58
  Speaker 2: To say organic satellite exactly, or farm raised satellites.
• 14:04
  Speaker 1: But natural satellite is kind of a mouthful, and so
• 14:06
  Speaker 1: now people, even scientists, sometimes say moons. Technically, we have
• 14:11
  Speaker 1: artificial satellites, things we have launched in due space, and
• 14:14
  Speaker 1: then we have natural satellites, things that are in orbit anyway,
• 14:18
  Speaker 1: naturally without the influence of humans.
• 14:20
  Speaker 2: But wait, wait, I think I've seen NASA call the
• 14:23
  Speaker 2: moons of Jupiter the moons of Jupiter. They never say
• 14:25
  Speaker 2: the satellites of Jupiter.
• 14:27
  Speaker 1: That's right. So technically we have artificial satellite and we
• 14:29
  Speaker 1: have natural satellite, though typically we just say satellite for
• 14:33
  Speaker 1: artificial satellite, and now we say moon for natural satellite,
• 14:36
  Speaker 1: even in scientific publications and like official press releases. So
• 14:39
  Speaker 1: now moon has come to mean natural satellite.
• 14:43
  Speaker 2: I see. But I guess if you put the in
• 14:45
  Speaker 2: front of it, then it's our moon. Like the moon
• 14:47
  Speaker 2: is our moon, but then other moons are just moons.
• 14:51
  Speaker 1: Yeah, exactly, the moon is our moon or Luna if
• 14:55
  Speaker 1: you prefer. And moon with a lowercase M means any
• 14:58
  Speaker 1: kind of natural satellite.
• 15:00
  Speaker 2: I guess you can have rocks, and you can have
• 15:02
  Speaker 2: the rock.
• 15:05
  Speaker 1: Exactly. We have lots of rocks in orbit, but I
• 15:07
  Speaker 1: don't think we have the rock in orbit yet, though
• 15:09
  Speaker 1: I haven't seen fast and Furious twenty seven or whichever
• 15:12
  Speaker 1: one has space.
• 15:14
  Speaker 2: I'm assureing the next one there, they'll you know, speed
• 15:17
  Speaker 2: up a ramp and somehow make it up to space
• 15:20
  Speaker 2: and crash into a space station. While he jumps and
• 15:23
  Speaker 2: also launches a rocket launcher.
• 15:25
  Speaker 1: He's got to flex his muscles at some point. Another
• 15:27
  Speaker 1: question is size, Like, is every object that's orbiting the
• 15:30
  Speaker 1: Earth a moon? Every tiny little rock is at a
• 15:34
  Speaker 1: moon of the Earth. Officially, there's no lower limit, right,
• 15:37
  Speaker 1: Like every natural object with an orbit around the planet,
• 15:40
  Speaker 1: technically you could call it a moon.
• 15:42
  Speaker 2: Wait what I mean? No, at some point, it's just
• 15:44
  Speaker 2: the rock, right.
• 15:45
  Speaker 1: The moon is just a rock. Also makes the Moon
• 15:48
  Speaker 1: different from other rocks orbiting the planet is just the size,
• 15:52
  Speaker 1: and there is no official lower limit to the size
• 15:55
  Speaker 1: of a moon. You could have a moon of any size,
• 15:58
  Speaker 1: and any limit you place is going to be totally ourary, right.
• 16:01
  Speaker 2: I wonder if the definition also has to do with
• 16:03
  Speaker 2: how stable its orbit is. Like, if I just throw
• 16:07
  Speaker 2: a rock and into space, it's kind of orbiting the
• 16:10
  Speaker 2: Earth for a little bit, does that mean it's a.
• 16:12
  Speaker 1: Moon that's not really in orbit? Right? I don't know
• 16:14
  Speaker 1: how strong you are. Recently haven't seen you in a while,
• 16:17
  Speaker 1: But I don't think you could throw a rock and
• 16:18
  Speaker 1: actually get it into orbit. It has to be in orbit.
• 16:21
  Speaker 2: Oh yeah, do you want to make that bet? I'll
• 16:24
  Speaker 2: bet you a billion dollars because with a billion dollars
• 16:27
  Speaker 2: I can come into space and throw the rock.
• 16:30
  Speaker 1: If you get a rock orbiting the Earth, I will
• 16:32
  Speaker 1: campaign NASA to let you name it officially.
• 16:35
  Speaker 2: Well, if you get me on a rocket ship into
• 16:37
  Speaker 2: space to throw a rock, we'll start the whole process.
• 16:40
  Speaker 1: But we can look at the typical sizes of these things,
• 16:43
  Speaker 1: and like in our Solar system there are a few
• 16:46
  Speaker 1: hundred of these moons. There's six planets that have moons,
• 16:49
  Speaker 1: for a total of two hundred and twenty six moons,
• 16:51
  Speaker 1: and typically the planet to moon mass ratio is at
• 16:55
  Speaker 1: least ten thousand to one, so moons typically have a
• 16:58
  Speaker 1: much smaller mass than the planet they orbit.
• 17:01
  Speaker 2: Wait, there are six planets in our Solar system with moons.
• 17:04
  Speaker 2: Who doesn't have a moon?
• 17:05
  Speaker 1: Neither Mercury nor Venus have moons. That's probably because they're
• 17:09
  Speaker 1: too close to the Sun and so tidal disruption basically
• 17:12
  Speaker 1: pulls those moons away.
• 17:14
  Speaker 2: Oh interesting, and I just figured out that's probably what
• 17:16
  Speaker 2: the listener meant when they said at least six ways.
• 17:19
  Speaker 1: Oh nice. Probably every moon has a unique story, m
• 17:26
  Speaker 1: they have their own origin story. Of course, our moon
• 17:29
  Speaker 1: is a big exception to this ten thousand to one rule, right,
• 17:32
  Speaker 1: because the mass of the Moon is about one eightieth
• 17:35
  Speaker 1: of the mass of the Earth. It's like more than
• 17:37
  Speaker 1: one percent of the mass of the Earth. So it's
• 17:40
  Speaker 1: a big honk and moon it's very unusual.
• 17:43
  Speaker 2: So most of the moons in the Solar System, some
• 17:46
  Speaker 2: of them are as big as our moon, but you're
• 17:49
  Speaker 2: saying that the ratio compared to their planet, most of
• 17:52
  Speaker 2: them are small.
• 17:53
  Speaker 1: Most of them are small exactly. And then there's the case,
• 17:56
  Speaker 1: for example, of Pluto. Pluto has a moon which is Sharon,
• 17:59
  Speaker 1: which is one eighth of its mass, and so like
• 18:02
  Speaker 1: we call Pluto a dwarf planet, and we call Sharon
• 18:05
  Speaker 1: a moon of Pluto. But you know, you could also
• 18:08
  Speaker 1: argue that it's really like a dwarf planet binary system,
• 18:12
  Speaker 1: which one is a planet and which one is the moon?
• 18:14
  Speaker 1: It all gets kind of fuzzy.
• 18:15
  Speaker 2: Whoa, it's like a double planet.
• 18:19
  Speaker 7: Man.
• 18:21
  Speaker 1: One way to distinguish the two scenarios, like having a
• 18:23
  Speaker 1: double planet or a planet with a moon. Is whether
• 18:26
  Speaker 1: the center of mass of the system is within the
• 18:30
  Speaker 1: surface of one of them. If you find the point
• 18:32
  Speaker 1: that averages where all the mass is, the point around
• 18:35
  Speaker 1: which the two objects really are orbiting, if that is
• 18:38
  Speaker 1: underground one of the two objects, and you call the
• 18:41
  Speaker 1: more massive one a planet and the other one a moon.
• 18:43
  Speaker 1: Otherwise you call it a binary system. Again, that's still
• 18:46
  Speaker 1: kind of arbitrary, right, We're just like giving these things
• 18:49
  Speaker 1: names and drawing lines between them. Really, there's just a
• 18:52
  Speaker 1: bunch of different rocks out there in the universe orbiting
• 18:54
  Speaker 1: each other.
• 18:55
  Speaker 2: Except also, Pluto is not a planet, So can you
• 18:58
  Speaker 2: have a moon around something that's not planet? Like can
• 19:01
  Speaker 2: you can moon or can a moon have a moon?
• 19:03
  Speaker 1: You can have a moon around a dwarf planet, though
• 19:05
  Speaker 1: maybe you would want to call it a dwarf moon.
• 19:07
  Speaker 1: I don't know. And it's possible in principle to have
• 19:11
  Speaker 1: moons around moons. There are asteroids that have moons.
• 19:15
  Speaker 2: Wait what, and you still call them moons, not master moons.
• 19:19
  Speaker 1: Some people want to call them moonlits or moon moons
• 19:22
  Speaker 1: like the moon of a.
• 19:23
  Speaker 2: Moon or moony's or mini moons.
• 19:26
  Speaker 1: And there are even some moons, like Rhea has its
• 19:28
  Speaker 1: own ring system Saturn's moon Rhea.
• 19:30
  Speaker 2: Wait what some moons can have rings? Yeah, because they
• 19:34
  Speaker 2: have so many mini moons.
• 19:36
  Speaker 1: If you're big enough that you dominate the gravitational environment nearby,
• 19:39
  Speaker 1: then yeah, you can have your own rings.
• 19:41
  Speaker 2: I mean, I guess technically anything can have a satellite, right,
• 19:44
  Speaker 2: Like I can take a baseball, put in into space
• 19:46
  Speaker 2: and then knock a you know, a speck of dust
• 19:49
  Speaker 2: in orbit around it.
• 19:50
  Speaker 1: Right, yeah, exactly. That wouldn't be a planet or even
• 19:53
  Speaker 1: a dwarf planet, but it would have an orbiting object.
• 19:56
  Speaker 1: Is that a natural satellite? I'm not quite sure.
• 19:59
  Speaker 2: A what else do we know about moons?
• 20:01
  Speaker 1: If you try to dig into the ancient history of moons,
• 20:03
  Speaker 1: it gets quite confusing to read about because until Copernicus,
• 20:07
  Speaker 1: moons were actually called planets, like the Moon itself was
• 20:10
  Speaker 1: referred to as a planet. Like when you talked about
• 20:13
  Speaker 1: astronomy in the fifteen hundreds, you said the planet Mars,
• 20:16
  Speaker 1: the planet Venus, the planet Luna. And it wasn't until Kepler,
• 20:20
  Speaker 1: who was thinking about how these things orbit each other,
• 20:22
  Speaker 1: who had a better understanding of these orbits, that we
• 20:25
  Speaker 1: started calling the moon a satellite of the Earth, and
• 20:28
  Speaker 1: then the satellites of Jupiter are of course the moons
• 20:31
  Speaker 1: of Jupiter. So there's a really fun interesting history to
• 20:34
  Speaker 1: these words.
• 20:34
  Speaker 2: Wait, really, so like, for a moment in human history,
• 20:37
  Speaker 2: we thought the Moon was another planet orbiting the Solar System.
• 20:41
  Speaker 2: Technically it is orbiting the Sun.
• 20:43
  Speaker 1: Yeah, it is orbiting the Sun, and it is orbiting
• 20:45
  Speaker 1: the Earth. Right, it's not that we thought the Moon
• 20:47
  Speaker 1: was a planet like Mars. It's just that we categorized
• 20:50
  Speaker 1: all these things the same way. All these words are
• 20:52
  Speaker 1: just buckets, right, and they're just like grab a bunch
• 20:54
  Speaker 1: of the stuff that's out there and gather it all
• 20:56
  Speaker 1: into a conceptual bucket. And where the lines between these
• 20:59
  Speaker 1: buckets is a little bit arbitrary. And so it used
• 21:02
  Speaker 1: to be that we lumped the moon in with the planets.
• 21:04
  Speaker 1: Now we have a separate category for things that orbit
• 21:07
  Speaker 1: the planets.
• 21:09
  Speaker 2: Shoot for the Moon. I guess when you're naming things,
• 21:11
  Speaker 2: all right, well, let's get a little deeper into where
• 21:14
  Speaker 2: the Moon came from, Where do moons in general come from,
• 21:16
  Speaker 2: how do other planets get their moons, and what does
• 21:19
  Speaker 2: it all mean about the history of the Solar System.
• 21:22
  Speaker 2: But first let's take a quick break, all right, we're
• 21:37
  Speaker 2: getting a little looney here talking about the moon and
• 21:40
  Speaker 2: how we got it and how do planets get their moons.
• 21:43
  Speaker 1: It is really fun in ancient question to wonder why
• 21:46
  Speaker 1: that thing is in our sky and why Jupiter has
• 21:48
  Speaker 1: more moons than we do. And if history had been different,
• 21:51
  Speaker 1: would we have had a bunch of moons? What would
• 21:53
  Speaker 1: it be like to live in that scenario? Could we
• 21:56
  Speaker 1: sail as well? If the ties were crazy and complicated
• 21:59
  Speaker 1: from having like fifteen different little moons? Hmmm?
• 22:02
  Speaker 2: Interesting? Yeah, that would affect the tides, right, But that
• 22:05
  Speaker 2: wouldn't affect navigation, would it.
• 22:06
  Speaker 1: It wouldn't affect navigation, but it would affect when it's
• 22:09
  Speaker 1: easy to launch your ships or not, and so it
• 22:11
  Speaker 1: might affect lots of industries and exploration.
• 22:14
  Speaker 2: M Also, if you're a were wolf, it would be
• 22:16
  Speaker 2: pretty complicated, right, probably, just you know, just the planet ahead.
• 22:20
  Speaker 1: Maybe you change into one kind of wolf for one
• 22:22
  Speaker 1: moon and another kind of wolf for another moon, and
• 22:24
  Speaker 1: like a Pomeranian for the little moon or a shitsu.
• 22:29
  Speaker 2: Yeah, there you go, different moons for different breeds.
• 22:31
  Speaker 1: Two moons up in the sky. Then you're a hybrid, right,
• 22:33
  Speaker 1: This sounds like a fun science fiction story.
• 22:35
  Speaker 2: It sounds like a great Ya novel.
• 22:39
  Speaker 1: So many spin offs.
• 22:40
  Speaker 2: All right, we talked about the word moon is kind
• 22:42
  Speaker 2: of flexible and it's not quite super well defined, but
• 22:46
  Speaker 2: basically it just kind of means like a big rock
• 22:48
  Speaker 2: circling around a bigger rock. Right, that's right.
• 22:50
  Speaker 1: It's a big rock orbiting another big rock.
• 22:53
  Speaker 2: And as you said, six of the planets in our
• 22:55
  Speaker 2: Solar system have them. Venus and Mercury don't because I
• 22:59
  Speaker 2: guess they're too hot, you said. And if they had moons,
• 23:01
  Speaker 2: then the Sun would have disrupted its orbit and probably
• 23:04
  Speaker 2: made it crash into the planet, right or fly away.
• 23:07
  Speaker 1: Yeah, it's all about the tidal forces. It makes it
• 23:08
  Speaker 1: basically impossible for Mercury or Venus to have moons and
• 23:12
  Speaker 1: to keep them. It's because they're so close to the Sun.
• 23:14
  Speaker 1: It's not their actual temperature, it's the gravitational tidal forces
• 23:18
  Speaker 1: from the Sun.
• 23:18
  Speaker 2: All right, Well, what do we know about where moons
• 23:21
  Speaker 2: come from and how they're form?
• 23:22
  Speaker 1: So you can tell a lot about where a moon
• 23:24
  Speaker 1: came from based on what it's made out of and
• 23:26
  Speaker 1: how it's orbiting. If a moon is mostly in a
• 23:29
  Speaker 1: circular orbit, and the circular orbit follows the tilt of
• 23:32
  Speaker 1: the planet, so for example, it's orbiting around the equator
• 23:36
  Speaker 1: in mostly a circle. Then it's very likely that that
• 23:39
  Speaker 1: moon came from the same stuff that formed the planet.
• 23:43
  Speaker 1: Remember how planets form in the beginning, it's a big
• 23:45
  Speaker 1: cloud of gas and dust that forms the whole Solar System.
• 23:48
  Speaker 1: Most of the gas is gobbled up by the star
• 23:50
  Speaker 1: as it forms, and our Sun has ninety ninety percent
• 23:53
  Speaker 1: of the mass of the Solar System. But if you
• 23:55
  Speaker 1: get a little isolated pocket of heavy stuff that has
• 23:57
  Speaker 1: its own gravity and can gather itself together, then you
• 24:00
  Speaker 1: can get a planet. So a planet sort of forms
• 24:02
  Speaker 1: the same way the Solar System does. It's the gravitational
• 24:05
  Speaker 1: collapse of a big blob of.
• 24:06
  Speaker 2: Stuff, right, And initially it's just kind of like a
• 24:09
  Speaker 2: big cloud of rocks and dust that's spinning or has
• 24:13
  Speaker 2: kind of an overall spin.
• 24:14
  Speaker 1: Exactly. The reason you get moons around planets is the
• 24:17
  Speaker 1: same reason you get planets around stars. Right. You don't
• 24:20
  Speaker 1: just get all the mass of the Solar System collapsing
• 24:22
  Speaker 1: into the Sun. You get these little pockets that have
• 24:24
  Speaker 1: enough gravity to form themselves together and then are moving
• 24:27
  Speaker 1: at high enough speed that they can resist falling into
• 24:30
  Speaker 1: the Sun. Now, around those planets, of course, you also
• 24:33
  Speaker 1: have little clouds of gas and dust. Some of it
• 24:35
  Speaker 1: collapses into the planet, most of it, but some of
• 24:38
  Speaker 1: it pulls itself together and has enough velocity to avoid
• 24:42
  Speaker 1: falling into the planet. And so if you have enough
• 24:45
  Speaker 1: velocity and you can pull yourself together, then you can
• 24:47
  Speaker 1: form like a little planet's planet, a little miniature system
• 24:50
  Speaker 1: around the planet, the same way the planet is going
• 24:52
  Speaker 1: around the Sun.
• 24:53
  Speaker 2: Right, because I guess gravity. That's how gravity works, right,
• 24:56
  Speaker 2: Like everything is attracted to everything else. It's not just
• 24:59
  Speaker 2: like we're attract it to the Sun or juice attracted
• 25:02
  Speaker 2: to the planet Earth. It's like I'm attracted to my
• 25:06
  Speaker 2: car and to this base bomb, the base will attracted
• 25:08
  Speaker 2: to me. And so if we were out in space,
• 25:11
  Speaker 2: we would both be falling towards the Earth, but then
• 25:13
  Speaker 2: we would there would also be an attraction between us.
• 25:15
  Speaker 2: And sometimes I think what you're saying is that if
• 25:18
  Speaker 2: a clump of dirt and rocks when the planet is forming,
• 25:21
  Speaker 2: it's kind of far enough out there, it will clump
• 25:24
  Speaker 2: together before it clumps with the Earth.
• 25:26
  Speaker 1: Yeah, that's exactly right. And there's sort of two steps there.
• 25:29
  Speaker 1: One is have enough velocity, like are you spinning fast
• 25:32
  Speaker 1: enough that you can basically get in orbit around the planet,
• 25:35
  Speaker 1: And that's how you get like a protoplanetary disc. The
• 25:38
  Speaker 1: planet forms and have some stuff out there that hasn't
• 25:41
  Speaker 1: fallen into the planet. So initially it's like a disc
• 25:44
  Speaker 1: and that can pull itself together using gravity into a ring.
• 25:47
  Speaker 1: And then there's a question of whether that ring can
• 25:49
  Speaker 1: pull itself together into a moon or not. Sometimes it
• 25:52
  Speaker 1: stays a ring and sometimes it forms a moon, and
• 25:55
  Speaker 1: that depends on how close you are to that planet.
• 25:59
  Speaker 1: If you're really really close to that planet, close to
• 26:01
  Speaker 1: than what we call the Roche limit, then tile forces
• 26:04
  Speaker 1: from the planet are too strong. If you try to
• 26:05
  Speaker 1: form a moon, the tile forces will tear it apart.
• 26:08
  Speaker 1: If you're outpast the Roche limit, then the tidle forces
• 26:11
  Speaker 1: are weak and you can gather together into a moon.
• 26:14
  Speaker 1: So you have to have enough velocity to avoid falling
• 26:16
  Speaker 1: into the planet, and then you have to be out
• 26:19
  Speaker 1: past the Roche limit to have a ring get turned
• 26:22
  Speaker 1: into a moon.
• 26:23
  Speaker 2: Because I think, as we've talked about before, gravity kind
• 26:26
  Speaker 2: of depends on the distance between two things. Right. So
• 26:29
  Speaker 2: if you're really close to the Earth, then like the
• 26:32
  Speaker 2: difference between one side of the Moon and the other
• 26:34
  Speaker 2: side of the Moon is they experience very different gravitational forces.
• 26:38
  Speaker 2: But maybe if you're far out and beyond this limit,
• 26:41
  Speaker 2: then you don't see this difference in pull from the
• 26:44
  Speaker 2: Earth between one and and the other, which kind of
• 26:48
  Speaker 2: lets you clump together.
• 26:49
  Speaker 1: You'll still always feel that difference, right, and like the
• 26:52
  Speaker 1: Moon does feel that difference. That's why we talked about earlier.
• 26:55
  Speaker 1: The Moon is a football. It is being pulled by
• 26:58
  Speaker 1: the Earth's tidal forces, but it's far and away that
• 27:00
  Speaker 1: those tidle forces are not strong enough to tear it apart.
• 27:03
  Speaker 1: The roach limit for the Earth is around ten thousand kilometers.
• 27:06
  Speaker 1: The Moon is like three hundred and eighty five thousand
• 27:08
  Speaker 1: kilometers away, so it's well past the roach limit. If
• 27:11
  Speaker 1: the Moon was much much closer, if it was like
• 27:14
  Speaker 1: less than ten thousand kilometers from the surface of the Earth,
• 27:17
  Speaker 1: the Earth would tear it apart with those tidal forces
• 27:19
  Speaker 1: into a massive ring system instead.
• 27:21
  Speaker 2: Where some of the rocks in that ring are going
• 27:23
  Speaker 2: at different speeds.
• 27:24
  Speaker 1: Right, it would be pretty cool to see the Moon
• 27:26
  Speaker 1: get torn up into rocks. Not all of them would
• 27:28
  Speaker 1: have the same velocity originally as the Moon. I'm sure
• 27:31
  Speaker 1: it would be somewhat destructive and chaotic. Some of them
• 27:34
  Speaker 1: would end up falling to the Earth, some of them
• 27:35
  Speaker 1: would get lost, and some of them would end up
• 27:37
  Speaker 1: in orbit.
• 27:37
  Speaker 2: Cool And I think that, as you said, also applies
• 27:40
  Speaker 2: to planets, right like you kind of have to be
• 27:42
  Speaker 2: a certain distance away from the Sun just to form
• 27:44
  Speaker 2: a planet, too.
• 27:45
  Speaker 1: Exactly, if you're too close to the Sun, then the
• 27:47
  Speaker 1: Sun's tidal forces, which are very powerful, will pull you apart.
• 27:51
  Speaker 1: So the roche limit for the Sun is like seven
• 27:53
  Speaker 1: hundred and fifty thousand kilometers. So if the Earth was
• 27:56
  Speaker 1: that close to the Sun, not only will we be fried,
• 27:59
  Speaker 1: of course, but the Sun would pull us apart with
• 28:01
  Speaker 1: its tidal forces. As you said, the gravitational force depends
• 28:05
  Speaker 1: on the distance, and so the Sun's gravit on the
• 28:07
  Speaker 1: near side of the Earth would be so much more
• 28:09
  Speaker 1: powerful than the Sun's gravity in the far side of
• 28:11
  Speaker 1: the Earth. It's effectively pulling us apart, and the Earth
• 28:14
  Speaker 1: is not strong enough to survive if it's closer than
• 28:17
  Speaker 1: seven hundred and fifty thousand kilometers. Fortunately, we're like one
• 28:20
  Speaker 1: hundred and fifty million kilometers from the Sun, so we're
• 28:24
  Speaker 1: nowhere near the Roche limit. And this isn't like an exact,
• 28:27
  Speaker 1: hard and fast number, it's like approximate. It depends on
• 28:29
  Speaker 1: the mass of the object, and it depends on structural
• 28:32
  Speaker 1: features of it, Like if you had a planet made
• 28:34
  Speaker 1: out of diamond, it could get closer to the Sun
• 28:36
  Speaker 1: than a planet made out of gravel.
• 28:39
  Speaker 2: But I guess generally speaking, it depends on the size
• 28:41
  Speaker 2: of the thing in the middle, Like the Sun has
• 28:44
  Speaker 2: a very big roach limit and the Earth as a
• 28:47
  Speaker 2: smaller one.
• 28:47
  Speaker 1: Yeah, that's true. You can get closer to the Earth,
• 28:50
  Speaker 1: then you can get to the Sun. But if you
• 28:51
  Speaker 1: see a moon around a planet and it's orbiting in
• 28:54
  Speaker 1: a circular orbit and it mostly has the same angle
• 28:58
  Speaker 1: or momentum as the planet, then you suspect that probably
• 29:01
  Speaker 1: came from the same stuff that made the planet, and
• 29:03
  Speaker 1: when that planet coalesced into stuff, not all of it
• 29:06
  Speaker 1: got turned into the planet, some of it got left
• 29:08
  Speaker 1: over and turned into a moon. So circular orbits with
• 29:12
  Speaker 1: the same anglermentum probably came from the same protoplanetary disk
• 29:17
  Speaker 1: that formed the planet.
• 29:19
  Speaker 2: Okay, So then if a moon is orbiting a planet
• 29:23
  Speaker 2: kind of in the same plane as the planet is spinning,
• 29:27
  Speaker 2: then most likely they're like siblings, kind of like they
• 29:30
  Speaker 2: were born at the same time from the same stuff.
• 29:33
  Speaker 1: Yeah, I suppose you could say so though, sort of
• 29:36
  Speaker 1: the scenario where like one twin is really big and
• 29:38
  Speaker 1: the other one is tiny.
• 29:39
  Speaker 2: Yeah, they're fraternal twins.
• 29:42
  Speaker 1: Exactly, and probably one it's pretty grumpy about not getting.
• 29:44
  Speaker 2: As much of dinner, all right. So that's one way
• 29:46
  Speaker 2: that maybe a moon can form, which is like it's
• 29:49
  Speaker 2: borne along with the planet, and you can sort of
• 29:51
  Speaker 2: tell which ones those are, Which of those do we
• 29:53
  Speaker 2: have in our Solar system, Like, is our moon one
• 29:56
  Speaker 2: of them?
• 29:56
  Speaker 1: Our moon is not one of those. Our moon is
• 29:58
  Speaker 1: actually a very weird case. Most of the moons in
• 30:01
  Speaker 1: the Solar System do not have nice circular orbits that
• 30:03
  Speaker 1: are orbiting with the planets. In fact, most of them
• 30:06
  Speaker 1: have elliptical orbits that have weird tilts. And that suggests
• 30:09
  Speaker 1: a completely different history for how.
• 30:11
  Speaker 2: That moon formed, necessarily, because like I wonder if maybe
• 30:14
  Speaker 2: the moon was formed as a sibling, but then it
• 30:16
  Speaker 2: got not by something and then it got a skewed orbit.
• 30:21
  Speaker 1: Yeah, that's certainly possible, but we think that most of
• 30:24
  Speaker 1: the ones with skewed orbits, that with tilted orbits that precess,
• 30:27
  Speaker 1: for example, are probably captured objects, things that came nearby
• 30:31
  Speaker 1: and were grabbed onto by the gravity of that planet.
• 30:34
  Speaker 1: You're right, it's possible for moon to be formed with
• 30:36
  Speaker 1: a planet and then get tilted through a collision. You
• 30:38
  Speaker 1: can tell the difference by looking at what that moon
• 30:40
  Speaker 1: is made out of. Is it made out of basically
• 30:42
  Speaker 1: the same stuff that formed the planet, or is it
• 30:45
  Speaker 1: made out of something totally weird and different. So that's
• 30:47
  Speaker 1: sort of like the key piece of information for distinguishing.
• 30:50
  Speaker 2: Like a DNA test prove of your siblings or not.
• 30:54
  Speaker 2: All right, well, then what does not having a circular
• 30:56
  Speaker 2: orbit tell you about the moon.
• 30:58
  Speaker 1: It tells you that probably it was captured, that the
• 31:01
  Speaker 1: planet is formed, and the moon comes from somewhere else.
• 31:04
  Speaker 1: It's like an asteroid or a dwarf planet or something
• 31:07
  Speaker 1: that was floating around and just came too close to
• 31:09
  Speaker 1: this massive object and its gravity took over. There's a
• 31:12
  Speaker 1: vicinity of a massive object we called the hill sphere,
• 31:15
  Speaker 1: which is the region sort of where its gravity dominates,
• 31:18
  Speaker 1: where everything else that's far away can basically be neglected,
• 31:21
  Speaker 1: and if an object passes within the hillsphere, it's a
• 31:24
  Speaker 1: candidate for getting captured.
• 31:26
  Speaker 2: But isn't that kind of weird? Or isn't it kind
• 31:28
  Speaker 2: of unlikely that you'll just kind of catch a big
• 31:30
  Speaker 2: rock out there and it'll have just the right speed
• 31:33
  Speaker 2: and distance to fall into a stable orbit, Like, aren't
• 31:35
  Speaker 2: stable orbits kind of hard to get into?
• 31:38
  Speaker 1: It is unlikely and it is weird. You're right. You
• 31:40
  Speaker 1: have to match the radius and the velocity. Like the
• 31:43
  Speaker 1: reason the Earth is in a stable orbit is because
• 31:46
  Speaker 1: it has the right velocity for our radius. You have
• 31:48
  Speaker 1: to be moving in a certain velocity at a given radius.
• 31:51
  Speaker 2: Like if we slowed down at all in our orbit,
• 31:53
  Speaker 2: we would start to spiral into the Sun. Right.
• 31:55
  Speaker 1: First orbit is actually quasi stable. So if we slowed
• 31:58
  Speaker 1: down a little bit, gravitational forces what actually pushes back
• 32:01
  Speaker 1: towards our orbit? But that's a whole other topic.
• 32:04
  Speaker 2: Like if you slow down a lot, though.
• 32:06
  Speaker 1: Yes, if we slowed down a lot, we would fall
• 32:07
  Speaker 1: in towards the Sun. If we sped up a bunch,
• 32:09
  Speaker 1: we would be ejected from the Solar system. And so
• 32:12
  Speaker 1: you have to have this match between these two quantities,
• 32:15
  Speaker 1: and it's not trivial for that to happen. Not only
• 32:17
  Speaker 1: do you have to have the right velocity and the
• 32:19
  Speaker 1: right radius, but you also have to lose energy in
• 32:21
  Speaker 1: order to fall into an orbit. Any object that falls
• 32:24
  Speaker 1: into the Solar System by definition has enough energy to
• 32:27
  Speaker 1: escape because it came from outside the Solar System. And
• 32:30
  Speaker 1: so if it just passes through on like a hyperbolic trajectory,
• 32:33
  Speaker 1: you know it has enough kinetic energy to climb out
• 32:36
  Speaker 1: of the gravitational well of the Solar System because it
• 32:38
  Speaker 1: came from outside the gravitational well. So in order to
• 32:41
  Speaker 1: get captured it not only does it have to come
• 32:43
  Speaker 1: in at the right radius and the right velocity, got
• 32:45
  Speaker 1: to lose a little bit of energy so that no
• 32:48
  Speaker 1: longer has the energy to escape. That can happen if
• 32:50
  Speaker 1: you like drag on the atmosphere the planet a little bit,
• 32:53
  Speaker 1: which gives you a little bit of friction, or maybe
• 32:55
  Speaker 1: another moon steals a little bit of your energy. So like,
• 32:58
  Speaker 1: the more moons you have and the puffier your atmosphere,
• 33:01
  Speaker 1: the more likely you are to be able to capture
• 33:03
  Speaker 1: an object that comes near you.
• 33:06
  Speaker 2: M it's kind of interesting to think of this idea
• 33:09
  Speaker 2: that planets like the Earth has a kind of a
• 33:11
  Speaker 2: halo kind of right, like a big sphere around it.
• 33:14
  Speaker 2: It's basically like a giant net. Like whatever falls into it,
• 33:17
  Speaker 2: it's gonna get sucked in.
• 33:19
  Speaker 1: Yeah, exactly. And if you fall in too far and
• 33:21
  Speaker 1: you slow don too far, then of course you're going
• 33:23
  Speaker 1: to burn up as you enter the atmosphere. So it's
• 33:25
  Speaker 1: a delicate operation. This is also think that sometimes a
• 33:28
  Speaker 1: pair of objects that are orbiting each other can fall
• 33:31
  Speaker 1: in the hillsphere and then one of them can get
• 33:33
  Speaker 1: captured and the other one can get ejected. So all
• 33:36
  Speaker 1: these sort of complicated things have to go just right
• 33:39
  Speaker 1: in order for a planet to capture a moon.
• 33:42
  Speaker 2: And by capturing, that's a nice word for stealing, right right,
• 33:45
  Speaker 2: I guess you're like trapping.
• 33:48
  Speaker 1: You're dancing, you're dancing with them, have of that?
• 33:50
  Speaker 2: Oh I see see?
• 33:52
  Speaker 3: Is that?
• 33:52
  Speaker 2: Where our that listener who mentioned earlier that maybe we
• 33:55
  Speaker 2: got our moon by stealing it from Venus? Is that?
• 33:58
  Speaker 2: Is there some truth to that?
• 34:00
  Speaker 1: We don't think that our moon was stolen from Venus,
• 34:02
  Speaker 1: but we do think that lots of the moons of
• 34:04
  Speaker 1: Jupiter and Saturn, for example, and these guys have like
• 34:07
  Speaker 1: dozens of moons come from scattered objects in the early
• 34:10
  Speaker 1: Solar system. Remember that very early on things were forming.
• 34:14
  Speaker 1: There may even have been more planets than the ones
• 34:16
  Speaker 1: we have now, and everything was quite chaotic. So now
• 34:20
  Speaker 1: we have sort of an orderly solar system where everything
• 34:22
  Speaker 1: is in place because it's been in place for so long,
• 34:25
  Speaker 1: and things that were not in place have been lost
• 34:28
  Speaker 1: or captured or fallen into the Sun. But in the
• 34:30
  Speaker 1: early days there were a lot of things going in
• 34:32
  Speaker 1: crazy orbits and crazy trajectories, and so Jupiter and Saturn
• 34:35
  Speaker 1: sort of like hoovered up a bunch of them.
• 34:37
  Speaker 2: So like, if you look at the moons of Jupiter,
• 34:39
  Speaker 2: for example, they're not all going to be like lined
• 34:41
  Speaker 2: up in a plane like our solar system. They probably
• 34:44
  Speaker 2: all have like crazy orbits around Jupiter.
• 34:46
  Speaker 1: Right, Yeah, that's exactly right, and that's why we think
• 34:49
  Speaker 1: that most of these were captured. Also, in the cases
• 34:51
  Speaker 1: that we've been able to try to study what these
• 34:53
  Speaker 1: moons are made out of, they're all made out of
• 34:55
  Speaker 1: totally different things, and so it doesn't look like they
• 34:57
  Speaker 1: formed from the same sort of scoop of solar systems
• 35:00
  Speaker 1: off that Jupiter did.
• 35:02
  Speaker 2: That's what you were saying, like you can check the
• 35:04
  Speaker 2: DNA basically the DNA of the moon and the planet
• 35:06
  Speaker 2: to see if they came from the same stuff, and
• 35:08
  Speaker 2: sometimes they don't, right.
• 35:10
  Speaker 1: Yeah, exactly. That's still tricky to do because we haven't
• 35:13
  Speaker 1: landed on those moons and like really taken samples that
• 35:15
  Speaker 1: we can study. But we can like do spectroscopy, we
• 35:18
  Speaker 1: can see the light that bounces off of them, we
• 35:20
  Speaker 1: can see what they emit, these kind of things. We
• 35:23
  Speaker 1: have done some flybys, and so we have ideas for
• 35:25
  Speaker 1: what these moons are probably made out of.
• 35:29
  Speaker 2: And in the early Solar system, like you said, things
• 35:31
  Speaker 2: were like there were probably like rock giant rocks flying
• 35:34
  Speaker 2: all over the place, and so it wouldn't be that
• 35:37
  Speaker 2: weird for some of them to fall into orbit around
• 35:40
  Speaker 2: like a passing Jupiter or Centurn. So is that how
• 35:43
  Speaker 2: we got our moon? Did we capture it or steal
• 35:45
  Speaker 2: it from somebody?
• 35:45
  Speaker 1: So we think our moon is unusual because it doesn't
• 35:47
  Speaker 1: fall into either of these categories. We don't think that
• 35:50
  Speaker 1: the Moon was formed with the Earth. We also don't
• 35:53
  Speaker 1: think that a wholly formed moon was captured by the Earth. Instead,
• 35:56
  Speaker 1: we think it comes from a collision. We think that
• 35:59
  Speaker 1: there was the proto Earth, this early planet, and then
• 36:02
  Speaker 1: there was another Mars like planet that came by and
• 36:05
  Speaker 1: smashed into the Earth, and there was this incredible collision
• 36:09
  Speaker 1: where essentially these two planets merged, but they left a
• 36:12
  Speaker 1: huge debris ring, and then that debris ring pulled together
• 36:16
  Speaker 1: and made the Moon.
• 36:17
  Speaker 2: Does our moon have an orbit that's around our equator
• 36:20
  Speaker 2: or is it tilted?
• 36:21
  Speaker 1: The Moon doesn't have a totally random orbit relatively angular
• 36:24
  Speaker 1: momentum of the Earth, because the two objects are essentially
• 36:27
  Speaker 1: formed by the combined angularmentum of this collision. So you
• 36:30
  Speaker 1: get this collision and basically you start from scratch. You
• 36:33
  Speaker 1: have a new blob of stuff which is then going
• 36:35
  Speaker 1: to coalesce again into a planet and a moon. And
• 36:38
  Speaker 1: so there is a relationship of course between the Earth's
• 36:40
  Speaker 1: spin and the Moon's orbit, and that's because they come
• 36:43
  Speaker 1: from this combined blob from this collision.
• 36:46
  Speaker 2: It's pretty dramatic. I think you can look up videos
• 36:49
  Speaker 2: of simulations of it online. It's like the Earth, the
• 36:51
  Speaker 2: proto Earth before Earth was just hanging out and then
• 36:54
  Speaker 2: this giant rock just slams into it. It all sort
• 36:57
  Speaker 2: of explodes together, but then gravity pulls it together into
• 37:01
  Speaker 2: Earth and the Moon.
• 37:02
  Speaker 1: Exactly, and the early Moon, we think, was much much
• 37:04
  Speaker 1: closer to the Earth, something like a tenth of its
• 37:07
  Speaker 1: current orbit, and then over time it spirals out and
• 37:11
  Speaker 1: ends up becoming tightly locked to the Earth. One reason
• 37:13
  Speaker 1: we think this is that we've been to the Moon
• 37:15
  Speaker 1: and we've been able to land on it and study
• 37:17
  Speaker 1: what it's made out of, and we see that it's
• 37:19
  Speaker 1: made out of a lot of stuff that's very very
• 37:21
  Speaker 1: similar to what the Earth is made out of, which
• 37:23
  Speaker 1: suggests that they do have some sort of common origin.
• 37:27
  Speaker 2: And does the Earth also sort of have moon like
• 37:30
  Speaker 2: materials in it that are not like the rest of
• 37:32
  Speaker 2: the Earth.
• 37:33
  Speaker 1: Well, we see that the Earth and the Moon have
• 37:34
  Speaker 1: a lot of very similar elements, which sugg they all
• 37:37
  Speaker 1: came from the same stuff, But the Moon has fewer
• 37:39
  Speaker 1: of like volatile elements things that vaporize at low temperatures
• 37:43
  Speaker 1: we're probably lost in this high energy event, and the
• 37:45
  Speaker 1: Moon has smaller gravity and so it's not able to
• 37:48
  Speaker 1: recapture these things the way the Earth did, so the
• 37:50
  Speaker 1: Earth and the Moon don't have exactly the same kinds
• 37:53
  Speaker 1: of stuff. The Moon also has a sort of surprisingly
• 37:55
  Speaker 1: small iron core which overall makes the Moon have lower density.
• 38:00
  Speaker 1: Simulations confirmed that this is what you would expect from
• 38:02
  Speaker 1: this kind of collision, that the Moon was formed more
• 38:05
  Speaker 1: out of the sort of external debris and the Earth
• 38:07
  Speaker 1: sort of got a bigger sampling of the core stuff.
• 38:11
  Speaker 2: I guess the Moon is also smaller, so it doesn't
• 38:13
  Speaker 2: have as much gravity compressing it, right, making it denser exactly.
• 38:17
  Speaker 1: And when they study like what's inside the Moon, they
• 38:19
  Speaker 1: find samples that suggest the Moon was molten down to
• 38:23
  Speaker 1: like a surprising depth. And you don't expect the small
• 38:26
  Speaker 1: body like the Moon to have the gravitational pressure to
• 38:29
  Speaker 1: like melt its inerts the way the Earth does. So
• 38:31
  Speaker 1: they think that the Moon was probably molten because of
• 38:34
  Speaker 1: this collision, not because of its like gravitational pressure.
• 38:37
  Speaker 4: Hmm.
• 38:37
  Speaker 2: Interesting. And I think they also found like the same
• 38:40
  Speaker 2: cheese inside of the Moon as some of the cheese
• 38:43
  Speaker 2: we have on Earth too, Right, that's part of the theory.
• 38:49
  Speaker 1: Yeah, they found pan pizzas rejected on the surface of
• 38:51
  Speaker 1: the Moon that nobody could eat.
• 38:53
  Speaker 2: That's right, the same mozzarella, cheese, the same cows, even
• 38:57
  Speaker 2: space cows. All right, well, that's the origin of our moon.
• 39:00
  Speaker 2: Let's get a little bit into what that means about
• 39:03
  Speaker 2: the formation of all moons and the formation of our
• 39:07
  Speaker 2: whole Solar system, why we're here, and why are things
• 39:10
  Speaker 2: the way they are. But first, let's take another quick break.
• 39:25
  Speaker 2: All right, we are coming face to face with the
• 39:28
  Speaker 2: lunacy here in the podcast talking about the origin of
• 39:31
  Speaker 2: moons and in particular our moon. You're saying, it's interesting because,
• 39:35
  Speaker 2: like our moon is sort of a combination of how
• 39:37
  Speaker 2: some of these other moons can form. Right, Like, we
• 39:40
  Speaker 2: had a proto planet Earth, and when there was a
• 39:43
  Speaker 2: visitor that was flying around came near us, it sort
• 39:47
  Speaker 2: of got captured or collided with our Earth, and then
• 39:49
  Speaker 2: it all became a big mess. And out of that mess,
• 39:52
  Speaker 2: you know, the Earth and the Moon forms sort of
• 39:54
  Speaker 2: a siblings, but also not siblings, because there was it
• 39:58
  Speaker 2: came from a different planet. The stuff.
• 40:01
  Speaker 1: There was a big fight early on, and we were left
• 40:03
  Speaker 1: over cleaning up the mess. Yeah, it is really fascinating,
• 40:06
  Speaker 1: and I love this sort of archaeology, this like detective
• 40:09
  Speaker 1: story figuring out what happened billions of years ago, reconstructing
• 40:13
  Speaker 1: the story from the clues that are left behind, these
• 40:15
  Speaker 1: really subtle hints. You know, why does the Moon seem
• 40:17
  Speaker 1: to be made of the same stuff as the Earth,
• 40:19
  Speaker 1: but it doesn't have sort of a close circular orbit
• 40:22
  Speaker 1: the way you would expect. Why exactly is it so big?
• 40:24
  Speaker 1: These stories are really fascinating because we missed so much
• 40:27
  Speaker 1: of the Solar System history. You know, like billions of
• 40:30
  Speaker 1: years happened with crazy fireworks in the sky and we
• 40:33
  Speaker 1: weren't here to look at it. But we can still
• 40:35
  Speaker 1: get hints about what happened.
• 40:37
  Speaker 2: Hmmm, do you think that's an official job title out there,
• 40:39
  Speaker 2: like space archaeologists.
• 40:42
  Speaker 1: Space murder mystery, you know, exactly.
• 40:45
  Speaker 2: Give me like Indiana solo a combination of Indiana Jones
• 40:49
  Speaker 2: and Hands solo.
• 40:51
  Speaker 1: And you know, we're still learning stuff about moons, like
• 40:54
  Speaker 1: Mars has some funny moons, Phobos and Demos, And the
• 40:57
  Speaker 1: smaller of those two moons, Demos, is really tiny. It's
• 41:01
  Speaker 1: only like nine miles across, has a really weird shorwt
• 41:04
  Speaker 1: of blobby shape to it, and for a long time
• 41:07
  Speaker 1: people thought it was probably a captured asteroid because of
• 41:10
  Speaker 1: its orbit, but they recently send an orbiter very very
• 41:13
  Speaker 1: close to it, super close approach by this spacecraft from
• 41:16
  Speaker 1: the UA Emirates. Actually it's called Hope, and they were
• 41:18
  Speaker 1: able to study what it's made out of and discover
• 41:21
  Speaker 1: that it has sort of the same carbon and organics
• 41:24
  Speaker 1: that Mars does, unlike the asteroids, sort of like the
• 41:27
  Speaker 1: DNA test you were saying before, which means that Demos
• 41:30
  Speaker 1: probably is a chunk of Mars that got blown off
• 41:34
  Speaker 1: in some sort of prehistoric collision.
• 41:36
  Speaker 2: Isn't that also kind of the theey of how we
• 41:38
  Speaker 2: got life on Earth, like a possible way that maybe
• 41:41
  Speaker 2: Mars got hit by something. It threw a bunch of
• 41:43
  Speaker 2: rocks out into space. Some of them became Demos, the
• 41:46
  Speaker 2: moon of Mars, and maybe some of them came to
• 41:48
  Speaker 2: Earth bringing like little bacteria.
• 41:50
  Speaker 1: Perhaps we're very sure that rocks from Mars have landed
• 41:53
  Speaker 1: on Earth. We have found them and their geology matches
• 41:56
  Speaker 1: Mars and doesn't match Earth. So there's no controversy about
• 41:59
  Speaker 1: whether visions from asteroids on planets can knock stuff off
• 42:03
  Speaker 1: into outer space and have it land on other planets.
• 42:05
  Speaker 1: Whether there's life in those rocks that then seeded life
• 42:08
  Speaker 1: on Earth totally open question. There was this famous misdiscovery
• 42:12
  Speaker 1: about twenty years ago when they found these weird little
• 42:15
  Speaker 1: shapes inside a Martian rock on Earth, and they made
• 42:18
  Speaker 1: this announcement that they were certain that there was life
• 42:20
  Speaker 1: in them, that these shapes could only be made by life.
• 42:23
  Speaker 1: But then later analysis demonstrated that you could make those
• 42:25
  Speaker 1: things without life. So there's no concrete proof that life
• 42:29
  Speaker 1: has traveled between planets on an asteroid, but it's totally
• 42:32
  Speaker 1: possible for it to happen. And Demos definitely is a
• 42:35
  Speaker 1: chunk of Mars floating in space. Sort of like if
• 42:38
  Speaker 1: you went out into space and you found like Manhattan
• 42:41
  Speaker 1: floating out in space, you'd be like, whoa, Where'd this
• 42:43
  Speaker 1: come from?
• 42:44
  Speaker 2: Yeah, well people wonder about that.
• 42:46
  Speaker 1: Now, what's the story? How did Manhattan get so weird?
• 42:50
  Speaker 2: Where did New Yorkers come from their lunatics?
• 42:53
  Speaker 1: But they have the best pizza, right, so I don't
• 42:56
  Speaker 1: want to have to go out of space to get
• 42:57
  Speaker 1: my pizza.
• 43:00
  Speaker 2: You just insulted everyone in Chicago. He lost a big
• 43:02
  Speaker 2: chunk of our listenership.
• 43:04
  Speaker 1: I love Chicago, I love Chicago wins, and I love
• 43:06
  Speaker 1: the Chicagoans love Chicago pizza. That's all fine with me.
• 43:09
  Speaker 2: All right, Well, what does all of this tells about
• 43:11
  Speaker 2: the formation of the Solar System and how we ended
• 43:14
  Speaker 2: up where we are and how we are.
• 43:16
  Speaker 1: It's a story that we are still unraveling.
• 43:18
  Speaker 5: Right.
• 43:18
  Speaker 1: We're still learning about our moon, We're still learning about
• 43:21
  Speaker 1: our neighbor's moons. We're still discovering moons. Right. Saturn recently
• 43:25
  Speaker 1: past Jupiter. I think in the number of moons that
• 43:28
  Speaker 1: it has, each one tells us a little bit of
• 43:30
  Speaker 1: the story of the Solar system, and what we're looking
• 43:33
  Speaker 1: for now are like more details for that story. As
• 43:35
  Speaker 1: you said earlier, we're asking questions like can moons have moons?
• 43:39
  Speaker 1: A lot of people think that it's impossible for the
• 43:42
  Speaker 1: same reason that like Mercury and Venus don't have moons
• 43:44
  Speaker 1: from the tidal forces of the Sun, that Jupiter's moons
• 43:47
  Speaker 1: probably can't have their own moons because of the tidal
• 43:50
  Speaker 1: forces of Jupiter. But you know, Saturn's moon Rhea probably
• 43:53
  Speaker 1: has rings which even though they're disrupted by the title forces,
• 43:57
  Speaker 1: they can still be in orbit around Rhea. And there's
• 44:00
  Speaker 1: like hundreds of minor planets deep out there in the
• 44:03
  Speaker 1: Solar system that do have their own moons, like Pluto.
• 44:06
  Speaker 1: But beyond that, we're also looking into other solar systems
• 44:09
  Speaker 1: to try to understand whether the moons that we have
• 44:11
  Speaker 1: are weird or typical? Right, Like, we only so far
• 44:15
  Speaker 1: have this one solar system to study at this level
• 44:18
  Speaker 1: of detail. Twenty years ago, we were able to see
• 44:20
  Speaker 1: planets around other stars, which tells us a lot about
• 44:22
  Speaker 1: whether the planets in our solar systems are weird. Now
• 44:25
  Speaker 1: we're pushing those boundaries to try to look for moons
• 44:28
  Speaker 1: in other solar systems. This thing we call exo moons
• 44:32
  Speaker 1: to try to discover if the distribution of moons that
• 44:34
  Speaker 1: we have is strange or pretty typical in the universe.
• 44:38
  Speaker 2: Well, that's wild. How are we seeing moons and other
• 44:40
  Speaker 2: planets outside of our solar system? Can we see them
• 44:43
  Speaker 2: or do we have to infer them from the gravity.
• 44:46
  Speaker 1: So there's a few ways that we discover planets, and
• 44:48
  Speaker 1: we can try to apply those ways to discover moons.
• 44:51
  Speaker 1: One of the early ways we discovered planets around other
• 44:54
  Speaker 1: stars was seeing their gravitational impact on the star, and
• 44:58
  Speaker 1: that would wiggle the star and cause like a change
• 45:01
  Speaker 1: in the frequency of the light, this Doppler shift, and
• 45:04
  Speaker 1: so we could discover that there was something pulling on
• 45:06
  Speaker 1: that star. We don't think that method will work for
• 45:08
  Speaker 1: discovering moons because it's really hard to distinguish the gravitational
• 45:11
  Speaker 1: effect of a little moon around a planet from the
• 45:13
  Speaker 1: planet itself. What we do think is possible is the
• 45:16
  Speaker 1: transit method, this eclipse method, where a planet passes in
• 45:20
  Speaker 1: front of a star and dips the light that comes
• 45:22
  Speaker 1: from it, And if that happens in a regular way,
• 45:24
  Speaker 1: we can tell that these little microeclipses come from a planet. Well,
• 45:27
  Speaker 1: if those eclipses have their own little dips in them,
• 45:30
  Speaker 1: because the moon going around the planet sometimes blocks this
• 45:33
  Speaker 1: life from the star and sometimes doesn't, then you can
• 45:36
  Speaker 1: discover moons around those planets. So like microeclipses within microeclipses.
• 45:42
  Speaker 2: Wow, exo eclipses exo exo moon eclipses.
• 45:45
  Speaker 1: Yeah, they're like eclipses squared. And we don't have any
• 45:47
  Speaker 1: confirmed exo moons yet, though there are a couple of
• 45:50
  Speaker 1: candidates from the Kepler telescope that look promising, but people
• 45:54
  Speaker 1: can't yet agree whether that actually is the discovery of
• 45:58
  Speaker 1: a moon. And more recently, we've developed this incredible technology
• 46:01
  Speaker 1: to do direct imaging of exoplanets, like telescopes that actually
• 46:05
  Speaker 1: take pictures of planets around other stars. Blows my mind.
• 46:09
  Speaker 1: I never thought that would be possible. A lot of
• 46:11
  Speaker 1: it involves like blocking out the light from the star
• 46:14
  Speaker 1: itself so you can see the ring around it. And
• 46:16
  Speaker 1: sometimes that lets us see planets being formed. So we
• 46:19
  Speaker 1: can see, for example, a star with a planetary disc
• 46:22
  Speaker 1: around it. And in one case we have a direct
• 46:25
  Speaker 1: image of a protoplanetary disc which seems to have a
• 46:28
  Speaker 1: planet with its own disc around it. So like you
• 46:31
  Speaker 1: can see the planet and it's got like a bunch
• 46:33
  Speaker 1: of stuff around it, and maybe that stuff will form
• 46:36
  Speaker 1: into a moon.
• 46:37
  Speaker 2: You can see the rings in it.
• 46:39
  Speaker 1: Yeah, exactly. You can see this disc that's going to
• 46:41
  Speaker 1: form it either into rings or moons or something.
• 46:44
  Speaker 2: Yeah, it's pretty mind blowing because I wonder like if
• 46:46
  Speaker 2: a lot of people know that you can actually see
• 46:48
  Speaker 2: the moons of Jupiter kind of with your naked eye,
• 46:50
  Speaker 2: or at least with a small telescope. You don't need
• 46:52
  Speaker 2: like a super amazing telescope. You can just use something
• 46:54
  Speaker 2: you can buy for your house and you can see
• 46:55
  Speaker 2: the moons of Jupiter.
• 46:56
  Speaker 1: Yeah, it doesn't take a fancy telescope. It was one
• 46:59
  Speaker 1: of the first things that Galla saw when he pointed
• 47:01
  Speaker 1: a telescope at the sky. It was one of the
• 47:02
  Speaker 1: first people to ever do this, and he saw the
• 47:04
  Speaker 1: moons of Jupiter. It's not hard. You can do it,
• 47:06
  Speaker 1: and it's pretty exciting to see Jupiter expand from this
• 47:09
  Speaker 1: tiny dot you can see with the naked eye to
• 47:11
  Speaker 1: this whole orbital system with its own dynamics.
• 47:14
  Speaker 2: H pretty cool. All right. Well, one thing that's day
• 47:18
  Speaker 2: announced recently is that we're sending more people to the Moon.
• 47:20
  Speaker 1: That's right, if Elon Musk ever gets that starship off
• 47:23
  Speaker 1: the ground.
• 47:23
  Speaker 2: No, the new artem is missions right, It isn't one
• 47:26
  Speaker 2: of the plants to send more people to the moon.
• 47:28
  Speaker 1: Yeah, that's exciting. It'd be cool to go back to
• 47:30
  Speaker 1: the Moon. With all of our advanced technology, we can
• 47:32
  Speaker 1: take more detailed measurements. We can map its magnetic field,
• 47:35
  Speaker 1: we can understand its geology and its history even better. Yeah.
• 47:38
  Speaker 2: I wonder why kind of pizza they would eat there though?
• 47:40
  Speaker 2: It's a deep dish because there's not much that much gravity.
• 47:43
  Speaker 2: So can you have a deep dish pizza?
• 47:46
  Speaker 1: Probably every pizza would rise a lot more because there
• 47:48
  Speaker 1: isn't gravity, right.
• 47:49
  Speaker 2: Oh, my goodness. In space, every pizza is a deep
• 47:51
  Speaker 2: dish pizza. That's why you're not going to Earth.
• 47:53
  Speaker 1: Danu or maybe astronaut pizza is just freeze dried and
• 47:57
  Speaker 1: gross no matter where it comes from.
• 48:01
  Speaker 2: I guess there's something one way to find out to
• 48:03
  Speaker 2: take the podcast to space. All right, Well that kind
• 48:06
  Speaker 2: of answers our question. How the Moon's form basically two
• 48:09
  Speaker 2: main ways, right, They either capture something flying by in space,
• 48:13
  Speaker 2: or they form together with the planet, or some combination
• 48:16
  Speaker 2: of the tube where something comes from space crashes into you,
• 48:20
  Speaker 2: creates a big mess, and then you both sort of
• 48:22
  Speaker 2: form together or reform together.
• 48:24
  Speaker 1: And the incredible thing is that by looking at the
• 48:26
  Speaker 1: Moon today we can mostly figure out how that happened,
• 48:29
  Speaker 1: how this huge space rock ended up in orbit around
• 48:32
  Speaker 1: the planet. Yeah.
• 48:33
  Speaker 2: And the cool thing is that you can see the
• 48:34
  Speaker 2: Moon almost every night. Every night you step outside of
• 48:37
  Speaker 2: your house, you can see this giant rock floating in
• 48:39
  Speaker 2: space there for us to see, pretty shiny, pretty bright.
• 48:44
  Speaker 1: It's nice to have one big, fat moon. I agree.
• 48:47
  Speaker 2: All right, Well, we hope you enjoyed that. Thanks for
• 48:49
  Speaker 2: joining us, See you next time.
• 48:59
  Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain
• 49:02
  Speaker 1: the Universe is a production of iHeartRadio. For more podcasts
• 49:06
  Speaker 1: from iHeartRadio, visit the iHeartRadio, app, Apple podcasts, or wherever
• 49:11
  Speaker 1: you listen to your favorite shows.