How do planets get their moons?

Daniel and Jorge talk about how a planets gets its natural satellites and the stories that each one reveals.

See omnystudio.com/listener for privacy information.

Episode Transcript

Speaker 1 (00:08):
Hey, do you ever wish that we had more moons
in our night sky?

Speaker 2 (00:14):
Hmmm? I think the universe as moon does enough times.

Speaker 1 (00:18):
Actually, well, I like the moons, and I sometimes wish
we had more going on in the night sky, like
lots of little moons.

Speaker 2 (00:28):
But then I wonder if we had the same line
in Star Wars, you know, where he says that's no moon.
That wouldn't work.

Speaker 1 (00:36):
Maybe instead of the Death Star, they would have had
the death constellation.

Speaker 2 (00:40):
Or that song when the moon hits your eye like
a big pizza pie. That wouldn't work with a lot
of little moons. I guess it would work with lots
of mini pizzas.

Speaker 1 (00:50):
The personal pan pizza would have been invented earlier.

Speaker 2 (01:08):
Hi am Horehea, ma cartoonist and the creator of PhD comics.

Speaker 1 (01:11):
Hi I'm Daniel. I'm a particle physicist and a professor
at UC Irvine, and I'd never really been a fan
of the pan pizza, of.

Speaker 2 (01:19):
The pan or the pizza or just a combination of
the two.

Speaker 1 (01:22):
The pizza in the pan. Definitely a thin crust kind
of guy over here, not.

Speaker 2 (01:26):
A bread fan trying to curb your carbs.

Speaker 1 (01:30):
I like tomato sauce. But I don't like the kiddie
pool of marinera that they call pizza in Chicago.

Speaker 2 (01:34):
I feel like there's a thin line between a pan
pizza and like a casserole or like a pot pie.

Speaker 1 (01:40):
It's really just a Midwestern hot dish.

Speaker 2 (01:42):
There you go, But anyways, welcome to our podcast, Daniel
and Jorge Explain the Universe, a production of iHeartRadio.

Speaker 1 (01:48):
Where we love everything about the universe, the thick ready
questions and the thin crunchy ones we wonder about how
everything out there in the universe works. We take a
big curiosity motivated by it, of the universe and try
to chew through all of it for you.

Speaker 2 (02:02):
That's right, because the universe is a deep dish of
amazing facts and incredible things happening in it, full of
mysteries and wonderful conundrums for us to try to figure out.

Speaker 1 (02:12):
And while physics has made incredible progress in understanding the
way the world works, we're still answering the kinds of
questions we've been asking basically forever, just looking around us,
seeing how the world is and wondering like, why is
it this way? How did it get to be this way?

Speaker 2 (02:28):
Why does Deep Dish Pizza exist? Fundamental questions? That's what
we ask here on the podcast, and why doesn't Daniel
like them?

Speaker 1 (02:36):
We know why Deep Dish Pizza exist for the same
reason vanilla ice cream exists, because you know, there's a
whole spectrum of people out there and everybody loves different things.

Speaker 2 (02:44):
Are you saying the universe is kind of cheesy? I
guess it will definitely give you a heart attack as well.
There's no topping that joke, but yeah, we like to
think about the universe and all of the perfecting things
in it, like how did things come to be the
way they are? Why are we here? And where are
we in the universe?

Speaker 1 (02:59):
And what is One of the real, simple but enduring
joys of being a curious person is just looking up
at the night sky. Not just being amazed at it's
beauty and odd at the depth of the view that
you were looking at, but this shared feeling through time
that humans one hundred years ago, a thousand years ago,
twenty five thousand years ago probably looked up at almost

(03:20):
the same night sky and wondered what was up there
and why it looked the way it did, and whether
it could have been different.

Speaker 2 (03:27):
Yeah, you're looking at the exact same sky that our
ancestors did, full of stars, comments, and even a moon.
And they probably asked the same question that maybe a
lot of you have out there, which is, why do
we have a moon? And is it made out of cheese?
Is it just a big, flat, giant, floating deep dish
of cheese.

Speaker 1 (03:47):
It's a spherical pizza. In the end, I have my
spherical pizza theory of the moon.

Speaker 2 (03:51):
Do you do tell? Give us a slice of that
knowledge there?

Speaker 1 (03:57):
All right? You called my bluff.

Speaker 2 (03:58):
I got nothing and it was a crusty joke. But yeah,
sometimes we look out into the universe, into the night sky,
and we wonder why are things there, and how did
they come to be the way they are? What's going on?
And it wasn't just our ancestors that looked up at
the moon. It's like all of the planet that is
looking up at the moon, right, it's feeling its facts
and howling at it and rolling with the tides that

(04:20):
go along with the moon. The moon has. It makes
a big difference here on this planet.

Speaker 1 (04:23):
Yeah, and these are not just questions asked by amateur astronomers,
but planet heiogeologist at the cunning edge are still trying
to figure out the details of how everything came to
be in our night sky.

Speaker 2 (04:34):
So to the other podcast, we'll be tackling the question
how the planets get their moon or moons. Some planets
have lots of moons, right.

Speaker 1 (04:45):
Yeah, that's right. It turns out our planet is quite
unusual in having approximately one moon.

Speaker 2 (04:50):
So you do believe in the moon. The moon does exist, right.

Speaker 1 (04:54):
I can see the moon. I know it's there, But.

Speaker 2 (04:56):
How you know it's round? It always looks the same.

Speaker 1 (04:58):
Well, we've been to the moon, so we can see
all around it, and you can tell that is round. Also,
the curved edge between the bright side and the dark
side of the moon tell us that it's going to
be round.

Speaker 2 (05:09):
Oh right, you get sort of like the shadow of
it tells you it's round.

Speaker 1 (05:13):
Exactly?

Speaker 2 (05:14):
Is it perfectly round? Is the Moon perfectly round? Or
is it kind of an ellipsoid like the Earth.

Speaker 1 (05:18):
Nothing in the universe is perfectly round. There are no
actual circles out there, maybe even not the event horizons
of black holes due to quantum effects. So the Moon
is definitely not perfectly round, and it's also pulled into
something of a football shape thanks to the Earth's gravity.
Tidal forces on the Moon by the Earth make it
a little bit oblong.

Speaker 2 (05:39):
Whoa, I guess it's not spinning in the way that
the Earth is so that you get this centropical force.
But you're saying that the fact that the Earth is
pulling on it kind of stretches it out.

Speaker 1 (05:48):
Yeah, it is spinning. It's just spinning at exactly the
right rate so that the same side of it is
always facing the Earth. This is called a tidal locking. Eventually,
the Earth pulls on the Moon to make it oblong,
and then they get stuck in this stable equilibrium where
that long bit is always pointing towards the Earth because
gravity on that long bit is a little stronger, so
it's sort of like a pendulum dangling towards the Earth.

Speaker 2 (06:10):
Well, it is cool that we have a moon. I
guess it would to inspire all of these songs and
all these stories and legends about the moon.

Speaker 1 (06:16):
It is nice to have a moon. It lights up
otherwise very dark nights, and it's something very close by
to look at, right, So much of the rest of
the night sky are just dots. They're so far away
they look like pinpricks. But the Moon has features on it.
I remember as a kid looking up at it and
studying those and like wondering what it would be like
to walk across it and to be on it, or
to look at the Earth from the moon. It's cool

(06:38):
that it's both in the night sky and kind of
close by.

Speaker 2 (06:41):
Yeah, I guess it's kind of scary to think about it. Actually,
it's just kind of swinging around the Earth. It's constantly
falling around the Earth. That's what the Moon is doing.
And it's big, Like you don't want to mess with
the moon either.

Speaker 1 (06:53):
Yeah, the Moon is pretty massive. And not only is
the Earth tugging on the Moon and forcing it to
face us the same way, but the Moon is doing
the same thing to Earth. Eventually, the Earth of the
Moon will both be tidally locked to each other.

Speaker 2 (07:07):
Mmmmm, wait what does that mean? That means that we
will be going around the moon.

Speaker 1 (07:14):
It means that, given enough time, the Moon will stay
on the same side of the Earth. The Earth's spin
and the Moon's spin will balance so that only one
side of the Earth ever sees the Moon the same way,
only one side of the Moon ever sees the Earth.

Speaker 2 (07:29):
Wait, what for real. When is that going to happen.

Speaker 1 (07:31):
It's not going to be for billions of years, but
it has already had an impact, Like the rate that
the Earth is spinning has slowed down to twenty four
hours per spin over the last four billion years. Four
billion years ago, it took about six hours for the
Earth to spin, So the Moon is slowing down the
spin of the Earth. Eventually, it will take about forty

(07:52):
seven of our current days to spin the Earth. That
will match the Moon's orbital period, and the Earth and
the Sun will be tidally locked to each other. But
that wouldn't be for billions of years, and that would
be assuming that the Sun doesn't gobble the Earth first.

Speaker 2 (08:05):
Yeah, we would have bigger problems in the Moon at
that point.

Speaker 1 (08:09):
But it would be kind of amazing if you could
only see the Moon from one half of the Earth.
It would mean you could grow up your whole life
and not see the Moon, and then travel to another
part of the Earth and see the Moon for the
first time. That would be incredible.

Speaker 2 (08:21):
Whoa which sid gets to have the moon? Can they
predict that? Or we even have the same We probably
won't even have the same continents.

Speaker 1 (08:27):
Right, Yeah, not in billions of years exactly.

Speaker 2 (08:31):
I guess we have the moon to thank for having
more time in our day. Then without the moon that
things will be a lot more hectic.

Speaker 1 (08:37):
Yeah, that's true. Those of you who like to work
late at night would have much shorter nights to get
stuff done.

Speaker 2 (08:42):
I think the people during the day would also have
a shorter time, right, But it is an interesting question
how did we get this moon? Like how do planets
get moons at all? And why do we only have
one moon versus having lots of moons like other planets
which have up to eighty four moons.

Speaker 1 (08:59):
It is really fun, fascinating question, and the answer tells
us a lot about how solar systems form, whether our
planet is weird, and maybe whether our solar system itself
is kind of weird.

Speaker 2 (09:09):
Well, you can get all that from the moon.

Speaker 1 (09:12):
You can learn a lot just by asking questions.

Speaker 2 (09:14):
Well, as usual, we were wondering how many people out there?
I thought about the question of where moons come from
and how are they form? How do we get ours?
So as usual Daniel went out there into the internet
to ask people how do moons form?

Speaker 1 (09:27):
Thanks very much to everybody who participates in this segment
of the podcast. If you've been listening for a while
and thinking about participating, please let me encourage you. It's fun,
it's easy. Everybody enjoys it. Write to me two questions
at Danielandjorge dot com.

Speaker 2 (09:42):
So think about it for a second. How do you
think planets get their moons? Here's what people had to say.

Speaker 3 (09:47):
I think that most moons form from cloud discs around planets,
and that Satan's rings are a picture of that process
going on.

Speaker 4 (09:58):
Moons on form? How planet form? So they're small rocks
and then they hit each other and create bigger ones.
So when a planet is created, maybe when it gets created,
some debris goes out and then creates like a miniature
planet aka a moon.

Speaker 2 (10:12):
Maybe I suppose the moon is just a small planet.
It's kind of just a planet that gets trapped by
another planet. Right, they're just rocks.

Speaker 5 (10:22):
There's got to be like at least six ways moon forms.
I don't know, like things crashing together. Apparently we might
have stolen the Moon from Venus. Maybe probably a bunch
of other ways they could form too.

Speaker 6 (10:35):
I think Moon's form either just sort of alongside they're
planet like Lucky, or from collisions like our own moon
came from an impact. Those are, I guess, the only
two I really know.

Speaker 7 (10:52):
I would say that this is a collisions between among
asteroids planets, and then you have planet that has been
hit by an asteroid, and a small chunk of this
planet would be placed in a sort of an orbit,
and then you get the Moon.

Speaker 8 (11:08):
I think it's when space dust is orbiting a planet
and then it clumps together into the Moon eventually, or if,
like an asteroid, is caught in the gravitational pool of
a planet and falls into its orbit.

Speaker 1 (11:24):
I think Moon's form from asteroids and other bits of
space debris that get trapped in a planet's orbit.

Speaker 9 (11:31):
I think that moon's form around planets the same way
that planets form around stars. I think that basically there's
a bunch of junk floating around the planet that aggregates
into a moon or moons.

Speaker 2 (11:42):
All right, a lot of interesting answers here. Somebody said
at least six ways, that's all they said, But only
at least six he or she had six ways in mind.

Speaker 1 (11:55):
M reminds me that Paul Simon's song just get on
the bus, gus don't need to discuss much. Yeah, there
must be six ways to get a moon.

Speaker 2 (12:04):
Sounds like clickbait. Six ways so we can get a moon.
The sixth one will totally amaze you. Maybe we should
be learning from this listener and how to title our
podcast episodes. Although that you hear BuzzFeed is going down,
it's going out of business or BuzzFeed news.

Speaker 1 (12:20):
Do you think there's a lesson there for us podcasters?

Speaker 2 (12:22):
Yeah, I think there are six amazing lessons. The sixth
one will totally astound you.

Speaker 1 (12:27):
I can't wait to hear.

Speaker 2 (12:28):
But yeah, a lot of interesting theories here from people.
Some people think it happens from like a collision. Some
people think we stole it from another planet? Is that true?

Speaker 1 (12:37):
The truth is that there are lots of different ways
to get moons, and we'll dig into several of them today.

Speaker 2 (12:42):
M The sixth one will amaze you.

Speaker 1 (12:46):
If we get there.

Speaker 2 (12:47):
If we get that right, know for sure we'll get there.
Question is how long before we get there? Will we
do it before the hour is up? Towards a close call?
All right, Well, let's start with the basics, Daniel, how
would you define a moon? Like what is a moon?
And what's the difference between a moon and like a
satellite or an asteroid or just a space jump.

Speaker 1 (13:06):
Yeah, this is an interesting question in astronomy. We have
all these categories we've invented to describe the kinds of
things we've seen out there, and then we find things
that break those categories, and it turns out there are
no real hard divisions and bright lines between stuff. It's
just sort of like where humans like to draw a
dotted line between things, and so it's kind of a
mess what a moon is signs. Originally they called these

(13:29):
things natural satellites, Like when you look at Jupiter and
you see things going around it, you call those satellites
of Jupiter. And for a long time, like before the
space age, the word moon just referred to the moon
of the Earth, which is the name of our moon.
But then we started launching artificial satellites, and so when
Sputnik went up, people called it an artificial satellite. But

(13:49):
that's sort of awkward and a mouthful, so people didn't
like saying artificial satellite. They just start calling it satellite,
and so that makes natural satellite kind of awkward.

Speaker 2 (13:58):
To say organic satellite exactly, or farm raised satellites.

Speaker 1 (14:04):
But natural satellite is kind of a mouthful, and so
now people, even scientists, sometimes say moons. Technically, we have
artificial satellites, things we have launched in due space, and
then we have natural satellites, things that are in orbit anyway,
naturally without the influence of humans.

Speaker 2 (14:20):
But wait, wait, I think I've seen NASA call the
moons of Jupiter the moons of Jupiter. They never say
the satellites of Jupiter.

Speaker 1 (14:27):
That's right. So technically we have artificial satellite and we
have natural satellite, though typically we just say satellite for
artificial satellite, and now we say moon for natural satellite,
even in scientific publications and like official press releases. So
now moon has come to mean natural satellite.

Speaker 2 (14:43):
I see. But I guess if you put the in
front of it, then it's our moon. Like the moon
is our moon, but then other moons are just moons.

Speaker 1 (14:51):
Yeah, exactly, the moon is our moon or Luna if
you prefer. And moon with a lowercase M means any
kind of natural satellite.

Speaker 2 (15:00):
I guess you can have rocks, and you can have
the rock.

Speaker 1 (15:05):
Exactly. We have lots of rocks in orbit, but I
don't think we have the rock in orbit yet, though
I haven't seen fast and Furious twenty seven or whichever
one has space.

Speaker 2 (15:14):
I'm assureing the next one there, they'll you know, speed
up a ramp and somehow make it up to space
and crash into a space station. While he jumps and
also launches a rocket launcher.

Speaker 1 (15:25):
He's got to flex his muscles at some point. Another
question is size, Like, is every object that's orbiting the
Earth a moon? Every tiny little rock is at a
moon of the Earth. Officially, there's no lower limit, right,
Like every natural object with an orbit around the planet,
technically you could call it a moon.

Speaker 2 (15:42):
Wait what I mean? No, at some point, it's just
the rock, right.

Speaker 1 (15:45):
The moon is just a rock. Also makes the Moon
different from other rocks orbiting the planet is just the size,
and there is no official lower limit to the size
of a moon. You could have a moon of any size,
and any limit you place is going to be totally ourary, right.

Speaker 2 (16:01):
I wonder if the definition also has to do with
how stable its orbit is. Like, if I just throw
a rock and into space, it's kind of orbiting the
Earth for a little bit, does that mean it's a.

Speaker 1 (16:12):
Moon that's not really in orbit? Right? I don't know
how strong you are. Recently haven't seen you in a while,
But I don't think you could throw a rock and
actually get it into orbit. It has to be in orbit.

Speaker 2 (16:21):
Oh yeah, do you want to make that bet? I'll
bet you a billion dollars because with a billion dollars
I can come into space and throw the rock.

Speaker 1 (16:30):
If you get a rock orbiting the Earth, I will
campaign NASA to let you name it officially.

Speaker 2 (16:35):
Well, if you get me on a rocket ship into
space to throw a rock, we'll start the whole process.

Speaker 1 (16:40):
But we can look at the typical sizes of these things,
and like in our Solar system there are a few
hundred of these moons. There's six planets that have moons,
for a total of two hundred and twenty six moons,
and typically the planet to moon mass ratio is at
least ten thousand to one, so moons typically have a
much smaller mass than the planet they orbit.

Speaker 2 (17:01):
Wait, there are six planets in our Solar system with moons.
Who doesn't have a moon?

Speaker 1 (17:05):
Neither Mercury nor Venus have moons. That's probably because they're
too close to the Sun and so tidal disruption basically
pulls those moons away.

Speaker 2 (17:14):
Oh interesting, and I just figured out that's probably what
the listener meant when they said at least six ways.

Speaker 1 (17:19):
Oh nice. Probably every moon has a unique story, m
they have their own origin story. Of course, our moon
is a big exception to this ten thousand to one rule, right,
because the mass of the Moon is about one eightieth
of the mass of the Earth. It's like more than
one percent of the mass of the Earth. So it's

(17:40):
a big honk and moon it's very unusual.

Speaker 2 (17:43):
So most of the moons in the Solar System, some
of them are as big as our moon, but you're
saying that the ratio compared to their planet, most of
them are small.

Speaker 1 (17:53):
Most of them are small exactly. And then there's the case,
for example, of Pluto. Pluto has a moon which is Sharon,
which is one eighth of its mass, and so like
we call Pluto a dwarf planet, and we call Sharon
a moon of Pluto. But you know, you could also
argue that it's really like a dwarf planet binary system,
which one is a planet and which one is the moon?

(18:14):
It all gets kind of fuzzy.

Speaker 2 (18:15):
Whoa, it's like a double planet.

Speaker 7 (18:19):
Man.

Speaker 1 (18:21):
One way to distinguish the two scenarios, like having a
double planet or a planet with a moon. Is whether
the center of mass of the system is within the
surface of one of them. If you find the point
that averages where all the mass is, the point around
which the two objects really are orbiting, if that is
underground one of the two objects, and you call the

(18:41):
more massive one a planet and the other one a moon.
Otherwise you call it a binary system. Again, that's still
kind of arbitrary, right, We're just like giving these things
names and drawing lines between them. Really, there's just a
bunch of different rocks out there in the universe orbiting
each other.

Speaker 2 (18:55):
Except also, Pluto is not a planet, So can you
have a moon around something that's not planet? Like can
you can moon or can a moon have a moon?

Speaker 1 (19:03):
You can have a moon around a dwarf planet, though
maybe you would want to call it a dwarf moon.
I don't know. And it's possible in principle to have
moons around moons. There are asteroids that have moons.

Speaker 2 (19:15):
Wait what, and you still call them moons, not master moons.

Speaker 1 (19:19):
Some people want to call them moonlits or moon moons
like the moon of a.

Speaker 2 (19:23):
Moon or moony's or mini moons.

Speaker 1 (19:26):
And there are even some moons, like Rhea has its
own ring system Saturn's moon Rhea.

Speaker 2 (19:30):
Wait what some moons can have rings? Yeah, because they
have so many mini moons.

Speaker 1 (19:36):
If you're big enough that you dominate the gravitational environment nearby,
then yeah, you can have your own rings.

Speaker 2 (19:41):
I mean, I guess technically anything can have a satellite, right,
Like I can take a baseball, put in into space
and then knock a you know, a speck of dust
in orbit around it.

Speaker 1 (19:50):
Right, yeah, exactly. That wouldn't be a planet or even
a dwarf planet, but it would have an orbiting object.
Is that a natural satellite? I'm not quite sure.

Speaker 2 (19:59):
A what else do we know about moons?

Speaker 1 (20:01):
If you try to dig into the ancient history of moons,
it gets quite confusing to read about because until Copernicus,
moons were actually called planets, like the Moon itself was
referred to as a planet. Like when you talked about
astronomy in the fifteen hundreds, you said the planet Mars,
the planet Venus, the planet Luna. And it wasn't until Kepler,
who was thinking about how these things orbit each other,

(20:22):
who had a better understanding of these orbits, that we
started calling the moon a satellite of the Earth, and
then the satellites of Jupiter are of course the moons
of Jupiter. So there's a really fun interesting history to
these words.

Speaker 2 (20:34):
Wait, really, so like, for a moment in human history,
we thought the Moon was another planet orbiting the Solar System.
Technically it is orbiting the Sun.

Speaker 1 (20:43):
Yeah, it is orbiting the Sun, and it is orbiting
the Earth. Right, it's not that we thought the Moon
was a planet like Mars. It's just that we categorized
all these things the same way. All these words are
just buckets, right, and they're just like grab a bunch
of the stuff that's out there and gather it all
into a conceptual bucket. And where the lines between these
buckets is a little bit arbitrary. And so it used
to be that we lumped the moon in with the planets.

(21:04):
Now we have a separate category for things that orbit
the planets.

Speaker 2 (21:09):
Shoot for the Moon. I guess when you're naming things,
all right, well, let's get a little deeper into where
the Moon came from, Where do moons in general come from,
how do other planets get their moons, and what does
it all mean about the history of the Solar System.
But first let's take a quick break, all right, we're

(21:37):
getting a little looney here talking about the moon and
how we got it and how do planets get their moons.

Speaker 1 (21:43):
It is really fun in ancient question to wonder why
that thing is in our sky and why Jupiter has
more moons than we do. And if history had been different,
would we have had a bunch of moons? What would
it be like to live in that scenario? Could we
sail as well? If the ties were crazy and complicated
from having like fifteen different little moons? Hmmm?

Speaker 2 (22:02):
Interesting? Yeah, that would affect the tides, right, But that
wouldn't affect navigation, would it.

Speaker 1 (22:06):
It wouldn't affect navigation, but it would affect when it's
easy to launch your ships or not, and so it
might affect lots of industries and exploration.

Speaker 2 (22:14):
M Also, if you're a were wolf, it would be
pretty complicated, right, probably, just you know, just the planet ahead.

Speaker 1 (22:20):
Maybe you change into one kind of wolf for one
moon and another kind of wolf for another moon, and
like a Pomeranian for the little moon or a shitsu.

Speaker 2 (22:29):
Yeah, there you go, different moons for different breeds.

Speaker 1 (22:31):
Two moons up in the sky. Then you're a hybrid, right,
This sounds like a fun science fiction story.

Speaker 2 (22:35):
It sounds like a great Ya novel.

Speaker 1 (22:39):
So many spin offs.

Speaker 2 (22:40):
All right, we talked about the word moon is kind
of flexible and it's not quite super well defined, but
basically it just kind of means like a big rock
circling around a bigger rock. Right, that's right.

Speaker 1 (22:50):
It's a big rock orbiting another big rock.

Speaker 2 (22:53):
And as you said, six of the planets in our
Solar system have them. Venus and Mercury don't because I
guess they're too hot, you said. And if they had moons,
then the Sun would have disrupted its orbit and probably
made it crash into the planet, right or fly away.

Speaker 1 (23:07):
Yeah, it's all about the tidal forces. It makes it
basically impossible for Mercury or Venus to have moons and
to keep them. It's because they're so close to the Sun.
It's not their actual temperature, it's the gravitational tidal forces
from the Sun.

Speaker 2 (23:18):
All right, Well, what do we know about where moons
come from and how they're form?

Speaker 1 (23:22):
So you can tell a lot about where a moon
came from based on what it's made out of and
how it's orbiting. If a moon is mostly in a
circular orbit, and the circular orbit follows the tilt of
the planet, so for example, it's orbiting around the equator
in mostly a circle. Then it's very likely that that
moon came from the same stuff that formed the planet.

(23:43):
Remember how planets form in the beginning, it's a big
cloud of gas and dust that forms the whole Solar System.
Most of the gas is gobbled up by the star
as it forms, and our Sun has ninety ninety percent
of the mass of the Solar System. But if you
get a little isolated pocket of heavy stuff that has
its own gravity and can gather itself together, then you
can get a planet. So a planet sort of forms
the same way the Solar System does. It's the gravitational

(24:05):
collapse of a big blob of.

Speaker 2 (24:06):
Stuff, right, And initially it's just kind of like a
big cloud of rocks and dust that's spinning or has
kind of an overall spin.

Speaker 1 (24:14):
Exactly. The reason you get moons around planets is the
same reason you get planets around stars. Right. You don't
just get all the mass of the Solar System collapsing
into the Sun. You get these little pockets that have
enough gravity to form themselves together and then are moving
at high enough speed that they can resist falling into
the Sun. Now, around those planets, of course, you also
have little clouds of gas and dust. Some of it

(24:35):
collapses into the planet, most of it, but some of
it pulls itself together and has enough velocity to avoid
falling into the planet. And so if you have enough
velocity and you can pull yourself together, then you can
form like a little planet's planet, a little miniature system
around the planet, the same way the planet is going
around the Sun.

Speaker 2 (24:53):
Right, because I guess gravity. That's how gravity works, right,
Like everything is attracted to everything else. It's not just
like we're attract it to the Sun or juice attracted
to the planet Earth. It's like I'm attracted to my
car and to this base bomb, the base will attracted
to me. And so if we were out in space,
we would both be falling towards the Earth, but then
we would there would also be an attraction between us.

(25:15):
And sometimes I think what you're saying is that if
a clump of dirt and rocks when the planet is forming,
it's kind of far enough out there, it will clump
together before it clumps with the Earth.

Speaker 1 (25:26):
Yeah, that's exactly right. And there's sort of two steps there.
One is have enough velocity, like are you spinning fast
enough that you can basically get in orbit around the planet,
And that's how you get like a protoplanetary disc. The
planet forms and have some stuff out there that hasn't
fallen into the planet. So initially it's like a disc
and that can pull itself together using gravity into a ring.

(25:47):
And then there's a question of whether that ring can
pull itself together into a moon or not. Sometimes it
stays a ring and sometimes it forms a moon, and
that depends on how close you are to that planet.
If you're really really close to that planet, close to
than what we call the Roche limit, then tile forces
from the planet are too strong. If you try to
form a moon, the tile forces will tear it apart.

(26:08):
If you're outpast the Roche limit, then the tidle forces
are weak and you can gather together into a moon.
So you have to have enough velocity to avoid falling
into the planet, and then you have to be out
past the Roche limit to have a ring get turned
into a moon.

Speaker 2 (26:23):
Because I think, as we've talked about before, gravity kind
of depends on the distance between two things. Right. So
if you're really close to the Earth, then like the
difference between one side of the Moon and the other
side of the Moon is they experience very different gravitational forces.
But maybe if you're far out and beyond this limit,
then you don't see this difference in pull from the

(26:44):
Earth between one and and the other, which kind of
lets you clump together.

Speaker 1 (26:49):
You'll still always feel that difference, right, and like the
Moon does feel that difference. That's why we talked about earlier.
The Moon is a football. It is being pulled by
the Earth's tidal forces, but it's far and away that
those tidle forces are not strong enough to tear it apart.
The roach limit for the Earth is around ten thousand kilometers.
The Moon is like three hundred and eighty five thousand
kilometers away, so it's well past the roach limit. If

(27:11):
the Moon was much much closer, if it was like
less than ten thousand kilometers from the surface of the Earth,
the Earth would tear it apart with those tidal forces
into a massive ring system instead.

Speaker 2 (27:21):
Where some of the rocks in that ring are going
at different speeds.

Speaker 1 (27:24):
Right, it would be pretty cool to see the Moon
get torn up into rocks. Not all of them would
have the same velocity originally as the Moon. I'm sure
it would be somewhat destructive and chaotic. Some of them
would end up falling to the Earth, some of them
would get lost, and some of them would end up
in orbit.

Speaker 2 (27:37):
Cool And I think that, as you said, also applies
to planets, right like you kind of have to be
a certain distance away from the Sun just to form
a planet, too.

Speaker 1 (27:45):
Exactly, if you're too close to the Sun, then the
Sun's tidal forces, which are very powerful, will pull you apart.
So the roche limit for the Sun is like seven
hundred and fifty thousand kilometers. So if the Earth was
that close to the Sun, not only will we be fried,
of course, but the Sun would pull us apart with
its tidal forces. As you said, the gravitational force depends
on the distance, and so the Sun's gravit on the

(28:07):
near side of the Earth would be so much more
powerful than the Sun's gravity in the far side of
the Earth. It's effectively pulling us apart, and the Earth
is not strong enough to survive if it's closer than
seven hundred and fifty thousand kilometers. Fortunately, we're like one
hundred and fifty million kilometers from the Sun, so we're
nowhere near the Roche limit. And this isn't like an exact,
hard and fast number, it's like approximate. It depends on

(28:29):
the mass of the object, and it depends on structural
features of it, Like if you had a planet made
out of diamond, it could get closer to the Sun
than a planet made out of gravel.

Speaker 2 (28:39):
But I guess generally speaking, it depends on the size
of the thing in the middle, Like the Sun has
a very big roach limit and the Earth as a
smaller one.

Speaker 1 (28:47):
Yeah, that's true. You can get closer to the Earth,
then you can get to the Sun. But if you
see a moon around a planet and it's orbiting in
a circular orbit and it mostly has the same angle
or momentum as the planet, then you suspect that probably
came from the same stuff that made the planet, and
when that planet coalesced into stuff, not all of it
got turned into the planet, some of it got left

(29:08):
over and turned into a moon. So circular orbits with
the same anglermentum probably came from the same protoplanetary disk
that formed the planet.

Speaker 2 (29:19):
Okay, So then if a moon is orbiting a planet
kind of in the same plane as the planet is spinning,
then most likely they're like siblings, kind of like they
were born at the same time from the same stuff.

Speaker 1 (29:33):
Yeah, I suppose you could say so though, sort of
the scenario where like one twin is really big and
the other one is tiny.

Speaker 2 (29:39):
Yeah, they're fraternal twins.

Speaker 1 (29:42):
Exactly, and probably one it's pretty grumpy about not getting.

Speaker 2 (29:44):
As much of dinner, all right. So that's one way
that maybe a moon can form, which is like it's
borne along with the planet, and you can sort of
tell which ones those are, Which of those do we
have in our Solar system, Like, is our moon one
of them?

Speaker 1 (29:56):
Our moon is not one of those. Our moon is
actually a very weird case. Most of the moons in
the Solar System do not have nice circular orbits that
are orbiting with the planets. In fact, most of them
have elliptical orbits that have weird tilts. And that suggests
a completely different history for how.

Speaker 2 (30:11):
That moon formed, necessarily, because like I wonder if maybe
the moon was formed as a sibling, but then it
got not by something and then it got a skewed orbit.

Speaker 1 (30:21):
Yeah, that's certainly possible, but we think that most of
the ones with skewed orbits, that with tilted orbits that precess,
for example, are probably captured objects, things that came nearby
and were grabbed onto by the gravity of that planet.
You're right, it's possible for moon to be formed with
a planet and then get tilted through a collision. You
can tell the difference by looking at what that moon
is made out of. Is it made out of basically

(30:42):
the same stuff that formed the planet, or is it
made out of something totally weird and different. So that's
sort of like the key piece of information for distinguishing.

Speaker 2 (30:50):
Like a DNA test prove of your siblings or not.
All right, well, then what does not having a circular
orbit tell you about the moon.

Speaker 1 (30:58):
It tells you that probably it was captured, that the
planet is formed, and the moon comes from somewhere else.
It's like an asteroid or a dwarf planet or something
that was floating around and just came too close to
this massive object and its gravity took over. There's a
vicinity of a massive object we called the hill sphere,
which is the region sort of where its gravity dominates,
where everything else that's far away can basically be neglected,

(31:21):
and if an object passes within the hillsphere, it's a
candidate for getting captured.

Speaker 2 (31:26):
But isn't that kind of weird? Or isn't it kind
of unlikely that you'll just kind of catch a big
rock out there and it'll have just the right speed
and distance to fall into a stable orbit, Like, aren't
stable orbits kind of hard to get into?

Speaker 1 (31:38):
It is unlikely and it is weird. You're right. You
have to match the radius and the velocity. Like the
reason the Earth is in a stable orbit is because
it has the right velocity for our radius. You have
to be moving in a certain velocity at a given radius.

Speaker 2 (31:51):
Like if we slowed down at all in our orbit,
we would start to spiral into the Sun. Right.

Speaker 1 (31:55):
First orbit is actually quasi stable. So if we slowed
down a little bit, gravitational forces what actually pushes back
towards our orbit? But that's a whole other topic.

Speaker 2 (32:04):
Like if you slow down a lot, though.

Speaker 1 (32:06):
Yes, if we slowed down a lot, we would fall
in towards the Sun. If we sped up a bunch,
we would be ejected from the Solar system. And so
you have to have this match between these two quantities,
and it's not trivial for that to happen. Not only
do you have to have the right velocity and the
right radius, but you also have to lose energy in
order to fall into an orbit. Any object that falls
into the Solar System by definition has enough energy to

(32:27):
escape because it came from outside the Solar System. And
so if it just passes through on like a hyperbolic trajectory,
you know it has enough kinetic energy to climb out
of the gravitational well of the Solar System because it
came from outside the gravitational well. So in order to
get captured it not only does it have to come
in at the right radius and the right velocity, got
to lose a little bit of energy so that no

(32:48):
longer has the energy to escape. That can happen if
you like drag on the atmosphere the planet a little bit,
which gives you a little bit of friction, or maybe
another moon steals a little bit of your energy. So like,
the more moons you have and the puffier your atmosphere,
the more likely you are to be able to capture
an object that comes near you.

Speaker 2 (33:06):
M it's kind of interesting to think of this idea
that planets like the Earth has a kind of a
halo kind of right, like a big sphere around it.
It's basically like a giant net. Like whatever falls into it,
it's gonna get sucked in.

Speaker 1 (33:19):
Yeah, exactly. And if you fall in too far and
you slow don too far, then of course you're going
to burn up as you enter the atmosphere. So it's
a delicate operation. This is also think that sometimes a
pair of objects that are orbiting each other can fall
in the hillsphere and then one of them can get
captured and the other one can get ejected. So all
these sort of complicated things have to go just right
in order for a planet to capture a moon.

Speaker 2 (33:42):
And by capturing, that's a nice word for stealing, right right,
I guess you're like trapping.

Speaker 1 (33:48):
You're dancing, you're dancing with them, have of that?

Speaker 2 (33:50):
Oh I see see?

Speaker 3 (33:52):
Is that?

Speaker 2 (33:52):
Where our that listener who mentioned earlier that maybe we
got our moon by stealing it from Venus? Is that?
Is there some truth to that?

Speaker 1 (34:00):
We don't think that our moon was stolen from Venus,
but we do think that lots of the moons of
Jupiter and Saturn, for example, and these guys have like
dozens of moons come from scattered objects in the early
Solar system. Remember that very early on things were forming.
There may even have been more planets than the ones
we have now, and everything was quite chaotic. So now
we have sort of an orderly solar system where everything

(34:22):
is in place because it's been in place for so long,
and things that were not in place have been lost
or captured or fallen into the Sun. But in the
early days there were a lot of things going in
crazy orbits and crazy trajectories, and so Jupiter and Saturn
sort of like hoovered up a bunch of them.

Speaker 2 (34:37):
So like, if you look at the moons of Jupiter,
for example, they're not all going to be like lined
up in a plane like our solar system. They probably
all have like crazy orbits around Jupiter.

Speaker 1 (34:46):
Right, Yeah, that's exactly right, and that's why we think
that most of these were captured. Also, in the cases
that we've been able to try to study what these
moons are made out of, they're all made out of
totally different things, and so it doesn't look like they
formed from the same sort of scoop of solar systems
off that Jupiter did.

Speaker 2 (35:02):
That's what you were saying, like you can check the
DNA basically the DNA of the moon and the planet
to see if they came from the same stuff, and
sometimes they don't, right.

Speaker 1 (35:10):
Yeah, exactly. That's still tricky to do because we haven't
landed on those moons and like really taken samples that
we can study. But we can like do spectroscopy, we
can see the light that bounces off of them, we
can see what they emit, these kind of things. We
have done some flybys, and so we have ideas for
what these moons are probably made out of.

Speaker 2 (35:29):
And in the early Solar system, like you said, things
were like there were probably like rock giant rocks flying
all over the place, and so it wouldn't be that
weird for some of them to fall into orbit around
like a passing Jupiter or Centurn. So is that how
we got our moon? Did we capture it or steal
it from somebody?

Speaker 1 (35:45):
So we think our moon is unusual because it doesn't
fall into either of these categories. We don't think that
the Moon was formed with the Earth. We also don't
think that a wholly formed moon was captured by the Earth. Instead,
we think it comes from a collision. We think that
there was the proto Earth, this early planet, and then
there was another Mars like planet that came by and

(36:05):
smashed into the Earth, and there was this incredible collision
where essentially these two planets merged, but they left a
huge debris ring, and then that debris ring pulled together
and made the Moon.

Speaker 2 (36:17):
Does our moon have an orbit that's around our equator
or is it tilted?

Speaker 1 (36:21):
The Moon doesn't have a totally random orbit relatively angular
momentum of the Earth, because the two objects are essentially
formed by the combined angularmentum of this collision. So you
get this collision and basically you start from scratch. You
have a new blob of stuff which is then going
to coalesce again into a planet and a moon. And
so there is a relationship of course between the Earth's
spin and the Moon's orbit, and that's because they come

(36:43):
from this combined blob from this collision.

Speaker 2 (36:46):
It's pretty dramatic. I think you can look up videos
of simulations of it online. It's like the Earth, the
proto Earth before Earth was just hanging out and then
this giant rock just slams into it. It all sort
of explodes together, but then gravity pulls it together into
Earth and the Moon.

Speaker 1 (37:02):
Exactly, and the early Moon, we think, was much much
closer to the Earth, something like a tenth of its
current orbit, and then over time it spirals out and
ends up becoming tightly locked to the Earth. One reason
we think this is that we've been to the Moon
and we've been able to land on it and study
what it's made out of, and we see that it's
made out of a lot of stuff that's very very
similar to what the Earth is made out of, which

(37:23):
suggests that they do have some sort of common origin.

Speaker 2 (37:27):
And does the Earth also sort of have moon like
materials in it that are not like the rest of
the Earth.

Speaker 1 (37:33):
Well, we see that the Earth and the Moon have
a lot of very similar elements, which sugg they all
came from the same stuff, But the Moon has fewer
of like volatile elements things that vaporize at low temperatures
we're probably lost in this high energy event, and the
Moon has smaller gravity and so it's not able to
recapture these things the way the Earth did, so the
Earth and the Moon don't have exactly the same kinds
of stuff. The Moon also has a sort of surprisingly

(37:55):
small iron core which overall makes the Moon have lower density.
Simulations confirmed that this is what you would expect from
this kind of collision, that the Moon was formed more
out of the sort of external debris and the Earth
sort of got a bigger sampling of the core stuff.

Speaker 2 (38:11):
I guess the Moon is also smaller, so it doesn't
have as much gravity compressing it, right, making it denser exactly.

Speaker 1 (38:17):
And when they study like what's inside the Moon, they
find samples that suggest the Moon was molten down to
like a surprising depth. And you don't expect the small
body like the Moon to have the gravitational pressure to
like melt its inerts the way the Earth does. So
they think that the Moon was probably molten because of
this collision, not because of its like gravitational pressure.

Speaker 4 (38:37):
Hmm.

Speaker 2 (38:37):
Interesting. And I think they also found like the same
cheese inside of the Moon as some of the cheese
we have on Earth too, Right, that's part of the theory.

Speaker 1 (38:49):
Yeah, they found pan pizzas rejected on the surface of
the Moon that nobody could eat.

Speaker 2 (38:53):
That's right, the same mozzarella, cheese, the same cows, even
space cows. All right, well, that's the origin of our moon.
Let's get a little bit into what that means about
the formation of all moons and the formation of our
whole Solar system, why we're here, and why are things
the way they are. But first, let's take another quick break.

(39:25):
All right, we are coming face to face with the
lunacy here in the podcast talking about the origin of
moons and in particular our moon. You're saying, it's interesting because,
like our moon is sort of a combination of how
some of these other moons can form. Right, Like, we
had a proto planet Earth, and when there was a
visitor that was flying around came near us, it sort

(39:47):
of got captured or collided with our Earth, and then
it all became a big mess. And out of that mess,
you know, the Earth and the Moon forms sort of
a siblings, but also not siblings, because there was it
came from a different planet. The stuff.

Speaker 1 (40:01):
There was a big fight early on, and we were left
over cleaning up the mess. Yeah, it is really fascinating,
and I love this sort of archaeology, this like detective
story figuring out what happened billions of years ago, reconstructing
the story from the clues that are left behind, these
really subtle hints. You know, why does the Moon seem
to be made of the same stuff as the Earth,
but it doesn't have sort of a close circular orbit

(40:22):
the way you would expect. Why exactly is it so big?
These stories are really fascinating because we missed so much
of the Solar System history. You know, like billions of
years happened with crazy fireworks in the sky and we
weren't here to look at it. But we can still
get hints about what happened.

Speaker 2 (40:37):
Hmmm, do you think that's an official job title out there,
like space archaeologists.

Speaker 1 (40:42):
Space murder mystery, you know, exactly.

Speaker 2 (40:45):
Give me like Indiana solo a combination of Indiana Jones
and Hands solo.

Speaker 1 (40:51):
And you know, we're still learning stuff about moons, like
Mars has some funny moons, Phobos and Demos, And the
smaller of those two moons, Demos, is really tiny. It's
only like nine miles across, has a really weird shorwt
of blobby shape to it, and for a long time
people thought it was probably a captured asteroid because of
its orbit, but they recently send an orbiter very very

(41:13):
close to it, super close approach by this spacecraft from
the UA Emirates. Actually it's called Hope, and they were
able to study what it's made out of and discover
that it has sort of the same carbon and organics
that Mars does, unlike the asteroids, sort of like the
DNA test you were saying before, which means that Demos
probably is a chunk of Mars that got blown off

(41:34):
in some sort of prehistoric collision.

Speaker 2 (41:36):
Isn't that also kind of the theey of how we
got life on Earth, like a possible way that maybe
Mars got hit by something. It threw a bunch of
rocks out into space. Some of them became Demos, the
moon of Mars, and maybe some of them came to
Earth bringing like little bacteria.

Speaker 1 (41:50):
Perhaps we're very sure that rocks from Mars have landed
on Earth. We have found them and their geology matches
Mars and doesn't match Earth. So there's no controversy about
whether visions from asteroids on planets can knock stuff off
into outer space and have it land on other planets.
Whether there's life in those rocks that then seeded life
on Earth totally open question. There was this famous misdiscovery

(42:12):
about twenty years ago when they found these weird little
shapes inside a Martian rock on Earth, and they made
this announcement that they were certain that there was life
in them, that these shapes could only be made by life.
But then later analysis demonstrated that you could make those
things without life. So there's no concrete proof that life
has traveled between planets on an asteroid, but it's totally

(42:32):
possible for it to happen. And Demos definitely is a
chunk of Mars floating in space. Sort of like if
you went out into space and you found like Manhattan
floating out in space, you'd be like, whoa, Where'd this
come from?

Speaker 2 (42:44):
Yeah, well people wonder about that.

Speaker 1 (42:46):
Now, what's the story? How did Manhattan get so weird?

Speaker 2 (42:50):
Where did New Yorkers come from their lunatics?

Speaker 1 (42:53):
But they have the best pizza, right, so I don't
want to have to go out of space to get
my pizza.

Speaker 2 (43:00):
You just insulted everyone in Chicago. He lost a big
chunk of our listenership.

Speaker 1 (43:04):
I love Chicago, I love Chicago wins, and I love
the Chicagoans love Chicago pizza. That's all fine with me.

Speaker 2 (43:09):
All right, Well, what does all of this tells about
the formation of the Solar System and how we ended
up where we are and how we are.

Speaker 1 (43:16):
It's a story that we are still unraveling.

Speaker 5 (43:18):
Right.

Speaker 1 (43:18):
We're still learning about our moon, We're still learning about
our neighbor's moons. We're still discovering moons. Right. Saturn recently
past Jupiter. I think in the number of moons that
it has, each one tells us a little bit of
the story of the Solar system, and what we're looking
for now are like more details for that story. As
you said earlier, we're asking questions like can moons have moons?

(43:39):
A lot of people think that it's impossible for the
same reason that like Mercury and Venus don't have moons
from the tidal forces of the Sun, that Jupiter's moons
probably can't have their own moons because of the tidal
forces of Jupiter. But you know, Saturn's moon Rhea probably
has rings which even though they're disrupted by the title forces,
they can still be in orbit around Rhea. And there's

(44:00):
like hundreds of minor planets deep out there in the
Solar system that do have their own moons, like Pluto.
But beyond that, we're also looking into other solar systems
to try to understand whether the moons that we have
are weird or typical? Right, Like, we only so far
have this one solar system to study at this level
of detail. Twenty years ago, we were able to see
planets around other stars, which tells us a lot about

(44:22):
whether the planets in our solar systems are weird. Now
we're pushing those boundaries to try to look for moons
in other solar systems. This thing we call exo moons
to try to discover if the distribution of moons that
we have is strange or pretty typical in the universe.

Speaker 2 (44:38):
Well, that's wild. How are we seeing moons and other
planets outside of our solar system? Can we see them
or do we have to infer them from the gravity.

Speaker 1 (44:46):
So there's a few ways that we discover planets, and
we can try to apply those ways to discover moons.
One of the early ways we discovered planets around other
stars was seeing their gravitational impact on the star, and
that would wiggle the star and cause like a change
in the frequency of the light, this Doppler shift, and
so we could discover that there was something pulling on
that star. We don't think that method will work for

(45:08):
discovering moons because it's really hard to distinguish the gravitational
effect of a little moon around a planet from the
planet itself. What we do think is possible is the
transit method, this eclipse method, where a planet passes in
front of a star and dips the light that comes
from it, And if that happens in a regular way,
we can tell that these little microeclipses come from a planet. Well,
if those eclipses have their own little dips in them,

(45:30):
because the moon going around the planet sometimes blocks this
life from the star and sometimes doesn't, then you can
discover moons around those planets. So like microeclipses within microeclipses.

Speaker 2 (45:42):
Wow, exo eclipses exo exo moon eclipses.

Speaker 1 (45:45):
Yeah, they're like eclipses squared. And we don't have any
confirmed exo moons yet, though there are a couple of
candidates from the Kepler telescope that look promising, but people
can't yet agree whether that actually is the discovery of
a moon. And more recently, we've developed this incredible technology
to do direct imaging of exoplanets, like telescopes that actually

(46:05):
take pictures of planets around other stars. Blows my mind.
I never thought that would be possible. A lot of
it involves like blocking out the light from the star
itself so you can see the ring around it. And
sometimes that lets us see planets being formed. So we
can see, for example, a star with a planetary disc
around it. And in one case we have a direct
image of a protoplanetary disc which seems to have a

(46:28):
planet with its own disc around it. So like you
can see the planet and it's got like a bunch
of stuff around it, and maybe that stuff will form
into a moon.

Speaker 2 (46:37):
You can see the rings in it.

Speaker 1 (46:39):
Yeah, exactly. You can see this disc that's going to
form it either into rings or moons or something.

Speaker 2 (46:44):
Yeah, it's pretty mind blowing because I wonder like if
a lot of people know that you can actually see
the moons of Jupiter kind of with your naked eye,
or at least with a small telescope. You don't need
like a super amazing telescope. You can just use something
you can buy for your house and you can see
the moons of Jupiter.

Speaker 1 (46:56):
Yeah, it doesn't take a fancy telescope. It was one
of the first things that Galla saw when he pointed
a telescope at the sky. It was one of the
first people to ever do this, and he saw the
moons of Jupiter. It's not hard. You can do it,
and it's pretty exciting to see Jupiter expand from this
tiny dot you can see with the naked eye to
this whole orbital system with its own dynamics.

Speaker 2 (47:14):
H pretty cool. All right. Well, one thing that's day
announced recently is that we're sending more people to the Moon.

Speaker 1 (47:20):
That's right, if Elon Musk ever gets that starship off
the ground.

Speaker 2 (47:23):
No, the new artem is missions right, It isn't one
of the plants to send more people to the moon.

Speaker 1 (47:28):
Yeah, that's exciting. It'd be cool to go back to
the Moon. With all of our advanced technology, we can
take more detailed measurements. We can map its magnetic field,
we can understand its geology and its history even better. Yeah.

Speaker 2 (47:38):
I wonder why kind of pizza they would eat there though?
It's a deep dish because there's not much that much gravity.
So can you have a deep dish pizza?

Speaker 1 (47:46):
Probably every pizza would rise a lot more because there
isn't gravity, right.

Speaker 2 (47:49):
Oh, my goodness. In space, every pizza is a deep
dish pizza. That's why you're not going to Earth.

Speaker 1 (47:53):
Danu or maybe astronaut pizza is just freeze dried and
gross no matter where it comes from.

Speaker 2 (48:01):
I guess there's something one way to find out to
take the podcast to space. All right, Well that kind
of answers our question. How the Moon's form basically two
main ways, right, They either capture something flying by in space,
or they form together with the planet, or some combination
of the tube where something comes from space crashes into you,
creates a big mess, and then you both sort of

(48:22):
form together or reform together.

Speaker 1 (48:24):
And the incredible thing is that by looking at the
Moon today we can mostly figure out how that happened,
how this huge space rock ended up in orbit around
the planet. Yeah.

Speaker 2 (48:33):
And the cool thing is that you can see the
Moon almost every night. Every night you step outside of
your house, you can see this giant rock floating in
space there for us to see, pretty shiny, pretty bright.

Speaker 1 (48:44):
It's nice to have one big, fat moon. I agree.

Speaker 2 (48:47):
All right, Well, we hope you enjoyed that. Thanks for
joining us, See you next time.

Speaker 1 (48:59):
Thanks for listening, and remember that Daniel and Jorge Explain
the Universe is a production of iHeartRadio. For more podcasts
from iHeartRadio, visit the iHeartRadio, app, Apple podcasts, or wherever
you listen to your favorite shows.