Speaker 1: Hey, Kelly, do you ever wish that our night sky
Speaker 1: was I don't know, a little bit more dramatic, more dramatic.
Speaker 1: We've got a huge moon, planets, stars, and all of
Speaker 1: the Milky Way. You've got pretty high standards for the
Speaker 1: night sky. What did you have in mind? I don't know.
Speaker 1: Sometimes I think it's boring to have just that one
Speaker 1: huge moon. It seems like it might be more exciting
Speaker 1: to have lots of little moons up there. Okay, all right,
Speaker 1: that's true. It's kind of like having an only child. Yeah,
Speaker 1: and not just an only child, like a single mega child.
Speaker 1: You want drama. What's more dramatic than the Earth's mega
Speaker 1: child hovering above you in the sky. Yeah, I guess
Speaker 1: I wanted drama. But now I'm worried that the idea
Speaker 1: of a mega child is going to give me nightmares. Yeah,
Speaker 1: me too. I like my two little ones. Hi. I'm Daniel.
Speaker 1: I'm a particle physicist, and I'm very happy to have
Speaker 1: too normal sized children instead of one mega child. And
Speaker 1: I'm Kelly. I'm a parasitologist, and I also have two
Speaker 1: normal sized children, and that works well for me. You
Speaker 1: having considered the concept of like combining them together into
Speaker 1: one child unification of the children. You know, Zach likes
Speaker 1: to joke that they stack when he stacks them. They
Speaker 1: don't seem very happy about it, and so you know,
Speaker 1: I haven't thought too hard about trying to combine them.
Speaker 1: I don't think they'd be big fans of that. I'm
Speaker 1: pretty sure my kids wouldn't be into that either. Well,
Speaker 1: Welcome to the podcast Daniel and Jorge explain the universe
Speaker 1: and which we ask the hard questions of the universe.
Speaker 1: We talked about the crazy stuff that's out there deep
Speaker 1: in the cosmos, and we talked about the tiny little
Speaker 1: particles that are wriggling around inside my children, your children,
Speaker 1: and everybody's children. We try to explore the entire universe
Speaker 1: and explain all of it to you. Normally we have
Speaker 1: my friend and co host Jorge him here on the podcast,
Speaker 1: but he's unavailable today, so we have our wonderful, hilarious
Speaker 1: guest host, Kelly Weener Smith. Hello, I'm excited to be back.
Speaker 1: Thanks very much for joining us and for talking to
Speaker 1: us about crazy stuff in the universe. So on the podcast,
Speaker 1: we sometimes like to dig into stuff that's really complicated,
Speaker 1: like how does quantum field theory work, and what is
Speaker 1: the real charge of the electron? Or what is it
Speaker 1: like to go inside a black hole? These are deep
Speaker 1: and complicated questions about the universe that we try to
Speaker 1: take apart and explain to you. But sometimes we also
Speaker 1: like to dive into simpler seeming in questions, questions that
Speaker 1: might seem like they have an obvious answer but then
Speaker 1: have some interesting little wrinkles. It's good to have diversity, yeah,
Speaker 1: because questions are at the heart of science, and they're
Speaker 1: not just the questions that scientists ask when they're doing
Speaker 1: their research, but we're also interested in the questions that
Speaker 1: everybody asks. And sometimes the best questions are the questions
Speaker 1: that children ask, the most obvious questions which sometimes have
Speaker 1: a tricky answer. And I remember looking up at the
Speaker 1: night sky with my kids, who are now twelve and fourteen,
Speaker 1: but earlier asked very simple, basic, fun questions about the universe,
Speaker 1: like why do we only have one moon? Or do
Speaker 1: we only have one moon? Kelly, what kind of questions
Speaker 1: do your kids ask when they look at the night sky?
Speaker 1: I was just trying to think of a good example
Speaker 1: of Like, my daughter is seven, and she's always asking
Speaker 1: me questions that I don't know the answer to some
Speaker 1: of them super fundamental, which makes me think, how is
Speaker 1: it that I'm walking around not knowing the answer to
Speaker 1: all of these fundamental things, but yet I still managed
Speaker 1: to survive. But no good example is coming to mind
Speaker 1: right now. But we've got one of those apps on
Speaker 1: our phone where you can sort of point it at
Speaker 1: whatever in the night sky and it tells you what
Speaker 1: it is. And we spend a lot of time sitting
Speaker 1: on our car at night looking up at stuff, and
Speaker 1: it's a lot of fun. She asked lots of questions,
Speaker 1: but nothing's coming to mind right now that I did
Speaker 1: not know the answer to. What's your favorite question your
Speaker 1: kids have asked you? One of my favorite questions my
Speaker 1: kids have asked me are questions like where are we
Speaker 1: in the universe. You know, they're just getting used to
Speaker 1: the idea of like our houses in the neighborhood, and
Speaker 1: the neighborhood is in the city, and that city is
Speaker 1: in a state somewhere we have like a location and address,
Speaker 1: and so they wanted to know, like, where are we
Speaker 1: in the universe? What's our like universe address? And of course,
Speaker 1: you know, the hardcore physics answer is that every place
Speaker 1: in the universe is the same, and physics doesn't care
Speaker 1: about location and translationally and variant and stuff. But that
Speaker 1: answer is not very satisfying for a four year old. Yeah,
Speaker 1: that's why it's a bummer to have a physicist for
Speaker 1: a dad. But instead I try to describe to them,
Speaker 1: you know, what the galaxy looks like, and how the
Speaker 1: galaxy fits in with other galaxies, and what we know
Speaker 1: about sort of our cosmic neighborhood. And the thing I
Speaker 1: love about their questions is that they are both easy
Speaker 1: and hard. They're like easy to ask but sometimes hard
Speaker 1: to answer. And they're the obvious questions, as you said,
Speaker 1: that you don't always think about when you're walking around
Speaker 1: the world. But that's why I think that children really
Speaker 1: are sometimes the most natural scientists, because they don't just
Speaker 1: accept things as they are. They ask questions about the
Speaker 1: and say why is it this way or is it
Speaker 1: that way? After all? Totally, And what I love about
Speaker 1: Ada is that she'll tell me that I'm wrong. I
Speaker 1: wish I had that confidence. So you know, not only
Speaker 1: do they ask good questions, but they still have the
Speaker 1: confidence of children to be like, no, I don't think so.
Speaker 1: And so today in the podcast, we'll be talking about
Speaker 1: a question which seems to have an obvious answer. So
Speaker 1: on today's program will be answering the question how many
Speaker 1: moons does the Earth have? So, Kelly, tell me what
Speaker 1: you thought when you saw that we would be talking
Speaker 1: about this today. So you sent me a list of
Speaker 1: topics we could talk about, And when I read this one,
Speaker 1: I thought, well, the answer seems obvious. The answer is one.
Speaker 1: And if the answer seems obvious, then either Daniel needs
Speaker 1: to be fired because he's not asking good questions anymore,
Speaker 1: or there's something fundamental that I'm missing, and it's probably
Speaker 1: the second. And so I suggested that we talked about
Speaker 1: this one because I figured this was a question that
Speaker 1: would teach me something new. Awesome. This is a fun
Speaker 1: question to dig into. We get to hear about like
Speaker 1: what exactly is a moon, what counts as a moon,
Speaker 1: even a little bit about the etymology of the word
Speaker 1: moon and when it came into use, and what else
Speaker 1: is out there orbiting around the Earth and could you
Speaker 1: call it a moon? So, as usual, before I dug
Speaker 1: into this, I wanted to know what everybody else out
Speaker 1: there thought. Sometimes I used to walk around the campus
Speaker 1: if you see Irvine and ask students there these questions
Speaker 1: to see what the general level of knowledge was or confusion.
Speaker 1: These days, of course, because the pandemic, I'm sending emails
Speaker 1: out into the Internet asking listeners to speculate baselessly without
Speaker 1: the chance to do any research on these difficult physics questions.
Speaker 1: Did you actually stop students on the campus and ask
Speaker 1: them how many moons does they are? Have? No, I
Speaker 1: haven't because this question is too recent, But I wonder
Speaker 1: what they would say. I've noticed that our listeners tend
Speaker 1: to give better informed answers than the random you see
Speaker 1: Irvine student. Nothing against you see Irvine. Of course, our
Speaker 1: listeners may just be like a subset of the universe
Speaker 1: that's more interested in understanding the universe. But I hope
Speaker 1: one day to get back to campus and getting to
Speaker 1: ask the students those questions. It was fun to sort
Speaker 1: of see their faces when I asked them these questions.
Speaker 1: I bet you have a reputation as being one of
Speaker 1: the like super weird professors. Well, you know, I don't
Speaker 1: dress very fancy, so maybe they just think I'm some
Speaker 1: random homeless person asking them hard physical questions. Every college
Speaker 1: has homeless person or physics professor, it can be hard
Speaker 1: to tell the difference, physics professor, you can't tell the
Speaker 1: difference between Yeah, anyway, Thank you to everybody who volunteered
Speaker 1: to answer these questions. If you'd like to participate for
Speaker 1: a future episode of the podcast, please write to me
Speaker 1: two questions at Daniel and Jorge dot com. Here's what
Speaker 1: some of our listeners had to say. The obvious answer
Speaker 1: that pops into my head immediately would be one. So
Speaker 1: I'm pretty sure that answer is wrong. Well, we have
Speaker 1: just our celebrity moon, the moon, and I don't know,
Speaker 1: maybe we might have caught up some small objects there,
Speaker 1: probably a Deslo car elon musk scent, who knows. I
Speaker 1: don't know exactly. I'm one sure that the Earth has
Speaker 1: two moons, the classic moon that we see in the
Speaker 1: sky and Keith Moon. I would say the Earth has
Speaker 1: one moon. I don't know if you would consider satellites
Speaker 1: or a space station a moon because the orbit the Earth,
Speaker 1: but I would probably just consider one moon. Well, I
Speaker 1: guess this depends on your definition of moon the natural moons.
Speaker 1: It has the one large natural moon, and I believe
Speaker 1: they've discovered a couple of asteroids that have been captured
Speaker 1: in loose enough for bits that they're probably temporary. If
Speaker 1: you're going to call any artificial uh satellite a moon,
Speaker 1: which they've been called artificial moons, then that number goes
Speaker 1: into the millions, depending on how small a particle you
Speaker 1: want to count. There's nuts and bolts and pieces of
Speaker 1: rocket and larger things that satellites, fragments of satellites that
Speaker 1: have collided with each other, so uh, a whole lot
Speaker 1: of them, all right, Kelly, So what do you think
Speaker 1: about our listeners responses here? I thought there were some
Speaker 1: very insightful responses, you know. One of them was essentially
Speaker 1: asking questions about maybe how do we define moons. I
Speaker 1: thought somebody had a clever thought that the Tesla car
Speaker 1: might now be sort of orbiting, although I think of
Speaker 1: the Tesla car was shot Mars word instead of moonword.
Speaker 1: But it was clear that people sort of thought through
Speaker 1: their answers, and yeah, they had some clever answers. What
Speaker 1: do you think? Yeah, I was impressed as well. In
Speaker 1: the end, of course, it's going to come down to
Speaker 1: the definition. I hope that we end up with the
Speaker 1: definition of moon that doesn't allow Elon Musk to have
Speaker 1: created his own personal moon. That would seems sort of unsatisfying.
Speaker 1: That would be too much power for one person. The
Speaker 1: dude's already a billionaire and owns three like really valuable
Speaker 1: companies like it, doesn't need to create astronomical objects on
Speaker 1: top of all of it. Although he wants to create
Speaker 1: a Mars colony, which is maybe even more powerful than
Speaker 1: creating a moon. So I guess we'll have to see
Speaker 1: what the future holds. Do you think that's because he
Speaker 1: wants to be dictator of Mars? I like joking about
Speaker 1: that with Zack. Yes, he claims he wants a representative
Speaker 1: not a direct democracy, So we'll see what happens when
Speaker 1: the time comes. Well, if he gets to pick who
Speaker 1: goes to Mars, and they're probably going to elect him
Speaker 1: president anyway. But let's get back to the topic. We're
Speaker 1: not talking about Elon Musk's plan to colonize Mars. We're
Speaker 1: talking about moons and how many moons the Earth has
Speaker 1: and what exactly is a moon? So let's dig into
Speaker 1: that first and talk about what qualifies as a moon. So,
Speaker 1: without doing any research, Kelly, what would you use to
Speaker 1: define a moon? So I would have guessed that a
Speaker 1: moon is a big thing that isn't bigger than the
Speaker 1: planet that it orbits. So a big thing that orbits
Speaker 1: around a planet, and it has to be big, but
Speaker 1: it can't be bigger than the thing that it's orbiting around.
Speaker 1: That's how I would have defined it. But but probably
Speaker 1: that's wrong. And then your definition would it have to
Speaker 1: be natural or could be manned? Me that? Could we
Speaker 1: build an artificial moon? Oh h no, No, I've always
Speaker 1: thought of it as being natural. Yeah, what about you? Well,
Speaker 1: I really wasn't sure because it seems like in lots
Speaker 1: of directions there are arbitrary distinctions you have to make.
Speaker 1: And that's the problem often in astronomy is that the
Speaker 1: categories between things get blurred, and you always find something
Speaker 1: right on the edge between the different categories, and in
Speaker 1: the end, you know, we're just we're looking at the
Speaker 1: universe and we're trying to categorize it to understand is
Speaker 1: that we can talk about it together. Doesn't mean that
Speaker 1: those categories actually reflect something deep and true about the universe.
Speaker 1: There's sometimes just the words we've used to describe stuff,
Speaker 1: and so as we see more stuff out there in
Speaker 1: the universe, we're gonna find things that break those categories.
Speaker 1: But the definition that I found for moon is that
Speaker 1: it has to be a quote natural body, right, So
Speaker 1: it needs to be a natural body that's orbiting a planet.
Speaker 1: And to me already this is problem that like a
Speaker 1: natural body means not like a human made satellite. So
Speaker 1: we built a death Star for example, Officially that wouldn't
Speaker 1: qualify as a moon. But what if we just like
Speaker 1: you know, pulled out a huge chunk of Earth and
Speaker 1: threw it out into space and then it went into
Speaker 1: orbit around the Earth. Is that a natural body? It's
Speaker 1: like made of rock, right, It's essentially the same process
Speaker 1: that created our moon as we understand it. But I
Speaker 1: think according to this definition, it wouldn't be a moon
Speaker 1: because you know, it would have been like as the
Speaker 1: result of a human process. It really does seem like
Speaker 1: if you just took a chunk of earth and you
Speaker 1: put it up there, it should count. But I suppose
Speaker 1: satellites are just chunks of Earth that we've we've done
Speaker 1: things too, that we send up into space, and so
Speaker 1: maybe it shouldn't count. Yeah, exactly, That's where I was going.
Speaker 1: What is a satellite other than like an ultra refined
Speaker 1: piece of Earth that you've somehow, you know, manipulated into
Speaker 1: a complex technological object. But in the end, it's a
Speaker 1: piece of the Earth that we've launched into space. And
Speaker 1: you know, for those of you who don't know the
Speaker 1: history of our moon, we think that our moon is
Speaker 1: basically a big chunk of Earth that was vaulted out
Speaker 1: into space when another proto planet hit Earth when it
Speaker 1: was very very young, and this collision led to this
Speaker 1: enormous blab of stuff getting tossed out there, which eventually
Speaker 1: coalesced into the Moon. And when we studied the surface
Speaker 1: of the Moon, we found elements of it which look
Speaker 1: exactly the same as elements of the surface of the Earth,
Speaker 1: which suggests that they really do have sort of a
Speaker 1: common origin. So this definition of a moon being a
Speaker 1: natural body not a human made object is a little tricky,
Speaker 1: and I don't think the definition there is very clear.
Speaker 1: Can I ask a sort of tangential question, of course, So, well,
Speaker 1: Zach and I were reading about the Moon. We came
Speaker 1: across this fact that the Moon is sort of carbon poor,
Speaker 1: like maybe there's some carbon up there, but you're gonna
Speaker 1: have trouble growing plants and stuff because there's not a
Speaker 1: lot of carbon. If the Moon is just a chunk
Speaker 1: of Earth that got expelled, why do we have so
Speaker 1: much carbon and they have so little. Is that the
Speaker 1: result of natal processes that happened after the Moon got
Speaker 1: cut off partly, Yeah, Mostly the Earth and the Moon
Speaker 1: are made up of very similar stuff. It's mostly oxygen
Speaker 1: and silicon and calcium and iron and that kind of stuff.
Speaker 1: That's because we think that the Moon and the Earth
Speaker 1: are made up of the remnants of a huge collision
Speaker 1: between the proto Earth and a Mars sized planet, like
Speaker 1: fifty million years after the Solar system formed, and the
Speaker 1: remnants of that huge collision coalesced into the Earth and
Speaker 1: into the Moon. But you're right that there is very
Speaker 1: little carbon on the Moon, but there is carbon on
Speaker 1: the Earth's surface, and we're not sure why. One theory
Speaker 1: is that carbon tends to form very volatile compounds, things
Speaker 1: that would end up in an atmosphere if the Moon
Speaker 1: could keep one. So the Earth hangs onto some of
Speaker 1: these things, some of this carbon, because it's big enough
Speaker 1: to keep hold of its atmosphere it has more gravity,
Speaker 1: But the Moon can't. Anything like an atmosphere on the
Speaker 1: Moon just boils away. Interesting okay, thanks. So the definition
Speaker 1: of a moon is that needs to be a natural
Speaker 1: a body in orbit around a planet, and you said
Speaker 1: that it needs to be big. Officially, technically there's no
Speaker 1: minimum size to a moon. A moon could be like huge,
Speaker 1: like our moon, or you know, according to astronomers, it's
Speaker 1: okay to have a moon that's like a kilometer in size.
Speaker 1: I find that very unsatisfying. Like to me, a moon
Speaker 1: is something that you should be able to, like put
Speaker 1: a settlement on one day, and you can't really do
Speaker 1: that with a one kilometer sized quote unquote moon. I
Speaker 1: don't know. I don't want to buy that, but apparently
Speaker 1: it's part of the definition. It would be like the
Speaker 1: little prints right walking around this tiny little planet. But
Speaker 1: I think that comes from our experience, right, just because
Speaker 1: we have this one big moon, we tend to think
Speaker 1: that's what you gotta have in a moon. But as
Speaker 1: well talk about later, so many planets in the Solar
Speaker 1: System don't have a huge moon, to have a lot
Speaker 1: of smaller moons, And so part of the joy of
Speaker 1: astronomy and and of exploring the universe is discovering that
Speaker 1: our corner of the universe is weird, is unusual, is
Speaker 1: not representative, and we've got to sort of like stretch
Speaker 1: our mind then get used to a different way of
Speaker 1: thinking about what a moon is. Yeah, it is really
Speaker 1: hard to wrap your mind around just how different it is.
Speaker 1: And yeah, I'm very earth centric. I guess I would
Speaker 1: like moons to all sort of fits in a nice
Speaker 1: little mold that matches the moon that I have, and
Speaker 1: you touch it on really all the important issues. I
Speaker 1: think that was really tremendous. The other thing you mentioned
Speaker 1: is that it shouldn't be bigger than the planet, right,
Speaker 1: And in the definition of a moon, officially, the upper
Speaker 1: limit on the size of a moon is pretty vague,
Speaker 1: Like what happens when the moon approaches the size of
Speaker 1: the planet. Then you might ask, like, well, which one
Speaker 1: is the planet and which one is the moon? Right?
Speaker 1: Or if they're exactly equal size, could you consider them
Speaker 1: to be like a binary planet system? So where does
Speaker 1: our moon fall relative? And they'll like Earth to Moon
Speaker 1: ratio side, Like, is our moon big for a moon?
Speaker 1: Is it the biggest relative to the size of the
Speaker 1: planet it orbits is? So is our moon weird relative
Speaker 1: to the other moons? Our moon is very weird. Our
Speaker 1: moon is basically that megachild. The diameter of the Moon
Speaker 1: is more than a quarter of the diameter of the Earth,
Speaker 1: and that's the biggest moon to planet ratio in the
Speaker 1: Solar System by like a factor of five. There's no
Speaker 1: other planet out there that has such a big moon
Speaker 1: relative to the planet. Like there are moons of Jupiter
Speaker 1: that are roughly the same size as our moon, but
Speaker 1: of course Jupiter is huge, and so relative to the
Speaker 1: size of Jupiter, those moons are very very small, So
Speaker 1: we have a really weird big moon. You know, it's
Speaker 1: kind of amazing that we've managed to figure out anything,
Speaker 1: which is sort of a phrase that, if I'm remembering correctly,
Speaker 1: I've said in almost every single one of these episodes
Speaker 1: we've done together. But it seems like, you know, our
Speaker 1: Solar System is so weird, and our planet and the
Speaker 1: moon is so weird. It gives us such a weird
Speaker 1: frame of reference. But I know, it's exciting that we
Speaker 1: can still figure stuff out. Yeah, and it's a real
Speaker 1: journey to peel away these preconceptions and understand that things
Speaker 1: we thought were fundamental, things we thought we're obvious or universal,
Speaker 1: are really just unusual. You know. It's just like when
Speaker 1: you go traveling and you discover like, oh, not everybody
Speaker 1: drinks coffee for breakfast. You know, it turns out there
Speaker 1: are other ways to live, and that's the joy of
Speaker 1: exploring the universe, you know, discovering the tea is also
Speaker 1: acceptable at breakfast times. No, no, no, no, no, no,
Speaker 1: that's just wrong. One fact that I really liked while
Speaker 1: I was reading through here was that those like one
Speaker 1: kilometer size moons are sometimes called moonlits. And I thought
Speaker 1: that was super cute. So I asked my seven year
Speaker 1: old today. I was like, how many moons does the
Speaker 1: Earth have? So she, being a very clever kid, was like, well,
Speaker 1: I thought it was one, but you're asking me this,
Speaker 1: so what does that mean? And and so I told
Speaker 1: her like, well, you know you can have these little
Speaker 1: things called moonlits. And she said, well, what does that mean?
Speaker 1: And so I tried to explain that let's means little
Speaker 1: things and she was like, well, when else does it
Speaker 1: mean that? And I had a like, uh, you know,
Speaker 1: like a moment of not being able to figure it out,
Speaker 1: but I came up with piglets and outlets, and I
Speaker 1: was very proud of myself. So anyway, that was a
Speaker 1: fun moment with the seven year old today. Yeah, I
Speaker 1: love those little endings lits and like, it's just like
Speaker 1: the diminutive in Spanish, you know, eto or eno or
Speaker 1: these kind of things in romance languages. So I'm glad
Speaker 1: that we have those in English. Also, you could really
Speaker 1: stick them on anything, you know, like I'm not having dessert,
Speaker 1: I'm having dessert lits. It makes everything cuter, it really does.
Speaker 1: So where are we with the moons? Moons have to
Speaker 1: be a natural body orbiting a planet. No minimum size.
Speaker 1: The oppera limit is kind of vague. One thing I
Speaker 1: read suggested that you could effectively describe an upper limit
Speaker 1: on the moon by requiring that the center of mass
Speaker 1: of the planet and moon together should be inside the
Speaker 1: diameter of the planet. Right, So the center of mass
Speaker 1: of two objects is sort of like the weighted average
Speaker 1: of all of their stuff. If you've got more stuff
Speaker 1: in the planet than in the moon, it's going to
Speaker 1: be closer to the planet mathematically and physically. It's actually
Speaker 1: the location that the two things are orbiting. Right. We
Speaker 1: say that the Moon, for example, orbits the Earth, but
Speaker 1: actually the two things are orbiting each other, or more precisely,
Speaker 1: they're both orbiting the center of mass of the two things.
Speaker 1: And if you have two things that are equal mass,
Speaker 1: then their center of masses right between them. If one
Speaker 1: of them is infinitely massive, then the center of mass
Speaker 1: is at the center of that very massive object. In
Speaker 1: a more realistic scenario, where one thing is very massive
Speaker 1: and one thing is much smaller, you can have the
Speaker 1: center of mass of the system of the two things
Speaker 1: be close to the center of the larger object. And
Speaker 1: so here the definition is like, is the center of
Speaker 1: mass of the two objects underneath the ground within the
Speaker 1: radius of the larger object. That's sort of a cool definition.
Speaker 1: That is a cool So I have a couple of
Speaker 1: questions to see if I understand. So one, does it
Speaker 1: depend on how far apart the things are or is
Speaker 1: it like you just when you make this comparison, you
Speaker 1: you know, sort of mentally put these things right next
Speaker 1: to each other and then compare the center of mass.
Speaker 1: It definitely depends on how far apart they are, right
Speaker 1: because for example, if they're equally massive, you'd be right
Speaker 1: between them, and that definitely depends on the distance between
Speaker 1: the two objects. Yes, and so that would mean you
Speaker 1: have two planets as opposed to a moon and a
Speaker 1: planet in that definition. And so so you have two
Speaker 1: things that are like one is just a little bit
Speaker 1: smaller than the other, and one is big er, but
Speaker 1: the smaller one is made out of something much more
Speaker 1: massive or dense or I'm not quite sure what word
Speaker 1: I'm looking for here. Could the smaller thing end up
Speaker 1: being the planet that gets orbited by a bigger thing
Speaker 1: because it has more like gravitational pull? Absolutely? Yeah. For example,
Speaker 1: if you had something orbiting a black hole, right, a
Speaker 1: super duper dense object, then the center of mass of
Speaker 1: the system is definitely going to be within the event horizon,
Speaker 1: even if though the black hole could be smaller. Right,
Speaker 1: black holes are very very compact. They don't have to
Speaker 1: be very very large, but they are supermassive. So that's awesome.
Speaker 1: You're really like pushing the boundaries of this definition. But
Speaker 1: I don't know. I guess a black hole could have
Speaker 1: a planet orbiting it. I'm not sure if you would
Speaker 1: call that a planet or a moon, right, if you're
Speaker 1: orbiting a black hole, Yeah, it's trippy, I guess, I,
Speaker 1: as a not physicist, find it sort of unsatisfying that
Speaker 1: if the moon is too far away, it might or
Speaker 1: if something that feels sort of moon like is too
Speaker 1: far away, it wouldn't count as a moon because the
Speaker 1: center of masses is not within the bigger body or something.
Speaker 1: It feels like distance shouldn't matter for the definition, But
Speaker 1: that's a biologist take on it. Well, it definitely has
Speaker 1: to be in orbit. And I think that one problem
Speaker 1: with this whole categorization is that this is like a
Speaker 1: natural hierarchy. I mean, you have the Sun and the
Speaker 1: stuff orbiting around the Sun, and then you call those planets,
Speaker 1: but that's sort of arbitrary because they're orbiting around the Sun.
Speaker 1: And then there's things orbiting around the planets, right, and
Speaker 1: you call those moons. In the end, it's just sort
Speaker 1: of a natural hierarchy of stuff orbiting stuff that's orbiting
Speaker 1: other stuff, and our categorization of it is you're really
Speaker 1: going to try to draw lines there where they really
Speaker 1: aren't lines. Yeah, but that's like a fundamental problem with science.
Speaker 1: You know, in biology, we categorize things, and constantly nature
Speaker 1: does not care how we categorize it. She moves away
Speaker 1: outside of our categories. Yeah, I guess it's tough just
Speaker 1: finding a definition that is useful I guess in biology
Speaker 1: there was a huge revolution a couple hundred years ago,
Speaker 1: right because you guys had been categorizing stuff based on
Speaker 1: how it looked and what it did, and then discovered
Speaker 1: the genetic relation ships between everything, and that there was
Speaker 1: actually a real, true organization to all these animals that
Speaker 1: didn't necessarily respect how they looked or how we observe
Speaker 1: them well. And then it turns out that, you know,
Speaker 1: how do you define species? That's actually a pretty difficult question.
Speaker 1: The tree of life doesn't just branch, it sort of comes,
Speaker 1: the branches come back together and you get horizontal gene transfer.
Speaker 1: And how do you categorize species of bacteria when they're
Speaker 1: swapping jeans all the time, and it gets complicated fast. Well,
Speaker 1: in physics, it's interesting they think about how these words
Speaker 1: were used for a long time. People use the word
Speaker 1: satellite to also refer to moons, and this is before
Speaker 1: we had things in space like GPS and telecommunications, satellites
Speaker 1: and you know, laser weapons and all that kind of stuff. Now,
Speaker 1: when you say satellite, you think of something people build,
Speaker 1: maybe electronics and launched into space. But before spot Nick,
Speaker 1: before ninety seven, astronomers used the word satellite to talk
Speaker 1: about anything orbiting another object, and so they didn't really
Speaker 1: use the word moon scientifically. They referred to Luna, for example,
Speaker 1: as Earth satellite. Then when they launched sput Nick, they realized,
Speaker 1: whole on a second, what are we going to call that?
Speaker 1: And so they started to use the word artificial satellite.
Speaker 1: But that was a little bit too cumbersome, and so
Speaker 1: now we just say satellite when we mean artificial satellite.
Speaker 1: And then moon, which was a word mostly used like
Speaker 1: in science fiction and a sort of popular culture, became
Speaker 1: a more official scientific word. I think that's sort of
Speaker 1: cool that the scientists adopted a word from sort of
Speaker 1: common usage. That's totally fascinating. And I've been reading about
Speaker 1: the space race and I didn't know this history of
Speaker 1: the word satellite. And when I saw that they named
Speaker 1: spot Nick an artificial satellite, I was like, well, that's
Speaker 1: sort of clunk. Why not just call it satellite? But
Speaker 1: it makes sense now. A lot of the fathers of
Speaker 1: rocket science or whatever. We're really into sci fi. I
Speaker 1: think almost all of the fathers of rocket science claimed
Speaker 1: that they were inspired by Jules Verns. What is it
Speaker 1: called to the moon? I wonder if the fact that
Speaker 1: they were all super into sci fi sort of helped
Speaker 1: get the word moon into the scientific literature. Yeah it
Speaker 1: makes me one or what else? Like will in the
Speaker 1: future be part of science. You know, things that we
Speaker 1: say but you wouldn't hear a scientists say, you know,
Speaker 1: like a shooting star is our word for a meteor,
Speaker 1: but you never see that in the science paper. But
Speaker 1: maybe someday in the future, you know, the language will
Speaker 1: transmogrify itself into official scientific physics speaker could be. All right,
Speaker 1: So we have our definition of a moon. It has
Speaker 1: to be a natural body, right, not something engineered by
Speaker 1: humanity or elon Musk. Has to orbit a planet. But
Speaker 1: there's really no minimum size to it, though there seems
Speaker 1: to be some sort of sense of an upper limit
Speaker 1: that you shouldn't have your moon being larger than your planet.
Speaker 1: All right, So, now that we have our definition, or
Speaker 1: at least a definition we're gonna work with for the
Speaker 1: rest of this episode, let's take a break before we
Speaker 1: move back to figuring out exactly how many moons Earth has.
Speaker 1: So we have a definition. Now, how many moons do
Speaker 1: we have, Daniel, So let's count them first. Of course,
Speaker 1: we have the number one candidate. The classic moon, the
Speaker 1: one you're familiar with, the one we all grew up loving. Right,
Speaker 1: this is the moon we call the moon, which is
Speaker 1: sort of a silly name, right, calling the moon the moon.
Speaker 1: It reminds me actually, when I was a kid, we
Speaker 1: had a cat and nobody could agree on what to
Speaker 1: call the cat, so we just called it the cat,
Speaker 1: and that just became its name. And for a while
Speaker 1: I felt sad for like, oh, poor cat doesn't get
Speaker 1: a name, But he didn't care. It got fed, it
Speaker 1: got pet it doesn't need a name. I think it's
Speaker 1: good that you became more creative that you got I
Speaker 1: can't tell if calling it the moon is very egocentric,
Speaker 1: like that is our moon, so it is the moon,
Speaker 1: or if it just represents a lack of creativity. Hard
Speaker 1: to say. Well, as we were saying earlier, it's really weird,
Speaker 1: Like it's huge. It's more than a quarter of the
Speaker 1: diameter of the Earth in the Solar System. The next
Speaker 1: largest moon relative to his planet is one of the
Speaker 1: moons of Neptune, which is almost six percent of the
Speaker 1: diameter of Neptune. So that's a pretty big gap. Like
Speaker 1: mostly moons are small compared to their planet. The moon
Speaker 1: is really a very weird and Or and I did
Speaker 1: a whole episode about how the Earth got its moon
Speaker 1: and the various theories and how people are testing those,
Speaker 1: and so if you're interested in the details of the
Speaker 1: history of the moon, then good check out that episode.
Speaker 1: But it's interesting that, you know, in the sort of
Speaker 1: the history of astronomy I was reading about this, people
Speaker 1: didn't really think about the Moon as a moon until
Speaker 1: they discovered Jupiter's moons. Like people were looking up in
Speaker 1: the sky and they saw, of course stars and they
Speaker 1: saw the moon, but they just thought of it as
Speaker 1: like another celestial object. They were wrong. And then you know,
Speaker 1: when Galileo and other folks saw the moons of Jupiter
Speaker 1: and they're like, hey, look at that, there are things
Speaker 1: orbiting Jupiter. That's when it clicked in the place and
Speaker 1: they're like, wait a second, what Jupiter's got over there
Speaker 1: is the same thing that we've got over here. And
Speaker 1: that's when they really eyes that this was a whole
Speaker 1: new kind of thing in space. That's so interesting. That's
Speaker 1: why it's so important to you know, to learn more
Speaker 1: and to step outside your comfort zone because there's so
Speaker 1: many things that become obvious when you see how other
Speaker 1: things are done, and the moon is actually considered a
Speaker 1: planet for a while, though the definition of a planet
Speaker 1: has also changed. Back then, a planet was just like
Speaker 1: another astronomical object. People didn't really understand the relationship between
Speaker 1: the planets and the stars and all this kind of stuff.
Speaker 1: So if you go back to very early astronomy, what
Speaker 1: these words mean is totally different from what they mean today.
Speaker 1: So it's pretty tricky to read, like you know, early
Speaker 1: astronomical texts. That sounds super confusing. So it makes me wonder.
Speaker 1: So if you can be changing what the definition of
Speaker 1: a planet is, can you have things that are not
Speaker 1: planets that have moons? You can definitely have things that
Speaker 1: are not planets that have stuff orbiting them, and we
Speaker 1: will talk about that later in the episode. There are
Speaker 1: things in the Solar System orbiting other things that are
Speaker 1: not planets, for sure. Sorry I got excited. It is
Speaker 1: very cool. And for example, you know, just as a teaser,
Speaker 1: Pluto no longer considered a planet, but it does have
Speaker 1: things orbiting it, right, Pluto has something which you would
Speaker 1: call a moon, Sharon, which is half the diameter of Pluto.
Speaker 1: So that's pretty fuzzy, like which one is a planet,
Speaker 1: which one is the moon. Pluto is only twice as
Speaker 1: big as its moon. So if Sharon or Charon, however
Speaker 1: you say, it ends up being called the moon, that
Speaker 1: makes our moon a little bit less exciting. Yeah, Or
Speaker 1: if Pluto gets repromoted back into it being a planet,
Speaker 1: then Sharon would be the largest moon relative to a
Speaker 1: planet in the Solar System. But because Pluto's no longer
Speaker 1: technically a planet, Sharon loses that distinction. Sharon shure, Sharon, Alright,
Speaker 1: so everybody knows about the moon. That's not what people
Speaker 1: want to hear about. Are there other things orbiting the
Speaker 1: Earth that could also be considered moons and so at?
Speaker 1: In fact, there are, but they're sort of on the
Speaker 1: border line of whether you would really technically call them
Speaker 1: a moon. One of my favorites, they say, the object
Speaker 1: which I won't even try to pronounce. You're gonna have
Speaker 1: to look it up, but it goes by the name
Speaker 1: of the space being, and it's this object like five
Speaker 1: kilometers in diameter that's orbiting the Sun in the vicinity
Speaker 1: of the Earth. But it seems like we've got to
Speaker 1: try to pronounce it, right, So I'm gonna try crew
Speaker 1: with me, Crew with crew with me. That sounds about right.
Speaker 1: If I had no idea how to pronounce it, I
Speaker 1: would guess that was correct. And I have no idea
Speaker 1: how to pronounce it, so I guess that's correct. I
Speaker 1: don't even know what the like, you know, origin of that,
Speaker 1: what language that comes from. It looks Irish to me,
Speaker 1: and I have I have no reason. I don't actually
Speaker 1: know anything about the Irish language. So mean, maybe I
Speaker 1: should stop. Maybe it's Gaelic for space being. Somebody out
Speaker 1: there who speaks Gaelic let us know how to say
Speaker 1: space being in Gaelic. So this is a fun object
Speaker 1: because it's in orbit technically around the Sun, but it's
Speaker 1: ring resonance with the Earth. This is something maybe people
Speaker 1: haven't realized that, like things that are orbiting the Sun
Speaker 1: are also interacting with each other. Right, our orbit around
Speaker 1: the Sun is mostly a big lips and it's dominated
Speaker 1: by the Sun. The shape of that lips is mostly
Speaker 1: controlled by the gravitational power of the Sun. But there
Speaker 1: are other things also orbiting with us, and they tug
Speaker 1: on us, they pull on us, and they can change
Speaker 1: our orbit. And sometimes you get two objects and what
Speaker 1: you call a resonance, which means that they are very
Speaker 1: regularly tugging on each other in a systematic way that
Speaker 1: changes both of their orbits and makes it stable, so that,
Speaker 1: for example, they will like meet two or four times
Speaker 1: while going around the Sun, depending on their relative speed,
Speaker 1: and nudge each other in just the right way. So,
Speaker 1: for example, Saturday and Jupiter are both really really powerful
Speaker 1: and they're in an orbital residence with each other. So
Speaker 1: this is an object that's moving around the Sun, but
Speaker 1: it's in resonance with the Earth, so it's strongly influenced
Speaker 1: by the Earth's gravity. But does it does it orbit
Speaker 1: in the same shape the Moon duns? So how is
Speaker 1: an orbit and a resonance different? So this thing moves
Speaker 1: around the Sun, you know, but so does the Moon.
Speaker 1: Right if you tracked the moon. The Moon goes around
Speaker 1: the Sun. The Earth goes around the Sun one but
Speaker 1: the Moon is gravitationally mostly bound to the Earth. This
Speaker 1: thing is primarily mostly bound to the Sun, but because
Speaker 1: of the influence of the Earth, if you look at
Speaker 1: its orbit from the Earth, it looks like it makes
Speaker 1: a bean shaped motion around the Earth. Like if you
Speaker 1: put the Earth, if you're sending of your reference frame
Speaker 1: and you plot where the space being is and you
Speaker 1: like take data points from day to day and imagine
Speaker 1: where it is. It makes a bean shape all the
Speaker 1: way around the Earth. So does that mean it doesn't
Speaker 1: quite fit the definition? Because like do orbits need to
Speaker 1: be elliptical and not not being shaped? It means that
Speaker 1: there's not really a clear distinction. We have a three
Speaker 1: body system. We have the Sun, we have the Earth,
Speaker 1: and we have the space being, and they're all tugging
Speaker 1: on each other. And so to ask the question like
Speaker 1: what is the space being orbiting? Is it orbiting the Earth?
Speaker 1: Is it orbiting just the Sun, doesn't have a clear
Speaker 1: precise answer unless you define an arbitrary distinction. But there
Speaker 1: is no natural distinction between these two scenarios. Is like
Speaker 1: a smooth continuum of being like the Moon where you're
Speaker 1: very clearly disorbiting the Earth and being like Mercury, where
Speaker 1: you're very clearly disorbiting the Sun. And then these quasi
Speaker 1: satellites of Earth that are very clearly affected by Earth
Speaker 1: and sort of moving around Earth as they move around
Speaker 1: the Sun. And that's what the space bean is. It's
Speaker 1: a quasi satellite of the Earth. All right, So two things. One,
Speaker 1: every time you say space being I'm going to continue
Speaker 1: to chuckle. I don't think I'm gonna stop doing that,
Speaker 1: because it's just funny and cute and too you know,
Speaker 1: I feel like it would be really nice in science
Speaker 1: classes if like, how hard it is to do these
Speaker 1: definitions and how so few things fit into these definitions
Speaker 1: was sort of made more clear, and maybe they do
Speaker 1: that in school today. It constantly blows my mind how
Speaker 1: much I think that we have the world bend nicely.
Speaker 1: But everything breaks the bins. Everything breaks the bins because
Speaker 1: the world is continuous, right, and it's huge, and so
Speaker 1: there's always going to be an example of something in between.
Speaker 1: These crisp distinctions are are our artificial way to try
Speaker 1: to impose order on the universe. And back when we
Speaker 1: hadn't seen so many things, those gaps might have seen meaningful.
Speaker 1: But as we keep looking at the universe, we find
Speaker 1: stuff that feels in those gaps, and you know, the
Speaker 1: same must be true in biology, right, that's what the
Speaker 1: duck bill platypus is. Right, It's like, hold on a second,
Speaker 1: what do you mean mammals? You know, right, right, it's
Speaker 1: nature's way of being, like, you cannot put me in
Speaker 1: a box. Yeah, so that's the space being. Also, I'm
Speaker 1: saying the space being because it is fun to say,
Speaker 1: and because I'm trying to avoid having to pronounce the
Speaker 1: actual name of the thing. Yeah. No, sure, that makes sense,
Speaker 1: It's okay. So here's what I want to know. So
Speaker 1: we're not taught that the space being is a moon
Speaker 1: in school, or at least I wasn't. So if you
Speaker 1: were to walk into a random astronomer's office at some
Speaker 1: university and ask them does the space being count as
Speaker 1: a moon? Are they gonna like roll their eyes and
Speaker 1: be like not this again. Or are they going to
Speaker 1: be like, oh, that's a really interesting question, Like how
Speaker 1: does the astronomy community do this question? That's a great question.
Speaker 1: I bet that half of them would roll our eyes
Speaker 1: and half of them would be like, you know, I
Speaker 1: was on the committee that decided what a quasi satellite is,
Speaker 1: and I have a very strong opinion about it, because
Speaker 1: you know, they get hotheaded about this stuff, right, And
Speaker 1: you will now sit for three hours while I explain
Speaker 1: the difference to you and you regret asking immediately. Yeah,
Speaker 1: And sometimes I wonder, like what does it matter? You know,
Speaker 1: people argue about whether Pluto is a planet or a
Speaker 1: dwarf planet, like, what are the consequences? Why does anybody
Speaker 1: really care? We're just making these names up. It doesn't
Speaker 1: change what Pluto is. It's not like Pluto shrinks if
Speaker 1: we call it a dwarf planet or grows in importance
Speaker 1: if we call it a real planet. These are just
Speaker 1: our arbitrary categorizations of the universe. So the affect how
Speaker 1: we think and how we talk, but really it's it's inconsequential.
Speaker 1: You know. I can see why it would matter to
Speaker 1: you if you are an astronomer, because maybe it affects
Speaker 1: the way you model things based on how these definitions
Speaker 1: fall out. But I imagine to the lay public it's like,
Speaker 1: what are we paying these people for. That's a good point.
Speaker 1: That's a good point. And so we have this thing
Speaker 1: that said the moons to the quasi satellite, and that's
Speaker 1: just one example. You know, there are lots of these
Speaker 1: things that are sort of loosely bound to the Earth
Speaker 1: orbiting the Sun that can be fairly small, like this
Speaker 1: thing is only five kilometers in diameter. As you get
Speaker 1: smaller and smaller, there are many many more of these things.
Speaker 1: Some of them are more loosely bound to the Earth.
Speaker 1: But you know, if you're gonna call this thing a moon,
Speaker 1: then you've got to call all those other little things
Speaker 1: moons also, So if you're gonna open the door that wide,
Speaker 1: then Earth is going to have a lot of little moons,
Speaker 1: and high school astronomy becomes totally untenable. And unfortunately, it
Speaker 1: doesn't change what it looks like in the sky, right,
Speaker 1: You can't look up in the sky and see this thing.
Speaker 1: The closest it ever comes to Earth is like seven
Speaker 1: and a half million miles away, which is thirty times
Speaker 1: further away from the Earth than our moon is. Plus,
Speaker 1: of course it's super tiny, so you have almost no
Speaker 1: change of spotting this thing. It was difficult for astronomers
Speaker 1: to even see it in the first place. It was
Speaker 1: only discovered in the last twenty years. Is it safe
Speaker 1: to assume that it's center of masses within the Earth
Speaker 1: or the center of mass for the two bodies falls
Speaker 1: within Earth? Absolutely? Yeah, because the Earth totally dominates this
Speaker 1: thing when it comes to mass. This thing is only
Speaker 1: five kilometers in diameter, and it's just a big chunk
Speaker 1: of rock, and so the Earth dwarfs this thing. Okay,
Speaker 1: even though it's super far away, it still works. Okay,
Speaker 1: that's our like best candidates, is there like a second
Speaker 1: best candidate. There's something else which I think is super fun,
Speaker 1: which astronomers and science communicators called a temporary moon for
Speaker 1: a while. And this is a weird object which at
Speaker 1: the end of last year sort of swooped in from
Speaker 1: deep space and orbiting the Earth a couple of times,
Speaker 1: and people are like, oh, what is this thing? It
Speaker 1: was like only forty ft long, and it has this
Speaker 1: strange cylindrical shape, and they spotted it on his telescope
Speaker 1: and they're like, wait a second, what is this thing?
Speaker 1: And it looks like a piece of a rocket. What
Speaker 1: it's space debris. It's space debris. And so it turns
Speaker 1: out this is a long lost piece of an ill
Speaker 1: faded NASA mission. There was this mission in nineteen sixty
Speaker 1: six called Surveyor two. Is a robotic spacecraft that was
Speaker 1: going to go land on the Moon and it was
Speaker 1: going to go explore the Moon, etcetera. But mid course
Speaker 1: there was a failure in the sort of ballistics and
Speaker 1: the trajection and they lost contact with the craft and
Speaker 1: one of the thrusters failed to ignite, and so basically
Speaker 1: they lost this thing. Part of it crashed on the Moon,
Speaker 1: and part of it just like tumbled out into deep
Speaker 1: space sort of lost, they thought forever. And so this
Speaker 1: thing has been like out there in space for you
Speaker 1: know what, seventy years, almost bouncing around, swooshing around, and
Speaker 1: somehow it ended up coming back to Earth. That's crazy,
Speaker 1: first of all, I think it's more like fifty years though, right,
Speaker 1: But like, it's amazing that we have that much resolution
Speaker 1: that we could find it again. It's really incredible. But
Speaker 1: you know, we are monitoring stuff that comes close to Earth,
Speaker 1: and we're looking for stuff that's sort of like tumbling
Speaker 1: towards the Earth. This is a pretty small object though
Speaker 1: that it's also a weird shape. Right. If you're looking
Speaker 1: out in the space and you see this forty ft
Speaker 1: long cylindrical object, my first guess is gonna be like aliens, right,
Speaker 1: And so how disappointed to look at it and then see,
Speaker 1: like you say, written down the side, it's just our
Speaker 1: old trash. But it's fascinating. People have done a study
Speaker 1: to figure out like what happened to it, and it
Speaker 1: turns out that when it tumbled out into space. It
Speaker 1: was very gently pushed further into space by the pressure
Speaker 1: of sunlight. We talked about this on the podcast, that
Speaker 1: you could build a spaceship that sails on light. It's
Speaker 1: called a solar sail. Just have a huge sheet of
Speaker 1: material and the photons from the sun when they hit
Speaker 1: it are going to transfer their momentum to that, just
Speaker 1: like wind on Earth transfers its momentum to a sail
Speaker 1: on a sailboat. And so that's like by design. But here,
Speaker 1: of course, it's just a rocket tumbling in space, was
Speaker 1: very gently, over decades and decades pushed deeper out into space.
Speaker 1: Are you familiar with Project Westward? No? Tell me, Oh
Speaker 1: my gosh. So the idea here was so this was
Speaker 1: like during the Cold War, and the US was worried
Speaker 1: that they would lose their ability to communicate with other
Speaker 1: nations if our undersea cables got cut by the Soviets,
Speaker 1: and so in that case we would have to rely
Speaker 1: on sending radio waves up and we would have to
Speaker 1: hope that they would bounce off the ionosphere. But that's
Speaker 1: sort of a not super reliable way of sending radio communications,
Speaker 1: and so I think it was m i T came
Speaker 1: up with the solution where they were like, well, we
Speaker 1: could be sure that the ionosphere would have stuff that
Speaker 1: would bounce the radio waves back if we put up
Speaker 1: over four hundred million copper needles. That's a great idea, right,
Speaker 1: And so the argument was that you would put these
Speaker 1: needles up and it would give us some information about
Speaker 1: how well this was gonna work. But in about two
Speaker 1: to three years, the combination of gravity and the sun
Speaker 1: pushing these needles back into the atmosphere would clear everything out,
Speaker 1: clear everything out. Does that mean these copper needles come
Speaker 1: raining back down to the service to impale people. Well,
Speaker 1: they do start raining back down towards Earth, but they're
Speaker 1: like literally only a couple of maybe centimeters long, like
Speaker 1: maybe two centimeters or something. These aren't huge, and that's
Speaker 1: why they needed four million of them. That sounds like
Speaker 1: approximately the size is of a bullet. You're talking about
Speaker 1: space bullets raining down on the Earth. But that would
Speaker 1: definitely burn up before it hits Earth, right, right, Yes,
Speaker 1: of course I think so. Yeah, so our atmosphere is
Speaker 1: like a bulletproof vest. Yes, thank you atmosphere. But so
Speaker 1: the first one that they shot up there, it didn't
Speaker 1: deploy the right way, so a bunch of these needles
Speaker 1: clumped instead of spreading nicely, and so some of these
Speaker 1: clumps fifty years later are still tracked as space debris
Speaker 1: because the clumps didn't de orbit the way that they
Speaker 1: thought they would. And then they did a second shot,
Speaker 1: and the second shot dispersed and they were able to confirm, yes,
Speaker 1: the radio waves bounced back more when we have supplemented
Speaker 1: the ionosphere with all of these needles. But then we
Speaker 1: had to go to the United Nations and promise we
Speaker 1: were going to stop messing up the space environment and
Speaker 1: that we were going to consult people from here on out.
Speaker 1: And one of the articles of the Outer Space Treaty
Speaker 1: actually requires people to do consultations. And that was motivated
Speaker 1: by Project Westward, because what the heck is the US doing?
Speaker 1: So anyway, tangent related to the Sun pushing things back
Speaker 1: into orbits or sorry, back into the atmosphere. Yeah, and
Speaker 1: we have a whole fun podcast episode about space junk
Speaker 1: and how dangerous it is and that's all smashing into itself.
Speaker 1: And if we don't get this stuff under control, all
Speaker 1: of space might be useless to us. We might be
Speaker 1: trapped down here on Earth because we'd be surrounded by
Speaker 1: our own garbage. So check out that episode if you're interested.
Speaker 1: But this is one particularly interesting object, and it came
Speaker 1: in November twenty and made a few large loops around
Speaker 1: the Earth. And so that's why they called this sort
Speaker 1: of like a temporary moon, because even though it was
Speaker 1: lost in deep space, somehow it ended up close enough
Speaker 1: for the Earth to grab it again and loop around.
Speaker 1: But it wasn't a stable orbit, which is really fascinating.
Speaker 1: It was like stable enough to loop around a few
Speaker 1: times and then get tossed back out into space. So
Speaker 1: in March continued his journey and is now back into
Speaker 1: deep space somewhere. WHOA. So, so was this like a
Speaker 1: sycom angle for getting people interested in this, because it
Speaker 1: seems like because it was artificial, it shouldn't count as
Speaker 1: a moon at all, not a temporary moon. It shouldn't
Speaker 1: be a moon. Or do different people use different definitions
Speaker 1: than the one that we settled upon at the beginning
Speaker 1: of the episode, Yeah, exactly. I think this was just
Speaker 1: a clickbait moon, not really by any definition. If you're
Speaker 1: going to require that moons be natural, may not be
Speaker 1: manufactured by humanity. Then this is definitely not a mood.
Speaker 1: But it's cool that we capture something from deep space
Speaker 1: and it orbited us a little while before going back
Speaker 1: out into the dark deep emptiness. Yeah, no, that's super cool.
Speaker 1: All right, So let's take our second break before we
Speaker 1: start to talk a bit more about moons on planets
Speaker 1: other than our own. Okay, so we've talked a bit.
Speaker 1: How about how Earth has one for sure moon and
Speaker 1: a couple maybe moons, quasi moons, quasi moons. Right, tell
Speaker 1: me a bit more about what else is typical in
Speaker 1: the Solar System. How many moons do the other planets have.
Speaker 1: It's really interesting because the Earth, as we were saying,
Speaker 1: is really weird, Like having a really big moon is weird. Also,
Speaker 1: having just one moon is weird. So the eight planets
Speaker 1: in the Solar System, of course, the Earth has one moon.
Speaker 1: Two of the planets have no moons, Mercury and Venus,
Speaker 1: and the other five planets have two hundred and four
Speaker 1: moons in between them. So that's really fascinating and you
Speaker 1: might wonder like, well, why do Mercury and Venus have
Speaker 1: no moons? And the reason is that they're so close
Speaker 1: to the Sun. The Sun is this like really terrible
Speaker 1: overwhelming gravitational force and it tugs on things. We talked
Speaker 1: to the program before about tidal forces. The closer you
Speaker 1: are to the Sun, the more it tugs on you.
Speaker 1: So if you're an object, it's not just like a point.
Speaker 1: If you have like an extent to you, and the
Speaker 1: Sun is going to tug harder on the bit that's
Speaker 1: closer and not as hard on the bid that's further away,
Speaker 1: and that's an effective force on you. So the Sun is,
Speaker 1: for example, squeezing mercury and venus all the time. It's
Speaker 1: pulling on them, and that makes it very hard for
Speaker 1: them to have any in a stable orbit around them. Basically,
Speaker 1: if they have a moon, the Sun is going to
Speaker 1: steal it when it swoops around the planet on the
Speaker 1: close side. So here I'm finding that I want to
Speaker 1: ask you if that means in other Solar systems, the
Speaker 1: close planets don't have moons. But I'm jumping if I
Speaker 1: do that, aren't I We don't know the answer to
Speaker 1: that question yet. We'll talk about that in a minute,
Speaker 1: but yeah, it's a fascinating question. We know that in
Speaker 1: our Solar system, the innermost planets Mercury and Venus have
Speaker 1: no moons, and you know, that might be part of
Speaker 1: the answer of why the Earth only has one moon
Speaker 1: and it's a really big one. It might be that
Speaker 1: anything else the Sun is basically going to steal, and
Speaker 1: that we're only capable of having like either really big
Speaker 1: moons or quasi moons that were sort of sharing with
Speaker 1: the Sun. That might be the partial answer to that question. Interesting,
Speaker 1: So we have the Sun to thank for the space being. Yeah,
Speaker 1: the Sun is toasting our space being for us. But
Speaker 1: then further out in the Solar system, there are lots
Speaker 1: and lots of moons. You know, the other five planets
Speaker 1: with moons have two hundred and four of these things combined,
Speaker 1: you know, in Jupiter and sat And have like dozens
Speaker 1: of them. And you know, Saturn has this crazy ring system,
Speaker 1: and inside those rings are rocks that are big enough
Speaker 1: to be considered moons. Sometimes they're called you know, moonlits,
Speaker 1: sometimes are called minor moons. But there are all sorts
Speaker 1: of things, and so the deeper you go out into
Speaker 1: our Solar system, the more you find these objects that
Speaker 1: have moons and lots and lots of moons. To do
Speaker 1: any of the moons have moons. I wish they did
Speaker 1: have moons. And what would you call that anyway? Would
Speaker 1: that be like a moon moon or squared? That's a
Speaker 1: great question. And so far we haven't found any moons
Speaker 1: that have moons. And the reason is similar to why
Speaker 1: Mercury doesn't have moons. If you're a moon, then you're
Speaker 1: near a big planet, and that means that there are
Speaker 1: tidal forces, and so it's pretty hard to hold onto
Speaker 1: something and not have it gets slurred up and just
Speaker 1: become another moon of the planet you're orbiting. So if
Speaker 1: you're Io and you're orbiting Jupiter, right, Jupiter is an
Speaker 1: enormous gravitational pull. The reason that Io is like hot inside,
Speaker 1: it's because of Jupiter's tidal forces, and so anything orbiting
Speaker 1: Io is just going to get pulled away. It's very
Speaker 1: very hard to have a stable orbit. Although there's this
Speaker 1: really crazy moon of Saturn. This moon is called Rhea,
Speaker 1: and recently they've spotted some stuff in orbit around Rhea,
Speaker 1: maybe sort of like these very small particles. It almost
Speaker 1: looks like this moon of Saturn has its own ring system.
Speaker 1: What I know, isn't that cool? I never thought about
Speaker 1: like a moon with rings around. It is pretty cool.
Speaker 1: That's awesome. So so how if it can't have moons,
Speaker 1: how does it manage to maintain its rings? Well, the
Speaker 1: reason you sometimes have rings instead of moons are because
Speaker 1: of tidal forces. Basically, rings are moons that have been
Speaker 1: torn apart by tidal forces. And so it might be
Speaker 1: that there was an object there and then it got
Speaker 1: sort of shredded by tidal forces, and what we're seeing
Speaker 1: is something transient that these rings might not last for
Speaker 1: very long. You know, by very long we mean on
Speaker 1: astrophysical time scale. So they might be there a million
Speaker 1: years or so. But if you leave the Solar system
Speaker 1: and come back and five million, you might find that
Speaker 1: they're not there anymore. Okay, so let's move out of
Speaker 1: our solar system. What does this look like in other
Speaker 1: solar system? So, for example, do the mercury and venus
Speaker 1: equivalents and other solar systems lack moons like we see
Speaker 1: in our solar system. It's such a good question and
Speaker 1: one we just don't know the answer to yet because
Speaker 1: we have never seen a moon in another solar system,
Speaker 1: Like every moon that any human has ever seen has
Speaker 1: only ever been in our solar system. Isn't that like
Speaker 1: crazy and slightly frustrating. It's both of those things, And
Speaker 1: it reveals to me, like just how often I assume
Speaker 1: that science has figured out so many things that are
Speaker 1: much harder than I apparently understand. So why do we
Speaker 1: know that all these other solar systems have planets but
Speaker 1: we don't know that they have moons? Well, moons are
Speaker 1: much smaller, and they're just harder to see them planets.
Speaker 1: You know, we now sort of take it for granted
Speaker 1: that we can see planets around other stars, But that's
Speaker 1: pretty recent. It was like that we started to be
Speaker 1: able to really do this and spot planets and other soldiers.
Speaker 1: Until then, we had never seen a planet around a
Speaker 1: star that wasn't our star. We didn't know until then, if,
Speaker 1: for example, our star was the only one that had planets,
Speaker 1: we could have been like the weirdest star in the universe. Now,
Speaker 1: of course, we know, because we've looked and we've seen
Speaker 1: that lots and lots and lots of stars have lots
Speaker 1: and lots of planets. We're also learning, of course, that
Speaker 1: our Solar system is weird in all sorts of interesting ways.
Speaker 1: But the problem is that the techniques we used to
Speaker 1: see those planets are better when the planets are large
Speaker 1: and when they're close to the Sun, and that makes
Speaker 1: it pretty hard to see moons, which tend to be
Speaker 1: small and further from the star. We haven't found any
Speaker 1: instances of a moon that's like huge or one of
Speaker 1: those instances where it's hard to determine which one is
Speaker 1: the planet and which one is the moon because they're
Speaker 1: both pretty big, and so there's no big things that
Speaker 1: break this rule. We haven't confirmed any moons and other
Speaker 1: solar systems are you're looking for the duck built platypus
Speaker 1: of moons out there somewhere No so far zero. There
Speaker 1: have been some candidates. People have some really clever ideas
Speaker 1: for how you might see moons around planets in other
Speaker 1: solar systems. Like one way that we see the planet
Speaker 1: is that the planet passes in front of the star
Speaker 1: makes like a little eclipse, it like dims the star
Speaker 1: a little bit. And if it does that several times,
Speaker 1: you can see a pattern, so you can get a
Speaker 1: sense for like, oh, this is really something that's passing
Speaker 1: in front of the star. It must be a planet. Now,
Speaker 1: if there's a moon around that planet and it's orbiting
Speaker 1: that planet. As it passes around the planet, it might
Speaker 1: add to that eclipse a little bit and then pass
Speaker 1: behind the planet and dip again. And so if you
Speaker 1: have really refined measurements, you might see these like wiggles
Speaker 1: on the wiggles that tell you that there's something going
Speaker 1: around that planet. And there are some cases where people
Speaker 1: look at the data and they're like, yeah, I think
Speaker 1: those are wiggles and wiggles, but other people analyze the
Speaker 1: same data and they're like, no, there's no evidence for that.
Speaker 1: So we're really at the edge of being able to
Speaker 1: detect XO moons. We haven't seen any yet. Well that's exciting, Like,
Speaker 1: hopefully in our lifetime we figure out how to do that. Well, yeah,
Speaker 1: hopefully in our lifetime. I mean, we're on the edge
Speaker 1: of learning so much about these other solars to times,
Speaker 1: like figuring out what's any atmosphere of those planets, seeing
Speaker 1: what moons there are. There was also a lot of excitement.
Speaker 1: I don't know if you remember about this one particular
Speaker 1: star called Tabby Star, which dimmed really weirdly all of
Speaker 1: a sudden, and people thought like, wait a second, what's
Speaker 1: blocking this star? Is this evidence of like an alien megastructure.
Speaker 1: Is somebody out there building a dison spear around this star,
Speaker 1: which was really fun and you know inspired, I'm sure
Speaker 1: a lot of science fiction novels. But it turns out
Speaker 1: that it was just like a big cloud of dust
Speaker 1: and debris. But it might be that, like, you know,
Speaker 1: there was a planet out there and it had a moon,
Speaker 1: and that moon got like tidally disrupted and torn up
Speaker 1: and ended up being this big cloud of stuff that
Speaker 1: partially blocked the star. So that might have been like,
Speaker 1: you know, evidence of the destruction of an excellent moon. WHOA,
Speaker 1: that's pretty cool. That's pretty cool. Yeah, But I'm looking
Speaker 1: forward to scientists figuring that out and so we can
Speaker 1: get a sense for like how unusual is it to
Speaker 1: have just like one big moon, How unusual is it
Speaker 1: to have inner planets with no moons? How weird is
Speaker 1: it to have huge gas giants with like a dozen moons.
Speaker 1: We ask these basic questions because we just don't know
Speaker 1: the answers, and really the only way to figure it
Speaker 1: out is to go out there and explore the universe
Speaker 1: and to like actually look with our eyeballs and our
Speaker 1: telescopes and get the answers. It's a cool time to
Speaker 1: be alive. It is a cool time to be alive. So, Kelly,
Speaker 1: what are you going to go back and tell your
Speaker 1: seven year old about how many moons the Earth has? Well,
Speaker 1: I think she's going to be super excited. She We've
Speaker 1: been talking to her about Apollo and the space race,
Speaker 1: and I think she'll be super excited to hear that
Speaker 1: one of those you know, boosters came back around again
Speaker 1: and is still floating in deep space. So I'll tell
Speaker 1: her about that, and I definitely think she's going to
Speaker 1: love that there's something called a space being or something
Speaker 1: we referred to as a space being because we can't
Speaker 1: pronounce its real name. I think she's going to get
Speaker 1: a total kick out of that information. What about you,
Speaker 1: what are you gonna tell your kids? Yeah, my kids
Speaker 1: also will tell them that there's weird stuff floating out there,
Speaker 1: and that in the end, it's all just sort of arbitrary.
Speaker 1: What we call a moon and what we call a
Speaker 1: quasi satellite is really just an arbitrary distinction, but that
Speaker 1: their questions are valuable questions, and that these really simple,
Speaker 1: basic questions about the universe are sometimes the most interesting,
Speaker 1: the hardest to answer and reveal something about you know,
Speaker 1: what we've thought about our place in the universe, what
Speaker 1: we think is natural, what we think is normal, what
Speaker 1: we think is typical, and it probably is really unusual.
Speaker 1: And that's somewhere out there there's an alien kid looking
Speaker 1: up at the sky and asking the alien mom, like,
Speaker 1: why do we have five moons? You know, it's just
Speaker 1: every planet to have five moons. I love that idea
Speaker 1: that we're all asking the same questions, but just very
Speaker 1: much separated. All right, So thank you very much everybody
Speaker 1: for going on this curiosity journey with us and listening
Speaker 1: to us talk about the number of moons around the Earth.
Speaker 1: If you have stuff you'd like to hear us talk about,
Speaker 1: please send them to us two questions at Daniel and
Speaker 1: Jorge dot com. Thanks again, Kelly for joining us today
Speaker 1: and thanks to all of you for tuning in. Thanks
Speaker 1: for having me. It was a lot of fun. Thanks
Speaker 1: for listening, and remember that Daniel and Jorge explained. The
Speaker 1: Universe is a production of I Heart Radio or more
Speaker 1: podcast from my Heart Radio visit the I Heart Radio app,
Speaker 1: Apple Podcasts, or wherever you listen to your favorite shows.