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Did the Earth ever have a ring? · Daniel and Kelly’s Extraordinary Universe

• 0:06
  Speaker 1: The message you often hear about space is that it's
• 0:08
  Speaker 1: vast and empty. The Earth and even the Sun are
• 0:11
  Speaker 1: these tiny dots and a huge ocean of black space.
• 0:15
  Speaker 1: That's all true, but it gives you the wrong idea
• 0:17
  Speaker 1: about our cosmic neighborhood. It suggests that the Earth is isolated, alone,
• 0:21
  Speaker 1: not affected by our neighbors, not in danger. The truth
• 0:25
  Speaker 1: is actually the opposite. Space is vast, but gravity is
• 0:29
  Speaker 1: also very patient. There are a lot of big dark
• 0:32
  Speaker 1: rocks out there that could get tugged by gravity towards
• 0:35
  Speaker 1: the Earth and then dramatically affect our way of life,
• 0:39
  Speaker 1: both positively or negatively. They could, of course smash into
• 0:42
  Speaker 1: us and cause an extinction event, but then they could
• 0:45
  Speaker 1: also create new snazzy bling around our planet. So today
• 0:50
  Speaker 1: we're going to dig deep into the history of Earth
• 0:52
  Speaker 1: within our cosmic neighborhood, understand the gravitational dance between all
• 0:56
  Speaker 1: of these objects, and ask the question about whether there
• 0:59
  Speaker 1: was ever a time when the universe put a ring
• 1:02
  Speaker 1: on the Earth. So, just in time for Valentine's Day,
• 1:05
  Speaker 1: we're getting cosmically romantic and asking did Earth ever have
• 1:10
  Speaker 1: a ring? Welcome to Daniel and Kelly's extraordinary universe. Hello.
• 1:28
  Speaker 2: I'm Kelly Wienersmith. I'm a parasitologist and I stopped wearing
• 1:32
  Speaker 2: rings because I got fish guts stuck in my ring
• 1:35
  Speaker 2: too many times and decided it was too gross.
• 1:39
  Speaker 1: Oh isn't that romantic though?
• 1:42
  Speaker 2: Fish guts in a ring? You got a weird sense
• 1:45
  Speaker 2: of romance, Daniel, I'm.
• 1:48
  Speaker 1: Trying to resonate with a biology. Hi. I'm Daniel. I'm
• 1:51
  Speaker 1: a particle physicist, and I bought my wedding rings for
• 1:55
  Speaker 1: two dollars on Telegraph Avenue in Berkeley.
• 1:58
  Speaker 2: I was going to ask you, are you and Katrina
• 2:01
  Speaker 2: ring people or not ring people?
• 2:03
  Speaker 1: We have rings which we feel sentimental about, but we're
• 2:05
  Speaker 1: not people who are into expensive fancy stuff. So like
• 2:08
  Speaker 1: her engagement ring has a piece of amber in it,
• 2:11
  Speaker 1: and I designed the ring myself. There's no like crazy
• 2:14
  Speaker 1: diamond in there. And we didn't want to spend a
• 2:16
  Speaker 1: lot of money on crazy rings, so we just walked
• 2:18
  Speaker 1: down Telegraph Avenue and found a guy who made silver
• 2:21
  Speaker 1: rings and bottom for a couple of bucks.
• 2:24
  Speaker 2: You designed a ring with amber and got it for
• 2:26
  Speaker 2: two bucks.
• 2:27
  Speaker 1: Oh no, the engagement ring I had a friend make,
• 2:29
  Speaker 1: so that was more than two dollars, but yes, I
• 2:32
  Speaker 1: designed it myself. It has a bunch of Danish ruins
• 2:34
  Speaker 1: in it and stuff and a piece of amber in
• 2:36
  Speaker 1: the middle.
• 2:37
  Speaker 2: Oh that's great.
• 2:38
  Speaker 1: How about you? What's your guys ring story?
• 2:40
  Speaker 2: Can I tell you our engagement story really quick? Oh?
• 2:42
  Speaker 1: Yes? Does it involve fish cuts? No?
• 2:44
  Speaker 2: No, the rest of our life involves fish cuts, but no,
• 2:46
  Speaker 2: our engagement story. So Zach is like not a super
• 2:49
  Speaker 2: sentimental guy, and so, like, a couple months earlier, I
• 2:52
  Speaker 2: had said to him, like, hey, you know we've been
• 2:54
  Speaker 2: together for a year, do you think you could ever
• 2:57
  Speaker 2: see yourself marrying me? Because if still, let's keep going.
• 2:59
  Speaker 2: But if not, let's like cut our losses and bee
• 3:02
  Speaker 2: like this was fun. And so his response, and this
• 3:05
  Speaker 2: is amazing. His response was I think you're really nice, wow,
• 3:09
  Speaker 2: which I thought was him being like I don't want
• 3:12
  Speaker 2: to answer this question because it's going to be uncomfortable,
• 3:15
  Speaker 2: but like, that's not what I was looking for, right,
• 3:17
  Speaker 2: And so I thought to myself, like, Okay, in a
• 3:19
  Speaker 2: couple more months, I'm going to ask him this again,
• 3:22
  Speaker 2: and if I don't get a better answer, it's over.
• 3:24
  Speaker 2: But so Zach thought, well, you marry the person who
• 3:27
  Speaker 2: you think is really nice. So he thought he had
• 3:29
  Speaker 2: said like, yeah, I could marry you one day, and
• 3:31
  Speaker 2: he thought after that conversation that it was locked in
• 3:33
  Speaker 2: and that he didn't even really need to ask.
• 3:35
  Speaker 1: That was like the most positive thing he could think
• 3:37
  Speaker 1: of saying, I think you're really nice.
• 3:40
  Speaker 2: No, he's not a super sentimental side. So it was
• 3:43
  Speaker 2: Pie Day, March fourteenth, and he gave me a little
• 3:46
  Speaker 2: card with a pie on it that said don't open
• 3:48
  Speaker 2: until what are the extended digits of pie? So three
• 3:51
  Speaker 2: fourteen is the date, and then it's nine okay, yeah,
• 3:54
  Speaker 2: so don't open until one fifty nine. And I thought
• 3:57
  Speaker 2: it was going to be a poem about how like
• 3:58
  Speaker 2: I eat too much pie he writes like weird poems,
• 4:02
  Speaker 2: and I forgot about it, and so later in the day,
• 4:05
  Speaker 2: it was like four pm and he was in the
• 4:07
  Speaker 2: restroom and I reached into my pocket and I was like, oh,
• 4:09
  Speaker 2: I've got this card in my pocket and it's after
• 4:11
  Speaker 2: one fifty nine, so I can open it. And it
• 4:13
  Speaker 2: said something to the effect of, like, you get frustrated
• 4:16
  Speaker 2: because I forgot our anniversary. But if we got engaged
• 4:18
  Speaker 2: on Pie Day, that's a date I'd always remember.
• 4:20
  Speaker 1: Oh my gosh.
• 4:21
  Speaker 2: And so he came out of the bathroom and I
• 4:23
  Speaker 2: was like, are you asking me to marry you? And
• 4:26
  Speaker 2: so I'll note that he forgot when one fifty nine passed,
• 4:29
  Speaker 2: so he wasn't worried about the answer. He knew what
• 4:31
  Speaker 2: the answer was gonna be.
• 4:32
  Speaker 1: And I love that there's a bathroom visit in the
• 4:34
  Speaker 1: middle of this story. That's very Kelly and Zach.
• 4:38
  Speaker 2: Exactly, very scatological. And so I was like, wait, so
• 4:41
  Speaker 2: are we engaged now? And all he said was, well,
• 4:43
  Speaker 2: you weren't supposed to read it while I was on
• 4:45
  Speaker 2: the hut. Anyway, he didn't have a ring, he didn't
• 4:51
  Speaker 2: have anything. We're not very sentimental. So anyway, we went out.
• 4:54
  Speaker 2: We got a ring. I got fish guts in it,
• 4:56
  Speaker 2: so I stopped wearing it because while I was doing dissections,
• 4:58
  Speaker 2: it kept getting in the way. I got him a ring,
• 5:01
  Speaker 2: and when we were walking around Rice University, our daughter
• 5:04
  Speaker 2: was playing with it, and I was like, Zach, and
• 5:06
  Speaker 2: she was like two as like, Zach, she's gonna drop it.
• 5:08
  Speaker 2: You're gonna lose your wedding ring. You probably shouldn't let
• 5:11
  Speaker 2: her play with it. And we got back into the
• 5:12
  Speaker 2: car and he sat down and he goes, uh oh.
• 5:17
  Speaker 2: And anyway, so he lost his ring, and I don't
• 5:19
  Speaker 2: wear mine because of fish guts and we are not
• 5:22
  Speaker 2: super sentimental. But you know, it's been almost twenty years
• 5:25
  Speaker 2: since we've been together, so it's working out.
• 5:27
  Speaker 1: So Zach's ring is somewhere on the campus of Rice University, or.
• 5:31
  Speaker 2: Some undergrad plays drinking games with it or something. I
• 5:34
  Speaker 2: don't know. I don't know where it ended up. We
• 5:36
  Speaker 2: never found it.
• 5:37
  Speaker 1: All right, Rice students, if you see a ring on campus,
• 5:39
  Speaker 1: send it to Kelly.
• 5:41
  Speaker 2: Yeah, I'll take all the random rings that get lost
• 5:44
  Speaker 2: on campus. All right, Well, I've gotten us off topic.
• 5:47
  Speaker 2: Your story was lovely. Mine was hopefully good for a laugh.
• 5:50
  Speaker 2: But today we're talking about whether or not Earth ever
• 5:53
  Speaker 2: had a ring, which is a fun question to think about.
• 5:56
  Speaker 1: It's fun to think about because it makes us think
• 5:58
  Speaker 1: about the deep past and how we think of the
• 6:01
  Speaker 1: Earth as a certain way and having the moon and
• 6:04
  Speaker 1: the sky looks a certain way and the solar systems
• 6:06
  Speaker 1: arranged a certain way, and we imagine it's always been
• 6:09
  Speaker 1: that way or forzillions of years. But it turns out
• 6:12
  Speaker 1: that on a cosmic time scale, the solar system has
• 6:15
  Speaker 1: a very chaotic history, and things used to look quite
• 6:18
  Speaker 1: a bit different. So it's really fun for me to
• 6:21
  Speaker 1: go deep into the past and learn about how the
• 6:24
  Speaker 1: Solar system used to be quite different, how life on
• 6:27
  Speaker 1: Earth could have been different. You could have looked up
• 6:28
  Speaker 1: at the sky and seeing different stuff out there.
• 6:31
  Speaker 2: And I got to say, when you sent me this
• 6:32
  Speaker 2: idea for a podcast episode topic, it had not been
• 6:36
  Speaker 2: on my radar at all that Earth could have ever
• 6:38
  Speaker 2: had a ring. So I'm excited about hearing the answer
• 6:41
  Speaker 2: to this.
• 6:42
  Speaker 1: So I was wondering if folks out there had considered
• 6:45
  Speaker 1: the possibility of whether Earth had ever had a ring.
• 6:48
  Speaker 1: So I sent this question to our intrepid volunteers. Thank
• 6:50
  Speaker 1: you very much to everybody who plays along. If you
• 6:53
  Speaker 1: would like to hear your voice answering questions on the podcast,
• 6:56
  Speaker 1: please don't be shy. We would love to have you
• 6:58
  Speaker 1: as part of the chorus. To us two questions at
• 7:01
  Speaker 1: Danielankelly dot org and we will set you up in
• 7:04
  Speaker 1: the meantime. Think about it for a minute. Do you
• 7:06
  Speaker 1: think Earth could have ever had a ring? Here's what
• 7:10
  Speaker 1: our listeners had to say. A big meteorite smashed into
• 7:15
  Speaker 1: the Earth all the debris shot up into the into space.
• 7:19
  Speaker 1: The Earth did have a ring with the material that
• 7:22
  Speaker 1: eventually call us into the Moon.
• 7:24
  Speaker 2: Yes, it did have a ring, and it still does.
• 7:27
  Speaker 3: Maybe it did, like with all the rocks flying around
• 7:31
  Speaker 3: it right at the beginning when it was being formed,
• 7:34
  Speaker 3: had like a wriggled rocks around it. And maybe when
• 7:40
  Speaker 3: the ice it happens and been a thing of vice
• 7:44
  Speaker 3: around it when there was the ice. Say, I don't
• 7:47
  Speaker 3: really think that could have happened.
• 7:49
  Speaker 2: So, yes, the Earth probably had a ring when the
• 7:52
  Speaker 2: Moon was born. As bodies coal started to fall into
• 7:55
  Speaker 2: planet olids and eventually planets that would have been rings.
• 7:57
  Speaker 1: Earth might have had a ring after the collision with Theata.
• 8:00
  Speaker 1: If you're referring to a persistent ring system akin to Saturns,
• 8:03
  Speaker 1: then that's more of a complex question open to interpretation.
• 8:06
  Speaker 1: The ejecta from that collision temporarily formed a ring.
• 8:10
  Speaker 2: There is a chance that's to be some sort of
• 8:12
  Speaker 2: ring during its creation.
• 8:15
  Speaker 1: It no longer has a ring because it is divorced.
• 8:19
  Speaker 1: Middle Earth did and it was a big freaking deal.
• 8:22
  Speaker 1: Is that one of the theories or hypotheses behind where
• 8:25
  Speaker 1: the Moon came from.
• 8:26
  Speaker 2: When a Mars sized object collided with Earth. Do Bear's
• 8:31
  Speaker 2: poop in the woods?
• 8:33
  Speaker 1: Do taco taste better on Tuesdays?
• 8:35
  Speaker 2: Does Tom Cruise will have to sprint like a maniac
• 8:37
  Speaker 2: in every one of his movies? Yes, yes, the Earth
• 8:40
  Speaker 2: had a ring, but.
• 8:41
  Speaker 1: I'll do notize that Liberachi had rings during the formation
• 8:44
  Speaker 1: of the Moon.
• 8:45
  Speaker 2: No, I mean Saturn offered, but long distance relationships just
• 8:48
  Speaker 2: never work out.
• 8:49
  Speaker 1: And a protope planet hits it to form the Moon.
• 8:52
  Speaker 2: While the moon was being formed.
• 8:56
  Speaker 1: I really don't know, but I imagine not since the
• 8:58
  Speaker 1: moon has been there.
• 9:00
  Speaker 2: That was an amazing mix of like serious good answers
• 9:03
  Speaker 2: and some really clever not answers.
• 9:07
  Speaker 1: I think Tom Cruise does sprint in every movie he's in.
• 9:10
  Speaker 1: I think that's true every.
• 9:12
  Speaker 2: Movie I can think of. Did he sprint in Jerry Maguire,
• 9:16
  Speaker 2: He must have. There must have been a reason to sprint.
• 9:18
  Speaker 2: Somebody check the footage, Okay, let us know.
• 9:20
  Speaker 1: And I was a little surprised, though I guess I
• 9:22
  Speaker 1: shouldn't have been that most people went to the sort
• 9:24
  Speaker 1: of early formation of the Earth, the impact with the
• 9:28
  Speaker 1: protoplanet that formed the Moon, and thinking about how that
• 9:31
  Speaker 1: might have been a ring as well, and that's a
• 9:33
  Speaker 1: totally reasonable answer. That it's not what I was going
• 9:36
  Speaker 1: for for today's episode.
• 9:38
  Speaker 2: Well, I think probably it would help to know how
• 9:41
  Speaker 2: rings are formed in general. So I'm guessing you're going
• 9:44
  Speaker 2: to tell us that today, but let's start even earlier. So, like,
• 9:48
  Speaker 2: what are rings? I guess I realized, Well, I was
• 9:50
  Speaker 2: thinking about this question, like, you know, the moon orbits
• 9:53
  Speaker 2: in a ring, but that's not a ring. How continuous
• 9:56
  Speaker 2: does the line need to be before you have a
• 9:58
  Speaker 2: satellite versus a ring?
• 9:59
  Speaker 1: Yeah, so it's astronomy, which means we're going to do
• 10:03
  Speaker 1: our best to draw arbitrary dotted lines between the continuous
• 10:06
  Speaker 1: concepts that really exist on a spectrum. But you know,
• 10:10
  Speaker 1: some things we call moons, some things we call rings.
• 10:12
  Speaker 1: What's the difference? How many tiny moons does it take
• 10:15
  Speaker 1: before you start calling it a ring? Typically we call
• 10:18
  Speaker 1: something a ring if it's composed of solid materials such
• 10:22
  Speaker 1: as dust or moonlits, But it's not in one single object.
• 10:26
  Speaker 1: So you know, basically there's a spectrum between Like you
• 10:30
  Speaker 1: have one single object, you call that a moon. If
• 10:32
  Speaker 1: you break that moon up into little rocks, you could
• 10:35
  Speaker 1: call those moonlits, Or you could say if they're fine
• 10:38
  Speaker 1: enough you could call it a ring.
• 10:40
  Speaker 2: But if you had two objects as big as the
• 10:42
  Speaker 2: Moon that somehow didn't run into each other, would that
• 10:45
  Speaker 2: be a ring. Does Mars have a ring or does
• 10:47
  Speaker 2: it just have two moons?
• 10:48
  Speaker 1: Mars has two moons, so I think there isn't a
• 10:52
  Speaker 1: very crisp distinction. I couldn't find a crisp distinction online.
• 10:56
  Speaker 1: I don't think like the astronomers have had a meeting
• 10:59
  Speaker 1: arguing about this yet.
• 11:00
  Speaker 2: Nature doesn't care about our criteria in our categories.
• 11:04
  Speaker 1: But I think one thing that is important for a
• 11:06
  Speaker 1: ring is that it's basically in a plane. So, you know,
• 11:10
  Speaker 1: a swarm of objects surrounding a planet, you wouldn't call
• 11:13
  Speaker 1: that a ring. If it's like in a sphere. If
• 11:15
  Speaker 1: it's orbiting in every direction and completely surrounding the planet
• 11:18
  Speaker 1: with little rocks, that isn't a ring. When distinguishing feature
• 11:21
  Speaker 1: of a ring is that it does orbit in a plane, right, that, like,
• 11:24
  Speaker 1: the vertical motion relative to the ring is small compared
• 11:28
  Speaker 1: to the motion around the planet.
• 11:30
  Speaker 2: Does it happen that you get junk like all around
• 11:34
  Speaker 2: a planet or does it always end up in the
• 11:36
  Speaker 2: same plane as a ring?
• 11:37
  Speaker 1: Yeah? Great question. You can get junk around a planet,
• 11:41
  Speaker 1: but that's sort of temporary. That's not a very stable
• 11:43
  Speaker 1: situation because gravity will eventually pull it down together into
• 11:47
  Speaker 1: a plane. There's a reason that planets have rings and
• 11:51
  Speaker 1: not swarms of stuff. And there's a reason that moons
• 11:53
  Speaker 1: typically form in a single plane around a planet, which
• 11:57
  Speaker 1: aligns with the planet's spin usually, And it's the same
• 12:00
  Speaker 1: reason why the planets all spin in the same plane
• 12:04
  Speaker 1: as their motion around the Sun, which aligns with the
• 12:08
  Speaker 1: rotation of the Sun. And the reason is angular momentum.
• 12:12
  Speaker 1: Gravity would like to pull everything down together into a
• 12:14
  Speaker 1: little dot. What resists that, Well, sometimes it's like structural
• 12:18
  Speaker 1: or integrity. The Earth doesn't collapse into a black hole
• 12:21
  Speaker 1: because it's solid, right, and the rocks resist being crushed.
• 12:24
  Speaker 1: But there's another factor there, which is the Earth is spinning,
• 12:27
  Speaker 1: and the spinning of the Earth sort of fluffs it
• 12:29
  Speaker 1: up a little bit and makes it larger. So like
• 12:32
  Speaker 1: the Earth's radius from the core to the surface is
• 12:35
  Speaker 1: larger at the equator because it's spinning, and if the
• 12:38
  Speaker 1: Earth was softer like pizza dough, it would get flatter
• 12:41
  Speaker 1: and flatter as that spinning resists gravity. But the spinning
• 12:45
  Speaker 1: only resists gravity along the plane. Right, So if you
• 12:48
  Speaker 1: have like the Earth spin axis, the spinning helps resist gravity,
• 12:52
  Speaker 1: helps keep Earth fluffed out along the plane of that
• 12:56
  Speaker 1: spin right, so the axis is perpendicular to the plane,
• 13:00
  Speaker 1: but it doesn't prevent things from collapsing to the plane.
• 13:03
  Speaker 1: So now I imagine you have a big swarm of
• 13:05
  Speaker 1: stuff that's swirling around the Earth. Gravity can pull it
• 13:08
  Speaker 1: down into that plane, making a disk, but the spinning
• 13:12
  Speaker 1: keeps gravity from pulling it down into the Earth necessarily.
• 13:15
  Speaker 1: That's why a big swarm of stuff would collapse into
• 13:18
  Speaker 1: a plane. And it's the same reason why the whole
• 13:20
  Speaker 1: solar system has collapsed into a plane. The original blob
• 13:25
  Speaker 1: of gas and dust that formed our solar system collapse
• 13:28
  Speaker 1: due to gravity, but didn't collapse as far along that plane.
• 13:32
  Speaker 1: Because everything is spinning, it keeps stuff from falling all
• 13:35
  Speaker 1: the way in.
• 13:37
  Speaker 2: So if you had a speck around the Earth, not
• 13:42
  Speaker 2: around like the plane where you get the ring, would
• 13:46
  Speaker 2: it get thrown out or pulled in or either?
• 13:49
  Speaker 1: Yeah? So say, for example, Earth has a big ring
• 13:53
  Speaker 1: and now you add a rock in a random orientation
• 13:56
  Speaker 1: to the Earth. What's going to happen to it? Well,
• 13:59
  Speaker 1: it has a lot of al so it's not going
• 14:01
  Speaker 1: to fall to the Earth. It's going to be an orbit,
• 14:03
  Speaker 1: but it's going to get gravitated towards the ring. The
• 14:05
  Speaker 1: ring is going to pull it in, and so while
• 14:08
  Speaker 1: it's going to maintain an orbit because of its speed,
• 14:10
  Speaker 1: that orbit's going to shift until it joins the ring.
• 14:13
  Speaker 1: The ring, because of its gravity, is going to pull
• 14:16
  Speaker 1: that new rock into it. So gravity pulls things together,
• 14:18
  Speaker 1: but it can't overcome angular momentum.
• 14:21
  Speaker 2: Okay, And are rings always at the equator of the
• 14:26
  Speaker 2: thing that they're orbiting around, And if the thing is
• 14:28
  Speaker 2: at a tilt, that's why it doesn't look like it's
• 14:30
  Speaker 2: straight around. So like Saturn, is that a tilt and
• 14:34
  Speaker 2: that's why it's rings are kind of tilty.
• 14:35
  Speaker 1: Yes, great question, And it depends a little bit on
• 14:38
  Speaker 1: the formation. And this is actually a question people have
• 14:40
  Speaker 1: about how rings form, Like if the ring formed from
• 14:43
  Speaker 1: the original blob of stuff that made the planet. And
• 14:47
  Speaker 1: one of the theories for how rings formed is you
• 14:49
  Speaker 1: have a big blob of stuff and some of it
• 14:51
  Speaker 1: collapses into a planet, and some of it doesn't because
• 14:54
  Speaker 1: it's moving too fast and it stays outside and forms
• 14:56
  Speaker 1: a ring. Then it all comes from the initial blob
• 14:59
  Speaker 1: of stuff that's spin, and then you expect it to
• 15:01
  Speaker 1: have the same spin on the same plane and basically
• 15:04
  Speaker 1: be around the equator of the planet. But another theory
• 15:06
  Speaker 1: is that these rings come from the outside. You have
• 15:08
  Speaker 1: a planet that forms, it's already spinning and hard and compact,
• 15:12
  Speaker 1: and now some material comes from the outside is captured
• 15:15
  Speaker 1: by the planet into a ring that will collapse on
• 15:18
  Speaker 1: its own, but its axis doesn't have to align with
• 15:20
  Speaker 1: the axis of the planet. Gravity will pull it down
• 15:23
  Speaker 1: into a single ring and it will orbit around its
• 15:26
  Speaker 1: own spin axis. It doesn't have to align with the planet.
• 15:29
  Speaker 1: There's nothing the planet can do to change its spin
• 15:32
  Speaker 1: axis because angular momentum is conserved.
• 15:34
  Speaker 2: All right, Is there anything else we need to know
• 15:36
  Speaker 2: about how rings are formed? Are we all now experts?
• 15:40
  Speaker 1: Another thing to think about is the difference between the
• 15:43
  Speaker 1: formation of moons and rings, Like, why do some planets
• 15:46
  Speaker 1: have rings and some of them have moons and some
• 15:48
  Speaker 1: of them have both? You know, why doesn't gravity always
• 15:51
  Speaker 1: pull a ring together into a moon? Right? You could
• 15:54
  Speaker 1: imagine like a string of little moonlits orbiting together in
• 15:59
  Speaker 1: a circle r planet. Why doesn't gravity always pull those together.
• 16:03
  Speaker 1: It can do that without violating anyngular momentum. And the
• 16:05
  Speaker 1: answer there is tidal forces. Usually when we think about
• 16:09
  Speaker 1: the Solar System, we're thinking about gravity as just like
• 16:12
  Speaker 1: here you have a rock and there you have a rock,
• 16:13
  Speaker 1: and there's gravity between them and they're pulling on each other.
• 16:16
  Speaker 1: But gravity is a little bit more complex than that.
• 16:19
  Speaker 1: If your rocks are not just points objects. If they're
• 16:21
  Speaker 1: just points, then you can just think about the gravity
• 16:24
  Speaker 1: on the objects. But if it's big, then you have
• 16:27
  Speaker 1: one side that's closer and another side that's further, and
• 16:30
  Speaker 1: gravity depends on distance. So gravity is going to pull
• 16:33
  Speaker 1: on the closer part harder than it's pulling on the
• 16:36
  Speaker 1: further part. And that's true always. So for example, if
• 16:39
  Speaker 1: you're an astronaut and you're in space and you're doing
• 16:42
  Speaker 1: an ev or whatever, the Earth is pulling on your
• 16:45
  Speaker 1: feet harder than it's pulling on your head. You might think,
• 16:49
  Speaker 1: no big deal, But those are relative forces. You can
• 16:53
  Speaker 1: think of it as pulling on your feet harder than
• 16:55
  Speaker 1: your head, or equivalently, you can think the Earth is
• 16:57
  Speaker 1: trying to pull your head off of your body, because
• 16:59
  Speaker 1: that's really what it's doing, right, It's pulling on one
• 17:02
  Speaker 1: side harder than the other side. It's trying to tear
• 17:04
  Speaker 1: you apart. And normally your neck is strong enough that
• 17:07
  Speaker 1: the Earth's not going to decapitate you. But if you
• 17:09
  Speaker 1: are close to a very powerful body like a black hole,
• 17:13
  Speaker 1: then those tidle forces are powerful enough to pull you apart.
• 17:15
  Speaker 1: That's what spaghetification is. And so planets pull on things.
• 17:19
  Speaker 1: The Earth, for example, is tugging on the Moon. It's
• 17:22
  Speaker 1: trying to squeeze the Moon into a football. It's trying
• 17:24
  Speaker 1: to pull rocks off the surface of the Moon that's
• 17:27
  Speaker 1: closer to it.
• 17:28
  Speaker 2: I can imagine how that pulling over time would start
• 17:30
  Speaker 2: to pull off pieces and result in a ring. So
• 17:34
  Speaker 2: does that mean that a lot of the rings around
• 17:36
  Speaker 2: planets are moons that just got kind of crushed? And
• 17:38
  Speaker 2: then why didn't our moon end up succumbing to that?
• 17:41
  Speaker 1: Sure, it depends on distance. It also depends on structural
• 17:45
  Speaker 1: integrity what your moon is made out of. But basically,
• 17:48
  Speaker 1: if a moon gets too close to a planet, the
• 17:50
  Speaker 1: tidle forces will pull it apart. If the moon is
• 17:52
  Speaker 1: far enough away, then the structural integrity of the moon
• 17:55
  Speaker 1: is more powerful than the tidal forces. It'll stay together.
• 17:59
  Speaker 1: So if you look at all the planets in the
• 18:00
  Speaker 1: Solar System, you notice that it's usually rings on the
• 18:03
  Speaker 1: inside and moons on the outside. And you can calculate
• 18:06
  Speaker 1: this sort of dividing line. It's called the Roche limit.
• 18:09
  Speaker 1: Things that are closer than the roach limit, the tidal
• 18:11
  Speaker 1: forces will probably pull it apart. Things that are further
• 18:13
  Speaker 1: things will coalesce into a moon. The self gravity will
• 18:16
  Speaker 1: pull it together, and then the structural forces will hold it.
• 18:19
  Speaker 2: Is it an interplay between distance and size or is
• 18:22
  Speaker 2: it just size or distance? Size and what you're made
• 18:26
  Speaker 2: out of, like a chunk of metal, would be harder
• 18:29
  Speaker 2: to pull apart than something else.
• 18:30
  Speaker 1: It's mostly distance from the planet and what you're made
• 18:33
  Speaker 1: out of. So, for example, there's a different roach limit
• 18:36
  Speaker 1: for a blob of water than there is for like
• 18:38
  Speaker 1: a moon made of diamond, which would be much harder
• 18:41
  Speaker 1: to pull apart, but for like a typical rock. You
• 18:44
  Speaker 1: can calculate these distances. For the moon, for example, if
• 18:47
  Speaker 1: it came within ten thousand kilometers of the surface of
• 18:49
  Speaker 1: the Earth, it would be pulled apart. Its orbit is
• 18:52
  Speaker 1: safely outside that. It's like three hundred and ninety thousand kilometers,
• 18:55
  Speaker 1: so it's well past the Roach limit. And you know,
• 18:58
  Speaker 1: the Sun has a roach limit. If a planet gets
• 19:00
  Speaker 1: too close to the Sun, it would get pulled apart
• 19:02
  Speaker 1: by its tidal forces. So, for example, the Earth came
• 19:05
  Speaker 1: within almost a million kilometers of the Sun, it would
• 19:09
  Speaker 1: get pulled apart. We're like one hundred and fifty million kilometers,
• 19:12
  Speaker 1: so we're in no danger. But this is the distinguishing
• 19:14
  Speaker 1: feature between rings and moons, basically how far you are
• 19:17
  Speaker 1: from the surface of the planet.
• 19:19
  Speaker 2: You know. Now, anytime we discuss something that's named after someone,
• 19:22
  Speaker 2: and I'm guessing the roof limit is named after it Roach. Yeah,
• 19:24
  Speaker 2: I find myself wanting to have Kathy Johnson back because
• 19:28
  Speaker 2: I want to be like, Kathy, did Roche really come
• 19:30
  Speaker 2: up with this? Or who was he building on? What
• 19:32
  Speaker 2: were people thinking at the time? She should just always
• 19:34
  Speaker 2: give us the background on everything, because she's wonderful.
• 19:36
  Speaker 1: M m yeah. And science is a human story, which
• 19:39
  Speaker 1: means that every time you learn a little bit of knowledge,
• 19:42
  Speaker 1: there's a fascinating, probably tortured history for how we figure
• 19:46
  Speaker 1: that out and how it is named after this person
• 19:48
  Speaker 1: and whether that person was actually a jerk, and if
• 19:50
  Speaker 1: their paper was full of mistakes, and whether they deserve
• 19:53
  Speaker 1: the credit for that or not. Human history is always fascinating.
• 19:55
  Speaker 1: Every time you lift up the rug you find really
• 19:58
  Speaker 1: interesting stuff under there.
• 20:00
  Speaker 2: I want you check out if you missed it, our
• 20:01
  Speaker 2: episode on Maxwell's equation, to hear Kathy's amazing history, and
• 20:04
  Speaker 2: also to make you feel better if you're not good at.
• 20:06
  Speaker 1: Math, because neither was fair Day or Maxwell. Apparently Maxwell
• 20:13
  Speaker 1: was good at math. He just wasn't good at keeping
• 20:14
  Speaker 1: track of minus signs. But hey, who is He got.
• 20:17
  Speaker 2: Away with a lot of mistakes. Yes, all right, that's true.
• 20:22
  Speaker 1: I have fewer published math errors than Max.
• 20:24
  Speaker 2: There you go. You should feel good about that. You
• 20:25
  Speaker 2: should get a plaque to put over your desk.
• 20:28
  Speaker 1: Maybe just a T shirt.
• 20:29
  Speaker 2: There you go, that's right here, mistakes than Maxwell. It's
• 20:33
  Speaker 2: got to be a pretty niche audience for that T shirt. Okay,
• 20:37
  Speaker 2: all right, Well, we're all missing Kathy right now, but
• 20:40
  Speaker 2: there's nothing we can do about it at the moment.
• 20:42
  Speaker 2: So let's take a break to think about how great
• 20:44
  Speaker 2: Kathy is, and when we come back, we'll talk about
• 20:46
  Speaker 2: what those rings tend to be made of. All right, So,
• 21:05
  Speaker 2: based on our earlier conversation, I'm guessing that a lot
• 21:07
  Speaker 2: of rings are made out of you know, like moves
• 21:10
  Speaker 2: that got crushed, so probably you know, rocks and metal
• 21:13
  Speaker 2: and stuff. What else do we get out there.
• 21:15
  Speaker 1: Yeah, so the rings tend to be made out of
• 21:17
  Speaker 1: the same stuff that the solar system is made out of.
• 21:20
  Speaker 1: So the inner Solar system it's mostly rocky because you
• 21:22
  Speaker 1: know the solar system, well, it starts out mostly gas,
• 21:25
  Speaker 1: but all that gas gets gobbled up by the Sun
• 21:28
  Speaker 1: and any gas left over and the inner Solar system
• 21:31
  Speaker 1: got blasted out of it by the Sun's radiation, so
• 21:34
  Speaker 1: you don't have a whole lot of gas left in
• 21:35
  Speaker 1: the inner Solar system. The rings closer to the Sun
• 21:38
  Speaker 1: are going to be rockier. Further out, you're more distant
• 21:40
  Speaker 1: from the Sun, so you can have things like water crystals,
• 21:43
  Speaker 1: and outpast what we call the frost line, where water
• 21:47
  Speaker 1: isn't vaporized by the Sun, you have ice. And so,
• 21:50
  Speaker 1: for example, beyond Jupiter, there's a lot of ice in
• 21:54
  Speaker 1: those rings.
• 21:55
  Speaker 2: So you don't get any ice in rings between the
• 21:58
  Speaker 2: Sun and Jupiter, but outwards you can get ice and rings.
• 22:02
  Speaker 1: Yeah, exactly right, And so we have some pretty spectacular
• 22:05
  Speaker 1: ring systems in the solar system right, and one of
• 22:07
  Speaker 1: the first ever to be seen was Saturn's This is
• 22:10
  Speaker 1: one of the first things actually that Galileo saw through
• 22:13
  Speaker 1: his telescope on those cold Italian nights in the early
• 22:16
  Speaker 1: sixteen hundreds are the rings of Saturn, which of you know,
• 22:20
  Speaker 1: anybody who's used a telescope in their backyard knows that
• 22:23
  Speaker 1: this is an amazing thing to see.
• 22:24
  Speaker 2: I can't imagine being the first one to see that
• 22:26
  Speaker 2: must have been just absolutely mind blowing right.
• 22:29
  Speaker 1: Right to me. It's always exciting when you can resolve
• 22:32
  Speaker 1: any feature on these objects in the night sky. Like
• 22:34
  Speaker 1: you look at the Moon and you can see things
• 22:36
  Speaker 1: on the surface. That's super cool because it's not just
• 22:39
  Speaker 1: like a point, and seeing the rings of Saturn is
• 22:41
  Speaker 1: the same way. You're like, I'm seeing something that's really
• 22:43
  Speaker 1: out there. I don't know about you, but when I
• 22:45
  Speaker 1: look at the night sky, it's just too easy to
• 22:48
  Speaker 1: think of it as like a screen with dots on it.
• 22:51
  Speaker 1: But when you can resolve features on something, then suddenly
• 22:54
  Speaker 1: I'm transported to this mode where I understand I'm looking
• 22:58
  Speaker 1: across an incredibly vast ocean of nothingness to huge objects
• 23:03
  Speaker 1: that are incredibly distant you know, it's so difficult for
• 23:06
  Speaker 1: your mind to really put yourself in that vast three
• 23:09
  Speaker 1: D space. But on a clear night when you can
• 23:11
  Speaker 1: see the rings of Saturn or the moons of Jupiter,
• 23:14
  Speaker 1: I feel like it's easier to visualize yourself in this
• 23:17
  Speaker 1: vast space rather than thinking of it as a screen.
• 23:20
  Speaker 2: Well, part of me feels like this is cheating, but
• 23:22
  Speaker 2: I love those apps on my iPhone where you look
• 23:24
  Speaker 2: up at the night sky and it tells you like,
• 23:26
  Speaker 2: that's Saturn, that's Venus, and like, to me, I get
• 23:29
  Speaker 2: all philosophical when I get that extra detail. It makes
• 23:32
  Speaker 2: me feel like I'm more of a small speck than
• 23:35
  Speaker 2: if I just look out at it. Like you said,
• 23:36
  Speaker 2: it's almost like you've got a sheet with little pin
• 23:38
  Speaker 2: pricks in it and lights coming through. It's like easy
• 23:40
  Speaker 2: to not think about it as a vast expanse out there.
• 23:43
  Speaker 2: But anyway, yea for technology, there's an app for that.
• 23:49
  Speaker 1: Well. The rings of Saturn are really incredible because they're
• 23:51
  Speaker 1: so very There are a bunch of different rings are separated,
• 23:55
  Speaker 1: and NASA has given them really creative names. There's the
• 23:58
  Speaker 1: A ring, the B ring, the C you know, goes
• 24:01
  Speaker 1: out to the G ring and the E ring, which
• 24:03
  Speaker 1: are sort of harder to see with your naked eye.
• 24:06
  Speaker 1: Some of these things have like a lot of dark
• 24:08
  Speaker 1: organic compounds, so they're not as easy to see. The
• 24:11
  Speaker 1: inner ones have more ice, like they're just basically a
• 24:14
  Speaker 1: bunch of icy particles spread out in these vast, very
• 24:17
  Speaker 1: flat rings.
• 24:19
  Speaker 2: Who should be naming these right? You know? So NASA
• 24:21
  Speaker 2: clearly shouldn't be allowed to name things because they're not
• 24:24
  Speaker 2: doing a good job. But you like, if you let
• 24:25
  Speaker 2: the Internet name them, it would have been like ringy
• 24:27
  Speaker 2: mcring face. What is the right solution here for these
• 24:31
  Speaker 2: amazing celestial objects. I think they should be renamed, That's
• 24:34
  Speaker 2: what I think.
• 24:35
  Speaker 1: Yeah, absolutely, I think they should not be named by scientists.
• 24:38
  Speaker 1: Maybe we should have Joge on the podcast to suggest names.
• 24:41
  Speaker 1: He was always good at.
• 24:41
  Speaker 2: That sounds good.
• 24:43
  Speaker 1: But there are these fascinating gaps between the rings, like
• 24:45
  Speaker 1: there's the A ring and the B ring, And we've
• 24:48
  Speaker 1: known about these gaps forever. It was Cassini, in like
• 24:51
  Speaker 1: the latest sixteen hundreds who first saw these gaps. And
• 24:54
  Speaker 1: that's why we call that spacecraft that visited Sounder and
• 24:57
  Speaker 1: the Cassini spacecraft, because he was the first one and
• 25:00
  Speaker 1: see them. And these gaps in the rings come from
• 25:02
  Speaker 1: actually the interactions of the ring material with little moons,
• 25:07
  Speaker 1: you know. So we talked about how like they are
• 25:08
  Speaker 1: only moons out past the rings, but if you're small enough,
• 25:11
  Speaker 1: you're gonna avoid those tidal forces. You're like basically a
• 25:14
  Speaker 1: big chunk of rock within the ring. Is it really
• 25:18
  Speaker 1: part of the ring? Is it a moonlit Now we're
• 25:20
  Speaker 1: getting into that murky territory where the dotted lines don't
• 25:22
  Speaker 1: make any sense. But these rings sometimes are called shepherd
• 25:26
  Speaker 1: rings shepherd moons because they orbit near the edges of
• 25:29
  Speaker 1: these rings and they can help keep the material in place.
• 25:32
  Speaker 1: There's these fascinating gravitational interactions between the ring and the moon.
• 25:38
  Speaker 2: Huh And okay, so the moon is countering Saturn's gravity
• 25:41
  Speaker 2: to keep some of the stuff in the ring in
• 25:42
  Speaker 2: its place. How is the moon clearing its own orbit?
• 25:45
  Speaker 2: Is it's gravity pulling anything else that might have been
• 25:48
  Speaker 2: in a ring in that location, It's pulling it into itself.
• 25:51
  Speaker 1: Yeah, essentially, it's acting like a little shepherd. It helps
• 25:54
  Speaker 1: keep the edge of the ring sharply defined because anything
• 25:57
  Speaker 1: that gets too close gets secreted onto the moon, or
• 26:00
  Speaker 1: it can make a near miss and can get accelerated
• 26:03
  Speaker 1: by the Moon and then deflect it back away from
• 26:05
  Speaker 1: the Moon like a slingshot back into the ring. That's
• 26:09
  Speaker 1: how it keeps its own like a little lane. That's
• 26:11
  Speaker 1: why you get these gaps in the rings. It's really
• 26:13
  Speaker 1: fascinating that these rings are really really broad, right, they're
• 26:17
  Speaker 1: like seventy thousand kilometers wide, the rings of Saturn, and
• 26:22
  Speaker 1: they're only twenty meters thick. That's meters, not kilometers.
• 26:27
  Speaker 2: Oh wow.
• 26:28
  Speaker 1: Yeah, it's the scale of like if you had a
• 26:29
  Speaker 1: sheet of paper, the sheet of paper would be like
• 26:31
  Speaker 1: a kilometer wide. Right. It's incredibly thin compared to the
• 26:36
  Speaker 1: breadth of it, and that's due to anglar momentum and gravity.
• 26:39
  Speaker 1: Gravity has done its work to collapse it down to
• 26:41
  Speaker 1: a thin sheet, but it can't do it in the
• 26:44
  Speaker 1: sort of plane of rotation because of angular momentum.
• 26:47
  Speaker 2: Kind of amazing that we can see anything that thin
• 26:49
  Speaker 2: from all the way here.
• 26:50
  Speaker 1: It's because it's reflective. It's the icy particles that make
• 26:53
  Speaker 1: it possible to see it.
• 26:54
  Speaker 2: Oh okay, all right, so then where did Saturn get
• 26:56
  Speaker 2: this ring in the first place. Was Jupiter feeling amorous
• 27:00
  Speaker 2: at some point.
• 27:02
  Speaker 1: You know, the story of Saturn's rings is interesting history.
• 27:05
  Speaker 1: It used to be that people thought this is probably
• 27:07
  Speaker 1: left over from formation of Saturn because it does orbit
• 27:11
  Speaker 1: in the plane of Saturn, and it seemed like, wow,
• 27:14
  Speaker 1: this must have been here for a long time. But
• 27:16
  Speaker 1: Cassini's visits revealed that the rings are quite low mass.
• 27:20
  Speaker 1: You know, there's like less stuff in there than we thought,
• 27:22
  Speaker 1: and it's still very sharp and bright, Like the edges
• 27:25
  Speaker 1: of these ice crystals are still very sharp, which isn't
• 27:29
  Speaker 1: consistent with like being there a long time. You know,
• 27:32
  Speaker 1: things tit to get rounded and collisions tend to soften stuff.
• 27:35
  Speaker 1: And more recent theory is that some moons of Saturn
• 27:38
  Speaker 1: might have collided and left a huge spray of debris
• 27:41
  Speaker 1: which basically formed into a ring, which might mean that
• 27:44
  Speaker 1: these rings themselves are temporary. It might be the Saturn
• 27:47
  Speaker 1: gathers them back together into moons. We don't quite know,
• 27:52
  Speaker 1: because the roche limit is a little bit fuzzy, you know,
• 27:54
  Speaker 1: the structural integrity. If those rings will be there in
• 27:58
  Speaker 1: one hundred million.
• 27:58
  Speaker 2: Years, oh man, and we're not gonna be around to know.
• 28:01
  Speaker 1: How do you know? Come on, We're gonna have great, great,
• 28:04
  Speaker 1: great great great grandkids making non sentimental marriage proposals to
• 28:07
  Speaker 1: each other using ice from the rings of Saturn.
• 28:11
  Speaker 2: Your grand kids are going to are we getting into
• 28:14
  Speaker 2: incestuous to Oh?
• 28:15
  Speaker 1: I mean humanity's descendants. I couldn't say enough great great
• 28:19
  Speaker 1: grades to get us one hundred million years. But are
• 28:21
  Speaker 1: you not optimistic that people will be living in the
• 28:23
  Speaker 1: Solar System in one hundred million years? Hi?
• 28:25
  Speaker 2: No, I'm optimistic all right.
• 28:27
  Speaker 1: Somebody will be here to see the new moons of
• 28:29
  Speaker 1: Saturn and to give them a creative name.
• 28:31
  Speaker 2: I hope somebody gets on that much sooner. I don't
• 28:34
  Speaker 2: want to wait for that to happen.
• 28:38
  Speaker 1: And other planets in the Solar System have fascinating histories
• 28:41
  Speaker 1: with rings, Like Astronomers think that Mars has gone through
• 28:44
  Speaker 1: several cycles of having rings and moons and rings and moons.
• 28:48
  Speaker 2: Wait, so does that mean that like Phobos and Demos
• 28:51
  Speaker 2: have broken up and come back together multiple times or well,
• 28:54
  Speaker 2: we don't.
• 28:54
  Speaker 1: Know how long phobos and demos will last, but we
• 28:57
  Speaker 1: think that Phobos and Demos formed from a ring that
• 29:01
  Speaker 1: was created from a giant impact. So like something hit
• 29:04
  Speaker 1: Mars and then ejected a huge amount of stuff like
• 29:08
  Speaker 1: ten to the twenty three kilograms of stuff into orbit
• 29:12
  Speaker 1: and left this huge debris cloud around Mars, which then
• 29:16
  Speaker 1: collapsed into a ring which then got gathered together into
• 29:19
  Speaker 1: these small moons.
• 29:21
  Speaker 2: So is it possible to look at a moon and
• 29:24
  Speaker 2: figure out if it's gathered up ring or not? Like
• 29:27
  Speaker 2: that's got to be hard.
• 29:30
  Speaker 1: It's not always possible to tell the history, but you
• 29:33
  Speaker 1: can get some clues, like, for example, Phobos and Demos
• 29:36
  Speaker 1: have very circular orbits, which suggests that you had like
• 29:39
  Speaker 1: a lot of stuff which formed a ring and then
• 29:41
  Speaker 1: gathered together, rather than being single objects that were like
• 29:45
  Speaker 1: captured as they floated near Mars, which would tend to
• 29:48
  Speaker 1: be like more elliptical orbits and not necessarily in the
• 29:51
  Speaker 1: same plane as Mars, So that suggests that it formed
• 29:55
  Speaker 1: from a ring. Also, you can look at the composition
• 29:57
  Speaker 1: of the stuff, and Phobos and Demo are made of
• 30:00
  Speaker 1: the same stuff as Mars is, which suggests, like our moon,
• 30:05
  Speaker 1: that it formed due to a giant impact rather than
• 30:08
  Speaker 1: like was captured. Sometimes moons can be captured. Some of
• 30:10
  Speaker 1: the moons of Saturn and Jupiter, we think are just
• 30:13
  Speaker 1: like big rocks that floated too close and got gobbled
• 30:16
  Speaker 1: up into the gravitational system of those planets not yet torn.
• 30:20
  Speaker 2: Apart, but hit the cosmic lottery and didn't get pulled
• 30:23
  Speaker 2: into the center.
• 30:26
  Speaker 1: Exactly. And if these things form moons and then they're
• 30:29
  Speaker 1: too close to the planet, like they'll drag, if there's
• 30:32
  Speaker 1: an atmosphere there, they'll drag and then eventually just fall
• 30:35
  Speaker 1: into the planet and so that you can lose your moon.
• 30:38
  Speaker 1: So there's evidence on Mars of several of these cycles,
• 30:41
  Speaker 1: like impact forms. A cloud makes a ring, then makes
• 30:45
  Speaker 1: a little moon, and that moon gets dragged down into
• 30:47
  Speaker 1: the planet and lost and you start again. So Mars
• 30:51
  Speaker 1: is like a really kind of checkered history with its moons.
• 30:53
  Speaker 1: It's got like a bunch of x's that it's gobbled up.
• 30:56
  Speaker 2: Oh man, yet, one more reason and not go to Mars.
• 31:00
  Speaker 2: So it sounds like these transitions are very chaotic and
• 31:03
  Speaker 2: would be dangerous if humans were living on the surface
• 31:05
  Speaker 2: at the time.
• 31:06
  Speaker 1: Oh yeah, No, you don't want to be around during
• 31:08
  Speaker 1: one of these transitions. And you don't want to be
• 31:10
  Speaker 1: around when you have like a huge dust cloud around
• 31:13
  Speaker 1: your planet either, because it's going to block a lot
• 31:15
  Speaker 1: of light. So you know, the temperature probably plummets on
• 31:18
  Speaker 1: the planet when you have a situation like that. In general,
• 31:21
  Speaker 1: it's probably really fun to watch from far away, but
• 31:23
  Speaker 1: not fun to watch from the surface.
• 31:25
  Speaker 2: And the connection with the dust cloud is because when
• 31:27
  Speaker 2: something plummets, it kicks up a bunch of dust.
• 31:29
  Speaker 1: Is that right, Yeah, a lot of these are formed
• 31:31
  Speaker 1: from an impact. So either you have something that comes
• 31:34
  Speaker 1: nearby and is torn apart and then you get a
• 31:36
  Speaker 1: cloud a debris, or you get actual impact on the
• 31:38
  Speaker 1: planet which kicks up huge piles of stuff from the planet,
• 31:42
  Speaker 1: which then coalesces into a ring and then a moon.
• 31:45
  Speaker 1: And so we used to think that Saturn was the
• 31:48
  Speaker 1: only planet in the Solar System that had rings, but
• 31:50
  Speaker 1: now we've discovered that rings are much more common. So,
• 31:53
  Speaker 1: for example, Jupiter has rings, but we've only known that
• 31:56
  Speaker 1: since nineteen seventy nine when Voyager went to visit. These
• 32:00
  Speaker 1: things are so faint that you either need to send
• 32:02
  Speaker 1: a probe to see them or have a very powerful
• 32:04
  Speaker 1: space telescope like Hubble. Can see the rings of Jupiter now,
• 32:07
  Speaker 1: but otherwise we couldn't see them from Earth.
• 32:09
  Speaker 2: And what are they named? One?
• 32:12
  Speaker 1: Two?
• 32:15
  Speaker 2: I hope we've done better with Jupiter's rings.
• 32:20
  Speaker 1: Maybe alpha beta, gamma delta. Yeah, that's a good question.
• 32:24
  Speaker 1: But these rings around Jupiter are very faint because they
• 32:26
  Speaker 1: mostly consist of these little dust particles that come from
• 32:30
  Speaker 1: like tiny meteors hitting the planet's moons and then being vaporized.
• 32:34
  Speaker 1: But this dust also doesn't last very long in the
• 32:37
  Speaker 1: Jovian System because Jupiter is crazy. It has really powerful
• 32:41
  Speaker 1: magnetic fields, and these basically pull these rings apart and
• 32:45
  Speaker 1: shepherd them up to the poles, and so a piece
• 32:48
  Speaker 1: of dust can only last in these rings for like
• 32:51
  Speaker 1: a few hundred years or a few thousand years, which
• 32:54
  Speaker 1: means that like Jupiter's rings are constantly being degraded and replenished,
• 32:59
  Speaker 1: like micro ears are hitting the moons, which them to
• 33:02
  Speaker 1: get vaporized and then they enjoin the ring. But there's
• 33:05
  Speaker 1: also an outflow, so it's not like a constant structure.
• 33:08
  Speaker 1: It's more like a river of dust that's moving through
• 33:11
  Speaker 1: this sort of like dust cycle around Jupiter.
• 33:13
  Speaker 2: It's probably nice to get some new bling from time
• 33:15
  Speaker 2: to time, you know, out with the old in with
• 33:17
  Speaker 2: the new ring.
• 33:20
  Speaker 1: Yeah, maybe you and Zac stually get new rings sometime.
• 33:23
  Speaker 2: Yeah. No, he'd just lose them and I would get
• 33:25
  Speaker 2: bug guts in them, and it would just not It
• 33:27
  Speaker 2: wouldn't work for us. It's all right.
• 33:28
  Speaker 1: Yeah, you know. I'm the same way. I lose stuff.
• 33:30
  Speaker 1: I put stuff down, I can't remember it, so I've
• 33:33
  Speaker 1: always been terrified I was gonna lose my ring. So
• 33:35
  Speaker 1: I just never ever ever take it off, Like that's
• 33:37
  Speaker 1: my rule. Not in the shower, I never take it
• 33:40
  Speaker 1: off because I'm afraid I lose it. Same with my glasses,
• 33:42
  Speaker 1: Like I wear glasses all the time. I actually only
• 33:45
  Speaker 1: need them for reading. Really, if I ever took them off,
• 33:47
  Speaker 1: they would be gone within a day. So I just
• 33:49
  Speaker 1: wear them all the time because I can't manage the other.
• 33:53
  Speaker 2: I'm just totally blind without mine, So I never take
• 33:55
  Speaker 2: mine off. But lately my kids think it's funny to
• 33:58
  Speaker 2: try to pull them off, and I do not think
• 34:00
  Speaker 2: that's funny at all, So we're working on that.
• 34:06
  Speaker 1: They think it's hilarious when mom bumps into stuff in
• 34:08
  Speaker 1: the kitchen.
• 34:09
  Speaker 2: I mean, yeah, I guess so. But then I remind
• 34:11
  Speaker 2: them like, oh, I can't drive you to go get
• 34:13
  Speaker 2: ice cream, And then they're like, oh, we found your glasses.
• 34:15
  Speaker 2: Like all that was easy.
• 34:18
  Speaker 1: Isn't it wonderful? As your kids grow up to be
• 34:20
  Speaker 1: real people.
• 34:21
  Speaker 2: Yeah, I know they're growing up to be bullies. I'll
• 34:25
  Speaker 2: do better, all right. So we've talked about how Mars
• 34:28
  Speaker 2: maybe had rings, Jupiter Saturn definitely have rings. How about Urytus,
• 34:34
  Speaker 2: She says with glee.
• 34:35
  Speaker 1: You're just desperate to talk about rings around Urinus.
• 34:37
  Speaker 2: I mean, what would an episode be without it?
• 34:41
  Speaker 1: So there are actually Uranian rings. The individual particles in
• 34:45
  Speaker 1: these rings are jet black like lumps of coal. And
• 34:49
  Speaker 1: we haven't visited close enough or been able to study
• 34:52
  Speaker 1: these enough to know exactly what they're made out of,
• 34:55
  Speaker 1: but they seem like some kind of carbon or hydrocarbon compounds.
• 34:58
  Speaker 1: They're not very well understood because they're so far out,
• 35:01
  Speaker 1: and they're so hard to see because they're black. Like, remember,
• 35:04
  Speaker 1: we can only see stuff that reflects light unless we
• 35:07
  Speaker 1: go and visit, and so jet black stuff out there
• 35:10
  Speaker 1: in the deep dark Solar system, it's very hard to study.
• 35:13
  Speaker 2: I would have so much fun naming things on a
• 35:16
  Speaker 2: Uranus mission rings and all that. Okay, let's take a break.
• 35:20
  Speaker 2: You think of what you would name Uranus rings if
• 35:23
  Speaker 2: you discovered them, And when we get back, let's talk
• 35:25
  Speaker 2: about whether or not Earth ever had a ring. All right,
• 35:44
  Speaker 2: So I am going to hope that Earth never has
• 35:48
  Speaker 2: another ring because I think that would probably result in
• 35:50
  Speaker 2: something catastrophic for the humans living on the planet. And actually,
• 35:53
  Speaker 2: have you ever read Seven Eves by I think it's
• 35:56
  Speaker 2: Neil Stevenson.
• 35:57
  Speaker 1: I have read Seven Eves and greatly enjoy it. It's
• 36:00
  Speaker 1: a fun book. I really wanted to know more about
• 36:03
  Speaker 1: what blows up the ring in that book. It's not
• 36:05
  Speaker 1: a spoiler because it happens in like chapter one, and
• 36:08
  Speaker 1: I thought, oh, this book is going to be about
• 36:10
  Speaker 1: understanding the mystery of what destroyed the moon, But he
• 36:12
  Speaker 1: just basically moves on to like what it's like to
• 36:14
  Speaker 1: live in that system, never answers the question like was
• 36:18
  Speaker 1: it an alien attack? Was it a random impactor? I
• 36:21
  Speaker 1: found that very unsatisfying. I mean, it's a great book. Otherwise,
• 36:24
  Speaker 1: I kind.
• 36:24
  Speaker 2: Of appreciated that. I felt like, you know, there's just
• 36:27
  Speaker 2: a lot of things we don't know the answer to,
• 36:28
  Speaker 2: and probably, like in a situation like that where you
• 36:31
  Speaker 2: think humanity is in peril, that probably goes to the
• 36:35
  Speaker 2: bottom of your to do list, like figuring out the
• 36:37
  Speaker 2: answer to that. But I had some questions about the
• 36:40
  Speaker 2: evolutionary biology stuff.
• 36:41
  Speaker 1: There, No we're science people. We're curious. You can't like
• 36:44
  Speaker 1: give us a huge mystery and then leave it unsolved.
• 36:46
  Speaker 1: That's the point of these books is to inflame your curiosity,
• 36:49
  Speaker 1: itch and then scratch it. You can't just inflame it.
• 36:52
  Speaker 1: That's really unfair.
• 36:53
  Speaker 2: I mean, there was a lot of other hard science
• 36:55
  Speaker 2: in that book.
• 36:55
  Speaker 1: No, there definitely was.
• 36:56
  Speaker 2: Yeah, if anyone knows mister Stevens said, we would love
• 36:59
  Speaker 2: to talk to him all the show let us see.
• 37:01
  Speaker 1: Yes, absolutely, please mister Stevenson, come talk to us. We
• 37:04
  Speaker 1: will be very nice.
• 37:05
  Speaker 2: We'll be huge nerds. All right, So let's hope that
• 37:08
  Speaker 2: Earth never has a ring into the future, but let's
• 37:10
  Speaker 2: look into our past when might we have had a ring?
• 37:13
  Speaker 1: So a lot of the answers from listeners were really insightful.
• 37:16
  Speaker 1: They were thinking about the early formation of the moon
• 37:20
  Speaker 1: and how that probably got gathered together from a big
• 37:22
  Speaker 1: cloud of stuff which probably initially formed into a ring.
• 37:26
  Speaker 1: And that's a very insightful answer. I think my only
• 37:28
  Speaker 1: quibble with that would be, like, was the Earth really
• 37:31
  Speaker 1: formed at that time? You know, we had the proto Earth,
• 37:34
  Speaker 1: which then got collided with Fea and formed a huge
• 37:38
  Speaker 1: swirling system which coalesced into the Earth and the Moon simultaneously.
• 37:42
  Speaker 1: So like, I don't know if that counts as the
• 37:44
  Speaker 1: Earth having a ring because the Earth itself was still forming.
• 37:48
  Speaker 1: But it's true that the Moon was likely a ring
• 37:50
  Speaker 1: of material before it formed a moon.
• 37:52
  Speaker 2: Oh interesting, But.
• 37:54
  Speaker 1: That was over four billion years ago, very very early
• 37:56
  Speaker 1: in the Solar system. There was actually another period much more,
• 38:00
  Speaker 1: only four hundred and sixty six million years ago, when
• 38:03
  Speaker 1: scientists think the Earth might have temporarily had a ring system.
• 38:07
  Speaker 2: Oh man, all right, what catastrophic thing happened to make
• 38:09
  Speaker 2: that happen.
• 38:10
  Speaker 1: So what we do know and has been well established,
• 38:12
  Speaker 1: is that around four hundred and sixty six million years
• 38:14
  Speaker 1: ago there was a time of heavy bombardment. It's the
• 38:18
  Speaker 1: Ordovician period of the Earth. And we know from fossil
• 38:21
  Speaker 1: records and from other crazy pieces of evidence we have
• 38:24
  Speaker 1: that there was just a lot of impacts on Earth.
• 38:27
  Speaker 1: Like there are these quarries in Sweden where you like
• 38:29
  Speaker 1: dig down to get limestone. Each layer is older and older,
• 38:32
  Speaker 1: and there's a layer that corresponds to this time period
• 38:35
  Speaker 1: with all these fossil meteorites in it. Like they found
• 38:39
  Speaker 1: these weird green rocks down there. They're like, what is this,
• 38:41
  Speaker 1: and you find them in this one particular strand, and
• 38:45
  Speaker 1: they dug into them and discovered these are meteorites. You
• 38:47
  Speaker 1: can tell like chemically and also from the shape of
• 38:50
  Speaker 1: these things that they are meteorites are not just like
• 38:52
  Speaker 1: rocks from Earth. And then they found similar impact sites
• 38:56
  Speaker 1: in other places around the Earth. That tells us like, wow,
• 38:58
  Speaker 1: there was a period here, like the weather was bad
• 39:01
  Speaker 1: on Earth.
• 39:02
  Speaker 2: So it's the idea then that there was something that
• 39:04
  Speaker 2: got within the roach limit and it got broken up
• 39:07
  Speaker 2: into a ring and then it fell all over the planet.
• 39:12
  Speaker 2: And that's why there's a lot of it.
• 39:14
  Speaker 1: Yes, So the theory used to be that there was
• 39:16
  Speaker 1: probably some impact between asteroids out in the asteroid belt
• 39:21
  Speaker 1: or near Jupiter or something that created a lot of
• 39:24
  Speaker 1: shrapnel and then the Earth basically flew through a cloud
• 39:27
  Speaker 1: of this shrapnel. That was the original idea. So we
• 39:29
  Speaker 1: know that there was a lot of impacts. You see
• 39:31
  Speaker 1: them all over the planet. There's even evidence of like
• 39:34
  Speaker 1: enhanced seismic and tsunami activity from all this time ago.
• 39:37
  Speaker 1: It's incredible what you can learn from geology from like
• 39:41
  Speaker 1: seeing these fragments of rock that got broken up and
• 39:43
  Speaker 1: stuck back together. In ways you only get from like
• 39:46
  Speaker 1: really cataclysmic tsunamis and seismic events. Anyway, the theory used
• 39:50
  Speaker 1: to be, Okay, there's a cloud of stuff that's created
• 39:53
  Speaker 1: far from Earth, and the Earth flies through this cloud
• 39:56
  Speaker 1: which creates all these impacts. Right. But a recent study
• 40:00
  Speaker 1: they analyzed where on the surface these craters were and
• 40:04
  Speaker 1: they discovered that there were suspiciously all along the equator.
• 40:08
  Speaker 1: That suggests that there was time for this thing to
• 40:10
  Speaker 1: form into a ring around the Earth. And probably your
• 40:14
  Speaker 1: description was more accurate that some big thing came pretty
• 40:17
  Speaker 1: close to the Earth within its roach limit, was then
• 40:21
  Speaker 1: torn apart into bits, which orbited for a while formed
• 40:25
  Speaker 1: a ring before the atmosphere dragged it down into impacts
• 40:29
  Speaker 1: on Earth.
• 40:29
  Speaker 2: Oh my gosh, So was there an extinction that happened
• 40:32
  Speaker 2: concurrent with this?
• 40:33
  Speaker 1: There is a moment called the Great Order Vision biodiversification event,
• 40:37
  Speaker 1: and there was definitely a change in the Earth's temperature.
• 40:40
  Speaker 1: If you look at the temperature records, they call this
• 40:42
  Speaker 1: a global ice house. It's like a big dip in
• 40:45
  Speaker 1: the history of the temperature on Earth. And so this
• 40:48
  Speaker 1: paper suggests, oh, this could explain that as well, because
• 40:50
  Speaker 1: if you have a huge ring that forms over the equator.
• 40:53
  Speaker 1: It's going to significantly shade the planet. And this is
• 40:56
  Speaker 1: a really hard study to do because if you want
• 40:59
  Speaker 1: to think about where these things land on the Earth,
• 41:02
  Speaker 1: you have to know where that land was at the time.
• 41:05
  Speaker 1: Right continents move, and you might be thinking, hold on,
• 41:08
  Speaker 1: didn't Daniel say there were a bunch of fossil meteors
• 41:10
  Speaker 1: that landed in Sweden? And Sweden isn't close to the equator. Yeah,
• 41:14
  Speaker 1: it isn't today, but four hundred and sixty six million
• 41:17
  Speaker 1: years ago it actually was. So what they had to
• 41:20
  Speaker 1: do was figure out where are all these craters that
• 41:23
  Speaker 1: you can associate with this time period, which isn't always
• 41:26
  Speaker 1: easy because sometimes you can date these things very well.
• 41:29
  Speaker 1: Sometimes you can't because the layers therein Then they had
• 41:32
  Speaker 1: to rewind the history of the Earth to understand where
• 41:35
  Speaker 1: were these craters when the impact actually happened. And so
• 41:39
  Speaker 1: they computed this amazing word. I love this, the paleo latitude,
• 41:43
  Speaker 1: right like, where on the Earth was this when it happened?
• 41:47
  Speaker 1: I love that.
• 41:47
  Speaker 2: That's a good word. So those people should be in
• 41:50
  Speaker 2: charge of naming the rings.
• 41:53
  Speaker 1: Yes, exactly. Riot Sometimes you hear words and signs. You're like, Okay,
• 41:57
  Speaker 1: that's well done, that's nice, and that's nice. And so
• 42:03
  Speaker 1: they did this calculation. They found all these things, but
• 42:06
  Speaker 1: you know, we're talking about a handful of things, not
• 42:08
  Speaker 1: like millions of examples. They have like a couple of dozen,
• 42:12
  Speaker 1: maybe three dozen craters that they can definitively pinpoint are
• 42:16
  Speaker 1: from the Ordovician period, and so you might wonder, like, well,
• 42:19
  Speaker 1: how do you really know these are within the equator.
• 42:21
  Speaker 1: It's not like they all line up perfectly on the equator.
• 42:24
  Speaker 1: They're sort of like loosely associated with the equator. Their
• 42:27
  Speaker 1: paleo latitude tends to be less than thirty degrees. And
• 42:31
  Speaker 1: so they did a pretty robust statistical analysis. I've read
• 42:34
  Speaker 1: this paper carefully because honestly, I'm kind of skeptical about
• 42:38
  Speaker 1: the ability of lots of folks out there to do
• 42:40
  Speaker 1: statistics in a robust way, because not that many people
• 42:43
  Speaker 1: really understand statistics. And I've been shocked to read papers
• 42:46
  Speaker 1: in other fields, especially biology, and be like, hmm, I'm
• 42:49
  Speaker 1: pretty sure that statistical analysis is totally wrong.
• 42:53
  Speaker 2: But I'll give you that.
• 42:56
  Speaker 1: But I read this paper. I thought they did a
• 42:57
  Speaker 1: great job. They thought about, like, what are the chances
• 43:00
  Speaker 1: of getting this kind of distribution of paleo latitudes if
• 43:05
  Speaker 1: things actually were evenly spread, And they did some good
• 43:08
  Speaker 1: calculations and some good simulations. They look, for example, at
• 43:11
  Speaker 1: the distribution of modern impacts and show that they're much
• 43:14
  Speaker 1: more broadly distributed than these, So they calculate it's very
• 43:18
  Speaker 1: unlikely that these things, by random chance just happened to
• 43:21
  Speaker 1: fall along the equator, and that suggests that they probably
• 43:24
  Speaker 1: were in a ring above the Earth for a while.
• 43:27
  Speaker 1: This is four hundred and sixty six million years ago.
• 43:31
  Speaker 1: They also looked at some of these rocks, these actual
• 43:33
  Speaker 1: fossil metiors, and they can study the chemical composition of
• 43:37
  Speaker 1: these things and understand how much space radiation they were
• 43:41
  Speaker 1: exposed to. This is super awesome, yeah, because you know,
• 43:45
  Speaker 1: there's a lot more radiation out in space than there
• 43:47
  Speaker 1: is here on Earth. Because out in space you don't
• 43:49
  Speaker 1: have the benefit of our atmosphere protecting you, and so like,
• 43:53
  Speaker 1: there are all these high speed particles, cosmic rays and
• 43:55
  Speaker 1: solar wind constantly penetrating it, and that changes the chemical
• 44:00
  Speaker 1: position of stuff, right. It matches into the rocks, it
• 44:03
  Speaker 1: degrades some of those isotopes, so you can basically count
• 44:07
  Speaker 1: how long something has been in space by looking at
• 44:09
  Speaker 1: the chemical makeup of a rock, and it looks like
• 44:13
  Speaker 1: these rocks were not exposed to space for very long,
• 44:17
  Speaker 1: only like a few tens of thousands of years, not millions,
• 44:21
  Speaker 1: and that means that probably they were like on the
• 44:23
  Speaker 1: inside of some large asteroid for many, many, many millions
• 44:27
  Speaker 1: or billions of years, basically protected from the radiation of space,
• 44:31
  Speaker 1: then torn apart by the Earth's tidal forces into a
• 44:34
  Speaker 1: bunch of little rocks which were not protected by the
• 44:36
  Speaker 1: radiation of space, but only for a few tens of
• 44:38
  Speaker 1: thousands of years before they fell to the surface of
• 44:41
  Speaker 1: the Earth and then protected again. So you know they
• 44:44
  Speaker 1: were near the surface of an asteroid out in space,
• 44:48
  Speaker 1: exposed to radiation for only a few tens of thousands
• 44:51
  Speaker 1: of years, So that's also suggestive. None of this is
• 44:54
  Speaker 1: completely conclusive, but you know, this is like solving a mystery.
• 44:58
  Speaker 1: You have a few clues you're trying to piece together story.
• 45:00
  Speaker 1: All this is very circumstantial, but it all points in
• 45:03
  Speaker 1: the same direction.
• 45:03
  Speaker 2: You mentioned that there was like a shrapnel theory. Wouldn't
• 45:06
  Speaker 2: the shrapnel theory also have something big where most of
• 45:10
  Speaker 2: it was protected by space radiation, and then it got
• 45:13
  Speaker 2: broken into pieces, and those pieces worked both to space
• 45:16
  Speaker 2: radiation for a short period of time before Earth hit it.
• 45:19
  Speaker 2: How would you tell the difference between those two options?
• 45:21
  Speaker 1: Yes, a short period of time, but longer, like if
• 45:24
  Speaker 1: there was a collision out on the asteroid belts that
• 45:26
  Speaker 1: created all this shrapnel, it would take much longer to
• 45:29
  Speaker 1: get to Earth, probably millions of years, not just ten thousand,
• 45:33
  Speaker 1: and so that's how they can tell the difference.
• 45:35
  Speaker 2: Got it. That's very cool. Who was the first author
• 45:37
  Speaker 2: in this study? Let's give them some credit? This sounds
• 45:39
  Speaker 2: awesome as scientists who understand statistics.
• 45:42
  Speaker 1: Yeah, so this is Andrew Tompkins, Aaron Martin, and Peter
• 45:46
  Speaker 1: Kaywood and a paper in Earth and Planetary Studies in
• 45:49
  Speaker 1: November twenty twenty four. It's really quite readable, even for
• 45:54
  Speaker 1: somebody outside their field. So congrats on the exciting result
• 45:57
  Speaker 1: and the nicely written paper.
• 45:58
  Speaker 2: And where did you come across this? How did we
• 46:00
  Speaker 2: come to talk about this today?
• 46:02
  Speaker 1: I think a bunch of listeners might have heard press
• 46:04
  Speaker 1: releases about it and send me an email asking me
• 46:07
  Speaker 1: to explain it. So I put it on my list,
• 46:09
  Speaker 1: and eventually I actually do get to everything on my list,
• 46:12
  Speaker 1: as I promise, but we got along backlog, so it
• 46:15
  Speaker 1: might take me a while. But if you are curious
• 46:18
  Speaker 1: about something you've heard about in the news and you'd
• 46:20
  Speaker 1: like for us to break it down and explain it
• 46:22
  Speaker 1: to you, for Kelly to ask me hard questions, for
• 46:24
  Speaker 1: me to ask Kelly naive biology questions, then please send
• 46:28
  Speaker 1: us your questions. We'd love to dig into something you'd
• 46:31
  Speaker 1: like to hear more about.
• 46:32
  Speaker 2: So write us at question I always forget our email address.
• 46:35
  Speaker 2: What's our email address?
• 46:36
  Speaker 1: Daniel Questions at Daniel and Kelly dot org. You can
• 46:39
  Speaker 1: write to us and ask us like, what is our
• 46:41
  Speaker 1: email address?
• 46:42
  Speaker 2: Yes you probably I can be super successful on that one,
• 46:44
  Speaker 2: but good luck and we hope to hear.
• 46:46
  Speaker 1: From you until next time. Put a ring on it.
• 46:49
  Speaker 2: That's right. My daughter would be absolutely appalled if I
• 46:54
  Speaker 2: say so. Anyway, Thanks everyone.
• 46:56
  Speaker 1: Tune in next time.
• 47:04
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• 47:08
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