Did the Earth ever have a ring?

Daniel and Kelly talk about whether the Universe ever put a ring on the Earth

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Episode Transcript

Speaker 1 (00:06):
The message you often hear about space is that it's
vast and empty. The Earth and even the Sun are
these tiny dots and a huge ocean of black space.
That's all true, but it gives you the wrong idea
about our cosmic neighborhood. It suggests that the Earth is isolated, alone,
not affected by our neighbors, not in danger. The truth
is actually the opposite. Space is vast, but gravity is

(00:29):
also very patient. There are a lot of big dark
rocks out there that could get tugged by gravity towards
the Earth and then dramatically affect our way of life,
both positively or negatively. They could, of course smash into
us and cause an extinction event, but then they could
also create new snazzy bling around our planet. So today

(00:50):
we're going to dig deep into the history of Earth
within our cosmic neighborhood, understand the gravitational dance between all
of these objects, and ask the question about whether there
was ever a time when the universe put a ring
on the Earth. So, just in time for Valentine's Day,
we're getting cosmically romantic and asking did Earth ever have

(01:10):
a ring? Welcome to Daniel and Kelly's extraordinary universe. Hello.

Speaker 2 (01:28):
I'm Kelly Wienersmith. I'm a parasitologist and I stopped wearing
rings because I got fish guts stuck in my ring
too many times and decided it was too gross.

Speaker 1 (01:39):
Oh isn't that romantic though?

Speaker 2 (01:42):
Fish guts in a ring? You got a weird sense
of romance, Daniel, I'm.

Speaker 1 (01:48):
Trying to resonate with a biology. Hi. I'm Daniel. I'm
a particle physicist, and I bought my wedding rings for
two dollars on Telegraph Avenue in Berkeley.

Speaker 2 (01:58):
I was going to ask you, are you and Katrina
ring people or not ring people?

Speaker 1 (02:03):
We have rings which we feel sentimental about, but we're
not people who are into expensive fancy stuff. So like
her engagement ring has a piece of amber in it,
and I designed the ring myself. There's no like crazy
diamond in there. And we didn't want to spend a
lot of money on crazy rings, so we just walked
down Telegraph Avenue and found a guy who made silver
rings and bottom for a couple of bucks.

Speaker 2 (02:24):
You designed a ring with amber and got it for
two bucks.

Speaker 1 (02:27):
Oh no, the engagement ring I had a friend make,
so that was more than two dollars, but yes, I
designed it myself. It has a bunch of Danish ruins
in it and stuff and a piece of amber in
the middle.

Speaker 2 (02:37):
Oh that's great.

Speaker 1 (02:38):
How about you? What's your guys ring story?

Speaker 2 (02:40):
Can I tell you our engagement story really quick? Oh?

Speaker 1 (02:42):
Yes? Does it involve fish cuts? No?

Speaker 2 (02:44):
No, the rest of our life involves fish cuts, but no,
our engagement story. So Zach is like not a super
sentimental guy, and so, like, a couple months earlier, I
had said to him, like, hey, you know we've been
together for a year, do you think you could ever
see yourself marrying me? Because if still, let's keep going.
But if not, let's like cut our losses and bee
like this was fun. And so his response, and this

(03:05):
is amazing. His response was I think you're really nice, wow,
which I thought was him being like I don't want
to answer this question because it's going to be uncomfortable,
but like, that's not what I was looking for, right,
And so I thought to myself, like, Okay, in a
couple more months, I'm going to ask him this again,
and if I don't get a better answer, it's over.
But so Zach thought, well, you marry the person who

(03:27):
you think is really nice. So he thought he had
said like, yeah, I could marry you one day, and
he thought after that conversation that it was locked in
and that he didn't even really need to ask.

Speaker 1 (03:35):
That was like the most positive thing he could think
of saying, I think you're really nice.

Speaker 2 (03:40):
No, he's not a super sentimental side. So it was
Pie Day, March fourteenth, and he gave me a little
card with a pie on it that said don't open
until what are the extended digits of pie? So three
fourteen is the date, and then it's nine okay, yeah,
so don't open until one fifty nine. And I thought
it was going to be a poem about how like
I eat too much pie he writes like weird poems,

(04:02):
and I forgot about it, and so later in the day,
it was like four pm and he was in the
restroom and I reached into my pocket and I was like, oh,
I've got this card in my pocket and it's after
one fifty nine, so I can open it. And it
said something to the effect of, like, you get frustrated
because I forgot our anniversary. But if we got engaged
on Pie Day, that's a date I'd always remember.

Speaker 1 (04:20):
Oh my gosh.

Speaker 2 (04:21):
And so he came out of the bathroom and I
was like, are you asking me to marry you? And
so I'll note that he forgot when one fifty nine passed,
so he wasn't worried about the answer. He knew what
the answer was gonna be.

Speaker 1 (04:32):
And I love that there's a bathroom visit in the
middle of this story. That's very Kelly and Zach.

Speaker 2 (04:38):
Exactly, very scatological. And so I was like, wait, so
are we engaged now? And all he said was, well,
you weren't supposed to read it while I was on
the hut. Anyway, he didn't have a ring, he didn't
have anything. We're not very sentimental. So anyway, we went out.
We got a ring. I got fish guts in it,
so I stopped wearing it because while I was doing dissections,

(04:58):
it kept getting in the way. I got him a ring,
and when we were walking around Rice University, our daughter
was playing with it, and I was like, Zach, and
she was like two as like, Zach, she's gonna drop it.
You're gonna lose your wedding ring. You probably shouldn't let
her play with it. And we got back into the
car and he sat down and he goes, uh oh.
And anyway, so he lost his ring, and I don't

(05:19):
wear mine because of fish guts and we are not
super sentimental. But you know, it's been almost twenty years
since we've been together, so it's working out.

Speaker 1 (05:27):
So Zach's ring is somewhere on the campus of Rice University, or.

Speaker 2 (05:31):
Some undergrad plays drinking games with it or something. I
don't know. I don't know where it ended up. We
never found it.

Speaker 1 (05:37):
All right, Rice students, if you see a ring on campus,
send it to Kelly.

Speaker 2 (05:41):
Yeah, I'll take all the random rings that get lost
on campus. All right, Well, I've gotten us off topic.
Your story was lovely. Mine was hopefully good for a laugh.
But today we're talking about whether or not Earth ever
had a ring, which is a fun question to think about.

Speaker 1 (05:56):
It's fun to think about because it makes us think
about the deep past and how we think of the
Earth as a certain way and having the moon and
the sky looks a certain way and the solar systems
arranged a certain way, and we imagine it's always been
that way or forzillions of years. But it turns out
that on a cosmic time scale, the solar system has
a very chaotic history, and things used to look quite

(06:18):
a bit different. So it's really fun for me to
go deep into the past and learn about how the
Solar system used to be quite different, how life on
Earth could have been different. You could have looked up
at the sky and seeing different stuff out there.

Speaker 2 (06:31):
And I got to say, when you sent me this
idea for a podcast episode topic, it had not been
on my radar at all that Earth could have ever
had a ring. So I'm excited about hearing the answer
to this.

Speaker 1 (06:42):
So I was wondering if folks out there had considered
the possibility of whether Earth had ever had a ring.
So I sent this question to our intrepid volunteers. Thank
you very much to everybody who plays along. If you
would like to hear your voice answering questions on the podcast,
please don't be shy. We would love to have you
as part of the chorus. To us two questions at
Danielankelly dot org and we will set you up in

(07:04):
the meantime. Think about it for a minute. Do you
think Earth could have ever had a ring? Here's what
our listeners had to say. A big meteorite smashed into
the Earth all the debris shot up into the into space.
The Earth did have a ring with the material that
eventually call us into the Moon.

Speaker 2 (07:24):
Yes, it did have a ring, and it still does.

Speaker 3 (07:27):
Maybe it did, like with all the rocks flying around
it right at the beginning when it was being formed,
had like a wriggled rocks around it. And maybe when
the ice it happens and been a thing of vice
around it when there was the ice. Say, I don't

(07:47):
really think that could have happened.

Speaker 2 (07:49):
So, yes, the Earth probably had a ring when the
Moon was born. As bodies coal started to fall into
planet olids and eventually planets that would have been rings.

Speaker 1 (07:57):
Earth might have had a ring after the collision with Theata.
If you're referring to a persistent ring system akin to Saturns,
then that's more of a complex question open to interpretation.
The ejecta from that collision temporarily formed a ring.

Speaker 2 (08:10):
There is a chance that's to be some sort of
ring during its creation.

Speaker 1 (08:15):
It no longer has a ring because it is divorced.
Middle Earth did and it was a big freaking deal.
Is that one of the theories or hypotheses behind where
the Moon came from.

Speaker 2 (08:26):
When a Mars sized object collided with Earth. Do Bear's
poop in the woods?

Speaker 1 (08:33):
Do taco taste better on Tuesdays?

Speaker 2 (08:35):
Does Tom Cruise will have to sprint like a maniac
in every one of his movies? Yes, yes, the Earth
had a ring, but.

Speaker 1 (08:41):
I'll do notize that Liberachi had rings during the formation
of the Moon.

Speaker 2 (08:45):
No, I mean Saturn offered, but long distance relationships just
never work out.

Speaker 1 (08:49):
And a protope planet hits it to form the Moon.

Speaker 2 (08:52):
While the moon was being formed.

Speaker 1 (08:56):
I really don't know, but I imagine not since the
moon has been there.

Speaker 2 (09:00):
That was an amazing mix of like serious good answers
and some really clever not answers.

Speaker 1 (09:07):
I think Tom Cruise does sprint in every movie he's in.
I think that's true every.

Speaker 2 (09:12):
Movie I can think of. Did he sprint in Jerry Maguire,
He must have. There must have been a reason to sprint.
Somebody check the footage, Okay, let us know.

Speaker 1 (09:20):
And I was a little surprised, though I guess I
shouldn't have been that most people went to the sort
of early formation of the Earth, the impact with the
protoplanet that formed the Moon, and thinking about how that
might have been a ring as well, and that's a
totally reasonable answer. That it's not what I was going
for for today's episode.

Speaker 2 (09:38):
Well, I think probably it would help to know how
rings are formed in general. So I'm guessing you're going
to tell us that today, but let's start even earlier. So, like,
what are rings? I guess I realized, Well, I was
thinking about this question, like, you know, the moon orbits
in a ring, but that's not a ring. How continuous
does the line need to be before you have a
satellite versus a ring?

Speaker 1 (09:59):
Yeah, so it's astronomy, which means we're going to do
our best to draw arbitrary dotted lines between the continuous
concepts that really exist on a spectrum. But you know,
some things we call moons, some things we call rings.
What's the difference? How many tiny moons does it take
before you start calling it a ring? Typically we call
something a ring if it's composed of solid materials such

(10:22):
as dust or moonlits, But it's not in one single object.
So you know, basically there's a spectrum between Like you
have one single object, you call that a moon. If
you break that moon up into little rocks, you could
call those moonlits, Or you could say if they're fine
enough you could call it a ring.

Speaker 2 (10:40):
But if you had two objects as big as the
Moon that somehow didn't run into each other, would that
be a ring. Does Mars have a ring or does
it just have two moons?

Speaker 1 (10:48):
Mars has two moons, so I think there isn't a
very crisp distinction. I couldn't find a crisp distinction online.
I don't think like the astronomers have had a meeting
arguing about this yet.

Speaker 2 (11:00):
Nature doesn't care about our criteria in our categories.

Speaker 1 (11:04):
But I think one thing that is important for a
ring is that it's basically in a plane. So, you know,
a swarm of objects surrounding a planet, you wouldn't call
that a ring. If it's like in a sphere. If
it's orbiting in every direction and completely surrounding the planet
with little rocks, that isn't a ring. When distinguishing feature
of a ring is that it does orbit in a plane, right, that, like,

(11:24):
the vertical motion relative to the ring is small compared
to the motion around the planet.

Speaker 2 (11:30):
Does it happen that you get junk like all around
a planet or does it always end up in the
same plane as a ring?

Speaker 1 (11:37):
Yeah? Great question. You can get junk around a planet,
but that's sort of temporary. That's not a very stable
situation because gravity will eventually pull it down together into
a plane. There's a reason that planets have rings and
not swarms of stuff. And there's a reason that moons
typically form in a single plane around a planet, which
aligns with the planet's spin usually, And it's the same

(12:00):
reason why the planets all spin in the same plane
as their motion around the Sun, which aligns with the
rotation of the Sun. And the reason is angular momentum.
Gravity would like to pull everything down together into a
little dot. What resists that, Well, sometimes it's like structural
or integrity. The Earth doesn't collapse into a black hole

(12:21):
because it's solid, right, and the rocks resist being crushed.
But there's another factor there, which is the Earth is spinning,
and the spinning of the Earth sort of fluffs it
up a little bit and makes it larger. So like
the Earth's radius from the core to the surface is
larger at the equator because it's spinning, and if the
Earth was softer like pizza dough, it would get flatter
and flatter as that spinning resists gravity. But the spinning

(12:45):
only resists gravity along the plane. Right, So if you
have like the Earth spin axis, the spinning helps resist gravity,
helps keep Earth fluffed out along the plane of that
spin right, so the axis is perpendicular to the plane,
but it doesn't prevent things from collapsing to the plane.
So now I imagine you have a big swarm of
stuff that's swirling around the Earth. Gravity can pull it

(13:08):
down into that plane, making a disk, but the spinning
keeps gravity from pulling it down into the Earth necessarily.
That's why a big swarm of stuff would collapse into
a plane. And it's the same reason why the whole
solar system has collapsed into a plane. The original blob
of gas and dust that formed our solar system collapse

(13:28):
due to gravity, but didn't collapse as far along that plane.
Because everything is spinning, it keeps stuff from falling all
the way in.

Speaker 2 (13:37):
So if you had a speck around the Earth, not
around like the plane where you get the ring, would
it get thrown out or pulled in or either?

Speaker 1 (13:49):
Yeah? So say, for example, Earth has a big ring
and now you add a rock in a random orientation
to the Earth. What's going to happen to it? Well,
it has a lot of al so it's not going
to fall to the Earth. It's going to be an orbit,
but it's going to get gravitated towards the ring. The
ring is going to pull it in, and so while
it's going to maintain an orbit because of its speed,

(14:10):
that orbit's going to shift until it joins the ring.
The ring, because of its gravity, is going to pull
that new rock into it. So gravity pulls things together,
but it can't overcome angular momentum.

Speaker 2 (14:21):
Okay, And are rings always at the equator of the
thing that they're orbiting around, And if the thing is
at a tilt, that's why it doesn't look like it's
straight around. So like Saturn, is that a tilt and
that's why it's rings are kind of tilty.

Speaker 1 (14:35):
Yes, great question, And it depends a little bit on
the formation. And this is actually a question people have
about how rings form, Like if the ring formed from
the original blob of stuff that made the planet. And
one of the theories for how rings formed is you
have a big blob of stuff and some of it
collapses into a planet, and some of it doesn't because
it's moving too fast and it stays outside and forms

(14:56):
a ring. Then it all comes from the initial blob
of stuff that's spin, and then you expect it to
have the same spin on the same plane and basically
be around the equator of the planet. But another theory
is that these rings come from the outside. You have
a planet that forms, it's already spinning and hard and compact,
and now some material comes from the outside is captured
by the planet into a ring that will collapse on

(15:18):
its own, but its axis doesn't have to align with
the axis of the planet. Gravity will pull it down
into a single ring and it will orbit around its
own spin axis. It doesn't have to align with the planet.
There's nothing the planet can do to change its spin
axis because angular momentum is conserved.

Speaker 2 (15:34):
All right, Is there anything else we need to know
about how rings are formed? Are we all now experts?

Speaker 1 (15:40):
Another thing to think about is the difference between the
formation of moons and rings, Like, why do some planets
have rings and some of them have moons and some
of them have both? You know, why doesn't gravity always
pull a ring together into a moon? Right? You could
imagine like a string of little moonlits orbiting together in
a circle r planet. Why doesn't gravity always pull those together.

(16:03):
It can do that without violating anyngular momentum. And the
answer there is tidal forces. Usually when we think about
the Solar System, we're thinking about gravity as just like
here you have a rock and there you have a rock,
and there's gravity between them and they're pulling on each other.
But gravity is a little bit more complex than that.
If your rocks are not just points objects. If they're
just points, then you can just think about the gravity

(16:24):
on the objects. But if it's big, then you have
one side that's closer and another side that's further, and
gravity depends on distance. So gravity is going to pull
on the closer part harder than it's pulling on the
further part. And that's true always. So for example, if
you're an astronaut and you're in space and you're doing
an ev or whatever, the Earth is pulling on your

(16:45):
feet harder than it's pulling on your head. You might think,
no big deal, But those are relative forces. You can
think of it as pulling on your feet harder than
your head, or equivalently, you can think the Earth is
trying to pull your head off of your body, because
that's really what it's doing, right, It's pulling on one
side harder than the other side. It's trying to tear
you apart. And normally your neck is strong enough that

(17:07):
the Earth's not going to decapitate you. But if you
are close to a very powerful body like a black hole,
then those tidle forces are powerful enough to pull you apart.
That's what spaghetification is. And so planets pull on things.
The Earth, for example, is tugging on the Moon. It's
trying to squeeze the Moon into a football. It's trying
to pull rocks off the surface of the Moon that's
closer to it.

Speaker 2 (17:28):
I can imagine how that pulling over time would start
to pull off pieces and result in a ring. So
does that mean that a lot of the rings around
planets are moons that just got kind of crushed? And
then why didn't our moon end up succumbing to that?

Speaker 1 (17:41):
Sure, it depends on distance. It also depends on structural
integrity what your moon is made out of. But basically,
if a moon gets too close to a planet, the
tidle forces will pull it apart. If the moon is
far enough away, then the structural integrity of the moon
is more powerful than the tidal forces. It'll stay together.
So if you look at all the planets in the
Solar System, you notice that it's usually rings on the

(18:03):
inside and moons on the outside. And you can calculate
this sort of dividing line. It's called the Roche limit.
Things that are closer than the roach limit, the tidal
forces will probably pull it apart. Things that are further
things will coalesce into a moon. The self gravity will
pull it together, and then the structural forces will hold it.

Speaker 2 (18:19):
Is it an interplay between distance and size or is
it just size or distance? Size and what you're made
out of, like a chunk of metal, would be harder
to pull apart than something else.

Speaker 1 (18:30):
It's mostly distance from the planet and what you're made
out of. So, for example, there's a different roach limit
for a blob of water than there is for like
a moon made of diamond, which would be much harder
to pull apart, but for like a typical rock. You
can calculate these distances. For the moon, for example, if
it came within ten thousand kilometers of the surface of
the Earth, it would be pulled apart. Its orbit is

(18:52):
safely outside that. It's like three hundred and ninety thousand kilometers,
so it's well past the Roach limit. And you know,
the Sun has a roach limit. If a planet gets
too close to the Sun, it would get pulled apart
by its tidal forces. So, for example, the Earth came
within almost a million kilometers of the Sun, it would
get pulled apart. We're like one hundred and fifty million kilometers,

(19:12):
so we're in no danger. But this is the distinguishing
feature between rings and moons, basically how far you are
from the surface of the planet.

Speaker 2 (19:19):
You know. Now, anytime we discuss something that's named after someone,
and I'm guessing the roof limit is named after it Roach. Yeah,
I find myself wanting to have Kathy Johnson back because
I want to be like, Kathy, did Roche really come
up with this? Or who was he building on? What
were people thinking at the time? She should just always
give us the background on everything, because she's wonderful.

Speaker 1 (19:36):
M m yeah. And science is a human story, which
means that every time you learn a little bit of knowledge,
there's a fascinating, probably tortured history for how we figure
that out and how it is named after this person
and whether that person was actually a jerk, and if
their paper was full of mistakes, and whether they deserve
the credit for that or not. Human history is always fascinating.
Every time you lift up the rug you find really

(19:58):
interesting stuff under there.

Speaker 2 (20:00):
I want you check out if you missed it, our
episode on Maxwell's equation, to hear Kathy's amazing history, and
also to make you feel better if you're not good at.

Speaker 1 (20:06):
Math, because neither was fair Day or Maxwell. Apparently Maxwell
was good at math. He just wasn't good at keeping
track of minus signs. But hey, who is He got.

Speaker 2 (20:17):
Away with a lot of mistakes. Yes, all right, that's true.

Speaker 1 (20:22):
I have fewer published math errors than Max.

Speaker 2 (20:24):
There you go. You should feel good about that. You
should get a plaque to put over your desk.

Speaker 1 (20:28):
Maybe just a T shirt.

Speaker 2 (20:29):
There you go, that's right here, mistakes than Maxwell. It's
got to be a pretty niche audience for that T shirt. Okay,
all right, Well, we're all missing Kathy right now, but
there's nothing we can do about it at the moment.
So let's take a break to think about how great
Kathy is, and when we come back, we'll talk about
what those rings tend to be made of. All right, So,

(21:05):
based on our earlier conversation, I'm guessing that a lot
of rings are made out of you know, like moves
that got crushed, so probably you know, rocks and metal
and stuff. What else do we get out there.

Speaker 1 (21:15):
Yeah, so the rings tend to be made out of
the same stuff that the solar system is made out of.
So the inner Solar system it's mostly rocky because you
know the solar system, well, it starts out mostly gas,
but all that gas gets gobbled up by the Sun
and any gas left over and the inner Solar system
got blasted out of it by the Sun's radiation, so
you don't have a whole lot of gas left in
the inner Solar system. The rings closer to the Sun

(21:38):
are going to be rockier. Further out, you're more distant
from the Sun, so you can have things like water crystals,
and outpast what we call the frost line, where water
isn't vaporized by the Sun, you have ice. And so,
for example, beyond Jupiter, there's a lot of ice in
those rings.

Speaker 2 (21:55):
So you don't get any ice in rings between the
Sun and Jupiter, but outwards you can get ice and rings.

Speaker 1 (22:02):
Yeah, exactly right, And so we have some pretty spectacular
ring systems in the solar system right, and one of
the first ever to be seen was Saturn's This is
one of the first things actually that Galileo saw through
his telescope on those cold Italian nights in the early
sixteen hundreds are the rings of Saturn, which of you know,
anybody who's used a telescope in their backyard knows that

(22:23):
this is an amazing thing to see.

Speaker 2 (22:24):
I can't imagine being the first one to see that
must have been just absolutely mind blowing right.

Speaker 1 (22:29):
Right to me. It's always exciting when you can resolve
any feature on these objects in the night sky. Like
you look at the Moon and you can see things
on the surface. That's super cool because it's not just
like a point, and seeing the rings of Saturn is
the same way. You're like, I'm seeing something that's really
out there. I don't know about you, but when I
look at the night sky, it's just too easy to
think of it as like a screen with dots on it.

(22:51):
But when you can resolve features on something, then suddenly
I'm transported to this mode where I understand I'm looking
across an incredibly vast ocean of nothingness to huge objects
that are incredibly distant you know, it's so difficult for
your mind to really put yourself in that vast three
D space. But on a clear night when you can

(23:11):
see the rings of Saturn or the moons of Jupiter,
I feel like it's easier to visualize yourself in this
vast space rather than thinking of it as a screen.

Speaker 2 (23:20):
Well, part of me feels like this is cheating, but
I love those apps on my iPhone where you look
up at the night sky and it tells you like,
that's Saturn, that's Venus, and like, to me, I get
all philosophical when I get that extra detail. It makes
me feel like I'm more of a small speck than
if I just look out at it. Like you said,
it's almost like you've got a sheet with little pin
pricks in it and lights coming through. It's like easy

(23:40):
to not think about it as a vast expanse out there.
But anyway, yea for technology, there's an app for that.

Speaker 1 (23:49):
Well. The rings of Saturn are really incredible because they're
so very There are a bunch of different rings are separated,
and NASA has given them really creative names. There's the
A ring, the B ring, the C you know, goes
out to the G ring and the E ring, which
are sort of harder to see with your naked eye.
Some of these things have like a lot of dark
organic compounds, so they're not as easy to see. The

(24:11):
inner ones have more ice, like they're just basically a
bunch of icy particles spread out in these vast, very
flat rings.

Speaker 2 (24:19):
Who should be naming these right? You know? So NASA
clearly shouldn't be allowed to name things because they're not
doing a good job. But you like, if you let
the Internet name them, it would have been like ringy
mcring face. What is the right solution here for these
amazing celestial objects. I think they should be renamed, That's
what I think.

Speaker 1 (24:35):
Yeah, absolutely, I think they should not be named by scientists.
Maybe we should have Joge on the podcast to suggest names.
He was always good at.

Speaker 2 (24:41):
That sounds good.

Speaker 1 (24:43):
But there are these fascinating gaps between the rings, like
there's the A ring and the B ring, And we've
known about these gaps forever. It was Cassini, in like
the latest sixteen hundreds who first saw these gaps. And
that's why we call that spacecraft that visited Sounder and
the Cassini spacecraft, because he was the first one and
see them. And these gaps in the rings come from
actually the interactions of the ring material with little moons,

(25:07):
you know. So we talked about how like they are
only moons out past the rings, but if you're small enough,
you're gonna avoid those tidal forces. You're like basically a
big chunk of rock within the ring. Is it really
part of the ring? Is it a moonlit Now we're
getting into that murky territory where the dotted lines don't
make any sense. But these rings sometimes are called shepherd
rings shepherd moons because they orbit near the edges of

(25:29):
these rings and they can help keep the material in place.
There's these fascinating gravitational interactions between the ring and the moon.

Speaker 2 (25:38):
Huh And okay, so the moon is countering Saturn's gravity
to keep some of the stuff in the ring in
its place. How is the moon clearing its own orbit?
Is it's gravity pulling anything else that might have been
in a ring in that location, It's pulling it into itself.

Speaker 1 (25:51):
Yeah, essentially, it's acting like a little shepherd. It helps
keep the edge of the ring sharply defined because anything
that gets too close gets secreted onto the moon, or
it can make a near miss and can get accelerated
by the Moon and then deflect it back away from
the Moon like a slingshot back into the ring. That's
how it keeps its own like a little lane. That's
why you get these gaps in the rings. It's really

(26:13):
fascinating that these rings are really really broad, right, they're
like seventy thousand kilometers wide, the rings of Saturn, and
they're only twenty meters thick. That's meters, not kilometers.

Speaker 2 (26:27):
Oh wow.

Speaker 1 (26:28):
Yeah, it's the scale of like if you had a
sheet of paper, the sheet of paper would be like
a kilometer wide. Right. It's incredibly thin compared to the
breadth of it, and that's due to anglar momentum and gravity.
Gravity has done its work to collapse it down to
a thin sheet, but it can't do it in the
sort of plane of rotation because of angular momentum.

Speaker 2 (26:47):
Kind of amazing that we can see anything that thin
from all the way here.

Speaker 1 (26:50):
It's because it's reflective. It's the icy particles that make
it possible to see it.

Speaker 2 (26:54):
Oh okay, all right, so then where did Saturn get
this ring in the first place. Was Jupiter feeling amorous
at some point.

Speaker 1 (27:02):
You know, the story of Saturn's rings is interesting history.
It used to be that people thought this is probably
left over from formation of Saturn because it does orbit
in the plane of Saturn, and it seemed like, wow,
this must have been here for a long time. But
Cassini's visits revealed that the rings are quite low mass.
You know, there's like less stuff in there than we thought,
and it's still very sharp and bright, Like the edges

(27:25):
of these ice crystals are still very sharp, which isn't
consistent with like being there a long time. You know,
things tit to get rounded and collisions tend to soften stuff.
And more recent theory is that some moons of Saturn
might have collided and left a huge spray of debris
which basically formed into a ring, which might mean that
these rings themselves are temporary. It might be the Saturn

(27:47):
gathers them back together into moons. We don't quite know,
because the roche limit is a little bit fuzzy, you know,
the structural integrity. If those rings will be there in
one hundred million.

Speaker 2 (27:58):
Years, oh man, and we're not gonna be around to know.

Speaker 1 (28:01):
How do you know? Come on, We're gonna have great, great,
great great great grandkids making non sentimental marriage proposals to
each other using ice from the rings of Saturn.

Speaker 2 (28:11):
Your grand kids are going to are we getting into
incestuous to Oh?

Speaker 1 (28:15):
I mean humanity's descendants. I couldn't say enough great great
grades to get us one hundred million years. But are
you not optimistic that people will be living in the
Solar System in one hundred million years? Hi?

Speaker 2 (28:25):
No, I'm optimistic all right.

Speaker 1 (28:27):
Somebody will be here to see the new moons of
Saturn and to give them a creative name.

Speaker 2 (28:31):
I hope somebody gets on that much sooner. I don't
want to wait for that to happen.

Speaker 1 (28:38):
And other planets in the Solar System have fascinating histories
with rings, Like Astronomers think that Mars has gone through
several cycles of having rings and moons and rings and moons.

Speaker 2 (28:48):
Wait, so does that mean that like Phobos and Demos
have broken up and come back together multiple times or well,
we don't.

Speaker 1 (28:54):
Know how long phobos and demos will last, but we
think that Phobos and Demos formed from a ring that
was created from a giant impact. So like something hit
Mars and then ejected a huge amount of stuff like
ten to the twenty three kilograms of stuff into orbit
and left this huge debris cloud around Mars, which then

(29:16):
collapsed into a ring which then got gathered together into
these small moons.

Speaker 2 (29:21):
So is it possible to look at a moon and
figure out if it's gathered up ring or not? Like
that's got to be hard.

Speaker 1 (29:30):
It's not always possible to tell the history, but you
can get some clues, like, for example, Phobos and Demos
have very circular orbits, which suggests that you had like
a lot of stuff which formed a ring and then
gathered together, rather than being single objects that were like
captured as they floated near Mars, which would tend to
be like more elliptical orbits and not necessarily in the

(29:51):
same plane as Mars, So that suggests that it formed
from a ring. Also, you can look at the composition
of the stuff, and Phobos and Demo are made of
the same stuff as Mars is, which suggests, like our moon,
that it formed due to a giant impact rather than
like was captured. Sometimes moons can be captured. Some of
the moons of Saturn and Jupiter, we think are just

(30:13):
like big rocks that floated too close and got gobbled
up into the gravitational system of those planets not yet torn.

Speaker 2 (30:20):
Apart, but hit the cosmic lottery and didn't get pulled
into the center.

Speaker 1 (30:26):
Exactly. And if these things form moons and then they're
too close to the planet, like they'll drag, if there's
an atmosphere there, they'll drag and then eventually just fall
into the planet and so that you can lose your moon.
So there's evidence on Mars of several of these cycles,
like impact forms. A cloud makes a ring, then makes
a little moon, and that moon gets dragged down into

(30:47):
the planet and lost and you start again. So Mars
is like a really kind of checkered history with its moons.
It's got like a bunch of x's that it's gobbled up.

Speaker 2 (30:56):
Oh man, yet, one more reason and not go to Mars.
So it sounds like these transitions are very chaotic and
would be dangerous if humans were living on the surface
at the time.

Speaker 1 (31:06):
Oh yeah, No, you don't want to be around during
one of these transitions. And you don't want to be
around when you have like a huge dust cloud around
your planet either, because it's going to block a lot
of light. So you know, the temperature probably plummets on
the planet when you have a situation like that. In general,
it's probably really fun to watch from far away, but
not fun to watch from the surface.

Speaker 2 (31:25):
And the connection with the dust cloud is because when
something plummets, it kicks up a bunch of dust.

Speaker 1 (31:29):
Is that right, Yeah, a lot of these are formed
from an impact. So either you have something that comes
nearby and is torn apart and then you get a
cloud a debris, or you get actual impact on the
planet which kicks up huge piles of stuff from the planet,
which then coalesces into a ring and then a moon.
And so we used to think that Saturn was the
only planet in the Solar System that had rings, but

(31:50):
now we've discovered that rings are much more common. So,
for example, Jupiter has rings, but we've only known that
since nineteen seventy nine when Voyager went to visit. These
things are so faint that you either need to send
a probe to see them or have a very powerful
space telescope like Hubble. Can see the rings of Jupiter now,
but otherwise we couldn't see them from Earth.

Speaker 2 (32:09):
And what are they named? One?

Speaker 1 (32:12):
Two?

Speaker 2 (32:15):
I hope we've done better with Jupiter's rings.

Speaker 1 (32:20):
Maybe alpha beta, gamma delta. Yeah, that's a good question.
But these rings around Jupiter are very faint because they
mostly consist of these little dust particles that come from
like tiny meteors hitting the planet's moons and then being vaporized.
But this dust also doesn't last very long in the
Jovian System because Jupiter is crazy. It has really powerful

(32:41):
magnetic fields, and these basically pull these rings apart and
shepherd them up to the poles, and so a piece
of dust can only last in these rings for like
a few hundred years or a few thousand years, which
means that like Jupiter's rings are constantly being degraded and replenished,
like micro ears are hitting the moons, which them to

(33:02):
get vaporized and then they enjoin the ring. But there's
also an outflow, so it's not like a constant structure.
It's more like a river of dust that's moving through
this sort of like dust cycle around Jupiter.

Speaker 2 (33:13):
It's probably nice to get some new bling from time
to time, you know, out with the old in with
the new ring.

Speaker 1 (33:20):
Yeah, maybe you and Zac stually get new rings sometime.

Speaker 2 (33:23):
Yeah. No, he'd just lose them and I would get
bug guts in them, and it would just not It
wouldn't work for us. It's all right.

Speaker 1 (33:28):
Yeah, you know. I'm the same way. I lose stuff.
I put stuff down, I can't remember it, so I've
always been terrified I was gonna lose my ring. So
I just never ever ever take it off, Like that's
my rule. Not in the shower, I never take it
off because I'm afraid I lose it. Same with my glasses,
Like I wear glasses all the time. I actually only
need them for reading. Really, if I ever took them off,
they would be gone within a day. So I just

(33:49):
wear them all the time because I can't manage the other.

Speaker 2 (33:53):
I'm just totally blind without mine, So I never take
mine off. But lately my kids think it's funny to
try to pull them off, and I do not think
that's funny at all, So we're working on that.

Speaker 1 (34:06):
They think it's hilarious when mom bumps into stuff in
the kitchen.

Speaker 2 (34:09):
I mean, yeah, I guess so. But then I remind
them like, oh, I can't drive you to go get
ice cream, And then they're like, oh, we found your glasses.
Like all that was easy.

Speaker 1 (34:18):
Isn't it wonderful? As your kids grow up to be
real people.

Speaker 2 (34:21):
Yeah, I know they're growing up to be bullies. I'll
do better, all right. So we've talked about how Mars
maybe had rings, Jupiter Saturn definitely have rings. How about Urytus,
She says with glee.

Speaker 1 (34:35):
You're just desperate to talk about rings around Urinus.

Speaker 2 (34:37):
I mean, what would an episode be without it?

Speaker 1 (34:41):
So there are actually Uranian rings. The individual particles in
these rings are jet black like lumps of coal. And
we haven't visited close enough or been able to study
these enough to know exactly what they're made out of,
but they seem like some kind of carbon or hydrocarbon compounds.
They're not very well understood because they're so far out,

(35:01):
and they're so hard to see because they're black. Like, remember,
we can only see stuff that reflects light unless we
go and visit, and so jet black stuff out there
in the deep dark Solar system, it's very hard to study.

Speaker 2 (35:13):
I would have so much fun naming things on a
Uranus mission rings and all that. Okay, let's take a break.
You think of what you would name Uranus rings if
you discovered them, And when we get back, let's talk
about whether or not Earth ever had a ring. All right,

(35:44):
So I am going to hope that Earth never has
another ring because I think that would probably result in
something catastrophic for the humans living on the planet. And actually,
have you ever read Seven Eves by I think it's
Neil Stevenson.

Speaker 1 (35:57):
I have read Seven Eves and greatly enjoy it. It's
a fun book. I really wanted to know more about
what blows up the ring in that book. It's not
a spoiler because it happens in like chapter one, and
I thought, oh, this book is going to be about
understanding the mystery of what destroyed the moon, But he
just basically moves on to like what it's like to
live in that system, never answers the question like was

(36:18):
it an alien attack? Was it a random impactor? I
found that very unsatisfying. I mean, it's a great book. Otherwise,
I kind.

Speaker 2 (36:24):
Of appreciated that. I felt like, you know, there's just
a lot of things we don't know the answer to,
and probably, like in a situation like that where you
think humanity is in peril, that probably goes to the
bottom of your to do list, like figuring out the
answer to that. But I had some questions about the
evolutionary biology stuff.

Speaker 1 (36:41):
There, No we're science people. We're curious. You can't like
give us a huge mystery and then leave it unsolved.
That's the point of these books is to inflame your curiosity,
itch and then scratch it. You can't just inflame it.
That's really unfair.

Speaker 2 (36:53):
I mean, there was a lot of other hard science
in that book.

Speaker 1 (36:55):
No, there definitely was.

Speaker 2 (36:56):
Yeah, if anyone knows mister Stevens said, we would love
to talk to him all the show let us see.

Speaker 1 (37:01):
Yes, absolutely, please mister Stevenson, come talk to us. We
will be very nice.

Speaker 2 (37:05):
We'll be huge nerds. All right, So let's hope that
Earth never has a ring into the future, but let's
look into our past when might we have had a ring?

Speaker 1 (37:13):
So a lot of the answers from listeners were really insightful.
They were thinking about the early formation of the moon
and how that probably got gathered together from a big
cloud of stuff which probably initially formed into a ring.
And that's a very insightful answer. I think my only
quibble with that would be, like, was the Earth really
formed at that time? You know, we had the proto Earth,

(37:34):
which then got collided with Fea and formed a huge
swirling system which coalesced into the Earth and the Moon simultaneously.
So like, I don't know if that counts as the
Earth having a ring because the Earth itself was still forming.
But it's true that the Moon was likely a ring
of material before it formed a moon.

Speaker 2 (37:52):
Oh interesting, But.

Speaker 1 (37:54):
That was over four billion years ago, very very early
in the Solar system. There was actually another period much more,
only four hundred and sixty six million years ago, when
scientists think the Earth might have temporarily had a ring system.

Speaker 2 (38:07):
Oh man, all right, what catastrophic thing happened to make
that happen.

Speaker 1 (38:10):
So what we do know and has been well established,
is that around four hundred and sixty six million years
ago there was a time of heavy bombardment. It's the
Ordovician period of the Earth. And we know from fossil
records and from other crazy pieces of evidence we have
that there was just a lot of impacts on Earth.
Like there are these quarries in Sweden where you like
dig down to get limestone. Each layer is older and older,

(38:32):
and there's a layer that corresponds to this time period
with all these fossil meteorites in it. Like they found
these weird green rocks down there. They're like, what is this,
and you find them in this one particular strand, and
they dug into them and discovered these are meteorites. You
can tell like chemically and also from the shape of
these things that they are meteorites are not just like

(38:52):
rocks from Earth. And then they found similar impact sites
in other places around the Earth. That tells us like, wow,
there was a period here, like the weather was bad
on Earth.

Speaker 2 (39:02):
So it's the idea then that there was something that
got within the roach limit and it got broken up
into a ring and then it fell all over the planet.
And that's why there's a lot of it.

Speaker 1 (39:14):
Yes, So the theory used to be that there was
probably some impact between asteroids out in the asteroid belt
or near Jupiter or something that created a lot of
shrapnel and then the Earth basically flew through a cloud
of this shrapnel. That was the original idea. So we
know that there was a lot of impacts. You see
them all over the planet. There's even evidence of like
enhanced seismic and tsunami activity from all this time ago.

(39:37):
It's incredible what you can learn from geology from like
seeing these fragments of rock that got broken up and
stuck back together. In ways you only get from like
really cataclysmic tsunamis and seismic events. Anyway, the theory used
to be, Okay, there's a cloud of stuff that's created
far from Earth, and the Earth flies through this cloud
which creates all these impacts. Right. But a recent study

(40:00):
they analyzed where on the surface these craters were and
they discovered that there were suspiciously all along the equator.
That suggests that there was time for this thing to
form into a ring around the Earth. And probably your
description was more accurate that some big thing came pretty
close to the Earth within its roach limit, was then

(40:21):
torn apart into bits, which orbited for a while formed
a ring before the atmosphere dragged it down into impacts
on Earth.

Speaker 2 (40:29):
Oh my gosh, So was there an extinction that happened
concurrent with this?

Speaker 1 (40:33):
There is a moment called the Great Order Vision biodiversification event,
and there was definitely a change in the Earth's temperature.
If you look at the temperature records, they call this
a global ice house. It's like a big dip in
the history of the temperature on Earth. And so this
paper suggests, oh, this could explain that as well, because
if you have a huge ring that forms over the equator.

(40:53):
It's going to significantly shade the planet. And this is
a really hard study to do because if you want
to think about where these things land on the Earth,
you have to know where that land was at the time.
Right continents move, and you might be thinking, hold on,
didn't Daniel say there were a bunch of fossil meteors
that landed in Sweden? And Sweden isn't close to the equator. Yeah,

(41:14):
it isn't today, but four hundred and sixty six million
years ago it actually was. So what they had to
do was figure out where are all these craters that
you can associate with this time period, which isn't always
easy because sometimes you can date these things very well.
Sometimes you can't because the layers therein Then they had
to rewind the history of the Earth to understand where

(41:35):
were these craters when the impact actually happened. And so
they computed this amazing word. I love this, the paleo latitude,
right like, where on the Earth was this when it happened?
I love that.

Speaker 2 (41:47):
That's a good word. So those people should be in
charge of naming the rings.

Speaker 1 (41:53):
Yes, exactly. Riot Sometimes you hear words and signs. You're like, Okay,
that's well done, that's nice, and that's nice. And so
they did this calculation. They found all these things, but
you know, we're talking about a handful of things, not
like millions of examples. They have like a couple of dozen,
maybe three dozen craters that they can definitively pinpoint are

(42:16):
from the Ordovician period, and so you might wonder, like, well,
how do you really know these are within the equator.
It's not like they all line up perfectly on the equator.
They're sort of like loosely associated with the equator. Their
paleo latitude tends to be less than thirty degrees. And
so they did a pretty robust statistical analysis. I've read
this paper carefully because honestly, I'm kind of skeptical about

(42:38):
the ability of lots of folks out there to do
statistics in a robust way, because not that many people
really understand statistics. And I've been shocked to read papers
in other fields, especially biology, and be like, hmm, I'm
pretty sure that statistical analysis is totally wrong.

Speaker 2 (42:53):
But I'll give you that.

Speaker 1 (42:56):
But I read this paper. I thought they did a
great job. They thought about, like, what are the chances
of getting this kind of distribution of paleo latitudes if
things actually were evenly spread, And they did some good
calculations and some good simulations. They look, for example, at
the distribution of modern impacts and show that they're much
more broadly distributed than these, So they calculate it's very

(43:18):
unlikely that these things, by random chance just happened to
fall along the equator, and that suggests that they probably
were in a ring above the Earth for a while.
This is four hundred and sixty six million years ago.
They also looked at some of these rocks, these actual
fossil metiors, and they can study the chemical composition of
these things and understand how much space radiation they were

(43:41):
exposed to. This is super awesome, yeah, because you know,
there's a lot more radiation out in space than there
is here on Earth. Because out in space you don't
have the benefit of our atmosphere protecting you, and so like,
there are all these high speed particles, cosmic rays and
solar wind constantly penetrating it, and that changes the chemical
position of stuff, right. It matches into the rocks, it

(44:03):
degrades some of those isotopes, so you can basically count
how long something has been in space by looking at
the chemical makeup of a rock, and it looks like
these rocks were not exposed to space for very long,
only like a few tens of thousands of years, not millions,
and that means that probably they were like on the

(44:23):
inside of some large asteroid for many, many, many millions
or billions of years, basically protected from the radiation of space,
then torn apart by the Earth's tidal forces into a
bunch of little rocks which were not protected by the
radiation of space, but only for a few tens of
thousands of years before they fell to the surface of
the Earth and then protected again. So you know they

(44:44):
were near the surface of an asteroid out in space,
exposed to radiation for only a few tens of thousands
of years, So that's also suggestive. None of this is
completely conclusive, but you know, this is like solving a mystery.
You have a few clues you're trying to piece together story.
All this is very circumstantial, but it all points in
the same direction.

Speaker 2 (45:03):
You mentioned that there was like a shrapnel theory. Wouldn't
the shrapnel theory also have something big where most of
it was protected by space radiation, and then it got
broken into pieces, and those pieces worked both to space
radiation for a short period of time before Earth hit it.
How would you tell the difference between those two options?

Speaker 1 (45:21):
Yes, a short period of time, but longer, like if
there was a collision out on the asteroid belts that
created all this shrapnel, it would take much longer to
get to Earth, probably millions of years, not just ten thousand,
and so that's how they can tell the difference.

Speaker 2 (45:35):
Got it. That's very cool. Who was the first author
in this study? Let's give them some credit? This sounds
awesome as scientists who understand statistics.

Speaker 1 (45:42):
Yeah, so this is Andrew Tompkins, Aaron Martin, and Peter
Kaywood and a paper in Earth and Planetary Studies in
November twenty twenty four. It's really quite readable, even for
somebody outside their field. So congrats on the exciting result
and the nicely written paper.

Speaker 2 (45:58):
And where did you come across this? How did we
come to talk about this today?

Speaker 1 (46:02):
I think a bunch of listeners might have heard press
releases about it and send me an email asking me
to explain it. So I put it on my list,
and eventually I actually do get to everything on my list,
as I promise, but we got along backlog, so it
might take me a while. But if you are curious
about something you've heard about in the news and you'd
like for us to break it down and explain it
to you, for Kelly to ask me hard questions, for

(46:24):
me to ask Kelly naive biology questions, then please send
us your questions. We'd love to dig into something you'd
like to hear more about.

Speaker 2 (46:32):
So write us at question I always forget our email address.
What's our email address?

Speaker 1 (46:36):
Daniel Questions at Daniel and Kelly dot org. You can
write to us and ask us like, what is our
email address?

Speaker 2 (46:42):
Yes you probably I can be super successful on that one,
but good luck and we hope to hear.

Speaker 1 (46:46):
From you until next time. Put a ring on it.

Speaker 2 (46:49):
That's right. My daughter would be absolutely appalled if I
say so. Anyway, Thanks everyone.

Speaker 1 (46:56):
Tune in next time.

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Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We
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