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Lecture 3.10: Types of meteorites: Chondrites
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The Science of the Solar System
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From the lesson
Unit 3: Big questions from small bodies (week 1)
Meet the Instructors
Mike BrownProfessor
Planetary Astronomy
There is so much we have learned about meteorites and I, I can spend
this entire class nine weeks without going
through things that we know from meteorites.
It's just an amazing thing to get parts of the solar system landing on
the Earth as I've said and be able to study them in the lab.
And study the details.
That we could never study from telescopes looking at things in the broad sense, or
even from going there and and using our robotic rovers to, to look at things.
Picking up those meteorites, looking at them, at them, at their microscopic
scale, picking out little piece of
them, measuring chemical compositions in isotopes.
It's just tremendous.
I'm going to give you now a brief kind of
overview of the sorts of meteorites that we find.
And we'll talk a little bit more about
the science that we learned from them, but it's
going to be, just, I'm sad to say, just a, a sort of cursory brush of the things.
So, the important thing to, to keep in
mind though about meteorites versus the rest of
planetary science, is that there's still this interesting
schism, I- schism is not even the right word.
But there's, there are people who study meteorites and they can
tell you incredible detail about these little pieces of the solar system.
And there are people who study the
asteroids, the planets, fly there, study things there.
And they can tell you a lot about the big picture about what they're talking about.
And it is still exceedingly difficult to connect those two things.
Now, the one thing that I showed you in
the last lecture was that you, we can at least
connect the time scales, we can use the asteroids
to measure the time scales, learn something very specific here.
The rest of the stuff I'm going to tell you
about meteorites is going to teach you a lot about, meteorites.
And untangling what that story means for the grander scale of the solar system
is, still work that people are trying to do now that's that's been very difficult.
First off, a quick primer on, on how to find a meteorite.
Walk around and look okay, it's not the greatest answer
in the world walk around the right places and look.
There are a couple places that if you were to
walk around long enough, I can guarantee you would find a
meteorite and that's because the places rather generally aren't other
rocks and you find a rock and sure that's a meteorite.
Where are those places?
One of the famous ones these days is Antarctica.
It's pretty easy to think about the fact that if you find a rock
sitting on top of the ice, that there's something funny going on about it.
But more importantly, this particular place in Antarctica where the
meteorites are found, it's not just that they've fallen right there.
It's that they, they've fell over a much wider
area and they landed on the ice, got buried.
And then glaciers carried them downhill.
Where the glaciers started to evaporate and deposited meteorites down here at the
bottom so you get this huge collection
area finding all these meteorites fantastic place.
Going to Antarctica is a little bit tough so maybe that's not something you
can go do and find your own but, that's one way to do it.
Another place these days that meteorites are
found in abundance is the Sahara Desert.
You could imagine that the Sahara Desert is this expanse of sand and if
you are going along Expanse of sand, you suddenly come across a black rock.
Well, you might guess that there's something funny going on
with that rock and it's not from the Sahara Dessert.
And, you're probably right.
They often are found in big clumps with many different pieces strewn around.
These days expeditions to the Sahara are mounted
because selling meteorites is now pretty big business.
So this, these are actually commercial ventures.
I don't think commercial vendors make it to Antarctica to go pick
them up there but the Sahara's not a bad place to go.
And then of course there are many other
places that, that meteorites have been found, sometimes it's
just people bending down and finding a strange
looking rock, it turns out to be a meteorite.
More often than not, if you bend down find
a strange looking rock it's just a strange looking rock.
It's not a meteorite.
But every once in awhile, people really uncover real meteorites.
Every once in a while they find them
because they saw them streaking across the sky,
calculated where they would have fallen and, and
go out and search and find them there.
That's happening increasingly these days as monitoring is happening more and more.
Let me show you pictures, at least, of some of
the types of meteorites that have been found on the Earth.
In general, I'm going to break up the meteorites into two types.
stones, clever name and, and irons.
And I will show you pictures of all of them, and then
we'll talk about the different types of stones, which are important things.
First let me show you what the irons look like, here's one right here.
I showed you this one earlier.
Here's another one right here.
This one is from Argentina and it fell in not recorded
history but it fell in story telling history.
It, it was- it fell in Argentina recently enough that
there were legends that this rock had fallen from the sky.
Not this particular one this is part of it.
But a much, much larger iron meteorite and which in fact was
buried there in the ground and was known about for a long time.
This one comes from, the Meteor Crater in, in Arizona.
And it's just one of a million pieces that
you can find scattered quite far from Meteor Crater.
I found this in the desert well outside of Meteor Crater.
And, as I said, it's just a little piece of iron.
You can go along with a magnet and pick up little pieces of iron.
These are the irons.
Irons are most distinct when you find them, because they're made out of iron.
You usually don't find pieces of iron sitting around on the Earth.
But the interesting ones that we're going to
talk about also are the, the stony meteorites.
The stony meteorites are made out of
things that we think of as rocks, [UNKNOWN].
Let me show you a picture of some of these.
This is the type, type of stony meteorite called a Chondrite.
We looked at some of those in the last lecture we were in,
particularly interested in the, in the
chondrules and the calcium and aluminum inclusions.
And here you can see another one of these you can tell, you probably
can't tell very well, but there's some sort of bumpy things on the outside here.
Those bumpy things are these round chondrules.
And you can sort of see them.
In through here.
These, the lot of round things.
All of these round things, are chondrules that together, make up this, chondrite.
Clever naming systems, I know.
chondrites, these stony meteorites, are, are, a
lot of them are these chondrites that are,
that are basically constructed of these sort of
millimeter sized round, formerly molten balls of rock.
It's a very strange thing that's telling you
something very specific about the solar system that the,
the bulk of these rocky meteorites are made up of this one sort of type of thing.
This one sort of type of thing must have been incredibly common in
the early solar system as these bodies were first starting to [UNKNOWN].
Here's a slice of one of these chondrites,
where you can really see the chondrules really well.
It's hard to know what the scale is
here, except to remind yourself that these these chondrils,
these sliced open chondrils are again a couple millimeters
across, so that's that's what that scale is there.
And you can see they're they are.
Beautiful round things, these spheres.
You can tell they're spheres because when you slice them across, you get
the, the little tops of them, you get the nice round versions of them.
Sometimes, you see things like they're cracked.
So you can see a cracked one right in through here.
You occasionally see, this one, you can't see very well but
this is, this is a pair of them that have merged together.
Sometimes you see they've broken apart.
This is parts of a chondrule that broke.
Chondrules the early solar system these meteorites that are landing
on us are made out of tremendous amounts of chondrules.
Almost like like little b b's in space a very very strange thing.
I could show you pictures of chondrites all day long
it's not as satisfying as seeing them in real life.
If you get a chance go see some of these things.
Here's a beautiful one from the American
Museum of Natural History in New York City.
Go there.
Check this one out.
You can see it's been sliced open.
This is a slice of one of the most famous carbonaceous chondrites,
we'll talk about that in a minute, and it's called the Allende chondrite.
And they get their names based on where they fell on the Earth.
And you can tell this one's different.
You see the chondrules, all over the place, nice round globules.
You see there's some beautiful big splotches
of calcium aluminum inclusions in through here but
mostly you'll see chondrules but what you also
see, is between, in between the chondrules, is
this black stuff that's called the, the matrix
the stuff that holds the chondrules together so
it's not that everything is chondrules, there's is
glue in between, and what is this glue?
Well.
In the previous chondrites we were looking at, it was just more of the same
sort of material that the chondrites are made out of, the sort of rocky material.
But in carbonaceous chondrites, the, the matrix in through here is carbon.
In forms like, like graphite, just pure carbon.
Carbon now, when I say carbon, you should suddenly
sit up and think woo, this is really interesting.
Carbon of course, is one of the key components
of organic matter of life of all these things.
We're looking for where stores of this carbon could have been.
Certainly could've been wherever these things, these carbonation chondrites
were forming and eventually falling down to the Earth.
Here's another carbonaceous chondrite.
These are just I find these spectacular.
These dark matrix of carbon and then just full
of all of these Chondrules in the middle of there.
So what is going on with chondrites?
We find them all over the place in the meteorites that we find on the Earth.
We think of them as the very first
primitive things that were made, in the solar system,
a, after the calcium aluminum inclusions, or perhaps
at the same time as the calcium aluminum inclusions.
And yet when we think about the accretion of things in the solar system
we think about the way, things start to stick together and get bigger and bigger.
It doesn't make chondrules, it doesn't make little millimeter sized b b's that
makes maybe big dust bunnies or something
or irregular globs not chondrules not chondrules.
Why chondrules?
Well you can study chondrules for your entire
life and what you would find is that you
can figure out things like chondrules were heated
to very high temperatures, and then cooled very quickly.
You'd find that they come in a range of sizes,
but that any individual meteorite, they tend to be all kind
of the same size, the range is not very big,
but the tend to be all sort of the same size.
There are a million different little aspects of chondrules that you need to
understand if you're going to put this sort of together where they came from.
I'll give you a couple different ideas, this is still unsettled,
it's not one of these things where no one has any
idea where chondrites came from, it's that there are too many
ideas and nobody has settled on yet what the story is.
There are some ideas that material is starting to grow and
shock waves came in through the big nebula of gas and dust
and those shock waves quickly shock heated this stuff it formed into
these little blobs and then cooled back down as the chocolate went.
There are other ideas that they were formed by, by material
being pulled close to the sun and then being ejected away from
the sun and heated up to very high temperatures very briefly
and just pulled close and then cooling as it was ejected away.
Other ideas that these, all these little chondrules were sort of sorted together
into similar sized balls by eddies and
currents that were flowing in through there.
There have been ideas that the chondrils were
melted by lightning that occurred inside the nebula.
None of these things is really certain.
It's an area of extremely active research,
and extremely detailed research that I'm, I'm sort
of sad that we don't have time to get into in, in the gory detail here.
What the key point really to take home is that there was some process that was seems
to have been fairly ubiquitous in the early
solar system that led to chondrules being strewn everywhere.
And by everywhere, I would point out that I really mean everywhere.
Pieces of chondrules have been found in the dust from
comets, there have been, has been one fly by of
a comet where the dust was collected brought back to
the Earth and that dust was analyzed, pieces of chondrules.
Chondrules, they are everywhere.
In the next lecture we'll talk about the other source of meteorites that we find.
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