This is John G B with all of us, trampled, most of us think of
the solar system as the sun, plus a set of planets in orbit
around it. But that leaves out the asteroid
belt a region lying between the orbits of Mars and Jupiter which
contains billions and billions of asteroids ranging in size,
from Pebbles to dwarf planets. It turns out that asteroids
contain, Tell us a great deal about the origin of the Earth in
many ways more than we can learn by looking at the other planets
such as Venus. And Mars.
Sarah Russell is Professor of planetary, sciences and leader
of the planetary materials group at the Natural History Museum in
London using asteroids as snapshots of the early solar
system, how research seeks to unravel, how the solar system
formed and answer questions such as how the Earth got its water
and organic. Ariel's.
She even has an asteroid named after.
So Russell. Welcome to geology, B.
Thank you very much for inviting.
Me Oliver, what are the asteroids?
So, an asteroid is basically a rocky body that is in orbit
around our sun. And we can differentiate it from
comets, which are the other small bodies that go around the
Sun and that comets tend to be much more.
I see full of volatile materials and they originated further out
in the outermost reaches of the solar system.
But have eccentric orbits, so they come As the inner solar
system where we can see them. And in contrast, asteroids are
made almost entirely of Rocky materials, that means
silica-based minerals and metals and things like that.
And we can distinguish both asteroids and comets from
meteorites, which is any natural, extraterrestrial
material that lands on the surface of the Earth.
So some of the things that land on the earth, then I'm not
asteroids at all. Know me traits can be anything.
So, actually, the vast majority, See our pieces of asteroids,
which is brilliant for those of us who are interested in
asteroids, but also some meteorites are pieces of the
Moon and some are pieces of Mars.
And some we just don't know what they are.
So so, so there's a whole variety of stuff that falls from
space for us to try to figure out.
So why are asteroids concentrated just in a region
between the orbits of Mars and Jupiter?
Yeah, and we think the answer to that goes.
Right back to the beginning of the solar system.
So the solar system formed from a disk of dust and gas that was
orbiting around the evolving young son, and these bits of
dust gradually accreted together to make larger and larger
Pebbles, and then Boulders and larger and larger objects, until
they eventually formed the planets that we see today and
Jupiter is the biggest planet in our solar system.
It from very early on, and Jupiter was so massive that it
caused all sorts of forces. Has in this area between Mars
and Jupiter, that kept forcing these bodies apart and cause
them to be quite energetic and have lots of impacts on.
That means that no Planet could form in that region.
So now we just see this debris of this material from the early
solar system, which is now our asteroid belt.
As I mentioned in the introduction, there are billions
of asteroids and if that concentrated are they like the
artist Impressions often show them as pretty close packed in
space. No, so if you see a sci-fi film
when they go through an asteroid belt, you can see these pictures
right? Of loads of Boulders all over
the place crashing into the astronaut spaceship, but
actually, it's not like that. So you would get one Boulder and
then the next one will be thousands and thousands of miles
away. There's a lot of space out there
so even though there's a lot of asteroids, they're not all that
densely packed and all of the spacecraft that have gone to the
outer solar system like New Horizons and Voyager, they've
all gone through the asteroid belt.
Out with absolutely no problem at all.
So that shows they're actually not very densely packed at all.
There are several different types of asteroid.
Yeah, there are several different types of asteroids, so
we can investigate this from Earth, looking at the spectral
features of the asteroids, I presume.
These are features that appear in the Spectra of the near
infrared and visible light, reflected, by the asteroids.
Yes, I'm from that kind of work. We know that there's an amazing
compositional diversity of asteroids.
So, I'm asteroids are very rich in carbon.
Some seem to be Rocky, some seem to be made of Basalt much like
the surface of the Earth. Some are made of metal.
We know the largest asteroid in the asteroid belt Series has got
an ice volcano on it. So there's an amazing diversity
of different compositions across the asteroid belt.
And yet it's one of the fun things about studying asteroids
is actually they're much more diverse in composition than the
inner planets for example. So It accounts for this
diversity, we don't know in detail, but it could be that in
the earliest times in the solar system, the giant planets
Jupiter and Saturn were actually migrated they moved in and out
of the protoplanetary disk and that could have disrupted, small
bodies that were forming another region.
So it could cause for example, bodies that were rich and
volatiles that formed in the outer solar system to be thrown
into the inner solar system. So we end up with this mismatch
over loads and loads of different body.
That's actually formed different parts of the solar system and
also, depending on how big they are, they have very different
histories. So a lot of asteroids seem to
have not changed at all since the beginning of the solar
system, but others have undergone some geology and so
they've changed since they first formed.
How can asteroids actually then tell us anything about the Earth
in lots of ways Oliver? So in some ways, the Earth has
kind of forgotten about its early history because on Earth
is so much joy. Elegy going on, everything's
been mushed up and mixed and melted, but many of these
asteroids have not changed since the beginning of the solar
system. And so they tell us something
about the primordial material that all the planets, including
the Earth came from. So the majority of asteroids and
meteorites, that we have to study on Earth.
Have we look at them in detail? They've never melted and they're
made up of particles of different sizes or mixed up
together and these particles. Some of them formed at very high
temperatures, and some of them formed at low temperatures.
So, that's telling us that the solar system formed from this
dust cloud, where there are lots of different environments and
lots of different things got mixed up together.
And this was probably the primordial material that made
the Earth and looking at these asteroid or meteorites.
We can learn how old the Earth is because we think they formed
at the same time as the Earth and they can tell us that the
Earth was about four and a half billion years old and we can
even unpick the components and Look at how long these particles
existed in the protoplanetary dusty disc and we get these ages
from radiometric dating methods. Most commonly using the decay of
uranium to lead, just as we do for the Earth rocks.
So, you said that among the different kinds of asteroid.
There are the kinds that are Rocky and the kinds that are
more metallic and the ones that seem to be more metallic.
What To the rocky stuff. Did they just never have it to
begin with or did it vaporize when they're?
Yes, as I said. So most asteroids, we think
never melted at all and they just made up this primordial
stuff that solar system was made of, but there are some asteroids
that seem to be made mostly of metal.
And we see these in our meteorite collections, we have
meteorites that are made of iron nickel alloy.
And we think that these formed from asteroids that became big
enough and had enough heat in them that they melted.
And when they melted the The iron in them, sank down to form
a core and so they had a core of metal and then that was
surrounded by igneous, Rocky material and actually an Army
Track collections. We also have samples of this
differentiated igneous, Rocky material that made up the
mantle, or crust of these asteroids.
But one, a kind of weird things in meteorite science is that we
have basaltic meteorites, which would have been the crust of
these asteroids. But we don't really have so much
of the mantle material. And so we have this missing
Mantle and we don't really know what happened to it.
So it could have been. As you say that it was vaporized
during impacts in the asteroid belt and we've just lost that
record but the but the iron which caused are more resilient
to impacts and so maybe they survive better.
And so maybe that's why we see so many of these.
But the iron-rich meteorites are interesting because they might
provide an analog to the Earth's core.
We know that the Earth has gone through this process of heating
and melting and forming a metal core, but we can't access our
own Nurse Corps to look at what the composition is, but we can
use these iron meteorites of some kind of analogy to what
might have happened during Earth's differentiation.
That's interesting. So, the metallic ones like a
naked core, that we know she look at.
Yeah. Well, that's what we're
thinking. Yeah, no.
Actually, there's a space mission called psyche.
That's going to visit one of these metal-rich asteroids, and
that should provide some clues about their origin and see if
that is the case. So, if the Earth was hot enough
to melt metal and have it sink down to form, Cool.
How did it get to be covered with water?
Well, so we can also thank Asteroids for that because many
asteroids contain writes, a lot of water and they contain a lot
of organic material as well. And the Earth has been
continuously bombarded with asteroid or meteorite since its
formation and in the early stages of the solar system, the
impact rate would have been even higher when the solar system was
a more energetic and chaotic kind of place.
And so after the Earth, had differentiated the water that's
created. The Earth's oceans could have
been brought there by meteorite impacts.
That's a hell of a lot of meteorites.
Well, I don't think it's, I mean, we look at the Earth from
space and it looks like a watery planet, right?
Because two-thirds of the Earth is covered in water and that
water from a human perspective. These look like really deep
oceans. But from a planetary
perspective, this is a very, very thin skin on the surface of
the planet. So there's not from a planetary
bulk composition perspective. There's not that much water,
whereas, meteorites can contain loads of water.
So carbonaceous chondrites, which seemed to be the
predominant flux of material for at least very tiny particles.
They can contain up to 20% water in the form of clay minerals.
So they contain these Clays that can trap water in their
structure. And so they can actually deliver
huge amounts of water to the Earth that way.
We're actually in a very exciting time from an asteroid
point of view because there are two missions currently underway
to fetch samples from the surface of two different,
asteroids, and return it to us. And you're a member of the
science team for both of them. Yes.
So the two currently in Flight missions, there's a Japanese one
called Hayabusa 2 which has already collected a sample from
its asteroid Raghu and It's on its way back to Earth.
Now it's going to return to Earth in December 2020 and the
other mission is a NASA mission called Osiris Rex, and that is
currently in orbit around the asteroid bennu, and it's going
to collect a sample next month in October 20 20, and then it's
due back to Earth in 2023. How big are these?
Asteroids, they're not very big at all.
So Raghu, the target for Hayabusa 2 is about a kilometer
across. And I knew the target for
asaurus Rex is about 500 meters across, so it's kind of about
the size of a skyscraper really. It's not very big in the grand
scheme of things but that's what makes it really exciting because
the smaller it is, the more likely it is to have this
primordial material and not have too much geology of happened to
it. So it's more likely to be a
pristine sample of the early solar system and do these things
have enough gravity to hold a space probe in orbit around
them. Well, they, yeah, they only have
a teeny, tiny fraction of the gravity of Earth because there's
such tiny bodies, though, Cyrus Rex.
For example, it is in orbit around been, oh, but to be in
orbit around Benny, what has to be super super close.
So it's only about a kilometer away from the center of the
asteroid. So it's actually has the world
record for being the closest orbiting satellite around a
body. So it's an incredible feat.
Out of the rocket scientists and the engineers to have actually
managed to successfully, put the spacecraft in orbit around this
sign Iraq. And then it's actually going to
go down to the surface to scoop up a little bit.
Yes. So this is the most dramatic
moment of the mission perhaps. So it's going to go down to the
surface and it has a kind of reverse vacuum cleaner.
So blast of gas will be pointed at the surface of been 0 and
that will disrupt the Rocks and fragments on the surface of the
asteroid which will then get captured into the collection
capsule and then hopefully brought back to Earth for us to
take a look at. So what are we hoping to learn
from these samples? That will be returned with great
difficulty to Earth. Yes, I spent my career studying
meteorites and mostly meteorites that come from asteroids.
And these missions are like the dream for scientists like me
because we love our meteorites, but the problem with me try,
It's is that they fall on Earth. We don't really know where
they've come from. We don't have a chance to do
fieldwork like terrestrial just to.
We can't choose that the samples that we get.
We just get whatever's lands on Earth.
But these missions are the chance for us to look at a
sample of a primordial, asteroid or body.
That we think came from the very earliest times in the solar
system that will tell us about the origins of our solar system.
And it will tell us that with the A global geological
perspective of all the mapping, that's these missions have been
doing at the same time. So it will really give us some
geological and astronomical context of these samples which
are so important to try to learn about their Origins.
Will it be like this? So called Ground.
Truth that we have with these Earth missions where we have
lots of pictures of the Earth for it to be able to correlate
the two. You actually have to go down to
the bit that you're looking at and grab a bit of it.
Is that going to enable you to? To link what we get back from
bennu with some of the asteroid. So that in your collection and
then you can just say oh well those definitely came from
asteroids, absolutely. So the Hayabusa to Mission is
actually that as you might expect from the name, it's the
second. Asteroid return mission that the
Japanese have done and the first asteroid return.
Mission Hayabusa went to a type of asteroid called the S-Type
asteroids that we'd always suspected were similar to a type
of meat right in our collection called Ordinary chondrite.
We didn't know for sure. And it was only when we had that
sample return, that we could make that connection
definitively and that then enables us to understand our
meteorite collections much, much better.
So, yeah, one of the important things about these missions is
that they help us to understand. Not just me, try to look
identical to these these Roxbury, they'll help us
understand our whole meteorite collection.
And the other thing, it will help us do is to understand the
diversity of asteroids that we can observe from Earth because
it will ground truth, our spectral data so that it will
help us to have that one connection of.
We have a sample on Earth and we can also see it in space that
will help us to calibrate and looking at all of asteroids and
small bodies in our solar system.
How did we select been you out of all the thousands of
asteroids? We could have picked one big
reason that it was picked is because it's what we call.
The c-type asteroid which we think contain organic material.
And one of the main aims of the mission is to learn about
Organics in the solar system are how they may have come to Earth
and seeded life on Earth and tell us about our Origins as
earthlings how we got our water and what it can tell us about
the formation of the earth. So the type of asteroid was very
important. And the other thing that was
very important was where it was. So benno is a near-earth
asteroid and so it's Not in the asteroid belt between Mars and
Jupiter. It probably was once but it's
been knocked out into an orbit. That's much closer to the
Earth's orbit around the Sun so that makes it much more
accessible and much easier for us to go there and Sample it
there's something else that I think you mentioned to me when
we were talking earlier that by studying the details of the
Albedo that is the fraction of the incident radiation that is
reflected by the surface of the asteroid we can tell in detail.
Tell what its future orbit is going to be and we really care
about that because it has a finite chance of colliding with
the earth. Oh yes, of course.
That's another important reason for looking at bennu and
near-earth, asteroids in general.
So we know on Earth that we do get hit by asteroids, sometimes
their big asteroids and can do a huge amount of damage on Earth
but we want to understand that risk as well as we can.
And one of the ways that we can do that is to Study asteroids
like bennu in details. So bennu is a potentially
hazardous asteroids in that. It's got a tiny probability of
hitting the Earth, in about 200 years time, but what we want to
do is try to make our calculations about whether it's
likely to hit or not a bit more precise.
And we can do that by making very precise measurements of its
lb do and the heterogeneity of the asteroid and so on and that
will help us to understand what's called the yarkovsky
effect. Switch has an effect on small
bodies of solar radiation. Pushing them as a very, very
gentle Force, but it's something that we need to understand to be
able to have accurate models of how the orbits of these objects
are going to evolve over the next centuries.
This yarkovsky effect that you mentioned is to do with solo
radiation pressure, which depends and turn on the Albedo,
which is how much of the the incident solar radiation gets
reflected and therefore how much it pushes on the asteroid and
changes its orbit. So if bennu did wind up hitting
the Earth in some catastrophe. Now, how would that compare with
the asteroid that we think hit the earth?
66 million years ago and caused the extinction of the dinosaurs
and much of Life? Yeah, well, I was going to say,
great thing about asteroids, but another interesting thing about
asteroids is that You have this capacity to cause global
destruction. And the last time that happened,
of course, was about 66 million years ago, an asteroid impacted
off the coast of Mexico in chicxulub.
And we think this impact caused massive Devastation and mass
extinctions of the dinosaurs and other animals, but then that led
to the rise of the mammals and and eventually to humans.
So these are catastrophic Vents do change the course of
evolution but they can sometimes change them in potentially
interesting ways. So we think an asteroid about a
kilometer in size, that's about the size of Raghu if that hits
the Earth that would cause global Devastation will have
catastrophic Global effects. So that so that's the target of
the very worst level of impact and we think such a globally
destructive impact might happen about once.
Every hundred And million years or so.
So it's not something that's likely to happen on our watch
but it can happen and it probably will happen over the
four or five billion years that the Earth has got remaining to
exist. So something that we're
interested in mapping what near-earth, asteroids might be
potentially hazardous and how hazardous they might be.
So for my last question, I want to ask you if you had unlimited
resources for your research, How would you use them, right?
I love that question. So if I had unlimited resources,
what I think I would love to do. I Love sample, return missions
for all the reasons that we've talked about actually going into
space and bring a sample back that we can study in the lab
tells us so much about the origins and age and
characteristics of this object. So it would have to be a
mission, a sample return mission, that will bring stuff
back to Earth for us to have in our collections.
And the places that I would love to get a sample from these
Interstellar Interlopers. So couple of years ago, the
first Interstellar asteroid struck combat was observed
coming into our solar system called omura so we don't know
where it came from, it came into our solar system and then it
disappeared off again. But having a sample of something
that is from beyond our solar system.
Could tell us so much about our place in the Galaxy, whether
there's anything Peculiar about our solar system that led to the
evolution of life and ultimately us or whether we're very common
and that is the one thing that we could do so much science on
to learn about, not only our solar system, but the universe
beyond us. So Russell.
Thank you very much, Oliver. Thank you so much.
I really enjoyed talking to you, and thanks very much for
including me in your podcasts for more about geology b, as
well as pictures and diagrams that illustrate this podcast.
You can go to geology B.com.