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Generally, when humans launch a robot into space to explore other worlds,
it’s a one-way trip.
But not always.
A special few get to bring samples back to Earth.
And this month, NASA’s OSIRIS-REx began its preparations to depart the asteroid Bennu,
carrying pieces of the tiny space potato which will clue us into the origins of our solar
system,
and maybe even life itself.
Bennu is an ancient pitch-black rubble-pile asteroid
currently located around 300 million kilometers from Earth.
And by rubble pile, astronomers mean that almost literally.
It’s an agglomeration of rocks holding itself together by force of will;
it’s actually force of gravity, with a bunch of empty space in between the pieces.
It is also a cosmic time capsule.
Those rocks, specifically the ones below the surface,
which haven’t been irradiated by the Sun,
haven’t gone through any significant chemical changes since they formed,
likely within the first ten million years of the Solar System’s existence.
Those pristine rocks are thought to share the
same ingredients that went into making the Earth.
Like organic compounds… the building blocks of the compounds
that are themselves the building blocks of life.
That’s one reason why Bennu is the target of OSIRIS-REx,
which arrived in orbit back in December 2018.
In addition to taking some very nifty pictures,
which revealed just how boulder-y the surface is,
in October 2020 the spacecraft actually flew down and
punched Bennu to collect some samples.
And when I say punched, I mean it shot a bunch of pressurized nitrogen gas
at Bennu to kick up and collect a bunch of debris.
This Touch and Go operation, or TAG for short,
grabbed at least sixty grams of material,
which doesn’t sound like much, but it was enough to overfill the collector head.
Since one last observation pass on April 7th, OSIRIS-REx has been drifting away,
but it won’t officially leave Bennu until May.
After that, it’ll be two more years before it arrives back on Earth.
Or at least before the capsule containing those precious rocks arrives back on Earth.
OSIRIS-REx will toss the capsule at us and then go on to orbit the Sun.
If it has enough fuel left, it might even do some more exploring.
Meanwhile, the samples will be distributed to labs around the world
so we can all work together to solve this ancient puzzle.
Speaking of studying samples of space rocks back on Earth,
our second story concerns some rocks that got here the old fashioned way…
by smashing into us.
Last week in Nature Astronomy, scientists revealed what the Earth’s atmosphere
may have been made of after it first formed.
And they learned that from baking meteorites.
Just like Bennu, certain meteorites, or at least the insides of them,
have stayed mostly the same since they formed in the early solar system.
That includes gases that are trapped inside,
like individual molecules incorporated into the different minerals’ crystal structures.
And if the rock gets too hot, these molecules gain the energy needed
to break their bonds and leak out as a gas.
If the rocks are part of a sufficiently large planet,
there would be enough gravity to hold onto that gas in the form of an atmosphere.
So that’s where some of the Earth’s early air may have come from,
a bunch of rocks heating up as all the materials making up the Earth
squished themselves into a ball.
But so far we haven’t found a connection between the
total composition of a baby planet, and the composition of its first atmosphere.
One team decided to look for that connection by
studying the gases produced by a sample of meteorites.
These meteorites are thought to have the same composition
as the building blocks of the rocky planets in our solar system.
And unlike other meteorites out there, these particular samples
never got hot enough to melt and lose their record-keeping abilities.
Degassing these meteorites, and that is the technical term,
required crushing them up and then chucking them into the science lab version
of a furnace to heat them up to twelve hundred degrees Celsius.
That furnace was connected to a machine which could measure
the masses of the gas molecules as they forced themselves out of the rock powder,
and from there we could figure out what the gases actually were.
It turned out to be mostly water vapor,
followed by carbon monoxide and carbon dioxide,
with a little hydrogen and hydrogen sulfide, too.
While the team only sampled three meteorites, the relatively consistent results
between them demonstrate that planetary formation models aren’t one size fits all.
The idea was to show, on a small scale, how rocky planets might
acquire their atmosphere in a different way from gas giants.
And the composition of that atmosphere appears to be
very different from the hydrogen and helium you see on Jupiter, for example.
So this research helps us understand how to
model the atmosphere formation on different planets,
especially planets outside our solar system.
That’s right.
Baking meteorites doesn’t just help us understand how the Earth got its air,
it helps figure out what might have happened on the other potential Earths out there.
From the origins of life to worlds too far to touch,
it’s pretty cool that we can learn about all that’s out there in space and
in time just by getting our actual hands on some space rocks.
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