Name: 小惑星探査における3つの歴史的ファースト (3 Historic Firsts in Asteroid Exploration)
Uploaded: 2021-01-14T10:31:32.000Z
Duration: 6 min 20 s
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Over the last 60 years, we've visited a lot of places in the solar system.

The Sun, the Moon, all eight planets, some comets, even Pluto!

Every time it seems like we've been everywhere worth going,

And these days, many of those objects are asteroids.

Astronomers have been discovering asteroids

since the early 1800s, but modern technology

has turned them into the hottest new frontier

So let's look at three exciting discoveries that marked firsts

in asteroid research and gave us great reasons

First up is asteroid  24 Themis, discovered in 1853

It's the parent body of one of the largest families of asteroids,

made up of thousands of objects that all seem to have been

knocked off Themis by ancient collisions.

But more recent telescope observations made in the mid-2000s

gave astronomers even more reason to be interested in this rock.

Their observations suggested that asteroids like Themis

could be responsible for something pretty important: Earth's water.

For a long time, planetary scientists had imagined

a clear distinction between asteroids and comets.

They thought asteroids were bone-dry, and only comets,

which orbit farther from the Sun, were covered with ice and snow —

and therefore, could have hit Earth and left behind water molecules.

The only problem was, they didn't see that clean division in their observations.

Some meteorites (which mostly come from asteroids)

show evidence of having formed in the presence of water.

And a few objects in the Themis family also had features

So that made it natural to check out the parent body in more detail.

When two separate teams used NASA's Infrared Telescope Facility

in Hawai'i to study Themis in the mid-2000s,

A thin layer of frost seemed to be covering its surface.

And embedded in that frost were carbon-based molecules —

the building blocks of life here on Earth.

Themis seems to orbit just far enough from the Sun to keep it all stable.

The fact that it's possible for an asteroid to hold onto ice is pretty fascinating,

because planets like ours probably formed from asteroids like Themis.

And as all that rock clumped together to form planets,

the water and organic molecules must have come along for the ride.

Themis isn't the only asteroid where we've discovered something

And for 87 Sylvia, that “something” was pretty big:

not just one, but two of its very own moons!

Astronomers first spotted Sylvia orbiting in the main asteroid belt

way back in 1866, but it took until the 21st century

Scientists noticed its first moon in 2001

We'd found lots of double-asteroids by then,

Now we know they exist — and they can be pretty useful!

By tracking the paths of the smaller moons, astronomers

were able to pin down details about Sylvia's mass and density.

Those gave them clues to its composition,

which can be tricky to figure out in an asteroid.

But of course, the first order of business

Sylvia was named after Rhea Sylvia, the woman ancient Romans

So, of course, the moons are named for her sons Romulus and Remus.

But the names are more than just some good, clean historical fun.

The evidence suggests that the moons might literally be

from Sylvia itself, knocked off during an ancient collision.

In fact, researchers think there could be even more moons,

because Sylvia is what astronomers call a rubble pile.

Basically, instead of being one big, solid object,

it's more like a collection of rocks held together by gravity.

That means it would be especially easy to knock off

Research suggests that up to 6% of asteroids

might have at least one companion, but Sylvia was the first one

Our final nifty asteroid is 163693 Atira,

And when it was discovered in 2003, Atira was the first known asteroid

that was always orbiting closer to the Sun than Earth.

Since then, astronomers have found around 20 more,

but these objects remain really tough to study.

For one, Atira is small, with a diameter around five kilometers.

But more importantly, it can be tricky to study objects

Because, you know what else is in that direction?

The Sun, which is definitely not an astronomer's friend.

But these objects are definitely worth studying,

because it's sort of surprising that asteroids like Atira can stick around at all.

Atira's orbit is really elongated — sometimes it nearly reaches Earth,

while at other points it can be just half as far from the Sun.

That means that, while it never crosses Earth's orbit,

it does pass through the part of space occupied by Venus.

Usually, crossing paths with a planet is bad news — over time,

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小惑星探査における3つの歴史的ファースト (3 Historic Firsts in Asteroid Exploration)

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