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- Did you know
that our solar system

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is made up of more than just
the Sun, planets, and moons.

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[music playing]

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Our solar system
has lots of small bodies

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made up of tons of
rocky fragments

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that orbit the Sun
just like the planets.

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In fact, you could say that
our whole solar system rocks.

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These small bodies
aren't all the same.

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But how do you
tell the difference?

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Let's talk to a rock star
from NASA

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to see what makes
each of these objects unique.

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- Yeah, so asteroids,
comets, and meteorites--meteors

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are all very different objects.

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Most of the asteroids
that we see

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are basically rock, clays--
some are metal.

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And they didn't get
large enough to form a planet,

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so we classify them
as asteroids.

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Most of them are found
in the asteroid belt

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in between Mars and Jupiter.

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Comets, on the other hand,

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form much further out
in the solar system.

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We call it the Kuiper belt,

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which is past
the orbit of Neptune,

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and out towards Pluto.

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So comets, we think,
formed much further out

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and thus,
are very cold objects.

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They've got ice,
a lot of ice.

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They also have rocks
and organic material as well.

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So asteroids are
the remnants of

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the earliest part
of the solar system,

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that formed about
4.6 billion years ago.

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The first materials
that condensed into rocks,

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called chondrules,
basically came together

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in little blebs and gradually
grew into larger bodies.

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The interesting thing
about asteroids is that

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they never grew large enough
to form a planet.

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And the reason for that
is because

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you had Jupiter, which is
a giant--a gas giant,

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basically causing all these
gravitational disruptions.

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So you have material coming
together and breaking apart

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between Mars and Jupiter.

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And so that asteroid belt

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really was never
able to come together.

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They range in size,
you know,

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from a few meters
to several hundred meters

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in diameter--

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even larger, hundreds
of kilometers in some cases.

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We estimate that
there are probably

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1 million to 2 million
objects

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with diameters greater
than a kilometer

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out in the asteroid belt.

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There are certainly much
smaller asteroids as well.

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And we're discovering them
every day.

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So most asteroids that
we observe in our solar system

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have kind of an irregular

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polygon,
like a spheroidal shape.

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So it looks something like
a top that you might spin.

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And, in fact,
asteroids do spin

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at various rates.

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But there are unusual
asteroids as well.

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We recently had one that
came from interstellar space.

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It passed through
our solar system,

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and it looked like
a cigar shape,

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so very unusual.

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- So it seems like asteroids

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come in different
shapes and sizes.

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And with more than
700,000 asteroids

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orbiting the Sun,
our solar system

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is a lot more crowded
than I thought.

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For "Real World,"
I'm Mishay.

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Rock on.

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