- If you had to guess,
where would you think our solar system starts,
and where do you think it ends?
If you think our solar system starts at the Sun,
then you would be right.
How about where it ends?
Does it end at A, just past Neptune;
B, at the Kuiper Belt;
or C, past the Oort Cloud?
The answer is...
If you guessed C, past the Oort Cloud,
you're correct.
- The Oort Cloud is a giant cloud
or collection of comets that surrounds the Sun.
It's huge, and all of these comets
are--are bound to the Sun gravitationally,
which means they are in orbit around the Sun.
They're not escaping into interstellar space.
So they really belong to our solar system.
The limits of our solar system are really defined
by the limits of the Sun's gravity,
and that extends, basically,
to the edges of the Oort Cloud.
The solar system begins at the Sun.
That's the main body in the solar system, gravitationally.
The solar system ends where
the gravitational influence of the Sun stops or fades out.
- I get it!
So if you thought our solar system ended
with our planets, you're wrong.
The solar system begins with our Sun
and extends way beyond the planets.
But how does NASA know that?
- One way to tell where the solar system ends
is by actually going there with a spacecraft.
NASA studies the solar system through missions
that go out and investigate planets.
For example, Voyager was launched in the 1970s
to go to Jupiter, Saturn, Uranus, and Neptune,
to study those planets up close, and their moons.
And Voyager went to the edge of the Heliosphere,
and it passed through a-- kind of a boundary
into interstellar space,
and that's one definition of where the solar system ends.
Another way is to track the orbits of comets,
and we can see that they come from this--
these extremities of the Oort Cloud
that are so far away from the Sun.
So we get a feeling for how large the Oort Cloud is
by looking at the orbits of these comets.
- And that's what is so exciting about science.
New technologies continue to help us learn more
about our vast solar system.
How vast is our solar system?
Tune into part two, "Scaling the Solar System,"
to learn more.
[exciting music]
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