- [Narrator] The Earth isn't flat, but the solar system is.
About 4.6 billion years ago,
the material that makes up our solar system
was in the form of a nebula,
which is pretty much a big cloud of gas and dust in space.
Gravity flattened this material into a disc like this one
and then pulled everything towards the center.
Eventually, the pressure became so great
that the star was formed.
The sun, the remaining dust
and gas particles collided with each other
and eventually formed larger objects like Earth.
Together, the sun and all the objects in space
that as gravity keeps an orbit, make up our solar system.
We call the biggest objects that orbit the sun, planets.
Our solar system has eight of them;
Mercury, Venus, Earth, Mars, Jupiter,
Saturn, Uranus, and Neptune.
These eight planets are divided by the asteroid belt.
Asteroids are rocks that orbit the sun
that are much smaller than planets
and they're made up of nickel and iron.
And unlike the planets, most asteroids aren't round.
Beyond Neptune is the Oort cloud,
a space at the very edge of the solar system
that's filled with comets, which are like space snowballs
that are made up of ice and dust.
Sometimes comets enter the inner part
of our solar system and can even be seen from Earth
with long tails of ionized gases.
One of the most famous comets
is Halley's comet,
which only comes near Earth every 75 years or so.
Be on the lookout for it in 2061.
The four planets on the side of the asteroid belt,
closer to the sun, are called the inner
or terrestrial planets.
The word terrestrial comes from the Latin word for Earth.
Terrestrial planets have solid, rocky surfaces,
thin atmospheres, few or no moons and no rings.
The closest planet to the sun
is called Mercury.
It's the smallest planet in the solar system
and it doesn't have any moons.
Next, there's Venus.
It's the closest planet to Earth
and like Mercury, it doesn't have a moon.
Venus shines bright in the sky, like a star.
It's about the same size as Earth,
but you wouldn't wanna live on it.
It's the hottest planet in the solar system
and its atmosphere contains an unbreathable mixture
of carbon dioxide and sulfuric acid.
Next is our home planet, Earth.
Earth is the only planet known to have life on it.
The last terrestrial planet in our solar system is Mars.
Mars has a very thin atmosphere of carbon dioxide
and it has two moons.
We've sent robots called rovers to Mars
in order to explore the planet surface.
The planets on the other side of the asteroid belt
are called the outer planets.
And unlike the inner planets, they're not made out of rock,
instead, they're made out of gases and liquids
and they have many moons and rings
and they're much, much colder
and much, much bigger than the terrestrial planets.
For instance, the planet Jupiter is so big
that it could fit about 1,300 Earths inside of it.
We call Jupiter a gas giant, because,
you guessed it, it's giant and made up of gas.
Its atmosphere is mostly made up of hydrogen and helium.
It has more than 50 moons.
One of Jupiter's moons, Ganymede,
is bigger by volume than the planet Mercury is.
Jupiter spins really fast on its axis.
This means that a day on Jupiter
is a little less than 10 hours long.
If you travel another 650 million kilometers
or so from Jupiter, you'd see Saturn,
another gas giant.
In 1610, Galileo Galilei became the first person
to see Saturn's rings.
Because his telescope wasn't strong enough,
he couldn't tell what they were.
He thought it looked like the planet had ears.
Even though Saturn's rings look smooth from a distance,
they're actually made out of rocks and pieces of ice
that orbit the planet
because of Saturn's gravitational pull.
The next planet is called Uranus.
It's the sideways planet.
Uranus has smaller rings than Saturn does
and it's so far away from the Earth
that we can only see it with a telescope.
Even farther away from Earth,
is the big and blue planet, Neptune.
Because Neptune is so far away from the sun,
it's really cold here.
The average temperature of Neptune
is about negative 214 degree Celsius.
It's also the windiest planet in our solar system
with winds going at more than 2000 kilometers per hour.
So if you ever visit, bundle up.
The planets don't all take the same amount of time
to orbit the sun.
For example, it takes Jupiter 12 years
to orbit the sun just once.
And the same amount of time,
Mercury has already orbited the sun nearly 50 times
and Neptune hasn't even made it around once.
Although humans have visited the moon,
we haven't built a rocket ship that can allow us
to visit our neighboring planets yet.
We've been able to learn more about our solar system
by using other kinds of technology.
Humans have built incredible telescopes
that allow us to see into our solar system and beyond,
and we've sent probes to other planets
and captured stunning images.
Even with all this research,
scientists are still learning new things
about our solar system
and its place in the rest of the universe.
So maybe one day you could help solve some
of the solar system's great mysteries too.