No matter where you are on Earth, you can usually look up into the night sky and see

the Moon.

Our Moon appears so big and bright because it's closer to Earth than any other planet

or moon.

But, our Moon isn't the only moon out there.

That's right!

In fact, some planets have a lot of moons.

A moon is a natural object that orbits anything larger than itself.

Moons come in many shapes and sizes.

Our solar system has eight planets and dozens of moons.

Almost every planet has 'em.

Mercury and Venus—the two planets closest to the Sun—have no moons at all.

Earth, on the other hand, has one rocky and rather large Moon.

It's about one-quarter the size of Earth.

Our Moon is the only other place in our solar system where humans have set foot.

What are some of the other interesting moons we know about?

Well, Mars has two moons named Phobos and Deimos.

They're dark and lumpy and at least 100 times smaller than Earth's moon.

Jupiter has more than 70 moons!

Several of them have very unusual features.

For example, Ganymede is the largest known moon in our solar system.

You can actually see it from Earth with just a pair or binoculars.

Jupiter's moon Io is covered in volcanos

And there is thought to be a giant salt water ocean under the icy surface of Jupiter's

moon Europa!

NASA is planning a future mission to investigate Europa and its underground ocean.

Saturn has more than 80 moons in total.

And at least two of those are ocean moons, too!

They are called Titan and Enceladus.

NASA's Cassini mission discovered that the underground ocean on Enceladus shoots jets

of icy particles from cracks in the moon's surface and out into space!

Uranus has more than 20 moons.

Its larger moons, like this one named Ariel, are thought to be made of half water ice and

half rock.

Scientists have discovered more than a dozen moons orbiting Neptune.

It's largest moon, called Triton, has volcanoes with icy lava flows.

Brr!

Volcanoes, underground oceans, and icy jets—what do you think we'll discover on moons next?

Find out more about moons at NASA Space Place.