Wikijunior:Solar System/Saturn/Iapetus

Iapetus is a moon of Saturn.

How big is Iapetus?

Iapetus is the third-biggest moon of Saturn, and is about 1436 km wide.

What is its surface like?

Iapetus features two hemispheres of differing colors.

From space, Ieaptus' two-tone colour is quite obvious. One hemisphere is a dark reddish-brown colour, while the other, while the other is bright and heavily cratered. The effect is like a ying-yang symbol.

Scientists don't know where the material covering the dark hemisphere comes from, but they think it might come from space or from inside Iapetus. If it came from space, it might have come from meteroites or the surface of comets, or it might have been knocked off from another moon of Saturn, Phoebe. If the material came from the inside of Iapetus, it might have come from cryovolcanoes or evaporation of water ice.

The equatorial ridge of Iapetus.

When Cassini flew by on Decembr 31, 2004, a ridge was discovered on Iapetus. It is 1300 km long, 20 km wide, and 13 km high. It follows Iapetus' equator almost perfectly, and is heavily cratered, and therefore ancient.

For now, scientists are not sure of the origins of the ridge. One theory is that the ridge is icy material that rose from inside the moon and solidified. The other is that Iapetus once grazed the outer edges of Saturn's rings.

How long is a day on Iapetus?

One day on Iapetus is equal to 79.32 days on Earth, or about 79 days, 7 hours and 41 minutes. It takes the same amount of time to finish an orbit around Saturn. This means that the same side of this moon is always facing Saturn.

What is it made of?

Iapetus is made of mostly ice, with a small amount of rock.

How much would Iapetus' gravity pull on me?

If you were standing on Iapetus, you would weigh about 1/40 of what you do on Earth.

Who is it named after?

When Iapetus, Tethys, Dione, and Rhea were discovered, they were named Sidera Lodoicea ("the stars of Louis") to honour king Louis XIV. However, astronomers called them and Titan Saturn I through Saturn V. Once Mimas and Enceladus were discovered, in 1789, the numbering scheme was extended to Saturn VII.

The name Iapetus was suggested by astronomer John Herschel (son of William Herschel, also an astronomer) in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope

Iapetus is a Titan from Greek mythology. He was son of Uranus and Gaia, and father (by an Oceanid named Clymene or Asia) of Atlas, Prometheus, Epimetheus, and Menoetius. Through Prometheus and Epimetheus and Atlas he is an ancestor of the human race.

How was it discovered?

Iapetus was discovered by Giovanni Cassini on October 25, 1671.