Astronomy Journal Entry

New Moons Discovered Around Jupiter (May 23, 2003)

Astronomers at the University of Hawaii report finding at least twenty new moons in orbit around Jupiter. The satellites are moving in wildly erratic orbits. Some are flying in backwards or retrograde orbits that go in the opposite direction of Jupiter's rotation. Some of the moons orbit within 5 million miles (8 million kilometers) of the planet. At least one of them swings up to 40 million miles (64 million km) away.

The newly-found satellites likely formed from collisions of other moons of Jupiter. Their discovery brings the total number of moons orbiting Jupiter to at least 60, although most are quite small.

Until a few years ago, only 16 of the moons had been discovered. But more advanced telescopes and large digital cameras have led to an explosion of discoveries since 1999.

The new discoveries put Jupiter way ahead of Saturn, the planet with the next highest total. It has "only" 31 moons.

Galileo discovered Jupiter's first four moons, Io, Europa, Ganymede, and Callisto, about 400 years ago. He was the first person to use a telescope to observe the sky.