Summary

Description	NASA's Hubble Space Telescope recently caught an extraordinary planetary show that takes place only once a decade. With giant Jupiter taking center stage, the telescope witnessed a rare alignment of three moons around the enormous planet. The largest object in the Hubble image is the moon named Ganymede. Ganymede is more than 3,000 miles across and would be big enough to be called a planet if it orbited the sun. Joining Ganymede is Io - Jupiter's most unsettled moon. Slightly larger than our own moon, Io is the most volcanically active body in our Solar System. Io's elliptical orbit around Jupiter produces an irregular gravitational pull on the moon. This uneven tug of gravity causes Io's surface to swell and recede more than 300 feet and remain violently unstable. Hidden in the wings was the third moon, Callisto. Only detectable by its shadow, Callisto is a battered world devoid of any atmosphere or surface activity. From a front row seat the Hubble Space Telescope captured
Date	2004-12-03
Source	images.nasa.gov

Licensing

Public Domain (US Government Work)