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Ganymede

Ganymede is the largest satellite in the solar system. It is larger in diameter than Mercury but only about half its mass. Ganymede is much larger than Pluto.

Ganymede's surface is a roughly equal mix of two types of terrain: very old, highly cratered dark regions (left), and somewhat younger (but still ancient) lighter regions marked with an extensive array of grooves and ridges (right). Their origin is clearly of a tectonic nature, but the details are unknown. In this respect, Ganymede may more similar to the Earth than either Venus or Mars (though there is no evidence of recent tectonic activity).

Galileo's first flyby of Ganymede discovered that Ganymede has its own magnetosphere field embedded inside Jupiter's huge one. This is probably generated in a similar fashion to the Earth's: as a result of motion of conducting material in the interior.

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Metis

Metis was a Titaness who was the first wife of Zeus (Jupiter).

Metis (together with another moon, Adrastea) lie within Jupiter's main ring. They may be the source of the material comprising the ring.

This image of Metis was taken by Galileo's solid state imaging system between November 1996 and June 1997. Although Metis was discovered by Voyager, it was no more than a point of light on images. This Galileo image is the the first image of the small moon that shows its irregular shape. Metis orbits Jupiter in the zone between the planet's ring and the larger Galilean satellites. The longest dimension of Metis is approximately 60 kilometers (37 miles) across. (Courtesy of NASA/Cornell University)

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Leda

Leda was the queen of Sparta and the mother of Helen and the twins Castor and Pollux.
The picture shown on the left is the Discovery image of Leda.

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Overview

Jupiter has 39 fascinating moons and a ring system. The four Galilean satellites; Io, Europa, Ganymede, and Callisto, are among the most interesting of all solar system bodies, particularly Io, with its active volcanism, and Europa with the possibility of a water environment habitable to life. The Galileo spacecraft, in exploring the moons of Jupiter will search for signs of an atmosphere around the moons, and look for clues about the interior. Scientists are very curious to discover whether Europa, in particular, has a detectable atmosphere.

Other moons, in order are; Metis, Adrastea, Amalthea, Thebe, Leda, Himalia, Lysithea, Elara, Ananke, Carme, Pasiphae, Sinope and S/1999 J1. These moons are part of a class of moons called the "Small Moons". Jupiter's moons are named after mythological figures.

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Europa

Europa's surface is not at all like anything in the inner solar system. It is exceedingly smooth: few features more than a few hundred meters high have been seen. The prominent markings seem to be only albedo features with very low relief.

There are very few craters on Europa; only three craters larger than 5 km in diameter have been found. This would seem to indicate a young and active surface. However, the Voyagers mapped only a fraction of the surface at high resolution. The precise age of Europa's surface is an open question.