NASA spacecraft, Galileo, has found evidence that a vast sea of liquid water lies beneath the surface of Jupiter's planet-sized moon Ganymede. Magnetic field measurements taken by Galileo suggested that a thick layer of water is hidden about 120 miles beneath the moon's ice-and-frost-covered surface. The discovery was announced by Margaret Kivelson at a meeting of the American Geophysical Union at Los Angeles. Kivelson is a planetary scientist at the University Of California.

Kivelson's team had in August announced compelling evidence of a liquid ocean less than five miles beneath the surface of another jovian moon Europa.
Frozen water is plentiful in the solar system. But water in liquid form is considered a crucial ingredient for life to develop and a key signpost in the search for extra-terrestrial life.
Ganymede now joins the few bodies in the solar system showing signs of liquid water below the surface, the others being Europa, the geologically dead jovian moon Callisto and the planet Mars. Earth has the only confirmed bodies of water in liquid form anywhere in the cosmos. Bureaui Report