Callisto

From Gwn

Callisto

Discovered:	1610 CE
Named After:	Named after the Greek Princess
Relative Size:	.018 Earths
Satellites:	Satellite of Jupiter

Callisto is a moon of the planet Jupiter, discovered in 1610 by Galileo Galilei. It is the third-largest moon in the solar system, about 99% the size of the planet Mercury but much less massive.

Callisto's battered surface lies on top of an icy layer that is about 150 kilometers thick. A salty ocean in excess of 10 kilometers thick lay beneath the crust. The Ocean's presence is alters the magnetic fields around Jupiter and its moons. It was found that the Callistoan magnetic field varies (flows in various directions at different times) in response to the background magnetic field generated by Jupiter.

Beneath the ocean, Callisto has a strange interior that is not entirely uniform but does not vary dramatically. The interior is composed of compressed rock and ice, with the amount of rock increasing with depth due to partial settling of its constituents. Callisto has the lowest density of the four Galilean moons of Jupiter, only 1.86 g/cm³, and is about 40% ice and 60% rock/iron.