Jupiter has a total of 63 known satellites. The four great moons
of Jupiter were discovered by Galileo Galilei (1564–1642) in
Jan. 1610, and are called the Galilean satellites after their
discoverer. Their names are Io, Europa, Ganymede, and Callisto.
Like our Moon, the satellites always keep the same face turned
toward the planet they circle. Jupiter's four largest moons all
have thin atmospheres. A carbon dioxide atmosphere envelops
Callisto; Europa and Ganymede each have thin oxygen atmospheres;
and Io's contains sulfur dioxide. Information Please® Database,
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