Its rings are probably composed of very small grains of rocky material, but no ice unlike Saturn's rings. These ring particles are probably lost to Jupiter's atmospheric and magnetic drag comparatively quickly. At latest count in early 2001, Jupiter has been found to have at least 28 satellites orbiting outside of its rings. By order of their increasing distance from the giant planet, the four moons are Io, Europa, Ganymede, and Callisto. As with Earth and its Moon , Jupiter's rotation is gradually slowing down from the tidal drag of the large Galilean moons, and these tidal forces are also gradually causing the moons' orbits to move farther away from the planet.
Tidal forces are also significantly heating the two innermost Galilean moons.
The gravitational pull of the mother planet and sister moons constantly yank and bend Io, heating it up in the same way repeated twisting heats up a metal wire. Two percent larger than Earth's Moon, Io has a molten interior and occasionally tremendous volcanic eruptions. This the intense heat probably caused any water present to evaporate billions of years ago, but it has generated a thin atmosphere of sulfur dioxide. NASA Cassini-Huygens Mission to Saturn and Titan Larger image. Jupiter with Europa and its shadow.