<P> Some models predict that there may have been several generations of Galilean satellites in Jupiter 's early history . Each generation of moons to have formed would have spiraled into Jupiter and been destroyed , due to tidal interactions with Jupiter 's proto - satellite disk , with new moons forming from the remaining debris . By the time the present generation formed , the gas in the proto - satellite disk had thinned out to the point that it no longer greatly interfered with the moons ' orbits . Other models suggest that Galilean satellites formed in a proto - satellite disk , in which formation timescales were comparable to or shorter than orbital migration timescales . Io is anhydrous and likely has an interior of rock and metal . Europa is thought to contain 8 % ice and water by mass with the remainder rock . These moons are , in increasing order of distance from Jupiter : </P>
<P> Some models predict that there may have been several generations of Galilean satellites in Jupiter 's early history . Each generation of moons to have formed would have spiraled into Jupiter and been destroyed , due to tidal interactions with Jupiter 's proto - satellite disk , with new moons forming from the remaining debris . By the time the present generation formed , the gas in the proto - satellite disk had thinned out to the point that it no longer greatly interfered with the moons ' orbits . Other models suggest that Galilean satellites formed in a proto - satellite disk , in which formation timescales were comparable to or shorter than orbital migration timescales . Io is anhydrous and likely has an interior of rock and metal . Europa is thought to contain 8 % ice and water by mass with the remainder rock . These moons are , in increasing order of distance from Jupiter : </P>
which of jupiter 's moons is believed to be covered with water ice
which of jupiter 's moons is believed to be covered with water ice
Europa
Europa