which of jupiter’s moons is believed to be covered with water ice
Galilean moons 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.[14][15] 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.[16] Io is anhydrous and likely has an interior of rock and metal.[14] Europa is thought to contain 8% ice and water by mass with the remainder rock.[14] These moons are, in increasing order of distance from Jupiter:
Formation and evolution of the Solar System The giant planets (Jupiter, Saturn, Uranus, and Neptune) formed further out, beyond the frost line, which is the point between the orbits of Mars and Jupiter where the material is cool enough for volatile icy compounds to remain solid. The ices that formed the Jovian planets were more abundant than the metals and silicates that formed the terrestrial planets, allowing the giant planets to grow massive enough to capture hydrogen and helium, the lightest and most abundant elements.[10] Planetesimals beyond the frost line accumulated up to 4 M⊕ within about 3 million years.[30] Today, the four giant planets comprise just under 99% of all the mass orbiting the Sun.[note 2] Theorists believe it is no accident that Jupiter lies just beyond the frost line. Because the frost line accumulated large amounts of water via evaporation from infalling icy material, it created a region of lower pressure that increased the speed of orbiting dust particles and halted their motion toward the Sun. In effect, the frost line acted as a barrier that caused material to accumulate rapidly at ~5 AU from the Sun. This excess material coalesced into a large embryo (or core) on the order of 10 M⊕, which began to accumulate an envelope via accretion of gas from the surrounding disc at an ever-increasing rate.[34][35] Once the envelope mass became about equal to the solid core mass, growth proceeded very rapidly, reaching about 150 Earth masses ~105 years thereafter and finally topping out at 318 M⊕.[36] Saturn may owe its substantially lower mass simply to having formed a few million years after Jupiter, when there was less gas available to consume.[30][37]