Icy moon

Icy moons are believed to be a common class of natural satellites or planetoids with surfaces composed mostly of ice. An icy moon may harbor an ocean underneath the surface, and possibly include a rocky core of silicate or metallic rocks. It is thought that they may be composed of ice II. The prototype of this class of object is Europa.

Icy moons warmed by tides may be the most common type of object to have liquid water, and thus the type of object most likely to have water-based life.

Some icy moons exhibit cryovolcanism, as well as geysers. The best studied example is Enceladus.

Icy moons

Known icy moons belong to giant planets, whose orbits lie beyond the Solar Systems frost line. An additional requirement is that a moon did not form in the inner region of a proto-satellite disk, which is too warm for ices to condense.

Jupiter's 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. Jupiter's outer two Galilean moons Ganymede and Callisto contain more ice since they formed further from the hot proto-Jupiter.

Saturn's moon Titan looks and behaves more like Earth than any other body in the Solar System. Titan is known to have stable pools of liquid on the surface.

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  Europa is believed to have a subsurface ocean

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  False-color image of Ganymede

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  Callisto showing frost deposits

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  Titan showing surface and atmospheric details

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  Plumes above the limb of Enceladus

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  A potential frost deposit on Umbriel

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  A cloud over the limb of Triton

small icy moons

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  Mimas 400km in diameter with a density of 1.1 g/cm³

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  Proteus^{[citation needed]} also 400km is non-spherical

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  Miranda 470km

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  Active Enceladus 500km