Icy moons are a class of

natural satellite A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are colloquially referred to as moons, a deriv ...

s with surfaces composed mostly of

ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...

. 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 or other polymorph of water ice. The prime example of this class of object is Europa. Icy moons warmed by

tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...

s may be the most common type of

celestial body An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists within the observable universe. In astronomy, the terms ''object'' and ''body'' are of ...

in the galaxy to have liquid

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

, and thus the most likely type of object to possibly have

-based

life Life, also known as biota, refers to matter that has biological processes, such as Cell signaling, signaling and self-sustaining processes. It is defined descriptively by the capacity for homeostasis, Structure#Biological, organisation, met ...

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

Orbits

Most known large icy moons belong to giant planets, whose orbits lie beyond the Solar System's frost line; the remainder (such as Charon and Dysnomia) formed around dwarf planets such as

Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of Trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Su ...

and , typically in large impacts not unlike the impact thought to have formed Earth's moon. In the case of icy gas giant satellites, 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. Europa is thought to contain 8% ice and water by mass with the remainder rock. Jupiter's outer two

Galilean moons The Galilean moons (), or Galilean satellites, are the four largest moons of Jupiter. They are, in descending-size order, Ganymede (moon), Ganymede, Callisto (moon), Callisto, Io (moon), Io, and Europa (moon), Europa. They are the most apparent m ...

Ganymede and Callisto contain more ice since they formed further from the hot proto-Jupiter. Saturn's moon

Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...

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

Images

Image:PIA01130 Interior of Europa.jpg, Europa is thought to have a subsurface ocean Image:Ganymede-moon.jpg, False-color image of Ganymede Image:Callisto_-_July_8_1979_(38926064465).jpg, Callisto showing frost deposits Image:Mimas moon.jpg, Mimas has a density of 1.1 g/cm³ Image:Successful Flight Through Enceladus Plume.jpg, Active plumes on Enceladus Image:Titan multi spectral overlay.jpg, False-color image of

showing surface and atmospheric details Image:Miranda - January 24 1986 (30906319004).jpg, Miranda has a scarred surface File:PIA00040 Umbrielx2.47.jpg, A potential frost deposit on Umbriel's pole Image:Tritoncloud.jpg, A cloud over the limb of Triton

References

{{DEFAULTSORT:Icy Moon Moons

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

Orbits

Images

See also

References