||This article needs attention from an expert in Volcanoes or Solar System. (February 2008)|
A cryovolcano (colloquially known as an ice volcano) is a volcano that erupts volatiles such as water, ammonia or methane, instead of molten rock. Collectively referred to as cryomagma or ice-volcanic melt, these substances are usually liquids and form plumes, but can also be in vapour form. After eruption, cryomagma condenses to a solid form when exposed to the very low surrounding temperature. Cryovolcanoes form on icy moons, and possibly on other low-temperature astronomical objects (e.g. Kuiper belt objects).
One potential energy source on some solar system bodies for melting ices and producing cryovolcanoes is tidal friction. It has also been suggested[by whom?] that translucent deposits of frozen materials could create a subsurface greenhouse effect that would accumulate the required heat.
Signs of past warming of the Kuiper belt object Quaoar have led scientists to speculate that it exhibited cryovolcanism in the past. Radioactive decay could provide the energy necessary for such activity, as cryovolcanoes can emit water mixed with ammonia, which would melt at 180 K (−95 °C) and create an extremely cold liquid that would flow out of the volcano.
Indirect evidence of cryovolcanic activity was later observed on several other icy moons of the Solar System, including Europa, Titan, Ganymede, and Miranda. Cassini has observed several features thought to be cryovolcanoes on Titan, notably Sotra Patera, a feature regarded as "the very best evidence, by far, for volcanic topography anywhere documented on an icy satellite". Cryovolcanism is one process hypothesized to be a significant source of the methane found in Titan's atmosphere.
In 2007, observations by the Gemini Observatory showing patches of ammonia hydrates and water crystals on the surface of Pluto's moon Charon suggested the presence of active cryovolcanoes/cryogeysers. Subsequent observations by New Horizons in 2015 found that Charon has a youthful surface, supporting this idea. Pluto itself is also known to have several likely cryovolcanoes. 
|Cryovolcanism on Enceladus|
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