Ice planet

An ice planet is a type of planet with an icy surface. Ice planets consist of a global cryosphere. Ice planets are bigger versions of Solar System's icy moons such as Europa, Enceladus, and Triton; dwarf planets Pluto and Eris, and many other icy Solar System bodies.
== Characteristics and habitability ==
Ice planets usually appear nearly white with geometric albedos of more than 0.9. An ice planet's surface can be composed of water, methane, ammonia, carbon dioxide (known as "dry ice"), carbon monoxide, or other volatiles, depending on its surface temperature. Ice planets would have surface temperatures below 260 K if composed primarily of water, below 180 K if primarily composed of CO and ammonia, and below 80 K if composed primarily of methane.
Ice planets are usually hostile to life as we know it because they are very cold, at least on the surface. Many ice planets may have subsurface oceans, warmed by their cores or tidal forces from another nearby body, specifically gas giants. Liquid subsurface water would provide habitable conditions for life, including fish, plankton, and microorganisms. Subsurface plants and microorganisms would not perform photosynthesis because sunlight is blocked by overlying ice; instead they produce nutrients using specific chemicals called chemosynthesis. Some worlds, if conditions are right, may have significant atmospheres and surface liquids like Saturn's moon Titan which could be habitable for exotic life forms.
== Pluto and candidates ==
Although there are many icy objects in the Solar System, there are no known ice planets (though Pluto was considered an ice planet until its reclassification in 2006). There are several extrasolar ice planet candidates, including OGLE-2005-BLG-390Lb, OGLE-2013-BLG-0341L b and MOA-2007-BLG-192Lb.
== See also ==
* Ocean planet
* Ice giant
* Snowball Earth
* Ice planets in science fiction
== References ==
Category:Types of planet
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