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ice
A term used by planetary scientists to refer to a variety of volatile substances, including water, methane, and ammonia, when in their solid state. Water-ice is an important geological material on many of the outer planet satellites.
Under various conditions ice can have viscosities and flow properties similar to those different types of molten rock, and therefore can result in the formation of similar geologic structures. Ice that is at near freezing temperatures (273 K) and low pressure (less than 1,000 bars) – Ice I – has different physical properties than ice at lower temperatures and higher pressures. (E.g. Ice II is stable at 200 K and 6,000 bars, while Ice VI is stable at 200 K and 15,000 bars.) These phases of ice have different densities and flow properties that may be expressed through tectonic and volcanic processes on icy satellites. When these ices contain small amounts of impurities, such as ammonia, they are known as clathrates, and have a lower melting temperature than pure water-ice. This may be a factor in volcanic processes on certain large outer satellites.
Related category
• INORGANIC CHEMISTRY
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