Volatiles: Difference between revisions
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In [[planetary science]], '''volatiles''' are that group of [[chemical elements]] and [[chemical compounds]] with [[Volatility (chemistry)|low boiling points]] that are associated with a [[planet]]'s or [[moon]]'s [[crust]] and/or [[atmosphere]]. Examples include [[nitrogen]], [[water]], [[carbon dioxide]], [[ammonia]], [[hydrogen]], and [[methane]], all compounds of C, H, O and/or N, as well as [[sulfur dioxide]]. In astrogeology, these compounds, in their solid state, often comprise large proportions of the crusts of [[moons]] and [[dwarf planet]]s. In terrestrial geology, the term more specifically refers to components of [[magma]] (mostly [[water vapor]] and carbon dioxide) that affect the appearance and strength of [[volcanoes]]. Volatiles in a magma with a high viscosity, generally [[felsic]] with a higher silica (SiO<sub>2</sub>) content, tend to eruptions that are explosive. Volatiles in a magma with a low viscosity, generally mafic with a lower silica content, tend to vent and can give rise to a [[lava fountain]].
Planetary scientists often class volatiles with exceptionally low melting points, such as [[hydrogen]] and [[helium]], as '''gases''' (as in [[gas giant]]), while those volatiles with melting points above about 100 K are referred to as '''ices'''. The terms "gas" and "ice" in this context can apply to compounds that may be solids, liquids or gases. Thus, [[Jupiter]] and [[Saturn]] are referred to as "gas giants", and [[Uranus]] and [[Neptune]] are referred to as "ice giants", even though the vast majority of the "gas" and "ice" in their interiors is liquid.