Volatile

Definition

In planetary science, volatiles are chemical elements and compounds with low boiling points typically associated with a planet’s or Moon’s crust and/or atmosphere. Some examples include nitrogen (N or N₂), water, carbon dioxide, ammonia, hydrogen (H or H₂), methane, and sulfur dioxide. These compounds or elements, in the solid state, are often significant components of the crusts of moons and planets. Planetary scientists often classify volatiles with exceptionally low melting points, such as hydrogen and helium, as gases, while those volatiles with melting points above about 100 K are classified as ices. Here, the terms “gas” and “ice” can be applied 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 majority of the “gas” and “ice” in their interiors is liquid. The Earth’s Moon has a very low volatile content. Its crust contains oxygen...