The atmospheres of planets in the solar system vary greatly in composition. The gas giants (Jupiter, Saturn, Uranus, and Neptune) are dominated by hydrogen (H₂) captured during their formation, so the principal trace elements in their atmospheres appear as fully hydrogenated gases (such as CH₄, NH₃, and H₂O). Atmospheres of the terrestrial planets (Venus, Earth, and Mars) are deficient in hydrogen and thus are strongly oxidizing. Consequently, hydrocarbon gases should be absent from their atmospheres if atmospheric processes alone govern their production and destruction.