This illustration portrays possible ways that methane might be added to Mars' atmosphere (sources) and removed from the atmosphere (sinks). A molecule of methane consists of one atom of carbon and four atoms of hydrogen. Comet dust brings organic chemicals to Mars from space. Ultraviolet radiation (UV) from the Sun can induce reactions that generate methane from these chemicals, which is probably responsible for a low, global background level of methane everywhere in the atmosphere of Mars. UV can also generate methane from organic materials in the Martian surface. Other possible sources for methane on Mars include reactions between water and olivine, and, hypothetically, microbes. Methane generated underground in the distant or recent past might be stored within lattice-structured methane hydrates called clathrates, and released by the clathrates at a later time, so that methane being released to the atmosphere today might have formed in the past.
Winds on Mars can quickly distribute methane coming from any individual source, reducing localized concentration of methane. Methane can be removed from the atmosphere by sunlight-induced reactions (photochemistry). These reactions can oxidize the methane, through intermediary chemicals such as formaldehyde and methanol, into carbon dioxide, the predominant ingredient in Mars' atmosphere.