Simple organic element with one carbon atom and four hydrogen atoms. Methane gas has been detected from Earth on Mars in localized concentrations, but is intermittent and some controversy. It is a mystery how Methane could exist on Mars, when it would be destroyed in the atmosphere quickly. It would need to be replenished somehow. As Methane is a by-product of life on Earth, it is tantalizing to say that it is a sign of life. Other processes could generate it, such as Mud Volcanoes. Mars Trace Gas Orbiter will attempt to characterized Methane on Mars.