The first definitive detection of methane gas on Mars was reported in 2009. The atmosphere of Mars is highly oxidized, consisting mainly of carbon dioxide gas (95%). With a photochemical lifetime of only 400 years, methane should not be present unless it was released on an ongoing basis. On Earth, about 95% of the methane is produced by biological organisms and the rest is produced by geochemistry. The presence of methane on Mars demonstrates that Mars is an active planet which is actively releasing trace gases that provide a window into its internal processes.
The release of methane on Mars suggests that Mars might now harbor an active microbial life below the surface, but it is also possible that the release of methane is driven by chemical reactions of hot rock with water and carbon dioxide deep underground. The seasonal release of methane suggests thermal control of the release mechanism.
A possibility that thus far has not been considered is that methane can be trapped within the crystal structure of water to form methane clathrate which on the Earth is found in permafrost and at the bottom of the ocean. The phase diagram of methane clathrate shows that it may be possible that methane clathrate would be stable in the Martian environment with an atmospheric pressure of 600 Pa and temperatures averaging 218 K at the surface. Underground, the pressure would be higher making the formation of methane clathrate more likely.
Although scientists are very eager to find some kind of life on Mars, the seasonal variation of atmospheric methane could just be due to the decomposition and regeneration of methane clathrate, or some other physical or chemical process. Let us not forget that Titan, one of Saturn’s moons, has lakes of liquid methane on its surface. Jumping to the conclusion that the presence of methane indicates life is not good science. Proof of life will have to come from biology, and not necessarily from chemistry.
 Mumma, MJ; Villanueva, GL; Novak, RE; Hewagama, T; Bonev, BP; DiSanti, MA; Mandell, AM; Smith, MD, Strong release of methane on Mars in northern summer 2003, Science, Volume: 323, Issue: 5917, Page: 1041-1045, Year: FEB 20 2009
 Laura A. Stern, Stephen H. Kirby, William B. Durham, Peculiarities of Methane Clathrate Hydrate Formation and Solid-State Deformation, Including Possible Superheating of Water Ice, Science, 27 September 1996, Vol. 273 no. 5283 pp. 1843-1848