Martian Atmospheric Composition
METHANE ON MARS.
Although methane is not a major gas in the Martian atmosphere, it was recently discovered venting from three areas and identified as possible evidence for life below the surface (Krasnopolsky et al. 2004). Three areas in question are shown. Note that the Viking found no organic chemistry on Mars. Methane is the basic building block of all organic chemistry.
New on December 17, 2014: There is a new report that methane spikes have been found by MSL at Gale Crater. We are just now hearing the report. See the 52-minute press conference at http://mars.jpl.nasa.gov/msl/mission/science/researchpapers/. The methane and other organic molecules found might be due to bacterial life on Mars now.