Methane
Methane is the lightest of the hydrocarbons, consisting of a single carbon atom bonded to four hydrogen atoms in a tetrahedral configuration. It is volatile, and tends to break down quite quickly by being oxidized, so presence of atmospheric methane is often considered to be an indication of the presence of life. However, methane can also be produced be non-biological processes such as volcanic activity.
In 2004, the Mars Express mission detected methane in the Martian atmosphere at a level of approx. 10 parts per billion. This was later confirmed by Earth-based spectroscopy.
Methane is of particular interest for missions to Mars, as it may be possible to produce it in situ using locally-available raw materials. This would make it an ideal fuel for rovers and rocket engines. A number of LOX/methane fueled rockets are under development, including the XCOR XR5M15 and Northrop Grumman TR408.
