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.
Synthesis of methane
Production of methane on the surface of Mars would likely be via the Sabatier reaction:
- CO2 + 4H2 ↔ CH4 + 2H2O
The forward reaction takes place in the presence of high temperatures and pressures, in the presence of a nickel catalyst. All of the raw materials should be available on the surface of Mars:
- The atmosphere contains a high proportion of carbon dioxide.
- Hydrogen could be obtained by electrolysis of indigenous water (although some schemes call for the hydrogen to be imported).
This process could also be used during a trip to or from Mars to scrub CO2 from a spacecraft atmosphere.
Instead of nickel, a catalyst made out of ruthenium on alumina could be used.
Uses for methane
Methane works well as a rocket fuel, and a number of LOX/methane fueled rockets are under development, including the XCOR XR5M15 and Northrop Grumman TR408.
Methane fuel cells have recently been demonstrated, and these would work well for powering rovers, semi-portable equipment or as backup generators.
Carbon in the form of pyrolytic graphite could be recovered from methane by pyrolyzing it:
- CH4 + heat   →   2H2 + C
The graphite so formed could be used for ablative surfaces, reinforcement of polymer materials, furnace linings or control elements in nuclear reactors.
