Samenvatting

The goal of this study was to explain various measurements of atmospheric methane on Mars performed by the PFS instrument on-board the European Mars Express mission and from ground based observations. In order to reach this goal a layer of methane was assumed to exist in porous near surface layers of Mars. Simulations using varying sets of parameters with respect to the subsurface composition of Mars have indicated that a scenario where subsurface methane ice is found is most likely to be present at a methane concentration of 2%.
In order to explain the measured gas flux of 4 gs-1 using earlier measurements as a reference, the total surface area of the subsurface methane deposits has been found to be about only 25,000 square metres. After 55 orbits, the methane ice deposits within the subsurface are found at > 75 metres depth. These deposits have been evaluated in their long-time stability. It has been found that methane gas flux over the Martian surface decreases with an order of magnitude in a time span of 300 years. The stability of ice deposits is thus still contested.
Whilst the introduction of a larger surface area for methane sources increases the gas flux, the methane would still disappear within a time span of 10,000 years. Therefore it is concluded that methane is not stable over geological time scales and that the measurements can only be explained by a very recent excavation of such an area below the surface.