Modeling Subsurface Origins and Transport of Methane on Mars

Abstract:

Methane has been detected in the Martian atmosphere by both remote sensing and in situ measurements. A variety of subsurface methane production mechanisms have been proposed, such as (1) abiotic synthesis associated with water–rock reactions in the Martian crust, (2) breakdown of organic matter in Martian soils and crust, and (3) biotic formation through a metabolic process. Following methane production, there are also a variety of transport mechanisms that can bring methane to the surface. The six methane spikes detected by the Tunable Laser Spectrometer, on board the Curiosity rover in Gale crater, suggest that a pulse transport mechanism is at work. One possible mechanism is as follows. The transport of methane from the warmer subterranean region to the surface can also include transport of water vapor, brine water and dissolved minerals. Closer to the surface where temperatures are lower, ice can form and minerals precipitate, sequestering methane in the form of clathrate, adsorbed on minerals or trapped as gas bubbles in ice. In spring, when the temperatures on Mars return to warmer values, some of the ice collapses or partially melts, releasing methane into the atmosphere. If the methane emission site is close to the detector, a pulse emission event will result in a methane spike. In this study, we model this subsurface transport mechanism, and explore what characteristics of the source can be preserved at the surface that can be used to constrain the origin of methane, such as the chemical compositions of the released gas plume, e.g., H₂ and C₂H₆. The results from this study will help future Mars missions design their observational techniques and strategies.