Data and model investigation of Martian methane and other trace gases

Derived trace abundances of methane from recent observations of the Mars atmosphere (Krasnopolsky et al. 2004; Krasnopolsky 2012; Formisano et al. 2004; Geminale et al. 2008, 2011; Mumma et al. 2009; Fonti & Marzo 2010) showed that methane gas is unexpectedly variable in both abundance (~0-70 parts per billion) and spatial distribution. Interest has arisen in investigating possible source and removal mechanisms because of implications of current or recent biological or geological activity, but available seasonal and spatial information is sparse. Questions have been raised regarding derived methane abundances (Zahnle et al. 2011), and MSL's first measurements have not confirmed detection of methane (Webster et al., 2013), but the observations include commonalities suggesting they are observing a common species. To increase the temporal coverage of available methane observations, an expansion of the work of Fonti & Marzo (2010) was carried out, increasing the twelve 5 degree L8 interval average maps to all available 10 degree L8 intervals with enough spectra in the 3 Martian years of Mars Global Surveyor Thermal Emission Spectrometer data (L8 103° MY 24 to L8 90° MY 27). A procedure was developed to significantly accelerate the analysis process to allow for this expansion work, and resulting maps have been produced. The NASA Ames Mars Global Circulation Model (GCM) was utilized to investigate possible source locations, sizes and release rates, and destruction timescales required to reproduce the observed methane spatial and temporal distributions of Mumma et al. (2009); Fonti & Marzo (2010) and Geminale et al. (2011). Parameters required to reasonably reproduce the observed variations in each scenario were established and compared to determine whether common source characteristics exist. The different observations do not suggest similar source locations or seasonal behavior, but do share similar peak mixing ratios and destruction lifetimes ~2 orders of magnitude shorter than expected through photochemical removal only. An additional GCM investigation has been conducted to explore temperature dependent fractionation of isotopic CO2 using tools developed in methane simulations and provide predictions for future spatially resolved measurements (Livengood et al. 2013).