Curiosity rover TLS-SAM measurements consistent with localized methane containment and transport by 3-D atmospheric circulation in Gale crater

The Curiosity rover has traversed more than 30 km from the landing site at the very bottom of Gale crater and has climbed more than ∼800 m into the Mt. Sharp foothills over more than five Martian years. During nighttime, downslope winds originating from both Mt. Sharp and crater rims would prevent the nighttime accumulation of methane released along the slopes above the cold pool and facilitate the convergence and accumulation of methane in the bottom of the crater [Figure, Panel A]. As a result, any methane released along the slopes at night is quickly transported downslope. After sunrise [Figure, Panel B], the crater circulation transitions to an upslope regime. The reversal of the circulation should transport the methane accumulated in the bottom of the crater upslope as shown in MRAMS model tracer fields, that also indicate a substantial horizontal mixing that rapidly dilutes the methane-enriched air mass. Any methane released along the slopes is transported horizontally and vented out of the crater. MRAMS model predicts a methane front of peak values to pass higher elevations at increasingly later times after sunrise, moreover later in the morning (~10:00 LMST), but usually with highly and increasingly diluted with time methane values. At mid-morning (Figure, Panel C), upslope circulation along surface rims is fully developed and there is a clear horizontal divergence at bottom of crater where methane is highly diluted due to 3-D atmospheric mixing and increasingly advected upslope out of crater. At dusk, downslope winds starts to develop through sloped surfaces of Mt. Sharp, as well as the cold pool of air at the bottom of the crater, which begins to trap methane released from the ground to start the cycle again (Figure, Panel D). Consistent with [Pla-García et al. 2019] and [Moores et al. 2019] the 3-D crater circulation supplemented by the growth and collapse of the PBL is necessary to explain the TLS-SAM methane observations.