Seasonality in Mars atmospheric methane driven by microseepage, barometric pumping, and adsorption

Abstract

Measurements of atmospheric methane by the Curiosity rover's SAM-TLS instrument are providing evidence of seasonality with bimodal peaks in concentration. Given methane's short atmospheric lifetime relative to geological timescales, its presence implies a replenishing source, and the observed seasonality demands the proposition of a modulation mechanism. This paper focuses on the modulation mechanism. Our modeling study shows that barometric pumping driven by seasonal variation of atmospheric pressure, along with adsorption and desorption of methane in the shallow subsurface driven by temperature change, can explain the observed bimodal peaks in the seasonal variations of methane concentration. In the model, an active, continuous, steady-state deep source of methane is assumed, and carbon dioxide serves as the carrier gas for producing seasonal variation in the upper part of the sedimentary column for methane and other possible trace gaseous constituents. Our work also presents a comprehensive flow chart for modeling the microseepage of methane on Mars from first principles.