Sub-diurnal methane variations on Mars driven by barometric pumping and
planetary boundary layer evolution
Abstract
In recent years, the Sample Analysis at Mars (SAM) instrument on board
the Mars Science Laboratory (MSL) Curiosity rover has detected methane
variations in the atmosphere at Gale crater. Methane concentrations
appear to fluctuate seasonally as well as sub-diurnally, which is
difficult to reconcile with an as-yet-unknown transport mechanism
delivering the gas from underground to the atmosphere. To potentially
explain the fluctuations, we consider barometrically-induced transport
of methane from an underground source to the surface, modulated by
temperature-dependent adsorption. The subsurface fractured-rock seepage
model is coupled to a simplified atmospheric mixing model to provide
insights on the pattern of atmospheric methane concentrations in
response to transient surface methane emissions, as well as to predict
sub-diurnal variation in methane abundance for the northern summer
period, which is a candidate time frame for Curiosity’s potentially
final sampling campaign. The best-performing scenarios indicate a
significant, short-lived methane pulse just prior to sunrise, the
detection of which by SAM-TLS would be a potential indicator of the
contribution of barometric pumping to Mars’ atmospheric methane
variations.