Modeling barometric pumping of martian methane: Implications for Perseverance sample timing and gas loss from drilled cores

Abstract

There are many challenges surrounding the interpretation of martian methane signatures. Atmospheric methane variations detected by the Sample Analysis at Mars (SAM) instrument on board the Curiosity rover remain difficult to explain given the lack of a confirmed methane transport mechanism from subsurface sources. Furthermore, the biogenic or abiogenic origin of martian methane cannot be determined outside of isotopic analysis in an Earth-based laboratory. Building on our previous work modeling barometrically driven seepage of methane through fractured rock coupled to a simplified atmospheric mixing scheme, we now use the same model framework to estimate the methane concentration in the shallow subsurface. Our results indicate that subsurface methane levels also exhibit strong seasonal and diurnal variability, with peak concentrations occurring during specific windows of time that depend on both solar and atmospheric forcing.

This insight has implications beyond Gale crater. At Jezero crater, where the Perseverance rover is collecting samples for potential return to Earth, strategic selection of sampling times could enhance the chances of recovering methane-bearing rock. Our results suggest that the timing of sample collection – both time of day and time of year – can significantly affect the likelihood of capturing methane within the collected cores if barometric pumping is a significant driving factor. Sample timing optimization could increase the potential for detecting organics or signatures of habitability in Mars Sample Return, augmenting the overall scientific return of the Mars 2020 mission and possibly bringing us closer to understanding the origin of methane on Mars. However, a preliminary analysis of methane loss rates from collected samples indicate that unless sample tubes can be sealed within a few hours of collection, the majority mass fraction of methane is likely to escape.