Formation and Stability of Salty Soil Seals in Mars‐Like Conditions. Implications for Methane Variability on Mars

Abstract

Methane spikes observed in the Martian atmosphere require the abrupt release of large amounts of methane from the Martian subsurface. The mechanism for such release has not been identified. We tested whether gas traps can form under Mars‐like conditions in the shallow Martian regolith due to salt migration in the icy soil. Experiments were performed on various soil samples in a Mars Simulation Chamber comprising different perchlorate salts and water concentrations mixed with JSC Mars‐1A. Inside the chamber, the samples were exposed to a range of temperatures from −20°C to 10°C and maintained CO2 gaseous pressure between 8 and 10 mbars. As a methane analog, Neon was injected periodically underneath the soil sample. It was found that over a wide range of Mars‐like soil parameters, a gas impermeable soil seal can form over a relatively short period (3–13 days) but requires 5%–10% of perchlorate salt content in the soil. It was determined that such a seal could sustain several mbars of neon above the Martian atmospheric pressure in the soil. Based on our experiments, substantial amounts of gaseous methane may accumulate under the soil seal and get released abruptly into the atmosphere upon seal cracking. An abrupt release of methane from the shallow subsurface may help explain methane variability at the Martian surface, as the Mars Science Laboratory detected.

Reaction of size-selected iron-oxide cluster cations with methane: a model study of rapid methane loss in Mars’ atmosphere

“…14 Observation by the Curiosity rover found temporary spikes of methane and its rapid loss, but the mechanism of the loss has not been elucidated yet. Although some previous studies suggested a very local, small methane source near the landing site of the Curiosity rover, 15,16 an alternative possibility is the effective loss of methane via chemical reaction that is not considered in photochemical models. Mars’ soil is rich in iron oxides, where storms of iron-oxide particles (dust devils) occur very frequently.…”