Mars Methane Mystery Linked to Daily Ground Temperature Swings

Methane detection on Mars has intrigued scientists since the early 2000s, with NASA's Curiosity rover measuring variable methane levels near the surface of Gale Crater since 2012. These measurements showed seasonal cycles, day-night differences, and occasional sharp methane spikes. However, the European ExoMars Trace Gas Orbiter, designed for highly sensitive atmospheric gas detection, failed to detect methane above Gale Crater, creating a puzzling discrepancy.

A new study published in Icarus, involving Prof. Hovav Tsafrir from Bar-Ilan University and Prof. Yuval Raubvani from Ariel University, proposes that daily temperature gradients in the Martian ground could drive subsurface gases into the atmosphere. Mars’ thin atmosphere causes rapid surface temperature changes, creating strong temperature gradients between the surface and subsurface layers that fluctuate daily. The researchers compared thermal data from Curiosity and Perseverance rovers with Earth-based laboratory and field experiments, focusing on how temperature gradients in porous media can influence gas movement.

Prof. Raubvani explained that similar thermal-driven gas movements occur on Earth, and the Martian soil might act as a natural "thermal pump." The study contrasts this mechanism with barometric pumping, where atmospheric pressure changes push gases through soil pores, a known Earth process. Their lab experiments showed that typical Martian pressure changes are too small to explain significant gas movement alone, suggesting temperature-driven flow is a more plausible explanation for the observed methane variability.

The researchers emphasize that their proposed mechanism does not determine whether the methane is biological or geological in origin but addresses how methane, regardless of source, could migrate from underground reservoirs to the atmosphere. Understanding this transport process is crucial because methane presence on Mars is a key factor in assessing potential past or present biological activity. The study highlights the importance of applying Earth-based physics to Martian conditions to unravel planetary processes.

In summary, the daily heating and cooling cycle on Mars may naturally pump methane and other gases from beneath the surface into the atmosphere, explaining the observed seasonal and diurnal methane fluctuations detected by rovers but not by orbiters.