Variability of the methane trapping in martian subsurface clathrate hydrates

TL;DR

This study models the composition of Martian subsurface clathrate hydrates, revealing their potential to trap methane under certain atmospheric and temperature conditions, which could explain observed methane traces.

Contribution

It introduces a hybrid thermodynamic model that accurately predicts clathrate hydrate composition considering Mars's main atmospheric gases and a wide temperature range.

Findings

Methane-enriched hydrates are stable only with a primitive CH4-rich atmosphere.

Clathrate composition depends on temperature and initial atmospheric composition.

Model accounts for Mars's main gases and extreme polar temperatures.

Abstract

Recent observations have evidenced traces of methane CH4 heterogeneously distributed in the martian atmosphere. However, because the lifetime of CH4 in the atmosphere of Mars is estimated to be around 300-600 years on the basis of photochemistry, its release from a subsurface reservoir or an active primary source of methane have been invoked in the recent literature. Among the existing scenarios, it has been proposed that clathrate hydrates located in the near subsurface of Mars could be at the origin of the small quantities of the detected CH4. Here, we accurately determine the composition of these clathrate hydrates, as a function of temperature and gas phase composition, by using a hybrid statistical thermodynamic model based on experimental data. Compared to other recent works, our model allows us to calculate the composition of clathrate hydrates formed from a more plausible composition of the martian atmosphere by considering its main compounds, i.e. carbon dioxyde, nitrogen and argon, together with methane. Besides, because there is no low temperature restriction in our model, we are able to determine the composition of clathrate hydrates formed at temperatures corresponding to the extreme ones measured in the polar caps. Our results show that methane enriched clathrate hydrates could be stable in the subsurface of Mars only if a primitive CH4-rich atmosphere has existed or if a subsurface source of CH4 has been (or is still) present.