Clathrates as a Source of Mars’ Methane

This “flammable ice” is the result of methane being released from a clathrate. On Mars, underground ice clathrates may be the source of the methane that has been intermittently detected in the atmosphere. Credit: U.S. Department of Energy.

Periodic detections of methane in Mars’ atmosphere have provoked considerable curiosity as to its source and variability over time. On Earth, methane can be produced by microbial life, but it also has many abiotic sources, including formation by active geologic processes. Due to methane’s short lifetime in Mars’ atmosphere, many investigations have focused on active, ongoing processes that could create methane from localized sources. A new study by researchers at the Royal Observatory of Belgium, led by Elodie Gloesener, suggests a different approach: methane on Mars could have formed earlier in Mars’ history, been stored in subsurface clathrate deposits, and intermittently released over time.

Clathrates are a form of crystalline water ice that can trap gas molecules inside their structure, effectively sequestering it until the ice is destabilized by heat or force. On Earth, gas clathrates can be found beneath the sea floor where there is enough pressure to keep their molecular structure stable. The authors modeled the depths, temperatures, and pressures at which similar clathrates would be stable in the martian subsurface and found that clathrates could exist within tens of meters of the surface, even at Mars’ equator, where subsurface temperatures are highest. Further, the locations where methane has been previously detected in Mars’ atmosphere have the deepest modeled stability zones, beginning at depths of about 70 meters. This depth is significantly deeper than the near-surface layer affected by seasonal temperature variations, which is typically within a few meters of the surface. Instead, the authors suggest that seismic activity or meteorite impacts could disrupt deep deposits of clathrates, releasing the methane gas.

The authors also studied the effects of briny liquids on methane storage in clathrates. They suggest that clathrates deeper in the subsurface might interact with highly saline crustal fluids, which could then destabilize clathrates and potentially free methane gas to rise toward the surface. They further suggest that the most likely region for this to occur would be near the equator where methane has been detected. Thus, it is possible that the irregular “puffs” of methane observed on Mars are from a deeper, longer-lived source than previously thought. Further measurements investigating the seasonality of methane detections and study of the effects of local subsurface composition are needed. If the proposed model is correct, then the methane detected would likely be ancient methane produced on early Mars, rather than methane produced by recent events like biological activity or ongoing magmatism. READ MORE