Ancient Mars may have been warmed by explosive bursts of methane trapped in its subsurface, according to a study published online in Nature Geoscience this week. This finding explains the evidence of episodic wet climates on an otherwise freezing planet.
Sediments on Mars - such as those currently being explored by the Curiosity rover at Gale crater - suggest that lakes of liquid water existed on Mars later than three billion years ago, despite evidence that Mars was largely cold and dry at this time. It has been difficult to explain how sufficient climate warming occurred to allow these lakes to form, and also how warm climates lasted long enough to allow the lakes to persist for several thousand years, as geological evidence suggests.
Edwin Kite and colleagues use numerical simulations to propose that warming due to release of the potent greenhouse gas methane into the atmosphere can explain both the existence and persistence of the lakes. In this scenario, shifts in the tilt of the planet’s axis can cause the planet’s ice cover to shrink. Like on Earth, methane can be stored in Martian soils and trapped beneath ice. If the ice cover is removed, the stored methane is destabilized, causing the methane to explosively erupt into the atmosphere. The authors calculate that sufficient methane could have been released by this process to produce a lake-forming climate on ancient Mars. Although the methane would gradually break down in the Martian atmosphere, they estimate that each warming episode would persist for up to a million years.
In an accompanying News & Views article, Alberto Fairen writes that: “The methane burst scenario proposed by Kite et al. contributes to an emerging view that the existence of liquid water on early Mars arose from a combination of diverse astronomical, geochemical and geological factors.”