Investigating the contribution of methane produced by ablating micrometeorites to the atmosphere of Mars
The presence of methane in the atmosphere of Mars has been suggested as evidence of life, as methane has a short lifetime in the atmosphere of Mars of just a few hundred years, requiring replacement by mechanisms, continuous or episodic, such as biology, volcanism, serpentinization of ultramafic crust or large cometary or asteroidal impacts. The potential of meteoritic infall to deliver significant quantities of methane is restricted by the low abundance of free methane in carbonaceous meteorites. However, the delivery of meteoritic material to the surface of a planet is an energetic process, and the ability of carbonaceous meteorites to generate methane upon ablation during atmospheric entry has not been previously considered. Here, we use analytical pyrolysis to simulate the ablation and pyrolysis of carbonaceous micrometeorites upon atmospheric entry, and Fourier-transform infrared spectroscopy to quantify the subsequent yield of methane. We show that ablation produces a yield of methane that is approximately two orders of magnitude greater than the measured free methane present in the CM2 carbonaceous chondrite, Murchison, but that this previously overlooked source of methane can only account for less than 10 kg of methane annually, a mass far below that required to maintain the abundance of methane observed in the atmosphere of Mars. Our data support attempts to search for life and explore subsurface chemical processes on the Red Planet.