Modelling UV Degradation of Airfall Organic Material on Mars

The Martian surface receives a constant flux of organic material through accretion of almost 1.7 x 10⁸ kg Interplanetary Dust Particle (IDPs) every Mars year, of which a significant fraction is unaltered. Due to poor attenuation of UV insolation by the Martian atmosphere, this organic carbon present in IDPs is subject to UV photolysis, which laboratory studies have found will result in the release of Methane. However, before these particles can be completely degraded, many are likely buried by airfall dust. Indeed, observed sedimentary rhythmites with quasiperiodic bedding are hypothesized to have formed through accumulation of aeolian dust fall during the present era. These forming rhythmites can provide a UV shielding environment to any IDPs that become embedded within. We will present work to: (a) characterize the UV shielding provided by layers of sediment by studying the transmission of UV light through samples of JSC Mars-1, (b) model the degradation of buried organics in IDPs at Gale crater, and (c) model the degradation of buried IDPs globally to constrain the total surface load of organic carbon available for photolysis to methane. Preliminary results from the model focusing on Gale Crater with deposition rates of 25 μm/year indicate a long-term surface load of ~ 3.046 10^-6 g/m², yielding an organic carbon mass fraction of ~ 0.00015. Because the dust being deposited is highly opaque and the photolysis lifetime of IDPs is from decades to centuries, this suggests that exogenous carbon deposited by IDPs can be largely sequestered in areas of Mars that are accumulating dust. This sequestration by burial prevents this carbon from contributing to methane in the Martian atmosphere and makes modern rhythmites excellent candidates for preserving a record of the modern organic carbon accretion rate to Mars.