UV production of methane from surface and sedimenting IDPs on Mars in light of REMS data and with insights for TGO

Abstract

This paper refines model predictions for the production of methane from UV-irradiated interplanetary dust particles (IDPs) now that the Rover Environmental Monitoring Station (REMS) instrument onboard the Mars Science Laboratory (MSL) Rover has made the first measurements of the UV environment on the surface of Mars, at Gale Crater.Once these measurements are included in a UV radiative transfer model, we find that . An examination of IDP-derived methane production during atmospheric settling indicates that no more than 0.32% of organic carbon from meteor streams may be deposited in the atmosphere. Thus, such a process cannot explain either the spikes observed in methane nor the low equilibrium values observed by MSL. Instead, this discrepancy may be explained if < 80 tons per year of organic carbon survives to the surface, the atmospheric lifetime of methane is < 110 years or the efficiency of the UV-CH 4 process is < 7%. Under the assumption of reduced carbon input cycling in the Martian system from these processes, both soil concentrations of organic carbon and atmospheric measurements of methane observed by MSL are consistent with the UV-CH 4 process. This refinement of methane production from IDPs and its geographical and vertical distribution will be an important input for models attempting to understand the results to be derived 2 Moores et al., 2017, P&SS_2017_232 R1 Martian Methane in the light of REMSfrom the Trace Gas Orbiter (TGO) mission that will map methane concentrations in the martian atmosphere in 2018 at 0.01 ppbv.

The Methane Diurnal Variation and Microseepage Flux at Gale Crater, Mars as Constrained by the ExoMars Trace Gas Orbiter and Curiosity Observations

“…Furthermore, the history of Gale indicates that it once had habitable standing liquid water (Grotzinger et al, ), the sediments of which are now located on and below the surface of Gale crater. At the very least, such an environment could have collected organic carbon from interplanetary dust particles and protected them from their initial UV‐mediated destruction (e.g., Moores et al, ), providing a substantial source of raw materials for methane production (Eigenbrode et al, ).…”

UV Reflectance of Spacecraft Materials and Analog Soils: Implications for Bioburden Reductions on the Undersides of Mars Rovers

“…For example, an LD 90 rate of 275 J m −2 for Bacillus anthracis was reported by Nicholson and Galeano (2003). Using this dosage rate, and the radiative transfer models of Moores et al (2007Moores et al ( , 2017, the direct UVC beam LD 90 rate for unshaded spacecraft surfaces would be ∼240 s (column 5) on equatorial Mars at Ls of 180 (i.e., autumnal equinox). Averaging all the UVC LD 90 rates for the 20 bacterial species given in Table 4, an LD 90 rate of ∼377 s would be achieved in a direct UVC beam on horizontal and upward-facing spacecraft surfaces, assuming an optical depth of the Martian atmosphere at tau = 0.5, as appropriate for equatorial latitudes near Ls = 180.…”

“…Note that the Moores et al. (2017) and Smith and Moores (2020) models have been updated and validated against the Mars Science Laboratory (MSL) Rover Environmental Monitoring Station (REMS) UV data set returned from the Curiosity Rover.…”

“…pumilus were calculated according to the formalisms of the Lunar Microbial Survival (LMS) (Schuerger et al., 2019) and the Cruise Phase Microbial Survival (CPMS) models (Moores & Schuerger, 2020) with the amount of downwelling radiation on each sol provided by the models of Moores et al. (2017) and Smith and Moores (2020). Note that the Moores et al.…”

“…The Perseverance rover landed on 18-Feb-2021 at a solar longitude (Ls) of 5.3 degrees, which formed the start of the calculation. From that time-step onward, times to sterility (-12 logs; seeCraven et al, 2021) for B. subtilis and B. pumilus were calculated according to the formalisms of the Lunar Microbial Survival (LMS)(Schuerger et al, 2019) and the Cruise Phase Microbial Survival (CPMS) models(Moores and Schuerger, 2020) with the amount of downwelling radiation on each sol provided by the models ofMoores et al (2017) andSmith and Moores (2020). Note that the Moores et al(2017) and Smith and Moores (2020) models have been updated and validated against the Mars Science Laboratory (MSL) Rover Environmental Monitoring Station (REMS) UV data set returned from the Curiosity Rover.…”