Title

Methane Evolution From Uv-Irradiated Spacecraft Materials Under Simulated Martian Conditions: Implications For The Mars Science Laboratory (Msl) Mission

Keywords

Astrobiology; Mars

Abstract

Fifteen organic and three inorganic compounds were tested for methane (CH4) evolution under simulated martian conditions of 6.9mbar; UVC (200-280nm) flux of 4Wm-2; 20°C; simulated optical depth of 0.1; and a Mars gas composition of CO2 (95.3%), N2 (2.7%), Ar (1.7%), O2 (0.13%), and water vapor (0.03%). All three inorganic compounds (i.e., NaCl, CaCO3, graphite) failed to evolve methane at the minimum detection level 0.5ppm, or above. In contrast, all organic compounds evolved methane when exposed to UV irradiation under simulated martian conditions. The polycyclic aromatic hydrocarbon, pyrene, released the most methane per unit of time at 0.175nmol CH4 g-1h-1, and a spectral reflectance target material used for the MER rovers and Phoenix lander released the least methane at 0.00065nmol CH4cm-2h-1. Methane was also released from UV-killed bacterial endospores of Bacillus subtilis. Although all organic compounds evolved methane when irradiated with UV photons under martian conditions, the concentrations of residual organics, biogenic signature molecules, and dead microbial cells should be relatively low on the exterior surfaces of the MSL rover, and, thus, not significant sources of methane contamination. In contrast, kapton tape was found to evolve methane at the rate of 0.00165nmol CH4 cm-2h-1 (16.5nmolm-2h-1) under the UV and martian conditions tested. Although the evolution of methane from kapton tape was found to decline over time, the large amount of kapton tape used on the MSL rover (lower bound estimated at 3m2) is likely to create a significant source of terrestrial methane contamination during the early part of the mission. © 2011 Elsevier Inc.

Publication Date

5-1-2011

Publication Title

Icarus

Volume

213

Issue

1

Number of Pages

393-403

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1016/j.icarus.2011.02.017

Socpus ID

79955165835 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/79955165835

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