Open AccessUV degradation of accreted organics on Mars: IDP longevity, surface reservoir of organics, and relevance to the detection of methane in the atmosphere
Author(s) -
Moores John E.,
Schuerger Andrew C.
Publication year - 2012
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2012je004060
Subject(s) - mars exploration program , latitude , methane , atmospheric sciences , total organic carbon , atmosphere of mars , atmosphere (unit) , environmental science , carbon fibers , atmospheric methane , astrobiology , geology , environmental chemistry , chemistry , materials science , martian , meteorology , physics , organic chemistry , geodesy , composite number , composite material
Reanalysis of the Viking Lander results on Mars has suggested a surface reservoir of organic carbon at the ppm level. The size of this putative reservoir could be explained if the source of carbon on Mars is meteoritic in origin and is destroyed primarily by UV irradiation, yielding methane. By combining a numerical UV model for the surface of Mars with published laboratory measurements of organic UV photolysis, the times required to completely convert the carbon within individual particles to methane may be calculated. For interplanetary dust particles (IDPs) initially containing 10 wt% carbon, lifetimes of organics range from 3.9 years for a 0.2 μ m diameter particle at equatorial latitudes to 4900 years for a 200 μ m diameter particle at polar latitudes, and implies a median time for IDP organics by UV photolysis of 320 years at equatorial latitudes and 1500 years at polar latitudes. Assuming no redistribution of organics over the surface, the IDP organic reservoir at the surface would range from 1.1 × 10 −6 kg m −2 at equatorial latitudes to 6.6 × 10 −6 kg m −2 at polar latitudes. If accreted carbon is evenly mixed with the soil, up to 3.4 ppm of organic carbon at the VL1 landing site can be explained from a meteoritic origin and up to 4.9 ppm at the VL2 landing site. Derived from the IDP organic reservoir, small fluctuations in methane would exist due to variations in UV irradiation with latitude and L S . Production of methane is expected to range up to 0.35 pptv sol −1 .