06.07

Diffusion of Photochemically Produced Hydrogen Peroxide in the Martian Regolith and Estimates of the Depth of Oxidized Strata on the Surface of Mars

R. C. Quinn (SETI Institute), A. P. Zent (NASA Ames)

The initial biological examination of Mars by Viking failed to detect life; instead the Viking experiments revealed that the Martian soil appeared to contain chemical oxidants (e.g., Klein, 1979). Any reducing materials that are relict of pre-biotic chemical evolution are susceptible to chemical attack by such oxidants, and their recovery is contingent upon penetrating oxidized strata. Zent and McKay (1993) concluded that the most consistent explanation for the Viking results calls on photochemically produced oxidants (odd-hydrogen and odd-oxygen species), which originate in the atmosphere and diffuse into the regolith. One study of the diffusion of hydrogen peroxide into the regolith (Bullock, et al., 1993) has suggested that the depth of the oxidized layer may be no more than several meters, although that modeling study was limited by the lack of data on the lifetime of hydrogen peroxide against reaction in the regolith, and it's adsorptive behavior. We report on the experimental determination of diffusion rates of hydrogen peroxide vapor through Mars soil analogs. Peroxide penetration rates, depths, and adsorptive coverage are examined as a function of regolith surface area and temperature. Further constraints on the depth of oxidation based on mixing by impact cratering will be reported (Zent and Quinn, 1997).

References: Bullock, M., C. R. Stoker, C. P. McKay, A. P. Zent, (1993). Icarus, 107, 142-154. Klein, H. P., (1979). Rev. Geophys. and Space Phys., 17, 1655-1662. Zent, A. P., C. P. McKay, (1994). Icarus, 108. 146-157. Zent, A. P., R. C. Quinn, (1997). Planet. Space Sci., submitted.