LIFE IN MARTIAN SNOWS – MEASUREMENTS OF UV PROTECTION UNDER NATURAL ANTARCTIC SNOWS IN THE UVC (254 nm)

Introduction: Ultraviolet radiation down to 195 nm penetrates to the surface of the Martian north polar ice cap during the polar summer on account of the lack of an ozone column, in contrast to the Earth where only radiation above ~290 nm penetrates to the surface (except under ozone depletion, when radiation down to ~280 nm may penetrate). During the winter, spring and fall some ozone production does occur over the Martian poles, but the column abundance is about two orders of magnitude lower than terrestrial stratospheric ozone values. Although this ozone will provide some protection from UVC (200-280 nm) radiation, it is transient. The DNA-damage experienced on the surface of the Martian poles is approximately (under clear, dust-free skies at vernal equinox) three orders of magnitude higher than that experienced by terrestrial polar organisms (under an undepleted ozone column at the same orbital position). UV in Antarctic and Martian Snows: To investigate the potential of Martian snow to act as a protection mechanism for contaminant microorganisms or organics, the penetration of 254 nm radiation (produced from a field-portable mercury vapor source) into natural snows was measured at Mars Oasis, Antarctica (72°S) during the 2001 austral summer. Sections of icy snow-pack of approximate dimensions 10 x 10 cm were placed between the cosinecorrected collector of a calibrated Ocean Optics S2000 spectrometer and the radiation source. A control measurment was taken before each snow-pack measurement and the ratio of the value under the snow-pack to the control was calculated as the attenuation coefficient. The thickness of each snow-pack sample was measured.