A photohabitable zone in the martian snowpack? A laboratory and radiative-transfer study of dusty water-ice snow

Dusty water-ice snowpacks on Mars may provide a habitable zone for DNA based photosynthetic life. Previous work has over estimated the depths and thicknesses of such photohabitable zones by not considering the effect of red dust within the snowpack. For the summer solar solstice, at 80 degrees N and a surface albedo of 0.45, there is a calculated photohabitable zone in the snowpack between depths of 5.5 and 7.5 cm. For an albedo of 0.62, there is a calculated photohabitable zone in the snowpack between depths of 8 and 11 cm. A coupled atmosphere-snow radiative-transfer model was set to model the Photosynthetic Active Radiation and DNA dose rates through water-ice snow at the north polar region of Mars. The optical properties of the polar caps were determined by creating a laboratory analogue to the Mars north polar deposits, and directly measuring light penetration and albedo. It is important for future exobiology missions to the polar regions of Mars to consider the implications of these findings, as drilling to depths of similar to 11 cm should be sufficient to determine whether life exists within the martian snows, whether it is photosynthetic or otherwise, as at this depth the snow cover will provide a permanent protection from DNA damaging UV radiation. (C) 2009 Elsevier Inc. All rights reserved