Potential for photosynthesis on Mars within snow and ice

On Earth, solar radiation can transmit down to multiple metres within ice, depending on its optical properties. Organisms within ice can harness energy from photosynthetically active radiation while being protected from damaging ultraviolet radiation. On Mars, the lack of an effective ozone shield allows ~30% more damaging ultraviolet radiation to reach the surface in comparison with Earth. However, our radiative transfer modelling shows that despite the intense surface ultraviolet radiation, there are radiatively habitable zones within exposed mid-latitude ice on Mars, at depths ranging from a few centimetres for ice with 0.01–0.1% dust, and up to a few metres within cleaner ice. Numerical models predict that dense dusty snow in the martian mid-latitudes can melt below the surface at present. Thus, if small amounts of liquid water are available at these depths, mid-latitude ice exposures could represent the most easily accessible locations to search for extant life on Mars.