Potential for photosynthesis on Mars within snow and ice
Communications Earth & Environment volume 5, Article number: 583 (2024 ) Cite this article
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.
Dusty water ice (<~1% dust by mass) is exposed at the surface of Mars at latitudes poleward of 75°1,2. In the martian mid-latitudes (\({{30}}{{-}}{{60}}{{^{\circ} \, }}\) latitude), dusty ice is typically overlain by desiccated material3,4,5. However, recent observations indicate that the overlying desiccated material can be removed by impact processes6 or by slumping on steep slopes, to expose dusty ice at the surface in the mid-latitude regions of Mars7,8,9. The ice is thought to have been deposited as dusty snow during numerous periods of high obliquity that occurred over the last few million years4,10,11. While the precise grain size and density of exposed martian ice is currently unknown, snow on Mars is estimated to metamorphose into coarser-grained firn and eventually glacier ice on timescales ranging from decades/centuries12,13 to millions of years14.
