Sunday, October 26, 2014

Adaptation of Antarctic Lichens to Conditions on Mars

Billions of years ago, Mars was a warm and wet planet. Life could have evolved on Mars and then receded to micro-habitats as the planet subsequently became colder and dryer. Present-day micro-habitats for life on Mars can include subterranean aquifers and cracks or fissures in rocks. J.-P. de Vera et al. (2014) conducted a study using the lichen Pleopsidium chlorophanum and found that this Antarctic lichen can adapt, within a span of 34 days, to the conditions expected to be present in the micro-habitats on Mars today.

The sample used in the study was collected from the granites and volcanic rocks of North Victoria Land in Antarctica during the 10th German North Victoria Land Expedition in 2009/2010. Pleopsidium chlorophanum is an extremophile that lives in very cold and dry places. Its native habitat in Antarctica somewhat approximates the conditions on Mars. Pleopsidium chlorophanum is usually found within cracks and fissures in rocks. It can remain metabolically active down to -20°C and can absorb water directly from snow.

To simulate Mars-like environmental conditions, the lichens were placed in the Mars Simulation Chamber (MSC) at the Mars Simulation Facility (MSF) of the DLR Institute of Planetary Research in Berlin. The atmosphere in the MSC was 95 percent carbon dioxide, 4 percent nitrogen and 1 percent oxygen. The pressure was held at 800 Pa, with a diurnal relative humidity cycling of 0.1 to 75 percent and a diurnal temperature cycling of 21°C to -50°C (i.e. similar to the temperatures observed in the equatorial to mid-latitude regions on Mars).

The lichens were embedded within a Mars analogue soil material. In the experiment, 3 samples of lichens were subjected to Mars-like niche conditions (i.e. conditions expected in the micro-habitats on Mars) and another 3 samples of lichens were subjected to the unprotected Mars-like surface conditions for 34 days. For lichens in the unprotected Mars-like surface conditions, they were subjected to much more intense UV irradiation.

Results from the experiment indicated that for Mars-like surface conditions, photosynthetic activity dropped to 18 percent of pre-experiment levels and it was unclear if the lichens remained photosynthetically active at the end of the 34 days. However, lichens that were subjected to Mars-like niche conditions and experienced a much lower radiation dose fared very differently. For these lichens, photosynthetic activity only dropped to 55 percent of pre-experiment levels after the 34 days. In fact, photosynthetic activity at the end of the experiment was 17 percent higher than what was measured for the lichens in their native habitat in Antarctica.

Under simulated Mars-like niche conditions, the lichens appeared to have experienced an initial period of shock lasting ~7 days. Following that, the lichens rapidly adapted. Photosynthetic activity increased over the subsequent days and the increase continued to the end of the experiment. It appears that the lichens were much more sensitive to the intensity of UV irradiation than to other Mars-like parameters such as high carbon dioxide concentration, very low temperatures, extreme humidity fluctuations and very low atmospheric pressure. This study supports the notion that Earthly life can adapt to the present-day conditions on Mars. Furthermore, life which may have originated during the early warm and wet Mars might still survive and thrive in present-day micro-habitats on Mars.

J.-P. de Vera et al., “Adaptation of an Antarctic lichen to Martian niche conditions can occur within 34 days”, Planetary and Space Science 98 (2014) 182-190