Some shadowed areas of the lunar South Pole could keep microbes from Earth alive, despite an environment considered extremely hostile.
This possibility emerges from a study conducted by researchers from NASA and the University of Maryland. The team combined detailed maps of the lunar terrain with the known resistance limits of several bacteria and fungi.
Relief view of the lunar South Pole obtained from the first altimetric measurements by LRO/LOLA. The Scott, Amundsen, Faustini, Shoemaker, Haworth, Malapert, Shackleton and Wiechert craters are visible.
Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio
The lunar surface nevertheless presents serious obstacles for a cell. It undergoes extreme temperature variations and ultraviolet radiation capable of rapidly damaging living organisms. But near the South Pole, the Sun remains very low on the horizon. The terrain therefore creates many areas shielded from its direct light.
The researchers studied three regions: Nobile Rim, Connecting Ridge and De Gerlache Rim. The temperature and terrain maps came in particular from the Lunar Reconnaissance Orbiter satellite. They made it possible to calculate exposure to solar radiation depending on location, and then compare it with the limits tolerated by different microbes.
Five types of microorganisms common in human or space environments were taken into account. Among them is Aspergillus niger, a fungus found notably in warm, humid places. It had already been detected on the International Space Station and proved particularly resistant to ultraviolet radiation.
In concrete terms, some areas compatible with survival could cover the floor of a crater. Others could be tiny, down to the scale of a boot print. A slight irregularity in the ground is sometimes enough to create permanent shade. According to the models, microorganisms could then remain viable for several days in some of these refuges.
This survival does not mean, however, that colonies could develop independently on the Moon. The researchers refer to cells remaining alive, possibly in a dormant state. They found no evidence that these locations provide the conditions needed for reproduction. Stable liquid water, in particular, is lacking on the lunar surface.
The issue will become concrete with future crewed missions. Astronauts naturally carry very large numbers of microorganisms, some of which can escape from spacesuits or habitats. Earth-based contamination could then complicate the analysis of ancient molecules present on site. The researchers now plan to use even more precise terrain and illumination maps to better locate these potential refuges.