Microbes Could Survive at Lunar South Pole for Days

Microbes from Earth could survive for days in certain permanently shadowed regions at the Moon's south pole. This finding from NASA and University of Maryland researchers means future crewed missions like Artemis IV must carefully limit the unintended transfer of Earth life forms.

High ultraviolet radiation and extreme temperatures make most of the lunar surface hostile to life. The polar regions are different. Because the Moon's axial tilt is only 1.5 degrees, sunlight strikes these areas at a low angle. This creates long, permanent shadows where temperatures are cooler. Rugged terrain with mountains and deep craters adds more protection from solar heat and UV flux. These conditions also allow for water ice.

Future manned missions are targeting the south pole. NASA's Artemis IV is scheduled to go there. The region has been observed by spacecraft including ESA's SMART-1, India's Chandrayaan, Japan's Kaguya, and NASA's Lunar Reconnaissance Orbiter (LRO). Despite stringent sterilization, astronauts will inevitably carry millions of microbes on their skin and inside their bodies.

Modeling Microbial Survival

To investigate, researchers led by Prabal Saxena of NASA's Goddard Space Flight Center and Stefano Bertone of the University of Maryland modeled the fate of common skin bacteria and fungi. They focused on three candidate Artemis IV landing sites. The team created high-resolution spatial maps of topography, including ruggedness, slopes, and shadows. They modeled UV exposure and temperature to find locations where microbes could survive at least 24 hours.

Seasonal temperature data came from LRO's Diviner instrument at a 240-meter scale. Estimated regional UV fluxes were gleaned from averaged illumination maps with a 60-meter pixel scale, based on LRO Lunar Orbiter Laser Altimeter (LOLA) topography.

Since the temperatures at the lunar poles are rarely high enough to kill bacteria and low temperatures can preserve microbes on Earth, UV radiation is generally likely to be more dangerous in these regions, says Saxena. The team analyzed UV fluxes at finer scales using ray tracing, incorporating optical effects like reflection and refraction with updated LOLA maps at a 5-meter per pixel scale.

Findings on Survival Duration

The simulations revealed that the studied microbes could survive in certain niches for up to, or potentially beyond, seven days. One fungus, Aspergillus, is particularly UV-resistant. It could potentially survive in 15 to 30 percent of the assessed areas, even those receiving some sunlight during the lunar winter.

The reconstructions showed all five studied microbes could possibly survive in certain areas of the De Gerlache Rim's permanently shaded regions. This held true even when simulations included scattered UV light.

Dormancy Versus Growth

Survival does not mean growth, Saxena stresses. Surviving microbes would be in a dormant, cryptobiotic state. They would only grow if conditions were amenable to life, which the Moon lacks. "Cells may also be dead," he tells Physics World. "But even dead cells may persist in the environment as another potential source of contamination."

The work has implications beyond the Moon. Airless bodies like Mercury, Ceres, some asteroids, comets, and certain exoplanets could have similar survivable niches. Understanding these niches, and how human exploration leaves a mark, serves as a testbed for future Mars missions. Mars likely has more habitable environments, making contamination a greater concern.

We need to understand what was there before us, because when we search for signs of life beyond our planet on these bodies, we will want to make sure it's not stuff we brought, says Saxena. The research is described in Science Advances.