The “small step” for an astronaut could have significant consequences for the Moon, Mars and Co. Because when future astronauts visit the moon or Mars, billions of terrestrial microorganisms will also travel with them. While unmanned space probes are sterilized at 200 degrees before their launch, this is not possible for astronauts. Bacteria and microbial fungi from their skin or breath therefore spread inside the space capsule, on space suits and utensils before landing.
The lunar south pole is different
The so-called COSPAR guidelines prescribe certain protective measures against contamination of foreign celestial bodies. How strict these requirements are depends on the expected liveability of the destination. And the moon was therefore previously considered to be at little risk: all introduced organisms – it was believed – would die immediately due to the harsh radiation, the vacuum and the low temperatures.
But that is apparently a mistake, as Prabal Saxena from NASA’s Goddard Space Flight Center and his colleagues have now found out. “Strong UV radiation, high-energy cosmic particles and extreme temperatures make the unprotected lunar surface largely hostile to life,” they explain. But the lunar south polar region – the area where the landing sites of upcoming lunar missions are located – could be an exception. There, towering crater edges protect against sunlight and UV radiation, and water ice also exists at the bottom of these shadow zones.
In the craters at the lunar south pole there are shadow zones that are permanently protected from UV radiation and extreme solar heat. — © NASA’s Scientific Visualization Studio/Ernie Wright
Five species of microbes as test objects
Could this be enough to allow some terrestrial microbes to survive? To test this, Saxena and his team chose five microorganisms as test objects: the bacteria Staphylococcus aureus and Bacillus subtilis, which are common on our skin, the common molds Aspergillus niger and Fusarium, and the bacteria Deinococcus radiodurans, which is known to be particularly “indestructible”. “These genera are resistant to vacuum, temperature extremes and high-energy particle bombardment,” explains the team.
For their study, the researchers first determined what maximum UV radiation dose and temperature these five types of microbes can tolerate. They then used a virtual model of the South Pole landscape to test where survivable conditions might exist for these bacteria and fungi. The focus was on the shadow zones in the Nobile and de Gerlache craters and an adjacent ridge.
Lunar survival niches for all five species
The surprising result: For all five microorganisms, there are places at the lunar south pole where they could survive for at least a few days. Some of these niches span an entire lunar crater, others are only as small as an astronaut’s footprint. “When we created lunar maps that marked different microbial species and their survival niches in purple, red, and blue, the maps were surprisingly colorful,” says co-author Stefano Bertone of the University of Maryland.
Areas at the lunar North Pole (left) and South Pole where the tested bacteria and fungi could survive. — © Saxena et al./ Science Advances, CC by 4.0
The mold Aspergillus proved to be particularly resilient: the team identified life-friendly niches for it in three percent of all South Pole areas examined. This fungus could even survive in 15 to 30 percent of areas that still receive scattered or reflected UV radiation despite the shade, as the researchers report. The shadow zone in the De Gerlache crater could also provide survivable conditions for all five microorganisms.
Better protection against microbial contamination needed
These results suggest that terrestrial microbes are more resilient than is often assumed – and the moon is by no means completely hostile to life. “We don’t typically think of the moon in terms of life or biology – but it appears to be a place where cells can survive,” says co-author Heather Graham from NASA. The researchers emphasize that terrestrial microbes cannot reproduce under lunar conditions. But their very presence could contaminate the moon and distort scientific studies.
“As we explore these areas in the near future, we should be particularly careful not to spread our microbial fellow travelers,” Graham said. “This is the only way we can explore lunar chemistry without our presence having already changed it.” Manned lunar landings such as NASA’s Artemis mission or China’s planned lunar flights should therefore be subject to even stricter decontamination measures in the future than has previously been the case.
The findings could be even more important for future space missions to Mars and other potentially more habitable planets. “If we go to Mars to look for evidence of extraterrestrial life, we need to make sure we don’t find the same microorganisms that we brought with us,” says NASA researcher Andrew Needham.
Source: Science Advances, 2026; doi: 10.1126/sciadv.aec0811