Roughly a million bacteria sit on every patch of human skin the size of a pencil eraser. Send people to the Moon and those passengers go too.
A team at NASA has now worked out where some of them might survive once they get there. Their paper, published on Aug. 19, 2026, in Science Advances, concludes that microbes carried by astronauts could persist in cold, shadowed pockets near the lunar South Pole. Some of those refuges are no bigger than a boot print.
“Humans are natural explorers, and with them come their voices, their memories … and their microbes,” said Prabal Saxena, the planetary scientist at NASA’s Goddard Space Flight Center who led the work. “For some scientists, myself included, that reality can be unsettling. But it also creates an opportunity to turn an imperfect situation into a useful experiment.”
Why the poles are odd
The geometry is the detail that matters. The Moon has only a slight axial tilt, so from the poles the Sun hangs close to the horizon and its light rakes across the ground like a torch laid flat on a table. Crater rims, ridges and mountains block that light from reaching lower terrain, and so do small bumps. What results is a patchwork of permanent shade that stays extremely cold, can preserve water, and shields fragile molecules, and possibly microorganisms, from radiation.
The team picked five organisms, drawn from spaceflight settings and from the microbes people commonly carry: Aspergillus niger, Bacillus subtilis, Staphylococcus aureus, Deinococcus radiodurans and several species of Fusarium. Using earlier research, they worked out how much heat and ultraviolet radiation each could take. They then modelled three sites near the South Pole, Nobile Rim, Connecting Ridge and De Gerlache Rim, using elevation and temperature maps built from data gathered by NASA’s Lunar Reconnaissance Orbiter, plus models of how radiation reaches the surface.
The maps showed “survivable niches” of every size, from crater floors several miles across down to patches the width of an astronaut’s boot. Here survival has a narrow meaning: a microbe stays alive for at least one Earth day. It says nothing about growing or reproducing.
The fungus that likes bathrooms
Aspergillus niger came out best. It grows readily in warm, humid places such as bathrooms and air conditioning systems, and astronauts have collected it aboard the International Space Station. Earlier experiments showed it could also live outside the station. It resisted ultraviolet light better than the other four, which means it could conceivably survive in spots that get some sunlight. Hospitals use UV to sterilise equipment because so many microorganisms die under it.
That result surprised people. Aaron Regberg, a geomicrobiologist at NASA’s Johnson Space Center in Houston and a co-author, noted that such organisms are not normally classed as extremophiles able to cope with the vacuum of space. “I would have expected these microbes to have dried out,” he said.
A contamination problem with no easy fix
Robotic spacecraft can be cleaned by baking them at more than 400 degrees Fahrenheit. Crews cannot be treated that way. And even thorough sterilisation does not remove every hardy organism.
The worry is scientific rather than medical. As people spend longer on the Moon, microbes escaping from suits and habitats could make it harder to tell ancient lunar chemistry from material humans brought along. Andrew Needham, a Goddard co-author who works on contamination control for Artemis lunar samples, put it plainly: “We need to understand what was there before us, because when we go to Mars to search for signs of life beyond our planet, we will want to make sure it’s not stuff we brought.”
The researchers see an upside, too. Carefully monitored shadowed regions could serve as a natural laboratory for testing the real limits of microbial survival, under conditions that are very hard to reproduce on Earth. First, though, someone has to establish a baseline of what humans introduce.
Heather Graham, a Goddard co-author who helps develop tools for detecting biology that may look nothing like Earth’s, said early visits should treat the hitchhikers with care. “The Moon is a place where a cell can survive, so our first exploration of these sites should pay extra attention to our microbial hitchhikers and work hard to characterize lunar chemistry before our visits change what we will find,” she said.
The authors stress that surviving is not thriving. They found no evidence that the Moon offers what microbes need to grow and reproduce, and liquid water, which generally needs an atmosphere and moderate temperatures, is one of the missing ingredients.
