A NASA study has shown that shadowed regions near the Moon’s south pole are cold enough for human-borne microbes to remain alive for a week. The findings were published in the journal Science Advances.
Every time a person takes a step on the Moon, they leave behind more than just a bootprint. Human skin constantly sheds bacteria, and a spacesuit boot can press some of these microbes directly into the lunar dust.
A new study has identified shadowed areas near the Moon’s south pole that remain cold and dark enough for some of these microbes to survive for at least a week.
Even the researchers who created the models were surprised by the results. They color-coded survival maps by species: purple for one microbe, red for another, and blue for a third. The resulting pattern looked less like a lifeless lunar landscape and more like paint splatters.
“So much for the idea that ‘nothing survives on the Moon,'” said Stefano Bertone, a planetary scientist at the University of Maryland who conducted the research while working at NASA’s Goddard Space Flight Center.
Mars raises similar concerns. NASA’s next major crewed missions are headed there, and any search for extraterrestrial life will face a similar risk of contamination.
“We need to understand what was there before us, because when we go to Mars looking for signs of life beyond our planet, we want to be sure that what we find isn’t something we brought with us,” said study lead Prabal Saxena of NASA’s Goddard Space Flight Center. Humans never travel alone. A patch of skin the size of a little-finger nail can harbor a million bacteria, and every person constantly sheds cells without even realizing it. Even after rigorous pre-launch cleaning, a single bootprint on the Moon could leave behind hundreds of millions of living bacteria.
This poses a problem for scientists attempting to study the Moon’s natural chemical composition. If microbes left by astronauts make their way into the lunar soil, distinguishing ancient lunar material from recent human-induced contamination becomes much more difficult. In the future, crews searching for ancient life on Mars will face the same challenge.
Near the lunar poles, the Sun never rises high in the sky. The Moon’s axis has almost no tilt, so the Sun always remains low above the horizon at the poles; it never reaches the heights seen at the equator.
Due to this shallow angle, even a small ridge or boulder can cast a shadow on the ground nearby. Some of these shadows never shift, because the Sun does not rise high enough to clear the objects casting them. Consequently, the landscape is dotted with areas that remain bitterly cold and dark year-round. These hollows can preserve buried ice and block most of the radiation that would otherwise kill a microbe within hours.
To determine the extent of this protection, the team mapped three regions near the Moon’s south pole. All three are potential landing sites for NASA’s Artemis III mission: Nobile Rim, Connecting Ridge, and de Gerlache Rim. Researchers combined elevation and temperature data from NASA’s Lunar Reconnaissance Orbiter with a method that tracks sunlight reflecting off the terrain before reaching the lunar surface.
“Accounting for surface roughness and craters was key to this study,” said Bertone. “The question was how well the lunar terrain could shield certain areas from ultraviolet radiation, and whether that protection was sufficient for the survival of any of the organisms we were studying.”
The team selected five microorganisms commonly found on human skin or inside spacecraft: the bacteria Bacillus and Staphylococcus, the radiation-resistant bacterium Deinococcus, and the fungi Aspergillus and Fusarium.
Geomicrobiologists at NASA’s Johnson Space Center used data from earlier laboratory studies on spacecraft surfaces to determine the heat and radiation exposure limits each microorganism could withstand.
The size of the potentially habitable crater areas varied widely, ranging from crater floors the size of a small city to patches no larger than a bootprint.
The fungus Aspergillus—which also grows in damp corners of buildings on Earth—proved to be the most resilient of the five microorganisms studied. It is capable of surviving on 15–30 percent of the lunar surface area receiving sunlight during the lunar winter. This makes it the only microbe in the study capable of withstanding direct sunlight and remaining alive. Furthermore, it could survive for at least seven days in an area comprising approximately 3% of the total mapped territory across all three regions.
An even more striking result was obtained for the darkest parts of the de Gerlache Rim. Researchers also factored in scattered light—sunlight reflected off nearby slopes rather than arriving directly from the sun. Once the team incorporated indirect light into their models, all five microbes were potentially able to survive somewhere within the permanently shadowed terrain.
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