Researchers who tested fungal strains collected during the Mars 2020 mission found that Aspergillus calidoustus spores withstood almost all radiation, dryness, low pressure and rheological tests – a finding that heightens the challenges of planetary defense
Terrestrial microbes may be tougher than expected, raising new questions about extraterrestrial survival.
Scientists have long considered fungi to be tough survivors, but new research suggests that some of them may be able to withstand a more extreme test: the journey from Earth to Mars.
The study examined fungal microbes collected from NASA cleanrooms, the highly controlled spaces where spacecraft are built and tested. These facilities are designed to eliminate contamination, yet certain microbes survive. When scientists exposed these survivors to conditions that simulate space travel and the surface of Mars, spores of the fungus Aspergillus calidoustus survived.
שFungal infections in extreme conditions
“This doesn’t mean Mars is likely to be contaminated, but it helps us better quantify potential risks of microbial survival,” said microbiologist and study leader Dr. Kasthuri Venkateshwaran. His unit implements NASA’s policy on various missions to prevent extraterrestrial cross-contamination with terrestrial microbes, and vice versa. “Microbes can be very resilient to environmental shocks.”
Unlike bacteria, fungi are less commonly studied in planetary defense research, but they can present unique challenges. Fungal spores are naturally designed to withstand desiccation, radiation, and food shortages, traits that mirror conditions found in spaceflight.
This study provides some of the first evidence that complex cells (eukaryotes) could potentially survive all phases of the mission, from assembly in clean rooms to operation on another planet.
The reason clean rooms aren't completely clean
NASA cleanrooms are some of the most tightly controlled environments on Earth. The air is constantly filtered, surfaces are disinfected, and workers follow strict protocols to limit contamination. However, some microbes adapt to these conditions. Over time, they can develop resistance to disinfectants, low humidity, and limited food.
That's why they're especially important in planetary defense operations, which aim to prevent life from Earth from reaching other worlds and to hinder the search for extraterrestrial biology. If a microbe can survive a clean room, it may have already adapted to the rigors of space.
Testing survivability on the way to Mars
To investigate this possibility, the research team analyzed 27 fungal strains collected during the Mars 2020 mission, which successfully delivered the Mars Perseverance rover to its destination. They also added two additional microbes known to be resistant to radiation.
The fungal spores were exposed to a series of simulations designed to mimic key phases of a Mars mission. These included extreme cold, intense UV and ionizing radiation, low atmospheric pressure, and exposure to Martian tuff (the loose, dusty rocky material on the surface of Mars). These conditions reflect not only the Martian environment but also the vacuum and radiation encountered during months of space travel.
Of all the samples, A. calidoustus stood out. Its spores survived almost all the tests. Only the combined stress of very low temperatures and high radiation levels proved fatal. "Survival of microbes is not determined by a single environmental stress but by combinations of stress resistance mechanisms," Venkataswaran said.
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