Of all the organisms on Earth, fungi seem almost designed for somewhere else. They don’t photosynthesize. They breathe oxygen like animals, don’t require sunlight, and can colonize environments that would kill most other living things within seconds. For decades, scientists treated them as biological background noise. Now, some of the most serious astrobiology research in the world is centered entirely on them.
What researchers have discovered over the last few years is genuinely difficult to frame in ordinary terms. Certain fungi don’t just tolerate the harshness of outer space. They appear to grow faster in it, absorb radiation that would kill a human many times over, and return from a two-year stint on the exterior of the International Space Station still capable of reproducing. The question of whether these organisms are simply survivors, or something more peculiar than that, is now a legitimate part of mainstream science.
Two Years in the Vacuum – and Still Alive
A 2024 study published in Scientific Reports confirmed that after a two-year exposure on the outside of the International Space Station, the fungus species Aureobasidium pullulans was able to survive, with researchers suggesting that the main factors for this long-term survival were likely dehydration and partial lyophilization in the vacuum of near-Earth space. This wasn’t a controlled lab simulation. The samples were mounted directly to the exterior of the station, exposed to the full reality of open space.
During the experiment, the number of colony-forming units of bacteria, archaea, and fungus decreased by three orders of magnitude in the first year, then by another two orders of magnitude in the second year, compared to the initial number. The fact that any fungi survived at all given those losses is, to put it plainly, remarkable. A population that dwindles that severely and still produces viable cells afterward tells a different story about fungal biology than we’ve been accustomed to telling.
The Chernobyl Connection: A Fungus That Feeds on Radiation
After the Chernobyl nuclear disaster in 1986, scientists expected to find a dead zone where almost nothing could survive. Instead, they found life that had found ways to adapt, including a common black fungus called Cladosporium sphaerospermum, which researchers had known about for more than a century but whose behavior at Chernobyl caught their attention in entirely new ways.
It didn’t just tolerate radiation. It appeared to grow toward it, colonizing surfaces where radiation levels were highest. This adaptation of some molds to areas such as the Chernobyl Exclusion Zone coined the terms “radiotropism” and “radiotrophy,” reflecting the affinity to and stimulation by radiation, and sometimes even enhanced growth under ionizing conditions. That’s a biological process with no real parallel anywhere else in nature.
Radiosynthesis: Eating Radiation Like Plants Eat Light
Radiotrophic fungi are fungi that can perform the biological process called radiosynthesis, which means using ionizing radiation as a main energy source to drive metabolization. The fungus’s ability to harness radiation is due to melanin, the pigment that gives human skin its color. In Cladosporium sphaerospermum, melanin absorbs gamma radiation and converts it into chemical energy through this process of radiosynthesis.
Based on the observed “radiostimulation” of melanogenesis and the growth advantage that putatively results from the exposure of these molds to high radiation, the concept of radiosynthesis has been developed. If found veritable, melanin could be perceived as loosely analogous to chlorophyll in photosynthesis. The science is still being verified, but the analogy is hard to ignore. A fungus using radiation the way a fern uses sunlight is an extraordinary thing, if true.
Tested Aboard the ISS: Growing Faster in Space Than on Earth
An experiment taking place at the International Space Station in December 2018 through January 2019 was conducted to test whether radiotrophic fungi could provide protection from ionizing radiation in space, as part of research efforts preceding a possible trip to Mars. This experiment used the radiotrophic strain of the fungus Cladosporium sphaerospermum, and the growth and its ability to deflect the effects of ionizing radiation were studied for 30 days aboard the ISS.
At full maturity, radiation beneath a roughly 1.7 mm thick layer of the radiotrophic fungus was approximately 0.84% lower compared to the negative control. In addition, a growth advantage in space of around 21% was observed, substantiating the thesis that the fungus’s radiotropism is extendable to space radiation. A 21% growth advantage in the hostile environment of orbit is not a trivial number. It suggests the fungus isn’t merely surviving space conditions. It may be benefiting from them.
Radiation Resistance Far Beyond Human Limits
Researchers discovered that fungal spores could survive radiation doses of 500 to 1,000 gray, depending on which type of radiation they were exposed to. Humans, by contrast, get radiation sickness at doses of 0.5 gray and are killed by 5 gray. That comparison is striking even stated plainly. The threshold that would kill a person is effectively irrelevant to these organisms.
The fungi withstood radiation exposure 200 times the dose that would kill a human, according to research presented at the Astrobiology Science Conference. In approximately 30% of Aureobasidium pullulans strains isolated after a two-year stay in outer space, the resistance to gamma radiation had actually increased compared to the control strain. Space exposure wasn’t just something the fungus endured. It made some strains demonstrably tougher.
The Mir Incident: When Fungi Nearly Wrecked a Space Station
The first serious hint that fungi could survive, if not thrive, in outer space came in 1988, when the Russian space station Mir was attacked by what Soviet microbiologist Natalia Novikova later described as an “aggressive space fungus.” The organism was not a typical space invader but a rapidly growing web of fungal hyphae that threatened windows, control panels, and was gradually eating away at the interior of the space station and a Soyuz transport vehicle.
Fungus found on one of Mir’s Soyuz transports was caught eating away at the hardened quartz glass of the vessel’s viewports. It etched webs of cracks and corroded the rubber seals connecting the windows to their titanium frames. The significance here extends beyond a maintenance problem. Although NASA asserted these fungal stowaways were of Earthly origin, their presence in space offered the first opportunity to examine astromycology, the study of Earth-derived mushrooms in space, up close and personal.
The Melanin Shield: How Fungi Protect Themselves
Melanins are a family of dark-colored, naturally occurring pigments with radiation-shielding properties. These pigments can absorb electromagnetic radiation due to their molecular structure, which results in their dark color. It has been suggested that melanin’s radiation-shielding properties are due to its ability to trap free radicals formed during radiolysis of water.
Researchers are particularly interested in observing the importance of fungi’s natural protective qualities, such as DNA repair and melanin synthesis. How DNA repairs itself after damage caused by radiation can affect the adaptation and survival of an organism. Melanin, a pigment that helps block damaging ultraviolet rays, could also be key to surviving in harsh environments outside of Earth, according to NASA. Estimations indicate that approximately a 21 cm thick layer of radiotrophic Cladosporium sphaerospermum could significantly deflect the annual amount of radiation received on Mars’ surface.
Space Mold and the Panspermia Hypothesis
Panspermia suggests that fungal spores could have arrived on Earth over a billion years ago by comets, asteroids, or other space debris, which could explain why fungi adapt so well to life in space, though this theory remains unproven. The role of fungal spores in the panspermia debate is underlined by the possibility of a high survival probability during an interplanetary trip.
Mushroom spores are electron-dense and can survive in the vacuum of space. Additionally, their outer layer has properties that can naturally allow the spore to deflect ultraviolet light. These aren’t theoretical attributes constructed for a hypothesis. They’re measurable physical characteristics of real spore structures. Whether that constitutes evidence of cosmic origin or simply a very well-adapted Earth organism remains an open and genuinely contested question in astrobiology.
Growing Habitats on the Moon and Mars from Fungi
As NASA prepares for long-duration missions to the Moon and Mars, a habitat-growing concept selected by the agency could help “grow” homes using fungi for future explorers. A team of researchers at NASA Ames Research Center will receive new funding under NASA’s Innovative Advanced Concepts program, with a Phase III NIAC award providing 2 million dollars over two years to continue technology development of the Mycotecture Off Planet project.
The mycotecture project team is developing technologies that could “grow” habitats on the Moon, Mars, and beyond using fungi and the underground threads known as mycelia. With this development, explorers could travel with a compact habitat built out of lightweight material containing dormant fungi. By adding water, fungi can potentially grow around that framework into a fully functional human habitat, while being safely contained to avoid contaminating the environment. Fungal mycelium makes for a great building material for multiple reasons: it’s lightweight, biodegradable, insulated, and fire retardant.
What This Means for Planetary Protection and the Future of Space Biology
If fungi survive trips to other worlds, scientists will need to develop measures to prevent these spores from contaminating other celestial bodies. Just because the fungi can tolerate radiation doesn’t make them invulnerable, and space is still a harsh environment. These are practical concerns, not philosophical ones. Any mission to Mars that carries fungal hitchhikers risks altering the very evidence scientists hope to find there.
Researchers want to learn how fungi can be used in space biomanufacturing. Fungi could help eventually produce biomaterials, medicine, and even food used to sustain life on other planets. The ability to “make, not take” certain supplies eliminates the need to transport them from Earth, saving costs. A fungus like Cladosporium sphaerospermum can start from a small sample, grow into a thicker layer, and repair itself after damage, at least in theory. The authors also discuss mixing fungal biomass or melanin with local materials such as lunar or Martian soil to create “living composites” that could combine structural and protective roles.
What began as a maintenance nuisance aboard the Mir station has evolved into one of the more serious lines of research in human spaceflight. The organism we once tried to scrub off control panels may eventually be the one that shields our astronauts from radiation, grows their shelters, and keeps them alive on another planet. That’s a strange arc, but science has a habit of finding its most useful tools in unexpected places.
