The sporophyte capsules of the model moss Physcomitrium patens were attached to the outside of the ISS for nine months. After return, more than 80% of spores still germinated, and chlorophyll a levels fell by about 20% without harming viability. Researchers say these results point to intrinsic cellular mechanisms for surviving extreme conditions and may inform future efforts to develop biological systems on the Moon or Mars.
Moss Spores Survive Nine Months in Space — Over 80% Still Germinate After ISS Exposure
The sporophyte capsules of the model moss Physcomitrium patens were attached to the outside of the ISS for nine months. After return, more than 80% of spores still germinated, and chlorophyll a levels fell by about 20% without harming viability. Researchers say these results point to intrinsic cellular mechanisms for surviving extreme conditions and may inform future efforts to develop biological systems on the Moon or Mars.
09:21 AM, 11/21/2025Science
Moss spores endured nine months exposed on the exterior of the International Space Station and returned to Earth largely intact. Researchers report that more than 80% of the spores of the model moss Physcomitrium patens were still able to germinate after direct exposure to the vacuum, ultraviolet radiation, and temperature extremes of space.
Hokkaido University biologist Tomomichi Fujita, who led the experiment, said the team was surprised by the results.
"We expected almost zero survival, but the result was the opposite: most of the spores survived," Fujita said. "We were genuinely astonished by the extraordinary durability of these tiny plant cells."
The researchers mounted spore-containing capsules (sporophytes) on the outside of the ISS for nine months. On return, laboratory culturing showed robust germination in the majority of samples. The team measured only about a 20% reduction in chlorophyll a levels, while other chlorophyll forms remained at normal concentrations — a loss that did not appear to impair spore viability.
Previous ground-based experiments had suggested that the sporophyte—an encased reproductive structure—provides exceptional protection against ultraviolet radiation, extreme heat and cold, and dehydration. The space exposure results reinforce the idea that certain cellular and structural traits help these reproductive units survive harsh conditions.
These findings have broader implications. Bryophytes (mosses, liverworts and hornworts) are thought to have been among the first plants to colonize land about 500 million years ago. Their resilience likely helped early plants extract nutrients from rock and form the soils that allowed terrestrial ecosystems to develop.
Because of that hardiness, mosses are gaining attention from astrobiologists and researchers exploring the possibility of establishing biological systems on the Moon or Mars. Fujita cautioned that survival as spores in space does not mean full ecosystems can yet be sustained off Earth, but he suggested the results open new avenues for studying how terrestrial life might be adapted or supported in extraterrestrial environments.
The study was led by Tomomichi Fujita and colleagues and was published in the journal iScience.