Mosses are already known for coping with harsh radiation, dehydration, and long freezes. Now scientists have pushed them even further by exposing their spore capsules to open space for nine months, and most of them survived.
The team worked with spreading earthmoss (Physcomitrium patens), a small moss species used widely as a plant model by researchers. Its spore-containing capsules were mounted on the outside of the International Space Station (ISS), where they experienced direct solar radiation, vacuum conditions, and sharp temperature swings during each orbit.
Under those conditions, cells usually break down quickly. So the researchers were surprised by what came back. “We expected almost zero survival, but the result was the opposite,” says Hokkaido University biologist Tomomichi Fujita. More than 80 percent of the spores still germinated once they returned to Earth.
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The team detected a small drop in chlorophyll a, but the other pigments remained stable. The spores grew normally in follow-up tests, showing no signs of major stress from their time in orbit.
This kind of toughness fits with the evolutionary history of mosses. Bryophytes — the group that includes mosses, liverworts, and hornworts — were among the first plants to move from water onto land about 500 million years ago. Their spores had to withstand drying and direct sunlight long before soils existed, which may explain why their protective structures still hold up so well today.
The results place moss spores alongside the few organisms known to tolerate direct space exposure, including tardigrades and certain microbes. Their survival also adds to ongoing discussions about what types of life might endure extreme environments beyond Earth.
According to the researchers, this durability could matter for future experiments on the Moon or Mars. Mosses need very little soil and can pull nutrients directly from rock, making them candidates for early ecosystem tests in extraterrestrial settings.
“Ultimately, we hope this work opens a new frontier toward constructing ecosystems in extraterrestrial environments such as the Moon and Mars,” says Fujita. “I hope that our moss research will serve as a starting point.”
The research was published in iScience. Read the study here.