Spores from the moss Physcomitrium patens survived 283 days exposed to the vacuum of space on the International Space Station, retaining the ability to germinate upon return to Earth. More than 80% of the spores endured the harsh conditions, surprising researchers who expected near-total failure. The findings, published in iScience, highlight moss resilience and potential for off-world agriculture.
Mosses have long been recognized for thriving in Earth's extreme environments, from Himalayan peaks to Antarctic tundra. This durability prompted researchers at Hokkaido University to test whether they could withstand space. Led by Tomomichi Fujita, the team focused on sporophytes—the reproductive structures containing spores—of Physcomitrium patens, commonly known as spreading earthmoss.
Initial lab simulations exposed different moss structures to intense UV radiation, temperature swings from −196°C to 55°C, and vacuum conditions. Sporophytes proved far superior, showing about 1,000 times greater UV tolerance than juvenile forms or brood cells. The spores' protective coating likely shielded them from harm, an adaptation that may have aided ancient plants' transition from water to land 500 million years ago.
To verify in real space, hundreds of sporophytes launched aboard the Cygnus NG-17 spacecraft in March 2022. Astronauts mounted them outside the ISS for 283 days, until retrieval via SpaceX CRS-16 in January 2023. Back in the lab, over 80% of the spores survived intact. Of those, all but 11% germinated successfully, with chlorophyll levels mostly normal except for a 20% drop in chlorophyll a.
"We expected almost zero survival, but the result was the opposite: most of the spores survived," Fujita said. "This provides striking evidence that the life that has evolved on Earth possesses, at the cellular level, intrinsic mechanisms to endure the conditions of space."
A mathematical model based on the data estimates spores could last up to 5,600 days—about 15 years—in similar conditions, though more research is needed. The study suggests moss could support ecosystems on the Moon or Mars, opening paths for extraterrestrial agriculture.