Moss spores withstand long term exposure outside space station

by Riko Seibo
Tokyo, Japan (SPX) Nov 21, 2025

Researchers have demonstrated that moss sporophytes can withstand nine months of direct exposure to outer space and remain reproductively viable upon return to Earth. The study, published November 20 in the journal iScience, tested the durability of Physcomitrium patens spores affixed to the outside of the International Space Station.

Lead author Tomomichi Fujita of Hokkaido University explained, "Most living organisms, including humans, cannot survive even briefly in the vacuum of space. However, the moss spores retained their vitality after nine months of direct exposure. 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."

Fujita and colleagues selected three structures from the moss for space tests: protenemata (juvenile moss), brood cells (stem cells that emerge under stress), and sporophytes (spore capsules). The team subjected these forms to conditions simulating space, including high ultraviolet radiation, severe temperature extremes, and deep vacuum.

UV radiation proved most damaging, with only the sporophyte spores displaying significant survival. Encased in protective layers, the spores tolerated high UV, freezing at minus 196 Celsius for a week, or 55 Celsius heat for a month. "We anticipated that the combined stresses of space, including vacuum, cosmic radiation, extreme temperature fluctuations, and microgravity, would cause far greater damage than any single stress alone," said Fujita.

The spores launched to the International Space Station in March 2022 aboard Cygnus NG-17, were attached externally for 283 days, then returned to Earth by SpaceX CRS-16. More than 80 percent survived, and of those, almost 90 percent germinated successfully in laboratory trials. Chlorophyll analyses found normal pigment levels, except for a modest decrease in chlorophyll a.

Mathematical modeling based on the experimental data suggested the spores could potentially endure up to 15 years in space conditions, though the team noted this is an estimate, and broader testing is needed.

Fujita said, "We expected almost zero survival, but the result was the opposite: most of the spores survived. We were genuinely astonished by the extraordinary durability of these tiny plant cells." He concluded, "Ultimately, we hope this work opens a new frontier toward constructing ecosystems in extraterrestrial environments such as the Moon and Mars. I hope that our moss research will serve as a starting point."

Research Report:Extreme Environmental Tolerance and Space Survivability of the Moss, Physcomitrium patens