Moss Spores Survive 283 Days of Direct Space Exposure, Return Viable

Astronauts have successfully returned spores of the moss species *Physcomitrium patens* (spreading earthmoss) to Earth after they endured 283 days attached to the exterior of the International Space Station (ISS). The experiment concluded with the spores being brought back via a SpaceX capsule for germination testing, which revealed a high rate of survival.

The samples were installed on March 4, 2022, and exposed directly to the extreme conditions of the space environment, including vacuum, severe temperature fluctuations, microgravity, and unfiltered cosmic and ultraviolet (UV) radiation. Research led by Professor Tomomichi Fujita of Hokkaido University in Japan, whose findings were published in the journal *iScience* on November 20, 2025, indicated that over 80% of the spores fully exposed to space retained their viability. Upon return to Earth, these spores successfully germinated into normal plants.

Professor Fujita, a member of the Japanese Society for Biological Sciences in Space, has conducted extensive research into the molecular mechanisms of plant environmental response, including how mosses adapt to harsh terrestrial environments such as volcanic fields and Antarctic regions. This investigation was prompted by the moss's natural ability to colonize difficult terrestrial settings. Initial tests on other moss structures, like filaments, showed rapid failure when subjected to a single stressor, such as UV radiation.

The directly exposed, unprotected spores achieved an 86% germination rate, contrasting with the control group maintained on Earth, which reached 97%. A group protected only from UV radiation also showed a high 97% germination rate. Professor Fujita theorizes that the double layer of the spore wall provides an inherent evolutionary defense, acting as a passive shield against external space pressures. Mathematical modeling by the research team estimates these spores could remain functional in space for up to 15 years.

This study represents the first time a land plant has demonstrated long-term survival while directly exposed to outer space conditions. The resilience of *Physcomitrium patens* spores significantly surpasses historical data for flowering plant seeds, such as *Arabidopsis thaliana* and *Nicotiana tabacum*, which showed survival rates near a quarter after over a year and a half in space, though subsequent generations exhibited growth and fertility disruptions. This finding reinforces the robustness of life evolved on Earth and provides a foundation for future space agriculture on the Moon or Mars.

Researchers noted a 20% decrease in chlorophyll a, a light-sensitive pigment, in the space-exposed spores; however, this reduction did not appear to compromise the overall health of the organisms. Professor Fujita emphasized that this result provides clear evidence of intrinsic cellular mechanisms enabling Earth life to endure space conditions. Future steps will involve assessing the DNA damage accumulated during the nine months in orbit and monitoring the plants' capacity for repair following exposure to the combined cosmic and solar radiation.