Photo: NASA
Scientists have discovered that Physcomitrium patens spores remained viable after enduring the extreme conditions of orbit.
Moss spores that spent nine months on the exterior of the International Space Station (ISS) successfully returned to Earth and retained their ability to reproduce, according to LiveScience. Researchers report that over 80% of P. patens spores survived prolonged exposure to outer space.
Moss is known for its resilience in harsh environments such as the Himalayas or Death Valley. This durability made it a promising candidate for space experiments, where organisms are exposed to radiation, temperature fluctuations, and altered gravity. Previous plant experiments in space have largely focused on bacteria or crops rather than mosses.
In the new study, published in the journal iScience, the team first tested three types of P. patens cells for resistance to ultraviolet radiation, cold, and heat. Sporophytes—the structures containing spores and responsible for reproduction—showed the strongest resilience. These were placed in a specialized exposure unit on the exterior panel of Japan’s Kibo module, where the moss remained for approximately nine months in 2022. Based on the data, researchers developed a model predicting that moss spores could withstand space conditions for up to 5,600 days, nearly 15 years.
“Remarkably, over 80% of the spores survived, and many germinated normally,” said lead author Tomomichi Fujita from Hokkaido University, as reported by LiveScience.
Upon returning to Earth, the team found that most space factors—vacuum, microgravity, and temperature fluctuations—did not cause significant damage. However, light exposure, especially ultraviolet radiation, did affect the moss: chlorophyll A and other photosynthetic pigments decreased, impacting subsequent growth. Despite partial damage from the harsh space environment, P. patens spores demonstrated far greater viability than other plant species previously tested in similar conditions. Researchers suggest that the spores’ protective, sponge-like coating helps shield them from UV radiation and dehydration.
“This protective function likely evolved early in the history of land plants to help mosses colonize terrestrial habitats,” Fujita explained.
The findings could have practical implications for future space missions. “The success of spores in space may provide a biological springboard for building ecosystems beyond our planet,” Fujita said. Researchers plan to expand experiments to other plant species to better understand the limits of plant survival in space environments.
