This Hokkaido University study, published in iScience, found that multiple moss strains mounted outside the International Space Station for nine months largely survived and could still germinate after return. Over 80% of spores remained viable despite chlorophyll loss. Distinct strain-specific resistances suggest potential for planetary greening and life-support applications in future off-Earth habitats.
Moss Spores Survive Nine Months on the ISS — Still Able to Germinate Back on Earth
This Hokkaido University study, published in iScience, found that multiple moss strains mounted outside the International Space Station for nine months largely survived and could still germinate after return. Over 80% of spores remained viable despite chlorophyll loss. Distinct strain-specific resistances suggest potential for planetary greening and life-support applications in future off-Earth habitats.
05:08 AM, 11/21/2025Science
Researchers at Hokkaido University report that moss spores exposed to outer space for most of 2022 survived extreme conditions on the exterior of the International Space Station and were still able to germinate after being returned to Earth. The findings, published in the journal iScience, point to the remarkable resilience of certain terrestrial plants and suggest potential applications for future off-world habitats.
Study setup and conditions
Moss samples (bryophytes) were affixed to the exterior of the ISS and left exposed to vacuum, intense radiation, wide temperature swings and strong light for nine months. These conditions mimic many of the extreme stressors organisms would encounter in space and on other planetary surfaces.
Key results
Although chlorophyll—the pigment that gives moss its green color—degraded during exposure, the researchers found that more than 80% of spores across the experiment remained viable after nine months in space. Importantly, when the samples were returned to Earth, many spores were still capable of germination and normal growth.
The team also tested multiple moss strains and observed distinct differences in tolerance. One strain showed traits that likely protect against ultraviolet radiation, heat and intense light; another displayed characteristics that the authors say could make it a candidate for "planetary greening" and integration into life-support systems.
Why bryophytes were chosen
Bryophytes have a deep evolutionary history on land, dating back roughly 500 million years. Their natural tolerance for desiccation, freezing and radiation made them ideal subjects for testing survival limits in an extraterrestrial setting.
Implications and next steps
These results expand our understanding of how simple land plants respond to space environments and support the idea that hardy vegetation could play roles in future lunar or Martian habitats—both for ecological engineering and as components of life-support systems. The authors note that further research is needed to explore long-term growth, reproduction under reduced gravity, and how different species might be combined for practical off-world ecosystems.
"Understanding the resilience of Earth-born organisms in extreme and unfamiliar conditions, such as the space environment, is a crucial step toward expanding human habitats other than Earth like the Moon or Mars," the authors write.
Overall, the study highlights that simple plants like mosses may be more capable of surviving—and later reproducing—after exposure to space than previously recognized.