Mosses are among Earth's hardiest plants, thriving from Antarctic coasts to Mount Everest and even on fresh lava flows. As bryophytes — the group that includes mosses, liverworts and hornworts — they were among the first plants to colonize land roughly 500 million years ago and have endured intense ultraviolet radiation, extreme temperature swings and long dry spells.
From lab simulations to the vacuum of space
New research now adds the vacuum and radiation of space to the list of extreme environments moss can withstand. Scientists tested the moss species Physcomitrium patens in the lab under simulated space-like conditions — extreme temperature cycles, very high UV radiation and vacuum — then exposed different life stages to see which survived best.
They compared juvenile moss, specialized stem cells and spores protected inside reproductive capsules called sporangia. The shielded spores proved vastly more resilient: they tolerated UV radiation about 1,000 times better than stem cells, a resilience the authors attribute to the protective properties of the sporangium.
Real orbital exposure on the ISS
In March 2022 the researchers sent hundreds of spores to the International Space Station aboard the Cygnus NG-17 spacecraft. Crew members mounted the spores on the station's exterior and divided them into three groups: uncovered but protected from UV by a filter (visible light only), completely blocked from all light (dark control), and fully exposed to both visible and ultraviolet radiation encountered in low Earth orbit. After 283 days the samples returned to Earth for analysis.
“We expected almost zero survival, but the result was the opposite: Most of the spores survived,”
said Tomomichi Fujita, a plant evolutionary and developmental biologist at Hokkaido University and co-author of the study.
Testing showed that more than 80% of the spores remained viable after nine months in orbit. Germination reached up to 97% for spores that were shielded from UV in space, while spores exposed to full space light and UV still germinated at 86%. The team observed signs of chlorophyll damage in spores exposed to space light that were not present in the dark-kept controls.
What this means — and what it doesn't
Combining laboratory simulations and orbital exposure data, the researchers estimate these moss spores could survive on the order of 15 years in space. That places moss alongside other extremophiles known to withstand space conditions, such as tardigrades and some fungi.
The authors suggest moss could someday support long-duration human missions by producing oxygen or helping to improve soil fertility for crops aboard spacecraft or on extraterrestrial outposts. However, experts urge caution: survival of spores is only an initial step. “The ISS does not fully replicate deep-space conditions,” Agata Zupanska, a biologist at the SETI Institute, noted, and successfully cultivating actively growing plants away from Earth presents many additional challenges.
Overall, the findings demonstrate remarkable durability in a tiny plant life stage and open new questions about how terrestrial life might persist beyond our planet — and how we might harness that resilience for future space exploration.
