Astronauts exposed 20,000 moss spores to space conditions outside the International Space Station for 283 days starting on 4 March 2022. The spores, from the species Physcomitrium patens, were returned to Earth via a SpaceX capsule and successfully germinated. Over 80 percent of the fully exposed spores remained viable, highlighting the resilience of moss in extreme environments.
On 4 March 2022, astronauts attached 20,000 spores of the moss species Physcomitrium patens to the exterior of the International Space Station (ISS), exposing them to the vacuum of space, extreme temperatures, microgravity, ultraviolet (UV) radiation, and cosmic radiation for 283 days. The samples were retrieved and returned to Earth aboard a SpaceX capsule, allowing researchers to test their viability.
Tomomichi Fujita at Hokkaido University in Japan, who led the experiment, noted that mosses are among the earliest land plants known for thriving in harsh Earth environments like Antarctica and deserts. "We wondered whether their spores might also survive exposure to outer space – one of the most extreme environments imaginable," he said.
The results were striking: a control group of spores kept on Earth germinated at 97 percent, as did spores exposed to space but shielded from UV radiation. Most surprisingly, over 80 percent of the spores fully exposed to space conditions germinated into normal plants. The team estimates that such spores could remain viable in space for up to 15 years.
"Opening the samples felt like unlocking a biological time capsule: life that had endured the void of space and returned fully functional," Fujita said. He attributes the spores' survival to multiple protective layers in their walls, acting like "passive shielding against space stresses." These layers may have evolved to handle early terrestrial challenges when life transitioned from oceans to land.
"Spores are essentially compact life capsules – dormant but ready to reactivate when conditions become favourable," Fujita explained. "It’s as though evolution equipped them with their own tiny survival pods, built for dispersal across both space and time."
Prior lab tests showed other moss parts, like filaments, succumbing to individual stressors such as UV, freezing, or dehydration within days to weeks. However, the spores withstood the combined space rigors.
While the study does not prove extraterrestrial life exists, Fujita says it demonstrates life's robustness: "The fact that terrestrial life forms can endure space-like conditions suggests that life’s building blocks may be more widespread and persistent than we often assume."
David Eldridge at the University of New South Wales in Sydney cautioned that true endurance requires testing growth and reproduction in space itself. "The trick will be to check the growth rates of these taxa in space and see whether they can reproduce," he said.
This marks the first real-space test for moss spores, building on simulations for Mars-like conditions. The findings were published in iScience (DOI: 10.1016/j.isci.2025.113827).