By Harshit
TOKYO, NOV. 25, 2025 —
Mosses are known for colonizing the harshest corners of Earth — from Himalayan peaks to Antarctic deserts — but new research reveals that their resilience reaches even farther. According to a study published November 20 in iScience, moss spores mounted on the exterior of the International Space Station (ISS) survived nine months in open space, enduring vacuum, cosmic radiation, extreme temperature swings, and intense ultraviolet light. More than 80% returned to Earth still capable of germination.
This is the first confirmed evidence that an early land plant can withstand direct space exposure for such an extended period.
“Most living organisms, including humans, cannot survive even briefly in the vacuum of space,” said lead author Tomomichi Fujita of Hokkaido University. “But these moss spores retained their vitality after nine months of direct exposure. This shows that Earth-evolved life has intrinsic cellular mechanisms to endure space conditions.”
A Question Born from Evolution: Could Moss Survive in Space?
Fujita began asking whether moss might withstand space while studying the evolution of early land plants. Mosses thrive in conditions that crush most life — on volcanoes, desert heat, and freezing polar climates. That durability sparked a deeper question: if moss can dominate Earth’s extremes, what about the extremes of space?
To explore this, Fujita’s team focused on Physcomitrium patens, a common laboratory moss. They tested three structures:
- Protonemata (juvenile growth)
- Brood cells (stress-induced stem cells)
- Sporophytes containing encased spores
The aim was to see which form could withstand the combined punishment of vacuum, UV radiation, heat, cold, and microgravity.
Encased Spores Show Exceptional Survival
Laboratory experiments revealed that UV radiation was the most lethal factor. Protonemata died under strong UV and extreme temperatures. Brood cells performed slightly better but still suffered significant damage.
Sporophyte-encased spores, however, were in a class of their own.
They showed:
- ~1,000× higher UV tolerance
- Survival after −196°C for over a week
- Survival after 55°C for a month
- Ability to germinate after exposure to simulated vacuum and cosmic radiation
The team concluded that the protective capsule around each spore absorbs harmful UV radiation and shields the cellular interior — a trait that may have played a role in early plants colonizing land 500 million years ago.
This durability warranted a real-world test in orbit.
A Real-World Test on the ISS
In March 2022, hundreds of moss sporophytes were launched aboard the Cygnus NG-17 spacecraft and mounted on the exterior of the ISS. They remained exposed to full space conditions for 283 days, with:
- Direct cosmic radiation
- Repeated freeze-thaw cycles
- Full vacuum
- Harsh UV rays
- Microgravity
The spores returned to Earth in January 2023 aboard SpaceX CRS-16.
What researchers expected to find was near-total destruction. Instead, they found the opposite.
Over 80% Survived — and Most Remained Fully Functional
Back in the lab, more than 80% of the moss spores were intact. Even more impressively, 89% of the survivors successfully germinated. Pigment analyses showed normal chlorophyll levels, except for a modest 20% reduction in chlorophyll-a.
“Seeing such strong survival was genuinely astonishing,” Fujita said. “This demonstrates the extraordinary resilience of life that originated on Earth.”
Using the radiation and environmental data, the team modeled potential survival time in similar conditions. Their estimates suggest moss spores could withstand space exposure for up to 15 years — though more research is needed.
Implications: Plants May One Day Thrive on the Moon or Mars
The findings bolster the idea that life on Earth possesses innate survival mechanisms that could function elsewhere in the solar system.
The research opens doors to:
- Growing plants in extraterrestrial environments
- Studying how early life spreads between planets
- Understanding which organisms are best suited for off-world agriculture
- Using mosses as pioneer species for lunar or Martian ecosystems
“Ultimately, we hope this work opens a new frontier toward constructing ecosystems in extraterrestrial environments such as the Moon and Mars,” Fujita said.
The study was supported by Hokkaido University, JSPS KAKENHI, and Japan’s Astrobiology Center.