When astronauts retrieved Earth moss that had been outside the International Space Station (ISS) for nine months, where
it had been exposed to the harsh environment of outer space, they were shocked to find that 80% of its spores were still
Once the spores were returned to Earth, scientists also discovered that most were capable of reproducing.
The Hokkaido University research team behind the unexpected discovery suggests that understanding this extreme Earth
organism’s durability could help mission planners evaluate potential Earth-based life forms for adaptation to future
human colonies in extraterrestrial environments like the Moon or Mars.
Selecting an Earth Organism to Test in Space
Project leader and lead author Tomomichi Fujita of Hokkaido University said the idea of exposing moss to space came to
him when his studies of plant evolution revealed the resilient Earth organism’s uncanny ability to colonize the planet’s
“I began to wonder: could this small yet remarkably robust plant also survive in space?” the researcher explained.
Before spending the resources necessary for an actual space mission, the Hokkaido scientist designed a series of
laboratory experiments to verify the plant’s potential for survival in outer space. According to Fujita, the best
candidate was Physcomitrium patens, a well-studied moss commonly known as spreading earthmoss.
In the experiments, the researchers selected three structures from the candidate moss. These included protenemata, which
are juvenile mosses; brood cells, which the team described as a specialized stem cell that “emerges under stress
conditions”; and encapsulated spores called sporophytes.
Next, the team exposed the moss to a simulated space environment. This included subjecting the three structures to high
levels of UV radiation, extreme temperatures (both high and low), and extremely low-pressure, vacuum-like conditions.
Fujita said the team anticipated that exposing the moss structures to all the combined stresses of space, such as
microgravity, extreme radiation and temperatures, and vacuum, instead of just one or two, would cause far greater damage
“than any single stress alone.”
Encouraging Lab Results Prompted ISS Goals
When examining the results, the team found that extreme UV radiation posed the greatest challenge to survival,
ultimately killing all the juvenile moss. Some of the brood cells did survive, but the researchers said the highest
survival rate under extreme UV radiation was among the sporophytes.
Compared to the other moss components, the encased spores exhibited roughly 1,000 times more UV tolerance. The team
suggests that the spore’s outer layer offers protection by physically absorbing UV radiation and blanketing the inner
spore structure “both physically and chemically.”
When comparing the results of the extreme-temperature tests, the team found that all juvenile structures had perished.
However, the spores survived after being held at 55°C for a month and then exposed to −196°C for over a week; they
remained alive and able to germinate.
Although further study is needed to determine the reason for this protective ability against temperature and radiation
extremes, the team said it is likely a 500-million-year-old evolutionary adaptation that allowed ancient bryophytes to
transition from aquatic to terrestrial environments. They suspect the same ability helped these extreme Earth organisms
survive several mass extinction events since that first adaptation.
ISS Tests Show Moss Sporophytes Possess Remarkable Ability to Survive in Space
According to a statement, the research team prepared several sporophyte samples for transport to space aboard the March
2022 Cygnus NG-17 spacecraft bound for the ISS. Upon arrival, astronauts aboard the station attached the moss spores to
the outside of the ISS, where they would be exposed to the full range of space conditions.
After 283 days of continuous exposure, the Earth organism samples were transported back home on SpaceX CRS-16 in January
2023. When the Hokkaido University team brought the samples into the lab for detailed testing, they said they had little
optimism they would have survived such lengthy space exposure.
“We expected almost zero survival,” Fujita said.
Instead, the researcher said the team found the exact opposite result: most of the spores were still alive. Upon further
examination, the team determined that 80% of the spores appeared alive and largely intact.
“Most living organisms, including humans, cannot survive even briefly in the vacuum of space,” Fujita explained.
“However, the moss spores retained their vitality after nine months of direct exposure.”
After testing spore chlorophyll levels, the team found normal levels for all types except chlorophyll a, which showed a
20% reduction below normal. The team said this reduction “didn’t seem to impact” the spores’ overall health.
Beyond the sporophyte’s ability to survive in space, the team said the most surprising result occurred when the spores
were encouraged to germinate. Shockingly, after nine months in outer space, all but 11% of the surviving spores
“This study demonstrates the astonishing resilience of life that originated on Earth,” Fujita said of the astonishing
test results. “This provides striking evidence that the life that has evolved on Earth possesses, at the cellular level,
intrinsic mechanisms to endure the conditions of space.”
“We were genuinely astonished by the extraordinary durability of these tiny plant cells,” the researcher added.
Resilient Earth Organism Could Support Future Colonies on the Moon and Mars
When discussing the application of their unexpected findings, the Hokkaido team suggested that mission planners
designing food and material systems for permanent space colonies on the moon and Mars should take a closer look at the
versatility and durability of the ancient Earth organism.
In one example, a mathematical model designed by Fujita’s team to predict how long moss could survive in space showed it
could, in theory, endure the extreme radiation, pressure, and temperature environment for as long as 5,600 days, or
While they emphasize that their model used limited data and that more research is needed to confirm the 15-year
projection, the clear durability and versatility of this extreme Earth organism, which can be used to make food, fuels,
and materials, make it an ideal study subject for potential space colonies. They also said they hope that their findings
help “advance research on the potential of extraterrestrial soils for facilitating plant growth” and inspire further
research into using mosses in agricultural systems in space.
“Ultimately, we hope this work opens a new frontier toward constructing ecosystems in extraterrestrial environments such
as the Moon and Mars,” Fujita said. “I hope that our moss research will serve as a starting point.”
The study “Extreme Environmental Tolerance and Space Survivability of the Moss, Physcomitrium patens” was published in