Moss Survives Outside Space Station For 9 Months, Marking Historic First

‘Astonished’ Scientists Believe Study Could Help Support Colonization Of Mars

Life finds a way, even in the extreme conditions of outer space. A common moss survived nine months bolted to the outside of the International Space Station and came back ready to grow. More than 80% of the spores stayed viable after enduring the vacuum of space, radiation bombardment, and temperature swings from extreme heat to deep freeze.

This marks the first time any bryophyte has been exposed to actual space conditions and returned alive, according to research published in iScience. The findings could reshape how scientists think about establishing life on other planets, with mosses potentially serving as pioneers for transforming barren worlds into habitable environments.

The research team at Hokkaido University in Japan found that the vast majority of spores survived after 9 months in space, retaining their ability to germinate. Incredibly, when brought back to Earth and placed in growing conditions, the moss spores sprouted into healthy green filaments as if their cosmic journey had been just another day.

The moss in question, Physcomitrium patens, is a common model organism scientists have studied for decades, chosen precisely because it represents typical plant biology. Establishing that this ordinary moss can survive in space opens the door for understanding how Earth’s plant life might thrive elsewhere in the solar system.

Nine Months Beyond Earth’s Protection

Starting in March 2022, researchers placed moss spores encased in their protective sporangia onto an exposure facility mounted on the outside of the ISS. For 283 days, these tiny packages of life faced the vacuum of space, cosmic radiation, and UV radiation hitting at full intensity without Earth’s atmospheric filter.

The research team tested the moss under different conditions. Some samples were shielded from UV light but exposed to vacuum, radiation, and temperature extremes. Others faced the full assault. A ground control stayed in darkness on Earth, and another set of spores sat in a shaded part of the exposure unit outside the station.

When the samples returned to Earth in January 2023, scientists extracted the spores and attempted to grow them. The results exceeded expectations. Spores kept in darkness in space showed a 95% germination rate. Those exposed to visible and infrared light hit 97%. Even the group blasted with UV radiation managed 86% germination.

Better Than Nature’s Toughest Survivors

Before launching moss into orbit, the research team conducted extensive ground tests to see which life stage of the moss could handle extreme conditions. They tested three types: actively growing filaments called protonemata, stress-resistant cells called brood cells, and spores encased in their protective sporangium.

The comparisons revealed a clear hierarchy of survival. Regular growing cells died quickly under most extreme conditions. Stress-resistant brood cells fared better but still showed significant mortality. Spores protected by their sporangium, however, demonstrated extraordinary tolerance.

When blasted with UV radiation at 254 nanometers, regular cells died at exposures that barely scratched the spores. The spores survived doses of 12 million joules per square meter, roughly 1,000 times more than the brood cells could handle. That kind of radiation would sterilize most surfaces on Earth.

The team also compared moss spores to other organisms known for extreme survival. Tardigrades, microscopic animals famous for tolerating harsh conditions, couldn’t match the moss’s UV resistance. Spores from certain bacteria showed similar vulnerability. Even other supposedly hardy organisms failed where moss spores succeeded.

Perhaps most telling, some plant seeds showed comparable or even greater UV tolerance than the moss spores. This pattern suggests that plants, with their protective structures and biochemical defenses, may be better suited for space survival than many animals.

“Most living organisms, including humans, cannot survive even briefly in the vacuum of space,” says lead author Tomomichi Fujita of Hokkaido University, in a statement. “However, the moss spores retained their vitality after nine months of direct exposure. 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 Sporangium Shield

What makes these spores so tough? The answer lies in their packaging. In mosses, spores develop inside a sporangium, layers of protective tissue that form a biological shield. When researchers examined what happened during space exposure, chlorophyll levels in the sporangium’s outer tissues dropped by about 20% after light exposure, suggesting this coating absorbed punishment that would otherwise destroy the spores inside.

Seeds in flowering plants have seed coats serving a similar protective function. Moss sporangia represent an earlier evolutionary solution to the same problem: keeping reproductive cells safe until conditions favor growth.

The moss spores also appear to have intrinsic defenses beyond their packaging. The sporangium contains pigments like flavonoids and carotenoids that can absorb UV radiation, turning it into harmless heat before it reaches critical cellular machinery. These compounds evolved to protect against Earth’s UV exposure, but they work even better in space’s unfiltered radiation environment.

From Earth to Mars

The research team didn’t conduct this experiment just to see if moss could survive space. They’re thinking about practical applications for human expansion beyond Earth.

Bryophytes like mosses were the first plants to colonize land roughly 500 million years ago. They transformed Earth’s early terrestrial environment, creating conditions that allowed other life forms to follow. The researchers suggest mosses could play a similar pioneering role on other worlds.

“Bryophyte could be used for planetary greening and life support systems,” the study states.

Picture a Mars base in its early stages. Sealed habitats provide temporary shelter, but long-term colonization needs more sustainable solutions. Mosses could serve multiple roles in such scenarios. They produce oxygen through photosynthesis. They can help convert rocky regolith into something closer to soil by breaking down minerals and adding organic matter. They’re efficient at carbon dioxide removal, which matters in closed environments.

The researchers specifically note mosses’ “efficient carbon fixation, oxygen production, and adaptability to low-light conditions.” These traits make them ideal for life support systems where resources are limited.

Some moss species already grow in Earth’s extreme environments, from Antarctica to hot deserts. The desert moss Syntrichia caninervis, tested in separate experiments, showed even greater tolerance than the species used in this study. When dried, that moss survived Mars-like simulated conditions for seven days without significant loss of viability.

What This Means for Space Exploration

Space agencies have long studied how to establish sustainable human presence beyond Earth. Current life support systems on the ISS rely heavily on mechanical and chemical processes. Plants provide some support but remain secondary to engineered solutions.

This research suggests a different approach might be possible. If mosses can survive the journey through space and establish themselves in harsh conditions, they could become foundational to extraterrestrial ecosystems. Rather than building everything from scratch with imported materials, future colonists might work with biology to create self-sustaining environments.

The timeline for such applications remains uncertain. Crewed missions to Mars and long-term lunar bases are still in planning, and the exact timelines are unclear. Still, knowing that common Earth mosses can survive space exposure changes what’s theoretically possible.

The researchers calculated that at the observed rate of degradation, moss spores could potentially survive up to 5,600 days in space conditions, roughly 15 years. They cautioned this estimate comes from limited data points and should be interpreted carefully. But even if the actual survival time is shorter, it’s long enough for interplanetary transport and establishment.

Questions Still Remaining

The study opened as many questions as it answered. Researchers only measured whether spores could germinate after space exposure. They didn’t track what happened during later developmental stages or whether the plants showed any abnormalities in structure or function.

Space radiation might cause genetic mutations that don’t immediately affect germination but could appear in subsequent generations. Temperature extremes might damage cellular machinery in ways that only become apparent during complex developmental processes. The study’s scope didn’t extend to these longer-term effects.

The experiment also used spores specifically, not growing plants. Spores represent dormant life stages designed to withstand stress. Active photosynthesis, cell division, and growth might face different challenges in space conditions. Some of the protective mechanisms that work for dormant spores might not apply to actively growing tissues.

In conclusion, while mosses might tolerate space during transport, establishing them in extraterrestrial environments presents additional challenges. Mars has one-third Earth’s gravity, a thin carbon dioxide atmosphere, no liquid water on the surface, and temperatures that regularly drop far below freezing. Surviving nine months in orbit doesn’t automatically mean moss will thrive in Martian regolith.

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