Key Takeaways:
- A study led by Tomomichi Fujita investigated the survivability of the extremophile moss *Physcomitrium patens* in space, a critical inquiry for establishing extraterrestrial human habitats.
- Pre-flight experiments identified the sporophyte stage, which encases spores, as the most resilient structure, demonstrating exceptional resistance to simulated space conditions including extreme temperatures and UV radiation.
- Hundreds of *P. patens* sporophyte samples were exposed for 283 days on the International Space Station to the vacuum of space, temperature fluctuations, microgravity, and direct UV radiation, with over 80% retaining vitality and germinating upon return to Earth.
- These findings indicate that bryophytes possess inherent mechanisms and protective structures enabling their endurance in space, suggesting their potential utility in transforming extraterrestrial regolith and contributing to self-sustaining ecosystems on the Moon or Mars.
If humans are to expand our habitat beyond Earth’s bounds, we will undoubtedly need the support of plant life: to remove carbon dioxide, provide oxygen, and create fertile soil. But is it possible for plants originating on Earth to survive in the extreme conditions of space? A team of scientists led by Tomomichi Fujita, a biologist at Hokkaido University, put that question to the test with one of Earth’s toughest plants: moss.
Moss belongs to the group bryophyte. These extremophiles (plants adapted to the most extreme conditions) reproduce not through flowers or seeds, but spores. As one of the first plants to adapt to terrestrial life on Earth, bryophytes have proven their resilience over the last 500 million years, thriving in some of the planet’s harshest conditions: the Himalayas, Death Valley, active volcanic lava fields, and the Antarctic tundra. Scientists have also proven the extent of their toughness in even more extreme environments, such as simulated Mars-like atmospheric conditions. For the first time, however, Fujita and his team tested whether these extremophiles could actually survive in outer space.
They launched hundreds of spore samples of the moss species Physcomitrium patens into orbit in 2022, and exposed them to the vacuum of space for nine months on the exterior of the International Space Station (ISS). The results, published Nov. 20 in iScience, were impressive: over 80 percent of the samples were able to germinate once returned to Earth.
“[T]he 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,” Fujita said in a press release.
Staying grounded
Before launching the spores into space, Fujita and his team first conducted experiments on the ground. The team chose Physcomitrium patens as their test subject because it has been well-studied over the past several decades, its genome is fully sequenced, and its genes are easy to manipulate. They tested the moss’s response to several of the environmental factors that it would be exposed to in space: UV radiation, extreme temperatures, and vacuum conditions.
“We anticipated that the combined stresses of space, including vacuum, cosmic radiation, extreme temperature fluctuations, and microgravity, would cause far greater damage than any single stress alone,” Fujita said in the press release.
To determine which stage of the moss’s life cycle would be the most resilient, the team subjected three different structures of the plant to the extreme conditions: juvenile moss, also known as protonemata; special stress-resistant cells that form in drought conditions known as brood cells; and sporophytes, the specialized structures that produce spores and shelter them within a protective capsule called the sporangium.
The sporophytes proved to be the toughest of the bunch. None of the protonemata survived the extreme temperatures or UV radiation. And while the brood cells fared better than the protonemata, their resilience paled in comparison to the sporophytes. The encased spores exhibited around 1,000 times more resistance to the UV radiation than the brood cells and were able to germinate successfully after prolonged exposure to extreme conditions, including 131 degrees Fahrenheit (55 degrees Celsius) for 30 days and -112 F (-80 C) for 30 days. They even showed a 9 percent germination rate after being subjected to -321 F (-196 C), a simulation of deep space.
Into the void
To further investigate the moss’s resistance to extreme conditions, the team launched hundreds of sporophyte samples to orbit in February 2022 aboard the Cygnus NG-17. The samples were divided into four groups: a control group that was left on Earth and shielded from light (ground dark), a space control group shielded from light (space dark), a space group shielded from UV (space non-UV), and a space group that was not shielded from UV (space UV). Upon arrival at the ISS, the astronauts placed the samples in the station’s exposure-testing facility, where they remained for 283 days.
Once the samples were returned to Earth, the team attempted to germinate the sporophytes. The ground dark and space dark groups had 97 and 95 percent germination rates, respectively. The space non-UV group had a 97 percent germination rate, revealing that exposure to vacuum conditions, temperature fluctuations, and microgravity had limited effects on the sporophyte’s survival. However, the most impressive result was the 86 percent germination rate of the spores from the space UV group.
Evolutionary armor
Bryophytes were some of the first plants to survive the transition from the aquatic to the terrestrial environment on Earth, a leap that required evolving defenses against a much harsher world. The team believes the exceptional resilience of the sporophytes results from a powerful synergy: the spores’ inherent durability combined with the sporangium’s external protection. While this structure originally evolved to protect the moss from the harsh conditions of land — including desiccation, intense UV radiation, and temperature extremes — it inadvertently provided the perfect armor for the vacuum of space. With the moss’s durability established, the team sought to determine the upper limits of its survival.
Pioneering a new frontier
Using a computer model based on the collected data, the researchers believe that sporophytes could potentially survive up to 15 years in space conditions. The team points out, however, that this data is just an estimate: “This estimation is based only on two points … and should therefore be interpreted with caution,” they warn in the paper.
Regardless, the results suggest that bryophytes like Physcomitrium patens could play a huge role in humanity’s journey beyond Earth. The team proposes that the moss could be used to help transform lunar or martian regolith into fertile soil and aid in the creation of self-sustaining ecosystems on other planets.
“Ultimately, we hope this work opens a new frontier toward constructing ecosystems in extraterrestrial environments such as the Moon and Mars. I hope that our moss research will serve as a starting point,” Fujita said in the press release.
