Life on Earth is remarkably resilient, thriving in environments ranging from deep-sea hydrothermal vents to frigid glaciers. However, the harshness of outer space—with its vacuum, extreme temperatures, and intense ultraviolet (UV) radiation—poses a challenge unlike any found on our planet. Yet, an increasing number of terrestrial organisms have demonstrated the extraordinary ability to survive these hostile conditions. Recently, scientists have added a new member to this elite group: a species of moss known as Physcomitrium patens. This discovery, led by researchers from Hokkaido University in Japan and published in the journal iScience, broadens our understanding of life’s potential to endure beyond Earth.
Outer space is an unforgiving environment. It lacks breathable air, exposes organisms to damaging UV radiation, and fluctuates between freezing cold and scorching heat. Despite these extremes, certain life forms have shown surprising tenacity. Among the most famous are tardigrades—microscopic animals also known as water bears—that can survive complete dehydration and exposure to space. Additionally, the small flowering plant Arabidopsis thaliana, commonly known as thale-cress, has demonstrated resilience in space conditions. Now, Physcomitrium patens joins this remarkable list, illustrating that mosses, one of the earliest groups of land plants, can also persist beyond our atmosphere.
Mosses are a particularly fascinating group of plants. They were among the first to colonize terrestrial environments roughly 500 million years ago, transitioning from aquatic habitats to land during a pivotal period in Earth’s evolutionary history. Physcomitrium patens is a species commonly found near pools of water in temperate regions across Europe, North America, and East Asia. The research team set out to test how different stages of this moss would respond to space-like conditions.
To simulate the rigors of space, the scientists exposed three distinct stages of the moss to UV radiation, freezing temperatures, and heat. These stages included the protonemata—the juvenile phase of the moss; brood cells, which are specialized cells that form under stressful conditions; and spores, the reproductive units contained within a tough capsule called a sporangium. Among these, the spores exhibited the greatest resilience, outperforming the juvenile and brood cells in surviving the simulated space environment.
The spores’ robustness surprised the researchers. Plant biologist Tomomichi Fujita, a co-author of the study, expressed particular interest in how much stronger the spores were than anticipated. To further assess their durability, the spores were sent to the International Space Station (ISS) where they were mounted on an exposure platform from early March to late December 2022. After spending approximately nine months in orbit, the spores were returned to Earth and cultivated in petri dishes. Remarkably, over 80 percent of the spores germinated successfully, demonstrating their ability to endure the extreme conditions of space.
While the spores’ survival rate was impressive, the researchers noted that their growth was slower than expected. This delayed germination raised intriguing questions about the mechanisms underlying their resilience. Fujita noted that the spores might survive space due to their dormant state during exposure, which could protect them from damage. However, the team does not yet fully understand why these spores are so hardy or the exact biological processes that enable their survival.
The next phase of the research aims to uncover the genetic factors that contribute to the spores’ tolerance. Scientists want to determine if the spores suffered any UV-induced DNA damage during their time in space and, if so, how they repaired it. Understanding these mechanisms could provide valuable insights into how terrestrial life withstands the challenges of space environments.
This research holds profound implications for the future of space exploration and the possibility of sustaining life beyond Earth. By studying how various forms of terrestrial life—including mosses, flowering plants, and microorganisms—respond to space conditions, scientists gain clues about how life might be supported in extraterrestrial habitats. While the idea of expanding human presence into the stars remains a distant goal, investigations like these lay the groundwork for future endeavors in space colonization and biological sustainability.
The discovery that moss spores can survive in space not only expands our knowledge of extremophiles but also challenges existing perceptions about the limits of life. As University of Florida space biology expert Robert Ferl, who was not involved in the study, remarked, “The fact that another major group of terrestrial life can survive in space, as far as physical findings, is cool. Terrestrial life may not be limited to the Earth.” This perspective