Physcomitrium patens Moss Spores Show Remarkable Survival After Nine Months in Open Space

A recent investigation conducted by Japanese biologists has confirmed the extraordinary resilience of spores belonging to the common moss Physcomitrium patens when subjected to the harsh environment of open space. Samples of this ancient terrestrial plant, which first colonized Earth approximately 500 million years ago, endured an exposure period of 283 days—roughly nine months—attached to the exterior panel of the International Space Station (ISS). The findings, officially released on November 20, 2025, indicated that a substantial fraction of these microscopic structures retained complete viability, opening exciting new avenues for concepts related to extraterrestrial life support.

The research initiative was spearheaded by Professor Tomomichi Fujita of Hokkaido University. His team was motivated by the known hardiness of mosses, which thrive even in extreme terrestrial settings such as the high altitudes of the Himalayas and the frigid plains of Antarctica. The spores were launched into orbit in March 2022 aboard the Cygnus NG-17 cargo vessel. Their return journey to Earth took place in January 2023, facilitated by the SpaceX CRS-16 mission. Prior to the space exposure, laboratory tests simulating the space environment revealed that sporophytes—the encapsulated spores—exhibited roughly a thousand times greater resistance to ultraviolet (UV) radiation compared to more delicate cellular structures, such as gemmae, which registered a 70% mortality rate under simulated UV stress.

The conditions faced by the samples mounted on the ISS exterior were extreme, encompassing a complete vacuum, microgravity, and severe thermal fluctuations ranging dramatically from about -196°C to 55°C. Intense UV radiation proved to be the most damaging element. Nevertheless, the spore’s protective casing, the sporangium, functioned effectively as a biological shield. Upon retrieval and return to Earth, the spores that endured the full spectrum of space stressors demonstrated an impressive survival rate of 86%. Furthermore, samples that were shielded from direct UV exposure achieved an even higher success rate, showing 97% germination, a figure comparable to the ground-based control group.

Given this high level of persistence, Professor Fujita and his colleagues developed preliminary projections for the spores' potential viability duration in space, estimating it could extend up to 5600 days, or roughly 15 years. This projection offers a solid foundation for planning the biological components of future long-duration interplanetary voyages. However, Dr. Agata Zupanska from the SETI Institute offered a necessary analytical perspective, cautioning that surviving in a dormant state is not equivalent to actively growing and flourishing in an alien environment. The critical questions regarding P. patens's capacity for active proliferation under reduced gravity and altered atmospheric compositions on locations like the Moon or Mars remain subjects for forthcoming scientific inquiry.

From the standpoint of applied astrobiology, these results hold direct relevance for developing bioregenerative life support systems (BLSS). Such systems are crucial for providing astronauts with oxygen and facilitating soil creation at off-world outposts. Mosses, being pioneers in terrestrial colonization, are considered prime candidates for these applications, possessing the ability to convert regolith into habitable substrate. Although the surviving specimens showed a minor reduction—specifically 20% less chlorophyll 'a'—their demonstrated capacity to germinate underscores the powerful evolutionary reserve embedded within plant spores.