Could one of Earth’s earliest plants hold the key to building life-support systems beyond our planet? The question gained new weight after an experiment revealed that moss spores can survive almost nine months in the raw environment of outer space, attached on the outside of the International Space Station.
Researchers at Hokkaido University, under the guidance of Tomomichi Fujita, exposed three structures of the model moss Physcomitrium patens: juvenile protonemata, stress-induced brood cells, and sporophytes diploid structures that encase reproductive spores to space conditions simulated in the laboratory. Juvenile moss, when subjected to UV radiation and extreme temperatures, did not survive, while brood cells exhibited only moderate resistance. But the sporophytes proved to be exceptional: the spores showed ~1,000 times greater UV tolerance than the brood cells, remained viable after freezing at −196°C for more than a week, and survived at 55°C for a month.
This resilience is due to the sporangium: a multi-layered capsule covering every spore. It functions both as a physical and chemical barrier, absorbing harmful UV wavelengths and buffering against desiccation and thermal extremes, a characteristic that may have developed when bryophytes first colonized land some 500 million years ago. Fujita said, “We expected almost zero survival, but the result was the opposite: most of the spores survived. We were genuinely astonished by the extraordinary durability of these tiny plant cells.”
Hundreds of sporophytes were launched in March 2022 aboard the Cygnus NG-17 spacecraft and mounted on Japan’s Kibo Exposed Facility, a platform for performing direct space exposure experiments. For 283 days, they were exposed to vacuum, cosmic radiation, microgravity, and temperature fluctuations between -196°C and 55°C. Four groups of samples had been prepared to test their resistance to light and radiation: shielded “space dark” controls, UV-filtered “space non-UV” samples, and fully exposed “space UV” samples. The germination rate remained above 95% for the shielded groups, but fell to 86% under full UV exposure, confirming that ultraviolet radiation was the most significant hazard.
Pigment analysis showed that chlorophyll a in sporophytes exposed to space was reduced by 20% reduction in chlorophyll a, implicating visible and infrared in photodegradation. Chlorophyll b and carotenoid levels showed no change, indicating that chlorophyll a may be a good indicator of photodamage relevant for extraterrestrial agriculture.
Modeling the decline in germination mathematically suggested that, under similar conditions, spores could survive for as long as 5,600 days about 15 years, although the researchers emphasize that this number is very rough. The robustness of the spores rivals or surpasses that of many extremophiles and plant seeds, making them among the most UV-resistant biological structures known.
The implications go far beyond curiosity. Mosses are pioneer plants that can initiate the processes of soil formation, moisture retention, and microbial communities. Given their low-level resource requirements and tolerance of desiccation, mosses may be among the most promising candidates for early-stage biological infrastructure in extraterrestrial habitats. Incorporating such species into bioregenerative life-support systems would contribute significantly to oxygen generation, carbon dioxide removal, and nutrient cycling on either the Moon or Mars.
Engineering hurdles are still to be overcome. Space-based crop systems need to be designed to address water delivery issues caused by microgravity, the shielding of radiation, and microbial contamination risks. NASA’s ongoing work with hydroponics, aeroponics, and plasma-based water treatment, along with autonomous plant health monitoring, offers pathways toward incorporating resilient species such as P. patens into closed-loop ecosystems. Such life support systems could incorporate moss with fast-growing microgreens or other extremotolerant crops to optimize volume use and crew dietary needs.
Historical concerns related to biological contamination in space include, but are not limited to, the debated microbial survival on Apollo 12’s recovered Surveyor 3 camera. The survival of moss spores on the exterior of the ISS reinforces both promise and caution: life from Earth can survive beyond it, an invaluable aspect of building extraterrestrial ecosystems, yet that demands strict control in order to prevent any kind of unwanted contamination. Fujita’s team regards the study as a starting point. “Ultimately, we hope this work opens a new frontier toward constructing ecosystems in extraterrestrial environments such as the Moon and Mars,” he said. The extraordinary survival of moss spores suggests that some of Earth’s simplest plants may one day play a central role in sustaining human life far from home.
