Moss in space: spores survive nine-month ride on outside of ISS

Matt Damon grew potatoes for survival in The Martian, but researchers say mosses could one day help turn the dust and rocks of other planets into fertile soil. Physcomitrella patens, or spreading earthmoss, is already known as a pioneering species – albeit for being an early plant on the scene in areas of barren mud. Now researchers have found that spores of the moss can survive for at least nine months stuck to the outside of the International Space Station (ISS) and still reproduce once back on Earth. Although the plant is inedible, researchers say the findings could be important for space exploration. Dr Tomomichi Fujita, the lead author of the study, from Hokkaido University in Japan, said: “While moss may not be on the menu, its resilience offers insights into developing sustainable life-support systems in space. Mosses could help with oxygen generation, humidity control or even soil formation.” It is not the first time researchers have highlighted the remarkable survival abilities of moss, or sent such species to the ISS. Indeed, such plants are known to tolerate a host of extreme conditions on Earth, while scientists have found that the desert moss species Syntrichia caninervis can withstand Mars-like conditions in experiments on Earth. Writing in the journal iScience, Fujita and colleagues report how they exposed three different moss structures to a simulated space environment on Earth. They found that moss spores encased in a structure known as a sporangium were the most resilient and were able to germinate after exposure to UVC radiation levels that exceeded 100,000 joules per square metre. Further tests suggested these encased spores were also resilient towards vacuum conditions, deep-freezing, high temperatures and radiation within a vacuum. The researchers then sent encased spores to the ISS onboard the Cygnus NG-17 spacecraft. These were attached to the outside of the ISS in sample holders with different filter settings and left for nine months. After the samples were returned to Earth, the researchers found all showed high rates of germination, noting that even those that had been fully exposed to UV radiation in space had a 86% germination rate – compared with a 97% germination rate for spores that had remained on Earth. However, a type of chlorophyll in the space-exposed samples showed signs of degradation. “If such spores can endure long-term exposure during interplanetary travel and then successfully revive upon rehydration and warming, they could one day contribute to establishing basic ecosystems beyond Earth,” Fujita said. He noted that the study focused only on survival under space exposure. “Whether moss can germinate and grow under various extraterrestrial conditions – including different gravity levels, atmospheric compositions and radiation levels – remains an open question,’” Fujita said. Dr Agata Zupanska, of the Seti Institute, who was not involved in the work, welcomed the study but said it was already known that dormant, desiccated biological forms such as spores or seeds exhibited significantly greater resistance to environmental extremes than hydrated cells or tissues. She said similar seed exposure experiments, including on space crop seeds, had already been conducted outside the ISS. Zupanska also stressed that the external ISS environment, while harsh, did not fully represent the complexities of true deep space conditions, including those on the moon or Mars. “The value of space plants is realised only if they can actively grow and thrive away from Earth,” she said. “While spore resilience is important, it represents only an initial step toward the broader goals of growing plants in extraterrestrial environments.”