Scientists put moss on the outside of the International Space Station for 9 months — then kept it growing back on Earth
Moss spores survived a long journey through space, scientists reveal. The spores spent nine months outside the International Space Station (ISS) before returning to our planet, and more than 80% of the spores were still capable of reproducing upon their return to Earth.
This discovery improves our understanding of how plant species survive in extreme conditions, the researchers wrote in their findings, published Thursday (November 20) in the journal iScience.
Previous experiments have explored how plants might behave in space, but so far they have focused on larger organisms such as bacteria or plant cultures. Now, researchers have shown that samples of moss Physcomitrium patens (P.. Patens) can not only survive but thrive in space.
First, the researchers tested three types of cells from P. patens coming from different stages of the moss reproduction cycle. They found that sporophytes – cellular structures that enclose spores – had the greatest stress tolerance when exposed to ultraviolet (UV) light, frost and heat.
Sporophyte samples were then placed outside the ISS in a exhibition facility attached to the Japanese Kibo module, where the samples lived for about nine months in 2022. After this time, the samples were returned to Earth.
“Surprisingly, more than 80% of the spores survived and many germinated normally,” said the study’s lead author. Tomomichi Fujitaprofessor of plant biology at Hokkaido University in Japan, told Live Science in an email. From this study, Fujita and his team developed a model that suggests moss spores could survive for up to 5,600 days in space, or about 15 years.
Back on Earth, the team found that most conditions, including the vacuum of space, microgravity and extreme temperature fluctuations, had a limited impact on the moss spores. However, samples exposed to light, particularly at the high-energy wavelengths of UV light, performed less well. Levels of pigments used by the foam to photosynthesislike chlorophyll a, were significantly reduced due to light damage, which affected further growth of moss.
Although some foam samples were damaged by space conditions, P. patens always performs much better than other plant species that have already been tested under similar conditions. Fujita believes the protective, spongy coating surrounding the spores may help defend against UV rays and dehydration.
“This protective role may have evolved early in the history of land plants to help mosses colonize terrestrial habitats,” he said.
While it may seem like an exercise in testing the limits of a single species, “spore success in space could provide a biological springboard for building ecosystems beyond our planet,” Fujita said. In the future, he hopes to test other species and better understand how these resilient cells survive such stressful conditions.
