Moss spores survive and germinate after 283-day ‘space walk’

On March 4, 2022, astronauts locked 20,000 moss spores outside the International Space Station and exposed them to the rigors of space for 283 days. They then collected the spores and brought them back to Earth aboard a SpaceX capsule so that scientists could attempt to germinate them. Surprisingly, these attempts were successful.

Mosses were among the first land plants and are well known for colonizing some of the harshest environments on Earth – Antarctica, volcanic fields and deserts, says Tomomichi Fujita of Hokkaido University in Japan, who was part of the team that conducted the experiment.

“We wondered whether their spores could also survive exposure to space – one of the most extreme environments imaginable,” he says.

Many studies have already simulated the ability of various mosses and other plants to survive conditions beyond Earth, including those that might be expected on Mars. But this is the first time researchers have tested whether a species of moss can adapt to real-world space conditions. The spores came from the species Physcomitrium patens.

A control group of spores that remained on Earth had a 97% germination rate, as did another set of spores exposed to space but protected from the harmful ultraviolet rays there.

Most astonishingly, more than 80% of the spores exposed to the full weight of space – vacuum, extreme temperatures, microgravity, UV and cosmic radiation – remained viable and germinated into normal plants. The team predicted that it is possible that, based on the results of these experiments, some spores could remain viable in space for 15 years.

“Opening the samples was like opening a biological time capsule: life that had endured the vacuum of space and returned fully functional,” Fujita says.

Before deployment, the researchers had already tested other living parts of the moss, such as its filaments, under simulated conditions. They found that other moss life stages succumbed to UV rays, freezing and heating, high salinity and dehydration within days or weeks.

But the spores seemed capable of meeting all these challenges. This is particularly impressive for the spores that were locked outside the space station, since they were hit by everything at once, whereas the tests on Earth involved each testing just one stressor at a time.

Fujita says the multiple layers of spore walls that envelop reproductive tissue appear to offer “passive protection against spatial stresses.”

He says it’s like the spores are inside their own spaceship. This may be an adaptive feature they evolved to cope with the harsh environmental conditions that existed on earth when life first left the oceans, hundreds of millions of years ago.

“Spores are essentially compact life capsules – dormant but ready to reactivate when conditions become favorable,” he says. “It’s as if evolution has equipped them with their own tiny survival modules, designed to disperse in both space and time.”

Fujita says that while the research in no way proves the existence of extraterrestrial life, it reinforces the idea that life, once it appears, can be incredibly robust. “The fact that terrestrial life forms can withstand space-like conditions suggests that the building blocks of life may be more widespread and persistent than often thought.”

David Eldridge, of the University of New South Wales in Sydney, says the real test is not whether the spores will germinate once they return to Earth, but whether they can also germinate in space.

“The trick will be to check the growth rates of these taxa in space and see if they can reproduce,” he explains.