Moss spores survive and germinate after 283 days of ‘spacewalk’

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

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

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

A number of studies have already simulated whether various mosses and other plants could survive conditions outside Earth, including those that could expected on Mars. But this is the first time researchers have tested whether a type of moss can cope with real space conditions. The spores came from the species Physcomitrium open

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

Most surprisingly, more than 80 percent of the spores that were exposed to the greatest impact of space—vacuum, extreme temperatures, microgravity, UV, and cosmic radiation—remained viable and germinated into normal plants. The team predicted that it was possible that, based on the results of these experiments, some of the spores could remain viable in space for 15 years.

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

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

But the spores seemed to be able to cope with all these challenges. This is particularly impressive for the spores that were locked outside the space station, as they were hit with everything at once, whereas the tests on Earth involved only testing one stressor at a time.

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

He says it’s like being slow inside your own spacecraft. This may have been an adaptive feature they developed to cope with the harsh environmental conditions that existed on land when life first moved out of the oceans hundreds of millions of years ago.

“Spores are essentially compact capsules of life – dormant but ready to be reactivated when conditions become favorable,” he says. “It’s as if evolution has equipped them with their own tiny survival pods, built to disperse through space and time.”

Fujita says that while the research in no way proves that extraterrestrial life exists, it does make the case that life, once it emerges, 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 we often assume.”

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

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

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