This moss grew from a spore that was in space for nine months.
Tomomichi Fujita
On March 4, 2022, astronauts trapped 20,000 moss spores outside the International Space Station and left them exposed to the harsh conditions of space for 283 days. They then rescued the spores and returned them to Earth on a SpaceX capsule so scientists could try 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 from Hokkaido University in Japan, who was on the team that conducted the experiment.
“We wondered whether their spores could survive exposure to outer space, one of the most extreme environments imaginable,” he says.
Numerous studies have already modeled whether various mosses and other plants can survive in conditions beyond Earth, including one that can expect on Mars. But for the first time, researchers are testing whether a particular type of moss can cope with real space conditions. The controversy originated from the species Physcomitrium open
A control group of spores remaining on Earth had a germination rate of 97 percent, as did another set of spores that were exposed to space but protected from the damaging ultraviolet radiation found there.
Most amazingly, more than 80 percent of the spores that were exposed to the full effects of space—vacuum, extreme temperatures, microgravity, UV, and cosmic radiation—remained viable and grew into normal plants. Based on the results of these experiments, the team predicted that some spores could remain viable in space for 15 years.
“Opening the samples was like opening a biological time capsule: life that had survived the void of space and returned fully functional,” says Fujita.
Before the launch, 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 are susceptible to exposure to UV radiation, freezing and heating, high salinity and dehydration over a period of days or weeks.
But spores seem to have overcome all these problems. This is especially impressive for the spores that were locked outside the space station, since they were hit all at once, whereas each ground test involved testing only one stressor at a time.
Fujita says the multiple layers of spore walls that surround reproductive tissue appear to provide “passive protection against cosmic stress.”
He says it's like the spores are inside their own spaceship. This may have been an adaptive feature that they developed to cope with the harsh environmental conditions that existed on land when life first emerged from 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 capsules designed to disperse across space and time.”
Fujita says that while the study in no way proves the existence of extraterrestrial life, it does reinforce the fact that life, once it arises, can be incredibly resilient. “The fact that terrestrial life forms can survive conditions similar to those in space suggests that the building blocks of life may be more widespread and resilient than we often think.”
David Eldridge at the University of New South Wales in Sydney say the real test is not whether the spores will germinate on Earth, but whether they can also germinate in space.
“The challenge will be to test the growth rates of these taxa in space and see if they can reproduce,” he says.
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