Mosses survive in some of the world’s most extreme environments, from the scorching sands of Death Valley to the heights of the Himalayas. Now scientists can top that list with an even more extreme example: outer space!
In a new study, samples of moss spores were exposed to space over a 9 month period outside the International Space Station (ISS). Incredibly, when returned to Earth, over 80% germinated. Publishing their work in iScience, the Japanese scientists behind the work explain how they initially subjected the well-studied moss Physcomitrium patens to a simulated space environment in their lab, which included extremes of temperatures, high levels of UV radiation, and vacuum conditions.
In their study, they tested three different moss structures to determine which had the best chance of survival in space. These were protenemata (or juvenile moss); brood cells that are specialised stem cells which emerge under stress conditions; and encapsulated reproductive spores known as sporophytes.
“We anticipated that the combined stresses of space, including vacuum, cosmic radiation, extreme temperature fluctuations, and microgravity, would cause far greater damage than any single stress alone,” says Tomomichi Fujita, of Hokkaido University.
They found that UV radiation was the toughest element to survive. Whilst none of the juvenile moss samples tolerated extreme temperatures or high UV radiation, and brood cells fared only marginally better, the sporophytes displayed a 1000-fold superior tolerance to UV. They were also able to survive and germinate after being exposed to freezing temperatures of -196°C for over a week and hot temperatures of 55°C for a month.
The case around these spores, the scientists speculate, likely acts as a physical and chemical barrier to protect the inner spore from damage. The team suggest that this is likely an evolutionary adaptation stemming from the time that the first bryophytes, the plant group in which mosses belong, transitioned from aquatic to terrestrial environments and invaded the land, 500 million years ago. The same adaptations may also have allowed these species to survive several mass extinction events since then.
“Mosses are a really interesting plant in that they were the first colonisers of the land,” points out Jen Bromley, a plant researcher at Churchill College, Cambridge, who was not involved in the study. “They were the true pioneers of surviving, going from what is a relatively stable aquatic environment – because you don’t get huge fluctuations in temperature and light UV radiation – to get out onto the land.”
To test whether these adaptations allow moss to survive in space, hundreds of sporophytes were jetted to the ISS on the Cygnus NG-17 spacecraft in March 2022. Astronauts then attached the sporophytes to the outside of the ISS and left them exposed to space for a total of 283 days, before they were returned back to the lab on Earth for testing in January 2023.
“We expected almost zero survival, but the result was the opposite: most of the spores survived,” says Fujita. “The moss spores retained their vitality after nine months of direct exposure. This provides striking evidence that the life that has evolved on Earth possesses, at a cellular level, intrinsic mechanisms to endure the conditions of space.”
Over 80% of the spores survived their time in space, and 89% of the remaining spores were able to germinate back in the lab. Using data from before and after the moss’ journey to space, the team created a mathematical model to predict that sporophytes could have survived up to 5,600 days – or approximately 15 years – in space. However, they emphasise this is a rough estimate and a larger data set is needed to generate more realistic predictions.
They hope their work aids in furthering research on the potential of extraterrestrial soils to facilitate plant growth, and also inspire the use of mosses to develop agricultural systems in space.
“Ultimately, we hope this work opens a new frontier toward constructing ecosystems in extraterrestrial environments such as the Moon and Mars,” says Fujita.
To hear more about this, listen to our interview with Dr Jen Bromley here: https://www.thenakedscientists.com/articles/interviews/moss-grows-space.