Extract from ABC News
Spores from spreading earth moss were exposed to space for nine months before returning to Earth. (iNaturalist: Robert Klips, Spreading-leaved earth moss, CC BY-NC 4.0)
In short:
Spores from a species of moss have survived nine months exposed to space outside the International Space Station.
Eighty per cent of the spores could reproduce when brought back to Earth.
What's next?
Several research teams are investigating the potential for different moss species in future space exploration and potential colonisation projects.
Without a space suit a human would last seconds outside the International Space Station (ISS) orbiting Earth.
But a smaller and greener plant resident of our planet is a lot hardier.
A handful of moss spores have survived nine months exposed to low-orbit conditions with 80 per cent of them still able to reproduce once back in a lab on the ground.
The results, published in the journal iScience, is the latest in a series of experiments by different scientific groups testing the capabilities of moss species for future space exploration.
That's because moss, which were some of the earliest forms of terrestrial plants on Earth, is one of the toughest oxygen-creating species on the planet.
The experiment took place on Japan's Kibō module on the ISS. (Wikimedia: NASA)
Senior study author and molecular biologist Tomomichi Fujita, from Hokkaido University, said the study demonstrated the plant's ability to survive in extreme environments.
"Our findings, together with previous seed studies, suggest that certain reproductive tissues of land plants — both seeds and spores — can exhibit remarkable tolerance to the harsh conditions of space."
Understanding the capabilities of moss could be useful in supporting genetic engineering of food crops that could thrive in deep space conditions.
Which would mean reliable food production for astronauts on long missions.
"They are small, resilient, and capable of photosynthesis under low-light conditions," Professor Fujita said.
"Their spores are light and can survive extreme desiccation.
"In the future, mosses might help create closed-loop ecosystems on the Moon or Mars, contribute to oxygen production, or even assist in soil formation for plant growth in extraterrestrial environments."
Exposing spores in space
There have been several studies on Earth to try replicate the conditions on planets like Mars for growing different species of moss.
And the ISS has also been used to test another moss species, Grimmia sessitana, which had a survival rate of 80 per cent after 31 days in a Martian-like atmosphere.
But Professor Fujita and his co-authors wanted to expose more moss for longer to see how it would fare under ultraviolet radiation and extreme temperatures (like -196 degrees Celsius).
Study co-authors Chang-hyun Maeng and Tomomichi Fujita. (Supplied: Tomomichi Fujita)
The research team selected spreading earth moss (Physcomitrium patens), found in most temperate locations around the world except South America, because of the moss' status as a model organism in biology experimentation.
This species has two main life stages.
In the "gametophyte" green photosynthetic stage, the moss grows from reproductive cells known as spores and also produces gametes (sperm and eggs).
In the second "sporophyte" stage, which follows fertilisation, the moss grows on the gametophyte and forms a capsule filled with thousands of spores.
Dried spore capsules were placed on a panel outside the Japanese experiment module on the ISS.
There, in orbit about 400 kilometres above the Earth, the spores were exposed to direct cosmic radiation, vacuum, microgravity, temperature fluctuations and full spectrum solar UV.
Ultimate survivors
Once brought back to Earth, the spores were tested for their reproductive capability.
About 80 per cent of the spores retained the ability to germinate.
Professor Fujita said so far they had not observed any major developmental abnormalities in moss grown from the returned spores.
"However, molecular and genomic analyses are ongoing to assess whether subtle damage or mutations may have occurred," he said.
Moss spores germinating after space exposure. (Supplied: Chang-hyun Maeng and Maika Kobayashi)
The study estimated the spores could last about 15 years under the same exposure conditions from the experiment.
"Future studies with longer-duration space exposure missions will be necessary to determine the true upper limits of spore viability under real space conditions," Professor Fujita said.
Climate change biologist Sharon Robinson, from the University of Wollongong, said the study showed this moss species could survive conditions worse than it currently faces on Earth.
"[That's because] these plants first evolved before they had helped create the ozone layer which now protects us all from space radiation," Professor Robinson, who was not involved in the study, said.
SETI Institute astrobiologist Agata Zupanska who was also not involved in the study, said it was always exciting to see new experimentation on the ISS with mosses.
"Exposing biological systems to environments entirely outside terrestrial evolutionary experience continues to demonstrate how remarkably adaptable life is. I am in awe every single time," she said.
But Dr Zupanska said there were limitations in the experiment conditions when trying to figure out how mosses may fare in future exploration into deeper parts of space.
"Although the external ISS environment is harsh, it does not fully represent the complexities of true deep space conditions,"Dr Zupanska said.
"To venture into deep space, and certainly to consider the possibility of terraforming other planets, we need to understand how terrestrial biology responds to the ionising radiation that permeates deep space."
Could Antarctic moss be the key to deep space travel?
Dr Zupanska is running her own space-exploration tests on a different species of moss called redshank (Ceratodon purpureus) that was collected in Antarctica.
"I needed a plant originating from one of the most extreme terrestrial environments, with naturally high tolerance to ionising radiation," she said.
"We suspect that Antarctic plants have evolved adaptations to sustain life under such harsh conditions and thus are likely to harbour genes that confer an advantage in human space exploration.
Dr Zupanska tests the moss under conditions that combine ionising radiation with microgravity, the latter of which is thought to hinder the plant's damage-repair processes.
Other species of moss like redshank (Ceratodon purpureus) are being investigated by scientists for their prospective-use in human space exploration. (iNaturalist: John Reynolds, Redshank, CC BY-NC 4.0)
Antarctic mosses are extremely tough.
Professor Robinson said C. purpureus survived in Australia's hot deserts at above 50C and Antarctic winters at -40C.
"Our work in Antarctica shows that that same moss also produces special sunscreens in its cell walls to survive under the ozone hole in Antarctica," Professor Robinson said.
"Mosses have superpowers when it comes to surviving extreme environments on Earth, we find them in both hot and cold deserts and high up mountains.
"They can survive these harsh environments because many mosses can dry out and then survive pretty much anything the natural environment throws at them, until conditions improve and they can start growing again."
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