Tough Moss Spores Weather Space’s Harsh Conditions

The tiny tardigrade is often hailed as one of the most resilient animals, but it's far from the only organism capable of surviving extreme conditions. In fact, certain types of moss can endure everything from scorching heat to freezing cold, high levels of UV radiation, and much more here on Earth. But how would moss fare in space?

This question motivated Tomomichi Fujita, a plant evolutionary and developmental biologist at Hokkaido University, to investigate the model moss Physcomitrium patens’ ability to endure space. The findings, published in iScience, demonstrated that the moss spores were highly resilient against UV radiation and extreme temperatures when exposed to space outside of the International Space Station (ISS).¹ Not only did these spores survive for a grueling nine months, but they also retained their ability to germinate back on Earth. "Ultimately, we hope this work opens a new frontier toward constructing ecosystems in extraterrestrial environments such as the Moon and Mars,” said Fujita in a press release.

First, Fujita and his colleagues subjected P. patens to a simulated space environment which included high levels of UV radiation, extreme temperature fluctuations, and vacuum conditions. They studied three different moss tissues: protenemata, or juvenile moss; brood cells, or specialized stem cells that emerge under stress conditions; and sporophytes, or encapsulated spores.

Of these, the juvenile moss succumbed to the harsh conditions, while the brood cells fared only slightly better. However, the sporophytes were the most resilient. Notably, the encapsulated spores exhibited approximately 1,000 times more tolerance to UV radiation than the brood cells. The researchers noted that this structure may provide a protective barrier against the elements.

With this in mind, the researchers prepared to send these spores into space aboard Cygnus NG-17. In March of 2022, they sent hundreds of sporophytes to the ISS, where astronauts attached the samples to the outside structure. The moss endured three different conditions for nine months within a two-layered space exposure unit: space darkness (samples in the bottom section that are not exposed to light), space exposure (samples in the top section exposed to light) with a UV-blocking filter, and space exposure without a UV filter.

Back on Earth, the researchers found that more than 80 percent of the spores survived across all three groups. Of these, the space exposure with UV group had the lowest germination rate (86 percent). This suggested that visible and infrared light have negligible effects on germination, whereas UV radiation was more of a detrimental factor. “We expected almost zero survival, but the result was the opposite: Most of the spores survived,” said Fujita in the statement. “We were genuinely astonished by the extraordinary durability of these tiny plant cells.”

In addition, the researchers created a mathematical model to predict how long the spores could survive in space. It came up with approximately 15 years. While further research is needed to identify the factors that contribute to this resilience, the researchers hope that this work helps advance research for future endeavors in space agriculture on the Moon and Mars.