A collaborative effort by Japanese scientists has subjected various life stages of the model moss species, Physcomitrium patens, including its juvenile forms (protonemata), specialized stress-induced stem cells (brood cells), and encapsulated spore structures (sporophytes), to simulated extraterrestrial conditions. Their investigations pinpointed spores as possessing the highest degree of hardiness. Subsequently, these resilient spores were exposed directly to the harsh realities of the space environment aboard the International Space Station (ISS). Following an exposure period spanning nine months, a remarkable survival rate exceeding 80% was observed, with the spores retaining their fundamental capacity for germination. These findings underscore the extraordinary robustness of Physcomitrium patens spores when confronted with space conditions and illuminate the potential for terrestrial flora to withstand extreme environmental stressors.
Physcomitrium patens spores survive simulated space conditions with high resilience. Image credit: Maeng et al., doi: 10.1016/j.isci.2025.113827.
Given the rapid environmental transformations occurring on Earth in contemporary times, the pursuit of novel avenues for life’s persistence beyond our home planet has gained considerable significance.
Ascertaining the capacity of Earth-originating organisms to endure austere and alien conditions, such as those encountered in outer space, represents a critical preliminary phase in the endeavor to establish human settlements on celestial bodies like the Moon or Mars.
An in-depth examination of the survival thresholds of biological entities across both terrestrial and extraterrestrial settings will not only deepen our comprehension of their adaptive capabilities but also furnish valuable insights for preparing to sustain complex ecosystems.
“The vast majority of living entities, including humankind, are incapable of enduring even brief exposure to the vacuum of space,” stated Dr. Tomomichi Fujita, a researcher affiliated with Hokkaido University.
“Nevertheless, the moss spores managed to preserve their viability after enduring direct exposure for a duration of nine months.”
“This observation provides compelling corroboration that life, as it has evolved on Earth, possesses inherent mechanisms at the cellular stratum that enable it to withstand the rigors of space conditions.”
In the course of their scientific inquiry, Dr. Fujita and his associates subjected Physcomitrium patens, a widely studied moss species colloquially referred to as spreading earthmoss, to an environment meticulously engineered to mimic space conditions. This simulation encompassed intense ultraviolet (UV) radiation, extreme thermal fluctuations (both high and low), and the pervasive vacuum.
They systematically evaluated three distinct developmental stages of Physcomitrium patens – protonemata, brood cells, and sporophytes – with the objective of identifying which offered the greatest potential for survival in an extraterrestrial context.
“Our hypothesis was that the composite stresses characteristic of space, encompassing vacuum, cosmic radiation, drastic temperature variations, and microgravity, would inflict substantially more profound damage than any individual stressor alone,” remarked Dr. Fujita.
The research team concluded that UV radiation presented the most formidable challenge to survival, and the sporophytes emerged as unequivocally the most robust among the three moss structures examined.
No instances of survival were recorded for the juvenile moss specimens when subjected to high UV levels or extreme temperatures.
While the brood cells demonstrated a superior survival rate, the spores, when enclosed within sporophytes, exhibited a tolerance to UV radiation that was an order of magnitude greater, approximately 1,000 times more resilient.
Furthermore, the spores proved capable of surviving and subsequently germinating after being subjected to temperatures as low as minus 196 degrees Celsius for over a week, as well as enduring temperatures of 55 degrees Celsius for an entire month.
The scientific consensus suggests that the protective casing encompassing the spore acts as a robust shield, effectively absorbing incident UV radiation and providing both physical and chemical insulation to the inner spore, thereby averting damage.
This phenomenon is likely an evolutionary adaptation that facilitated the transition of bryophytes—the plant division to which mosses belong—from aquatic to terrestrial existence approximately 500 million years ago, and enabled their survival through multiple mass extinction events in the intervening epochs.
In March 2022, the researchers successfully dispatched hundreds of sporophytes to the ISS via the Cygnus NG-17 spacecraft.
Upon their arrival, astronauts affixed the sporophyte specimens to the exterior of the ISS, where they remained exposed to the space environment for a cumulative total of 283 days.
The moss samples then commenced their return journey to Earth aboard the SpaceX CRS-16 mission in January 2023, ultimately being transported back to the laboratory for rigorous examination.
“We had anticipated a near-total absence of survival, but the outcome was the inverse: the majority of the spores persevered,” conveyed Dr. Fujita.
“We were genuinely taken aback by the extraordinary fortitude exhibited by these microscopic plant cells.”
In excess of 80% of the spores successfully navigated their cosmic voyage, and all but 11% of the surviving spores subsequently demonstrated the ability to germinate upon their return to the laboratory.
The research team also conducted an analysis of the chlorophyll content within the spores, observing normal levels across all specimens. The sole anomaly detected was a 20% reduction in chlorophyll a—a pigment particularly sensitive to variations in visible light—though this alteration did not appear to adversely affect the overall vitality of the spores.
“This investigation serves as a testament to the astonishing resilience inherent in life forms that originated on Earth,” affirmed Dr. Fujita.
Motivated by curiosity regarding the potential duration of the spores’ survival in space, the researchers leveraged the data collected both prior to and following the moss’s extraterrestrial expedition to construct a predictive mathematical model.
Based on this model, they projected that the encased spores could potentially endure space conditions for a maximum of 5,600 days, which approximates to 15 years.
However, they strongly emphasize that this figure represents a preliminary estimation, and a more comprehensive dataset is imperative for formulating more precise projections concerning the longevity of moss survivability in space.
“Ultimately, our aspiration is that this research will pave the way for the establishment of entirely new paradigms in the construction of ecosystems within extraterrestrial locales such as the Moon and Mars,” articulated Dr. Fujita.
“It is my sincere hope that our investigations into moss will serve as a foundational catalyst for such advancements.”
The findings derived from this research are meticulously detailed in a scholarly publication featured in the esteemed journal iScience.
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Chang-hyun Maeng et al. Extreme environmental tolerance and space survivability of the moss, Physcomitrium patens. iScience, published online November 20, 2025; doi: 10.1016/j.isci.2025.113827
