How resilient is life? Scientists are now presenting new findings on the survivability of particularly robust bacterial species in space: When clumped together in clumps, they can survive the harsh conditions for years, according to experiments on the outer shell of the International Space Station. Thus, in the form of such aggregates, they could also survive a journey between Earth and Mars, say the scientists.
Does life develop independently of one another or can it also pass from one heavenly body to another as a kind of seed? The hypothesis known as “panspermia” states that microbial life forms travel through space and trigger an evolution after landing on suitable celestial bodies. This idea implies that such life forms can withstand the vacuum, temperature fluctuations and radiation exposure in space for long periods of time. Scientists working with Akihiko Yamagishi from the Japanese Space Agency (JAXA) in Tokyo have been researching the possibility of panspermia for some time. As part of the “Tanpopo” project, they are investigating the resistance of certain organisms under the conditions of space.
It is already known from previous studies that some life forms can survive in space for a certain time under certain circumstances. Especially when microbes are surrounded by protective material such as rock, long survival spans seem conceivable. This form of a corresponding expansion in space is known as lithopanspermia. But to what extent is it possible for microbial space travelers to survive without the stone capsules?
Exposure tests on the ISS
The current study started with the discovery of viable bacteria in the outer areas of the terrestrial atmosphere. Research balloons have collected these representatives of the Deinococci at a height of twelve kilometers above the earth. Results of laboratory experiments then suggested that these microbes have great resistance to extreme conditions. It was also shown that the deinococci form what are known as aggregates – clumps of bacteria that can reach sizes of over a millimeter. So the question arose to what extent the microbes in this form can withstand the conditions in space. The cell aggregates may act as a kind of ark in the interplanetary transfer of microbes, so the hypothesis.
To test this, the scientists carried out long-term experiments on the International Space Station (ISS). For this purpose, deinococcal aggregates of different sizes were exposed to the conditions of near-earth space on exposure plates outside the station. The samples were brought back inside the ISS after one, two or three years. Then culture experiments made it clear to what extent some of the microbes were still viable.
It turned out that in aggregates with a thickness of more than 0.5 millimeters, the bacteria had survived after three years and were able to repair genetic damage suffered. However, the investigations showed that the bacteria had died on the surface of the aggregates. As the researchers explain, these dead apparently formed a protective layer for the bacteria underneath and thus enabled the colony to survive. Based on the survival rates after exposure for one, two and three years, the researchers were also able to estimate the time course of death and thus draw conclusions about the maximum abilities. According to this, an aggregate more than 0.5 millimeters thick could survive significantly longer periods of time in near-Earth space: between 15 and 45 years.
Possible journeys between Earth and Mars
As far as the assessments of the survivability when traveling through the interplanetary areas are concerned, the scientists come to the following assessment: Under these aggravated conditions, a colony with a diameter of one millimeter could still survive for up to eight years. “The results therefore suggest that radiation-resistant deinococcal aggregates could survive a journey from Earth to Mars and vice versa that would take several months or years,” says Yamagishi. While earlier experiments had shown the possibility of lithopanspermia in rocks, the current study now provides an indication of the possibility of so-called “Massapanspermia” through aggregates of microbes, say the scientists.
Nevertheless, the transmission of life between celestial bodies has so far naturally remained a hypothesis that needs to be explored further, the scientists emphasize. In addition to the ability to survive in space, it is also questionable how the forms of life taking off and landing could survive. Yamagishi and his colleagues will now continue to research the possibility of panspermia as the origin of life on celestial bodies. The researcher is particularly interested in one thought: “If panspermia is possible, life could exist in space much more often than we previously thought,” says Yamagishi.
Source: Frontiers, Frontiers in Microbiology, doi: 10.3389 / fmicb.2020.02050