Scientists have assessed the survival of terrestrial microbes on the Moon
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- Scientists have assessed the survival of terrestrial microbes on the Moon
Terrestrial bacteria and fungi trapped on the Moon with astronauts can persist in the shaded areas of its poles for several days, and some species for at least a week. This creates a risk of contamination of samples that are planned to be collected during future manned expeditions. About which microorganisms are able to survive the lunar conditions, how they can get to the Earth's satellite and why scientists will have to reconsider the rules of research — in the material of Izvestia.
Microbes can survive the Moon landing
Bacteria and fungi associated with humans are able to remain viable on certain parts of the moon much longer than expected. This is the conclusion reached by experts from NASA and the University of Maryland.
The authors of the study examined the conditions under which five common terrestrial microorganisms can remain alive in the polar regions of the satellite. Scientists expected that the potentially suitable zones would be concentrated mainly inside permanently shaded craters. However, modeling has shown that such sites are found almost throughout the entire territory of the poles, including far beyond areas where direct sunlight never hits.
This does not mean that life has been discovered on the moon or that microorganisms imported from Earth will be able to reproduce there. We are talking only about their calculated ability to remain viable in an inactive state for some time.
Nevertheless, even this may be enough to influence the results of scientific research. Bacteria, fungal spores, and cell fragments can get into soil samples that astronauts will later deliver to Earth. In this case, it will be more difficult for scientists to determine which substances were originally present on the Moon and which were introduced by humans.
How can terrestrial bacteria get to a satellite
Humans constantly carry a large number of microorganisms on their skin, hair, clothing, and equipment. According to NASA estimates, there may be about 1 million bacteria on a piece of skin about the size of an eraser on a pencil. It is impossible to completely exclude their entry into a spacecraft or a residential module, even with strict compliance with sanitary requirements.
Life support systems, airlocks, scientific equipment, landing vehicles and spacesuits can become sources of contamination of the lunar surface. The latter are not completely isolated systems: during operation, they discharge some of the gases into the external environment. Microscopic skin particles and human-related organisms can enter the surface along with the escaping air.
In addition, microbes left inside the spacecraft may end up outside during the opening of the airlock or the movement of equipment. Purification methods can significantly reduce the number of microorganisms, but they do not ensure absolute sterility.
"Humans are natural explorers, and their voices, memories, and microbes go into space with them," said Prabal Saxena, head of the study and planetary scientist at NASA's Goddard Space Flight Center.
For automatic devices, NASA uses rather harsh disinfection methods. Some components can be heated to temperatures above 200 degrees Celsius to destroy most of the living organisms. It is impossible to use such treatment for spacesuits, living quarters and necessary equipment for people. Therefore, manned missions inevitably carry a higher risk of biological contamination.
Why are the poles particularly dangerous?
In 1969-1972, participants in the Apollo program landed in areas relatively close to the lunar equator. There, the Sun rises high enough above the horizon, and the surface receives an intense dose of ultraviolet radiation. It quickly damages cells and the genetic material of microorganisms.
Future manned expeditions are planned to be sent to the area of the Moon's south pole. It is of particular interest because of the reserves of water ice that can be found at the bottom of permanently shaded craters. In the future, this resource can be used to produce water and oxygen, as well as to produce rocket fuel components.
Geographical features that allow the ice to persist, at the same time create more favorable conditions for terrestrial microorganisms. The moon's axis is tilted only slightly, so the Sun remains low above the horizon in the polar regions. Even small hills, rocks, crater edges, and other irregularities form long shadows.
Such areas are protected from direct ultraviolet radiation, which turned out to be the main limiting factor for the studied bacteria and fungi. Low temperatures and vacuum alone do not necessarily lead to their immediate death. Freezing is used to preserve biological samples on Earth, and some organisms are able to spend a long time in a vacuum, remaining inactive.
How scientists searched for sites suitable for life
As part of the study, microorganisms were not sent to the moon. Scientists have created a computer model by combining the results of previously conducted biological experiments with detailed maps of the temperature, terrain and illumination of the satellite.
The bacteria Bacillus subtilis, Staphylococcus aureus and Deinococcus radiodurans, the fungus Aspergillus niger, known as black mold, as well as several species of the genus Fusarium were selected for analysis. These microorganisms are found near humans, and some of them have previously been found inside the International Space Station. They are also known for their increased resistance to adverse conditions.
First, experts studied the results of experiments showing what doses of ultraviolet radiation and temperature levels each organism is able to withstand. Based on this information, the survival threshold was calculated for all species.
The biological data was then compared with the characteristics of the lunar surface. First, the scientists made maps of both poles with a resolution of about 60 meters per pixel. After that, they studied in detail three possible areas of future astronaut landings — the edge of the Nobile crater, the Connecting Ridge and the edge of the De Gerlach crater. At the second stage, the model's resolution was increased to 5 m per pixel.
The ray tracing method was used to calculate the illumination. It allowed us to take into account the movement of sunlight, the reflection of radiation from the surrounding surface and the influence of individual hills, slopes and craters.
Earlier models focused mainly on latitude and actually represented the surface of the Moon as flat. Because of this, small but potentially important areas of the shadow could remain unnoticed.
"The key to this study was to account for irregularities and craters. The question was how well the relief of the Moon protects certain areas from ultraviolet radiation and whether this protection is enough to save the life of at least one of the studied organisms," said Stefano Bertone, co—author of the work, an employee of the University of Maryland.
Black mold proved to be the most resistant
Staphylococcus and Bacillus bacteria tolerated the worst simulated lunar conditions. The zones suitable for them were limited to small shaded areas, mostly located near the edges of the craters. Deinococcus and Fusarium have demonstrated somewhat greater resistance.
The Aspergillus niger fungus turned out to be the hardiest organism. It is widespread on Earth and is found in soil, humid rooms, ventilation systems and on various surfaces. Samples of this fungus have also been found inside the ISS, and previous experiments have shown that individual members of the genus are able to withstand the effects of outer space.
The resistance of Aspergillus niger to accumulated ultraviolet radiation can be ten times higher than that of the studied bacteria. Compared to fungi of the Fusarium genus, the permissible radiation dose was about nine times higher.
The model showed that in summer, Aspergillus could persist in about 2-9% of the illuminated territory of the studied polar regions, and in winter — by 15-30%. In some areas, the fungus is theoretically able to remain viable for at least seven days.
Suitable sites for it were found in all three studied areas of possible planting in detail. Moreover, some of them were located not only inside permanently shaded craters, but also in areas that periodically receive sunlight.
"When we created the lunar maps, which showed the survival areas of different species in purple, red and blue, we were surprised by how colorful they turned out to be. After that, it's already difficult to say that nothing on the moon can survive," Bertone said.
Why aren't we talking about colonizing the moon?
An organism's ability to remain viable does not mean that it will be able to grow and reproduce. Bacteria and fungal spores can survive adverse conditions in a dehydrated or dormant state, but they need a suitable environment to form a colony.
There is no confirmed combination of conditions necessary for the full development of terrestrial life on the surface of the moon. In particular, there is no stable liquid water, and vacuum, radiation and sudden temperature changes interfere with the normal course of biological processes.
Therefore, the study does not prove the possibility of spreading mold or independently developing bacterial colonies on the moon. It only shows that some cells may not die immediately after entering a shaded area.
How pollution threatens lunar expeditions
Terrestrial microorganisms can distort the results of searching for organic substances, studying the history of water, and analyzing the chemical composition of the lunar soil. Samples with an extremely low content of biological material will be particularly sensitive. Even a small number of introduced cells or their fragments can affect the results of laboratory tests.
The most valuable materials are those from permanently shaded areas that could have remained virtually unchanged for millions or billions of years. They potentially contain information about the early history of the Solar System, the origin of water, and organic compounds brought to the Moon by asteroids and comets.
After the start of regular manned expeditions, it will become more difficult to separate the initial composition of such areas from the effects of human presence. Therefore, scientists consider it necessary to collect basic information about the environment before building permanent residential modules and other infrastructure.
The problem may arise even during one expedition. If an astronaut passes through a certain area and returns there a few hours later to collect a sample, there may be microorganisms left in the ground by the spacesuit during the first visit.
In such cases, specialists will have to take into account the routes of the expedition participants, the time of collecting the material and the location of possible sources of contamination. Microbial survival maps can be used to select areas for primary soil extraction and determine the sequence of work.
"We need to understand what was there before our arrival. When we go to Mars to look for signs of life beyond Earth, we will want to make sure that we did not bring the detected organisms with us," said Andrew Needham, NASA's lunar sample pollution control specialist.
The moon will become a natural laboratory
The authors of the study consider the presence of terrestrial microorganisms not only as a threat. The polar regions of the moon can become a natural laboratory to test the real limits of bacterial and fungal resistance.
It is difficult to fully reproduce the combination of vacuum, low temperatures, radiation and unusual lighting conditions in an Earth laboratory. The controlled placement of microorganisms on the lunar surface will help determine how long they remain viable and what protection mechanisms they use.
In the future, the researchers plan to improve the accuracy of the models, obtain more detailed information about the terrain and expand the list of organisms studied. They will also have to determine how the preservation of microbes is affected by moon dust, cosmic radiation and the possible presence of soil particles inside.
The data obtained can also be useful in the preparation of expeditions to Mars. However, the results cannot be directly transferred to the Red Planet. Mars has an atmosphere, it is located further from the Sun, and the radiation intensity, pressure and temperature regime there are noticeably different from those on the moon.
At the same time, the very principle of mapping potential survival can be adapted to Martian conditions. The main task of such research is to learn how to distinguish possible traces of extraterrestrial life from organisms delivered by spacecraft and humans.
Переведено сервисом «Яндекс Переводчик»
