Bacteria from Earth could quickly colonize the surface of Mars, according to new research conducted aboard the International Space Station (ISS).

Research into bacterial colonization on the red planet was not part of the plan to terraform the alien world ahead of human occupation. Instead, three teams investigated how to prevent microbes from Earth from hitching a ride to the red planet aboard spacecraft.

It is nearly impossible to remove all biological contaminants from equipment headed to other planets. By better understanding what organisms can survive in space or on the surfaces of other worlds, mission planners can learn which forms of microscopic life to concentrate on during the sanitation process.

"If you are able to reduce the numbers to acceptable levels, a proxy for cleanliness, the assumption is that the life forms will not survive under harsh space conditions," Kasthuri Venkateswaran of the Jet Propulsion Laboratory and co-author of all three papers, said.

Researchers investigated the problem using independent experiments. The first used the EXPOSE-E facility aboard the ISS. The team then proceeded to expose organisms known to be hardy on Earth to 18 months in space.

"It was found that some... are also partially resistant to the even more hostile environment of outer space, including high vacuum, temperature fluctuation, the full spectrum of extraterrestrial solar electromagnetic radiation, and cosmic ionizing radiation," a group of international researchers wrote.

A second team, composed of researchers from the German Aerospace Center, California Institute of Technology and Jet Propulsion Laboratory exposed bacteria to space conditions, also for a year and a half. They used the European Technology Exposure Facility (EuTEF) on the space station to conduct their experiment.

"After 18 months of exposure... under dark space conditions... spores showed 10-40% survivability, whereas a survival rate of 85-100% was observed when these spores were kept aboard the ISS under dark simulated martian atmospheric conditions," the team reported.

When bacteria of the Firmicute phylum come under stress, they can form protective shells, called endospores. These coatings protect the organisms from harm from extreme environmental conditions like droughts. Biologists wanted to know if these structures could protect bacteria from sanitation processes and the harsh environment of space.

A team from Germany, France and the United States subjected bacteria to conditions similar to those expected on a trip to, and on the surface of, Mars. Only ultraviolet light was proven to be effective at killing the organisms.

"All other environmental parameters encountered by the 'trip to Mars' or 'stay on Mars' spores did little harm to the spores, which showed about 50% survival or more. The data demonstrate the high chance of survival of spores on a Mars mission, if protected against solar irradiation," the investigators wrote in the article announcing their results.

The investigations of interplanetary microbe contamination were all published together in the Astrobiology Journal.

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