May 4, 2014
Scientists Working Hard To Prevent Microbial Invasion On Other Worlds
redOrbit Staff & Wire Reports - Your Universe Online
In order to avoid potential microbial contamination while searching for signs of microbial life on other planets, the authors of three recently-published studies have used research from the International Space Station to analyze the risks of accidentally transporting organisms from Earth into outer space.
Currently, spacecraft that land on Mars or other potentially habitable worlds have to meet strict requirements for the maximum level of microbial life, also known as bioburden. These permissible levels have been based on studies of how various life forms can survive traveling aboard a spacecraft or landing vehicle.
“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 J. Venkateswaran, a co-author on all three studies and a researcher with the Biotechnology and Planetary Protection Group at NASA's Jet Propulsion Laboratory, said in a statement Friday.
However, recent studies have indicated that such an assumption might not be valid, since some types of microbial live have proven to be hardier than previously believed and others could develop a variety of protective mechanisms in order to handle the rigors of space travel. To that end, each of the three new studies set out to investigate different types of organisms to find out how they might react to an interplanetary voyage.
The researchers are most concerned with spore-forming bacteria, since they are able to survive following some types of sterilization procedures and could be most capable of surviving after leaving Earth. In particular, Bacillus pumilus SAFR-032 spores have demonstrated high resistance to the techniques typically used to clear spacecraft, including ultraviolet radiation and treatment with peroxide, the researchers said.
They exposed Bacillus pumilus SAFR-032 to simulated conditions on Mars – an environment capable of killing many other types of bacteria in just 30 seconds – and found that it was able to remain alive for 30 minutes. In another experiment, they exposed the spores to 18 months on the European Technology Exposure Facility (EuTEF) external testing ground, and found that some of them were able to survive for the entire duration.
According to NASA, the surviving Bacillus pumilus SAFR-032 spores “had higher concentrations of proteins associated with UV radiation resistance and, in fact, showed elevated UV resistance when revived and re-exposed on Earth. The findings also provide insight into how robust microbial communities are able to survive in extremely hostile regions on Earth and how these microbes are affected by radiation.”
A second study involved drying out spores of Bacillus pumilus SAFR-032 and another spore-forming microbe, Bacillus subtilis 168, on pieces of spacecraft-quality aluminum. They were then subjected to 18 months of the vacuum of space, as well as cosmic and extraterrestrial solar radiation and temperature changes, on EuTEF. The samples were then subjected to a simulated Martian atmosphere using the external testing facility.
“Most of the organisms exposed to solar UV radiation in space and in the Mars spectrum were killed, but when UV rays were filtered out and samples were kept in the dark, about 50 percent or more of those subjected to other space- and Mars-like conditions survived,” the US space agency explained. “That makes it likely that spores could survive a trip on a spacecraft to Mars if they are sheltered against solar radiation.”
“The third study placed rock-colonizing cellular organisms in the EuTEF facility for 1.5 years, further testing a theory of how organisms might move from one planet to another, known as lithopanspermia,” the space agency added. “In this scenario, rocks ejected from a planet by impact with, say, a meteor, carried organisms on their surface through space and then landed on another planet, bringing that life with them.”
As part of this research project, scientists selected microbes that were specifically adapted to survive in some of the most extreme environmental conditions on Earth. They discovered that some of these organisms were also able to thrive in the harsher conditions of outer space. While it would require at least thousands of years, the study provided the first evidence that lithopanspermia could survive on rocks carried through space from one planet to another.
“Future exploration missions can use the results of these investigations to help find ways to minimize the risk of contaminating another planet,” NASA said. “The findings also will help prevent scientists from incorrectly identifying an organism that hitchhiked on the exploring spacecraft as a native of the planet, when in fact it's an invader. That's a good thing, because no one wants to be responsible for an alien invasion of Mars.”
All three of the papers detailing the research - Survival of Rock-Colonizing Organisms After 1.5 Years in Outer Space, Resistance of Bacterial Endospores to Outer Space for Planetary Protection Purposes and Survival of Bacillus pumilus Spores for a Prolonged Period of Time in Real Space Conditions – were published in the Astrobiology Journal.