WASHINGTON -- NASA faces a dilemma in planning to send people to Mars: The scientific desire to search for life there versus the need to prevent any such life from endangering the astronauts or the Earth.
The National Research Council is recommending that safety take precedence and that missions to the Red Planet try to avoid encountering any possible life forms there.
"While the threat to Earth's ecosystem from the release of Martian biological agents is very low, the risk of harmful effects is not zero and cannot be ignored," the council said in a report released Wednesday.
The NRC urged NASA to establish "zones of minimal biological risk" by sending automated probes to test for organic chemicals or other life forms.
Astronauts could then be sent to areas with the lowest possible risk of encountering life that might either pose a threat to them or to Earth if it returned with them.
And in an additional step to avoid bringing back contamination, the study said, the returning spacecraft might have to be abandoned in space with the astronauts transferred to another vehicle to get back to Earth.
While NASA has not scheduled a human mission to Mars, it asked the council to study what measurements and studies need to be done in advance. Unmanned space probes have studied the planet in flybys and by landing on its surface.
Mars has long fascinated astronomers. The planet is known to once have had considerable water on its surface, making it a prime candidate for life forms such as bacteria, which many scientists believe could still exist in the Martian soil.
A Mars landing craft would inevitably become coated with dust, and astronauts walking on the planet to do scientific work would bring some dust back inside with them, as happened on the trips to the moon.
To prevent a return of this material to Earth, the report suggested a transfer in space where the returning craft is docked to another vehicle and the astronauts are transferred in a sterile atmosphere.
If the return vehicle could not be sterilized in space it might have to be discarded and never come back to Earth, the report said.
And NASA "might be faced with requiring quarantine and surveillance of returning astronauts until it is determined that a threat no longer exists."
Other recommendations in the study:
-NASA should determine the rock size, shape and abrasiveness at potential landing sites.
-An unmanned Mars lander needs to study the adhesiveness of dust on that planet.
-Potential radiation exposure at planned landing areas need to be assessed.
-NASA should study the threat of toxic elements on Mars and design filters to protect the astronauts from them. A particular concern is hexavalent chromium, a rare material on Earth which, studies suggest, may be present in larger amounts on Mars.
-The presence of high concentrations of sulfur and chlorine on Mars suggest the possibility of acidity in the soil and airborne dust. This needs to be measured and prepared for.
The National Research Council is a part of the National Academy of Sciences, an independent agency chartered by Congress to provide advice to the government on scientific issues.
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