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Fall 2005 Vol. 5 No. 3



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©Photodisc Alien Invaders


Preventing Earth Microbes from Contaminating Mars




The setting is Mars. The year is 2016. A rover is searching the planet's surface for traces of life. Weeks later and millions of miles away on Earth, scientists begin analyzing the data they have received and cannot believe what they see: DNA. What's more, the DNA belongs to organisms that look like the bacteria found on Earth.

Could this scenario happen in the future? Twelve spacecraft have already landed or crashed on Mars, possibly carrying microorganisms from Earth. Although each craft was cleaned before takeoff, the level of cleanliness is now being questioned. Some microorganisms called extremophiles might survive and grow in extreme, Mars-like conditions -- such as very low-temperature and high-salt environments. But since many of these microbes were undiscovered until recently, detection and cleaning techniques currently in use may only be spotting and eliminating a fraction of them. Should these organisms go undetected and survive the trip to Mars, their chance of survival is increased if they encounter water -- although the presence of liquid water on or below the Martian surface today has not been confirmed.

To prevent contamination of Mars and avoid hampering efforts to find life there, NASA should develop over the coming decade new measures to detect and eliminate microorganisms on robotic spacecraft before they leave Earth, says a new report from the National Research Council.

"We don't know enough about how many and which of these hardy microorganisms may be on our spacecraft," said study chair Christopher F. Chyba, professor of astrophysics and international affairs at Princeton University, Princeton, N.J. "We need to better understand which of those organisms found on the spacecraft have the best chances for growing in Martian environments and then devise techniques to get rid of them."

Pre-launch preparation of Mars Explorer Rover 1 at the Kennedy Space Center in Florida, photo courtesy NASA/JPL/KSC

NASA currently uses procedures that detect heat-resistant and spore-forming bacteria and then attempts to eradicate them by cleaning the spacecraft and, in certain circumstances, baking parts of it with dry heat. NASA has been developing other methods but greater resources are needed, the report says.

To identify a larger variety of microorganisms, NASA should apply techniques already used by biologists that do not require extra time for culturing the organisms in a laboratory and adapt these methods to provide more accurate estimates of the types and number of microorganisms present on and inside spacecraft and in their assembly areas. These advanced methods -- which can determine genetic sequences of organisms and link them to known microbial species -- could allow NASA to tailor sterilization techniques toward spacecraft contaminants of greatest concern, the report says.

NASA should investigate and test alternative cleaning methods -- such as radiation or vapor disinfectants -- for their effectiveness in killing different types of microorganisms and for their effects on various spacecraft materials. If such techniques are fully tested and implemented in time for spacecraft launching in 2016, the scenario described above can be averted. By preventing the introduction of Earth microbes to Mars, scientists may one day find life forms genuinely native to the red planet. Once humans set foot there -- as envisioned by NASA's new Vision for Space Exploration -- it will be tougher to avoid contamination.   -- Patrice Pages


Preventing the Forward Contamination of Mars. Committee on Preventing the Forward Contamination of Mars, Division on Engineering and Physical Sciences (2005, approx. 180 pp.; ISBN 0-309-09724-X; available from the National Academies Press, tel. 1-800-624-6242; $38.00 plus $4.50 shipping for single copies).

Christopher F. Chyba, professor of astrophysics and international affairs at Princeton University, Princeton, N.J., chaired the committee. The study was funded by NASA.



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Copyright 2005 by the National Academy of Sciences