In a move that might seem like something out of Hollywood, American scientists are taking serious steps to safeguard against an invasion from outer space.
The potential visitants aren't Martians or meteorites but microscopic organisms that could be brought back to earth in rock and soil samples collected during US missions to other parts of the solar system.
Thirty years ago, during the Apollo program, the United States was similarly concerned about contamination of Earth's environment and the need to quarantine samples collected on the moon.
But today, with a series of flights planned to Mars and proposed for other celestial bodies that are considered more likely homes for microscopic life forms, the need to take precautionary steps is becoming more acute. "Now the situation is quite different," says Michael Carr, a planetary geologist with the US Geological Survey and a member of a National Research Council (NRC) panel that yesterday released recommendations on how to deal with the problem. "The prospect for organisms is considered to be much greater" on Mars.
No one is overplaying the potential threat of contamination. Earth serves as a catcher's mitt for about 110 pounds of Martian meteors each year. They have been landing on earth for millions of years. Given this history, says Dr. Carr, the chances of anything untoward happening from samples NASA's machines pluck "are almost zero. But we can't prove it won't happen."
Thus, the US needs to have safeguards in place until samples can clear the biological equivalent of an interplanetary customs search. A Mars sample-return mission could be launched as early as 2003. Already, planetary scientists are awaiting the chance to pick potential landing spots. Before 1997 ends, researchers likely will start poring over images from the Mars Global Surveyor - one of two US spacecraft currently bound for the Red Planet - in the hunt for intriguing sites for a robotic rock hound.
Largely devoid of organic material and bathed in ultraviolet radiation, Mars's surface is thought to be sterile. But if a closer look reveals subterranean water, or that the planet has active volcanoes, the likelihood that simple organisms inhabit the planet "becomes more plausible," says the panel.
As a result, the team says, any material brought back should be treated as "potentially hazardous" until proved otherwise. Even spacecraft surfaces exposed to Mars's environment should be sterilized before returning to Earth. If mission engineers fail to verify that sample containers haven't leaked during the return trip, the samples and any part of the spacecraft they could come in contact with should be jettisoned in space.
Once in the lab, the samples would be released to researchers only after tests indicate the material contains no biological hazards. This means NASA may have to build a facility capable of handling potentially hazardous biological materials. One option is to add it to the Johnson Space Center's building that archives moon rocks, says Todd Stevens, a microbiologist at the Pacific Northwest Laboratory in Richland, Wash.
"We don't have unanimity in the scientific community that these are reasonable things to do," says Bruce Jakosky, a planetary geologist at the University of Colorado in Boulder. But when it comes to Earth's biosphere, "the prudent thing is to be cautious."