If you imagined each planet, moon, comet, and asteroid to be an isolated and unique test tube, you would understand why a growing number of people are upset about NASA’s sample return plans.

Researchers, environmentalists and policymakers want NASA to consider carefully its plans to visit and bring back samples from Mars, Europa, and other solar system bodies.

"This is a very serious issue, and there are clearly many concerns," says Norine Noonan, director of the U.S. Environmental Protection Agency's research arm who also recently chaired a NASA-sponsored panel on planetary protection.

The recommendation has stirred some concern among scientists, who fear that a high-level advisory panel consisting of policymakers as well as scientists could put restrictions on their ability to conduct research. But Noonan and NASA officials say that providing a broad-based committee now could avoid charges in the future that scientists are downplaying the threat of contamination of Earth or other worlds for the sake of not disrupting their projects.

"You can pay me now or you can pay me later," Noonan recently told a panel of NASA space scientists at agency headquarters in Washington. She compares the proposal for the planetary protection committee to the 1970s panel set up by the National Institutes of Health to examine the potential consequences of recombinant DNA research -- an action which Noonan says helped open the issue to public debate and ultimately diffuse controversy over its dangers.

Worry about contaminating other worlds is an old one that stretches back to a 1958 paper published in Science Magazine on international cooperation to avoid contamination of extraterrestrial bodies. The 1967 Outer Space Treaty states that spacefaring nations will avoid "harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter" just two years before Apollo astronauts brought back the first rocks.

NASA's longstanding policy is to both protect the Earth and "preserve planetary conditions for future biological and organic constituent exploration," according to an agency policy document. The returned lunar rocks were carefully contained, while Viking spacecraft which landed on Mars were sterilized. In recent years, NASA has commissioned the National Research Council to conduct several studies on the potential for contaminating other worlds. Now that the space agency also is considering a variety of sample return missions, researchers are becoming increasingly aware that they must put clear standards in place to protect against the highly unlikely but possible introduction -- and escape -- of extraterrestrial life to Earth. While minimal, the risk level "is not zero," warns one NRC study.

Both a 1997 NRC report on Mars sample return and a 1998 report on the potential for biological samples to be brought back to Earth urged NASA to consider ways to reduce contamination of outgoing and incoming spacecraft with biological agents and set up strict controls on handling returned samples. The study of "forward contamination" -- that is, spreading life through spacecraft sent to other bodies -- has taken on a new urgency given recent findings by researchers that life can exist on Earth in extreme environments ranging from near-boiling pools to crevices in rocks deep beneath the ocean.

A 1999 NRC study of the exploration of Europa, a moon of Jupiter which shows strong evidence of oceans beneath an oxygen atmosphere and a water-ice crust, called particular attention to this issue. A spacecraft which plunged into those presumed oceans, the report warns, "could emplace material at depths where terrestrial organisms might survive for extremely long periods of time." U.S. and Russian researchers on Earth right now are trying to cope with the problem of how to explore Lake Vostok which lies pristine underneath the Antarctic ice sheet without introducing biota from the surface through the drill. That experiment could provide a model for how to proceed on other planets, say researchers.

Noonan's panel, which included a host of scientists as well as government managers and even one lawyer, was set up to review NASA's current policies. They will also consider how to plan for the next decade, and recommend how to deal with small bodies which have an extremely low likelihood -- given lack of atmosphere and presence of radiation -- of harboring life. Last fall the panel recommended that a planned sample-return mission to an asteroid -- the Muses-C flight slated for a 2002 launch -- does not require special containment or handling given the harsh environment on the asteroid. The panel also called for NASA to set up a permanent planetary protection committee made up of 15 members appointed by the administrator.

That recommendation stirred some concern at February's space science advisory subcommittee meeting in Washington, where several scientists raised concerns about a panel made partly of non-scientists who could dictate scientific procedures to researchers.

"They were concerned that this could interfere with their ability to do science," says John Rummel, NASA's planetary protection officer. But a majority of the subcommittee ultimately backed the proposal, which now goes to the NAC for approval in June.