Long before the MER missions were readied for their highly public launch, NASAs scientists and engineers have worried behind the scenes about all the little things that could impact the mission -- some literally down to the invisible microbes that could contaminate the spacecraft, or interfere with the scientific equipment or the environments theyll visit.

Since the early years of the space program, scientists have expressed concern about planetary protection --that is, the prevention of human-caused biological cross-contamination between Earth and other bodies in the solar system. "Hitchhiker" bacteria and other organisms on spacecraft and equipment might cause irreversible changes in the environments of other planets or interfere with scientific exploration on them. In practical terms, the concerns are twofold: avoiding (1) forward contamination, the transport of terrestrial microbes on outbound spacecraft, and (2) back contamination, the introduction onto Earth of contamination or life-forms that could be returned from space. Both concerns are covered in provision of the Outer Space Treaty of 1967, as well as in NASA policies and requirements.

Just as there are laws and regulations about the movement of certain types of organisms from one place to another on Earth, so it is with space explorationeven though we dont know for sure whether extraterrestrial life exists. For all missions to Mars (and to other locations in the solar system that could potentially support or harbor life) planetary protection controls are an integral part of mission preparations. Its like environmental impact avoidance for the solar system -- better safe than sorry. In fact, NASAs Planetary Protection Officer has summed it up succinctly on a bumper sticker: "Planetary Protection: All of the Planets, All of the time."

When planetary protection controls are required, they can come in the form of various procedures and measures depending on the mission. For example, prior to launch, spacecraft are assembled in clean rooms and scientific instruments may be heat treated or specially packaged to reduce the number of microbes they carry. Spacecraft trajectories are designed to avoid unintended impacts on other bodies. For future sample return missions, in addition to extensive cleaning and decontamination of the outbound spacecraft, the sample return portion will also require a fail-safe, remotely-sealed, durable container that is cleanly separated from the planet, monitored en route, and opened in an appropriate quarantine facility for rigorous testing. Although the likelihood of releasing and spreading a contained living organism is low, it is appropriate to take precautions in order to minimize harmful effects if an extraterrestrial life-form is discovered.

As solar system exploration has expanded, so too have discussions about applying planetary protection policies. In recent years, discussions have extended into areas barely imagined a decade ago. For example:

Mars Sample Return Missions: NASA recently completed a two year international workshop series that developed a Draft Protocol for handling, containing and testing samples when they are returned from Mars. In addition to specifying the types of containment that will be required, the protocol also outlines a conceptual approach for conducting the physical/chemical analyses, life detection tests, and biohazard assays that will be done on returned samples. The report also outlines a process for designing, constructing and staffing a specialized receiving facility in advance of sample return.

Human Missions to Mars: NASA recently sponsored a summer workshop that analyzed the implications of future human missions to Mars. The assembled experts examined whether and how it may be possible to undertake human exploration consistent with planetary protection policies. The workshop addressed a range of operations and activities having planetary protection implicationsfrom food supply and waste handling, to rover exploration, space suit design, in situ scientific testing, and astronaut health. While human missions are undoubtedly a long way off, it is appropriate that engineers and scientists tackle the logistical and planning issues well in advance.

Societal and Ethical Concerns: In addition to focusing on the scientific and technical aspects of planetary protection, NASA has also broadened discussions to explore topics not directly related to mission planning. The prospect of discovering evidence of extraterrestrial life raises significant societal, legal, ethical, philosophical and cultural issues beyond the realm of science and technology. NASA is co-sponsoring a workshop series with the American Association for the Advancement of Science (AAAS) to explore the implications of finding evidence for extraterrestrial lifewhether intelligent life via a SETI signal, microbial life in the solar system, or created life in the laboratory via replicating the appropriate pre-precursor conditions and cosmo-chemistry. The potential implications and perhaps the very meaning of other life may depend on where and how a discovery is made.

As we learn more about the tenacity and diversity of life on our home planet, it appears increasingly likely that there are extraterrestrial environments that could support Earth organisms. Equally important, missions like MER or others in the solar system may find distant environments that support their own extraterrestrial life. As we undertake future missions beyond Earth, planetary protection provisions will be essential to the study and conservation of such environments -- as well as to the success of the missions themselves.