Planetary Protection

Since the early days of the space program, there has been concern about planetary protection: the prevention of human-caused biological cross-contamination between Earth and other bodies in the solar system. After the launch of Sputnik in 1957, scientists cautioned about the possibility of contaminating other places in the solar system with microbes from Earth: "Hitchhiker" bacteria and other organisms on spacecraft and equipment might cause irreversible changes in the environments of other planets. Moreover, these changes could also interfere with scientific exploration. In addition, it was felt that spacecraft or extraterrestrial samples returned from space might harm Earth's inhabitants and ecosystems.

The Outer Space Treaty of 1967 requires that exploration of outer space and other celestial bodies "avoid their harmful contamination" and "adverse changes in the environment of Earth" caused by the "introduction of extraterrestrial matter." 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 on Earth of contamination by life-forms that could be returned from space.

Protection Policies

The issues involved in planetary protection are similar to those associated with environmental and health policies. Just as there are rules and laws about moving certain types of organisms from one place to another on Earth, so it is with space exploration. But there is a difference. On Earth, those regulations are intended to prevent the spread of serious disease-causing microbes (e.g., HIV/AIDs, tuberculosis, or Dutch Elm disease) or limit the movement of invasive pests (e.g., Medflies, gypsy moths, zebra mussels, kudzu vine, or water hyancinth). In space exploration, the issues are the same, although the existence of extraterrestrial organisms is unknown. Nonetheless, in space exploration there are domestic and international policies to regulate spacecraft and mission activities before launch and upon return to Earth.

Worldwide, planetary protection policies are recommended by the international Committee on Space Research (COSPAR), which reviews the latest scientific information. In the United States the National Aeronautics and Space Administration (NASA) issues guidelines and requirements for solar system exploration missions. Planning planetary protection measures requires synthesizing information about biological systems and extraterrestrial environments while acknowledging uncertainties about the conditions that exist in the locations that spacecraft will visit or where samples might be collected. Planetary protection policies must take into account these uncertainties, even while exploration tries to determine whether life exists elsewhere. It is necessary to be conservative to prevent the act of exploration from disrupting or interfering with extraterrestrial life.

Controls to implement planetary protection policies may consist of procedures and measures that depend on the solar system body that will be explored and whether its environment could harbor living organisms or support Earth life. For example, before launch, spacecraft are assembled in clean rooms and scientific instruments may be heat treated or specially packaged to reduce the bioload, or the number of microbes they carry. Spacecraft trajectories are designed to avoid unintended impacts on other bodies. For round-trip missions to places such as Mars, returned samples are treated as potentially hazardous until proven otherwise.

In addition to extensive cleaning and decontamination of the outbound spacecraft, the return portion of the mission requires a fail-safe durable container that can be remotely sealed, cleanly separated from the planet, monitored en route, and opened in an appropriate quarantine facility. If containment cannot be verified during the return flight to Earth, the sample and any spacecraft components that have been exposed to the extraterrestrial environment will be sterilized in space or not returned to the planet. Pristine sample materials will not be removed from containment until they are sterilized or certified as nonhazardous, using a rigorous battery of life detection and biohazard tests. Although the likelihood of releasing and spreading a contained living organism is low, special equipment, personnel, and handling are warranted to minimize harmful effects if a life-form is discovered.

The Apollo Missions

A similar approach to extraterrestrial quarantine was used during the Apollo program, when lunar samples were returned to Earth along with lunar-exposed astronauts. Before the first Moon landing, the Interagency Committee on Back Contamination (ICBC) was formed to coordinate requirements for the quarantine of astronauts, spacecraft, and samples returned from the Moon. The ICBC also developed and oversaw plans for a special Lunar Receiving Laboratory (LRL) at what is now the Johnson Space Center in Houston, Texas. At the LRL, an elaborate series of tests and analyses were conducted before astronauts and samples could be released from quarantine. Strict quarantine testing ended with the Apollo 14 mission because lunar samples were determined to be lifeless and not biohazardous. There were a variety of problems in implementing the Apollo quarantine, but it provided a wealth of information useful in planning future missions that will require planetary protection and quarantine on Earth.

Future Missions

Future round-trip missions to Mars or other extraterrestrial locations will differ from Apollo in several ways. Because no astronauts will be involved in the initial sample-return missions and because sample amounts are anticipated to be limited (less than 1 kilogram [2.2 pounds] of rocks and soils), quarantine procedures and flight operations will be less complex. However, the missions will still be challenging because of the distances involved. In addition, advances in microbiological and chemical techniques since Apollo have increased knowledge about life in extreme environments on Earth and expanded the ability to detect life or life-related molecules in samples. A heightened awareness of microbial capabilities and microbe-caused diseases has developed, with corresponding public concern about the risks of sample-return missions.

As solar system exploration continues, so too will planetary protection policies. Revisions to planetary protection policies will depend on an improved understanding of extraterrestrial environments and the emerging awareness of the tenacity of life in extreme environments on Earth. It appears increasingly likely that there are extraterrestrial environments that could support Earth organisms. Equally important, future missions may find distant environments that support their own extraterrestrial life. Planetary protection provisions will be essential to the study and conservation of such environments.

see also Astrobiology (volume 4); Environmental Changes (volume 4); Human Missions to Mars (volume 3); Mars Missions (volume 4).

Margaret S. Race and John D. Rummel

Bibliography

Task Group on Issues in Sample Return, Space Studies Board, National ResearchCouncil. "Mars Sample Return: Issues and Recommendations." Washington, DC: National Academy Press, 1997.<http://www.nas.edu/ssb/mrsrmenu.html>.

Task Group on Planetary Protection, Space Studies Board, National Research Council. "Biological Contamination of Mars: Issues and Recommendations." Washington, DC: National Academy Press, 1992.<http://www.nas.edu/ssb/ssb.html>.

Task Group on Sample Return from Small Solar System Bodies, Space Studies Board,National Research Council. "Evaluating the Biological Potential in Samples Returned from Planetary Satellites and Small Solar System Bodies." Washington, DC: National Academy Press, 1998.<http://www.nas.edu/ssb/ssb.html>.

"Planetary Protection: Safeguarding Islands of Life."Planetary Report XIV, no. 4(1994):3-23.

Rummel, John D."Planetary Exploration in the Time of Astrobiology: Protecting against Biological Contamination."Proceedings of the National Academy of Sciences 98 (2001):2,128-2,131.<http://www.pnas.org/cgi/content/abstract/98/5/2128>.