Planetary Protection

Planning for space exploration in the solar system involves far more than rockets, astronauts, and planets. Mission planners must also consider planetary protection, the prevention of human-caused cross-contamination of planets and other solar system bodies during exploration. From the earliest days of the space program, scientists recognized the very real possibility of contaminating extraterrestrial locations by the inadvertent delivery of microbes in or on spacecraft and equipment launched from Earth. International deliberations about these concerns began in the Sputnik era in the late 1950s and led eventually to the passage of the United Nations Outer Space Treaty (OST) of 1967, which stipulates that exploration of outer space and other celestial bodies shall be done in ways that avoid harmful contamination of planetary bodies as well as adverse changes in the environment of the Earth caused by the introduction of extraterrestrial matter. Planetary protection policies are an important component of the space programs of the United States and other countries, yet rarely appear in news accounts.

In many ways, planetary protection is similar to policies on Earth that seek to control the movements of exotic pests or pathogenic organisms from one place to another so as to prevent the human-aided spread of potentially harmful or invasive species beyond their natural hosts, habitats, or ecosystems. “Hitchhiker” microbes or biological contaminants on spacecraft and equipment could cause irreversible changes in environments beyond Earth. Not only might the presence of such hitchhikers interfere with scientific study of other bodies in their natural states, it could also compromise the search for indigenous extraterrestrial life, should it exist. Thus, even though we remain uncertain about whether or not extraterrestrial life exists, planetary protection policy takes a deliberately conservative approach and aims to ensure that the very act of exploring beyond Earth does not significantly disrupt the environments and possible life there.

The term planetary protection (PP) is often used in several different ways. It refers formally to international and national policies that are rooted in the OST and have the objective of minimizing the transfer of Earth microbes and biological contaminants on outbound spacecraft (forward contamination) and controlling the return of extraterrestrial life forms or materials to Earth that could harm our planet's inhabitants or biosphere (back contamination). PP also refers to the management requirements and controls imposed by space agencies to regulate spacecraft and mission activities prior to launch and on return to Earth to meet the treaty's policy goals. Finally, PP additionally refers to the implementation practices and methods used to clean and prepare spacecraft in ways that minimize both forward and back contamination. Under current policy, planetary protection applies to planets as well as moons, asteroids, comets, and other celestial objects within the solar system.

Over time, the OST has been signed by more than 90 countries, each of which agrees to abide by its policies when conducting or participating in space exploration. In practice, PP policies are recommended and overseen by the international Committee on Space Research (COSPAR). Aided by scientists and experts from many space-faring nations, COSPAR regularly reviews up-to-date scientific findings and methods and revises planetary protection policy accordingly. In the United States, the National Aeronautics and Space Administration (NASA) is the agency that issues specific guidelines and requirements on how to conduct solar system exploration for U.S.-launched robotic and human missions. NASA's Planetary Protection Officer is the designated individual for ensuring compliance with PP policy, prescribing standards and procedures to achieve policy guidelines, undertaking needed research and development, and certifying that missions have met appropriate requirements. NASA regularly consults with the Space Studies Board (SSB) of the National Research Council (NRC) for expert advice on matters related to planetary protection.

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