National Aeronautics and Space Administration Planetary Protection Office


About the Office

Mission Categories I-V

Annotated Requirements

List of Missions


Contact NASA PPO

About the Office





Mission Categories

Solar System Bodies

List of Missions

Mission Design & Requirements

Methods & Implementation

International Policy

Research in Planetary Protection

History of Planetary Protection

Course in Planetary Protection

Glossary of Terms




What is Planetary Protection?

Planetary protection is the term given to the practice of protecting solar system bodies (i.e., planets, moons, comets, and asteroids) from contamination by Earth life, and protecting Earth from possible life forms that may be returned from other solar system bodies.

Why is Planetary Protection Important?

Planetary protection is essential for several important reasons: to preserve our ability to study other worlds as they exist in their natural states; to avoid contamination that would obscure our ability to find life elsewhere — if it exists; and to ensure that we take prudent precautions to protect Earth’s biosphere in case it does. Typically, planetary protection is divided into two major components: forward contamination, which refers to the biological contamination of explored solar system bodies; and backward contamination, which refers to the biological contamination of Earth as a result of returned extraterrestrial samples.

NASA Planetary Protection Policy

NASA maintains a planetary protection policy that is defined by the NASA Policy Directive (NPD) 8020.7G: Biological Contamination Control for Outbound and Inbound Planetary Spacecraft. In turn, the NASA Office of Planetary Protection administers associated procedures to ensure compliance with NPD 8020.7G using the guidelines and requirements described in the NASA Procedural Requirements (NPR) 8020.12D: Planetary Protection Provisions for Robotic Extraterrestrial Missions. As described in the following section, the NASA policy, and its associated guidelines and requirements, are well aligned with the COSPAR Planetary Protection Policy, and is consistent with Article IX of the ‘Outer Space Treaty’. More information is provided in the history of planetary protection and international policy pages of this site. NASA’s Planetary Protection Officer oversees compliance with formal implementation requirements that are assigned to each mission, and is typically directly involved in the development and planning stages of solar system missions. More information on the requirements is provided below, and a summary of the planetary protection mission categories, planetary protection requirements, and methods & implementation used to ensure compliance with NASA policy are found on the respective pages of this site. In accordance with the NASA policy, requirements are based on the most current scientific information available about the target bodies and about life on Earth. The Planetary Protection Officer requests recommendations on implementation requirements for missions to a specific solar system body, or class of bodies, from internal and external advisory committees (for example, the National Advisory Council Planetary Protection Subcommittee); but most notably from the Space Studies Board of the National Research Council. In recent years the Space Studies Board has provided recommendations on planetary protection requirements for Mars, Europa, and sample return missions from a variety of small solar system bodies such as moons, comets, and asteroids. Many of the Space Studies Board reports are posted on the Documents page. Recommendations from the Space Studies Board are routinely reassessed as new information becomes available.

International Treaties and Organizations with Cognizance of Planetary Protection Activities

Agreements regarding planetary protection stem from the 1967 United Nations Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Bodies, which states that all countries party to the treaty “shall pursue studies of outer space, including the moon and other celestial bodies, and conduct exploration of them so as to avoid their harmful contamination.” Internationally, technical aspects of planetary protection are developed through deliberations by the Committee on Space Research (COSPAR), part of the International Council of Science (ICSU), which consults with the United Nations in this area. The COSPAR Panel on Planetary Protection develops and makes recommendations on planetary protection policy to COSPAR, which may adopt them as part of the official COSPAR Planetary Protection Policy. More information on the history of planetary protection and international policy is provided on the respective pages of this site.

Requirements for Protecting Life on Other Bodies

Planetary protection requirements for each mission and target body are determined based on the scientific advice of the Space Studies Board and on NASA or international policy guidelines. Each mission is categorized according to the type of mission (e.g., flyby, orbiter, or lander), the nature of its destination (e.g., a planet, moon, comet, or asteroid), and the planetary bodies that may be encountered during the mission (e.g., Mars and Europa). The corresponding requirements are, in turn, formalized and developed in consultation with the Planetary Protection Officer. In general, if the target body has the potential to provide clues about life or prebiotic chemical evolution, a spacecraft going there must meet a higher level of cleanliness, and some operating restrictions will be imposed. If non-target bodies of interest to life or prebiotic chemical evolution may be encountered during mission, the spacecraft may also be required to meet a higher level of cleanliness, and some operating restrictions may be imposed. Spacecraft traveling to target bodies with the potential to support Earth life must undergo stringent cleaning and sterilization processes, and greater operating restrictions. Further information can be obtained from the following pages: