National Aeronautics and Space Administration Planetary Protection Office

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 and/or international policy guidelines. Each mission is categorized according to the type of encounter it will have (e.g., flyby, orbiter, or lander) and the nature of its destination (e.g., a planet, moon, comet, or asteroid). 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. Spacecraft going to target bodies with the potential to support Earth life must undergo stringent cleaning and sterilization processes, and greater operating restrictions.

Planetary Protection Mission Category Definitions

Types of Planetary Bodies Mission Type1 Mission Category2
Bodies “not of direct interest for understanding the process of chemical evolution or the origin of life.” Any I
Bodies of “significant interest relative to the process of chemical evolution and the origin of life, but where there is only a remote chance that contamination carried by a spacecraft could compromise future investigations.” Any II & II*
Bodies of significant interest to the process of “chemical evolution and/or the origin of life”, and where “scientific opinion provides a significant chance that contamination could compromise future investigations.” Flyby, Orbiter III
Lander, Probe IV3
Earth-return missions from bodies “deemed by scientific opinion to have no indigenous life forms.” unrestricted Earth-Return V (unrestricted)
Earth-return missions from bodies deemed by scientific opinion to be of significant interest to the process of chemical evolution and/or the origin of life. restricted Earth-Return V (restricted)
1If gravity assist is utilized during a flyby, constraints for the planetary body with the highest degree of protection may be required.
2For missions that target or encounter multiple planets, more than one PP category may be specified.
3Category IV missions for Mars are subdivided into IVa, IVb, and IVc.

Planetary Targets for all Mission Categories

Planetary Targets/Locations Mission Type Mission Category
Undifferentiated, metamorphosed asteroids; Io; others TBD. Flyby, Orbiter, Lander I
Venus; Earth’s Moon; Comets; non-Category I Asteroids; Jupiter; Jovian Satellites (except Io and Europa); Saturn; Saturnian Satellites (except Titan and Enceladus); Uranus; Uranian Satellites; Neptune; Neptunian Satellites (except Triton); Kuiper-Belt Objects (< 1/2 the size of Pluto); others TBD. Flyby, Orbiter, Lander II
Icy satellites, where there is a remote potential for contamination of the liquid-water environments, such as Ganymede (Jupiter); Titan (Saturn); Triton, Pluto and Charon (Neptune); others TBD. Flyby, Orbiter, Lander II*
Mars; Europa; Enceladus; others TBD (Categories IVa-c are for Mars). Flyby, Orbiter III
Lander, Probe IV(a-c)
Venus, Moon; others TBD: “unrestricted Earth return” unrestricted Earth-Return V (unrestricted)
Mars; Europa; Enceladus; others TBD: “restricted Earth return” restricted Earth-Return V (restricted)

Category IV Subdivisions for Mars (IVa-c)

Types of Mars Missions Mission Type Mission Category
Lander systems not carrying instruments for the investigations of extant Mars Life. Lander, Probe IVa
Lander systems designed to investigate extant Martian Life. Lander, Probe IVb
Missions investigating Martian Special Regions, even if they do not include life detection experiments. Martian Special Regions include those within which terrestrial organisms are likely to replicate and those potentially harboring extant Martian Life. Lander, Probe IVc