Planetary Protection


Planetary protection is the practice of protecting solar system bodies (planets, moons, asteroids and comets) from Earth life and protecting the Earth from life that may be brought back from other solar system bodies. Planetary protection requirements for solar system exploration missions are established in consideration of the nature, goals and destination of a mission. For some worlds, where conditions are severe, there are no particular planetary protection requirements. When a world (whether a planet, comet, etc.) has material relevant to the study of life, there are requirements to limit contamination and to record where a spacecraft may have impacted. If such a world might support Earth life, then the spacecraft must be very clean – nearly sterile. And of course, material returned to Earth from bodies that are capable of supporting life must be reliably contained and tested before being released for further study.

Key Concepts

  • One of the primary motivations for space exploration is to understand the origin and distribution of life in the solar system.
  • The study, by spacecraft, of life and organic chemistry in the solar system can be confounded by the presence of organic or microbial contamination carried by that same spacecraft.
  • Because space systems are quite complex and in some ways fragile, sophisticated designs and methods must be used to remove organic and biological contamination or the spacecraft may fail during a mission.
  • Some places in the solar system (Europa's subsurface ocean, certain places on Mars referred to as ‘Special Regions, the source of plumes from Saturn's moon, Enceladus’) appear to be capable of supporting Earth life.
  • Samples returned from places with the potential for endemic lifeforms will be contained and returned in a highly reliable manner and tested for biohazards before being released for further scientific study.
  • Human exploration of the Moon and Mars is compatible with planetary protection objectives within our current understanding of the habitats available on those bodies.

Keywords: astrobiology; microbiology; mars; europa; sample return; solar system exploration

Figure 1. Europa, a moon of the planet Jupiter, is a target in the search for evidence of extraterrestrial life. Scientists believe Europa has a liquid water ocean beneath its icy surface. Reproduced courtesy of NASA/JPL‐Caltech.
Figure 2. Mars Global Surveyor took this picture of the northern Martian polar ice cap in 1998. Evidence of frozen water on the surface of Mars leads scientists to believe that liquid water could exist in warmer regions beneath the surface of the planet. Reproduced courtesy of NASA/JPL‐Caltech.
Figure 3. Technician samples surface of a Mars Exploration Rover spacecraft for microbial contamination before launch. Reproduced courtesy of NASA/JPL‐Caltech.


COSPAR (2002) COSPAR Planetary Protection Policy, 20 October 2002 (updated to March 2011). (accessed 15 Nov 2015).

NASA (1999) Biological Contamination Control for Outbound and Inbound Planetary Spacecraft. NASA Policy Directive (NPD) 8020.7G. Washington, DC: NASA Headquarters. (accessed 15 Nov 2015).

NASA (2002) A Draft Test Protocol for Detecting Possible Biohazards in Martian Samples Returned to Earth (NASA/CP‐2002‐211842). Hanover, MD: NASA Center for AeroSpace Information. (accessed 15 Nov 2015).

NASA (2011) Planetary Protection Provisions for Robotic Extraterrestrial Missions. NASA Procedural Requirements (NPR) 8020.12D. Washington, DC: NASA Headquarters. (accessed 15 Nov 2015).

Further Reading

Gladman BJ, Burns JA, Duncan M, Lee P and Levison HF (1996) The exchange of impact ejecta between terrestrial planets. Science 271: 1387–1392.

McEwen AS, Ojha L, Dundas CM, et al. (2011) Seasonal flows on warm martian slopes. Science 333: 740–743.

McKay DS, Gibson EK Jr Thomas‐Keprta KL, et al. (1996) Search for past life on Mars: possible relic biogenic activity in Martian meteorite ALH84001. Science 273: 924–930.

Mitrofanov IG, Zuber MT, Litvak ML, et al. (2003) CO2 snow depth and subsurface water‐ice abundance in the northern hemisphere of Mars. Science 300: 2081–2084.

Nicholson WL, Munakata N, Horneck G, Melosh HJ and Setlow P (2000) Resistance of Bacillus endospores to extreme terrestrial and extraterrestrial environments. Microbiology and Molecular Biology Reviews 64: 548–572.

Rummel JD, Beaty DW, Jones MA, et al. (2014) A new analysis of Mars “Special Regions”: findings of the second MEPAG Special Regions Science Analysis Group (SR‐SAG2). Astrobiology 14: 887–968.

Space Studies Board, National Research Council (1998) Evaluating the Biological Potential in Samples Returned from Planetary Satellites and Small Solar System Bodies. Task Group on Sample Return from Small Solar System Bodies. Washington, DC: National Academy of Sciences. (accessed 15 Nov 2015).

Space Studies Board (Committee on the Review of Planetary Protection Requirements for Mars Sample Return Missions), National Research Council (2009) Assessment of Planetary Protection Requirements for Mars Sample Return Missions. Washington, DC: National Academy of Sciences. (accessed 15 Nov 2015).

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How to Cite close
Rummel, John D, Billings, Linda, and Stabekis, Pericles(Jan 2016) Planetary Protection. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0004034.pub2]