National Aeronautics and Space Administration Planetary Protection Office

About the Office





Mission Categories

Solar System Bodies

List of Missions

Mission Design & Planning

Mission Requirements

Mars Requirements

International Policy

History of Planetary Protection

Course in Planetary Protection

Glossary of Terms



glossary of terms

Assay (also referred to as Bioassay) – Any activities related to gathering of microbial data, through the use of appropriate sampling techniques (swabs, wipes or other approved methods) to obtain microbial samples in order to estimate the number or types of microorganisms associated with an item of interest.

Biological monitoring – The data management and visual surveillance activities that are performed so that the microbial burden of an item of interest may be verified.

Biosignature molecule – A molecule that scientists agree is a clear sign of life as we understand it.

Constraints – Bounding conditions governing aspects of the implementation of planetary protection requirements.

Encapsulated burden – Microbial burden buried inside non-metallic spacecraft material.

Exposed surface – Those surfaces whose microbial burden will likely reach a planetary environment following the normal landing of a spacecraft. For dry heat considerations, a surface that is free for gas exchange.

Inadvertent impact – An undesired event during a space mission in which the spacecraft accidently impacts the surface of a taget body. Such an event could be caused by navigation uncertainties or spacecraft failures. For bodies with little or no atmosphere, such as moons and asteroids, the entire intact spacecraft could impact the body. For bodies with an appreciable atmosphere, such as Mars or Saturn’s moon, Titan, a spacecraft not designed for atmospheric entry would likely break apart and burn during passage through the atmosphere; only pieces that survive this entry would impact the surface.

Mated surface – Surfaces joined by fasteners rather than by adhesive.

Microbial assay – Biological methods that are conducted to assess the cleanliness of spaceflight hardware and the assembly facilitites and ground support systems associated with flight items. The methods are approved by NASA for deriving an estimate of the number or kind or microorganisms associated with an item of interest.

Microbial barrier – A means to protect a spacecraft or associated component(s) against microbial recontamination following the application of microbial reduction procedures.

Microbial burden (also referred to as Bioburden) – The level of microbial contamination (total number of microbes, spores and non-heat shocked, or microbial density) in or on an item of interest.

Microbial burden density – Surface burden density: the number of microbes per unit surface area. Volume burden density: the number of microbes per unit volume (of non-metallic material).

Microbial monitoring – The collection, analysis, and associated activities that are performed to verify the biological condition of an item of interest.

Microbial reduction (also referred to as Bioburden reduction) – Any activities designed to remove or destroy microbes and that are performed in order to reduce microbial burden levels on or in an item of interest.

Microbial spore — An inactive form of a bacterium or fungus that can survive in a dormant phase and, in some cases, can survive extreme environments (e.g., high or low temperature, high or low pressure, very wet or very dry conditions). Spores have the capability of returning to their active form under conditions that support growth.

Organics archive – A stored collection of bulk organic constituents (materials) of all launched hardware.

Organics inventory – An itemized list of bulk organic materials used in launched hardware.

Planetary protection – The protection of a planet from terrestrial contaminants and the protection of the Earth’s biosphere from potentially harmful extraterrestrial material.

Spore (or Endospore) – A structure formed by the actively growing (vegetative) stage of some bacteria that is able to remain viable under extremely harsh environmental conditions (heat, dryness, radiation) and, when the environment improves, once again actively grow and proliferate. As used in the context of planetary protection and in its appropriate requirements and specifications, spore refers to a heat-shock surviving microbe culturable in the NASA standard assay.

Sterilization – As used in the context of planetary protection, the process of actively reducing the microbial burden on flight hardware so that the hardware is nearly free of all living microorganisms (consistent with the appropriate specifications).

Target body – The solar system body (e.g., planet, moon, comet, asteroid) which is the scientific focus of a space exploration mission. A mission may have more than one taget body; for example, the Galileo mission explored the planet Jupiter, several of its moons, and two asteriods while enroute to Jupiter.

Terminal microbiological assay – The last assay done prior to terminal sterilization.

Terminal sterilization – A final sterilization process applied to the entire spacecraft system.

Total microbial burden – Total of exposed, mated and encapsulated microbial burden.

Trajectory biasing – A technique used in the design of a deep-space mission to ensure that the spacecraft will not inadvertently impact the target body of interest. The spacecraft’s planned trajectory is initially offset (biased) away from its ultimate desired position (called the aim point) at the target by hundreds to thousands of kilometers, depending on the size of the target body. As mission contollers’ knowledge of the spacecraft’s actual trajectory (relative to its planned trajectory) improves through radio tracking and optical navigation, the trajectory bias is removed in progressive steps using the spacecraft’s propulsion system until the desired aim point is reached. Should contact with the spacecraft be lost for any reason before the bias is removed, mission managers will have high confidence that it will not inadvertently impact the target body.

Verification assay – A microbiological assay performed as requested and directed by the Planetary Protection Officer to verify compliance with planetary protection requirements.