Aeolian—Geologic processes involving wind.
Archaea—Organisms making up one of the three branches on the phylogenetic tree of life. Their cells do not contain a defined nucleus, and they are genetically and biochemically distinct from the Bacteria. See Eukaryotes and Bacteria.
Astrobiology—The study of the origin, evolution, and distribution of life in the universe.
Autotroph—An organism that can use carbon dioxide as its sole source of carbon. See Heterotroph.
Bacteria—Organisms making up one of the three branches of the phylogenetic tree of life. Their cells do not contain a defined nucleus, and they are genetically and biochemically distinct from the Archaea. See Eukaryotes and Archaea.
Centaurs—A family of small solar system bodies found between the orbits of Jupiter and Neptune, having appearances ranging from asteroidal to cometlike. Their orbital characteristics indicate that they have not resided in their present locations very long, leading to the suggestion that they are recently migrated Kuiper belt objects.
Chemoautotroph—An organism with the ability to synthesize organic nutrients directly from simple inorganic compounds using the energy derived from chemical rather than photochemical reactions.
Chemolithoautotroph—An organism deriving all of its carbon and energy requirements from inorganic compounds. The “litho” component of the name implies that the organism derives energy from the oxidation of hydrogen.
Clathrate—A compound in which one component is enclosed by the structure of another.
Coleman-Sagan—A methodology used to calculate the probability that terrestrial organisms on or within a spacecraft could survive and proliferate while transiting through space to an extraterrestrial planetary environment.
Commensurability—A location (e.g., in the asteroid belt) where a body orbits with a period that is a simple fraction (e.g., 2/5 or 1/3) of the period of another large body (e.g., Jupiter) where resonant effects can build up.
Containment—Physical and biological isolation and handling of returned samples as specified for samples returned from Mars.
COSPAR (Committee on Space Research of the International Council for Science)—An international body responsible for setting planetary protection policies.
COSPAR categories—Categories, I-V, are a series of rules and requirements that have to be met depending on the object visited and the type of mission.
Category I—Includes any mission to a target body that is not of direct interest for understanding the process of chemical evolution or the origin of life. No protection of such bodies is warranted, and no planetary protection requirements are imposed by this policy.
Category II—Includes types of missions to those target bodies where there is 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 jeopardize future exploration. The requirements are for simple documentation only. Preparation is required for these flight projects primarily to outline intended or potential impact targets, provide brief pre- and post-launch analyses detailing impact strategies, and supply a post-encounter and end-of-mission report that will provide the location of impact if such an event occurs.
Categories III and IV—Include certain types of missions to a target body of interest with respect to chemical evolution and/or origin of life or for which scientific opinion posits a significant chance of contamination that could jeopardize future biological experiments. For Category III, mostly flyby and orbiter missions, the requirements consist of documentation (more involved than that for Category II) and some implementing procedures, including trajectory biasing, the use of clean rooms during spacecraft assembly and testing, and possibly bioburden reduction. For Category IV, mostly probe and lander missions, the requirements include rather detailed documentation (more involved than that for Category III), including a bioassay to enumerate the bioburden, an analysis of the probability of contamination, an inventory of the bulk constituent organics, and an increased number procedures governing implementing.
Category V—Includes Earth-return missions. The concern for these missions is the protection of the terrestrial system, Earth and the Moon. For solar system bodies deemed by scientific opinion to have no indigenous life forms, a subcategory, “unrestricted Earth return,” is defined. For all other Category V missions, in a subcategory defined as “restricted Earth return,” the highest degree of concern is expressed as the absolute prohibition of destructive impact upon return, the need for containment throughout the return phase of all returned hardware that directly contacted the target body or unsterilized material from the body, and the need for containment of any unsterilized sample collected and returned to Earth.
Cryovolcanism—A low-temperature analog of silicate volcanism in which a volatile, such as water, ammonia, or methane, plays the role of lava on the surface of a planetary body.
Diapir—A dome or anticlinal fold in which a mobile plastic core has ruptured the more brittle overlying rock.
DNA (deoxyribonucleic acid)—A polymer of nucleotides connected via a sugar-phosphate backbone. This complex biomolecule encodes genetic information in all terrestrial organisms.
Downwelling—The downward movement of material of a body driven by buoyancy forces, as in the case of a high-density fluid sinking beneath a low-density fluid.
Ejecta—Material thrown up from an event, such as an impact.
EJSM—Europa Jupiter System Mission.
Endogenic—Relating to a geologic process of internal origin (volcanism, tectonism).
ESA—European Space Agency.
Eukaryote—An organism making up one of the three branches on the phylogenetic tree of life. The characteristic feature is that their cells have a defined nucleus containing most of the organism’s DNA. See Archaea and Bacteria.
Extremophile—A microorganism capable of growing under extreme physicochemical conditions such as high temperatures, pressures, and acidity.
Facultative anaerobe—An organism with the capacity to grow in both the presence and the absence of oxygen.
Fluvial—Pertaining to or produced by the action of a river or stream.
Forward contamination—The biological contamination of an extraterrestrial body by terrestrial organisms inadvertently carried aboard a spacecraft.
Gram-negative bacteria—Bacteria that show a red color from Gram’s stain procedure.
Gram-positive bacteria—Bacteria that show a purple color from Gram’s stain procedure. The structure of a bacterium’s cell wall determines its ability to retain the dye used in Gram’s stain procedure.
Gray—Unit of absorbed dose of ionizing radiation defined in terms of the total amount of energy absorbed per unit mass of the absorbing material. One gray is equal to 1 joule of energy deposition per kilogram of the target material. Because the amount of energy absorbed depends on the nature of the target material, the unit is often qualified to indicate the nature of the target. One gray is equal to 100 rad.
Habitable zone—The notional region around a star within which an Earth-like planet would experience environmental conditions compatible with life as we know it. The solar system’s habitable zone stretches, approximately, from the orbit of Venus to the orbit of Mars.
Heterotroph—An organism that survives by the ingestion and breakdown of complex organic materials. See Autotroph.
Hydrothermal vents—Springs of hot seawater on the deep ocean floor. They are formed when cold seawater seeps through cracks in the ocean floor, circulates through volcanically heated rock, and returns to the seafloor rich in dissolved minerals.
Hyperthermophile—An organism adapted to living in temperatures of 80°C or higher.
Impact gardening—The process by which the surface of atmosphere-less bodies is stirred and resurfaced by impacts.
JEO—Jupiter Europa Orbiter.
JPL—Jet Propulsion Laboratory.
KBO—Kuiper belt object.
Kuiper belt—A torus-shaped volume beyond the orbit of Neptune populated by bodies ranging up to many hundreds of kilometers in size; the source region for most short-period comets.
Lacustrine—Relating to lakes.
Magnetosphere—The volume of space surrounding a planetary body that is under the dynamical influence of that body’s magnetic field.
Mesophilic—Preferring moderate temperatures.
NASA—National Aeronautics and Space Administration.
NRC—National Research Council.
Outgassing—The emanation of gases from within an object.
Pg—Probability of growth.
Phenotype—An organism’s observed characteristics or traits that result from the expression of the organism’s genes, environmental factors, and the interaction between the two.
Photosynthesis—The process by which certain organisms use the energy derived from sunlight to sustain their metabolism.
Pluvial—Involving abundant rainfall.
Psychrophile—An organism that has a maximum growth temperature of 20°C, an optimal growth temperature of 15°C or lower, and a minimum growth temperature of 0°C or lower.
Psychrotolerant organism—An organism that has a maximum growth temperature of 35°C, an optimal growth temperature of 15°C or lower, and a minimum growth temperature of 0°C or lower.
Rad—Unit of absorbed dose of radiation defined in terms of the total amount of energy absorbed per unit mass of the absorbing material. One rad is equal to 100 erg of energy deposition per gram of the target material. Because the amount of energy absorbed depends on the nature of the target material, the unit is often qualified to indicate the nature of the target, e.g., 5 krad [water] per month.
Radiation-resistant organism—An organism that can survive and grow following acute exposure to radiation.
Radiolysis—The breakdown of molecules as a result of exposure to ionizing radiation.
Redox couples—A coupled series of chemical reactions driven by the simultaneous loss of electrons from one species (oxidation) and the gain of electrons from a second species (reduction).
Regolith—The layer of fragmented, incoherent rocky debris on the surface of a planetary body.
Retrograde—Rotational or orbital motion in the direction opposite to that of Earth.
RNA (ribonucleic acid)—A polymer of nucleotides connected via a sugar-phosphate backbone. It plays an important role in protein synthesis and other chemical activities in cells.
Spore—A single-celled asexual reproductive unit created by a variety of microorganisms to aid in their dispersal and survival over extended periods of time in adverse environmental conditions.
Sterilization—A procedure that destroys all living microorganisms, including vegetative forms and spores. In practice, a completely sterile state is rarely achieved.
TBD—To be determined.
Tectonism—Processes acting within the lithospheres of planetary bodies responsible for the creation of large-scale structures.
Thermophile—An organism that can survive and grow in high-temperature environments.
Tidal heating—Heating of a planet or satellite as a result of the work performed on the object’s materials by the flexing due to gravitational interactions between bodies.
Trojan asteroid—An asteroid located at the 1/1 mean-motion resonance (commensurability) with Jupiter, librating about the L4 and L5 points 60 degrees ahead of, and behind, Jupiter in its orbit.
TSA (trypticase soy agar)—A solid growth medium used to culture microorganisms.
TSSM—Titan Saturn System Mission.
Upwelling—The upward movement of material of a body driven by buoyancy forces, as in the case of a low-density fluid rising above a high-density fluid.
Vegetative bacteria—Bacteria that can grow and reproduce in moist, nutrient-rich environments.
VIMS—Visible and Infrared Mapping Spectrometer.