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.

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