E Glossary


Ablation—

the process whereby material is heated, vaporized, and lost from the surface of a projectile penetrating Earth's atmosphere

Allotrope—

one of two or more existing forms of an element

Astronomical unit (AU)—

mean distance of the Earth from the Sun


Back contamination—

biological contamination of Earth as a result of samples returned from solar system bodies


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 Mars1

Crater palimpsests—

circular features of very little relief that are apparently vestiges of large ancient impacts


Endolithic—

living on the surface of rocks, e.g., lichens

Eukaryotic cells—

cells with a defined nucleus that contains most of a cell's DNA and is enclosed by a membrane, e.g., fungi

Extremophiles—

microorganisms capable of growing under extreme physicochemical conditions such as high temperatures and pressures


Forward contamination—

biological contamination of a solar system body from a sample return mission


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

Hydrolase—

any of a class of enzymes that break hydrogen bonds

1  

 National Research Council (NRC). 1997. Mars Sample Return: Issues and Recommendations. Washington D.C.: National Academy Press.



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Evaluating the Biological Potential in Samples Returned from Planetary Satellites and Small Solar System Bodies: Framework for Decision Making E Glossary Ablation— the process whereby material is heated, vaporized, and lost from the surface of a projectile penetrating Earth's atmosphere Allotrope— one of two or more existing forms of an element Astronomical unit (AU)— mean distance of the Earth from the Sun Back contamination— biological contamination of Earth as a result of samples returned from solar system bodies 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 Mars1 Crater palimpsests— circular features of very little relief that are apparently vestiges of large ancient impacts Endolithic— living on the surface of rocks, e.g., lichens Eukaryotic cells— cells with a defined nucleus that contains most of a cell's DNA and is enclosed by a membrane, e.g., fungi Extremophiles— microorganisms capable of growing under extreme physicochemical conditions such as high temperatures and pressures Forward contamination— biological contamination of a solar system body from a sample return mission 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 Hydrolase— any of a class of enzymes that break hydrogen bonds 1    National Research Council (NRC). 1997. Mars Sample Return: Issues and Recommendations. Washington D.C.: National Academy Press.

OCR for page 99
Evaluating the Biological Potential in Samples Returned from Planetary Satellites and Small Solar System Bodies: Framework for Decision Making Interplanetary debris complex (IDC)— the ensemble of dust and larger particles (e.g., boulder size) in interplanetary space, generated by the gradual erosion and disintegration of asteroids, comets, and other bodies; components of the complex are manifested in diverse ways (e.g., zodiacal light, IDPs collected in Earth's stratosphere, and so on) and are generally small enough so that their motions are governed not only by gravitational forces but also by radiation forces (e.g., light pressure or Yarkovsky forces) and forces sensitive to particle charge Kirkwood gap— a narrow zone in the asteroid belt (generally surrounding a commensurability) that has been depleted of asteroids 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 Laplace orbital resonance— a commensurability in the mean motions that causes repeated alignment of planetary satellites at identical points in their orbits Nuclease— an enzyme that degrades nucleic acids Oort Cloud— a spherical zone beyond the outer solar system, extending part way to the nearest star, where long-period comets originate Poynting-Robertson drag— forces interplanetary dust particles into Earth-crossing, inwardly spiraling circular orbits around the Sun Prokaryotic cells— cells without a defined nucleus, e.g., bacteria Protease— an enzyme that degrades proteins Protoplanetary disk— another term for the solar nebula at the time it was flattened into a disk, or an analogous disk from which a single planet (e.g., Jupiter) and its satellites were formed Secular resonance— occurs where the frequency for an asteroidal orbital precession rate matches a main frequency for planetary eccentricities in Brouwer and van Woerkom's secular theory SNC meteorites— achondrites that originate from Mars Sterilization— the destruction of all living microorganisms including vegetative forms and spores Stickney— the largest crater on Phobos Tektites— glassy meteorite-like objects formed when the ejecta of large terrestrial craters was lofted above Earth's atmosphere and then reentered 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 asteroids— asteroids 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 Vibrios— comma-shaped bacteria that are common to aquatic environments