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


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


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


the destruction of all living microorganisms including vegetative forms and spores


the largest crater on Phobos


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


comma-shaped bacteria that are common to aquatic environments

The National Academies of Sciences, Engineering, and Medicine
500 Fifth St. N.W. | Washington, D.C. 20001

Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement