Carbonaceous chondriteA rare type of stony meteorite that is rich in carbon compounds and is thought to be relatively unaltered since the beginning of the solar system. Its spectrum (and probably also its composition) closely resembles that of the C-type asteroids.

CatalystA substance that enhances the rate of reaction by providing a lower-energy alternative pathway.

CentaursA family of small solar system bodies found between the orbits of Jupiter and Neptune. Their orbital characteristics indicate that they have not resided in their present locations for very long, leading to the suggestion that they are recently migrated Kuiper belt objects and that further evolution of their orbits might turn them into short-period comets.

ChiralDescribing a molecule configured such that it cannot be superimposed on its mirror image.

ChromatographyA family of techniques for separating components from a mixture. All take advantage of the fact that different substances diffuse through a given medium at different rates. Gas chromatography is a technique for separating gas mixtures, in which the gas is passed through a long column containing a fixed absorbent phase that partitions the gas mixture into its component parts.

ComaThe quasispherical envelope of gas and dust surrounding the nucleus of an active comet, created when the ambient heat causes the sublimation of cometary ices.

Cosmic raysHigh-energy charged particles consisting of atomic nuclei, electrons, and protons, which originate from the Sun and from energetic astrophysical processes (e.g., those associated with supernovas).

DesorptionA physical or chemical process by which a substance that has been adsorbed or absorbed by a liquid or solid material is removed from the material.

DiastereoisomersStereoisomers that are not mirror images of each other.

Diffuse interstellar bands (DIBs)Unidentified absorption bands detected mostly in the visible spectrum of reddened O- and B-type stars and observed ubiquitously in space. Recent results point strongly toward a gas-phase molecular origin, but the DIB carriers’ identification remains an extremely puzzling issue.

EnantiomerStereoisomers that are mirror images of each other. Enantiomers are optically active and rotate the plane of polarized light.

Exogenous deliveryDelivery of matter to a planetary environment via asteroidal or cometary impact.

Fischer-Tropsch (FT) catalytic processA method for the synthesis of hydrocarbons and other aliphatic compounds. Typically, a mixture of hydrogen and carbon monoxide is reacted in the presence of an iron or cobalt catalyst to produce methane, synthetic gasoline, and other aliphatic compounds, with water and carbon dioxide as byproducts.

Free radicalA highly reactive chemical species carrying no charge and having a single unpaired electron in an orbital.

FullereneAny of various cagelike molecules that constitute the third form of pure carbon (along with the forms diamond and graphite), whose prototype C60 (buckyball) is the roundest molecule that exists. Fullerenes are a class of discrete molecules, soccerball-shaped forms of carbon with extraordinary stability (so named because their configuration suggests the shape of Buckminster Fuller’s famous geodesic dome).

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