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Pages 30-32

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From page 30...
... Glossary Absorption features Minima in spectra produced by absorption of certain wavelengths of light by surface materials Accrete To combine materials physically to form a larger object Achondrite A stony meteorite that crystallized from molten liquid Albedo The proportion of incoming light that is reflected from a surface Aqueous alteration A process by which minerals react with liquid water or a hydrothermal fluid Asteroid family Asteroids with similar orbital elements that were probably once parts of a larger asteroid Asteroids Main-belt Small bodies with orbits between those of Mars and Jupiter Near-Earth Small bodies whose orbits approach that of Earth Astronomical unit (AU) Measurement of distance equal to the mean distance from Earth to the Sun Breccia Rock composed of broken fragments cemented together Chondrite A common class of meteorites that has not been melted or differentiated Coma The atmosphere surrounding the nucleus of a comet, produced by gas and dust expelled from the nucleus Condensation A process by which solids form directly from a cooling gas Cosmogenic See Isotopes 30
From page 31...
... GLOSSARY Delta-V Impulse (change in velocity) required to accomplish a specific manuever in space 31 Differentiation Internal stratification of a body, caused by heating and usually resulting in a core, mantle, and crust Ecliptic The plane defined by Earth's orbit around the Sun Electromagnetic induction heating Method proposed for asteroid heating, using electric currents induced by variations in a strong solar wind Emission band Radiation emitted by an object at a particular range of wavelengths Interplanetary dust particles Tiny particles that once orbited in the spaces between planets, normally collected in the stratosphere by high-flying aircraft Iron meteorite One composed primarily of iron-nickel alloy Isotopes Cosmogenic Isotope produced by exposure to cosmic rays Radioactive Unstable isotope that decays spontaneously Radiogenic Isotope formed by radioactive decay Kuiper Belt Zone of presumably icy planetesimals located outside the orbit of Neptune Light curve Variations in amplitude observed as an asteroid rotates Metamorphic grade Relative intensity of heating and recrystallization Nodes Two points at which an object's orbit intersects Earth's orbital plane Oort Cloud Spherical halo of icy planetesimals located between approximately 1,000 and 50,000 AU from the Sun Orbital precession Slow, periodic rotation of the long axis of an orbit Parent body Object of asteroidal size from which meteorites were derived Petrology Study of the mineralogy, texture, structures, and origin of rocks Photometry Measurement of light intensities Phyllosilicate Silicate mineral with layered crystal structure Plutonic Rocks that crystallized from magma at depth Radioactive See Isotopes Radiogenic See Isotopes Radiometric dating Determining the age of a sample from measurement of its radionuclides
From page 32...
... 32 Radionuclide Radioactive isotope Regolith Layer of fragmented, incoherent rocky debris on the surface of an object THE EXPLORATION OF NEAR-EARTH OBJECTS Solar electric propulsion Reaction drive that utilizes solar energy to power an ion engine Space weathering Alteration of an asteroid's surface materials by exposure to the space environment Spall surface Dislodged slab of rock Spectra Reflection or absorption of different wavelengths of incident light Spectroscopy Measurement of spectra Thermal Inertia Parameter indicating the rate at which a body's temperature responds to changing heat input Model Calculated history of temperature variations with time Tholin Complex organic compound producing a dark reddish spectrum Trace element Element present in small abundance Ureilites Complex igneous rocks composed mostly of pyroxene, olivine, and carbon Volatiles Elements that condense from or exist as a gas at low temperatures Water of hydration Water bound into crystal structures of hydrated silicate materials, such as clays

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