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
Delta-V
Impulse (change in velocity) required to accomplish a specific manuever in space
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
Radionuclide
Radioactive isotope
Regolith
Layer of fragmented, incoherent rocky debris on the surface of an object
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
