What is Asteroid spectral types?
Asteroids are assigned a type based on [[emission spectrum|spectral]] shape, [[color]], and sometimes [[albedo]]. These types are thought to correspond to an asteroid's surface composition. For small bodies which are not internally differentiated, the surface and internal compositions are presumably similar, while large bodies such as [[1 Ceres]] and [[4 Vesta]] are known to have internal structure. A list of types can be found at [[:Category:asteroid spectral classes|asteroid spectral classes]]. == Present-day classifications == The present-day classification was initiated by Clark R. Chapman, David Morrison, and Ben Zellner in 1975 <sup>[[#Chapman1975|&#91;1&#93;]]</sup> with three categories: [[C-type asteroid|C]] for dark carbonaceous objects, [[S-type asteroid|S]] for stony (silicaceous) objects, and U for those which did not fit into either C or S. This classification has since been expanded and clarified. A number of classification schemes are currently in existence <sup>[[#PDS|&#91;2&#93;]][[#BusAsteroidsIII|&#91;3&#93;]]</sup>, and while they strive to retain some mutual consistency, quite a few asteroids are sorted into different classes depending on the particular scheme. This is due to the use of different criteria for each approach. The two most widely used classifications are described below: === Tholen classification === The most widely used taxonomy for over a decade has been that of [[David J. Tholen]], first proposed in 1984. This classification was developed from broad band spectra (between 0.31μm and 1.06μm) obtained during the Eight-Color Asteroid Survey (ECAS) in the 1980s, in combination with [[albedo]] measurements <sup>[[#Tholen1989|&#91;4&#93;]]</sup>. The original formulation was based on 978 asteroids. This scheme includes 14 types with the majority of asteroids falling into one of three broad categories, and several smaller types. They are, with their largest exemplars: * '''[[C-type asteroid#C-group asteroids|C-group]]''' dark carbonaceous objects, including several sub-types: *