Asteroid spectral types

Over the years, there has been a number of surveys that resulted in a set of different taxonomic systems such as the Tholen, SMASS and Bus–DeMeo classifications.

[1] In 1975, astronomers Clark R. Chapman, David Morrison, and Ben Zellner developed a simple taxonomic system for asteroids based on color, albedo, and spectral shape.

For the Tholen-like classification, the survey introduced a new "Caa-type", which shows a broad absorption band associated indicating an aqueous alteration of the body's surface.

[1] The Bus-DeMeo classification is an asteroid taxonomic system designed by Francesca DeMeo, Schelte Bus and Stephen Slivan in 2009.

The letter "U" is a qualifying flag, used for asteroids with an "unusual" spectrum, that falls far from the determined cluster center in the numerical analysis.

For example, the Mars-crosser 1747 Wright has an "AU:" class, which means that it is an A-type asteroid, though with an unusual and noisy spectrum.

[9] This survey produced spectra of a far higher resolution than ECAS (see Tholen classification above), and was able to resolve a variety of narrow spectral features.

[citation needed] The characterization of an asteroid includes the measurement of its color indices derived from a photometric system.

This is done by measuring the object's brightness through a set of different, wavelength-specific filters, so-called passbands.