Geologic minerals have their own characteristic features in the ultraviolet (UV), visible (Vis), and near infrared (NIR) wavelength regions (e.g., 0.3 to 2.6 μm) of their reflectance spectra. Therefore, meteorites and rocks, which are mixtures of many different minerals, show various, complex, overlapping features in their spectra. Reflectance spectra of asteroids indicate varying surface mineral compositions, some of which are similar to but others are different from meteorites. By classifying asteroids based on their reflectance spectra, their surface materials are shown to vary from high to low temperature materials as they go farther from the Sun. This may imply both that planetesimals in the early solar system had such zoned distribution by (electromagnetic) heating from the Sun or that the inner asteroids grew rapidly enough to make use of short-life radioactive nuclides such as 26Al as a heat source. If we look into the details, however, there are many unresolved questions as to the relationship between asteroids and meteorites such as the issues on the S asteroids and ordinary chondrites.
