How are asteroid classes identified from reflected sunlight?

Asteroid classes are identified by analyzing the albedo—the fraction of sunlight reflected—and the spectral reflectance of the asteroid's surface.12

Astronomers measure the amount of sunlight reflected at specific wavelengths, typically between 0.3 and 1.1 micrometres, to determine these properties. By comparing this observational data with laboratory measurements of terrestrial rocks and meteorites, scientists can infer the surface composition of the asteroid.12

Because some classes, such as E, M, and P, may appear spectrally indistinguishable at certain wavelengths, independent albedo measurements are often required for unambiguous classification. Furthermore, researchers must account for space weathering—processes like solar wind and micrometeorite impacts—which can alter the surface properties of asteroids over time, sometimes creating discrepancies between the observed spectra and the underlying composition of the body.12