A class of asteroid, fairly common in the main asteroid belt, having featureless reflectance spectra, flat to slightly reddish over the wavelength range 0.3–1.1 μm. M-class asteroids are distinguished from the spectrally identical classes E and P by their moderate albedos (0.10–0.18). The ‘M’ is for metallic, since they are believed to have metallic (nickel–iron) compositions. Members of this class include (16) Psyche, diameter 253 km, and (21) Lutetia, diameter 96 km.
Subjects: Astronomy and Astrophysics.