M-type (metal-rich) asteroids are typically found in the middle of the main belt, and they make up much of the remainder of the total population. Their spectra resemble that of iron-nickel. Some are believed to have formed from the metallic cores of differentiated progenitor bodies that were disrupted through collision. However, some silicate compounds also can produce a similar appearance. For example, the large M-type asteroid 22 Kalliope does not appear to be primarily composed of metal. Within the asteroid belt, the number distribution of M-type asteroids peaks at a semimajor axis of about 2.7 AU. Whether all M-types are compositionally similar, or whether it is a label for several varieties which do not fit neatly into the main C and S classes is not yet clear.
M-type (metal-rich) asteroids are typically found in the middle of the main belt and they make up much of the remainder of the total population Their spectra resemble that of iron-nickel Some are believed to have formed from the metallic cores of differentiated progenitor bodies that were disrupted through collision However some silicate compounds also can produce a similar appearance For example the large M-type asteroid 22 Kalliope does not appear to be primarily composed of metal Within the asteroid belt the number distribution of M-type asteroids peaks at a semimajor axis of about 27 AU Whether all M-types are compositionally similar or whether it is a label for several varieties which do not fit neatly into the main C and S classes is not yet clear