Searching for minor absorptions on D-type asteroids

Preferably located in the outer main belt, D-type asteroids experienced less heating and represent an important population for studies on the origin and evolution of the asteroid belt, as well as the relations between asteroidal and cometary bodies. Their surface mineralogy is currently related to a mixture of organics, anhydrous silicates, opaque material and ice. However, like other taxonomic classes, a large spectral diversity can be seen among D-type objects. We use the Visible spectra of 100 D-type objects available in the literature to search for minor absorptions in those objects. The presence of minor absorptions around 0.6 and 0.8 microns is reported for a large number of objects in the sample. The presence of such bands is not related to the heliocentric distance of the objects, since the absorptions can be seen in the whole main belt, up to the the Trojans region.