Minor bodies: Spectral gradients and relationships with meteorites

The observational evidence of a gradient in composition of the solid matter in the Solar System as a function of heliocentric distance, with more volatile elements increasingly abundant at larger heliocentric distances, is in general agreement with commonly accepted ideas about condensation of solid material in the early protoplanetary disk. In this respect, the gradual transition from regions mostly populated by S-type objects in the inner asteroid belt to the C-type dominated outer belt, and to the D-type dominated Trojan clouds has generally been interpreted as diagnostic of a zoning of the asteroid population in terms of mineralogic composition and thermal history. The situation, however, is not completely clear, and several contradictory facts still need an explanation. Another major problem concerns the origin of meteorites. Understanding the history of these bodies is critically important, since most of our ideas about the composition of the original protosolar nebula and protoplanetary matter come from meteoritic data. In this respect, very recent advances have been achieved in the knowledge of dynamical transport mechanisms. This can have important consequences for the characterization of plausible meteorite parent bodies.