The composition of the Trojan asteroids

Abstract

Physical studies have shown that most asteroids are covered with material of low visual albedo (p_v∼0.04) having flat, nearly featureless reflection spectra between 0.4 and 1.1 µm (ref. 1). This large class of objects, the C asteroids, accounts for a progressively larger fraction of minor planets as one goes from the inner to the outer regions of the asteroid belt, a trend which has been interpreted as evidence of a decrease in effective condensation temperature in the original solar nebula with increasing distance from the proto-Sun². We suggest here that the very low albedos and red spectra of some Trojan asteroids can be explained by the presence of kerogen-like organic compounds. Materials containing these types of carbonaceous substances, rather than those found in the more familiar carbonaceous chondrite matrix, may have been the primary rocky condensate in the outer Solar System and may therefore be typical of the rocky component of comet nuclei.