Hydrated Silicates on M-, S-, and E-Type Asteroids as Possible Traces of Collisions with Bodies from the Jupiter Growth Zone

Absorption bands near 0.43 and 0.60–0.80 m, with a relative intensity of approximately 5–10%, were discovered in the reflectance spectra of five M asteroids (21, 75, 161, 201, and 497) and two S asteroids (11 and 198). It is highly probable that these absorption bands are related to oxidized and/or hydrated silicates that incorporate OH structural groups. Absorbed water in the surface material of about 24% of the known M asteroids and three E asteroids has been identified by a group of astronomers at the University of Arizona (Rivkin et al., 1995; Rivkin, 1997; Rivkin et al., 2000) on the basis of the characteristic 3-m absorption band. In addition to this, four of the six E-type asteroids observed spectrally in the visible region quite recently were found to have an absorption band at 0.5 m (Burbine et al., 1998; Fornasier and Lazzarin, 2001), which could likewise be associated with the presence of hydrated silicates in their material. The above data contradict the generally accepted viewpoint on the nature of M, S, and E asteroids, which is based on their common observed characteristics as bodies that arose at high temperatures (in the 1000–2000°C range). This contradiction, however, can be eliminated if use is made of the cosmogonic model developed by V.S. Safronov and co- workers. According to this model, the initial evolution of the main-belt asteroids was directly influenced by the process of the growth of Jupiter and was later controlled by its gravitational field.