A hypothesis on the origin of C-type asteroids and carbonaceous chondrites

Abstract

A hypothesis based on observational and theoretical results on the origin of C-type asteroids and carbonaceous chondrites is proposed. Asteroids of C-type and close BGF-types could form from hydrated silicate-organic matter accumulated in the cores of water-differentiated (due to 26Al and other short-lived isotopes decay) bodies existed in the growth zones of Jupiter. Gravitational scattering of such bodies by Jupiter at its final stage of formation to the main asteroid belt might have led to fragmentation and re-accretion of their primitive materials on the surfaces of many asteroids and/or asteroid parent bodies. The hypothesis makes clear a row of long-standing puzzling facts, the main of which are as follows. The low-albedo and carbonaceous-chondritic surface properties of (1) Ceres contradict to its probable differentiated structure and icy crust (e. g., Thomas et al., 2005, Nature 437: 224-226; Castillo-Rogez et al., 2010, Icarus 205, 443-459), but it could be explained by the process of primitive matter fall. Atypical hydrated silicates (probably, as a component of carbonaceous-chondritic matter) are found on the surfaces of many asteroids of high-temperature types (Rivkin et al., 1995, Icarus 117: 90-100; Rivkin et al., 2000, Icarus 145: 351-368; Busarev, 1998, Icarus 131: 32-40; Busarev, 2002, Solar System Research 36: 39-47) that may be a consequence of the carbonaceous-chondritic matter precipitation on their surfaces. Some carbonaceous chondrites are unidirectionly magnetized (e. g., Stacey et al., 1961, J. Geophys. Res. 66: 1523-1534; Butler, 1972, Earth Planet. Sci. Lett. 17: 120-128) which may be a result of their stay on the surface of an early differentiated asteroid parent body having melted interiors and a strong magnetic field.