The early Solar system produced a variety of bodies with different properties. Among the small bodies, objects that contain notable amounts of water ice are of particular interest. Water-rock separation on such worlds is probable and has been confirmed in some cases. We couple accretion and water-rock separation in a numerical model. The model is applicable to Ceres, icy satellites, and Kuiper belt objects, and is suited to assess the thermal metamorphism of the interior and the present-day internal structures. The relative amount of ice determines the differentiation regime according to porous flow or Stokes flow. Porous flow considers differentiation in a rock matrix with a small degree of ice melting and is typically modelled either with the Darcy law or two-phase flow. We find that for small icy bodies two-phase flow differs from the Darcy law. Velocities derived from two-phase flow are at least one order of magnitude smaller than Darcy velocities. The latter do not account for the matrix resistance against the deformation and overestimate the separation velocity. In the Stokes regime that should be used for large ice fractions, differentiation is at least four orders of magnitude faster than porous flow with the parameters used here.

Almost all meteorites (about 99% by number) are samples from a few hundreds of asteroids that are leftover from planetesimals and protoplanets formed within several million years after the birth of the Solar System. These meteorites record detailed evolutionary history of dust to planets, including condensation, accretion, aqueous alteration, thermal metamorphism, partial and total melting.

We numerically investigate the conditions for planetesimal accretion in the circumprimary disk under the perturbing presence of a companion star, with focus on the γ Cephei system. Gas drag is included with a dissipating time scale of 105 years. We show at the beginning(within 103 ∼ 104 years), gas drag damps the ΔV between planetesimals of same sizes and increases ΔV between planetesimals of different sizes. However, after increasing to high values(300∼800m/s), we find the ΔV between bodies of different sizes decrease to very low values (below 10m/s) in a few 105yrs (depending on the gas-dissipating time scale Tdamp, radial size Rp and semi-major axis ap of planetesimals). Hence, the high ΔV is somewhat short-lived, and runaway accretion can be turned on later. We conclude that the conditions for planetary formation in binary systems (even close binary systems) are much better than what we expected before.