Formation and Migration of Trans-neptunian Objects and Asteroids

The evolution of thousands of orbits of Jupiter-family comets and asteroids under the gravitational influence of planets was calculated. Comparison of the results obtained by a symplectic method with those obtained by direct integration showed that a symplectic method is not always good for investigations of the orbital evolution of such bodies. Basing on the results of orbital evolution of bodies, we concluded that a considerable portion of near-Earth objects could have come from the trans-Neptunian region. Some large trans-Neptunian objects could be formed by the compression of rarefied dust condensations, but not by the accumulation of smaller planetesimals. 1. FORMATION OF TRANS-NEPTUNIAN OBJECTS AND ASTEROIDS It is considered by many authors that a dust disk around the forming Sun became thinner until its density reached a critical value about equal to the Roche density. At this density, the disk became unstable to perturbations by its own self-gravity and developed dust condensations. These initial condensations coagulated under collisions and formed larger condensations, which compressed and formed solid planetesimals. Usually it is considered that asteroids and trans-Neptunian objects (TNOs) were formed by accumulation of smaller planetesimals. As it was obtained by several authors, the process of accumulation of TNOs from smaller planetesimals needs small (∼0.001) eccentricities and a massive belt. Our runs showed that maximal eccentricities of typical TNOs always exceed 0.05 during 20 Myr under the gravitational influence of the giant planets. Gas drag could decrease eccentricities of planetesimals, and the gravitational influence of the forming giant planets could be less than that of the present planets. Nevertheless, to our opinion, it is probable that, due to the gravitational influence of the forming giant planets and migrating planetesimals, small eccentricities of TNOs could not exist during all the time needed for the accumulation of TNOs with diameter d > 100 km. Therefore, we support the Eneev’s suggestion that TNOs with d ≥ 100 km moving now in not very eccentric orbits could be formed directly by the compression of large rarefied dust condensations (with a > 30 AU), but not by the accretion of smaller solid planetesimals. The role of turbulence could decrease with an increase of distance from the Sun, so, probably, condensations could be formed at least beyond Saturn’s orbit. Probably, some planetesimals with d ∼ 100−1000 km in the feeding zone of the giant planets and even large main-belt asteroids also could be formed directly by the compression of rarefied dust condensations. Some smaller objects (TNOs, planetesimals, asteroids) could be debris of larger objects, and other such objects could be formed directly by compression of condensations. Even if at some instants of time at approximately the same distance from the Sun, the dimensions of initial condensations, which had been formed from the dust layer due to gravitational instability, had been almost identical, there was a distribution in masses of