Dynamical orbital evolution of asteroids and planetesimals across distinct chemical reservoirs due to accretion growth of planets in the early solar system

Abstract

N-body numerical simulations code for the orbital motion of asteroids/planetesimals within the asteroid belt under the gravitational influence of the Sun and the accreting planets, has been developed. The aim is to make qualitative, and to an extent a semi-quantitative argument, regarding the possible extent of radial mixing and homogenization of planetesimal reservoirs of the two observed distinct spectral types, viz., the S- and C-types, across the heliocentric distances due to their dynamical orbital evolution, thereby, eventually leading to the possible accretion of asteroids with chemically diverse constituents. The spectral S- and C-type asteroids are broadly considered as the parent bodies of the two observed major meteoritic dichotomy classes, namely the non-carbonaceous (NC) and carbonaceous (CC) meteorites, respectively. The present analysis is performed to understand the evolution of the observed dichotomy and its implications due to the nebula and early planetary processes during the initial 10 Myr (million years). The homogenization across the two classes is studied in context to the accretion timescales of the planetesimals with respect to the half-life of the potent planetary heat source, ²⁶Al. The accretion over a timescale of ~1.5 Myr, possibly resulted in the planetary-scale differentiation of planetesimals to produce CC and NC achondrites and iron meteorite parent bodies, whereas the prolonged accretion over a timescale of 2–5 Myr resulted in the formation of CC and NC chondrites. Our simulation results indicate a significant role of the initial eccentricities and the masses of the accreting giant planets, specifically, Jupiter and Saturn, in triggering the eccentricity churning of the planetesimals across the radial distances. The rapid accretion of the giant planets with appropriate eccentricities, critically influences the triggering of the orbital resonances that are in turn responsible for the radial mixing of the two distinct chemical reservoirs across early solar system. This would influence the chemical composition and mixing of the various planetary reservoirs. The observed dichotomy among the NC and CC reservoirs can be preserved within the initial 5 Myr in the early solar system in case the accretion of the two giant planets is prolonged. The present work provides a semi-quantitative formulation in terms of radial homogenization. A rigorous computational formulation of the evolving ensemble of distinct chemical reservoirs is beyond the scope of the present computational work.