Dynamical Evolution of Planetesimals in the Outer Solar System: I. The Jupiter/Saturn Zone

• Published in: Icarus (New York, N.Y. 1962) Vol. 140; no. 2; pp. 341 - 352
• Main Authors: Grazier, Kevin R, Newman, William I, Kaula, William M, Hyman, James M
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.08.1999
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1006/icar.1999.6146

We report on numerical simulations designed to understand the distribution of small bodies in the Solar System and the winnowing of planetesimals accreted from the early solar nebula. The primordial planetesimal swarm evolved in a phase space divided into regimes by separatrices which define their trajectories and fate. This sorting process is driven by the energy and angular momentum and continues to the present day. We reconsider the existence and importance of stable niches in the Jupiter/Saturn zone using highly accurate numerical techniques based on high-order optimized multistep integration schemes coupled to roundoff error minimizing methods. We repeat the investigations of W. M. Weibel et al. (Icarus83, 382–390, 1990) with one hundred thousand massless particles—nearly 103 time more particles than our 1990 investigation. Previous studies of the Jupiter/Saturn zone have employed only hundreds of particles, usually starting on circular and zero inclination orbits. By employing 105 particles on both inclinded and eccentric orbits, we can perform a near-exhaustive search for test particle stability as a function of initial orbital elements. The increase in the numbers of test particles also facilitates robust statistical inference and comparison with analytic results. In our simulations, we observed three stages in the planetesimal dynamics. At the start of the simulation many planetesimals are quickly eliminated by close approaches to Jupiter or Saturn. Next there is a gravitational relaxation phase where the surviving particles are exponentially eliminated by random gravitational encounters with Jupiter or Saturn. Finally, the only long-lived particles in the simulation were initially located either at a Lagrange point or in an orbit nearly commensurable with Jupiter or Saturn. We conclude that although niches for planetesimal material are rare, extremely high-accuracy long-duration simulations employing many particles will be able to capture even the qualitative nature of early Solar System planetesimal evolution.