A population of main belt asteroids co-orbiting with Ceres and Vesta

Apostolos A. Christou, Paul Wiegert

Evolution of main belt asteroid 157214 during episodes of tadpole (bold line) and horseshoe (dashed-dotted line) libration with respect to Ceres. These last for 2.4*10⁵ yr and 1.6*10⁵ yr respectively. The location of Ceres ('C') - averaged over one orbital period - and that of the Sun ('S') in a frame rotating with the mean motion of Ceres are indicated, as are the triangular equilibrium points L4 and L5 of the Sun-Ceres-Asteroid system.

Abstract

We have carried out a search for Main Belt Asteroids (MBAs) co-orbiting with the large MBA Vesta and the dwarf planet Ceres. Through improving the search criteria used in Christou (2000b) and numerical integrations of candidate coorbitals, we have identified approximately 51 (44) objects currently in co-orbital libration with Ceres (Vesta). We show that these form part of a larger population of transient coorbitals; 129 (94) MBAs undergo episodes of co-orbital libration with Ceres (Vesta) within a 2 Myr interval centred on the present. The lifetime in the resonance is typically a few times òÈ® 10⁵ yr but can exceed 2 †× 10⁶ yr. The variational properties of the orbits of several co-orbitals were examined. It was found that their present states with respect to the secondary are well determined but knowledge of it is lost typically after òÈ® 2 †× 10⁵ years. Objects initially deeper into the coorbital region maintain their coorbital state for longer. Using the model of Namouni et al. (1999) we show that their dynamics are similar to those of temporary coorbital NEAs of the Earth and Venus. As in that case, the lifetime of resonant libration is dictated by planetary secular perturbations, the inherent chaoticity of the orbits and close encounters with massive objects other than the secondary. In particular we present evidence that, while in the coorbital state, close encounters with the secondary are generally avoided and that Ceres affects the stability of tadpole librators of Vesta. Finally we demonstrate the existence of Quasi-satellite orbiters of both Ceres and Vesta and conclude that decametre-sized objects detected in the vicinity of Vesta by the DAWN mission may, in fact, belong to this dynamical class rather than be bona-fide (i.e. keplerian) satellites of Vesta.

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Last Revised: 2011 October 24th