Minor planets and related objects. XIII. Long-term orbital evolution of (1685) Toro

The orbital evolution of (1685) Toro has been investigated over 5000 yr. The asteroid exhibits a locked resonance through an 8:5 commensurability with the Earth for the first 3400 yr of integration and a locked resonance with Venus through a 13:5 commensurability for the last 1000 yr. Control of these resonances passes from the Earth to Venus as the distance from the Earth's orbit gets greater and the distance to Venus' orbit gets closer as a consequence of the precession of the argument of perihelion. The double resonance may give Toro the ability to avoid collisions with the Earth and Venus at the present time but this is stili uncertain. Mars perturbations could remove Toro from the deepest part of the resonance in about 3000000 ?rs. Thus Toro's llfetime can be ouly marginally lengthened over the normally expected value of 1030 million years by the resonance.