Can a jumping-Jupiter trigger the Moon’s formation impact?

Abstract

ABSTRACT We investigate the possibility that the Moon’s formation impact was triggered by an early dynamical instability of the giant planets. We consider the well-studied ‘jumping Jupiter’ hypothesis for the Solar system’s instability, where Jupiter and Saturn’s semimajor axes evolve in step-wise manner from their primordially compact architecture to their present locations. Moreover, we test multiple different configurations for the primordial system of terrestrial planets and the Moon-forming projectile, with particular focus on the almost equal masses impact. We find that the instability/migration of the giant planets excites the orbits of the terrestrial planets through dynamical perturbations, thus allowing collisions between them. About 10 per cent of the simulations lead to a collision with the proto-Earth which resulted in a final configuration of the terrestrial system that reproduces, to some extent, its present architecture. Most of these collisions occur in the hit-and-run domain, but about 15 per cent occur in the partial accretion regime, with the right conditions for a Moon-forming impact. In most of the simulations, there is a delay of more than ∼20 My between the time of the instability and the Moon-forming impact. This supports the occurrence of an early instability (<10 My after dissipation of the gas in the protoplanetary disc), compatible with the time of the Moon-forming impact (30–60 My) inferred from cosmochemical constraints. In general, the final states of the inner Solar system in our simulations show an excess of Angular Momentum Deficit, mostly attributed to the overexcitation of Mercury’s eccentricity and inclination.