Oort cloud asteroids: Collisional evolution, the Nice Model, and the Grand Tack

If the Solar system had a history of planet migration, the signature of that migration may be imprinted on the populations of asteroids and comets that were scattered in the planets' wake. Here, we consider the dynamical and collisional evolution of the inner Solar system asteroids that join the Oort cloud. We compare the Oort cloud asteroid populations produced by migration scenarios based on the 'Nice' and 'Grand Tack' scenarios, as well as a null hypothesis where the planets have not migrated, to the detection of one such object, C/2014 S3 (PANSTARRS). Our simulations find that the discovery of C/2014 S3 (PANSTARRS) only has a > 1 per cent chance of occurring if the Oort cloud asteroids evolved on to Oort cloud orbits when the Solar system was 1 Myr old, as this early transfer to the Oort cloud is necessary to keep the amount of collisional evolution low. We argue that this only occurs when a giant (30m) planet orbits at 1 ∼ 2 au, and thus our results strongly favour a 'Grand Tack'-like migration having occurred early in the Solar system's history.