Capture of interstellar objects: a source of long-period comets

Abstract

ABSTRACT We simulate the passage through the Sun–Jupiter system of interstellar objects (ISOs) similar to 1I/‘Oumuamua or 2I/Borisov. Capture of such objects is rare and overwhelmingly from low incoming speeds on to orbits akin to those of known long-period comets. This suggests that some of these comets could be of extrasolar origin, in particular inactive ones. Assuming ISOs follow the local stellar velocity distribution, we infer a volume capture rate of $0.051\, \mathrm{au}^3\, \mathrm{yr}^{-1}$. Current estimates for orbital lifetimes and space densities then imply steady-state captured populations of ∼102 comets and ∼105 ‘Oumuamua-like rocks, of which 0.033 per cent are within 6 au at any time.