The Dynamics of Interstellar Asteroids and Comets within the Galaxy: An Assessment of Local Candidate Source Regions for 1I/Oumuamua and 2I/Borisov

The first detection of an interstellar asteroid occurred in 2017. Dubbed '1I/’Oumuamua', a Hawaiian term loosely meaning 'Messenger From Afar', its discovery has ushered in a new era in the study of planetary objects. A second interstellar interloper, comet '2I/Borisov' was discovered in 2019. Studies of these objects as they pass through the solar system can be augmented by knowledge of their birthplaces, provided they can be traced backward in time to their home systems. 1I/’Oumuamua's low velocity with respect to the Local Standard of Rest of our galaxy is an indication (though not proof) that it is young, providing motivation for studies of its origin. We first outline the effect of gravitational scattering by galactic components (so-called, 'disk heating') on attempts to trace interstellar objects' orbits through the galaxy. We find that disk heating introduces large errors even as far back as 10 Myr, when orbital calculations can only expect to be accurate to within 15 pc and 2 km s^-1. We nevertheless show that there is a reasonable chance that 'Oumuamua is local in origin, coming to us from within the Orion Arm. We extend these results by searching for close, slow (<5 km s^-1) encounters between 1I/'Oumuamua and young, nearby moving groups, accounting for uncertainties due to disk heating along the way. We show that ’Oumuamua passed through a considerable subset of the Carina and Columba moving groups when those groups were forming, at speeds consistent with an origin there. This makes them perhaps the most plausible source region, if ’Oumuamua was ejected during planet formation or via intra-cluster interactions. A similar analysis for 2I/Borisov reveals three stars in the Ursa Major group, one brown dwarf, and seven other stars to have encounters with 2I/Borisov, within 2 pc and 30 km s^-1. However, these encounters’ high relative speeds mean none are likely to be the home of 2I/Borisov.