Interstellar objects are a new messenger in stellar astrophysics. A complex picture is emerging of their role in multiple facets of Galactic processes: from planetesimal formation with equivalencies to outer Solar System objects, to dynamical evolution in the Galactic potential. Unlocking these connections requires combining factors ranging from the remote sensing and modelling of protoplanetary disks, to compositional measurements of the surfaces and comae of Solar System-visiting ISOs. We will explore the current state of each part of this picture, identifying the big questions that need resolving, with a focus on the dynamical effects and their relative importance.
One key part is the ISO velocity distribution. Using a debiased stellar population derived from the Gaia DR3 stellar sample, we infer that the velocity distribution of ISOs is highly textured. The moving groups caused by Galactic resonances dominate the distribution. 1I/‘Oumuamua and 2I/Borisov have entirely normal places within these distributions; 1I is within the non-coeval moving group that includes the Matariki (Pleiades) cluster, and 2I within the Coma Berenices moving group. We show that for the composition of planetesimals formed beyond the ice line, these velocity structures also have a chemodynamic component.