Predicting Interstellar Object Chemodynamics with Gaia

The interstellar object (ISO) population of the Milky Way is a product of its stars. Traditionally the ISO velocity distribution has been modelled as a smooth Gaussian. Using a debiased stellar population derived from the Gaia DR3 stellar sample we infer the velocity distribution of ISOs to be far more textured and complex. 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, like stars, ISOs have a correlation between their velocities and compositions, resulting in a detectable difference in the velocities of water-rich and water-poor ISOs; this includes the directions from which they will approach the Solar system. We predict that this richly textured distribution will be distinguishable from a Gaussian in samples that are within the expected discovery capacity of the Vera C. Rubin Observatory. Solar neighbourhood ISOs come from a dynamic mix of stars with a wide range of ages and chemical abundances, originating all around the Milky Way. This makes the observable population an interesting probe of Galactic dynamics, with an entirely different set of biases to stellar surveys.