2021ApJ...917...20H

The appearance of interstellar objects (ISOs) in the solar system-and specifically the arrival of 1I/'Oumuamua-points to a significant number density of free-floating bodies in the solar neighborhood. We review the details of 'Oumuamua's pre-encounter Galactic orbit, which intersected the solar system at very nearly its maximum vertical and radial excursion relative to the Galactic plane. These kinematic features are strongly emblematic of nearby young stellar associations. We obtain an a priori order-of-magnitude age estimate for 'Oumuamua by comparing its orbit to the orbits of 50,899 F-type stars drawn from Gaia DR2; a diffusion model then suggests a ∼35 Myr dynamical age. We compare 'Oumuamua's orbit with the trajectories of individual nearby moving groups, confirming that its motion is fully consistent with membership in the Carina (CAR) moving group with an age of ∼30 Myr. We conduct Monte Carlo simulations that trace the orbits of test particles ejected from the stars in the CAR association. The simulations indicate that in order to uniformly populate the ∼10⁶ pc³ volume occupied by CAR members with the inferred number density, n = 0.2 au^–3, of ISOs implied by Pan-STARRS's detection of 'Oumuamua, the required ejection mass is M ∼ 500 M_Jup per known star within the CAR association. This suggests that the Pan-STARRS observation is in significant tension with scenarios that posit 'Oumuamua's formation and ejection from a protostellar disk.