Sedna as the Footprint of the Sun's Migration in the Milky Way

Nathan Kaib

Queen's University

The trans-Neptunian object (TNO) Sedna is puzzling because its orbit displays evidence of significant gravitational perturbations from the local galactic environment even though its proximity to the Sun implies the odds of a "Sedna-perturbing" field star passage are improbably small. Consequently, many alternative formation scenarios have been proposed. However, new galactic evolution models suggest the Sun's radial position in the Milky Way (and hence its local galactic environment) has varied dramatically during its history. In particular, they find that the Sun may have formed closer to the Galactic center where local stellar densities are higher. Using numerical simulations that account for the Sun's migration within the Galaxy, we demonstrate that it is in fact quite plausible for normal passing field stars to generate Sedna-like orbits. Depending on the Sun's orbital history, the probability of Sedna being generated by a simple field star passage varies between 2 and 50%. In contrast to other models, we predict a small population of Sedna-like bodies whose orbits could have been sculpted Gyrs after solar system formation. Thus, Sedna's orbit may not require a special dynamical mechanism and may fit within the framework of an Oort Cloud sculpted by the conventional perturbations of passing field stars and the Milky Way tide.