Thursday, July 14, 2016

Tracking Neptune's Migration History through High-Perihelion Resonant Trans-Neptunian Objects

Tracking Neptune's Migration History through High-Perihelion Resonant Trans-Neptunian Objects


Kaib et al


Recently, Sheppard et al. (2016) presented the discovery of 7 new trans-Neptunian objects with perihelia beyond 40 AU with moderate eccentricities and semimajor axes over 50 AU. Like the handful of previously known bodies on similar orbits, these objects' semimajor axes are just beyond the Kuiper belt edge and clustered around mean motion resonances (MMRs) with Neptune. The objects likely obtained their observed orbits while trapped in a MMR, where the Kozai-Lidov mechanism can raise their perihelia. This mechanism generates a high-perihelion population and also weakens Neptune's dynamical influence over these objects. Here we numerically model the production of this population under a variety of different migration scenarios for Neptune, varying both migration speed and migration smoothness. We find that high-perihelion objects near Neptunian MMRs constrain the nature of Neptune's migration. In particular, the population near the 3:1 MMR (near 62 AU) is especially useful due to its large population and short dynamical evolution timescale. If Neptune reaches its modern orbit after just ~100 Myrs or less of total migration time, we predict that ~90% of the high-perihelion objects near the 3:1 MMR will all have semimajor axes within 1 AU of each other, residing very near the modern resonance's center. On the other hand, if Neptune takes ~300 Myrs of total time to migrate to its final orbit, we expect ~50% of this population to be in dynamically fossilized orbits slightly closer (>~1 AU) to the Sun than the modern resonance location. We highlight 2015 KH162 as a likely member of this fossilized 3:1 population. Under any plausible migration scenario, the vast majority of high-perihelion objects in resonances more distant than the 4:1 MMR (near 76 AU) reach their orbits well after Neptune stops migrating and represent a recently generated, dynamically active population.

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