OSSOS: IV. Discovery of a dwarf planet candidate in the 9:2 resonance with Neptune

TL;DR

This paper reports the discovery of a new dwarf planet candidate, 2015 RR$_{245}$, in the 9:2 resonance with Neptune, highlighting the importance of resonances in the evolution of trans-Neptunian objects.

Contribution

First identification of a TNO in the 9:2 resonance with Neptune, providing insights into resonance dynamics and the metastable population of distant TNOs.

Findings

2015 RR$_{245}$ is securely in the 9:2 resonance with Neptune.

The object has an estimated diameter of ~670 km.

Resonance trapping influences the long-term evolution of TNOs.

Abstract

We report the discovery and orbit of a new dwarf planet candidate, 2015 RR$_{245}$, by the Outer Solar System Origins Survey (OSSOS). 2015 RR$_{245}$'s orbit is eccentric ($e=0.586$), with a semi-major axis near 82 au, yielding a perihelion distance of 34 au. 2015 RR$_{245}$ has $g-r = 0.59 \pm 0.11$ and absolute magnitude $H_{r} = 3.6 \pm 0.1$; for an assumed albedo of $p_V = 12$% the object has a diameter of $\sim670$ km. Based on astrometric measurements from OSSOS and Pan-STARRS1, we find that 2015 RR$_{245}$ is securely trapped on ten-Myr timescales in the 9:2 mean-motion resonance with Neptune. It is the first TNO identified in this resonance. On hundred-Myr timescales, particles in 2015 RR$_{245}$-like orbits depart and sometimes return to the resonance, indicating that 2015 RR$_{245}$ likely forms part of the long-lived metastable population of distant TNOs that drift between resonance sticking and actively scattering via gravitational encounters with Neptune. The discovery of a 9:2 TNO stresses the role of resonances in the long-term evolution of objects in the scattering disk, and reinforces the view that distant resonances are heavily populated in the current Solar System. This object further motivates detailed modelling of the transient sticking population.