OSSOS: V. Diffusion in the orbit of a high-perihelion distant Solar System object

TL;DR

This paper reports the discovery of a highly distant, eccentric trans-Neptunian object with the largest known semi-major axis, and explores its orbital evolution driven by Neptune's weak influence, suggesting a connection to the Oort cloud.

Contribution

It presents the discovery of 2013 SY$_{99}$ with the largest semi-major axis among high-perihelion TNOs and analyzes its dynamical evolution through simulations, proposing a new formation mechanism.

Findings

2013 SY$_{99}$ has a semi-major axis of 730 au and perihelion of 50 au.

Dynamical simulations show diffusion in semi-major axis over 4 Gyr due to Neptune.

Diffusion can populate the orbital space from the inner Oort cloud fringe.

Abstract

We report the discovery of the minor planet 2013 SY$_{99}$, on an exceptionally distant, highly eccentric orbit. With a perihelion of 50.0 au, 2013 SY$_{99}$'s orbit has a semi-major axis of $730 \pm 40$ au, the largest known for a high-perihelion trans-Neptunian object (TNO), well beyond those of (90377) Sedna and 2012 VP$_{113}$. Yet, with an aphelion of $1420 \pm 90$ au, 2013 SY$_{99}$'s orbit is interior to the region influenced by Galactic tides. Such TNOs are not thought to be produced in the current known planetary architecture of the Solar System, and they have informed the recent debate on the existence of a distant giant planet. Photometry from the Canada-France-Hawaii Telescope, Gemini North and Subaru indicate 2013 SY$_{99}$ is $\sim 250$ km in diameter and moderately red in colour, similar to other dynamically excited TNOs. Our dynamical simulations show that Neptune's weak influence during 2013 SY$_{99}$'s perihelia encounters drives diffusion in its semi-major axis of hundreds of astronomical units over 4 Gyr. The overall symmetry of random walks in semi-major axis allow diffusion to populate 2013 SY$_{99}$'s orbital parameter space from the 1000-2000 au inner fringe of the Oort cloud. Diffusion affects other known TNOs on orbits with perihelia of 45 to 49 au and semi-major axes beyond 250 au, providing a formation mechanism that implies an extended population, gently cycling into and returning from the inner fringe of the Oort cloud.