Observational Signatures of a Massive Distant Planet on the Scattering Disk

TL;DR

This study simulates the impact of a hypothetical distant massive planet on the distribution of trans-Neptunian objects, finding that its effects are subtle and difficult to detect with current surveys, but may influence the Kuiper Belt's mass.

Contribution

First detailed N-body simulation of a massive distant planet's effects on the Kuiper Belt, highlighting observational challenges in detecting such a planet.

Findings

Distant massive planet alters TNO orbital distribution, raising pericenters and inclinations.

Current surveys cannot distinguish models with or without the ninth planet.

Kuiper Belt mass estimates increase significantly with the additional planet.

Abstract

The orbital element distribution of trans-Neptunian objects (TNOs) with large pericenters has been suggested to be influenced by the presence of an undetected, large planet at >200 AU from the Sun. To find additional observables caused by this scenario, we here present the first detailed emplacement simulation in the presence of a massive ninth planet on the distant Kuiper Belt. We perform 4 Gyr N-body simulations with the currently known Solar System planetary architecture, plus a 10 Earth mass planet with similar orbital parameters to those suggested by Trujillo & Sheppard (2014) or Batygin & Brown (2016), and 10^5 test particles in an initial planetesimal disk. We find that including a distant superearth-mass planet produces a substantially different orbital distribution for the scattering and detached TNOs, raising the pericenters and inclinations of moderate semimajor axis (50<a<500 AU) objects. We test whether this signature is detectable via a simulator with the observational characteristics of four precisely characterized TNO surveys. We find that the qualitatively very distinct Solar System models that include a ninth planet are essentially observationally indistinguishable from an outer Solar System produced solely by the four giant planets. We also find that the mass of the Kuiper Belt's current scattering and detached populations is required to be 3-10 times larger in the presence of an additional planet. We do not find any evidence for clustering of orbital angles in our simulated TNO population. Wide-field, deep surveys targeting inclined high-pericenter objects will be required to distinguish between these different scenarios.