Observational Constraints on Planet Nine: Astrometry of Pluto and Other Trans-Neptunian Objects

TL;DR

This study uses precise astrometry of Pluto and other TNOs to place observational constraints on the possible location, distance, and mass of Planet Nine, finding that certain regions improve fit quality while others do not.

Contribution

It provides new observational constraints on Planet Nine's properties using astrometry, suggesting it may be more massive or closer than previously thought.

Findings

Certain sky regions improve fit with a massive, distant planet

Astrometric residuals favor larger, closer perturbing planets

Potential systematic errors or additional bodies may explain declination trends

Abstract

We use astrometry of Pluto and other TNOs to constrain the sky location, distance, and mass of the possible additional planet (Planet Nine) hypothesized by Batygin and Brown (2016). We find that over broad regions of the sky, the inclusion of a massive, distant planet degrades the fits to the observations. However, in other regions, the fits are significantly improved by the addition of such a planet. Our best fits suggest a planet that is either more massive or closer than argued for by Batygin and Brown (2016) based on the orbital distribution of distant trans-neptunian objects (or by Fienga et al. (2016) based on range measured to the Cassini spacecraft). The trend to favor larger and closer perturbing planets is driven by the residuals to the astrometry of Pluto, remeasured from photographic plates using modern stellar catalogs (Buie and Folkner 2015), which show a clear trend in declination, over the course of two decades, that drive a preference for large perturbations. Although this trend may be the result of systematic errors of unknown origin in the observations, a possible resolution is that the declination trend may be due to perturbations from a body, additional to Planet Nine , that is closer to Pluto, but less massive than, Planet Nine .