We use astrometry of Pluto and other trans-neptunian objects to constrain the sky location, distance, and mass of the possible additional planet (Planet Nine) hypothesized by Batygin & Brown. 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 & Brown based on the orbital distribution of distant trans-neptunian objects (or by Fienga et al. 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, which show a clear trend in decl. 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 decl. trend may be due to perturbations from a body, in addition to Planet Nine, that is closer to Pluto but less massive than Planet Nine.
