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

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 . 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 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 .

The Curiously Warped Mean Plane of the Kuiper Belt

“…Recent suggestions (Trujillo & Sheppard 2014;Holman & Payne 2016a, 2016bMalhotra et al 2016;Sheppard & Trujillo 2016) of a M 10 Å planet in the very distant solar system (beyond several hundred au) would not explain the observed deviation of the mean plane in the 50-150 au semimajor axis range. An additional M 10 Å planet at a 600 au » has a negligible effect on the forced plane of the Kuiper Belt at semimajor axes interior to ∼100 au, even if the additional planet is highly inclined.…”

“…We are also motivated by recent intriguing but not conclusive evidence of a large unseen planet on an inclined orbit in the distant solar system (Trujillo & Sheppard 2014;Holman & Payne 2016a, 2016bMalhotra et al 2016;Sheppard & Trujillo 2016), as well as previous suggestions of unseen planetary-mass objects perturbing the orbits of KBOs (e.g., Gladman et al 2002;Lykawka & Mukai 2008). Unseen planetary-mass objects in the outer solar system could result in KBOs having a mean plane that deviates from that expected due to the known planets.…”

Dynamical Evolution Induced by Planet Nine

“…Thus, the final evaluation of the Planet Nine hypothesis will not simply correspond to a detection of a planet beyond Neptune, but the confrontation of the outlined theory with the dynamical evolution induced by this planet. Thankfully, the observational prospects for the direct detection of Planet Nine either through ongoing or future surveys are quite promising Fortney et al 2016;Holman & Payne 2016aMillholland & Laughlin 2017), and it is likely that the concluding assessment of the theoretical model outlined in this paper will occur on a timescale considerably shorter than a decade.…”

Consequences of a Distant Massive Planet on the Large Semimajor Axis Trans-Neptunian Objects

“…These arguments launched a flurry of discussions and studies on the origins, location, and implications of a ninth planet. The studies have covered formation and capture scenarios Cowan et al 2016;Li & Adams 2016;Mustill et al 2016), constraints on the location, detectability and physical properties of P9 de la Fuente Marcos & de la Fuente Marcos 2016aFienga et al 2016;Fortney et al 2016;Ginzburg et al 2016;Holman & Payne 2016aLinder & Mordasini 2016;Philippov & Chobanu 2016;Toth 2016;Veras 2016), the dynamical implications of P9 in the solar system (de la Fuente Marcos et al 2016c;Lawler et al 2016), P9 producing inclined TNOs (Batygin & Brown 2016b), resonances and P9 (Beust 2016;Malhotra et al 2016), a dark matter P9 (Sivaram et al 2016), and impacts of P9 on the Sun's obliquity (Bailey et al 2016;Lai 2016).…”