How Well Do We Know the Orbits of the Outer Planets?

TL;DR

This paper evaluates the accuracy of astrometric methods in determining outer planet orbits, highlighting the limitations of simplified models and clarifying misconceptions about the Pioneer effect and orbital data.

Contribution

It critically assesses current astrometric techniques, emphasizing the need for careful modeling and analysis to avoid misleading conclusions about planetary dynamics.

Findings

Current Pluto ephemeris does not rule out the Pioneer effect.

Pluto's orbit is not well enough characterized to confirm or deny the Pioneer effect.

Simplified models can mislead interpretations of orbital perturbations.

Abstract

This paper deals with the problem of astrometric determination of the orbital elements of the outer planets, in particular by assessing the ability of astrometric observations to detect perturbations of the sort expected from the Pioneer effect or other small perturbations to gravity. We also show that while using simplified models of the dynamics can lead to some insights, one must be careful to not over-simplify the issues involved lest one be misled by the analysis onto false paths. Specifically, we show that the current ephemeris of Pluto does not preclude the existence of the Pioneer effect. We show that the orbit of Pluto is simply not well enough characterized at present to make such an assertion. A number of misunderstandings related to these topics have now propagated through the literature and have been used as a basis for drawing conclusions about the dynamics of the solar system. Thus, the objective of this paper is to address these issues. Finally, we offer some comments dealing with the complex topic of model selection and comparison.