The fates of Solar system analogues with one additional distant planet

TL;DR

This paper investigates how a distant, massive planet in the Solar system could cause future orbital instabilities during the Sun's evolution into a white dwarf, with implications for planetary system dynamics and white dwarf pollution.

Contribution

It estimates bounds on the mass and orbit of a distant planet that would induce instability in Solar system analogues during stellar evolution.

Findings

Instability more likely if the distant planet has a mass similar to Jupiter and orbits beyond 300 au.

Super-Earth mass planets beyond 3000 au also induce instability.

The likelihood of instability depends strongly on the planet's orbital parameters.

Abstract

The potential existence of a distant planet ("Planet Nine") in the Solar system has prompted a re-think about the evolution of planetary systems. As the Sun transitions from a main sequence star into a white dwarf, Jupiter, Saturn, Uranus and Neptune are currently assumed to survive in expanded but otherwise unchanged orbits. However, a sufficiently-distant and sufficiently-massive extra planet would alter this quiescent end scenario through the combined effects of Solar giant branch mass loss and Galactic tides. Here, I estimate bounds for the mass and orbit of a distant extra planet that would incite future instability in systems with a Sun-like star and giant planets with masses and orbits equivalent to those of Jupiter, Saturn, Uranus and Neptune. I find that this boundary is diffuse and strongly dependent on each of the distant planet's orbital parameters. Nevertheless, I claim that instability occurs more often than not when the planet is as massive as Jupiter and harbours a semimajor axis exceeding about 300 au, or has a mass of a super-Earth and a semimajor axis exceeding about 3000 au. These results hold for orbital pericentres ranging from 100 to at least 400 au. This instability scenario might represent a common occurrence, as potentially evidenced by the ubiquity of metal pollution in white dwarf atmospheres throughout the Galaxy.