An Exoplanet's Response to Anisotropic Stellar Mass-Loss During Birth and Death

TL;DR

This paper develops equations to study how anisotropic stellar mass loss during star evolution affects planetary orbits, revealing that isotropic models are generally sufficient except for certain asymmetric outflows that can tilt exoplanetary orbits.

Contribution

It introduces a comprehensive set of equations for planetary orbital evolution under anisotropic stellar mass loss, extending previous isotropic models.

Findings

Isotropic mass-loss models are adequate within hundreds of au during giant phases.

Latitudinal mass loss variations only affect orbits if asymmetric about the stellar equator.

Asymmetric bipolar outflows can tilt exoplanetary orbits by degrees.

Abstract

The birth and death of planets may be affected by mass outflows from their parent stars during the T-Tauri or post-main-sequence phases of stellar evolution. These outflows are often modelled to be isotropic, but this assumption is not realistic for fast rotators, bipolar jets and supernovae. Here we derive the general equations of motion for the time evolution of a single planet, brown dwarf, comet or asteroid perturbed by anisotropic mass loss in terms of a complete set of planetary orbital elements, the ejecta velocity, and the parent star's co-latitude and longitude. We restrict our application of these equations to 1) rapidly rotating giant stars, and 2) arbitrarily-directed jet outflows. We conclude that the isotropic mass-loss assumption can safely be used to model planetary motion during giant branch phases of stellar evolution within distances of hundreds of au. In fact, latitudinal mass loss variations anisotropically affect planetary motion only if the mass loss is asymmetric about the stellar equator. Also, we demonstrate how constant-velocity, asymmetric bipolar outflows in young systems incite orbital inclination changes. Consequently, this phenomenon readily tilts exoplanetary orbits external to a nascent disc on the order of degrees.