Disrupting Primordial Planet Signatures: The Close Encounter of Two Single-Planet Exosystems in the Galactic Disc

TL;DR

This paper investigates how close stellar encounters in the Galactic Disc can significantly alter the orbits of single-planet exosystems, potentially obscuring their primordial orbital characteristics.

Contribution

It provides analytical limits and numerical cross-sections for the effects of stellar encounters on planetary orbits, highlighting the disruption of primordial orbital features.

Findings

A few percent of wide-orbit planets may escape due to encounters.

Eccentricities of planets can change by at least 0.1.

Primordial orbital properties of tight-orbit exoplanets are likely disrupted.

Abstract

During their main sequence lifetimes, the majority of all Galactic Disc field stars must endure at least one stellar intruder passing within a few hundred AU. Mounting observations of planet-star separations near or beyond this distance suggest that these close encounters may fundamentally shape currently-observed orbital architectures and hence obscure primordial orbital features. We consider the commonly-occurring fast close encounters of two single-planet systems in the Galactic Disc, and investigate the resulting change in the planetary eccentricity and semimajor axis. We derive explicit 4-body analytical limits for these variations and present numerical cross-sections which can be applied to localized regions of the Galaxy. We find that each wide-orbit planet has a few percent chance of escape and an eccentricity that will typically change by at least 0.1 due to these encounters. The orbital properties established at formation of millions of tight-orbit Milky Way exoplanets are likely to be disrupted.