Explaining Neptune's Eccentricity

TL;DR

This paper proposes that a close stellar flyby approximately 4.5 billion years ago could explain Neptune's current eccentric orbit, supplementing earlier migration models that damped its eccentricity.

Contribution

It introduces a stellar flyby scenario as a mechanism for Neptune's eccentricity, which was previously not considered in detail.

Findings

A stellar flyby of about 0.1 solar masses at 1000 AU can account for Neptune's eccentricity.

The flyby event likely occurred within the first few billion years of the Solar System.

This scenario complements existing models of planetary migration and eccentricity damping.

Abstract

Early migration damped Neptune's eccentricity. Here, we assume that the damped value was much smaller than the value observed today, and show that the closest flyby of $\sim 0.1 \; \mathrm{M_{\odot}}$ star over $\sim 4.5 \mathrm{\; Gyr}$ in the field, at a distance of $\sim 10^3 \mathrm{\; AU}$ would explain the value of Neptune's eccentricity observed today.