A substellar flyby that shaped the orbits of the giant planets

TL;DR

This paper proposes that a single flyby of a substellar object could explain the current eccentric and inclined orbits of the giant planets, challenging traditional formation theories.

Contribution

It introduces a new dynamical scenario where a close flyby event shapes the giant planets' orbits, supported by a metric for matching observed orbital modes.

Findings

A flyby with a 2-50 Jupiter-mass object can produce observed orbital eccentricities and inclinations.

Estimated 1-in-9000 chance of such a flyby occurring in the solar system's early environment.

The flyby scenario offers a plausible origin for the solar system's planetary architecture.

Abstract

The modestly eccentric and non-coplanar orbits of the giant planets pose a challenge to solar system formation theories which generally indicate that the giant planets emerged from the protoplanetary disk in nearly perfectly circular and coplanar orbits. We demonstrate that a single encounter with a 2-50 Jupiter-mass object, passing through the solar system at a perihelion distance less than 20 AU and a hyperbolic excess velocity of 1-3 km/s, can excite the giant planets' eccentricities and mutual inclinations to values comparable to those observed. We describe a metric to evaluate how closely a simulated flyby system matches the eccentricity and inclination secular modes of the solar system. We estimate that there is about a 1-in-9000 chance that such a flyby occurs during the solar system's residence in its primordial cluster and produces a dynamical architecture similar to that of the solar system. The scenario of an ancient close encounter with a substellar object offers a plausible explanation for the origin of the moderate eccentricities and inclinations and the secular architecture of the planets. We discuss some broader implications of disruptive flyby encounters on planetary systems in the Galaxy.