How Jupiters save or destroy inner Neptunes around evolved stars

TL;DR

This study models the complex evolution of Neptune-Jupiter systems around stars as they become red giants, revealing how gravitational, tidal, and stellar effects influence planetary fates, including engulfment, collision, ejection, or survival.

Contribution

It introduces a novel multi-planet, multi-effect simulation combining stellar evolution, tides, and interactions to predict planetary outcomes during stellar aging.

Findings

Neptune's fate varies significantly due to interactions and resonances.

Mean motion resonances can lead to planet engulfment or ejection.

Planetary survival depends on initial positions and system dynamics.

Abstract

In about 6 Giga years our Sun will evolve into a red giant and finally end its life as a white dwarf. This stellar metamorphosis will occur to virtually all known host stars of exo-planetary systems and is therefore crucial for their final fate. It is clear that the innermost planets will be engulfed and evaporated during the giant phase and that planets located farther out will survive. However, the destiny of planets in-between, at ~ 1 - 10 au, has not yet been investigated with a multi-planet tidal treatment. We here combine for the first time multi-planet interactions, stellar evolution, and tidal effects in an N-body code to study the evolution of a Neptune-Jupiter planetary system. We report that the fate of the Neptune-mass planet, located closer to the star than the Jupiter-mass planet, can be very different from the fate of a single Neptune. The simultaneous effects of gravitational interactions, mass loss and tides can drive the planetary system towards mean motion resonances. Crossing these resonances affects particularly the eccentricity of the Neptune and thereby also its fate, which can be engulfment, collision with the Jupiter-mass planet, ejection from the system, or survival at a larger separation.