Inner mean-motion resonances with eccentric planets: A possible origin for exozodiacal dust clouds

TL;DR

This paper investigates how mean-motion resonances with eccentric planets can scatter planetesimals into cometary orbits, potentially explaining the persistent exozodiacal dust around stars over billions of years.

Contribution

It combines analytical and numerical methods to demonstrate that this resonance mechanism can sustain long-term comet scattering and dust production in planetary systems.

Findings

Resonance-driven scattering can explain exozodi presence in old systems.

Low-mass Kuiper-like discs can sustain comet activity compatible with observations.

Eccentric Jupiter-like planets could maintain dust levels around stars like Vega.

Abstract

High levels of dust have been detected in the immediate vicinity of many stars, both young and old. A promising scenario to explain the presence of this short-lived dust is that these analogues to the Zodiacal cloud (or exozodis) are refilled in situ through cometary activity and sublimation. As the reservoir of comets is not expected to be replenished, the presence of these exozodis in old systems has yet to be adequately explained. It was recently suggested that mean-motion resonances (MMR) with exterior planets on moderately eccentric ($\mathrm{e_p}\gtrsim 0.1$) orbits could scatter planetesimals on to cometary orbits with delays of the order of several 100 Myr. Theoretically, this mechanism is also expected to sustain continuous production of active comets once it has started, potentially over Gyr-timescales. We aim here to investigate the ability of this mechanism to generate scattering on to cometary orbits compatible with the production of an exozodi on long timescales. We combine analytical predictions and complementary numerical N-body simulations to study its characteristics. We show, using order of magnitude estimates, that via this mechanism, low mass discs comparable to the Kuiper Belt could sustain comet scattering at rates compatible with the presence of the exozodis which are detected around Solar-type stars, and on Gyr timescales. We also find that the levels of dust detected around Vega could be sustained via our proposed mechanism if an eccentric Jupiter-like planet were present exterior to the system's cold debris disc.