On The Applicability of Ring-Moon Cycles to Exoplanets

TL;DR

This paper investigates the potential for coupled ring-moon cycles around exoplanets, their observability during transits, and how they might explain certain anomalous density measurements, extending theories from our Solar System.

Contribution

It introduces models for ring-moon cycles around exoplanets, assesses their detectability, and explores their role in explaining low-density exoplanet observations.

Findings

Ring-moon cycles can produce long-lived rings with significant transit depths.

Secular spin-orbit resonances can enable detectable rings in multi-planet systems.

Ring features may explain some low-density exoplanet observations.

Abstract

The presence of rings and moons around exoplanets is likely to be one of the next great discoveries in exoplanet research. Using theories developed for the Solar System, we explore the possibility of coupled ring-moon cycles around exoplanets and what these processes mean for the observability of these features. Around Neptune- and Earth-like planets, we find that ring-moon cycles are capable of producing long-lived rings of comparable and greater relative transit depths than Saturn's. In multi-planet systems, secular spin-orbit resonances can provide the necessary planetary obliquity for these rings to contribute noticeably to transit lightcurves. We model the geometry of a ring's cross-section at various angles in comparison to the cross-section of a transiting planet to determine whether the ring may be detectable during the planet's transit. Ringed planets have also been proposed as an alternative to inflated planetary radii seen in transit, leading to abnormally low observed densities. Ring-moon cycles can produce late-forming and sometimes long-lived rings that can have the potential of explaining at least some of these observations. We also discuss some inconsistencies in the calculation of exoplanet oblateness due to rotation that we have come across in the course of this work.