Improved Analysis of Clarke Exobelt Detectability

TL;DR

This paper refines the analysis of exoplanet Clarke exobelts' detectability, showing they are harder to detect than previously thought due to limb-darkening effects and dynamical instability, making their observation unlikely.

Contribution

It incorporates limb-darkening and an observer-centered approach into transit analysis, and assesses the dynamical stability and collision risks of exobelts around habitable zone planets.

Findings

Detectability of exobelts is lower than previous estimates.

Synchronous exobelts are dynamically unstable around habitable zone M stars.

High satellite densities needed for detection lead to significant collision risks.

Abstract

We analyze the potential transit light curve effects due to a Clarke belt of satellites around an exoplanet. Building on code and analysis from Korpela, Sallmen, & Leystra Greene (2015), we refine the transit analysis of Socas-Navarro (2018) by incorporating limb-darkening and taking an observer-centered approach to examining residuals. These considerations make Clarke exobelt detectability more difficult than previous estimates. We also consider practical dynamical issues for exobelts, confirming that synchronously orbiting belts are dynamically unstable around planets in the habitable zones of M stars, and determining the maximum quasi-stable belt size in these situations. Using simulations for both G and M stars, we conclude that to have an even marginally detectable impact on transit light curves, exobelts must be substantially denser than previous estimates. We also estimate collision rates for the required satellite densities assuming random orbits, and find they would present significant monitoring and guidance challenges. If detectable belts exist, they would require some (possibly high) degree of ordering to avoid collisions, and must be actively maintained or they will dissipate on relatively short astronomical timescales. We conclude that detectable exobelts are likely to be rare, and have extremely low prospects for detection by transit monitoring from both current and upcoming missions.