# Worlds Without Moons: Exomoon Constraints for Compact Planetary Systems

## TL;DR

This paper investigates the likelihood of exomoons in compact planetary systems, especially around low-mass stars, using Hill radius and Roche limit constraints, with a focus on the TRAPPIST-1 system, concluding most planets probably lack moons.

## Contribution

It introduces a method to constrain exomoon presence in compact systems based on Hill and Roche limits, applied specifically to TRAPPIST-1.

## Key findings

- Most planets in TRAPPIST-1 are likely moonless.
- Constraints suggest moons are unlikely in compact systems.
- Exomoon presence depends on Hill and Roche limit considerations.

## Abstract

One of the primary surprises of exoplanet detections has been the discovery of compact planetary systems, whereby numerous planets reside within ~0.5 AU of the host star. Many of these kinds of systems have been discovered in recent years, indicating that they are fairly common orbital architecture. Of particular interest are those systems for which the host star is low-mass, thus potentially enabling one or more of the planets to lie within the Habitable Zone of the host star. One of the contributors to the habitability of the Earth is the presence of a substantial moon whose tidal effects can stabilize axial tilt variations and increase the rate of tidal pool formation. Here we explore the constraints on the presence of moons for planets in compact systems based on Hill radii and Roche limit considerations. We apply these constraints to the TRAPPIST-1 system and demonstrate that most of the planets are very likely to be worlds without moons.