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arXiv · 2608.04512

A Formation-Stage Bottleneck for Exomoons around Close-in Rocky Planets

Rongxi Bi·Hongping Deng·Christian Reinhardt·Shangfei Liu·Yun Liu
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Abstract

Massive moons around rocky exoplanets are expected outcomes of giant impacts, yet no exomoon has been securely confirmed. We address this problem using meshless finite-mass simulations of giant impacts between differentiated rocky planets that include stellar tidal and Coriolis forces in a local co-rotating frame for orbital periods of 1--300 days, and compare these simulations with otherwise identical collisions in isolation. We find that stellar perturbations impose a severe formation-stage bottleneck on moon-forming disks. Ultra-short-period impacts leave essentially no surviving circumplanetary disk, whereas 10-day systems retain only strongly depleted, radially truncated, and dynamically compact disks. High impact velocities, expected for close-in planets, are devastating for disk generation, while retrograde impacts can slightly compensate for disk mass depletion. These results show that stellar perturbations can suppress exomoon formation around close-in rocky planets, reshaping expectations for the demographics of exomoons.

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Rongxi Bi, Hongping Deng, Christian Reinhardt, Shangfei Liu, Yun Liu. 2026-08-05. A Formation-Stage Bottleneck for Exomoons around Close-in Rocky Planets. https://arxiv.org/abs/2608.04512

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