![Schematic overview of instability-inducing mechanisms through which planets may be ejected from a system. These mechanisms, each discussed throughout this work, include close approaches between neighboring planets (top left; Section 2), binary-induced instabilities (top center and right, and bottom left; Section 3), flyby encounters (bottom center; Section 4), and post-main-sequence orbital evolution (bottom right; Section 5).-- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/08/The-Dynamics.png?fit=1200%2C676&ssl=1)
[astro-ph.EP] The ubiquity of free-floating planets inferred from microlensing and direct imaging surveys suggests that planetary ejection—a process in which planets initially born encircling a stellar host become gravitationally unbound—is common.
Four overarching mechanisms have been proposed to induce planetary ejection: close approaches of neighboring planets, instabilities in binary or multi-star systems, stellar and planetary flybys, and post-main-sequence stellar evolution.
Here we review the mechanisms underlying planetary ejection, as well as predictions derived from each. Current and upcoming microlensing surveys offer the potential to test existing models and distinguish between potential planetary ejection mechanisms, offering further insight into the demographic-level architectures of exoplanets across stellar environments.
Malena Rice, William DeRocco, Sean N. Raymond
Comments: invited review; accepted to PASP
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2608.00173 [astro-ph.EP] (or arXiv:2608.00173v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2608.00173
Focus to learn more
Submission history
From: Malena Rice
[v1] Fri, 31 Jul 2026 18:00:09 UTC (9,428 KB)
https://arxiv.org/abs/2608.00173
Astrobiology
