Exoplanetology: Exoplanets & Exomoons

Long-term Stability and Dynamical Spacing of Compact Planetary Systems

By Keith Cowing
Status Report
astro-ph.EP
December 29, 2024
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Long-term Stability and Dynamical Spacing of Compact Planetary Systems
LEFT: Evolution in the period ratios plane. The points are colour-coded according to their time before the close encounter. We note that the system spends almost all of its time very close to its starting location. Green oblique lines correspond the loci of the zeroth-order threeplanet MMRs. The first-order two-planet MMRs, 7:6 and 6:5, are plotted in grey. The second-order resonance 13:11 is plotted in red. Adapted from Petit et al. (2020). RIGHT: Number of resonances covering the period ratios space for equal-mass planets, with masses 10−5 M⊙. At first order, the number of resonances can be compared to the resonance optical depth ρtot. We plot the two-planet circular Hillstability limits (Petit et al. 2018) for both planet pairs in green and the predicted overlap limit for the three-planet MMRs (Eq. 2.7) in blue. Adapted from Petit et al. (2020). — astro-ph.EP

Exoplanet detection surveys revealed the existence of numerous multi-planetary systems packed close to their stability limit.

In this proceeding, we review the mechanism driving the instability of compact systems, originally published in Petit et al. (2020). Compact systems dynamics are dominated by the interactions between resonances involving triplets of planets.

The complex network of three-planet mean motion resonances drives a slow chaotic semi-major axes diffusion, leading to a fast and destructive scattering phase. This model reproduces quantitatively the instability timescale found numerically.

We can observe signpost of this process on exoplanet systems architecture. The critical spacing ensuring stability scales as the planet-to star mass ratio to the power 1/4. It explains why the Hill radius is not an adapted measure of dynamical compactness of exoplanet systems, particularly for terrestrial planets.

We also provide some insight on the theoretical tools developed in the original work and how they can be of interest in other problems.

Antoine C. Petit

Comments: Contribution to the Proceedings Kavli-IAU Symposium No. 382, 2024 (Complex Planetary Systems II, July 2023). Beyond the review, section 3 discusses observational implications on from the dynamical spacing
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2411.19590 [astro-ph.EP](or arXiv:2411.19590v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2411.19590
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Journal reference: Proceedings of the International Astronomical Union. 2022;18(S382):20-29
Related DOI:
https://doi.org/10.1017/S1743921323004167
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Submission history
From: Antoine Petit C.
[v1] Fri, 29 Nov 2024 10:13:17 UTC (1,709 KB)
https://arxiv.org/abs/2411.19590
Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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