Exoplanetology: Exoplanets & Exomoons

From Stability to Instability: Characterizing the Eccentricities of Multi-planet Systems in the California Kepler Survey as a Means of Studying Stability

By Keith Cowing
Status Report
astro-ph.EP
January 14, 2025
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From Stability to Instability: Characterizing the Eccentricities of Multi-planet Systems in the California Kepler Survey as a Means of Studying Stability
A KDE plot of SPOCK Stability vs. Eccentricity for KOI-82 on the left and KOI-70 on the right. Color denotes the density of samples. The KDE is normalized with 1 being the highest density of points for the system and 0 being the lowest density of points for the system. A small range of possible eccentricities for a specific stability are denoted by a lighter colored area, while a large range of possible eccentricities for a specific stability are denoted by a darker colored area. As eccentricity increases, stability decreases. Note how there are two well constrained regions of stability and instability with a transition region between the two. The eccentricity that describes the location of this transition region, as marked by a SPOCK Stability of 50%, we called the ”characteristic” eccentricity of the system. — astro-ph.EP

Understanding the stability of exoplanet systems is crucial for constraining planetary formation and evolution theories.

We use the machine-learning stability indicator, SPOCK, to characterize the stability of 126 high-multiplicity systems from the California Kepler Survey (CKS). We constrain the range of stable eccentricities for each system, adopting the value associated with a 50% chance of stability as the characteristic eccentricity. We confirm characteristic eccentricities via a small suite of N-body integrations.

In studying correlations between characteristic eccentricity and various planet-pair and system-level metrics we find that minimum period ratio correlates most strongly with characteristic eccentricity. These characteristic eccentricities are approximately 20% of the eccentricities necessary for two-body mean-motion resonance overlap, suggesting three-body dynamics are needed to drive future instabilities.

Systems in which the eccentricities would need to be high (> 0.15) to drive instability are likely dynamically relaxed and might be the fossils of a previous epoch of giant impacts that increased the typical planet-planet spacing.

Matthew J. Doty, Lauren M. Weiss, Matthias Y. He, Antoine C. Petit

Comments: 39 pages, 4 figures, 3 tables, Submitted to AJ October 20 2024
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2501.06358 [astro-ph.EP] (or arXiv:2501.06358v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2501.06358
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Submission history
From: Matthew Doty
[v1] Fri, 10 Jan 2025 21:41:59 UTC (30,586 KB)
https://arxiv.org/abs/2501.06358
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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