Architecture Classification For Extrasolar Planetary Systems

This paper presents a classification framework for the architectures of planetary systems based on a complete survey of the confirmed exoplanet population.
With nearly 6,000 confirmed exoplanets discovered, including more than 300 multiplanet systems with three or more planets, the current observational sample has reached the point where it is both feasible and useful to build a classification system that divides the observed population into meaningful categories.
This framework provides a criterion to split planetary systems into inner and outer regimes, and then further divides inner systems into dynamical classes. The resulting categories include “peas-in-a-pod systems” with uniformly small planets and “warm Jupiter systems” with a mix of large and small planets, as well as “closely-spaced systems” and “gapped systems,” with further subdivisions based on the locations of gaps and other features. These categories can classify nearly all of the confirmed systems with three or more planets with minimal ambiguity.
We qualitatively examine the relative prevalence of each type of system, subject to observational selection effects, as well as other notable features such as the presence of hot Jupiters. A small number of outlier systems are also discussed. Potential additional classes of systems yet to be discovered are proposed.

Cumulative distributions of confirmed exoplanets with period, comparing total numbers of planets (dashed) to those in single-planet systems (solid), according to the same color scheme as Figure 1. Hot Jupiters show far fewer companions than other planet types, as illustrated by the near-coincidence of the two Jupiter distributions at <10 days. — astro-ph.EP

Quick-reference chart for our classification of planetary system architectures, with representative model systems for each category. Each row corresponds to one planetary system, with horizontal spacing corresponding to orbital period on a log scale and point sizes corresponding to planet size. Colors correspond to planet type, as described in Section 2.3: Jupiters (>6 R⊕, red), Neptunes (3.5-6 R⊕, gold), Sub-Neptunes (1.75-3.5 R⊕, blue), and Earths (<1.75 R⊕, green). (However, the exact composition of non-Jupiters in this figure is arbitrary.) This format is used for all plots of planetary system architectures throughout this paper. Framework summary: Each system is divided into inner and outer planets (if both are detected). Systems with N ≥3 inner planets are classified based on whether their inner planets include any Jupiters, and whether (and if so where) their inner planets include large gaps with a period ratio >5. Other dynamical features are addressed separately from the overall classification system (see Section 6). — astro-ph.EP
Alex R. Howe, Juliette C. Becker, Christopher C. Stark, Fred C. Adams
Comments: 35 pages, 17 figures, 5 tables, in review with AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2501.08191 [astro-ph.EP] (or arXiv:2501.08191v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2501.08191
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Submission history
From: Alex Howe
[v1] Tue, 14 Jan 2025 15:13:38 UTC (6,336 KB)
https://arxiv.org/abs/2501.08191
Astrobiology,