A Dynamical Systems Approach to the Theory of Circumbinary Orbits in the Circular Restricted Problem


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Abstract

jats:titleAbstract</jats:title> jats:pTo better understand the orbital dynamics of exoplanets around close binary stars, i.e., circumbinary planets (CBPs), we applied techniques from dynamical systems theory to a physically motivated set of solutions in the Circular Restricted Three-Body Problem (CR3BP). We applied Floquet theory to characterize the linear dynamical behavior—static, oscillatory, or exponential—surrounding planar circumbinary periodic trajectories (limit cycles). We computed prograde and retrograde limit cycles and analyzed their geometries, stability bifurcations, and dynamical structures. Orbit and stability calculations are exact computations in the CR3BP and reproducible through the open-source Python package jats:monospacepyraa</jats:monospace>. The periodic trajectories (doi.org/10.5281/zenodo.7532982) produce a set of noncrossing, dynamically cool circumbinary orbits conducive to planetesimal growth. For mass ratios jats:italicμ</jats:italic> ∈ [0.01, 0.50], we found recurring features in the prograde families. These features include (1) an innermost near-circular trajectory, inside which solutions have resonant geometries, (2) an innermost stable trajectory (jats:italica</jats:italic> jats:sub jats:italicc</jats:italic> </jats:sub> ≈ 1.61 − 1.85 jats:italica</jats:italic> jats:subbin</jats:sub>) characterized by a tangent bifurcating limit cycle, and (3) a region of dynamical instability (jats:italica</jats:italic> ≈ 2.1 jats:italica</jats:italic> jats:subbin</jats:sub>; Δjats:italica</jats:italic> ≈ 0.1 jats:italica</jats:italic> jats:subbin</jats:sub>), the exclusion zone, bounded by a pair of critically stable trajectories bifurcating limit cycles. The exterior boundary of the exclusion zone is consistent with prior determinations of jats:italica</jats:italic> jats:sub jats:italicc</jats:italic> </jats:sub> around a circular binary. We validate our analytic results with jats:italicN</jats:italic>-body simulations and apply them to the Pluto–Charon system. The absence of detected CBPs in the inner stable region, between the prograde exclusion zone and jats:italica</jats:italic> jats:sub jats:italicc</jats:italic> </jats:sub>, suggests that the exclusion zone may inhibit the inward migration of CBPs.</jats:p>

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Keywords
5109 Space Sciences, 51 Physical Sciences
Journal Title
The Astronomical Journal
Conference Name
Journal ISSN
0004-6256
1538-3881
Volume Title
Publisher
American Astronomical Society
Sponsorship
National Science Foundation (NSF) (DGE-1842166)