Retrograde resonances in compact multi-planetary systems: a feasible stabilizing mechanism

TL;DR

This paper explores how retrograde mean-motion resonances can serve as a stabilizing mechanism in compact multi-planet systems, potentially offering more robust stability than prograde resonances.

Contribution

It introduces the concept of retrograde resonances as a novel stabilizing mechanism for compact multi-planetary systems, highlighting their unique structures and stability benefits.

Findings

Retrograde resonances exhibit characteristic structures relevant for stability.

Retrograde MMRs can provide more robust stability than prograde MMRs.

Specific behaviors of apsidal precessions are involved in stabilization.

Abstract

Multi-planet systems detected until now are in most cases characterized by hot-Jupiters close to their central star as well as high eccentricities. As a consequence, from a dynamical point of view, compact multi-planetary systems form a variety of the general N-body problem (with N >= 3), whose solutions are not necessarily known. Extrasolar planets are up to now found in prograde (i.e. direct) orbital motions about their host star and often in mean-motion resonances (MMR). In the present paper, we investigate a theoretical alternative suitable for the stability of compact multi-planetary systems. When the outer planet moves on a retrograde orbit in MMR with respect to the inner planet, we find that the so-called retrograde resonances present fine and characteristic structures particularly relevant for dynamical stability. We show that retrograde resonances and their resources open a family of stabilizing mechanisms involving specific behaviors of apsidal precessions. We also point up that for particular orbital data, retrograde MMRs may provide more robust stability compared to the corresponding prograde MMRs.