Gabriele Pichierri – The onset of instability in resonant chains – Exoplanets III Conference
Channel: Gabriele Pichierri
Date: 17/07/2020

This is a pre-recording of my talk for the Exoplanets III conference. The talk is scheduled for Friday, 31 July 2020, 18h15 – 18h30 (CEST).

Parallel Session: Planetary System Architectures and Dynamics 2

Title of the talk: The onset of instability in resonant chains

Abstract: Planets smaller than Saturn, typically Super-Earths and Mini-Neptunes, undergo type-I migration in the protoplanetary disc in which they form. When multiple planets are orbiting the same star, the inner one stops migrating at the inner edge of the disc and a favoured outcome of the slow, convergent orbital transport of the planets is the formation of a chain of mean motion resonances. When the disc is dissipated away and the damping forces applied by the disc are removed, the resulting system may be dynamically stable or unstable. Observations show that only a small fraction of these resonant chains should be stable, and these instabilities are indeed found in N-body simulations. In particular, previous numerical simulations showed that the maximum planetary mass for a resonant to remain stable decreases with increasing number of planets and increasing compactness of the system, but the origin of the instability was not understood. We focus on the case of three equal-mass planets in the 3:2 - 3:2 mean motion resonant chain and we study which dynamical phenomena lead to a loss of stability if the planetary mass is larger than some threshold. We identify a set of secondary resonances between the libration frequencies in the mean motion resonance and a sub-frequency of the synodic period 2 pi (1/P1-1/P2). These secondary resonances excite the amplitudes of libration of the mean motion resonances. We generalise this mechanism to different chains of mean motion resonances involving a larger number N of planets and/or a higher index k of the k:k-1 mean motion resonances, obtaining a scaling for the maximal planetary mass that guarantees stability, as a function of N and k. The results are in qualitative agreement with the numerical experiments mentioned above, thus giving a theoretical understanding of the instabilities observed in the simulations, as well as a better grasp on the fingerprint of the planetary dynamical history contained in the current exoplanets sample.
Authors: Pichierri, Gabriele; Morbidelli, Alessandro; Crida, Aurélien

This talk is based on the following papers: 
Pichierri G., Morbidelli A., Crida A., 2018, CeMDA, 130, 54 (https://ui.adsabs.harvard.edu/abs/2018CeMDA.130...54P/abstract)
Pichierri G., Morbidelli A., 2020, MNRAS, 494, 4950 (https://ui.adsabs.harvard.edu/abs/2020MNRAS.494.4950P/abstract)

Gabriele Pichierri, post-doc at MPIA
Comments and questions are extremely welcome (email: pichierri@mpia.de)