Spin and Obliquity Distributions of Low-mass Planets Shaped by Dynamical Instability

Dieran Wang, Jiaru Li, and Dong Lai

Publication: arXiv::2510.11785

Abstract: Exoplanetary systems hosting multiple low-mass planets are thought to have experienced dynamical instability, during which planet-planet collisions and mergers occur; these collisions can impart a substantial amount of angular momentum to the merger remnants, changing the obliquities of the resulting planets significantly. In this work, we carry out a series of N-body experiments to investigate the spin magnitude and obliquity distributions of low-mass exoplanets that have gone through planetary collisions. In our fiducial super-Earth and mini-Neptune systems, the collision products follow a nearly uniform distribution in and the spin-magnitude distribution is approximately linear. Parameter studies and theoretical analysis show that increasing planetary radii or masses, or decreasing the initial planet-planet mutual inclinations, tend to polarize the obliquity distribution toward alignment or anti-alignment. Experiments with initially two-planet and three-planet systems produce qualitatively similar outcomes, suggesting that the trends in this study may generalize to systems with higher planetary multiplicities.

Paper links: [publisher] [arXiv] [NASA ADS]