2025/10/13 by Wang, Dieran, Li, Jiaru, Lai, Dong
#Earth and Planetary Astrophysics (astro-ph.EP) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2510.11785
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 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 (|S|) and obliquity (θ\rm SL) distributions of low-mass exoplanets that have gone through planetary collisions. In our fiducial super-Earth (with m=3M⊕, R=1.3R⊕) and mini-Neptune systems (with m=9M⊕, R=2.5R⊕), the collision products follow a nearly uniform distribution in cosθ\rm SL and the spin-magnitude distribution is approximately linear in |S|. 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 (i.e., excess probability near cosθ\rm SL=±1). 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.