Low-energy ring particle accretion as the origin of Pan's equatorial ridge
arXiv:2609.03060
Abstract
Pan is a small Saturnian satellite embedded within the planet's A ring, characterized by a polygonal equatorial ridge whose formation mechanism remains debated. A proposed explanation is ring particle accretion, yet previous simplified models could not address the ridge's complex multi-lobed morphology without ad hoc assumptions, and the cause of its latitudinal spread remains unclear. This work studies the complex low-energy dynamics around Pan to verify whether the ring particle accretion paths are consistent with the observed ridge morphology. We model particle motion using a CR3BP with spherical harmonic perturbations. Accretion paths are analyzed via grid-search simulations of trajectories transiting the and necks, using backward propagation from Pan's surface to determine the impacting material's original orbital characteristics. Asymmetric accreting particle populations, with inner-ring particles located closer to Pan and contributing more significantly to the impact flux, produce impact distributions that correlate with the ridge structure, especially for the Saturn-facing hemisphere. The ridge latitudinal spread is recovered only when the out-of-plane position and velocity of the accreting particles are strictly limited, consistent with accretion from a thin disk such as Saturn's rings. Furthermore, analysis of the particles' impact conditions revises the previously estimated minimum accretion duration downward by an order of magnitude, to yr, while accreting material is shown to originate from ring particles that once populated the Encke Gap. By systematically sampling admissible low-energy trajectories near Pan, our grid-search approach resolves the complex accretion dynamics that previous simplified narrow-stream models do not capture, revealing that the ridge's main morphological features emerge naturally from the local low-energy dynamical environment.
12 pages, submitted to Astronomy & Astrophysics