Monte Carlo simulations of magnetospheric ion precipitation into Triton's upper atmosphere: Sputtering, energy deposition, charge exchange, and ionization

¹ Planetary Environmental and Astrobiological Research Laboratory (PEARL), School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, Guangdong, PR China
² Center for Excellence in Comparative Planetology, Chinese Academy of Sciences, Hefei, Anhui, PR China

^★ Corresponding author: guhao7@mail.sysu.edu.cn

Received: 5 July 2025
Accepted: 18 August 2025

Abstract

Context. Magnetospheric ion precipitation is an important driver of energy and mass transfer in a planet’s upper atmosphere. When energetic ions penetrate an atmosphere, they undergo a cascade of interactions with background species, including elastic scattering, charge exchange, excitation, dissociation, and ionization. These processes can alter the atmospheric composition and potentially contribute to atmospheric escape, a process known as sputtering.

Aims. We investigated the effects of magnetospheric N⁺ and H⁺ precipitation on Triton’s upper atmosphere.

Methods. We established a one-dimensional test particle Monte Carlo model to simulate the process.

Results. Our simulations indicate a total nitrogen escape rate of approximately (0.2-2)× 10²⁶ s⁻¹, primarily resulting from incident N⁺ ions. This rate is comparable to the previously reported values for Jeans escape and chemical escape, indicating that ion precipitation is a substantial contributor to Triton’s atmospheric loss. We also quantified the energy deposition, charge exchange, and ionization rates along with the energy degradation of incident ions, and assessed their sensitivities to ion energy, incidence angle, and scattering angle distribution.

Conclusions. While magnetospheric electron precipitation likely dominates atmospheric ionization on Triton, our estimations suggest that the contribution of ion precipitation is non-negligible.