Jovian Auroral Proton Precipitation

Abstract

The total power of the Jovian aurora is about 10 ¹³ –10 ¹⁴  W with ultraviolet emission observed in the Lyman and Werner bands of molecular hydrogen. X‐ray, radio, and infrared emissions have also been observed. The Jovian Auroral Distributions Experiment and the Jovian Energetic Particle Detector Instrument onboard the Juno spacecraft, orbiting Jupiter, measured large downward and upward fluxes of energetic electrons and ions in the polar regions. The main auroral oval is mainly due to energetic electron precipitation, but proton and heavy ion (sulfur and oxygen) precipitation contribute to the aurora poleward of the main oval. The current paper presents the results of a Monte Carlo model of energy deposition by proton precipitation into Jupiter's molecular hydrogen atmosphere for incident energies ranging from tens of keV up to 25 MeV. Cross sections for H ⁺ , H, and H ⁻ collisions with H ₂ were determined using a classical trajectory Monte Carlo method. The model generates ionization, dissociation, and excitation rates of H ₂ for a wide range of incident proton energy and altitude. The contribution of secondary electrons to the overall energy deposition is included. The model results indicate that 50 keV protons deposit their energy near 500 km, where the H ₂ density is about 3 × 10 ¹¹  cm ⁻³ , with 10 MeV protons depositing their energy near 200 km, where the H ₂ density is about 5 × 10 ¹⁵  cm ⁻³ , which is in the stratosphere.