Precipitation of energetic electrons in Io's atmosphere: production of UV emissions

Abstract

Recent observations of Io by Galileo spacecraft showed the presence of a dense ionosphere, which is identified by a cold dense plasma that is at rest with respect to Io, and a tentative possibility of an intrinsic magnetic field. Also, there are measurements of intense magnetic field-aligned energetic bidirectional electron beams of tens of keV in the wake region of Io. These energetic electrons may enter into the atmosphere of Io, where they can degrade their energy via collisions with the neutral atmospheric gases. A Monte Carlo model has been generated to study the spatial degradation of electrons of energy ≤ 10 keV in the SO₂-dominated atmosphere of Io. This model is employed to study the excitation of Io's atmosphere. The intensities of neutral atomic oxygen (OI) and sulfur (SI) ultraviolet emissions due to the energetic electron impact on SO₂ are calculated and are compared with the Hubble Space Telescope-observed intensities and the intensities produced due to photoelectron impact excitation.