Simulations of Electron Beam Interactions with Substellar Atmospheres

The atmospheric evolution of substellar objects is governed by thermospheric and exospheric
conditions, which modulate atmospheric mass-loss processes. Electrons (produced via
magnetospheric dynamics or host-satellite interactions) incident on predominantly H_2
atmospheres can ionize H_2, driving the formation of H_3^+. For gas giant planets in the Solar
System, H_3^+ cools the upper atmosphere through infrared emission. Future observations of
H_3^+ in extrasolar substellar atmospheres could serve as a powerful diagnostic of atmospheric
structure and temperature. Furthermore, electron impact excitation of H_2 can produce UV
aurorae, and the observation of such aurorae would provide evidence of electron precipitation.
The discovery of radio aurorae in brown dwarf atmospheres demonstrates the presence of
auroral processes beyond the Solar System, with UV, optical, and IR aurorae also theoretically
predicted. Simulations of high energy electron interactions with substellar hydrogen dominated
atmospheres will guide observational searches for multi-wavelength auroral features in
exoplanetary atmospheres. We present initial results of a simulated electron beam interaction
with various H_2 atmospheres. As a first step, we focus on the ionization profile, which is
needed to understand the atmospheric chemistry effects of the electron beam, including the
formation of H_3^+. We consider electron beam interactions with atmospheres of both gas
giants and brown dwarfs.