Auroral emissions of the giant planets

Auroras are (generally) high-latitude atmospheric emissions that result fro m the precipitation of energetic charged particles from a planet's magnetos phere. Auroral emissions from the giant planets have been observed from gro und-based observatories, Earth-orbiting satellites (e.g., international Ult raviolet Explorer (IUE), Hubble Space Telescope (HST), and Roentgensatellit (ROSAT)), flyby spacecraft (e.g., Voyager 1 and 2), and orbiting spacecraf t platforms (e.g., Galileo) at X-ray, ultraviolet (UV), visible, infrared ( IR), and radio wavelengths, UV, visible, and TR auroras are atmospheric emi ssions, produced or initiated when ambient atmospheric species are excited through collisions with the precipitating particles, while radio and X-ray auroras are beam emissions, produced by the precipitating species themselve s. The emissions at different wavelengths provide unique and complementary information, accessible to remote sensing, about the key physical processes operating in the atmospheric and magnetospheric regions where they origina te. This paper reviews the development of our current understanding of auro ral emissions from Jupiter, Saturn, Uranus, and Neptune, as revealed throug h multispectral observations and supplemented by plasma measurements.