Current ideas about the production of the electroglow of Uranus

Abstract

A process known as ``electroglow'' was identified by Broadfoot et al. /1/ shortly after the Voyager Uranus encounter as soft charged particle excitation of atmospheric gas in the presence of sunlight and in excess of the available photoelectron energy. Localized aurora and diffuse H and H₂ band emissions have been observed from Uranus, and the H Ly α is highly variable. A high upper atmospheric temperature of 800 K and enhanced ionization layers were also observed at Uranus, and these phenomena are all similar to (but more pronounced than) those observed at Jupiter and Saturn. It is clear that the upper atmospheres of the outer planets are driven by more than solar EUV radiation. A theory has been advanced for the energization of photoelectrons and ions by ionospheric fields produced by the dynamo action of the atmosphere, and the potential contribution of scattering processes to these emissions is being re- analyzed.