Intense Lyα emission from Uranus

Abstract

The existence of intense atomic hydrogen Lyα emission from Uranus is demonstrated here by utilizing the monochromatic imaging capabilities of the International Ultraviolet Explorer (IUE) spectrograph. Our observations show increased emission in the vicinity of Uranus superimposed on the geocoronal/interplanetary background. If resonant scattering of solar Lyα is the source of the 1.6+/-0.4 kR disk averaged brightness, then very high column densities of atomic H above the absorbing methane are required. Precipitation of trapped charged particles-aurora-could explain the emissions. This would imply a planetary magnetic field.