VARIATION IN THE H-3(+) EMISSION OF URANUS

Infrared images of Uranus, obtained in 1993 April, at wavelengths sens itive to the H-3(+) molecular ion, are presented. These show that spat ial variation in the emission from the planet is discernible. Comparis on with magnetic field modeling of Uranus indicates that sources of th is variation may include auroral activity and other features, but the images show that the spatial variation is more limited than in the cas e of Jupiter. This conclusion is born out by spectra obtained on four consecutive nights during 1995 June, which show that the overall tempo ral variability of the H-3(+) emission is similar to 20%. Comparison o f the 1995 June spectra with data obtained in 1992, and the 1993 image s, shows that the overall brightness of H-3(+) emission of Uranus can vary by a factor of 2 on a timescale of years.