Infrared observations of the Uranian rings

Abstract

ABSTRACTWe present maps of the Uranian rings at an effective wavelength of 2.2 µm, and spectrophotometric observations covering the ranges 2.0 – 2.4 µm and 2.9 – 3.9 µm. The maps, constructed from data obtained in May 1978 and July 1979, reveal a 2:1 azimuthal brightness variation whose amplitude and phase are consistent with the known width variation and apsidal precession of the eccentric e ring. A detailed comparison of the maps with models based on stellar occultation data leads to an upper limit of ~0.01 on the normal optical depth of any broad (5000 km wide), diffuse component of the ring system. An unexplained feature of the 1978 map is a significant east-west asymmetry, corresponding to a brightening of the near side of the rings relative to the far side.