The Satellites of Uranus

Abstract

AbstractThe Uranian satellite system contains five known members, all of which are difficult to study owing to their faintness and proximity to Uranus. The photometry of these objects is not in a satisfactory state, nor is the photovisual spectrophotometry. Infrared observations are in some sense easier and more precise because Uranus itself is faint in the near infrared and interferes but little with the satellite studies. The near infrared work reveals water ice or frost on the satellite surfaces, perhaps in a very pure state. The satellites are most similar to Ganymede in terms of the strength of the ice bands, but subtle differences, now under study, may be present. The diameters and masses of the satellites, while not readily measurable directly, can be estimated from generalizations about the surface geometric albedos, assumed mean densities, and certain dynamical arguments. Most of the data and theories are consistent with bodies with radii in the range 160-520 km (similar to the larger asteroids) and albedos on the order of 0.5, consistent with ice and snow. The mean densities are probably similar to those of the icy Saturn satellites, about 1.3 g/cm3. Uranus’ satellites probably formed after the event that caused the planet to tilt to the presently observed obliquity.