PHYSICAL PROPERTIES OF THE URANIAN SATELLITES.

Radiometric measurements have shown that Ariel, Umbriel, Titania and Oberon have diameters which range from 1630 to 1110 km and albedos which range from 0. 30 to 0. 18. Spectrophotometric observations of Miranda suggest that it may have the highest albedo of the known Uranian satellites and a diameter of about 500 km. Near-infrared measurements show that Ariel, Titania and Oberon have the largest known opposition surges. All five known satellites of Uranus have surfaces which are composed of water ice contaminated with small amounts of a dark material. Recent density determinations suggest that there may be large density differences among Ariel, Umbriel, Titania and Oberon, with density increasing with distance from Uranus.