Uranus Rings and Two Moons

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    Voyager 2 has discovered two "shepherd" satellites associated with the
    rings of Uranus. The two moons -- designated 1986U7 and 1986U8 -- are
    seen here on either side of the bright epsilon ring; all nine of the
    known Uranian rings are visible. The image was taken Jan. 21, 1986,
    at a distance of 4.1 million kilometers (2.5 million miles) and
    resolution of about 36 km (22 mi). The image was processed to enhance
    narrow features. The epsilon ring appears surrounded by a dark halo
    as a result of this processing; occasional blips seen on the ring are
    also artifacts. Lying inward from the epsilon ring are the delta,
    gamma and eta rings; then the beta and alpha rings; and finally the
    barely visible 4, 5 and 6 rings. The rings have been studied since
    their discovery in 1977, through observations of how they diminish the
    light of stars they pass in front of. This image is the first direct
    observation of all nine rings in reflected sunlight. They range in
    width from about 1OO km (6O mi) at the widest part of the epsilon ring
    to only a few kilometers for most of the others. The discovery of the
    two ring moons 1986U7 and 1986U8 is a major advance in our
    understanding of the structure of the Uranian rings and is in good
    agreement with theoretical predictions of how these narrow rings are
    kept from spreading out. Based on likely surface brightness
    properties, the moons are of roughly 2O- and 3O-km diameter,
    respectively. The Voyager project is managed for NASA by the Jet
    Propulsion Laboratory.

    credit: NASA/JPL

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