Examining Uranus’ ζ Ring in Voyager 2 Wide-angle Camera Observations: Quantifying the Ring’s Structure in 1986 and Its Modifications Prior to the Year 2007

Abstract

The ζ ring is the innermost component of the Uranian ring system. It is of scientific interest because its morphology changed significantly between the Voyager 2 encounter in 1986 and subsequent Earth-based observations around 2007. It is also of practical interest because some Uranus mission concepts have the spacecraft pass through the inner flank of this ring. Recent reexaminations of the Voyager 2 images have revealed additional information about this ring that provide a more complete picture of the ring’s radial brightness profile and phase function. These data reveal that this ring’s brightness varies with phase angle in a manner similar to other tenuous rings, consistent with it being composed primarily of submillimeter-sized particles. The total cross section of particles within this ring can also be estimated from these data, but translating that number into the actual risk to a spacecraft flying through this region depends on a number of model-dependent parameters. Fortunately, comparisons with Saturn’s G and D rings allows the ζ ring’s particle number density to be compared with regions previously encountered by the Voyager and Cassini spacecraft. Finally, these data indicate that the observed changes in the ζ ring’s structure between 1986 and 2007 are primarily due to a substantial increase in the amount of dust at distances between 38,000 and 40,000 km from Uranus’ center.