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Evidence from Voyager II photometry for early resurfacing of Umbriel


THE uranian satellite UmbriePs dark, heavily cratered surface is remarkable for its apparent uniformity in Voyager II images1. Its most conspicuous geological feature is a comparatively high-albedo, annulus-shaped deposit which covers the floor of the 40-km diameter crater Wunda1. Here we present new Voyager II albedo maps of Umbriel which reveal that its surface is subdivided into low-contrast, crudely polygonal areas ranging in size from tens to hundreds of kilometres (Fig. 1). The largest polygons are elongate with systematically trending northeast–southwest boundaries. Some of the polygonal areas form topographic depressions several kilometres in depth. We suggest that this newly discovered global albedo pattern is a relic of the early tectonic disruption of Umbriel's surface.

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Helfenstein, P., Thomas, P. & Veverka, J. Evidence from Voyager II photometry for early resurfacing of Umbriel. Nature 338, 324–326 (1989).

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