DISCOVERY OF GROOVES ON GASPRA

We report the discovery of grooves in Galileo high-resolution images o f Gaspra. These features, previously seen only on Mars' satellite Phob os, are most likely related to severe impacts. Grooves on Gaspra occur as linear and pitted depressions, typically 100-200 m wide, 0.8 to 2. 5 km long, and 10-20 m deep. Most occur in two major groups, one of wh ich trends approximately parallel to the asteroid's long axis, but is offset by some 15-degrees; the other is approximately perpendicular to this trend. The first of these directions falls along a family of pla nes which parallel three extensive flat facets identified by Thomas et al., Icarus 107. The occurrence of grooves on Gaspra is consistent wi th other indications (irregular shape, cratering record) that this ast eroid has evolved through a violent collisional history. The bodywide congruence of major groove directions and other structural elements su ggests that present-day Gaspra is a globally coherent body. (C) 1994 A cademic Press, Inc.