Discovery of Grooves on Gaspra

Abstract

We report the discovery of grooves in Galileo high-resolution images of Gaspra. These features, previously seen only on Mars' satellite Phobos, 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 which trends approximately parallel to the asteroid's long axis, but is offset by some 15 deg.; the other is approximately perpendicular to this trends. The first of extensive flat facets identified by Thomas et al., Icarus 107. The occurence of grooves on Gaspra is inconsistent with other indications (irregular shape, cratering record) that this asteroid has evolved through a violent collisional history. The bodywide congruence of major groove directions and other structural elements suggests that the present- day Gaspra is a globally coherent body.