This picture of asteroid 951 Gaspra is a mosaic of two images taken by the Galileo
     spacecraft from a range of 5,300 kilometers (3,300 miles), some 10 minutes before
     closest approach on October 29, 1991. The Sun is shining from the right; phase angle
     is 50 degrees. The resolution, about 54 meters/pixel, is the highest for the Gaspra
     encounter and is about three times better than that in the view released in November
     1991. Additional images of Gaspra remain stored on Galileo's tape recorder, awaiting
     playback in November. Gaspra is an irregular body with dimensions about 19 x 12 x
     11 kilometers (12 x 7.5 x 7 miles). The portion illuminated in this view is about 18
     kilometers (11 miles) from lower left to upper right. The north pole is located at upper
     left; Gaspra rotates counterclockwise every 7 hours. The large concavity on the lower
     right limb is about 6 kilometers (3.7 miles) across, the prominent crater on the
     terminator, center left, about 1.5 kilometers (1 mile). A striking feature of Gaspra's
     surface is the abundance of small craters. More than 600 craters, 100-500 meters
     (330-1650 feet) in diameter are visible here. The number of such small craters
     compared to larger ones is much greater for Gaspra than for previously studied bodies
     of comparable size such as the satellites of Mars. Gaspra's very irregular shape
     suggests that the asteroid was derived from a larger body by nearly catastrophic
     collisions. Consistent with such a history is the prominence of groove-like linear
     features, believed to be related to fractures. These linear depressions, 100-300 meters
     wide and tens of meters deep, are in two crossing groups with slightly different
     morphology, one group wider and more pitted than the other. Grooves had previously
     been seen only on Mars's moon Phobos, but were predicted for asteroids as well.
     Gaspra also shows a variety of enigmatic curved depressions and ridges in the
     terminator region at left. The Galileo project, whose primary mission is the exploration
     of the Jupiter system in 1995-97, is managed for NASA's Office of Space Science
     and Applications by the Jet Propulsion Laboratory.