Sibling sandblasting and the smoothness of Gaspra and Ida

Both Asteroid 951 Gaspra and 243 Ida look like smooth, rounded pebbles and neither have the expected angular, jagged-faceted appearance of a rock fragment produced by a hypervelocity impact. We suggest that they were both rough and sharp-edged at birth and that the rounding off that we now see is the result of a multitude of low-velocity collisions (at around 0.065 to 0.1 km s−1) with the much smaller sibling asteroidal fragments that were born at the same time by the collisions that produced the respective asteroidal families.