Interpretation of the impact record on Asteroid 951 Gaspra requires un
derstanding of the effects of collisions on a target body of Gaspra's
size and shape. Recent hydrocode models show that major impacts on Gas
pra may leave craters larger than previously thought possible and that
they can create substantial regolith and produce global jolting capab
le of erasing many smaller craters. A Gaspra-size body has a mean life
time of about 10(9) years and is likely to have several impact craters
of 4 km diameter or larger, which is consistent with the number of ob
served concavities on Gaspra. The steep size distribution of small cra
ters on Gaspra implies an even steeper distribution for small asteroid
s, and the relative paucity of kilometer-size craters seems to require
a twice-in-a-Gaspra-lifetime impact to have occurred about 50 myr ago
. All of these considerations consistently point to a scenario in whic
h several of the very large concavities (>4 km diameter) on Gaspra are
probably impact craters. (C) 1994 Academic Press, Inc.