Interpretation of the impact record on asteroid 951 Gaspra
requires understanding of the effects of collisions on a target
body of Gaspra's size and shape. Recent hydrocode modesl show
that major impacts on Gaspra may leave craters larger than previously
thought possible and that they can create substantial regolith
and produce global jolting capable of erasing smaller craters. A
Gaspra-size body has a mean lifetime of 1E+9 years and is likely
to have several impact craters of 4 km diameter or larger, which
is consistent with the number of observed concavities on Gaspra.
The steep size distribution of small craters on Gaspra implies
an even steeper distribution for small asteroids, and the relative
paucity of kilometer-size craters seems to require a twice-in-a-lifetime
impact to have occurred about 50 Myr ago. All of these considerations
consistently point to a scenario in which several of the very
large concavities (> 4 km diameter) on Gaspra are probably impact
craters.