Lunar and Planetary Institute  Compiled by Nadine G. Barlow
Virgil L. Sharpton  View Slides Now  Impact craters are the
predominant landforms on most planetary surfaces and provide
important insight into age relationships and surface
characteristics. Martian surface ages have been deduced solely
from the distribution of impact craters on various geologic
units. Crater morphology provides clues to the nature of the
martian surface: lobate ejecta blankets and central pit craters
common on Mars but uncommon on the Moon may indicate the
presence of near-surface volatiles (ice and water). Degraded
impact structures record variations in volcanic, fluvial, and
aeolian activity. Finally, the shergottite, nakhlite, and
chassignite (SNC) meteorites are believed to be fragments of
Mars, ejected off the surface by a large impact event. Thus, an
as yet unidentified impact crater may have provided us with the
only samples of the martian surface to date.  Many of the
martian landforms produced by the interplay of cratering