Hawai'i Space Grant College, Hawai'i Institute of Geophysics and
Planetology, University of Hawai'i, 1996 To determine the
factors affecting the appearance of impact craters The circular
features so obvious on the Moon's surface are impact craters
formed when impactors smashed into the surface. The explosion
and excavation of materials at the impacted site created piles
of rock (called ejecta) around the circular hole as well as
bright streaks of target material (called rays) thrown for great
Two basic methods that form craters in nature are: 1) impact of
a projectile on the surface and 2) collapse of the top of a
volcano creating a crater termed caldera. By studying all types
of craters on Earth and by creating impact craters in
experimental laboratories, geologists concluded that the Moon's
craters are impact in origin. The factors affecting the
appearance of impact craters and ejecta are the size and
velocity of the impactor, and the geology of the target By
recording the number, size, and extent of erosio