Geologic processes have not erased the craters with time. The shock wave fractures the rock and excavates a large cavity (much larger than the impactor).The impact sprays material — ejecta — out in all directions.Impact cratering is the excavation of a planet's surface when it is struck by a meteoroid. Craters are the most common surface features on many solid planets and moons—Mercury and our Moon are covered with craters. The circular shape is due to material flying out in all directions as a result of the explosion upon impact, not a result of the impactor having a circular shape (almost no impactors are spherical).The LROC WAC mosaic of Karpinskiy crater overlaid with the GLD100 color topography presents a clearer outline of the older crater (WAC mosaic below).The top portion of the image is black because the GLD100 product does not have coverage at that latitude (79°N).We now have over 380 kg of rocks from nine places on the Moon, rocks that have been analyzed by hundreds of scientists from many different countries.
The large number of craters in this region indicates that this part of the Moon is quite ancient. When an impactor strikes the solid surface of a planet, a shock wave spreads out from the site of the impact.
In many ways the Moon is a geologic Rosetta stone: an airless, waterless body untouched by erosion, containing clues to events that occurred in the early years of the solar system, which have revealed some of the details regarding its origin and providing new insight about the evolution of Earth.
Although they also posed new questions, the thousands of satellite photographs brought back from the Moon have permitted us to map its surface with greater accuracy than Earth could be mapped a few decades ago.
As it turns out, the Moon is truly a whole new world, with rocks and surface features that provide a record of events that occurred during the first billion years of the solar system.
This record is not preserved on Earth because all rocks formed during the first 800 million years of Earth's history were recycled back into the interior.
For example, a lava flow that spreads out and fills a large impact crater is likely to be younger than the crater.