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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 crater is about 1.2 kilometers (a little more than 0.5 miles) across and 200 meters (650 feet) deep.
Its features, such as the ejecta blanket beyond its rim, are well preserved because of the crater's youth; it has not experienced extensive erosion. The Vredefort impact crater, about 100 kilometers (60 miles) from Johannesburg, South Africa, was formed just a little over 2 billion years ago.
Early in the formation of our solar system (before 3.9 billion years ago) there was lots of large debris striking the surfaces of the young planets and moons; these older impact basins are larger than the more recent craters.
As a rule of thumb, older surfaces have been exposed to impacting bodies (meteoroids, asteroids, and comets) for a longer period of time than younger surfaces.
Very large impact craters greater than 300 kilometers (185 miles) across are called impact basins. The size and shape of the crater and the amount of material excavated depends on factors such as the velocity and mass of the impacting body and the geology of the surface.
The Moon lacks water, an atmosphere, and tectonic activity, three forces that erode Earth's surface and erase all but the most recent impacts.The large circular dark areas in the image are impact basins, created as huge impactors struck the Moon. Small craters often are simple bowl-shaped depressions.Lava later flowed across the low floors of the basins, giving them a darker, smoother appearance than the surrounding, brighter highlands. The structure of large craters is more complex because they collapse, forming terraces, central peaks, central pits, or multiple rings.Copernicus is a large crater (93 kilometers or 60 miles wide) on the Moon. This crater is about 20 kilometers (12 miles) across and has a large central peak and terraces around its rim.The inner walls of the crater have collapsed to form a series of step-like terraces, and a central peak is visible in the center of the image. The ejecta blanket has lobes, which may indicate wet material was ejected, suggesting that subsurface water or melted ice was mixed into the debris.