There are two basic types of impact craters: simple and complex. Simple craters form a bowl-like rimmed depression, and complex craters (such as Kepler) display central peaks, terraces, and flat floors. Complex craters occur above a certain diameter crater, the cutoff diameter is dependent on gravity, so it varies from planet to planet (or moon to moon). On the Moon the size cutoff between simple and complex craters is between 10 and 20 km, on the Earth it is between 2 and 5 km.
Despite the label "central peak," a central peak is not always exactly in the center of a crater, nor is it always symmetrically shaped; Kepler crater is an example. Instead of having a nice central peak, Kepler crater has an irregular off-center peak. This form is most likely due to the crater being close to the boundary diameter between a simple and complex crater. Larger craters, such as King crater, can also display oddly shaped central peaks that are likely the result of an oblique impact.
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Posted by Drew Enns on November 12, 2010 10:00 UTC.