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Complex cratering relationships on Mercury

Complex cratering relationships on Mercury
Complex cratering relationships on Mercury This mosaic of two images was captured by MESSENGER shortly after its closest approach to its first flyby of Mercury on January 14, 2008. The image is about 370 kilometers (230 miles) across. It shows part of a large, fresh crater with secondary crater chains located near Mercury's equator on the side of the planet not seen by Mariner 10. Large, flat-floored craters often have terraced rims from post-impact collapse of their newly formed walls. The hundreds of secondary impactors that are excavated from the planet's surface by the incoming object create long, linear crater chains radial to the main crater. These chains, in addition to the rest of the ejecta blanket, create the complicated, hilly terrain surrounding the primary crater. By counting craters on the ejecta blanket that have formed since the impact event, the age of the crater can be estimated. This count can then be compared with a similar count for the crater floor to determine whether any material has partially filled the crater since its formation. With their large size and production of abundant secondary craters, these flat-floored craters both illuminate and confound the study of the geological history of Mercury. NASA / JHUAPL / CIW