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ejecta blanket The blanket of debris surrounding an impact crater. It is composed of material ejected from the crater during its formation, and is laid down with stratigraphy inverted from that of the bedrock. There is typically a star-shaped distribution of ejecta around the crater rim. In addition to rock fragments excavated from the crater, and melted material, surface material from outside the crater may be incorporated by base surge erosion or excavated by secondary craters caused by large ejected blocks. There is a chaotic size distribution of ejected material. Many Martian craters are surrounded by fluidized ejecta blankets which have flowed across the surface. In contrast, lunar ejecta blankets are due mostly to ballistic sedimentation.