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THE NATURE OF SECONDARY CRATERS PHOTOGRAPHED BY RANGER VII,
BOEING SCIENTIFIC RESEARCH LABS SEATTLE WASH MATHEMATICS RESEARCH LAB
A mathematical theory of the ejection of secondary fragments from the focus of primary impacts on the Moon has been developed for the case of a spherical bounding surface. An application of the results to the frequency - distribution of the secondary lunar craters in the region of Mare Cognitum, as determined from photographs secured by Ranger VII in July 1964, leads to a conclusion that the sum total of the mass required to produce all observed craters or crater-like formation in Mare Cognitum overlying Tychos rays by secondary impacts of particles ejected from Tycho would - if spread evenly over the surface - cover the ground by a layer of debris about half a metre in thickness at the distance of 1000 km from the focus of ejection and the volume of the material thus splashed out all over the Moon would exceed the volume excavated by the primary impact at least ten to twenty times. On the strength of this evidence a hypothesis is advanced that a large fraction of depressions, smaller than 1 km in size, counted as craters due to secondary impacts, are in reality subsidence formations, possibly triggered by moonquakes which must occur in the wake of all major primary impacts on the Moon. Author
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