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Energy and mass distributions of impact ejecta blankets on the moon and Mercury

Ahrens, Thomas J. and O'Keefe, John D. (1978) Energy and mass distributions of impact ejecta blankets on the moon and Mercury. In: 9th Lunar and Planetary Science Conference. Geochimica et cosmochimica acta. Supplement. Vol.3. No.10. Pergamon Press , New York, NY, pp. 3787-3802. ISBN 0080229662.

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The distribution of the mass and energy of the ejecta from the impact of gabbroic anorthosite objects at 7 .5, 15, and 30 km/sec. on a half-space of similar material is described for planetary objects having the mass and radius of the moon and Mercury. For impact flows for which the peak stresses have decayed to a few kilobars, both the resulting mass and total energy distribution per unit area, S, decrease with radius, R, more slowly than the - 3 power of the radius, and the formula of the form: /n_(10)S = A + B /n_(10)R + C(/n^(10)R)^2 always displays a negative sign for the constant, C. The value of C is more negative for ejecta distributions on Mercury versus the moon. A newly recognized feature of the ejecta cloud is the near constancy with range of the ratio of internal energy to kinetic energy of ~1.1 to ~3 for material launched within a few shock transit times of the meteorite, whereas at times corresponding to many shock transit times in the meteorite this ratio exceeds ~10 when R ≥ l0^4 cm. Calculated "stratigraphic" sections indicate characteristics such that such units might be recognized in Apollo drill core on the basis of shock metamorphic zoning. The initial fast ejecta which arrives at great distances from the impact zone is lightly shocked, and largely represents target material which was near or at the free surface. Where resolved, this layer is overlain by a 5 to 10 times thicker, more heavily shocked ejecta layer. The latter is again overlain by a layer of lightly shocked material. The latter thickens rapidly toward the crater.

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Additional Information:© 1978 Lunar and Planetary Institute. We appreciate the computational assistance of Mary and Robert Johnson. Research supported under NASA Grant NSG 7129. Contribution No. 3077, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125. We are indebted to Hitoshi Mizutani for several important corrections in the manuscript.
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Caltech Division of Geological and Planetary Sciences 3077
Series Name:Geochimica et cosmochimica acta. Supplement
Issue or Number:10
Record Number:CaltechAUTHORS:20150902-153359119
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Official Citation:Energy and mass distributions of impact ejecta blankets on the moon and Mercury Ahrens, T. J. & Okeefe, J. D. In: Lunar and Planetary Science Conference, 9th, Houston, Tex., Volume 3. (A79-39253 16-91) New York, Pergamon Press, Inc., 1978, p. 3787-3802
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:60038
Deposited By: Ruth Sustaita
Deposited On:11 Sep 2015 18:11
Last Modified:03 Oct 2019 08:52

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