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Low-velocity impact craters in ice and ice-saturated sand with implications for Martian crater count ages

Croft, S. K. and Kieffer, S. W. and Ahrens, T. J. (1979) Low-velocity impact craters in ice and ice-saturated sand with implications for Martian crater count ages. Journal of Geophysical Research B, 84 (B14). pp. 8023-8032. ISSN 0148-0227.

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We produced a series of decimeter-sized impact craters in blocks of ice near 0°C and −70°C and in ice-saturated sand near −70°C as a preliminary investigation of cratering in materials analogous to those found on Mars and the outer solar system satellites. The projectiles used were standard 0.22 and 0.30 caliber bullets fired at velocities between 0.3 and 1.5 km/s, with kinetic energies at impact between 10^9 and 4×10^(10) ergs. Crater diameters in the ice-saturated sand were ∼2 times larger than craters in the same energy and velocity range in competent blocks of granite, basalt and cement. Craters in ice were ∼3 times larger. If this dependence of crater size on strength persists to large hypervelocity impact craters, then surfaces of geologic units composed of ice or ice-saturated soil would have greater crater count ages than rocky surfaces with identical influx histories. The magnitude of the correction to crater counts required by this strength effect is comparable to the magnitudes of corrections required by variations in impact velocity and surface gravity used in determining relative interplanetary chronologies. The relative sizes of craters in ice and ice-saturated sand imply that the tensile strength of ice-saturated sand is a strong inverse function of temperature. If this is true, then Martian impact crater energy versus diameter scaling may also be a function of latitude.

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Additional Information:Copyright 1979 by the American Geophysical Union. (Received April 2, 1979; revised July 19, 1979; accepted August 31, 1979.) Paper number 9B1305. We thank Henry Moore and Joseph Boyce for critical reviews and Eloise Luera and Gayle Croft for assistance in preparation of the manuscript. We are also grateful to G. Hager, 31st Naval Construction Regiment, for permission to use the Sea Bee C Rifle Range at Port Hueneme, California, to perform these experiments, and to David F. Wismen for courteous and helpful assistance in logistics at the rifle range. This work was partially supported by NASA grants NGL 05-007-002, NSG 7052 (University of California, Los Angeles) and NGL 05-002-105 (California Institute of Technology). Contribution 3292, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125.
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NASANGL 05-007-002
NASANGL 05-002-105
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Caltech Division of Geological and Planetary Sciences3292
Issue or Number:B14
Record Number:CaltechAUTHORS:20141105-150851681
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Official Citation:Croft, S. K., S. W. Kieffer, and T. J. Ahrens (1979), Low-velocity impact craters in ice and ice-saturated sand with implications for Martian crater count ages, J. Geophys. Res., 84(B14), 8023–8032, doi:10.1029/JB084iB14p08023.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51335
Deposited By: George Porter
Deposited On:06 Nov 2014 16:47
Last Modified:03 Oct 2019 07:32

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