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Atmospheric effects on cratering on Venus

Takata, T. and Ahrens, T. J. and Phillips, R. J. (1995) Atmospheric effects on cratering on Venus. Journal of Geophysical Research E, 100 (E11). pp. 23329-23348. ISSN 0148-0227. doi:10.1029/95JE02641.

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A paraboloidal bow shock model is developed in order to estimate the surface distribution of gas shock-induced modifications surrounding Venusian impact craters. We apply two-dimensional oblique shock dynamics to describe a three-dimensional paraboloidal-shaped bow shock impinging upon an assumed incompressible Venusian surface. The effects of the hypersonic atmospheric shock acting on the Venusian surface are considered in terms of induced maximum gas pressure, density, particle velocity, and temperature, for varying angles and velocities of impact. The maximum boulder size that can be saltated by the shock wave induced gas flow and the degree of mutual collision of the surface materials are also considered. The present calculations quantitatively predict the areal extent of the gas shock perturbed surface for normal and oblique impact as a function of impact angle and velocity, and radii of impactors. For a 1-km radius stony meteorite impacting normally at 20 km/s, the radius of the disturbed area extends ∼10–17 times the 3–5 km crater radius. The perturbed surface affects the surface radar properties, and the present results can provide an explanation of the wide “dark/bright halos” surrounding some of the Venusian impact craters observed via Magellan imagery. For example, a ∼50-km radius bright halo surrounding a ∼20-km dark halo is observed around the 3.1-km radius crater located at 16.5° north latitude and 334.4° longitude. The average value of the radar backscatter cross section of the ∼20-km radius dark halo indicates that ∼50-cm-thick layer of porous lithologic material is superimposed upon an assumed undisturbed basement rock surface. The bright halo indicates that the surface roughness in this region is ∼30 % greater than that of the surrounding original surface. These features can be induced by atmospheric shock waves. The present model can relate the observed crater halo radii to the impact parameters, such as projectile radius and density, and the impact velocity and angle.

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Additional Information:© 1995 American Geophysical Union. Received November 25, 1991; revised August 10, 1995. We thank all the personnel associated with the Magellan mission for their efforts. We thank H. Hornung (Caltech) for valuable suggestionsa nd comments which lead to the development of the present shock model. We thank J. D. O'Keefe (Caltech), B. A. Ivanov (Russian Academy of Science), and B. Sturtevant (Caltech), for their valuable suggestions and comments on the shock interactions with Venus. We also thank C. Elachi (JPL) for discussions on interpretation of the relationship of SAR data and surface properties, J. J. Plant (JPL) for help on the SAR data analysis, C. Left (JPL) for providing Magellan data; R. Herrick (LPI), J. W. Holt (Caltech), and K. A. Tryka (Caltech) for their help on data analysis, and G. E. Danielson for producing the crater pictures. We thank R. M. Schmidt and an anonymous reviewer for their constructive advice and criticism. Research was supported under NAG1953. Division of Geological and Planetary Sciences, California Institute of Technology contribution 5086.
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Caltech Division of Geological and Planetary Sciences5086
Issue or Number:E11
Record Number:CaltechAUTHORS:20141023-092917436
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Official Citation:Takata, T., T. J. Ahrens, and R. J. Phillips (1995), Atmospheric effects on cratering on Venus, J. Geophys. Res., 100(E11), 23329–23348, doi:10.1029/95JE02641.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50724
Deposited On:24 Oct 2014 18:06
Last Modified:10 Nov 2021 18:59

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