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Angular momentum transfer in low velocity oblique impacts: Implications for asteroids

Yanagisawa, Masahisa and Eluszkiewicz, Janusz and Ahrens, Thomas J. (1991) Angular momentum transfer in low velocity oblique impacts: Implications for asteroids. Icarus, 94 (2). pp. 272-282. ISSN 0019-1035. doi:10.1016/0019-1035(91)90227-K.

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The efficiency of angular momentum transfer ζ in low velocity oblique impacts was studied experimentally. ζ is defined as the fraction of incident angular momentum transferred to the rotation of the target. Plaster, mortar, cement, and one granite target were studied. Lead and aluminum projectiles were used. Only cratering impacts were considered. ζ was found to decrease with increasing incidence angle φ (relative to the surface normal). For example, for impacts into cylindrical mortar targets a least-squares fit of the form ζ = A(cos φ)β with A = 0.9 and β = 1.7 was found to match the data points reasonably well. In addition, β decreased from 1.9 to 1.4 as the kinetic energy density ϵ (= kinetic energy of the projectile/projectile volume) increased from 0.5 to 1.8 × 10^9 J m^(−3). This suggests that more energetic impacts transfer angular momentum more efficiently. ζ decreased as the indentation hardness H of the target increased: at φ ∼ 35°, ζ = 0.07 for granite (H = 850 kg mm^(−2) and ζ = 0.7 for plaster (H = 7.5 kg mm^(−2)). Cement and mortar (H = 76 kg mm^(−2)) yielded intermediate values, although the values for cement (ζ ∼ 0.3) were appreciably lower than for mortar (ζ ∼ 0.6). In all cases where the velocity of the ricochetted projectile was determined, the fraction of angular momentum carried away by ejecta was found to be less than 30%. Finally, the results were only weakly dependent on the material of the projectile.

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Additional Information:© 1991 Academic Press. Inc. Received January 28, 1991: Revised August 22, 1991. We thank Dr. W. Knauss for the use of the framing camera, M. Long for his assistance in the experiments, and W. Yang for conducting the hardness measurements. We thank H. J. Melosh for providing the Kornhauser (1964) reference to us. The careful reviews by P. Cerroni and A. Fujiwara are also appreciated. The experimental work was supported by NASA and M.Y. derived support from the Japanese Ministry of Education. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, contribution 4982.
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Ministry of Education, Culture, Sports, Science and Technology (MEXT)UNSPECIFIED
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Caltech Division of Geological and Planetary Sciences4982
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Official Citation:Yanagisawa, M., Eluszkiewicz, J., & Ahrens, T. J. (1991). Angular momentum transfer in low velocity oblique impacts: Implications for asteroids. Icarus, 94(2), 272-282. doi:
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ID Code:50840
Deposited On:27 Oct 2014 18:31
Last Modified:10 Nov 2021 19:01

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