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Impact cratering experiments in brittle targets with variable thickness: implications for deep pit craters on Mars

Michikami, T.; Hagermann, A.; Miyamoto, H.; Miura, S.; Haruyama, J. and Lykawka, P. S. (2014). Impact cratering experiments in brittle targets with variable thickness: implications for deep pit craters on Mars. Planetary and Space Science, 96 pp. 71–80.

DOI (Digital Object Identifier) Link: https://doi.org/10.1016/j.pss.2014.03.010
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Abstract

High-resolution images reveal that numerous pit craters exist on the surface of Mars. For some pit craters, the depth-to-diameter ratios are much greater than for ordinary craters. Such deep pit craters are generally considered to be the results of material drainage into a subsurface void space, which might be formed by a lava tube, dike injection, extensional fracturing, and dilational normal faulting. Morphological studies indicate that the formation of a pit crater might be triggered by the impact event, and followed by collapse of the ceiling. To test this hypothesis, we carried out laboratory experiments of impact cratering into brittle targets with variable roof thickness. In particular, the effect of the target thickness on the crater formation is studied to understand the penetration process by an impact. For this purpose, we produced mortar targets with roof thickness of 1–6 cm, and a bulk density of 1550 kg/m3 by using a mixture of cement, water and sand (0.2 mm) in the ratio of 1:1:10, by weight. The compressive strength of the resulting targets is 3.2±0.9 MPa. A spherical nylon projectile (diameter 7 mm) is shot perpendicularly into the target surface at the nominal velocity of 1.2 km/s, using a two-stage light-gas gun. Craters are formed on the opposite side of the impact even when no target penetration occurs. Penetration of the target is achieved when craters on the opposite sides of the target connect with each other. In this case, the cross section of crater somehow attains a flat hourglass-like shape. We also find that the crater diameter on the opposite side is larger than that on the impact side, and more fragments are ejected from the crater on the opposite side than from the crater on the impact side. This result gives a qualitative explanation for the observation that the Martian deep pit craters lack a raised rim and have the ejecta deposit on their floor instead.

Item Type: Journal Item
Copyright Holders: 2014 Published by Elsevier Ltd.
ISSN: 0032-0633
Project Funding Details:
Funded Project NameProject IDFunding Body
Not SetNot SetSTFC (Science & Technology Facilities Council)
Not SetNot SetUK Space Agency
Keywords: impact cratering process; pit crater; penetration regime; subsurface cavity; laboratory experiments
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Item ID: 40363
Depositing User: Axel Hagermann
Date Deposited: 11 Jun 2014 13:21
Last Modified: 07 Dec 2018 10:23
URI: http://oro.open.ac.uk/id/eprint/40363
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