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Science 14 August 1987:
Vol. 237. no. 4816, pp. 738 - 743
DOI: 10.1126/science.237.4816.738
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Articles

The Large Crater Origin of SNC Meteorites

A. M. VICKERY 1 and H. J. MELOSH 1

1 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721.

A large body of evidence strongly suggests that the shergottite, nakhlite, and Chassigny (SNC) meteorites are from Mars. Various mechanisms for the ejection of large rocks at martian escape velocity (5 kilometers per second) have been investigated, but none has proved wholly satisfactory. This article examines a number of possible ejection and cosmic-ray exposure histories to determine which is most plausible. For each possible history, the Melosh spallation model is used to estimate the size of the crater required to produce ejecta fragments of the required size with velocities ge5 kilometers per second and to produce a total mass of solid ejecta consistent with the observed mass flux of SNC meteorites. Estimates of crater production rates on Mars are then used to evaluate the probability that sufficiently large craters have formed during the available time. The results indicate that the SNC meteorites were probably ejected from a very large crater (> 100 kilometers in diameter) about 200 million years ago, and that cosmic-ray exposure of the recovered meteorites was initiated after collisional fragmentation of the original ejecta in space at much later times (0.5 to 10 million years ago).


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Martian Meteorite Launch: High-Speed Ejecta from Small Craters.
J. N. Head, H. J. Melosh, and B. A. Ivanov (2002)
Science 298, 1752-1756
   Abstract »    Full Text »    PDF »
Resistance of Bacillus Endospores to Extreme Terrestrial and Extraterrestrial Environments.
W. L. Nicholson, N. Munakata, G. Horneck, H. J. Melosh, and P. Setlow (2000)
Microbiol. Mol. Biol. Rev. 64, 548-572
   Abstract »    Full Text »    PDF »
Martian Meteorites Are Arriving: The eight SNC meteorites found on Earth are probably from Mars, most researchers now agree, but how they ever got off their home planet remains a question.
R. A. Kerr and R. A. KERR (1987)
Science 237, 721-723
   PDF »


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Science. ISSN 0036-8075 (print), 1095-9203 (online)