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The large crater origin of SNC meteoritesA 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 km/sec) 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 (1984, 1985, 1987) spallation model is used to estimate the size of the crater required to produce ejecta fragments of the required size with velocities not less than 5 km/sec 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 (greater than 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).
Document ID
19870064550
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Vickery, A. M.
(Arizona Univ. Tucson, AZ, United States)
Melosh, H. J.
(Arizona, University Tucson, United States)
Date Acquired
August 13, 2013
Publication Date
August 14, 1987
Publication Information
Publication: Science
Volume: 237
ISSN: 0036-8075
Subject Category
Lunar And Planetary Exploration
Accession Number
87A51824
Funding Number(s)
CONTRACT_GRANT: NAGW-428
Distribution Limits
Public
Copyright
Other

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