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The Shergottite Age Paradox and the Relative Probabilities of Ejecting Martian Meteorites of Differing AgesThe apparent paradox that the majority of impacts yielding Martian meteorites appear to have taken place on only a few percent of the Martian surface can be resolved if all the shergottites were ejected in a single event rather than in multiple events as expected from variations in their cosmic ray exposure and crystallization ages. If the shergottite-ejection event is assigned to one of three craters in the vicinity of Olympus Mons that were previously identified as candidate source craters for the SNC (Shergottites, Nakhlites, Chassigny) meteorites, and the nakhlite event to another candidate crater in the vicinity of Ceraunius Tholus, the implied ages of the surrounding terranes agree well with crater density ages. EN,en for high cratering rates (minimum ages), the likely origin of the shergottites is in the Tharsis region, and the paradox of too many meteorites from too little terrane remains for multiple shergottite-ejection events. However, for high cratering rates it is possible to consider sources for the nakhlltes which are away from the Tharsis region. The meteorite-yielding impacts may have been widely dispersed with sources of the young SNC meteorites in the northern plains, and the source of the ancient orthopyroxenite, ALH84001, in the ancient southern uplands. Oblique-impact craters can be identified with the sources of the nakhlites and the orthopyroxenite,, respectively, in the nominal cratering rate model, and with the shergottites and orthopyroxenite, respectively, in the high cratering rate model. Thus, oblique impacts deserve renewed attention as an ejection mechanism for Martian meteorites.
Document ID
19980018466
Document Type
Contractor Report (CR)
Authors
Borg, L. E.
(National Academy of Sciences - National Research Council Houston, TX United States)
Shih, C.-Y.
(Lockheed Martin Engineering and Sciences Co. Houston, TX United States)
Nyquist, L. E.
(NASA Johnson Space Center Houston, TX United States)
Date Acquired
September 6, 2013
Publication Date
February 1, 1998
Publication Information
Publication: Journal of Geophysical Research-Planets
Publisher: American Geophysical Union
Subject Category
Lunar And Planetary Exploration
Report/Patent Number
NAS 1.26:207153
NASA/CR-1998-207153
Funding Number(s)
PROJECT: RTOP 344-31-30-21
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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