Mathematics – Logic
Scientific paper
Jun 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.0205b&link_type=abstract
American Astronomical Society, DPS meeting #28, #02.05; Bulletin of the American Astronomical Society, Vol. 28, p.1058
Mathematics
Logic
1
Scientific paper
The "Catalog of Large Martian Impact Craters" has been used to search for possible source craters of the martian meteorite ALH84001. ALH84001 has an igneous crystallization age of 4.5 Gyr, a pre-ejection shock age of about 4.0 Gyr, an ejection shock age of 16 Myr, and a cosmic ray exposure age of about 15 Myr. The meteorite contains carbonates and features recently interpreted to be biogenic material and microfossils. The low amount of aqueous alteration of the meteorite's minerals, however, indicate that any exposure to water, necessary to create the carbonates, must have been short-lived. Possible source craters for this meteorite were determined using the following criteria to search through the Crater Catalog: (1) the 4.5 Gyr formation age limited the search to the ancient (Noachian-aged) terrain units, (2) the 16 Myr ejection age limited the search to fresh (sharp rim, pristine ejecta blanket) craters, and (3) our understanding of how material can be ejected off Mars limited the search to large (>100-km-D) circular craters and smaller (<10-km-D) elliptical craters. Twenty-three possible craters resulted from this search of the Crater Catalog, of which 21 were eliminated by subsequent photogeologic analysis which suggested the craters were likely older than 16 Myr. Two craters remain as possible source craters, both of which show evidence of ancient near-by impacts (which can explain the approximate 4.0 Gyr pre-ejection shock age) and ancient fluvial activity. Crater 1 is a slightly elliptical 11.3 km x 9.0 km crater with an asymmetric ejecta blanket located east of Hesperia Planitia (11.7S 243.3W). Crater 2 is a 22.9 km x 14.6 km crater with a prominent "butterfly" ejecta pattern located south of the Schiaparelli impact basin on the rim of a degraded 60-km-D crater (14.0S 343.5W).
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