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N. G. Barlow (Northern Arizona University)
Crater size-frequency distribution analysis incorporating the very small martian craters revealed by MOC has led to reports of extremely young surface ages for some martian terrain units. The absolute ages of these surface units are derived by extrapolation of the lunar crater chronology to Mars. These studies are almost certainly including secondary craters among the small crater counts. However, these crater studies typically ignore the effects of secondary crater inclusion in the statistics by assuming that the rate of secondary crater production on Mars is similar to that on the Moon.
We are investigating the claim that secondary crater production is similar for the Moon and Mars. We are comparing the crater size-frequency distribution curves of obvious secondaries surrounding relatively-fresh lunar and martian craters. The craters have been selected as representative of those which result from similar energy impacts on the two bodies. We have utilized MOC and THEMIS (VIS and daytime IR) imagery for martian craters and Clementine and Lunar Orbiter data for the lunar craters. We have looked at the secondaries produced by 1-km, 5-km, and 10-km diameter asteroids impacting on basaltic lava flows on the Moon and Mars. Our results reveal that secondary crater production is reduced on Mars compared to the Moon for impacts of similar energies.
The vapor plume mechanism which produces the layered ejecta morphology on Mars likely decreases the ejection of secondary material along ballistic trajectories, thus reducing the number of secondary craters. These results have important implications for the very young absolute ages being cited for some martian terrain units. The lower production of secondary craters on Mars will lead to fewer craters being produced by impacts of similar age and energy on Mars compared to the Moon. This lower frequency of primary+secondary craters would be interpreted as younger ages for Martian terrain units. Thus many of the areas currently cited as being extremely young on Mars may actually be significantly older.
The author(s) of this abstract have provided an email address for comments about the abstract: Nadine.Barlow@nau.edu
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.