Mathematics – Logic
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p53c1539l&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P53C-1539
Mathematics
Logic
[5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering
Scientific paper
We model the cratering of the Moon and terrestrial planets from the present knowledge of the orbital and size distribution of asteroids and comets in the inner solar system (Bottke et al., 2002; Stuart and Binzel, 2004; Brown, 2002; Harris, 2002; Minor Planet Center), in order to refine the crater chronology method. Impact occurrences, locations, velocities and incidence angles are calculated semi-analytically, and scaling laws (Holsapple and Housen, 2007) are used to convert impactor sizes into crater sizes. Our approach is generalizable to other moons or planets. The lunar cratering rate varies with both latitude and longitude: with respect to the global average, it is about 25% lower at (65N, 90E) and larger by the same amount at the apex of motion (0N, 90W) for the present Earth-Moon distance. The measured size-frequency distributions of lunar craters (see Neukum et al., 2001) are reconciled with the observed population of near-Earth objects for standard parameter values under the assumption that craters smaller than a few kilometers in diameter form in a porous megaregolith (as proposed by Ivanov, 2007). Varying depths of this megaregolith between the mare and highlands is a plausible explanation for differences in previously reported measured size-frequency distributions. We give a revised analytical relationship between the number of craters and the age of a lunar surface. For the inner planets, expected size-frequency crater distributions are calculated that account for differences in impact conditions, and the age of a few key geologic units is given. We estimate Orientale Basin to be 3.76 Ga old, Caloris exterior plains to be 2.20 Ga old, and the surface of Venus to be 200 Ma old, significantly younger than most previous estimates. The terrestrial cratering record is consistent with the revised chronology and a constant impact rate over the last 400 Ma. Fig. 1: Model production function of lunar craters, for one year, in comparison with Hartmann and Neukum measured production functions, and the model production function of Marchi et al. (2009). Respective megaregolith thicknesses T of ~750 and ~250 m allow to fit either the Neukum or Hartmann distributions in the diameter range 2-20 km.
Le Feuvre Mathieu
Wieczorek Mark A.
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