Constraining the Recent Impactor Flux on the Earth and Moon

Details Constraining the Recent Impactor Flux on the Earth and Moon Constraining the Recent Impactor Flux on the Earth and Moon

Sep 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999dps....31.2007g&link_type=abstract

American Astronomical Society, DPS meeting #31, #20.07

Astronomy and Astrophysics

Astronomy

Scientific paper

McEwen et al. (1997, JGR 102) reported a possible increase in the cratering rate during the Copernican (< 800 Ma) based on crater counts of large rayed craters on the lunar farside. This was consistent with the hypothesis of Shoemaker (1998, GSA SP 140) that there was an increase in the impactor flux of ~ 2x during the past 300 Ma. To further test these observations, we have undertaken an improved analysis of lunar craters using the Clementine global multispectral image mosaics. We have grouped craters based on the relative optical maturity of their ejecta using the technique developed by Lucey et al., (1998, JGR 103). Our revised inventory of lunar craters is composed from a survey of all craters > 20km in diameter from +/- 60 deg latitude which possess, or have been suspected to possess, immature ejecta. We have generated radially averaged maturity profiles for each crater, and binned them into relative age categories. The profiles allow younger craters, with fresher, more immature ejecta and thus steeper profiles, to be distinguished from older craters which possess flatter profiles. Craters have been categorized as ``Young" (ejecta similar too or less mature than Tycho), ``Old" (ejecta apparently more mature than Copernicus), and ``Intermediate" (ejecta of intermediate maturity). We have calibrated these relative age categories using the absolute ages of Tycho and Copernicus, which have been radiometrically dated. Our age-dating scheme does not indicate an increase in the impactor flux over the last ~ 110 Ma, and therefore does not support Shoemaker's hypothesis. Continued refinement of the technique and a survey of the smaller (1-20km) craters will allow for additional constraints to be placed on in the impactor flux during the Phanerozoic, and may reveal variation, if present.

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