Physics – Geophysics
Scientific paper
Sep 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.5712w&link_type=abstract
American Astronomical Society, DPS meeting #38, #57.12; Bulletin of the American Astronomical Society, Vol. 38, p.590
Physics
Geophysics
Scientific paper
Secondary impact craters can cause significant uncertainties when small (primary) craters are used to date young surfaces in our Solar System. To help address this issue, we present size-frequency distribution (SFD) measurements from 20-m resolution, 13 cm wavelength Arecibo radar data of lunar craters with 350 m < D < 12.6 km located in an apparent ray of the 85 km Tycho crater stretching across the craters Newton and Newton-A. Secondary craters were identified by clustering and the presence of "tails” of bright ejecta which show up clearly in images of the circular polarization ratio (CPR, the ratio of the radar echo strength in the same sense of circular polarization as transmitted to that in the opposite sense). The direction of these tails indicates that the secondary craters on the floors of Newton and Newton-A, both of which are about 60 km in diameter, were formed by ejecta from the young primary Tycho, roughly 1000 km to the north.
Approximately 190 and 134 secondary craters were identified on the floors of Newton and Newton-A, in areas of 2535 and 1900 km2, respectively. Examination of the best-fit power-laws of the SFD's of these fields reveals a shallow slope for the total population of secondaries in this size range (a power law index of b=1.9 for Newton and 2.2 for Newton-A), a result which we attribute to a saturation effect for secondaries with D < 1 km. Considering only craters with D > 1 km, the SFDs have considerably steeper slopes with power-law indices of b=3.6 for Newton and 4.3 for Newton-A. These values are in reasonable agreement with the values obtained by Hirata and Nakamura (J. Geophysics. Res., 111, E03005, 2006) for Tycho secondaries at distances of 130 to 370 km from Tycho. Funding by NASA's Planetary Astronomy program is acknowledged.
Campbell Bruce A.
Campbell Don B.
Carter Lynn Marie
Wells Kassandra S.
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