Detection of small lunar secondary craters in circular polarization ratio radar images
Article first published online: 17 JUN 2010
Copyright 2010 by the American Geophysical Union.
Journal of Geophysical Research: Planets (1991–2012)
Volume 115, Issue E6, June 2010
How to Cite
2010), Detection of small lunar secondary craters in circular polarization ratio radar images, J. Geophys. Res., 115, E06008, doi:10.1029/2009JE003491., , , and (
- Issue published online: 17 JUN 2010
- Article first published online: 17 JUN 2010
- Manuscript Accepted: 22 FEB 2010
- Manuscript Revised: 4 FEB 2010
- Manuscript Received: 20 AUG 2009
- lunar cratering
 The identification of small (D < a few kilometers) secondary craters and their global distributions are of critical importance to improving our knowledge of surface ages in the solar system. We investigate a technique by which small, distal secondary craters can be discerned from the surrounding primary population of equivalent size based on asymmetries in their ejecta blankets. The asymmetric ejecta blankets are visible in radar circular polarization ratio (CPR) but not as optical albedo features. Measurements with our new technique reveal 94 secondary craters on the Newton and Newton-A crater floors near the lunar south pole. These regions are not in an obvious optical ray, but the orientation of asymmetric secondary ejecta blankets suggests that they represent an extension of the Tycho crater ray that crosses Clavius crater. Including the secondary craters at Newton and Newton-A skews the terrain age inferred by crater counts. It is reduced by few percentages by their removal, from 3.8 to 3.75 Gyr at Newton-A. Because “hidden rays” like that identified here may also occur beyond the edges of other optically bright lunar crater rays, we assess the effect that similar but hypothetical populations would have on lunar terrains of various ages. The average secondary crater density measured at 1 km diameter is equivalent to the crater density at 1 km on a 3.4 Gyr surface [Neukum et al., 2001]. Younger surfaces (i.e., younger crater ejecta blankets) would be dominated by secondary craters below 1 km if superposed by a hidden ray.