1A Serenitatis origin for the Imbrian grooves and South Pole-Aitken thorium anomaly

• Main Authors: Mark A. Wieczorek, Maria T. Zuber
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Aitken; South Pole; South pole
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.555.2761; http://www-geodyn.mit.edu/imbrium.grooves.pdf

Abstract. The northwest corner of the MoonÕs South Pole-Aitken (SPA) basin contains a high abundance of thorium and a unique Imbrian aged geomorphologic unit that consists of Ògrooves and moundsÓ (referred to here as the Imbrian grooves). Because the location of these features are almost antipodal to the Imbrium basin, where high-thorium ejecta and seismic energy are expected to have converged, an Imbrium origin for these units has long seemed certain. By modeling the deposition of impact ejecta on the Moon, we have investigated whether the convergence of ImbriumÕs ejecta at its antipode could be the origin of both the Imbrian grooves and SPA thorium anomaly. As a result of the MoonÕs rotation, our results show that ejecta from this basin should converge more than 12 ° west of its antipode. Both the Imbrian grooves and thorium anomaly within SPA, however, reside slightly to the east of ImbriumÕs antipode. In an attempt to reconcile this disparity, the effects of a putative oblique Imbrium impact have been qualitatively investigated. While this model can distribute ejecta in the general vicinity of the Imbrian grooves, the planform of our modeled antipodal ejecta is distinctly different from that which is observed. As an alternative explanation for the origin of these features, we find that the modeled distribution of ejecta from an oblique Serenitatis impact is surprisingly similar to the planform of the Imbrian grooves, with the exception that it is offset directly to the east. This