Impact Generation of Holes in the Early Lunar Crust: Scaling Relations

Abstract

The most widely accepted hypothesis for the origin of Earth's Moon is the giant impact hypothesis, in which the young Earth is struck by another planetary-sized body (e.g., Cameron & Ward, 1976;Canup, 2004;Hartmann & Davis, 1975). The Canonical model, developed over several decades, settled on a low velocity, glancing impact between a roughly Mars-sized body (commonly known as "Theia" after the mother of Selene, goddess of the Moon in Greek mythology) and the proto-Earth in the late stages of its formation (see Canup, 2004, for a review). The Canonical model readily explains the high ratio of angular momentum in the lunar orbit relative to the whole Earth-Moon system, and the depletion of the Moon in iron and volatile elements relative to Earth (Taylor et al., 2006). More recently, doubts have been cast on the Canonical model as a result of geochemical analyses that have revealed the Moon to have nearly identical isotopic signatures to Earth (e.g., Spicuzza et al., 2007;Zhang et al., 2012), which conflicts with the prediction of the Canonical model that lunar material should be predominantly sourced from Theia (e.g., Canup, 2014). This has led to a number of proposals for modified giant impact scenarios (e.g.