An Alternative Hypothesis for the Formation of the Moon

Introduction: The giant impact hypothesis [1,2] is the cornerstone of current lunar formation research. However, recent analyses of the elemental and isotopic composition of lunar samples show degrees of similarity between Moon and Bulk Silicate Earth (BSE) that are inconsistent with hydrodynamic models of the Moon-forming giant impact showing 60-90% of the Moon is made up of impactor rather than terrestrial material [3]. At present, this inconsistency is dealt with by invoking full post-collisional elemental and isotopic equilibration between Earth and proto-Moon as proposed for oxygen by [4] for elements from H to W. In essence, the giant impact hypothesis currently relies on the applicability of a equilibration scenario that is untested for elements other than oxygen. Here we propose an alternative explanation for the compositional correspondence between Moon and BSE, namely that the Moon was formed from the ejection of terrestrial mantle material in a heat-propelled jet, triggered by a run-away natural georeactor at Earth’s core-mantle boundary (CMB). Our hypothesis straightforwardly explains the identical isotopic composition of bulk silicate Earth and Moon for many elements withour relying on full post-collisional equilibration.