Fig. 3: Mechanisms for mantle fO2 difference between the lunar nearside and farside.
From: A more reduced mantle beneath the lunar South Pole–Aitken basin
The black dot represents the lunar center of figure; the red dot represents the lunar center of mass. In the mechanism ①, the Fe metal sank to the core from the nearside mantle and elevated its Fe3+/∑Fe, resulting in a relatively oxidized nearside mantle than the farside mantle. This process should result in an asymmetry between the nearside and the farside. In the mechanism ②, the abundant S2 and CO degassing induced by the SPA massive impact occurred and caused Fe2+ → Fe0, and consequently, a relatively reduced mantle beneath SPA basin. This process should lead to an asymmetry between the SPA basin and PKT. Future comparative studies on the lunar northern hemisphere of the farside and southern hemisphere of the nearside are required to validate these two mechanisms. SPA South Pole–Aitken, PKT Procellarum KREEP Terrane.
