Chisenga, and 4 co-authors reported in 2019 that the Von Kármán Crater, within the South Pole-Aitken (SPA) Basin, is the landing site of China’s Chang’E-4 mission on the far side of the Moon. To complement the in situ exploration mission and provide initial subsurface interpretation, the authors applied a 3D density inversion using the Gravity Recovery and Interior Laboratory (GRAIL) gravity data. They constrained our inversion method using known geological and geophysical lunar parameters to reduce the non-uniqueness associated with gravity inversion.
The 3D density models reveal vertical and lateral density variations, 2600–3200 kg/m3, assigned to the changing porosity beneath the Von Kármán Crater. They also identified two mass excess anomalies in the crust with a steep density contrast of 150 kg/m3, which were likely caused by multiple impact cratering. The anomalies from recovered near surface density models, together with the gravity derivative maps extending to the lower crust, are consistent with surface geological manifestation of excavated mantle materials from remote sensing studies. Therefore, the authors suggested that the density distribution of the Von Kármán Crater indicates multiple episodes of impact cratering that resulted in formation and destruction of ancient craters, with crustal reworking and excavation of mantle materials.
The authors performed a 3-D inversion of the GRAIL gravity data to produce a density model of the Von Kármán Crater. Our results reveal that the region is underlain by a mass excess anomaly beneath the Von Kármán M Crater with a density of ~3200 kg/m3, on the southern rim of the Von Kármán basin. A relatively high-density mass excess anomaly with a density value of up to 3100 kg/m3 connects to the first anomaly in the northern part. Basaltic rocks covering the Von Kármán basin show an extended body on the surface, with the northern part of the Von Kármán basin indicating a more feldspathic composition.
The authors concluded that this was as the result of the buried mare basalts that created a buried impact basin in the Von Kármán M Crater. The inversion results are consistent with the spectral and geological results from remote sensing and gravity derivative data. The occurrence of high-density materials that extend to the lower crust correlates with excavated mantle materials observed on the floor of the Von Kármán basin, indicating that the impact cratering likely brought upper mantle materials to the surface. The authors inferred that the evolution of the Von Kármán basin was due to multiple episodes of impact cratering that resulted in crustal reworking and secondary excavation of mantle materials.
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