Mercury's crustal heterogeneity revealed by gravity data modelling 

The study of the internal structure of Mercury is fundamental for understanding the formation and evolution of the planet and of the entire Solar System. The main purpose of this work was the analysis of the MESS160A gravity field model [1] to show the presence of crustal heterogeneities in density. According to the flexural isostatic response curve, we noted that the lithospheric flexure occurs in the spherical harmonic degree range 5-80, consistently with a flexural compensation model, while for degrees lower than 5 the flexural rigidity tends to 0 and a local compensation model can be assumed. Removing spherical harmonic components up to degree 4, as they are associated with the polar mass deficit and to the morphological contrasts, we assumed a flexural compensation model [2] to first estimate a mean elastic thickness of 30 ± 10 km. We, then, modeled the lithospheric flexure regardless of the gravity field and calculated the isostatic gravity anomalies by subtracting the gravity effect caused by the isostatic compensation to Bouguer anomalies. In this way, we proved that considerable lateral density variations occur within the Mercury's crust [3]. We also estimated the curst-mante interface depth, varying from 19 to 42 km. Isostatic anomalies are mainly related to density variations in the crust: gravity highs mostly correspond to large-impact basins, suggesting intra-crustal magmatic intrusions as the main origin of these anomalies. Isostatic gravity lows prevail, instead, above intercrater plains and may represent the signature of a heavily fractured crust.   Acknowledgements: We gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2017-47-H.0.   References: [1] Konopliv, A. S. et al. (2020). Icarus, 335. [2] Turcotte, D. L. et al. (1981). J. Geophys. Res., 86. [3] Buoninfante, S. et al. (2023). Sci. Rep., 13.