Computing the size of Mercury’s impact basins and ring systems through gravity data modelling

Impact basins on terrestrial planets have been thoroughly investigated from imagery and topography data. Previous work has already shown the presence of peak-ring basins on terrestrial planets and estimated their size (e.g., [1]), utilising topography and morphological data. However, the modelling of gravity and crustal thickness data can be a powerful approach in detecting hidden impact basins and estimating the diameters of their rim and inner rings. This is also useful in updating the basin catalogue of terrestrial planets and provides valuable constraints to accurately estimate the impact rate during the early Solar System.

NASA’s MESSENGER mission provided most datasets used in the last decade to model the internal structure of Mercury and characterize its surface. Image products derived after MESSENGER have been widely used to detect impact basins and provide a consistent database [2, 3]. More recently, Mercury’s gravity anomalies have also been used to re-update this catalogue [4].

Here we model Bouguer gravity anomalies of Mercury using the MESS160A gravity field model [5] to properly estimate the size of inner rings. We first quantify a regional value of the Bouguer gravity anomaly, which is defined as the average value obtained from azimuthally averaged profiles in the spatial range 1.5D to 2D, where D is the basin diameter. The size of the Bouguer gravity high is derived as the radius where the profiles first intersect the regional values. The uncertainties represent the ±1σ values of the regional values taken in the same spatial range. We performed tests on filtered GRAIL gravity data, consistently with the spatial resolution of Mercury’s gravity field, to understand how the resolution affects the size estimates of certain lunar basins [6]. The used approach can be reliable for inner ring diameters ≳ 70 km when considering the highest gravity resolution for Mercury.

We present preliminary results for selected certain impact basins [2, 3, 7] in the northern hemisphere where the current gravity data is characterized by higher resolution, and for putative or uncertain basins [2, 3]. The results confirm the existence of the investigated certain and putative basins, and provide updated inner ring sizes.

This approach will be first used to identify potential unknown impact basins, re-evaluate the existing databases of impact basins on Mercury, and it can be valuable in assessing the existence and number of multi-ring basins on Mercury. Though our current database focuses on basins in the northern hemisphere, the approaching ESA-JAXA BepiColombo mission will provide higher-resolution gravity data in the southern hemisphere, allowing us to better quantify the impact basins size at these latitudes.

References

[1] Baker D. M. H. et al. (2011). Planet. Space Sci., 59(15).

[2] Fassett C. I. et al. (2012). JGR: Planets, 117(E12).

[3] Orgel C. et al. (2020). JGR: Planets, 125(8).

[4] Szczech C. C. et al. (2024). Icarus, 422.

[5] Konopliv A. S. et al. (2020). Icarus, 335.

[6] Neumann, G. A. et al. (2015). Sci. Adv., 1(9).

[7] Hall G. P. et al. (2021). JGR: Planets, 126(9).

 

Acknowledgements: We gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2024-18-HH.0.