Quantifying the size of impact basins through analysis of gravity and crustal thickness data

The surface and crustal structure of the terrestrial planets in the inner solar system have been influenced by large and energetic impact events. GRAIL data showed that the size of the central gravitational anomaly of lunar basins corresponds closely to the diameter of the inner peak-ring [1].

We present an improved technique based on the analysis of gravity and crustal thickness data to estimate the inner ring and rim crest diameters. This technique expands upon the work of [1] and allows us to better identify highly degraded basins. From this analysis, we also quantify how lower resolution gravity and crustal thickness datasets (such as for Mars and Mercury) might bias the peak ring and main rim diameter estimates.

In our approach, we first quantify the regional value of the Bouguer gravity anomaly and crustal thickness, which is defined as the average value obtained from azimuthally averaged profiles in the radius range 1.5 D to 2 D, where D is the crater diameter. The diameter of the Bouguer gravity high, as well as the diameter of the crustal thickness anomaly, were then estimated as the radius where the profiles first intersect the background regional values. After the initial estimate of D was obtained, the procedure was iterated until there was no change in the obtained diameters.

We tested this method using Bouguer gravity data for certain lunar peak-ring and multi-ring basins, by considering the spherical harmonic degree range from 6 to 540. We then filtered the data using the spherical harmonic degree range 6-49 in order to simulate the lower resolution of the Mars gravity models (e.g., [2]). We then used the same approach using crustal thickness maps derived after GRAIL [3], both for the degree ranges 6-310 and 6-46, to simulate the loss of spatial resolution of Mars [4]. Uncertainty estimates were obtained for the crustal thickness and the Bouguer anomaly diameter by considering the ±1σ values for the background values in the spatial range of 1.5 D to 2 D.

Our method properly detects peak-ring or inner ring sizes for lunar basins with main rim diameter greater than 250 km. Nevertheless, when considering filtered versions of these datasets that correspond to the effective spatial resolution of the Mars gravity models, only basins with rim crest diameters greater than about 450 km can be detected with acceptable accuracy. Finally, results from these analyses will allow us to better constrain the impact rate during the early solar system.

 

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References:

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

[2] Genova A., et al. (2016). Icarus.

[3] Wieczorek M. A., et al. (2013). Science.

[4] Wieczorek M. A., et al. (2022). JGR: Planets.

 

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