Crustal Porosity of Lunar Impact Basins. Issue 4 (18th April 2020)

• Record Type: Journal Article
• Authors: Wahl, D.; Wieczorek, M. A.; Wünnemann, K.; Oberst, J.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 4(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-04-18
• Subjects: Moon -- GRAIL -- LOLA -- LRO; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2019JE006335
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: Lateral variations in bulk density and porosity of the upper lunar highland crust are mapped using a high‐resolution Gravity Recovery and Interior Laboratory (GRAIL) gravity field model and Lunar Reconnaissance Orbiter (LRO) derived topography. With a higher spatial resolution gravity model than previous studies, we focus on individual impact basins with diameters greater than 200 km. The bulk density of the upper few kilometers of the lunar crust is estimated by minimizing the correlation between the topography and Bouguer gravity at short wavelengths that are unaffected by lithospheric flexure. Porosity is then derived using estimates of the grain density obtained from remote sensing data of the surface composition. The near surface crust in proximity to many large basins is found to exhibit distinct radial porosity signatures. Low porosities are found in the basin centers within the peak ring, whereas high porosities are identified near and just exterior to the main rim. The larger basins exhibit a more pronounced porosity signature than the smaller basins. Though the number of basins investigated in this study is limited, younger basins appear to be associated with the largest amplitude variations in porosity. For basins with increasing age the magnitude of the porosity variations decreases. Plain Language Summary: The gravity field surrounding an impact basin allows us to investigate the properties of the underlying crust and to better understand how craters form and evolve. In the center of the largest lunar craters, the impact basins, positive mass anomalies can be found that are caused by the excavation of crustal materials and the uplift of the mantle during formation. When using only the short wavelength portion of the gravity field, signals from these deeper regions are masked, and this allows us to estimate both the density and porosity of the upper crust. We investigated the crustal porosity of impact basins located in the lunar highlands, with diameters larger than 200 km. Many of these basins reveal similar porosity signatures, having low porosities in their center and high porosities near the crater rim. For the most pristine basins, the magnitude of the porosity variations increases with increasing basin size. Furthermore, the crustal porosity is influenced by the formation age of a basin, where the older basins have more muted signatures than younger basins. Key Points: The bulk density and porosity of the upper highland crust are revisited using a high‐resolution GRAIL gravity field model in combination with LOLA topography and independently estimated grain densities For many impact basins, porosity is reduced within their peak ring and increased near and just exterior to the main rim Large impact basins show a stronger pronounced porosity signature than smaller basins, and old impact basins reveal a muted porosity signature compared to younger basins