Lateral Variations in Bulk Density and Porosity of the Upper Lunar Crust from High-Resolution Gravity and Topography Data: Comparison of Different Analysis Techniques

Kurzfassung

We map lateral variations in bulk density of the upper lunar highland crust using the most recent GRAIL gravity field solution of degreeand order 1500 in combination with LOLA topography data, both truncated to an upper limit of degree and order 700. Our maps havea spatial resolution of 0.75°, where each grid point was calculated using circular analysis regions of 3° radius. We apply two methods,which yield similar results for most parts of the study area. The first method minimizes the correlation between topography and Bougueranomalies, the second maximizes the smoothness of the Bouguer anomalies. Both approaches suffer in the case that terrain is flat andlacks topographic features; consequently, this is where results from the two methods differ. We also mapped porosity of the crust usinggrain densities derived from Lunar Prospector spectrometry and sample analysis. It appears that variations in bulk density are mostlyrelated to differences in crustal porosity. We find that high porosity is often associated with areas of impact basins. This confirms earlierstudies, that impacts changed the geophysical characteristics of the lithosphere sustainably and that the high porosity of the upper lunarcrust is most likely impact induced.