Top panel: a histogram of Al/Si line ratios (purple) measured over the entire surface shows a clear bimodal distribution, corresponding to the mare and highland terranes. The Gaussian fits to this distribution are shown by the dashed–dotted orange line. Bottom panel: a two-dimensional distribution of the Mg/Si and Al/Si line ratios also shows a multimodal distribution. The color map shows the density of data points in the 2D space, going from low (blue) to high (red) density.