Figure 4. Maps of Mercury’s chemical composition. The K abundance map (measured in parts per million), for the northern hemisphere, is derived from MESSENGER GRS data (Peplowski et al., 2012a). The Mg/Si, Al/Si, S/Si, Ca/Si, and Fe/Si elemental weight ratio maps are derived from MESSENGER X-Ray Spectrometer data (Nittler et al., 2016; Weider et al., 2015). Coverage is complete for the Mg/Si and Al/Si maps, whereas portions of the S/Si, Ca/Si, and Fe/Si maps (mostly in the northern hemisphere) were not mapped during the MESSENGER campaign. All maps are shown in a Mollweide projection, centered on 0°N, 0°E.