MESSENGER X-Ray Observations of Electron Precipitation on the Dayside of Mercury

The first maps of electron-induced X-ray emission from the dayside of Mercury's surface are presented, generated by the development of a solar X-ray flux filter. This enables the isolation of the X-ray fluorescence of calcium driven by probable electron precipitation. A catalog of such events has been generated and dayside maps of implied electron precipitation zones have been produced. We find that, similar to electron induced emission events on the nightside, these zones are strongly organized by latitude and magnetic local time. The majority of the dayside events appear in the southern hemisphere and there is a strong enhancement observed centered about local dawn (06:00 LT). There is apparent poleward continuation of emission in the north, but very few events were observed on the duskward hemisphere. These results carry implications for Mercury's magnetosphere by constraining zones of electron precipitation, for the exosphere as a potential source of exospheric species, and for surface science as an additional source of X-ray fluorescence.