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A. E. Potter (Lunar and Planetary Institute), R. M. Killen (Southwest Research Institute), T. H. Morgan (NASA Headquarters)
We imaged Mercury in sodium D1 and D2 emission for six days during the period November 13-20, 1997 using a 10x10 arcsec aperture image slicer coupled to a high-resolution spectrograph. During the period of observation, large daily changes took place in both the total amount of sodium and its distribution over the planet. In 24 hours, from November 13 to November 14, the total amount of sodium on Mercury doubled. By November 20, the total sodium amount had tripled relative to that of November 13. We corrected the sodium images for atmospheric smearing by computing the actual seeing function from surface reflection images, and using this function to correct the sodium images. The resulting images showed sodium emission to be brightest at longitudes near the subsolar longitude at about 140 degrees. There are no obviously outstanding geologic features at this longitude. On November 15, sodium was excess at southern latitudes. On November 16, the excess moved to northern latitudes, and then changed back to southern latitudes by November 18. In order to explain the large and rapid changes in the amount of sodium, and the shift of excess sodium from southern latitudes to northern latitudes, and back again, we suggest that sodium is released from the surface by magnetospheric processes, perhaps initiated by CME events that expose the planet’s surface to solar particles (Luhmann, et al., 1998). CME activity was high during this period of observation.
References: Luhmann, et al. (1998), Disturbances in Mercury’s magnetosphere: Are the Mariner 10 “substorms” simply driven?, JGR 103 9113