Major-Element Abundances on the Surface of Mercury: Results from the MESSENGER Gamma-Ray Spectrometer

Solomon, Sean C.; Evans, Larry G.; Peplowski, Patrick N.; Rhodes, Edgar A.; Lawrence, David J.; McCoy, Timothy J.; Nittler, Larry R.; Sprague, Ann L.; Stockstill-Cahill, Karen R.; Starr, Richard D.; Weider, Shoshana Z.; Boynton, William V.; Hamara, David K.; Goldsten, John O.

Orbital gamma-ray measurements obtained by the MESSENGER spacecraft have been analyzed to determine the abundances of the major elements Al, Ca, S, Fe, and Na on the surface of Mercury. The Si abundance was determined and used to normalize those of the other reported elements. The Na analysis provides the first abundance estimate of 2.9 plus or minus 0.1 wt% for this element on Mercury's surface. The other elemental results (S/Si = 0.092 plus or minus 0.015, Ca/Si = 0.24 plus or minus 0.05, and Fe/Si = 0.077 plus or minus 0.013) are consistent with those previously obtained by the MESSENGER X-Ray Spectrometer, including the high sulfur and low iron abundances. Because of different sampling depths for the two techniques, this agreement indicates that Mercury's regolith is, on average, homogenous to a depth of tens of centimeters. The elemental results from gamma-ray and X-ray spectrometry are most consistent with petrologic models suggesting that Mercury's surface is dominated by Mg-rich silicates. We also compare the results with those obtained during the MESSENGER flybys and with ground-based observations of Mercury's surface and exosphere.


Also Published In

Journal of Geophysical Research: Planets

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Academic Units
Lamont-Doherty Earth Observatory
Published Here
September 11, 2013