Date Presented: May 3, 2011, in a MESSENGER Science Highlight article.
Instrument: Gamma-ray and Neutron Spectrometer (GRNS)

Of Interest: Two example gamma-ray spectra acquired by the MESSENGER Gamma-Ray Spectrometer, with gamma-ray count rates shown as a function of energy (keV, or kilo-electron volt, is a unit of energy). To the left is shown a gamma-ray spectrum collected while MESSENGER was far from the planet; to the right is a spectrum obtained close to the surface (less than 2000 km altitude). “BG” denotes background gamma-ray peaks. Two particular gamma rays, at 1460-keV resulting from potassium and at 1779-keV resulting from silicon, are highlighted, as they show clear enhancements near the surface. These data demonstrate the presence of potassium and silicon on Mercury's surface. Other unlabeled peaks in the gamma-ray spectra in this energy range result from galactic cosmic-ray interactions with the spacecraft and detector material.

The MESSENGER spacecraft is the first ever to orbit the planet Mercury, and the spacecraft's seven scientific instruments and radio science investigation are unraveling the history and evolution of the Solar System's innermost planet. Visit the Why Mercury? section of this website to learn more about the key science questions that the MESSENGER mission is addressing.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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