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Loading contentAn instrument that measures the gamma rays and neutrons emitted by a surface under cosmic-ray bombardment, revealing elemental composition — and, through neutrons, the presence of water or ice.
MESSENGER's spectrometer, which measured the elemental composition of Mercury's surface and helped confirm water ice in its permanently shadowed polar craters.
Facts on this topic will be cited from these primary and reference sources.
Mission data, planetary science, space telescopes, and public-domain imagery.
Most NASA-produced imagery is in the public domain; individual items are checked for usage terms before publication.