Last updated on April 19, 2014 at 7:10 EDT

Illustration of MESSENGER’s Gamma-Ray Spectrometer

September 29, 2011

Galactic cosmic rays interact with Mercury’s surface to a depth of tens of centimeters, producing high-energy neutrons. These neutrons interact with surface material, resulting in the emission of gamma rays with energies characteristic of the emitting elements and low-energy neutrons. Naturally occurring elements such as potassium, thorium, and uranium also emit gamma rays. Detection of the gamma rays and neutrons by GRS allows determination of the chemical composition of the surface.  credit:  NASA