The elemental composition of both Vesta and Ceres will be measured with the Gamma Ray and Neutron Detector. This instrument uses a total of 21 sensors with a very wide field of view to measure the energy from gamma rays and neutrons that either bounce off or are emitted by a celestial body. Gamma rays are a form of light, while neutrons are particles that normally reside in the nuclei of atoms. Together, gamma rays and neutrons reveal many of the important atomic constituents of the celestial body’s surface down to a depth of one meter (three feet). Gamma rays and neutrons emanating from the surface of Vesta and Ceres will tell us much about the elemental composition of each. Many scientists believe that Ceres may be rich in water; if that is the case, the signature of the water may be contained in this instrument’s data. Unlike the other instruments aboard Dawn, the detector has no internal data storage. The instrument was developed by Los Alamos National Laboratory, Los Alamos, N.M.