GRNS packages separate gamma-ray and neutron spectrometers to collect complementary data on elements that form Mercury's crust.
Gamma-Ray Spectrometer (GRS)
Mass: 9.2 kilograms (20.3 pounds)
Power: 16.5 watts
Development: Johns Hopkins University Applied Physics Laboratory, Patriot Engineering, Lawrence Berkeley National Laboratory, Lawrence Livermore National Laboratory
GRS measures gamma rays emitted by the nuclei of atoms on Mercury’s surface that are struck by cosmic rays. Each element has a signature emission, and the instrument will look for geologically important elements such as hydrogen, magnesium, silicon, oxygen, iron, titanium, sodium, and calcium. It may also detect naturally radioactive elements such as potassium, thorium, and uranium.
Neutron Spectrometer (NS)
Mass: 3.9 kilograms (8.6 pounds)
Power: 6.0 watts
Development: Johns Hopkins University Applied Physics Laboratory, Patriot Engineering, Los Alamos National Laboratory
NS maps variations in the fast, thermal, and epithermal neutrons Mercury’s surface emits when struck by cosmic rays. “Fast” neutrons shoot directly into space; others collide with neighboring atoms in the crust before escaping. If a neutron collides with a light atom (like hydrogen), it will lose energy and be detected as a slow (or thermal) neutron. Scientists can look at the ratio of thermal to epithermal (slightly faster) neutrons across Mercury’s surface to estimate the amount of hydrogen – possibly locked up in water molecules – and other elements.