File:MESSENGER - NS.jpg

English: "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."