NASA engineers are working on a new instrument that could peer through rock and dirt on Mars to see evidence of life under the surface. The Neutron/Gamma ray Geologic Tomography (NUGGET) would be wielded by a Martian rover, and aimed at suspicious rocks. By releasing a focused beam of neutrons, some of atoms in the target rock will capture them and give off a characteristic gamma ray signature, measurable by the instrument. Ancient fossils embedded in the rock would be revealed by their chemicals.