They empirically identified that a certain reflectance correlates with a given abundance. Elphic's findings indicate there is half as much titanium in the basalt regions as the previous data suggested. Lunar Prospector carried neutron detectors that measured neutrons in three energy ranges emitted by the lunar surface. The first neutrons that escape after the lunar soil is hit by cosmic rays are indicative of the composition of the soil. Different elements, when hit by cosmic rays, will produce fast, thermal or epithermal neutrons.
Fast neutrons are indicative of iron and titanium.
This information helps determine the elemental composition of the soil. The remarkable difference in composition between the two faces of the moon is surprising for a small planet. Gasnault also analyzed fast neutron data and thorium abundance on the lunar surface. Thorium is a subsurface material brought to the surface by meteor impacts and volcanic activity. Using this analysis Gasnault believes they have found another impact basin near the large Imbrium basin.