In this image, which was mapped from Lunar Prospector, we see a global map of the element thorium, a radioactive trace element showing the location of KREEP (an acronym built from the letters K: the atomic symbol for potassium, REE: rare Earth elements, and P: the atomic symbol for phosphorus, is a geochemical component of some lunar impact breccia and basaltic rocks), an important key to lunar igneous history. Lunar Prospector is the third mission selected by NASA for full development and construction as part of the Discovery Program. At a cost of $62.8 million, the 19 month mission was designed for a low polar orbit investigation of the Moon, including mapping of surface composition and possible polar ice deposits, measurements of magnetic and gravity fields, and study of lunar outgassing events. The mission ended July 31, 1999, when the orbiter was deliberately crashed into a crater near the lunar south pole after the presence of water ice was successfully detected.