AN ORIGIN FOR THE SOUTH POLE-AITKEN BASIN THORIUM. ... Moscow University. ... Introduction: The lunar South Pole-Aitken (SPA) impact basin is one of the largest and oldest impact basins and has thus been heavily degraded by postbasin-formation primary impacts and their ejecta [1]. ... The SPA basin thorium map: The using data Lunar Prospector [4] the thorium distribution map demonstrated a hemisphere of the Moon which contains the SPA basin structure and its environs was constructed. ...