Map of the abundance of the element thorium on the Moon made with data from the Lunar Prospector, a space mission launched in 1998, shows that most of this radioactive element is concentrated in a region on the Moon's near side (left). But there is also a small hot spot called the Compton-Belkovich Thorium Anomaly (labeled C-B in the map) on the side of the Moon that faces away from Earth.

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