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Mercury's strange potassium-thorium ratio

Mercury's strange potassium-thorium ratio
Mercury's strange potassium-thorium ratio Ratio by weight of potassium to thorium for the terrestrial planets and Moon, plotted versus distance from the Sun. Because K is a volatile element and Th a refractory one, this ratio is a sensitive measure of thermal processes that fractionate elements by volatility. For example, the ratio for the Moon (360) is much lower than that for Earth (3000), reflecting volatile loss during the Moon's formation by a giant impact. The ratio for Mercury (~6000), determined by GRNS, is comparable to that of Venus, Earth, and Mars, indicating that Mercury is not highly depleted in volatile elements, ruling out some models for its formation and early history. NASA / JHUAPL / CIW