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Why does Mercury have such a large core?

Philip Lynch, Tony, Wisconsin
Planet-interiors
One of the enduring enigmas of Mercury is why such a small planet, roughly 38 percent of Earth’s diameter, is so dense. From Mariner 10’s 1974–5 flybys of the innermost world and now the orbiting MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, we know Mercury has an average density of 5.43 grams per cubic centimeter. (Earth’s average density is 5.52 g/cm3.) This value means the planet . . .

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