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How large is Mercury’s iron core?
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Mercury
Mercury as seen by the Messenger probe, January 14, 2008. This image shows half of the hemisphere missed by Mariner 10 in 1974–75 and was snapped by Messenger's Wide Angle Camera when it was about 27,000 km (17,000 miles) from the planet.
Mercury’s iron-rich core is exceptionally large, accounting for nearly two-thirds of the planet's total mass. It extends from the center of the planet to a radius of approximately 2,100 km (1,300 miles), which reaches about 85 percent of the way to the surface.1
In contrast, the planet's rocky outer shell—comprising its mantle and crust—is relatively thin, measuring only about 300 km (200 miles) in thickness. This massive core is the primary reason why Mercury possesses the highest density of any planet when corrected for self-compression.1