MARK GARLICK / SCIENCE PHOTO LIBRARY MARK GARLICK / SCIENCE PHOTO LIBRARY
Diagram showing the interior of the terrestrial planet Mars. The outermost layer is the crust, which is about 50 km deep on average - quite thick compared to Earth's. The convecting mantle, immediately below the crust, is a thick shell of silicate rocks. Lastly there is a substantial core which occupies up to 52 per cent of the planet's radius. Like the Earth's it's probably made up mostly of nickel-iron with about 17 percent sulfur.
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