Figure 7.8 The interior structure of Mars.

compared to Earth's core, which makes up about 32 per cent of its mass. A weak magnetic field suggests the core is no longer liquid or that currents within it are slow. Surrounding the core is a molten rocky mantle about 2200 km thick that is less dense than the core. The outer crust of the planet varies in thickness from about 20 km to 150 km.

The strength of gravity on Mars is about a third of that on Earth. A 75 kg person weighs 735 N on Earth, but would weigh only 270 N on Mars.

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