MARK GARLICK / SCIENCE PHOTO LIBRARY MARK GARLICK / SCIENCE PHOTO LIBRARY
Internal structure of Mars, cutaway artwork. The inset at lower right shows Earth and Mars at the same scale. Mars is a rocky planet. It has a partially molten core of iron and iron sulphides (yellow). Overlying the core is a thick mantle (orange), which underlies the crust (brown). The crust of Mars is around 100 kilometres thick, compared to the 10-70km thick crust of Earth. The lack of a completely molten region around the core means that Mars does not generate a uniform strong magnetic field, which would have protected the planet's atmosphere from the solar wind. It is thought the Martian atmosphere was stripped away after the core cooled.
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