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Extinct volcanoes on Mars
The highest mountain in the Solar System is Olympus Mons, an extinct volcano on Mars. A description is provided of how volcanoes rely on heat from the middle of planets. Mars' smaller size suggests that its heat was lost to the Solar System faster than that of the Earth, so all its volcanoes are now extinct. Published as part of the Solar System website: bbc.co.uk/solarsystem/. Please note this clip is only available in Flash.
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