Why is Mercury covered in so many large cliffs and scarps?
Quick Answer
Mercury shrank as its interior cooled, causing its crust to wrinkle and break into huge thrust faults. Some of these scarps are hundreds of kilometres long and up to about 3 km high.
The Full Story
Mercury has a very large iron core and a comparatively thin rocky shell, so as the planet cooled over billions of years, its interior contracted. That contraction forced the crust to compress and buckle, creating long cliffs called scarps. NASA's MESSENGER mission showed that some scarps are enormous, stretching for hundreds of kilometres across the surface. The planet is still thought to be shrinking slightly today, although the biggest deformation happened long ago. These features are one of the clearest signs that Mercury is geologically different from Earth and the Moon.
Key Facts
YouTube Angle
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"Mercury is literally crumpling like a giant cooling ball!"
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