Mars famously has the largest volcanoes known to science. The largest is Olympus Mons, pictured above, which towers 22km above the surrounding plains – over two and a half times taller than Mount Everest. This extinct volcano is 640km wide even at its narrowest point, greater than the distance between London and Glasgow, or Los Angeles and San Francisco. And Olympus Mons isn’t alone in the Earth-beating stakes – three other Martian volcanoes are more than 10km high.