Mars hosts Olympus Mons, the tallest volcano in the Solar System

Olympus Mons is the largest known volcano in the Solar System, a colossal shield volcano on Mars that towers roughly 22 kilometres above the surrounding plains, with an outer cliff that climbs as much as 10 kilometres on its own. Stack that against Mount Everest, which reaches about 8.8 kilometres above sea level, and Olympus Mons stands roughly three times taller. Its base sprawls some 600 kilometres across, wide enough to blanket an entire country.

The secret to its scale is geology Earth lacks. Our planet’s crust is broken into plates that creep over hot spots in the mantle, so a single hot spot produces a chain of modest volcanoes rather than one giant, much as the Hawaiian islands trail across the Pacific.

Mars has no such conveyor belt. Its crust sits still over a fixed plume of rising magma, so lava piled up in the same spot for hundreds of millions of years, building a mountain to a height that would be impossible on a tectonically restless world like ours.