Curiosity 9 of 10
9. Mars has the largest known volcano in the Solar System
Olympus Mons, on Mars, is about 22 kilometers tall, nearly two and a half times the height of Everest. Its base is about 600 kilometers wide, an area almost the size of Italy.
Why Mars's volcanoes grow so big
Olympus Mons is a shield volcano, with gentle slopes, formed by lava that flowed for a very long time. It is so wide that someone at the top would not see its edges: they would be hidden beyond the planet's horizon.
Mars has no tectonic plates that move as on Earth. Here, the plate slides over a hot spot in the mantle and forms a line of volcanoes, as in Hawaii. There, the crust stays still over the same magma source, and the lava always piles up in the same place.
Mars's weaker gravity, about 38% of Earth's, also helps. Heavier mountains can hold themselves up without collapsing under their own weight, and the volcano can grow much larger than it could here.
The planet also has Valles Marineris, a canyon system more than 4,000 kilometers long and up to 7 kilometers deep. If it were on Earth, it would stretch from one coast of the United States to the other.
Did you know? On Mars, the sunset is blue. The fine dust in the Martian atmosphere scatters light in a way that gives the region around the Sun a blue tint, the opposite of what happens on Earth.
