When Mariner 9 reached Mars in 1971, a global dust storm had hidden the entire planet. As the dust settled, a few peaks poked through the clouds, and scientists realized they were looking at volcanoes so tall their summits pierced a planet-wide storm. One of them, once named Nix Olympica by 19th-century astronomers, was confirmed as Olympus Mons, the largest planetary mountain in the solar system. This episode is dedicated to understanding its almost comical scale.

We cover the numbers: up to 26 kilometers high, about 600 kilometers across, a base that would cover Italy, a summit pressure of just 72 pascals, and a slope so gradual that an astronaut on its flank could not see the top or the bottom because of the planet's curvature. We explain why Mars, without mobile tectonic plates and with a 70-kilometer-thick lithosphere and lower gravity ...