Picture a 40 hour nonstop drive from New York to California along the edge of a single cliff whose bottom disappears into haze. That is the scale of Valles Marineris, the Martian canyon system over 4,000 kilometers long, 200 kilometers wide and up to seven kilometers deep, stretching across nearly a quarter of the planet's circumference. This episode recounts its 1971 discovery by Mariner 9 as a global dust storm cleared, then explains the leading theory: a tectonic rift fault created when magma upwelling and the enormous weight of the Tharsis volcanic plateau overloaded a stagnant lid crust that, unlike Earth's, has no plate tectonics to relieve the stress.

The hosts tour the canyon west to east. Noctis Labyrinthus, the labyrinth of the night, formed by downward block faulting and is now an astrobiology target after the 2024 identification ...