Mars

Mars is the fourth planet of the Solar System and the world where Pierce Brown's Red Rising saga opens. Under the rule of the color-coded Society, it serves as the chief source of helium-3, mined by Reds who live and die in subterranean colonies such as Lykos, taught that their labor is preparing the planet for the generations to come. Above them the surface has long since been terraformed, green with forests and cropland, crossed by seas, and studded with a thousand cities that answer to the Golds.

The planet's dry land is divided among continents named Cimmeria, Apollonia, Sirenia, and Arabia Terra, with the capital, Agea, set in the vast canyon of the Valles Marineris. Its climate is temperate away from the storm-wracked poles, its day is nearly the same length as Earth's, and its wildlife, from haemanthus blossoms to the pitvipers of the tunnels, was seeded by the terraformers.