The closest planet to the sun has a mass comparable to Luna but is a great deal denser due to its iron-nickel core. Mercury rotates slowly and has no atmosphere, so that its day side is hot enough to melt most metals, while its night side is bitterly cold. Because it lacks many of the elements needed for transhuman colonies to be self-sufficient, Mercury is sparsely inhabited, save for a handful of solar power relays, a few underground mining stations, and a single large surface mining concern, Cannon.

Most of Mercury’s economy is based on mining. Iron, nickel, and other metals make up 70% of the planet’s mass, making it the richest source of ferrous metals outside of the asteroids. Mercury also does a brisk business in relaying solar power and serves as a jumping-off point for solar research concerns unwilling or unable to support stations in the solar corona. Mercury has limited helium-3 deposits, although these are predominantly mined for local use. It is an open secret that several powers have antimatter production stations here. Officially, these stations are massive solar power relays, but the immense toroid particle accelerators and large spherical magnetic containment units required for antimatter production and storage are nearly impossible to disguise.