The Asteroid Belt, often referred to as The Belt, also known as the main asteroid belt (to distinguish it from the farther out Kuiper belt), is a torus-shaped region in the Sol system, located roughly between the orbits of Mars and Jupiter. It consists of numerous smaller and bigger asteroids, and is part of the outer planets region of the system.
The four biggest asteroids of the belt, Ceres, Vesta, Pallas, and Hygiea, contain half of its overall mass. In total, the mass of all objects in the asteroid belt is approx. 4% that of Luna, or roughly twice that of Charon, and is estimated to be around 2.39 × 1021 kg. The size of objects in the belt varies from small rocks up to dwarf planets. The temperatures depend on the distance from the sun and typically range from -73 — -108 °C.
The Belt was colonized by humans roughly in the 2200s, after the invention of the Epstein Drive by the Martian engineer Solomon Epstein. In exchange for their independence, Mars thereafter shared the Epstein-technology with Earth, leading to the exploitation of resources and later to colonization of asteroids and moons in the belt and the outer system by the two superpowers. People born on the colonized asteroids are called Belters.
Driven by "Gold Rush" mentality, humanity spread across the Belt into hundreds of settlements, stations, and ships. Eros was among the first asteroids to be colonized, followed after by Ceres and Vesta. The internal caverns of Eros had been the birthplace of the Belter culture and history. From raw ore to smelting furnace to annealing platform and then into the spines of water haulers and gas harvesters and prospecting ships. Eros had been a port of call in the first generation of humanity’s expansion. The economics of the Belt had then moved on. Ceres Station had spun up with newer docks, more industrial backing, more people. The commerce of shipping moved to Ceres, while Eros remained a center of ship manufacture and repair. Eros would later become a den of crime and violence, often being labeled by as the "murder capital of the Belt."
In 2250, Ceres has become the primary "port city" of the Belt, with most of the Belt's wealth passing through its docks. Water ice from Ceres was slowly stripped and taken by Mars to be used on their terraforming project. On Pallas, the massive refineries the station is now known for begin smelting the ore Belters. All the major moons of Jupiter and Saturn have fully functioning settlements on them. Last of the ice is mined away from Ceres and new sources sought.
In 2300, the Canterbury is no longer needed as a colony ship, and is repurposed by the Pur'n'Kleen Water Company as an ice hauling vessel, and begins scooping ice out of Saturn's rings for distribution to the Belt, and to Mars insatiable appetite for terraforming materials. In 2334, the Anderson Station Massacre occurs, further galvanizing the Belter's ire toward Earth. On Pallas, in 2335, Marco Inaros's militant OPA cell commit a terrorist act by destroying the Augustin Gamarra, a UN science ship with 516 people on board. When Naomi Nagata was young and in love with Marco Inaros, they had a crazy plan. Naomi would hack reactor control programs, while Marco had a way to insert them into Inner ships. Then they could turn off the drive, leave them on the drift, rescue them for a price later, and it wouldn't look like piracy because the affected individuals would be so grateful that they were saved. The first one they tried was the civilian vessel Augustín Gamarra. Marco intentionally used the code to overload the ship's reactor: the ship blew up in the Lovell City docks at Luna, killing 516 innocent people. Today, a memorial for the ship can be found at Lovell City.