Asteroid belts
Asteroid Belts, also known as Asteroid Fields, are bands of asteroids which encircle a star, often where a planet would normally have formed. Asteroids are rocks floating in space and while significantly larger than a human being, they're usually too small to land a ship on. Asteroid fields are collars of giant rocks, if you will, that circle the stars.
Origin
Asteroid belts have a number of possible origins. Generally, a planet failed to coalesce during the formation of its star system, usually because of gravitational forces from a nearby gas giant, or because of the disruptive influence of multiple stars (Belts are for this reason far more common in systems with multiple suns than in one star systems).
Much more rarely, a planet has been torn apart by tidal forces, leaving a path of scattered debris. There are also a few instances where planet killer weapons were used to destroy a world, turning it into a belt of asteroids.
Uses
Mining
Asteroid belts are often seen by galactic governments as a sought-after resource. Many asteroids, most particularly nickel-iron rocks, contain varying amounts of minerals: platinum, iridium, and sometimes radioactives, while carbonaceous chondrites are prized for being a rich source of volatiles. More exotic substances such as dragonium and fullerenes can also be located in some rarer types of asteroid fields.
Because of their small and easily manageable size, individual asteroids are very valuable. They have no gravity wells, making it relatively easy to move materials to habitat constructions in orbit. Even a small asteroid of a few hundred meters diameter can contain bllions of tons of raw material. For this reason, individual prospectors are willing to gamble life-savings against the cost of relativistic transport, mining rights, and so on, and quite a few do make it rich.
In addition to straightforward strip-mining, nanotechnological recycling can also be used on asteroid bodies, turning their entire mass into base elements suitable for the production of programmable nanomatter.
Colonization and space travel
Somewhat rarer is the use of asteroids in creating space habitats by hollowing them out or establishing biodomes on their surfaces. Generally, only the largest of asteroids are considered suitable for colonization; smaller ones are often simply not worth the effort.
In some rare occasions, eccentric shipbuilders have even turned entire asteroids into starships, equipping them with propulsion systems. Similarly, asteroids have been used as weapons when used as projectiles for mass drivers.
Scanning an asteroid field is usually done to find interesting asteroids within the field and may result in finding an asteroid with high amounts of a mineral or large asteroids that can be used to land a ship on. Sometimes small planets are hidden inside asteroid fields and will be discovered by scanning the field.
Trying to land in an asteroid field is only meaningful, if you have discovered an asteroid large enough to land on trough prior scans. Warning, spacepirates are known to use asteroid fields to evade sensors and ambush unprepared ships.
