The solar asteroid belt, typically shortened to the Sol Belt or simply the Belt, is an orbital band between Mars and Jupiter in the Sol system filled with leftover protoplanetary debris. Roughly half of the Belt's mass (just 4% the mass of Luna) is contained in the four largest asteroids: Ceres, Vesta, Pallas, and Hygiea. The Belt is an industrial hub for humans, as well as the location of the Solar System Defense Complex, the ark asteroid Apophis, and the Belt capital Proserpina on the dwarf planet Ceres. Belt colonies are common stopovers for flights between the inner and outer system, though smaller debris can present a serious travel hazard.
The Belt is composed of some 2 million asteroids, both rocky and metallic, which orbit Sol approximately between 2 and 6 astronomical units (AU). Due to orbital resonances with Jupiter and Mars, there are large gaps in asteroid orbital distribution, funneling the vast majority of Belt objects to the "main belt" between 2.06 and 3.27 AU. Most bodies in this region have roughly circular orbits more or less within the ecliptic plane of the system, but some (such as Pallas) have unusually high orbital inclinations that make accessing them difficult and planning-intensive. However, most of the largest objects have some form of human presence. Major settlements can be found on the following Sol Belt objects:
- Apophis, a self-contained ark asteroid that regularly passes close to Earth
- Vesta, one of the major orbital manufacturing centers of the system
- Ceres, the largest body in the Belt and, functionally, its capital settlement
- Pallas, a large object isolated from the main belt due to its high inclination
The Belt was settled over the course of a few centuries by humans
, the native inhabitants of the Sol system. However, over generations, humans living on and in the asteroids of the belt have adapted fairly well to their unusual environments.
Thanks to the extremely low gravity of belt objects, "Belters" (the umbrella term for the humans of the Belt) have become leaner and more gracile than planetbound humans, with increased dexterity and flexibility. Curiously, in a few populations some fine motor control has reemerged in the feet. Belters are typically very pale, with dark eyes to absorb as much light as possible. This has lent them the unfortunate nickname "morlocks," in reference to H.G. Wells' The Time Machine
The exact physiology of a Belter depends largely on which population they hail from. Cereans are by far the stockiest of the Belter groups, and have the least trouble adjusting to planetary life. Vestans and Palladians are very similar to each other, but Palladians tend to have darker skin than most other Belters and are one of the rare clans which have minor manipulative ability in the feet. Physiologically, Vestans are simply lankier Cereans, since the two gene pools tend to overlap.
Apophese and Erosian Belters, by contrast, are nearly indistinguishable from planetbound humans, as their respective homeworlds have been converted to self-contained arks with centrifugal pseudogravity that closely mirrors that of Earth. This allows ark-dwelling Belters to travel around known space without having to worry about the effects of higher gravity and increased sunlight on their physiology.
The settlement of the Belt was a very patchwork affair, accomplished over several centuries by an assortment of organizations for a few key reasons.
First and foremost, naturally, was the obvious motivation: resources
. With so much raw material floating haphazardly between Mars and Jupiter, its inevitable exploitation had been looming more or less since the dawn of interplanetary human spaceflight. Mining is still the primary industry of the Belt, and likely will be until its trove is exhausted.
Secondarily, however, was the (perhaps moderately paranoid) desire for protected redundancy. 99942 Apophis, the first celestial object to be hollowed out and "arked," was reshaped and colonized as a sort of "doomsday vault" for terrestrial life, though it is far too small to be an effective emergency backup sample of Earth's biodiversity.
When permanent human presence spread to the outer system, it became apparent that interplanetary transit between the inner and outer system would be considerably more efficient if the long-haul vessels stopped at Belt settlements to refuel and replenish their supplies, causing a boom in the Belt's resource exportation.