Main page: Asteroids (theoretical models)
The Kiuper Belt is an area behind the orbit of Neptune. It contains some dwarf planets and a lot of smaller objects. The Kuiper Belt might contain in fact the largest amount of asteroids inside the Solar System.
Asteroids inside the Kuiper Belt are considered to be the blocks of planetary formation, left from the time when Solar System was not finished. However, the asteroids left there have changed since 4 billion years ago. They have been exposed to what little heat reaches them from Sol, by solar and interstellar wind, by meteorite impacts and also by gravity perturbations from planets that still exist or were once exiled from the Solar System by gravitational pull from the remaining planets. It is also possible that some asteroids originated in much hotter areas and were pulled away. There is also a chance that bodies from the further Oort Cloud were perturbed and moved closer to the Sun.
So, in theory, there should be 3 different types of asteroids inside the Kuiper Belt:
- Asteroids with ice and other volatiles (formed there or that moved from the Oort Cloud)
- Icy asteroids (they lost much of their volatiles after a collision who melted them)
- Rocky asteroids (moved from the inner parts of Solar System).
As for now (2016), no space probe has ever visited a Kuiper Belt asteroid. What we know about them comes from the following sources:
- Large Earth-based telescopes and the Hubble can see objects in the Kuiper Belt as tiny dots of light. Spectral analysis can give us an idea about what can be on their surface, if the light is enough for gathering data. What we can know for sure is their rotation period, based on repeated changings in their light curve.
- Majority of comets originate in the Kuiper Belt. Solar heating has affected comets, but we still can make an idea how they looked like before coming close to Sol. For sure, we know their composition.
- Pluto's four tiny moons have been examined by New Horizons.
- Theoretical models suggest that, at temperatures below 60 K, some gasses might be solid, some should slowly sublimate and some should remain captive beneath the surface.
Asteroids inside the Kuiper Belt live in a cold environment. Even if their surface is completely black, temperatures should not reach above 60 K (or -210 degrees Celsius). At these conditions, water ice is solid as a rock. Ammonia and carbon dioxide should also be solid and not sublimate. Other gasses, like methane, carbon monoxide or nitrogen, will sublimate and after millions of years they should be lost in space. If an asteroid moves from the Oort Cloud into the Kuiper Belt, it should slowly lose its volatiles. However, reservoirs of methane and other gasses with low melting point can remain beneath the surface forever, brought there after meteorite impacts or from the time the asteroid was in a colder place.
Solar wind is still present. From time to time, when solar magnetosphere is weak, cosmic radiation can reach the Kuiper Belt very easy. The asteroids are cold and lack of any magnetic field, so that they are completely exposed to ionized particles. This leads to formation of tholins from existing methane, nitrogen and ammonia. However, since methane is expected to sublimate, there should not be high amounts of tholins.
The rotation period is usually around 10 hours. The year should last for 200 to 500 years. In these conditions, if the asteroid has a tilted axis, at one pole we will see day and on the opposite pole a long night, for a longer period then a human lifetime. A base will have tens of years available to slowly change the rotation axis, keeping the illuminated parts of the asteroid towards the Sun.
- Detection of exposed water .
- Detection of organics , including the amino acid glycine
- Detection of argon (one of Earth's noble gasses) 
- Detection of salt (sodium and magnesium) .
- Detection of methane .
- Detection of solid compounds .
- Detection of carbon dioxide .
- Detection of molecular oxygen , showing that the comet formed somewhere where temperatures are cold enough for oxygen to not sublimate.
- Comets have high differences of hydrogen - deuterium ratios and Rosetta's comet is very rich in deuterium .
After all these chemical discoveries, Rosetta has successfully made other analysis. They all give us ideas about what we should find on a Kuiper Belt asteroid:
- Comets appear not to be magnetized .
- Rosetta's comet has no large caverns inside and appears to be homogenous .
- Rosetta's lander, Philae, discovered that the comet is made of solid materials, as hard as rock . The lander could not drill into the ground at its final landing spot. Also, at its first landing spot, it recorded the sound of touchdown, proving that beneath a layer of dust, there is hard, solid ice.
However, the most amazing of all findings on 67/P is stratification . This is something that gives us an idea of how comets are made. 67/P is made of two lobes who slowly collided into one larger body. They are both made of an alternation of strata, each one with a slightly different composition. An interesting discovery happened when a hole appeared in one layer. Below it, the newly exposed layer started to sublimate and after a few weeks it pulled away the previous layer. This proves that the two layers had different chemical composition .
Rosetta's comet was analyzed in high detail, but similarities can be found on other comets. Stratification was proven to exist also on Deep Impact's Tempel 1 [. Also, the impactor that penetrated Tempel 1's surface, showed that the comet is made of solid materials.
Based on all these findings, we can conclude that Kuiper Belt asteroids are usually solid bodies and not piles of rubble. They contain dirty ice with many volatiles inside, but also with salt and solids. They have a homogenous composition (with stratification) and are not magnetized.
Until now, there is no clear theory that can explain stratification. Personally, I suppose that during formation, comets had an elliptical orbit. At aphelion, they entered a cloud of frozen gasses, water ice and dust, while at perihelion, heat from the Sun, reaching -200 C, could affect the surface. This change in temperature made possible for the formation of layers of material. If at some point any better theory appears, please correct me.
Reasons for colonization Edit
Why should someone try to get to Kuiper Belt and settle on an icy asteroid? Well, there are a few reasons.
First of all, some terraforming processes will need water and gasses. As shown on this wiki, terraforming of Luna, Mercury and Venus is not possible without adding extra water and gasses for the atmosphere. As shown above, comets have all the ingredients (but in various proportions) needed to create an atmosphere and an ocean. Smashing all existing comets would not create enough water on the Moon. Also, we need to add water with exactly the same hydrogen-deuterium ratio like the water on Earth. It has been proven that water with less deuterium can increase lifespan  and can be an efficient medicine against cancer . We still don't know how does deuterium interacts with living organisms.
When space pioneers will terraform Venus, Mercury and Moon (and other similar bodies in other solar systems), they will look for suitable Kuiper Belt asteroids, will try to divert their orbits and force them collide with the targeted planet. For doing this, settlers will first have to set bases somewhere inside the Kuiper Belt, with all facilities needed. Later, these bases will remain operational for other settlers.
Industrial colonization will target the Kuiper Belt twice. First, during terraforming era. Then, researchers will look after raw materials. They will look after tholins and other organic compounds. In a world without petroleum, industrial corporations will still need organics for plastic, rubber, medicine and many branches if the industry, from the IT to children toys, from clothes to high tech space probes.
There also will be pioneers willing to break all frontiers and looking for freedom. Setting home in the Kuiper Belt will be a real challenge.
Building a colony Edit
Inside the Kuiper Belt, temperatures are extremely low and there is no way one can survive without a source of energy. The central piece of the colony must be a nuclear generator. In a world where almost everything is made of ices, it will be hard to find uranium to power-up a nuclear generator. An alternative source of energy should be a fusion generator, using hydrogen or deuterium. The colony would not survive without a source of energy, so it should be a good idea to build also a second generator.
Earth plants can survive as far as the orbit of Neptune (see Plants on new worlds for more details), but they only survive and not produce the required food. In Kuiper Belt, you need an extra source of light, to keep them alive. A greenhouse can be built on the surface, close to a pole (to benefit from the endless polar day) or can be created beneath the ground, to be protected from radiation. The colony itself should be built underground, to be protected. The walls protecting the colony have to be impermeable, to avoid any of the gasses trapped inside the ice to enter the inhabited area. Also, the walls must keep all the heat inside and avoid to dissipate it inside the asteroid.
On the surface, there should be a base, with platforms for spaceships and a communication relay system. Using the ice, settlers will replenish the hydrogen and oxygen needed for rocket fuel.
So far from the planets of the Solar System, settlers will find themselves completely on their own. If anything bad happens, no rescue team will reach them in time. Also, because communications travel with the speed of light, they will get all the news with some delay. There will not be something like a live basketball game or TV show. Everything will be seen with hours of delay.
Being so far from Sol, has a major advantage. Sun's gravity is weak. The Earth moves around the Sun with over 30 km/s, while Pluto only moves with a bit over 4 km/s. As a direct result, with only some fuel spent, you can make your spaceship stop relative to the Sun. This will result in going directly towards the inner Solar System. By conducting a Jupiter gravity assist and a controlled Earth aerobreaking, you can send cargo to Earth without spending much fuel. It is far more easy to send cargo from the Kuiper Belt to the inner Solar System then to send from the inner Solar System to Kuiper Belt. However, with current chemical engines and current technology, each transport will require around 10 years.