Global Paraterraforming is the only way to transform an asteroid into an Earth-like paradise. The system has some major advantages, including small costs and a full control of the environment. Major disadvantage is that the system is exposed to meteor impacts.
In the following, two models are displayed, both are proposed for asteroid Vesta.
High altitude paraterraforming
In this model, an elastic and transparent shield is built at an average height of 10 km above surface.
Shield details
The shield can be made of various materials, from glass to plastic. Major problem is that it will be exposed to extreme temperatures, from values close to zero Celsius during day and down to below -200 C in night. Temperature fluctuations influence elasticity. If the shield is rigid, it will be exposed to fissures, because as temperature varies, dilatation occurs. We can see this on Earth, where railway rails are separated into pieces of about 30 meters long. If they were a single piece, dilatation during summer will make them leave the tracks. More elastic rails can be longer. One more expensive version is to add some heating devices inside the shield, to protect it against extreme cold in night time. The shield must have an ultraviolet protective layer, combined with another layer to reflect solar wind and other kinds of radiation.
Atmospheric pressure will tend to blow the shield into outer space. In order to keep it at the required height, another force is needed, to push it back. One idea is to anchor the shield to the ground, with strong cables and elastic towers. The other idea is to add weight suspended to the shield, like chunks of rock. Perhaps the best solution is to use both techniques.
A water shield is different. It is known that a layer of 10 meters of water can absorb almost all ultraviolet, X and gamma radiations and can slow even the solar wind. In order to keep water liquid at low temperatures, something must be added in it, like glycol. For paraterraforming Vesta, this will be good, because water will generate some greenhouse effect, increasing temperature. Also, since water accumulates temperature during day, the shield will survive more easy during night.
Compartimentation
Major thread for paraterraformed worlds are meteor impacts. They will make holes in the shield. A special response unit is needed, to immediately close any hole that is formed. In case of a water shield, the water layer will slow a bit the meteor, maybe just enough to stop it from falling below the shield. In order to limit the risk, it is good to create elastic walls that will separate asteroid surface into parcels. By controlling greenhouse effect in each parcel, we will generate different climates.
If the held atmosphere is not compartmented, the climate will be interesting. Air will circle around. Asteroids have shorter day-night cycles, so that temperature variations will not be so long. Also, since their size is low, air will migrate more easy between equator and poles. The result will be a more undifferentiated climate then what is on Earth. Assuming that half of the surface is covered with water, there will be no deserts, because moistured air will not have enough time to lose all its water as it circles around.
One interesting way of compartmentation is the slice model. In this scenario, each compartment stretches from pole to pole, just the slices of an orange. Each parcel hosts a central warm zone and two cold polar regions. In this model, hot air will rise and move to the poles, where it cools. Air will circulate and rain will fall. This is the closer an asteroid can get to Earth.
Another model of compartmentation is the square model. In case of Vesta, we can imagine this moon separated by walls along parallels and meridians. Each one will have its own climate. The major advantage is that, depending on the amount of greenhouse gas used, you can create any climatic model you want. The major problem is that air will not circulate like on Earth. In this model, each parcel will tend to increase humidity. We will have fog instead of rain. In order for rain to be generated, air must first achieve moisture, then it needs to cool. Artificial temperature changes can be made possible, by manipulating greenhouse effect. Also, flexible doors can allow air to circle between compartments.
Low altitude paraterraforming
This model is much cheaper, but it will create a greenhouse and not an Earth-like paradise.
The shield
In this case, the shield is located at low altitude, between 20 and 100 meters above ground. It can be even at 5 meters above in some places. It will be cheaper to build. The shield can be connected to the ground by shorter and smaller cables, but in higher number. And because there will be more cables, distance between them will be smaller and tensions inside the shield will also be small.
Since atmosphere will be thinner, the shield must create a stronger greenhouse effect. If you enter a greenhouse on Earth, you will notice that, during day, temperature increases, but dramatically falls during night, close to the external environment. We cannot allow temperatures to drop to -200 C.
A major problem is that the shield will be threatened from above (by meteors), but also from below. On Vesta, gravity is 3% of that on Earth. If someone is playing tennis and throws the ball up, it will go for kilometers! For sure, it will hit the shield. Even birds, flying fast, will collide into the shield. We know them sometimes crashing into windows. So, in places with risk, like terrains for sports, kids playing areas and others, the shield must be strengthen. There will be many dangers.
Internal side of the shield will need permanent cleanup. Each time temperature (of the shield or of the environment) changes, there will be a risk that water condensates. Drops of water on the shield will attract algae and bacteria. Later, lichens will find this a good place to grow. In time, this will block part of the sunlight.
Compartments
Compartmentation is vital for this kind of world. Even if the shield covers entire asteroid, air will not circulate easy. There will be required many walls, splitting land into small parcels. Each one will be created for a specified destination.
Many, if not majority of compartments, will be designed for agriculture. They will produce all food needed for settlers. Other, smaller ones, will host towns. It is possible that settlers will want some places to be parks for recreation. If they want meat, they will need to grow also animals somewhere. Finally, some places will be left for maintenance purposes, for hosting air, water and minerals required.
Very important is the air circulation. Left alone, each compartment will increase humidity up to high levels, will face population explosions of various species, will face different concentrations of carbon dioxide and will encounter abnormal air ionization. The air circulation facility needs to be connected to all adjacent compartments. There, air is cooled, to extract excess humidity and to replenish water. Air is mixed between compartments. Tests are constantly running, to detect presence of ammonia, sulfur dioxide and other dangerous gasses.
Special care must be taken with fire, mainly if the shield is flammable. A quick response fire department is needed.
Air entering compartments will need to be ionized.
Living on a paraterraformed asteroid
In case of a high altitude shield, settlers will have the feeling that they are on a planet. There will be two major differences. First of all, they will see on the sky structure details of the shield. Second, because asteroids are small, they will see the horizon far closer then on Earth. In case of a low altitude shield, it will be like living in a greenhouse and walking through gardens. You will always see the roof instead of a sky.
Nature will look completely different from what we see on Earth. First thing to see is that water drops are growing a lot larger and are falling much slower. On a pond, waves are also moving a lot slower and will tend to be larger. An artificial river will flow so slowly, that it might get confused with a lake. Water will be always in slow motion. However, there is one thing else with water and that is superficial tension. On Earth, if you put water into a glass, you see that water is rising a few millimeters on the glass wall, above the average level in the glass. The glass itself is attracting water, while Earth gravity is working against this attraction. Well, in case of Vesta, where gravity is 3% of that on Earth, there will be less gravity to counter superficial tension. Water will climb 35 times higher, rising to 100 mm instead of 3, as it does on Earth. This means that water will slowly move out of a glass. Also, because superficial tension brings underground water closer to the surface, the ground will always be wet.
Plants will require only a limited amount of strength in order to grow. They will be extremely fragile for Earth, but strong enough for the world where they live. Less need for stronger branches means more resources for growing and food generation. For animals, things will be completely different. Suppose you can jump two meters on Earth. On Vesta, you will be able to jump over 2000 meters! What does this mean? It means that you have to be very careful while moving, or you will get in (or above) trees. Walking will be useless, even jumping will be. So, the best way to move around will be flying and pushing/pulling nearby objects. Humans will adapt fast to this. But animals? Let's see:
- Birds are made for flying, only that on Earth, they push the air down, to keep themselves up. Here, they will need to push the air behind and less down. Wings will need a different movement. The same is for insects.
- Ground insects are moving by climbing. They are always in contact with ground and on Earth, they easily climb trees. No problem for them on Vesta.
- Rodents are also able to move on various terrains and to climb. They will find it more easy in low gravity and maybe they will be able to move on the roof.
- Fish will still swim in water, but will need to be careful close to the surface. Their moves will generate waves. Also, if they try to jump to the surface, they might end-up in (or above) trees.
- Dogs and cats will find this world interesting. Cats will have the advantage of claws. In case of dogs, things are a bit different, but in low gravity they will be able to hang on everything. Walking will be useless and jumping risky. When they will first arrive, they will most often go above tree tops and will make desperate convulsive movements trying to reach the ground again. Then, they will learn how to move in here. They will be able even to swim in the air, moving their feet as they would move while swimming.
- Horses and cows will face major problems, because their muscles and joints are made for walking on ground. They don't have claws or fingers to grab something with them. They are unable to turn their body around, like humans, dogs and cats do. I don't think they will be able to adapt in this environment. The same is with pigs. Soon after insertion, pigs will literally fly in all directions.
- Rabbits will have a chance, since they are smaller, have a greater mobility and have claws. But, don't expect them to stay on the ground for long. They will jump in the trees like squirrels.
Human life
As for humans, the first thing to change is the body. Future races will develop, like the cosmic race.
Every aspect of our life will be different. As shown above, drinking water from a glass will not be a good idea, since water will flow out by superficial tensions. Eating your lunch from a plate will also be strange, because food will move in the air. Sleeping in a bed will be a strange experiment. If you have a nightmare and move fast, you will push yourself out from the bed. These problems are faced by any human community living in a spaceship or a colony with low gravity.
Transportation needs to be based on different principles. Driving a car in low gravity is a tricky job because the vehicle might easy lose contact with the ground. Railway vehicles will be more adapted. They will need to have tiny wheels above and below the track, just like roller-coaster vehicles, to keep contact with the tracks. A global, scheduled and automated transport system is required.
Energy generation is very important for the entire community, for all systems and all compartments. Electricity would be the most easy to transport. On outer space, fossil fuels are not an option, so settlers will have to turn their attention to two major sources: solar panels and nuclear fusion/fission, depending on available resources. In case of a low shield, it is very important to keep energy supply always running. If we use solar panels, they must be placed in different spots all around the asteroid, so that there will always enough panels facing the sun. If we use atomic energy, the power plant must have at least two large generators, so that when the main generator is off-line for maintenance, the second one is running. Maybe three generators should be the best solution. A global network of cables is needed to provide energy to every unit that demands it.
The economy will be divided into two main sectors: internal and external economy.
Internal economy is where many people will get employed. Agriculture is important, since it will provide all the food required for the local population. Every aspect of agriculture is different from what we see on Earth. In a low-gravity environment, preparing the soil will be harder. A tractor will need a thruster (or, more likely, a fan) on its cabin to keep it on the ground. However, in low gravity, plants will need less energy for their strength and will use their resources for growing and to make fruits. So, we expect higher productions then on Earth. Another important task is that we need to give the plants all they need. There must be a biological recycling facility. It will use microbes and worms to transform excrements, waste water and other remaining biological matter into compost and minerals needed for plant life. We must do all what nature is doing on Earth on its own. There is a very strict balance between the amount of carbon dioxide in the air and the carbon fixed in plants. Also, other chemical elements needed for life will be located both in plants (or animals, humans) and in ground, water or air. Keeping the equilibrium is very important. In case of a high altitude shield, the balance is not so delicate, but in case of a low altitude shield, there is only a limited amount of air, ground or water. So, all the maintenance systems need to be correlated to agriculture. All of them need to be under the same department. Transportation and energy generation are also important for the community, but are not so connected to agriculture and maintenance. They can be under a different department.
External economy includes all branches of the economy related to outer world. This is what generates export and manages imports. Industry can be developed on a global paraterraformed body, but will never grow large enough, because of pollution and other risks involved. Bodies with low gravity are good targets for industrial centers, because it will be cheaper to ship the goods out and because many industrial activities are more easy to be made in low gravity. However, a global terraformed body will not have enough empty land for this. Most probably, they will be residential areas, while the industrial centers can be located on nearby asteroids or on a space station. Agriculture can be a better way to make money. Because of the low gravity, it will be more easy to ship food from Vesta then it is from Earth. Shipping food from Vesta to industrial centers within the Asteroid Belt will require less then 1/10 of the fuel needed for the same transport, from Earth. In addition to do this, the asteroid needs to import organic residual waste, to replenish the lost minerals and carbon.
Interplanetary transport needs to be possible. A base has to be built, with platforms for the majority of ship models that will exist at that time. In future, we might even see scheduled interplanetary transport, like today we see for trains and airplanes. A base also requires a powerful computer to guide all traffic and also reserves of all kind of fuel (hydrogen, hydrazine, oxygen, xenon for ion engines, plutonium for atomic engines and other types of fuel).
Demography
A global paraterraformed body will be very attractive for many settlers. I think that people working on nearby industrial centers will like to stay on a body that has some nature around instead of spending all the life in an apartment without any living nature around. They will be targeted by the rich and by medium-class people. Also, since they can produce food, they will be inhabited by people working in space farms.
Population will rise fast and will come quick to a maximum. From that point, the asteroid has two options: become a completely residential place or use an immigration embargo to keep its agriculture alive. Most probably, people will look for an alternative solution, like trying to paraterraform another asteroid.