Colonization of a planet or moon reaches a maturity stage at a certain point. This is the point where population stops increasing fast and when most of the land is owned. Depending on various conditions, this phase might last a few Earth years or centuries. Then, economy, population and biosphere parameters can enter a decline phase, from where, a planet can be recovered to a second life or can enter a terminal decline phase.
Advanced Planetary Colonization can be detected by the following parameters:
- Population is increasing fast.
- The economy is growing fast.
- A significant development of infrastructure is visible.
- Taxes are low, to facilitate colonization and economical growth.
Planetary colonization at apogee can be detected by the following parameters:
- Population is not changing fast and is close to the Population Limit.
- The economy is not growing fast, but it is not pushed into recession.
- There are no or only few global infrastructure projects, but there is investment in small, local projects.
- Taxes are higher, but they don't destroy the economy.
Planetary Colonization Decline can be detected by the following parameters:
- Population is decreasing and is aging.
- The economy has entered in recession.
- There are environmental problems.
- Sometimes, taxes are high or debts are increasing.
The population limit is strongly connected to the Solar Constant (the amount of energy received by a planet or moon from its sun) and the visual constant (the amount of visible light that reaches the planet).
Population limit Edit
In case of an Inner Planet, population limit is inverse proportional to the solar constant. Mercury will support less people per square km then Venus. This is because Anti Greenhouse Technology is very important to avoid sending such a planet on a runaway greenhouse effect. Too many people means too much human activity, which can affect protective layers of Micro Helium Balloons, Anti Greenhouse Gasses or other technologies used to shield the planet.
In case of an limit is directly proportional to the solar constant. With less light, plants will produce less food and oxygen. Also, air currents will be slower. Human activities produce heat and heat produces vertical currents that can create a hole in the layer of Greenhouse Gases, which will automatically send the planet to an ice age. This is why, on an outer planet, not only population limit is lower, but also population density must be lower. Large cities cannot exist.
In case of an Earth - like planet, population density can be similar to Earth. However, population limit for Earth should be around 5 billion people and not 7.5 as we are in 2017. Human pressure on Earth's ecosystems is too much.
Limits for largest cities Edit
As shown above, in case of an outer planet, population density cannot be too high. For a terraformed moon of Uranus and for Triton, towns with 10000 inhabitants will be the maximum which can be tolerated. Again, in case of very close inner planets, large cities cannot exist.
In places where population density is restricted, large cities cannot exist. We could see a city with one million people, lasting over 100 km from one end to the other, composed of houses (and no sky-scrappers), separated by forests and farm land. In order to make such a city work, we will need very fast transport routes. One good way will be a metro system, with very small automated trains. These trains will carry up to 16 passengers and will detach every 15 minutes, traveling with an average 300 km/h. In such a city, many activities will be done online or in the virtual reality. School will be held like this. Much office work will be done from home, using an interactive screen. Also, there will be no need to go shopping. Goods, ordered online, will be delivered with special vehicles that will use the metro rail network. Then, from the last station, drones will take all the goods and deliver them to the final clients.
There are planets that can support large cities. For Earth, which has the best solar constant, it is questionable how large can a city be. We have cities with 30 million people, but at that size, there are major problems. Pollution is the main problem. However, even if we will use no fossil fuel, a large city, with 100 million inhabitants, will be too large for nature to support. In summer, heat from buildings and cooling devices, together with heat produced by human bodies, will alter air currents. In winter, there is more heat, as we need to warm our homes. And if we only account for the carbon dioxide produced by 100 million breathing people, this simply is too much for nature to handle on a local scale. On the other hand, the infrastructure needed to handle so many people is huge and simply cannot exist. No matter how many subway lines we build, no matter how many underground or above ground highways are created, at some point, there will simply be not enough rooms. Buildings will not support so much weight.
At some point, there is a limit, which can be passed only by building large cities in outer space.
Agriculture limit Edit
Today, Eastern China, India and Bangladesh are too populated, with a density over 400 people per square km. Farm land is used at maximum efficiency. The problem is that land cannot feed so many people for too long. We see massive droughts in India, desertification in Northern China and many other warnings that nature is starting to fail supporting so many people. Some people warn that China and India might face a future famine.
Shipping food from a planet to another is not feasible, because food has a large weight and low cost. Together with food, oxygen must be shipped. Then, carbon dioxide and excrements have to be transported back, to produce food. So, at least for a few centuries, each planet will have to produce its own food.
Each region of a planet has a different food productivity. Also, we cannot transform all land into agriculture land. We must keep some wilderness in place, if we don't want to alter climate and wildlife.
Population structure Edit
The population consists of people of all ages, in a equilibrium. There are children, adults and elders. We can see a number of immigrants, but they don't account for a significant part of the population. Also, we can see emigrants.
The economy of a planet living at its apogee in development is stable, without major increases and decreases. The planet is self-sufficient, producing what it needs, importing and exporting. Imports and exports balance each other.
Unlike a planet during advanced colonization phase, state money comes from taxes, which are higher, but not too high. There is not much land left to sale or if there is, there are not many interested clients.
Population age structure is in equilibrium, which means there will be money allocated for schools, for hospitals and for elders. But as long as the economy is working, this will not be a problem.
State investments Edit
At this point, the state needs to maintain the planet. Maintaining a terrafomed world requires some activities, like replenishing the atmosphere and the oceans, diverting asteroids and keeping an eye on the biosphere.
This is the point where the state should focus on expanding. The planet cannot support a population increase, the economy is mature and is growing slowly (if at all) and the only way to progress is to terraform another planet.
Maybe, at that point, there will be an international convention that each state will divert 1% of its internal product for terraforming other worlds or that some planets will try to terraform other worlds, to increase their power. Nobody knows this for now. What is for sure, is that as Cartagena, a Phoenician colony, started to make its own colonies, space colonization will not stop at the borders of the Solar System.