Europa: The Key to colonizing Mars, Neptune and Uranus.
According to NASA, the Jupiter's Moon Europa is believed to be covered in about 100km layer of liquid water and water ice. I have taken the liberty of calculating the volume of this much water.
2.901*10^9 km^3 of water!
2.901*10^21 liters (or kilograms) of water
1.6117*10^23 Mol of Water
or the equivalent of
1.6117*10^23 Mol of H2 gas plus 8.053*10^22 Mol of O2 gas.
In fact, according to my calculations, there is more than enough water on Europa to use for terraforming Mars, as well as providing all the liquid water needed for the biospheres I will shortly discuss for Neptune and Uranus (several millenia from now). Some of this water can also be used to create rocket fuel and also for Nuclear fusion. The oxygen will be used in the biosphere on mars and eventually both Neptune and Uranus.
From Wikipedia Fusion article
Fusion power commonly proposes the use of deuterium, an isotope of hydrogen, as fuel and in many current designs also use lithium. Assuming a fusion energy output equal to the 1995 global output of about 100 EJ/yr (= 1 x 1020 J/yr) and that this does not increase in the future, then the known current lithium reserves would last 3000 years, lithium from sea water would last 60 million years, and a more complicated fusion process using only deuterium from sea water would have fuel for 150 billion years
Actually Terraforming Mars (Sort of).
Earth's moon does not make a good candidate for terraforming nor long term living, because its surface gravity is far too low to be of long term habitation. Additionally, there simply aren't any available "human needs" resources on the Moon as far as we know from current knowledge.
Notice, all "buildings" and "transportation mechanisms" discussed here are designed in a way that they are "air tight", unless otherwise specified. WE don't want to waste any energy, and the atmosphere of mars is mostly CO2, which we will eventually harvest for usage in our biodomes (archologies) to feed to plants in the artificial biosphere.
Essentially, we are encasing the entire surface of the planet in a shell of metals, glasses and polycarbonates. Most of the materials for this project come from the planet itself and the asteroids and minor moons. This is done so that our precious oxygen cannot escape, and because the way I have imagined to do this, it becomes a natural consequence of the most efficient construction process and civilization development anyway.
Because the surface gravities and escape velocities of Mars, Europa, and the various minor moons and dwarf planets are so low, this means we can very, very easily move enormous payloads from planet to planet or moon to moon (except in the case of earth). In fact, based on my estimates, launching a spacecraft from the surface of Europa requires only about 2.43% as much total energy as launching the exact same spacecraft from the surface of the earth. In other words, a rocket system with the same total energy of the existing space shuttle could launch a ship and payload 41.15 times as massive from the surface of Europa using the same amount of fuel.
Launching the same craft (with different, but equal mass payload) from the surface of mars requires approximately 16.9% as much energy as launching it from earth.
This means that it would be possible to construct massively efficient transport mechanisms between Mars and Europa. The scientists now tell us that Mars has some usable water trapped in its poles which could be used for drinking and also for fusion. however, this is a really small scale operation by comparison of what I am going to suggest.
Europa has about enough water to completely cover the entire surface of Mars to a depth of about 12.5km! We do not need ANYWHERE near that much water on mars. We don't need oceans that support 10,000,000 species of obscure creatures. We don't need, or even want, obscenely deep ocean trenches. We want manageable artificial oceans, whether freshwater or salted, which can be farmed as needed and complement a stable biosphere. These "artificial oceans" are contained in air tight arcology structures, and the primary energy source which powers this biosphere is nuclear fusion, with solar radiation coming in a distant second.
We need man made oceans in biodomes and archologies which support algaes, plankton, and the fish that feed on these, as well as edible "bottom feeders" such as oysters, etc. Along with the land based crops grown in biodomes during the early epochs of the martian colonies, these man made oceans would serve our needs well, coverting CO2 and other less useful materials efficiently into food supplies and oxygen for us. Electricity from Fusion powers lamps which provide the energy for these oceans, in addition to pumping in the water carrying "waste heat" from the fusion reactions. Thus maintaining survivable temperatures for the entire artificial ecosystem. Eventually the artificial oceans fill up the entire basement level and several other levels of the megastructure. This is one possibility anyway. The power from the sun is converted to electricity and ambient heat through solar cells or other process. The power from fusion however, is the primary source of energy which powers this artificial biosphere.
Because Mars is so far away, it recieves only about 43% as much sunlight per square meter as the earth does. This is the second to last planet that receives enough sunlight to even be worth mentioning, with Jupiter receiving about 1/27 as much sunlight per square meter as the earth. Now, this means that the sun alone cannot provide enough energy to sustain "normal" earth-like life on Mars. This is not really a problem, however. With all that hydrogen from Europa, we can use fusion to provide ambient heat, light, and electricity to our civilization, and indeed, the entire biosphere. Hydrogen fusion eventually leads to the production of carbon, nitrogen, oxygen, and even iron. These are all good things as they are used to feed the biosphere or to build structures.
In the special case of Mars, because it is a terrestrial planet, we will build a ring on the surface of the planet starting at the poles and wrapping around perpendicular to the equator. (we need to blast away any mountain ranges in the way, and fill in any valleys. But since we need billions of tons of metals and agregates anyway from the construction of this megastructure, we would need to do that anyway.
The reason we want to build the polar ring first on mars is because the water appears to be most concentrated on the poles. With this ring filled with pipes and with all the living quarters, we can mass transport materials, namely water, hydrogen, oxygen, nitrogen, carbon dioxide and other liquids and gases through sorted piping networks with almost no net energy cost. With forward thinking, a series of valves and T's are installed in the most likely places ahead of time(i.e. where each ring intersects another right, as well as equidistantly along those rings, say every kilometer or ten), so that future projects already have their infrastructure laid out for them. (Unlike the U.S. government, anyone embarking on this project would actually give a damn about future generations.)
Because we need not be concerned with established "traditional" city, suburb, urban structure (or lack thereof) as on earth, we can start with an "ideal" organized layout of transport mechanisms for the surface of Mars. The second ring is installed on the same plane as the martian equator, perpendicular to the first, and the third ring is another polar ring perpendicular to both rings one and two.
The equatorial ring is designed such that its transport mechanisms pass over the top of the other two. Each ring will use some sort of mass transport such as monorails or maglev as follows. There are about 2/3 of the tracks in the center of this massive transport mechanism, used for transporting solid goods and people(as stated, liquids and gases are simply piped around the planet as needed). One third of the total tracks on the equatorial ring move only to the east. The other 1/3 move only to the west. The remaining 1/3 of the tracks have the ability to turn onto the polar rings tracks going north or south, eventually reaching the junctions at the poles and turning back. Essentially, trains only move in one direction, because they either circle the entire globe, or else circle one half of one quadrant of the globe. Further, we could add two more smaller rings parrallel to the equator, but roughly half way to the poles, but behaving the same way as the one at the equator.
A computer knows where each compartment of a train/maglev/whatever needs to stop, thus moving the train (preferabily some sort of planetary scale magnetic ring shapped sled) only as needed. In this way materials at the equator are transported with almost no net energy cost. The computer program would know based on a human entering in the cargo start point and its destination when and where to stop the rotation for each destination. This is technology similar to what Amazon.com currently uses in its warehouses, only this would be on a global "megastructure" scale.
Homes, farms, factories, and other businesses and industries are built in Archology structures, along with farms and artificial oceans. Most jobs in this civilization, especially during the first several centuries, would be related to farming or construction of the polar and equatorial rings. Once these structures are in place, population of the planet in archologies built along and outward from this rings, filling in the 8 major zones between them, would be incredibly easy and efficient. The top floor of all buildings covered in solar panels.
Due to the low surface gravity of Mars, it would be possible to construct buildings as much as 3-5km tall or more, which can eventually house hundreds and hundreds of thousands of people per square kilometer of land area. It is much more cost effective and energy efficient to build structures that are more cubicle as opposed to flat or sky scrapers, particularly when everything should be absolutely "air tight". Thus we might consider a building which is 3km*3km*3km in size, having a footprint of 9km^2 and a volume of 27km^3. These would be constructed in a modular fashion along the rings as human needs demand, with further individual modular transport mechanisms which tie into the primary ring structures. Eventually the entire surface of mars would be covered in these.
Thus we "terraform" mars, but not in the science fiction manner, but rather in a realistic manner. When we need oxygen, simply suck the CO2 out of the atmosphere and feed it to plants and algae, trapping the Oxygen INSIDE the megastructure, which coats the entire surface of mars (eventually). Most of the building materials for this structure come from Mars itself, or else from teh martian moons and the asteroids.
Between Earth, Mars, Europa, and the asteroids, dwarf planets, and minor moons, this stage of civilization could support theoretically upwards of 25-50 billion human beings. About 12 billion on earth, and about another 12-25 billion or more on mars, easily (see below).
The reason mars could possibly support more life than earth, even given our current technologies, is because of the lower gravity. Mar's gravity is high enough to actually be "human friendly," but low enough for the constructure of truly mega mega structures. Everything, organic and non-organic, would work far more efficiently, and you could just build bigger, better, safer more efficient structures. One advantage Mars has over the Earth's moon is the fact that it already has a huge amount of oxygen, water, and other organic compounds and elements on the planet in one form or another.
A 3km high building might have 600 - 1000 floors. A 1km high building might have 200-333 floors. Imagine if the entire surface of the planet were covered in these modularly over centuries or millenia (essentially 200-1000 concentric spheres). Though it may not actually be possible to establish a stable artificial ecosystem that massive, nevertheless, the human population that could potentially live here even with existing technologies, in equilibrium wiht a biosphere of plants and animals populated from earth, (plus fusion,) is certainly in the tens of billions.
Remember, there is literally about a couple hundred times as much water as this civilization will ever need sitting in Europa.
Techniques and technologies developed during this phase of human civilization would come in quite useful during the next phase.
If only I could draw a diagram of what I have in mind for Mars, but I don't know of any CAD software that supports and adequate scale, and there is nothing I know of other than video game development software that supports drawing the 3d the way I'd need to do anyway.