Transforming the environment of Titan into something livable for humans presents a new set of challenges when compared to ideas for terraforming Mars. Titan has several qualities--such as a thick atmosphere, an abundance of atmospheric nitrogen, and the presence of water ice--that make it an attractive candidate for human colonization. Furthermore, the atmosphere of Titan could even be oxygenated by using water ices present on the planet or by importing photosynthetic microorganisms. However, Titan’s small size and icy crust will present problems for any future colonists attempting to terraform the planet into a habitable Earth-like condition.
Titan’s surface temperature is about -180 degrees (Celsius) below freezing, which means that a massive increase in the greenhouse effect is required to warm the planet and allow liquid water to form. One way of accomplishing this would be to place giant mirrors or lenses in space around Titan that would focus the Sun’s energy and increase the total amount of sunlight reaching the surface. This would likely cause massive alterations to the global climate patterns on Titan from those observed today. Another option would be to increase Titan’s greenhouse effect by releasing chlorofluorocarbons, ammonia, carbon dioxide, water vapor, or additional methane into the atmosphere. Achieving this large of an increase in surface temperature is a daunting task, and a very large volume of greenhouse gas, or a large array of mirrors, would be required to bring Titan’s surface temperature above freezing.
If this artificial increase in surface temperature were to happen, then future colonists would face another problem: Titan’s crust is completely frozen and would completely melt into oceans. Titan today shows a solid surface, mostly composed of methane and ethane ices, with water perhaps underneath and an icy mantle beneath. Terraforming projects to warm Titan by a small amount may be possible, but any attempt to bring the average temperature above the boiling point of methane (near -160 degrees Celsius or less on Titan) will result in the loss of any methane surface; likewise any attempt to bring the average temperature above the freezing point of water will result in the melting of any stable icy surfaces. Thus, any attempts at warming the climate of Titan will result in the loss of any solid surface features and essentially convert Titan into a waterworld.
Titan also lacks a magnetic field and is bathed in high-energy radiation during much of its orbit around Saturn. This means that any human colonists may risk damage due to high doses of radiation. Shielding against such damaging radiation requires a thick layer of high-density material that can absorb any high energy particles well before they reach the surface. Because of this potentially lethal danger of radiation, future Titan colonists may decide to spend most of their time inside large and well-insulated enclosed shelters.
A couple plausible methods for terraforming Titan exist, but these all come with significant challenges. One strategy to introduce oxygen and Earth-like temperatures could work by artificially warming the planet, but this would turn Titan into a waterworld with no solid surface and would require artificial floating islands for human habitation. Another strategy to keep Titan close to its current conditions would refrain from changing temperatures or atmospheric composition and instead would build artificial enclosed structures that protect human colonists against the dangers of Titan. This latter strategy seems more robust, as shelters could also be designed to withstand potentially damaging radiation.
Terraforming Titan is not an easy endeavor, and many unpredictable climatic outcomes will likely occur if such a project ever unfolds. Even so, any future human colonists that make it as far as Titan certainly will be a determined bunch and perhaps may have the stamina to transform Titan--at least a little bit--into something more like home.