Terraforming is the process of reshaping or otherwise modifying the ecology of a planet or moon to make it more habitable for human life.
Background
Very few, if any, worlds in the Firefly solar system were entirely suitable for human habitation when colonists first arrived on their multi-generational ships. Atmospheric temperature and composition, among other factors, were usually well outside human tolerances. Colonists can wear space-suits and other environmental hazard gear when outside protected areas, yet they ideally need a more permanent solution to claim a planet as truly their own. Enter terraforming.
In general, terraforming is the process of "tweaking" key traits of a planet or moon to make them more like Earth. This technology is quite widespread in the Firefly universe as characters make reference to terraformed worlds frequently. The exact technology is unknown but is described as taking decades; large machines are seen moving across the surface of a planet undergoing terraforming. Apparently this can even include altering the gravity and sunlight levels of a body by unknown means. As part of the terraforming process, Earthly plant and animal life are also seeded across a world to form a hopefully balanced ecology; types of ecosystems seen incude desert, temperate, forest and ocean. Terraforming is also referred to as dangerous work that often kills laborers.
The central planets are much better off than the border planets, possessing much more earth-like environments with easily accessible resources. These inner planets were probably required little or no terraforming to become sufficiently livable. They were the first worlds terraformed, and by the time of the War of Independance have well-established ecologies and industries supporting large populations and cities.
Many border planets face a worse fate. Some of the outer Rim planets are still being terraformed and have harsh conditions and no infrastructure to support human civilization. It often takes more work to get the same results on planets which are more hostile. Also, not all planets react the same way to the terraforming process. "The Train Job" centers on unexpected problems arising from the terraformed moon of a gas giant. This moon thrives solely on its mining industry. Unfortunately, the terraformed surface air mixing with rubble and subterranean air lead to the rise of Bowden's Malady, a degenerative disease which targets muscles and bones. Surprises like this are quite common, with most worlds having a few of their own little quirks.
A planet where terraforming fails to "take" and reverts back to uninhabitable condition is called a blackrock.
Criteria
Terraforming can be performed on any body that meets the following criteria:
- It has to be large enough for Hydrostatic Equilibrium to form it into a sphere. For a rocky body with a composition that would be useful to settlers, the minimum size is 970km in diameter, or the size of the asteroid Ceres. Anything smaller would have an irregular shape that wouldn't hold an atmosphere all over.
- Its diameter cannot be greater than 1.4 times ETW (Earth That Was) due to limitations in terraforming technology.
- The target must lie in a 13.5 AU wide band around the star. The inner and outer boundaries for this band depend on the star's temperature. Terraforming technology is much better at warming cold places than cooling hot places.
What needs to be done?
- The gravity needs to be adjusted to ETW-normal. Here's the reason for the upper size limit. It is much easier with our current technology to increase the gravity of a planet than it is to decrease the gravity. A less dense world can be compressed to increase its density and gravity. A world with more than twice the surface area of ETW (1.4 x the diameter) is too big to terraform.
- Continents and seabeds need to be sculpted.
- Atmospheric gases need to be released from the crust – water as well.
- What may well be lifeless rock needs to be processed into soil that will grow plants and crops.
- The planet's rotation and axial tilt need to be adjusted so that the planet has a 24 hour day and a standard 365-day seasonal year.
- Plant and animal life needs to be introduced.
- Atmosphere processors are set to a maintenance mode to help maintain an ideal mixture of gases until the biosphere develops enough to handle that function.
The planet is now ready for colonization.
Axial tilting
One of the biggest challenges faced by terraforming crews is the introduction of plant and animal life into a created environment on an alien world. How are plants and animals going to cope with seasons that will last for years? And how will colonists cope with calendars that are different for every world? They won't have to.
The terraforming crews will adjust the rotation period of the planet for a 24-hour day. They'll adjust the axial tilt to 23.439 degrees. Then they'll add a second rotational axis at 0 degrees (perpendicular to the plane of the system) with a rotation period of 365.25 days. This second axis will cause the planet to cycle through one complete seasonal year in 365.25 days, regardless of where the planet is in its orbit around its sun. That will create a seasonal change that will mirror Earth. After that, it's a simple matter to ignore the planet's orbital revolution and go with the calendar.
Summers will last just long enough to ripen crops, and not so long as to bake them in the fields. Animals with millions of years of migrations wired into their brains will know when to migrate away, and when to come home.