The twelfth planet of the primary of the Nivenia System, A12, is currently a mining colony of the Nivenian Empire. Like A11, it is highly urbanized, but it is a lot larger and focuses on methane extraction instead of ammonia. Large amounts of ionic salts also exist in the subsurface oceans, making A12 the primary source of calcium and magnesium in the Nivenian Empire.
Even though A12 was not the first planet colonized by the Nivenian Empire, it is the largest terrestrial one, and functions as a major spaceport. A12 is actually part of the A12-A12.1 binary planet, and both are colonized and developed as mining colonies for the Nivenian Empire. A carbon nanotube tether connects the two planets, allowing for a huge station at the center of mass and space elevators going to both planets.
A12 is the most populated conventionally inhabited terrestrial planet in the Nivenian Empire, save Nivenia Prime, not due to population density, but due to surface area.
The economy of A12 is based on the alkaline earth metals and methane being extracted from the subsurface oceans. It is also one of the largest trading hubs in the Nivenian Empire, so trading and storage are major planetary industries as well. Being closely linked with A12.1, prices for most items are closer on the two objects than would otherwise be expected.Things that cannot be made on-planet, like electronics and shields, are imported from Nivenia Prime, but the main imports are food and metals, as the water on the planet is too salty to easily be used for hydroponics, and there are very few transition metals on the planet.