Empyrrean is a sparkling Temperate world covered in thick prairies and open forests. It is the homeworld of the ARM Rebellion, one of the two factions and it reflects the retainment of nature that the ARM sought in its rebellion against the CORE Empire. Empyrrean itself is covered from pole to pole in wide oceans and long, thin continents. It has no deserts and a small polar region. It can only be assumed that the massive oceans that cover Empyrrean are somehow accountable for this.
Empyrrean is not an artificial world like Core Prime but owing to the nature of the ARM this actually benefits them. Spider nerve cells from the Empyrrean biosphere no doubt were instrumental in the creation of the Spider tanks which can often paralyse whole squadrons and allow much smaller ARM squadrons to destroy them with ease. Empyrrean's oceans are also likely used at the most desperate of times to provide ARM forces with water. Empyrrean also has reserves of metal and geothermal resources at its disposal, although these are never likely exploited by the ARM to the extent that other planets, such as Barathrum, have been. Although in crisis cases the appearance of Mines and Geothermal Powerplants across battlefields is a common sight.