Tarnis 2a is the shattered moon of Taranis II, the second planet from the sun of the unclaimed Taranis system.
During the Messer Era, the geo-development company Ophion, Inc. used Taranis 2a and its parent planet as testbeds for various new terraforming technologies, including a dubiously-designed platform that was meant to utilize the moon's orbital energy as a power source. A combination of errors in math from the overworked and underpaid engineers, mistakes in construction from the exhausted workers, overall poor design, and the use of shoddy parts led to a catastrophic energy discharge from the largest platform that ruptured the mantle of Taranis 2a, eventually causing the moon to break apart.
The "Broken Moon of Taranis" map featured in the popular space flight simulator Arena Commander was inspired by Taranis 2a.