Kira II was the only planet in the system that was habitable and suitable for colonization.
The planet was initially surveyed during the time of the Old Republic. It was the only planet in the system deemed worthy of further developement, as all others were classified as uninhabitable.
When Republic explorers returned to the system years later, they found the three inner planets had been mysteriously destroyed, and gave the name Kira Prime to the asteroid field orbiting Kira.
When the Kira Run was established years later, the asteroids remained a small, but constant hazard for hyperspace travel.