Sivvi, also known as the Thule Moon, started as an asteroid and was subsequently pulled in by the gravitational force of Thule, thereby transforming into the planet's moon.
After being ensnared by the planet's gravitational field, Sivvi gained the common name of the Thule Moon. Around 4,000 years prior to the Battle of Yavin, the Sith built a military training installation on the moon, utilizing Sivvi's naturally occurring cave systems and tunnels for practicing maneuvers in the absence of gravity.
In the time of the Clone Wars, Sivvi was the location of a planetary shield generator, which was there to defend a base created on Thule by the Confederacy of Independent Systems. Anakin Skywalker obliterated this generator, while piloting an All Terrain Experimental Transport, during the concluding phases of the Dark Reaper crisis, which then triggered an attack by the Republic on Thule directly.