In the fringes of the Subterrel sector of the Outer Rim Territories, Polis Massa was once an intact world that was home to the underground-dwelling Eellayin people. The people mysteriously vanished when the world was destroyed by an unknown and ancient cataclysm.
Polis Massa is now a jumbled collection of lazily floating asteroids, and has a small Outer Rim mining settlement far removed from the more populated areas of the galaxy. The airless rocks are host to sealed outposts inhabited by the strangely silent Polis Massan aliens.
Over 500 years ago, an archeological expedition began combing the rocky fragments for the remains of the Eellayin. The alien researchers, believing themselves to be descendants of the Eellayin, became so entrenched in the asteroid remains over the centuries that they simply became known as Polis Massans to all who dealt with them.
One of the largest topside facilities is called the Local Dig, and it is situated above the remains of
Wiyentaah, an Eellayin city that the Polis Massans are meticulously uncovering. The interior of the Local Dig's scientific chambers are kept in pristine and sterile conditions, preserving any fragile artifacts that are found. The medical centers are stocked with the latest in recuperative technology, though it is tailored for the physiology of the alien researchers. The Polis Massans employ cloning technology in attempts to recreate extinct or vanished pre-cataclysm life-forms from any scraps of usable genetic material found within the rocks.
It was at one of these outposts that Jedi fugitives Yoda and Obi-Wan Kenobi regrouped following the disastrous decimation of their order by the rise of Empire. Having failed to thwart Palpatine, Yoda fled to Polis Massa with Bail Organa to recover. Obi-Wan Kenobi, having defeated Darth Vader on Mustafar, soon joined them.
During the Galactic Civil War shortly before the Battle of Yavin, Imperial intelligence tracked the Death Star plans to a small Rebel outpost in the medical center. The 501st Legion stormed the facility, and managed to obtain one holodisc. Overall, the raid was only a partial success, with the Rebels beaming the remainder of the plans to Princess Leia Organa's corvette the Tantive IV orbiting over Tatooine.