Mass Effect & Mass Effect 3
Ploba is the second, and by far the largest, of Anataeus' two gas giants. Active scans by survey ships have returned tantalizing indications of massive, solid structures deep within the atmosphere, too regular in pattern to be anything natural.
Some believe Ploba is a "Jupiter Brain," a planet-sized supercomputer. Adherents of this theory have fruitlessly beamed signals toward the sunken megastructures, hoping to get the machine's attention.
Others believe that an ancient spacefaring race disposed of their weapons of war by dumping them into the planet. The last attempt to reach and salvage Ploba's "Deep Anomalies" went tragically wrong, and ended with a crew of 12 being trapped and crushed in the gas giant's lower atmosphere.