Adelphous IV was the fourth planet in the Adelphous system which sustained a population prior to 2381. The USS Enterprise was headed for this world in 2367 when Data relieved Worf of command at the beginning of the night shift. (TNG episode: "Data's Day") During the Borg Invasion of 2381, over seven thousand Borg cubes launched a simultaneous attack on the Alpha and Beta Quadrants from the Azure Nebula; Adelphous IV was one of the planets attacked and its population wiped out. (ST - Destiny novel: Mere Mortals) Startrek.com spells the planet as Adelphus IV.