Delphi Ardu IV was the fourth planet of the Delphi Ardu system. The planet was classified as class M, and prior to 2364, had only been charted by the Federation via long-range scans, which indicated no lifeforms, sentient or otherwise.
Delphi Ardu IV was an outpost of the extinct Tkon Empire, known as Outpost 63, and was guarded by a Portal. Portal 63 was encountered by away teams from the USS Enterprise-D and a Ferengi Marauder in 2364. (TNG: "The Last Outpost")
Timothy Sinclair visited Delphi Ardu several times in the late 24th century, as part of his quest for knowledge of the Preservers. (Star Trek: Pendragon: "Missing Person", "Odyssey, Part I", "Starkindler")