Alexandra's Planet was an inhabitable planet.
On stardate 44765, Elias Vaughn was involved in an encounter with Romulans on Alexandra's Planet after an Iconian gateway was located there, with Vaughn forced to destroy the gateway to stop the Romulans from using it. Vaughn's mission was later classified, although Admiral William Ross provided some redacted information to the crews of the USS Enterprise and Deep Space 9 in 2376. The information from Alexandra's Planet was helpful to Geordi La Forge, Nog and Thirishar ch'Thane during the Gateways Crisis. (TNG - Gateways novel: Doors Into Chaos; DS9 - Gateways novel: Demons of Air and Darkness; TNG - What Lay Beyond short story: "The Other Side")