Delta IV (or Delta) was the fourth planet of the Delta Triciatu system. (TOS novel: The Fearful Summons) It had at least two moons, Cinera and Seyann. (ST reference: Star Trek: Star Charts)
Delta IV was homeworld of the Deltan species. (ST movie: The Motion Picture) It was governed by the Deltan Union, which joined the United Federation of Planets in 2223. As of 2380, the planet had a population of 3.8 billion Deltans. (ST reference: Star Trek: Star Charts)
History
One of the closest inhabited planets to Delta IV was Carrea. The Carreon and the Deltans have been rivals since first contact, sometime prior to the late 22nd century. (Star Trek: Gateways novel: Doors Into Chaos; ST novel: Articles of the Federation)
In 2294, James T. Kirk claimed Delta IV was the intended destination of the Plush Princess. (TOS novel: The Fearful Summons)
Emblem of the Deltans.
Delta IV was attacked by Dominion forces during the Dominion War, resulting in the contamination of their water table. This resulted, by 2379, in the breakdown of their water reclamation system. Delta attempted to obtain a new Carreon-designed system, and after four months of negotiation, agreed to allow a Carreon scientific base on planet Brannik IV in exchange for this new system. (ST novel: Articles of the Federation)
- Star Charts indicates the Deltans became warp capable in 2223. This was later contradicted by the Star Trek: Enterprise episode "Bound", which establishes they were warp-capable as early as 2141.