Delta IV Delta IV ( or simply Delta ) was the inhabited fourth planet of its star system and was the homeworld of the humanoid Deltan s . The planet was a Federation member world . ( ; ) Several years before his assignment to the in the 2270s , Will Decker met Ilia on Delta IV , where they became romantically involved . After " V ' Ger " had replaced her with a near - duplicate , Christine Chapel tried to activate her original memories with a head dress she used to wear back on Delta . ( ) In 2371 , the location of Delta IV was labeled in the star chart Data and Picard were studying in stellar cartography aboard the . ( , " okudagram " ) Appendices . Background information . In the writers / directors guide for " " , the Deltan homeworld was referred to as 114 - Delta V . The same document also stated that the planet had " recently joined the Federation . " ( " " , p . 90 ) In the first - draft script for " In Thy Image " ( the story that gradually transformed into " The Motion Picture " – the script was dated ) , the Deltan homeworld was referred to as Delta 14 . ( " " , pp . 121 & 139 ) In , consultant company de Forest Research addressed the naming of the Deltan homeworld , stating that the word " Delta " being used as a planet name presents a problem in astronomy , since it ( in common with other Greek letters ) is commonly used to identify a particular star in a generic , recognized constellation . " " That it would ever be used as a planetary name is very unlikely , " " the research company declared . They concluded , " " We would be happy to consult on other possibilities which might be more in accord with standard astronomical usage . " " ( " " , p . 64 ) Evidently , the production crew did not adhere to the advice from De Forest Research , and variations of the name were included in several examples of documentation that were much more closely related to " The Motion Picture " than they were to " Phase II " . In a character study of Ilia that Gene Roddenberry wrote for the film , the Deltan homeworld was referred to as Delta . ( " " , p . 108 ) The planet was also mentioned in notes that costume designer Robert Fletcher wrote , regarding the various aliens in the movie . In that case , the Deltan homeworld was called " Planet Delta 4 . " ( " The Making of Star Trek : The Motion Picture " , p . 133 ) According to " The Worlds of the Federation " ( p . 64 ) , Delta was the fifth planet orbiting Delta Triciatu , a white dwarf star . The indigenous name for the planet Delta was Seyalia . The planet was covered by vast forests and had two moons , Seyann and Cinera . According to " Who ' s Who in Star Trek 1 " , Delta was the fifth planet in the 114 - Delta system . According to the " Star Trek IV Sourcebook Update " , Delta was the fourth planet in the Delta Principius system . However , the " The Federation " sourcebook says it ' s the fifth planet in that system . According to the novel " Uncertain Logic " , " Delta " is an anglicized version of its native name Dhei - Lta . It is located in the V2292 Ophiuchi system . According to " " ( p . 33 ; " United Federation of Planets I " ) and " " ( " Federation Historical Highlights , 2161 - 2385 " ) , the M - class planet Delta IV was governed by the Delta Union . This world joined the Federation in 2223 , the year the Deltans became warp - capable . In the 2370s , there were 3 . 8 billion Deltans living on the planet . Instead of exposing offworld humanoid s to Deltan pheromones , they were directed to the moon s of Seyann and Cinera . This planet was located in the Delta system , a star system in the Alpha Quadrant . The system ' s primary was a . Apocrypha . In " Articles of the Federation " , Delta IV is mentioned to be attacked by the Dominion during the Dominion War . In " " , Delta IV is attacked by a combined force of Borg and Cybermen as their first attack against the Federation .