(covers information from several alternate timelines)
|Ceti Alpha V|
|Native Species:||Ceti eel|
|Location:||Ceti Alpha system|
Ceti Alpha V was located a considerable distance from the Delphic Expanse and the planet Denobula as well as three days away from Regula I at an unspecified warp speed. The nearest starbase was Starbase 12. (ENT: "Twilight"; TOS: "Space Seed"; Star Trek II: The Wrath of Khan)
Only six months later, Ceti Alpha VI exploded, shifting Ceti Alpha V's orbit and turning it into a desert-like world, dominated by craylon gas and high-velocity winds. The planet became incapable of supporting life, with the only remaining known indigenous lifeform being the Ceti eel.
In 2285, the USS Reliant visited the planet as part of Project Genesis. Mistaking it for Ceti Alpha VI, Captain Clark Terrell and XO Commander Pavel Chekov beamed down to the surface, only to be taken prisoner by Khan and his surviving followers. Khan then hijacked Reliant and stranded its crew on the planet's surface. The crew were later recovered by the USS Enterprise, following Khan's death at the Battle of the Mutara Nebula. (Star Trek II: The Wrath of Khan)
In an alternate timeline, Ceti Alpha V was the refuge for the last 6,000 members of the Human race from 2156 to 2165 – survivors of the devastating Xindi attacks on Earth and its colonies – as it was far from the Delphic Expanse. The colony's location was kept secret for a great deal of time, but a Yridian discovered it by tailing Doctor Phlox, thus allowing the Xindi to attack. (ENT: "Twilight")
In the script of "Twilight", the surface view of Ceti Alpha V was described thus; "Dozens of makeshift human dwellings are clustered in this small valley. We’re on a harsh but habitable Class-M world... only a few occasional patches of vegetation are visible here and there." The writers have joked on the audio commentary for "Twilight" that, if it wasn't bad enough the Xindi killed off almost all of Humanity, a hundred years from "Twilight", Ceti Alpha V would have been destroyed as well.
Due to its dry nature, Ceti Alpha V was apparently a Class H planet or almost matching that classification after the destruction of Ceti Alpha VI.
There was no explanation given as to how the loss of one planet in a star system could affect others to the degree shown.
The spin-off novel To Reign in Hell: The Exile of Khan Noonien Singh explicitly addressed the above issue. Spock postulated that Ceti Alpha VI's destruction and the environmental impacts on Ceti Alpha V had another, shared cause (possibly a small black hole passing through the system), while apparently the miscounting resulted from the Reliant's crew counting inward, finding the outermost planet (and mistaking the remains of Ceti Alpha VI for part of an outer asteroid belt).
In Vonda N. McIntyre's novelization of Star Trek II: The Wrath of Khan, there was some dialog between the Reliant's bridge crew speculating about the cause of the discrepancy between the planet count of the system reported by an old interstellar probe (20) and the current count (19) – one possible conclusion they drew was that the limitations of the probe's imaging systems had led to inaccurate data being reported. This dialog occurred shortly before Terrell and Chekov decided to beam down to the planet.