E-Space - alternately known as Exo-Space, Ecto-Space or Exo-Space-time continuum - was a smaller universe existing alongside the prime universe, N-Space.
Characteristics
E-Space was not a parallel universe as that term is generally understood, having its own astronomy and unique inhabitants. [statement unclear] However it wasn't quite a perpendicular universe either, since it had humanoids and other sentient life forms that were similar to ones of N-Space; thus it was more of an oblique universe or pocket universe.[source needed] However the fact that the Doctor's TARDIS was still able to draw the energy it needed to function from E-Space suggested that it shared some similarity to N-Space, as the ship was starved of energy upon entering a "true" alternate dimension (TV: Rise of the Cybermen). The Doctor's companion, Adric, originated from E-Space (TV: Full Circle) and travelled with the Fourth Doctor back to N-Space (TV: The Keeper of Traken), where he ultimately died (TV: Earthshock) The Doctor's longtime companion, Romana II, chose to stay in E-Space along with K9 Mark II rather than return to N-Space with the Doctor and Adric. (TV: Warriors' Gate)
E-Space was visually distinct from N-Space in that it possessed an unusual greenish tint. It was also considerably smaller than N-Space. (TV: Full Circle, State of Decay)
Locations in E-Space apparently had negative co-ordinates, where N-Space was positive. When the Doctor's TARDIS materialised on the planet Alzarius after it had travelled into E-space, the TARDIS scanner continued to show images of Gallifrey, which had the positive equivalent of Alzarius' spatial co-ordinates. Rather than being a simple optical relay, the system apparently depicted whatever existed at the ship's current co-ordinates. The Doctor suggested that the system operated off the absolute value of the co-ordinates and thus could not process negative co-ordinates. The scanner system was made functional again simply by replacing its original N-Space image translator with one native to E-Space. (TV: Full Circle)
Transit between the universes
The Fifth Doctor stated that the negative co-ordinates would make it very difficult for his TARDIS to travel there deliberately and not accidentally. (TV: Earthshock)
By his seventh incarnation the Doctor was able to pilot his TARDIS between E- and N-space, and was able to retrieve Romana from E-space. (PROSE: Blood Harvest) K9 was also later retrieved. (PROSE: Lungbarrow)
CVEs
Travel between N-Space and E-Space could occur via a Charged Vacuum Emboitment, or "CVE". This was a hazardous and apparently random process, even using a TARDIS. (TV: Full Circle)
The Logopolitans revealed they had created the CVEs which linked together the two universes as part of their plan to forestall the overdue entropic collapse of their universe (N-Space), by opening up what had previously been a closed system and thus dissipating the accumulated entropy. Following the disastrous consequences of the Master's visit to Logopolis, only one CVE remained open, in the constellation of Cassiopeia (from Earth's perspective). (TV: Logopolis) Unless further CVEs were later created, it was highly likely this was the route through which the Hydrax would later enter E-Space (TV: State of Decay) in the 22nd century. (PROSE: Lucifer Rising)
The Gateway
On his return journey to N-Space the Fourth Doctor and his companions passed through a strange white void known to its most frequent inhabitants, the Tharils, as the Gateway. (TV: Warriors' Gate)
- (The Gateway zone between N-Space and E-Space had zero co-ordinates, thus adding credence to the 'positive and negative universes' theory.) It is not known whether it was possible to travel from E-Space to N-Space without physically visiting the Gateway.
Planets of E-Space
Known planets in E-Space include Alzarius, Ballustra, the unnamed planet which was the hiding place of the last Great Vampire, and Terradon, the origin world of the starliner which crashed on Alzarius. (TV: Full Circle, State of Decay, Earthshock, AUDIO: The Invasion of E-Space). The Tharils presumably had a homeworld of some kind as well, as did the unidentified humanoid races which they variously enslaved and were enslaved by; Shapeer was a place named for hunting them. (TV: Warriors' Gate)