Lost colonies in the Aquila region with surviving cultures shown in white; extinct colonies shown in red
Lost colonies are colonies that have been totally isolated from the remainder of Terragen civilization for a long period of time (the exact timeframe varies depending on various circumstances). They are typically found in the Outer Volumes, although there are still sizeable numbers in the Middle Regions. Of course, by definition no-one can know how many lost colonies there are at any one time.
Lost colonies are generally technologically impoverished worlds, since a world of lower Middle Tech level or higher is usually easily detectable to other colonies from its radio transmissions. The lost colony of Guanche persisted for several hundred years at a Bronze Age level and all transmissions naturally ceased until the only surviving copy of the Encyclopaedia Everythingiana was discovered.
High tech lost colonies are usually either very far from any other colonies or were settled by isolationists who deliberately conceal any radio emissions. There are a variety of ways for a colony to become technologically impoverished. It may be founded by extreme ludds who shun technology, it may suffer some disaster which destroys the established technological base, or a technological base may be inadequately established from the outset. Such lost colonies were relatively common in the early days of interstellar colonisation, as at Tjetvir (Zeta 2 Reticuli) or Eoestromonath (61 Virginis).
Inadequate establishment of the technological base usually results from poor initial preparation of the colonial expedition. Such expeditions usually consist of refugees, marginalized groups, or other similar populations; for instance the early colonies around 40 Eridani were badly prepared backyarders, refugees from the Nanoswarms, who did not survive.
Under astropolitical circumstances conducive to isolation a lost colony can easily remain undetected for thousands of years. Several known lost colonies have been isolated for so long that they have developed an independent culture and technological base that owes nothing to mainstream Terragen civilization, making them close to true aliens. The classic examples of this phenomenon are the Refugium and the dusty entities of Gammergan, both of which were taken to be xenosophont civilisations when first discovered.
Historically, large numbers of lost colonies have been created whenever the Wormhole Nexus is closed down locally, usually as a result of conflict. This happened during the Version War, in the Enif prefecture and the Serpens region; in Cygexpa, following the dissolution of the local House; and most recently in the MPA following the Oracle War. Many of the colonies isolated following the latter conflict are still uncontacted, although hopefully this will be remedied within the next few hundred years.