Early discovered chlorine ecology. The curious atmosphere of Tytalus was detected in the Interplanetary Age via spectroscopy, but it was not until the planet was reached in 3219AT that the cause of its peculiar composition was discovered; a complex biosphere which produces free chlorine as a byproduct of photosynthesis.
In 3344 AT the results of this survey were collated at Tycho City on Luna by Irene Habelsein-Io; she realised that the life on this planet was almost identical to that found on Outland, a second chlorogaian found in Andromeda, more than a thousand lightyears from Tytalus. Because of this wide separation she formulated the theory that the two planets (and possibly several others, found by spectroscopy but not yet reached) had been seeded hundreds of millions of years ago by a hypothetical xenosophont species which she called the Halogenics.
In the Current Era several hundred Halogenic worlds have been surveyed, and Habelsein-Io's theory has been largely vindicated. This xenobiological type is one of several different artificial biochemistries that have been discovered in the Terragen Sphere.