In 9847 a Sophic long range probeship, exploring along a line to anti-spinward and Rimward of the Periphery discovered an anomalous light signature while travelling through interstellar space. Upon altering course and performing a high-speed flyby of the phenomenon, the probe was able to determine that the light signature was reflected star light. The probe had detected the reflection of a gigantic mirror in the middle of interstellar space.
Thinking at first that they had found evidence of either alien technology or terragens activity, the probe and eir crew initiated deceleration and rendezvous manoeuvres that placed them in close proximity to the array some 18 weeks after the initial detection event. What the probe found was indeed a product of alien manufacture. But not exactly a product of alien technology.
Drifting between the stars, light-years from any sun, the probe discovered a huge array of thin film mirrors some thirty thousand kilometers across. The mirrors acted to focus sunlight on a point nearby in space. Floating at this point was the first deepwood ever discovered.
A deepwood is, in outward appearance, very similar to the more familiar orwoods of terragens space. However, there are a number of crucial differences. While terragens orwoods can grow to hundreds of kilometers across, the largest deepwood so far discovered is only 3 kilometers in diameter (after some initial study, the probeship signalled back to its base station and then travelled to the nearest star system where it nanofactured telescopes and several million short range probes to explore space in the area of the first deepwood for others of its kind. To date some 11,000 deepwoods have been identified across a volume some 10 light-years across with no indication that their numbers are thinning.).
Deepwoods have much darker leaves then standard orwoods (the better to absorb reflected starlight) and a much slower, more efficient metabolism, allowing them to consume the resources of their host comet very gradually. And, of course, there is the mirror array. The mirror array of a deepwood is a bionano produced construct made from the metals available in the host comet. Each array is made up of many smaller mirrors all acting in coordination to reflect starlight onto the central tree.
The output of the mirrors is sufficient to closely approximate the light level of a near-solar environment and provides the energy for the deepwood to metabolize the resources of its comet as well as maintaining a low level electric charge across its entire structure. While the exact purpose of this charge is not entirely clear, it is theorized that the deepwood uses this effect to gradually direct its course through space by reacting against the magnetic field lines of the galaxy.
While the exact origins of the deepwood have yet to be determined, the most popular theory to date is that deepwoods are the product of an alien biotechnology. It is hypothesized that at some point in the far past an alien species engineered the deepwoods to serve as deep space habitats for their population, much as orwoods are used as habitats by terragens. At some point, some of the deepwoods 'escaped into the wild' perhaps due to the extinction of their creators, and have been gradually spreading through deep space ever since. A second, less generally accepted, hypothesis is that terragens civilization has encountered the outer edges of an expanding alien civilization (perhaps the builders of the Whisper sonic virtchcosm and alien Biogeocomputing worlds) and that it is only a matter of time until the deepwood's creators are encountered along with their creations.