The Artifact
From Tardis Wiki, the free Doctor Who reference
The Artifact was an organism that lived in outer space.
When Earth humans colonised the Elysium system, they discovered the Artifact already existing there. It siphoned water from planets to survive. It was large enough to support numerous ecosystems. The Seventh Doctor was able to link with it, encouraging it to make its progeny symbiotic instead of parasitic. (PROSE: Parasite)
