Tyrus VIIA was a moon of Tyrus VII, an inhabited planet in the Tyran system. The moon was orbited by the Tyrus VIIA station, and was the location of the experimental particle fountain mining technology.
In 2364, Dr. Farallon initiated the project as its inventor and supervisor. She remained as project leader at least as late as 2369 when the USS Enterprise-D visited Tyrus VIIA to monitor the project's progress. Starfleet wanted a feasibility study for possible use of a particle fountain on Carema III. (TNG: "The Quality of Life")
However, according to the Star Trek Encyclopedia, 4th ed., vol. 2, p. 431 and StarTrek.com, this was a planet. StarTrek.com described it as "one of a double planet". [2](X)