Tyrus VIIa was a moon of Tyrus VII, an inhabited planet in the Tyran system. The moon was the site of the experimental Particle Fountain Project, which was designed as a new mining technology.

In 2364, Dr. Farallon intiated 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")

According to the Star Trek Encyclopedia (4th ed., vol. 2, p. 431) and, this was a planet. described it as "one of a double planet". However, the script describes Tyrus VIIa as a moon.