Bre'el IV is a heavily populated planet whose moon was falling out of orbit when a powerless Q appeared on the Enterprise.
Bre'el IV is a densely populated planet whose moon began to slip from its orbit, threatening to crash into the world below. In Déjà Q the Enterprise was trying to push the moon back into place when Q appeared on the bridge, stripped of his powers by the Q Continuum.
While Q lived as a mortal aboard the ship, the crew worked with scientists on Bre'el IV and tried his suggestion of changing the gravitational constant of the universe. After Q regained his powers, he restored the moon to its proper orbit, the planet was saved, and he left.