(coexisting on another dimensional plane)
A starship from the future prime universe was being held inside a moon of said gas giant. In 2155 this was discovered by Commander Jonathan Archer. After successfully staging a mutiny against Captain Forrest, Archer commandeered and forced the Terran battle cruiser ISS Enterprise to the Vintaak system in order to retrieve the captured starship, identified as the USS Defiant. Though Forrest eventually regained command of the Enterprise, Archer had locked the helm controls on course for Vintaak. Forrest's attempts to change Enterprise's course ultimately proved futile.
When an away team under Archer's command beamed aboard the Defiant, the Enterprise was attacked and captured in a Tholian web. Some of the Enterprise's crew was able to abandon ship in escape pods, but the ship itself was destroyed with Forrest still on board. (ENT: "In a Mirror, Darkly")