A moon covered in violent electrical storms, where the consciousnesses of exiled criminals were held prisoner for centuries.
Mab-Bu VI is an uninhabitable moon whose atmosphere is filled with powerful electrical storms. It was used as a penal colony, where the disembodied minds of criminals from another world were exiled and left trapped.
In Power Play, the Enterprise investigates what seems to be a distress signal from the long-lost USS Essex. Troi, Data and O'Brien are possessed by entities that at first claim to be the Essex crew, but the beings are really the prisoners of Mab-Bu VI seeking escape.