A planet surrounded by an energy distortion field, where a transporter accident created Thomas Riker.
Nervala IV is an inhospitable planet with a Federation research station. A distortion field around the planet makes transport possible only during brief windows every few years.
In Second Chances, the Enterprise returns to recover data from the station eight years after its evacuation. The away team finds a second William Riker, created when the distortion field split his transporter beam during the evacuation. That Riker had lived alone on the planet ever since and later takes the name Thomas Riker.