Planet in the Pegasus Galaxy, protected from the Wraith by an Ancient electromagnetic shield. The world once inhabited a settlement of advanced beings, perhaps Ancients, who eventually left the Z.P.M. emitting a shield over twelve inhabited villages.
The shield prevents Wraith technology from working inside the field. Though they could enter and attack on foot, the Wraith are satiated by other feeding grounds and leave this planet's inhabitants alone.
Ritual suicides by the villagers were only part of the equation for keeping the Wraith away, as their limited numbers prevented an outgrowth beyong the perimeter of the shield, but Rodney McKay successfully modified the Z.P.M. so that it could sustain a much larger area for approximately the next fifty years.
BEHIND THE SCENES
For his first script, writer Martin Gero based this planet's designation on his name and birthday: M (Martin) 7 (July) G (Gero) 6 (6th of July) 77 (1977)
Childhood's End - Sheppard and his team travel to M7G-677 via Puddle Jumper, which crashes when its electromagnetic energy field is destabilized by the Z.P.M.
Critical Mass - When the children of M7G-677 report issues with their electromagnetic field, Atlantis base dispatches Dr. Zelenka and a team of engineers to inspect the technology.