Arch Travel is the most efficient known way to travel between planets. They are claimed to be established by the Seraphi, so far no evidence to the contrary has been found. It is generally accept as a truth, because it is know that the Farside civilization had other means of inter-planetary travel.
Giant Arches, some with diameter to be as large as several kilometers, are found already on some worlds, some are found on land others partially submerge in oceans or seas.
Once entering such an arch a large mist forms obscuring everything from view, except the land or water that is traveled upon. After a certain amount of time ranging from a half day to nearly a week, depending on the size of the gate, the mist will start to clear and the travelers will find themselves on a new planet.
Arch travel is generally unrestricted as controlling the entrance to the sometimes massive structures is inherently problematic. Surveillance is generally all that is kept to make sure that those who enter one end of the Arch exits at the far end.