I would say Janus used the Stargate to get back both in time and space using a solar flare. I guess his time ship would have all the power the gate would need to dial Atlantis. Also, being one of the Ancients' top scientists he would have the knowledge and the means to predict, possibly using the time ship, the solar flare he would need so he could leave the planet in his future to return to his past in Atlantis leaving the time ship behind for SG-1 to find.
Comment