But to GlobalSecurity.org director John Pike, there’s an easy explanation: “It is obviously an airplane.”
“The aircraft is flying towards the observer; the air over the Pacific is clear, so the contrail is visible all the way to the horizon. This creates the optical illusion of a rocket flying up, rather than the actual situation of an airplane flying horizontally,” Pike tells Danger Room. “The object generating the contrail is moving too slowly to be a rocket; the contrail is not expanding as the ‘rocket’ gains ‘altitude’ — which would be the case as the exhaust plume expanding into less dense high altitude air.”
MIT astronomer Jonathan McDowell tells New Scientist pretty much the same thing. Although he does note that the Navy owns a missile target and launch facility at nearby San Nicolas Island.