U.S. officials said Tuesday they couldn't say what might have created a mysterious plume that set off an Internet frenzy after it streaked across the Southern California sky Monday night. But they said they were confident there was no threat to the United States.
Speculation immediately arose that some sort of rocket or missile must have been fired after Los Angeles television station KCBS videotaped the spectacular trail from one of its traffic helicopters.
But a Federal Aviation Administration official told NBC News that there were "no reports of unusual sightings" and that a review of radar replays "did not reveal a fast-moving object in that area."
That's in line with the observations of scientists interviewed by NBC News and msnbc.com, who said that for all the sensation the video created on the Internet, the contrail was consistent what you'd see behind a normal jetliner or other large aircraft if you happened to spot it at sunset from the unusual aerial angle of the TV helicopter — in other words, it was probably an optical illusion.
Jonathan McDowell, an astrophysicist at Harvard University who tracks suborbital launches, said the last known such test was Oct. 21. He endorsed the conclusion of other scientists and satellite observers who said the contrail appeared to be moving too slowly to be the result of any sort of missile launch.
Whatever it was, "there is no indication of any threat to our nation," the North American Aerospace Defense Command said in a statement.
NASA and the U.S. Missile Defense Agency didn't immediately respond to requests for information.
By Alex Johnson of msnbc.com with Jay Blackman and Jim Miklaszewski of NBC News.