The phenomenon recorded Monday evening by a TV news helicopter created a media sensation and a vapor trail of commentary across the Internet about the possibility of a secret missile firing. But the military insisted it knew of no rockets launched in the area.
Defense Department spokesman Col. Dave Lapan said Wednesday that officials were satisfied it was an airplane contrail distorted by camera angle, winds and other environmental factors including a setting sun.
Military experts studied the video and talked to all government agencies that might have been involved in a missile launch and none reported having launched one, Lapan said.
The conclusion was independently supported by Al Bowers, associate director of research at NASA's Dryden Flight Research Center in the Mojave Desert, and Patrick Minnis, a senior research scientist at NASA's Langley Research Center in Virginia, who studies remote sensing of the atmosphere and Earth's surface.
"A missile would look like that," said Bowers, whose 27-year career has included stints as chief or lead engineer on such programs as the SR-71 spyplanes turned over to NASA by the Air Force.
"It could potentially have a contrail that shape," he told the AP. "(But) the motion looks a little suspect to me, and my conclusion would be that, yeah, it's most probably an aircraft."
At Langley Research Center, Minnis and colleague Doug Spangenberg analyzed a sequence of infrared images of the area collected between 5 p.m. and 6:45 p.m. Monday by GOES-11, a geostationary operational environmental satellite.
At 5:30 p.m., "suddenly there is contrail extending horizontally from the left side of the image ... that bends toward the (northeast) pointing directly at Catalina Island," Minnis said in an e-mail to the AP.
The contrail had to have started 15 to 45 minutes earlier and become quite wide to be visible to the satellite, he said.
Minnis accounted in his analysis for earlier and later contrails, conditions that would cause a contrail to persist, movement of the contrail, and nearby clouds.
Missile and satellite launches are routine along the California coast.
The area of ocean perceived as the seeming liftoff point Monday night is in the vicinity of a Navy ocean range where missiles are often launched from vessels, platforms and San Nicolas Island.
Up the coast is Vandenberg Air Force Base, where satellites are lofted into polar orbit and intercontinental ballistic missiles are launched on unarmed test flights to targets thousands of miles away in the Pacific Ocean. Three ICBMS were launched between June and September.
Many of these launches are invisible to the metropolitan area, shrouded by the layer of moist marine air that often rolls in from the Pacific. Others are lost in the brightness of daytime.
But launches on very clear nights or at twilight sometimes trigger numerous calls to media or authorities reporting unusual sky sightings from hundreds of miles away, even from neighboring states.
No such spontaneous public response occurred Monday night in the nation's second-largest city, suggesting that the image captured by the airborne camera was not apparent to ground observers.