The orange tail of vapor seemed to hurtle skyward off the coast of Los Angeles.
And it didn't take long for the video footage, shot by a television news helicopter just before sunset Monday, of what looked like a missile to set off fierce speculation about a rogue missile or a secret government rocket test.
But the curiosity over what exactly was spotted some 35 miles off the coast was met Tuesday only by a puzzling lack of answers from federal officials.
Military and aviation authorities denied any knowledge of a scheduled launch and the Pentagon said only that it was looking into a report of an "unexplained contrail," or vapor trail, left by an aircraft.
Whatever it was, it never posed a threat, officials said, and there's no evidence it was a missile.
That didn't stop aerospace experts, news outlets and curious onlookers from snapping photos and guessing the true nature of the "mystery missile" and who may have launched it.
Was it a intercontinental ballistic missile fired in error? Not according to the North American Aerospace Defense Command, which monitors the continent's airspace.
Did a submarine launch the rocket as a test? Negative.
Was it an act of aggression by a foreign government? Absolutely not, the Pentagon quickly confirmed; there had been no threat to national security.
Or maybe, as some experts suggest, it was just an optical illusion that made an aircraft's condensation trail look like something much more menacing.
John Pike, director of Globalsecurity.org, a military policy research website, said the idea that the government would carry out a secret launch at sunset within view of millions of people, is hard to believe.
"If it were secret, we'd do it at night in Alaska where only the caribou could see it," Pike said. "It's an airplane contrail pure and simple."
Rocket launches are a common sight in Southern California and rarely go unnoticed. And if it were a planned event, military officials should have known weeks in advance.
Perhaps no one had a better view of the alleged rocket than KCBS-TV Channel 2 cameraman Gil Leyvas.
He was aboard the station's helicopter shooting footage of sunset over the ocean about 5 p.m. when he noticed a spiral-shaped vapor trail and zoomed in to get a better look.
The on-board camera showed a plume twisting up from the horizon and narrowing as it climbed into the sky northwest of Santa Catalina Island, he said.
"Whatever it was, it was spinning up into the sky kind of like a spiral," he said. "It was quite a sight to see. It was spectacular."
He wasn't the only one to see it.
When Kelly Spear looked out the back window of her San Pedro home to see a rising orange line on the horizon, she thought it might be a rocket launch from Vandenberg Air Force Base, a sight unusual enough for her to grab her telephoto lens and take a few shots.
"I told myself it was just a plane, but I really had no idea," she said. "We have a pretty expansive view, and I've never seen anything like that before."
Some aerospace experts who reviewed the footage said the size of the plume hinted that it was a government operation.
"It can't belong to anyone but the military," said Marco Caceres, an analyst with Teal Group Corp., a Fairfax, Va.-based aerospace research firm. The appearance of such a massive rocket contrail near military bases that are known for regularly testing missiles is unlikely to be a coincidence, Caceres said.
A more likely explanation, Caceres said: It was a mistake, perhaps a defense exercise launched by accident.
The military does, after all, operate a floating ocean platform and regularly carries out tests at San Nicolas Island, one of the Channel Islands, and Point Mugu Naval Air Station is a missile defense testing site.
All branches of the Department of Defense with rocket and missile programs reported no launches, scheduled or inadvertent, a Pentagon spokesman affirmed in a statement late Tuesday.
The Pentagon has not shed much light on what happened, but one official said an examination by multiple U.S. government agencies of radar data, satellite imagery and other sophisticated monitoring technology has turned up no conclusive evidence that a missile was fired in that vicinity and at that time.
The official, who spoke on condition of anonymity because the investigation is ongoing, said that Federal Aviation Administration records showed commercial airliners were flying in the area at the time, and that most government experts were coming to the conclusion that the condensation trail was caused by an aircraft.
"The best we can tell, it was probably caused by an aircraft," the official said.
The FAA did not approve any commercial space launches in the area Monday and did not receive reports of any unusual sightings from pilots, said FAA spokesman Ian Gregor.
After reports of the projectile surfaced, the agency ran radar replays of a large area west of Los Angeles and did not spot any fast-moving, unidentified targets in that area, Gregor said.
Mike Gruntman, a USC professor of astronautics, reviewed the video but said any definitive answer on the mysterious projectile lies with the military.
The video that generated all the hoopla, he said, is so close up and of such low resolution that it's hard to draw conclusions.
"It looks like a missile to me," he said. "But I cannot rule out that this is some kind of jet aircraft."
Times staff writer David S. Cloud contributed to this report from Washington, D.C.