Military officials remain stumped about the mysterious projectile spotted in the sky off the Southern California coast, but aerospace experts said it appeared to be an errant missile launch.

Pentagon officials are looking into what they have called an "unexplained contrail" after a KCBS news helicopter shot video late Monday of a luminous point hurtling through the sky followed by a long vapor trail.

Each branch of the military has denied involvement, and the Pentagon has been cryptic about the object and who may have launched it. Despite this, officials said the event was not a threat to national security. They also said it was not a launch by a foreign military.

While rocket launches are a common sight in Southern California, getting proper authorization is a weeks-long process. Authorities that oversee commercial and military launches have denied any knowledge of a scheduled launch.

The Federal Aviation Administration did not approve any commercial space launches around the area Monday, said spokesman Ian Gregor. In addition, the agency did not receive reports of any unusual sightings from pilots who were flying in the area.

After reports of the event, 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.

Officials at nearby military bases where rocket launches regularly take place also said they were not involved.

Aerospace experts who reviewed the footage said the size of the plume suggests it was a large military rocket or missile.

"The launch of a rocket that size doesn't belong to any commercial entity without them issuing a press release," said Marco Caceres, analyst with Teal Group Corp., a Fairfax, Va.-based aerospace research firm. "It can't belong to anyone but the military."

The lack of explanation from the Pentagon makes Caceres believe it may have been a mistake -- perhaps a defense exercise launched by accident.

Based on the footage, it is unclear where exactly the missile was coming from, but many analysts believe it originated near Naval Air Station Point Mugu in Ventura County, where missiles and missile defense exercises are regularly carried out.

Officials at the base, however, denied it was their missile.

"It didn't happen here," said Naval Base Ventura County spokeswoman Teri Reid. "There was no firing on the range yesterday."

The military also operates a floating ocean platform and regularly carries out tests at San Nicolas Island, one of the Channel Islands.

Riki Ellison, founder and chairman of the Missile Defense Advocacy Alliance, said it could have been launched from an island off the mainland or a submarine in the Pacific Ocean.

In any case, if this were a planned event, military officials would have known weeks in advance.

"There is a safety routine that the government goes through," Ellison said. "Everything needs to be cleared away. They're not going to take any risks."

-- W.J. Hennigan and Tony Barboza