Military officials are still unclear as to what caused the "mystery missile" contrail spotted off the Southern California coast last night, but the most likely theory appears to be that an airplane was responsible.
Some experts believe the "mystery missile" is an optical illusion involving atmospherics and the contrails of a plane flying off in the distance.
Military officials have spent all day trying to determine who or what may have been responsible for what seemed like a mysterious missile launch caught on tape Monday night by a news helicopter off the Southern California coast.
There has been much speculation that the mysterious contrail may have been caused by a missile, a plane or an optical illusion of a plane's contrails.
Defense Department officials say that though there is nothing conclusive, it appears that a plane may have caused the mysterious contrail.
A defense official says the Pentagon has determined there were no scheduled or inadvertent missile launches off the California coast last night and that U.S. Northern Command has confirmed that there was no foreign military launch off the coast.
In a statement earlier today, Northern Command said they were continuing to investigate the origin of the apparent missile launch, but said they had determined "that there is no threat to our nation, and from all indications this was not a launch by a foreign military."
The contrail of what appears to be a missile streaking into the California sunset was captured on video by a KCBS-TV news helicopter flying above Los Angeles at around 5 p.m. Pacific time.
The crew aboard the helicopter estimated the contrail was approximately 35 miles west out to sea, north of Catalina Island.
The video drew more attention when local news stations were told by Navy and Air Force officials that they did not launch a missile Monday night.
Because the video shows what appears to have been a missile launch at sea, there was speculation that a Navy vessel, perhaps even a submarine, might have launched a missile off the California coast. However, Navy officials determined that none of their vessels had fired a missile.
Vandenberg Air Force Base, north of Los Angeles, is a regular launch point for missile tests, but Air Force officials confirmed that they had no missile activity either on Monday night.
Ivan Oelrich, with the Federation of American Scientists, screened the KCBS-TV video for ABC News and said he could not be certain about what the video shows because it shows characteristics of both a missile launch or perhaps an optical illusion involving a plane's contrail.
Oelrich said it could be a jet contrail because if "it's horizontal goes a long, long distance, almost to the horizon, (then) it looks vertical." But he also said that a plane would have had multiple separate contrails that do not seem to appear on the video.
He speculated that a glint of light seen at the top of the contrail might be the exhaust from a rocket engine, but it "doesn't appear earlier, which is unusual, because if it were a rocket, you would see that continuously."
That could mean the glint of light might be the sun's reflection off the top of a plane, "up high, still in the sunlight while you're down below in the darkness so that could be sun glint."
Oelrich said he does not believe it could have been a secret missile test.