A video that appears to show a missile launch off the coast of California is so far "unexplained" by anyone in the military, a Pentagon spokesman told reporters Tuesday -- but what seems mysterious could be nothing more than an airplane.

Federal officials do not consider the event a threat. And they aren't the only ones.

According to a post on ContrailScience.com, the visible exhaust from a jet engine, a trail of condensed water vapor called a contrail, resembles a missile trail when seen from some angles.

The confusion between a missile launch and a jet plane launch is caused by several common misconceptions, the site notes, explaining that the angle of launch, the direction of flight, and even the shape of the Earth can lead to the illusion. And indeed, when you look at certain images of jet launches, they do look a fair bit like missiles.

The site's author goes on to note other factors that could connect the unexplained launch to a jet engine. There's no bright rocket flare, just a few flashes of sunlight, and a sunlit trail. Plus the unexplained craft is incredibly slow, the site notes, while rockets move incredibly fast.

A senior military official told Fox News late Tuesday that indications are that the contrail "was more likely caused by an airplane than anything else because the other possibilities of rockets or missiles are turning up negative." But officials still aren't 100 percent sure, so the military is taking steps to review its missile inventory and make sure they're all accounted for.

A similar mystery event took place on Dec. 31, 2009, when a launch in the skies over Orange County mystified people. The Orange Country Register noted a few days later that the event was variously described as a rocket launch or jet contrails. ContrailScience.com argues that both events were simply planes -- seen from an unexpected angle, that is.

Military officials remain puzzled. The Missile Defense Agency told Fox News it did not launch any test missile last night that could explain the dramatic images. The Navy and the Air Force were also unable to offer an explanation.

A Boeing spokesman could not immediately confirm this potential explanation for the event.

"It does not appear that this was a regularly scheduled missile test," Boeing spokesman David Lapan said. "Before a missile test the military sends notifications to mariners, airmen and air traffic controllers to stay clear of the area." And, according to Lapan, it doesn't appear those warnings were sent.

ContrailScience.com's plane theory may explain why the military simply doesn't know what the so-called mystery missile was.

Click here to see the video captured by KCBS in Los Angeles.

EDITOR'S NOTE: Following questions about Kevin Martin, a self-described "meteorologist" who was quoted in the original report, FoxNews.com removed his comment from the story.