Feb. 16--DALLAS -- The fireball that blazed across the Texas sky and sparked numerous weekend calls to law enforcement agencies is closer to being considered an identified flying object.

The Federal Aviation Administration said Monday that the fireball was a natural phenomenon -- not flying space junk -- and a North Texas astronomer said more specifically that it was probably a pickup truck-sized meteor with the consistency of concrete.

The object was visible Sunday morning from Austin to Dallas and into East Texas. In Central Texas, the Williamson County sheriff's office received so many emergency calls that it sent a helicopter aloft to look for debris from a plane crash.

The FAA backed off its weekend statement that the fireball possibly was caused by falling debris from colliding satellites plummeting into earth's atmosphere.

On Sunday, the FAA said the fireball, accompanied by a sonic boom, was probably a piece of space debris, which officials thought may have come from a collision that destroyed two satellites last week.

The U.S. Strategic Command said there was no connection to the sightings over Texas and Tuesday's collision of satellites from the U.S. and Russia.

"There is no correlation between the debris from that collision and those reports of re-entry," said Maj. Regina Winchester, with STRATCOM.

The satellites collided over Siberia and sent thousands of pieces of debris into the Earth's orbit, pieces that experts said could remain there for thousands of years.

The sightings prompted several calls to law enforcement, including to agencies in Collin County, officials said. In Williamson County, north of Austin, the fireball sent authorities scrambling in vain to search for what they thought was a crashing aircraft, The Associated Press reported.

Across Texas, callers described a red-and-orange burning object that eventually turned white and appeared to burn out. Nobody was injured, and officials had yet to find any debris by late Sunday.

In North Texas, the Plano Police Department fielded at least two calls, said officer Andrae Smith, police spokesman. One Plano officer captured some of the falling debris on a dash-mounted video camera during a midafternoon traffic stop, he said, but officials hadn't reviewed the footage late Sunday and weren't sure about its quality.

Officials at the Fort Worth Police Department and sheriff's departments in Tarrant, Parker, Johnson and Denton counties said they didn't have any reports of similar sightings. But someone describing himself as an SMU professor posted an item on a blog at the Austin American-Statesman saying he had seen something while traveling south on Central Expressway in Dallas.

An Austin TV station captured the object on tape. According to the Federal Aviation Administration, authorities in Limestone County, east of Waco, had also received a report.

A spokesman for the FAA, which issued a warning to pilots about the falling debris, said law enforcement agencies started contacting the agency about 11 a.m.

"People started reporting to law enforcement that there was a 'fireball' and some people reported an explosion, which we suspect was probably a sonic boom," FAA spokesman Roland Herwig said during a conference call with reporters Sunday.

Ron DiIulio, director of the astronomy laboratory at the University of North Texas, said what callers reported could have been a natural object, such as a meteor, or space junk, but the fact that people reported sightings all across Texas made it more likely that it was a piece of space debris.

A meteor, he said, would have come in at a high speed and burned up much more quickly, meaning that it would probably have taken a bus-sized object to pass across Texas and still be visible to those below.

Pieces of space junk "come in so slowly that they last for quite a while," he said. "If there's an idea that people are seeing a ball of flame in Austin and also seeing it in Plano, then it's probably a satellite."

Herwig, of the FAA, said unless a piece of debris is actually found intact, investigators won't be able to make a definite determination.

"Until somebody comes up with a chunk of something and someone goes to investigate it, we won't know for sure" what it is, he said.

Michael Hibbs, an astronomy instructor at Tarleton State University, said pieces of debris generally disintegrate as they pass through the atmosphere.

"It has to be a very large piece to actually ever hit the ground," Hibbs said.

DiIulio said it would probably take a piece of space junk the size of a pickup to generate Sunday's event.

He said the increased availability of digital imaging technology to consumers and cellphones has led to an increase in reporting.

"We're getting pictures of these coming in now much more than we used to," he said.

The report contains material from The Associated Press.