By The Associated Press
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The agency did not give a more specific location in a midday update on its website, http://www.nasa.gov/mission_pages/uars/index.html , which also said officials were not aware of any reports of injuries or property damage. Most of the spacecraft was believed to have burned up.
The bus-sized satellite first penetrated Earth's atmosphere somewhere over the Pacific Ocean, according to NASA and the U.S. Air Force's Joint Space Operations Center. But that doesn't necessarily mean it all fell into the sea.
NASA's earlier calculations had predicted that the 20-year-old former climate research satellite would fall over a 500-mile swath and could include land.
Because the plummet began over the ocean and given the lack of any reports of people being hit, that "gives us a good feeling that no one was hurt," but officials didn't know for certain, NASA spokesman Steve Cole told The Associated Press.
The two government agencies said the 35-foot satellite fell sometime between 8:23 p.m. PDT and 10:09 PDT Friday, but with no precise time or location.
There was rampant speculation on the Internet and Twitter, much of it focusing on unconfirmed reports and even video of debris from the Upper Atmosphere Research Satellite over Alberta, Canada.
Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics said the spacecraft entered the atmosphere around 9:15 a.m. PDT over the coast of Washington. He said much of the debris likely fell over the Pacific Ocean, though its trajectory suggests some of it could have fallen over more heavily populated areas in the U.S. and Canada, including Portland, Ore.; Seattle; Calgary, Alberta; and Saskatoon, Saskatchewan.
"Pieces are falling off of this flaming fireball, and some of it has enough momentum to go hundreds of miles," he said.
Cole said that was possible because the last track for the satellite included Canada, starting north of Seattle and then in a large arc north then south. From there, the track continued through the Atlantic south toward Africa, but it was unlikely the satellite got that far if it started falling over the Pacific.
Cole said NASA was hoping for more details from the Air Force, which was responsible for tracking debris.
But given where the satellite may have fallen, officials may never quite know precisely.
"Most space debris is in the ocean. It'll be hard to confirm," Cole said.
Some 26 pieces of the satellite representing 1,200 pounds of heavy metal had been expected to rain down somewhere. The biggest surviving chunk should be no more than 300 pounds.
UARS is the biggest NASA spacecraft to crash back to Earth, uncontrolled, since the post-Apollo 75-ton Skylab space station and the more than 10-ton Pegasus 2 satellite, both in 1979.
Russia's 135-ton Mir space station slammed through the atmosphere in 2001, but it was a controlled dive into the Pacific.
Before UARS fell, no one had ever been hit by falling space junk and NASA expected that not to change.
NASA put the chances that somebody somewhere on Earth would get hurt at 1-in-3,200. But any one person's odds of being struck were estimated at 1-in-22 trillion, given there are 7 billion people on the planet.
The satellite ran out of fuel and died in 2005. UARS was built and launched before NASA and other nations started new programs that prevent this type of uncontrolled crashes of satellite.