NASA's decommissioned 6.3-ton Upper Atmosphere Research Satellite, out of gas and out of control after two decades in space, plunged back into the atmosphere early Saturday, heating up, breaking apart and presumably showering chunks of debris along a 500-mile-long Pacific Ocean impact zone.

Maybe.

U.S. Strategic Command radar tracking indicated re-entry would occur around 12:16 a.m. EDT (GMT-4) Saturday as the satellite was descending across the Pacific Ocean on a southwest-to-northeast trajectory approaching Canada's west coast. If re-entry occurred on or before the predicted time, any wreckage that survived atmospheric heating almost certainly fell into the Pacific Ocean.

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Nick Johnson, chief scientist with NASA's Orbital Debris Program at the Johnson Space Center in Houston, says the space agency has received "no credible" reports of observers seeing the UARS re-entry. Officials think the satellite most likely fell into atmosphere over the open Pacific Ocean around 12 a.m. EDT (0400 GMT) and the surviving debris would have landed in the sea before reaching North America.

We'll have live streaming coverage of NASA's audio-only teleconference with reporters at 2 p.m. EDT (1800 GMT).

And also join us later today at 4 p.m. EDT (2000 GMT) for live coverage of today's Sea Launch rocket blastoff.

The Joint Space Operations Center at Vandenberg Air Force Base in California says UARS re-entered over the North Pacific Ocean, off the west coast of the United States.

"The precise re-entry time and location of any debris impacts are still being determined. NASA is not aware of any reports of injury or property damage," the space agency said in a statement.

NASA plans a news briefing today at 2 p.m. EDT.

According to a NASA spokesman, Air Force space-tracking specialists report UARS entered the atmosphere over the Pacific Ocean. However, the precise time and locale aren't yet known.

RE-ENTRY CONFIRMED. The Upper Atmosphere Research Satellite, launched from the shuttle Discovery in 1991 to begin a new era of studying the Earth's environment from space, has fallen from orbit.

But NASA still doesn't know exactly when or where the re-entry happened.

"NASA's decommissioned Upper Atmosphere Research Satellite fell back to Earth between 11:23 p.m. EDT Friday, Sept. 23 and 1:09 a.m. EDT Sept. 24. The satellite was passing eastward over Canada and Africa as well as vast portions of the Pacific, Atlantic and Indian oceans during that period. The precise re-entry time and location are not yet known with certainty," the space agency says.

Natural processes caused the large spacecraft's orbital altitude to gradually lower over time, finally tumbling into the atmosphere today where it burned up. It had spent 7,316 days in space.

NASA expected 26 fragments of the satellite would survive the superhot re-entry and hit the ground, such as titanium fuel tanks, antenna structures and beryllium brackets. The combined mass of the pieces was predicted to be 1,173 pounds (532 kg).

Authorities urge anyone finding the satellite pieces to avoid touching the objects and contact local officials.

A NASA spokesman just tweeted: "As we thought, a lot of hoax data and false info going viral. We'll have an official update soon."

NASA says it continues to wait for final confirmation of re-entry. "If debris fell on land (and that's still a BIG if), Canada is most likely area," the space agency just said.

Still awaiting official word.

NASA says the agency is working to confirm the re-entry location and time. It will provide an update shortly.

"It's possible that UARS is down by now," NASA just said. "We're waiting for confirmation from U.S. Strategic Command."

If UARS is still up there, it has passed over North America. We'll post official confirmation of the re-entry when it is announced.

The likely re-entry window has opened. NASA predicts UARS will make its fiery plunge into the atmosphere within the next 60 minutes. The satellite is south of Australia at the current time, about to fly over the Pacific Ocean toward a crossing of Canada, then the Atlantic Ocean and Africa, if UARS remains in orbit that long.

The streaming video you are watching shows satellite tracking software. The program is illustrating the most recent orbital data for the UARS satellite's flight path.

This video won't depict the actual re-entry whenever it occurs, and the stream will continue playing until confirmation is received that UARS has fallen from space.

The latest numbers show UARS flying in an orbit of 85 miles by 90 miles (135 km by 140 km). NASA officially predicts re-entry will happen sometime between 11:45 p.m. and 12:45 a.m. EDT (0345-0445 GMT). The satellite's orbital flight path will be crossing the Pacific, North America, the Atlantic, Africa and Indian Ocean during the upcoming hour-long re-entry window.

Strategic Command's final prediction has been issued for re-entry at approximately 12:16 a.m. EDT (0416 GMT). The satellite would be approaching the coast of North America at that time, crossing Washington before flying over Canada. But the margin of error remains plus or minus two hours.

Based on a potential re-entry coming up during UARS' next few orbits, the satellite will be passing over the Pacific, Atlantic and Indian oceans, plus Canada, Africa and Australia. The most recent altitude numbers showed the satellite was flying in an orbit of just 90 miles by 95 miles (145 km by 150 km). The craft is likely to come down sometime between 11 p.m. and 3 a.m. EDT (0300-0700 GMT).

NASA's decommissioned Upper Atmosphere Research Satellite, out of gas and out of control, is not descending toward re-entry as rapidly as expected, officials say, likely delaying the satellite's kamikaze plunge to Earth by a few hours to late Friday or early Saturday. Experts expect more than two dozen chunks of debris to survive re-entry and hit the ground in a 500-mile-long footprint somewhere along the satellite's orbital track.

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U.S. Strategic Command's latest projection shows re-entry occurring around 12:50 a.m. EDT (0450 GMT). But the margin of error is plus or minus four hours.

The latest tracking of UARS shows the satellite's orbit has fallen to 100 miles by 105 miles (160 km by 170 km). The likely re-entry time period has shift later -- now late tonight or early tomorrow (Eastern Daylight Time).

"Solar activity is no longer the major factor in the satellite's rate of descent. The satellite's orientation or configuration apparently has changed, and that is now slowing its descent," NASA officials say.

"There is a low probability any debris that survives re-entry will land in the United States, but the possibility cannot be discounted because of this changing rate of descent. It is still too early to predict the time and location of re-entry with any certainty, but predictions will become more refined in the next 12 to 18 hours."

No one knows for sure when and where the Upper Atmosphere Research Satellite will fall back to Earth today, some 20 years after being launched from the shuttle Discovery to begin a new era of scientific study of our planet's environment from space.

Blasting away from the Kennedy Space Center at sunset on Sept. 12, 1991, the UARS spacecraft was deployed into orbit by the astronauts using the shuttle's robotic arm on Sept. 15, 1991.

Its suite of sensors probed the atmosphere's chemistry and human afflictions to the ozone layer for more than 5,000 days as the initial piece of NASA's Mission to Planet Earth program. UARS eventual gave way to newer satellite platforms that continue to observe Earth's climate and environmental health.

UARS was decommissioned on Dec. 15, 2005, becoming a dead satellite whose altitude would slowly decay until tumbling into the atmosphere.

With the satellite turned off and no fuel left to maneuver the craft, the precise moment in which the satellite will hit the atmosphere is unknown. The fiery re-entry will be completely uncontrolled.

Continuous tracking is orbit enables engineers to predict in broad terms when the re-entry is likely to occur. The current guess is Friday afternoon or evening (Eastern Daylight Time).

Although old space hardware and orbital debris fall back to Earth almost daily, the size of UARS and the likelihood that several large pieces will survive the catastrophic breakup in the atmosphere to hit the ground has given this re-entry unusual amounts of public attention.

NASA predicts 26 chunks of the satellite will endure the superhot re-entry and remain intact, such as titanium fuel tanks, antenna structures and beryllium brackets. The combined mass of the pieces is estimated at 1,173 pounds (532 kg).

The swath of falling debris could stretch 500 miles long. Authorities urge anyone finding the satellite pieces to avoid touching the objects and contact local officials.

"Satellites re-entering is actually very commonplace," said Nick Johnson, chief scientist with NASA's Orbital Debris Program at the Johnson Space Center in Houston.

"Last year, for example, we averaged over one object per day falling back uncontrolled into the atmosphere. The majority of these, of course, were very, very small, they burn up completely and no parts reach the surface of the Earth.

"On the order of one moderate-sized object, on average, falls back to Earth every week, an old intact spacecraft or intact rocket body. Some of these vehicles do have components that reach the surface of the Earth. When they do, they typically fall into an ocean area or some desolate region. Typically, we find one piece a year from one of these re-entries."

But something as large as UARS re-enter about once per year on average.

"Last year, there were 75 metric tons of spacecraft and rocket bodies falling back to Earth in an uncontrolled manner," he said. "In perspective, UARS is less than six metric tons. So it's a very small percentage of the annual re-entry of satellites.

"Finally, just to remind everyone, throughout the entire 54 years of the space age, there have been no reports of anybody in the world being injured or severely impacted by any re-entering debris."

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Here is the history of UARS orbital data and re-entry predictions over the past two weeks:

• As of Sept. 12, the orbit of UARS was 145 mi by 165 mi (235 km by 265 km). Re-entry is expected during the last week of September.
  
  
• As of Sept. 15, the orbit of UARS was 143 mi by 158 mi (230 km by 255 km). Re-entry is expected Sept. 24, plus or minus a day.
  
  
• As of Sept. 16, the orbit of UARS was 140 mi by 155 mi (225 km by 250 km). Re-entry is expected Sept. 23, plus or minus a day. The re-entry of UARS is advancing because of a sharp increase in solar activity since the beginning of this week.
  
  
• As of Sept. 18, the orbit of UARS was 133 mi by 149 mi (215 km by 240 km). Re-entry is expected Sept. 23, plus or minus a day.
  
  
• As of Sept. 19, the orbit of UARS was 130 mi by 143 mi (210 km by 230 km). Re-entry is expected Sept. 23, plus or minus a day.
  
  
• As of 1:30 p.m. EDT Sept. 21, the orbit of UARS was 120 mi by 130 mi (190 km by 205 km). Re-entry is expected sometime during the afternoon of Sept. 23, Eastern Daylight Time.
  
  
• As of 7 a.m. EDT Sept. 22, the orbit of UARS was 115 mi by 120 mi (185 km by 195 km). Re-entry still expected sometime during the afternoon of Sept. 23.
  
  
• As of 9:30 p.m. EDT Sept. 22, the orbit of UARS was 110 mi by 115 mi (175 km by 185 km). Re-entry is possible sometime during the afternoon or early evening of Sept. 23, Eastern Daylight Time.

Armchair satellite trackers hoping to catch a glimpse of NASA's doomed Upper Atmosphere Research Satellite -- UARS -- when it plunges back to Earth Friday will need patience, access to the internet, a clear sky and a large helping of luck to have any chance of spotting the spacecraft's fiery demise, experts say.

Even with last-minute updates from NASA and U.S. Strategic Command pinpointing when and where UARS will begin its final plunge, the sheer size of the planet, with its vast stretches of ocean and remote terrain, means the odds of catching a glimpse -- or of being anywhere near any falling debris -- will be remote.

But as re-entry footage of the old Russian Mir space station and the more recent flaming fall of a European cargo craft show, satellite "decays" offer the public and experienced amateurs alike a chance to witness a fairly spectacular show.

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NASA expects an abandoned research satellite to crash back to Earth later this month, scattering more than 1,000 pounds of debris somewhere on the surface as the rest of the craft vaporizes in the upper atmosphere.

Discussing the pending re-entry with reporters Friday, NASA and U.S. military officials said the satellite should plunge back into the atmosphere in late September, but it's impossible to predict when or where the spacecraft will fall.

"We just won't know precisely where it's going to come down until it's come down," said Nick Johnson, chief scientist for NASA's orbital debris program at the Johnson Space Center in Houston.

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