National Geographic News
The UARS satellite is deployed into orbit in 1992.

An astronaut picture of the UARS satellite being deployed in 1991.

Photograph courtesy NASA

Traci Watson

for National Geographic News

Updated September 24, 2011, at 6:05 p.m. ET

After 20 years in orbit, NASA's UARS satellite has fallen to Earth, most likely into a watery grave at the bottom of the Pacific Ocean. But its exact resting spot may remain a mystery forever, NASA said.

(Also see "Space Debris: Five Unexpected Objects That Fell to Earth.")

The U.S. military's Joint Space Operations Center estimated that the Upper Atmosphere Research Satellite, or UARS, toppled from the sky at 12:16 a.m. ET Saturday.

(See "NASA Satellite Falling Faster Due to Solar Activity.")

If that's correct, the 1,100 pounds (500 kilograms) of debris that were predicted to survive reentry would have splashed down in the northern Pacific, far west of California.

But "we may never know" exactly where the spacecraft met its fate, NASA's Nick Johnson said on Saturday.

NASA needs observations from the public to be certain of the location of remnants from the satellite, which is the biggest NASA spacecraft to make an uncontrolled reentry in more than 30 years, Johnson said.

He hopes eyewitness accounts from ships or airliners will eventually confirm that any surviving pieces of UARS dove harmlessly into the sea.

Amateur satellite trackers in places such as San Antonio, Texas, and northern Minnesota reported catching glimpses of UARS as it made its final circles around Earth.

But so far there have been no credible reports of debris either found on the ground or seen streaming through the sky, Johnson said. Nor have there been reports of injuries or damage.

If the satellite actually slammed down just a few minutes later than estimated, it's possible some pieces landed in western Canada. But so far rumors of debris there have proven to be only rumors.

Satellite Pieces Not For Sale

UARS, which weighed more than six tons, was lofted into orbit by the space shuttle Discovery in 1991. The craft recorded data on Earth’s atmosphere until it was switched off in 2005.

The biggest intact piece to survive the superheated descent through the atmosphere was most likely a 300-pound (140-kilogram) chunk of the spacecraft's structure, NASA said.

NASA continues to warn the curious not to touch any pieces of the spacecraft that may have made it to the ground, because of the risk of sharp edges.

The space agency also tried to head off sales of UARS remnants on Internet auction sites such as eBay.

"Any pieces of UARS found are still the property of the country that made it," NASA warned via Twitter this morning. "You'll have to give 'em back to U.S."

Also see "Space Station to Fall to Earth—Find Out How and Where" >>

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