A SIX-TONNE NASA science satellite plunged through the atmosphere early today, breaking up and possibly scattering debris in Canada, NASA said.
There were reports on Twitter of debris falling over Okotoks, a town south of Calgary in western Canada, most likely the remains of the Upper Atmosphere Research Satellite, or UARS, which had been in orbit for 20 years.
Scientists were unable to pinpoint the exact time and place where UARS would return to Earth due to the satellite's unpredictable tumbles as it ploughed through the upper atmosphere.
Re-entry was believed to have occurred on Saturday between 3.45am and 4.45am.
Stretching 10.6m long and 4.5m in diameter, UARS was among the largest spacecrafts to plummet uncontrollably through the atmosphere, although it is a slim cousin to NASA's 75-tonne skylab station, which crashed to Earth in 1979.
Russia's last space station, the 135-tonne Mir, crashed into the Pacific Ocean in 2001, but it was a guided descent.
NASA now plans for the controlled re-entry of large spacecrafts, but it did not when UARS was designed.
The 5,897kg satellite was dispatched into orbit by a space shuttle crew in 1991 to study ozone and other chemicals in the Earth's atmosphere. It completed its mission in 2005 and had been slowly losing altitude ever since, pulled by the planet's gravity.
Most of the spacecraft burned up during the fiery plunge through the atmosphere, but about 26 individual pieces, weighing a total of about 500kg could have survived the incineration and landed somewhere on Earth.
The debris field spans about 805km.
The chance that someone would be hit by falling debris was one in 3,200, NASA said.