An old NASA satellite is expected to fall to Earth in pieces as early as Thursday.

The Upper Atmosphere Research Satellite (UARS), which was decommissioned in 2005, is expected to re-enter the Earth's atmosphere on Sept. 23, plus or minus a day, NASA reported Monday afternoon.

"Although the spacecraft will break into pieces during re-entry, not all of it will burn up in the atmosphere," NASA acknowledged in a statement. However, it added that "the risk to public safety or property is extremely small."

According to The Canadian Press, about 26 potentially hazardous pieces of the satellite are expected to survive re-entry and more than 450 kilograms of debris may make it to the ground, resulting in an estimated 1 in 3,200 chance of hitting someone.

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The Upper Atmosphere Research Satellite, shown here being launched using a robotic arm from the Space Shuttle Discovery in 1991, has a mass of nearly six tonnes. ((NASA))

If the satellite does cause any damage, the U.S. government could be held legally responsible, since it is the country of origin for the satelitte, Peter Brown, a University of Western Ontario space scientist, told The Canadian Press.

However, Brown, who uses radar data to track meteorites around the Earth's atmosphere, said most likely the satellite will come down over the ocean.

The UARS satellite, launched in 1991 to take measurements of the ozone layer, has a mass of almost six tonnes and is a little over 10 metres long with a diameter of about 4.5 metres. Other satellites have taken over the types of measurements it used to make.

NASA expects any surviving components to land between 57 north degrees latitude – about 300 kilometres south of the boundary between the territories and the provinces — and 57 degrees south latitude. The debris is expected to be scattered across an area about 800 kilometres long, but NASA said the location of that zone is "impossible to pinpoint."

The U.S. space agency warned members of the public not to touch any objects that could be pieces of the satellite. Instead, it advised them to contact police for help.

NASA said it will provide daily updates until 24 hours before the satellite's re-entry, with additional updates at 12, six and two hours before re-entry.

Phil Langill, director of Calgary's Rothney Astrophysical Observatory, told the Canadian Press that the satellite could put on a good show if it falls during the night.

"People will be lucky enough to see a very spectacular streak across the sky — like the biggest fireball they have ever seen."

With files from The Canadian Press