For weeks NASA's defunct 7-ton research satellite has been falling towards Earth with the potential of shattering on the earth's surface and raining debris on densely populated areas, but the Space agency has confirmed the impeding threat saying it is set to crash by the end of the week.

But where will the The Upper Atmosphere Research Satellite ( UARS) hit exactly and should people be worried?

The risk to public safety or property is extremely small, and safety is NASA's top priority, the space agency wrote in an advisory. Since the beginning of the Space Age in the late-1950s, there have been no confirmed reports of an injury resulting from re-entering space objects. Nor is there a record of significant property damage resulting from a satellite re-entry.

But senior space agency officials admitted they were concerned about the risk to billions of people when it starts falling uncontrolled out of orbit at any stage from later this month, the Telegraph reported

The debris is expected to leave a 500-mile long footprint but the chances of a piece of the craft hitting the ground of a densely populated area is extremely low, experts say.

The Satellite has been in orbit for six years in what NASA calls a productive scientific life. Although it will break into pieces during re-entry, not all of it will burn up in the sky, according to a report.

More than 500,000 pieces of debris, or space junk, are tracked as they orbit the Earth. They all travel at speeds up to 17,500 mph, fast enough for a relatively small piece of orbital debris to damage a satellite or a spacecraft, NASA reported.

Orbital debris is any man-made object in orbit about the Earth, which no longer serves a useful function. Such debris includes nonfunctional spacecraft, abandoned launch vehicle stages, mission-related debris and fragmentation debris. 

NASA has said it is hard to predict the exact date of the re-entry as it is dependent on solar flux and the spacecraft's orientation as the orbit decays but the space agency will be posting weekly updated and then daily updates as the craft approaches.

As of Sept. 18, 2011, 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. Because the satellite's orbit is inclined 57 degrees to the equator, any surviving components of UARS will land within a zone between 57 degrees north latitude and 57 degrees south latitude, NASA reported.

UARS was a $750 million mission deployed from the shuttle Discovery in 1991 to study the Earth's atmosphere and its interactions with the sun. It measures important ozone depletion related to climate change. According to NASA reading from UARS gave evidence that Chorine in the atmosphere is at the root of the polar ozone hole.