A defunct NASA science satellite will be plunging back to Earth soon, sparking concerns that some debris might shower down on populated areas.

Most of the 6.5-ton Upper Atmosphere Research Satellite, known by its acronym UARS, will burn up in Earth's atmosphere when it finally falls from orbit later this month or early October.

NASA says the 20-year-old UARS ran out of fuel in 2005 and probably will fall uncontrolled sometime between late September and October. Pieces of it could land anywhere in the six inhabited continents in a worldwide swath from south of Juneau, Alaska, to just north of the tip of South America.

NASA has estimated a 1-in-3,200 chance that a satellite part could hit someone. Most of it will burn up after entering the atmosphere. Only about 1,200 pounds should survive, scattered over perhaps a 500-mile-wide area, NASA said.

UARS was deployed from the shuttle Discovery in 1991 to study Earth's atmosphere and its interactions with the sun. The $750 million mission measured the concentrations and distribution of gases important to ozone depletion, climate change and other atmospheric phenomena. NASA says readings from UARS provided conclusive evidence that chlorine in the atmosphere, originating from human-produced chlorofluorocarbons, is at the root of the polar ozone hole.

NASA says it plans to post updates about UARS' status weekly until four days before the anticipated re-entry, and then daily until about 24 hours before re-entry.

The satellite's current orbit is 155 by 174 miles (250 by 280 kilometers), with an inclination of 57 degrees, NASA said. That means the satellite would have to descend into the atmosphere somewhere between 57 degrees north latitude and 57 degrees south. NASA estimated that the debris footprint would stretch about 500 miles.

That means pieces could fall over most of the world's six inhabited continents as well as its three largest oceans.

The risk to public safety or property is extremely small. 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.

The agency said it's too early to say exactly when UARS will make its final plunge, or exactly where any debris will fall.