A defunct NASA science satellite is expected to plunge back to Earth soon, sparking concerns that some debris might shower down on populated areas.

The 6.5-ton Upper Atmosphere Research Satellite will burn up in Earth's atmosphere when it finally falls from orbit later this month or early October, the U.S. space agency says.

NASA said it's too early to say exactly when UARS will make its final plunge, or where any debris will come down.

Fragments of the 20-year-old probe, which ran out of fuel in 2005, could land anywhere in the inhabited continents in a worldwide swath from the 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 500 miles.

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