A dead NASA satellite is expected to re-enter Earth's atmosphere Friday, but the U.S. space agency says it has no clue where it will land.

The satellite has finished its productive scientific life and is being watched closely by NASA scientists.

Most of the 6.5-ton Upper Atmosphere Research Satellite will burn up in Earth's atmosphere when it falls from the orbit.

The re-entry of the satellite has advanced due to a sharp increase in solar activity since the beginning of this week. According to the calculations made by NASA scientists, the satellite will break into 26 pieces as it gets closer to earth. The chances of it hurting someone anywhere on the planet are 1 in 3,200.

NASA says the 20-year-old UARS ran out of fuel in 2005. Pieces of the satellite 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.

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, from human-produced chlorofluorocarbons, is at the root of the polar ozone hole.

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.

NASA estimated that the debris footprint would stretch about 500 miles.