A defunct NASA satellite is set to descend into the Earth's atmosphere this weekend, but the U.S. space agency says it has no clue where it will land.

According to the latest projections, the six and a half-ton bus-sized Upper Atmosphere Research Satellite, known by its acronym UARS, is scheduled to reach the surface of the planet sometime on Friday, Sept. 23.

The 6.5 ton satellite was originally expected to re-enter the Earth's atmosphere either late September or early October but the re-entry has advanced due to a sharp increase in solar activity since the beginning of this week.

It's a little bit unpredictable, and as a result, it's coming in a little faster than we originally anticipated. said Dr. Mark Mateny of the Orbital Debris Program at Johnson Space Center in Houston, Texas.

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 Antarctica.

It's a hard calculation problem; we don't know the exact instant when it's going to come down, and it's moving really fast. It actually orbits the Earth every 90 minutes, says Steve White, a Fresno State Physics Professor.

Most of the vessel is expected to burn up in the atmosphere, but the agency says there is little chance that the falling debris will create risk to public safety or property.

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, NASA said in a report.

According to a NASA statement issued on Monday, the satellite's current orbit is 145 miles by 165 miles (235 km by 265 km).

NASA estimates a 1-in-3,200 chance that a satellite part could hit someone, though 1,200 pounds should survive the re-entry.

NASA experts suggest at least 26 durable parts will remain intact on re-entry and may crash in a wide area, up to 400 to 500 miles. Some experts are believed Ohio will be the crash site.

If you find something you think may be a piece of UARS, do not touch it. Contact a local law enforcement official for assistance, said NASA.

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.

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