Almost six years after ceasing operation, NASA's defunct 6.5-ton Upper Atmosphere Research Satellite is expected to plummet to Earth on Friday. But the U.S. space agency still has no idea as to where exactly it would fall.

On Sept. 15, 1991, the satellite was launched from the space shuttle Discovery. The $750 million spacecraft was deployed to collect data on Earth's atmosphere and its interactions with the sun. It orbited the planet more than 78,000 times before ceasing operations on Dec. 14, 2005.

The re-entry of the bus-size satellite has advanced because of 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 and burn in the atmosphere as it gets closer to earth. Hence, the chances of it hurting someone anywhere on the planet are remote or 1 in 3,200.

Look at how much of Earth is covered with water, Victoria Samson, the Washington Office Director of the Secure World Foundation, an organization dedicated to the peaceful use of outer space, told SPACE.com. There's a really good chance it's going to go straight into the ocean.

It was in 2005, when the 20-year-old UARS ran out of fuel. Pieces of the dead 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. Since water covers almost 75 percent of the Earth's surface, an ocean splashdown of the satellite is likely, NASA said.

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 estimated that most parts of the satellite will burn up after entering the atmosphere. Only about 1,200 pounds should survive, scattered over perhaps a 500-mile-wide area. The falling debris could include titanium pieces and onboard tanks, but the UARS carries no toxic propellant, according to NASA.

UARS measured the concentrations and distribution of gases important to ozone depletion, climate change and other atmospheric phenomena. NASA said 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 Climate change Space International Space Station