NASA has recently announced that an out-of-control, retired satellite will come crashing into the earth's surface "sometime" towards the end of September. Furthermore, the satellite, which is about the size of a school bus and weights over 6 tonnes (6.6 tons), will impact the earth in an unknown location between Canada and South America. The exact time and location will remain a mystery until two hours before the event, and that's with six thousand miles (10,000 km) of uncertainty.

"It is too early to say exactly when UARS will re-enter and what geographic area may be affected," states NASA.

The Upper Atmosphere Research Satellite (UARS) will come crashing back to Earth after it was placed into orbit almost twenty years ago. Although the spacecraft will break into pieces during re-entry, not all of it will burn up in the atmosphere beforehand. It is anticipated that 26 large fragments of the UARS satellite will actually fall to Earth, in a rain of debris altogether weighing about 1,170 pounds/532 kg (the largest weighing 300 pounds/150 kg). Though it is impossible to predict the exact impact zones, NASA estimates the debris footprint will be approximately 500 miles (800 km) long.

The US$750 million UARS satellite will be the largest NASA satellite to make an uncontrolled dive back to Earth in years. However, NASA assures that the risk to public safety or property is extremely low. "Throughout the entire 54 years of the Space Age there has been no report of anyone being injured or impacted by any re-entering debris," said Nick Johnson, the chief scientist of NASA's Orbital Debris Program at the agency's Johnson Space Center in Houston. That's keeping in mind that during this time, on average, one piece of debris has fallen back to Earth each day.

UARS was originally put into orbit in 1991 to collect data on the ozone layer and measures 35 feet (10.7 meters) long and 15 feet (4.5 m) wide. In 2005, NASA decommissioned the spacecraft, causing it to make a six-year plunge back to Earth. NASA will post constant updates before the anticipated re-entry of UARS, which will come directly from the Joint Space Operations Center of U.S. Strategic Command at Vandenberg Air Force Base, California. The center works 24/7 detecting, identifying and tracking all man-made objects in Earth orbit, including space junk.

NASA also warns people to not touch any pieces of UARS debris and to contact a local law enforcement official for assistance.

You can read updates on the falling UARS on the NASA website.