The ROSAT scientific research satellite is about the size of a minivan.
It is expected to break up during re-entry, but as many as 30 fragments weighing a total of nearly 2 tons could crash into Earth with a speed of up to 280 mph.
The satellite orbits the Earth every 90 minutes and scientists can only say that it could hit Earth anywhere along its path, between 53-degrees north and 53-degrees south - a vast swath of territory that includes much of the planet outside the poles.
This is the second time in as many months that a dead satellite has plummeted toward Earth.
A 6-ton NASA satellite fell on Sept. 23, landing in the middle of the Pacific Ocean. NASA says UARS broke into pieces upon re-entry, and most of it burned up in the atmosphere.
The Associated Press contributed to this report.