The U.S. space agency NASA says debris from a decommissioned satellite, the size of a city bus, is moving slower than expected and will make its fiery re-entry into the Earth's atmosphere late Friday or early Saturday.

Officials said there now is a slim chance that debris from the 5.4-ton satellite might land in the United States. NASA had previously ruled out North America as a crash site.

When it re-enters the atmosphere, the satellite is expected to burn brightly enough to be spotted during daylight hours, and to break apart into about 26 pieces.

NASA officials have warned people not to touch any of the debris, which could be scattered along a path more than 800 kilometers long.

The prospect of space junk falling from the sky has generated considerable interest among U.S. media and users of social media.

NASA launched the Upper Atmosphere Research Satellite in 1991 on a three-year mission to study ozone levels in the atmosphere. NASA took it out of service in 2005.

Since then, the satellite was placed into lower orbit to avoid any collision with the International Space Station.

The satellite is the largest piece of space debris to fall to Earth since NASA's Skylab space station crashed in western Australia 32 years ago. No one was hurt.