NASA satellite to crash into earth, but where?

It’s coming but everyone is clueless about its destination. A defunct NASA science satellite is expected to fall back to Earth on Friday, showering debris somewhere on the planet although scientists cannot predict exactly where.

The 6.5-ton bus-sized Upper Atmosphere Research Satellite, or UARS, was carried into orbit during a space shuttle mission in 1991. It operated for 14 years, collecting measurements of ozone and other chemicals in the atmosphere.

Since completing its mission in 2005, UARS has been slowly losing altitude, tugged by Earth's gravity. On Friday, the 35-foot-long, 15-foot diameter (10.6-metres long, 4.5-metres diameter) satellite is expected to plunge into the atmosphere, NASA reported on its website.

On re-entry the satellite is expected to break into over 100 pieces out which 26 may survive the burn and crash onto earth’s surface.

The largest chunk may weigh around 136 kilograms. The satellite's orbit passes over most of the planet, from as far north as northern Canada to the southern part of South America.

However, the debris spread area would be around 805 kilometres, the location of which would be determined by the precise time at which the spacecraft will make the re-entry.

Assuaging fears about its impact on earth, NASA said the chance a piece of UARS debris will strike a person is about one in 3,200. The debris will mostly likely fall into an ocean or land in an uninhabited region of Earth.

Satellites as large as UARS re-enter Earth's atmosphere about once a year.

NASA said there have been no reports of any deaths or injuries to people from falling debris.