Mystery shrouds NASA’s defunct Upper Atmosphere Research Satellite (UARS) that recently crashed to the Earth --- neither has the exact pre-entry time of the satellite been determined nor is there any clue about the precise location where one tonne of the space debris has landed! And, experts are of the opinion that this mystery may never be solved!

According to reports, UARS fell back to Earth between 11:23 p. m. EDT on September 23 and 1:09 a. m. on September 24 --- two decades after it was officially launched on a 14-year mission, which brought forth some of the first long-term records pertaining to the chemicals present in the atmosphere.

The satellite, which weight a mammoth 5897-kilogram, was sent into orbit by a space shuttle crew in 1991. Ever since the completion of its mission – involving the study of ozone and other chemicals in Earth’s atmosphere -, the satellite had been gradually losing altitude.

The satellite broke up and plummeted towards Earth over the weekend, and NASA had revealed that during its fiery re-entry period, the satellite will be passing from the east coast of Africa over the Indian Ocean; then over the Pacific Ocean and across northern Canada; before finally passing across the northern Atlantic Ocean to a point over West Africa.

Since a large part of the satellite’s transit was over water and its precise pre-entry point remained undetermined, Nicholas Johnson - chief orbital debris scientist at NASA's Johnson Space Centre in Houston – said: “We don't know where the debris field might be. We may never know.”