The American space agency said decommissioned Upper Atmosphere Research Satellite fell back to Earth between 11.23pm and 1.09am on Saturday morning (3.23am GMT to 5.09am GMT).
Tracking of the satellite, which broke up during its re-entry through the atmosphere, showed it was passing eastwards over Canada and areas of open ocean.
Nasa said it was still trying to determine the precise re-entry time and location. Unconfirmed reports on Twitter suggested some of the debris may have fallen near a town south of Calgary in western Canada…
Most of the satellite was expected to have burned up during re-entry but 26 fragments weighing up to half a tonne in total are expected to hit the Earth’s surface.
Officials said the risk to the public from the satellite was very remote…
Mark Matney, an orbital debris scientist at Nasa, said: “In the entire 50 plus year history of the space program, no person has ever been injured by a piece of re-entering space debris.
“Keep in mind we have bits of debris re-entering the atmosphere every single day.” The US Department of Defence and Nasa were tracking the debris. The US Federal Aviation Administration issued a notice to pilots and flight crews of the potential hazard, and urged them to report any falling space debris and take note of its position and time…
The surviving chunks of the UARS satellite are likely to include titanium fuel tanks, beryllium housing and stainless steel batteries and wheel rims.
Nasa added: “Pieces of UARS landing on Earth will not be very hot. Heating stops 20 miles up, and it cools after that.” Any surviving wreckage belongs to Nasa, and it is against the law to keep or sell even the smallest piece.
There space said sharp edges could be dangerous and warned people not to pick up pieces if they find them, urging them to contact local law enforcement authorities instead.
Canadians: For goodness sake, just leave the stuff alone! Heaven forbid you may just cut yourselves, or worse, catch some sort of weird space alien sickness. Dialing 911 (you have 911 don’t you?) on your telephone is the fastest way you will get help when confronted with this dangerous, fallen space litter!