Editor: Tang Danlu
BEIJING, Sept. 24 (Xinhuanet) --A defunct six-ton satellite is hurtling towards earth and is expected to crash within the next 24 hours, but experts have no idea where it will land.
The Nasa Upper Atmosphere Research Satellite (Uars) could shower debris anywhere over the six inhabited continents - from as far north as Alaska to the bottom tip of South America.
Satellites as large as Uars re-enter Earth's atmosphere about once a year and Nasa said there have been no reports of any deaths or injuries to people from falling debris.
But space expert Doug Millard at London's Science Museum thinks this one is worth watching.
He said: "This is one of the largest satellites up there.
"It's about the size of a double-decker bus. Most satellites when they come down, they are smaller, they burn up and no one notices. Because of the size it's a little more significant."
Nasa has said the odds of a piece of the Uars debris striking a person is about one in 3,200.
The agency insists most of the 20-year-old probe will burn up in the atmosphere and that the debris will most likely fall into an ocean or land in an uninhabited region of Earth.
The probe is being tracked by radar stations and experts around the world.
Flight Lieutenant Mike Farrington and his team at RAF Fylingdales have been monitoring the 35ft long satellite since its launch.
He says the tumbling probe is causing tracking difficulty because of its shape, size and speed.
"There's a great deal of uncertainty over where it will re-enter. Due to the irregular size and shape of this object it's impossible to say.
"These things move at about 7.5 kilometres (4.6 miles) per second in space and something moving at that speed is very difficult to predict.
"We've got some world class analysts here who've been working round the clock.
"But it's impossible for anyone using any of the resources anywhere across the globe to actually predict when and where this object will land."
Scientists expect up to 26 pieces - with a combined mass of about 540kg - to survive the fiery re-entry.
Launched in 1991, the satellite has been monitoring chemicals in the atmosphere, slowly losing altitude since completing its mission in 2005.
This satellite has caused a scare already. In 2010 it forced the International Space Station into a collision avoiding manoeuvre.
Nasa said that in 50 years of space travel no one has ever been hurt by falling debris.
But cosmic junk is not rocket science. This is a case of watch this space. Literally.
Editor: Tang Danlu