A five tonne, 20-year-old satellite has fallen out of orbit and is expected to crash somewhere on Earth on or around 24 September, according to Nasa.
Nasa says the risk to life from the UARS –Upper Atmosphere Research Satellite – is just 1 in 3,200.
Hurtling at 5m (8km) per second, it could land anywhere between 57 degrees north and 57 degrees south of the equator – most of the populated world.
However, most of the satellite will break or burn up before reaching Earth.
Scientists have identified 26 separate pieces that could survive the fall through the earth’s atmosphere, and debris could rain across an area 400-500km (250-310 miles) wide.
Nasa said scientists would only be able to make more accurate predictions about where the satellite might land two hours before it enters the Earth’s atmosphere.
The 1 in 3,200 risk to public safety is higher than the 1 in 10,000 limit that Nasa aims for.Twitter