Fragments of stricken Russian spaceship Phobos-Grunt are expected to come crashing back to Earth next week.
The 13.5 tonne craft became stranded in Earth's orbit in November after its rocket boosters failed to ignite following take off.
A computer malfunction was blamed for the failure meaning the spaceship, the largest planetary rocket ever built by Russia, had to abandon its mission to Mars to collect rock samples from the moon Phobos.
The mission would have been the first time samples had been extracted from a moon orbiting another planet. The craft also carried a Chinese Mars orbiter and bacteria containers, intended to test their survival in space.
Twenty to thirty pieces of debris from the vessel, weighing a total of around 200kg, are expected to fall back to Earth by January 14.
As the spacecraft nears re-entry into the Earth's atmosphere, space agency officials from around the world will track its trajectory hour by hour. However, experts from Roscosmos, the Russian space agency, admitted they have no idea where the pieces will fall and that plotting its landing site is subject to a high degree of uncertainty.
Space debris is normally expected to fall into the ocean or sparsely populated areas although many parts simply vaporise upon re-entry.
However, Russian, German and US space agencies have been assessing whether toxic fuel, known as unsymmetrical dimethylhydrazine (UDMH) and dinitrogen tetroxide (DTO), could contaminate the landing site of the debris.
Heiner Klinkrad, head of the space debris office at the European Space Agency, said the re-entry of the spaceship was not a significant risk to members of the public.
"All came up with same conclusion that Phobos-Grunt will not be a very high risk re-entry object," Mr Klinkrad told The Guardian newspaper. "It's a very delicate structure and it will break up fairly quickly."
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