China's first space station is expected to come crashing down to Earth within weeks, but scientists have not been able to predict where the 8.5-tonne module will hit.
The US-funded Aerospace Corporation estimates Tiangong-1 will re-enter the atmosphere during the first week of April, give or take a week. The European Space Agency says the module will come down between 24 March and 19 April.
In 2016 China admitted it had lost control of Tiangong-1 and would be unable to perform a controlled re-entry.
The statement from Aerospace said there was "a chance that a small amount of debris" from the module will survive re-entry and hit the Earth.
"If this should happen, any surviving debris would fall within a region that is a few hundred kilometres in size," said Aerospace, a research organisation that advises government and private enterprise on space flight.