The unmanned Rosetta craft has already flown past Earth once

Professor Alan Fitzsimmons of Queen's University Astrophysics Research Centre told the BBC there is "no longer any need for concern".

"The 'asteroid' has been identified as the European spacecraft Rosetta," he said.

The spacecraft is en route to a comet near Jupiter.

Earlier this year, the unmanned Rosetta craft, which has already flown past Earth once, passed within 250 km (150 miles) of Mars.

In a precise move, the probe used the planet's gravity to change course on its voyage to the Churyumov-Gerasimenko comet.