An alert over a close shave by a threatening asteroid has been called off after it was found to be a passing spaceprobe called Rosetta. The alarm was raised by the Minor Planet Center, the world’s official HQ for logging newly discovered space rocks and checking for any “Near Earth Objects” that threaten a devastating impact.

They issued an email circular to professional observatories last week announcing that an asteroid had been detected that would miss the Earth by a whisker on Tuesday, November 13.

The near miss, by 5,600 km – less than half the diameter of the Earth – looked set to be one of the closest on record. The MPC, which is run by the Smithsonian Astrophysical Observatory, Massachusetts, for the International Astronomical Union, even gave the body an official label, 2007 VN84.

Detailed observations by astronomers worldwide who discover and monitor potentially deadly asteroids were used to calculate an accurate track for the incoming “missile”.

Britain’s Royal Astronomical Society was preparing a special announcement to the media on Monday to reveal one of the closest cosmic shaves with disaster ever recorded. Then one sharp-eyed scientist, Denis Denisenko, 36, of Moscow, spotted that the asteroid’s track matched that of a European comet-chasing spaceprobe called Rosetta.

The craft, which is the size of a box van, is scheduled to make a swing past Earth on Tuesday for a gravity boost to speed it like a slingshot on its ten-year journey to Comet Churyumov-Gerasimenko.

Rosetta, launched in March, 2004, by the European Space Agency (ESA) has already made one swing-by of Earth in March 2005, another past Mars in February this year, and it will pass us again in November 2009.

Ironically, the unmanned probe will also fly close to and study two minor planets, Steins and Lutetia, during two journeys through the asteroid belt in 2008 and 2010.

Denisenko emailed an online discussion group for asteroid observers revealing his discovery. Embarrassed officials at the Minor Planet Center were forced to email a fresh circular announcing: “The minor planet 2007 VN84 does not exist and the designation is to be retired.”

But they added: “This incident highlights the deplorable state of availability of positional information on distant artificial objects (whether in earth orbit or in solar orbit). A single source for information on all distant artificial objects would be very desirable.”

Despite the red faces, the MPC perform vital work and there have been very real near misses by genuinely threatening asteroids that demand monitoring. The world’s biggest digital camera recently joined the search for them.

The Rosetta probe, which is due to plant a lander on its target comet in 2014, measures 2.8 x 2.1 x 2.0 metres. Its enormous solar panel “wings” stretch 32 metres from tip to tip and each is 32 sq metres in area.

Update: Rosetta’s flyby was a complete success with the probe right on course and producing some spectacular photos of the Earth as it approached.

Our picture is an ESA artist’s impression of Tuesday’s flyby by Rosetta.

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