By Helen Briggs BBC News Online science reporter

European space officials are preparing back-up plans in case the flagship Rosetta mission has to be postponed, BBC News Online has learned.

The �600m mission to orbit and land on a comet faces a delay of weeks or even months following a failed rocket launch in December.

We're not about to take any risk of the best part of a billion euros investment Prof David Southwood

Europe's new super rocket, the Ariane 5-ECA, exploded over the Atlantic on its maiden flight, casting a shadow on the daring project.

An independent investigation into the loss is due to report on Monday.

Meanwhile, Arianespace, the company that operates Europe's rockets from the Kourou spaceport in French Guiana, has suspended flight preparations.

No compromise

Rosetta must leave Earth by the end of January if it is to reach its destination, Comet Wirtanen, an icy space rock which orbits the planet Jupiter and the Sun.

Comet Wirtanen: It may elude detailed scientific scrutiny

It had been scheduled to launch on 12 January but has been delayed by a few days at least.

Scientists fear it could miss its launch window altogether, forcing a delay of months or even years, and giving the probe no second chance to visit Comet Wirtanen.

Professor David Southwood, director of science at the European Space Agency, said he was confident that another target comet could be found, in the worst case scenario.

This would mean additional costs and a lengthy delay to ensure the science of the original mission was not compromised, he said.

He told BBC News Online: "Although it will cost us money we're not about to take any risk on the best part of a billion euros investment on the grounds of not risking another few tens of millions."

New targets

Professor Southwood said a number of new comets have been discovered in recent years that are worthy of scientific scrutiny.

"In terms of finding a potential new target and being able to do everything that the mission requires, I'm fairly confident I will be able to find a new target," he explained.

Rosetta is designed to drop a robot on a comet (Photo: Astrium)

"My concern will be to try to make sure we balance the additional expenditure of money against making sure that we get the science we were going to get."

He said he was hopeful that the launch would go ahead as planned in January.

Engineers hope that the fault can be traced to new components in the super rocket. This would clear Rosetta to fly on the standard version of the rocket.

A media conference in London set for Monday has been postponed until the full results of the inquiry are known.

Peter Barratt, of the UK Particle Physics and Astronomy Research Council, said: "The launch will be delayed certainly by a few days but all the indications at the moment are that it is going to go ahead."

Anxious wait

A new launch date for Rosetta is expected to be announced on 11 January. Until then, British scientists on the project can do little more than keep their fingers crossed.

"Year 2003 has been put on an 'anxious' hold until we get a final decision on the launch," said Dr Christopher Lee of Imperial College London.

"Indications are that they expecting to launch this January which is what I am personally hoping for."

He said whatever the decision, the launch itself would be much worse than the wait.

"Our launch will still use new components which have not yet been flown and we will not know if the launch has been successful until several hours after the rocket has (hopefully) disappeared from view," he explained.

He said scientists had been assured that Arianespace had taken all possible steps to ensure a successful launch "but there is always that little doubt which since the last failure has grown a bit larger".

Dr Andrew Coates from University College London's Mullard Space Science Laboratory said UK scientists had played important roles in previous comet missions such as Giotto.

"Let's hope Europe can maintain its hard-gained lead in cometary science with a good launch for Rosetta," he told BBC News Online.