London and Paris

The European Space Agency's Rosetta mission faces an uncertain future this week after an agency inquiry failed to give it clearance for take off.

Rosetta, a US$700-million plan to land a probe on the comet Wirtanen, was originally scheduled to launch on 12 January. But it was postponed after the failure of the Ariane 5 ECA 'heavy lifter' on its maiden flight last month (see Nature 420, 723; 200210.1038/420723a).

An inquiry into whether the accident has any bearing on the classic Ariane 5 design, which will be used to take Rosetta on the first leg of its journey, reported on 7 January but failed to give the mission a green light. Rosetta has a very narrow launch window and must blast off by 31 January if it is to meet the comet.

At a press conference in Paris, Jean-Yves Le Gall, chief executive of Arianespace, which operates the Ariane rockets, said that the accident was caused by a cooling fault on the new engine, which suggests that the older Ariane 5 model is not at risk. But there are still doubts over whether the fault will affect Ariane 5 under the unusual conditions of the Rosetta launch, which requires the rocket to enter an Earth orbit and then re-fire. A separate investigation is now checking this, and will report on 14 January.