Minutes after it took off on 11 December from Kourou, French Guiana, the Ariane 5 rocket plunged into the Atlantic Ocean with two telecommunications satellites on board. The mishap means the European Space Agency’s ambitious comet probe, Rosetta, will be delayed—and must find a new target.
Rosetta was supposed to set off on 22 January for a 2011 rendezvous with Comet Wirtanen. It would have used a smaller version of the Ariane 5 rocket than the one that failed. But Arianespace, the launch company, suspended all sendoffs for several weeks to conduct an internal review. As a result, Rosetta missed its launch window for Wirtanen.
In any case, ESA wants to wait until it has confidence in a successful launch before slinging the €1 billion (roughly $1.1 billion) Rosetta into space. Out of 14 launches, the Ariane 5 has had four failures—including its maiden flight on 4 June 1996, which...
