Rosetta

Paolo Ferri, head of mission operations, describes the moment of relief when engineers confirmed the Philae comet lander separated from its Rosetta mothership. But anxiety is building over touchdown after telemetry data raised questions about the status of an important cold gas thruster designed to keep the lander from bouncing off the comet.

A potential problem with a rocket thruster designed to keep the Philae lander from bouncing off comet 67P/Churyumov-Gerasimenko after touchdown Wednesday will make the probe’s daring descent even more challenging, officials said.