The Philae comet lander has fallen silent again after its brief revival last month, raising fears it has moved again.
The European Space Agency (ESA) lander – the first mission to land on a comet – reached its comet 67P/Churyumov-Gerasimenko in November, but bounced on landing and ended up in a position too shadowy to power its solar panels.
It powered down after using up its battery supply late last year, but woke up again in June as the comet moved closer to the sun. However, the fridge-sized robotic lab last made contact on July 9 and efforts to reach it again have so far failed said its operators.
The latest data suggests something, possibly a gas emission, may have moved it again. There was no answer to a command sent to activate Philae's ROMAP instrument to determine the comet's plasma environment and magnetic field.
"The profile of how strongly the sun is falling on which panels has changed from June to July and this does not seem to be explained by the course of the seasons on the comet alone," Stephan Ulamec, Philae project manager at the DLR German Aerospace Centre said in a statement.
The team believe Philae's antenna may have been obstructed and one of its transmitters appears to have stopped working so scientists have now sent a command telling Philae to use just one transmitter.
As the comet gets closer to the Sun the amount of dust it throws off is increasing, making it hard for the Rosetta orbiter to stay close to the comet, which increases the difficulty of communication between it and the lander. The scientists have started moving the orbiter to a safer distance around 170-190 km from the comet
Until July 24, Rosetta will orbit a path that may allow it to contact the lander and then it will fly over the southern hemisphere of the comet to observe it with its own 11 instruments.
"Philae is obviously still functional, because it sends us data, even if it does so at irregular intervals and at surprising times," Ulamec said.