The Philae comet lander has fallen silent, European scientists said on Monday, raising fears that it has moved again on its new home millions of miles from Earth.
The fridge-sized robotic lab, which landed on comet 67P/Churyumov-Gerasimenko in November, last made contact on July 9 and efforts to reach it again have so far failed, experts working for the historic European Space Agency project said.
The lander -- the first mission to land on a comet, this one traveling as fast as 135,000 kph -- initially bounced and landed in a position too shadowy to power its solar panels.
It woke up in June as the comet moved closer to the sun. But the latest data suggests something, possibly a gas emission, may have moved it again, the scientists said.
"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.
Philae's antenna may have been obstructed, and one of its transmitters appears to have stopped working, the team said.
There was no answer to a command sent to activate Philae's ROMAP instrument to determine the comet's plasma environment and magnetic field.