Scientists with the European Space Agency's comet-hunting Rosetta mission say they've lost contact with the Philae lander on the comet's surface, raising fears the lander may have moved.
Released from the Rosetta spacecraft, the lander originally bounced on its landing attempt on Comet 67P/Churyumov-Gerasimenko last November, coming to rest in a shadowed area that deprived its solar panels of sunlight needed to power it.
It was able to power up in June and made contact with Earth through the Rosetta craft, but now, scientists say it's been silent since July 9.
There are fears the lander may have been moved again, possibly by jets of gas and dust shooting from the comet's surface as it comes closer to the sun and warms up.
That may have shifted it so that it's no longer properly aligned to maintain contact with the Rosetta spacecraft, the scientists say.
"In the telemetry received, we have observed signs that Philae could have moved and that its antennas are thus perhaps more concealed or their orientation might have changed," says project leader Stephan Ulamec of the German Aerospace Center.
The possibility of the lander being moved by activity on the comet's surface is also suggested by data received that shows how its different solar panels are receiving sunlight, he says.
"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," he explains in an ESA blog.
There has been no response to recent commands sent to activate an instrument on Philae intended to investigate the comet's magnetic field, controllers say.
They say they may try to modify Rosetta's orbit around the comet to improve its communication with the lander, but they note that Rosetta's star-reading system by which it navigates has been confused by dust streaming off the comet, making any such adjustments difficult.
Despite the communications difficulties, mission scientists say they have not given up on Philae.
"There have been several times when we feared that the lander would not switch back on, but it has repeatedly taught us otherwise," says Ulamec.
Moving at more than 20 miles per second, Comet 67P will reach the point of its closest approach to the sun — known as perihelion — on Aug. 13, when it will be around 116 million miles away.