Scientists of the European Space Agency are a worried lot because their Philae comet lander has gone missing after it landed, and the latest imaging search by the overflying Rosetta "mothership" is unable to identify its present location. In fact, they are putting up their hands and saying, there is no trace of the probe.

Philae had touched down on 67P/Churyumov-Gerasimenko on November 12 and sent back a large amount of data before going silent when its battery ran flat. The ESA scientists are now waiting for Philae to reveal its position once it garners enough power to call home.

Researchers have a rough idea of where the robot should be, but pinpointing its exact location is tricky because, after touchdown, it had bounced twice before coming to rest in a dark ditch. This much is evident from the pictures it took of its surroundings, and this particular spot is, in the opinion of the mission team, just off the top of the "head" of the duck-shaped comet.

It seems the orbiting Rosetta satellite had photographed this general location on December 12, 13 and 14, and each image was subsequently scanned for any bright pixels that might be Philae.

However, there was no positive detection and Rosetta has now moved further from 67P. Its altitude has now gone up from 20km to 30km, and there is no immediate plan to go back down.

The scientists are not losing hope, because even if they cannot locate it, the little probe will eventually make its whereabouts known once 67P moves closer to the Sun. At that time, the lighting conditions for the robot should improve and that would, in turn, make way for it to charge its solar cells and recharge the battery system.