The Philae lander launched by the European Space Agency (ESA) is missing soon after it landed on comet 67P/Churyumov-Gerasimenko. Scientists are still waiting to get a signal from the sleeping lander.

Philae lander was accompanied by the Rosetta spacecraft that was launched from the Earth in March 2004. Rosetta reached the comet in August 2014, making it the first spacecraft to orbit a comet. Philae made a landing on the comet in November 2014, but its primary battery went flat soon after the landing that cut off communications with Rosetta and ESA scientists.

Rosetta has taken high-resolution images of the comet but has still not been successful to find the sleeping lander. ESA scientists suggest that now they will just wait for the lander to send a signal when it wakes up.

An ESA blog suggests that Philae touched down on the surface of the comet four times that also included the final landing. Scientists suggest that Rosetta's Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) had captured some images of the first landing of Philae. They are working with other clues to get exact location of the lander but they are still waiting for visual confirmation.

ESA scientists explain that the lander is not getting illumination from the Sun, which is required to wake it up. Philae was expected to get about 6.5 hours of solar illumination per 12.4 hours of the comet day at the original touch down site. However, at the new location it is only getting about 1.3 hours of illumination.

"Now we need the extra solar illumination provided by the comet's closer proximity to the Sun by that time in order to bring the lander back to life," says Stephan Ulamec, Lander Project Manager.

The scientists are hoping that the landing site of Philae will be warm enough to wake up Philae by late March. However, it can still take a few months before the lander starts transmitting signals. ESA suggests that Philae is in need of 17 watts, which will wake it up and send signals.

The scientists suggest that by May this year, the sun's inclination over the lander's estimated landing zone will be enough to provide sufficient illumination. However, the direction of Philae is in a way that it will not take full solar illumination.

ESA scientists will hope that the lander wakes up and starts its communications as soon as possible. 

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