Researchers have again lost contact with the Philae comet lander. The lander landed on comet 67P/Churyumov-Gerasimenko in November, but it bounced off and settled at a place where no sunlight was available for its solar panels to generate enough power to help it operate.

Researchers eventually made contact with the lander on July 9 after the comet moved closer to the sun. The side on which the lander was lying started facing the sun, thereby allowing the lander to harness the sunlight to get power.

However, it has been learnt from the latest data that gas emissions have again moved the lander, said experts at the European Space Agency project. Philae's antenna is not working and it appears that one of its transmitters has also stopped working.

Researchers failed to get any answer from Philae lander after sending a command to activate its ROMAP instrument to determine the ROMAP instrument.

Ground controllers said on Monday that comet-riding robot lab Philae has again gone silent. They fear that the lander has been pushed to the rough, alien surface, out of radio range. It is no longer communicating with its orbiting mothership, Rosetta.

"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", said project leader Stephan Ulamec of the German Aerospace Center (DLR).

ESA researchers said they have not given up on Philae and have high hopes for its revival.