Attempts to detect signals from the Philae comet lander have ceased after more than seven months of silence.
The German Aerospace Centre, managing the mission, last heard from the spacecraft, which has entered history books as the first man-made object to soft land on a comet's surface, on 9 July 2015. And with comet 67P/Churyumov-Gerasimenko now retreating away from the Sun, temperatures have become too cold (minus 180 °C) for the lander’s instruments to operate.
"Unfortunately, the probability of Philae re-establishing contact with our team at the DLR Lander Control Centre is almost zero, and we will no longer be sending any commands," said project manager Stephan Ulamec.
"It would be very surprising if we received a signal now."
Philae touched down on the surface of comet 67P/Churyumov-Gerasimenko on 12 November 2014. The landing almost ended in a fiasco as the lander failed to deploy its three harpoon-like legs to attach itself to the comet’s surface and bounced off several times instead before coming to rest. As a result the lander’s solar panels were shielded from the Sun and the lander fell silent after depleting its primary battery.
Contact was briefly regained in June 2015, enabling researchers to download more precious scientific data that will take years to analyse.
"The Philae mission was one-of-a-kind – it was not only the first time that a lander was ever placed on a comet's surface, but we also received fascinating data," said Pascale Ehrenfreund, chair of the DLR Executive Board and a participating scientist on the mission. "Rosetta and Philae have shown how aerospace research can expand humankind’s horizon and make the public a part of what we do."
After about a month of occasional contact, scientists downloaded the last data from the Philae lander about its status in July 2015. Contact was lost afterwards as the Rosetta orbiter, which delivered the lander to the comet and served as its data relay satellite, got too far away from the lander and was unable to receive its signals.
"There were also times last year when we did not understand why Philae had made no contact with us," Ulmanec admitted. "We repeatedly sent various commands to try to stabilise contact with Philae and conduct measurements with its instruments, but unfortunately it was not possible."
The project engineers believe that the reason for the irregular contact and subsequent silence could have been a failure in the lander's transmitter.
The mother craft, Rosetta, will continue to carry out scientific measurements in orbit around comet 67P until September, when it will be steered to land on the surface as well.
The comet is currently 138 million miles away from Earth, between the orbits of Mars and Jupiter.