Silent since its last call to mothership Rosetta seven months ago, the Philae lander is facing conditions on Comet 67P/Churyumov–Gerasimenko from which it is unlikely to recover.
Reconstructing Philae’s flight
Rosetta, which continues its scientific investigations at the comet until September before its own comet-landing finale, has in recent months been balancing science observations with flying dedicated trajectories optimised to listen out for Philae. But the lander has remained silent since 9 July 2015.
“The chances for Philae to contact our team at our lander control centre are unfortunately getting close to zero,” says Stephan Ulamec, Philae project manager at the German Aerospace Center, DLR. “We are not sending commands any more and it would be very surprising if we were to receive a signal again.”
Philae’s team of expert engineers and scientists at the German, French and Italian space centres and across Europe have carried out extensive investigations to try to understand the status of the lander, piecing together clues since it completed its first set of scientific activities after its historic landing on 12 November 2014.
A story with incredible twists and turns unfolded on that day. In addition to a faulty thruster, Philae also failed to fire its harpoons and lock itself onto the surface of the comet after its seven-hour descent, bouncing from its initial touchdown point at Agilkia, to a new landing site, Abydos, over 1 km away. The precise location of the lander has yet to be confirmed in high-resolution images.
A reconstruction of the flight of the lander suggested that it made contact with the comet four times during its two-hour additional flight across the small comet lobe. After bouncing from Agilkia it grazed the rim of the Hatmehit depression, bounced again, and then finally settled on the surface at Abydos.
Even after this unplanned excursion, the lander was still able to make an impressive array of science measurements, with some even as it was flying above the surface after the first bounce.
Once the lander had made its final touchdown, science and operations teams worked around the clock to adapt the experiments to make the most of the unanticipated situation. About 80% of its initial planned scientific activities were completed.
In the 64 hours following its separation from Rosetta, Philae took detailed images of the comet from above and on the surface, sniffed out organic compounds, and profiled the local environment and surface properties of the comet, providing revolutionary insights into this fascinating world.
But with insufficient sunlight falling on Philae’s new home to charge its secondary batteries, the race was on to collect and transmit the data to Rosetta and across 510 million kilometres of space back to Earth before the lander’s primary battery was exhausted as expected. Thus, on the evening of 14–15 November 2014, Philae fell into hibernation.