Rosetta’s Philae lander has completed its primary science mission after two days on Comet 67P/Churyumov-Gerasimenko. With its batteries depleted and not enough sunlight available to recharge, the lander has fallen into ‘sleep mode’ – all its instruments and most systems are shut down.
Philae at work on the comet. Image credit: ESA / AOES Medialab.
“Despite the unplanned series of three touchdowns, all of Philae’s instruments could be operated and now it’s time to see what we’ve got,” said Dr Stephan Ulamec, lander manager at the DLR German Aerospace Agency.
After being out of communication visibility with Philae since 4:58 a.m. EDT (1:58 a.m. PDT, 9:58 a.m. GMT, 10:58 a.m. CET) on 14 November, Rosetta regained contact with the probe at 5:19 p.m. EDT (2:19 p.m. PDT, 10:19 p.m. GMT, 11:19 p.m. CET).
The signal was initially intermittent, but quickly stabilized and remained very good until 7:36 p.m. EDT (4:36 p.m. PDT, 0:36 a.m. GMT, 1:36 a.m. CET).
In that time, the lander returned all of its housekeeping data, as well as science data from the targeted instruments, including ROLIS, COSAC, Ptolemy, SD2 and CONSERT. This completed the measurements planned for the final block of experiments on the surface.
“Prior to falling silent, the lander was able to transmit all science data gathered during the First Science Sequence. This machine performed magnificently under tough conditions, and we can be fully proud of the incredible scientific success Philae has delivered,” Dr Ulamec said.
In addition, the Philae’s body was lifted by about 4 cm and rotated about 35 degrees in an attempt to receive more solar energy. But as the last science data fed back to Earth, Philae’s power rapidly depleted.
The search for Philae’s final landing site continues, with high-resolution images from the orbiter being closely scrutinized. Meanwhile, the lander has returned unprecedented images of its surroundings.
While descent images show that the surface of the comet is covered by dust and debris ranging from millimeter to meter sizes, panoramic images show layered walls of harder-looking material.
The science teams are now studying their data to see if they have sampled any of this material with Philae’s drill.
“We still hope that at a later stage of the mission, perhaps when we are nearer to the Sun, that we might have enough solar illumination to wake up the lander and re-establish communication,” Dr Ulamec said.
From now on, no contact will be possible unless sufficient sunlight falls on the solar panels to generate enough power to wake it up.
The possibility that this may happen later in the mission was boosted when mission controllers sent commands to rotate the lander’s main body with its fixed solar panels. This should have exposed more panel area to sunlight.
The Rosetta orbiter has been moving back into a 30 km orbit around the comet. It will return to a 20 km orbit on 6 December and continue its mission to study the body in great detail as the comet becomes more active, en route to its closest encounter with the Sun on 13 August 2015.
Over the coming months, Rosetta will start to fly in more distant ‘unbound’ orbits, while performing a series of daring flybys past the comet, some within just 8 km of its center.
Data collected by the orbiter will allow scientists to watch the short- and long-term changes that take place on the comet, helping to answer some of the biggest and most important questions regarding the history of our Solar System.
