On 30 September 2016 at 13:19 CEST, the final signal from the Rosetta orbiter was received back on Earth. The ESA mission ended when the spacecraft touched down on Comet 67P/Churyumov-Gerasimenko. The international team of scientists had already said their farewells to the Philae lander back in February 2016, when its prolonged radio silence indicated that it would no longer report back to the team in the control centre at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR).
The Philae landing craft touched down on comet on 12 November 2014. It has now been found: it is not located at the convenient site originally selected for its landing, but rather – following a series of three bounces – in a grim and dark environment.
The comet lander Philae has been found. The OSIRIS camera on board the Rosetta orbiter took the revealing images of the surface of Comet 67P/Churyumov-Gerasimenko on 2 September 2016. They show the landing craft lying sideways in a crevasse. Two of the three landing legs are clearly visible.
The last prolonged silence had already indicated that contact with the Philae lander will be increasingly unlikely, and the conditions on Comet 67P/Churyumov-Gerasimenko have become more hostile. "Unfortunately, the probability of Philae re-establishing contact with our team at the DLR Lander Control Center (LCC) is almost zero, and we will no longer be sending any commands; it would be very surprising if we received a signal now," said Stephan Ulamec Philae Project Manager of the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR).
Philae was more than 500 million kilometres from Earth when it touched down on Comet 67P/Churyumov-Gerasimenko one year ago, on 12 November 2014. "We looked after and planned this mission for almost 20 years and launched the Rosetta orbiter and Philae lander on their journey through space – so landing day really was quite special," says Philae Project Manager Stephan Ulamec from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) to sum up the mood on the day.
Shaped like a rubber duck – this was the talk upon the discovery of Comet 67P/Churyumov-Gerasimenko's surprising shape in July 2014. Scientists were amazed at the celestial body's extraordinary shape, which was revealed by the European Rosetta spacecraft.
Gas and dust streams from the ‘neck’ of Comet 67P/ Churyumov-Gerasimenko
Since its arrival at the comet, Rosetta has observed jets of gas and dust. Numerous gas eruptions have been observed originating from the ‘neck’ of the comet. Using the measurements performed by the VIRTIS spectrometer, it has been possible to recognise a day/night cycle of cometary activity and identify the mechanism responsible.
For weeks, comet Churyumov-Gerasimenko has been active, hurling dust and gas into space – but it will not reach the closest point to the Sun in its orbit, the perihelion, until 13 August 2015 at exactly 4:03 CEST. It will take another six-and-a-half years to get this close to the Sun once again.
On 12 November 2014, as the Philae lander slowly descended onto Comet 67P/Churyumov-Gerasimenko, the first instruments on board began to take measurements. Philae touched down three times during the first ever landing on a comet, scraped against a crater rim, and finally arrived at the unforeseen landing site, called Abydos, at 18:31 CEST.
On 9 July 2015 at 19:45 CEST, Philae reported back to the team at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Lander Control Center (LCC) – only to then go back to 'silent mode'. Since then, the team has been working hard to get back in contact with the lander and operate it to conduct scientific measurements.
The Philae lander communicated with the Rosetta orbiter again between 19:45 and 20:07 CEST on 9 July 2015 and transmitted measurement data from the COmet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) instrument. Although the connection failed repeatedly after that, it remained completely stable for those 12 minutes.
Despite a new trajectory for Rosetta and a reduction of the distance between the orbiter and Comet 67P/Churyumov-Gerasimenko from 200 to 180 kilometres, contact with the Philae lander remains irregular and short. After the initial contact on 13 June 2015, Philae has reported to the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Lander Control Center (LCC) in Cologne a total of six times.
The team at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) received data from the Philae lander for the third time on 19 June 2015. Between 15:20 and 15:39 CEST, Philae sent 185 data packets.
The Philae lander reported back on 14 June 2015. From 23:22 to 23:26 CEST, the lander sent some data packets that are now being evaluated at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR). "But this time, the connection to the lander was relatively unstable," says DLR Philae Lander Project Leader Stephan Ulamec.
The Philae lander has reported back on 13 June 2015 at 22:28 (CEST), coming out of hibernation and sending the first data to Earth. More than 300 data packets have been analysed by the team at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Lander Control Center: "Philae is doing very well – it has an operating temperature of minus 35 degrees Celsius and has 24 watts of power available," explains DLR’s Philae Project Manager, Stephan Ulamec. "The lander is ready for operations." Philae 'spoke' for 85 seconds with its team on ground in its first contact since it went into hibernation.
On 15 November 2014 at 01:15 CET, Philae's battery was exhausted and, after nearly 60 hours of operation on Comet 67P/Churyumov-Gerasimenko, the lander went into hibernation – in an unexpected place. Philae 'bounced' several times before landing in its current location, and its exact position has still not been determined.
Comets eject gas and dust into space. Primarily, this takes place on the areas of the comet's surface exposed to direct sunlight. In mid-March, from a distance of 75 kilometres, the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) on board the Rosetta orbiter acquired images of an extraordinary phenomenon occurring on Comet 67P/Churyumov-Gerasimenko.
Although from 28 March 2015, following difficulties with its star trackers and navigation system, the Rosetta orbiter is now following a new and more distant trajectory around Comet 67P/Churyumov-Gerasimenko, the team at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Lander Control Center (LCC) will begin listening again for signals from the Philae lander at 02:00 CET on 12 April 2015.
Perhaps it is still too cold for the Philae lander to wake up on Comet 67P/Churyumov-Gerasimenko. Maybe its power resources are not yet sufficient to send a signal to the team at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Lander Control Center.
It would be very lucky if a signal were to be received from Rosetta's Philae lander at 05:00 CET on 12 March 2015. The lander finally came to rest in a rather shaded location on Comet 67P/Churyumov-Gerasimenko and it needs to receive sufficient energy before it can wake up and begin communicating.