OSIRIS spots Philae's drifting journey across the comet

OSIRIS camera on board of the Rosetta spacecraft images the journey of the lander above the nucleus of 67P / Churyumov-Gerasimenko

After the Philae lander was separated from Rosetta on 12 November, it remained in view of its mother space probe. The OSIRIS camera system captured a stunning sequence of images showing Philae drifting above the surface of comet 67P / Churyumov-Gerasimenko, inbound to its landing spot. In one image, the touchdown marks of Philae's landing can be seen.

"While the image sequence was planned, we're still very excited to see such beautiful view at the lander," says the head of the OSIRIS team, Holger Sierks, from the Max Planck Institute for Solar System Research in Göttingen. The newly released mosaic comprises a series of images showing Philae at different times: at 16:14 CET, 16:19 CET, 16:23 CET and 16.43 CET (the time in the image provided is in GMT).

When OSIRIS was taking the images, Rosetta was at a distance of just 15 kilometres from the surface. "From the image data, we are unable to tell the height at which Philae was drifting above the comet's nucleus", says Sierks. The detail resolution is 28 centimetres per pixel, and the square insets on the image have an side length of 17 meters.

The picture of the landing site at 16.43 CET is particularly interesting. A change in the surface structure is clearly visible compared with the image of 16.18 CET. In fact, Philae's first touchdown was at 16.34 CET. Could these be marks left by the landing legs? "That is a possibility," says Holger Sierks. "However, the illumination conditions could deceive us."

The last part of the mosaic shows the lander near a rock at 16.43 CET. Sierks and his colleagues have not found the site of the second touchdown or the final resting place of the sleeping Philae. "We are intensively searching for it. There are certainly possible candidates, which are in discussion in the OSIRIS Team ", says the Max Planck researcher. In his opinion, it would be important to manoeuvre Rosetta closer to 67P / Churyumov-Gerasimenko in the next few days, to a distance of less than 20 km. At the moment, the spacecraft is about 40 kilometres away from the comet.

For Rosetta itself, the scientific mission phase now kicks off. Until the end of December 2015, it will continue to explore the comet from up close. Scientists, however, are already thinking at this point of extending the mission by nine months. In August 2015, the comet will have moved up to a distance of 186 million kilometres to the sun; 1.24 times the Earth's distance to the sun. By the end of 2015, the comet will have moved out again to a distance of 300 million kilometres.

"It would be ideal if we could accompany the comet even further, up to a solar distance of 600 million kilometres," says Sierks. While 67P / Churyumov-Gerasimenko then gradually falls back into hibernation, further insights into changes in its surface could be won.

Rosetta is an ESA mission with contributions from its member states and NASA. Rosetta's Philae lander is provided by a consortium led by DLR, MPS, CNES and ASI. Rosetta will be the first mission in history to rendezvous with a comet, escort it as it orbits the Sun, and deploy a lander to its surface.

The scientific imaging system OSIRIS was built by a consortium led by the Max Planck Institute for Solar System Research (Germany) in collaboration with CISAS, University of Padova (Italy), the Laboratoire d'Astrophysique de Marseille (France), the Instituto de Astrofísica de Andalucia, CSIC (Spain), the Scientific Support Office of the European Space Agency (The Netherlands), the Instituto Nacional de Técnica Aeroespacial (Spain), the Universidad Politéchnica de Madrid (Spain), the Department of Physics and Astronomy of Uppsala University (Sweden), and the Institute of Computer and Network Engineering of the TU Braunschweig (Germany). OSIRIS was financially supported by the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), and Sweden (SNSB) and the ESA Technical Directorate.