COMET 67P
Images taken by Philae's Rosetta Lander Imaging System, ROLIS, trace the lander's descent to the first landing site, Agilkia, on Comet 67P/Churyumov–Gerasimenko on 12 November 2014. The first image was taken just over 3 km from the comet, and indicates the position of Agilkia and the area covered by the next image in the sequence, taken just 67 m away. The six images that follow were taken at approximately 10 second intervals prior to landing, with the final image of the sequence acquired 9 m above the touchdown site. ESA/Rosetta/Philae/ROLIS/DLR

Analysis of data obtained during the touchdown of the Philae lander on Comet 67P/Churyumov-Gerasimenko (nicknamed Chury) has thrown up interesting details ranging from the presence of life-forming complex organic molecules to varied surface structures on Chury.

"Although it remains to be seen whether these observations hold true for all comets, the discoveries made by Philae — including these initial results — will continue to shape our view of the history of the solar system," write the authors of eight research papers that analysed the findings in the 31 July issue of Science.

The data was collected by ten instruments in the 63 hours between November 12-14, 2014 when Philae separated from Rosetta and landed and bounced before settling down. Philae took flight for an additional two hours some 100m above the comet between the two landings.

Philae's initial sniffing of chemicals, 25 minutes after first contact, identified 16 compounds in six classes of organic molecules. Four of these have been detected for the first time on a comet.
These particles are precursors of molecules important for life such as sugars, amino acids and DNA bases whose presence has not been confirmed on the comet.

The COSAC (Cometary Sampling and Composition experiment) carried out the first chemical analysis by examining particles that entered the instrument following the dust raised by the landing.

All the compounds detected result from each other, pointing to chemical processes at work in a cometary nucleus and hence to the collapsing solar nebula in the very early Solar System.

The cameras of the CIVA experiment (Comet Infrared and Visible Analyser) show dark clumps at Philae's final landing site that are probably large grains made up of organic compounds.

Since cometary material does not alter much since its origins, the clumps indicate organic compounds were granular in early solar system. These grains when introduced into the oceans of the planets could have seeded them with life.

COSAC was not able to pick sulphur compounds observed by Rosina instrument on board Rosetta. This could imply varying chemical composition on the comet.

Hard and soft surfaces
The bounce by itself provided information on the nature of the surface. From granular Agilkia where Philae first touched down to hard Abydos where it finally rested, Chury displays a diversity of surfaces.

Images taken by ROLIS on the descent to Agilkia, and the CIVA images taken at Abydos provide a visual comparison of the topography at these two locations.

The largest boulder in the ROLIS field-of-view measures about 5m high, with a peculiar bumpy structure and fracture lines running through it.

However, as revealed by the radar experiment CONSERT (Comet Nucleus Sounding Experiment by Radio wave Transmission) sending a signal through the upper part of smaller lobe and measured by Rosetta, the comet has a homogenous interior.

High porosity seen shows the electrical properties of the dust are comparable to those of carbonaceous chondrites.

The CIVA-P image from seven microcameras confirms fractures seen by Rosette, at a millimetre scale.

The fractures are caused by thermal stress from large temperature differences on the comet as it travels around the Sun.

Philae's trench
The panoramic image also revealed Philae's position. It rests in a hole about its own size, lying on its side. This was then confirmed using cameras on Rosetta when in positions of direct visibility.

"Taken together, these first pioneering measurements performed on the surface of a comet are profoundly changing our view of these worlds and continuing to shape our impression of the history of the Solar System," says Jean-Pierre Bibring, a lead lander scientist and principal investigator of the CIVA instrument at the IAS in Orsay, France.

The analysis was carried out as part of ESA's Rosetta mission, involving researchers from the CNRS, Aix-Marseille Université, Université Joseph Fourier, Université Nice Sophia Antipolis, UPEC, UPMC, Université Paris-Sud, Université Toulouse III – Paul Sabatier and UVSQ, with support from CNES.

"With Philae making contact again in mid-June, we still hope that it can be reactivated to continue this exciting adventure, with the chance for more scientific measurements and new images which could show us surface changes or shifts in Philae's position since landing over eight months ago," says DLR's Lander Manager Stephan Ulamec.

The probe briefly woke up twice last month after a long hibernation since November to make contact, but communications have been erratic.

Scientists are expecting a big break in two weeks when the comet will be at perihelion on 13 August, nearest to the sun before it recedes.

More about Rosetta mission