A new analysis of several studies on data sent back Philae has helped the scientists understand the nature of comets better than ever, and may be beneficial for future missions.
In a detailed account, Jens Biele et al. describe the critical moments where Philae descends on 67P, only to bounce off the soft, intended landing area and finally settle on a harder surface farther away.
Previously, scientists trying to understand comet surface material strength had to rely on indirect observations, which have ranged widely, and include some very low values that have raised questions about whether a comet could successfully dock on such weak material.
After analysing the depth profile of the lander footprint features with imaging tools, Biele and colleagues believe that the Philae’s feet first came in contact with a soft granular surface, which was approximately 0.25 meters (0.82 feet) thick, with a harder layer below. This layering creates a compressive strength of about 1 kilopascal, whereas the compression strength of Philae’s final, much harder landing site exceeded 2 megapascals (2,000 kilopascals), possibly contributing to why only one leg was able to anchor to this latter surface, and partially at that.
In a research article by Wlodek Kofman et al., the team found the composition of the head of the comet to be fairly homogenous. To get a better idea of 67P’s interior, the team directed electromagnetic signals through the nucleus of the comet to Rosetta on the opposite side. The signals Rosetta received lacked a scattering pattern, indicating that the interior of the comet is uniform throughout.
Research by Fred Goesmann and colleagues further analysed the composition of 67P using the COmetary SAmpling and Composition (COSAC) instrument, designed to identify organic compounds in the comet and thus contribute to a deeper understanding of the history of life on Earth. This process detected 16 organic compounds, four of which – methyl isocyanate, acetone, propionaldehyde, and acetamide – were previously unknown to exist on comets.
In a study by Jean-Pierre Bibring and colleagues, the surface of 67P is analysed in panoramic images taken by a set of seven cameras as part of the Comet Infrared and Visible Analyser (CIVA). By analysing thermal inertia and soil composition, the team found that the surface at the final landing spot has been covered with a highly compact, microporous, dust-ice layer with a porosity of 30 to 65 percent.
The findings are published in Science.