Geomorphology and spectrophotometry of Philae's landing site on comet 67P/Churyumov-Gerasimenko

La Forgia, F.; Giacomini, L.; Lazzarin, M.; Massironi, M.; Oklay, N.; Scholten, F.; Pajola, M.; Bertini, I.; Cremonese, G.; Barbieri, C.; Naletto, G.; Simioni, E.; Preusker, F.; Thomas, Nicolas; Sierks, H.; Lamy, P.; Rodrigo, R.; Koschny, D.; Rickman, H.; Keller, H. U.; ... (2015). Geomorphology and spectrophotometry of Philae's landing site on comet 67P/Churyumov-Gerasimenko. Astronomy and astrophysics, 583(A41), p. 18. EDP Sciences 10.1051/0004-6361/201525983

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Context. On 12 November 2014 the European mission Rosetta succeeded in delivering a lander, named Philae, on the surface of one of the smallest, low-gravity and most primitive bodies of the solar system, the comet 67P/Churyumov-Gerasimenko (67P). Aims. The aim of this paper is to provide a comprehensive geomorphological and spectrophotometric analysis of Philae's landing site (Agilkia) to give an essential framework for the interpretation of its in situ measurements. Methods. OSIRIS images, coupled with gravitational slopes derived from the 3D shape model based on stereo-photogrammetry were used to interpret the geomorphology of the site. We adopted the Hapke model, using previously derived parameters, to photometrically correct the images in orange filter (649.2 nm). The best approximation to the Hapke model, given by the Akimov parameter-less function, was used to correct the reflectance for the effects of viewing and illumination conditions in the other filters. Spectral analyses on coregistered color cubes were used to retrieve spectrophotometric properties. Results. The landing site shows an average normal albedo of 6.7% in the orange filter with variations of similar to 15% and a global featureless spectrum with an average red spectral slope of 15.2%/100 nm between 480.7 nm (blue filter) and 882.1 nm (near-IR filter). The spatial analysis shows a well-established correlation between the geomorphological units and the photometric characteristics of the surface. In particular, smooth deposits have the highest reflectance a bluer spectrum than the outcropping material across the area. Conclusions. The featureless spectrum and the redness of the material are compatible with the results by other instruments that have suggested an organic composition. The observed small spectral variegation could be due to grain size effects. However, the combination of photometric and spectral variegation suggests that a compositional differentiation is more likely. This might be tentatively interpreted as the effect of the efficient dust-transport processes acting on 67P. High-activity regions might be the original sources for smooth fine-grained materials that then covered Agilkia as a consequence of airfall of residual material. More observations performed by OSIRIS as the comet approaches the Sun would help interpreting the processes that work at shaping the landing site and the overall nucleus.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences
08 Faculty of Science > Physics Institute

UniBE Contributor:

Thomas, Nicolas; Elmaarry, Mohamed Ramy and Pommerol, Antoine

Subjects:

500 Science > 520 Astronomy
600 Technology > 620 Engineering
500 Science > 530 Physics

ISSN:

0004-6361

Publisher:

EDP Sciences

Language:

English

Submitter:

Katharina Weyeneth-Moser

Date Deposited:

14 Jun 2016 14:08

Last Modified:

06 Jul 2016 16:56

Publisher DOI:

10.1051/0004-6361/201525983

Web of Science ID:

000365072200042

BORIS DOI:

10.7892/boris.81675

URI:

https://boris.unibe.ch/id/eprint/81675

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