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    Aswan site on comet 67P/Churyumov-Gerasimenko: Morphology, boulder evolution, and spectrophotometry

    Pajola, M. and Oklay, N. and La Forgia, F. and Giacomini, L. and Massironi, M. and Bertini, I. and El-Maarry, Mohamed Ramy and Marzari, F. and Preusker, F. and Scholten, F. and Höfner, S. and Lee, J.-C. and Vincent, J.-B. and Groussin, O. and Naletto, G. and Lazzarin, M. and Barbieri, C. and Sierks, H. and Lamy, P. and Rodrigo, R. and Koschny, D. and Rickman, H. and Keller, H.U. and Agarwal, J. and A’Hearn, M.F. and Barucci, M.A. and Bertaux, J.-L. and Cremonese, G. and Deppo, V. D. and Davidsson, B. and De Cecco, M. and Debei, S. and Ferri, F. and Fornasier, S. and Fulle, M. and Güttler, C. and Gutierrez, P. J. and Hviid, S.F. and Ip, W.-H. and Jorda, L. and Knollenberg, J. and Kramm, J.-R. and Küppers, M. and Kürt, E. and Lara, L.M. and Lin, Z.-Y. and Lopez Moreno, J.J. and Magrin, S. and Michalik, H. and Mottola, S. and Thomas, N. and Tubiana, C. (2016) Aswan site on comet 67P/Churyumov-Gerasimenko: Morphology, boulder evolution, and spectrophotometry. Astronomy & Astrophysics 592 , A69. ISSN 0004-6361.

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    Abstract

    Aims. We provide a detailed morphological analysis of the Aswan site on comet 67P/Churyumov-Gerasimenko (67P). We derive the size-frequency distribution of boulders ≥2 m and correlate this distribution with the gravitational slopes for the first time on a comet. We perform the spectral analysis of this region to understand if possible surface variegation is related to thedifferent surface textures observable on the different units. Methods. We used two OSIRIS Narrow Angle Camera (NAC) image data sets acquired on September 19 and 22, 2014, with a scale of 0.5 m/px. Gravitational slopes derived from the 3D shape model of 67P were used to identify and interpret the different units of the site. By means of the high-resolution NAC data sets, boulders ≥2.0 m can be unambiguously identified and extracted using the software ArcGIS. Coregistered and photometrically corrected color cubes were used to perform the spectral analyses, and we retrieved the spectral properties of the Aswan units. Results. The high-resolution morphological map of the Aswan site (0.68 km2) shows that this site is characterized by four different units: fine-particle deposits located on layered terrains, gravitational accumulation deposits, taluses, and the outcropping layered terrain. Multiple lineaments are identified on the Aswan cliff, such as fractures, exposed layered outcrops, niches, and terraces. Close to the terrace margin, several arched features observed in plan view suggest that the margin progressively retreats as a result of erosion. The size-frequency of boulders ≥2 m in the entire study area has a power-law index of −3.9 +0.2/−0.3 (1499 boulders ≥2 m/km2), suggesting that the Aswan site is mainly dominated by gravitational events triggered by sublimation and/or thermal insolation weathering causing regressive erosion. The boulder size-frequency distribution versus gravitational slopes indicates that when higher gravitational slope terrains are considered, only boulders ≤10 m are identified, as well as steeper power-slope indices. In addition, no boulders ≥2 m are observed on slopes ≥50°. This may indicate that larger blocks detached from a sublimating cliff cannot rest at these slopes and consequently fall down. The spectral analysis performed on the site shows that despite different morphologic units, no spectral differences appear in the multiple textures. This may confirm a redistribution of particles across the nucleus as a consequence of airfall, whether coming from Hapi or from the southern hemisphere when it is active during perihelion.

    Metadata

    Item Type: Article
    Keyword(s) / Subject(s): comets: general / comets: individual: 67P/Churyumov-Gerasimenko / methods: data analysis
    School: Birkbeck Schools and Departments > School of Science > Earth and Planetary Sciences
    Depositing User: Administrator
    Date Deposited: 26 Oct 2018 11:48
    Last Modified: 26 Oct 2018 11:48
    URI: http://eprints.bbk.ac.uk/id/eprint/24836

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