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    Size-frequency distribution of boulders ≥7 m on comet 67P/Churyumov-Gerasimenko

    Pajola, M. and Vincent, J.-B. and Güttler, C. and Lee, J.-C. and Bertini, I. and Massironi, M. and Simioni, E. and Marzari, F. and Giacomini, L. and Lucchetti, A. and Barbieri, C. and Cremonese, G. and Naletto, G. and Pommerol, A. and El-Maarry, Mohamed Ramy and Besse, S. and Küppers, M. and La Forgia, F. and Lazzarin, M. and Thomas, N. and Auger, A.-T. 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 Deppo, V.D. and Davidsson, B. and De Cecco, M. and Debei, S. and Ferri, F. and Fornasier, S. and Fulle, M. and Groussin, O. and Gutierrez, P.J. and Hviid, S.F. and Ip, W.-H. and Jorda, L. and Knollenberg, J. and Kramm, J.-R. and Kürt, E. and Lara, L.M. and Lin, Z.-Y. and Moreno, J.J.L. and Magrin, S. and Marchi, S. and Michalik, H. and Moissl, R. and Mottola, S. and Oklay, N. and Preusker, F. and Scholten, F. and Tubiana, C. (2015) Size-frequency distribution of boulders ≥7 m on comet 67P/Churyumov-Gerasimenko. Astronomy & Astrophysics 583 , A37. ISSN 0004-6361.

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    Abstract

    Aims. We derive for the first time the size-frequency distribution of boulders on a comet, 67P/Churyumov-Gerasimenko (67P), computed from the images taken by the Rosetta/OSIRIS imaging system. We highlight the possible physical processes that lead to these boulder size distributions. Methods. We used images acquired by the OSIRIS Narrow Angle Camera, NAC, on 5 and 6 August 2014. The scale of these images (2.44−2.03 m/px) is such that boulders ≥7 m can be identified and manually extracted from the datasets with the software ArcGIS. We derived both global and localized size-frequency distributions. The three-pixel sampling detection, coupled with the favorable shadowing of the surface (observation phase angle ranging from 48° to 53°), enables unequivocally detecting boulders scattered all over the illuminated side of 67P. Results. We identify 3546 boulders larger than 7 m on the imaged surface (36.4 km2), with a global number density of nearly 100/km2 and a cumulative size-frequency distribution represented by a power-law with index of −3.6 +0.2/−0.3. The two lobes of 67P appear to have slightly different distributions, with an index of −3.5 +0.2/−0.3 for the main lobe (body) and −4.0 +0.3/−0.2 for the small lobe (head). The steeper distribution of the small lobe might be due to a more pervasive fracturing. The difference of the distribution for the connecting region (neck) is much more significant, with an index value of −2.2 +0.2/−0.2. We propose that the boulder field located in the neck area is the result of blocks falling from the contiguous Hathor cliff. The lower slope of the size-frequency distribution we see today in the neck area might be due to the concurrent processes acting on the smallest boulders, such as i) disintegration or fragmentation and vanishing through sublimation; ii) uplifting by gas drag and consequent redistribution; and iii) burial beneath a debris blanket. We also derived the cumulative size-frequency distribution per km2 of localized areas on 67P. By comparing the cumulative size-frequency distributions of similar geomorphological settings, we derived similar power-law index values. This suggests that despite the selected locations on different and often opposite sides of the comet, similar sublimation or activity processes, pit formation or collapses, as well as thermal stresses or fracturing events occurred on multiple areas of the comet, shaping its surface into the appearance we see today.

    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: 20 Nov 2018 14:09
    Last Modified: 20 Nov 2018 14:09
    URI: http://eprints.bbk.ac.uk/id/eprint/25198

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