Gravitational slopes, geomorphology, and material strengths of the nucleus of comet 67P/Churyumov-Gerasimenko from OSIRIS observations
Journal
Date Issued
2015
Author(s)
Groussin, O.
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Jorda, L.
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Auger, A. -T.
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Kührt, E.
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Gaskell, R.
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Capanna, C.
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Scholten, F.
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Preusker, F.
•
Lamy, P.
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Hviid, S.
•
Knollenberg, J.
•
Keller, U.
•
Huettig, C.
•
Sierks, H.
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Barbieri, C.
•
Rodrigo, R.
•
Koschny, D.
•
Rickman, H.
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A'Hearn, M. F.
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Agarwal, J.
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Barucci, M. A.
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Bertaux, J. -L.
•
Bertini, I.
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Boudreault, S.
•
•
Da Deppo, V.
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Davidsson, B.
•
Debei, S.
•
De Cecco, M.
•
El-Maarry, M. R.
•
Fornasier, S.
•
•
Gutiérrez, P. J.
•
Güttler, C.
•
Ip, W. -H.
•
Kramm, J. -R.
•
Küppers, M.
•
Lazzarin, M.
•
Lara, L. M.
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Lopez Moreno, J. J.
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Marchi, S.
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Marzari, F.
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Massironi, M.
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Michalik, H.
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Naletto, G.
•
Oklay, N.
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Pommerol, A.
•
•
Thomas, N.
•
Toth, I.
•
•
Vincent, J. -B.
Description
OSIRIS was built by a consortium of the Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany; CISAS University of Padova, Italy; the Laboratoire d’Astrophysique de Marseille, France; the Instituto de Astrofísica de Andalucia, CSIC, Granada, Spain; the Research and Scientific Support Department of the ESA, Noordwijk, Netherlands; the Instituto Nacional de Técnica Aeroespacial, Madrid, Spain; the Universidad Politéchnica de Madrid, Spain; the Department of Physics and Astronomy of Uppsala University, Sweden; and the Institut für Datentechnik und Kommunikationsnetze der Technischen Universität Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB), and the ESA Technical Directorate is gratefully acknowledged. We thank the Rosetta Science Operations Centre and the Rosetta Mission Operations Centre for the successful rendezvous with comet 67P/Churyumov-Gerasimenko. We thank David Romeuf from the University Claude Bernard Lyon 1 (France) for creating the red/blue anaglyph in Fig. 11 . We thank the referee, J. Blum, for his helpful and constructive report.
Abstract
Aims. We study the link between gravitational slopes and the surface morphology on the nucleus of comet 67P/Churyumov-Gerasimenko and provide constraints on the mechanical properties of the cometary material (tensile, shear, and compressive strengths).
Methods. We computed the gravitational slopes for five regions on the nucleus that are representative of the different morphologies observed on the surface (Imhotep, Ash, Seth, Hathor, and Agilkia), using two shape models computed from OSIRIS images by the stereo-photoclinometry (SPC) and stereo-photogrammetry (SPG) techniques. We estimated the tensile, shear, and compressive strengths using different surface morphologies (overhangs, collapsed structures, boulders, cliffs, and Philae’s footprint) and mechanical considerations.
Results. The different regions show a similar general pattern in terms of the relation between gravitational slopes and terrain morphology: i) low-slope terrains (0−20°) are covered by a fine material and contain a few large (>10 m) and isolated boulders; ii) intermediate-slope terrains (20−45°) are mainly fallen consolidated materials and debris fields, with numerous intermediate-size boulders from <1 m to 10 m for the majority of them; and iii) high-slope terrains (45−90°) are cliffs that expose a consolidated material and do not show boulders or fine materials. The best range for the tensile strength of overhangs is 3−15 Pa (upper limit of 150 Pa), 4−30 Pa for the shear strength of fine surface materials and boulders, and 30−150 Pa for the compressive strength of overhangs (upper limit of 1500 Pa). The strength-to-gravity ratio is similar for 67P and weak rocks on Earth. As a result of the low compressive strength, the interior of the nucleus may have been compressed sufficiently to initiate diagenesis, which could have contributed to the formation of layers. Our value for the tensile strength is comparable to that of dust aggregates formed by gravitational instability and tends to favor a formation of comets by the accrection of pebbles at low velocities.
Volume
583
Start page
A32
Issn Identifier
0004-6361
Ads BibCode
2015A&A...583A..32G
Rights
open.access
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