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Comet 67P/Churyumov-Gerasimenko: Constraints on its origin from OSIRIS observations

H. Rickman 1, 2 S. Marchi 3 Michael F. A'Hearn 4 C. Barbieri 5 M. R. El-Maarry 6 C. Güttler 7 W.-H. Ip 8 H. U. Keller 9 P. Lamy 10 F. Marzari 5 M. Massironi 11, 12 G. Naletto 12, 13, 14 M. Pajola 12 H. Sierks 7 D. Koschny 15 R. Rodrigo 16, 17 M. A. Barucci 18 Jean-Loup Bertaux 19 I. Bertini 12 Gabriele Cremonese 20 V. da Deppo 14 S. Debei 13 M. de Cecco 21 S. Fornasier 18 M. Fulle 22 O. Groussin 10 Pedro J. Gutiérrez 23 S. F. Hviid 24 L. Jorda 10 J. Knollenberg 24 J.-R. Kramm 7 Ekkehard Kührt 24 M. Küppers 25 L. M. Lara 23 M. Lazzarin 5 J. J. Lopez Moreno 23 H. Michalik 26 L. Sabau 27 N. Thomas 6 J.-B. Vincent 7 K.-P. Wenzel 15 
Abstract : One of the main aims of the ESA Rosetta mission is to study the origin of the solar system by exploring comet 67P/Churyumov-Gerasimenko at close range. Aims. In this paper we discuss the origin and evolution of comet 67P/Churyumov-Gerasimenko in relation to that of comets in general and in the framework of current solar system formation models. Methods. We use data from the OSIRIS scientific cameras as basic constraints. In particular, we discuss the overall bi-lobate shape and the presence of key geological features, such as layers and fractures. We also treat the problem of collisional evolution of comet nuclei by a particle-in-a-box calculation for an estimate of the probability of survival for 67P/Churyumov-Gerasimenko during the early epochs of the solar system. Results. We argue that the two lobes of the 67P/Churyumov-Gerasimenko nucleus are derived from two distinct objects that have formed a contact binary via a gentle merger. The lobes are separate bodies, though sufficiently similar to have formed in the same environment. An estimate of the collisional rate in the primordial, trans-planetary disk shows that most comets of similar size to 67P/Churyumov-Gerasimenko are likely collisional fragments, although survival of primordial planetesimals cannot be excluded. Conclusions. A collisional origin of the contact binary is suggested, and the low bulk density of the aggregate and abundance of volatile species show that a very gentle merger must have occurred. We thus consider two main scenarios: the primordial accretion of planetesimals, and the re-accretion of fragments after an energetic impact onto a larger parent body. We point to the primordial signatures exhibited by 67P/Churyumov-Gerasimenko and other comet nuclei as critical tests of the collisional evolution.
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Submitted on : Friday, November 20, 2020 - 1:30:41 PM
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H. Rickman, S. Marchi, Michael F. A'Hearn, C. Barbieri, M. R. El-Maarry, et al.. Comet 67P/Churyumov-Gerasimenko: Constraints on its origin from OSIRIS observations. Astronomy and Astrophysics - A&A, EDP Sciences, 2015, 583, pp.A44. ⟨10.1051/0004-6361/201526093⟩. ⟨insu-01200792⟩



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