The pristine interior of comet 67P revealed by the combined Aswan outburst and cliff collapse

Maurizio Pajola 1, 2 S. Höfner 3 Jean-Baptiste Vincent 3, 4 Nilda Oklay 3, 4 Frank Scholten 4 Frank Preusker 5 S. Mottola 5 Giampiero Naletto 6, 7, 2 Sonia Fornasier 8 S. Lowry 9 C. Feller 8 H. Hasselmann 8 Carsten Güttler 3 Cécilia Tubiana 3 Holger Sierks 3 Cesare Barbieri 2 Philippe L. Lamy 10 R. Rodrigo 11, 12 Detlef Koschny 13 H. Rickman 14, 15 H. Keller 5, 16 Jessica Agarwal 3 Michael A’hearn 17 A. Barucci 8 Jean-Loup Bertaux 18 Ivano Bertini 2 Sebastien Besse 19 S. Boudreault 3 G. Cremonese 20 Vania Da Deppo 6 Björn Davidsson 14 Stefano Debei 21 M. De Cecco 22 J. Deller 3 J. Deshapriya 8 Mohamed Ramy El-Maarry 23, 24 S. Ferrari 2 F. Ferri 2 Marco Fulle 25 Olivier Groussin 10 P. Gutierrez 26 M. Hofmann 3 Stubbe F. Hviid 5 Wing-Huen Ip 27 Laurent Jorda 10 Jörg Knollenberg 4 Gabor Kovacs 3 J. R. Kramm 3 Ekkehard Kührt 4 Michael Küppers 19 Luisa M. Lara 26 Z.-Y. Lin 27 Monica Lazzarin 28 A. Lucchetti 20 J. J. Lopez Moreno 26 F. Marzari 28 M. Massironi 29 H. Michalik 16 L. Penasa 29 A. Pommerol 24 E. Simioni 20 Nicolas Thomas 24 Imre Toth 30 E. Baratti 31
18 IMPEC - LATMOS
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
Abstract : Outbursts occur commonly on comets1 with different frequencies and scales2,3. Despite multiple observations suggesting various triggering processes4,5, the driving mechanism of such outbursts is still poorly understood. Landslides have been invoked6 to explain some outbursts on comet 103P/Hartley 2, although the process required a pre-existing dust layer on the verge of failure. The Rosetta mission observed several outbursts from its target comet 67P/Churyumov–Gerasimenko, which were attributed to dust generated by the crumbling of materials from collapsing cliffs7,8. However, none of the aforementioned works included definitive evidence that landslides occur on comets. Amongst the many features observed by Rosetta on the nucleus of the comet, one peculiar fracture, 70 m long and 1 m wide, was identified on images obtained in September 2014 at the edge of a cliff named Aswan9. On 10 July 2015, the Rosetta Navigation Camera captured a large plume of dust that could be traced back to an area encompassing the Aswan escarpment7. Five days later, the OSIRIS camera observed a fresh, sharp and bright edge on the Aswan cliff. Here we report the first unambiguous link between an outburst and a cliff collapse on a comet. We establish a new dust-plume formation mechanism that does not necessarily require the breakup of pressurized crust or the presence of supervolatile material, as suggested by previous studies7. Moreover, the collapse revealed the fresh icy interior of the comet, which is characterized by an albedo >0.4, and provided the opportunity to study how the crumbling wall settled down to form a new talus. The evolution of the collapse of the Aswan cliff9, observed by the OSIRIS Narrow Angle Camera (NAC)10 and the Rosetta Navigation camera (NavCam), is shown in Fig. 1. We estimated a total outburst ejected mass of cometary material between 0.5 × 106 and 1.0 × 106 kg for the 10 July event. By applying stereo-photogrammetric methods11 using multiple OSIRIS images (Supplementary Table 1), we determined the total volume of material that collapsed from the Aswan cliff. In Fig. 2, the dataset that depicts the aspect of the cliff before and after the collapse is presented. By using pre- and post-collapse three-dimensional (3D) models (see Methods), we have been able to measure the dimensions of the collapsed overhang (Supplementary Figs 1–2), deriving a total volume of 2.20 × 104 m3, with a 1σ uncertainty of 0.34 × 104 m3.
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Soumis le : jeudi 27 avril 2017 - 16:53:23
Dernière modification le : jeudi 9 novembre 2017 - 09:36:02

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Maurizio Pajola, S. Höfner, Jean-Baptiste Vincent, Nilda Oklay, Frank Scholten, et al.. The pristine interior of comet 67P revealed by the combined Aswan outburst and cliff collapse. Nature Astronomy, Nature Publishing Group, 2017, 1, pp.0092. 〈10.1038/s41550-017-0092〉. 〈insu-01515572〉

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