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OSIRIS observations of meter-size exposures of H2O ice at the surface of 67P/Churyumov-Gerasimenko and interpretation using laboratory experiments

Antoine Pommerol 1 Nicholas Thomas 1 Mohamed R. El-Maarry 1 Maurizio Pajola 2 Olivier Groussin 3 Anne-Thérèse Auger 3 Nilda Oklay 4 Sonia Fornasier 5 C. Feller 5 Björn Davidsson 6 A. Gracia-Berna 1 B. Jost 1 R. Marschall 1 O. Poch 1 M. A. Barucci 5 Jean-Loup Bertaux 7 F. La Forgia 8 H. U. Keller 9, 10 Ekkehard Kührt 10 S. C. Lowry 11 S. Mottola 10 G. Naletto 12, 13, 2 H. Sierks 4 Cesare Barbieri 8 Philippe L. Lamy 3 R. Rodrigo 14, 15 Detlef Koschny 16 Hans Rickman 6, 17 Jessica Agarwal 4 Michael F. A'Hearn 18 Ivano Bertini 2 S. Boudreault 4 Gabriele Cremonese 19 Vania da Deppo 13 Mariolino de Cecco 20 Stefano Debei 12 Carsten Güttler 4 M. Fulle 21 Pedro J. Gutiérrez 22 Stubbe F. Hviid 10 W. -H. Ip 23 Laurent Jorda 3 J. Knollenberg 10 G. Kovacs 4 J.-R. Kramm 4 Michael Küppers 24 Luisa M. Lara 22 Monica Lazzarin 8 Jose L. Lopez Moreno 22 Francesco Marzari 8 Harald Michalik 25 Frank Preusker 10 Frank Scholten 10 Cécilia Tubiana 4 Jean-Baptiste Vincent 4
Abstract : Since OSIRIS started acquiring high-resolution observations of the surface of the nucleus of comet 67P/Churyumov-Gerasimenko, over one hundred meter-sized bright spots have been identified in numerous types of geomorphologic regions, but mostly located in areas receiving low insolation. The bright spots are either clustered, in debris fields close to decameter-high cliffs, or isolated without structural relation to the surrounding terrain. They can be up to ten times brighter than the average surface of the comet at visible wavelengths and display a significantly bluer spectrum. They do not exhibit significant changes over a period of a few weeks. All these observations are consistent with exposure of water ice at the surface of boulders produced by dislocation of the weakly consolidated layers that cover large areas of the nucleus. Laboratory experiments show that under simulated comet surface conditions, analog samples acquire a vertical stratification with an uppermost porous mantle of refractory dust overlaying a layer of hard ice formed by recondensation or sintering under the insulating dust mantle. The evolution of the visible spectrophotometric properties of samples during sublimation is consistent with the contrasts of brightness and color seen at the surface of the nucleus. Clustered bright spots are formed by the collapse of overhangs that is triggered by mass wasting of deeper layers. Isolated spots might be the result of the emission of boulders at low velocity that are redepositioned in other regions.
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Antoine Pommerol, Nicholas Thomas, Mohamed R. El-Maarry, Maurizio Pajola, Olivier Groussin, et al.. OSIRIS observations of meter-size exposures of H2O ice at the surface of 67P/Churyumov-Gerasimenko and interpretation using laboratory experiments. Astronomy and Astrophysics - A&A, EDP Sciences, 2015, 583, A25 (16 p.). ⟨10.1051/0004-6361/201525977⟩. ⟨insu-01182702⟩



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