1. Correlation of Comet 67P/CG'S Morphology with the Occurrence of Exposed Water Ice Patches
- Author
-
Arnold, Gabriele, Weller, D., Zeilinger, G., Kappel, David, Hviid, Stubbe F., Kührt, Ekkehard, Moroz, Lyuba V., Markus, Kathrin, Henckel, D., Capaccioni, Fabrizio, Filacchione, Gianrico, Erard, Stéphane, Bockelée-Morvan, Dominique, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik und Astronomie, Universität Potsdam, DLR, Istituto di Astrofisica e Planetologia Spaziali, INAF (IAPS), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Pôle Planétologie du LESIA, Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)
- Subjects
[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] - Abstract
International audience; Introduction: Comet 67P's surface is quite homogeneously covered by dark refractory materials rich in organics [1,2]. Rare water ice expo- sures on the surface, most likely originating from sub-surface layers, have recently been discovered [3,4]. Such H2O ice patches on 67P's Imhotep region in the pre-perihelion phase were ex- amined and related to the local morphology to understand the exposure mechanisms [5]. Methods: H2O ice was identified in two study areas using characteristic H2O spectral features observed by the VIRTIS-M instrument [1]: absorption bands at 1.04, 1.25, 1.52, 2.02, 2.96 mum, and the VIS spectral slope (0.5-0.8 mum). Corresponding normalized spectral indicators were projected onto a 3D digital shape model (DSM) of 67P [6], along with high spatial resolution images acquired by OSIRIS [7] for morphological context. Results and conclusions: The 2.0-mum absorption band proved to be the most sensitive H2O indicator in the IR. Flat (bluer) normalized VIS slopes correlate very well with depths of H2O ice absorption bands. The DSM projections show a significant spatial correlation between spectral H2O indicators and morphological features. H2O ice deposits were identified in two areas, each extending over hundreds of square meters. Both are located at the bases of steep-sloped (>60°) walls of Consolidated Cometary Material (CCM) on debris falls that came to rest on moderately inclined (20°-30°) terrain, pointing towards gravitational lows. Both deposits are located in poorly illuminated areas due to shadowing from close-by steep walls. The morphological and photometrical properties of these deposits appear to be stable over months. Spectral modeling [3,4] indicated the presence of large (mm-sized) H2O ice grains. Such grains form through vapor diffusion in ice-rich colder layers or by sintering and are exposed by erosion [3]. The CCM in both study areas was fractured and weakened by thermal fatigue and sublimation, leading to the collapse of overhangs in one single event or in small steps over a longer time. For study area 1 this interpretation is supported by a small remnant H2O ice patch in the upper part of the steep wall indicating the original location of the collapse overhang. Sinkhole-structures on the CCM in study area 2 indicate sub-surface activity connected to ice sublimation, thermal stress, and occasional outbursts. Even though the nucleus structure probably is mostly homogeneous and primordial, the variable size and irregular distribution of sink-holes and erosional features strongly imply a highly active and heterogeneous sub-surface layer of at least tens of meters [8,9]. References: [1] Capaccioni F. et al. (2015) Sci- ence, 347, 628. [2] Quirico E. et al. (2016) Ica- rus, 272, 32-47. [3] Filacchione G. et al. (2016) Nature, 529, 368-372. [4] Barucci A. et al. (2016) A&A, 595, A102. [5] Weller D. (2016) Master thesis, University of Potsdam. [6] Preusker F. et al. (2015) A&A, 583, A33. [7] Keller H. et al. (2007) Space Sci. Rev., 128(1), 433-506. [8] Thomas N. et al. (2015) Science, 347, 440. [9] Vincent J.B. et al. (2015) Nature, 523, 63-66.
- Published
- 2017