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1. Ceres observed at low phase angles by VIR-Dawn

Author

Andrea Longobardo, Federico Tosi, Mauro Ciarniello, Filippo Giacomo Carrozzo, Jian-Yang Li, Batiste Rousseau, Andrea Raponi, Eleonora Ammannito, Stefan Schröder, Edoardo Rognini, Christopher T. Russell, Carol A. Raymond, M. C. De Sanctis, Francesca Zambon, Alessandro Frigeri, ITA, USA, and DEU

Subjects
Physics, asteroids: individual: Ceres, 010504 meteorology & atmospheric sciences, Astronomy and Astrophysics, Astrophysics, planets and satellites: surfaces, 01 natural sciences, methods: data analysis, Planetengeologie, techniques: photometric, Space and Planetary Science, Asteroid, radiative transfer, techniques: imaging spectroscopy, 0103 physical sciences, Radiative transfer, minor planets, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract

Context.Particulate surfaces exhibit a surge of reflectance at low phase angles, a phenomenon referred to as the opposition effect (OE). Two mechanisms are recognized as responsible for the OE: shadow hiding (SH) and coherent backscattering. The latter is typically characterized by a small angular width of a few degrees at most and according to the theoretical prediction should exhibit wavelength and albedo dependence.Aims.We characterize the OE on the surface of Ceres using Dawn Visible InfraRed mapping spectrometer hyperspectral images at low phase angles. Furthermore, this dataset, coupled with previous observations, allows us to perform a complete spectrophotometric modeling at visual-to-infrared (VIS-IR) wavelengths (0.465–4.05μm) in the broad phase angle range ≈0°−132°.Methods.We applied Hapke’s theory to the average phase curve for Ceres. Disk-resolved properties of the OE were investigated through an empirical model.Results.Across the investigated phase angle interval, Ceres’ average phase curve exhibits a smaller back-scattering contribution for increasing wavelengths. This determines a progressive spectral reddening at larger phase angles that we hypothesize as being related to the effect of submicron roughness on the grain surface. In the OE region, the shape of the phase curves is fairly constant across the VIS range and no sharp opposition surge at very small phase angles (α< 2°) can be recognized. This would suggest a major contribution from SH to Ceres’ OE. Assuming SH as the dominant mechanism, from the OE angular width we infer a high surface porosity (≈0.9), which appears in good qualitative agreement with Ceres’ low thermal inertia. Thanks to the OE observations we derive Ceres’ VIS-IR geometric albedo with a reference value at 0.55μm of 0.098 ± 0.007. Mapping of the VIS normal albedo and OE angular width across a portion of the surface of Ceres does not reveal a spatial correlation between these quantities, consistent with SH dominating in theα= 0°−7° interval. The comparison of Ceres’V-band magnitude curve with that of other asteroids indicates that Ceres’ OE is typical of a low-albedo object and compatible with the C-class type.

Published
2020

2. Detection of exposed H2O ice on the nucleus of comet 67P/Churyumov-Gerasimenko

Author

Ivano Bertini, Ekkehard Kührt, Michael Küppers, Cesare Barbieri, Monica Lazzarin, P. L. Lamy, S. Fornasier, Gianrico Filacchione, Bernard Schmitt, Antoine Pommerol, Laurent Jorda, J. D. P. Deshapriya, Matteo Massironi, Gabriele Arnold, Holger Sierks, Dominique Bockelée-Morvan, Stubbe F. Hviid, C. Güttler, S. Fonti, F. Merlin, C. Leyrat, Cecilia Tubiana, J. B. Vincent, V. Da Deppo, A. Guilbert-Lepoutre, J.-R. Kramm, Marco Fulle, Mauro Ciarniello, Mohamed Ramy El-Maarry, Olivier Groussin, Detlef Koschny, Hans Rickman, F. Mancarella, L. M. Lara, Nicolas Thomas, M. T. Capria, N. Oklay, M. A. Barucci, W-H. Ip, Stéphane Erard, Maurizio Pajola, Priscilla Cerroni, G. Cremonese, Clement Feller, D. Perna, Andrea Raponi, Eric Quirico, J. J. Lopez Moreno, C. de Sanctis, Stefano Mottola, P. Drossart, B. J. R. Davidsson, Batiste Rousseau, Ernesto Palomba, R. Rodrigo, M. F. A'Hearn, J. L. Bertaux, Horst Uwe Keller, Pedro Hasselmann, Jörg Knollenberg, Marcello Fulchignoni, David Kappel, Fabrizio Capaccioni, Federico Tosi, Giampiero Naletto, Francesco Marzari, 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), Istituto di Astrofisica e Planetologia Spaziali - INAF (IAPS), Istituto Nazionale di Astrofisica (INAF), Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research (MPS), Max-Planck-Gesellschaft, Physikalisches Institut [Bern], Universität Bern [Bern] (UNIBE), Dipartimento di Geoscienze [Padova], Università degli Studi di Padova = University of Padua (Unipd), Univers, Transport, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UMR 6213) (UTINAM), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC), Dipartimento di Fisica e Astronomia 'Galileo Galilei', Laboratoire d'Astrophysique de Marseille (LAM), Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), International Space Science Institute [Bern] (ISSI), European Space Research and Technology Centre (ESTEC), Agence Spatiale Européenne = European Space Agency (ESA), Space Research Centre of Polish Academy of Sciences (CBK), Polska Akademia Nauk = Polish Academy of Sciences (PAN), Department of Physics and Astronomy [Uppsala], Uppsala University, Institut für Geophysik und Extraterrestrische Physik [Braunschweig] (IGEP), Technische Universität Braunschweig = Technical University of Braunschweig [Braunschweig], Department of Astronomy [College Park], University of Maryland [College Park], University of Maryland System-University of Maryland System, DLR Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt [Berlin] (DLR), PLANETO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), INAF - Osservatorio Astronomico di Padova (OAPD), Department of Information Engineering [Padova] (DEI), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Department of Physics [Lecce], Università del Salento [Lecce], INAF - Osservatorio Astronomico di Trieste (OAT), Institute of Space Science [Taiwan], National Central University [Taiwan] (NCU), Operations Department (ESAC), European Space Astronomy Centre (ESAC), Agence Spatiale Européenne = European Space Agency (ESA)-Agence Spatiale Européenne = European Space Agency (ESA), Instituto de Astrofísica de Andalucía (IAA), Consejo Superior de Investigaciones Científicas [Madrid] (CSIC), NASA Ames Research Center (ARC), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Ministerio de Economía y Competitividad (España), European Space Agency, Swedish National Space Agency, Agenzia Spaziale Italiana, German Centre for Air and Space Travel, Centre National D'Etudes Spatiales (France), Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Max-Planck-Institut für Sonnensystemforschung (MPS), Universität Bern [Bern], Universita degli Studi di Padova, European Space Agency (ESA), Polska Akademia Nauk (PAN), Technische Universität Braunschweig [Braunschweig], IMPEC - LATMOS, European Space Agency (ESA)-European Space Agency (ESA), Consejo Superior de Investigaciones Científicas [Spain] (CSIC), Centre National d'Études Spatiales [Toulouse] (CNES)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS), California Institute of Technology (CALTECH)-NASA, Université de Franche-Comté (UFC)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Aix Marseille Université (AMU)-Centre National d'Études Spatiales [Toulouse] (CNES), ITA, USA, FRA, DEU, ESP, TWN, NLD, POL, SWE, and CHE

Subjects
67P/Churyumov-Gerasimenko, 010504 meteorology & atmospheric sciences, Comet, Data analysis, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], Techniques: image processing, Context (language use), 01 natural sciences, Spectral line, Photometry, individual: 67P/Churyumov-Gerasimenko [Comets], Methods: data analysis, 0103 physical sciences, Comets, medicine, image processing [Techniques], data analysis [Methods], Techniques: imaging spectroscopy, 010303 astronomy & astrophysics, Spectroscopy, 0105 earth and related environmental sciences, Comets: individual: 67P/Churyumov-Gerasimenko, Physics, biology, Pixel, Spots, Techniques: photometric, imaging spectroscopy [Techniques], photometric [Techniques], Astronomy, Astronomy and Astrophysics, comets: individual: 67P/Churyumov-Gerasimenko – techniques: imaging spectroscopy – techniques: photometric – techniques: image processing – methods: data analysis, biology.organism_classification, comets: individual: 67P/Churyumov-Gerasimenko / techniques: imaging spectroscopy / techniques: photometric / techniques: image processing / methods: data analysis, medicine.anatomical_structure, Space and Planetary Science, Absorption band, Osiris, Nucleus
Abstract

[Context] Since the orbital insertion of the Rosetta spacecraft, comet 67P/Churyumov-Gerasimenko (67P) has been mapped by OSIRIS camera and VIRTIS spectro-imager, producing a huge quantity of images and spectra of the comet's nucleus., [Aims] The aim of this work is to search for the presence of HO on the nucleus which, in general, appears very dark and rich in dehydrated organic material. After selecting images of the bright spots which could be good candidates to search for HO ice, taken at high resolution by OSIRIS, we check for spectral cubes of the selected coordinates to identify these spots observed by VIRTIS., [Methods] The selected OSIRIS images were processed with the OSIRIS standard pipeline and corrected for the illumination conditions for each pixel using the Lommel-Seeliger disk law. The spots with higher I/F were selected and then analysed spectrophotometrically and compared with the surrounding area. We selected 13 spots as good targets to be analysed by VIRTIS to search for the 2 μm absorption band of water ice in the VIRTIS spectral cubes., [Results] Out of the 13 selected bright spots, eight of them present positive HO ice detection on the VIRTIS data. A spectral analysis was performed and the approximate temperature of each spot was computed. The HO ice content was confirmed by modeling the spectra with mixing (areal and intimate) of HO ice and dark terrain, using Hapke's radiative transfer modeling. We also present a detailed analysis of the detected spots., 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.

Published
2016

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