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1. VIS-IR Spectroscopy of Mixtures of Water Ice, Organic Matter, and Opaque Mineral in Support of Small Body Remote Sensing Observations

Author

Mauro Ciarniello, Lyuba V. Moroz, Olivier Poch, Vassilissa Vinogradoff, Pierre Beck, Batiste Rousseau, Istiqomah Istiqomah, Robin Sultana, Andrea Raponi, Gianrico Filacchione, David Kappel, Antoine Pommerol, Stefan E. Schröder, Cedric Pilorget, Eric Quirico, Vito Mennella, and Bernard Schmitt

Subjects
water ice, organics, VIS-IR spectroscopy, spectral modelling, small bodies, Mineralogy, QE351-399.2
Abstract

Visual-to-infrared (VIS-IR) remote sensing observations of different classes of outer solar system objects indicate the presence of water ice and organics. Here, we present laboratory reflectance spectra in the 0.5–4.2 μm spectral range of binary particulate mixtures of water ice, organics analogue (kerite), and an opaque iron sulphide phase (pyrrhotite) to investigate the spectral effects of varying mixing ratios, endmember grain size, and mixing modality. The laboratory spectra are also compared to different implementations of the Hapke reflectance model (Hapke, 2012). We find that minor amounts (≲1 wt%) of kerite (investigated grain sizes of 45–63 μm and μm) can remain undetected when mixed in coarse-grained (67 ± 31 μm) water ice, suggesting that organics similar to meteoritic insoluble organic matter (IOM) might be characterized by larger detectability thresholds. Additionally, our measurements indicate that the VIS absolute reflectance of water ice-containing mixtures is not necessarily monotonically linked to water ice abundance. The latter is better constrained by spectral indicators such as the band depths of water ice VIS-IR diagnostic absorptions and spectral slopes. Simulation of laboratory spectra of intimate mixtures with a semi-empirical formulation of the Hapke model suggests that simplistic assumptions on the endmember grain size distribution and shape may lead to estimated mixing ratios considerably offset from the nominal values. Finally, laboratory spectra of water ice grains with fine-grained pyrrhotite inclusions (intraparticle mixture) have been positively compared with a modified version of the Hapke model from Lucey and Riner (2011).

Published
2021
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2. Organic Material on Ceres: Insights from Visible and Infrared Space Observations

Author

Andrea Raponi, Maria Cristina De Sanctis, Filippo Giacomo Carrozzo, Mauro Ciarniello, Batiste Rousseau, Marco Ferrari, Eleonora Ammannito, Simone De Angelis, Vassilissa Vinogradoff, Julie C. Castillo-Rogez, Federico Tosi, Alessandro Frigeri, Michelangelo Formisano, Francesca Zambon, Carol A. Raymond, and Christopher T. Russell

Subjects
astrobiology, organic material, Ceres, small bodies, Science
Abstract

The NASA/Dawn mission has acquired unprecedented measurements of the surface of the dwarf planet Ceres, the composition of which is a mixture of ultra-carbonaceous material, phyllosilicates, carbonates, organics, Fe-oxides, and volatiles as determined by remote sensing instruments including the VIR imaging spectrometer. We performed a refined analysis merging visible and infrared observations of Ceres’ surface for the first time. The overall shape of the combined spectrum suggests another type of silicate not previously considered, and we confirmed a large abundance of carbon material. More importantly, by analyzing the local spectra of the organic-rich region of the Ernutet crater, we identified a reddening in the visible range, strongly correlated to the aliphatic signature at 3.4 µm. Similar reddening was found in the bright material making up Cerealia Facula in the Occator crater. This implies that organic material might be present in the source of the faculae, where brines and organics are mixed in an environment that may be favorable for prebiotic chemistry.

Published
2020
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3. Macro and micro structures of pebble-made cometary nuclei reconciled by seasonal evolution

Author

Mauro Ciarniello, Marco Fulle, Andrea Raponi, Gianrico Filacchione, Fabrizio Capaccioni, Alessandra Rotundi, Giovanna Rinaldi, Michelangelo Formisano, Gianfranco Magni, Federico Tosi, Maria Cristina De Sanctis, Maria Teresa Capria, Andrea Longobardo, Pierre Beck, Sonia Fornasier, David Kappel, Vito Mennella, Stefano Mottola, Batiste Rousseau, Gabriele Arnold, ITA, FRA, and DEU

Subjects
Comets, 67P/Churyumov–Gerasimenko, Astronomy and Astrophysics
Abstract

Comets evolve due to sublimation of ices embedded inside porous dust, triggering dust emission (that is, erosion) followed by mass loss, mass redistribution and surface modifications. Surface changes were revealed by the Deep Impact and Stardust NExT missions for comet 9P/Tempel 1 (ref. 1), and a full inventory of the processes modifying cometary nuclei was provided by Rosetta while it escorted comet 67P/Churyumov–Gerasimenko for approximately two years2–4. Such observations also showed puzzling water-ice-rich spots that stood out as patches optically brighter and spectrally bluer than the average cometary surface5–9. These are up to tens of metres large and indicate macroscopic compositional dishomogeneities apparently in contrast with the structural homogeneity above centimetre scales of pebble-made nuclei10. Here we show that the occurrence of blue patches determines the seasonal variability of the nucleus colour4,11,12 and gives insight into the internal structure of comets. We define a new model that links the centimetre-sized pebbles composing the nucleus10 and driving cometary activity13,14 to metre-sized water-ice-enriched blocks embedded in a drier matrix. The emergence of blue patches is due to the matrix erosion driven by CO2-ice sublimation that exposes the water-ice-enriched blocks, which in turn are eroded by water-ice sublimation when exposed to sunlight. Our model explains the observed seasonal evolution of the nucleus and reconciles the available data at micro (sub-centimetre) and macro (metre) scales.

Published
2022

4. Seasonal evolution unveils the internal structure of cometary nuclei

Author

Mauro Ciarniello, Marco Fulle, Andrea Raponi, Gianrico Filacchione, Fabrizio Capaccioni, Alessandra Rotundi, Giovanna Rinaldi, Michelangelo Formisano, Gianfranco Magni, Federico Tosi, Maria Cristina De Sanctis, Maria Teresa Capria, Andrea Longobardo, Pierre Beck, Sonia Fornasier, David Kappel, Vito Mennella, Stefano Mottola, Batiste Rousseau, and Gabriele Arnold

Subjects
67P/Churyumov-Gerasimenko, comets, Rosetta mission
Abstract

Remote sensing data of comets 9P/Tempel 1 and 67P/Churyumov-Gerasimenko (67P hereafter) indicate the occurrence of water-ice-rich spots on the surface of cometary nuclei [1-5]. These spots are up to tens of metres in size and appear brighter and bluer than the average surface at visible wavelengths. In addition, the extensive observation campaign performed by the Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS, [6]) and the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS, [7]) during the Rosetta escort phase at 67P revealed a seasonal cycle of the nucleus colour. This is characterised by blueing of the surface while approaching perihelion followed by progressive reddening and restoral of the original colour along the outbound orbit. The temporal evolution of the colour has been interpreted in previous studies as the result of increasing exposure of water ice at smaller heliocentric distances [8, 9], however, an explanation of such seasonal cycle in the context of a quantitative cometary activity model was not yet been provided. Recently, in [10] we showed that the seasonal colour cycle observed on comet 67P is determined by the occurrence of the above-mentioned water-ice-rich spots (referred to as Blue Patches – BPs –, given their colour). This can be explained in the context of activity models [11, 12] of pebble-made cometary nuclei [13], i.e. in terms of nucleus surface erosion induced by H2O and CO2 ices sublimation, driving the cometary activity. According to the scenario proposed in [10] (Fig. 1), the presence of the BPs is due to the exposure of subsurface sub-metre-sized Water-ice-Enriched Blocks (WEBs) thanks to surface erosion triggered by CO2 sublimation ejecting decimetre-sized chunks [12]. The WEBs are composed of ice-rich pebbles (dust-to-ice mass ratio δ=2, [14]), embedded in a matrix of drier pebbles (δ>>5) forming most of the nucleus. Once exposed to illumination as BPs, the WEBs are eroded by water-ice sublimation ejecting sub-cm dust [11]. By means of dedicated spectral and thermophysical modelling, we match the nucleus colour temporal evolution measured by the VIRTIS Mapping channel in the 0.55-0.8 µm spectral range. In doing this, we take into account the competing effects of CO2- and H2O-driven erosion that expose and remove the BPs, respectively, and are seasonally modulated by the insolation conditions, primarily depending on the heliocentric distance. The new nucleus model proposed in [10], implying an uneven distribution of water ice in cometary nuclei, reconciles the compositional dishomogeneities observed on comets (the BPs) at macroscopic (up to tens of metres) scale, with a structurally homogeneous pebble-made nucleus at small (centimetre) scale, and with the processes determining the cometary activity at microscopic (sub-pebble) scales. Figure 1. 67P surface gets bluer approaching perihelion as a consequence of the progressive exposure to sunlight of subsurface WEBs (from Figure 4 in Ciarniello et al., 2022, Nature Astronomy, https://doi.org/10.1038/s41550-022-01625-y). The comet nucleus is made of two types of pebbles, both including refractories and CO2 ice, with different water ice content: pebbles with high content of H2O ice form the WEBs, while H2O-ice-poor pebbles represent the rest of the nucleus. CO2 ice is stable beneath the CO2 sublimation front at depths >0.1 m [12]. Approaching perihelion, the CO2 ice sublimation rate increases, eroding the surface by chunk ejection and exposing the WEBs. Once exposed, WEBs lose CO2 and are observable as BPs. Water-ice sublimation erodes the BPs ejecting sub-cm dust from their surface and preventing the formation of a dry crust [11]. The BPs survive until their water-ice fraction is sublimated, producing the observed surface blueing. Please refer to ref. [10] for complete details. References [1] Sunshine, J. M. et al. (2006) Science 311, 1453–1455. [2] Filacchione, G. et al. (2016) Nature 529, 368–372. [3] Raponi, A. et al. (2016) Mon. Not. R. Astron. Soc. 462, S476-S490. [4] Barucci, M. A. et al. (2016) Astron. Astrophys. 595, A102. [5] Oklay, N. et al. (2017) Mon. Not. R. Astron. Soc. 469, S582–S597. [6] Coradini, A. et al. (2007) Space Sci. Rev. 128, 529–559. [7] Keller, H. U. et al. (2007) Space Sci. Rev. 128, 433–506. [8] Fornasier, S. et al. (2016) Science 354, 1566–1570. [9] Filacchione, G. et al. (2020) Nature 578, 49-52. [10] Ciarniello, M. et al. (2022) Nat. Astron. doi:10.1038/s41550-022-01625-y. [11] Fulle, M. et al. (2020) Mon. Not. R. Astron. Soc. 493, 4039–4044. [12] Gundlach, B. et al (2020). Mon. Not. R. Astron. Soc. 493, 3690–3715. [13] Blum, J. et al. (2017) Mon. Not. R. Astron. Soc. 469, S755–S77. [14] O’Rourke, L. et al. (2020) Nature 586, 697–701. Acknowledgements We thank the Italian Space Agency (ASI, Italy; ASI-INAF agreements I/032/05/0 and I/024/12/0), Centre National d’Etudes Spatiales (CNES, France), and Deutsches Zentrum für Luft-und Raumfahrt (DLR, Germany) for supporting this work. VIRTIS was built by a consortium from Italy, France and Germany, under the scientific responsibility of IAPS, Istituto di Astrofisica e Planetologia Spaziali of INAF, Rome, which also led the scientific operations. The VIRTIS instrument development for ESA has been funded and managed by ASI (Italy), with contributions from Observatoire de Meudon (France) financed by CNES and from DLR (Germany). The VIRTIS instrument industrial prime contractor was former Officine Galileo, now Leonardo Company, in Campi Bisenzio, Florence, Italy. Part of this research was supported by the ESA Express Procurement (EXPRO) RFP for IPL-PSS/JD/190.2016. D.K. acknowledges DFG-grant KA 3757/2-1. This work was supported by the International Space Science Institute (ISSI) through the ISSI International Team "Characterization of cometary activity of 67P/Churyumov-Gerasimenko comet". This research has made use of NASA’s Astrophysics Data System.

Published
2022

5. VIS-IR Spectroscopy of Mixtures of Water Ice, Organic Matter, and Opaque Mineral in Support of Small Body Remote Sensing Observations

Author

Bernard Schmitt, Batiste Rousseau, David Kappel, Vassilissa Vinogradoff, Robin Sultana, Stefan Schröder, Mauro Ciarniello, L. V. Moroz, Eric Quirico, Vito Mennella, Cedric Pilorget, Istiqomah Istiqomah, Antoine Pommerol, Gianrico Filacchione, Olivier Poch, Andrea Raponi, Pierre Beck, IAPS–INAF, Istituto di Astrofisica e Planetologia Spaziali, Deutsches Zentrum für Luft- und Raumfahrt [Berlin] (DLR), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Centre National d'Études Spatiales [Toulouse] (CNES)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Météo-France -Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Météo-France, Physique des interactions ioniques et moléculaires (PIIM), Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS), Istituto di Astrofisica e Planetologia Spaziali - INAF (IAPS), Istituto Nazionale di Astrofisica (INAF), Deutsches Zentrum für Luft- und Raumfahrt (DLR), Physikalisches Institut [Bern], Universität Bern [Bern] (UNIBE), Institut d'astrophysique spatiale (IAS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), INAF - Osservatorio Astronomico di Capodimonte (OAC), and ITA

Subjects
Materials science, VIS-IR spectroscopy, Opacity, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], engineering.material, Spectral line, water ice, spectral modelling, Phase (matter), organics, Organic matter, Pyrrhotite, Remote sensing, chemistry.chemical_classification, 520 Astronomy, Lead (sea ice), Geology, Geotechnical Engineering and Engineering Geology, Mineralogy, 620 Engineering, Grain size, chemistry, Particle-size distribution, engineering, small bodies, QE351-399.2
Abstract

Visual-to-infrared (VIS-IR) remote sensing observations of different classes of outer solar system objects indicate the presence of water ice and organics. Here, we present laboratory reflectance spectra in the 0.5–4.2 μm spectral range of binary particulate mixtures of water ice, organics analogue (kerite), and an opaque iron sulphide phase (pyrrhotite) to investigate the spectral effects of varying mixing ratios, endmember grain size, and mixing modality. The laboratory spectra are also compared to different implementations of the Hapke reflectance model (Hapke, 2012). We find that minor amounts (≲1 wt%) of kerite (investigated grain sizes of 45–63 μm and &lt, 25 μm) can remain undetected when mixed in coarse-grained (67 ± 31 μm) water ice, suggesting that organics similar to meteoritic insoluble organic matter (IOM) might be characterized by larger detectability thresholds. Additionally, our measurements indicate that the VIS absolute reflectance of water ice-containing mixtures is not necessarily monotonically linked to water ice abundance. The latter is better constrained by spectral indicators such as the band depths of water ice VIS-IR diagnostic absorptions and spectral slopes. Simulation of laboratory spectra of intimate mixtures with a semi-empirical formulation of the Hapke model suggests that simplistic assumptions on the endmember grain size distribution and shape may lead to estimated mixing ratios considerably offset from the nominal values. Finally, laboratory spectra of water ice grains with fine-grained pyrrhotite inclusions (intraparticle mixture) have been positively compared with a modified version of the Hapke model from Lucey and Riner (2011).

Published
2021
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6. The surface of (4) Vesta in visible light as seen by Dawn/VIR

Author

Federico Tosi, S. Fonte, C. T. Russel, M. C. De Sanctis, Filippo Giacomo Carrozzo, Batiste Rousseau, Carol A. Raymond, Mauro Ciarniello, Eleonora Ammannito, P. Scarica, Andrea Raponi, Alessandro Frigeri, Istituto di Astrofisica e Planetologia Spaziali - INAF (IAPS), Istituto Nazionale di Astrofisica (INAF), Italian Space Agency, Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), University of California [Los Angeles] (UCLA), University of California, and ASI-INAF grant I/004/12/0

Subjects
asteroids, 010504 meteorology & atmospheric sciences, Infrared, Lithology, data analysis, FOS: Physical sciences, Astrophysics, imaging spectroscopy, 01 natural sciences, [SDU.STU.PL]Sciences of the Universe [physics]/Earth Sciences/Planetology, Impact crater, 0103 physical sciences, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Earth and Planetary Astrophysics (astro-ph.EP), Spectrometer, Surfaces - satellites of asteroids, Astronomy and Astrophysics, Meteorite, (4) Vesta -planets and satellites, Space and Planetary Science, Asteroid, [SDU]Sciences of the Universe [physics], Radiance, Geology, Astrophysics - Earth and Planetary Astrophysics, Visible spectrum
Abstract

We analyzed the surface of Vesta at visible wavelengths, using the data of the Visible and InfraRed mapping spectrometer (VIR) on board the Dawn spacecraft. We mapped the variations of various spectral parameters on the entire surface of the asteroid, and also derived a map of the lithology. We took advantage of the recent corrected VIR visible data to map the radiance factor at 550 nm, three color composites, two spectral slopes, and a band area parameter relative to the 930 nm crystal field signature in pyroxene. Using the howardite-eucrite-diogenite (HED) meteorites data as a reference, we derived the lithology of Vesta using the variations of the 930 nm and 506 nm (spin-forbidden) band centers observed in the VIR dataset. Our spectral parameters highlight a significant spectral diversity at the surface of Vesta. This diversity is mainly evidenced by impact craters and illustrates the heterogeneous subsurface and upper crust of Vesta. Impact craters also participate directly in this spectral diversity by bringing dark exogenous material to an almost entire hemisphere. Our derived lithology agrees with previous results obtained using a combination of infrared and visible data. We therefore demonstrate that it is possible to obtain crucial mineralogical information from visible wavelengths alone. In addition to the 506 nm band, we identified the 550 nm spin-forbidden one. As reported by a laboratory study for synthetic pyroxenes, we also do not observe any shift of the band center of this feature across the surface of Vesta, and thus across different mineralogies, preventing use of the 550 nm spin-forbidden band for the lithology derivation. Finally, the largest previously identified olivine rich-spot shows a peculiar behavior in two color composites but not in the other spectral parameters., Comment: 23 pages, 11+7 figures

Published
2021

7. The surface of (1) Ceres in visible light as seen by Dawn/VIR

Author

M. Ferrari, F. C. Carrozzo, Mauro Ciarniello, Alessandro Frigeri, Andrea Raponi, Christopher T. Russell, S. De Angelis, M. C. De Sanctis, Batiste Rousseau, Carol A. Raymond, E. Ammannito, Stefan Schröder, Federico Tosi, Istituto di Astrofisica e Planetologia Spaziali - INAF (IAPS), Istituto Nazionale di Astrofisica (INAF), Agenzia Spaziale Italiana (ASI), Deutsches Zentrum für Luft- und Raumfahrt [Berlin] (DLR), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), and Earth, Planetary and Space Sciences, University of California, Los Angeles, CA, USA

Subjects
010504 meteorology & atmospheric sciences, Infrared, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], FOS: Physical sciences, Pyroxene, Astrophysics, planets and satellites: surfaces, 01 natural sciences, MESH: methods: data analysis, [SDU.STU.PL]Sciences of the Universe [physics]/Earth Sciences/Planetology, Impact crater, 0103 physical sciences, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Physics, Earth and Planetary Astrophysics (astro-ph.EP), asteroids: individual: Ceres, Spectrometer, MESH: planets and satellites: surfaces, Astronomy and Astrophysics, methods: data analysis, Planetengeologie, MESH: minor planets, asteroids: individual: Ceres, Meteorite, techniques: imaging spectroscopy, Space and Planetary Science, Asteroid, MESH: techniques: imaging spectroscopy, minor planets, Radiance, Astrophysics - Earth and Planetary Astrophysics, Visible spectrum
Abstract

We study the surface of Ceres at visible wavelengths, as observed by the Visible and InfraRed mapping spectrometer (VIR) onboard the Dawn spacecraft, and analyze the variations of various spectral parameters across the whole surface. We also focus on several noteworthy areas of the surface of this dwarf planet. We made use of the newly corrected VIR visible data to build global maps of a calibrated radiance factor at 550 nm, with two color composites and three spectral slopes between 400 and 950 nm. We have made these maps available for the community via the Aladin Desktop software. Ceres surface shows diverse spectral behaviors in the visible range. The color composite and the spectral slope between 480 and 800 nm highlight fresh impact craters and young geologic formations of endogenous origin, which appear bluer than the rest of the surface. The steep slope before 465 nm displays very distinct variations and may be a proxy for the absorptions caused by the $O_2^{-}$ -> $Fe^{3+}$ or the $2Fe^{3+}$ -> $Fe^{2+} + Fe^{4+}$ charge transfer, if the latter are found to be responsible for the drop in this spectral range. We notice several similarities between the spectral slopes and the abundance of phyllosilicates detected in the infrared by the VIR, whereas no correlation can be clearly established with carbonate species. The region of the Dantu impact crater presents a peculiar spectral behavior (especially through the color and the spectral slope before 465 nm) suggesting a change in composition or in the surface physical properties that is not observed elsewhere on Ceres., 22 pages, 14 + 5 figures. Published online on Astronomy and Astrophysics on 07-10-2020

Published
2020

8. Infrared detection of aliphatic organics on a cometary nucleus

Author

Robert W. Carlson, D. Bockelée-Morvan, J. P. Combe, Antoine Pommerol, Vito Mennella, Federico Tosi, Cedric Leyrat, Giovanna Rinaldi, Batiste Rousseau, F. Mancarella, L. Moroz, Michelangelo Formisano, Ernesto Palomba, Pierre Beck, M. C. De Sanctis, I. Istiqomah, Eric Quirico, David Kappel, Stéphane Erard, Antonella Barucci, Gabriele Arnold, Vassilissa Vinogradoff, Giancarlo Bellucci, Fabrizio Capaccioni, Mauro Ciarniello, C. Pilorget, Andrea Longobardo, Andrea Raponi, Sonia Fornasier, Gianrico Filacchione, Olivier Poch, Istituto di Astrofisica e Planetologia Spaziali - INAF (IAPS), Istituto Nazionale di Astrofisica (INAF), Physique des interactions ioniques et moléculaires (PIIM), Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Centre National d'Études Spatiales [Toulouse] (CNES)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA), Istituto di Fisica dello Spazio Interplanetario (IFSI), Consiglio Nazionale delle Ricerche (CNR), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), 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 de Paris (UP), Institut Universitaire de France (IUF), Ministère de l'Education nationale, de l’Enseignement supérieur et de la Recherche (M.E.N.E.S.R.), National Research Council of Italy | Consiglio Nazionale delle Ricerche (CNR), Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Météo-France -Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Météo-France, Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), 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
Earth and Planetary Astrophysics (astro-ph.EP), In situ, Physics, Solar System, 010504 meteorology & atmospheric sciences, Infrared, Comet, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], FOS: Physical sciences, Hyperspectral imaging, Astronomy and Astrophysics, 01 natural sciences, Astrobiology, medicine.anatomical_structure, [SDU]Sciences of the Universe [physics], 13. Climate action, Comet nucleus, 0103 physical sciences, medicine, Absorption (electromagnetic radiation), 010303 astronomy & astrophysics, Nucleus, Astrophysics - Earth and Planetary Astrophysics, 0105 earth and related environmental sciences
Abstract

The European Space Agency’s Rosetta mission1 has acquired unprecedented measurements of the surface of the nucleus of comet 67P/Churyumov–Gerasimenko (hereafter, 67P), the composition of which, as determined by in situ and remote-sensing instruments, including the VIRTIS instrument2, seems to be an assemblage of ices, minerals and organic material3. We performed a refined analysis of infrared observations of the nucleus of 67P carried out by the VIRTIS-M hyperspectral imager. We find that the overall shape of the infrared spectrum of 67P is similar to that of other carbon-rich outer Solar System objects, suggesting a possible genetic link with them. More importantly, we also confirm the complex spectral structure of the wide 2.8–3.6 µm absorption feature populated by fainter bands. Among these, we unambiguously identify the presence of aliphatic organics by their ubiquitous 3.38 µm, 3.42 µm and 3.47 µm bands. This infrared detection of aliphatic species on a cometary surface has strong implications for the evolutionary history of the primordial Solar System and is evidence that comets provide an evolutionary link between interstellar material and Solar System bodies4. A refined analysis of infrared observations of comet 67P/Churyumov–Gerasimenko from the VIRTIS instrument on board the Rosetta spacecraft has revealed the presence of aliphatic organic molecules on the comet nucleus.

Published
2020

9. Ammonium salts are a reservoir of nitrogen on a cometary nucleus and possibly on some asteroids

Author

Gabriele Arnold, Vassilissa Vinogradoff, Andrea Raponi, Lydie Bonal, Eric Quirico, Antoine Pommerol, Dominique Bockelée-Morvan, Gianrico Filacchione, Vito Mennella, S. Potin, P. Beck, Federico Tosi, L. Moroz, Olivier Poch, Alexandre Faure, Batiste Rousseau, Nicolas Thomas, L. Flandinet, Bernard Schmitt, F. Mancarella, M. C. De Sanctis, Stéphane Erard, P. Hily-Blant, Ernesto Palomba, Istiqomah Istiqomah, Mauro Ciarniello, Andrea Longobardo, O. Brissaud, Patrice Theulé, David Kappel, C. Leyrat, Fabrizio Capaccioni, Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Centre National d'Études Spatiales [Toulouse] (CNES)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA), Physique des interactions ioniques et moléculaires (PIIM), Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), 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 de Paris (UP), Istituto di Astrofisica e Planetologia Spaziali - INAF (IAPS), Istituto Nazionale di Astrofisica (INAF), ANR-17-CE31-0004,CLASSY,Composition des surfaces du Système Solaire de bas albédo(2017), European Project: ERC-CoG2017-771691,SOLARYS, Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Météo-France -Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Météo-France, Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), 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
animal structures, 010504 meteorology & atmospheric sciences, Interstellar cloud, Comet, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], chemistry.chemical_element, FOS: Physical sciences, 01 natural sciences, complex mixtures, Astrobiology, chemistry.chemical_compound, 0103 physical sciences, Ammonium, Absorption (electromagnetic radiation), 010303 astronomy & astrophysics, Refractory (planetary science), 0105 earth and related environmental sciences, Earth and Planetary Astrophysics (astro-ph.EP), Multidisciplinary, 520 Astronomy, food and beverages, 620 Engineering, Nitrogen, chemistry, 13. Climate action, Asteroid, Absorption band, sense organs, biological phenomena, cell phenomena, and immunity, Astrophysics - Earth and Planetary Astrophysics
Abstract

The measured nitrogen-to-carbon ratio in comets is lower than for the Sun, a discrepancy which could be alleviated if there is an unknown reservoir of nitrogen in comets. The nucleus of comet 67P/Churyumov-Gerasimenko exhibits an unidentified broad spectral reflectance feature around 3.2 micrometers, which is ubiquitous across its surface. On the basis of laboratory experiments, we attribute this absorption band to ammonium salts mixed with dust on the surface. The depth of the band indicates that semivolatile ammonium salts are a substantial reservoir of nitrogen in the comet, potentially dominating over refractory organic matter and more volatile species. Similar absorption features appear in the spectra of some asteroids, implying a compositional link between asteroids, comets, and the parent interstellar cloud., Comment: Main manuscript and Supplementary material document, Accepted for publication in Science on February 14, 2020

Published
2020

10. 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

11. Fresh emplacement of hydrated sodium chloride on Ceres from ascending salty fluids

Author

Francesca Zambon, Michelangelo Formisano, Alessandro Frigeri, Andrea Raponi, Filippo Giacomo Carrozzo, Batiste Rousseau, M. Ferrari, Federico Tosi, Eleonora Ammannito, Carol A. Raymond, Christopher T. Russell, Mauro Ciarniello, M. C. De Sanctis, and ITA

Subjects
Solar System, Aqueous solution, 010504 meteorology & atmospheric sciences, Sodium, Dwarf planet, Geochemistry, chemistry.chemical_element, Astronomy and Astrophysics, 01 natural sciences, Chloride, Hydrothermal circulation, chemistry, Impact crater, 0103 physical sciences, medicine, Upwelling, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, medicine.drug
Abstract

The surface and internal structure of Ceres show evidence of a global process of aqueous alteration, indicating the existence of an ocean in the past. However, it is not clear whether part of this ocean is still present and whether residual fluids are still circulating in the dwarf planet. These fluids may be exposed in a geologically young surface, and the most promising site to verify the occurrence of present fluids on Ceres is Cerealia Facula dome, in Occator crater. This very young facula exhibits minerals that are relatively rare in our Solar System, the formation of which requires the presence of liquid water in combination with hydrothermal activity. Here we report the discovery of hydrated sodium chloride on Cerealia Facula. These newly identified chloride salts are concentrated on the top of the dome, close to a system of radial fractures. The spatial distribution of the hydrated phase suggests that chloride salts are the solid residue of deep brines that reached the surface only recently, or are still ascending. These salts are very efficient in maintaining Ceres’s warm internal temperature and lowering the eutectic temperature of the brines, in which case ascending salty fluids may exist in Ceres today. Spectroscopic data obtained at high spatial resolution from Dawn detected the presence of fresh chloride salts at Cerealia Facula on Ceres. The spatial distribution of the hydration level of these salts suggests that they surfaced a maximum of a few centuries ago and that the upwelling of salty fluids may still be active.

Published
2020

12. The changing temperature of the nucleus of comet 67P induced by morphological and seasonal effects

Author

Ernesto Palomba, T. B. McCord, Batiste Rousseau, F. Mancarella, Sergio Fonti, Bernard Schmitt, Dominique Bockelée-Morvan, David Kappel, Mark Hofstadter, A. Zinzi, Gabriele Arnold, Mauro Ciarniello, J. Ph. Combe, Fabrizio Capaccioni, Giuseppe Piccioni, Alessandra Migliorini, Federico Tosi, J.-B. Vincent, Stéphane Erard, Giancarlo Bellucci, Priscilla Cerroni, Andrea Raponi, Johannes Benkhoff, D. Despan, Stefano Mottola, M. T. Capria, M. A. Barucci, Vincenzo Orofino, Gianrico Filacchione, Michelangelo Formisano, C. Leyrat, Andrea Longobardo, Ekkehard Kührt, M. C. De Sanctis, Istituto di Astrofisica e Planetologia Spaziali - INAF (IAPS), Istituto Nazionale di Astrofisica (INAF), German Aerospace Center (DLR), Agenzia Spaziale Italiana (ASI), Istituto di Astrofisica Spaziale e Fisica cosmica - Roma (IASF-Roma), Jet Propulsion Laboratory (JPL), California Institute of Technology (CALTECH)-NASA, Dipartimento di Fisica, Università degli studi di Lecce, DLR Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt [Berlin] (DLR), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), 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)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Max-Planck-Institut für Sonnensystemforschung (MPS), Max-Planck-Gesellschaft, 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]), Istituto di Fisica dello Spazio Interplanetario (IFSI), Consiglio Nazionale delle Ricerche (CNR), European Space Research and Technology Centre (ESTEC), European Space Agency (ESA), Department of Physics [Lecce], Università del Salento [Lecce], Department of Earth and Space Sciences [Seattle], University of Washington [Seattle], Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), 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), Institut de recherches sur la catalyse (IRC), Centre National de la Recherche Scientifique (CNRS), 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), Observatoire de Paris - Site de Meudon (OBSPM), Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Planétologie et Géodynamique UMR6112 (LPG), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Nantes - Faculté des Sciences et des Techniques, Université de Nantes (UN)-Université de Nantes (UN)-Université d'Angers (UA), ITA, USA, FRA, DEU, Tosi, F., Capaccioni, F., Capria, M. T., Mottola, S., Zinzi, A., Ciarniello, M., Filacchione, G., Hofstadter, M., Fonti, S., Formisano, M., Kappel, D., Kührt, E., Leyrat, C., Vincent, J. -B., Arnold, G., De Sanctis, M. C., Longobardo, A., Palomba, E., Raponi, A., Rousseau, B., Schmitt, B., Barucci, M. A., Bellucci, G., Benkhoff, J., Bockelée-Morvan, D., Cerroni, P., Combe, J. -Ph., Despan, D., Erard, S., Mancarella, F., Mccord, T. B., Migliorini, A., Orofino, V., and Piccioni, G.

Subjects
Daytime, 010504 meteorology & atmospheric sciences, Infrared, Comet, Imaging spectrometer, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], Astrophysics, 01 natural sciences, law.invention, Orbiter, law, Phase (matter), 0103 physical sciences, medicine, Comets, Rosetta mission, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Physics, Diurnal temperature variation, Comet 67P/Churyumov-Gerasimenko thermal modeling temperature, Institut für Physik und Astronomie, Astronomy and Astrophysics, medicine.anatomical_structure, 13. Climate action, ddc:520, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Nucleus
Abstract

International audience; K nowledge of the surface temperature distribution of a comet's nucleus proves to be of fundamental importance for a number of reasons: the evaluation of the thermophysical properties (thermal inertia and roughness, at several spatial scales), the characterization of the thermal behaviour of peculiar surface units (for example, local ice exposures, or inherently cold material units not to be confused with shaded areas), and for the understanding of the physical processes affecting the surface and the shallow subsur-face layers (for example, sublimation of volatile compounds). The distribution of surface temperatures of a cometary nucleus, closely measured by a spacecraft, can be compared with theoretical models meant to predict the thermophysical properties of the nucleus at various depths and with previous thermal observations carried out by both Earth-based and space-based telescopes, with the goal of validating and/or improving those models 1. Furthermore, the temporal evolution of the surface temperatures, primarily driven by insolation, is critical in triggering the activity of a comet, allowing the migration of volatile compounds from the interior of the nucleus and the production of gas and dust observable with different techniques 2. In the past, thermal surveys of minor bodies were carried out using ground-based and space-based facilities. However, due to the limited spatial resolution of those observations, in most cases the derived thermal properties were only global averages, and the determined temperatures were highly model dependent. Before Rosetta, direct measurements of cometary nuclei surface temperatures were obtained during short periods for a handful of comets, namely 1P/ Halley 3 , 19P/Borrelly 4 , 9P/Tempel 1 1 and 103P/Hartley 2 5 , with a maximum spatial resolution of approximately 30 m per pixel. Here we study the surface temperature distribution of the nucleus of comet 67P/Churyumov-Gerasimenko as derived by the Visible InfraRed and Thermal Imaging Spectrometer, Mapping channel (VIRTIS-M, hereafter VIRTIS) 6 in Rosetta's early global mapping phase after comet encounter. These data cover the pre-perihelion period from 1 August to 23 September 2014, when the heliocentric distance decreased from 3.62 to 3.31 au and the spacecraft was in the altitude range 61-13 km above the surface, resulting in a spatial resolution from approximately 15 to 3 m per pixel (most data showing a resolution of 13 to 15 m per pixel). In this period, the solar phase angle ranged from 17° to 93°, which Knowledge of the surface temperature distribution on a comet's nucleus and its temporal evolution at different timescales is key to constraining its thermophysical properties and understanding the physical processes that take place at and below the surface. Here we report on time-resolved maps of comet 67P/Churyumov-Gerasimenko retrieved on the basis of infra-red data acquired by the Visible InfraRed and Thermal Imaging Spectrometer (VIRTIS) onboard the Rosetta orbiter in 2014, over a roughly two-month period in the pre-perihelion phase at heliocentric distances between 3.62 and 3.31 au from the Sun. We find that at a spatial resolution ≤15 m per pixel, the measured temperatures point out the major effect that self-heating, due to the complex shape of the nucleus, has on the diurnal temperature variation. The bilobate nucleus of comet 67P also induces daytime shadowing effects, which result in large thermal gradients. Over longer periods, VIRTIS-derived temperature values reveal seasonal changes driven by decreasing heliocentric distance combined with an increasing abundance of ice within the uppermost centimetre-thick layer, which implies the possibility of having a largely pristine nucleus interior already in the shallow subsurface.

Published
2019

13. Mapping polar atmospheric features on Titan with VIMS: from the dissipation of the northern cloud to the onset of a southern polar vortex

Author

Robert H. Brown, Thomas Cornet, Jason W. Barnes, S. Le Mouélic, Sebastien Rodriguez, Pascal Rannou, Batiste Rousseau, P. D. Nicholson, Roger N. Clark, B. J. Buratti, Benoît Seignovert, Christophe Sotin, R. Robidel, Kevin H. Baines, Laboratoire de Planétologie et Géodynamique [UMR 6112] (LPG), Université d'Angers (UA)-Université de Nantes - Faculté des Sciences et des Techniques, Université de Nantes (UN)-Université de Nantes (UN)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7), Alcatel-Thalès III-V lab (III-V Lab), THALES-ALCATEL, Department of Physics [Moscow,USA], University of Idaho [Moscow, USA], Lunar and Planetary Laboratory [Tucson] (LPL), University of Arizona, Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), California Institute of Technology (CALTECH), Groupe de spectrométrie moléculaire et atmosphérique (GSMA), Université de Reims Champagne-Ardenne (URCA)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Planétologie et Géodynamique UMR6112 (LPG), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Nantes - Faculté des Sciences et des Techniques, Université de Nantes (UN)-Université de Nantes (UN)-Université d'Angers (UA), California Institute of Technology (CALTECH)-NASA, Université d'Angers (UA)-Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), 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]), Centre de Formation et de Recherche sur les Environnements Méditérranéens (CEFREM), Université de Perpignan Via Domitia (UPVD)-Centre National de la Recherche Scientifique (CNRS), Department of Astronomy [Ithaca], and Cornell University [New York]

Subjects
Haze, 010504 meteorology & atmospheric sciences, FOS: Physical sciences, Equinox, 01 natural sciences, symbols.namesake, Polar vortex, 0103 physical sciences, Atmosphere of Titan, [MATH]Mathematics [math], 010303 astronomy & astrophysics, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, [PHYS]Physics [physics], Earth and Planetary Astrophysics (astro-ph.EP), Spectral signature, Spectrometer, Astronomy and Astrophysics, 13. Climate action, Space and Planetary Science, [SDU]Sciences of the Universe [physics], Climatology, symbols, Polar, Titan (rocket family), [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Geology, Astrophysics - Earth and Planetary Astrophysics
Abstract

We have analyzed the complete archive of the Visual and Infrared Mapping Spectrometer (VIMS) data in order to monitor and analyze the evolution of the clouds and haze coverage at both poles of Titan during the entire Cassini mission. Our objective is to give a cartographic synopsis from a VIMS perspective, to provide a global view of the seasonal evolution of Titan's atmosphere over the poles. We leave the detailed comparison with the Imaging Science Subsystem (ISS) and the Composite Infrared Spectrometer (CIRS) data sets to further studies. We have computed global hyperspectral mosaics for each of the 127 targeted flybys of Titan to produce synthetic color maps emphasizing the main atmospheric features. The north pole appears fully covered by a huge cloud as soon as the first observations in 2004 and up to the equinox in 2009 (Le Mou\'elic et al. 2012). The northern skies then became progressively clearer, after the circulation turnover in 2009, revealing the underlying lakes and seas to the optical instruments up to 2017. The reverse situation is observed over the south pole, which was mostly clear of such a high obscuring cloud during the first years of the mission, but started to develop a polar cloud in 2012. This feature grew up month after month until the end of the mission in 2017, with a poleward latitudinal extent of 75$^\circ$S in 2013 up to 58$^\circ$S in April 2017. Thanks to the spectral capabilities of VIMS, we have detected HCN spectral signatures over the north pole in almost all flybys between 2004 and 2008. These HCN signatures started then to show up over the south pole in almost all flybys between 2012 and 2017, so perfectly matching the timing and spatial extent of the northern and southern polar atmospheric features.

Published
2018

14. VESPA: A community-driven Virtual Observatory in Planetary Science

Author

S. Ivanoski, Bernard Schmitt, Anthony Lagain, Andrea Longobardo, F. Andrieu, R. Hueso, Angelo Pio Rossi, Stéphane Erard, N. Jourdane, Nicholas Achilleos, O. Delaa, N. André, Kevin Benson, M. Bouchemit, Vincent Génot, Manuel Scherf, Damien Albert, T. Al-Ubaidi, Ann Carine Vandaele, Anni Määttänen, P. Le Sidaner, William Thuillot, L. Beigbeder, Pierre Fernique, M. Gangloff, David Pisa, Batiste Rousseau, Josselin Desmars, Baptiste Cecconi, M. Minin, Ondrej Santolik, J. M. Glorian, Ehouarn Millour, Loïc Trompet, P. Bollard, Chiara Marmo, J. Soucek, C. Chauvin, Benoit Carry, Jon Juaristi, M. T. Capria, Patrick Guio, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Direction Informatique de l'Observatoire - Composante PADC (DIO - PADC), Observatoire de Paris - Site de Paris (OP), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS), Jacobs University [Bremen], Istituto di Astrofisica e Planetologia Spaziali - INAF (IAPS), Istituto Nazionale di Astrofisica (INAF), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), 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), Institut de recherche en astrophysique et planétologie (IRAP), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Belgian Institute for Space Aeronomy / Institut d'Aéronomie Spatiale de Belgique (BIRA-IASB), Institut für Weltraumforschung [Graz] (IWF), Osterreichische Akademie der Wissenschaften (ÖAW), Escuela Técnica Superior de Ingenieria (ETSI), Universidad del Pais Vasco / Euskal Herriko Unibertsitatea [Espagne] (UPV/EHU), IMPEC - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Institut de Mécanique Céleste et de Calcul des Ephémérides (IMCCE), PSL Research University (PSL)-PSL Research University (PSL)-Université de Lille-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Joseph Louis LAGRANGE (LAGRANGE), Université Nice Sophia Antipolis (... - 2019) (UNS), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Department of Physics and Astronomy [UCL London], University College of London [London] (UCL), Géosciences Paris Sud (GEOPS), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), Institute of Atmospheric Physics [Prague] (IAP), Czech Academy of Sciences [Prague] (ASCR), Mullard Space Science Laboratory (MSSL), Observatoire astronomique de Strasbourg (ObAS), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), GFI Informatique, Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), Space Research Institute of Austrian Academy of Sciences (IWF), Austrian Academy of Sciences (OeAW), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS), 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]), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Escuela de Ingeniería de Bilbao, PLANETO - LATMOS, Sorbonne Université (SU)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Lille-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Czech Academy of Sciences [Prague] (CAS), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Institut für Weltraumforschung = Space Research institute [Graz] (IWF), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Paris (ENS-PSL), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL)

Subjects
Earth and Planetary Astrophysics (astro-ph.EP), [PHYS]Physics [physics], 010504 meteorology & atmospheric sciences, Computer science, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], FOS: Physical sciences, Astronomy and Astrophysics, Virtual observatory, GIS, Virtual Observatory, 01 natural sciences, Data science, Planetary science, Data access, Space and Planetary Science, 0103 physical sciences, Use case, Solar System, Astrophysics - Instrumentation and Methods for Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Astrophysics - Earth and Planetary Astrophysics, 0105 earth and related environmental sciences, Remote sensing
Abstract

The VESPA data access system focuses on applying Virtual Observatory (VO) standards and tools to Planetary Science. Building on a previous EC-funded Europlanet program, it has reached maturity during the first year of a new Europlanet 2020 program (started in 2015 for 4 years). The infrastructure has been upgraded to handle many fields of Solar System studies, with a focus both on users and data providers. This paper describes the broad lines of the current VESPA infrastructure as seen by a potential user, and provides examples of real use cases in several thematic areas. These use cases are also intended to identify hints for future developments and adaptations of VO tools to Planetary Science., Comment: Planetary and Space Sciences (in press), Special Issue "Enabling Open and Interoperable Access to Planetary Science and Heliophysics Databases and Tools". 43 pages, 14 figures, 1 table

Published
2018

15. The temporal evolution of exposed water ice-rich areas on the surface of 67P/Churyumov-Gerasimenko: spectral analysis

Author

Eric Quirico, Federico Tosi, Gianrico Filacchione, M. A. Barucci, C. Leyrat, Gabriele Arnold, David Kappel, Stefano Mottola, Fabrizio Capaccioni, Andrea Raponi, D. Bockelee-Morvan, M. T. Capria, Giovanna Rinaldi, Stéphane Erard, Batiste Rousseau, Andrea Longobardo, M. C. De Sanctis, Ernesto Palomba, Mauro Ciarniello, Istituto di Astrofisica e Planetologia Spaziali - INAF (IAPS), Istituto Nazionale di Astrofisica (INAF), Istituto di Astrofisica Spaziale e Fisica cosmica - Roma (IASF-Roma), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), 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), DLR Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt [Berlin] (DLR), Laboratoire de Chimie Physique D'Orsay (LCPO), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), 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), IASI (IASI), Consiglio Nazionale delle Ricerche (CNR), 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), Université Paris-Sud - Paris 11 (UP11)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), 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]), and National Research Council of Italy | Consiglio Nazionale delle Ricerche (CNR)

Subjects
Physics, Earth and Planetary Astrophysics (astro-ph.EP), radiative transfer – techniques: imaging spectroscopy – comets: individual: 67P – planets and satellites: surfaces – infrared: planetary systems, 010504 meteorology & atmospheric sciences, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], FOS: Physical sciences, Astronomy and Astrophysics, Landslide, Spatial distribution, Atmospheric sciences, 01 natural sciences, Grain size, Atmospheric radiative transfer codes, 13. Climate action, Space and Planetary Science, [SDU]Sciences of the Universe [physics], 0103 physical sciences, Radiative transfer, Sublimation (phase transition), Water ice, Water cycle, 010303 astronomy & astrophysics, Astrophysics - Earth and Planetary Astrophysics, 0105 earth and related environmental sciences
Abstract

Water ice-rich patches have been detected on the surface of comet 67P/Churyumov-Gerasimenko by the VIRTIS hyperspectral imager on-board the Rosetta spacecraft, since the orbital insertion in late August 2014. Among those, three icy patches have been selected, and VIRTIS data are used to analyse their properties and their temporal evolution while the comet was moving towards the Sun. We performed an extensive analysis of the spectral parameters, and we applied the Hapke radiative transfer model to retrieve the abundance and grain size of water ice, as well as the mixing modalities of water ice and dark terrains on the three selected water ice rich areas. Study of the spatial distribution of the spectral parameters within the ice-rich patches has revealed that water ice follows different patterns associated to a bimodal distribution of the grains: ~50 {\mu}m sized and ~2000 {\mu}m sized. In all three cases, after the first detections at about 3.5 AU heliocentric distance, the spatial extension and intensity of the water ice spectral features increased, it reached a maximum after 60-100 days at about 3.0 AU, and was followed by an approximately equally timed decrease and disappearanceat about ~2.2 AU, before perihelion. The behaviour of the analysed patches can be assimilated to a seasonal cycle. In addition we found evidence of short-term variability associated to a diurnal water cycle. The similar lifecycle of the three icy regions indicates that water ice is uniformly distributed in the subsurface layers, and no large water ice reservoirs are present., Comment: submitted to MNRAS

Published
2016

16. The global surface composition of 67P/Churyumov-Gerasimenko nucleus by Rosetta/VIRTIS. II) Diurnal and seasonal variability

Author

M. A. Barucci, Stefano Mottola, Alessandra Migliorini, Federico Tosi, Gabriele Arnold, Priscilla Cerroni, Andrea Longobardo, M. T. Capria, Giovanna Rinaldi, M. Salatti, Bernard Schmitt, Andrea Raponi, W-H. Ip, Angelo Zinzi, Mauro Ciarniello, C. Leyrat, Giuseppe Piccioni, Batiste Rousseau, David Kappel, Fabrizio Capaccioni, Eric Quirico, Stéphane Erard, Gianrico Filacchione, Ernesto Palomba, E. Kuehrt, D. Bockelee-Morvan, M.C. Desanctis, ITA, FRA, DEU, TWN, SGP, Istituto di Astrofisica e Planetologia Spaziali - INAF (IAPS), Istituto Nazionale di Astrofisica (INAF), Istituto di Astrofisica Spaziale e Fisica cosmica - Roma (IASF-Roma), DLR Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt [Berlin] (DLR), Laboratoire de Chimie Physique D'Orsay (LCPO), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), 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), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), 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), German Aerospace Center (DLR), Agenzia Spaziale Italiana (ASI), Space Science Institute [Macau] (SSI), Macau University of Science and Technology (MUST), IASI (IASI), Consiglio Nazionale delle Ricerche (CNR), Université Paris-Sud - Paris 11 (UP11)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), 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), 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]), and National Research Council of Italy | Consiglio Nazionale delle Ricerche (CNR)

Subjects
67P/Churyumov-Gerasimenko, Asteroiden und Kometen, 010504 meteorology & atmospheric sciences, Infrared, imaging spectroscopy, Atmospheric sciences, 01 natural sciences, Spectral line, Diurnal cycle, 0103 physical sciences, Radiative transfer, comets, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Sunlight, Physics, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Leitungsbereich PF, comets: individual: 67P/Churyumov-Gerasimenko, Astronomy and Astrophysics, methods: data analysis, 13. Climate action, Space and Planetary Science, techniques: imaging spectroscopy, [SDU]Sciences of the Universe [physics], radiative transfer, Spatial ecology, Sublimation (phase transition), Surface water, padc
Abstract

International audience; VIRTIS-M observations of the nucleus of comet 67P/Churyumov-Gerasimenko acquired from 2014 August to 2015 May have been analysed to investigate surface temporal variability at both seasonal and diurnal scales. The measured reflectance spectra are studied by means of comet spectral indicators (CSI) such as slopes in the visible and infrared ranges, and 3.2 mum band area and band centre. CSI maps derived from data acquired at different heliocentric distances (from 3.62 to 1.72 au) along the inbound leg of the comet's orbit are used to infer surface water ice abundance. We measure a global scale enrichment of water ice from 2014 August to 2015 May across the body of the comet, along with variability at small spatial scale, possibly related with the local insolation conditions. Analysis of water ice diurnal variability is performed on 2014 August observations. Water ice appears at the border of receding shadows in the neck of the comet (Hapi), sublimating in less than 1 h, after exposure to sunlight. As similar variability is not observed in other regions of the comet, we interpreted this as the expression of a diurnal cycle of sublimation and re-condensation of water ice, triggered by sudden shadowing produced on the neck by the body and the head of the nucleus.

Published
2016

17. The global surface composition of 67P/CG nucleus by Rosetta/VIRTIS. (I) Prelanding mission phase

Author

M. Faure, David Kappel, Priscilla Cerroni, Antonella Barucci, Alessandra Migliorini, Fabrizio Capaccioni, Batiste Rousseau, Dominique Morvan, Sonia Fornasier, C. Leyrat, Eric Quirico, D. Despan, Federico Tosi, Gabriele Arnold, Andrea Longobardo, Stéphane Erard, Andrea Raponi, Ralf Jaumann, Sergio Fonti, L. V. Moroz, Ernesto Palomba, F. Mancarella, Maria Teresa Capria, Maria Cristina De Sanctis, Robert W. Carlson, Bernard Schmitt, Mauro Ciarniello, Katrin Stephan, Gianrico Filacchione, Giuseppe Piccioni, Istituto di Astrofisica e Planetologia Spaziali - INAF (IAPS), Istituto Nazionale di Astrofisica (INAF), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Deutsches Zentrum für Luft- und Raumfahrt [Berlin] (DLR), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), 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), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Dipartimento di Matematica e Fisica 'Ennio de Georgi', Università del Salento [Lecce], ITA, USA, FRA, DEU, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), 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]), and California Institute of Technology (CALTECH)-NASA

Subjects
Asteroiden und Kometen, 010504 meteorology & atmospheric sciences, Institut für Planetenforschung, Comet, FOS: Physical sciences, Spatial distribution, 01 natural sciences, Nucleus, Flattening, Spectral line, law.invention, Orbiter, law, Rosetta, 0103 physical sciences, Spectroscopy, 010303 astronomy & astrophysics, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Earth and Planetary Astrophysics (astro-ph.EP), Physics, [PHYS]Physics [physics], Single-scattering albedo, Hyperspectral imaging, Astronomy, Astronomy and Astrophysics, Planetengeologie, 13. Climate action, Space and Planetary Science, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Composition, Astrophysics - Earth and Planetary Astrophysics
Abstract

From August to November 2014 the Rosetta orbiter has performed an extensive observation campaign aimed at the characterization of 67P/CG nucleus properties and to the selection of the Philae landing site. The campaign led to the production of a global map of the illuminated portion of 67P/CG nucleus. During this prelanding phase the comet's heliocentric distance decreased from 3.62 to 2.93 AU while Rosetta was orbiting around the nucleus at distances between 100 to 10 km. VIRTIS-M, the Visible and InfraRed Thermal Imaging Spectrometer - Mapping channel (Coradini et al. 2007) onboard the orbiter, has acquired 0.25-5.1 micron hyperspectral data of the entire illuminated surface, e.g. the north hemisphere and the equatorial regions, with spatial resolution between 2.5 and 25 m/pixel. I/F spectra have been corrected for thermal emission removal in the 3.5-5.1 micron range and for surface's photometric response. The resulting reflectance spectra have been used to compute several Cometary Spectral Indicators (CSI): single scattering albedo at 0.55 micron, 0.5-0.8 micron and 1.0-2.5 micron spectral slopes, 3.2 micron organic material and 2.0 micron water ice band parameters (center, depth) with the aim to map their spatial distribution on the surface and to study their temporal variability as the nucleus moved towards the Sun. Indeed, throughout the investigated period, the nucleus surface shows a significant increase of the single scattering albedo along with a decrease of the 0.5-0.8 and 1.0-2.5 micron spectral slopes, indicating a flattening of the reflectance. We attribute the origin of this effect to the partial removal of the dust layer caused by the increased contribution of water sublimation to the gaseous activity as comet crossed the frost-line., 19 Figures, 5 Tables. Accepted for publication in Icarus journal on 29 February 2016

Published
2016

18. Sulfides and refractory organic matter at the surface of 67P/Churyumov-Gerasimenko: evidence from VIRTIS data and laboratory measurements

Author

Batiste Rousseau, Érard, Stéphane, Beck, Pierre, Quirico, Eric, Schmitt, Bernard, Bonal, Lydie, Montes-Hernandez, German, Moroz, Lyuba, Kappel, David, Markus, Kathrin, Arnold, Gabriele, Ciarniello, Mauro, Raponi, Andrea, Longobardo, Andrea, Capaccioni, Fabrizio, Filacchione, Gianrico, Bockelee-Morvan, Dominique, Leyrat, Cedric, Virtis, Rosetta Team, Henry, Florence, 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, 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 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]), Institut des Sciences de la Terre (ISTerre), Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-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]), University of Postdam, German Aerospace Center (DLR), and IAPS - INAF

Subjects
[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], [PHYS.ASTR] Physics [physics]/Astrophysics [astro-ph]
Abstract

International audience; From Aug. 2014 to Sept. 2016, Rosetta has been orbiting comet 67P and has obtained informations on the origin and evolution of comets. The imaging spectrometer VIRTIS collected reflectance spectra of the surface within the range 0.25-5.1 µm that revealed a low albedo and a homogeneous surface (Capaccioni et al., 2015; Ciarniello et al., 2015). The spectra are also characterized by red slopes in the visible and in the near infrared. These properties have been interpreted to be due to the presence of an organic polyaromatic material mixed with opaque minerals, presumably troilite-like sulfides according to the composition of presumed cometary grains (Quirico et al., 2016).In order to test this proposition, we have run a series of experimental measurements of granular mixtures of an analog of cometary polyaromatic organic matter (an immature coal) and different sulfides (pyrite, pyrrhotite and troilite). Bi-directional reflectance spectra were obtained at IPAG in the range 0.4-4 µm and under a range of viewing geometries. For the first time we are performing measurements on materials with sub-micrometer grains relevant to what is expected for cometary grains. Produced with a planetary grinder operating on colloidal solutions, these grains were characterized with SEM, X-ray diffraction and an electronic microprobe.The experiment confirms that the low albedo in the near infrared is controlled by the abundance of pyrrhotite or troilite, while pyrite is not a viable candidate. These sulfides also account very well for the red slopes in the visible and the near infrared ranges. Excellent match with VIRTIS spectra is obtained for coal pyrrhotite mixtures with a pyrrhotite abundance ranging from 30 to 50 wt%. Although the cometary grains composition include silicates and other organic compounds (see IDPs and Wild2 samples analysis), these results offer another interpretation of the reddish nature of some small bodies' surfaces, which has been interpreted so far as the presence of red organics or the consequence of space weathering. Finally, the suggestion that sulfides are major contributors to 67P dust might be generalized to other cometary nuclei that have similar VNIR spectra, as well as to P & D type asteroids.

Published
2016

19. Sub-pixel geometric modeling and spectral fitting for Rosetta/VIRTIS-M measurements of the nucleus of comet 67P

Author

Andrea Raponi, Gianrico Filacchione, Federico Tosi, David Kappel, Fabrizio Capaccioni, Mauro Ciarniello, Cedric Leyrat, Gabriele Arnold, Batiste Rousseau, Liubov Moroz, and Stéphane Erard

Subjects
Physics, Surface (mathematics), Pixel, Institut für Planetenforschung, Comet, Leitungsbereich PF, spectral modeling, Hyperspectral imaging, Astrophysics, VIRTIS, medicine.anatomical_structure, Rosetta, medicine, Comets, Spectral fitting, Geometric modeling, Nucleus
Abstract

AbstractWe aim at retrieving physical and compositional surface properties of the nucleus of comet 67P/Churyumov-Gerasimenko (hereafter 67P) from VIS-IR hyperspectral images (‘cubes’). Here we report on our progress in the geometric modeling and spectral fitting.IntroductionThe measured cubes have been acquired with VIRTIS-M instrument [1] aboard Rosetta. Starting from a digital shape model of 67P [2], the radiance measured by a pixel results from sub-pixel radiance contributions of several shape model facets weighted by the wavelength-dependent spatial point spread function (PSF) of the instrument. Based on a corresponding sub-pixel geometric modeling, we have computed the weighting coefficients and quantified the PSF [3]. The radiance contribution from a single facet can be simulated from physical and compositional parameters defined on this facet, using a photometric model (Hapke or Shkuratov [4,5]). Besides facilitating the consideration of PSF effects, this approach allows us to better approximate the rugged fine-scale topography of 67P that leads to varying observation/illumination/shadowing conditions on sub-pixel scales. Also, the retrieval of parameters common to multiple acquisitions requires a definition of surface parameters bound to the shape model instead of the respective pixel footprints. In this work, we focus on the spectral fitting of entire sets of cubes.Retrieval algorithmThe Bayesian Multi-Spectrum Retrieval algorithm MSR [6] fits the synthetic spectra to the measured ones by iteratively varying the facet properties. MSR takes into account constraints and Bayesian a priori information on the facet properties (mean values, standard deviations, correlation lengths/times/wavelengths) as well as measurement error information. Moreover, consistency requirements are respected. For instance, for measurements acquired at similar times, there are facet properties (surface roughness, particle size, composition, etc.) that do not change between repeated observations and can be treated and retrieved as common to those observations. To achieve this, MSR regards many measurements of a selected surface region under different illumination and observation conditions, shadowing state, spatial resolution, and at different wavelengths as a single meta-measurement. This is analogous to the meta-measurement formed by measurements at different single wavelengths, called a spectrum.Preliminary resultsAt the present stage, MSR is tested to retrieve maps of shape model facet properties from a meta-measurement encompassing tens of VIRTIS-M-cubes, corresponding to the order of a million measured spectra, see Fig. 1. Panel (a) shows a calibrated and pre-processed measured VIRTIS-M cube, represented at 1 µm, mainly showing 67P’s northern hemisphere.Panel (b) illustrates residual variations when the first-order effect of the complex topography of 67P is removed using the Akimov disk function [5], which describes the photometry of utterly rough surfaces. These residual variations can be due to limits in the applicability of the Akimov disk function or real physical variations in texture or composition. The phase angle (~40°) is too large for substantial opposition effects to show up.In the case where we fit the entire cube using the Hapke model, panel (c) shows very little residual variations that are mainly associated with local terminators and slight PSF model imprecisions. This image illustrates that our present setup allows us to fit the measurements very accurately when the facet properties can vary freely within the frame of our Bayesian regularization for one cube. For this comparison, we selected as free parameters the single-scattering albedo and phase function asymmetry parameter spectra for two intimately mixed endmembers as properties that are constant over all facets, and the relative abundance of the two endmembers along with the roughness angle and filling factor as properties that can vary between facets.Finally, panel (d) exhibits moderate residual variations. Here, we fitted a meta-measurement of 25 cubes at various illumination and observation conditions and displayed the one also represented in the other panels. The fitting took about one week on a desktop computer. Now the facet properties cannot vary as freely as for case (c), because simultaneously they also have to be compatible with all other considered cubes. The retrieved facet properties are therefore more well-grounded candidates for the actual surface properties. This panel demonstrates that using information from many hyperspectral images helps to reduce overfitting. We also note that the here utilized set of free parameters is not able to fully capture the spectral variability of the measurements within the frame of this model, pointing to the necessity of additional free parameters, or difficulties of the Hapke model to simultaneously parameterize the different cubes in a consistent way.At this stage, it is not clear yet, how the retrieved facet properties are related to actual surface properties of 67P. At the meeting we will present different parameter sets that lead to equally well fits and discuss their plausibility. A similar investigation based on the Shkuratov model as well as a detailed error analysis, based on synthetic VIRTIS-M cubes, to investigate interferences between the retrieved and other parameters, are the next steps in this ongoing work. Finally, we expect our approach to be capable of identifying local surface property variations in a physically and mathematically well-grounded way, and we will investigate their correlations with morphologic regions on 67P.AcknowledgementsWe thank the following institutions and agencies for support of this work: Italian Space Agency (ASI, Italy). Centre National d'Etudes Spatiales (CNES, France), DLR (Germany). D.K. acknowledges DFG-grant KA 3757/2-1.References[1] Coradini et al. (2007) Space Sci. Rev. 128, 529. [2] Preusker et al. (2017) A&A 607, L1. [3] Kappel et al. (2019) EPSC-DPS 2019, EPSC-DPS2019-456. [4] Hapke (2012) Theory of Reflectance and Emittance Spectroscopy, 2nd edn. (Cambridge University Press). [5] Shkuratov et al. (2011) Planet. Space Sci. 59, 1326. [6] Kappel (2014) J. Quant. Spectrosc. Rad. 133, 153.

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