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Spectral reflectance properties of refractory components of comet 67P/CG's nucleus - insights from laboratory studies

Moroz, Liubov and Markus, Kathrin and Arnold, Gabriele and Henckel, Daniela and Kappel, David and Schade, U. and Ciarniello, M. and Rousseau, Batiste and Quirico, E. and Schmitt, B. and Capaccioni, F. and Bockelee-Morvan, D. and Filacchione, G. and Erard, S. and Leyrat, C. and Longobardo, A (2017) Spectral reflectance properties of refractory components of comet 67P/CG's nucleus - insights from laboratory studies. In: Asteroids, Comets, Meteors 2017 Meeting (ACM 2017), 2.d.39. Asteroids, Comets, Meteors (ACM) 2017, 10. - 14. April 2017, Montevideo, Uruguay.

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Official URL: http://acm2017.uy/abstracts/Poster2.d.39.pdf


Analysis of 0.25-5 μm reflectance spectra acquired by the Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS) onboard Rosetta orbiter revealed that the surface of comet 67P/CG is dark from the near-UV to the IR and is enriched in refractory phases such as organic and opaque components. The broadness and complexity of the ubiquitous absorption feature around 3.2 μm suggest a variety of cometary organic constituents. For example, complex hydrocarbons can contribute to the feature between 3.2 and 3.5 μm and to the low reflectance of the surface in the visible. Relevance of natural macromolecular solids, such as solid oil bitumens (asphaltites, kerites, anthraxolites) and coals as spectral analogs for the hydrocarbon part of cometary refractory organics were discussed in detail in the literature. Fine-grained opaque refractory phases (e.g. iron sulfides, Fe-Ni alloys) are likely responsible for the low IR reflectance and low contrast of the 3.2 μm absorption band. Other non-icy constituents that may contribute to spectral reflectance properties of the 67P surface include amorphous and crystalline silicates. Here we report and discuss the 0.3-5 μm reflectance spectra of relevant Fe-sulfides (meteoritic troilite and several terrestrial pyrrhotites) ground and sieved to various particle sizes. We report the results of the synthesis, analyses, and/or spectral reflectance measurements of Fe-free low-Ca pyroxenes (ortho- and clinoenstatites), forsterites, and a high-Ca pyroxene (diopside). We present reflectance spectra of intimate mixtures of powdered Fe-sulfides with kerite (as an example of a relevant macromolecular organic solid) and synthetic orthoenstatite. We investigate and discuss the ability of Fe-sulfides to suppress absorption bands of other cometary refractory components and to affect the spectral slopes and reflectance values of the 67P/CG surface at different wavelengths from the near-UV to the IR. Finally, we discuss the evolution of organic absorption bands as a function of sulfide content in the mixtures and the possibility for detection of individual C-H stretching bands in the VIRTIS spectra of 67P/CG. We show that spectral reflectance of the ubiquitous dark material on the surface of 67P is mostly controlled by fine-grained opaques and organic refractories, while silicate components play a less significant role and are unlikely to contribute significantly to the VIRTIS spectra and to the observed spectral variations across the 67P surface. We demonstrate that fine-grained Fe-sulfides (troilite and pyrrhotite) are effective darkening agents from the near UV to IR that can explain the very low IR reflectance of the 67P nucleus. The shape of the VIRTIS spectra in the visible range is consistent with the presence of polyaromatic-rich organics together with Fe-sulfides. Fe-sulfides intimately mixed with other components significantly influence shapes and relative contrasts of absorption bands of other phases. If real, the fine structure in the VIRTIS spectra between 3.2 and 3.5 μm could be indicative of individual C-H absorption bands in aromatic structures, methyl and methylene groups. Further work is needed to clarify which species contribute to the broad complex 3.2-μm band in the VIRTIS spectra and to the spectral shape between 1.5 and 2.5 μm.

Item URL in elib:https://elib.dlr.de/115595/
Document Type:Conference or Workshop Item (Poster)
Title:Spectral reflectance properties of refractory components of comet 67P/CG's nucleus - insights from laboratory studies
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Markus, Kathrinwestfälische wilhelms-universität münsterUNSPECIFIEDUNSPECIFIED
Schade, U.helmholtz centre berlin for materials and energy, bessy ii, berlin, germanyUNSPECIFIEDUNSPECIFIED
Ciarniello, M.inaf-iasf, italyUNSPECIFIEDUNSPECIFIED
Quirico, E.laboratory of planetology, cnrs joseph fourier universityUNSPECIFIEDUNSPECIFIED
Schmitt, B.grenoble planetology laboratoryUNSPECIFIEDUNSPECIFIED
Capaccioni, F.inaf-iasf, italyUNSPECIFIEDUNSPECIFIED
Bockelee-Morvan, D.observatoire de paris, meudonUNSPECIFIEDUNSPECIFIED
Filacchione, G.inaf-iasf, rome, italyUNSPECIFIEDUNSPECIFIED
Longobardo, Ainaf-laps, via del fosso del cavaliere 100, i-00133 rome, italyUNSPECIFIEDUNSPECIFIED
Date:13 April 2017
Journal or Publication Title:Asteroids, Comets, Meteors 2017 Meeting (ACM 2017)
Refereed publication:No
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:No
Page Range:2.d.39
Keywords:Rosetta, 67P, comet, surface, composition, VIRTIS, laboratory
Event Title:Asteroids, Comets, Meteors (ACM) 2017
Event Location:Montevideo, Uruguay
Event Type:international Conference
Event Dates:10. - 14. April 2017
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Space Exploration
DLR - Research theme (Project):R - Project ROSETTA Instruments (old)
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Asteroids and Comets
Institute of Planetary Research > Leitungsbereich PF
Deposited By: Kappel, David
Deposited On:20 Nov 2017 15:51
Last Modified:31 Jul 2019 20:13

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