The opposition effect of 67P/Churyumov-Gerasimenko on post-perihelion Rosetta images
Date Issued
2017
Author(s)
Hasselmann, P. H.
•
Barucci, M. A.
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Fornasier, S.
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Feller, C.
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Deshapriya, J. D. P.
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Fulchignoni, M.
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Jost, B.
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Sierks, H.
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Barbieri, C.
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Lamy, P. L.
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Rodrigo, R.
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Koschny, D.
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Rickman, H.
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A'Hearn, M.
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Bertaux, J. -L.
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Bertini, I.
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•
Da Deppo, V.
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Davidsson, B.
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Debei, S.
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De Cecco, M.
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Deller, J.
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•
Gaskell, R. W.
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Groussin, O.
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Gutierrez, P. J.
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Güttler, C.
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Hofmann, M.
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Hviid, S. F.
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Ip, W. -H.
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Jorda, L.
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Keller, H. U.
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Knollenberg, J.
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Kovacs, G.
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Kramm, R.
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Kührt, E.
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Küppers, M.
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Lara, M. L.
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Lazzarin, M.
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Lopez-Moreno, J. J.
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Marzari, F.
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Mottola, S.
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Naletto, G.
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Oklay, N.
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Pommerol, A.
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Thomas, N.
•
•
Vincent, J. -B.
Abstract
High-resolution OSIRIS/Rosetta images of 67P/Churyumov-Gerasimenko acquired on the night run of 2016 April 9-10 show, at large scale, an opposition effect (OE) spot sweeping across Imhotep as the phase angle ranges from 0° to 17°. In this work, we fitted the phase curve of the whole surface imaged as well as three particular features using both the linear-exponential and Hapke models. These features encompass different types of spectral behaviour: a circular mesa, one venous structure and an assemblage of bright spots, going from red to blue colours. Both the Hapke and linear-exponential parameters indicate a stepwise sharpening of the OE from bright spots to circular mesa. Yet a very broad nonlinear phase curve is verified and no sign of sharp OE associated with a coherent-backscattering mechanism is observed. We estimate that the 67P surface is dominated by opaque, desiccated and larger-than-wavelength irregular grains. Veins and bright spots display photometric properties consistent with surfaces becoming slightly brighter as they are enriched by high-albedo ice grains. We also report the estimation of normal albedo for all cometary regions observed throughout the image sequence. Comparison to pre-perihelion results indicates that far better insolation of northern brighter regions, I.e. Hapi, Hathor and Seth, is sufficient to explain mismatches on the photometric parameters. However, metre-scale photometric analysis of the Imhotep-Ash boundary area advocates for mild darkening (<7 per cent) of the surface at local scale.
Volume
469
Start page
S550
Issn Identifier
0035-8711
Ads BibCode
2017MNRAS.469S.550H
Rights
open.access
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