The opposition effect of 67P/Churyumov-Gerasimenko on post-perihelion Rosetta images

DOI: 
10.1093/mnras/stx1834
Publication date: 
01/07/2017
Main author: 
Hasselmann, P. H.
IAA authors: 
Gutierrez, P. J.;Lara, M. L.;Lopez-Moreno, J. J.
Authors: 
Hasselmann, P. H.;Barucci, M. A.;Fornasier, S.;Feller, C.;Deshapriya, J. D. P.;Fulchignoni, M.;Jost, B.;Sierks, H.;Barbieri, C.;Lamy, P. L.;Rodrigo, R.;Koschny, D.;Rickman, H.;A'Hearn, M.;Bertaux, J. -L.;Bertini, I.;Cremonese, G.;Da Deppo, V.;Davidsson, B.;Debei, S.;De Cecco, M.;Deller, J.;Fulle, M.;Gaskell, R. W.;Groussin, O.;Gutierrez, P. J.;Güttler, C.;Hofmann, M.;Hviid, S. F.;Ip, W. -H.;Jorda, L.;Keller, H. U.;Knollenberg, J.;Kovacs, G.;Kramm, R.;Kührt, E.;Küppers, M.;Lara, M. L.;Lazzarin, M.;Lopez-Moreno, J. J.;Marzari, F.;Mottola, S.;Naletto, G.;Oklay, N.;Pommerol, A.;Thomas, N.;Tubiana, C.;Vincent, J. -B.
Journal: 
Monthly Notices of the Royal Astronomical Society
Refereed: 
Yes
Publication type: 
Article
Volume: 
469
Pages: 
S550
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.

Database: 
ADS
URL: 
https://ui.adsabs.harvard.edu/#abs/2017MNRAS.469S.550H/abstract
ADS Bibcode: 
2017MNRAS.469S.550H
Keywords: 
Rosetta: 67P/Churyumov-Gerasimenko;photometry