Hasselmann, P. H.P. H.HasselmannBarucci, M. A.M. A.BarucciFornasier, S.S.FornasierFeller, C.C.FellerDeshapriya, J. D. P.J. D. P.DeshapriyaFulchignoni, M.M.FulchignoniJost, B.B.JostSierks, H.H.SierksBarbieri, C.C.BarbieriLamy, P. L.P. L.LamyRodrigo, R.R.RodrigoKoschny, D.D.KoschnyRickman, H.H.RickmanA'Hearn, M.M.A'HearnBertaux, J. -L.J. -L.BertauxBertini, I.I.BertiniCREMONESE, GabrieleGabrieleCREMONESEDa Deppo, V.V.Da DeppoDavidsson, B.B.DavidssonDebei, S.S.DebeiDe Cecco, M.M.De CeccoDeller, J.J.DellerFULLE, MarcoMarcoFULLEGaskell, R. W.R. W.GaskellGroussin, O.O.GroussinGutierrez, P. J.P. J.GutierrezGüttler, C.C.GüttlerHofmann, M.M.HofmannHviid, S. F.S. F.HviidIp, W. -H.W. -H.IpJorda, L.L.JordaKeller, H. U.H. U.KellerKnollenberg, J.J.KnollenbergKovacs, G.G.KovacsKramm, R.R.KrammKührt, E.E.KührtKüppers, M.M.KüppersLara, M. L.M. L.LaraLazzarin, M.M.LazzarinLopez-Moreno, J. J.J. J.Lopez-MorenoMarzari, F.F.MarzariMottola, S.S.MottolaNaletto, G.G.NalettoOklay, N.N.OklayPommerol, A.A.PommerolThomas, N.N.ThomasTubiana, C.C.TubianaVincent, J. -B.J. -B.Vincent2020-11-092020-11-0920170035-8711http://hdl.handle.net/20.500.12386/28219High-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.STAMPAenArticle10.1093/mnras/stx18342-s2.0-85040810160000443940500051https://academic.oup.com/mnras/article/469/Suppl_2/S550/41035522017MNRAS.469S.550HFIS/05 - ASTRONOMIA E ASTROFISICA