Decimetre-scaled spectrophotometric properties of the nucleus of comet 67P/Churyumov–Gerasimenko from OSIRIS observations

Clément Feller 1 Sonia Fornasier 1 Pedro Henrique Hasselmann 1 Antonella Barucci 1 Frank Preusker 2 Frank Scholten 2 Laurent Jorda 3 Antoine Pommerol 4 Bernhard Jost 4 Olivier Poch 4 Mohamed Ramy Elmaary 4 Nicholas Thomas 4 Irina Belskaya 5 Maurizio Pajola 6, 7 Holder Sierks 8 Cesare Barbieri 9 Philippe L. Lamy 3 Detlef Koschny 10 Hans Rickman 11, 12 Rafael Rodrigo 13, 14 Jessica Agarwal 8 Michael F. A'Hearn 15 Jean-Loup Bertaux 16 Ivano Bertini 7 Steve Boudreault 8 Gabriele Cremonese 17 Vania Da Deppo 18 Björn J. R. Davidsson 19 Stefano Debei 20 Mariolino de Cecco 21 Jakob Deller 8 Marco Fulle 22 Adeline Giquel 8 Olivier Groussin 3 Pedro J. Gutierrez 23 Carsten Güttler 8 Marc Hofmann 8 Stubbe F. Hviid 2 Horst Keller 24 Wing-Huen Ip 25 J. Knollenberg 2 G. Kovacs 8 J.-R. Kramm 8 E. Kührt 2 M. Küppers 14 M. Lara 24 M. Lazzarin 9 C. Leyrat 1 J. J. Lopez Moreno 23 F. Marzari 9 N. Masoumzadeh 8 S. Mottola 2 G. Naletto 26 D. Perna 1 N. Oklay 8 X. Shi 8 C. Tubiana 8 Jean-Baptiste Vincent 8
Abstract : We present the results of the photometric and spectrophotometric properties of the 67P/Churyumov–Gerasimenko nucleus derived with the Optical, Spectroscopic and Infrared Remote Imaging System instrument during the closest fly-by over the comet, which took place on 2015 February 14 at a distance of ∼6 km from the surface. Several images covering the 0°–33° phase angle range were acquired, and the spatial resolution achieved was 11 cm pixel−1. The flown-by region is located on the big lobe of the comet, near the borders of the Ash, Apis and Imhotep regions. Our analysis shows that this region features local heterogeneities at the decimetre scale. We observed difference of reflectance up to 40 per cent between bright spots and sombre regions, and spectral slope variations up to 50 per cent. The spectral reddening effect observed globally on the comet surface by Fornasier et al. (2015) is also observed locally on this region, but with a less steep behaviour. We note that numerous metre-sized boulders, which exhibit a smaller opposition effect, also appear spectrally redder than their surroundings. In this region, we found no evidence linking observed bright spots to exposed water-ice-rich material. We fitted our data set using the Hapke 2008 photometric model. The region overflown is globally as dark as the whole nucleus (geometric albedo of 6.8 per cent) and it has a high porosity value in the uppermost layers (86 per cent). These results of the photometric analysis at a decimetre scale indicate that the photometric properties of the flown-by region are similar to those previously found for the whole nucleus.
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Clément Feller, Sonia Fornasier, Pedro Henrique Hasselmann, Antonella Barucci, Frank Preusker, et al.. Decimetre-scaled spectrophotometric properties of the nucleus of comet 67P/Churyumov–Gerasimenko from OSIRIS observations. Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP): Policy P - Oxford Open Option A, 2016, 462 (Suppl 1), pp.S287 - S303. ⟨10.1093/mnras/stw2511⟩. ⟨insu-01406412⟩



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