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

Feller, C. and Fornasier, S. and Hasselmann, P. H. and Barucci, A. and Preusker, F. and Scholten, F. and Jorda, L. and Pommerol, A. and Jost, B. and Poch, O. and ElMaary, M. R. and Thomas, N. and Belskaya, I. and Pajola, M. and Sierks, H. and Barbieri, C. and Lamy, P. L. and Koschny, D. and Rickman, H. and Rodrigo, R. and Agarwal, J. and A'Hearn, M. and Bertaux, J. -L. and Bertini, I. and Boudreault, S. and Cremonese, G. and Da, Deppo V. and Davidsson, B. J. R. and Debei, S. and De Cecco, M. and Kovács, Gábor (2016) Decimetre-scaled spectrophotometric properties of the nucleus of comet 67P/Churyumov-Gerasimenko from OSIRIS observations. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 462 (1). pp. 287-303. ISSN 0035-8711

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Abstract

We present the results of the photometric and spectrophotometric properties of the 67P/Churyumov-Gerasimenko nucleus derived with the OSIRIS instrument during the closest fly-by over the comet, which took place on 14th February 2015 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/pxl. The flown-by re- gion 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% between bright spots and sombre regions, and spectral slope variations up to 50%. The spectral red- dening 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 dataset using the Hapke 2008 photometric model. The region overflown is globally as dark as the whole nucleus (geometric albedo of 6.8%) and it has a high porosity value in the uppermost-layers (86%). 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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