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The scattering phase function of comet 67P/Churyumov-Gerasimenko coma as seen from the Rosetta/OSIRIS instrument

Ivano Bertini 1 Florangela La Forgia 1 Cécilia Tubiana 2 Carsten Güttler 2 Marco Fulle 3 Fernando Moreno 4 Elisa Frattin 5, 1 Gabor Kovacs 2 Maurizio Pajola 6, 7 Holger Sierks 2 Cesare Barbieri 1, 7 Philippe L. Lamy 8 Rafael Rodrigo 9, 10 Detlef Koschny 11 Hans Rickman 12, 13 Horst Uwe Keller 14, 15 Jessica Agarwal 2 Michael F. A'Hearn 2, 16 Maria Antonella Barucci 17 Jean-Loup Bertaux 18 Dennis Bodewits 16 Gabriele Cremonese 5 Vania da Deppo 19 Björn Davidsson 20 Stefano Debei 21 Mariolino de Cecco 22 Esther Drolshagen 23 Sabrina Ferrari 7 Francesca Ferri 7 Sonia Fornasier 17 Adeline Gicquel 2, 20 Olivier Groussin 8 Pedro J. Gutiérrez 4 Pedro H. Hasselmann 17 Stubbe F. Hviid 15 Wing-Huen Ip 24, 25 Laurent Jorda 8 Jörg Knollenberg 15 J.-Rainer Kramm 2 Ekkehard Kührt 15 Michael Küppers 26 Luisa Lara 4 Monica Lazzarin 1 Zhong-Yi Lin 25 José J. Lopez Moreno 4 Alice Lucchetti 5 Francesco Marzari 1 Matteo Massironi 7, 27 Stefano Mottola 15 Giampiero Naletto 7, 19, 28 Nilda Oklay 15 Theresa Ott 29 Luca Penasa 7 Nicolas Thomas 30 Jean-Baptiste Vincent 2 
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
Abstract : The study of dust, the most abundant material in cometary nuclei, is pivotal in understanding the original materials forming the solar system. Measuring the coma phase function provides a tool to investigate the nature of cometary dust. Rosetta/OSIRIS sampled the coma phase function of comet 67P/Churyumov-Gerasimenko, covering a large phase angle range in a small amount of time. Twelve series were acquired in March 2015 - February 2016 for this scientific purpose. This data allowed, after straylight removal, measuring the phase function shape, its reddening, and phase reddening while varying heliocentric and nucleocentric distances. Despite small dissimilarities within different series, we found a constant overall shape. The reflectance has a u-shape with minimum at intermediate phase angles, reaching similar values at the smallest and largest phase angle sampled. The comparison with cometary phase functions in literature indicates OSIRIS curves being consistent with the ones found in many other single comets. The dust has a negligible phase reddening at α < 90°, indicating a coma dominated by single scattering. We measured a reddening of [11-14]%/100 nm between 376 nm and 744 nm. No trend with heliocentric or nucleocentric distance was found, indicating the coma doesn’t change its spectrum with time. These results are consistent with single coma grains and close-nucleus coma photometric results. Comparison with nucleus photometry indicates a different backscattering phase function shape and similar reddening values only at α < 30°. At larger phase angles the nucleus becomes significantly redder than the coma.
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Ivano Bertini, Florangela La Forgia, Cécilia Tubiana, Carsten Güttler, Marco Fulle, et al.. The scattering phase function of comet 67P/Churyumov-Gerasimenko coma as seen from the Rosetta/OSIRIS instrument. Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP): Policy P - Oxford Open Option A, 2017, 469 (Suppl_2), pp.S404-S415. ⟨10.1093/mnras/stx1850⟩. ⟨insu-01574406⟩



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