The backscattering ratio of comet 67P/Churyumov-Gerasimenko dust coma as seen by OSIRIS onboard Rosetta

Ivano Bertini (1) , Fiorangela La Forgia (1) , Marco Fulle (2) , Cécilia Tubiana (3) , Carsten Güttler (3) , F. Moreno (4) , Jessica Agarwal (3) , Olga Muñoz (4) , Stefano Mottola (5) , S. Ivanovsky (6, 7) , Maurizio Pajola (8) , Alice Lucchetti (8) , V. Petropoulou (9) , Monica Lazzarin (1) , Alessandra Rotundi (6, 7) , Dennis Bodewits (10) , E. Frattin (1, 8) , Imre Toth (11, 12) , Nafiseh Masoumzadeh (3) , Gabor Kovacs (3) , Giovanna Rinaldi (6, 7) , Daniel Guirado (4) , Holger Sierks (3) , Giampiero Naletto (9, 1, 13) , Philippe L. Lamy (14) , Rafael Rodrigo (15, 16) , Detlef Koschny (17) , Björn Davidsson (18) , Cesare Barbieri (1) , Maria Antonella Barucci (19) , Jean-Loup Bertaux (14) , P. Cambianica (9) , Gabriele Cremonese (8) , Vania da Deppo (20) , Stefano Debei (21) , Mariolino de Cecco (22) , Jakob Deller (3) , Sabrina Ferrari (9) , Francesca Ferri (9) , Sonia Fornasier (19) , Pedro J. Gutiérrez (4) , Pedro Henrique Hasselmann (19) , Wing-Huen Ip (23, 24) , Horst U. Keller (25, 5) , Luisa-Maria Lara (4) , Josè Juan Lopez-Moreno (4) , Francesco Marzari (1) , Matteo Massironi (9, 26) , Luca Penasa (9) , Xian Shi (3)

1 Dipartimento di Fisica e Astronomia "Galileo Galilei"
2 OAT - INAF - Osservatorio Astronomico di Trieste
3 MPS - Max-Planck-Institut für Sonnensystemforschung
4 IAA - Instituto de Astrofísica de Andalucía
5 DLR Institut für Planetenforschung
6 IAPS - Istituto di Astrofisica e Planetologia Spaziali - INAF
7 DIST - Dipartimento di Scienze e Tecnologie [Napoli]
8 OAPD - INAF - Osservatorio Astronomico di Padova
9 CISAS - Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”
10 Department of Physics [Auburn]
11 Konkoly Observatory
12 LAM - Laboratoire d'Astrophysique de Marseille
13 IFN - CNR Istituto di Fotonica e Nanotecnologie [Padova]
14 PLANETO - LATMOS
15 CAB - Centro de Astrobiologia [Madrid]
16 ISSI - International Space Science Institute [Bern]
17 ESTEC - European Space Research and Technology Centre
18 JPL - Jet Propulsion Laboratory
19 LESIA (UMR_8109) - Laboratoire d'études spatiales et d'instrumentation en astrophysique
20 IFN - CNR Institute for Photonics and Nanotechnologies
21 Department of Industrial Engineering [Padova]
22 University of Trento [Trento]
23 IANCU - Institute of Astronomy [Taiwan]
24 SSI - Space Science Institute [Macau]
25 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
26 Dipartimento di Geoscienze [Padova]

Remote sensing observations of dust particles ejected from comets provide important hints on the intimate nature of the materials composing these primitive objects. The measurement of dust coma backscattering ratio, BSR, defined as the ratio of the reflectance at phase angle 0° and 30°, helps tuning theoretical models aimed at solving the inverse scattering problem deriving information on the nature of the ejected particles. The Rosetta/OSIRIS camera sampled the coma phase function of comet 67P, with four series acquired at low phase angles from 2015 January to 2016 May. We also added previously published data to our analysis to increase the temporal resolution of our findings. We measured a BSR in the range ˜ [1.7-3.6], broader than the range found in literature from ground-based observations of other comets. We found that during the post-perihelion phase, the BSR is systematically larger than the classical cometary dust values only for nucleocentric distances smaller than ˜100 km. We explain this trend in terms of a cloud of chunks orbiting the nucleus at distances <100 km ejected during perihelion and slowly collapsing on the nucleus over a few months because of the coma gas drag. This also implies that the threshold particle size for the dust phase function to become similar to the nucleus phase function is between 2.5 mm and 0.1 m, taking into account previous Rosetta findings.

Keywords: scattering; data analysis; image processing; photometry; 67P/Churyumov-Gerasimenko

Domains: Astrophysics [astro-ph]; Astrophysics [astro-ph]

Ivano Bertini, Fiorangela La Forgia, Marco Fulle, Cécilia Tubiana, Carsten Güttler, et al.. The backscattering ratio of comet 67P/Churyumov-Gerasimenko dust coma as seen by OSIRIS onboard Rosetta. Monthly Notices of the Royal Astronomical Society: Letters, 2019, 482 (3), pp.2924-2933. ⟨10.1093/mnras/sty2843⟩. ⟨insu-01933906⟩