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The dust environment of comet 67P/Churyumov-Gerasimenko from Rosetta OSIRIS/GIADA and VLT observations in the 4.5 to 2.9 AU heliocentric distance range inbound

F. Moreno 1 Colin Snodgrass 2 Olivier Hainaut 3 Cécilia Tubiana 4 Holger Sierks 4 Cesare Barbieri 5, 6 Philippe L. Lamy 7 R. Rodrigo 8, 9 Detlef Koschny 10 Hans Rickman 11 Horst Uwe Keller 12 Jessica Agarwal 13 Michael F. A'Hearn 14, 4, 15 Maria A. Barucci 16 Jean-Loup Bertaux 17 Ivano Bertini 6 Sebastien Besse 10 Dennis Bodewits 15 Gabriele Cremonese 18 Vania da Deppo 19 Björn Davidsson 11 S. Debei 20 M. de Cecco 21 Francesca Ferri 6 Sonia Fornasier 16 Marco Fulle 22 Olivier Groussin 7 Pedro J. Gutiérrez 1 Pablo Gutierrez-Marques 4 Carsten Guttler 4 Stubbe F. Hviid 23 W.-H. Ip 24 L. Jorda 7 Jörg Knollenberg 23 Gabor Kovacs 4 J.-Rainer Kramm 4 Ekkehard Kührt 23 Michael Küppers 25 L. M. Lara 1 Monica Lazzarin 5 José-Juan López-Moreno 1 Francesco Marzari 5 Stefano Mottola 23 Giampiero Naletto 6, 26, 19 Nilda Oklay 4 Maurizio Pajola 6 Nicholas Thomas 13 Jean-Baptiste Vincent 4 Vincenzo Della Corte 27 A. Fitzsimmons 28 S. Faggi 29 E. Jehin 30 Cyrielle Opitom 30 G.-P. Tozzi 29 
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
Abstract : The ESA Rosetta spacecraft, currently orbiting around comet 67P, has already provided in situ measurements of the dust grain properties from several instruments, particularly OSIRIS and GIADA. We propose adding value to those measurements by combining them with ground-based observations of the dust tail to monitor the overall, time-dependent dust-production rate and size distribution. To constrain the dust grain properties, we take Rosetta OSIRIS and GIADA results into account, and combine OSIRIS data during the approach phase (from late April to early June 2014) with a large data set of ground-based images that were acquired with the ESO Very Large Telescope (VLT) from February to November 2014. A Monte Carlo dust tail code has been applied to retrieve the dust parameters. Key properties of the grains (density, velocity, and size distribution) were obtained from Rosetta observations: these parameters were used as input of the code to considerably reduce the number of free parameters. In this way, the overall dust mass-loss rate and its dependence on the heliocentric distance could be obtained accurately. The dust parameters derived from the inner coma measurements by OSIRIS and GIADA and from distant imaging using VLT data are consistent, except for the power index of the size-distribution function, which is $\alpha$=--3, instead of $\alpha$=--2, for grains smaller than 1 mm. This is possibly linked to the presence of fluffy aggregates in the coma. The onset of cometary activity occurs at approximately 4.3 au, with a dust production rate of 0.5 kg/s, increasing up to 15 kg/s at 2.9 au. This implies a dust-to-gas mass ratio varying between 3.8 and 6.5 for the best-fit model when combined with water-production rates from the MIRO experiment.
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F. Moreno, Colin Snodgrass, Olivier Hainaut, Cécilia Tubiana, Holger Sierks, et al.. The dust environment of comet 67P/Churyumov-Gerasimenko from Rosetta OSIRIS/GIADA and VLT observations in the 4.5 to 2.9 AU heliocentric distance range inbound. Astronomy and Astrophysics - A&A, 2016, 587, A155 (12 p.). ⟨10.1051/0004-6361/201527564⟩. ⟨insu-01274855⟩



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