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)

1 IAA - Instituto de Astrofísica de Andalucía
2 School of Physical Sciences [Milton Keynes]
3 ESO - European Southern Observatory
4 MPS - Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research
5 Dipartimento di Fisica e Astronomia "Galileo Galilei"
6 CISAS - Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”
7 LAM - Laboratoire d'Astrophysique de Marseille
8 CAB - Centro de Astrobiologia [Madrid]
9 ISSI - International Space Science Institute [Bern]
10 RSSD - Research and Scientific Support Department, ESTEC
11 Department of Physics and Astronomy [Uppsala]
12 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
13 Physikalisches Institut [Bern]
14 Gauss Professor Akademie der Wissenschaften zu Göttingen
15 Department of Astronomy [College Park]
16 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
17 PLANETO - LATMOS
18 OAPD - INAF - Osservatorio Astronomico di Padova
19 IFN - CNR Institute for Photonics and Nanotechnologies
20 Department of Industrial Engineering [Padova]
21 UNITN - Università degli Studi di Trento = University of Trento
22 OAT - INAF - Osservatorio Astronomico di Trieste
23 DLR Institute of Planetary Research
24 Institute of Space Science, National Central University
25 Operations Department (ESAC)
26 DEI - Department of Information Engineering [Padova]
27 IAPS - Istituto di Astrofisica e Planetologia Spaziali - INAF
28 ARC - Astrophysics Research Centre [Belfast]
29 OAA - INAF - Osservatorio Astrofisico di Arcetri
30 Institut d'Astrophysique et de Géophysique [Liège]

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.

Mots clés: Data analysis; 67P/Churyumov-Gerasimenko; Photometry; Comets

Domaines: Planétologie et astrophysique de la terre [astro-ph.EP]; Astrophysique stellaire et solaire [astro-ph.SR]

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⟩