Large-scale dust jets in the coma of 67P/Churyumov-Gerasimenko as seen by the OSIRIS instrument onboard Rosetta

L.M. Lara (1) , S. Lowry (2) , J.B. Vincent (3) , P.J. Gutiérrez (1) , A. Rozek (2) , F. La Forgia (4) , N. Oklay (3) , H. Sierks (3) , C. Barbieri (4, 5) , P. L. Lamy (6) , R. Rodrigo (7, 8) , D. Koschny (9) , H. Rickman (10, 11) , H. U. Keller (12) , J. Agarwal (3) , A.-T. Auger (6) , Michael F. A'Hearn (13) , M. A. Barucci (14) , Jean-Loup Bertaux (15) , I. Bertini (5) , S. Besse (9) , Dennis Bodewits (13) , Gabriele Cremonese (16) , B. Davidsson (11) , V. da Deppo (17) , S. Debei (18) , M. de Cecco (19) , M.R. El-Maarry (20) , F. Ferri (5) , S. Fornasier (14) , M. Fulle (21) , O. Groussin (6) , P. Gutiérrez–marques (3) , C. Güttler (3) , S. F. Hviid (22) , W.-H. Ip (23) , L. Jorda (6) , J. Knollenberg (22) , G. Kovacs (3) , J.-R. Kramm (3) , Ekkehard Kührt (22) , M. Küppers (24) , M. Lazzarin (4) , Z.-Y. Lin (23) , J. J. López-Moreno (1) , S. Magrin (4) , F. Marzari (4) , H. Michalik (12) , R. Moissl–fraund (24) , F. Moreno (1) , S. Mottola (22) , G. Naletto (17, 18, 5) , M. Pajola (5) , A. Pommerol (20) , N. Thomas (20) , M. D. Sabau (25) , C. Tubiana (3)

1 IAA - Instituto de Astrofísica de Andalucía
2 CAPS - Centre for Astrophysics and Planetary Science [Canterbury]
3 MPS - Max-Planck-Institut für Sonnensystemforschung
4 Dipartimento di Fisica e Astronomia "Galileo Galilei"
5 CISAS - Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”
6 LAM - Laboratoire d'Astrophysique de Marseille
7 ISSI - International Space Science Institute [Bern]
8 CAB - Centro de Astrobiologia [Madrid]
9 RSSD - Research and Scientific Support Department, ESTEC
10 CBK - Space Research Centre of Polish Academy of Sciences
11 Department of Physics and Astronomy [Uppsala]
12 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
13 Department of Astronomy [College Park]
14 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
15 PLANETO - LATMOS
16 OAPD - INAF - Osservatorio Astronomico di Padova
17 IFN - CNR Institute for Photonics and Nanotechnologies
18 Department of Industrial Engineering [Padova]
19 University of Trento [Trento]
20 Physikalisches Institut [Bern]
21 OAT - INAF - Osservatorio Astronomico di Trieste
22 DLR Institute of Planetary Research
23 IANCU - Institute of Astronomy [Taiwan]
24 Operations Department (ESAC)
25 INTA - Instituto Nacional de Técnica Aeroespacial

During the most recent perihelion passage in 2009 of comet 67P/Churyumov-Gerasimenko (67P), ground-based observations showed an anisotropic dust coma where jet-like features were detected at ∼1.3 AU from the Sun. The current perihelion passage is exceptional as the Rosetta spacecraft is monitoring the nucleus activity since March 2014, when a clear dust coma was already surrounding the nucleus at 4.3 AU from the Sun. Subsequently, the OSIRIS camera also witnessed an outburst in activity between April 27 and 30, and since mid-July, the dust coma at rh ∼ 3.7−3.6 AU preperihelion is clearly non-isotropic, pointing to the existence of dust jet-like features. Aims. We aim to ascertain on the nucleus surface the origin of the dust jet-like features detected as early as in mid-July 2014. This will help to establish how the localized comet nucleus activity compares with that seen in previous apparitions and will also help following its evolution as the comet approaches its perihelion, at which phase most of the jets were detected from ground-based observations. Determining these areas also allows locating them in regions on the nucleus with spectroscopic or geomorphological distinct characteristics. Methods. Three series of dust images of comet 67P obtained with the Wide Angle Camera (WAC) of the OSIRIS instrument onboard the Rosetta spacecraft were processed with different enhancement techniques. This was made to clearly show the existence of jet-like features in the dust coma, whose appearance toward the observer changed as a result of the rotation of the comet nucleus and of the changing observing geometry from the spacecraft. The position angles of these features in the coma together with information on the observing geometry, nucleus shape, and rotation, allowed us to determine the most likely locations on the nucleus surface where the jets originate from. Results. Geometrical tracing of jet sources indicates that the activity of the nucleus of 67P gave rise during July and August 2014 to large-scale jet-like features from the Hapi, Hathor, Anuket, and Aten regions, confirming that active regions may be present on the nucleus localized at 60◦ northern latitude as deduced from previous comet apparitions. There are also hints that large-scale jets observed from the ground are possibly composed, at their place of origin on the nucleus surface, of numerous small-scale features.

Keywords: Comets; 67P/Churyumov-Gerasimenko

Domains: Earth and Planetary Astrophysics [astro-ph.EP]

L.M. Lara, S. Lowry, J.B. Vincent, P.J. Gutiérrez, A. Rozek, et al.. Large-scale dust jets in the coma of 67P/Churyumov-Gerasimenko as seen by the OSIRIS instrument onboard Rosetta. Astronomy and Astrophysics - A&A, 2015, 583, pp.A9. ⟨10.1051/0004-6361/201526103⟩. ⟨insu-01201821⟩