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

¹ Instituto de Astrofisica de Andalucia-CSIC, Glorieta de la Astronomia, 18008 Granada, Spain
e-mail: lara@iaa.csic.es
² Centre for Astrophysics and Planetary Science, School of Physical Sciences, The University of Kent, Canterbury CT2 7NH, UK
³ Max-Planck Institut fuer Sonnensystemforschung, Justus-von-Liebig-Weg, 3 37077 Goettingen, Germany
⁴ Department of Physics and Astronomy G. Galilei, University of Padova, Vic. Osservatorio 3, 35122 Padova, Italy
⁵ Center of Studies and Activities for Space (CISAS) “G. Colombo”, University of Padova, via Venezia 15, 35131 Padova, Italy
⁶ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astro-physique de Marseille) UMR 7326, 13388, Marseille, France
⁷ Centro de Astrobiologia (INTA-CSIC), European Space Agency (ESA), European Space Astronomy Centre (ESAC), PO Box 78, 28691 Villanueva de la Canada, Madrid, Spain
⁸ International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland
⁹ Research and Scientific Support Department, European Space Agency, 2201 Noordwijk, The Netherlands
¹⁰ PAS Space Reserch Center, Bartycka 18A, 00716 Warszawa, Poland
¹¹ Institute for Geophysics and Extraterrestrial Physics, TU Braunschweig, 38106 Braunschweig, Germany
¹² Department for Astronomy, University of Maryland, College Park, MD 20742-2421, USA
¹³ LESIA, Observatoire de Paris, CNRS, UPMC Univ Paris 06, Univ. Paris-Diderot, 5 place J. Janssen, 92195 Meudon Principal Cedex, France
¹⁴ LATMOS, CNRS/UVSQ/IPSL, 11 boulevard d’Alembert, 78280 Guyancourt, France
¹⁵ INAF Osservatorio Astronomico di Padova, vic. dell’Osservatorio 5, 35122 Padova, Italy
¹⁶ Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
¹⁷ CNR-IFN UOS Padova LUXOR, via Trasea 7, 35131 Padova, Italy
¹⁸ Department of Industrial Engineering, University of Padova, via Venezia 1, 35131 Padova, Italy
¹⁹ University of Trento, via Sommarive 9, 38123 Trento, Italy
²⁰ Physikalisches Institut, Sidlerstrasse 5, University of Bern, 3012 Bern, Switzerland
²¹ INAF–Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
²² Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Rutherfordstrasse 2, 12489 Berlin, Germany
²³ Institute for Space Science, National Central University, 32054 Chung-Li, Taiwan
²⁴ ESA/ESAC, PO Box 78, 28691 Villanueva de la Cañada, Spain
²⁵ Department of Information Engineering, University of Padova, via Gradenigo 6/B, 35131 Padova, Italy
²⁶ Instituto Nacional de Técnica Aeroespacial, 28850 Torrejón de Ardoz, Madrid, Spain

Received: 16 March 2015
Accepted: 23 July 2015

Abstract

Context. 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 r_h ~ 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.