Search for satellites near comet 67P/Churyumov-Gerasimenko using Rosetta/OSIRIS images

¹ Center of Studies and Activities for Space (CISAS) “G. Colombo”, University of Padova, via Venezia 15, 35131 Padova, Italy
e-mail: ivano.bertini@unipd.it
² Instituto de Astrofísica de Andalucía – CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
³ Department of Physics and Astronomy “G. Galilei”, University of Padova, Vicolo dell’ Osservatorio 3, 35122 Padova, Italy
⁴ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
⁵ Laboratoire de Astrophysique de Marseille UMR 7326, CNRS & Aix-Marseille Université, Cedex 13, 13388 Marseille, France
⁶ Centro de Astrobiología, CSIC-INTA, Torrejón de Ardoz, 28850 Madrid, Spain
⁷ International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland
⁸ Research and Scientific Support Department, European Space Agency, 2201 Noordwijk, The Netherlands
⁹ Department of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden
¹⁰ PAS Space Reserch Center, Bartycka 18A, 00716 Warszawa, Polond
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 Pricipal Cedex, France
¹⁴ LATMOS, CNRS/UVSQ/IPSL, 11 boulevard d’Alembert, 78280 Guyancourt, France
¹⁵ INAF–Osservatorio Astronomico di Padova, Vicolo dell’ Osservatorio 5, 35122 Padova, Italy
¹⁶ CNR–IFN UOS Padova LUXOR, via Trasea 7, 35131 Padova, Italy
¹⁷ Department of Industrial Engineering – University of Padova, via Venezia 1, 35131 Padova, Italy
¹⁸ UNITN, Universitá di Trento, via Mesiano, 77, 38100 Trento, Italy
¹⁹ Univ. Paris Diderot, Sorbonne Paris Cité, 4 rue Elsa Morante, 75205 Paris Cedex 13, France
²⁰ INAF–Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
²¹ Department of Geosciences, University of Padova, via Gradenigo 6, 35131 Padova, Italy
²² Aix-Marseille Université, CNRS, Laboratoire de Astrophysique de Marseille, UMR 7326, 13388 Marseille, France
²³ Institute of Planetary Research, DLR, Rutherfordstrasse 2, 12489 Berlin, Germany
²⁴ Institute of Astronomy, National Central University, 32054 Chung-Li, Taiwan
²⁵ Space Science Institute, Macau University of Science and Technology, Macau, PR China
²⁶ ESA/ESAC, PO Box 78, 28691 Villanueva de la Cañada, Spain
²⁷ Institut für Datentechnik und Kommunikationsnetze, Hans-Sommer-Str. 66, 38106 Braunschweig, Germany
²⁸ Department of Information Engineering, University of Padova, via Gradenigo 6/B, 35131 Padova, Italy
²⁹ Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland

Received: 27 February 2015
Accepted: 11 May 2015

Abstract

Context. TheEuropean Space Agency Rosetta mission reached and started escorting its main target, the Jupiter-family comet 67P/Churyumov-Gerasimenko, at the beginning of August 2014. Within the context of solar system small bodies, satellite searches from approaching spacecraft were extensively used in the past to study the nature of the visited bodies and their collisional environment.

Aims. During the approaching phase to the comet in July 2014, the OSIRIS instrument onboard Rosetta performed a campaign aimed at detecting objects in the vicinity of the comet nucleus and at measuring these objects’ possible bound orbits. In addition to the scientific purpose, the search also focused on spacecraft security to avoid hazardous material in the comet’s environment.

Methods. Images in the red spectral domain were acquired with the OSIRIS Narrow Angle Camera, when the spacecraft was at a distance between 5785 km and 5463 km to the comet, following an observational strategy tailored to maximize the scientific outcome. From the acquired images, sources were extracted and displayed to search for plausible displacements of all sources from image to image. After stars were identified, the remaining sources were thoroughly analyzed. To place constraints on the expected displacements of a potential satellite, we performed Monte Carlo simulations on the apparent motion of potential satellites within the Hill sphere.

Results. We found no unambiguous detections of objects larger than ~6 m within ~20 km and larger than ~1 m between ~20 km and ~110 km from the nucleus, using images with an exposure time of 0.14 s and 1.36 s, respectively. Our conclusions are consistent with independent works on dust grains in the comet coma and on boulders counting on the nucleus surface. Moreover, our analysis shows that the comet outburst detected at the end of April 2014 was not strong enough to eject large objects and to place them into a stable orbit around the nucleus. Our findings underline that it is highly unlikely that large objects survive for a long time around cometary nuclei.