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

Ivano Bertini (1) , Pedro J. Gutiérrez (2) , Luisa M. Lara (2) , Francesco Marzari (3) , F. Moreno (2) , Maurizio Pajola (1) , Florangela La Forgia , Holger Sierks (4) , Cesare Barbieri (3) , Philippe Lamy (5) , Rafael Rodrigo (6, 7) , Detlef Koschny (8) , Hans Rickman (9, 10) , Horst U. Keller (11) , Jessica Agarwal (4) , Michael F. A'Hearn (12) , M.A. Barucci (13) , Jean-Loup Bertaux (14) , Gabriele Cremonese (15) , Vania da Deppo (16) , Björn Davidsson (9) , Stefano Debei (17) , Mariolino de Cecco (18) , Fabio Ferri (1) , Sonia Fornasier (19, 13) , Marco Fulle (20) , Lorenza Giacomini (21) , Olivier Groussin (5) , Carsten Güttler (4) , Stubbe F. Hviid (22) , W. -H. Ip (23, 24) , Laurent Jorda (5) , Jörg Knollenberg (22) , J.-R. Kramm (4) , Ekkehard Kührt (22) , Michael Küppers (25) , M. Lazzarin (3) , Jose J. Lopez-Moreno (2) , Sara Magrin (3) , Matteo Massironi (21) , Harald Michalik (26) , Stefano Mottola (22) , Giampiero Naletto (27, 1, 16) , Nilda Oklay (4) , Nicholas Thomas (28) , Cécilia Tubiana (4) , Jean-Bapiste Vincent (4)

1 CISAS - Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”
2 IAA - Instituto de Astrofísica de Andalucía
3 Dipartimento di Fisica e Astronomia "Galileo Galilei"
4 MPS - Max-Planck-Institut für Sonnensystemforschung
5 LAM - Laboratoire d'Astrophysique de Marseille
6 CAB - Centro de Astrobiologia [Madrid]
7 ISSI - International Space Science Institute [Bern]
8 RSSD - Research and Scientific Support Department, ESTEC
9 Department of Physics and Astronomy [Uppsala]
10 CBK - Space Research Centre of Polish Academy of Sciences
11 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
12 Department of Astronomy [College Park]
13 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
14 PLANETO - LATMOS
15 OAPD - INAF - Osservatorio Astronomico di Padova
16 IFN - CNR Institute for Photonics and Nanotechnologies
17 Department of Industrial Engineering [Padova]
18 University of Trento [Trento]
19 UPD7 - Université Paris Diderot - Paris 7
20 OAT - INAF - Osservatorio Astronomico di Trieste
21 Dipartimento di Geoscienze [Padova]
22 DLR Institute of Planetary Research
23 IANCU - Institute of Astronomy [Taiwan]
24 SSI - Space Science Institute [Macau]
25 Operations Department (ESAC)
26 Institut für Datentechnik und Kommunikationsnetze
27 DEI - Department of Information Engineering [Padova]
28 Physikalisches Institut [Bern]

The European 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 environ- ment. 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 5 785 km and 5 463 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 Article number, page 1 of 9 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.

Keywords: 67P/Churyumov-Gerasimenko; Photometry; Comets

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

Ivano Bertini, Pedro J. Gutiérrez, Luisa M. Lara, Francesco Marzari, F. Moreno, et al.. Search for satellites near comet 67P/Churyumov-Gerasimenko using Rosetta/OSIRIS images. Astronomy and Astrophysics - A&A, 2015, 583, A19 (8 p.). ⟨10.1051/0004-6361/201525979⟩. ⟨insu-01203674⟩