Comet 67P/Churyumov-Gerasimenko: Constraints on its origin from OSIRIS observations
1 P.A.S. Space Research Center, Bartycka 18A, 00-716 Warszawa, Poland
2 Dept. of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
3 Southwest Research Institute, 1050 Walnut St., Boulder, CO 80302, USA
4 Department for Astronomy, University of Maryland, College Park, MD 20742-2421, USA
5 Department of Physics and Astronomy “G. Galilei”, University of Padova, Vic. Osservatorio 3, 35122 Padova, Italy
6 Physikalisches Institut, Sidlerstrasse 5, University of Bern, 3012 Bern, Switzerland
7 Max-Planck Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
8 Institute for Space Science, National Central University, 32054 Chung-Li, Taiwan
9 Institute for Geophysics and Extraterrestrial Physics, TU Braunschweig, 38106 Braunschweig, Germany
10 Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
11 Dipartimento di Geoscienze, University of Padova, via G. Gradenigo 6, 35131 Padova, Italy
12 Centro di Ateneo di Studi ed Attivitá Spaziali, “Giuseppe Colombo” (CISAS), University of Padova, via Venezia 15, 35131 Padova, Italy
13 Department of Information Engineering, University of Padova, via G. Gradenigo 6/B, 35131 Padova, Italy
14 CNR-IFN UOS Padova LUXOR, via Trasea 7, 35131 Padova, Italy
15 Scientific Support Office, European Space Agency, 2201 Noordwijk, The Netherlands
16 Centro de Astrobiologia (INTA-CSIC), 28691 Villanueva de la Canada, Madrid, Spain
17 International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland
18 LESIA, Obs. de Paris, CNRS, Univ. Paris 06, Univ. Paris-Diderot, 5 Pl. J. Janssen, 92195 Meudon, France
19 LATMOS, CNRS/UVSQ/IPSL, 11 bd d’Alembert, 78280 Guyancourt, France
20 INAF–Osservatorio Astronomico, vicolo dell’Osservatorio 2, 35122 Padova, Italy
21 Department of Mechanical Engineering, University of Padova, via Venezia 1, 35131 Padova, Italy
22 UNITN, Univ. di Trento, via Mesiano 77, 38100 Trento, Italy
23 INAF–Osservatorio Astronomico, via Tiepolo 11, 34143 Trieste, Italy
24 Instituto de Astrofisica de Andalucía (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
25 Institute of Planetary Research, DLR, Rutherfordstrasse 2, 12489 Berlin, Germany
26 Operations Department, European Space Astronomy Centre/ESA, PO Box 78, 28691 Villanueva de la Canada, Madrid, Spain
27 Institut für Datentechnik und Kommunikationsnetze der TU Braunschweig, Hans-Sommer-Str. 66, 38106 Braunschweig, Germany
28 Instituto Nacional de Técnica Aeroespacial, Carretera de Ajalvir, p.k. 4, 28850 Torrejon de Ardoz, Madrid, Spain
Received: 13 March 2015
Accepted: 12 May 2015
Context. One of the main aims of the ESA Rosetta mission is to study the origin of the solar system by exploring comet 67P/Churyumov-Gerasimenko at close range.
Aims. In this paper we discuss the origin and evolution of comet 67P/Churyumov-Gerasimenko in relation to that of comets in general and in the framework of current solar system formation models.
Methods. We use data from the OSIRIS scientific cameras as basic constraints. In particular, we discuss the overall bi-lobate shape and the presence of key geological features, such as layers and fractures. We also treat the problem of collisional evolution of comet nuclei by a particle-in-a-box calculation for an estimate of the probability of survival for 67P/Churyumov-Gerasimenko during the early epochs of the solar system.
Results. We argue that the two lobes of the 67P/Churyumov-Gerasimenko nucleus are derived from two distinct objects that have formed a contact binary via a gentle merger. The lobes are separate bodies, though sufficiently similar to have formed in the same environment. An estimate of the collisional rate in the primordial, trans-planetary disk shows that most comets of similar size to 67P/Churyumov-Gerasimenko are likely collisional fragments, although survival of primordial planetesimals cannot be excluded.
Conclusions. A collisional origin of the contact binary is suggested, and the low bulk density of the aggregate and abundance of volatile species show that a very gentle merger must have occurred. We thus consider two main scenarios: the primordial accretion of planetesimals, and the re-accretion of fragments after an energetic impact onto a larger parent body. We point to the primordial signatures exhibited by 67P/Churyumov-Gerasimenko and other comet nuclei as critical tests of the collisional evolution.
Key words: comets: individual: 67P/Churyumov-Gerasimenko
© ESO, 2015