Two independent and primitive envelopes of the bilobate nucleus of comet 67P

Matteo Massironi (1, 2) , Emanuele Simioni (3) , Francesco Marzari (4) , Gabriele Cremonese (5) , Lorenza Giacomini (2) , Maurizio Pajola (1) , Laurent Jorda (6) , Giampiero Naletto (1, 7, 3) , Stephen Lowry (8) , Mohamed Ramy El-Maarry (9) , Frank Preusker (10) , Frank Scholten (10) , Holger Sierks (11) , Cesare Barbieri (4) , Philippe Lamy (6) , Rafael Rodrigo (12, 13) , Detlef Koschny (14) , Hans Rickman (15, 16) , Horst Uwe Keller (17) , Michael F. A'Hearn (18, 19) , Jessica Agarwal (11) , Anne-Thérèse Auger (6) , M. Antonella Barucci (20) , Jean-Loup Bertaux (21) , Ivano, Bertini (1) , Sebastien Besse (22) , Dennis Bodewits (19) , Claire Capanna (6) , Vania da Deppo (3) , Björn Davidsson (16) , Stefano Debei (23) , Mariolino de Cecco (24) , Francesca Ferri (1) , Sonia Fornasier (20) , Marco Fulle (25) , Robert Gaskell (26) , Olivier Groussin (6) , Pedro J. Gutiérrez (27) , Carsten Güttler (11) , Stubbe F. Hviid (10, 11) , Wing-Huen Ip (28) , Jörg Knollenberg (10) , Gabor Kovacs (11) , Rainer Kramm (11) , Ekkehard Kührt (10) , Michael Küppers (29) , Fiorangela La Forgia (4) , Luisa M. Lara (27) , Monica Lazzarin (4) , Zhong-Yi Lin (28) , Josè J. Lopez Moreno (27) , Sara Magrin (4) , Harald Michalik (30) , Stefano Mottola (10) , Nilda Oklay (11) , Antoine Pommerol (9) , Nicolas Thomas (9) , Cecilia Tubiana (11) , Jean-Baptiste Vincent (11)

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

The factors shaping cometary nuclei are still largely unknown, but could be the result of concurrent effects of evolutionary and primordial processes. The peculiar bilobed shape of comet 67P/Churyumov-Gerasimenko may be the result of the fusion of two objects that were once separate or the result of a localized excavation by outgassing at the interface between the two lobes. Here we report that the comet's major lobe is enveloped by a nearly continuous set of strata, up to 650 metres thick, which are independent of an analogous stratified envelope on the minor lobe. Gravity vectors computed for the two lobes separately are closer to perpendicular to the strata than those calculated for the entire nucleus and adjacent to the neck separating the two lobes. Therefore comet 67P/Churyumov-Gerasimenko is an accreted body of two distinct objects with `onion-like' stratification, which formed before they merged. We conclude that gentle, low-velocity collisions occurred between two fully formed kilometre-sized cometesimals in the early stages of the Solar System. The notable structural similarities between the two lobes of comet 67P/Churyumov-Gerasimenko indicate that the early-forming cometesimals experienced similar primordial stratified accretion, even though they formed independently.

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

Matteo Massironi, Emanuele Simioni, Francesco Marzari, Gabriele Cremonese, Lorenza Giacomini, et al.. Two independent and primitive envelopes of the bilobate nucleus of comet 67P. Nature, 2015, 526, pp.402 - 405. ⟨10.1038/nature15511⟩. ⟨insu-01328952⟩