Meter-scale thermal contraction crack polygons on the nucleus of comet 67P/Churyumov-Gerasimenko

Anne-Thérèse Auger (1, 2) , Olivier Groussin (1) , Laurent Jorda (3) , Mohamed Ramy El-Maarry (4) , Sylvain Bouley (2, 5) , Antoine Séjourné (2) , Robert Gaskell (6) , Claire Capanna (1) , Björn Davidsson (7) , Simone Marchi (8) , Sebastian Höfner (9) , Philippe Lamy (1) , Holger Sierks (9) , Cesare Barbieri (10) , Rafael Rodrigo (11, 12) , Detlef Koschny (13) , Hans Rickman (14, 7) , Horst Uwe Keller (15) , Jessica Agarwal (9) , Michael F. A'Hearn (16) , Maria Antonella Barucci (17) , Jean-Loup Bertaux (18) , Ivano Bertini (19) , Gabriele Cremonese (20) , Vania da Deppo (21) , Stefano Debei (20) , Mariolino de Cecco (22) , Sonia Fornasier (17) , Marco Fulle (23) , Pedro J. Gutiérrez (24) , Carsten Güttler (9) , Stubbe Hviid (25) , Wing-Huen Ip (26) , Jörg Knollenberg (25) , Jörg-Rainer Kramm (9) , Ekkehard Kührt (25) , Michael Küppers (27) , Luisa-Maria Lara (24) , Monica Lazzarin (10) , Josè J. Lopez-Moreno (24) , Francesco Marzari (10) , Matteo Massironi (19, 28) , Harald Michalik (29) , Giampiero Naletto (19, 21, 30) , Nilda Oklay (25) , Antoine Pommerol (4) , Lola Sabau (31) , Nicolas Thomas (4) , Cécilia Tubiana (9) , Jean-Baptiste Vincent (9) , Klaus-Peter Wenzel (32)

1 LAM - Laboratoire d'Astrophysique de Marseille
2 GEOPS - Géosciences Paris Sud
3 AMU - Aix Marseille Université
4 Physikalisches Institut [Bern]
5 IMCCE - Institut de Mécanique Céleste et de Calcul des Ephémérides
6 PSI - Planetary Science Institute [Tucson]
7 JPL - Jet Propulsion Laboratory
8 SSERVI - Solar System Exploration Research Virtual Institute
9 MPS - Max-Planck-Institut für Sonnensystemforschung
10 Dipartimento di Fisica e Astronomia "Galileo Galilei"
11 CAB - Centro de Astrobiologia [Madrid]
12 ISSI - International Space Science Institute [Bern]
13 ESTEC - European Space Research and Technology Centre
14 CBK - Space Research Centre of Polish Academy of Sciences
15 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
16 Department of Astronomy [College Park]
17 LESIA (UMR_8109) - Laboratoire d'études spatiales et d'instrumentation en astrophysique
18 PLANETO - LATMOS
19 CISAS - Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”
20 Department of Industrial Engineering [Padova]
21 LUXOR - Laboratory for Ultraviolet and X-ray Optical Research [Padova]
22 University of Trento [Trento]
23 OAT - INAF - Osservatorio Astronomico di Trieste
24 IAA - Instituto de Astrofísica de Andalucía
25 DLR Institut für Planetenforschung
26 Institute of Space Science [Taiwan]
27 ESAC - European Space Astronomy Centre
28 OAPD - INAF - Osservatorio Astronomico di Padova
29 Institut für Datentechnik und Kommunikationsnetze
30 DEI - Department of Information Engineering [Padova]
31 INTA - Instituto Nacional de Técnica Aeroespacial
32 RSSD - Research and Scientific Support Department, ESTEC

We report on the detection and characterization of more than 6300 polygons on the surface of the nucleus of comet 67P/Churyumov-Gerasimenko, using images acquired by the OSIRIS camera onboard Rosetta between August 2014 and March 2015. They are found in consolidated terrains and grouped in localized networks. They are present at all latitudes (from North to South) and longitudes (head, neck, and body), sometimes on pit walls or following lineaments. About 1.5% of the observed surface is covered by polygons. Polygons have an homogeneous size across the nucleus, with 90% of them in the size range 1 – 5 m and a mean size of 3.0 ± 1.4 m. They show different morphologies, depending on the width and depth of their trough. They are found in networks with 3- or 4-crack intersection nodes. The polygons observed on 67P are consistent with thermal contraction crack polygons formed by the diurnal or seasonal temperature variations in a hard (MPa) and consolidated sintered layer of water ice, located a few centimeters below the surface. Our thermal analysis shows an evolution of thermal contraction crack polygons according to the local thermal environment, with more evolved polygons (i.e. deeper and larger troughs) where the temperature and the diurnal and seasonal temperature range are the highest. Thermal contraction crack polygons are young surface morphologies that probably formed after the injection of 67P in the inner solar system, typically 100 000 years ago, and could be as young as a few orbital periods, following the decreasing of its perihelion distance in 1959 from 2.7 to 1.3 a.u. Meter scale thermal contraction crack polygons should be common features on the nucleus of Jupiter family comets.

Keywords: Comets; Nucleus; Geological processes

Domains: Earth and Planetary Astrophysics [astro-ph.EP]; Solar and Stellar Astrophysics [astro-ph.SR]

Anne-Thérèse Auger, Olivier Groussin, Laurent Jorda, Mohamed Ramy El-Maarry, Sylvain Bouley, et al.. Meter-scale thermal contraction crack polygons on the nucleus of comet 67P/Churyumov-Gerasimenko. Icarus, 2018, 301, pp.173-188. ⟨10.1016/j.icarus.2017.09.037⟩. ⟨insu-01610197⟩