Thermophysics of fractures on comet 67P/Churyumov-Gerasimenko

¹ Max-Planck Institut fuer Sonnensystemforschung, Justus-von-Liebig-Weg, 3, 37077 Goettingen, Germany
e-mail: hoefner@mps.mpg.de
² Institute for Geophysics and Extraterrestrial Physics, TU Braunschweig, 38106 Braunschweig, Germany
³ Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
⁴ Jet Propulsion Laboratory, M/S 183-301, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
⁵ Physikalisches Institut, Sidlerstrasse 5, University of Bern, 3012 Bern, Switzerland
⁶ Department of Physics and Astronomy “G. Galilei”, University of Padova, Vic. Osservatorio 3, 35122 Padova, Italy
⁷ Centro di Ateneo di Studi ed Attivitá Spaziali “Giuseppe Colombo” (CISAS), University of Padova, via Venezia 15, 35131 Padova, Italy
⁸ Department of Physics and Astronomy “G. Galilei”, University of Padova, Vic. Osservatorio 3, 35122 Padova, Italy
⁹ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
¹⁰ Centro de Astrobiologia (INTA-CSIC), European Space Agency (ESA), European Space Astronomy Centre (ESAC), PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
¹¹ International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland
¹² Research and Scientific Support Department, European Space Agency, 2201 Noordwijk, The Netherlands
¹³ PAS Space Reserch Center, Bartycka 18A, 00716 Warszawa, Poland
¹⁴ Department for Astronomy, University of Maryland, College Park, MD 20742-2421, USA
¹⁵ Gauss Professor Akademie der Wissenschaften zu Göttingen, 37077 Göttingen, Germany
¹⁶ LESIA, Observatoire de Paris, CNRS, UPMC Univ. Paris 06, Univ. Paris-Diderot, 5 place J. Janssen, 92195 Meudon Principal Cedex, France
¹⁷ LATMOS, CNRS/UVSQ/IPSL, 11 boulevard d’Alembert, 78280 Guyancourt, France
¹⁸ INAF–Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
¹⁹ Instituto de Astrofisica de Andalucia-CSIC, Glorieta de la Astronomia, 18008 Granada, Spain
²⁰ Institute of Planetary Research, DLR, Rutherfordstrasse 2, 12489 Berlin, Germany
²¹ Institute for Space Science, National Central University, 32054 Chung-Li, Taiwan
²² Budapest University of Technology and Economics, Department of Mechatronics, Optics and Engineering Informatics, Muegyetem rkp 3, 1111 Budapest, Hungary
²³ ESA/ESAC, PO Box 78, 28691 Villanueva de la Cañada, Spain
²⁴ Department of Information Engineering, University of Padova, via Gradenigo 6/B, 35131 Padova, Italy
²⁵ Observatory of the Hungarian Academy of Sciences, PO Box 67, 1525 Budapest, Hungary

Received: 15 April 2016
Accepted: 16 May 2017

Abstract

Context. The camera OSIRIS on board Rosetta obtained high-resolution images of the nucleus of comet 67P/Churyumov-Gerasimenko (67P). Great parts of the nucleus surface are composed of fractured terrain.

Aims. Fracture formation, evolution, and their potential relationship to physical processes that drive activity are not yet fully understood. Observed temperatures and gas production rates can be explained or interpreted with the presence of fractures by applying appropriate modelling methods.

Methods. We followed a transient thermophysical model approach that includes radiative, conductive, and water-ice sublimation fluxes by considering a variety of heliocentric distances, illumination conditions, and thermophysical properties for a set of characteristic fracture geometries on the nucleus of 67P. We computed diurnal temperatures, heat fluxes, and outgassing behaviour in order to derive and distinguish the influence of the mentioned parameters on fractured terrain.

Results. Our analysis confirms that fractures, as already indicated by former studies about concavities, deviate from flat-terrain topographies with equivalent properties, mostly through the effect of self-heating. Compared to flat terrain, illuminated cometary fractures are generally warmer, with smaller diurnal temperature fluctuations. Maximum sublimation rates reach higher peaks, and dust mantle quenching effects on sublimation rates are weaker. Consequently, the rough structure of the fractured terrain leads to significantly higher inferred surface thermal inertia values than for flat areas with identical physical properties, which might explain the range of measured thermal inertia on 67P.

Conclusions. At 3.5 AU heliocentric distance, sublimation heat sinks in fractures converge to maximum values >50 W / m² and trigger dust activity that can be related mainly to H₂O. Fractures are likely to grow through the erosive interplay of alternating sublimation and thermal fatigue.