Redistribution of particles across the nucleus of comet 67P/Churyumov-Gerasimenko

¹ Physikalisches Institut, Universität Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
e-mail: nicolas.thomas@space.unibe.ch
² Department of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden
³ LESIA, Obs. de Paris, CNRS, Univ Paris 06, Univ. Paris-Diderot, 5 place J. Janssen, 92195 Meudon, France
⁴ Dipartimento di Geoscienze, University of Padova, via G. Gradenigo 6, 35131 Padova, Italy
⁵ Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Asteroiden und Kometen, Rutherfordstrasse 2, 12489 Berlin, Germany
⁶ National Central University, Graduate Institute of Astronomy, 300 Chung-Da Rd, 32054 Chung-Li, Taiwan
⁷ Laboratoire d’Astrophysique de Marseille, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
⁸ Institute for Geophysics and Extraterrestrial Physics, TU Braunschweig, 38106 Braunschweig, Germany
⁹ Centro di Ateneo di Studi ed Attivitia Spaziali, Giuseppe Colombo (CISAS), University of Padova, via Venezia 15, 35131 Padova, Italy
¹⁰ Department of Mechanical Engineering, National Chiao Tung University, 1001 Ta-Hsueh Road, 30010 Hsinchu, Taiwan
¹¹ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, 3, 37077 Göttingen, Germany
¹² Dipartimento di Fisica e Astronomia G. Galilei, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹³ International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland and Centro de Astrobiologíca, CSIC–INTA, 28850 Torrejon de Ardoz, Madrid, Spain
¹⁴ Scientific Support Office, European Space Agency, 2201 Noordwijk, The Netherlands
¹⁵ Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden and PAS Space Research Center, Bartycka 18A, 00716 Warszawa, Poland
¹⁶ Department of Astronomy, University of Maryland, College Park, MD, 20742-2421, USA
¹⁷ LATMOS, CNRS/UVSQ/IPSL, 11 boulevard d’Alembert, 78280 Guyancourt, France
¹⁸ INAF–Osservatorio Astronomico di Padova, Vicolo dell Osservatorio 5, 35122 Padova, Italy
¹⁹ CNR-IFN UOS Padova LUXOR, via Trasea 7, 35131 Padova, Italy
²⁰ Department of Mechanical Engineering University of Padova, via Venezia 1, 35131 Padova, Italy
²¹ UNITN, Universitá di Trento, via Mesiano 77, 38100 Trento, Italy
²² INAF–Osservatorio Astronomico, via Tiepolo 11, 34014 Trieste, Italy
²³ Instituto de Astrofisica de Andalucia (CSIC), c/ Glorieta de la Astronomia s/n, 18008 Granada, Spain
²⁴ ScienceOperations Department, European Space Astronomy Centre/ESA, PO Box 78, 28691 Villanueva de la Canada, Madrid, Spain
²⁵ Institut für Datentechnik und Kommunikationsnetze, 38106 Braunschweig, Germany

Received: 7 March 2015
Accepted: 9 June 2015

Abstract

Context. We present an investigation of the surface properties of areas on the nucleus of comet 67P/Churyumov-Gerasimenko.

Aims. We aim to show that transport of material from one part of the cometary nucleus to another is a significant mechanism that influences the appearance of the nucleus and the surface thermal properties.

Methods. We used data from the OSIRIS imaging system onboard the Rosetta spacecraft to identify surface features on the nucleus that can be produced by various transport mechanisms. We used simple calculations based on previous works to establish the plausibility of dust transport from one part of the nucleus to another.

Results. We show by observation and modeling that “airfall” as a consequence of non-escaping large particles emitted from the neck region of the nucleus is a plausible explanation for the smooth thin deposits in the northern hemisphere of the nucleus. The consequences are also discussed. We also present observations of aeolian ripples and ventifacts. We show by numerical modeling that a type of saltation is plausible even under the rarified gas densities seen at the surface of the nucleus. However, interparticle cohesive forces present difficulties for this model, and an alternative mechanism for the initiation of reptation and creep may result from the airfall mechanism. The requirements on gas density and other parameters of this alternative make it a more attractive explanation for the observations. The uncertainties and implications are discussed.