Tensile strength of 67P/Churyumov–Gerasimenko nucleus material from overhangs

¹ Aix Marseille Univ, CNRS, LAM, Laboratoire d’Astrophysique de Marseille, Marseille, France
e-mail: Nicholas.Attree@lam.fr
² Physikalisches Institut, Sidlerstr. 5, University of Bern, 3012 Bern, Switzerland
³ Institute of Planetary Research, DLR, Rutherfordstrasse 2, 12489, Berlin, Germany
⁴ Max-Planck-Institut für Sonnensystemforschung, 37077 Göttingen, Germany
⁵ Department of Physics and Astronomy, Padova University, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁶ Centro de Astrobiologia (INTA-CSIC), Villanueva de la Canada, 28691 Madrid, Spain
⁷ International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland
⁸ Scientific Support Office, European Space Agency, 2201 Noordwijk, The Netherlands
⁹ Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
¹⁰ PAS Space Research Center, Bartycka 18A, 00716 Warszawa, Poland
¹¹ Institute for Geophysics and Extraterrestrial Physics, TU Braunschweig, 38106 Braunschweig, Germany
¹² Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
¹³ LESIA, Obs. de Paris, CNRS, Univ Paris 06, Univ. Paris-Diderot, 5 place J. Janssen, 92195 Meudon, France
¹⁴ LATMOS, CNRS/UVSQ/IPSL, 11 boulevard d’Alembert, 78280 Guyancourt, France
¹⁵ Centro di Ateneo di Studi ed Attività Spaziali, “Giuseppe Colombo” (CISAS), University of Padova, via Venezia 15, 35131 Padova, Italy
¹⁶ Department of Industrial Engineering, University of Padova, 35131 Padova, Italy
¹⁷ CNR-IFN UOS Padova LUXOR, via Trasea 7, 35131 Padova, Italy
¹⁸ UNITN, Universit di Trento, via Mesiano, 77, 38100 Trento, Italy
¹⁹ INAF - Osservatorio Astronomico, Via Tiepolo 11, 34143 Trieste, Italy
²⁰ Instituto de Astrofisica de Andalucía (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
²¹ Institute for Space Science, Nat. Central Univ., 300 Chung Da Rd., 32054 Chung-Li, Taiwan
²² Operations Department, European Space Astronomy Centre/ESA, PO Box 78, Villanueva de la Canada, 28691 Madrid, Spain
²³ Centre for Astrophysics and Planetary Science, School of Physical Sciences (SEPnet), The University of Kent, Canterbury CT2 7NH, UK
²⁴ Southwest Research Institute, 1050 Walnut St., Boulder, CO 80302, USA
²⁵ NASA Ames Research Center, Moffett Field, CA 94035, USA
²⁶ MTA CSFK Konkoly Observatory, Konkoly Thege M. ut 15-17, 1121 Budapest, Hungary

Received: 23 October 2017
Accepted: 20 December 2017

Abstract

We directly measured twenty overhanging cliffs on the surface of comet 67P/Churyumov–Gerasimenko extracted from the latest shape model and estimated the minimum tensile strengths needed to support them against collapse under the comet’s gravity. We find extremely low strengths of around 1 Pa or less (1 to 5 Pa, when scaled to a metre length). The presence of eroded material at the base of most overhangs, as well as the observed collapse of two features andthe implied previous collapse of another, suggests that they are prone to failure and that the true material strengths are close to these lower limits (although we only consider static stresses and not dynamic stress from, for example, cometary activity). Thus, a tensile strength of a few pascals is a good approximation for the tensile strength of the 67P nucleus material, which is in agreement with previous work. We find no particular trends in overhang properties either with size over the ~10–100 m range studied here or location on the nucleus. There are no obvious differences, in terms of strength, height or evidence of collapse, between the populations of overhangs on the two cometary lobes, suggesting that 67P is relatively homogenous in terms of tensile strength. Low material strengths are supportive of cometary formation as a primordial rubble pile or by collisional fragmentation of a small body (tens of km).