Opposition effect on comet 67P/Churyumov-Gerasimenko using Rosetta-OSIRIS images

¹ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
² Centro di Ateneo di Studi ed Attivitá Spaziali “Giuseppe Colombo” (CISAS), University of Padova, via Venezia 15, 35131 Padova, Italy
³ Institute for Geophysics and Extraterrestrial Physics, TU Braunschweig, 38106 Braunschweig, Germany
⁴ Department of Physics and Astronomy “G. Galilei”, University of Padova, Vic. Osservatorio 3, 35122 Padova, Italy
⁵ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astro-physique de Marseille) UMR 7326, 13388 Marseille, France
⁶ Centro de Astrobiologia (INTA-CSIC), European Space Agency (ESA), European Space Astronomy Centre (ESAC), PO Box 78, 28691 Villanueva de la Canada, Madrid, Spain
⁷ International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland
⁸ Research and Scientific Support Department, 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 Department for Astronomy, University of Maryland, College Park, MD 20742-2421, USA
¹² Gauss Professor Akademie der Wissenschaften zu Göttingen, 37077 Göttingen, Germany
¹³ LESIA, Observatoire de Paris, CNRS, UPMC Univ Paris 06, Univ. Paris-Diderot, 5 Place J. Janssen, 92195 Meudon Principal Cedex, France
¹⁴ LATMOS, CNRS/UVSQ/IPSL, 11 Boulevard d’Alembert, 78280 Guyancourt, France
¹⁵ INAF Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹⁶ CNR-IFN UOS Padova LUXOR, via Trasea 7, 35131 Padova, Italy
¹⁷ Department of Industrial Engineering University of Padova via Venezia, 1, 35131 Padova, Italy
¹⁸ University of Trento, via Sommarive, 9, 38123 Trento, Italy
¹⁹ Physikalisches Institut, Sidlerstrasse 5, University of Bern, 3012 Bern, Switzerland
²⁰ INAF–Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
²¹ Instituto de Astrofisica de Andalucia-CSIC, Glorieta de la Astronomia, 18008 Granada, Spain
²² German Aerospace Center (DLR), Institute of Planetary Research, 12489 Berlin-Adlershof, Germany
²³ Institute for Space Science, National Central University, 32054 Chung-Li, Taiwan
²⁴ ESA/ESAC, PO Box 78, 28691 Villanueva de la Cañada, Spain
²⁵ Department of Information Engineering, University of Padova, via Gradenigo 6/B, 35131 Padova, Italy

^⋆ Corresponding author: N. Masoumzadeh, e-mail: masoumzadeh@mps.mpg.de

Received: 16 September 2016
Accepted: 11 November 2016

Abstract

Aims. We aim to explore the behavior of the opposition effect as an important tool in optical remote sensing on the nucleus of comet 67P/ Churyumov-Gerasimenko (67P), using Rosetta-OSIRIS images acquired in different filters during the approach phase, July-August 2014 and the close flyby images on 14 of February 2015, which contain the spacecraft shadow.

Methods. We based our investigation on the global and local brightness from the surface of 67P with respect to the phase angle, also known as phase curve. The local phase curve corresponds to a region that is located at the Imhotep-Ash boundary of 67P. Assuming that the region at the Imhotep-Ash boundary and the entire nucleus have similar albedo, we combined the global and local phase curves to study the opposition-surge morphology and constrain the structure and properties of 67P. The model parameters were furthermore compared with other bodies in the solar system and existing laboratory study.

Results. We found that the morphological parameters of the opposition surge decrease monotonically with wavelength, whereas in the case of coherent backscattering this behavior should be the reverse. The results from comparative analysis place 67P in the same category as the two Mars satellites, Phobos and Deimos, which are notably different from all airless bodies in the solar system. The similarity between the surface phase function of 67P and a carbon soot sample at extremely small angles is identified, introducing regolith at the boundary of the Imhotep-Ash region of 67P as a very dark and fluffy layer.