Exposed bright features on the comet 67P/Churyumov–Gerasimenko: distribution and evolution
LESIA, Observatoire de Paris, PSL Research University, CNRS, Univ. Paris Diderot, Sorbonne Paris Cité, UPMC Univ. Paris 06, Sorbonne Universités,
5 place Jules Janssen,
2 Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
3 INAF-OAPD, Astronomical Observatory of Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
4 NASA Ames Research Center, Mountain View, CA 94035, USA
5 Institut für Planetenforschung, DLR, Rutherfordstrasse 2, 12489 Berlin, Germany
6 Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università di Padova, Vic. Osservatorio 3, 35122 Padova, Italy
7 Laboratoire d’Astrophysique de Marseille UMR 7326, CNRS, Aix-Marseille Université, 13388 Marseille Cedex 13, France
8 Centro de Astrobiología, CSIC-INTA, 28850 Torrejón de Ardoz, Madrid, Spain
9 International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland
10 Research and Scientific Support Department, European Space Agency, 2201 Noordwijk, The Netherlands
11 Department of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden
12 Polish Academy of Sciences, Space Research Center, Bartycka 18A, 00716 Warszawa, Poland
13 LATMOS, CNRS/UVSQ/IPSL, 11 Boulevard d’Alembert, 78280 Guyancourt, France
14 Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
15 CNR–IFN UOS Padova LUXOR, Via Trasea 7, 35131 Padova, Italy
16 NASA Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
17 Dipartimento di Ingegneria Meccanica, Università di Padova, Via Venezia 1, 35131 Padova, Italy
18 UNITN, Universitá di Trento, Via Mesiano 77, 38100 Trento, Italy
19 INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34143 Trieste, Italy
20 Instituto de Astrofísica de Andalucía – CSIC, 18080 Granada, Spain
21 Institute for Space Science, National Central University, 32054 Chung-Li, Taiwan
22 Institut für Geophysik und Extraterrestrisch Physik, TU Braunschweig, 38106 Braunschweig, Germany
23 ESA/ESAC, PO Box 78, 28691 Villanueva de la Cañada, Spain
24 Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo” (CISAS), Università di Padova, Via Venezia 15, 35131 Padova, Italy
25 Dipartimento di Ingegneria dell’Informazione, Università di Padova, Via Gradenigo 6/B, 35131 Padova, Italy
26 Physikalisches Institut, Sidlerstrasse 5, Universität Bern, 3012 Bern, Switzerland
Accepted: 28 December 2017
Context. Since its arrival at the comet 67P/Churyumov–Gerasimenko in August 2014, the Rosetta spacecraft followed the comet as it went past the perihelion and beyond until September 2016. During this time there were many scientific instruments operating on board Rosetta to study the comet and its evolution in unprecedented detail. In this context, our study focusses on the distribution and evolution of exposed bright features that have been observed by OSIRIS, which is the scientific imaging instrument aboard Rosetta.
Aims. We envisage investigating various morphologies of exposed bright features and the mechanisms that triggered their appearance.
Methods. We co-registered multi-filter observations of OSIRIS images that are available in reflectance. The Lommel–Seeliger disk function was used to correct for the illumination conditions and the resulting colour cubes were used to perform spectrophotometric analyses on regions of interest.
Results. We present a catalogue of 57 exposed bright features observed on the nucleus of the comet, all of which are attributed to the presence of H2O ice on the comet. Furthermore, we categorise these patches under four different morphologies and present geometric albedos for each category.
Conclusions. Although the nucleus of 67P/Churyumov–Gerasimenko appears to be dark in general, there are localised H2O ice sources on the comet. Cometary activity escalates towards the perihelion passage and reveals such volatile ices. We propose that isolated H2O ice patches found in smooth terrains in regions, such as Imhotep, Bes, and Hapi, result from frost as an aftermath of the cessation of the diurnal water cycle on the comet as it recedes from perihelion. Upon the comet’s return to perihelion, such patches are revealed when sublimation-driven erosion removes the thin dust layers that got deposited earlier. More powerful activity sources such as cometary outbursts are capable of revealing much fresher, less contaminated H2O ice that is preserved with consolidated cometary material, as observed on exposed patches resting on boulders. This is corroborated by our albedo calculations that attribute higher albedos for bright features with formations related to outbursts.
Key words: comets: individual: 67P/Churyumov–Gerasimenko / techniques: photometric / methods: data analysis
© ESO 2018