Decimetre-scaled spectrophotometric properties of the nucleus of comet 67P/Churyumov–Gerasimenko from OSIRIS observations

Clément Feller (1) , Sonia Fornasier (1) , Pedro Henrique Hasselmann (1) , Antonella Barucci (1) , Frank Preusker (2) , Frank Scholten (2) , Laurent Jorda (3) , Antoine Pommerol (4) , Bernhard Jost (4) , Olivier Poch (4) , Mohamed Ramy Elmaary (4) , Nicholas Thomas (4) , Irina Belskaya (5) , Maurizio Pajola (6, 7) , Holder Sierks (8) , Cesare Barbieri (9) , Philippe L. Lamy (3) , Detlef Koschny (10) , Hans Rickman (11, 12) , Rafael Rodrigo (13, 14) , Jessica Agarwal (8) , Michael F. A'Hearn (15) , Jean-Loup Bertaux (16) , Ivano Bertini (7) , Steve Boudreault (8) , Gabriele Cremonese (17) , Vania da Deppo (18) , Björn J. R. Davidsson (19) , Stefano Debei (20) , Mariolino de Cecco (21) , Jakob Deller (8) , Marco Fulle (22) , Adeline Giquel (8) , Olivier Groussin (3) , Pedro J. Gutiérrez (23) , Carsten Güttler (8) , Marc Hofmann (8) , Stubbe F. Hviid (2) , Horst Keller (24) , Wing-Huen Ip (25) , J. Knollenberg (2) , G. Kovacs (8) , J.-R. Kramm (8) , Ekkehard Kührt (2) , M. Küppers (14) , M. L. Lara (24) , M. Lazzarin (9) , C. Leyrat (1) , J. J. Lopez Moreno (23) , F. Marzari (9) , N. Masoumzadeh (8) , S. Mottola (2) , G. Naletto (26) , D. Perna (1) , N. Oklay (8) , X. Shi (8) , C. Tubiana (8) , Jean-Baptiste Vincent (8)

1 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
2 DLR Institut für Planetenforschung
3 LAM - Laboratoire d'Astrophysique de Marseille
4 Physikalisches Institut [Bern]
5 KhNU - V.N. Karazin Kharkiv National University
6 ARC - NASA Ames Research Center
7 CISAS - Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”
8 MPS - Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research
9 Dipartimento di Fisica e Astronomia "Galileo Galilei"
10 RSSD - Research and Scientific Support Department, ESTEC
11 Department of Physics and Astronomy [Uppsala]
12 CBK - Space Research Centre of Polish Academy of Sciences
13 ISSI - International Space Science Institute [Bern]
14 CAB - Centro de Astrobiologia [Madrid]
15 Department of Astronomy [College Park]
16 PLANETO - LATMOS
17 OAPD - INAF - Osservatorio Astronomico di Padova
18 IFN - CNR Institute for Photonics and Nanotechnologies
19 JPL - Jet Propulsion Laboratory
20 Department of Industrial Engineering [Padova]
21 UNITN - Università degli Studi di Trento = University of Trento
22 OAT - INAF - Osservatorio Astronomico di Trieste
23 IAA - Instituto de Astrofísica de Andalucía
24 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
25 IANCU - Institute of Astronomy [Taiwan]
26 DEI - Department of Information Engineering [Padova]

We present the results of the photometric and spectrophotometric properties of the 67P/Churyumov–Gerasimenko nucleus derived with the Optical, Spectroscopic and Infrared Remote Imaging System instrument during the closest fly-by over the comet, which took place on 2015 February 14 at a distance of ∼6 km from the surface. Several images covering the 0°–33° phase angle range were acquired, and the spatial resolution achieved was 11 cm pixel⁻¹. The flown-by region is located on the big lobe of the comet, near the borders of the Ash, Apis and Imhotep regions. Our analysis shows that this region features local heterogeneities at the decimetre scale. We observed difference of reflectance up to 40 per cent between bright spots and sombre regions, and spectral slope variations up to 50 per cent. The spectral reddening effect observed globally on the comet surface by Fornasier et al. (2015) is also observed locally on this region, but with a less steep behaviour. We note that numerous metre-sized boulders, which exhibit a smaller opposition effect, also appear spectrally redder than their surroundings. In this region, we found no evidence linking observed bright spots to exposed water-ice-rich material. We fitted our data set using the Hapke 2008 photometric model. The region overflown is globally as dark as the whole nucleus (geometric albedo of 6.8 per cent) and it has a high porosity value in the uppermost layers (86 per cent). These results of the photometric analysis at a decimetre scale indicate that the photometric properties of the flown-by region are similar to those previously found for the whole nucleus.

Mots clés: Space vehicles; image processing; 7P/Churyumov Gerasimenko; comets; photometry; Data analysis

Domaines: Planétologie et astrophysique de la terre [astro-ph.EP]; Astrophysique stellaire et solaire [astro-ph.SR]

Clément Feller, Sonia Fornasier, Pedro Henrique Hasselmann, Antonella Barucci, Frank Preusker, et al.. Decimetre-scaled spectrophotometric properties of the nucleus of comet 67P/Churyumov–Gerasimenko from OSIRIS observations. Monthly Notices of the Royal Astronomical Society, 2016, 462 (Suppl 1), pp.S287 - S303. ⟨10.1093/mnras/stw2511⟩. ⟨insu-01406412⟩