Rosetta/OSIRIS observations of 67P nucleus during the April 2016 flyby: high-resolution spectrophotometry

Clément Feller (1) , Sonia Fornasier (1) , Sabrina Ferrari (2) , Pedro Henrique Hasselmann (1) , Antonella M. Barucci (1) , Matteo Massironi (2) , J. D. P. Deshapriya (1) , Holger Sierks (3) , Giampiero Naletto (4, 2, 5) , Philippe Lamy (6) , Rafael Rodrigo (7, 8) , Detlef Koschny (9) , Björn Davidsson (10) , Jean-Loup Bertaux (6) , Ivano Bertini (4) , Dennis Bodewits (11) , Gabriele Cremonese (12) , Vania da Deppo (13) , Stefano Debei (14) , Maurizio de Cecco (15) , Marco Fulle (16) , Pedro J. Gutiérrez (17) , Carsten Güttler (3) , Wing-Huen Ip (18, 19) , Horst U. Keller (20, 21) , Luisa-Maria Lara (17) , Monica Lazzarin (11) , Josè Juan Lopez-Moreno (17) , Francesco Marzari (4) , Xian Shi (3) , Cécilia Tubiana (3) , B. Gaskell (22) , Florangela La Forgia (4) , A. Lucchetti (12) , Sefano Mottola (21) , Maurizio Pajola (12) , Frank Preusker (21) , Frank Scholten (21)

1 LESIA (UMR_8109) - Laboratoire d'études spatiales et d'instrumentation en astrophysique
2 CISAS - Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”
3 MPS - Max-Planck-Institut für Sonnensystemforschung
4 Dipartimento di Fisica e Astronomia "Galileo Galilei"
5 IFN - CNR Istituto di Fotonica e Nanotecnologie [Padova]
6 PLANETO - LATMOS
7 ISSI - International Space Science Institute [Bern]
8 CAB - Centro de Astrobiologia [Madrid]
9 RSSD - Research and Scientific Support Department, ESTEC
10 JPL - Jet Propulsion Laboratory
11 Department of Physics [Auburn]
12 OAPD - INAF - Osservatorio Astronomico di Padova
13 IFN - CNR Institute for Photonics and Nanotechnologies
14 Department of Industrial Engineering [Padova]
15 University of Trento [Trento]
16 OAT - INAF - Osservatorio Astronomico di Trieste
17 IAA - Instituto de Astrofísica de Andalucía
18 IANCU - Institute of Astronomy [Taiwan]
19 SSI - Space Science Institute [Macau]
20 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
21 DLR Institut für Planetenforschung
22 PSI - Planetary Science Institute [Tucson]

From August 2014 to September 2016, the Rosetta spacecraft followed comet 67P/Churyumov–Gerasimenko along its orbit. After the comet passed perihelion, Rosetta performed a flyby manoeuvre over the Imhotep–Khepry transition in April 2016. The OSIRIS/Narrow-Angle-Camera (NAC) acquired 112 observations with mainly three broadband filters (centered at 480, 649, and 743 nm) at a resolution of up to 0.53 m/px and for phase angles between 0.095° and 62°. We have investigated the morphological and spectrophotometrical properties of this area using the OSIRIS/NAC high-resolution observations. We assembled the observations into coregistered color cubes. Using a 3D shape model, we produced the illumination conditions and georeference for each observation. We mapped the observations of the transition to investigate its geomorphology. Observations were photometrically corrected using the Lommel–Seeliger disk law. Spectrophotometric analyses were performed on the coregistered color cubes. These data were used to estimate the local phase reddening. The Imhotep–Khepry transition hosts numerous and varied types of terrains and features. We observe an association between a feature’s nature, its reflectance, and its spectral slopes. Fine material deposits exhibit an average reflectance and spectral slope, while terrains with diamictons, consolidated material, degraded outcrops, or features such as somber boulders present a lower-than-average reflectance and higher-than-average spectral slope. Bright surfaces present here a spectral behavior consistent with terrains enriched in water-ice. We find a phase-reddening slope of 0.064 ± 0.001%/100 nm/° at 2.7 au outbound, similar to the one obtained at 2.3 au inbound during the February 2015 flyby. Identified as the source region of multiple jets and a host of water-ice material, the Imhotep–Khepry transition appeared in April 2016, close to the frost line, to further harbor several potential locations with exposed water-ice material among its numerous different morphological terrain units.

Domains: Astrophysics [astro-ph]; Physics [physics]; Astrophysics [astro-ph]

Clément Feller, Sonia Fornasier, Sabrina Ferrari, Pedro Henrique Hasselmann, Antonella M. Barucci, et al.. Rosetta/OSIRIS observations of 67P nucleus during the April 2016 flyby: high-resolution spectrophotometry. Astronomy and Astrophysics - A&A, 2019, 630, A9 (20p.). ⟨10.1051/0004-6361/201833807⟩. ⟨insu-02115740⟩