Detection of exposed H₂O ice on the nucleus of comet 67P/Churyumov-Gerasimenko as observed by Rosetta OSIRIS and VIRTIS instruments

M. Antonella Barucci (1) , G. Filacchione (2) , Sonia Fornasier (1) , A. Raponi (2) , J. D.P. Deshapriya (1) , F. Tosi (2) , C. Feller (1) , M. Ciarniello (2) , Holger Sierks (3) , F. Capaccioni (2) , A. Pommerol (4) , Matteo Massironi (5) , Nilda Oklay (3) , F. Merlin (1) , Jean-Baptiste Vincent (3) , M. Fulchignoni (1) , A. Guilbert-Lepoutre (6) , D. Perna (1) , M.T. Capria (2) , P. H. Hasselmann (1) , B. Rousseau (1) , Cesare Barbieri (7) , D. Bockelée-Morvan (1) , Philippe L. Lamy (8) , C. de Sanctis (2) , Rafael Rodrigo (9) , S. Erard (2) , Detlef Koschny (10) , C. Leyrat (1) , H. Rickman (11, 12) , P. Drossart (1) , Horst U. Keller (13) , Michael F. A'Hearn (14) , G. Arnold (15) , Jean-Loup Bertaux (16) , Ivano Bertini (17) , P. Cerroni (2) , Gabriele Cremonese (17) , Vania da Deppo (18) , Björn J. R. Davidsson (19) , Mohamed R. El-Maarry (4) , S. Fonti (20) , M. Fulle (21) , O. Groussin (8) , C. Güttler (3) , S. F. Hviid (15) , W. Ip (22) , L. Jorda (8) , D. Kappel (15) , J. Knollenberg (15) , J.-R. Kramm (3) , Ekkehard Kührt (15) , M. Küppers (23) , L. Lara (24) , Monica Lazzarin (17) , J. J. Lopez Moreno (24) , F. Mancarella (20) , F. Marzari (7) , S. Mottola (15) , Giampiero Naletto (18) , Maurizio Pajola (25) , E. Palomba (2) , E. Quirico (26) , B. Schmitt (26) , Nicholas Thomas (4) , Cécilia Tubiana (3)

1 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
2 IAPS - Istituto di Astrofisica e Planetologia Spaziali - INAF
3 MPS - Max-Planck-Institut für Sonnensystemforschung
4 Physikalisches Institut [Bern]
5 Dipartimento di Geoscienze [Padova]
6 UTINAM - Univers, Transport, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UMR 6213)
7 Dipartimento di Fisica e Astronomia "Galileo Galilei"
8 LAM - Laboratoire d'Astrophysique de Marseille
9 ISSI - International Space Science Institute [Bern]
10 ESTEC - European Space Research and Technology Centre
11 CBK - Space Research Centre of Polish Academy of Sciences
12 Department of Physics and Astronomy [Uppsala]
13 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
14 Department of Astronomy [College Park]
15 DLR Institut für Planetenforschung
16 PLANETO - LATMOS
17 OAPD - INAF - Osservatorio Astronomico di Padova
18 DEI - Department of Information Engineering [Padova]
19 JPL - Jet Propulsion Laboratory
20 Department of Physics [Lecce]
21 OAT - INAF - Osservatorio Astronomico di Trieste
22 Institute of Space Science [Taiwan]
23 Operations Department (ESAC)
24 IAA - Instituto de Astrofísica de Andalucía
25 ARC - NASA Ames Research Center
26 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble

Since the orbital insertion of the Rosetta spacecraft, comet 67P/Churyumov-Gerasimenko (67P/C-G) has been mapped by OSIRIS camera and VIRTIS spectro-imager, producing a huge quantity of images and spectra of the comet’s nucleus. The aim of this work is to search for the presence of H₂O on the nucleus which, in general, appears very dark and rich in dehydrated organic material. After selecting images of the bright spots which could be good candidates to search for H₂O ice, taken at high resolution by OSIRIS, we check for spectral cubes of the selected coordinates to identify these spots observed by VIRTIS. Methods. The selected OSIRIS images were processed with the OSIRIS standard pipeline and corrected for the illumination condi- tions for each pixel using the Lommel-Seeliger disk law. The spots with higher I/F were selected and then analysed spectrophotomet- rically and compared with the surrounding area. We selected 13 spots as good targets to be analysed by VIRTIS to search for the 2 μm absorption band of water ice in the VIRTIS spectral cubes. Results. Out of the 13 selected bright spots, eight of them present positive H₂O ice detection on the VIRTIS data. A spectral analysis was performed and the approximate temperature of each spot was computed. The H₂O ice content was confirmed by modeling the spectra with mixing (areal and intimate) of H₂O ice and dark terrain, using Hapke’s radiative transfer modeling. We also present a detailed analysis of the detected spots.

Keywords: Photometry; Comets; Spectroscopy; Data analysis; 67P/Churyumov-Gerasimenko

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]; Earth and Planetary Astrophysics [astro-ph.EP]

M. Antonella Barucci, G. Filacchione, Sonia Fornasier, A. Raponi, J. D.P. Deshapriya, et al.. Detection of exposed H₂O ice on the nucleus of comet 67P/Churyumov-Gerasimenko as observed by Rosetta OSIRIS and VIRTIS instruments. Astronomy and Astrophysics - A&A, 2016, 595, A102 (13 p.). ⟨10.1051/0004-6361/201628764⟩. ⟨insu-01371174⟩