Geomorphological and spectrophotometric analysis of Seth's circular niches on comet 67P/Churyumov–Gerasimenko using OSIRIS images

Alice Lucchetti (1) , Maurizio Pajola (2) , Sonia Fornasier (3) , Stefano Mottola (4) , Luca Penasa (5) , Laurent Jorda (6) , Gabriele Cremonese (1) , Clément Feller (3) , Pedro H. Hasselmann (3) , Matteo Massironi (7) , Sabrina Ferrari (5) , Giampiero Naletto (5, 8, 9) , Nilda Oklay (4) , Holger Sierks (10) , Cesare Barbieri (2, 11) , Philippe L. Lamy (6) , Rafael Rodrigo (12, 13) , Detlef Koschny (14) , Hans Rickman (15, 16) , Horst Uwe Keller (17) , Jessica Agarwal (10) , Michael F. A'Hearn (18) , Maria Antonella Barucci (3) , Jean-Loup Bertaux (19) , Ivano Bertini (11) , Steve Boudreault (10) , Vania da Deppo (8) , Björn Davidsson (20) , Stefano Debei (21) , Mariolino de Cecco (22) , Jakob Deller (10) , Marco Fulle (23) , Olivier Groussin (6) , Pedro J. Gutiérrez (24) , Carsten Güttler (10) , Marc Hoffman (10) , Stubbe F. Hviid (4) , Wing-Huen Ip (25) , Jörg Knollenberg (4) , J.-Rainer Kramm (10) , Ekkehard Kührt (4) , Michael Küppers (26) , Luisa M. Lara (24) , Monica Lazzarin (11) , Florangela La Forgia (11) , L. Z. Lin (24) , José J. Lopez Moreno (24) , Francesco Marzari (11) , Frank Preusker (4) , Frank Scholten (4) , Xian Shi (10) , Nicolas Thomas (27) , Cécilia Tubiana (10) , Jean-Baptiste Vincent (10)

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

We provide a detailed geomorphological and spectrophotometric analysis of the circular niches located on the Seth region of 67P using OSIRIS images. The features can be related to landslide events that occurred on 67P and shaped its surface, as the recent Aswan cliff collapse detected in the same region. We therefore provide an analysis of the area pre- and post-perihelion suggesting that no specific changes have been observed. To assess this, after performing a geomorphological map of the area that allows us to identify different terrain units, we computed the boulders cumulative size frequency distribution (SFD) of the niches, before and after the perihelion passage. The niches SFDs are characterized by a similar trend with two different power-law indices within the same deposit: lower power-law value (between −2.3 and −2.7) for boulders smaller than 5 m and steeper power-law value (between −4.7 and −5.0) for boulders larger than 5 m. These trends suggest that smaller boulders have evolved and progressively have been depleted (lower power-law index), while bigger boulders are more representative of the event that generated the deposit and are less degraded. Then, we perform the spectrophotometric analysis of this region comparing pre- and post-perihelion results. We found colour changes within the area, in particular brighter patches related to the presence of exposed water ice mixed to the refractory materials have been detected in the post-perihelion images.

Keywords: Comets: general; 67P/Churyumov–Gerasimenko; Data analysis

Domains: Earth and Planetary Astrophysics [astro-ph.EP]; Solar and Stellar Astrophysics [astro-ph.SR]

Alice Lucchetti, Maurizio Pajola, Sonia Fornasier, Stefano Mottola, Luca Penasa, et al.. Geomorphological and spectrophotometric analysis of Seth's circular niches on comet 67P/Churyumov–Gerasimenko using OSIRIS images. Monthly Notices of the Royal Astronomical Society, 2017, 469 (Suppl_2), pp.S238 - S251. ⟨10.1093/mnras/stx1590⟩. ⟨insu-01574363⟩