The Agilkia boulders/pebbles size-frequency distributions: OSIRIS and ROLIS joint observations of 67P surface

Maurizio Pajola (1, 2) , Sefano Mottola (3) , Maximilian Hamm (3) , Marco Fulle (4) , B. Davidsson (5) , C. Güttler (6) , H. Sierks (6) , G. Naletto (7, 2, 8) , G. Arnold (3) , Hans Grothues (9) , R. Jaumann (10, 3) , H. Michaelis (3) , Jean-Pierre Bibring (11) , C. Barbieri (2, 12) , P. L. Lamy (13) , R. Rodrigo (14, 15) , D. Koschny (16) , H. Rickman (17, 18) , H. U. Keller (19) , J. Agarwal (6) , Michael F. A'Hearn (20) , M. A. Barucci (21) , Jean-Loup Bertaux (22) , I. Bertini (2) , S. Boudreault (6) , Gabriele Cremonese (23) , V. da Deppo (8) , S. Debei (24) , M. de Cecco (25) , J. Deller (6) , M. R. El Maarry (26) , Clément Feller (21) , Sonia Fornasier (21) , A. Gicquel (6) , Olivier Groussin (13) , Pedro J. Gutiérrez (27) , M. Hofmann (6) , S. F. Hviid (3) , H. Ip (28) , L. Jorda (13) , Jörg Knollenberg (3) , J.-Rainer Kramm (6) , Ekkehard Kührt (3) , Michael Küppers (29) , Florangela La Forgia (12) , L. M. Lara (27) , Z. Y. Lin (28) , Monica Lazzarin (12) , Josè Juan Lopez-Moreno (27) , A. Lucchetti (23) , Francesco Marzari (12) , Matteo Massironi (30) , Harald Michalik (31) , Nilda Oklay (6) , A. Pommerol (26) , Frank Preusker (3) , Frank Scholten (3) , Nicholas Thomas (26) , Cecilia Tubiana (6) , Jean-Baptiste Vincent (6)

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

By using the images acquired by the OSIRIS and ROLIS cameras, we derive the size-frequency distribution (SFD) of cometary pebbles and boulders covering the size range 0.05 - 30.0 m on the Agilkia landing site. The global SFD measured on OSIRIS images, reflects the different properties of the multiple morphological units present on Agilkia, combined with selection effects related to lifting, transport and redeposition. Contrarily, the different ROLIS SFD derived on the smooth and rough units may be related to their different regolith thickness present on Agilkia. In the thicker, smoother layer, ROLIS mainly measures the SFD of the airfall population that almost completely obliterate the signature of underlying boulders up to a size of the order of 1 m. This is well matched by the power-law index derived analysing coma particles identified by the grain analyser GIADA. This result confirms the important blanketing dynamism of Agilkia. The steeper SFD observed in rough terrains from 0.4 to 2 m could point out intrinsic differences between northern and southern dust size distributions, or it may suggest that the underlying boulders ”peek through” the thinner airfall layer in the rough terrain, thereby producing the observed excess in the decimeter size range. Eventually, the OSIRIS SFD performed on Philae landing unit may be due to water sublimation from a static population of boulders, affecting smaller boulders before the bigger ones, thus shallowing the original SFD.

Domaines: Planétologie et astrophysique de la terre [astro-ph.EP]

Maurizio Pajola, Sefano Mottola, Maximilian Hamm, Marco Fulle, B. Davidsson, et al.. The Agilkia boulders/pebbles size-frequency distributions: OSIRIS and ROLIS joint observations of 67P surface. Monthly Notices of the Royal Astronomical Society, 2016, 462 (Suppl. 1), pp.S242-S252. ⟨10.1093/mnras/stw2720⟩. ⟨insu-01387594⟩