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(216) Kleopatra, a low density critically rotating M-type asteroid

Marchis, F. and Jorda, L. and Vernazza, P. and Brož, M. and Hanuš, J. and Ferrais, M. and Vachier, F. and Rambaux, N. and Marsset, M. and Viikinkoski, M. and Jehin, E. and Benseguane, S. and Podlewska-Gaca, E. and Carry, B. and Drouard, A. and Fauvaud, S. and Birlan, M. and Berthier, J. and Bartczak, P. and Dumas, C. and Dudziński, G. and Ďurech, J. and Castillo-Rogez, J. C. and Cipriani, F. and Colas, F. and Fetick, R. and Fusco, T. and Grice, J. and Kryszczynska, A. and Lamy, P. and Marciniak, A. and Michalowski, T. and Michel, P. and Pajuelo, M. and Santana-Ros, T. and Tanga, P. and Vigan, A. and Witasse, O. and Yang, B. (2021) (216) Kleopatra, a low density critically rotating M-type asteroid. Astronomy and Astrophysics, 653 . Art. No. A57. ISSN 0004-6361. doi:10.1051/0004-6361/202140874.

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Context. The recent estimates of the 3D shape of the M/Xe-type triple asteroid system (216) Kleopatra indicated a density of ~5 g cm⁻³, which is by far the highest for a small Solar System body. Such a high density implies a high metal content as well as a low porosity which is not easy to reconcile with its peculiar “dumbbell” shape. Aims. Given the unprecedented angular resolution of the VLT/SPHERE/ZIMPOL camera, here, we aim to constrain the mass (via the characterization of the orbits of the moons) and the shape of (216) Kleopatra with high accuracy, hence its density. Methods. We combined our new VLT/SPHERE observations of (216) Kleopatra recorded during two apparitions in 2017 and 2018 with archival data from the W. M. Keck Observatory, as well as lightcurve, occultation, and delay-Doppler images, to derive a model of its 3D shape using two different algorithms (ADAM, MPCD). Furthermore, an N-body dynamical model allowed us to retrieve the orbital elements of the two moons as explained in the accompanying paper. Results. The shape of (216) Kleopatra is very close to an equilibrium dumbbell figure with two lobes and a thick neck. Its volume equivalent diameter (118.75 ± 1.40) km and mass (2.97 ± 0.32) × 10¹⁸ kg (i.e., 56% lower than previously reported) imply a bulk density of (3.38 ± 0.50) g cm⁻³. Such a low density for a supposedly metal-rich body indicates a substantial porosity within the primary. This porous structure along with its near equilibrium shape is compatible with a formation scenario including a giant impact followed by reaccumulation. (216) Kleopatra’s current rotation period and dumbbell shape imply that it is in a critically rotating state. The low effective gravity along the equator of the body, together with the equatorial orbits of the moons and possibly rubble-pile structure, opens the possibility that the moons formed via mass shedding. Conclusions. (216) Kleopatra is a puzzling multiple system due to the unique characteristics of the primary. This system certainly deserves particular attention in the future, with the Extremely Large Telescopes and possibly a dedicated space mission, to decipher its entire formation history.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Marchis, F.0000-0001-7016-7277
Vernazza, P.0000-0002-2564-6743
Brož, M.0000-0003-2763-1411
Hanuš, J.0000-0002-2934-3723
Ferrais, M.0000-0002-0535-652X
Marsset, M.0000-0001-8617-2425
Jehin, E.0000-0001-8923-488X
Carry, B.0000-0001-5242-3089
Castillo-Rogez, J. C.0000-0003-0400-1038
Fetick, R.0000-0002-1329-7603
Vigan, A.0000-0002-5902-7828
Additional Information:© ESO 2021. Article published by EDP Sciences. Received 25 March 2021; Accepted 12 June 2021; Published online 09 September 2021. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program 199.C-0074 (PI: Vernazza). This material is partially based upon work supported by the National Science Foundation under Grant No. 1743015. This work has been supported by the Czech Science Foundation through grant 20-08218S (J. Hanuš, J. Ďurech), 21-11058S (M. Brož) and by the Charles University Research program No. UNCE/SCI/023. P. Vernazza, A. Drouard, M. Ferrais and B. Carry were supported by CNRS/INSU/PNP. M.M. was supported by the National Aeronautics and Space Administration under grant No. 80NSSC18K0849 issued through the Planetary Astronomy Program. The work of TSR was carried out through grant APOSTD/2019/046 by Generalitat Valenciana (Spain). This work was supported by the MINECO (Spanish Ministry of Economy) through grant RTI2018-095076-B-C21 (MINECO/FEDER, UE). The research leading to these results has received funding from the ARC grant for Concerted Research Actions, financed by the Wallonia-Brussels Federation. TRAPPIST is a project funded by the Belgian Fonds (National) de la Recherche Scientifique (F.R.S.-FNRS) under grant FRFC 2.5.594.09.F. TRAPPIST-North is a project funded by the University of Liège, and performed in collaboration with Cadi Ayyad University of Marrakesh. E. Jehin is a FNRS Senior Research Associate. The data presented herein were obtained partially at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Group:Thirty Meter Telescope
Funding AgencyGrant Number
Czech Science Foundation20-08218S
Czech Science Foundation21-11058S
Charles UniversityUNCE/SCI/023
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Institut national des sciences de l'Univers (INSU)UNSPECIFIED
Programme National de Planétologie (PNP)UNSPECIFIED
Generalitat ValencianaAPOSTD/2019/046
Ministerio de Economía, Industria y Competitividad (MINECO)RTI2018-095076-B-C21
Australian Research CouncilUNSPECIFIED
Wallonia-Brussels FederationUNSPECIFIED
Fond National de la Recherche Scientifique (FNRS)FRFC 2.5.594.09.F
University of LiègeUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:techniques: high angular resolution – minor planets, asteroids: individual: 216 Kleopatra
Record Number:CaltechAUTHORS:20211007-144520717
Persistent URL:
Official Citation:(216) Kleopatra, a low density critically rotating M-type asteroid. F. Marchis, L. Jorda, P. Vernazza, M. Brož, J. Hanuš, M. Ferrais, F. Vachier, N. Rambaux, M. Marsset, M. Viikinkoski, E. Jehin, S. Benseguane, E. Podlewska-Gaca, B. Carry, A. Drouard, S. Fauvaud, M. Birlan, J. Berthier, P. Bartczak, C. Dumas, G. Dudziński, J. Ďurech, J. Castillo-Rogez, F. Cipriani, F. Colas, R. Fetick, T. Fusco, J. Grice, A. Kryszczynska, P. Lamy, A. Marciniak, T. Michalowski, P. Michel, M. Pajuelo, T. Santana-Ros, P. Tanga, A. Vigan, O. Witasse and B. Yang. A&A, 653 (2021) A57; DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111260
Deposited By: Tony Diaz
Deposited On:07 Oct 2021 15:58
Last Modified:07 Oct 2021 15:58

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