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M-type (22) Kalliope: A tiny Mercury

Ferrais, M. and Jorda, L. and Vernazza, P. and Carry, B. and Brož, M. and Rambaux, N. and Hanuš, J. and Dudziński, G. and Bartczak, P. and Vachier, F. and Aristidi, E. and Becker, P. and Marchis, F. and Marsset, M. and Viikinkoski, M. and Fetick, R. and Drouard, A. and Fusco, T. and Birlan, M. and Podlewska-Gaca, E. and Burbine, T. H. and Dyar, M. D. and Bendjoya, P. and Benkhaldoun, Z. and Berthier, J. and Castillo-Rogez, J. and Cipriani, F. and Colas, F. and Dumas, C. and Ďurech, J. and Fauvaud, S. and Grice, J. and Jehin, E. and Kaasalainen, M. and Kryszczynska, A. and Lamy, P. and Le Coroller, H. and Marciniak, A. and Michalowski, T. and Michel, P. and Prieur, J.-L. and Reddy, V. and Rivet, J.-P. and Santana-Ros, T. and Scardia, M. and Tanga, P. and Vigan, A. and Witasse, O. and Yang, B. (2022) M-type (22) Kalliope: A tiny Mercury. Astronomy and Astrophysics, 662 . Art. No. A71. ISSN 0004-6361. doi:10.1051/0004-6361/202243200.

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Context. Asteroid (22) Kalliope is the second largest M-type asteroid in the main belt and is orbited by a satellite, Linus. Whereas the mass of Kalliope is already well constrained thanks to the presence of a moon, its volume is still poorly known, leading to uncertainties on its bulk density and internal structure. Aims. We aim to refine the shape of (22) Kalliope and thus its diameter and bulk density, as well as the orbit of its moon to better constrain its mass, hence density and internal structure. Methods. We acquired disk-resolved observations of (22) Kalliope using the VLT/SPHERE/ZIMPOL instrument to reconstruct its three-dimensional (3D) shape using three different modeling techniques. These images were also used together with new speckle observations at the C2PU/PISCO instrument as well as archival images from other large ground-based telescopes to refine the orbit of Linus. Results. The volume of (22) Kalliope given by the shape models, corresponding to D = 150 ± 5 km, and the mass constrained by its satellite’s orbit yield a density of ρ = 4.40 ± 0.46 g cm⁻³. This high density potentially makes (22) Kalliope the densest known small body in the Solar System. A macroporosity in the 10–25% range (as expected for this mass and size), implies a grain density in the 4.8–5.9 g cm⁻³ range. Kalliope’s high bulk density, along with its silicate-rich surface implied by its low radar albedo, implies a differentiated interior with metal contributing to most of the mass of the body. Conclusions. Kalliope’s high metal content (40–60%) along with its metal-poor mantle makes it the smallest known Mercury-like body. A large impact at the origin of the formation of the moon Linus is likely the cause of its high metal content and density.

Item Type:Article
Related URLs:
URLURL TypeDescription
Ferrais, M.0000-0002-0535-652X
Jorda, L.0000-0001-8735-3308
Vernazza, P.0000-0002-2564-6743
Carry, B.0000-0001-5242-3089
Brož, M.0000-0003-2763-1411
Hanuš, J.0000-0002-2934-3723
Vachier, F.0000-0002-4289-4466
Marchis, F.0000-0001-7016-7277
Marsset, M.0000-0001-8617-2425
Viikinkoski, M.0000-0001-8601-9164
Fetick, R.0000-0002-1329-7603
Dyar, M. D.0000-0003-4272-793X
Benkhaldoun, Z.0000-0001-6285-9847
Castillo-Rogez, J.0000-0003-0400-1038
Jehin, E.0000-0001-8923-488X
Vigan, A.0000-0002-5902-7828
Witasse, O.0000-0003-3461-5604
Additional Information:© M. Ferrais et al. 2022. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Received: 26 January 2022 Accepted: 14 March 2022. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 199.C-0074 (PI: P. Vernazza). P. V., A. D., M. F. and B. C. were supported by CNRS/INSU/PNP. The research of J.H. has been supported by the Czech Science Foundation through grant 20-08218S and by Charles University Research program no. UNCE/SCI/023. M.B. was supported by the Czech Science Foundation, grant 21-11058S. F.M. is supported by the National Science Foundation under grant no. 1743015. TRAPPIST is a project funded by the Belgian Fonds (National) de la Recherche Scientifique (F.R.S.-FNRS) under grant PDR T.0120.21. TRAPPIST-North is a project funded by the University of Liège, in collaboration with the Cadi Ayyad University of Marrakech (Morocco). E.J. is F.R.S.-FNRS Senior Research Associate. The work of T.S.R. 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). Reduced images are only available at the CDS via anonymous ftp to ( or via Based on observations made with ESO Telescopes at the Paranal Observatory under program ID 199.C-0074 (PI: P. Vernazza).
Group:Thirty Meter Telescope
Funding AgencyGrant Number
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Institut national des sciences de l'Univers (INSU)UNSPECIFIED
Programme National de Planetologie (PNP)UNSPECIFIED
Czech Science Foundation20-08218S
Charles UniversityUNCE/SCI/023
Czech Science Foundation21-11058S
Fond National de la Recherche scientifique de Belgique (FNRS)PDR T.0120.21
University of LiègeUNSPECIFIED
Cadi Ayyad University of MarrakechUNSPECIFIED
Generalitat ValencianaAPOSTD/2019/046
Ministerio de Economía, Industria y Competitividad (MINECO)RTI2018-095076-B-C21
European Regional Development FundUNSPECIFIED
Subject Keywords:minor planets, asteroids: individual: (22) Kalliope / methods: observational / techniques: high angular resolution
Record Number:CaltechAUTHORS:20220721-8655000
Persistent URL:
Official Citation:M-type (22) Kalliope: A tiny Mercury. M. Ferrais, L. Jorda, P. Vernazza, B. Carry, M. Brož, N. Rambaux, J. Hanuš, G. Dudziński, P. Bartczak, F. Vachier, E. Aristidi, P. Beck, F. Marchis, M. Marsset, M. Viikinkoski, R. Fetick, A. Drouard, T. Fusco, M. Birlan, E. Podlewska-Gaca, T. H. Burbine, M. D. Dyar, P. Bendjoya, Z. Benkhaldoun, J. Berthier, J. Castillo-Rogez, F. Cipriani, F. Colas, C. Dumas, J. Ďurech, S. Fauvaud, J. Grice, E. Jehin, M. Kaasalainen, A. Kryszczynska, P. Lamy, H. Le Coroller, A. Marciniak, T. Michalowski, P. Michel, J.-L. Prieur, V. Reddy, J.-P. Rivet, T. Santana-Ros, M. Scardia, P. Tanga, A. Vigan, O. Witasse and B. Yang. A&A, 662 (2022) A71; DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:115739
Deposited By: George Porter
Deposited On:21 Jul 2022 22:43
Last Modified:21 Jul 2022 22:43

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