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Evidence for differentiation of the most primitive small bodies

Carry, B. and Vernazza, P. and Vachier, F. and Neveu, M. and Berthier, J. and Hanuš, J. and Ferrais, M. and Jorda, L. and Marsset, M. and Viikinkoski, M. and Bartczak, P. and Behrend, R. and Benkhaldoun, Z. and Birlan, M. and Castillo-Rogez, J. and Cipriani, F. and Colas, F. and Drouard, A. and Dudziński, G. P. and Desmars, J. and Dumas, C. and Ďurech, J. and Fetick, R. and Fusco, T. and Grice, J. and Jehin, E. and Kaasalainen, M. and Kryszczynska, A. and Lamy, P. and Marchis, F. and Marciniak, A. and Michalowski, T. and Michel, P. and Pajuelo, M. and Podlewska-Gaca, E. and Rambaux, N. and Santana-Ros, T. and Storrs, A. and Tanga, P. and Vigan, A. and Warner, B. and Wieczorek, M. and Witasse, O. and Yang, B. (2021) Evidence for differentiation of the most primitive small bodies. Astronomy and Astrophysics, 650 . Art. No. A129. ISSN 0004-6361. doi:10.1051/0004-6361/202140342.

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Context. Dynamical models of Solar System evolution have suggested that the so-called P- and D-type volatile-rich asteroids formed in the outer Solar System beyond Neptune’s orbit and may be genetically related to the Jupiter Trojans, comets, and small Kuiper belt objects (KBOs). Indeed, the spectral properties of P- and D-type asteroids resemble that of anhydrous cometary dust. Aims. We aim to gain insights into the above classes of bodies by characterizing the internal structure of a large P- and D-type asteroid. Methods. We report high-angular-resolution imaging observations of the P-type asteroid (87) Sylvia with the Very Large Telescope Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument. These images were used to reconstruct the 3D shape of Sylvia. Our images together with those obtained in the past with large ground-based telescopes were used to study the dynamics of its two satellites. We also modeled Sylvia’s thermal evolution. Results. The shape of Sylvia appears flattened and elongated (a/b ~1.45; a/c ~1.84). We derive a volume-equivalent diameter of 271 ± 5 km and a low density of 1378 ± 45 kg m⁻³. The two satellites orbit Sylvia on circular, equatorial orbits. The oblateness of Sylvia should imply a detectable nodal precession which contrasts with the fully-Keplerian dynamics of its two satellites. This reveals an inhomogeneous internal structure, suggesting that Sylvia is differentiated. Conclusions. Sylvia’s low density and differentiated interior can be explained by partial melting and mass redistribution through water percolation. The outer shell should be composed of material similar to interplanetary dust particles (IDPs) and the core should be similar to aqueously altered IDPs or carbonaceous chondrite meteorites such as the Tagish Lake meteorite. Numerical simulations of the thermal evolution of Sylvia show that for a body of such a size, partial melting was unavoidable due to the decay of long-lived radionuclides. In addition, we show that bodies as small as 130–150 km in diameter should have followed a similar thermal evolution, while smaller objects, such as comets and the KBO Arrokoth, must have remained pristine, which is in agreement with in situ observations of these bodies. NASA Lucy mission target (617) Patroclus (diameter ≈140 km) may, however, be differentiated.

Item Type:Article
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URLURL TypeDescription Paper ItemData ItemData
Carry, B.0000-0001-5242-3089
Hanuš, J.0000-0002-2934-3723
Fetick, R.0000-0002-1329-7603
Jehin, E.0000-0001-8923-488X
Marchis, F.0000-0001-7016-7277
Vigan, A.0000-0002-5902-7828
Additional Information:© B. Carry et al. 2021. 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 14 January 2021; Accepted 5 March 2021; Published online 17 June 2021. Tables A.1, B.1, C.1 and C.2 and the reduced and deconvolved SPHERE images are only available at the CDS via anonymous ftp to ( or via Based on observations made with ESO telescopes at the La Silla Paranal Observatory under program 073.C-0851 (PI Merline), 073.C-0062 (PI Marchis), 085.C-0480 (PI Nitschelm), 088.C-0528 (PI Rojo), 199.C-0074 (PI Vernazza). Some of the work presented here is based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programs 073.C-0851 (PI Merline), 073.C-0062 (PI Marchis), 085.C-0480 (PI Nitschelm), 088.C-0528 (PI Rojo), 199.C-0074 (PI Vernazza). Some of the data presented herein were obtained 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. This research has made use of the Keck Observatory Archive (KOA), which is operated by the W.M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under contract with the National Aeronautics and Space Administration. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. We thank the AGORA association which administrates the 60 cm telescope at Les Makes observatory, La Reunion island, under a financial agreement with Paris Observatory. Thanks to A. Peyrot, J.-P. Teng for local support, and A. Klotz for helping with the robotizing. B. Carry, P. Vernazza, A. Drouard, and J. Grice were supported by CNRS/INSU/PNP. This work has been supported by the Czech Science Foundation through grants 20-08218S (J. Hanuš, J. Ďurech) and by the Charles University Research program No. UNCE/SCI/023. 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). This material is partially based upon work supported by the National Science Foundation under Grant No. 1743015. Our colleague and co-author M. Kaasalainen passed away while this work was carried out. Mikko’s influence in asteroid 3D shape modeling has been enormous. This study is dedicated to his memory. This paper makes use of data from the DR1 of the WASP data (Butters et al. 2010) as provided by the WASP consortium, and the computing and storage facilities at the CERIT Scientific Cloud, reg. no. CZ.1.05/3.2.00/08.0144 which is operated by Masaryk University, Czech Republic. TRAPPIST-South is funded by the Belgian Fund for Scientific Research (Fond National de la Recherche Scientifique, FNRS) under the grant PDR T.0120.21, with the participation of the Swiss FNS. 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 Belgian FNRS Senior Research Associate. Thanks to all the amateurs worldwide who regularly observe asteroid lightcurves and stellar occultations. The great majority of observers have made these observations at their own expense, including occasions when they have travelled significant distances. Most of those observers are affiliated with one or more of (i) European Asteroidal Occultation Network (EAON), (ii) International Occultation Timing Association (IOTA), (iii) International Occultation Timing Association – European Section (IOTA–ES), (iv) Japanese Occultation Information Network (JOIN), (v) Trans Tasman Occultation Alliance (TTOA). The authors acknowledge the use of the Virtual Observatory tools Miriade ( (Berthier et al. 2008), TOPCAT (, and STILTS ( (Taylor 2005). This research used the SSOIS (http://www.cadc-ccda.hia-iha. facility of the Canadian Astronomy Data Centre operated by the National Research Council of Canada with the support of the Canadian Space Agency (Gwyn et al. 2012). Thanks to the developers and maintainers.
Group:Thirty Meter Telescope
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
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
Generalitat ValencianaAPOSTD/2019/046
Ministerio de Economía, Industria y Competitividad (MINECO)RTI2018-095076-B-C21
Fondo Europeo de Desarrollo Regional (FEDER)UNSPECIFIED
Fond National de la Recherche scientifique de Belgique (FNRS)PDR T.0120.21
Swiss National Science Foundation (SNSF)UNSPECIFIED
University of LiègeUNSPECIFIED
Subject Keywords:minor planets, asteroids: general – Kuiper belt: general – minor planets, asteroids: individual: Sylvia
Record Number:CaltechAUTHORS:20210716-193605013
Persistent URL:
Official Citation:Evidence for differentiation of the most primitive small bodies. B. Carry, P. Vernazza, F. Vachier, M. Neveu, J. Berthier, J. Hanuš, M. Ferrais, L. Jorda, M. Marsset, M. Viikinkoski, P. Bartczak, R. Behrend, Z. Benkhaldoun, M. Birlan, J. Castillo-Rogez, F. Cipriani, F. Colas, A. Drouard, G. P. Dudziński, J. Desmars, C. Dumas, J. Ďurech, R. Fetick, T. Fusco, J. Grice, E. Jehin, M. Kaasalainen, A. Kryszczynska, P. Lamy, F. Marchis, A. Marciniak, T. Michalowski, P. Michel, M. Pajuelo, E. Podlewska-Gaca, N. Rambaux, T. Santana-Ros, A. Storrs, P. Tanga, A. Vigan, B. Warner, M. Wieczorek, O. Witasse and B. Yang. A&A, 650 (2021) A129; DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109879
Deposited By: Tony Diaz
Deposited On:16 Jul 2021 20:09
Last Modified:16 Jul 2021 20:09

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