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Asteroid (16) Psyche’s primordial shape: A possible Jacobi ellipsoid

Ferrais, M. and Vernazza, P. and Jorda, L. and Rambaux, N. and Hanuš, J. and Carry, B. and Marchis, F. and Marsset, M. and Viikinkoski, M. and Brož, M. and Fetick, R. and Drouard, A. and Fusco, T. and Birlan, M. and Podlewska-Gaca, E. and Jehin, E. and Bartczak, P. and Berthier, J. and Castillo-Rogez, J. and Cipriani, F. and Colas, F. and Dudziński, G. and Dumas, C. and Ďurech, J. and Kaasalainen, M. and Kryszczynska, A. and Lamy, P. and Le Coroller, H. and Marciniak, A. and Michalowski, T. and Michel, P. and Santana-Ros, T. and Tanga, P. and Vachier, F. and Vigan, A. and Witasse, O. and Yang, B. (2020) Asteroid (16) Psyche’s primordial shape: A possible Jacobi ellipsoid. Astronomy and Astrophysics, 638 . Art. No. L15. ISSN 0004-6361. doi:10.1051/0004-6361/202038100.

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Context. Asteroid (16) Psyche is the largest M-type asteroid in the main belt and the target of the NASA Psyche mission. It is also the only asteroid of this size (D >  200 km) known to be metal rich. Although various hypotheses have been proposed to explain the rather unique physical properties of this asteroid, a perfect understanding of its formation and bulk composition is still missing. Aims. We aim to refine the shape and bulk density of (16) Psyche and to perform a thorough analysis of its shape to better constrain possible formation scenarios and the structure of its interior. Methods. We obtained disk-resolved VLT/SPHERE/ZIMPOL images acquired within our ESO large program (ID 199.C-0074), which complement similar data obtained in 2018. Both data sets offer a complete coverage of Psyche’s surface. These images were used to reconstruct the three-dimensional (3D) shape of Psyche with two independent shape modeling algorithms (MPCD and ADAM). A shape analysis was subsequently performed, including a comparison with equilibrium figures and the identification of mass deficit regions. Results. Our 3D shape along with existing mass estimates imply a density of 4.20  ±  0.60 g cm⁻³, which is so far the highest for a solar system object following the four telluric planets. Furthermore, the shape of Psyche presents small deviations from an ellipsoid, that is, prominently three large depressions along its equator. The flatness and density of Psyche are compatible with a formation at hydrostatic equilibrium as a Jacobi ellipsoid with a shorter rotation period of ∼3h. Later impacts may have slowed down Psyche’s rotation, which is currently ∼4.2 h, while also creating the imaged depressions. Conclusions. Our results open the possibility that Psyche acquired its primordial shape either after a giant impact while its interior was already frozen or while its interior was still molten owing to the decay of the short-lived radionuclide ²⁶Al.

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Additional Information:© 2020 M. Ferrais et al. 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 6 April 2020; Accepted 2 June 2020; Published online 29 June 2020. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 199.C-0074 (principal investigator: P. Vernazza). P. Vernazza, A. Drouard, M. Ferrais and B. Carry were supported by CNRS/INSU/PNP. J.H. and J.D. were supported by grant 18-09470S of the Czech Science Foundation and by the Charles University Research Programme no. UNCE/SCI/023. E.J. is F.R.S.-FNRS Senior Research Associate. 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).
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
Grantová Agentura České Republiky18-09470S
Charles UniversityUNCE/SCI/023
Fonds de la Recherche Scientifique (FNRS)UNSPECIFIED
Generalitat ValencianaAPOSTD/2019/046
Ministerio de Economía, Industria y Competitividad (MINECO)RTI2018-095076-B-C21
Fondo Europeo de Desarrollo Regional (FEDER)UNSPECIFIED
Subject Keywords:minor planets, asteroids: general – minor planets, asteroids: individual: (16) Psyche – methods: observational – techniques: high angular resolution
Record Number:CaltechAUTHORS:20200629-134223506
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Official Citation:Asteroid (16) Psyche’s primordial shape: A possible Jacobi ellipsoid. M. Ferrais, P. Vernazza, L. Jorda, N. Rambaux, J. Hanuš, B. Carry, F. Marchis, M. Marsset, M. Viikinkoski, M. Brož, R. Fetick, A. Drouard, T. Fusco, M. Birlan, E. Podlewska-Gaca, E. Jehin, P. Bartczak, J. Berthier, J. Castillo-Rogez, F. Cipriani, F. Colas, G. Dudziński, C. Dumas, J. Ďurech, M. Kaasalainen, A. Kryszczynska, P. Lamy, H. Le Coroller, A. Marciniak, T. Michalowski, P. Michel, T. Santana-Ros, P. Tanga, F. Vachier, A. Vigan, O. Witasse and B. Yang. A&A, 638 (2020) L15; DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:104135
Deposited By: Tony Diaz
Deposited On:29 Jun 2020 20:55
Last Modified:16 Nov 2021 18:28

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