[en] (10) Hygiea is the fourth largest main belt asteroid and the only known asteroid whose surface composition appears similar to that of the dwarf planet (1) Ceres[SUP]1,2[/SUP], suggesting a similar origin for these two objects. Hygiea suffered a giant impact more than 2 Gyr ago[SUP]3[/SUP] that is at the origin of one of the largest asteroid families. However, Hygeia has never been observed with sufficiently high resolution to resolve the details of its surface or to constrain its size and shape. Here, we report high-angular-resolution imaging observations of Hygiea with the VLT/SPHERE instrument ( 20 mas at 600 nm) that reveal a basin-free nearly spherical shape with a volume- equivalent radius of 217 ± 7 km, implying a density of 1,944 ± 250 kg m[SUP]-[/SUP][SUP]3[/SUP] to 1σ. In addition, we have determined a new rotation period for Hygiea of 13.8 h, which is half the currently accepted value. Numerical simulations of the family-forming event show that Hygiea's spherical shape and family can be explained by a collision with a large projectile (diameter 75-150 km). By comparing Hygiea's sphericity with that of other Solar System objects, it appears that Hygiea is nearly as spherical as Ceres, opening up the possibility for this object to be reclassified as a dwarf planet.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Vernazza, Pierre; LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, Aix Marseille Université, CNRS, Marseille, France
Jorda, Laurent; LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, Aix Marseille Université, CNRS, Marseille, France
Ševeček, P.; Institute of Astronomy, Charles University, Prague, Czech Republic
Brož, M.; Institute of Astronomy, Charles University, Prague, Czech Republic
Viikinkoski, Matti; Mathematics and Statistics, Tampere University, Tampere, Finland
Hanuš, Josef; Institute of Astronomy, Charles University, Prague, Czech Republic
Carry, B.; Laboratoire Lagrange, Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Nice, France
Drouard, Alexis; LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, Aix Marseille Université, CNRS, Marseille, France
Ferrais, Marin ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
Marsset, M.; Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA, USA
Marchis, F.; LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, Aix Marseille Université, CNRS, Marseille, France ; SETI Institute, Carl Sagan Center, Mountain View, CA, USA
Birlan, M.; IMCCE, Observatoire de Paris, Paris, France
Podlewska-Gaca, Edyta; Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz University, Poznań, Poland ; Institute of Physics, University of Szczecin, Szczecin, Poland
Jehin, Emmanuel ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
Bartczak, P.; Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz University, Poznań, Poland
Dudzinski, G.; Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz University, Poznań, Poland
Berthier, J.; IMCCE, Observatoire de Paris, Paris, France
Castillo-Rogez, J.; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
Cipriani, F.; European Space Agency, ESTEC - Scientific Support Office, Noordwijk, the Netherlands
Colas, F.; IMCCE, Observatoire de Paris, Paris, France
DeMeo, F.; Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA, USA
Dumas, C.; TMT Observatory, Pasadena, CA, USA
Durech, J.; Institute of Astronomy, Charles University, Prague, Czech Republic
Fetick, R.; LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, Aix Marseille Université, CNRS, Marseille, France ; ONERA, The French Aerospace Lab, Chatillon, France
Fusco, T.; LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, Aix Marseille Université, CNRS, Marseille, France ; ONERA, The French Aerospace Lab, Chatillon, France
Grice, J.; Laboratoire Lagrange, Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Nice, France ; School of Physical Sciences, The Open University, Milton Keynes, UK
Kaasalainen, M.; Mathematics and Statistics, Tampere University, Tampere, Finland
Kryszczynska, A.; Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz University, Poznań, Poland
Lamy, P.; LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, Aix Marseille Université, CNRS, Marseille, France
Le Coroller, H.; LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, Aix Marseille Université, CNRS, Marseille, France
Marciniak, A.; Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz University, Poznań, Poland
Michalowski, T.; Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz University, Poznań, Poland
Rambaux, N.; IMCCE, Observatoire de Paris, Paris, France
Santana-Ros, T.; Departamento de Fı́sica, Ingenierı́a de Sistemas y Teorı́a de la Señal, Universidad de Alicante, Alicante, Spain ; Institut de Ciències del Cosmos, Universitat de Barcelona, Barcelona, Spain
Tanga, P.; Laboratoire Lagrange, Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Nice, France
Vachier, F.; IMCCE, Observatoire de Paris, Paris, France
Vigan, A.; LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, Aix Marseille Université, CNRS, Marseille, France
Witasse, O.; European Space Agency, ESTEC - Scientific Support Office, Noordwijk, the Netherlands
Yang, B.; European Southern Observatory (ESO), Santiago, Chile
Gillon, Michaël ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Exotic
Benkhaldoun, Z.; Oukaimeden Observatory, High Energy Physics and Astrophysics Laboratory, Cadi Ayyad University, Marrakesh, Morocco
Szakats, R.; Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Budapest, Hungary
Hirsch, R.; Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz University, Poznań, Poland
Duffard, R.; Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía, Granada, Spain
Chapman, A.; Observatorio de Buenos Aires, Buenos Aires, Argentina
Maestre, J. L.; Observatorio de Albox, Albox, Spain)
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