Abstract
(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) Ceres1,2, suggesting a similar origin for these two objects. Hygiea suffered a giant impact more than 2 Gyr ago3 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−3 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.
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Data availability
As soon as papers for our large programme are accepted for publication, we will make the corresponding reduced and deconvolved adaptive optics images and 3D shape models publicly available at http://observations.lam.fr/astero/.
Code availability
The code used to generate the 3D shape is freely available at https://github.com/matvii/ADAM. The code used to perform the SPH simulations is freely available at https://gitlab.com/sevecekp/sph.
References
Takir, D. & Emery, J. P. Outer main belt asteroids: identification and distribution of four 3-μm spectral groups. Icarus 219, 641–654 (2012).
Vernazza, P. et al. Different origins or different evolutions? Decoding the spectral diversity among C-type asteroids. Astron. J. 153, 72 (2017).
Carruba, V., Domingos, R. C., Huaman, M. E., dos Santos, C. R. & Souami, D. Dynamical evolution and chronology of the Hygiea asteroid family. Mon. Not. R. Astron. Soc. 437, 2279–2290 (2014).
Vernazza, P. et al. The impact crater at the origin of the Julia family detected with VLT/SPHERE? Astron. Astrophys. 618, A154 (2018).
Thalmann, C. et al. SPHERE ZIMPOL: overview and performance simulation. Proc. SPIE 7014, 70143F (2008).
Fusco, T. et al. Deconvolution of astronomical images obtained from ground-based telescopes with adaptive optics. Proc. SPIE 4839, 1065–1075 (2003).
Fetick, R. et al. Closing the gap between Earth-based and interplanetary mission observations: Vesta seen by VLT/SPHERE. Astron. Astrophys. 623, A6 (2019).
Viikinkoski, M., Kaasalainen, M. & Durech, J. ADAM: a general method for using various data types in asteroid reconstruction. Astron. Astrophys. 576, A8 (2015).
Michalowski, T. et al. The spin vector of asteroid 10 Hygiea. Astron. Astrophys. Suppl. Ser. 91, 53–59 (1991).
Chandrasekhar, R. Ellipsoidal Figures of Equilibrium (Dover Publications, 1987).
Park, R. S. et al. High-resolution shape model of Ceres from stereophotoclinometry using Dawn imaging data. Icarus 319, 812–827 (2019).
Nesvorný, D., Brož, M. & Carruba, V. in Asteroids IV (eds Michel, P. et al.) 297–321 (Univ. Arizona Press, 2015).
Thomas, P. C. et al. Impact excavation on asteroid 4 Vesta: Hubble Space Telescope results. Science 277, 1492–1495 (1997).
Benz, W. & Asphaug, E. Impact simulations with fracture. I. Method and tests. Icarus 107, 98–116 (1994).
Jutzi, M., Holsapple, K., Wünneman, K. & Michel, P. in Asteroids IV (eds Michel, P. et al.) 679–699 (Univ. Arizona Press, 2015).
Ševeček, P. et al. SPH/N-body simulations of small (D = 10 km) asteroidal breakups and improved parametric relations for Monte-Carlo collisional models. Icarus 296, 239–256 (2017).
Tillotson, J. H. Metallic Equations of State for Hypervelocity Impact General Atomic Report GA-3216 (General Dynamics, 1962).
von Mises, R. Mechanik der festen Körper in plastisch-deformablen Zustand. Nachr. d. Kgl. Ges. Wiss. Göttingen, Math.-phys. Klasse 4, 582–592 (1913).
Grady, D. & Kipp, M. Continuum modelling of explosive fracture in oil shale. Int. J. Rock Mech. Min. Sci. 17, 147–157 (1980).
Barnes, J. & Hut, P. A hierarchical O(N log N) force-calculation algorithm. Nature 324, 446–449 (1986).
Michel, P., Benz, W., Tanga, P. & Richardson, D. C. Collisions and gravitational reaccumulation: forming asteroid families and satellites. Science 294, 1696–1700 (2001).
Tanga, P., Hestroffer, D., Delbo, M. & Richardson, D. C. Asteroid rotation and shapes from numerical simulations of gravitational re-accumulation. Planet. Space Sci. 57, 193–200 (2009).
Melosh, H. J. & Ivanov, B. A. Impact crater collapse. Ann. Rev. Earth Planet. Sci. 27, 385–415 (1999).
Riller, U. et al. Rock fluidization during peak-ring formation of large impact structures. Nature 562, 511–518 (2018).
Jutzi, M., Asphaug, E., Gillet, P., Barrat, J.-A. & Benz, W. The structure of the asteroid 4 Vesta as revealed by models of planet-scale collisions. Nature 494, 207–210 (2013).
Wadell, H. Volume, shape and roundness of quartz particles. J. Geol. 43, 250–280 (1935).
Warner, B. D., Harris, A. W. & Pravec, P. The asteroid lightcurve database. Icarus 202, 134–146 (2009).
Jehin, E. et al. TRAPPIST: TRAnsiting Planets and PlanetesImals Small Telescope. Messenger 145, 2–6 (2011).
Pettengill, G. H., Ford, P. G., Johnson, W. T. K., Raney, R. K. & Soderblom, L. A. Magellan: radar performance and data products. Science 252, 260–265 (1991).
Thomas, P. C. et al. The shape of Gaspra. Icarus 107, 23–36 (1994).
Hudson, R. S. et al. Asteroid Radar Shape Models, 6489 Golevka PDS ID EAR-A-5-DDR-RADARSHAPE-MODELS-V1.1:RSHAPES-6489GOLEVKA-200006 (NASA PDS, 2000).
Ostro, S. J. et al. Asteroid Radar Shape Models, 1620 Geographos PDS ID EAR-A-5-DDR-RADARSHAPE-MODELS-V1.1:RSHAPES-1620GEOGRAPHOS-200006 (NASA PDS, 2000).
Smith, D. E. et al. Mars Orbiter Laser Altimeter: experiment summary after the first year of global mapping of Mars. J. Geophys. Res. 106, 23689–23722 (2001).
Jorda, L. et al. Asteroid (2867) Steins: shape, topography and global physical properties from OSIRIS observations. Icarus 221, 1089–1100 (2012).
Preusker, F. et al. Stereo-photogrammetrically derived topography of asteroid (4) Vesta. Proc. American Geophysical Union, Meeting Number 93 abstr. P43E-05 (2012).
Jaumann, R. et al. Vesta’s shape and morphology. Science 336, 687–690 (2012).
Farnham, T. L. Shape Model of Asteroid 21 Lutetia PDS ID RO-A-OSINAC/OSIWAC-5-LUTETIA-SHAPE-V1.0 (NASA PDS, 2013).
Preusker, F. et al. Topography of Mercury: a global model from MESSENGER orbital stereo mapping. Proc. Ninth Conference European Planetary Science Congress Vol. 9 abstr. EPSC2014-709 (2014).
Preusker, F. et al. Dawn at Ceres—shape model and rotational state. Proc. 47th Lunar and Planetary Science Conference 1954 (LPI, 2016).
Viikinkoski, M. et al. (16) Psyche: a mesosiderite-like asteroid? Astron. Astrophys. 619, L3 (2018).
Hanuš, J. et al. The shape of (7) Iris as evidence of an ancient large impact? Astron. Astrophys. 624, A121 (2019).
Hiesinger, H. et al. Cratering on Ceres: implications for its crust and evolution. Science 353, aaf4759 (2016).
Bland, M. T. et al. Composition and structure of the shallow subsurface of Ceres revealed by crater morphology. Nat. Geosci. 9, 538–542 (2016).
Knezevic, Z. & Milani, A. Proper element catalogs and asteroid families. Astron. Astrophys. 403, 1165–1173 (2003).
Zappala, V., Cellino, A., Farinella, P. & Milani, A. Asteroid families. II. Extension to unnumbered multiopposition asteroids. Astron. J. 107, 772–801 (1994).
Ivezic, Ž. et al. Solar System objects observed in the Sloan Digital Sky Survey commissioning data. Astron. J. 122, 2749–2784 (2001).
Nugent, C. R. et al. NEOWISE Reactivation Mission Year One: preliminary asteroid diameters and albedos. Astrophys. J. 814, 117 (2015).
Usui, F. et al. Asteroid catalog using AKARI: AKARI/IRC Mid-infrared Asteroid Survey. Pub. Astron. Soc. Jpn 63, 1117–1138 (2011).
Schäfer, C. et al. A smooth particle hydrodynamics code to model collisions between solid, self-gravitating objects. Astron. Astrophys. 590, A19 (2016).
Collins, G. S., Melosh, H. J. & Ivanov, B. A. Modeling damage and deformation in impact simulations. Met. Planet. Sci. 39, 217–231 (2004).
Silber, E. A., Osinski, G. R., Johnson, B. C. & Grieve, R. A. F. Effect of impact velocity and acoustic fluidization on the simple-to-complex transition of lunar craters. J. Geophys. Res. Planets 122, 800–821 (2017).
Acknowledgements
P.V., A.D. and B.C. were supported by CNRS/INSU/PNP. M.Brož was supported by grant 18-04514J of the Czech Science Foundation. 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. This project has received funding from the European Union’s Horizon 2020 research and innovation programmes under grant agreement nos 730890 and 687378. This material reflects only the authors’ views, and the European Commission is not liable for any use that may be made of the information contained herein. TRAPPIST-North is a project funded by the University of Liège, in collaboration with Cadi Ayyad University of Marrakech (Morocco). TRAPPIST-South 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. E.J. and M.G. are F.R.S.-FNRS Senior Research Associates.
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P.V. designed the research. P.V., M.M., R.F. and T.F. reduced and deconvolved the SPHERE images. M.V. and J.H. reconstructed the 3D shape of Hygiea. L.J. and P.V. performed the analysis of Hygiea’s shape. P.Š. and M.Brož ran the SPH simulations. M.F. and E.J. acquired and reduced the TRAPPIST data. M.M. and L.J. produced the albedo map. P.V. and F.D. served as principal investigators to acquire the near-infrared spectral data. B.C. provided the mass estimate. P.V., L.J., P.Š. and M.Brož worked jointly to write the manuscript. All authors discussed the results and commented on the manuscript.
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Vernazza, P., Jorda, L., Ševeček, P. et al. A basin-free spherical shape as an outcome of a giant impact on asteroid Hygiea. Nat Astron 4, 136–141 (2020). https://doi.org/10.1038/s41550-019-0915-8
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DOI: https://doi.org/10.1038/s41550-019-0915-8
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