Closing the gap between Earth-based and interplanetary mission observations: Vesta seen by VLT/SPHERE^★,★★

¹ Aix-Marseille Université, CNRS, CNES, Laboratoire d’Astrophysique de Marseille, Marseille, France
e-mail: romain.fetick@lam.fr
² Department of Earth, Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
³ Astrophysics Research Centre, Queen’s University Belfast, BT7 1NN, UK
⁴ ONERA, The French Aerospace Lab BP72, 29 avenue de la Division Leclerc, 92322 Châtillon Cedex, France
⁵ Université Côte d’Azur, Observatoire de la Cote d’Azur, CNRS, Laboratoire Lagrange, France
⁶ SETI Institute, Carl Sagan Center, 189 Bernado Avenue, Mountain View CA 94043, USA
⁷ Institute of Astronomy, Charles University, Prague, V Holešovičkách 2, 18000, Prague 8, Czech Republic
⁸ Department of Mathematics, Tampere University of Technology, PO Box 553, 33101 Tampere, Finland
⁹ IMCCE, Observatoire de Paris, 77 avenue Denfert-Rochereau, 75014 Paris Cedex, France
¹⁰ Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz University, Słoneczna 36, 60-286 Poznań, Poland
¹¹ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
¹² European Space Agency, ESTEC – Scientific Support Office, Keplerlaan 1, Noordwijk 2200 AG, The Netherlands
¹³ TMT Observatory, 100 W. Walnut Street, Suite 300, Pasadena, CA 91124, USA
¹⁴ Space sciences, Technologies and Astrophysics Research Institute, Université de Liège, Allée du 6 Août 17, 4000 Liège, Belgium
¹⁵ Sección Física, Departamento de Ciencias, Pontificia Universidad Católica del Perú, Apartado, Lima 1761, Perú
¹⁶ Institute of Physics, University of Szczecin, Wielkopolska 15, 70-453 Szczecin, Poland
¹⁷ European Southern Observatory (ESO), Alonso de Cordova 3107, 1900 Casilla Vitacura, Santiago, Chile

Received: 30 November 2018
Accepted: 12 January 2019

Abstract

Context. Over the past decades, several interplanetary missions have studied small bodies in situ, leading to major advances in our understanding of their geological and geophysical properties. These missions, however, have had a limited number of targets. Among them, the NASA Dawn mission has characterised in detail the topography and albedo variegation across the surface of asteroid (4) Vesta down to a spatial resolution of ~20 m pixel⁻¹ scale.

Aims. Here our aim was to determine how much topographic and albedo information can be retrieved from the ground with VLT/SPHERE in the case of Vesta, having a former space mission (Dawn) providing us with the ground truth that can be used as a benchmark.

Methods. We observed Vesta with VLT/SPHERE/ZIMPOL as part of our ESO large programme (ID 199.C-0074) at six different epochs, and deconvolved the collected images with a parametric point spread function (PSF). We then compared our images with synthetic views of Vesta generated from the 3D shape model of the Dawn mission, on which we projected Vesta’s albedo information.

Results. We show that the deconvolution of the VLT/SPHERE images with a parametric PSF allows the retrieval of the main topographic and albedo features present across the surface of Vesta down to a spatial resolution of ~20–30 km. Contour extraction shows an accuracy of ~1 pixel (3.6 mas). The present study provides the very first quantitative estimate of the accuracy of ground-based adaptive-optics imaging observations of asteroid surfaces.

Conclusions. In the case of Vesta, the upcoming generation of 30–40 m telescopes (ELT, TMT, GMT) should in principle be able to resolve all of the main features present across its surface, including the troughs and the north–south crater dichotomy, provided that they operate at the diffraction limit.