  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 approximately 20 m/pixel 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
approximately 20-30 km. Contour extraction shows an accuracy of approximately 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 30-40m
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.

Earth and Planetary Astrophysics