  The processes by which red supergiants lose mass are not fully understood
thus-far and their mass-loss rates lack theoretical constraints. The ambient
surroundings of the nearby M0.5 Iab star Antares offers an ideal environment to
obtain detailed empirical information on the outflow properties at its onset,
and hence indirectly, on the mode(s) of mass loss. We present and analyse
optical VLT/SPHERE/ZIMPOL polarimetric imaging with angular resolution down to
23 milli-arcsec, sufficient to spatially resolve both the stellar disk and its
direct surroundings. We detect a conspicuous feature in polarised intensity
that we identify as a clump containing dust, which we characterise through 3D
radiative transfer modelling. The clump is positioned behind the plane of the
sky, therefore has been released from the backside of the star, and its inner
edge is only 0.3 stellar radii above the surface. The current dust mass in the
clump is $1.3^{+0.2}_{-1.0} \times 10^{-8}$ M$_{\odot}$, though its proximity
to the star implies that dust nucleation is probably still ongoing. The
ejection of clumps of gas and dust makes a non-negligible contribution to the
total mass lost from the star which could possibly be linked to localised
surface activity such as convective motions or non-radial pulsations.
