TheDawnexploration of (4) Vesta as the ‘ground truth’ to interpret asteroid polarimetry

The results of the in situ exploration of the asteroid (4) Vesta by the Dawn spacecraft open\udnew perspectives in the field of interpretation of remote-sensing polarimetric measurements of\udasteroids. (4) Vesta has long been known to be the only asteroid exhibiting a cyclic variation\udof the degree of linear polarization of the sunlight scattered by its surface, with a period which\udis synchronous with the object’s rotation. This variation must be the consequence of some\udheterogeneity of the asteroid’s surface, including regions characterized by different albedo,\udor composition, or regolith properties, or a combination of the above features. For a long\udtime, this kind of conclusion has remained essentially qualitative. Now, after the extensive\udexploration of Vesta’s surface by Dawn, it is possible to interpret the data set of polarimetric\udmeasurements of Vesta, including some unpublished data presented here for the first time, in\udterms of a correspondence between the degree of linear polarization and the variation of local\udproperties of the surface visible to ground-based observers during Vesta’s rotation, as seen at\uddifferent epochs and under different illumination conditions. This makes it possible to refine\udour knowledge of the empirical relation between polarization properties and albedo, which is\udcommonly used to derive the albedo from remote-sensing measurements of linear polarization\udof atmosphereless Solar system bodies