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 new perspectives in the field of interpretation of remote-sensing polarimetric measurements of asteroids. (4) Vesta has long been known to be the only asteroid exhibiting a cyclic variation of the degree of linear polarization of the sunlight scattered by its surface, with a period which is synchronous with the object's rotation. This variation must be the consequence of some heterogeneity of the asteroid's surface, including regions characterized by different albedo, or composition, or regolith properties, or a combination of the above features. For a long time, this kind of conclusion has remained essentially qualitative. Now, after the extensive exploration of Vesta's surface by Dawn, it is possible to interpret the data set of polarimetric measurements of Vesta, including some unpublished data presented here for the first time, in terms of a correspondence between the degree of linear polarization and the variation of local properties of the surface visible to ground-based observers during Vesta's rotation, as seen at different epochs and under different illumination conditions. This makes it possible to refine our knowledge of the empirical relation between polarization properties and albedo, which is commonly used to derive the albedo from remote-sensing measurements of linear polarization of atmosphereless Solar system bodies. Fil: Cellino, A.. Istituto Nazionale Di Astrofisica; Italia. Osservatorio Astrofisico di Torino; Italia Fil: Ammannito, E.. University of California at Los Angeles; Estados Unidos Fil: Magni, G.. Istituto Nazionale Di Astrofisica; Italia Fil: Gil Hutton, Ricardo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; Argentina Fil: Tedesco, E. F.. Planetary Science Institute; Estados Unidos Fil: Belskaya, I. N.. Kharkiv National University. Institute of Astronomy; Ucrania Fil: De Sanctis, M. C.. Istituto Nazionale Di Astrofisica; Italia Fil: Schröder, S.. DLR Institute of Planetary Research; Alemania Fil: Preusker, F.. DLR Institute of Planetary Research; Alemania Fil: Manara, A.. Istituto Nazionale Di Astrofisica; Italia. Osservatorio Astronomico di Brera; Italia