Puzzling asteroid 21 Lutetia: our knowledge prior to the Rosetta fly-by

Asteroid 21 Lutetia will be visited by the Rosetta spacecraft on July 10, 2010. Belskaya et al. analyze photometric and polarimetric measurements over a wide range of phase angles. They make predictions that should be directly tested by the fly-by observations: (i) Lutetia has a non-convex shape, probably caused by a large crater, and heterogeneous surface properties probably related to surface morphology; (ii) at least part of the surface is covered by a fine-grained regolith with a particle size less than 20 microns; (iii) the surface composition is similar to that of CO, CV, and/or CH carbonaceous chondrites.