COMPOSITIONAL TYPE CHARACTERIZATION OF ROSETTA ASTEROID CANDIDATES

The final selection of the two Rosetta target asteroids will be made i n a successive phase of the Rosetta project development, when the engi neering parameters will be frozen. In this paper we present spectrosco pic observations of the possible Rosetta candidates and we discuss the results obtained, particularly the definition of their compositional type. We examine the possibility to select some more ''primitive'' can didates. On the basis of its size and spectral type, we suggest includ ing the asteroid 140 Siwa as one of the asteroid targets of the Rosett a mission. (C) 1998 Elsevier Science Ltd.