  Asteroid 21 Lutetia, visited by the Rosetta spacecraft, plays a crucial role
in the reconstruction of primordial phases of planetary objects. Its high bulk
density and its primitive chondritic crust (Weiss et al. 2011) suggest that
Lutetia could be partially differentiated. We developed a numerical code, also
used for studying the geophysical history of Vesta (Formisano et al.,
submitted), to explore several scenarios of internal evolution of Lutetia,
differing in the strength of radiogenic sources and in the global
post-sintering porosity. The only significant heat source for partial
differentiation is represented by Al26, the other possible sources (Fe60,
accretion and differentiation) being negligible. In scenarios in which Lutetia
completed its accretion in less than 0.7 Ma from injection of Al26 in Solar
Nebula and for post-sintering values of macroporosity not exceeding 30 vol. %,
the asteroid experienced only partial differentiation. The formation of the
proto-core, a structure enriched in metals and also containing pristine
silicates, requires from 1 to 4 Ma: the size of the proto-core varies from 6 to
30 km.
