  Several pieces of evidence suggest that silicate grains in primitive
meteorites are not interstellar grains but condensates formed in the early
solar system. Moreover, the size distribution of matrix grains in chondrites
implies that these condensates might be formed as nanometer-sized grains.
Therefore, we propose a novel scenario for rocky planetesimal formation in
which nanometer-sized silicate grains are produced by evaporation and
recondensation events in early solar nebula, and rocky planetesimals are formed
via aggregation of these nanograins. We reveal that silicate nanograins can
grow into rocky planetesimals via direct aggregation without catastrophic
fragmentation and serious radial drift, and our results provide a suitable
condition for protoplanet formation in our solar system.
