  Two distinct thermal evolutionary pathways of irregular shaped small
planetesimals in the early solar system have been studied. We have taken a case
study of two S-type asteroids; (243) Ida and (951) Gaspra, on the basis of
their precise physical dimensions accessed by the Philip Stooke small body 3-D
shape models of the NASA Planetary Data System. The 3- D shape models for the
two asteroids are based on the Galileo spacecraft fly-by mission. Based on our
novel thermal evolutionary code for the precise shape of the asteroids we found
that the small planetary bodies that accreted within the initial 2-3 million
years (Myr) experienced sintering, whereas, the bodies formed afterwards were
left unconsolidated, e.g., as a rubble pile. The former set of bodies could
have formed by direct aggregation of nebula dust. Whereas, the majority of the
rubble pile type small planetary bodies accreted latter by the assemblage of
the fragmented debris of the initially existing planetesimals. These bodies
cooled over tens of million years. Generations of small planetesimals formed
over time in the early solar system evolved from an ensemble of compact
consolidated bodies to rubble pile bodies due to collision induced
fragmentation and re-accretion.
