Possible thermal evolutionary pathways of irregular shaped small asteroids and planetesimals

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, or by the accretion of sub km-sized planetary bodies. Whereas, the majority of the rubble pile type small planetary bodies accreted later by the assemblage of the fragmented debris of the initially existing planetesimals. These bodies cooled over tens of millions of years. The 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.