Possible thermal evolutionary pathways of irregular shaped small asteroids and planetesimals

TL;DR

This study explores two thermal evolutionary pathways of irregular small asteroids, showing that early-formed bodies sintered into solid forms while later ones remained as rubble piles, based on shape models of Ida and Gaspra.

Contribution

It introduces a novel thermal evolutionary code applied to irregular asteroid shapes, revealing distinct formation and cooling processes over millions of years.

Findings

Early bodies experienced sintering and consolidation.

Later bodies remained as rubble piles due to fragmentation.

Bodies cooled over tens of millions of years.

Abstract

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.