A Collective Trigger for Widespread Planetesimal Formation Revealed by Accretion Ages

TL;DR

This study develops a thermal evolution model to determine the formation ages of meteorite parent bodies, revealing a synchronized onset of planetesimal formation and disk motion around 0.95 million years after CAI formation, which constrains protoplanetary disk evolution.

Contribution

It introduces a refined thermal model incorporating chemical reactions and phase changes, linking planetesimal formation timing with disk dynamics and proposing a key phenomenon influencing planetesimal formation.

Findings

Parent bodies of NC and CC meteorites formed nearly simultaneously.

Onset of planetesimal formation coincided with disk motion around 0.95 Myr after CAI.

Proposes a semi-permeable barrier influencing disk evolution and planetesimal formation.

Abstract

The formation of planetesimals was an integral part of the cascading series of processes that built the terrestrial planets. To illuminate planetesimal formation, here we develop a refined thermal evolution model to calculate the formation ages of meteorite parent planetesimals. This model includes chemical reactions and phase changes during heating, as well as natural variations in the proportions of the constituent phases of these planetesimals. We find that the parent bodies of non-carbonaceous (NC) and carbonaceous (CC) iron meteorites start forming at very similar times (~0.95 Myr after calcium-aluminium-rich inclusion [CAI] formation) and occupy overlapping time windows. NC and CC chondrite parent bodies formed later during non-overlapping periods. We combine these ages with proportions of isotopic end-members we recover from mixing models to construct records of motion throughout the protoplanetary disk. These records argue that NC and CC material traversed the barrier in the disk after ~0.95 Myr after CAI formation. The onset of this motion coincided with planetesimal formation, indicating that the phenomenon that drove motion also triggered planetesimal formation. We argue that this feature also served as the semi-permeable barrier in the disk. Although its identity is uncertain, the effects this phenomenon had on the timing of planetesimal formation and motion through the disk can now serve as constraints on models of disk evolution. Models that reproduce these effects would elucidate the nature and implications of this phenomenon, which is key to unlocking a holistic model of terrestrial planet building.