Partitioning tungsten between matrix precursors and chondrule precursors through relative settling

TL;DR

This paper investigates how tungsten isotopic anomalies in chondrites suggest that different pre-solar grain families were sorted and interacted differently during chondrule formation, implying localized formation mechanisms.

Contribution

It demonstrates that dust sorting by relative settling was a key process influencing tungsten distribution and supports localized chondrule formation mechanisms over volume-filling ones.

Findings

W isotopic anomalies indicate multiple pre-solar grain families.

Dust sorting by settling was as effective as other mechanisms in separating grains.

Localized chondrule formation mechanisms are favored by the data.

Abstract

Recent studies of chondrites have found a tungsten isotopic anomaly between chondrules and matrix. Given the refractory nature of tungsten, this implies that W was carried into the solar nebula by at least two distinct families of pre-solar grains. The observed chondrule/matrix split requires that the distinct families were kept separate during the dust coagulation process, and that the two families of grain interacted with the chondrule formation mechanism differently. We take the co-existence of different families of solids in the same general orbital region at the chondrule-precursor size as given, and explore the requirements for them to have interacted with the chondrule formation process at significantly different rates. We show that this sorting of families of solids into chondrule and matrix destined dust had to have been at least as powerful a sorting mechanism as the relative settling of aerodynamically distinct grains at at least two scale heights above the midplane. The requirement that the chondrule formation mechanism was correlated in some fashion with a dust grain sorting mechanism argues strongly for spatially localized chondrule formation mechanisms such as turbulent dissipation in non-thermally ionized disk surface layers, and argues against volume filling mechanisms such as planetesimal bow shocks.