On the aerodynamic redistribution of chondrite components in protoplanetary disks

TL;DR

This paper analytically examines how gas drag influences the distribution of chondrite components in protoplanetary disks, revealing that their dynamics depend on a key decoupling parameter and suggesting a timeline for chondrite formation.

Contribution

It introduces the gas-solid decoupling parameter S to explain the distribution and formation timing of different chondrite components in protoplanetary disks.

Findings

Decoupling parameter S determines solid-gas dynamics.

Carbonaceous chondrites formed earlier with S<1.

Non-carbonaceous chondrites formed later with S>1.

Abstract

Despite being all roughly of solar composition, primitive meteorites (chondrites) present a diversity in their chemical, isotopic and petrographic properties, and in particular a first-order dichotomy between carbonaceous and non-carbonaceous chondrites. We investigate here analytically the dynamics of their components (chondrules, refractory inclusions, metal/sulfide and matrix grains) in protoplanetary disks prior to their incorporation in chondrite parent bodies. We find the dynamics of the solids, subject to gas drag, to be essentially controlled by the "gas-solid decoupling parameter" $S\equiv \textrm{St}/\alpha$, the ratio of the dimensionless stopping time to the turbulence parameter. The decoupling of the solid particles relative to the gas is significant when $S$ exceeds unity. $S$ is expected to increase with time and heliocentric distance. On the basis of (i) abundance of refractory inclusions (ii) proportion of matrix (iii) lithophile element abundances and (iv) oxygen isotopic composition of chondrules, we propose that non-matrix chondritic components had $S<1$ when carbonaceous chondrites accreted and $S>1$ when the other chondrites accreted. This suggests that accretion of carbonaceous chondrites predated on average that of the other chondrites and that refractory inclusions are genetically related to their host carbonaceous chondrites.