A critical analysis of shock models for chondrule formation

TL;DR

This paper critically examines the nebular shock model for chondrule formation, revealing that the model's temperature and cooling rate constraints make it unlikely to be the primary process responsible for chondrule creation.

Contribution

The study provides a detailed reanalysis of the shock model, highlighting issues with temperature and cooling rates that challenge its viability in chondrule formation.

Findings

Postshock equilibrium temperature too high for volatile retention

Radiative cooling rates too high for realistic chondrule textures

Global nebular shocks unlikely primary chondrule formation mechanism

Abstract

In recent years many models of chondrule formation have been proposed. One of those models is the processing of dust in shock waves in protoplanetary disks. In this model, the dust and the chondrule precursors are overrun by shock waves, which heat them up by frictional heating and thermal exchange with the gas. In this paper we reanalyze the nebular shock model of chondrule formation and focus on the downstream boundary condition. We show that for large-scale plane-parallel chondrule-melting shocks the postshock equilibrium temperature is too high to avoid volatile loss. Even if we include radiative cooling in lateral directions out of the disk plane into our model (thereby breaking strict plane-parallel geometry) we find that for a realistic vertical extent of the solar nebula disk the temperature decline is not fast enough. On the other hand, if we assume that the shock is entirely optically thin so that particles can radiate freely, the cooling rates are too high to produce the observed chondrules textures. Global nebular shocks are therefore problematic as the primary sources of chondrules.