[Paper Review] A proposed origin for chondrule-forming shocks in the solar nebula

Andrew Nelson, M. Ruffert|arXiv (Cornell University)|Oct 13, 2005

Astro and Planetary Science3 citations

TL;DR

This paper proposes that shocks generated by dynamical activity in the gaseous envelopes of forming Jovian planets in the solar nebula could be the origin of chondrules and other annealed silicates. Using 3D hydrodynamic simulations, the authors show that these envelopes are not hydrostatic but turbulent, producing shock conditions matching chondrule-forming parameters, suggesting a direct link between planet formation and chondrule production.

ABSTRACT

We propose that the nebular shocks currently favored as a model to form chondrules and other annealed silicates in the solar nebula originate in the dynamical activity present in the envelope of forming Jovian planets. In contrast to the classic `core accretion model', our 3D hydrodynamic simulations show that this envelope is not a 1D hydrostatic structure but is instead vigorously active and contains densities and temperatures that appear similar in magnitude and spatial extent to those thought to be responsible for the production of chondrules.

Motivation & Objective

• To investigate whether the gaseous envelopes of forming Jovian planets are truly hydrostatic, as assumed in the core accretion model.
• To explore whether dynamical activity in these envelopes can generate shocks with properties suitable for chondrule formation.
• To test the hypothesis that chondrules and other annealed silicates originate from shock heating in the protoplanetary envelope of nascent gas giants.
• To establish a physical link between chondrule formation timescales and the early stages of Jovian planet formation.
• To assess the viability of this mechanism as an alternative or complement to existing chondrule-forming shock models.

Proposed method

• 3D hydrodynamic simulations of a local Cartesian region around a 10 M⊕ core at 5.2 AU in a circumstellar disk.
• Use of a modified 'shearing box' approximation that includes non-linear terms and avoids linearized shear, improving correspondence with global disk conditions.
• Initial conditions derived from a global disk model with power-law surface density and temperature profiles, assuming 500 g cm⁻² surface density and 200 K temperature at 5.2 AU.
• Incorporation of core gravity and local disk self-gravity, while neglecting vertical gravity components to simplify the model.
• Use of the relation ρ = Σ/H to convert global surface density to local volume density, introducing a small physical inconsistency.
• Streamline analysis to trace fluid paths and estimate shock conditions, though with limitations due to the use of fixed flow fields.

Experimental results

Research questions

• RQ1 Can dynamical activity in the envelopes of forming Jovian planets produce shocks with the required density, temperature, and velocity conditions for chondrule formation?
• RQ2 How do the shock properties from 3D hydrodynamic simulations compare to the inferred parameters of chondrule-forming events?
• RQ3 Is the standard assumption of hydrostatic equilibrium in Jovian planet envelopes valid, or is the flow significantly turbulent?
• RQ4 What fraction of solid material passing near a forming Jovian core might experience chondrule-forming conditions?
• RQ5 Can this mechanism explain the observed distribution and abundance of chondrules and annealed silicates in meteorites?

Key findings

• The gaseous envelope of a forming Jovian planet is not hydrostatic but dynamically active, with vigorous turbulence and shock formation.
• The simulations produce shock regions with temperatures and densities comparable to those inferred for chondrule formation, particularly in the envelope's outer layers.
• Shock velocities in the flow are estimated at 1–2 km s⁻¹, though this may be too low compared to values required by some chondrule models.
• The activity persists over a significant fraction of the planet formation timescale, enabling prolonged and repeated chondrule processing.
• The model suggests a physical link between chondrule formation and the early stages of Jovian planet formation, potentially explaining the co-occurrence of chondrules and volatile-rich planetesimals.
• The results imply that the core accretion model may require revision to account for dynamical activity in planetary envelopes.