Planetesimal Impact Vapor Plumes and Nebular Shocks Form Chondritic Mixtures
The origin of chondrules, and the chondritic sedimentary rocks that dominate the meteoritic record, is a long-standing problem in planetary science. Here, we develop a physical model for the formation of chondritic mixtures as an outcome of vaporizing collisions between planetesimals that were dynamically excited by the growth and migration of planets.
We present calculations of nebular shock waves generated by impact vapor plumes and focus on aspects of the plume interaction with the nebular gas and dust that have been neglected in previous studies of impact ejecta. We find that, when water dominates the vapor, the plumes are relatively cool.
However, the plume expansion is supersonic and can drive strong shock waves in the dusty nebular gas. Portions of these nebular shock fronts initially melt nebular dust, forming chondrules that are coupled to the moving front. As the shock front expands and cools, the chondrules solidify while the shock front entrains additional dust.
Eventually, the plume expansion stalls and then hydrodynamically collapses, turbulently mixing variably processed dust and size-sorted chondrules. For probable impact parameters and nebular conditions during giant planet growth and migration, the impact-generated mixtures have characteristics that span the range observed in chondritic meteorites, providing an environment for rapid formation of chondritic assemblages after chondrule formation.
Our impact vapor and nebular shocks (IVANS) model links chondrule formation to the overall context of planet formation and provides a framework for interpreting the detailed chronological and geochemical record contained in chondritic meteorites.
Schematic overview of the hydrodynamics of impact vapor plumes and nebular shocks. A. Planetesimals comprised of refractory dust and ice collide in a disruptive and vaporizing event surrounded by dusty nebular gas. B. The impact generates an expanding cloud of cooling water vapor and debris from the planetesimal. The vapor plume expands supersonically (inner blue region), driving a warmer shock wave into the solar nebula (outer ring with warm colors). The elongated expanding shell of shocked nebula is hotter in the principal impact direction and cooler in the opposite and lateral dimensions (indicated by the color gradient). Portions of the shocked nebula are warm enough to melt free-floating nebular dust and form chondrules; other regions experience less thermal processing. C. The nebular shock decays to a sound wave as it expands. Expansion of the vapor plume leads to a pressure low in the solar nebula and subsequent hydrodynamic reversal in the flow field. The nebular gas, dust, and chondrules flow into the low pressure region, mixing materials that were processed in different regions. The collapsed mixture has the characteristics observed in chondritic mixtures: quenched chondrules mixed with dust and ice. The mixed region is orders of magnitude larger in scale than the original planetesimals (e.g., Mm-scale mixed regions). The timescale of the collapse is order 10s hours. — astro-ph.EP
Sarah T. Stewart, Simon J. Lock, Philip J. Carter, Erik J. Davies, Michail I. Petaev, Stein B. Jacobsen
Comments: 51 pages, 24 figures, accepted in The Planetary Science Journal. Supplemental materials at this https URL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2503.05636 [astro-ph.EP] (or arXiv:2503.05636v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2503.05636
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From: Sarah Stewart
[v1] Fri, 7 Mar 2025 17:57:48 UTC (18,818 KB)
https://arxiv.org/abs/2503.05636
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