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Impact jetting as the origin of chondrules



Chondrules are the millimetre-scale, previously molten, spherules found in most meteorites1. Before chondrules formed, large differentiating planetesimals had already accreted2. Volatile-rich olivine reveals that chondrules formed in extremely solid-rich environments, more like impact plumes than the solar nebula3,4,5. The unique chondrules in CB chondrites probably formed in a vapour-melt plume produced by a hypervelocity impact6 with an impact velocity greater than 10 kilometres per second. An acceptable formation model for the overwhelming majority of chondrules, however, has not been established. Here we report that impacts can produce enough chondrules during the first five million years of planetary accretion to explain their observed abundance. Building on a previous study of impact jetting7, we simulate protoplanetary impacts, finding that material is melted and ejected at high speed when the impact velocity exceeds 2.5 kilometres per second. Using a Monte Carlo accretion code, we estimate the location, timing, sizes, and velocities of chondrule-forming impacts. Ejecta size estimates8 indicate that jetted melt will form millimetre-scale droplets. Our radiative transfer models show that these droplets experience the expected cooling rates of ten to a thousand kelvin per hour9,10. An impact origin for chondrules implies that meteorites are a byproduct of planet formation rather than leftover building material.

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Figure 1: Jetting of melted material during an accretionary impact.
Figure 2: Timing and location of chondrule-forming impact.
Figure 3: The cumulative mass of chondrules created by accretionary impacts.
Figure 4: Chondrule cooling rates as a function of impactor size.

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We thank I. Sanders for his review, which improved the manuscript. We gratefully acknowledge the developers of iSALE (, especially G. Collins, K. Wünnemann, D. Elbeshausen and B. Ivanov. This research was supported by NASA grant number PGG NNX10AU88G.

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Authors and Affiliations



While working on calculating the cooling rates of impact-produced chondrules with H.J.M., B.C.J. conceived the idea that chondrules could form by jetting during low-velocity accretionary impacts. D.A.M. produced the Monte Carlo accretion code results. B.C.J. produced the hydrocode and radiative transfer code results. All authors contributed to preparation of the manuscript and the conclusions presented in this work.

Corresponding author

Correspondence to Brandon C. Johnson.

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The authors declare no competing financial interests.

Extended data figures and tables

Extended Data Figure 1 Timing and velocity of chondrule-forming impact.

Chondrule-forming impacts with velocities above 2.5 km s−1 for the MMSN model (a) and the 3MMSN model (b). The points are coloured according to vimp/vesc (shown on the colour scale). Note that vimp/vesc may be less than one because vesc is considered to be the escape velocity after the target and impactor have combined to form a more massive body.

Extended Data Figure 2 Maximum size of droplets created by jetting.

The different lines represent different impact velocities, as indicated.

Extended Data Figure 3 Schematic showing the geometry of our radiative transfer models.

The horizontal axis shows radial distance from the point of impact. The vertical axis marks the thickness of the jet. We model a portion of the jet as an annulus that moves outward radially. The width of this annulus also grows with time. BC, boundary condition; h, the thickness of the jet.

Extended Data Figure 4 Temperature time history for a jet consisting of 1-mm-diameter droplets created by a 1,000-km-diameter impactor.

The different coloured curves represent different computational cells, as indicated, where cell 1 is the innermost cell, which has a reflective boundary condition on one side, and cell 400 is the outermost cell, which radiates into a background at 300 K. The thick grey curve is the mass-averaged temperature, which we use as proxy for the average temperature of material in the plume. Panel a shows the temperature as a function of time, while b shows the cooling rate as a function of time.

Extended Data Figure 5 Chondrule density and collision rates.

a, The number density of chondrules is plotted as a function of time for 100-km-diameter and 1,000-km-diameter impactors. b, Relative collision velocity plotted as a function of time. c, Rate of collisions a single chondrule experiences plotted as a function of time. d, Cumulative number of impacts a chondrule experiences plotted as a function of time.

Extended Data Table 1 iSALE input parameters

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Johnson, B., Minton, D., Melosh, H. et al. Impact jetting as the origin of chondrules. Nature 517, 339–341 (2015).

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