Chondrule formation via impact jetting in the icy outer solar system

Abstract

Impact jetting during planetesimal collisions is a process that ejects small amounts of highly shocked material during the earliest stages of an impact. Jetting can produce melted and vaporized material during relatively low velocity collisions and has previously been presented as a mechanism for producing chondrules in the inner solar system during impacts between rocky planetesimals. However, chondrules are observed in both non‑carbonaceous and carbonaceous chondrites, which are thought to have formed in the inner and outer solar system, respectively. In this work, we use the iSALE2D hydrocode to investigate the viability of jetting for producing chondrules in the outer solar system, where ice-rich bodies begin to be incorporated into the planetesimal population. We create mixed material equations of state for ice mass fractions of 10–50% intimately combined with dunite to emulate the compositions of ice-rich outer solar system planetesimals. We account for collisions between a sphere and flat target at 2–7 km/s. Our results indicate that the presence of ice lowers the total mass of chondrule forming material jetting can produce, but a significant mass of chondrules is likely to form nonetheless even through collisions of bodies with relatively high ice concentrations. For example, for collisions at 4 km/s, pure dunite bodies create ~1% the mass of a 10-km-diameter projectile of chondrules, while bodies that include 50% ice by mass produce ~0.004% the mass of an impactor of chondrules. The presence of ice results in water vapor in the jet plume which may generate an oxidizing environment that favors the production of chondrules relatively enriched in 17O and 18O due to 16O-poor composition of water ice in the outer solar system.