Nebular shock waves generated by planetesimals passing through Jovian resonances: Possible sites for chondrule formation

Abstract

The primordial asteroid belt contained at least several hundred and possibly as many as 10,000 bodies with diameters of 1000 km or larger. Following the formation of Jupiter, nebular gas drag combined with passage of such bodies through Jovian resonances produced high eccentricities (e = 0.3-0.5), low inclinations (i < 0.5 degrees), and, therefore, high velocities (3-10 km/s) for resonant bodies relative to both nebular gas and non-resonant planetesimals. These high velocities would have produced shock waves in the nebular gas through two mechanisms. First, bow shocks would be produced by supersonic motion of resonant bodies relative to the nebula. Second, high-velocity collisions of resonant bodies with non-resonant bodies would have generated impact vapor plume shocks near the collision sites. Both types of shocks would be sufficient to melt chondrule precursors in the nebula, and both are consistent with isotopic evidence for a time delay of ~1-1.5 Myr between the formation of CAIs and most chondrules. Here initial simulations are first reported of impact shock wave generation in the nebula and of the local nebular volumes that would be processed by these shocks as a function of impactor size and relative velocity. Second, the approximate maximum chondrule mass production is estimated for both bow shocks and impact-generated shocks assuming a simplified planetesimal population and a rate of inward migration into resonances consistent with previous simulations. Based on these initial first-order calculations, impact-generated shocks can explain only a small fraction of the minimum likely mass of chondrules in the primordial asteroid belt (~10^24-10^25 g). However, bow shocks are potentially a more efficient source of chondrule production and can explain up to 10-100 times the estimated minimum chondrule mass.