Abstract

We attempt to estimate the size range of particles that are ejected from a protostellar accretion disk by a protostellar jet. An n-body code is used to determine the subsequent motion of the ejected particles, where the particles are subject to two forces: the gravitational attraction from the protostar and the gas drag from the halo gas of the accretion disk. It is highly probable that a protosolar jet existed at the very beginning of the Solar System. Such a jet may have influenced the chemical structure of the solar nebula by recycling heated material back into the nebula. Protostellar jets eject a considerable amount of mass (10 ^-3-10 ^-1M ⊙) over a long lifetime (10 ⁶-10 ⁷ years), so some evidence of a protosolar jet may still be detectable in the most primitive surviving objects of the solar nebula, chondritic meteorites. Protostellar jets appear to be formed from the innermost regions (≤0.1 AUえーゆー) of protostellar accretion disks. At such close proximity to the protostar, one would expect any nongaseous disk material to be in a molten or semimolten state. We have made an analysis of the expected droplet size that can be ejected by the jet flow and find that the droplet radius is <1 cm. The gas densities and speeds required to eject such large objects from the close environs of a protostar have been shown (in previous studies) to be well within theoretically expected and observationally confirmed ranges. Our calculations, however, suggest that ejection of such large objects requires the scale height of the inner accretion disk to be compressed by two orders of magnitude relative to the usual isothermal scale height. Using a parameterized solution to an outflow jet, we find that 0.1-cm-sized projectiles can become decoupled from the outflow at distances in excess of 0.01 AUえーゆー above the midplane of the accretion disk. The subsequent motion of these objects is shown to be a linear path across the face of the accretion disk. If these ejected particles pass through a sufficiently large section of the accretion disk's upper atmosphere, then their speed will become smaller than the escape velocity, and the particles will settle back to the accretion disk. It is shown that the denser and larger a particle is, the further it can travel through the gas halo of an accretion disk, thereby producing density-dependent size-sorting of particles. Since chondrules have radii (≤1 cm) that are inversely proportional to their density, it is suggested that chondrules are ablation droplets produced by a protostellar jet.