Chondrule Survivability in the Solar Nebula

Abstract

The lifetime of millimeter-sized dust grains, such as chondrules, in the nominal solar nebula model is limited to ∼10 ^5 yr, due to an inward drift driven by gas drag. However, isotopic and petrological studies of primitive meteorites indicate a discrepancy of ≳10 ^6 yr between the formation time of chondrules and that of chondritic parent bodies. Therefore, chondrules should survive for ≳10 ^6 yr in the solar nebula against the inward drift without subsequent growth (i.e., planetesimal formation). Here, we investigate the conditions of the solar nebula that are suitable for the long lifetime of chondrule-sized dust particles. We take the turbulent strength, the radial pressure gradient force, and the disk metallicity of the solar nebula as free parameters. For 1 mm radius chondrules to survive and keep their size for ≳10 ^6 yr, the suitable condition is a weak turbulence ( α ∼ 10 ^−6 ), a flat radial profile ( η ≲ 10 ^−3 ), and a high metallicity ( Z ∼ 0.1). This condition is qualitatively consistent with the characteristics of protoplanetary disks suggested by recent observations. We eventually propose that planetesimal formation may be induced by disk evolution, e.g., the inside-out dispersal of the gas component due to the disk wind.

Keywords

• Chondrules
• Solar nebulae
• Planetesimals
• Planetary system formation
• Protoplanetary disks
• Carbonaceous chondrites