Chondrule survivability in the solar nebula

The lifetime of mm size dust grains, such as chondrules, in the nominal solar nebula model is limited to $\sim 10^{5}$ yr due to an inward drift driven by gas drag. However, isotopic and petrological studies on primitive meteorites indicate a discrepancy of $\gtrsim 10^{6}$ yr between the formation time of chondrules and that of chondritic parent bodies. Therefore chondrules should survive for $\gtrsim 10^{6}$ 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 $\gtrsim 10^{6}$ yr, the suitable condition is a weak turbulence ($\alpha \sim 10^{-6}$), a flat radial profile ($\eta \lesssim 10^{-3}$), and a high metallicity ($Z\sim 0.1$). 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 the disk evolution, e.g., the inside-out dispersal of the gas component due to the disk wind.