Forming the Noncarbonaceous Chondrite Parent Bodies in the Presence of the Jupiter Barrier

Abstract Meteorites can be divided into two groups—noncarbonaceous chondrite like (NC) and carbonaceous chondrite like (CC)—with distinct stable-isotope compositions. Parent bodies of NC and CC meteorites have overlapping formation ages. This suggests they formed in different regions of the solar nebula, separated by a dynamical barrier that prevented small solids (pebbles) from mixing. NC chondrites would have formed 1–2 Myr after the barrier appeared. Pebbles in the NC region moved inwards due to radial drift and the inward flow of gas. Outward turbulent diffusion partly offset inward advection, but pebble lifetimes were finite. Survival of enough pebbles to form the NC chondrites requires that the gas flow was mainly confined to the surface layers of the solar nebula, and that pebbles remained near the midplane. This sets an upper limit on the strength of turbulence. If pebble size was set by mutual collision speeds, then turbulence strength has a lower limit as well, set by the maximum acceptable drift rate. For a barrier at 5 au from the Sun, the turbulence parameter α should lie between 2 × 10 −5 and 10 −3 . The maximum collision speed <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>v</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">max</mml:mi> </mml:mrow> </mml:msub> </mml:math> should not exceed 0.8 m s −1 . If the pebble radius remained fixed, it should not exceed 2 mm, which is a few times larger than the mass peak seen in NC chondrules.