Using CAIs and Refractory Abundances in Meteorites to Constrain Our Protoplanetary Disk's Evolution
Steven Desch



I present a comprehensive model of the evolution of our Sun's protoplanetary disk, constructed to resolve the "CAI Storage" problem of meteoritics. The model predicts from first principles the abundances of calcium-rich, aluminum-rich inclusions (CAIs) and refractory elements (Ca, Al, Ti, etc.), as well as gas densities and temperatures, at various times and places in the solar nebula. The model is consistent with the constraints on time of accretion, CAI and refractory abundances, water content, etc., for all chondrites and all achondrites for which such information exists, including Earth and Mars. The consistency of the model strongly suggests the time and place of formation of each meteorite are knowable. We argue that formation of planetary embryos was very rapid, within < 2 Myr. We argue that dynamical scattering of meteorite parent bodies was limited. We argue that CI chondrites were inevitably depleted in refractory elements relative to the Sun, by about 9%. We present tentative evidence for such a depletion. Although CI chondrites do not chemically match the Sun exactly, the close match places severe constraints on the level of turbulence in the outer disk; based on the low inferred value of alpha ~ 10-5, we infer that hydrodynamic instabilities, not the magnetorotational instability, dominate turbulent transport there. We constrain alpha ~ 10-4 in the inner disk, arguing for a combination of hydrodynamic instabilities and magnetic disk winds. We argue that the disk interior to Jupiter was depleted by about 4 Myr, but the disk exterior to Jupiter persisted longer; the solar nebula therefore resembled a transition disk. In the process of explaining the abundances of CAIs and refractory elements in meteorites, our model predicts where and when each meteorite formed, and provides unique insights into protoplanetary disk evolution.