Chondrule Formation in Bow Shocks around Eccentric Planetary Embryos

Recent isotopic studies of Martian meteorites by Dauphas & Pourmond (2011) have established that large (~ 3000 km radius) planetary embryos existed in the solar nebula at the same time that chondrules - millimeter-sized igneous inclusions found in meteorites - were forming. We model the formation of chondrules by passage through bow shocks around such a planetary embryo on an eccentric orbit. We numerically model the hydrodynamics of the flow, and find that such large bodies retain an atmosphere, with Kelvin-Helmholtz instabilities allowing mixing of this atmosphere with the gas and particles flowing past the embryo. We calculate the trajectories of chondrules flowing past the body, and find that they are not accreted by the protoplanet, but may instead flow through volatiles outgassed from the planet's magma ocean. In contrast, chondrules are accreted onto smaller planetesimals. We calculate the thermal histories of chondrules passing through the bow shock. We find that peak temperatures and cooling rates are consistent with the formation of the dominant, porphyritic texture of most chondrules, assuming a modest enhancement above the likely solar nebula average value of chondrule densities (by a factor of 10), attributable to settling of chondrule precursors to the midplane of the disk or turbulent concentration. We calculate the rate at which a planetary embryo's eccentricity is damped and conclude that a single planetary embryo scattered into an eccentric orbit can, over ~ 10e5 years, produce ~ 10e24 g of chondrules. In principle, a small number (1-10) of eccentric planetary embryos can melt the observed mass of chondrules in a manner consistent with all known constraints.Comment: Accepted for publication in The Astrophysical Journa

On Silicon Group Elements Ejected by Supernovae Type Ia

There is compelling evidence that the peak brightness of a Type Ia supernova is affected by the electron fraction Ye at the time of the explosion. The electron fraction is set by the aboriginal composition of the white dwarf and the reactions that occur during the pre explosive convective burning. To date, determining the makeup of the white dwarf progenitor has relied on indirect proxies, such as the average metallicity of the host stellar population. In this paper, we present analytical calculations supporting the idea that the electron fraction of the progenitor systematically influences the nucleosynthesis of silicon group ejecta in Type Ia supernovae. In particular, we suggest the abundances generated in quasi nuclear statistical equilibrium are preserved during the subsequent freezeout. This allows one to potential recovery of Ye at explosion from the abundances recovered from an observed spectra. We show that measurement of 28Si, 32S, 40Ca, and 54Fe abundances can be used to construct Ye in the silicon rich regions of the supernovae. If these four abundances are determined exactly, they are sufficient to recover Ye to 6 percent. This is because these isotopes dominate the composition of silicon-rich material and iron rich material in quasi nuclear statistical equilibrium. Analytical analysis shows that the 28Si abundance is insensitive to Ye, the 32S abundance has a nearly linear trend with Ye, and the 40Ca abundance has a nearly quadratic trend with Ye. We verify these trends with post-processing of 1D models and show that these trends are reflected in model synthetic spectra.Comment: Submitted to the Ap

Penetration of supernova radioactivities in the solar system

We investigate the mechanism by which supernova ejecta can penetrate the solar system, and in particular, directly deposit live radioactivities on Earth. This study is motivated by the discovery of live undersea 60Fe from an event 2.8 Myr ago. The 60Fe signal is consistent with a nearby supernova explosion - occuring within a few tens of parsecs from the solar system. We present the first numerical hydrodynamic simulation of the interaction between a supernova blast and the solar wind, using the FLASH code. We find that the supernova ejecta can penetrate the solar system within the orbit of the Earth if the supernova explosion is within 10pe of the Sun. Since 10 pc marks the nominal "kill radius" within which biosphere damage is severe and could lead to species extinction events, the absence of paleontological evidence of such an extinction coeval with the 6°Fe deposition leads us to consider a more subtle mechanism of ejecta delivery. There exists evidence that the vast majority of heavy elements in a supernova remnant may be depleted onto grains, hence they can be considered as charged particles which do not participate in the plasma dynamics of the interaction of the supernova plasma and the solar wind. We examine the motion of these charged particles as they decouple from the supernova plasma and are influenced by the solar magnetic, radiation and gravitational field. We find that given the large incoming velocities of the charged grains, they suffer little or no deflection within the solar system. Consequently, the dust penetration to 1 AU has essentially 100% transmission probability, and the dust capture onto the Earth should have a geometric cross section.U of I Onlythesis/dissertatio