Understanding mixing in the solar nebula, the nature of solar and presolar components present, and origin of terrestrial bodies including accretion and early differentiation, is fundamental to…

This is a $702,316.92 grant awarded by NASA to the University of Houston System to conduct research on the origins and early evolution of the solar system. The research aims to gain a better understanding of the mixing processes in the solar nebula, the nature of solar and presolar components, and the origin and early differentiation of terrestrial bodies. The grant will fund high-precision isotopic measurements of bulk chondrites using neodymium, samarium, and osmium to investigate these issues. The research is aligned with NASA's Emerging Worlds program and is intended to provide insights relevant to planning future solar system exploration missions. This award does not have a set-aside designation and is not associated with a larger contract vehicle.

Understanding mixing in the solar nebula, the nature of solar and presolar components present, and origin of terrestrial bodies including accretion and early differentiation, is fundamental to constraining the origin of our solar system and its early evolution. To examine these issues high precision ND, SM, and OS isotope measurements will be performed on a wide range of bulk chondrites. New refinements for measuring ND using the multistatic technique, results in improved external precisions of 3 to 5 PPM 2 sigma for 142ND 144ND. Measurements to date on chondrites largely used the static technique which has been shown to produce analytical artifacts such that internal precisions on 142ND 144ND of up to 5 to 8 PPM cannot be reproduced to better than 15 PPM from external reproducibility. Because the range of 142ND 144ND for all chondrites is 50 PPM with large overlaps between different chondrite groups, determining the types of materials that make up terrestrial planets, or resolving distinct differences in their nucleosynthetic components on the bulk sample scale cannot be achieved with the present dataset. We will measure bulk chondrites spanning a wide range of metamorphic conditions, to determine whether the variability in ND isotope abundances reflect acid resistant presolar grains with large s or r process isotope anomalies that were not accessed in the digestions. In addition, we will use the established alkali fusion technique on a subset of the samples to independently examine whether acid resistant pre solar grains are accessed in bulk sample digestions. Further, correlations between s process 142ND with r process dominated 145ND and 148ND are hinted at within the present database but with unconvincing, large scatter. The new, higher precision data proposed in this study will examine how much of this may reflect unmixing of s and r process ND in bulk chondrites. Complementary SM isotope data will be obtained on the same bulk chondrite fractions to investigate the previously observed effect on 144SM of p process deficiencies and how these impact production of 142ND from p process 146SM and potentially leverage observed variation on 142ND 144ND. High precision OS isotope measurements will be performed on bulk fractions of CV CK and ordinary chondrites spanning a wide range of metamorphic conditions. With these new bulk rock data we will examine the issue of nucleosynthetic component distribution and variability on the scale of chondrite parent bodies. Leaching residue combustion experiments will also be performed on unequilibrated ordinary chondrites. These complement studies on leaching residue combustion of carbonaceous and enstatite chondrites elsewhere and examines whether the s and r process components for OS are from the same stellar environments between the chondrite groups or whether multiple nucleosynthetic components were dispersed in the nebula heterogeneously. Neodymiun, SM, and OS are all refractory elements and hence provide complementary constraints on the distribution of nucleosynthetic isotope anomalies in these materials. This issue can only be examined by obtaining high precision isotope data from these early formed solar system samples. Hence this will lead to a better understanding of the earliest history of the solar system from the seeding of nucleosynthetic components, nebular condensation, accretion into terrestrial bodies and their early differentiation. This research is consistent with the scope of the emerging worlds program. Our new data will provide fresh insights into how the solar system formed and evolved from protoplanetary disk formation and evolution, chemical and physical processing of nebular dust, bulk properties of solar system bodies, formation, accretion, early thermal and chemical processing, and global differentiation of solar system bodies. Such data will also help in planning for missions that will target specific bodies in our solar system.