Selected on-going projects
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Isotopic clues to the evolution of the early solar system: The objective of this NASA Cosmochemistry-funded research is to further our understanding of the time scales and conditions attending the formation of the earliest rocks in the solar system. In this program we: 1) characterize the distribution of the short-lived isotope 26Al in calcium-aluminum-rich inclusions (CAIs) and in the early solar system as a whole; 2) constrain temperatures and pressures during CAI formation using silicon and magnesium isotope fractionation; 3) develop a new intra-mineral isotope geothermometer using carbon and oxygen isotope “clumping” in carbonates with application to aqueously altered carbonaceous chondrites; and 4) acquire high--precision measurements of oxygen isotope ratios in meteorites to further understand the origin of isotope anomalies in the solar system. The figure at right (Shahar and Young, 2007) shows laser ablation Mg and Si isotope ratio measurements across a CAI (R is radius of object). Comparisons with calculations (e.g., the curves shown here as a function of pressure) show that the object could have been molten for no more than about one month in the ealry solar system.
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Photochemistry in protoplanetary disks and the early solar system: In this NASA Origins-funded research program we are creating and identifying analogues for the early solar circumstellar disk through observations and calculations. We are observingCO isotopologue ratios using the NIRSPEC spectrometer on the Keck II telescope. We also process data already collected from other young stellar objects to extract the relevant isotopologue ratios. In parallel with these observations we construct reaction network models for N2 as well as CO photodissociation in disks and compare our results with the O and N isotopic compositions of constituents of primitive meteorites. The observations test predictions of the CO self-shielding model while the calculations provide new predictions. Shown at right is a curve of growth for four isotopologues of CO for IRAS 19110+1045 and resulting isotope ratios based on columm densities (Smith et al., 2007 LPSC). This target is a massive young stellar object. |
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Non-traditional stable isotope fractionation at high temperatures and pressures - an experimental approach: In this NSF-funded research program, a collaboration with Prof. Craig Manning and Prof. Edwin Schauble, both of UCLA, we test theoretical predictions ofFe and Mg isotope fractionation among mineral phases experimentally. Iron and Mg were selected as the focus of the study because of the importance of these rock-forming elements in many geochemical and biogeochemical cycles. The research is composed of three related facets: 1) prediction of the ways that Fe and Mg isotopes partition themselves between different minerals; 2) implementation of so-called three-isotope experiments designed to determine equilibrium isotope partitioning of isotopes among minerals of interest; and 3) high-precision measurement of stable isotope ratios in the experimental products. The experiments involve subjecting minerals of interest to high temperatures and pressures in a heated “piston cylinder” until isotopic equilibrium is achieved. The three isotope technique, by which samples are artificially enriched (“spiked”) with a particular isotope, permits quantitative assessment of the degree to which the experimental products achieved equilibrium. The figure at right shows early results on Fe isotope fractionation between magnetite and fayalite (Shahar et al., 2007, Goldschmidt Conference). |
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Astrobiology: Dr. Young is the Principle Investigator of the UCLA lead team of the NASA Astrobiolog Institute. He is also director of the IGPP Center for Astrobiology. Our astrobiology program at UCLA is wideranging. In our laboratory we focus on: 1) comparisons between protoplanets forming today and the record of ealry solar system history recorded in meteorites and 2) on the use of stable isotope ratios as biosignatures. The image at right shows results of our recent analysis of the oxygen isotopic composition of the troposphere compared with terrestrial rocks. The "big delta 17O" values reflects departures from equilibrium mass fractionation. The departure from equilibrium exhibited by tropospheric molecular oxygen matches that predicted for respiration. This result must now be squred with previous findings indicating that some of the departure from equilibrium fractionation is a result of transfer of a mass-independent fractionation effect downward from the stratosphere via CO2. |
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