Ernst K. Zinner

Research Professor (also Department of Physics)
Ph.D. Washington University, 1972

Astrophysics and Space Physics

Scanning electron micrograph of a presolar graphite spherule from the Murchison meteorite. The isotopic composition of this unusually large grain, which has an onion-like external morphology, indicates a supernova origin. Scale bar is 1 µm. Photo courtesy of S. Amari.

The research interests of Professor Zinner are centered on the study of primitive meteorites and interplanetary dust, particularly their record of the nucleosynthesis of elements in stars and the formation of the solar system. The most important record is contained in the anomalous isotopic compositions of refractory phases from primitive meteorites. These phases are of two kinds: 1) solids that formed in the solar system, but that inherited isotopic anomalies from precursors that were not completely homogenized, and 2) presolar grains that condensed in the expanding atmospheres and the explosions of stars and survived the formation of the solar system. In the study of these objects, ion microprobe analysis has played an exceedingly important role. The reason is that this technique allows the chemical and isotopic analysis of microscopic samples, and that the largest isotopic anomalies (i.e., isotopic ratios different from average terrestrial values) are carried by small mineral grains.
An example of the first kind is hibonite (CaAl₁₂O₁₉). Small hibonite-bearing inclusions have large isotopic anomalies in Ca and Ti. Although the distribution of trace elements in the hibonite indicates a solar system origin, the dominant isotopic signature (excesses in ⁴⁸Ca and ⁵⁰Ti) gives evidence for a nucleosynthetic component produced in the cores of massive stars during supernova explosions. Another type of isotopic record present in certain small meteoritic phases are excesses of isotopes due to the decay of short-lived, now extinct radionuclides. Examples for the latter are ²⁶Al (half life 7.2 x 10⁵ y) and ⁵³Mn (half life 3.5 x 10⁶ y). Ion probe studies of their daughter products (²⁶Mg and ⁵³Cr, respectively) can provide information on the distribution of the parent nuclides and on the history of processes in the early solar system on a time scale of less than a million years.

Nitrogen and carbon isotopic ratios measured by secondary ion mass spectrometry in individual presolar SiC grains. Six different classes can be distinguished on the basis of the C, N, and Si isotopic ratios. The abundances of the different classes among all meteoritic SiC are indicated. Grains of different classes originated from different types of stars. For example, mainstream grains are believed to have originated from Asymptotic Giant Branch stars whereas grains of type X come from supernovae. Note that the numbers of grains of different types in the plot do not correspond to their observed frequencies but that grains from rare classes have been selectively located by ion imaging and are thus over-represented in the graph.

In recent years, Professor Zinner and co-workers have identified several types of presolar dust in meteorites: silicon carbide, graphite, corundum, spinel, silicon nitride, and silicates. The first two types carry exotic noble gases and all grains are characterized by isotopic compositions of the major (C, O, Si), minor, and trace elements (N, Mg, Ca, Ti, Ba, Nd) that are completely different from those found in the solar system, indicating a presolar origin for the dust grains in the cooling gas of stellar atmospheres. The ion microprobe and especially the NanoSIMS permits isotopic measurements in individual dust grains down to 0.1 µm in size. This in turn helps in identifying specific stellar sources for silicon carbide and graphite. Red giants, Wolf Rayet stars, novae, and supernovae are possible production sites of carbonaceous dust grains. Silicates, oxides, and most of the SiC grains are believed to come from red giant stars, stars that lose a large part of their atmosphere at the end of their lives, silicates and oxides from oxygen-rich stars, SiC from carbon stars. On the other hand, low density graphite grains, a rare subtype of SiC, and silicon nitride apparently come from supernovae, massive stars that explode after the exhaustion of the nuclear fuel in their interior. The presence of isotopes that are produced in very different layers of supernovae in the same grains are evidence for turbulent mixing during supernova explosions.

Zinner has been elected Fellow of the Meteoritical Society and the American Physical Society, Geochemistry Fellow of the Geochemical Society and the European Association for Geochemistry and corresponding member of the Austrian Academy of Sciences. He has received the Antarctic Service Medal of the National Science Foundation, the J Lawrence Smith Medal of the National Academy of Sciences and the Leonard Medal of the Meteoritical Society. He has twice served on NASA's Lunar and Planetary Geology Review Panel and for ten years was associate editor of Meteoritics & Planetary Science.

Zinner, E. (2003) An isotopic view of the early solar system. Science, 300, 265-267.

Zinner E., Amari S., Guinness R., Nguyen A., Stadermann F. J., Walker R. M. and Lewis R. S. (2003) Presolar spinel grains from the Murray and Murchison carbonaceous chondrites. Geochim. Cosmochim. Acta, 67, 5083-5095.

Zinner E. (2004) Presolar grains. In Treatise on Geochemistry, Vol. 1 (eds. K. K. Turekian and H. D. Holland; vol. ed. A. M. Davis), Elsevier, Oxford and San Diego, p. 17-39.

Nguyen A. and Zinner E. (2004) Discovery of ancient silicate stardust in a meteorite. Science, 303, 1496-1499.

José J., Hernanz M., Amari S., Lodders K. and Zinner E. (2004) The imprint of nova nucleosynthesis in presolar grains. Astrophys. J., 612, 414-428.

Zinner E., Nittler L. R., Hoppe P., Gallino R., Straniero O., and Alexander C. O’D. (2005) Oxygen and magnesium isotopic ratios of presolar spinel grains. Geochim. Cosmochim. Acta, 69, 4149-4165.

Meyer B. S. and Zinner E. (2006) Nucleosynthesis. In Meteorites and the Early Solar System II (eds. D. Lauretta, L. A. Leshin, and H. Y. McSween Jr.) Univ. of Arizona Press. p. 69-108.

Zinner E., Nittler L. R., Gallino R., Karakas A. I., Lugaro M., Straniero O. and Lattanzio J. C. (2006) Silicon and carbon isotopic ratios in AGB stars: SiC grain data, models, and the Galactic evolution of the Si isotopes, Astrophys. J., 650, 350-373.

Zinner E., Nittler L. R., Alexander C. O’D. and Gallino R. (2006) The study of radioisotopes in presolar dust grains. In Proc. Astronomy with Radioactivities V (eds. D. Hartmann, R. Diehl, N. Prantzos and E. Zinner). New Astronomy Reviews, 50,574-577.

Nguyen A. N., Stadermann F. J., Zinner E., Stroud R. M., Alexander C. M. O’D. and Nittler L. R. (2007) Characterization of presolar silicate and oxide grains in primitive carbonaceous chondrites. Astrophys. J., 656, 1223-1240.

See also Department Publications and http://presolar.wustl.edu/people/zinner.html

314-935-6240	ekz@wustl.edu
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