Research Interests: Formation and evolution of meteorites and planets; establishment of a time sequence of condensation and isolation of bodies from the solar nebula; study of correlated isotopic anomalies in meteorites and their connection with specific nucleosynthetic processes. The associated experimental techniques involve high precision mass spectrometry and ultra-clean sample processing and chemical separations. The research has centered on the creation of a fine resolution time scale for meteorites, the establishment of a lunar chronology, and the interpretation of these results in terms of a model for the accretion and the subsequent evolution of the moon as a planet. Major discoveries have included the identification of ²⁶Mg excesses and their correlation with short-lived, live ²⁶Al in the solar system, and the identification of correlated, general isotopic anomalies for many elements in early solar system condensates. The discoveries have provided strong evidence for the introduction of extremely short-lived nuclides in the early solar system and for the preservation of distinct, exotic nucleosynthetic products at the time of solar system formation. Research interests have addressed kinetic and equilibrium, mass dependent isotope fractionation effects on the Earth, on the surface of the Moon, in refractory condensates in the early solar system, and in systems of biological interest. The development of novel, sensitive analytical techniques has been critical. This has included the acquisition and development a high abundance sensitivity mass spectrometer (NSF, Instrumentation and Facilities, D. A. Papanastassiou, PI, Caltech). The instrument was redesigned to yield an abundance sensitivity of 3 x 10^-11 amu^-1, in the U-Th mass region, which approaches the levels for accelerator mass spectrometry. This instrumentation has been applied to U-Th series disequilibrium studies. Techniques for the thermal ionization of platinum group elements have been successfully developed (as negative oxide ions) and have resulted in improvements in sensitivity of factors of ~10⁴, and in key applications for the chronology of meteorites, terrestrial samples and the study of element transport in the environment. The techniques are being applied intensively to the Re-Os system in meteorites and lunar samples and to the study of platinum group elements (Ru, Mo, Re, Os, Ir). Starting in 1999, after appointment as the Mars Sample Handling Scientist, at the Jet Propulsion Laboratory, in anticipation of the 2003-2005 Mars Sample Return (MSR) missions, I designed, constructed, and operate new analytical facilities (sample preparation, analytical chemical separations, and mass spectrometry), with state-of-the-art instrumentation and capabilities. While the MSR missions have been postponed, these facilities are used for research on extraterrestrial materials, including for micro-samples from several on-going and planned missions. The most recent work, over the last two years has been development of thermal ionization techniques for isotopic analyses of Ni, once we tried and then decided that the universal use of ICP-MS by others is fraught with danger. Our recently published paper shows that reported effects by ICP-MS, by two other labs, in sulfides from iron meteorites are artifacts. In the period 2004-2005, I participated, as the Project Scientist, in a proposed mission to return samples from the South Pole-Aitken Basin, on the far side of the Moon, as highly recommended, for a New Frontiers mission, by the NRC Decadal Survey (2003), on which I also served. The proposal was selected for a Phase A, more extensive study, but was not the final selection. We have successfully resubmitted an updated South Pole-Aitken Basin proposal in the current New Frontiers competition and been selected and are currently working on a one year-long Phase A Concept Study for the mission. Final selection is expected in mid-2011. 

Version July 2010