2018 Nier Prize for Aki Takigawa

Abstract

The Nier Prize of the Meteoritical Society recognizes early career members of the Society whose achievements extend the frontiers of meteoritics. The 2019 Nier Prize winner, Dr. Aki Takigawa, is a true scientific pioneer, who has extended meteoritics across multiple disciplinary boundaries. She began her research as an undergraduate researcher in the lab of Dr. Shogo Tachibana at the University of Tokyo in 2006. Her first project was to develop a model to explain the abundances of short-lived radionuclides in the early solar system, which not only led to a first author publication (Takigawa et al. 2008), but remains in use today (Wasserburg et al. 2017). Notably, even in this first project, she made connections with researchers in a related field, in this case astrophysicists working on supernova nucleosynthesis, so that she could draw on cross-disciplinary knowledge to make progress on an important problem in meteoritics. For her second undergraduate project, Aki worked with both Dr. Tachibana and Dr. Hiroko Nagahara. She again considered important questions about early solar system materials that link astronomy and meteoritics, this time using the effects of shape anisotropy on the infrared spectra of forsterite crystals to constrain the temperature and gas conditions of circumstellar grain condensation, similar to the presolar grain building blocks of our solar system. To complete this project, she performed laboratory experiments on the anisotropic evaporation of forsterite, measured the optical properties of the heated grains, and applied the results to the interpretation of astronomical spectra (Takigawa et al. 2009). This work ultimately became the basis of her master’s thesis, and is an important scientific milestone. The results are among the first demonstrations that the features of individual mineral grains can be used to constrain their condensation histories, providing a potential link from presolar silicates found in meteorites to the conditions of the circumstellar envelopes in which they formed (Takigawa and Tachibana 2012). For her PhD thesis also under the guidance of Dr. Tachibana, Dr. Takigawa turned from silicates to oxides, focusing on corundum, which similar to forsterite, exhibits crystal anisotropy effects in infrared spectra that can be linked to condensation conditions. This anisotropy is important for interpreting the features of some O-rich Red Giant stars, because it can explain the relative intensities of the “13-micron” and “22-micron” features as being consistent with variations in the shape of corundum grains, and thus settled a debate among astronomers about which mineral to assign the 13-micron feature (Takigawa et al. 2015). At the end of her PhD, Dr. Takigawa was awarded a Japanese Society for the Promotion of Science Ikushi Prize, one of only 20 awarded across all academic fields for the entire country in 2012. This prestigious postdoctoral fellowship provided 3 years of support, including 18 months to be spent conducting research outside Japan. Most of these 18 months were spent in Washington, D.C., working jointly at the Carnegie Institution of Washington with Drs. Larry Nittler and Conel Alexander, and in my laboratory at the Naval Research Laboratory. During that time, Dr. Takigawa expanded her work on presolar Al2O3 to include oxygen isotope measurements with secondary ion mass spectrometry, transmission electron microscopy, cathodoluminescence, and electron backscatter diffraction (Takigawa et al. 2018). Working directly with Dr. Takigawa, I was greatly impressed with her drive to learn to make each of the measurements herself, and to build a comprehensive understanding of her samples that could be used to draw broad conclusions linking cosmochemistry, astromineralogy, materials science, and astronomy. Furthermore, during her postdoctoral fellowship, she also developed a proposal for time on the newly commissioned ALMA telescope, in order to directly measure circumstellar dust features in O-rich stars that could link to her modeling and laboratory studies. Despite the intense competition for telescope time, her proposal was selected and resulted in two published papers and one in press from her observations of silicate and alumina dust (Vlemmings et al. 2017; Takigawa et al. 2017; Tachibana et al. 2019). Now an assistant professor at the Hakubi Center for Advanced Research at Kyoto University, Dr. Takigawa is a co-investigator on the NASA CAESAR mission proposal, and has begun laboratory studies looking at the interactions between amorphous silicates and cometary ice analogs. Dr. Takigawa's unique synthesis of laboratory experiments, coordinated microanalysis of meteoritic materials, astronomical observations, and modeling make her an outstanding example of the interdisciplinary nature of meteoritical science. Her results have greatly improved our understanding of the formation of refractory dust in stars and the early solar system. She has worked as an international and intellectual ambassador for the meteoritic community. It is a great honor to present her as the 2019 Nier Prize awardee.