Hiroshi Takeda, an Emeritus Professor at the University of Tokyo, passed away on September 11, 2023, just one day short of his 89th birthday. Globally recognized for his groundbreaking work in mineralogy and crystallography for solid Earth and planetary material science, Takeda's accolades are numerous. Notably, he received the Leonard Medal from the society in 2010. Back home in Japan, he was honored with the Special Award during the Japan Mineralogical Society's 50th anniversary in 2002 and the esteemed 26th Manjiro Watanabe Award in 2009. His legacy was further cemented when a new Ca borate mineral was named "Takedaite" in his honor in 1995, and asteroid (4965) was dubbed "Takeda" in 2001. For his invaluable contributions to lunar sample studies and his research on meteorites for NASA, he was awarded NASA’s Public Service Medal in 1996.
After earning his PhD from the University of Tokyo, Takeda moved to the United States in 1962. At Johns Hopkins University and the U.S. Geological Survey, he embarked on extensive studies into minerals like micas and pyroxenes. Interestingly, this period coincided with the landmark Apollo 11 lunar mission, which had a profound influence on Takeda's research trajectory. Given the infancy of this field in Japan at the time, his forward-thinking approach was truly visionary. From 1970 to 1972, he worked at NASA's Manned Spaceflight Center, studying lunar samples and meteorites, building lasting professional relationships. A cornerstone of Takeda's research was understanding how differentiated meteorites and lunar rocks formed and cooled. His detailed analysis revealed how the earliest materials in our Solar System evolved. He was the mind behind the term "evolution of solid planetary materials". After his time with NASA, Takeda returned to the University of Tokyo around the time when numerous Antarctic meteorites were discovered in the Yamato Mountains. He was instrumental in shaping research around these Antarctic meteorites, ensuring they were accessible for global study.
Among Takeda's research achievements, one of the most significant is his work on HED (Howardite-Eucrite-Diogenite) meteorites. Through this research, he demonstrated that protoplanets, similar to asteroid Vesta, underwent differentiation, resulting in a layered crustal structure. Also, it was Takeda who proposed the now-commonly used term "HED” meteorites. By examining newly discovered Antarctic samples, he advanced the comparative study of the differentiation and cooling processes of pyroxenes in HED meteorites. He also suggested a grading system for thermal metamorphism of eucrites, ranging from 1 to 6, based on the differences in their pyroxene mineralogy. This index is still widely used today. Takeda's research on HED meteorites highlighted the differences between the crusts of the Moon and these meteorites. While HED meteorites showcase a relatively simple differentiation process of a protoplanet, the Moon's primordial crust underwent a more complex differentiation due to collisions.
From the 1980s onwards, Takeda conducted detailed mineralogical analyses of ureilites, suggesting that this group of meteorites might have originated from a body that underwent catastrophic disruption during the early stages of primordial planet formation. At that time, the prevailing theory posited that ureilites originated from a significantly differentiated body. In contrast, Takeda proposed, based on the chemical composition and crystal structure of pyroxenes and olivines, that ureilites formed from the removal of low-temperature melt. This model is now widely accepted as an explanation for the petrogenesis of ureilites. Subsequently, Takeda applied a similar model to primitive achondrites, highlighting the importance of localized movement of partial melt at low temperatures in the material evolution of the solar system's primitive substances.
Takeda's contributions were not limited to the analysis of solid planetary materials. He not only advanced research on meteorites but also extensively collaborated with the National Space Development Agency of Japan (NASDA) to guide the direction of Japan's future lunar exploration. He played a central role in the SELENE (Kaguya) lunar exploration program of the Japan Aerospace Exploration Agency (JAXA). During Kaguya's lunar exploration, many lunar meteorites were discovered in deserts in Africa and the Middle East, among which Takeda identified meteorites that had originated from the Moon's far side. Based on mineralogical and petrological studies of these meteorites and Kaguya's data on the far side of the Moon, he proposed a new model for the formation of the lunar crust, which garnered international attention.
In addition to his academic contributions, Takeda was active in academic organizations both in Japan and abroad, continuously showcasing the strength of Japan's solid planetary material science on the international stage. For our society, he was active in roles such as a council member (1981-1986) and associate editor of Meteoritics (1988-1992). He was a chair for the Cosmic Mineralogy Working Group of International Mineralogical Association (IMA) (1991-1995). In Japan, he served as vice-president during the founding of the Japanese Society for Planetary Science (1992-1996) and as a councilor of the Japan Mineralogical Society for two decades.
Takeda highlighted how foundational research in mineralogy and crystallography contributes to planetary science and meteoritics. He authored books on "Fundamental Techniques and Applications in Solid Planetary Material Science (in Japnaese)" and "Evolution of Solid Planetary Materials (in Japanese)". In addition to his research, he was dedicated to education, nurturing many talented students who now occupy pivotal positions in universities, national research institutes, and private-sector research organizations.
At the 1985 annual meeting of the Meteoritical Society in Bordeaux, France, Takeda became attracted to wine. He began pursuing the relationship between the nature of soils and the quality of wine. His contributions to the topic led to his being named “sommelier d'honneur” by the Japan Sommelier Association in 2005.
Takeda was an inspiring mentor to his students seeking to advance their careers by introducing them to international colleagues at important meetings such as MetSoc annual meetings, LPSC and NIPR Symposium. In remembrance of his devoted service to science and colleagues, we express heartfelt gratitude for his contributions and confidence in his peaceful rest.
Larry E. Nyquist