Caltech Honors the Passing of Dimitri Papanastassiou (BS '65, PhD '70)
Dimitri Papanastassiou, a staff scientist in the Division of Geological and Planetary Sciences (GPS), passed away on March 9, aged 82, following an illness.
Papanastassiou was a seminal figure in cosmochemistry and planetary science, and contributed enormously to Caltech's leadership in these fields throughout his career. He is remembered by colleagues for his sharp mind, wit, and life story that was interwoven with Caltech and JPL's evolution from the 1960s to today.
Papanastassiou was raised in Athens, Greece, and first found his way to Caltech as an undergraduate student, graduating in physics in 1965. After conducting research in nuclear physics under the supervision of Thomas Lauritsen and Thomas Tombrello, he joined GPS as a graduate student working primarily with Gerald Wasserburg. Papanastassiou's thesis research was truly groundbreaking, including the construction and first uses of the world's first digital mass spectrometer, the Lunatic I. This instrument revolutionized the speed and precision of isotope ratio mass spectrometry, vastly expanding the scope of geochronology and other applications to geo- and cosmochemistry. Papanastassiou first used it to precisely date basaltic achondrite meteorites, simultaneously establishing the Sr isotope evolution of the circumsolar disk over its first 5 million years of life—helping shape the first so-called "rough cut" of our understanding of the solar system's early chemical evolution.
After receiving his PhD in 1970, Papanastassiou stayed on to work as a research scientist in Wasserburg's lab, known as the Lunatic Asylum, initially focused on applying the new tool of high-precision Sr isotope analysis to the chronology of the Moon using samples returned from the Apollo program. He received the F. W. Clarke Medal in recognition for both his thesis research and this subsequent work.
Papanastassiou went on to a career filled with field-leading innovations and discoveries, including Pb isotope dating of lunar rocks, which help establish the chronology of magmatism and cratering on the Moon, and pioneering the study of short-lived 26Al in the early solar system, which radically improved our understanding of its first several million years of evolution.
Papanastassiou joined JPL as a senior research scientist in 1999 and went on to run a research group in mass spectrometry and geochemistry, and to serve significant roles in the Mars Sample Handling program, various New Frontiers missions, and the National Research Council's Decadal Survey.
Papanastassiou remained a dedicated scholar and an involved member of the division to his last days. He was a visitor in GPS in the years following his retirement at JPL and a fixture in weekly reading groups in cosmochemistry and petrology.