Caltech Mourns the Passing of Planetary Scientist Yuk Yung

Yuk L. Yung, professor of planetary science and Jet Propulsion Laboratory (JPL) senior research scientist, passed away on March 16, 2026 after a brief illness. He was 79.

"Yuk loved Caltech, JPL, and his many close colleagues, and it showed in the many ways he shared his scientific passion and understanding of this life we lead together," says John Eiler, the Robert P. Sharp Professor of Geology and Geochemistry and Ted and Ginger Jenkins Leadership Chair of the Division of Geological and Planetary Sciences. "He was delighted with exploring and understanding the natural world while also working selflessly to enhance everyone else's delight in it, through his teaching, mentoring or casual conversations. Yuk helped and encouraged me in all sorts of small, gentle ways; offering uplifting thoughts or a moment of scholarly collegiality in the midst of all the chaos of daily duties. I greatly appreciated him and will miss him very much."

Yung's research spanned planetary atmospheres, atmospheric chemistry and radiation, planetary evolution, astrobiology, and global climate change, with a strong emphasis on connecting theoretical models to observations. His work led to pioneering insights into the current properties and behavior of solar-system atmospheres, as well as their historical evolution. His models of the chemistry of planetary atmospheres have been widely used to interpret the results from spacecraft missions.

Yung's long career included many seminal contributions, such as the recognition of the roles trace gases such as methane and nitrous oxide play in driving the greenhouse effect and anthropogenic global warming on Earth; the first comprehensive explanation of the chemistry of the organic-rich atmosphere of Saturn's moon, Titan; and the proposal that atmospheric photochemistry on the early Earth created abundant formaldehyde—a key precursor in the chemistry that enabled life.

In awarding Yung the 2015 Gerard P. Kuiper Prize, the Division of Planetary Sciences of the American Astronomical Society described Yung as "a founding father of planetary atmospheric chemistry and one of the most influential researchers in the field."

In addition to his professorial roles on campus, Yung served as a coinvestigator on the Ultraviolet Imaging Spectrograph (UVIS) Experiment on NASA's Cassini mission to Saturn, and a team member on the NASA Orbital Carbon Observatory 2 (OCO-2) Mission to map CO2 concentrations on Earth. Yung was also involved with the New Horizons mission to Pluto and the Kuiper Belt and the European Space Agency's Venus Express.

Yung was born on August 23, 1946, and earned a BS in engineering physics from UC Berkeley in 1969 and a PhD in physics from Harvard University in 1974. After serving as a research fellow and lecturer in atmospheric sciences at Harvard from 1974–77, he joined the Caltech faculty as an assistant professor of planetary science, receiving tenure in 1986. In 2011, he was named the Smits Family Professor. He became a JPL research scientist in 2014 and a senior research scientist in 2015.

Yung was elected a fellow of several scientific societies, including the American Geophysical Union (2003), the American Association for the Advancement of Science (2005), the Academia Sinica (2010), and the American Academy of Arts and Sciences (2011). He was honored with a NASA Exceptional Scientific Achievement Medal in 2004 and an Achievement Award from the Chinese-American Engineers and Scientists Association of Southern California in 2014. In 2015, the American Astronomical Society named Asteroid 19370 for Yung.

Yung's award citation for his 2015 Kuiper Prize noted: "Key to his success has been his enormous enthusiasm and inexhaustible tenacity for research, his very broad knowledge in many fields, his creative and innovative approach to problems in planetary atmospheres. His continual flow of new ideas, his breadth of knowledge, and his big-picture understanding of planetary science have inspired generations of students and postdocs over the past four decades."

In 2025, Yung was recognized as the recipient of the 2025 Poynting Award on Radiative Transfer, a particularly significant honor for its association with John Henry Poynting—a founding figure in the modern understanding of electrical fields and their forces and an exemplar for Yung throughout his career.

Over his career, Yung published over 400 publications and mentored dozens of graduate students and postdoctoral scholars who have gone on to careers in academia, industry, and government laboratories around the world.

He is survived by his wife Shau M. Yung, daughter Wing Y. Taketa (BS '07), and son Wing Chi Yung.