A Planetary Cold Case: Using JWST to Uncover the Catastrophic History of Neptune’s Moons

The rings and small inner moons of the giant planets are remnants of past events that shaped their planetary systems. Around Uranus and Neptune, these faint “ring-moons” have remained largely unexplored, and their origins have been uncertain for decades. In this talk, I will show how new observations from the James Webb Space Telescope (JWST) allow us to use their surfaces to reconstruct that history. Neptune’s inner moons do not resemble the primitive icy bodies we might expect. Instead, their compositions point to a more complex origin—one that suggests they are the remnants of much larger ocean worlds that were broken apart and later reassembled. This points to a catastrophic destruction of Neptune’s original satellite system, likely associated with the capture of its largest moon, Triton. By turning faint points of light into detailed compositional measurements, JWST is opening a new window into the outer solar system. These observations show how even the smallest and most distant moons can be used to reconstruct the events that shaped planetary systems billions of years ago. About the Speaker: Ryleigh Davis investigates how the surfaces of icy satellites record their formation conditions, radiation history, thermochemical evolution, and interior composition. During her PhD, she has studied icy moons across the Jovian, Uranian, and Neptunian systems. Her work has examined how radiation alters Europa, how deeper material is exposed on Callisto, and how Europa’s surface chemistry evolves over millions of years. Most recently, she has used JWST to show that Neptune’s small ring-moons are likely the broken remnants of ancient, water-rich worlds that once hosted subsurface oceans. About the Series: The Everhart Lecture Series is a forum encouraging interdisciplinary interaction among graduate students and faculty, the sharing of ideas about research developments, as well as a space to discuss controversies. Everhart Lectures allow for the recognition of individual Caltech student's exemplary presentation and research abilities. Each year, three graduate student are selected as Lecturers and receive a $2000 honorarium and recognition at graduation. This series is cohosted by the Caltech Graduate Office and Graduate Student Council This lecture was recorded on April 21st, 2026 Produced in association with Caltech Academic Media Technologies. ©2026 California Institute of Technology