University of Idaho Physicist Helps Confirm Uranus Ring Is Made of Water Ice
Moscow Researcher Contributes to Landmark Planetary Science Study
A University of Idaho physicist has helped confirm that one of Uranus’s faint outer rings is composed primarily of water ice — a finding that is changing how scientists understand the origins and evolution of the distant planet’s ring system.
Matthew Hedman, a physics professor at the U of I in Moscow, contributed to an international study by analyzing telescope data to determine the chemical makeup of two of Uranus’s outermost rings. The research draws on observations from three major observatories: the W. M. Keck Observatory, the Hubble Space Telescope, and NASA’s James Webb Space Telescope.
Together, the research team assembled the first complete spectral profile of the rings known as the μ (mu) and ν (nu) rings. What they found surprised them: the two rings are fundamentally different from one another in composition and almost certainly formed through separate processes.
Two Rings, Two Very Different Stories
The ν ring appears to be dark and rocky, resembling the material found in other rings and small moons that orbit close to Uranus. Scientists believe it was likely formed from debris scattered by collisions between larger objects — a process consistent with how many planetary rings are thought to form.
The μ ring tells a different story. It is composed of extremely fine particles of water ice and, unusually, appears blue in visible light — a characteristic rarely seen among planetary rings. Researchers traced the source of this icy material to a tiny moon called Mab, which measures only about 10 kilometers across and is itself largely made of ice.
Because Mab’s gravitational pull is so weak, icy grains dislodged from its surface by small impacts cannot return to the moon — but they also cannot escape Uranus’s gravitational field. Instead, they spread outward into orbit around the planet.
“That material doesn’t fall back to the moon, but it can’t escape Uranus either,” Hedman said. “So, it ends up forming a ring.”
While scientists had long suspected the μ ring might be icy in nature, earlier instruments lacked the capability to confirm it. The James Webb Space Telescope proved decisive, detecting a clear water-ice signature that ground-based observatories struggle to identify because Earth’s own atmosphere contains water vapor that interferes with such measurements.
Active System Raises New Questions
The discovery has opened as many questions as it has answered. Mab and the μ ring appear significantly icier than nearby moons and ring structures, which are composed of darker, rockier material. Why this particular region of the Uranus system differs so sharply from its surroundings remains under investigation.
“There’s something unusual happening in this part of the Uranus system that we’re still trying to understand,” Hedman said.
Further complicating the picture, some observations suggest the brightness of the μ ring fluctuates over a span of years, hinting that Mab may be periodically releasing fresh material into orbit. That possibility points to a ring system that is not static but actively evolving.
“There are hints the ring may be changing over time,” Hedman said. “If that’s the case, it means we’re watching an active system, not something frozen in place.”
To answer these questions, Hedman and fellow researchers have been awarded observing time on the James Webb Space Telescope to study Uranus annually over the next five years. The repeated observations are intended to track any changes in the ring’s structure and brightness and to refine models of how the system develops.
The project received $18,663 in NASA funding through the Space Telescope Science Institute, with the full amount drawn from federal sources. The study was led by researchers at the University of California, Berkeley, and has been published in the Journal of Geophysical Research: Planets.
What Comes Next
With dedicated James Webb observing sessions scheduled annually through the coming years, the University of Idaho’s role in outer-planet research is set to continue. Hedman’s work is part of a broader pattern of scientific inquiry at U of I, where faculty researchers are engaging on fronts ranging from deep-space physics to practical agricultural science. For more on U of I research initiatives, see the university’s recent work on advancing Idaho fruit production and farm needs explored at the World Ag Expo. For additional Idaho education and science coverage, visit Idaho News.