Astronomers have discovered that the outermost rings of Uranus, known as the mu and nu rings, differ markedly in composition despite their similar appearance. The mu ring consists of tiny ice grains, likely from a small icy moon, while the nu ring is rich in dust and organic molecules. These findings, drawn from two decades of telescope observations, raise new questions about the planet's dynamic ring system.
Researchers led by Imke de Pater at the University of California, Berkeley analyzed nearly 20 years of data from the Keck Telescope in Hawai’i, the Hubble Space Telescope, and the James Webb Space Telescope. This effort revealed that the mu ring, the outermost of Uranus's faint rings, appears blue and is composed of tiny ice grains. In contrast, the adjacent nu ring looks red, containing dust and complex organic molecules called tholins, according to the study published in The Journal of Geophysical Research: Planets (DOI: 10.1029/2025JE009404).