DIX Planetary Science Seminar

In the 80's, Voyager 2 discovered the abundant satellites and complex ring systems around the ice giants, with 13 small moons around Uranus, and 7 around Neptune. While their dynamics have been the subject of significant study, the limitations posed by their size and scattered light from their host planets have left the compositional picture of these bodies and their associated rings mostly unchanged between the 1989 Voyager 2 fly-by and present day. With JWST spectroscopic observations from our program 4645 on the small moons of Uranus and Neptune, new compositional information for these moons has been revealed. The inner moons of Uranus are nearly identical to water-rich Kuiper belt objects, while the Uranian rings show clear signs of CO2 ice with a notably smaller abundance of water. Surprisingly, Neptune's inner moons are entirely distinct from the Uranian ones, with Larissa, Galatea and the rings showing asteroid belt-like phyllosilicate material, very little CO2, and no signs of water-ice suggesting a composition that is strikingly different from all other observed small bodies of the outer solar system past Jupiter. Our talk will combine the emerging compositional picture with our best understanding of the dynamical evolution of these satellite systems to determine the origin of these moons and discuss the implication of their composition for the early history of the ice giants.