Towards a new history of the Ice Giant Satellite Systems

Uranus and Neptune host rich satellite systems, comprised of rings and associated ring-moons, large regular satellites with geology as photographed by Voyager 2, and numerous irregular satellites found on distant, inclined and eccentric orbits. The composition and dynamics of these moons hold the key to unlocking the early history of Uranus and Neptune, potentially resolving the origin of Uranus’s tilt, the initial formation locations of the two planets, and their subsequent migration through the nascent Kuiper belt. Our new data from the James Webb Space Telescope has, for the first time, revealed the compositions of the small satellites around the ice giants, as well as provided key measurements of the ratio of deuterium-to-hydrogen on the larger moons. Our findings include strong observational evidence for certain models of satellite formation around the ice giants and distinct formation mechanisms of the Uranian and Neptunian rings. Through additional dynamical simulations of the proto-Neptunian system and interpretation of the spectroscopic data, we present a story for what happened to Neptune’s missing regular satellites.