Ice giants are a distinct type of planet that may be common beyond our own Solar System. Their relatively mixed combination of both light and heavy elements sets them apart from terrestrial planets (mostly heavy rock) and gas giants (mostly hydrogen and helium). The heavy elements in the ice giants are believed to be inherited from icy materials in the early Solar System, such as water, ammonia, and methane. Studying the structure and evolution of ice giant planets can therefore provide a unique window into the conditions of the early Solar System and can shed light on the general processes of planetary formation.

Our Solar System contains two ice giants, Uranus and Neptune, which were briefly explored by the Voyager 2 flybys in 1986 and 1989, respectively. Since then, studies of the ice giants have been limited to ground and space-based telescopes. A New Frontiers or Flagship-class mission to one of the ice giants could dramatically enhance our understanding of these planets by providing a means to study their interiors, atmospheres, magnetospheres, rings, and satellites with unprecedented detail and obtain measurements that are otherwise inaccessible from Earth. Such observations could be expected to yield new insights into the formation of the Solar System and the role that giant planets play in creating a habitable environment for Earth and potentially other Earth-like planets.

Gas Giants Too

Though the Solar System’s gas giants, Jupiter and Saturn, have enjoyed intensive exploration from dedicated spacecraft such as Galileo and Cassini, many questions remain about their origin and evolution. Atmospheric entry probes can provide crucial observations of giant planet atmospheres that are unable to be obtained from orbiting spacecraft. The Galileo mission deployed one such entry probe into Jupiter’s atmosphere and there is much interest in delivering a similar probe to Saturn. Studying the gas giants alongside the ice giants provides an important comparison of two very different types of giant planets.