Ice Giants: Uranus and Neptune

The Ice Giants, Uranus and Neptune, are among the least explored worlds in the Solar System, and yet they represent a planetary class that may be commonplace in the Galaxy. Their atmospheres represent two extremes: Uranus&s;s is forced by unusual solar heating due to its axial tilt, and Neptune&s;s climate is driven by a powerful source of internal energy. Like the Gas Giants, the atmospheres of the Ice Giants are primarily hydrogen and helium. On Uranus, methane scatters sunlight producing a distinct blue color. Unlike Jupiter and Saturn, Uranus&s;s equatorial winds move in retrograde. Uranus may have a high-pressure carbon shell thicker than Jupiter&s;s or Saturn&s;s. With almost the same size and mass as Uranus, Neptune has the same compositional characteristics as the other Jovian Planets. Neptune&s;s rings are as meager as Uranus&s;s. It has nine sets, the outermost of which consists of partial ring arcs concentrated into clumps, probably influenced by the gravity of small imbedded moons.