Uranus
The coldest planet in the Solar System, and the first of the ice giants. Learn more about the bulls-eye planet here!
Formation
The formation of the ice giants is controversial and shrouded in mystery. Models suggest that Uranus was able to form by gathering a core of about a few solar masses. Unlike the gas giants, the ice giants never reached the critical mass required to gather large amounts of gas and stopped becoming larger. Another model suggests that Uranus formed close to the Sun and migrated out towards the present-day position.
Composition
The composition of Uranus is thought to be similar to the composition of the young Solar nebula. Around 75% of the atmosphere is composed of hydrogen, 24% helium, and 1% other elements, mostly dominated by methane. Not much is known about the interior composition of Uranus, though the mass of the planet suggests that the composition is similar to the atmosphere with certain elements and compounds, besides hydrogen and helium, more unknown.
Structure
An ice giant such as Uranus has structural layers different from the ice giants. Suspected to have a rocky core surrounded by a mantle of ices, not much is known about this part of the planet. The icy mantle is surrounded by the lower atmosphere, which has a large composition of methane, ammonia, and water ice. Finally, the upper atmosphere of Uranus completes the structure.
Atmosphere
The atmosphere of Uranus is made up of mostly hydrogen, with methane clouds dominating. Unlike the gas giants, Uranus does not have prominent bands of weather across the whole planet. Due to the extreme axial tilt of the planet, only one hemisphere receives sunlight for decades at a time. This causes bands to form on the side which has been receiving sunlight, while the other side is featureless.
Magnetic Field
The magnetic field of Uranus is peculiar. Unlike the other planets, the field does not originate from the planet’s core. Instead, the magnetic field is offset from the center by about one-third of the planet’s radius. This causes a highly unsymmetrical magnetic field and the Solar wind reaches the Uranian surface once a Uranian day. The cause of this peculiar magnetic field is thought to be either the reason behind why Uranus has an extreme axial tilt, possibly by a collision long ago, or by electrodynamics within the mantle producing a strange magnetic field.
Planetary Rings
Uranus has 13 planetary rings, with the epsilon ring being the brightest. The planetary rings of Uranus are dark and made of material that is probably water ice and carbon material. The rings of Uranus are narrow, with only a couple of the rings contained by shepherd moons. The reason why some of the planetary rings are thin, but have no shepherd moons, is unknown.
Satellites
Voyager 2 is the only satellite to visit Uranus. Discovering two new rings and ten new moons, the Voyager 2 flyby was able to image the system in detail. Voyager 2 also was able to study the magnetic field, discovering the strange configuration that the magnetic field exhibits. While Voyager 2 was able to glean information from the flyby, a dedicated orbiter is required to learn more about Uranus.