Uranus, the seventh planet from the Sun, is classified as an “ice giant,” a designation it shares with Neptune, due to its distinct internal composition. Located nearly 19 times farther from the Sun than Earth, Uranus presents a unique celestial body, notably recognized for its extreme axial tilt, causing it to orbit the Sun on its side.
The Gaseous Atmosphere
The outermost layer of Uranus is a deep gaseous atmosphere primarily composed of hydrogen (83%) and helium (15%), along with a notable amount of methane (2%). Methane absorbs red wavelengths of sunlight while reflecting blue and green light, which gives Uranus its characteristic blue-green hue.
The atmosphere is structured into distinct layers, including a troposphere and a stratosphere. The troposphere, the lowest and densest part, hosts complex cloud layers, where temperatures can plummet to a minimum of 49 Kelvin (-224.2 degrees Celsius). Above this, the stratosphere experiences an increase in temperature with altitude, influenced by the absorption of solar radiation by methane and other hydrocarbons.
The Icy Mantle
Beneath the planet’s atmosphere lies the icy mantle, which constitutes the bulk of Uranus’s mass, estimated at around 13.4 Earth masses. The term “ice” in this context refers not to frozen solids, but to a hot, dense, and electrically conductive fluid. This fluid is a mixture of water, ammonia, and methane.
This unique state of matter is often described as a “supercritical fluid” or a “water-ammonia ocean,” where the distinct liquid and gas phases cease to exist. The extreme conditions within this layer, with temperatures reaching up to 4,982 degrees Celsius (9,000 degrees Fahrenheit), enable molecules to ionize. Some models even suggest the possibility of methane molecules breaking down, with carbon atoms condensing into diamond crystals that could “rain” through this dense fluid.
The Rocky Core
At the very center of Uranus is a relatively small, dense core. This innermost region is believed to be composed of rocky materials, likely silicates and iron-nickel. Models suggest it has a mass of approximately 0.55 Earth masses and a radius less than 20% of Uranus’s overall radius.
The conditions within this core are extreme, with pressures reaching around 8 million bars (800 GPa) and temperatures estimated to be about 5000 Kelvin (4727 degrees Celsius). This immense pressure and heat indicate that the core is a hot, dense, and potentially partially molten or highly compressed solid.