Uranus
The ice giant that rotates on its side
The Seventh Planet from the Sun
Overview
Uranus is the seventh planet from the Sun and the third-largest in our solar system. It is an ice giant, composed primarily of hydrogen, helium, and methane, with a small rocky core. The methane in its atmosphere gives Uranus its distinctive blue-green color.
Discovered in 1781 by William Herschel, Uranus was the first planet found with a telescope. It's named after the Greek god of the sky, Ouranos.
Uranus has the coldest planetary atmosphere in the Solar System, with a minimum temperature of -224°C (-371°F). It also has a complex ring system and 27 known moons, all named after characters from the works of William Shakespeare and Alexander Pope.
The Unique Axial Tilt
Uranus has the most extreme axial tilt of any planet in our solar system - 98 degrees. This means it essentially rotates on its side, with its poles lying where most other planets have their equators.
Extreme Seasons
This unusual orientation results in extreme seasonal variations. During summer at one pole, the Sun shines continuously for 42 years, while the other pole experiences a 42-year-long winter of complete darkness.
Temperature
Coldest planetary atmosphere
Axial Tilt
Rotates on its side
Moons
Known natural satellites
The cause of Uranus's extreme tilt is unknown, but the most widely accepted hypothesis is that during the formation of the Solar System, an Earth-sized protoplanet collided with Uranus, knocking it on its side.
The Moons of Uranus
Uranus has 27 known moons, all named after characters from the works of William Shakespeare and Alexander Pope. The five major moons are Miranda, Ariel, Umbriel, Titania, and Oberon.
Miranda
Features Verona Rupes, the tallest cliff in the solar system at 20 km (12 mi) high.
Ariel
The brightest moon with a young, complex surface of canyons and fault lines.
Umbriel
The darkest moon with an ancient, heavily cratered surface.
Titania
The largest moon with a system of enormous canyons and scarps.
Uranus Exploration
Only one spacecraft has visited Uranus - NASA's Voyager 2 in 1986. The flyby provided the first close-up images of the planet, its rings, and moons.
Voyager 2 Mission
Voyager 2 passed within 81,500 km (50,600 mi) of Uranus's cloud tops in January 1986. The spacecraft discovered 10 new moons, studied the planet's unique atmosphere, and examined its ring system.
Voyager 2 revealed that Uranus's magnetic field is tilted 59 degrees from its rotational axis and offset from the planet's center. The mission also discovered that Uranus radiates very little heat compared to other giant planets.
Fascinating Facts About Uranus
Ice Giant
Uranus is classified as an ice giant, with about 80% of its mass being a fluid mixture of water, methane, and ammonia ices.
Faint Rings
Uranus has 13 known rings, which are extremely dark and composed of water ice mixed with dark material.
Wind Speeds
Despite its cold temperatures, Uranus has winds that can reach up to 900 km/h (560 mph).
Long Year
One Uranian year lasts 84 Earth years, with each season lasting approximately 21 years.
Uranus's Scale
Uranus is the third-largest planet in our solar system, but its unique characteristics set it apart:
Diameter: 50,724 km
Volume: 63 Earths could fit inside Uranus
Despite being larger than Neptune, Uranus has less mass, making it the second least dense planet after Saturn. Its blue-green color comes from methane in its atmosphere, which absorbs red light and reflects blue-green light.
Future Exploration
Several missions to Uranus have been proposed to follow up on the discoveries made by Voyager 2. These missions would study the planet's atmosphere, interior structure, magnetic field, rings, and moons in greater detail.
Potential missions include orbiters that would spend years studying the Uranian system, and probes that would descend into the planet's atmosphere. These missions could help us understand the formation and evolution of ice giants, which are now known to be common around other stars.
Studying Uranus could provide crucial insights into planetary formation and the history of our solar system, as well as expand our understanding of exoplanets of similar size and composition.