An Unusual Orientation

Like a spinning top, planets rotate around an axis, usually in the same direction as they orbit (counterclockwise as viewed from the direction of Earth’s north pole). However, Uranus, its rings, and its moons are all tilted more than those of any other major body in the solar system. At a tilt (called “obliquity”) of 98°, Uranus’ axis points almost directly at the Sun during the solstices. This results in portions of Uranus and its moons being in shadow for dozens of Earth years at a time, leading to the most intense seasons in the solar system.

A Bevy of Moons

Uranus was discovered in 1787, and by 1851, its four largest moons—Oberon, Titania, Umbriel, and Ariel—had also been discovered. Uranus’ moons are named after characters in works of William Shakespeare and Alexander Pope. One of the most intriguing features of Uranus’ moons is found on Miranda, where the solar system’s tallest cliff­, Verona Rupes, can be found. This cliff­ is an impressive 12-mile drop! The inner moons of Uranus are smaller and have close orbits that nearly cross paths. This proximity raises the possibility of collisions in the future. Some of Uranus’ moons even orbit within the planet's rings. Unlike Saturn’s bright icy rings, Uranus' rings are dim and made of dark materials. They are likely much younger than Uranus itself, perhaps formed from recent collisions or breakups of the planet’s moons.

University of Arizona Legacy

In 1948, Gerard P. Kuiper, the founder of the University of Arizona’s Lunar and Planetary Laboratory, discovered Uranus’ fifth moon, Miranda. Miranda’s surface is one of the strangest in the solar system, covered in blocky terrains that barely fit together at all.


MASS: 8.9x10^25 kg 15 times Earth
DIAMETER: 50,724 km 4 times Earth
SURFACE GRAVITY: 8.9 m/s2 91% Earth Gravity
AVG. DISTANCE TO SUN: 2.9 billion km 19 au

Illustration of Uranus during a giant impact event on the left and at right the planet today with the orientation changed by 90 degrees.