Uranus

Uranus is the seventh planet from the Sun and has the third-largest diameter in our solar system. It was the first planet found with the aid of a telescope, discovered in 1781 by astronomer William Herschel, although he originally thought it was a comet or a star.

The Tilted Planet

Uranus is unique among the planets because it spins on its side. Its axis of rotation is tilted at an angle of 98 degrees, meaning its north and south poles lie where most other planets have their equators. This extreme tilt gives Uranus the most extreme seasons in the solar system. For nearly a quarter of each Uranian year (which lasts 84 Earth years), the sun shines directly over each pole, plunging the other half of the planet into a 21-year-long, dark winter.

An Ice Giant

Like its neighbor Neptune, Uranus is an “Ice Giant.” While it is composed mostly of hydrogen and helium like Jupiter and Saturn, it contains a higher proportion of “ices” such as water, ammonia, and methane. The methane in its upper atmosphere absorbs red light and reflects blue-green light, giving Uranus its distinctive cyan color.

Uranus is also the coldest planet in the solar system, with atmospheric temperatures dropping to -224°C (-371°F).

Rings and Moons

Uranus has 13 known rings. The inner rings are narrow and dark, while the outer rings are brightly colored. Unlike Saturn’s broad, bright rings, Uranus’s rings are likely young and short-lived.

The planet is orbited by 28 known moons, most of which are named after characters from the works of William Shakespeare and Alexander Pope. The five major moons are Miranda, Ariel, Umbriel, Titania, and Oberon. Miranda is particularly strange, with a chaotic landscape of canyons and cliffs that looks like a jigsaw puzzle put together incorrectly.

Exploration

Uranus has been visited by only one spacecraft: Voyager 2. In 1986, the probe flew past the planet, discovering 10 new moons, two new rings, and a magnetic field that is strangely tilted and offset from the planet’s center. No dedicated mission to Uranus is currently planned, but scientists are eager to return to unlock more of its secrets.