1.8 billion miles from the Sun, the first of the ice giants, blue Uranus orbits, encircled by faint rings. Unlike every other planet in the solar system, Uranus rotates sideways, like a wheel rolling along its orbit.
Uranus is named after the Greek God of the sky, and it is the only planet named directly after a character from Greek mythology. Originally, Herschel named the planet Georgium Sidus, which means “George’s Star,” after King George III. However, this decision was unpopular, and the planet was eventually named Uranus by Johan Bode. In Thai, the planet is sometimes known as Dao Maritayu, which references the Sanskrit word meaning “death.” In Hawaiian, it is known as Hele’ekala, after the discoverer, Herschel, and in Maori, it is known as Wherangi.
Out of its 27 moons, Uranus’s five major moons are Miranda, Ariel, Umbriel, Titania, and Oberon. These moons are named after characters from the works of Shakespeare and Alexander Pope. The moons are made of primarily of an even split between ice and rock.
The rings of Uranus are not so visible as the rings of Saturn. They are made of very small, dark particles. The ring system is so faint that, though it was hypothesized as early as 1789, its existence was not confirmed until 1977.
Unlike the gas giants Jupiter and Saturn, Uranus, and its sister planet Neptune, are known as ice giants. This means that they are primarily composed of elements such as water, ammonia, and methane. In turn, this unique chemical composition results in significantly different environments and colors when compared to the warm yellows and oranges of the gas giants.
Uranus gets its light blue color from methane gas in its atmosphere, which absorbs red light and reflects blue. However, most of the planet’s atmosphere consists of the elements, hydrogen and helium.
Its low density reveals that Uranus largely consists of water, ammonia, and methane ices—hence its categorization as an ice giant. Under the soft blue atmosphere, there is a water-ammonia ocean of high conductivity. And further below the mantle, crushing pressure breaks up methane molecules, condensing carbon atoms into crystals. This means that, on Uranus, it literally rains diamonds.
Compared to the gas giants, and its sister ice giant, Neptune, the inside of the planet is relatively cold, radiating very little, if any, excess heat. At its coldest, Uranus’s troposphere has been recorded at -224.2 degrees Celsius (-371.5 Fahrenheit), the coldest of any planet in the Solar system.
As mentioned, Uranus rotates on its side relative to the ecliptic plane of the Solar System. It is the only planet to orbit in such an orientation. Though there is evidence that Uranus experiences seasonal changes, as do other planets, research regarding these changes is limited because of how long it takes the ice giant to complete its orbit. It takes Uranus about 84 Earth-years to complete one orbit around the sun, which makes sense when you consider it is nearly two billion miles away from our home star.
Only one spacecraft has ever visited the lonely ice giant. Voyager 2, of the twin Voyager missions, swung past Uranus in 1986. Someday, more spacecraft may eventually visit the distant ice giants. But their distance makes missions difficult. Until then, much of their existence remains a mystery.
Watch and relax with the Wonder Science Uranus video, here.