Uranus, also known as the Tilted Giant for its unique tilted rotation that makes it appear to spin on its side, is the second outermost planet in our Solar System. It joins Neptune, Saturn, and Jupiter as one of the giant planets. Giant planets are unimaginably huge, stunningly beautiful, and sometimes a little weird. They are made mostly of gases instead of solid materials.
Discovery
The five planets visible to the naked eye had been known since ancient times. Uranus, however, was not discovered until the age of the telescope. British astronomer Sir William Herschel “discovered” Uranus in 1781. However, earlier observers had seen it many times but thought it was a star. Sir William Herschel discovered Uranus accidentally while conducting a star survey. One “star” seemed different. Years of earlier observations, some by German astronomer Johann Bode, revealed that it was indeed a planet.
Characteristics of Uranus
Uranus is an ice giant. An ice giant is a giant planet that is made up of a thick soup of water, methane, and ammonia which scientists refer to as "ices." Uranus’s core is rocky, and its mantle is made up of the icy water and ammonia associated with the ice giants. Its striking blue-green hue is due to the haze that is created by methane and hydrogen sulfide gases in its atmosphere. Like the other ice giant Neptune, large storms swirl in Uranus's the atmosphere.
Uranus’s odd tilt makes it unique among our solar system’s giant worlds. A collision with a planet-sized object may have caused Uranus to tip over early in its history.
With its axis tilted almost 98°, Uranus’s environment differs from other planets in our solar system. The Sun points directly at each pole for long stretches of the planet’s orbit. This produces years-long winters when half of the planet is in continuous darkness, shadowed from the Sun’s light. Uranus also rotates in the opposite direction from most other planets. Only Uranus and Venus spin clockwise.
All four giant planets have rings. Jupiter, Uranus, and Neptune have only a few faint, narrow rings that are difficult to observe.
The rings of Uranus were first observed by scientists using Earth-based telescopes and the Kuiper Airborne Observatory. The rings were discovered when they caused the light of a star to flicker as Uranus passed in front of it. Voyager 2 took the first images of the rings. This one shows five of the 13 rings identified around Uranus.
Uranus has 27 moons. The Voyager spacecraft revealed the moons of the giant planets to be surprisingly diverse worlds in their own right. Further exploration has unveiled intricate surfaces both young and old, volcanoes and impact features, huge plumes and geysers, deep canyons, subsurface oceans, and even clues to possible environments that might be friendly to simple forms of life.
Uranus’s moon Miranda, pictured here, looks like a sloppy patchwork of unconnected parts. Made of ice and rock, it has huge chasms 12 times deeper than the Grand Canyon. Miranda’s strange appearance mystifies scientists. Perhaps the moon was shattered and came back together. Or maybe huge impacts broke up its icy surface, which then refroze.