Keeping It Cool
The only planet in the Solar System named after a Greek deity, specifically the Greek god of the sky, Uranus is the seventh planet from the Sun, and the first one to be discovered with a use of a telescope, by a German-born British astronomer William Herschel in 1781, who at first thought Uranus was a comet. Orbiting at a distance of 2,88 billion kilometers from the Sun, it is the coldest of all eight planets, despite being closer to the Sun than Neptune. Contrary to the other planets, it gives off less heat than it absorbs, because at some point its core cooled down. The temperatures can reach as low as 49 degrees Kelvin, making it the coldest planet in the Solar System.
Uranus is also the second least dense planet in the Solar System, with Saturn being the first. We have already mentioned that, theoretically, Saturn could float on water. Although Uranus would sink, it still has very low density, only 1.27 g/cm3, meaning that even though it is roughly 14 times the size of the Earth, you would experience only 89% the force of gravity. Uranus, just like Jupiter, Saturn and Neptune, is a gas giant, and has no actual surface, and its atmosphere is comprised mostly of hydrogen and helium, and a small amount of methane, which gives the planet its characteristic pale blue color, due to the fact that methane filters out red light. Similar to all three gas giants, Uranus has a large number of moons orbiting the planet, 27 to be exact. Given the planet’s unique tilt, the moons appear to be going over and under the planet, as if mounted on a giant Ferris wheel. One additional shared similarity is the fact the Uranus has rings made up of ice and rocks particles, as well, although they are not easily discernible, and can be viewed using only special equipment.
Interesting fact about Uranus is the way it spins. Most planets are rotate around their axis, and are slightly tilted. However, the tilt of Uranus is 99 degrees, which effectively means the planet is rotating sideways, giving off the impression that it is rolling around the Sun, rather than spinning around it, like all the other planets. This was probably caused by the collision with an Earth-sized object billions of years ago when Uranus was formed. This extreme tilt is also the reason a night on one of its poles lasts for 21 Earth years, receiving little or no light and heat from Sun at all. Also, a day on Uranus last for 17 hours, a few hours shorter than a day on Earth, but, a year on Uranus lasts 84 Earth years.
Uranus has been visited only once, when Voyager 2 flew by at a distance of 81,500 kilometers in 1986, taking thousands of photographs of the planet and its moons, before moving on to research Neptune. No other spacecraft has ever been sent to Neptune, and currently there are no plans to send any more.