Uranus



Diameter: 51,500 km (32,000 miles)
Temperature: -197.15 C (-322.87° F)
Orbit: Takes 84 years to complete an orbit.
Average Distance: 2,870,972,200 km (1,783,939,400 miles - 19.2 AU) from Sun
Mass: 8.6849 x 1025 kg
Moons: 27
Period of Rotation: 17.24 hours (retrograde: spins backwards compared to most other planets)

Missions to Uranus:


Voyager 2 - January 24, 1986


Uranus in history:


Uranus was mistaken at first for a star first time in 1690 by Jon Flamsteed, cataloging it as 35 Tauri, then the French astronomer Pierre Lemonnier observed it at least twelve times between 1750 and 1769.


After this Sir William Herschel observed the planet on March 13, 1781 in his garden but initially reported it om April 26, 1781 as a "comet". Herschel was using a telescope of his own design.


In his journal he recorded On March 17:  "I looked for the Comet or Nebulous Star and found that it is a Comet, for it has changed its place". When he presented his discovery to the Royal Society, he continued to assert that he had found a comet while also implicitly comparing it to a planet.

Herschel notified the Astronomer Royal, Nevil Maskelyne, of his discovery and received this flummoxed reply from him on April 23: "I don't know what to call it. It is as likely to be a regular planet moving in an orbit nearly circular to the sun as a Comet moving in a very eccentric ellipsis. I have not yet seen any coma or tail to it".

While Herschel continued to cautiously describe his new object as a comet, other astronomers had already begun to suspect otherwise. Russian astronomer Anders Johan Lexell was the first to compute the orbit of the new object and its nearly circular orbit led him to a conclusion that it was a planet rather than a comet. Berlin astronomer Johann Elert Bode described Herschel's discovery as "a moving star that can be deemed a hitherto unknown planet-like object circulating beyond the orbit of Saturn". Bode concluded that its near-circular orbit was more like a planet than a comet.

The object was soon universally accepted as a new planet. By 1783, Herschel himself acknowledged this fact to Royal Society president Joseph Banks: "By the observation of the most eminent Astronomers in Europe it appears that the new star, which I had the honour of pointing out to them in March 1781, is a Primary Planet of our Solar System." In recognition of his achievement, King George III gave Herschel an annual stipend of £200 on the condition that he move to Windsor so that the Royal Family could have a chance to look through his telescopes.


Uranus internal structure: 



Uranus has a mass of roughly 14.5 times that of the Earth, making it the least massive giant planet. Its diameter is slightly larger than Neptune's at roughly four times Earth's. A resulting density of 1.27 g/cm3 makes Uranus the second least dense planet, after Saturn. This indicates that it is made primarily of various ices, such as water, ammonia and methane. The total mass of ice in Uranus's interior is not precisely known, it must be between 9.3 and 13.5 Earth masses. Hydrogen and helium constitute only a small part of the total, with  between 0.5 and 1.5 Earth masses, the remainder of the non-ice mass, 0.5 to 3.7 Earth masses, is accounted for by rocky material.


In standard model of Uranus internal structure consists of three layers: a rocky (silicate/iron-nickel) core in center, an icy mantle in the middle and an outer gaseous hydrogen/helium envelope. The core is relatively small, with a mass of only 0.55 Earth masses and a radius less than 20% of Uranus's; the mantle comprises the bulk of the planet, with around 13.4 Earth masses, while the upper atmosphere is relatively insubstantial, weighing about 0.5 Earth masses and extending for the last 20% of Uranus's radius. Uranus's core density is around 9 g/cm3, with a pressure in the center of 8 million bars and a temperature of 5000K. The ice mantle is not in fact composed of ice in the conventional sense, but of a hot and dense fluid consisting of water, ammonia and other volatiles. This fluid has a high electrical conductivity is sometimes called a water-ammonia ocean. The bulk compositions of Uranus and Neptune are very different from those of Jupiter and Saturn, with ice dominating over gases, hence justifying their separate classification as ice giants. There may be a layer of ionic water where the water molecules break down into a soup of hydrogen and oxygen ions and deeper down superionic water in which the oxygen crystallizes but the hydrogen ions move freely within the oxygen lattice.

Other models are also in satisfaction with the observations. For instance, if substantial amounts of hydrogen and rocky material are mixed in the ice mantle, the total mass of ices in the interior will be lower and correspondingly, the total mass of rocks and hydrogen will be higher. Presently available data does not allow science to determine which model is correct.


Rings of Uranus:





Uranus has a complicated planetary ring system (the second such system to be discovered in our Solar System after Saturn's). The rings composition is from a extremely dark particles, which vary in size from micrometers to a fraction of a meter. All rings are extremely narrow, except two of them. The rings are probably quite young and the dynamics considerations indicate that they did not form with Uranus so the matter in the rings may have been part of a moon or moons that was shattered by high speed impacts.

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