Portal:Uranus

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Uranus

A photo of Uranus taken by Voyager 2.

Uranus is the seventh planet from the Sun; it is the third largest and fourth most massive planet in the solar system. Uranus was the first planet discovered in modern times. Though it is visible to the naked eye like the five classical planets, it was never recognised as a planet by ancient observers due to its dimness. Sir William Herschel announced its discovery on March 13, 1781, expanding the known boundaries of the solar system. Uranus' atmosphere, although similar to Jupiter and Saturn in being composed primarily of hydrogen and helium, contains a higher proportion of "ices" such as water, ammonia and methane, along with the usual traces of hydrocarbons. It has the coldest planetary atmosphere in the solar system, with a minimum temperature of 49 K, and has a complex layered cloud structure in which water is thought to make up the lowest clouds, while methane makes up the uppermost layer of clouds. In 1986, images from the Voyager 2 space probe showed Uranus as a virtually featureless planet in visible light without the cloud bands or storms associated with the other giants. The wind speeds on Uranus can reach 250 m/s (560 mph).

More about...Uranus: its history, rings, atmosphere, climate, moons, and its exploration


Selected article

HST images show changes in the atmosphere of Uranus the planet approaches its equinox (right image).
The atmosphere of Uranus, like those of the larger gas giants, Jupiter and Saturn, is composed primarily of hydrogen and helium. At depth it is significantly enriched in volatiles (dubbed "ices") such as water, ammonia and methane. The opposite is true for the upper atmosphere, which contains very few gases heavier than hydrogen and helium due to its low temperature. Uranus's atmosphere is the coldest of all the planets, with its temperature reaching as low as 49 K.

The Uranian atmosphere can be divided into three main layers: the troposphere, between altitudes of −300 and 50 km and pressures from 100 to 0.1 bar; the stratosphere, spanning altitudes between 50 and 4000 km and pressures of between 0.1 and 10−10 bar; and the hot thermosphere (and exosphere) extending from an altitude of 4,000 km to several Uranian radii from the nominal surface at 1 bar pressure. Unlike Earth's, Uranus's atmosphere has no mesosphere.

The troposphere hosts four cloud layers: methane clouds at about 1.2 bar, hydrogen sulfide and ammonia clouds at 3–10 bar, ammonium hydrosulfide clouds at 20–40  bar, and finally water clouds below 50 bar. Only the upper two cloud layers have been observed directly—the deeper clouds remain speculative. Above the clouds lie several tenuous layers of photochemical haze. Discrete bright tropospheric clouds are rare on Uranus, probably due to sluggish convection in the planet's interior. Nevertheless observations of such clouds were used to measure the planet's zonal winds, which are remarkably fast with speeds up to 240 m/s.

Selected biography

William Herschel
Sir Frederick William Herschel, KH, FRS, German: Friedrich Wilhelm Herschel, (15 November 1738 – 25 August 1822) was a German-born English astronomer, technical expert and composer who became famous for discovering Uranus and its two satellites. He also discovered infrared radiation, devised the first model of the Milky Way galaxy and made many other discoveries in astronomy.

Topics

Uranus Atmosphere ˑ Climate ˑ Exploration (Voyager 2) ˑ Rings

Moons (Portia ˑ Puck ˑ Miranda ˑ Ariel ˑ Umbriel ˑ Titania ˑ Oberon ˑ Caliban ˑ Sycorax)

Astronomers: William Herschel ˑ William Lassell ˑ Gerard Kuiper ˑ James L. Elliot

See Also: Formation and evolution of the Solar System ˑ Gas Giant ˑ Nebular hypothesis

Bold articles are featured.
Italicized articles are on dwarf planets or major moons.


Selected picture

Elsinore Corona on Miranda
Credit: Hubble Space Telescope

One of three coronae on Miranda observed in 1986 by Voyager 2. Elsinore Corona shows a complicated pattern of ridges and troughs.

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