Thursday, 10 November 2011

Uranus




URANUS
THE ICY PLANET

(Hello! We are Aroa and Carmen and we're going to give you some information about Uranus. Enjoy it!)

Uranus is the seventh planet from the Sun. It has the third-largest planetary raidus of the Solar System, and It's one of the planets with the largest mass. It was discovered by Sir William Herschel on March 13, 1781. It was the first planet discovered with a telescope. He called the planet 'The Georgian Planet' to honour the King George III of England. However some time later the name was changed to Uranus by the astronomer JohannElert Bode (based on the mythological god of sky 'Ouranus'). The British astronomer, William, also discovered two of the moons of Uranus (Titania and Oberon) and some of the moons of Saturn. Thought it is part of the Five Classic Planets , it was never recognized as a planet by ancient observers because of its dimness and slow orbit. This icy planet has a blue color caused by the Methane (CH4) in Its atmosphere.

It's diameter is about 51,118 Km, about four times bigger than the diameter of the Earth (12,742Km). However, in this planet, it's rapidly spin causes it to have two different diameters. In other words, the diameter from pole to pole is slightly less than the diameter across the equator (from pole to pole: 49946 Km). The polar diameter is 1172 Km less than the equatorial diameter. The orbital speed of our icy planet is about 6,6km/second.


Uranus is one of the farthest planet from the Sun . It's exactly at 2,870,990,000 Km from the Sun , or what is the same 1,783,950,480 miles.

It mass is aproximally about 86.8*10^24 Kilograms, one of the hugest masses that we can find in the Solar System, and about 14 times the mass of the Earth.

Uranus is considered the coldest planet in the Solar System. Uranus suface's temperature is divided in three depending on the level of temperature we considered. Considering the maximum or minimum we find:

  • Minimum: 49 K

  • Average: 53 K

  • Maximum: 57 K

Each day on Uranus takes 17hours and 8 minutes in Earth hours. At the same time, a year on Uranus takes 84 Earth years. So , we can say that Uranus takes 84 Earth years to orbit the sun once. The density of this Icy planet is 1,27 grams/cubic centimeter.It's the second least dense planet in the Solar System after Saturn.

COMPOSITION

The composition of Uranus' interior is basically methane, in the form of ice. Ice begins forming in the atmosphere of Uranus, near the methane cloud deck. The amount of ice in the air continues increasing until there is slush and it solidificed. This ice is warm (for Uranus) and can flow like the rocky underground mantle layers of Earth. This planet has very little metallic hydrogen(it is liquid hydrogen), and there is much more ice. Beneath the atmosphere there is a liquid layer of hydrogen and helium. As depth increases, this layer becomes more viscous, and then partly solid. This layer is composed of compressed water with ammonia and methane. Uranus has a molten rocky core about 10,500 miles (17,000 km) in diameter and about 12,500°F (6927°C). It's made out of heavy rock and metal elements.

SATELLITES

Our icy planet, has 27 satellites or moons, all of which are named after characters from the works of some important poets as William Shakespeare or Alexander Pope. As we said , William Herschel discovered the first two, Titania and Oberon in 1787, and the other spherical moons were discovered in 1851 by William Lassel (Ariel and Umbriel) and in 1948 by Gerard Kuiper(Miranda).The rest of the moons were discovered in 1985. The moons are divided in three big groups:

  • Inner moons: Connected to the rings of Uranus.There are 13 which are: Cordelia, Ophelia, Miranda, Mab, Puck, Desdemona, Cressida, Juliet, Bianca, Portia, Rosalind, Belinda and Perdita.

  • Large moons: Miranda, Ariel, Umbriel, Titania and Oberon. They range in diameter from 472 KM for Miranda to 1578 KM to Titania. All major moons comprise approximately equal amounts of rock and ice, except Miranda, which is madre primarily of ive.

  • Irregular moons: Uranus has 9 irregular moons. All of them are probably captured objects that were trapped by Uranus soon after its formation. The names are: Margaret, Francisco, Caliban, Stephano, Trinculo, Sycorax, Prospero, Setebos and Ferdinand.

    ATMOSPHERE

    Uranus's atmosphere is not well-defined. The outermost part of Uranus's gaseous envelope is called atmosphere.The Uranian atmosphere can be divided into three layers: the troposphere,(lowest and most dense, contains many different and complex cloud structures. Changes in seasons, strong winds, convections and bright clouds are typical ocurrences of the troposphere) between altitudes of -300 and 50Km and pressures from 100 to 0,1 bar, the stratosphere,(Middle part, made up of acetylene and ethane) between altitudes of 50 and 4000 Km and pressures between 0,1 and 10-10 bar, and finally the thermosphere/corona(the outermost layer. Helium is absent. Has a great amount of molecular hydrogen) extending from 4,000 Km to as high as 50,000 Km from the surface. There is no mesosphere.
    The atmosphere consists mainly of molecular hydrogen and helium. A large part of it is also composed by water, ammonia and methane. The surface below is filled with a 'sea' ammonia , water and hydrogen. The part of the atmosphere that contains gas is principally composed by hydrogen and helium. The Uranian thermosphere, together with the upper
    part of the stratosphere, corresponds to the ionosphere of Uranus. Observations show that the ionosphere occupies altitudes from 2000 to 10000km. The Uranian ionosphere is denser than that of either Saturn or Neptune. The ionosphere is mainly sustained by solar UV radiation and its density depends on the solar activity .Auroral activity is insignificant as compared to Jupiter and Saturn.


    OTHER CHARACTERISTICS

    Magnetic Field: The magnetic dipole moment of Uranus is tilted at an angle of 59 grades to the spin axis of the planet. The extrapolated near-equatorial surface field is 23 µT,

    corresponding to a magnetic moment (equatorial surface field times radius cubed) of 3.9 x 1017 T m3, close to 50 times greater than the terrestrial magnetic moment. The contribution of the quadrupole moment to the surface magnetic field is large, almost comparable to the contribution from the dipole moment. This relative contribution is in fact
    only exceeded by that of Neptune. The Uranian magnetosphere is very similar to the terrestrial magnetosphere. There is a bow shock that deflects the supersonic flow of the solar wind in front of the magnetospheric cavity and a magnetic tail extending far downstream.

    Rings: Uranus has the most complex ring system in the Solar System. This rings were first observed 2 centuries ago by William Herschel. In 1977 it was confirmed the theory about the rings of Uranus. After more than a decade, two more rings were discovered. In 2003 and 2005 two more rings were discovered by the Hubble Space Telescope.They start at about a distance of 38,000 km from the center of Uranus, and then extend out to about 98,000 km. There is a total of 13 rings of Uranus, but the most important are : Epsilon, Delta, Gamma, Eta, Alpha and Beta, and rings 6,5 and 4.

      Inclination of the Axis: It's axial inclination is about 97 degrees and its rotation is direct.

      EXPLORATION MISSIONS

      Voyager 2 is the only spacecraft to have flown by Uranus in 24 January 1986. The planet displayed little detail, but gave evidence of an ocean of boiling water about 800 km below the cloud tops. Curiously, the average temperature of its sun-facing pole was found to be the same as that of the equator. The spacecraft discovered 10 new moons, two new rings, and a strangely tilted magnetic field stronger than that of Saturn. A gravity assist at Uranus propelled the spacecraft toward its next destination, Neptune.


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