URANUS

Data from Wikipedia and NASA (C)

Uranus is the seventh planet of the solar system in order of distance from the Sun, the third party for diameter and the quarter for mass. It came discovered on 13 March 1781 from William Herschel. A curiosity regard to its discovery is that it reached of unexpected: the visible planets to eye knot (until Saturno) were known from millenia, and nobody suspected the existence of other planets, until the discovery, more than other for case, of Herschel that it noticed as a particular star seemed to move itself. The more interesting characteristic of the planet is the orientation of its axis of rotation. All the other planets have just the nearly perpendicular axis to the plan of the orbit, while that one of Uranus is nearly parallel. It rotates therefore maintaining one of its poles towards the sun for half of the period of revolution with consequent long seasons. Moreover, since the axis is tilted little more than 90°, the rotation is technically retrograde: Uranus rotates in the opposite back to that one of all the other planets of the system solar, even if seen the particularity of the inclination the retrograde rotation is only a minor note. The period of its revolution around the sun is of 84 years approximately and therefore every 40 years it changes the exposed pole to the sun, that it has one advanced temperature regarding that one of the Equator. Its orbit lies in practical on the plan of the ecliptic (inclination of 0,7°). Uranus is a giant gaseous, similar to Neptune but a few larger. The inner structure of the planet is constituted from a atmosphere thick 7600 km. The probe Voyager 2 is the only probe spaces is approached the planet, and they are not in program missions for the future.

Atmosphere

Atmosphere the atmosphere is thick 7600 km and is composed from hydrogen (83%), helium (15%), methane (2%) and with traces of water and ammonia. In 1986 the probe spaces Voyager 2 found clouds transported from airflows comprised between the 100 and 600 km/h. In 1998 the telescope spaces Hubble has photographed, to different altitudes, approximately 20 cloudy formations between the most luminous presents in the external solar system. The clouds probably are formed from methane crystals that condense like warm gas bubbles going back from the depths of Uranus. The below part, more of 80% of the mass of the planet, is formed from a liquid composed mainly from iced materials of water, methane and ammonia, while the part central is formed from denser material. The ciano color of the planet has had to the atmosphere composed mostly of methane that absorbs the red light and reflects that blue. The temperature of the surface of the clouds that cover Uranus is approximately 55 K (-218 °C or -360 °F); Uranus is so distant from the Sun that the difference of temperature between the summer and the winter is nearly null. To the top of clouds the temperature is of approximately -220°C with small differences between the various zones of the planet, probably it possesses a particular system of redistribution of the solar energy. The several measurements have revealed that the heat amount that it receives from the sun is nearly the same one of that irradiates. The different speed of clouds between the poles and the Equator made to mean the presence of great flows, and the particularitity of Uranus of having a strongly inclination of the axis of rotation induced to believe that it had been a development of the winds and particular atmospheric conditions, but to the contrary these factors has been reorganizes and thin clouds cover parallels to the Equator, just as it happens on the Earth, to one speed that varies from 170 to 570 km hour.

Inner structure

Uranus is composed mainly of cliffs and varies types of ice, with approximately 15% of hydrogen and a small fraction of helium (this in contrast with Jupiter and Saturn that instead are composed mainly from hydrogen). Uranus (as Neptune) is in many ways similar to the inner part of Jupiter and Saturn, without but it presence of liquid metallic hydrogen that the two giant planets have thanks to the enormous pressures that they exercise on theirs you leave inner. Uranus, of smaller mass, cannot generate a sufficient pressure. It seems moreover that Uranus does not have a full of rocks nucleus, but instead the material that composes it seems more or less to be distributed in uniform way. Because Uranus possesses a density similar to Jupiter, but it has a mass 22 times smaller can be mainly deduced that in its inside there is not liquid hydrogen, but a full of rocks nucleus (of 7500 km of radius) compound of iron and silicon. Around the nucleus a cape (of 10500 km of thickness) with a composition of: ice, methane and ammonia. Finally there is the superficial layer (of 7500 km) that it wraps the entire planet made of molecular hydrogen, helium and ammonia. Thanks to some made tests of laboratory from the astrophysical William B. Hubbard have been said the hypothesis that not necessarily the nucleus of the planet was full of rocks, but made of a water mixture, ammonia and isopropano subordinate to a pressure of 2 million atmospheres; and this new hypothesis seems adapted to that it is the structure and the characteristic of the inside of Uranus. Inclination of the axis : one of the main characteristics of Uranus is the inclination of its axis of 98°. Consequently, for part of its orbit a pole is towards the Sun continuously, while the other pole is in the zone in shadow. From the other part of the orbit of Uranus the two poles are inverted and therefore what before it was in shadow constantly it is directed towards the Sun. Between these two ends the Sun rises and set around to the Equator normally. When Voyager 2 visited the planet in 1986, the South Pole of Uranus was directed towards the Sun. To notice that the allocation of this pole as South Pole is currently in argument. Uranus can be described like planet that has an inclination a few greater axis of 90° or like planet that it has a inclination inferior to 90° and a retrograde rotation. These two descriptions are exactly equivalent like physical description of a planet, but the result is that the definition of North Pole and South Pole is one the opposite one of the other. A result of this strange guideline is that the polar regions of Uranus receive a great amount of energy from the Sun in greater way regarding the regions near to the Equator. However Uranus is warmer to the Equator that to the poles even if the mechanism responsible of this currently is not known. The reason is disowned also for which the axis of rotation of Uranus therefore it is tilted. In order to explain this last fact it has been introduced a hypothesis that is based on a possible collision of Uranus, during the formation, with an other protopianeta, with final result of this strange inclination of the axis. It seems also that the extreme inclination of the axis of rotation of Uranus causes extreme variations in the seasons as far as the meteorological time. During the travel of the Voyager the 2 clouds of Uranus were extremely weak and myths, while recent observations (2005) made through the telescope space them Hubble have found a presence much more emphasized and turbulent now that the inclination of the axis is carrying the Equator in the perpendicular direction of the Sun (in the 2007 will have such alignment). Magnetic field : the magnetic field of Uranus is strange in how much does not have its center in the nucleus of the planet and is tilted at least 60° regarding the spin of rotation. Probably it is generated from the movement to relatively superficial depths to the inside of the planet. Neptune has a similar magnetic field and therefore it is believed that this thing is not due to the strange inclination of the axis of Uranus. The magnetosfera is coiled from the rotation of the planet in a spiral rear the same planet. The source of the magnetic field is currently (2005) disowned; currently the idea of the existence is not thought truer, between the nucleus of the planet and the atmosphere, of the super-pressurized ocean composed from water and ammonia that could have generated a conduction electrical worker. Uranus rings possess a hardly perceivable ring system, composed from dark and pulverized matter until 10 m of diameter. The ring system was discovered on 10 March 1977 from James L. Elliot, Edward W. Dunham and Douglas J. Mink thanks to the flying observatory Kuiper Airborne Observatory. The discovery was unexpected: the astronomers had predisposed the airplane purposely in order to study a phenomenon much rare : the occultation of a star from Uranus, with the attempt of being able to study its atmosphere, that it would have filtered the beams of the star, before that this disappeared behind the planet. The C141 transported a telescope of 90 cm. and an sensitive photoelectric photometer, able to measure the smallest variations of brightness. When the investigators analyzed their observations discovered that the star was passing shortly from the sight five times before and after the occultation from part of the planet. After repeated controls, in the doubt of a defect in the instrument, concluded that around to Uranus was analogous ring system to those of Saturn. Such ring system came found directly when the probe spaces them Voyager 2 passed near Uranus in 1986. In December 2005 the telescope spaces them Hubble has photographed two new rings previously disowned. Widest than these it has a greater diameter two times of rings previously known. The two rings are therefore far from the planet that have been call the "second of rings" of Uranus. The scientists who have carried out the study assume that the more external ring comes continuously fed from the Mab satellite, discovered in 2005 and from the diameter of approximately 20 km, than orbit inside to the ring.

Natural satellites

Uranus possesses a complex system of natural satellites; those discoveries until today (2006) are 27. Various from the others moons of planets of the solar system whose names are drawn from personages of mythology, the names of the uranian satellites come from works of the English poets William Shakespeare and Alexander Pope. Between 1994 to the December 2005 many orbits of the satellites of Uranus have varied, like have been possible to see from the comparison of the data collected by means of the telescope space them Hubble with the observations of the Voyager program. It seems that an accidental process causes a continuous exchange of energy and angular moment between the moons. According to the calculations the moons of Uranus would have to arrive to a collision every few million years, an extraordinarily short time regarding the 4,5 billions of years of life of the solar system. The system of satellites of Uranus demonstrates therefore much unstable young person and; the scientists think to use it as model in order to study the formation and the maintenance of a planetary system. The satellites of Uranus can be to great lines distinguished in two groups, the regular satellites and the irregular ones, to second of the type of orbit and their origin. The regular satellites of Uranus are distinguished for having orbits nearly relatively small circulars and (regarding the gravitational field of the planet) and in adding is situates much neighbor to you to the equatorial plan of the planet. The five main satellites - Miranda, Ariel, Umbriel, Titania and Oberon - make all part of the group of the regular satellites; their period of rotation is equal to orbital period (similarly to when it happens for the Moon with the Earth, that is, they turns always the same hemisphere towards the surface of Uranus, second a motion of rotation sincrona ). The group of the regular satellites comprises also 13 lune smaller, that is Cordelia, Ofelia, White woman, Cressida, Desdemona, Giulietta, Porzia, Rosalinda, Cupido, Belinda, Loss, Puck and Mab. It is thought that all the regular satellites, than altogether are eighteen, are form by means of the traditional process of orbiting protoplanetari disc increase around to Uranus, analogous to main planets of the solar system. The irregular satellites, contrarily to the group of the regular ones, introduce orbits of greater dimensions, plus eccentrics and tilted regarding the equatorial plan of Uranus. To this group nine smaller satellites belong: Francisco, Calibano, Stefano, Trinculo, Sicorace, Daisy, Prospero, Setebos and Ferdinand. It is thought that these satellites, to difference of the regular ones, are not form the inside of the uraniano system, but have been captured, in times succeeded, from the force of gravity of the planet. Chronology of discoveries 1787 - 13 March British astronomer William Herschel discovers Titania and Oberon by means of a telescope reflector from 60 cm near Liverpool. 1851 - William Lassell discovers to others two satellites, Ariel and Umbriel. 1852 - The son of John Herschel attributes to the four satellites discoveries their names. 1948 - American astronomer Gerard Kuiper discovers a fifth satellite, Miranda. 1986 - Thanks to the transmitted data to Earth from the probe space Voyager 2 come progressively characterize eleven new satellites, that they carry the total to 16; Cordelia, Ofelia, White woman, Cressida, Desdemona, Giulietta, Porzia, Rosalinda, Belinda, Perdita and Puck. 1997 - Discovery of Calibano, thanks to the observations completed from Brett Gladman, Philip Nicholson, Joseph Burns and John Kavelaars with the telescope from 200 inches Has them of Observatory Palomar the Mount, in California. It comes moreover discovered Sicorace. 1999 - The discovery of three new satellites : draft of Stefano (Brett Gladman), Prospero (Matthew Holman) and Setebos (John Kavelaars). 2001 - They come discovered Trinculo (Matthew Holman), Ferdinand (Matthew Holman, John Kavelaars, Dan Milisavljevic and Brett Gladman) and Francisco (Matthew Holman and Brett Gladman). 2003 - The observations of Hubble carry to the discovery of Cupido (Mark Showalter and Jack Lissauer), Mab (Mark Showalter and Jack Lissauer) and Daisy (Scott Sheppard). The total of the satellites arrives therefore to 27. It follows a prospect with the data of the 27 known satellites of Uranus, orders for period of revolution around to the planet. They are evidences to you in violetto the satellites enough massive to possess a spheroidal shape, and in dark gray the irregular satellites, probably captured in according to moment from the force of gravity of the planet.

Name		Diameter	Weight	Medium orbital radius	Orbital period	Discovery
Uranus VI	Cordelia	13 ± 2 km	0,8×10¹⁸ kg	49 752 km	0,3350338 giorni	1986
Uranus VII	Ofelia	15 ± 8 km	0,8×10¹⁸ kg	53 764	0,376400 giorni	1986
Uranus VIII	Bianca	21 ± 4 km	0,8×10¹⁸ kg	59 166	0,43457899 giorni	1986
Uranus IX	Cressida	80 ± 4 km	0,343×10¹⁸ kg	61 780 km	0,463570 giorni	1986
Uranus X	Desdemona	64 ± 8 km	0,178×10¹⁸ kg	62 680 km	0,473650 giorni	1986
Uranus XI	Giulietta	94 ± 8 km	0,557×10¹⁸ kg	64 350 km	0,493065 giorni	1986
Uranus XII	Porzia	135 ± 8 km	1,68×10¹⁸ kg	66 090 km	0,513196 giorni	1986
Uranus XIII	Rosalinda	72 ± 12 km	0,254×10¹⁸ kg	69 940 km	0,558460 giorni	1986
Uranus XXVII	Cupido	~17,8 km	3,8×10¹⁵ kg	74 800 km	0,618 giorni	2003
Uranus XIV	Belinda	81 ± 16 km	0,357×10¹⁸ kg	75 260 km	0,623527 giorni	1986
Uranus XXV	Perdita	~26,6 km	13×10¹⁵ kg	76 420 km	0,638 giorni	1986
Uranus XV	Puck	162 ± 4 km	2,89 × 10¹⁸ kg	86 010 km	0,761833 giorni	1986
Uranus XXVI	Mab	~24,8 km	1,0 × 10¹⁶ kg	97 734 km	0,923 giorni	2003
Uranus V	Miranda	471,6 ± 1,4 km	(66 ± 7) × 10¹⁸ kg	129 390 km	1,413479 giorni	1948
Uranus I	Ariel	1157,8 ± 1,2 km	(1,35 ± 0,12) × 10²¹ kg	191 020 km	2,520379 giorni	1851
Uranus II	Umbriel	1169,4 ± 5,6 km	(1,17 ± 0,13) × 10²¹ kg	266 300 km	4,144177 giorni	1851
Uranus III	Titania	1577,8 ± 3,6 km	(3,53 ± 0,09) × 10²¹ kg	435 910 km	8,705872 giorni	1787
Uranus IV	Oberon	1522,8 ± 5,2 km	(3,01 ± 0,07) × 10²¹ kg	583 520 km	13,463239 giorni	1787
Uranus XXII	Francisco	~12 km	1,3×10¹⁵ kg	4 276 000 km	-0,7299 anni	2001
Uranus XVI	Calibano	~98 km	0,73×10¹⁸ kg	7 231 000 km	-1,5871 anni	1997
Uranus XX	Stefano	~20 km	6×10¹⁵ kg	8 004 000 km	-1,8546 anni	1999
Uranus XXI	Trinculo	~10 km	0,75×10¹⁵ kg	8 504 000 km	-2,0780 anni	2001
Uranus XVII	Sicorace	~190 km	5,4×10¹⁸ kg	12 179 000 km	-3,5272 anni	1997
Uranus XXIII	Margherita	~11 km	1,3×10¹⁵ kg	14 345 000 km	4,6401 anni	2003
Uranus XVIII	Prospero	~30 km	21×10¹⁵ kg	16 256 000 km	-5,4136 anni	1999
Uranus XIX	Setebos	~30 km	21×10¹⁵ kg	17 418 000 km	-6,1185 anni	1999
Uranus XXIV	Ferdinando	~12 km	1,3×10¹⁵ kg	20 901 000 km	-7,7300 anni	2001