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TOPIC: Uranus


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Uranus

Average Distance From Sun: 2,870,990,000 Km
Diameter: 51,118 KM
Volume: 52 x Earth Standard
Mass: 1.4535e+01 x Earth Standard
Gravity: 1.17 x Earth StandardD
Atmosphere: Hydrogen, Helium, Methane
Moons: 27
Uranus Years: 84.01 Earth Years
Axis Tilt : 97.86 degrees
Uranus Day: 16hrs 10mins

The seventh planet from the Sun.

Uranus was discovered by William Herschel 1781. It is twice as far out as the sixth planet, Saturn.The spin axis of Uranus is tilted at 98 degrees, so that one pole points towards the Sun, giving extreme seasons.
Uranus spins from east to west, the opposite of the other planets, with the exception of Venus and possibly Pluto.

Data derived from the space probe Voyager 1 in 1986 revealed that Uranus is covered with a cloud layer under which an ocean of superheated water exists. The pressure caused by the thick atmosphere keeps the water from boiling away and the heat keeps the pressure from solidifying the water.

Voyager 2 detected ten rings, composed of rock pieces and large ice boulders, around the planet's equator, and found ten small moons in addition to the five visible from Earth. Titania, the largest moon, has a diameter of 1,610 km. The rings are charcoal black, and may be debris of former `moonlets' that have broken up.

Uranus can be spied with the unaided eye under a clear, dark sky. However, it is more easily seen in binoculars. At magnitude +5.7, it is located in Aquarius and is at opposition to the Sun on September 5, 2006.
Rings of Uranus

Name Distance* Width Thickness Mass Albedo
1986U2R 38,000 km2,500 km0.1 km?0.03
6 41,840 km1-3 km0.1 km?0.03
5 42,230 km2-3 km0.1 km?0.03
4 42,580 km2-3 km0.1 km?0.03
Alpha 44,720 km7-12 km0.1 km?0.03
Beta 45,670 km7-12 km0.1 km?0.03
Eta 47,190 km0-2 km0.1 km?0.03
Gamma 47,630 km1-4 km0.1 km?0.03
Delta 48,290 km3-9 km0.1 km?0.03
1986U1R 50,020 km1-2 km0.1 km?0.03
Epsilon 51,140 km20-100 km< 0.15 km?0.03
U2 66,000 km
2003R1 97,500 km
*The distance is measured from the planet-center to the inner edge of the ring.

The Uranus System Uranus moons

clickhere.gif to listen (realplayer)
Uranus is classed as a Gas Giant, although it is much smaller than Saturn & Jupiter.

Uranus, due to an ancient collision, is tilted by 98, so it is virtually orbiting on its side.


Moons



Moon # Radius
(km)
Mass
(kg)
Distance
(km)
Discoverer Date
Cordelia VI13?49,750Voyager 21986
Ophelia VII16?53,760Voyager 21986
Bianca VIII22?59,160Voyager 21986
Cressida IX33?61,770Voyager 21986
Desdemona X291.781017 kg62,659Voyager 21986
Juliet XI42?64,360Voyager 21986
Portia XII55?66,100Voyager 21986
Rosalind XIII27?69,930Voyager 21986
Belinda XIV34?75,260Voyager 21986
S/2003 U2 Cupid XXV61.21015 kg74,800Hubble2003
1986 U10 Perdita XVIII403.51017 kg76,416Karkoschka1999
Puck XV812.891018 kg86,004Voyager 21985
S/2003 U1 (Mab) XXVI82.81015 kg97,734Showalter2003
Miranda V235.86.33e+19129,780G. Kuiper1948
Ariel I578.91.27e+21191,240W. Lassell1851
Umbriel II584.71.27e+21265,970W. Lassell1851
Titania III788.93.49e+21435,840W. Herschel1787
Oberon IV761.43.03e+21582,600W. Herschel1787
S/2001 U3 FranciscoXXII61.31015 kg4,276,000Holman2001
Caliban XVI497.31017 kg7,231,000Gladman1997
StephanoXX106.01015 kg8,004,000Gladman1999
Trinculo S/2001 U1XX157.510148,578,000Holman2001
Sycorax XVII955.41018 kg12,179,000Nicholson1997
S/2003 U3 Margaret XXIII5.51.01015 kg14,345,000Sheppard2003
ProsperoXVIII152.11016 kg16,243,000Holman1999
SetebosXIX152.11016 kg17,501,000Kavelaars1999
2001 U2 Ferdinand XXIV61.31015 kg20,901,000Holman2001

Update



Atmosphere

Atmosphere

Atmosphere

Hydrogen and helium (83%H, 15% he) make up more than 98% of Uranus's atmosphere, which is about 8000 km thick, the remaining 2% is methane which condenses out to form light coloured clouds of ice crystals in the upper regions of Uranus's atmosphere.
Like the other gas planets, Uranus has bands of clouds that blow around rapidly; the amount of methane however is 10 times greater than either Jupiter or Saturn. Methane (by absorbing red light) is responsible for Uranus's blue-green colour.
The lower `atmosphere` may be composed of liquid water (perhaps as much as 50%), methane, and ammonia.
Uranus may not have a rocky core or massive liquid metallic hydrogen layer like Jupiter and Saturn.
Uranus's spectrum shows that its atmosphere is rich in hydrogen and methane.
Uranus has an average density of about 1.2 grams per cubic centimetre, implying that Uranus contains proportionately less hydrogen than Jupiter or Saturn. The density is too small for Uranus to contain much rock or iron material.
Spectrum

Spectrum

Atmospheric pressure 120 kPa
Hydrogen 83%
Helium 15%
Methane 1.99%
Ammonia 0.01%
Ethane 0.00025%
Acetylene 0.00001%
Carbon monoxide
Hydrogen sulfide trace
Astronomers have found two of the smallest moons ever spotted around Uranus, brining the distant planet's satellite tally to 24, the third most in the solar system.
The moons are 8 to 10 miles across (12 to 16 km) and were discovered with the Hubble Space Telescope.
The newly detected moons orbit closer to the planet than the five major Uranian satellites, which are each several hundred miles wide.
The newly discovered moons are temporarily designated as S/2003 U1 and S/2003 U2 until the IAU formally approves their discovery. S/2003 U1 is the larger of the two moons, measuring 10 miles (16 km) across. The Hubble telescope spotted this moon orbiting between the moons Puck, the largest satellite found by the Voyager spacecraft, and Miranda, the innermost of the five largest Uranian satellites.
Astronomers previously thought this region was empty space, according to a statement issued today by Hubble officials. S/2003 U1 is 60,600 miles (97,700 kilometers) away from Uranus, whirling around the giant planet in 22 hours and 9 minutes.
The smallest Uranian moon yet found, S/2003 U2, is 8 miles (12 kilometers) wide. Its orbital path is just 200 to 450 miles (300 to 700 km) from the moon Belinda. S/2003 U2 is 46,400 miles (74,800 km) away from Uranus and circles the planet in 14 hours and 50 minutes. The tiny moon is part of a densely crowded field of 11 other moons, all discovered from pictures taken by the Voyager spacecraft.
One idea
New Uranus moons

New moons

is that some of the moons are young and formed through collisions with wayward comets.
"Not all of Uranus's satellites formed over 4 billion years ago when the planet formed," Lissauer said. "The two small moons orbiting close to [the moon] Belinda, for example, probably were once part of Belinda. They broke off when a comet smashed into Belinda."
The astronomers hope to refine the orbits of the newly discovered moons with further observations.
"The orbits will show how the moons interact with one another, perhaps showing how such a crowded system of satellites can be stabilized," Showalter explained. "This could provide further insight into how the moon system formed. Refining their orbits also could reveal whether these moons have any special role in confining or 'shepherding' Uranus's 10 narrow rings."

"The inner swarm of 13 satellites is unlike any other system of planetary moons," says co-investigator Jack Lissauer of Ames. "The larger moons must be gravitationally perturbing the smaller moons. The region is so crowded that these moons could be gravitationally unstable. So, we are trying to understand how the moons can coexist with each other."
New images
Uranus

Uranus

of the planet Uranus reveal more diversity in cloud features than ever seen before.
The new images, from the Keck Telescope in Hawaii, provide insight into some of the most enigmatic weather in the solar system
A large storm in the southern hemisphere oscillates over 5 degrees of latitude during several years.
"It's weird behaviour that hasn't been recognized before on Uranus. It's similar to what's been seen on Neptune, although there the oscillation is much more rapid.
clickhere.gif to read more
Update:
22 December 2005
Astronomer Mark Showalter, using the Hubble Space Telescope have discovered two more rings around Uranus.
This is the first such discovery since the Voyager 2 spacecraft flew past the planet 20 years ago, in 1986 and discovered the 10th and 11th thin ring arcs.
The other nine rings were discovered from Earth.
The new rings orbit within the orbits of its large moons and just outside of Uranus' previously known 11 known rings. The newly discovered rings are made up of short-lived, faint bands of dust grains that are constantly being replenished by erosion of the orbiting moons. The moon Mab, that was discovered in 2003 restocks the outermost ring.
Scientists made the latest ring discoveries in 2004 after reprocessing hundreds of images taken by Voyager and found the rings had been imaged in the pictures. The rings were overlooked during the spacecraft flyby because of their faintness.
Astronomers have measured changes in the orbits of Uranus' inner moons since 1994. The new measurements suggest the moons are in a "random and chaotic" fashion
Because of the moons' instability, scientists think the satellites will lead to a collide with one another in the next couple of million years.


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New images yield clues to seasons of Uranus

Images of Uranus

Near-infrared images from the Keck II telescope show the planet Uranus in 2005 (left), with the rings at an angle of 8 degrees, and at equinox in 2007 (right pair), with the planets ring system edge-on. In all images, the south pole is at the left and the equator is directly below the rings. Uranus, which has an 84-year orbit around the sun, has seasons that last twenty-one years. With the aid of new imaging technologies and telescopes, scientists had their best chance to observe the change of seasons on the distant planet and to look for seasonal effects on some of the solar systems most mysterious weather features.

With an 84-year orbit around the sun, it isn't often that planetary scientists have an opportunity to observe the change of seasons on Uranus, a planet some 19 times farther from the sun than the Earth.
But in 2007, the planet reached equinox, the point in time where the sun is directly over the planet's equator and what little sunlight the planet gets is distributed evenly over its northern and southern hemispheres, giving scientists their best opportunity to probe the seasonal dynamics of the ringed planet.
Speaking in Ithaca, N.Y., today (Oct. 13) at a meeting of the American Astronomical Society's Division for Planetary Sciences, a team led by University of Wisconsin-Madison researcher Lawrence Sromovsky shared crisp new Keck II telescope images of the planet as it changed seasons.

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Now is the prime time to see Uranus up in the sky. Uranus, with its dingy rings and its entourage of 27 moons, was closest to the Earth for this year on the night of Sept. 13, an event called opposition. A keen-eyed observer who knows right where to look can spot Uranus with the naked eye. The best viewing time will be about 10 p.m. during late September and about 9 p.m. in early October.

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Title: Constraints to Uranus' Great Collision. IV. The Origin of Prospero
Authors: Gabriela Parisi (IAR-LaPlata), Giovanni Carraro (ESO-Santiago), Michele Maris (OATS), Adrian Brunini (LaPlata)

It is widely accepted that the large obliquity of Uranus is the result of a great tangential collision (GC) with an Earth size proto-planet at the end of the accretion. We attempt to constraint the GC scenario as the cause of Uranus' obliquity as well as on the mechanisms able to give origin to the Uranian irregulars. Different capture mechanisms for irregulars operate at different stages on the giant planets formation process. The mechanisms able to capture the Uranian irregulars before and after the GC are analysed. Assuming that they were captured before the GC, we calculate the orbital transfer of the nine irregulars by the impulse imparted by the GC. If their orbital transfer results dynamically implausible, they should have originated after the GC. We investigate and discuss the dissipative mechanisms able to operate later. In particular Prospero could not exist at the time of the GC. Different capture mechanisms for Prospero after the GC are investigated. Gas drag by Uranus' envelope and pull-down capture are not plausible mechanisms. Capture of Prospero through a collisionless interaction seems to be difficult. The GC itself provides a mechanism of permanent capture. However, the capture of Prospero by the GC is a low probable event. Catastrophic collisions could be a possible mechanism for the birth of Prospero and the other irregulars after the GC. Orbital and physical clustering should then be expected. Either Prospero had to originate after the GC or the GC did not occur. In the former case, the mechanism for the origin of Prospero after the GC remains an open question. In the latter case, another theory to account for Uranus' obliquity and the formation of the Uranian regular satellites on the equatorial plane of the planet would be needed.

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As the rings of Uranus swing edge-on to Earth - a short-lived view we get only once every 42 years - astronomers observing the event are getting an unprecedented, glare-free view of the rings and the fine dust that permeates them.
The rings were discovered in 1977, so this is the first opportunity astronomers have had to observe a Uranus ring crossing and perhaps to discover a new moon or two.

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uranus2
Credit: Imke de Pater (UC Berkeley), Heidi B. Hammel (SSI, Boulder) and the W. M. Keck Observatory

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Astronomers have captured remarkable new images of the rings of Uranus.
The rings are currently edge-on to Earth, in an event that only happens every 42 years.
A team, led by Imke de Pater from University of California, Berkeley, US, has analysed the rings' structure, with some surprising results.

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A rare edge-on view of the rings around Uranus has given astronomers their first glare-free peek at them since 1986, when the Voyager 2 probe flew past our solar system's seventh planet from the sun. The shaded glimpse, permitted by the heavens once every 42 years, revealed a surprisingly bright swath of faint dust that had been obscured by reflected sunlight glinting from other rings made of larger rocks, researchers report online today in Science.

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This series of images from NASA's Hubble Space Telescope shows how the ring system around the distant planet Uranus appears at ever more oblique (shallower) tilts as viewed from Earth - culminating in the rings being seen edge-on in three observing opportunities in 2007. The best of these events appears in the far right image taken with Hubble's Wide Field Planetary Camera 2 on August 14, 2007.
The edge-on rings appear as two spikes above and below the planet. The rings cannot be seen running fully across the face of the planet because the bright glare of the planet has been blocked out in the Hubble photo (a small amount of residual glare appears as a fan-shaped image artefact). A much shorter colour exposure of the planet has been photo-composited to show its size and position relative to the ring plane.
Earthbound astronomers only see the rings' edge every 42 years as the planet follows a leisurely 84-year orbit about the Sun. However, the last time the rings were tilted edge-on to Earth astronomers didn't even know they existed.

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Uranus on Edge

Credit: NASA, ESA, and M. Showalter (SETI Institute)


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The Planet Uranus
Exposure: 2 seconds
Date: 00:22 UT, Tuesday 7 August 2007

Uranus_022HUT0807
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mapUranus-2007-8-7-0h22m
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The Planet Uranus
Exposure: 250 ms
Time: 05:05 UTC, Wednesday 1 August 2007

Uranus1Aug07

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