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_Uranus_

_The important thing is not to stop questioning.
- Albert Einstein_

_Table of Contents_
Uranus Introduction
[10]Uranus' Rings
[11]Uranus Statistics
[12]Animations of Uranus
[13]Views of Uranus
[14]Rings of Uranus
[15]Uranus Moon Summary

_Satellites of Uranus_
[16]Ariel, [17]Belinda, [18]Caliban, [19]Cordelia,
[20]Cressida, [21]Desdemona, [22]Juliet,
[23]Miranda, [24]Oberon, [25]Ophelia,
[26]Portia, [27]Puck, [28]Rosalind,
[29]Sycorax,
[30]Titania, [31]Umbriel,
[32]New Moons of Uranus
[33]New Moons of Uranus

_Uranus Science_
[34]Uranus Science Summary
[35]Uranus Exploration Chronology
[36]Uranus Image/Animation Gallery

_Other Resources_
[37]The Uranian Ring System

[38][LINK] 

Uranus is the seventh planet from the Sun and is the third largest in
the solar system. It was discovered by [39]William Herschel in 1781.
It has an equatorial diameter of 51,800 kilometers (32,190 miles) and
orbits the Sun once every 84.01 Earth years. It has a mean distance
from the Sun of 2.87 billion kilometers (1.78 billion miles). The
length of a day on Uranus is 17 hours 14 minutes. Uranus has at least
22 moons. The two largest moons, [40]Titania and [41]Oberon, were
discovered by William Herschel in 1787.

The atmosphere of Uranus is composed of 83% hydrogen, 15% helium, 2%
methane and small amounts of acetylene and other hydrocarbons. Methane
in the upper atmosphere absorbs red light, giving Uranus its
blue-green color. The atmosphere is arranged into clouds running at
constant latitudes, similar to the orientation of the more vivid
latitudinal bands seen on Jupiter and Saturn. Winds at mid-latitudes
on Uranus blow in the direction of the planet's rotation. These winds
blow at velocities of 40 to 160 meters per second (90 to 360 miles per
hour). Radio science experiments found winds of about 100 meters per
second blowing in the opposite direction at the equator.

Uranus is distinguished by the fact that it is tipped on its side. Its
unusual position is thought to be the result of a collision with a
planet-sized body early in the solar system's history. [42]Voyager 2
found that one of the most striking influences of this sideways
position is its effect on the tail of the magnetic field, which is
itself tilted 60 degrees from the planet's axis of rotation. The
[43]magnetotail was shown to be twisted by the planet's rotation into
a long corkscrew shape behind the planet. The magnetic field source is
unknown; the electrically conductive, super-pressurized ocean of water
and ammonia once thought to lie between the core and the atmosphere
now appears to be nonexistent. The magnetic fields of Earth and other
planets are believed to arise from electrical currents produced in
their molten cores.

Uranus' Rings

In 1977, the first nine rings of Uranus were discovered. During the
Voyager encounters, these rings were photographed and measured, as
were two other new rings and ringlets. Uranus' rings are distinctly
different from those at [44]Jupiter and [45]Saturn. The outermost
_epsilon_ ring is composed mostly of ice boulders several feet across.
A very tenuous distribution of fine dust also seems to be spread
throughout the ring system.

There may be a large number of narrow rings, or possibly incomplete
rings or ring arcs, as small as 50 meters (160 feet) in width. The
individual ring particles were found to be of low reflectivity. At
least one ring, the epsilon, was found to be gray in color. The moons
Cordelia and Ophelia act as [46]shepherd satellites for the epsilon
ring.

Uranus Statistics
Discovered by William Herschel
Date of discovery 1781
Mass (kg) 8.686e+25
Mass (Earth = 1) 1.4535e+01
Equatorial radius (km) 25,559
Equatorial radius (Earth = 1) 4.0074
Mean density (gm/cm^3) 1.29
Mean distance from the Sun (km) 2,870,990,000
Mean distance from the Sun (Earth = 1) 19.1914
Rotational period (hours) -17.9
Orbital period (years) 84.01
Mean orbital velocity (km/sec) 6.81
Orbital eccentricity 0.0461
Tilt of axis (degrees) 97.86
Orbital inclination (degrees) 0.774
Equatorial surface gravity (m/sec^2) 7.77
Equatorial escape velocity (km/sec) 21.30
Visual geometric albedo 0.51
Magnitude (Vo) 5.52
Mean cloud temperature -193°C
Atmospheric pressure (bars) 1.2
Atmospheric composition
Hydrogen
Helium
Methane
83%
15%
2%

Animations of Uranus

* [47]Historical background: Discovery of Uranus.
* [48]Magnetic field of Uranus.
* [49]Core & magnetic field of Uranus.

Views of Uranus

_Uranus_
The greenish color of it atmosphere is due to methane and This view of
Uranus was acquired by [50]Voyager 2 on January 10, 1986. The
blue-green appearance of its atmosphere results from methane and
high-altitude photochemical smog. This gas absorbs red wavelengths
from the incoming sunlight, leaving the predominant bluish color seen
here. Towards the bottom of the image a few clouds can be seen. This
image is one of the few [51]Voyager pictures that shows this type of
cloud. _(Copyright Calvin J. Hamilton)_
_The Interior of Uranus_
Our knowledge of the internal structure of Uranus is inferred from the
planet's radius, mass, period of rotation, the shape of its
gravitational field and the behavior of hydrogen, helium, and water at
high pressure. Its internal structure is similar to that of
[52]Neptune except for the fact that it is less active in terms of
atmospheric dynamics and interior heat flow.

This cut-away view shows Uranus composed of an outer envelope of
molecular hydrogen, helium and methane roughly the mass of one to two
Earths. Below this region Uranus appears to be composed of a mantle
rich in water, methane, ammonia, and other elements. These elements
are under high temperatures and pressures deep within the planet. The
mantle is equivalent to 10 to 15 earth masses. Uranus's core is
composed of rock and ice, and is likely no more than one Earth mass.
_(Copyright Calvin J. Hamilton)_
_Uranus in True and False Color_
These two pictures of Uranus, one in true color (left) and the other
in false color, were compiled from images returned January 17, 1986,
by the narrow-angle camera of Voyager 2. The spacecraft was 9.1
million kilometers (5.7 million miles) from the planet, several days
from closest approach. The picture at left has been processed to show
Uranus as human eyes would see it from the vantage point of the
spacecraft. The picture is a composite of images taken through blue,
green and orange filters. The darker shadings at the upper right of
the disk correspond to the day-night boundary on the planet. Beyond
this boundary lies the hidden northern hemisphere of Uranus, which
remains in total darkness as the planet rotates. The blue-green color
results from the absorption of red light by methane gas in Uranus'
deep, cold and remarkably clear atmosphere. The picture at right uses
false color and extreme contrast enhancement to bring out subtle
details in the polar region of Uranus. Images obtained through
ultraviolet, violet and orange filters were respectively converted to
the same blue, green and red colors used to produce the picture at
left. The very slight contrasts visible in true color are greatly
exaggerated here. In this false-color picture, Uranus reveals a dark
polar hood surrounded by a series of progressively lighter concentric
bands. One possible explanation is that a brownish haze or smog,
concentrated over the pole, is arranged into bands by zonal motions of
the upper atmosphere. The bright orange and yellow strip at the lower
edge of the planet's limb is an artifact of the image enhancement. In
fact, the limb is dark and uniform in color around the planet.
_(Courtesy NASA/JPL)_
_Voyager Farewell Image_
This view of Uranus was recorded by [53]Voyager 2 on January 25, l986,
as the spacecraft left the planet behind and set forth on its cruise
to [54]Neptune. Voyager was 1 million kilometers (620,000 miles) from
Uranus when it acquired this wide-angle view. The picture has a
resolution of 140 kilometers (90 miles). The thin crescent of Uranus
is seen at an angle of 153 degrees between the spacecraft, the planet
and the [55]Sun. Even at this extreme angle, Uranus retains the pale
blue-green color seen by ground-based astronomers and recorded by
Voyager during its historic encounter. This color results from the
presence of methane in Uranus' atmosphere; the gas absorbs red
wavelengths of light, leaving the predominant hue seen here. The
tendency for the crescent to become white at the extreme edge is
caused by the presence of a high-altitude haze. _(Copyright Calvin J.
Hamilton)_
_Hubble Tracks Rotation of Uranus_
This view of Uranus was acquired by NASA's Hubble Space Telescope and
reveals a pair of bright clouds in the planet's southern hemisphere,
and a high altitude haze that forms a "cap" above the planet's south
pole. This is just one view of a sequence of three that can be
obtained by selecting the above gif image.

Hubble's new view was obtained on August 14, 1994, when Uranus was 2.8
billion kilometers (1.7 billion miles) from Earth. These atmospheric
details were only previously seen by the Voyager 2 spacecraft, which
flew by Uranus in 1986. Since then, detailed observations of Uranus's
atmospheric features have not been possible because the planet is at
the resolution limit of ground-based telescopes.

Hubble's Wide Field Planetary Camera 2 observed Uranus through a
filter that is sensitive to light reflected by a pair of high altitude
clouds. This makes a high altitude haze over Uranus' south polar
region clearly visible, along with a pair of high altitude clouds or
plume-type features that are 4,300 and 3,100 kilometers (2,500 and
1,800 miles) across, respectively. _(Credit Kenneth Seidelmann, U.S.
Naval Observatory, and NASA)_

Two additional Hubble Telescope images can be found here.
* [56]Uranus, Rings and Satellites
* [57]Uranus

_Uranus Ring System_
This dramatic Voyager 2 picture reveals a continuous distribution of
small particles throughout the Uranian ring system. The unique
geometry of this picture makes the previously unseen lanes of fine
dust particles visible. All the formerly known rings are visible here;
however, some of the brightest features in the image are bright dust
lanes not previously seen. The combination of this unique geometry and
a long, 96 second exposure allowed this spectacular observation. The
image was acquired through the clear filter of Voyager's wide-angle
camera. The long exposure produced a noticeable, non-uniform smear as
well as streaks due to trailed stars. _(Copyright Calvin J. Hamilton)_
_Shepherd Satellites_
The discovery of two [58]shepherd satellites has advanced our
understanding of the structure of the Uranian rings. The moons,
Cordelia (1986U7) and Ophelia (1986U8), are seen here on either side
of the bright epsilon ring; all 9 of the known Uranian rings are also
visible. The epsilon ring appears surrounded by a dark halo as a
result of image processing; occasional blips seen on the ring are also
artifacts. Lying inward from the epsilon ring are the delta, gamma and
eta rings; the beta and alpha rings; and finally the barely visible 4,
5 and 6 rings. The rings have been studied since their discovery in
1977. _(Courtesy NASA/JPL)_
_Pseudo-image of Uranus' Ring_
This pseudo-image of Uranus' rings was generated by using Voyager 2
frame FDS 26852.19. This image was taken in forward scattered light
and shows dust bands not seen in any other image. A 3 pixel wide slice
was taken from the most detailed part of the image, averaged to a 1
pixel wide image, then rotated 360 degrees and projected into
perspective view. The real color of the rings are neutral gray and
they are as dark as charcoal. _(Courtesy A. Tayfun Oner)_
_Uranus' Rings_
The 9 known rings of Uranus are visible here. The somewhat fainter,
pastel lines seen between the rings are artifacts of computer
enhancement. Six narrow-angle images were used to extract color
information from the extremely dark and faint rings. The final image
was made from three color averages and represents an enhanced,
false-color view. The image shows that the brightest, or epsilon, ring
at top is neutral in color, with the fainter 8 remaining rings showing
color differences between them. _(Courtesy NASA/JPL)_
_Uranian System_
This montage of the Uranian system was prepared from an assemblage of
images taken by the Voyager 2 spacecraft during its Uranus encounter
in January 1986. This artist's view shows [59]Ariel in the forefront,
with Uranus rising behind. Traversing clockwise from Ariel are the
satellites [60]Umbriel, [61]Oberon, [62]Titania, [63]Miranda, and the
small moon [64]Puck. _(Copyright Calvin J. Hamilton)_

Rings of Uranus

The following is a summary of the rings of Uranus.

Name Distance* Width Thickness Mass Albedo
1986U2R 38,000 km 2,500 km 0.1 km ? 0.03
6 41,840 km 1-3 km 0.1 km ? 0.03
5 42,230 km 2-3 km 0.1 km ? 0.03
4 42,580 km 2-3 km 0.1 km ? 0.03
Alpha 44,720 km 7-12 km 0.1 km ? 0.03
Beta 45,670 km 7-12 km 0.1 km ? 0.03
Eta 47,190 km 0-2 km 0.1 km ? 0.03
Gamma 47,630 km 1-4 km 0.1 km ? 0.03
Delta 48,290 km 3-9 km 0.1 km ? 0.03
1986U1R 50,020 km 1-2 km 0.1 km ? 0.03
Epsilon 51,140 km 20-100 km < 0.15 km ? 0.03

*The distance is measured from the planet center to the start of the
ring.

Uranus Moon Summary

The following table summarizes the radius, mass, distance from the
planet center, discoverer and the date of discovery of each of the
moons of Uranus:

Moon # Radius
(km) Mass
(kg) Distance
(km) Discoverer Date
[65]Cordelia VI 13 ? 49,750 [66]Voyager 2 1986
[67]Ophelia VII 16 ? 53,760 Voyager 2 1986
[68]Bianca VIII 22 ? 59,160 Voyager 2 1986
[69]Cressida IX 33 ? 61,770 Voyager 2 1986
[70]Desdemona X 29 ? 62,660 Voyager 2 1986
[71]Juliet XI 42 ? 64,360 Voyager 2 1986
[72]Portia XII 55 ? 66,100 Voyager 2 1986
[73]Rosalind XIII 27 ? 69,930 Voyager 2 1986
[74]Belinda XIV 34 ? 75,260 Voyager 2 1986
1986U10 XVIII 40 ? 75,000 Karkoschka 1999
[75]Puck XV 77 ? 86,010 Voyager 2 1985
[76]Miranda V 235.8 6.33e+19 129,780 [77]G. Kuiper 1948
[78]Ariel I 578.9 1.27e+21 191,240 [79]W. Lassell 1851
[80]Umbriel II 584.7 1.27e+21 265,970 W. Lassell 1851
[81]Titania III 788.9 3.49e+21 435,840 [82]W. Herschel 1787
[83]Oberon IV 761.4 3.03e+21 582,600 W. Herschel 1787
[84]Caliban XVI 49 ? 7,169,000 Gladman 1997
Stephano XX 10 ? 7,948,000 Gladman 1999
[85]Sycorax XVII 95 ? 12,213,000 Nicholson 1997
Prospero XVIII 15 ? 16,568,000 Holman 1999
Setebos XIX 15 ? 17,681,000 Kavelaars 1999

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_Copyright © 1997-2001 by [89]Calvin J. Hamilton. All rights reserved._
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