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Uranus

Uranus' Moons

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OverviewUranus

Uranus was the first planet to be discovered in modern history. It was actually discovered by accident in 1781 by William Herschel.

Like the other gas giants, Uranus has a very thick cloud cover and an atmosphere made up mostly of hydrogen, helium, methane, and ammonia. The trace amount of methane is what gives Uranus and its twin, Neptune, their blue color. Unlike Saturn and Jupiter, Uranus has a different internal structure.

The core of Uranus is probably composed of liquid rock. Then, farther up, the liquid rock slowly gives way to an ocean made mostly of hydrogen, helium, and water, with small amounts of ammonia and methane. This "ocean" accounts for most of Uranus's bulk. Then, the water slowly thins out into the bland, almost featureless atmosphere.

Uranus also has a system of about 11 rings - not nearly as large as Saturn's. Nine were found when Uranus passed in front of a bright star in 1977, for the rings causing the star to temporarily disappear when they passed in front of it. This was the first time astronomers had detected rings around any planet other than Saturn. It was the first time, also, that astronomers had detected thin rings around any planet. The other two rings were found when Voyager 2 passed by.

Uranus also has known moons, most of which little is known about.

Atmosphere

Composition of Uranus AtmosphereUranus is basically one big atmosphere - as far as we know, there is no real surface to the planet. Its composition is nearly all H2; the rest is approximately:

  • H2: 82.5±3.3%
  • He: 15.2±3.3%
  • CH4: 2.3%
  • HD: 0.0148%

Besides this, aerosols of ammonia ice, water ice, and ammonia hydrosulfide exist in the atmosphere. Methane ice may also be present.

The temperature at 1 bar is approximately 76 K, and at 0.1 bar it is 53 K. The density at 1 bar is 420 g/m3. Wind speeds range up to 200 m/s. The scale height of the Uranian atmosphere is about 27.7 km.

Unique Characteristics

Uranus has two main unique features:Uranus' Rings

  • First, there is absolutely no detail in the cloud cover. Only when pushed to the maximum level of color enhancement and contrast on computers do scientists start to see small swirls in the atmosphere.
  • Second, Uranus is the only planet rotates on its side. This produces the strangest seasons of any planet in the solar system. For 21 years, Uranus's moons are seen as one would view a dart board, with one pole facing the sun. The next 21 years Uranus has its side to the sun, and the moons move up and down across the equator. then the cycle repeats itself starting with the other pole. Scientists aren't sure why this is, but they think that a large body smashed into it with such force that it pushed the planet over.

Satellites that Have Visited

  1. Voyager 2 - 1 flyby in 1986

Mythology

Uranus was named for the ancient Greek god of the heavens. When Earth was first made, Uranus was the first thing she saw, and they fell in love.

Data for the Rings

Name

Radius (km)
Relative Radius
Optical Depth
Albedo (10-3)
Width (km)
Eccentricity
Uranus' Equator
25,559
1.000
N/A
N/A
N/A
N/A
6
41,837
1.637
0.3
15
1.5
0.0010
5
42,235
1.652
0.5
15
2
0.0019
4
42,571
1.66
0.3
15
2.5
0.0010
Alpha
44,718
1.750
0.4
15
4 - 10
0.0008
Beta
45,661
1.786
0.3
15
4 - 11
0.0004
Eta
47,176
1.834
0.4-
15
1.6
 
Gamma
47,626
1.863
1.5+
15
1 - 4
0.0001
Delta
48,303
1.900
0.5
15
3 - 7
 
Lambda
50,024
1.957
0.1
15
2
 
Epsilon
51,149
2.006
0.5 - 2.3
18
20 - 96
0.0079

Data for the Planets

Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune
Perihelion (106 km)
46.00
107.5
147.09
206.62
740.52
1352.55
2741.30
4444.45
Mean Orbital Distance (106 km)
57.91
108.2
149.60
227.92
778.57
1433.53
2872.46
4495.06
Aphelion (106 km)
69.82
108.9
152.10
249.23
816.62
1514.50
3003.62
4545.67
Average Orbital Velocity (km/s)
47.87
35
29.78
24.13
13.07
9.69
6.81
5.43
Orbital Inclination (from Earth's Orbit)
7.00°
3.4°
0.0°
1.850°
1.304°
2.485°
0.772°
1.769°
Orbital Eccentricity
0.2056
0.007
0.0167
0.0935
0.0489
0.0565
0.0457
0.0113
Equatorial Radius (km)
2439.7
6051.8
6378.1
3397
71,492
60,268
25,559
24,764
Polar Radius (km)
2439.7
6051.8
6,356.8
3375
66,854
54,364
24,973
24,341
Volume (1010 km3)
6.083
92.843
108.321
16.318
143,128
82,713
6833
6254
Ellipticity (Variation from Sphere)
0.0000
0.000
0.00335
0.00648
0.06487
0.09796
0.02293
0.01708
Axial Tilt (from Earth's geographic North)
0.01°
177.4°
23.45°
25.19°
3.13°
26.73°
97.77°
28.32°
Mass (1024 kg)
0.3302
4.87
5.9736
0.64185
1898.6
568.46
86.832
102.43
Density (water=1)
5.427
5.243
5.515
3.933
1.326
0.687
1.27
1.638
Escape Velocity (km/s)
4.3
10.36
11.19
5.03
59.5
35.5
21.3
23.5
Gravity (m/s2)
3.70
8.802
9.78
3.716
23.1
9
8.7
11
Surface Pressure (bars)
≈ 10-15
92
1.014
0.000636
N/A
N/A
N/A
N/A
Total Mass of Atmosphere (kg)
< 1000
4.8x1020
5.1x1018
2.5x1016
N/A
N/A
N/A
N/A
Sidereal Rotation Period (hours)
1407.6
-5832.5
23.9345
24.6229
9.9250
10.656
-17.24
16.11
Length of Day (hours)
4222.6
2802
24
24.6597
9.9259
10.656
17.24
16.11
Tropical Orbital Period (days)
87.968
224.7
365.256
686.980
4330.595
10,746.94
30,588.740
59,799.9
Bond Albedo 0.119 0.750 0.306 0.250 0.343 0.342 0.300 0.290
Visual Geometric Albedo 0.106 0.65 0.367 0.150 0.52 0.47 0.51 0.41
Visual Magnitude -0.42 -4.40 -3.86 -1.52 -9.40 -8.88 -7.19 -6.87
Solar Irradiance (W/m2) 9126.6 2613.9 1367.6 589.2 50.50 14.90 3.71 1.51
Black-Body Temperature (K) 442.5 231.7 254.3 210.1 110.0 81.1 58.2 46.6
Average Surface Temperature (Celsius) 167° 464° 15° -65° -110° -140° -195° -200°
Number of Moons
Rings? No No No No Yes Yes Yes Yes
Global Magnetic Field Strength (Gs) / Tilt 0.0033 / 169° - / - 0.3076 / 11.4° - / - 4.28 / 9.6° 0.210 / <1° 0.228 / 58.6° 0.142 / 46.9°
Discoverer Unknown Unknown Unknown Unknown Unknown Unknown William Herschel Johann Gottfried Galle
Discovery Date Prehistory Prehistory Prehistory Prehistory Prehistory Prehistory March 13, 1781 September 23, 1846

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