Mean orbital velocity: 4.2 miles (6.8 km) per second
Inclination of axis: 97.9
Orbital eccentricity: 0.047
Orbital inclination: 0.774
Diameter at equator: 31,770 miles (51,118 km)
4.01 x Earth's diameter
Oblateness: 0.023
Mass: 8.66 x 10^25 kg
14.6 x Earth's mass
Volume: 7.26 x 10^13 km^3
67 x Earth's volume
Density: 1.17 g/cm^3
0.23 x Earth's density
Surface gravity: 11.44 m/s^2
1.17 x Earth's gravity
Escape velocity: 13.2 miles (21.3 km) per second
Mean surface temperature: -353 F / -214 C / 59 K (at cloud tops)
Maximum apparent diameter as seen from Earth (seconds of arc): 3.7"
Number of known satellites: 15
Mean diameter of Sun as seen from the planet: 1' 41"
Satellite data
Cordelia (U6)
Mean distance from center of Uranus: 30,746 miles (49,471 km)
Inclination of axis: approx. 0
Rotation period: unknown
Orbital period: 0.335 days
Orbital eccentricity: 0
Orbital inclination to Uranus' equator: 0.14
Diameter: 16 miles (26 km)
Mass: unknown
Density: unknown
Escape velocity: approx. 0.006 mile (0.01 km) per second
Maximum apparent diameter as seen from Uranus: unknown
Ophelia (U7)
Mean distance from center of Uranus: 33,434 miles (53,796 km)
Inclination of axis: approx. 0
Rotation period: unknown
Orbital period: 0.372 days
Orbital eccentricity: 0.01
Orbital inclination to Uranus' equator: 0.09
Diameter: 19 miles (30 km)
Mass: unknown
Density: unknown
Escape velocity: approx. 0.006 mile (0.01 km) per second
Maximum apparent diameter as seen from Uranus: unknown
Bianca (U8)
Mean distance from center of Uranus: 36,776 miles (59,173 km)
Inclination of Axis: approx. 0
Rotation period: unknown
Orbital period: 0.431 days
Orbital eccentricity: 0
Orbital inclination to Uranus' equator: 0.16
Diameter: 26 miles (42 km)
Mass: unknown
Density: unknown
Escape velocity: approx.0.01 mile (0.02 km) per second
Maximum apparent diameter as seen from Uranus: unknown
Cressida (U9)
Mean distance from center of Uranus: 38,395 miles (61,777 km)
Inclination of axis: approx. 0
Rotation period: unknown
Orbital period: 0.463 days
Orbital eccentricity: 0
Orbital inclination to Uranus' equator: 0.04
Diameter: 39 miles (62 km)
Mass: unknown
Density: unknown
Escape velocity: approx. 0.02 mile (0.03 km) per second
Maximum apparent diameter as seen from Uranus: unknown
Desdemona (U10)
Mean distance from center of Uranus: 38,953 miles (62,676 km)
Inclination of Axis: approx. 0
Rotation period: unknown
Orbital period: 0.475 days
Orbital eccentricity: 0
Orbital inclination to Uranus' equator: 0.16
Diameter: 34 miles (54 km)
Mass: unknown
Density: unknown
Escape velocity: approx. 0.02 mile (0.03 km) per second
Maximum apparent diameter as seen from Uranus: unknown
Juliet (U11)
Mean distance from center of Uranus: 39,995 miles (64,352 km)
Inclination of Axis: approx. 0
Rotation period: unknown
Orbital period: 0.493 days
Orbital eccentricity: 0
Orbital inclination to Uranus equator: 0.06
Diameter: 52 miles (84 km)
Mass: unknown
Density: unknown
Escape velocity: approx. 0.025 mile (0.04 km) per second
Maximum apparent diameter as seen from Uranus: unknown
Portia (U12)
Mean distance from center of Uranus: 41,072 miles (66,085 km)
Inclination of axis: approx. 0
Rotation period: unknown
Orbital period: 0.513 days
Orbital eccentricity: 0
Orbital inclination to Uranus' equator: 0.09
Diameter: 67 miles (108 km)
Mass: unknown
Density: unknown
Escape velocity: approx. 0.03 mile (0.05 km) per second
Maximum apparent diameter as seen from Uranus: unknown
Rosalind (U13)
Mean distance from center of Uranus: 41,604 miles (69,941 km)
Inclination of axis: approx. 0
Rotation period: unknown
Orbital period: 0.558 days
Orbital eccentricity: 0
Orbital inclination to Uranus' equator: 0.28
Diameter: 34 miles (54 km)
Mass: unknown
Density: unknown
Escape velocity: approx. 0.02 mile (0.03 km) per second
Maximum apparent diameter as seen from Uranus: unknown
Belinda (U14)
Mean distance from center of Uranus: 46,773 miles (75,258 km)
Inclination of axis: approx. 0
Rotation period: unknown
Orbital period: 0.622 days
Orbital eccentricity: 0
Orbital inclination to Uranus' equator: 0.03
Diameter: 41 miles (66 km)
Mass: unknown
Density: unknown
Escape velocity: approx. 0.02 mile (0.03 km) per second
Maximum apparent diameter as seen from Uranus: unknown
Puck (U15)
Mean distance from center of Uranus: 53,450 miles (86,000 km)
Inclination of Axis: approx. 0
Rotation period: unknown
Orbital period: 0.762 days
Orbital eccentricity: 0
Orbital inclination to Uranus' equator: 0.31
Diameter: 96 miles (154 km)
Mass: unknown
Density: unknown
Escape velocity: approx. 0.04 mile (0.07 km) per second
Maximum apparent diameter as seen from Uranus: unknown
Miranda (U5)
Mean distance from center of Uranus: 80,423 miles (129,400 km)
Inclination of axis: 0
Rotation period: 1.414 days
Orbital period: 1.414 days
Orbital eccentricity: 0.0
Orbital inclination to Uranus' equator: 3.4
Diameter: 293 miles (472 km)
Mass: 6.89 x 10^19 kg
Density: 1.35 g/cm^3
Escape velocity: 0.12 mi (0.2 km) per second
Maximum apparent diameter as seen from Uranus: 17'54"
Ariel (U1)
Mean distance from center of Uranus: 118,710 miles (192,000 km)
Inclination of axis: 0
Rotation period: 2.520 days
Orbital period: 2.520 days
Orbital eccentricity: 0.003
Orbital inclination to Uranus' equator: 0.0
Diameter: 720 miles (1,158 km)
Mass: 1.26 x 10^21 kg
Density: 1.66 g/cm^3
Escape velocity: 0.35 mile (0.56 km) per second
Maximum apparent diameter as seen from Uranus: 30'54"
Umbriel (U2)
Mean distance from center of Uranus: 165,500 miles (266,300 km)
Inclination of axis: 0
Rotation period: 4.144 days
Orbital period: 4.144 days
Orbital eccentricity: 0.004
Orbital inclination to Uranus' equator: 0.0
Diameter: 727 miles (1,169 km)
Mass: 1.33 x 10^21 kg
Density: 1.51 g/cm^3
Escape velocity: 0.34 mi (0.54 km) per second
Maximum apparent diameter as seen from Uranus: 14'12"
Titania (U3)
Mean distance from center of Uranus: 270,300 miles (435,000 km)
Inclination of axis: 0
Rotation period: 8.706 days
Orbital period: 8.706 days
Orbital eccentricity: 0.002
Orbital inclination to Uranus' equator: 0.0
Diameter: 981 miles (1,578 km)
Mass: 3.48 x 10^21 kg
Density: 1.68 g/cm^3
Escape velocity: 0.48 mile (0.77 km) per second
Maximum apparent diameter as seen from Uranus: 15'00"
Oberon (U4)
Mean distance from center of Uranus: 362,600 miles (583,500 km)
Inclination of axis: 0
Rotation period: 13.463 days
Orbital period: 13.463 days
Orbital eccentricity: 0.001
Orbital inclination to Uranus' equator: 0.0
Diameter: 947 miles (1,523 km)
Mass: 3.03 x 10^21 kg
Density: 1.58 g/cm^3
Escape velocity: 0.44 mile (0.71 km) per second
Maximum apparent diameter as seen from Uranus: 9'48"
Planet composition
Uranus has a rocky core about the size of Earth, composed of heavy elements, mainly silicon and iron. An icy mantle of water, methane, and ammonia surrounds the core. Like Jupiter and Saturn, Uranus does not have a "surface"; above the ice a mixture of hydrogen, helium, and methane extends outward, gradually decreasing in density toward the top of the atmosphere. However, since a higher proportion of the planet is rock and ice, Uranus is more dense than its larger cousins.
Rocky Core: radius of 7,000 km
Ice and Water Layer: 8,000 km thick
Gas Layer: 10,500 km thick
Topography
Uranus has no distinct topographical features.
Atmosphere
Uranus has a cold, hydrogen-rich (83% by volume) atmosphere, with a higher percentage of methane (2%) than any other planet. Most of the remainder of the atmosphere is composed of helium. Temperatures near the upper atmosphere (at the tops of the clouds) average -353 F / -214 C / 59 K and wind speeds average 580 km (360 miles) per hour. These temperatures are so cold that even methane will condense from a gas to a liquid; it is proposed that overlying the cloud layers is a layer of liquid methane. It is this layer that causes the absortion of red and near infrared light, which in turn creates the planet's blue-green appearance. The cloud layers are probably similar to those of Jupiter and Saturn, with regions of ammonia, ammounium hydrosulfide, and water ice layers. However, these layers must lie deeper in the atmosphere in order for the temperatures to be conducive to cloud formation.
Magnetic fields and gravity
The intensity of the magnetic field at Uranus's surface is roughly comparable to that of Earth's, though it varies much more from point to point because of its large offset from the center of Uranus. 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 or metallic cores.
There is a magnetic tail extending millions of miles behind Uranus. Voyager measured the magnetotail to at least 10 million kilometers (6.2 million miles) behind the planet. The extreme tilt of the magnetic axis, combined with the tilt of the rotational axis, causes the field lines in this cylindrical magnetotail to be wound into a corkscrew shape.
The surface gravity on Uranus is 1.17 times the gravity on Earth.
Orbit and rotation
Though it is not generally considered to be so, the planet's rotation is technically retrograde due to the 98 axial inclination. The orbital period is 84 years, and recent studies suggest the rotation period to be 23.9 hours. However, the lack of visible surface features makes it difficult to measure precisely.
Moons and/or rings
For many years, there were only five known satellites: Titania, Oberon, Umbrial, Ariel, and Miranda. All are half rock, half ice satellites between 520 and 1,610 km (323 - 1,000 miles) across. In 1986, Voyager 2 provided proof of the existence of 10 new moons, all between 16 - 169 km (10 - 105 miles) in diameter.
The three brightest moons are Titania, Oberon, and Ariel. Their surfaces are completely covered with ice or frost, making this water the farthest from the Sun known to exist in the solar system. Miranda also features high cliffs, canyons, cratered plains, and winding valleys.
Uranus also features 11 dark rings, which were discovered in 1977 when they occulted a star. They are far less reflective than Saturn's rings, and appear to be composed of dust particles less than 5k in diameter.
Mythology
In Greek mythology, Uranus was the personification of the heaven and ruler of the world. He was also the father of Saturn. Miranda was named for the heroine and Ariel for the benevolent spirit in Shakespeare's play "The Tempest." Umbriel was named for the malevolent spirit in Pope's "Rape of the Lock." Titania was named for the Queen of the fairies and Oberon for the King of the fairies in Shakespeare's "Midsummer Night's Dream."
Discovery and exploration
Uranus was discovered in 1781 by William Herschel, who also discovered the satellites Titania and Oberon (in 1787). William Lassell recovered Umbriel (previously glimpsed by Herschel) and discovered Ariel in 1851. Gerard P. Kuiper discovered Miranda in 1948. Voyager 2 did first close-up survey of Uranus in January 1986.
