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The Planet Uranus
| Namesake |
Roman God, Father of the Titan |
| Distance from Sun |
2.871 Billion Kilometers |
| Period of revolution (1 Uranian
year) |
84.01 Earth Years |
| Equatorial Diameter |
51,118 Kilometers |
| Atmosphere (Main Components) |
Hydrogen and Helium |
Uranus
has a number of rings around it. Ten of them are dark and narrow, ranging in
width from less than 3 miles (5 kilometers) to 60 miles (100 kilometers). They
are no more than 33 feet (10 meters) thick. Image credit: NASA
Once considered one of the
blander-looking planets, Uranus (pronounced YOOR un nus) has been revealed as a
dynamic world with some of the brightest clouds in the outer solar system and 11
rings. The first planet found with the aid of a telescope, Uranus was discovered
in 1781 by astronomer William Herschel. The seventh planet from the Sun is so
distant that it takes 84 years to complete one orbit. Uranus, with no solid
surface, is one of the gas giant planets (the others are Jupiter, Saturn, and
Neptune).
The atmosphere of Uranus is
composed primarily of hydrogen and helium, with a small amount of methane and
traces of water and ammonia. Uranus gets its blue-green color from methane gas.
Sunlight is reflected from Uranus' cloud tops, which lie beneath a layer of
methane gas. As the reflected sunlight passes back through this layer, the
methane gas absorbs the red portion of the light, allowing the blue portion to
pass through, resulting in the blue-green color that we see. The planet's
atmospheric details are very difficult to see in visible light. The bulk (80
percent or more) of the mass of Uranus is contained in an extended liquid core
consisting primarily of 'icy' materials (water, methane, and ammonia), with
higher-density material at depth.
In 1986, Voyager 2 observed faint
cloud markings in the southern latitudes blowing westward between 100 and 600
kilometers (60 and 400 miles) per hour. In 2004, the Keck Observatory in Hawaii
used advanced optics to capture highly detailed images of Uranus as the planet
approached its southern autumnal equinox, when the equator will be vertically
illuminated by the Sun.
Uranus' rotation axis is nearly
horizontal with respect to the ecliptic plane, the imaginary plane containing
Earth's orbit, as well as the orbits of most of the planets, as though Uranus
had been knocked on its side. This unusual orientation may be the result of a
collision with a planet-sized body early in the planet's history, which
apparently radically changed Uranus' rotation. Additionally, while magnetic
fields are typically in alignment with a planet's rotation, Uranus' magnetic
field is tipped over: instead of aligning along the rotational axis, the
magnetic axis is tilted nearly 60 degrees from the planet's axis of rotation,
and is also offset from the center of the planet by one-third of the planet's
radius. Unlike the magnetic fields of Earth, Jupiter, and Saturn, which can be
thought of as acting like dipole bar magnets, the fields of Uranus (and Neptune
also) are very irregular. Uranus' magnetic field is about 48 times more powerful
than Earth's.
Even though Uranus is tipped on
its side and experiences seasons that last over 20 years, the temperature
differences on the summer and winter sides do not differ greatly because the
planet is so far from the Sun. Near the cloud tops, the temperature of Uranus is
-216 degrees Celsius (-357 degrees Fahrenheit).
The
Hubble Space Telescope photographed a new pair of rings around Uranus and two
new, small moons orbiting the planet. The largest ring is twice the diameter of
the planet's previously known rings; the rings are so far from the planet that
they are being called Uranus' "second ring system." One of the new
moons shares its orbit with one of the rings. Analysis of the Hubble data also
reveals the orbits of Uranus' family of inner moons have changed significantly
over the past decade.
Because of the planet's unusual
orientation, Uranus' rings are perpendicular to its orbital path about the Sun.
The 10 outer rings are dark, thin, and narrow, while the 11th ring is inside the
others and is broad and diffuse. Uranus has 27 known moons, named mostly for
characters from the works of William Shakespeare and Alexander Pope.
Uranus
27 known moons
Cordelia - Ophelia - Bianca-
Cressida - Desdemona - Juliet - Portia - Rosalind - Mab -. Belinda - Perdita -
Puck - Cupid - Miranda - Francisco - Ariel -. Umbriel - Titania - Oberon -
Caliban - Stephano - Trinculo - Sycorax - Margaret - Prospero - Setebos -
Ferdinand
Miranda was named
after the daughter of the magician Prospero in Shakespeare's play The Tempest.
Miranda is
the strangest-looking Uranian moon, appearing as though it were made of spare
parts. The high cliffs and winding valleys of the moon may indicate partial
melting of the interior, with icy material occasionally drifting to the surface
Uranus: Facts &
Figures
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Average Distance from the Sun
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Metric: 2,870,972,200 km
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English: 1,783,939,400
miles
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Scientific Notation:
2.8709722 x 109 km (19.191 A.U.)
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By Comparison: 19.191 x
Earth
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Metric: 2,735,560,000 km
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English: 1,699,800,000
miles
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Scientific Notation:
2.73556 x 109 km (18.286 A.U.)
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By Comparison: 18.60 x
Earth
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Metric: 3,006,390,000 km
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English: 1,868,080,000
miles
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Scientific Notation:
3.00639 x 109 km (20.096 A.U.)
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By Comparison: 19.76 x
Earth
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Metric: 25,559 km
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English: 15,882 miles
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Scientific Notation:
2.5559 x 104 km
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By Comparison: 4.007 x
Earth
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Metric: 160,592 km
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English: 99,787 miles
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Scientific Notation:
1.60592 x 105 km
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Metric:
69,142,000,000,000 km3
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Scientific Notation:
5.9142 x 1013 km3
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By Comparison: 63.1 x
Earth
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Metric:
86,849,000,000,000,000,000,000,000 kg
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Scientific Notation:
8.6849 x 1025 kg
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By Comparison: 14.371 x
Earth's
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Metric: 1.30 g/cm3
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By Comparison: 0.236 x
Earth
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Metric: 8,115,600,000 km2
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English: 3,133,400,000
square miles
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Scientific Notation:
8.1156 x 109 km2
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By Comparison: 15.91 x
Earth
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Equatorial Surface Gravity
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Metric: 8.43 m/s2
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English: 27.7 ft/s2
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By Comparison: If you
weigh 100 pounds on Earth, you would weigh 86 pounds
on Uranus.
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Metric: 76,640 km/h
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English: 47,620 mph
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Scientific Notation:
21,290 m/s
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By Comparison: 1.904 x
Earth
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Sidereal Rotation Period (Length
of Day)
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-0.7196 Earth days (retrograde)
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-17.24 hours (retrograde)
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By Comparison: 0.722 x
Earth
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Sidereal Orbit Period (Length of
Year)
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84.02 Earth years
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30,687.2 Earth days
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Metric: 24,607 km/h
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English: 15,290 mph
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Scientific Notation:
6,835.2 m/s
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By Comparison: 0.229 x
Earth
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.047168
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By Comparison: 2.823 x
Earth
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Orbital Inclination to Ecliptic
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Equatorial Inclination to Orbit
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97.86 degrees
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By Comparison: 4.173 x
Earth
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Metric: 17,620,000,000 km
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Scientific Notation:
1.762 x 1010 km
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By Comparison: 19.06 x
Earth
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Metric: -216 °C
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English: -357 °F
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Scientific Notation: 57 K
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Hydrogen, Helium, Methane
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Scientific Notation: H2,
He, CH4
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By Comparison: Earth's
atmosphere consists mostly of N2 and O2.
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Uranus/Earth
Comparison
Bulk parameters
Uranus Earth Ratio (Uranus/Earth)
Mass (1024 kg) 86.832 5.9736 14.536
Volume (1010 km3) 6,833 108.321 63.08
Radius (1 bar level) (km)
Equatorial 25,559 6,378.1 4.007
Polar 24,973 6,356.8 3.929
Volumetric mean radius (km) 25,362 6,371.0 3.981
Ellipticity (Flattening) 0.02293 0.00335 6.84
Mean density (kg/m3) 1,270 5,515 0.230
Gravity (eq., 1 bar) (m/s2) 8.87 9.80 0.905
Acceleration (eq., 1 bar) (m/s2) 8.69 9.78 0.889
Escape velocity (km/s) 21.3 11.19 1.903
GM (x 106 km3/s2) 5.794 0.3986 14.536
Bond albedo 0.300 0.306 0.980
Visual geometric albedo 0.51 0.367 1.390
Visual magnitude V(1,0) -7.19 -3.86 -
Solar irradiance (W/m2) 3.71 1,367.6 0.0027
Black-body temperature (K) 58.2 254.3 0.229
Moment of inertia (I/MR2) 0.225 0.3308 0.680
J2 (x 10-6) 3343.43 1082.63 3.088
Number of natural satellites 27 1
Planetary ring system Yes No
Orbital parameters
Uranus Earth Ratio (Uranus/Earth)
Semimajor axis (106 km) 2,872.46 149.60 19.201
Sidereal orbit period (days) 30,685.4 365.256 84.011
Tropical orbit period (days) 30,588.740 365.242 83.749
Perihelion (106 km) 2,741.30 147.09 18.637
Aphelion (106 km) 3,003.62 152.10 19.748
Synodic period (days) 369.66 - -
Mean orbital velocity (km/s) 6.81 29.78 0.229
Max. orbital velocity (km/s) 7.11 30.29 0.235
Min. orbital velocity (km/s) 6.49 29.29 0.222
Orbit inclination (deg) 0.772 0.000 -
Orbit eccentricity 0.0457 0.0167 2.737
Sidereal rotation period (hours) -17.24* 23.9345 0.720
Length of day (hrs) 17.24 24.0000 0.718
Obliquity to orbit (deg) 97.77 23.45 4.169
* Magnetic coordinates (as
determined by the Voyager 2 Radio Science experiment)
Uranus Observational Parameters
Discoverer: William Herschel
Discovery Date: 13 March 1781
Distance from Earth
Minimum (106 km) 2581.9
Maximum (106 km) 3157.3
Apparent diameter from Earth
Maximum (seconds of arc) 4.1
Minimum (seconds of arc) 3.3
Mean values at opposition from Earth
Distance from Earth (106 km) 2719.99
Apparent diameter (seconds of arc) 3.9
Apparent visual magnitude 5.5
Maximum apparent visual magnitude 5.32
Uranus Mean Orbital Elements
(J2000)
Semimajor axis (AU) 19.19126393
Orbital eccentricity 0.04716771
Orbital inclination (deg) 0.76986
Longitude of ascending node (deg) 74.22988
Longitude of perihelion (deg) 170.96424
Mean Longitude (deg) 313.23218
North Pole of Rotation
Right Ascension: 257.43
Declination : -15.10
Reference Date : 12:00 UT 1 Jan 2000 (JD 2451545.0)
Uranian Magnetosphere
Dipole field strength: 0.228 gauss-Ru3
Dipole tilt to rotational axis: 58.6 degrees
Dipole offset (planet center to dipole center) distance: 0.3 Ru along the rotation axis
Note: Ru denotes Uranian
radii, here defined to be 25,600 km
Uranian Atmosphere
Surface Pressure: >>1000 bars
Temperature at 1 bar: 76 K (-197 C)
Temperature at 0.1 bar: 53 K (-220 C)
Density at 1 bar: 0.42 kg/m3
Wind speeds: 0-200 m/s
Scale height: 27.7 km
Mean molecular weight: 2.64 g/mole
Atmospheric composition (by volume, uncertainty in parentheses)
Major: Molecular hydrogen (H2) - 82.5% (3.3%); Helium (He) - 15.2% (3.3%)
Methane (CH4) - 2.3%
Minor (ppm): Hydrogen Deuteride (HD) - 148
Aerosols: Ammonia ice, water ice, ammonia hydrosulfide, methane ice(?)
Credit: NASA
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