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Seventh planet
Larger in diameter but smaller in mass than Neptune.
Orbit: 19.218 AU
Diameter: 4.23 Earths
Mass: 14.5 Earths
History of Uranus
Greek deity of the Heavens, earliest supreme god.
Father of Cronus (Saturn)
Discovered by William Herschel while searching the sky on March 13, 1781.
Seen many times before but ignored as simply another star.
Spacecraft Visiting Uranus
Voyager 2, Jan 24 1986, flyby
Discovered 11 small moons in addition to the 5 large ones already known.
Rotation of Uranus
Most planets’ spin axes are nearly perpendicular to the plane of its orbit.
Uranus' axis is almost parallel to its orbital plane.
When Voyager 2 flew by, the south pole was pointed toward the Sun.
The polar region received more energy from the Sun than its equatorial regions.
However, it’s hotter at the equator.
Not known why.
Composition of Uranus
Rock
Various Ices
Only 15% hydrogen
Little Helium
Uranus is similar to the cores of Jupiter and Saturn minus the massive liquid metallic
hydrogen “layer”.
Material is more or less uniformly distributed.
Atmosphere of Uranus
83% hydrogen
15% helium
2% methane
Weather of Uranus
Bands of clouds blow around rapidly.
Extremely faint, visible only with enhancement of the Voyager 2 pictures.
HST shows larger and more pronounced streaks.
Further HST observations show even more activity as the Sun starts to shine directly onto
the equator.
A maximum effect in 2007!
Color of Uranus
Blue color is the result of absorption of red light by methane in the upper atmosphere.
There may be colored bands like Jupiter's but they are hidden by the methane layer.
Ring of Uranus
Uranus has rings!
Very dark.
Composed of particles ranging from dust to 10 meters in size.
11 known rings, all very faint
Brightest is known as the Epsilon ring. T
Uranian rings were the first after Saturn's to be discovered.
It is likely that there are several more tiny satellites within the rings.
Odd Magnetic Field
Not centered at center of Uranus
Tilted almost 60 degrees from rotation axis.
Probably generated by motion at depths within Uranus.
Uranus' Satellites
Uranus has 21 named moons and six unnamed ones:
Not named from classical mythology
Named from writings of Shakespeare and Pope.
Form three distinct classes:
11 small very dark inner ones discovered by Voyager 2;
5 large ones; and newly discovered, much more distant ones.
Most have nearly circular orbits in the plane of Uranus' equator;
the outer 4 are much more elliptical.