URANUS

Physical and Orbital Characteristics of Uranus

Mean Distance from Sun (Earth = 1) - 19.2,

Period of Revolution - 84.01 y,

Period of Rotation - 17.24 h

Inclination of Axis – 98 degrees,

Equatorial Diameter - 51,120 km,

Mass (Earth = 1) - 14.4

Volume (Earth = 1) - 63,

Density - 1.28 g/cm3,

Atmosphere (main components) - H2, He, CH4

(83% hydrogen, 15% helium and 2% methane)

Temperature at cloud tops) - 60 K,

Magnetic field (Earth = 1) - uncertain 0.25-2.75,

Gravity (at cloud tops) - 1.15

Known Satellites (20 named, at least 1 unnamed)

Uranus, the first planet discovered in modern times, was discovered by William Herschel while systematically searching the sky with his telescope on March 13, 1781.

Uranus' blue color is the result of absorption of red light by methane in the upper atmosphere.

Uranus lacks the mass to have a layer of metallic hydrogen.

Uranus, a large gas-and ice-rich outer planet, is the center of a system of satellites and nine dark rings. Uranus is unique in that its spin axis is tipped almost 90 degrees from the normal solar system orientation. It seems that Uranus was tipped on its side when it was struck by a large body during its accretion.

Uranus’ magnetic field is not centered on the spin axis and tilted almost 60 degrees with respect to the axis of rotation. Perhaps it is in the middle of a magnetic polarity shift, but more likely it is generated by motion at relatively shallow depths.

Miranda (470 km in diameter), the smallest of the Uranian is about half water ice and half rocky material. Miranda's surface is all mixed up with heavily cratered terrain intermixed with weird grooves, valleys and cliffs (one over 5 kilometers high). The surface has been shaped by tectonic events that postdate the era of heavy bombardment and may mark chunks of the planet redistributed by fragmentation and reaccretion.

The satellites Oberon (1520 km in diameter) and Umbirel (1170 km) both have heavily cratered surfaces that probably date to an early period of intense bombardment. Subsequent resurfacing by volcanism or tectonism was not significant.

The brigher, denser satellites, Titania (1580 km in diameter) and Ariel (1160 km), experienced resurfacing after the period of intense bombardment, probably as a result of internal melting and icy volcanism. Moreover, both of these moons also have systems of grabens, which indicates that global expansion occurred late in their histories, perhaps as a result of the more rapid cooling and contraction of the outer layers of these bodies compared to their warmer interiors.