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Planetary Ponderings - Part 7 of 9: Uranus

by Perry Pezzolanella, MVAS

Uranus, often considered the blandest of all the planets, is cloaked in a thick haze and lacks any detail, but it is a dynamic world to ponder with mysterious dark rings and a family of moons with weird terrain.

  • Uranus is the seventh planet from the Sun with an average distance of 1.78 billion miles. It can come as close as 1.70 billion miles or as far as 1.86 billion miles.

  • Uranus is the first planet discovered with a telescope when Sir William Herschel found it on March 13, 1781. He originally named the planet "Georgium Sidus" (the Georgian Star) to honor King George III.

  • Uranus is the third largest planet with an equatorial diameter of 31,771 miles and has 27 moons.

  • A day on Uranus lasts 17.2 hours, but its year lasts 84.01 Earth years.

  • Uranus can come within 1.61 billion miles of Earth, appear as large as 4.2 arc-seconds, and shine as bright as magnitude +5.5.

  • Under perfectly dark skies, Uranus can be glimpsed with the unaided eye.

  • Because Uranus orbits farther from the Sun than Earth, the phase always appears full.

  • Uranus has a small rocky core that is surrounded by a ball of mainly gas. The atmosphere is thousands of miles deep and is composed of 82% hydrogen, 14% helium, 2% methane, and the rest being a mixture of other gases.

  • Uranus is completely cloudy with a veil of haze obscuring the finer cloud details. Methane in its atmosphere gives Uranus a turquoise hue since it effectively absorbs the red component of sunlight and scatters the blue.

  • Uranus' cloud tops are cold at -350 degrees F, but for an unknown reason, unlike Jupiter, Saturn, and Neptune, there is very little heat radiating from the core.

  • Uranus is tilted way over on its axis at 97.9 degrees. This means that Uranus travels on its side as it orbits the Sun.

  • The strange tilt on its axis means that the poles of Uranus experience alternating daylight and night that lasts 42 Earth years each.

  • White clouds are rare, but are increasing as spring arrives in the northern hemisphere after nearly 42 years of twilight and darkness.

  • There is no solid surface on Uranus. The atmosphere thickens into slush with increasing depth, pressure, and heat, and is speculated to become a hot ocean of liquid water wrapped around a rocky core.

  • It has also been speculated that the core of Uranus may be wrapped with a layer of pressurized carbon, better known as diamonds.

  • The hot ocean may be conductive enough to create a bizarre magnetic field that is completely offset from the rotating core and tilted 59 degrees from the axis of rotation.

  • Uranus has aurora and lightning, although not as intense as Jupiter and Saturn, but still far more intense than Earth.

  • Uranus is surrounded by at least ten rings that were discovered on March 10, 1977. Unlike Saturn's icy rings, these carbon rings are as dark as coal.

  • Because Uranus is tipped over, the rings can make the planet appear like a giant bulls-eye at certain points in its orbit as seen from Earth.

  • Uranus has five major moons: Miranda, Ariel, Umbriel, Titania, and Oberon, which are all less than 1000 miles in diameter.

  • Miranda, the smallest of the major moons at 292 miles in diameter, may have been smashed to pieces by a powerful collision and reassembled itself into a patchwork quilt of dark rock and bright, icy chunks.

  • Miranda has an ice cliff known as Verona Rupes that towers up to 12 miles high and is the largest drop in the Solar System.

  • Ariel has large areas that are free of craters and is riddled with scarps and faults where fresh ice may have oozed out and resurfaced vast areas.

  • Umbriel is an oddity because it is considerably darker that the other moons. It is covered with craters, but there is one lone bright spot on the limb that possibly formed from an icy impact.

  • Titania is the largest of the major moons at 990 miles in diameter and is covered with craters and cut by deep rift valleys.

  • Oberon has several craters with bright, icy ejecta and dark floors where liquid water may have erupted from the impacts.

  • Oberon has one lone mountain that was seen along its limb, which is at least four miles high.

  • Voyager 2 flew past Uranus on January 24, 1986 for its only spacecraft encounter ever and took 330 pictures.

  • Uranus may be visited by another spacecraft as soon as 2014 when the proposed (although not yet approved) New Horizons 2 flies past it on its way to the Kuiper Belt.

Uranus is a fascinating world that may have had a violent history involving a massive impact that knocked it over, destroyed its original moons, and then in the midst of all the chaos, reassembled a whole new world that we see today. This in itself is enough to present a convincing argument that Uranus is not so bland after all.