Uranus

1. Characteristics

Uranus is the seventh closest planet to the Sun and, unlike the first six planets, it was not discovered until the invention of the telescope. Uranus was discovered by German-British astronomer William Herschel in 1781, who first thought it was a comet[1] It was identified as a planet once its orbit was found to be roughly circular in 1783[2].

Uranus is the third largest planet in the Solar System, after Jupiter and Saturn. It is larger than Neptune but less massive. It takes over 30,000 days for Uranus to orbit the Sun, this is over 80 years, and one day on Uranus is just over 17 hours long[3].

Photograph of Uranus

Uranus, image taken by the Hubble Space Telescope. Image credit: NASA, ESA, and M. Showalter/Public domain.

Unlike Mercury, Venus, Mars, Jupiter, and Saturn, Uranus was not named after a Roman god. It is instead named after the Ancient Greek god of the sky. Uranus is the father of the Greek god Kronos, which corresponds to the Roman god Saturn, and the grandfather of Zeus, known to the Roman's as Jupiter[4a].

Uranus is an ice giant, with an atmosphere primarily composed of hydrogen and helium, but it also contains trace amounts of hydrocarbons, and large amounts of frozen water, ammonia, and methane[4b].

Uranus has a liquid core composed mostly of water, methane, and ammonia. Uranus has a magnetosphere, but the whole planet is tilted on its side so that its magnetic poles are at the equator[4c].

Uranus has a ring system similar to Saturn's, except that it did not form when the planet did[5], and orbits at an angle of nearly 90°[6].

Planets in the Solar system, sizes are approximately to scale. Jupiter is the largest planet, followed by Saturn.

The planets, sizes approximately to scale. Image credit: Dave Jarvis/CC-SA.

2. Moons

2.1 Miranda, Ariel, Umbriel, Titania, and Oberon

Uranus has 27 moons, the five largest are Miranda, Ariel, Umbriel, Titania, and Oberon. The largest of these is Titania, which is about half the diameter of the Moon. These moons are mostly composed of frozen water and silicate rock[7].

Photographs of Uranus’ moons, where the size is to scale.

Uranus' five largest moons, images from Voyager 2 (to scale). Image credit: NASA/JPL/Public domain.

3. Missions to Uranus

NASA's Voyager 2 came within 82,000 km of Uranus in 1986, travelling past its five largest moons, and discovering 10 new ones[8]. There are currently no plans for a new mission to Uranus.

4. References

  1. Herschel, W., 1781, 'Account of a Comet. By Mr. Herschel, FRS; Communicated by Dr. Watson, Jun. of Bath, FRS.', Philosophical Transactions of the Royal Society of London, 71, pp.492-501.

  2. Lexell, A. J., 1783, 'Recherches sur la nouvelle planète, découverte par Herschell et nommée Georgium Sidus', Acta Academia Scientarum Imperialis Petropolitanae, 1, pp.303–329.

  3. NASA, 'Planetary Fact Sheet', accessed 15-02-16.

  4. (a, b, c) NASA, 'Uranus: In Depth', accessed 15-02-16.

  5. NASA, 'Rings of Uranus', accessed 15-02-16.

  6. NASA, 'Hubble Camera Snags Rare View of Uranus Rings', accessed 15-02-16.

  7. NASA, 'Uranus: Moons', accessed 15-02-16.

  8. NASA, 'Uranus', accessed 15-02-16.

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