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Planet Uranus: The Coldest Ice Giant

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Published on December 7th, 2011 | by Yellow Magpie


Planet Uranus: The Coldest Ice Giant


Planet Uranus

Planet Uranus has become the butt of many jokes mainly due to its oft-mispronounced name. However, this iced giant offers far more than one-dimensional scatological humour. Planet Uranus has a unique place in astronomy. The first of the planets to be discovered using a telescope by William Hershel it also possesses one of the most unique and oddest magnetic fields in the Solar System.

Planet Uranus, at 51,000 kilometres in width, is four times the diameter of our own Earth and has 14.5 times the mass of our planet. Which means it is not very dense, in fact it has the second lowest densities of all the planets in the Solar System after Saturn. The Earth is the most dense planet.

Planet Uranus orbits the Sun at a distance of 19 astronomical units (AU) or 2.8 billion kilometres (1.8 billion miles) taking 84 Earth-years to complete just one trip. While one day on the Icy Giant takes just over 17 hours.

Planet Uranus's 84-Year Orbit By Loo Kang Lawrence Wee

Planet Uranus Composition

Planet Uranus is classed as an ice giant which means it is composed mostly of materials that are frozen. This also means that its bulk composition is not hydrogen and helium, the two lightest elements.

The outermost layer of the planet consists of cloud that is methane-rich. Below that it has an inner atmosphere of helium, methane and hydrogen which becomes liquid as the pressure increase farther in.

Planet Uranus's Interior

Planet Uranus has a frozen mantle with a mixture of frozen chemicals which include methane, ammonia and water. Deep at its heart is a core of a mixture of rock and ice.

Atypical Tilt

One of the most singular aspects of planet Uranus’s rotation is the angle at which it tilts. The planet is effectively spinning on its side with its polar regions laying at the equators. This gives rise to a curious phenomenon when it comes to seasonal variations on the planet.

During its 84 year trek around the Sun one of its hemispheres is plunged into darkness while the other experiences daylight.

The Cold Planet

Planet Uranus, despite not being as far away from the Sun as Neptune, is the coldest planet in the Solar System. It’s atmosphere is minus 224 degrees Celsius (minus 371 degrees Fahrenheit).

The actuality of planet Uranus being colder than Neptune has created a puzzle. The planet that is the furthest away from the Sun should be the coldest. Somehow Uranus had less internal heat than astronomers anticipated.

Two of the most credible hypotheses state that either this peculiarity was a result of a massive impact in which much of its core heat was lost to Space while some scientists believe that there is some insulating barrier that is preventing the heat of the core from reaching the surface. The impact hypothesis could also account for planet Uranus’s strange tilt.

Planet Uranus Taken By Voyager

Magnetic Mystery

The magnetic field of planet Uranus is in a league of its own when its comes to strangeness. Unlike the magnetic fields of either the terrestrial planets or the Gas Giants, Uranus magnetic field does not originate in the polar regions. The strength of the magnetic field also varies according to the hemisphere with the northern being much weaker than the southern.

A hypothesis has been formulated to explain this phenomena as a product of magnetic fields being created through motion quite close to the surface of the planet. It is thought that if this is the case the magnetic fields are likely formed in oceans of water-ammonia mixtures.

Clear Climate

The wind on planet Uranus is unlike anything the Earth experiences with speeds of 900 kilometres per hour (560 miles) caused by the planet’s rapid rotation.

Unusually Uranus has very few clouds. In fact, in any given time there would be only a handful of clouds on the surface of the entire planet.

The Ring System

Planet Uranus has a comprehensive ring system with 13 distinctly segregated rings. They consist of dust particles in micron scale right up to larger boulders of 20 metres (65 feet) or more.

These particles and objects orbit planet Uranus at a distance of between 38,000  and 98,000 kilometres (23,600 to 60,800 miles).

Planet Uranus's Rings

The Moons Of Planet Uranus

As of today, astronomers have identified 27 moons orbiting planet Uranus. All of these satellites are either based on the characters of William Shakespeare of Alexander Pope. There are a five large moons with the largest being over 1,500 kilometres in width (900 miles). All the satellites are composed of a mixture of rock and ice.

Yellow Magpie will delve into more detail on Uranus’s moons soon.

Planet Uranus is a strange planet with many of its secrets yet to be revealed. Perhaps in time we may find out for certain why it is so cold and why it has such a funny tilt. Until now we will have to be content with educated and reasoned guesses.

Highly Recommended Reading

Check out Yellow Magpie’s The Planet Saturn: The Ringed Wonder Of The Solar System for more insight into the largest planet in the Solar System.

You may also wish to take a gander at The Solar System And Beyond: A Guide To The Cosmos.

Cosmos is a highly recommended book. It contains large, full-page pictures of the asteroids and writing on the subject by the highly competent author, Giles Sparrow.

For people living in Ireland or the United Kingdom, you can access: Cosmos from here.

For those who live in Canada, you can obtain: Cosmos here.

For Germany: Cosmos.

For France: Cosmos.

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