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Ariel Uranus's Bright Moon

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Published on February 13th, 2012 | by Yellow Magpie


Ariel Uranus’s Bright Moon


Uranus’s Moon Ariel

Uranus’s moon Ariel is a half-charted mysterious world that may have harboured a liquid water ocean in its past. Our only pictures of this far-away satellite are over two decades old – yet they have revealed a lot about this cold world.

The brightest of all the Uranian moons, Ariel is the forth-largest of Uranus’s 27 satellites at over 1,100 kilometres (over 700 miles) in width. The moon is named after a character in Alexander Pope’s poem, The Rape of the Lock.

A Tidally Locked Frozen World

Uranus’s moon Ariel orbits Uranus at a distance of 190,000 kilometres (118,000 miles) taking two and a half days (Earth-days) to do so. The satellite is one of the coldest moons in the Solar System with an average surface temperature of minus 213 degrees Celsius (minus 351 degrees Fahrenheit).

Infrared spectroscopic observation has confirmed that Uranus’s moon Ariel has water ice present on its surface. It is thought that the moon is differentiated into an icy mantle and an inner rocky core.

Like our own Moon, and many of the other satellites in the Solar System, Uranus’s moon Ariel is tidally locked. This means that one side of the moon always faces Uranus while the other is always pointed away from the planet.

Uranus’s Moon Ariel And The Voyager Fly-by

Voyager 2 flew by the satellite in 1986 imaging 35 per cent of the moon’s surface in the process.

Painting Of Voyager 2

The relatively close Voyager 2 fly-by has allowed more detailed mapping than those of Oberon or Umbriel. This has allowed scientists to build a fairly good picture of the type of geological features found on Uranus’s moon Ariel.


Scientists maintain that the moon is roughly equally made of ice and rock. The moon was more than likely formed from an accretion disk that was either left over after Uranus’s formation or the result of debris arising from the likely impact which resulted in the planet’s very odd tilt.

Uranus’s moon Ariel was also the subject of expansion which created many of its geological features. The expansion of the interior is estimated to have lasted 200 million years.

Odd Orbit And Long, Long Seasons

Uranus’s moon Ariel’s orbit resides completely within the magnetosphere of Uranus. This means that the moon is continuously struck by magnetospheric plasma which causes its trailing hemisphere to be darkened by charged particles.

Due to the unusual rotational tilt of Uranus, Ariel’s seasons are very extreme. The polar regions experience either complete darkness or continuous sunlight for periods of 42 years.

Uranus’s moon Ariel is extensively cratered and also has ridges and scarps as well as canyons. It is thought that geological activity probably arising from internal heating created some of these features.

The Chasmata

The main surface features of Uranus’s moon Ariel include canyons, ridges, scarps, troughs as well as impact craters.

The terrain of craters is thought to be Ariel’s oldest geological feature. The canyons, or chasmata, are believed to have been created by the freezing of liquid water deep within the moon. The longest chasmata is Jackina Chasma. This canyon is over 620 kilometres (385 miles) long.

The rigid terrain of ridges and troughs form a cris-crossing network hundreds of kilometres in size. Some of the ridges and troughs are up to 200 kilometres (124 miles) in length. These features are thought to be the result of failures of the crust.

Uranus's Moon Ariel Voyager 2 Close Up

The Craters

The plains are the youngest geological feature on Uranus’s moon Ariel. These are smooth, low-lying areas that took a long period of time to form as can be extrapolated by the differing levels of cratering. These plains are thought to be the result of volcanic activity.

The impact craters on the moon are not as large as those found on other Uranian moons. This suggests that Ariel’s surface is much younger than the date of the Solar System’s formation. Therefore, the moon must have undergone resurfacing after Ariel’s formation.

It is believed that tidal heating must have been the force behind this reshaping. It is thought this occurred when Ariel’s orbit was much more eccentric than it is today.

Ariel’s largest crater at 78 kilometres (48 miles) across is called Yangoor.

Liquid Ocean?

Like Umbriel, Uranus’s moon Ariel may once have had a frozen liquid-water ocean at the boundary layer between the icy mantle and the rocky core. The presence of ammonia and other anti-freezes would have helped to prevent freezing. If this ocean did exist it would long since have become frozen.

Ariel And The Future

So far Voyager 2 is the only spacecraft to visit Uranus’s moon Ariel over two decades ago. Currently, there are no planned missions to the satellite for the foreseeable future.

It may be many more decades before this moon is visited again.

Highly Recommended Reading

Check out Yellow Magpie’s Uranus: The Coldest Ice Giant 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.

About the Author

2 Responses to Ariel Uranus’s Bright Moon

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