No sniggering at the back! Astronomers discover the secret of vast cracks on the surface of the 'Frankenmoon' of Uranus

  • Miranda is a small icy moon of Uranus 
  • Covered in large cracks up to 200km across
  • Strange appearance has baffled astronomers for decades
  • Researchers now say a warming ice surface caused the deformities
  • Effect is similar to tectonic plate movement on Earth

By Mark Prigg for MailOnline

Published: 15:56 EST, 18 September 2014 | Updated: 17:05 EST, 18 September 2014

It is one of the oddest moons in the solar system.

Miranda, a small, icy moon of Uranus, is covered in giant fault canyons 12 times as deep as the Grand Canyon, giving it a unique look leading to it being called a 'Frankenstein moon'. 

Now, researchers say they have finally discovered why it looks so unusual.

A mosaic of high-resolution Voyager 2 images of Miranda, the 'Frankenstein moon' of Uranus. One wide-angle and eight narrow-angle camera images of Miranda were combined in this view to show off the bizarre deformed surface.

A mosaic of high-resolution Voyager 2 images of Miranda, the 'Frankenstein moon' of Uranus. One wide-angle and eight narrow-angle camera images of Miranda were combined in this view to show off the bizarre deformed surface.

A FRANKENMOON

At about 500 km in diameter, Miranda is only one-seventh as large as Earth's moon.

It sports one of the strangest and most varied landscapes among extraterrestrial bodies, including three large features known as 'coronae,' which are unique among known objects in our solar system. 

They are lightly cratered collections of ridges and valleys, separated from the more heavily cratered (and presumably older) terrain by sharp boundaries like mismatched patches on a moth-eaten coat. 

Miranda's giant fault canyons are as much as 12 times as deep as the Grand Canyon.

Due to Miranda's low gravity and large cliffs, a rock dropped off the edge of the highest cliff would take a full 10 minutes to reach the foot of the cliff.  

All of Uranus' larger moons, including Miranda, are thought to consist mostly of roughly equal amounts of water ice and silicate rock.

Despite its relatively small size, Miranda appears to have experienced an episode of intense resurfacing that resulted in the formation of at least three remarkable and unique surface features -- polygonal-shaped regions called coronae.

These coronae are visible in Miranda's southern hemisphere, and each one is at least 200 km across. 

Arden corona, the largest, has ridges and troughs with up to 2 km of relief. 

Elsinore corona has an outer belt that is approx. 80 km wide, relatively smooth, and elevated above the surrounding terrain by approx. 100m. 

Inverness corona has a trapezoidal shape with a large, bright chevron at its center.  

The giant fault canyons are as much as 12 times as deep as the Grand Canyon.

Due to Miranda's low gravity and large cliffs, a rock dropped off the edge of the highest cliff would take a full 10 minutes to reach the foot of the cliff.  

All of Uranus' larger moons, including Miranda, are thought to consist mostly of roughly equal amounts of water ice and silicate rock.

Voyager 2 image of Miranda taken shortly before closest approach on 24 January 1986 at a range of 19,000 miles. Miranda's giant fault canyons are as much as 12 times as deep as the Grand Canyon.

Voyager 2 image of Miranda taken shortly before closest approach on 24 January 1986 at a range of 19,000 miles. Miranda's giant fault canyons are as much as 12 times as deep as the Grand Canyon.

The northern hemisphere of Miranda was never imaged by the Voyager 2 spacecraft, so it is unknown whether additional coronae exist.

Using numerical models, Noah Hammond and Amy Barr from Brown proved that convection in Miranda's ice mantle likely formed the coronae.

'During convection, warm buoyant ice rose toward the surface, driving concentric surface extension beneath the locations of the coronae, causing the formation of extensional tectonic faults. 

'This style of resurfacing is similar to plate tectonics on Earth, in that convection is a primary driving force for surface deformation,' they wrote.

Hammond and Barr write that the internal energy that powered convection probably came from tidal heating. 

Tidal heating would have occurred when Miranda was in an eccentric orbit -- moving closer to and further from Uranus. 

This caused the tidal forces from Uranus to vary, periodically stretching and squeezing Miranda and generating heat in its ice shell.  

 

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