Miranda is the innermost of the five moons of Uranus that
were known purely from telescopic observations before space probes ventured in
its direction. Images returned by the Voyager 2 probe in 1986 revealed a
surprisingly complex world, with a mixture of heavily created and smooth
terrain, separated by deep canyons and towering cliffs. The most impressive
features are regions covered in parallel grooves, which are known as coronae.
It was originally thought that this small moon, with an
average diameter of only 293 miles (472 km), had shattered completely at some
point in the distant past and then reassembled. However, it is much more likely
that Miranda followed a much more eccentric orbit at some stage in its history
that it does today. This would have caused extreme gravitational tidal
pressures on the moon, leading to alternate periods of melting and re-forming.
Large areas of the crust would have subsided and new material welled up from
inside the moon to replace them.
With Miranda’s orbit becoming more regular, the tidal
pressures would have ceased, leaving the surface to freeze into its current
configuration.
© John Welford
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